0660 knee arthroplasty - aetna better health

Knee Arthroplasty - Medical Clinical Policy Bulletins | Aetna of 100

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Knee Arthroplasty

Policy History

Last Review

08/18/2020

Effective: 05/02/2003

Next

Review: 07/22/2021

Review History

Definitions

Additional Information

Clinical Policy Bulletin

Notes

Number: 0660

Policy *Please see amendment for Pennsylvania Medicaid at the end of this CPB.

I. Aetna considers a Food and Drug Administration (FDA)

approved total knee arthroplasty (TKA) prosthesis medically necessary for adult members when the

following criteria are met:

A. Member has advanced joint disease demonstrated

by:

1. Pain and functional disability that interferes with

ADLs from injury due to osteoarthritis,

rheumatoid arthritis, avascular necrosis, or posttraumatic arthritis of the knee joint; and

2. Limited range of motion, crepitus, or effusion or

swelling of knee joint on physical examination:

and

3. Member has either of the following:

a. Radiographic evidence of

moderate/severe osteoarthritis of knee joint

(i.e., Kellgren-Lawrence Grade 3 or 4) (see

Appendix); or Proprietary

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b. Radiographic evidence of avascular necrosis

(osteonecrosis) of tibial or femoral condyle;

c. Radiographic evidence or rheumatoid arthritis

(joint space narrowing); and

4. History of of unsuccessful conservative therapy

(non-surgical medical management) that is clearly

addressed in the medical record (see note).

Conservative therapy may be inappropriate for

severe osteoarthritis with bone-on-bone

articulation and severe angular deformity, or for

avascular necrosis with collapse of tibial or

femoral condyle. If conservative therapy is not

appropriate, the medical record must clearly

document why such approach is not reasonable;

or

B. Failure of a previous osteotomy with pain interfering

with ADLs; or

C. Distal femur or proximal tibia malunion by imaging

with pain interfering with ADLs;

D. Distal femur or proximal tibia fracture or nonunion;

or

E. Malignancy of the distal femur, proximal tibia, knee

joint or adjacent soft tissues by imaging; or

F. Failure of previous unicompartmental knee

replacement with pain interfering with ADLs.

Note: Members with osteoarthritis, traumatic

arthritis, or avascular necrosis should have at least

12 weeks of nonsurgical treatment documented in

the medical record (at least 24 weeks for persons

with a relative contraindication), including all of

the following, unless contraindicated:

1. Anti-inflammatory medications or analgesics; and

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2. Flexibility and muscle strengthening exercises;

and

3. Activity modification; and

4. Supervised physical therapy [Activities of daily

living (ADLs) diminished despite completing a

plan of care]; and

5. Assistive device use (required for persons with

relative contraindications* to joint replacement,

optional for others); and

6. Therapeutic injections into the knee (required for

persons with relative contraindications* to joint

replacement, optional for others).

* Relative contraindicaitons to joint replacement

include the following: morbid obesity (BMI

greater than 40), age less than 50

years). Members with relative contraindications

should exhaust all nonsurgical treatment options.

G. Total joint replacement is considered not medically

necessary in persons with any of the following

absolute contraindications:

1. Active infection of the joint or active systemic

bacteremia that has not been totally eradicated;

or

2. Active skin infection (exception recurrent

cutaneous staph infections) or open wound

within the planned surgical site of the knee; or

3. Vascular insufficiency, significant muscular

atrophy of the leg, or neuromuscular disease

severe enough to compromise implant stability or

post-operative recovery or quadriplegia; or

4. Osseous abnormalities that cannot be optimally

managed and which would increase the

likelihood of a poor surgical outcome (i.e.,

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inadequate bone stock to support the implant);

or

5. Allergy to components of the implant (e.g., cobalt,

chromium or alumina).

H. For members with significant conditions or co-

morbidities, the risk/benefit of total knee

arthroplasty should be appropriately addressed in

the medical record.

II. Aetna considers a revision or replacement of total knee

arthroplasty medically necessary for the following

indications when accompanied by pain and functional

disability (interference with ADLs):

A. Aseptic loosening of one or more prosthetic

components confirmed by imaging, or

B. Fracture of one or more components of the

prosthesis or worn or dislocated plastic

insert confirmed by imaging, or

C. Confirmed periprosthetic infection by gram stain and

culture, or

D. Periprosthetic fracture of distal femur, proximal tibia

or patella confirmed by imaging, or

E. Progressive or substantial periprosthetic bone loss

confirmed by imaging, or

F. Bearing surface wear leading to symptomatic

synovitis, or

G. Implant or knee malalignment (valgus/varus or

flextion/extension greater than 15 degrees), or

H. Knee arthrofibrosis, or

I. Instability of dislocation of the TKA, or

J. Extensor mechanism instability, or

K. Upon individual case review, persistent knee pain of

unknown etiology not responsive to a period of non

surgical care for 6 months.

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And member does not have any of the following

contraindications to revision surgery:

1. Persistent infection,

2. Poor bone quality,

3. Highly limited quadriceps or extensor function,

4. Poor skin coverage, and

5. Poor vascular status.

III. Aetna considers unicompartmental knee arthroplasty

using Food and Drug Administration (FDA)-approved

devices medically necessary for members with

advanced osteoarthritis or posttraumatic arthritis of the

knee affecting only a single compartment (medial,

lateral or patellofemoral), and who meet the following

criteria:

A. Pain and functional disability that interferes with

ADLs due to osteoarthritis or post-traumatic arthritis

of the knee joint; and

B. Limited range of motion, crepitus, or effusion or

swelling of knee joint on physical examination: and

C. Member must have intact, stable ligaments, in

particular the anterior cruciate ligament; and

D. Patient’s knee arc of motion (full extension to full

flexion) is not limited to 90 degrees or less; and

E. Radiographic evidence of moderate/severe

osteoarthritis (i.e., Kellgren-Lawrence Grade 3 or

4) (see Appendix) affecting only a single (medial,

lateral or patellofemoral) compartment of the knee

joint; and

F. History of of unsuccessful conservative therapy (non

surgical medical management) that is clearly

addressed in the medical record (see Note); and

Note: Members should have at least 12 weeks of

nonsurgical treatment documented in the medical

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record (at least 24 weeks for persons with a relative

contraindication), including all of the following,

unless contraindicated:

1. Anti-inflammatory medications or analgesics, and

2. Flexibility and muscle strengthening exercises,

and

3. Activity modification, and

4. Supervised physical therapy [Activities of daily

living (ADLs) diminished despite completing a

plan of care], and

5. Assistive device use (required for persons with

relative contraindications*: to joint replacement,

optional for others), and

6. Therapeutic injections into the knee (required for

persons with relative contraindications*: to joint

replacement, optional for others).

* Relative contraindicaitons to unicompartmental

knee arthroplasty include the following: morbid

obesity (BMI greater than 40), age less than 50

years). Members with relative contraindications

should exhaust all nonsurgical treatment options.

G. Member has none of the following contraindications

to unicompartmental knee arthroplasty:

1. Previous proximal tibial osteotomy or distal

femoral osteotomy; or

2. Tibial or femoral shaft deformity; or

3. Radiographic evidence of medial or lateral

subluxation; or

4. Flexion contracture greater than 15º; or

5. Varus deformity greater than 15º (medial

unicompartmental knee arthroplasty) or a valgus

deformity greater than 20º (lateral

unicompartmental knee arthroplasty); or

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6. Inflammatory or crystalline arthropathy; or

7. Subchondral bone loss due to large subchondral

cysts or extensive focal osteonecrosis.

H. Member has none of the following absolute

contraindications to joint replacement:

1. Active infection of the joint or active systemic

bacteremia that has not been totally eradicated;

or

2. Active skin infection (exception recurrent

cutaneous staph infections) or open wound

within the planned surgical site of the knee; or

3. Vascular insufficiency, significant muscular

atrophy of the leg, or neuromuscular disease

severe enough to compromise implant stability or

post-operative recovery or quadriplegia; or

4. Osseous abnormalities that cannot be optimally

managed and which would increase the

likelihood of a poor surgical outcome (i.e.,

inadequate bone stock to support the implant; or

5. Allergy to components of the implant (e.g., cobalt,

chromium or alumina).

I. For members with significant conditions or co-

morbidities, the risk/benefit

of unicompartmental knee arthroplasty should be

appropriately addressed in the medical record.

IV. Aetna considers the UniSpacer interpositional spacer for

the treatment of osteoarthritis affecting the medial

compartment of the knee experimental and

investigational because its effectiveness for this

indication has not been established.

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V. Aetna considers bicompartmental, staged

bicompartmental, and bi-unicompartmental knee

arthroplasty experimental and investigational for

osteoarthritis of the knee and all other indications

because their effectiveness has not been established.

VI. Aetna considers customized total knee implant

experimental and investigational because its

effectiveness has not been established.

VII. Aetna considers prophylactic radiation therapy following

total knee arthroplasty experimental and investigational

because its effectiveness has not been established.

VIII. Aetna considers computer-assisted musculoskeletal

surgical navigation (e.g., MAKOplasty) experimental and

investigational for knee arthroplasty because there is a

lack of reliable evidence that it improves surgical

outcomes. Note: Robotic assistance is considered

integral to the primary procedure and not separately

reimbursed.

Note: Intra-operative use of kinetic balance sensor for implant

stability during knee replacement arthroplasty is considered

incidental to the primary procedure being performed and is not

eligible for separate reimbursement.

See also CPB 0661 - Joint Resurfacing (0661.html) .

Background

Knee joint replacement is indicated for patients with significant

loss or erosion of cartilage to bone accompanied by pain and

limited range of motion (ROM), in patients who have had an

inadequate response to conservative measures. Guidelines

indicate that unicompartmental knee arthroplasty (UKA) is

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indicated when only 1 compartment is affected, and total knee

arthroplasty (TKA) is indicated when 2 or 3 compartments are

affected.

According to available literature, UKA is contraindicated in

persons with any of the following: active local or systemic

infection; loss of musculature, neuromuscular compromise or

vascular deficiency in the affected limb, rendering the

procedure unjustifiable; poor bone quality; severe instability

secondary to advanced loss of osteochondral structure;

absence of collateral ligament integrity; or individuals with over

30 degrees of fixed varus or valgus deformity.

The UniSpacer (Sulzer Orthopedics, Austin, TX) is a metallic

interpositional spacer for arthritis affecting primarily the medial

compartment of the knee. The device is a U-shaped metallic

shim, designed to be implanted in the knee joint following

removal of any damaged cartilage. The UniSpacer has been

used for the treatment of isolated, moderate degeneration of

the medial compartment (Grade III to IV chondromalacia) with

no more than minimal degeneration (Grade I to II

chondromalacia, no loss of joint space) in the lateral condyle

or patellofemoral compartment. The UniSpacer is intended to

restore the stability and alignment of the knee and relieve pain,

thereby delaying or avoiding the need for total knee

replacement (TKR).

The manufacturer states that an advantage of the UniSpacer

over TKR is that the procedure to implant the UniSpacer

involves no cutting of the patient's bone and no cementing of

the implant in the knee. A small incision is required before the

implant can be inserted. The UniSpacer is designed to center

itself in the knee, so that no alteration of the surrounding bone

or soft tissues is required for implantation. The manufacturer

states that surgery to implant the UniSpacer takes about 1

hour to complete, and the patient usually is only required to

stay over-night after the procedure, instead of the 3 to 4 days

required by a TKR.

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According to the manufacturer's website, approximately 90

patients have been implanted with the UniSpacer. The

manufacturer's website states that outcomes so far have been

"excellent", although the follow-up on these patients is

relatively short (the longest being approximately 1.5 years).

The manufacturer's website states that there have been no

revisions or complications in any of the cases.

The manufacturer's website states that the UniSpacer is

targeted for younger patients who have unicompartmental

arthritis involving the medial compartment of their knee. The

majority of the patients who have been implanted with the

UniSpacer are under 65 and, therefore, are not yet ideal

candidates for TKR.

According to the manufacturer's website, the UniSpacer is

currently only available through a small group of specially

trained surgeons who are participating in an assessment

research project of the device. However, there is insufficient

published evidence of the effectiveness and durability of this

device. Because of the lack of adequate prospective studies

in the peer-reviewed published medical literature, the clinical

value of UniSpacer has yet to be established.

Scott (2003) stated that the eventual role of the UniSpacer in

arthroplasty currently is uncertain. There are no published

reports of its effectiveness. Its indication should be similar to

those for McKeever arthroplasty. A patient with

unicompartmental osteoarthritis in whom an osteotomy is

contraindicated but is considered too young, heavy, or active

for a metal-to-plastic arthroplasty is ideal. Less than 1 % of

patients with osteoarthritis should be appropriate candidates.

Scott (2003) stated that procedure is technically demanding

and sensitive, making its widespread success unlikely.

A technology assessment by the California Technology

Assessment Forum (Tice, 2003) concluded that the UniSpacer

did not meet CTAF’s assessment criteria. The assessment

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concluded that “[s]urgical placement of knee joint spacer

devices requires evaluation in controlled trials in order to

assess the efficacy and safety of the procedure before its

widespread adoption can be advocated.”

The Washington State Department of Labor and Industries

(2005) has stated that it does not cover the UniSpacer device

because of an absence of clinical data and published literature

regarding its safety and efficacy.

Guidance from the National Institute for Health and Clinical

Excellence (NICE, 2009) concludes: "Current evidence on the

safety and efficacy of individually magnetic resonance imaging

(MRI)-designed unicompartmental interpositional implant

insertion for osteoarthritis of the knee is inadequate in quantity

and quality. Therefore, this procedure should only be used in

the context of research studies".

A technology assessment of TKA prepared for the Washington

State Health Care Authority (Dettori et al, 2010) identified

only 1 randomized controlled trial (RCT) that reported on a

comparison between UKA and standard TKA. Regarding knee

function, the report found that, in the 1 RCT comparing UKA

with TKA, the mean Bristol Knee Score was similar between

the UKA and TKA groups 5 and 15 years following surgery:

91.1 (range of 32 to 100) and 92 (range of 32 to 100)

compared with 86.7 (range of 48 to 98) and 88 (range of 48 to

98). The report observed that a larger percentage of the UKA

group reported excellent Bristol scores at 5- and 15-year follow-

up (76 % and 71 %, respectively) than in the TKA group (57 %

and 53 %, respectively), although this did not reach statistical

significance). Regarding failure rates, the report stated that

statistically significant differences in failure rate defined as

revision or a Bristol Knee Score less than 60 were not reported;

however, at 15-year follow-up, 17 % of the UKA group and 24

% of the TKA group had experienced failure. The report found

no statistically significant differences in revision rates between

UKA and TKA at 15-year follow-up.

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Thirteen percent of the UKA group and 16 % of the TKA group

had experienced revision. The report also found no

statistically significant differences in survival rate at 15-year

follow-up: 89.8 % (95 % confidence interval [CI]: 74.3 to 100)

for the UKA group and 78.7 % (95 % CI: 56.2 to 100) for the

TKA group (p > 0.05). The report also found knee pain,

function and revision rates were comparable between the

2 treatment groups in 14 cohort studies reporting over a

variety of follow-up times. The report identified 2 RCTs

providing data on the efficacy of UKA compared with TKA; in

these studies, there were no significant differences in knee

pain, knee function, failure or revision, or ROM between the

groups from 1 year to 10 years of follow-up. Regarding safety,

no deaths and few complications were reported in 1 RCT

and 9 cohort studies. No statistical significance between UKA

and TKA was reported in the number of patients experiencing

venous thromboembolism, the knees requiring manipulation

under anesthesia or the number of knees having delayed

wound healing. Three studies reported complications after

treatment with UKA or high tibial osteotomy (HTO); there were

no differences between groups.

Bailie and colleagues (2008) reported the findings of a

prospective study of 18 patients treated with the Unispacer.

The mean age of the patients was 49 years (40 to 57). A total

of 8 patients (44 %) required revision within 2 years. In 2

patients, revision to a larger spacer was required, and in 6

conversion to either a UKA or TKR was needed. At the most

recent review 12 patients (66.7 %) had a Unispacer remaining

in-situ. The mean modified visual analog score for these

patients at a mean follow-up of 19 months (12 to 26) was 3.0

(0 to 11.5). The mean pain level was 30 % that of the mean pre

operative level of 10. The early clinical results using this device

have been disappointing. This study demonstrated that use of

the Unispacer in isolated medial compartment osteoarthritis is

associated with a high rate of revision surgery and provides

unpredictable relief of pain.

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Clarius et al (2010) assessed clinical and radiological results

of the UniSpacer, whether alignment correction can be

achieved by UniSpacer arthroplasty and alignment change in

the first 5 post-operative years. Antero-posterior long leg

stance radiographs of 20 legs were digitally analysed to

assess alignment change: 2 relevant angles and the deviation

of the mechanical axis of the leg were analysed before and

after surgery. Additionally, the change of the post-operative

alignment was determined at 1 and 5 years post-operatively.

Analysing the mechanical tibio-femoral angle, a significant leg

axis correction was achieved, with a mean valgus change of

4.7 +/- 1.9 degrees ; a varus change occurred in the first post

operative year, while there was no significant further change of

alignment seen 5 years after surgery. The UniSpacer corrects

mal-alignment in patients with medial gonarthrosis; however, a

likely post-operative change in alignment due to implant

adaptation to the joint must be considered before

implantation. The authors concluded that these findings show

that good clinical and functional results can be achieved after

UniSpacer arthroplasty. However, 4 of 19 knees had to be

revised to a TKA or UKA due to persistent pain, which is an

unacceptably high revision rate when looking at the alternative

treatment options of medial osteoarthritis of the knee.

Kock et al (2011) examined if an interpositional knee implant

based on magnetic resonance imaging (MRI) data can be an

alternative treatment option to the established procedures of

high tibial osteotomy and UKA. From June 2004 to May 2008,

a total of 33 patients suffering from unicompartmental knee

arthritis received a patient-specific interpositional implant (31

medial and 2 lateral) within a single-arm trial. The mean follow-

up time was 26.6 months (range of 1 to 48 months) and the

mean age of the patients was 54.5 years (range of 39 to 65

years). In addition to the clinical results the Western Ontario

and McMaster Universities Osteoarthritis index (WOMAC)

function scale and the Knee Society scores were measured. A

descriptive data analysis, a variance analysis for repeated

measurements and a determination of significance

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level were carried out. The 2 to 4 year results showed a

significant improvement in the WOMAC function scale as well

as the Knee Society scores. The knee function after 2 years

was comparable to the pre-operative situation with an

extension to flexion of 0/2/130°. The dislocation rate was 6 %

and the overall revision rate 21 %. The authors concluded that

despite acceptable functional results a significant pain relief, a

complete preservation of bone and a lower rate of dislocations

compared to the off-the-shelf Unispacer implant there were

only limited indications for the customized interpositional knee

implant with respect to the given contraindications due to the

high 2-year revision rate.

Catier et al (2011) noted that a new concept has been recently

developed for use in the treatment of isolated medial tibio

femoral osteoarthritis: the Unispacer implant. This mobile

interpositional, self-centering implant replicates the meniscal

shape. This mini-invasive device does not require bone cuts

or component fixation. The implant trajectory is guided by the

medial condyle. These investigators hypothesized that the

Unispacer knee implant enhances knee function in the

treatment of isolated tibio-femoral osteoarthritis graded 2 and

3 according to Ahlbäck radiographic evaluation scale. This

prospective study involved 17 Unispacer knee systems

implanted in 16 patients between April 2003 and March 2009

within the frame of a clinical research project. Patients were

clinically (IKS score) and radiographically evaluated during a

mean follow-up period of 40 months. A total of 9 patients (10

implants) had a IKS score greater than 160. The mean overall

knee score at re-assessment, including failures, increased

from 51 points pre-operatively to 78 points post-operatively.

The mean overall Knee Society Function score increased from

55 pre-operatively to 75/100 post-operatively. The reported

complication rate was 35 % (pain or implant instability); 1/3 of

the failures were not technique- or implant-related but rather

induced by the use of an inappropriate width in the frontal

plane. The authors concluded that good results regarding pain

relief and function are reported when using a mobile implant

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with no peripheral overhang that could be responsible for

medial capsulo-ligamentous impingement. The Unispacer

has 3 theoretical advantages: (i) no bone resection, (ii) no

implant fixation, and (iii) no polyethylene wear debris. On

the basis of its uncertain clinical results and high revision rate

(6 cases out of 17), these researchers do not recommend this

system despite the expected improvements on this range of

implants.

It has been suggested that bicompartmental knee replacement

may be indicated for individuals with osteoarthritis limited to

the medial and patello-femoral compartments.

Bicompartmental knee replacement replaces only the inside

(medial) joint and knee-cap joint (patello-femoral) joint. It does

not re-surface the outside (lateral) part of the knee and allows

for the anterior cruciate ligament (ACL) and posterior cruciate

ligament to be retained.

A systematic evidence review of TKA prepared for the

Washington State Health Care Authority (Dettori et al, 2010)

found 2 registry studies providing comparative data between

bicompartmental and standard tricompartmental knee

arthroplasty. These 2 registry studies reported low revision

rates in both the bi- and tri-compartmental groups: 3.2 % and

2.8 %, respectively, at 2 to 4 years follow-up and 1.5 % and

1.6 %, respectively, at 2 years follow-up. No significant

differences in overall revision rates between the 2 treatment

groups were reported by either study. Complications were not

reported for 2 registry studies comparing bi- and tri

compartmental TKA.

In a meta-analysis, Callahan et al (1995) summarized the

literature describing patient outcomes following

unicompartmental as well as bicompartmental knee

arthroplasties. Original studies were included if they enrolled

10 or more patients at the time of an initial knee arthroplasty

and measured patient outcomes using a global knee rating

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scale. A total of 46 studies on unicompartmental prostheses

and 18 studies on bicompartmental prostheses met these

criteria. For unicompartmental studies, the total number of

enrolled patients was 2,391, with a mean enrollment of 47

patients and a mean follow-up period of 4.6 years. The mean

patient age was 66 years; 67 % were women, 75 % had

osteoarthritis, and 16 % underwent bilateral knee arthroplasty.

The mean post-operative global rating scale score was 80.9.

The overall complication rate was 18.5 % and the revision rate

was 9.2 %. Studies published after 1987 reported better

outcomes, but also tended to enroll older patients and patients

with osteoarthritis and higher pre-operative knee rating

scores. For bicompartmental studies, the total number of

enrolled patients was 884, with a mean enrollment of 44

patients and a mean follow-up period of 3.6 years. The mean

patient age was 61 years; 79 % were women, 31 % had

osteoarthritis, and 29 % underwent a bilateral arthroplasty.

The mean post-operative global rating scale score was 78.3.

The overall complication rate was 30 % and the revision rate

was 7.2 %. Although bicompartmental studies reported lower

mean post-operative global rating scale scores, these studies

tended to enroll patients with worse pre-operative knee rating

scores. Recent improvements in patient outcomes following

UKA appear to be due, at least partially, to changes in patient

selection criteria. Patient outcomes appear to be worse for

bicompartmental arthroplasties than for other prosthetic

designs; however, patients enrolled in these studies had more

poorly functioning knees before surgery and actually had

greater absolute improvements in global knee rating scores.

Rolston et al (2007) stated that in the past, treatment of knee

osteoarthritis has been limited to UKA or TKA. Neither option

is well-suited for the active patient with mid-stage osteoarthritis

of the medial and patello-femoral compartments. Now an

alternative treatment is available that targets the diseased

area without sacrifice of normal bone or both the cruciate

ligaments. Minimally invasive surgical techniques are easily

used, which reduces tissue trauma and results in a quicker

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recovery than TKA. Bicompartmental replacement offers

decreased pain, stability through normal ligament structure,

and the retention of normal bone for patients with medial and

patello-femoral osteoarthritis.

Bi-unicompartmental knee arthroplasty refers to UKA

performed in the contralateral compartment of a knee

previously treated with a UKA.

A systematic evidence review of TKA prepared for the

Washington State Health Care Authority (Dettori et al, 2010)

reported on studies comparing bi-unicompartmental knee

arthroplasty (bi-UKA) and standard TKA. The report found 1

small retrospective cohort study comparing bi-UKA with TKA.

No difference was found in functional scores at a minimum of 4

years of follow-up, and no revisions were recorded in either

group. No cases of radiological loosening or infection were

seen in either the bi-UKA or TKA groups. Two cases (9 %) of

intra-operative fracture of the tibial spine block occurred in the

bi-UKA group but did not have any adverse effect on the

outcome at last follow-up in either case.

Confalonieri and associates (2009) carried out a matched

paired study between 2 groups: (i) bi-unicompartmental (Bi-

UKR) and (ii) TKR for the treatment of isolated

bicompartmental tibio-femoral knee arthritis with an

asymptomatic patello-femoral joint. A total of 22 patients

with bicompartmental tibio-femoral knee arthritis, who

underwent Bi-UKR were included in the study (group A). In all

the knees the arthritic changes were graded according to the

classification of Alback. All patients had an asymptomatic

patello-femoral joint. All patients had a varus deformity lower

than 8 degrees, a body-mass index lower than 34, no clinical

evidence of ACL laxity or flexion deformity and a pre-operative

range of motion of a least 110 degrees. At a minimum follow-

up of 48 months, every single patient in group A was matched

with a patient who had undergone a computer-assisted TKR

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(group B). In the Bi-UKR group, in 2 cases these researchers

registered intra-operatively the avulsion of the treated tibial

spines, requiring intra-operative internal fixation and without

adverse effects on the final outcome. Statistical analysis of the

results was performed. At a minimum follow-up of 48 months

there were no statistical significant differences in the surgical

time while the hospital stay was statistically longer in TKR

group. No statistically significant difference was observed for

the Knee Society, Functional and GIUM scores between the 2

groups. Statistically significant better WOMAC Function and

Stiffness indexes were registered for the Bi-UKR group. Total

knee replacement implants were statistically better-aligned

with all the implants positioned within 4 degrees of an ideal

hip-knee-ankle angle of 180 degrees. The authors concluded

that the findings of this 48-month follow-up study suggested

that Bi-UKR is a viable option for bicompartmental tibio

femoral arthritis at least as well as TKR but maintaining a

higher level of function.

Available evidence does not provide strong conclusions

regarding optimal patient selection criteria as well as improved

patient outcomes with bicompartmental knee arthroplasty or bi-

UKA. Currently, there is no clinical practice guideline on either

of these procedures. In this regard, the American Academy of

Orthopaedic Surgeons' clinical guideline on osteoarthritis of

the knee (2003) did not discuss the use of bicompartmental

knee arthroplasty or bi-UKA as methods of treatment for

osteoarthritis of the knee. Furthermore, the Osteoarthritis

Research International's recommendations for the

management of hip and knee osteoarthritis (Zhang et al, 2008)

did not mention the use of bicompartmental or bi-UKA.

Available scientific evidence is insufficient to support the use

of bicompartmental knee arthroplasty and bi-UKA as

alternatives for TKR. At present, there is inadequate evidence

demonstrating improved patient outcomes from either of these

methods. Well-designed studies are needed to ascertain the

safety and effectiveness of these approaches.

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Unicompartmental knee arthroplasty is a popular treatment for

unicompartmental knee arthritis. Roche and associates (2009)

stated that a recently developed computer-assisted

surgery/robotic system has the potential to improve alignment

in and results of UKA. Pearle et al (2009) stated that

indications for UKA include mechanical axis of less than 10

degrees varus and less than 5 degrees valgus, intact ACL,

and absence of femoro-tibial subluxation. Appropriately

selected patients can expect UKA to last at least 10 years.

Failures in UKA are not common and involve technical errors

that are thought to be corrected with use of newly developed

robotic technology such as the MAKO robotic arm system

(MAKOplasty). The surgeon using this technology may be

able to arrive at a set target, enhance surgical precision, and

avoid outliers. However, whether improved precision will result

in improved long-term clinical outcome remains a subject of

research.

Sinha (2009) reported that the early outcomes of UKA

performed with a robotically assisted navigation system have

been favorable. The surgical technique enhances accuracy of

bone preparation and component positioning. Technical errors

of the system have been minimal. The surgeon's learning

curve is not adversely affected. Early patient outcomes are

excellent and complications minimal. The authors noted that

further follow-up studies will help to determine whether these

early outcomes are sustained over time.

Lonner (2009) noted that modular bicompartmental

arthroplasty is an emerging knee-resurfacing approach that

provides a conservative alternative to TKA. Isolated

bicompartmental arthritis involving the medial or lateral and

patello-femoral compartments, but with no significant deformity

or bone deficiency, preserved motion, and intact cruciate

ligaments, can be effectively managed with this treatment

method. For the many young and active patients with isolated

bicompartmental arthritis, given the potential durability of the

procedure and the prosthesis, it is appropriate to use an

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approach that is more conservative than TKA. Robotic arm

assistance for modular bicompartmental arthroplasty optimizes

component position and alignment, which may improve system

performance and long-term durability. In addition, a

percentage of patients who undergo isolated

unicompartmental or patello-femoral arthroplasty may later

develop progressive arthritis in an unresurfaced compartment.

Their cases may be effectively managed with a staged

modular approach to resurfacing the degenerating

compartment, but additional study is needed.

In a pilot study, Lonner et al (2010) compared the post

operative radiographical alignment of the tibial component with

the pre-operatively planned position in 31 knees in 31

consecutive patients undergoing UKA using robotic arm-

assisted bone preparation and in 27 consecutive patients who

underwent unilateral UKA using conventional manual

instrumentation to determine the error of bone preparation and

variance with each technique. Radiographically, the root

mean square error of the posterior tibial slope was 3.1 degrees

when using manual techniques compared with 1.9 degrees

when using robotic arm assistance for bone preparation. In

addition, the variance using manual instruments was 2.6 times

greater than the robotically guided procedures. In the coronal

plane, the average error was 2.7 degrees +/- 2.1 degrees

more varus of the tibial component relative to the mechanical

axis of the tibia using manual instruments compared with 0.2

degrees +/- 1.8 degrees with robotic technology, and the

varus/valgus root mean square error was 3.4 degrees

manually compared with 1.8 degrees robotically. The authors

concluded that further study will be necessary to determine

whether a reduction in alignment errors of these magnitudes

will ultimately influence implant function or survival.

Paratte and associates (2010) stated that recent literature

suggests patients achieve substantial short-term functional

improvement after combined bicompartmental implants but

longer-term durability has not been documented. These

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investigators examined if (i) bicompartmental arthroplasty

(either combined medial unicompartmental UKA and

femoro-patellar arthroplasty (PFA) or medial UKA/PFA, or

combined medial and lateral UKA or bicompartmental UKA)

reliably improved Knee Society pain and function scores; (ii)

bicompartmental arthroplasty was durable (survivorship,

radiographical loosening, or symptomatic disease

progression); (iii) durable alignment can be achieved; and

(iv) the arthritis would progress in the unresurfaced

compartment. These researchers retrospectively reviewed 84

patients (100 knees) with bicompartmental UKA and 71

patients (77 knees) with medial UKA/PFA. Clinical and

radiographical evaluations were performed at a minimum follow-

up of 5 years (mean of 12 years; range of 5 to 23 years).

Bicompartmental arthroplasty reliably alleviated pain and

improved function. Prosthesis survivorship at 17 years was 78

% in the bicompartmental UKA group and 54 % in the medial

UKA/PFA group. The high revision rate, compared with TKA,

may be related to several factors such as implant design, patient

selection, crude or absent instrumentation, or component mal

alignment, which can all contribute to the relatively high failure

rate in this series.

Palumbo et al (2011) evaluated the effectiveness of a novel

bicompartmental knee arthroplasty (BKA) prosthesis for the

treatment of degenerative disease affecting the medial and

patello-femoral compartments. The study included 36 knees

in 32 patients with a mean follow-up of 21 months. The mean

Knee Society functional survey and Western Ontario McMaster

Osteoarthritic Index Survey scores were 65.4 and 75.8,

respectively. Thirty-one percent of patients were unsatisfied

with the surgery, and 53 % stated that they would not repeat

the surgery. These researchers reported an overall survival

rate of 86 % with 1 catastrophically failed tibial baseplate. The

authors concluded that this prosthesis provides inconsistent

pain relief and unacceptable functional results for

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bicompartmental arthritis. The short-term survival of this

prosthesis was unacceptably low, and therefore, these

investigators no longer implant it at their institution.

Morrison and colleagues (2011) compared functional

outcomes of BKA and TKA in patients with osteoarthritis (OA)

of the patello-femoral and medial compartments. Eligibility

criteria included bicompartmental OA with less than grade 2

OA in the lateral compartment and intact cruciate ligaments. A

total fo 56 patients met eligibility criteria (21 BKA, 33 TKA).

Enrolled participants completed Short-Form 12 and Western

Ontario and McMaster Universities Osteoarthritis Index

assessments at baseline and post-operatively at 3 months, 1

year, and 2 years. In the early post-operative period, the BKA

cohort had significantly less pain (p = 0.020) and better

physical function (p = 0.015). These trends did not continue

past 3 months. When adjusting for age, sex, body mass index,

and pre-operative status, only 3-month Western Ontario and

McMaster Universities Osteoarthritis Index stiffness scores

significantly differed between cohorts (p = 0.048). Despite less

early stiffness in the BKA cohort, a significantly higher BKA

complication rate (p = 0.045) has led these investigators to

recommend TKA for patients with this pattern of OA.

Lyons et al (2012) examined if TKA would demonstrate (i)

better change in clinical outcome scores from pre-operative

to post-operative states and (ii) better survivorship than

UKA. These researchers evaluated 4,087 patients with 5,606

TKAs and 179 patients with 279 UKAs performed between

1978 and 2009. Patients with TKA were older and heavier

than patients with UKA (mean age of 68 versus 66 years;

mean BMI of 32 versus 29). They compared pre-operative,

latest post-operative, and change in Knee Society Clinical

Rating System (KSCRS), SF-12, and WOMAC scores.

Minimum follow-up was 2 years (UKA: mean of 7 years; range

of 2.0 to 23 years; TKA: mean of 6.5 years; range of 2.0 to 33

years). Pre-operative outcome measure scores (WOMAC, SF-

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12, KSCRS) were higher in the UKA group. Patients with UKA

had higher post-operative KSCRS and SF-12 mental scores.

Changes in score for all WOMAC domains were similar

between groups. Total KSCRS changes in score were similar

between groups, although patients with TKA had higher knee

scores (49 versus 43) but lower function scores than UKA (21

versus 26). Cumulative revision rate was higher for UKA than

for TKA (13 % versus 7 %). Kaplan-Meier survivorship at 5

and 10 years was 95 % and 90 %, respectively, for UKA and

98 % and 95 %, respectively, for TKA. The authors concluded

tht while patients with UKA had higher pre- and post-operative

scores than patients with TKA, the changes in scores were

similar in both groups and survival appeared higher in patients

with TKA.

Tria (2013) stated that replacement of the patella-femoral and

medial tibio-femoral joints has been performed since the

1980s. Bicompartmental replacement was modified. Two

different designs were developed: one custom implant and one

with multiple pre-determined sizes. The surgical technique

and instruments are unique and training is helpful. There are

no clinical reports for the custom design as of yet. The

standard implant has several reports in the literature with only

fair to good results and has subsequently been withdrawn from

the market. The author concluded that bicompartmental

arthroplasty remains a questionable area of knee surgery.

Chung et al (2013) noted that bicompartmental knee

arthroplasty features bone and ligament sparing as

unicompartmental knee arthroplasty and is presumably better

in the recovery of muscle strength and function compared to

TKA though not previously reported in the literature. These

researchers compared isokinetic knee muscle strength and

physical performance in patients who underwent either

bicompartmental knee arthroplasty or TKA. Each of 24

patients (31 knees) was prospectively examined pre

operatively, at 6 and 12 months after each surgery. Isokinetic

knee extensor and flexor strength as well as position sense

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were measured using the Biodex system. Timed up and go

test, stair climbing test, and the 6-min walk test were used to

assess physical performance. The results of each group were

also compared with those from the corresponding healthy

control, respectively. Demography showed significant

difference in the mean age between bicompartment (54.8 ± 5.6

years) and TKA groups (65.7 ± 6.7 years). Comparing

between the 2 groups, knee extensor and flexor torque,

hamstring/Quadriceps ratio, position sense, and physical

performance were not significantly different pre-operatively, at

6 and 12 months after surgery. In intra-group analysis, muscle

strength and position sense at each time-point were not

different in both groups. In physical performance, both groups

resulted in improvement in the 6-min walk test, and only TKA

group showed enhancement in stair climbing test. The

authors concluded that although theoretically plausible,

bicompartmental knee arthroplasty was not superior in knee

muscle strength and physical performance at 1 year compared

with TKA.

Thienpont and Price (2013) stated that studies have shown

that after TKA neither normal biomechanics nor function is

obtained. Selective resurfacing of diseased compartments

could be a solution. These investigators presented a narrative

review of the available literature on bicompartmental

arthroplasty. A literature review of all peer-reviewed published

articles on bicompartmental arthroplasty of the knee was

performed. Bicompartmental arthroplasty is by definition the

replacement of the tibio-femoral and the patella-femoral joint.

It can be performed with a modular unlinked or a monolithic

femoral component. Bicompartmental arthroplasty performed

with modular components obtained good to excellent results at

± 10 years follow-up. Function and biomechanics are superior

to TKA. Modern monolithic femoral components were reported

to give early failure and high revision rates and should be

avoided. The authors concluded that modular

bicompartmental arthroplasty is an excellent alternative to treat

bicompartmental arthritis of the knee leading to good

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functional results and superior biomechanics in well-selected

patients. However, they stated that caution is needed since

only a few peer-reviewed articles with small series and old

implant designs are available on this type of arthritis

treatment. Survivorship in these studies is inferior to TKA.

Furthermore, the Work Loss Data Institute’s guideline on

“Knee & leg (acute & chronic)” (2013) listed bicompartmental

knee replacement as one of the interventions that were

considered, but are not recommended.

Luring et al (2011) stated that isolated OA of the

patellofemoral joint occurs in 9 % of patients over 40 years of

age and women are more often affected. Options of treatment

are varied and not sufficiently justified by the literature. These

investigators performed a literature research with keywords in

the field of femoropatellar osteoarthritis in the relevant

databases. Studies were categorized into different treatment

options and analyzed. There are almost no level I studies

comparing the different treatment options. In the literature

there are indications that relief of pain can be achieved by

conservative treatment, arthroscopic surgery, cartilage

conserving surgery and isolated arthroplasty. The authors

concluded that in view of the fact that there are almost no

prospective randomized controlled trials (RCTs), none of the

options for treatment can be highly recommended. There is

still no gold standard for the treatment of isolated

patellofemoral osteoarthritis.

An assessment by the Canadian Agency for Drugs and

Technologies in Health (CADTH, 2013) summarized the

available evidence for patellofemoral knee implants: "Bietzel et

al. reported outcomes of patello-femoral knee implants in

terms of pain and knee functions. The study compared the

scores of patients for these outcomes at baseline and after two

years from the implant surgery. The exact scores were not

reported; however, the report showed that the scores for pain

and knee functions (Lyshlom score and WOMAC scores) were

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statistically significantly improved from baseline. The results

for maximum reflection showed no statistical difference. Starks

et al. reported the scores of knee functions after two years

from the implantation; however, these scores were not

compared to their baseline counterpart values; therefore, their

significance could not be interpreted".

Davies (2013) noted that unicompartmental patellofemoral

arthroplasties are uncommon however numbers are increasing

and there are a variety of new prostheses available. The

Femoro-Patella Vialla (FPV, Wright Medical UK) device was

the second most commonly used patellofemoral

unicompartmental prosthesis in the 2012 British National Joint

Register. There are however no published outcomes data for

this device. In this study, a total of 52 consecutive cases were

studied prospectively using Oxford Knee Score and American

Knee Society Scores pre-operatively and at follow-up to a

minimum of 2 years. Overall Oxford Knee Scores improved

from 30 points pre-operatively (36.6 %) to 19 points (60 %) at 1

year. American Knee Society Knee scores improved from 51

points pre-operatively to 81 points at 1-year. Function scores

improved from 42 points pre-operatively to 70 points at 1-year.

Moreover, 13 (25 %) patients had an excellent outcome with

pain abolished and near normal knee function; 11 (21 %)

patients gained very little improvement and scored their knees

similar or worse to their pre-operative state. There were no

infective or thromboembolic complications. Seven cases have

been revised to a total knee replacement for on- going pain in 6

cases and progression of arthritis in the tibio- femoral

compartments in 1 case. The patellar button was found to be

very poorly fixed in all cases that were revised.

The authors concluded that early results with the FPV

prosthesis demonstrated that successful outcomes can be

achieved; however the results were unpredictable and a

significant minority of patients had on-going symptoms that

they found unacceptable. They stated that the early revision

rate was high in this series.

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Al-Hadithy et al (2014) stated that isolated patellofemoral

joint OA affects approximately 10 % of patients aged over 40

years and treatment remains controversial. The FPV

patellofemoral joint replacement has been shown to restore

functional kinematics of the knee close to normal. Despite its

increasing popularity in recent years, there are no studies

evaluating the mid-term results with an objective scoring

assessment. These investigators reported the clinical and

radiological outcomes of FPV patellofemoral joint replacement

in patients with isolated patellofemoral arthritis. Between 2006

and 2012, these researchers performed 53 consecutive FPV

patellofemoral arthroplasties in 41 patients with isolated

patellofemoral joint osteoarthritis. The mean follow-up was 3

years. Mean Oxford Knee Scores improved from 19.7 to 37.7

at latest follow-up. The progression of tibiofemoral

osteoarthritis was seen 12 % of knees. Two knees required

revision to TKR at 7 months post-operatively, which these

researchers attributed to poor patient selection. There were

no cases of mal-tracking patellae, and no lateral releases were

performed. The authors concluded that these findings

suggested the FPV patellofemoral prosthesis provided good

pain relief and survivorship with no significant mal-tracking

patellae. This was a relatively small study (n = 41 patients)

with mid-term results. These findings need to be validated by

well-designed studies with larger sample size and long-term

follow-up.

King et al (2015) reported the incidence of patellar fracture

after PFA and determined associated factors as well as

outcomes of patients with and without this complication. A

total of 77 knees in 59 patients with minimum 2-year follow-up

were included; 7 (9.1 %) patients experienced a patellar

fracture at a mean of 34 (range of 16 to 64) months post

operatively. All were treated non-operatively. Lower BMI (p =

0.03), change in patellar thickness (p < 0.001), amount of bone

resected (p = 0.001), and larger trochlear component size (p =

0.01) were associated with a greater incidence of fracture.

Fewer fractures occurred when the post-operative patellar

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height exceeded the pre-operatively measured height. No

statistically significant differences were found in outcome

scores between groups at mean four-year follow-up. A fair

amount of fractures at mid-term; not sure if the incidence

would increase at long-term.

Parratte et al (2015) noted that partial knee arthroplasty (PKA),

either medial or lateral UKA or PFA are a good option in

suitable patients and have the advantages of reduced

operative trauma, preservation of both cruciate ligaments and

bone stock, and restoration of normal kinematics within the

knee joint. However, questions remain concerning long-term

survival. These researchers presented the long-term results of

medial and lateral UKA, PFA and combined compartmental

arthroplasty for multi-compartmental disease. Medium- and

long-term studies suggested reasonable outcomes at 10 years

with survival greater than 95 % in UKA performed for medial

OA or osteonecrosis, and similarly for lateral UKA, particularly

when fixed-bearing implants were used. Disappointing long

term outcomes have been observed with the 1st generation of

patella-femoral implants, as well as early Bi-Uni (i.e., combined

medial and lateral UKA) or bicompartmental (combined UKA

and PFA) implants due to design and fixation issues. The

authors concluded that promising short- and med-term results

with the newer generations of PFAs and bicompartmental

arthroplasties will require long-term confirmation.

Joseph, et al. (2020) reported on a pragmatic, single-center,

double-blind randomized clinical trial that was conducted in a

UK National Health Service (NHS) teaching hospital to

evaluate whether there is a difference in functional knee

scores, quality-of-life outcome assessments, and

complications at one-year after intervention between total knee

arthroplasty (TKA) and patellofemoral arthroplasty (PFA) in

patients with severe isolated patellofemoral arthritis.

The parallel, two-arm, superiority trial was powered at 80%,

and involved 64 patients with severe isolated patellofemoral

arthritis. The primary outcome measure was the functional

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section of the Western Ontario and McMaster Universities

Osteoarthritis Index (WOMAC) score at 12 months. Secondary

outcomes were the full 24-item WOMAC, Oxford Knee Score

(OKS), American Knee Society Score (AKSS), EuroQol five

dimension (EQ-5D) quality-of-life score, the University of

California, Los Angeles (UCLA) Physical Activity Rating Scale,

and complication rates collected at three, six, and 12 months.

For longer-term follow-up, OKS, EQ-5D, and self-reported

satisfaction score were collected at 24 and 60 months. Among

64 patients who were randomized, five patients did not receive

the allocated intervention, three withdrew, and one declined

the intervention. There were no statistically significant

differences in the patients' WOMAC function score at 12

months (adjusted mean difference, -1.2 (95% confidence

interval -9.19 to 6.80); p = 0.765). There were no clinically

significant differences in the secondary outcomes.

Complication rates were comparable (superficial surgical site

infections, four in the PFA group versus five in the TKA group).

There were no statistically significant differences in the

patients' OKS score at 24 and 60 months or self-reported

satisfaction score or pain-free years. The investigators

concluded that, among patients with severe isolated

patellofemoral arthritis, this study found similar functional

outcome at 12 months and mid-term in the use of PFA

compared with TKA.

Odgaard, et al. (2018) compared the outcome of

patellofemoral arthroplasty (PFA) with total knee arthroplasty

(TKA) in a blinded randomized controlled trial. Patients were

eligible if they had debilitating symptoms and isolated

patellofemoral disease. One hundred patients were included

from 2007 to 2014 and were randomized to PFA or TKA

(blinded for the first year; blinded to patient, therapists, primary

care physicians, etc; quasiblinded to assessor). Patients were

seen for four clinical followups and completed six sets of

questionnaires during the first 2 postoperative years. SF-36

bodily pain was the primary outcome. Other outcomes were

range of movement, PROs (SF-36, Oxford Knee Score [OKS],

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Knee injury and Osteoarthritis Outcome Score [KOOS]) as well

as complications and revisions. Four percent (two of 50) of

patients died within the first 2 years in the PFA group (none in

the TKA group), and 2% (one of 50) became ill and declined

further participation after 1 year in the PFA group (none in the

TKA group). The mean age at inclusion was 64 years (SD 8.9),

and 77% (77 of 100) were women. The area under the curve

(AUC) up to 2 years for SF-36 bodily pain of patients

undergoing PFA and those undergoing TKA was 9.2 (SD 4.3)

and 6.5 (SD 4.5) months, respectively (p = 0.008). The SF-36

physical functioning, KOOS symptoms, and OKS also showed

a better AUC up to 2 years for PFA compared with TKA (6.6

[SD 4.8] versus 4.2 [SD 4.3] months, p = 0.028; 5.6 [SD 4.1]

versus 2.8 [SD 4.5] months, p = 0.006; 7.5 [SD 2.7] versus 5.0

[SD 3.6] months, p = 0.001; respectively). The SF-36 bodily

pain improvement at 6 months for patients undergoing PFA

and those undergoing TKA was 38 (SD 24) and 27 (SD 23),

respectively (p = 0.041), and at 2 years, the improvement was

39 (SD 24) and 33 (SD 22), respectively (p = 0.199). The

KOOS symptoms improvement at 6 months for patients

undergoing PFA and those undergoing TKA was 24 (SD 20)

and 7 (SD 21), respectively (p < 0.001), and at 2 years, the

improvement was 27 (SD 19) and 17 (SD 21), respectively (p

= 0.023). Improvements from baseline for KOOS pain, SF-36

physical functioning, and OKS also differed in favor of PFA at

6 months, whereas only KOOS symptoms showed a difference

between the groups at 2 years. No patient-reported outcome

(PRO) dimension showed a difference in favor of TKA. At 4

months, 1 year, and 2 years, the range of motion (ROM)

change from baseline for patients undergoing PFA and those

undergoing TKA was (-7° [SD 13°] versus -18° [SD 14°], p <

0.001; -4° [SD 15°] versus -11° [SD 12°], p = 0.011; and -3°

[SD 12°] versus -10° [SD 12°], p = 0.010). There was no

difference in the number of complications. During the first 2

postoperative years, there were two revisions in patients

undergoing PFA (one to a new PFA and one to a TKA). The

investigators concluded that patients undergoing PFA obtain a

better overall knee-specific quality of life than patients

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undergoing TKA throughout the first 2 years after operation for

isolated patellofemoral osteoarthritis. At 2 years, only KOOS

function differs between patients undergoing PFA and those

undergoing TKA, whereas other PRO dimensions do not show

a difference between groups. The observations can be

explained by patients undergoing PFA recovering faster than

patients undergoing TKA and the functional outcome being

better for patients undergoing PFA up to 9 months. Patients

undergoing PFA regain their preoperative ROM, whereas

patients undergoing TKA at 2 years have lost 10° of ROM. The

investigators stated that they found no differences in

complications.

Bunyoz, et al. (2019) reported on a systematic review to

compare outcomes of second-generation PFA and TKA by

assessment of patient-reported outcome measures

(PROMs). A systematic search was made in PubMed,

Medline, Embase, Cinahl, Web of Science, Cochrane Library

and MeSH to identify studies using second-generation PFA

implants or TKA for treatment of PFOA. Only studies using

The American Knee Society (AKSS), The Oxford Knee Score

(OKS) or The Western Ontario and McMaster Universities

Osteoarthritis Index (WOMAC) to report on PROMs were

included. The postoperative weighted mean AKSS knee

scores were 88.6 in the second-generation PFA group and

91.8 in the TKA group. The postoperative weighted mean

AKSS function score was 79.5 in the second-generation PFA

group and 86.4 in the TKA group. There was no significant

difference in the mean AKSS knee or function scores between

the second-generation PFA group and the TKA group. The

postoperative weighted mean OKS score was 36.7 and the

postoperative weighted mean WOMAC score was 24.4. The

revision rate was higher in the second-generation PFA group

(113 revisions [8.4%]) than in the TKA group (3 revisions

[1.3%]). Progression of OA was most commonly noted as the

reason for revision of PFA, and it was noted in 60 cases

[53.1%]; this was followed by pain in 33 cases [29.2%]. The

authors concluded that excellent postoperative weighted mean

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AKSS knee scores were found in both the second-generation

PFA group and in the TKA group, suggesting that both surgical

options can result in a satisfying patient-reported outcome.

Higher revision rates in the second-generation PFA studies

may in part be due to challenges related to patient selection.

Based on evaluation of PROMs, the use of second-generation

PFA seems to be an equal option to TKA for treatment of

isolated PFOA in appropriately selected patients.

Dudhniwala et al (2016) evaluated the early functional

outcome and survivorship of a bicompartmental knee

arthroplasty implant (Journey-Deuce) in a cohort of patients

with combined medial and patella-femoral degenerative OA. A

total of 15 patients with a mean age of 57 years were followed-

up prospectively and evaluated with clinical examination,

Oxford knee score and radiology imaging. Poor pain scores,

concerns about the tibial fixation, early aseptic loosening of the

tibial component and a revision rate of 60 % at a minimum

follow-up of 54 months were reported. Implantation of this

prosthesis was stopped at the authors’ institution well before

the first revision due to an unfavorable early clinical response.

This was further endorsed by an unacceptable revision rate.

The authors concluded that the outcome of the Journey-

Deuce bicompartmental knee replacement was considerably

worse than the published outcome of TKR.

Sabatini et al (2016) stated that TKA is the most worldwide

practiced surgery for knee OA and its effectiveness is mightily

described by literature. Concerns about the invasiveness of

TKA let the introduction of segmental resurfacing of the joint

for younger patients with localized OA. Bone stock sparing

and ligaments preservation are the essence of both UKA and

BKA. Advantages related to BKA are the respect of knee

biomechanics, lower complications rates, shorter hospital stay,

faster rehabilitation. Moreover, in case of failure of the 1st

implant the conversion to TKA is undemanding and can be

compared to a standard prosthesis. The authors concluded

that their experience suggested that BKA is a reliable

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technique in selected cases and especially younger people

with higher functional requests can favorably profit from it.

They stated that although these results are encouraging,

there is still a need for further prospective, randomized, long

term studies to evaluate BKA indications and outcomes.

Staged Bicompartmental Knee Arthroplasty

Pandit and colleagues (2017) noted that lateral progression of

arthritis following medial UKA, although infrequent, is still the

most common reason for revision surgery. Treatment options

normally include conversion to TKA. An alternative strategy

for some patients may be addition of a lateral UKA. In an

observational study, these investigators reported the first

results of staged bi-compartmental UKA (Bi-UKA) strategy.

They retrospectively selected from their UKA database

patients who underwent a lateral UKA to treat a symptomatic

lateral OA progression after a medial UKA. The analysis

included a clinical and radiological assessment of each

patient. A total of 25 patients for a total of 27 knees of staged Bi-

UKA were performed in a single-center. The mean time interval

between primary medial UKA and the subsequent lateral UKA

was 8.1 years (SD ± 4.6 years). The mean age at the time of the

Bi-UKA was 77.1 years (SD ± 6.5 years). The median hospital

stay was 3 (range of 2 to 9 days) days, and the mean follow-up

after Bi-UKA was 4 years (SD ± 1.9 years). The functional

scores showed a significant improvement as compared to the

pre-operative status (paired-t test, p = 0.003). There were no

radiological evidences of failure. None of the patients needed

blood transfusion, and there was no significant complications

related to the surgical procedure without further surgeries or

revisions at final follow-up. The authors concluded that these

findings suggested that addition of a lateral UKA for arthritis

progression following medial UKA is a good option in

appropriately selected patients. Level of Evidence = IV. The

main drawbacks of this study were its

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small sample size (n = 25), observational design (thus the lack

of a control group), and medium term follow-up (mean of 4

years).

Customized Total Knee Implant

Beal et al (2016) stated that modern total knee arthroplasty

(TKA) is effective at treating the pain and disability associated

with osteoarthritis. The number of total knee replacements

done in the USA continues to increase. Despite the great care

taken during all of these procedures, some patients remain

dissatisfied with their outcome. While this dissatisfaction is

likely multi-factorial, malalignment of the prosthetic

components is a major cause of post-operative complications.

A neutral mechanical axis plus or minus 3° is felt to have a

positive impact on the survivorship of the prosthesis.

Conventional instrumentation has been shown to have a

significant number of total knee replacements (TKRs) that lie

well outside a neutral coronal alignment. With that in mind,

significant effort has been placed into the development of

technology to improve the overall alignment of the prosthesis .

In order to reduce the number of outliers, several companies

have developed cost-effective systems to aid the surgeon in

achieving a more predictably aligned prosthesis in all 3

planes. These researchers reviewed the literature that is

available regarding several of these tools to examine if

navigation or custom guides improve outcomes in TKA. The

authors stated that the review supported that while both

navigation and custom implants guides appeared to be a cos-

effective way to achieve a predictable mechanical alignment of

a total knee prosthesis therefore reducing the number of

outliers, the cost may be increased operative times with no

perceived difference in patient satisfaction with navigation

custom guides. They concluded that while navigation and

customized implants have found recent interest in the knee

arthroplasty marketplace, in a broad sense and in their current

forms, these technologies have yet to reach their full potential

in improving outcomes and patient experience. These

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researchers stated that while navigation and customized

implants have found recent interest in the knee arthroplasty

marketplace, in a broad sense and in their current forms, these

technologies have yet to reach their full potential in improving

outcomes and patient experience.

Culler et al (2017) compared selected hospital outcomes

between patients undergoing TKA using either a customized

individually made (CIM) implant or a standard off-the-shelf

(OTS) implant. A retrospective review was conducted on 248

consecutive TKA patients treated in a single institution, by the

same surgeon. Patients received either CIM (n = 126) or OTS

(n = 122) implants. Study data were collected from patients'

medical record or the hospital's administrative billing record.

Standard statistical methods tested for differences in selected

outcome measures between the 2 study arms. Compared with

the OTS implant study arm, the CIM implant study arm showed

significantly lower transfusion rates (2.4 % versus 11.6 %; p =

0.005); a lower adverse event (AEs) rate at both discharge

(CIM 3.3 % versus OTS 14.1 %; p = 0.003) and 90 days after

discharge (CIM 8.1 % versus OTS 18.2 %; p = 0.023); and a

smaller percentage of patients were discharged to a

rehabilitation or other acute care facility (4.8 % versus 16.4 %;

p = 0.003). Total average real hospital cost for the TKA

hospitalization between the 2 groups were nearly identical

(CIM $16,192 versus OTS $16,240; p = 0.913). Finally, the risk-

adjusted per patient total cost of care showed a net savings of

$913.87 (p = 0.240) per patient for the CIM-TKA group, for

bundle of care including the pre-operative computed

tomography scan, TKA hospitalization, and discharge

disposition. The authors concluded that patients treated with a

CIM implant had significantly lower transfusion rates and lower

AEs rates than patients treated with OTS implants. Patients

treated with a CIM implant showed a trend toward a shorter

length of stay (LOS) and a better discharge disposition than

patients in the OTS arm. These improved outcomes for the

CIM group were achieved without an increase in hospital

costs. They stated that future studies are needed to examine

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the potential hospital savings associated with lower inventory

management and sterilization cost-savings with the single

package CIM implant.

The authors stated that there were several limitations to this

analysis that warrant discussion. First, this analysis used a

retrospective study at a single institution with a single

surgeon. Care should be taken when extrapolating clinical

outcome to other providers. However, it should be pointed out

that the bias of the retrospective study was diminished due to

the consecutive nature of patient enrollment and consistent

patient management between both study arms. In addition,

some of the clinical outcomes in the CIM study arm may reflect

a learning curve associated with using a new implant device

and outcomes, in particular, operation time may reflect the

surgeons learning to use the device. A further limitation was

that the study population (248 hospitalizations) limited the

ability to reach statistical significance for some outcome

measures. Nevertheless, nearly all the observed trends in

outcomes would have reached significance with more study

patients and the same observed variance in the study. A third

limitation was that hospital costs were estimated from billed

charges. However, this was a well-established approach to

estimate costs, and it was unlikely that the approach used to

estimate cost would consistently over-estimate or under

estimate the cost of treating patients in either study group.

Finally, increased focus on discharge planning over the study

period may explain some of the observed differences in the

proportion of patients discharged to home or home health care

in the CIM study arm. However, this limitation was migrated

by the fact that all patients were treated and discharged by the

same surgeon.

Li et al (2017) noted that TKR has been performed for patients

with end-stage knee joint arthritis to relieve pain and gain

functions. Most knee replacement patients can gain

satisfactory knee functions; however, the range of motion of

the implanted knee is variable. There are many designs of

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TKR implants; it has been suggested by some researchers

that customized implants could offer a better option for

patients. Currently, the 3D knee model of a patient can be

created from magnetic resonance imaging (MRI) or computed

tomography (CT) data using image processing techniques.

The knee models can be used for PSI design, biomechanical

analysis, and creating bone cutting guide blocks. Researchers

have developed patient-specific musculoskeletal lower limb

model with TKR, and the models can be used to predict

muscle forces, joint forces on knee condyles, and wear of tibial

polyethylene insert. These available techniques make it

feasible to create customized implants for individual patients.

The authors concluded that customized TKR implant has the

potential to greatly improve knee kinematics and patient knee

functions compared to off-the-shelf TKR implant; however,

further studies are need to be carried out to make the

customized TKR implant available for patients.

Customized Unicompartmental Knee Arthroplasty

Fitz (2009) described the surgical technique with a patient-

specific resurfacing uni-compartmental knee arthroplasty

(UKA). The patient-specific implant is currently designed on

the basis of data from pre-operative computed tomography

(CT). The implant is provided with a set of patient-specific,

disposable cutting jigs. Biomechanical and anatomic axes are

factored into jigs from a scan obtained through the hip, knee,

and ankle, effectively achieving pre-navigation of the cut

planes without the need for a navigation system. The surgical

technique is reduced to 5 simple, reproducible steps. After

removing the articular cartilage, the knee is balanced to

determine the correct amount of tibial resection; this is

followed by femoral preparation, verification of balancing and

tibial preparation, and trial and cementing of the implant. The

introduction of personalized three-dimensional (3-D) image-

derived resurfacing implants, as well as personalized single-

use instrumentation, has the potential to change the common

surgical practice of uni-compartmental knee arthroplasty.

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Patient-specific resurfacing implants enable a femoral bone-

preserving approach and enhance cortical bone support on the

tibia, overcoming critical design limitations of commercial off-

the-shelf implants. The author concluded that patient-specific

resurfacing implants can restore normal anatomy, the position

of the joint line, and normal joint function, with the potential to

result in more normal knee kinematics.

Mahoney and Kinsey (2010) stated that recently, much

attention has been directed to femoral component overhang in

total knee arthroplasty (TKA). These researchers described

the prevalence of femoral component overhang among men

and women after TKA, to identify risk factors for overhang, and

to examine if overhang was associated with post-operative

knee pain or decreased range of motion (ROM). Femoral

component overhang was measured intra-operatively during

437 implantations of the same type of TKA prosthesis. The

overhang of metal beyond the bone cut edge was measured in

millimeters at the mid-point of 10 zones after permanent

fixation of the implant. Factors predictive of overhanging fit

were identified, and the effect of overhang on post-operative

pain and flexion was examined. Overhang of greater than or

equal to 3 mm occurred in at least 1 zone among 40 % (71) of

176 knees in men and 68 % (177) of 261 knees in women,

most frequently in lateral zones 2 (anterior-distal) and 3

(distal). Female sex, shorter height, and larger femoral

component size were highly predictive of greater overhang in

multivariate models. Femoral component overhang of greater

than or equal to 3 mm in at least 1 zone was associated with

an almost 2-fold increased risk of knee pain more severe than

occasional or mild at 2 years after surgery (odds ratio [OR],

1.9; 95 % confidence interval [CI]: 1.1 to 3.3). The authors

concluded that in this series, overhang of the femoral

component was highly prevalent, occurring more often and

with greater severity in women, and the prevalence and

magnitude of overhang increased with larger femoral

component sizes among both sexes. Femoral component

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overhang of greater than or equal to 3 mm approximately

doubled the odds of clinically important knee pain 2 years after

TKA.

The authors stated that the limitations of this study included its

retrospective design, restriction to a single device and surgical

technique, and lack of formally validated, more discriminating

outcomes instruments. It was not known how closely the

prevalence of overhang that was observed approximated that

of the general population of all patients with TKAs; however,

the distal aspect ratio of the femoral component used in this

study was similar to that of several other widely used designs.

Statistical models and attributable risk calculations were by

nature theoretical and have limitations; it is not known how

closely these findings and observations represented the status

of the general population, and evaluation of clinical importance

was ultimately a subjective process.

Koeck et al (2011) noted that implant positioning and knee

alignment are 2 primary goals of successful UKA. This

prospective study outlined the radiographic results following 32

patient-specific uni-compartmental medial resurfacing knee

arthroplasties. By means of standardized pre- and post

operative radiographs of the knee in strictly antero-posterior

(AP) and lateral view, AP weight bearing long leg images as

well as pre-operative CT-based planning drawings an analysis

of implant positioning and leg axis correction was performed.

The mean pre-operative coronal femoro-tibial angle was

corrected from 7° to 1° (p < 0.001). The pre-operative medial

proximal tibial angle of 87° was corrected to 89° (p < 0.001).

The pre-operative tibial slope of 5° could be maintained. The

extent of the dorsal femoral cut was equivalent to the desired

value of 5 mm given by the CT-based planning guide. The

mean accuracy of the tibial component fit was 0 mm in AP and

+1 mm in medio-lateral projection. The authors concluded that

patient-specific fixed bearing UKA could restore leg axis

reliably, obtain a medial proximal tibial angle of 90°, avoid an

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implant mal-positioning and ensure maximal tibial coverage.

This was a relatively small study (n = 32); the duration of

follow-up was unclear.

Sinha (2012) stated that the efficiency in surgical procedures

saves time and money and can decrease medical

complications. Several sources of inefficiency exist in the

operating room (OR), including pre-operative and intra-

operative. The instruments used during total knee arthroplasty

(TKA) are frequently redundant. Customized instruments and

implants can improve efficiency by reducing steps. Additional

benefits may include improved alignment and kinematics. The

author addressed the various sources of inefficiency, provided

suggestions to overcome them, and introduced the concept of

customized guides and implants as a method to improve

efficiency. The author concluded that besides the obvious

benefit of cost and resource conservation, one added benefit

may be improved accuracy and possibly outcomes; further

research is needed to confirm these possibilities.

Carpenter et al (2014) noted that poor tibial component fit can

lead to issues including pain, loosening and subsidence.

Morphometric data, from 30 patients undergoing UKA were

utilized; comparing size, match and fit between patient-specific

and off-the-shelf implants; CT images were prospectively

obtained and implants modeled in CAD, utilizing sizing

templates with off-the-shelf and CAD designs with patient-

specific implants. Virtual surgery was performed, maximizing

tibial plateau coverage while minimizing implant overhang.

Each implant evaluated to examine tibial fit. Patient-specific

implants provided significantly greater cortical rim surface area

coverage versus off-the-shelf implants: 77 % versus 43 %

medially and 60 % versus 37 % laterally. Significantly less

cortical rim over-hang and under-coverage were observed with

patient-specific implants. The authors concluded that patient-

specific implants provided superior cortical bone coverage and

fit while minimizing over-hang and under-coverage seen in off-

the-shelf implants.

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Ivie et al (2014) stated that patient-specific guides can improve

limb alignment and implant positioning in TKA, although not all

studies have supported this benefit. These researchers

compared the radiographs of 100 consecutively-performed

patient-specific total knees to a similar group that was

implanted with conventional instruments instead. The patient-

specific group showed more accurate reproduction of the

theoretically ideal mechanical axis, with fewer outliers, but

implant positioning was comparable between groups. The

odds ratio comparison showed that the patient-specific group

was 1.8 times more likely to be within the desired +3° from the

neutral mechanical axis when compared to the standard

control group. The authors concluded that these findings

suggested that reliable reproduction of the limb mechanical

axis may accrue from patient-specific guides in TKA when

compared to standard, intra-medullary instrumentation.

In a cohort study, Schwarzkopf et al (2015) examined if there

is a significant difference in surgical time, intra-operative blood

loss, post-operative range of motion (ROM), and length of stay

(LOS) between patient-specific implants (PSIs) and

conventional TKA. A consecutive series of 621 TKA patients,

307 with PSIs and 314 with conventional implants, was

reviewed. Differences in estimated blood loss, LOS, ROM and

surgical time/tourniquet time between the 2 cohorts were

analyzed. Linear regression analysis demonstrated that PSI

decreased estimated blood loss by 44.72 ml (p < 0.01),

decreased LOS by 0.39 days (p < 0.01), decreased post

operative ROM by 3.90° (p < 0.01), and had a negligible

difference on surgical and tourniquet time. The authors

concluded that the use of PSI was associated with decreased

estimated blood loss, decreased LOS, decreased ROM, and

no discernible difference in surgical or tourniquet time, all of

which are unlikely to be clinically significant; and future studies

are needed to address quality of life (QOL) and patient-

reported functional outcome measurements between the 2

cohorts. Level of evidence = III.

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Patil et al (2015) stated that nearly 14 % to 39 % TKA patients

reported dissatisfaction causing incomplete return of function.

These researchers proposed that the kinematics of knees

implanted with patient-specific prostheses using patient-

specific cutting guides would be closer to normal. A total of 18

matched cadaver lower limbs were randomly assigned to 2

groups: group A was implanted with patient-specific implants

using patient-specific cutting guides; group B, the contralateral

knee, was implanted with a standard design using

intramedullary alignment cutting guides. Knee kinematics

were measured on a dynamic closed-kinetic-chain Oxford

knee rig, simulating a deep knee bend and in a passive rig

testing varus-valgus laxity. The difference from normal

kinematics was lower for group A compared to group B for

active femoral rollback, active tibiofemoral adduction, and for

passive varus-valgus laxity. The authors concluded that these

findings supported the hypothesis that knees with patient-

specific implants generate kinematics more closely resembling

normal knee kinematics than standard knee designs. They

noted that restoring normal kinematics may improve function

and patient satisfaction after total knee arthroplasty.

Zeller et al (2017) examined if improving implant design

through customized TKA improves kinematic function. Using

state-of-the-art mobile fluoroscopy, tibio-femoral kinematics

were analyzed for 24 subjects with a customized individually

made (CIM), cruciate-retaining TKA, and 14 subjects having

an asymmetric condylar cruciate-retaining TKA. Subjects

performed a weight-bearing deep knee bend and a rise from a

seated position. Each patient was evaluated for weight-

bearing ROM, femoro-tibial translation, femoro-tibial axial

rotation, and condylar lift-off occurrence. Subjects having a

CIM TKA experienced greater weight-bearing knee flexion

compared with the traditional posterior cruciate-retaining

(PCR) TKA design. During flexion, the CIM TKA subjects

consistently exhibited more posterior femoral roll-back than the

traditional PCR TKA subjects. The CIM TKA was found to

have statistically greater axial rotation compared with the

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traditional PCR TKA (p = 0.05). Of note, only the CIM TKA

patients experienced femoral internal rotation at full extension,

as exhibited in a normal knee. Compared with the traditional

PCR TKA, the CIM TKAs demonstrated minimal occurrences

of paradoxical sliding and reverse rotation during flexion and

extension. The CIM TKA subjects showed minimal lift-off and

hence better stability in early-flexion to mid-flexion compared

with the traditional PCR subjects. The authors concluded that

the CIM TKA demonstrated kinematics more similar to a

normal knee; thus; using customized implant technology

through CIM TKA designs afforded benefits including more

normal motion compared with a traditional PCR TKA.

An assessment by the Ludwig Boltzmann Institute for Health

Technology Assessment of custom-made or customizable 3D

printed implants and cutting guides (2019) concluded: "3D

printed custom-made or customisable implants and cutting

guides are currently most frequently applied in knee,

maxillofacial, and cranial surgery. Evidence of very low or low

quality shows significant differences in precision, both in terms

of malalignment and deviation between 3D printed technology

and standard instrumentation in knee arthroplasty. Evidence of

higher quality is needed to validate these significant results

and draw final conclusions. No firm conclusions can be made

in mandibular reconstruction and cranioplasty, since no

outcomes were significant in favour of either technology. No

statements regarding long-term safety outcomes can be

made."

ConforMIS Knee Implant

Wang et al (2018) stated that newer TKR designs have been

introduced to the market with the aim of overcoming common

sizing problems with older TKR designs. Furthermore, since a

sizable percentage of patients with osteoarthritis (OA) present

with disease limited to the medial/lateral knee compartment in

addition to the patellofemoral joint, for whom, a customized bi-

compartmental knee replacement (BKR) is available as a

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therapeutic option. To-date, there is very little information

regarding knee strength and mechanics during gait for patients

implanted with these modern TKR and BKR designs. These

investigators evaluated knee strength and mechanics during

walking for patients with either a modern off-the-shelf TKR or a

customized BKR and compared these findings to a cohort of

healthy controls. A total of 12 healthy controls, 8 BKR, and 9

TKR patients participated in the study. Maximal isometric

knee strength was evaluated; 3D kinematic and kinetic

analyses were conducted for level walking. The TKR knee

exhibited less peak extensor torque when compared to, both

the BKR and control limbs (p < 0.05). The TKR knee had less

extensor moment at stance than both the BKR and control

knees (p < 0.05). Both the BKR and control knees displayed

larger internal rotation at stance than that of the TKR knee (p <

0.05). The authors concluded that the findings of this study

suggested that, for patients that exhibit isolated OA of the

tibiofemoral joint, using a customized BKR implant is a viable

therapeutic option and may contribute to superior mechanical

advantages.

The authors stated that there were several drawbacks that

need consideration when interpreting these results. The

sample size of participants in each group was smaller than the

typical follow-up studies that reported on functional and clinical

end-points. Though sample size played an important role in

interpreting results, the authors believed from their experience

with conducting such studies, that the sample size chosen was

adequate to enable them to make conclusions on their

analyses. Additionally, they were able to maintain a similar

sample size in each arm of the study. This should alleviate

any bias due to sample size in any one study arm. Although

participants in the control group were younger with smaller

BMI than the other groups, the 2 patient groups were age-,

mass-, and height-matched. These investigators believed that

any advantage drawn from this would affect the implant groups

equally, thus making comparisons between the implant groups

relevant, while still providing context on how they compare to

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healthy controls. Ideally, the authors would have liked to test

patients pre- and post-operatively and compare results with

the patient being their own control. However, this would mean

having to test patients that have end-stage OA, which the

authors felt would not provide a clear comparison to healthy

controls. Lastly, in this study, patients’ pre-operative Knee

Society scores and gait analysis data were not available due

to their cross-sectional study design. However, they believed

their patients’ pre-surgical conditions were similar to patients

used in other prospective studies examining functional

improvements after knee replacements. In those studies,

patients’ combined Knee Society scores were close to 100 and

knee range of motion was around 120° [19, 20, 21, 22]. In

general, patients with end-stage knee OA experience joint pain

and stiffness, which led to functional limitations of performing

daily activities such as walking, going up and down stairs, and

rising from a sitting position. The authors chose the KOS-ADL

because it is an effective instrument for measuring functional

limitations associated with pathological disorders of the knee.

However, the authors only administered the KOS-ADL during

patients’ post-operative laboratory visit. Ideally, if the KOS

ADL score was obtained prior to surgery, then it would have

been possible to quantify how much functional improvement

was made at the time of the post-operative laboratory testing.

Tammachote et al (2018) noted that customized cutting block

(CCB) was designed to ensure the accurate alignment of knee

prostheses during total knee arthroplasty (TKA). Given the

paucity of CCB efficacy data, these researchers compared

CCB with conventional cutting guide using a randomized

controlled trial (RCT). A total of 108 osteoarthritic knee

patients underwent TKA by 1 experienced surgeon were

randomized to receive CCB (n = 54) or conventional cutting

instrument (CCI) surgery (n = 54). The primary outcomes

were limb alignment, prostheses position, and operative time.

The secondary outcomes were hemodynamic alteration after

surgery, functional outcomes (modified Western Ontario and

McMaster University Osteoarthritis Index) and ROM at 2 years

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after surgery. Mean hip-knee-ankle angle in the CCB group

was 179.4° ± 1.8° versus 179.1° ± 2.4° in the CCI group, Δ = 0

(95 % confidence interval [CI]: -0.6 to 1.1, p = 0.55). Mean

operative time was faster in the CCB arm: 93 ± 12 versus 104

± 12 mins, Δ = 11 (95 % CI: -16.7 to -7.2, p < 0.0001). There

were no differences in hemodynamic parameters, mean blood

loss (446 [CCB] versus 514 ml [CCI], Δ = -68 [95 % CI: -138 to

31 ml, p = 0.21]), post-operative hemoglobin changes,

incidence of hypotension (systolic blood pressure less than 90

mmHg), oliguria, and rates of blood transfusion. Functional

outcomes and ROM were also similar. The authors concluded

that there was no improvement in alignment, hemodynamic

changes, blood loss, and knee functional outcomes; CCB

reduced surgical time by 11 mins in this cohort. These

researchers stated that CCB cost-effectiveness should be

further investigated.

Khosravipour et al (2018) noted that contact pressure and

stresses on the articulating surface of the tibial component of a

TKR are directly related to the joint contact forces and the

contact area. These stresses can result in wear and fatigue

damage of the ultra-high-molecular-weight polyethylene.

Thus, conducting stress analysis on a newly designed surface-

guided knee implant is needed to evaluate the design with

respect to the polyethylene wear. Finite element modeling is

used to analyze the design's performance in level walking,

stair ascending and squatting. Two different constitutive

material models have been used for the tibia component to

evaluate the effect of material properties on the stress

distribution. The contact pressure results of the finite element

analysis were compared with the results of contact pressure

using pressure-sensitive film tests. In both analyses, the

average contact pressure remained below the material limits of

ultra-high-molecular-weight polyethylene insert. The peak von

Mises stresses in 90° of flexion and 120° of flexion (squatting)

are 16.28 and 29.55 MPa, respectively. All the peak stresses

were less than the fatigue failure limit of ultra-high-molecular

weight polyethylene which was 32 MPa. The average contact

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pressure during 90° and 120° of flexion in squatting were 5.51

and 5.46 MPa according to finite element analysis and 5.67

and 8.14 MPa according to pressure-sensitive film

experiment. The authors concluded that customized surface-

guided knee implants are aimed to resolve the limitations in

activities of daily living (ADL) after TKR by providing close to

normal kinematics. The proposed knee implant model

provided patterns of motion much closer to the natural target,

especially as the knee flexes to higher degrees during

squatting. These laboratory findings need to be validated in

the clinical setting.

Levengood and Dupee (2018) determined the accuracy of a

customized individually made total knee implant used in

conjunction with patient-specific cutting guides in restoring

coronal plane mechanical axis alignment using computer-

assisted surgery (CAS). A consecutive series of 63 TKA

patients were prospectively measured with intra-operative

CAS. The patient-specific instruments and implants were

created utilizing a pre-operative CT scan; CAS system was

used for all patients, to determine mechanical alignment.

Bone cuts were made using the patient-specific instruments.

Both bone cuts and final coronal mechanical alignment were

recorded utilizing the navigation system for the assessment.

The patient-specific instruments and implants provided perfect

neutral coronal mechanical alignment (0°) in 53 patients. The

remaining 10 patients had a post-operative alignment within±2°

of neutral. The average pre-operative deformity was 5.57°

versus 0.18° post-operatively (p < 0.0001). The mean

correction angle was 5.68°. No patients had post-operative

extension deficits as measured with CAS (7.50° pre-op for

40/63 patients). Customized, individually made total knee

implant with patient-specific cutting jigs showed results that

were comparable to those of CAS systems in this study. The

authors concluded that this technology restored the neutral

coronal mechanical axis very accurately, while offering unique

benefits such as improved implant fit and restoration of the

patient's J-curves, which require further investigation.

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The authors stated that the use of a CAS as the reference for

the measurements of the mechanical axis pre- and post-

implantation could be one of the drawbacks of this study. The

measurements arising from CAS were dependent on what was

registered and data may be incorrect if the original registration

was not accurate. However, CAS has been commonly used

during surgery for aligning implant components. Also, the lead

author was trained in using CAS and has used them in more

than 600 surgeries prior to use in this study. The authors

believed that this had a mitigating impact on registration

errors. Additionally, CAS systems had been found to be more

accurate than radiographic and CT measurements and

prevented the patient from being exposed to additional ionizing

radiation. Another drawback of this study was the fact that this

study was conducted on a sample size that was smaller than

the average volume of an orthopedic surgeon in the time

window analyzed, though it was comparable to similar

previously published studies. This could be seen as a limiting

factor in powering the study. Nevertheless, these were

consecutively recruited patients at a sports medicine practice

and the results of this study indicated that the results were

highly reproducible; thus, these investigators did not anticipate

a deviation from the current results by increasing the sample

size. Also, the sample size used for this study was

comparable to previously published reports on mechanical

alignment using CAS. As part of the study data collection,

sagittal plane alignment of the femoral and tibial bones, pre

and post-implantation was not collected. Pre-surgery femoral

and tibial varus/valgus alignment was not assessed. The goal

of our study was to evaluate the iJig system used in

conjunction with the iTotal implant in reproducing overall

coronal plane mechanical alignment after implantation and the

ability of the system to return the patients to full extension.

These data have been presented in the study. Future studies

that investigate the sagittal alignment in conjunction with the

coronal alignment using these jigs will provide a deeper

understanding on the ability of the iJig system to restore

sagittal and coronal alignment post-surgery. Finally, the study

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did not include a control group, which would have provided a

direct comparison of outcomes. There were multiple studies

that had examined the use of patient specific instrumentation

blocks in conjunction with off-the-shelf implants. The authors

believed comparing their results to the results presented in

these manuscripts as an adequate criterion for comparing the

outcomes with the customized implant used with the iJigs

platform. Moreover, they stated that it was important to note,

however, that many of these studies investigated the use of

patient-specific jigs manufactured using MRI imaging. The

patient-specific jigs investigated in this study were

manufactured using computed tomography (CT) imaging. The

differences in the imaging modalities were not investigated in

this study.

Koh et al (2018) examined post-cam design via finite element

analysis to evaluate the most normal-like knee mechanics.

These researchers developed 5 different 3-D computational

models of customized posterior-stabilized (PS) TKA involving

identical surfaces with the exception of the post-cam

geometry. They included flat-and-flat, curve-and-curve

(concave), curve-and-curve (concave and convex), helical,

and asymmetrical post-cam designs. These investigators

compared the kinematics, collateral ligament force, and

quadriceps force in the customized PS-TKA with 5 different

post-cam designs and conventional PS-TKA to those of a

normal knee under deep-knee-bend conditions. The results

indicated that femoral rollback in curve-and-curve (concave)

post-cam design exhibited the most normal-like knee

kinematics, although the internal rotation was the closest to

that of a normal knee in the helical post-cam design. The curve

and-curve (concave) post-cam design showed a femoral

rollback of 4.4 mm less than the normal knee, and the helical

post-cam design showed an internal rotation of 5.6° less than

the normal knee. Lateral collateral ligament and quadriceps

forces in curve-and-curve (concave) post-cam design, and

medial collateral ligament forces in helical post-cam design

were the closest to that of a normal knee. The curve-and-

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curve (concave) post-cam design showed 20 % greater lateral

collateral ligament force than normal knee, and helical post-

cam design showed medial collateral ligament force 14 %

greater than normal knee. The authors concluded that the

results revealed the variation in each design that provided the

most normal-like biomechanical effect. The present

biomechanical data were expected to provide useful

information to improve post-cam design to restore normal-like

knee mechanics in customized PS-TKA.

The authors stated that this study had 4 limitations. First, the 5

specific post-cam designs used in this study did not represent

all the design features of contemporary TKA. Second, a deep-

knee-bend simulation was performed although simulations

related to more demanding activities (e.g., chair rising, sitting,

stair climbing, and stair descending) were required in the

future for a more reliable investigation. However, the

simulation was performed under deep-knee-bend motion

because it included both a wide range of flexion-extension and

a significant muscular endeavor around the knee joint. Third,

implant kinematics and quadriceps force were evaluated by

using computational simulations, and this did not fully

represent an in-vivo condition. Fourth, the anatomy for the

customized PS design was based on, and virtually implanted

in, only 1 subject. The use of subjects of various ages would

improve the validity of the results because the validity was also

dependent on the geometry of the knee joint. Most

significantly, the time and computational cost associated with

subject-specific FE model generation were not efficient. These

researchers stated that further design modifications to the

customized TKA are needed to achieve normal knee

mechanics during deep-knee-bend activity; and future

research will increase the number of subjects. Additionally, it

is necessary to consider the design for substituting ACL

function.

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Kay et al (2018) stated that manipulation under anesthesia

(MUA) is a standard treatment for arthrofibrosis after total knee

arthroplasty (TKA), with reported rates of 1.5 to 6 %.

Customized TKA may have better outcomes by matching

individual patient anatomy. However, a previous study

reported an unacceptably high rate of MUA for customized

TKAs. This study reported the incidence of MUA in a large

cohort of 2nd generation customized TKAs. Data were

collected prospectively on 360 2nd generation ConforMIS

iTotal cruciate retaining TKAs; MUA was performed for

clinically significant arthrofibrosis. Range of motion (ROM)

and New Knee Society Scores (KSS) were evaluated at

regular intervals for 2 years; 11/360 (3.05 %) knees underwent

MUA; ROM overall improved from 115° to 125°, and from 112°

to 122° in patients undergoing MUA; KSS objective and

functional scores in MUA patients increased from 57 to 98 and

41 to 90, respectively, and in the entire cohort increased from

65 to 96 and 45 to 86 at 2 years (p < 0.05). No MUA patients

underwent revision surgery. The authors concluded that

customized TKA with 2nd generation ConforMIS iTotal

implants resulted in a MUA rate consistent with the literature

for all designs. Additionally, patients exhibited significant

increases in ROM and Knee Society Scores. Moreover, these

researchers stated that further follow-up continues at all sites.

Data from longer term follow-up on the entire cohort as well as

the patients who experienced MUAs in this study population

will provide a deeper understanding of overall survival, patient

outcomes and long-term effects of MUA on patients receiving

this device.

The authors stated that drawbacks of this study included a

lack of standardized indications for undergoing MUA and

incomplete follow-up (298 of 360 patients at 1 years, including

8 of 11 patients who underwent MUA). However, patients who

did not complete 1 year follow-up did not report problems that

would be indications for MUA at the 6 week or 6 month visit.

Thus, it was unlikely that additional patients in the study will

require MUA in the future.

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Arbab et al (2018) noted that incorrect positioning and

malalignment of TKA components can result in implant

loosening. Restoration of neutral alignment of the leg is an

important factor affecting the long-term results of TKA. In a

retrospective study, these researchers compared mechanical

axis in patients with conventional and patient-specific TKAs. A

total of 232 patients who underwent TKA between January

2013 and December 2014 were included to compare post

operative mechanical axis; 125 patients received a patient-

specific TKA (iTotal CR®, Conformis) and 107 a conventional

TKA (Triathlon®, Stryker). Standardized pre- and post

operative long-leg standing radiographs were retrospectively

evaluated to compare the 2 patient cohorts; 113 (90 %)

radiographs of patient-specific TKA and 88 (82 %) of

conventional TKA were available for comparison. The pre

operative deviation from neutral limb axis was 9.0° (0.1 to

27.3°) in the patient-specific TKA cohort and 8.2° (0.2 to 18.2°)

in the conventional TKA group. Post-operatively the patient-

specific TKA group showed 3.2° (0.1 to 8.4°) and the

conventional TKA cohort 2.3° (0.1 to 12.5°) deviation.

However, the rate of ± 3° outliers from neutral limb axis was 16

% in the patient-specific TKA cohort and 26 % in the

conventional TKA group. The authors concluded that patient-

specific TKA demonstrated fewer outliers from neutral leg

alignment compared to conventional technique. Moreover,

these researchers stated that potential benefits in the long

term outcome and functional improvement require further

investigation.

The authors stated that this study had several drawbacks.

First, it was a retrospective comparative analysis and hence

selection bias could not be excluded. Second, these

investigators assessed only 1 patient-specific implant (PSI)

design and these findings might not be applicable to other

PSIs that currently are commercially available. They did not

perform a power analysis before starting this study. Third, the

findings of this study were limited to the coronal plane and did

not take into account lateral or rotational component

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positioning, which may play a role in long-term survivorship of

total knee implants. Finally, these investigators did not report

on clinical outcomes such as pain, stiffness, range of motion,

patient satisfaction, or outcome scoring systems, which may

limit the clinical relevance of the findings in this study.

Schroeder and Martin (2019) stated that in TKA, surgeons

often face the decision of maximizing tibial component fit and

achieving correct rotational alignment at the same time.

Customized implants (CIMs) address this difficulty by aiming to

replicate the anatomical joint structure, utilizing data from

patient-specific knee geometry during the manufacturing.

These investigators intra-operatively compared component fit

in 4 tibial zones of a CIM to that of 3 different off-the-shelf

(OTS) TKA designs in 44 knees. Additionally, they evaluated

the rotational alignment of the tibia using CT-based computer

aided design model analysis. Overall the CIM device showed

significantly better component fit than the OTS TKAs. While

18 % of OTS designs presented an implant overhang of 3 mm

or more, none of the CIM components did (p < 0.05). There

was a larger percentage of CIMs seen with optimal fit (less

than or equal to 1 mm implant overhang to less than or equal

to 1 mm tibial bone under-coverage) than in OTS TKAs. Also,

OTS implants showed significantly more component under-

hang of greater than or equal to 3 mm than the CIM design (37

% versus 18 %). The rotational analysis revealed that 45 % of

the OTS tibial components showed a rotational deviation of

more than 5 degrees and 4 % of more than 10 degrees to a

tibial rotational axis described by Cobb et al. No deviation was

seen for the CIM, as the device was designed along this axis.

Using the medial 1/3 of the tibial tubercle as the rotational

landmark, 95 % of the OTS trays demonstrated a rotational

deviation of more than 5 degrees and 73 % of more than 10

degrees compared with 73 % of CIM tibial trays with more than

5 degrees and 27 % with more than 10 degrees. Based on

these findings, the authors believed that the CIM TKA provided

both better rotational alignment and tibial fit without causing

overhang of the tibial tray than the 3 examined OTS implants.

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First, all TKAs and intra-operative measurements were done

by a single surgeon which may affect the results when

measuring tibial bone coverage of the 3 OTS implants from a

surgical technique stand-point. However, the surgeon had

used all of these implants previously and was especially

experienced with the OTS 3 and CIM brands. A 2nd drawback

was that patient-specific jigs manufactured for the iTotal CR

were used for the tibial bone resection. Yet, this tibial cut was

similar to any other cut in the resulting shape of the cut tibial

bone. Third, as the CAD analysis of the rotational deviation

from an axis described by Cobb et al and an axis to the medial

1/3 of the tibial tubercle was performed manually and for each

implant individually. This may have resulted in intra-observer

mistakes. Varying opinions exist on what landmarks to use

when assessing component alignment. These researchers did

not utilize all methods of tibial component rotation, only

methods based on the location of the tibial tubercle and by an

axis described by Cobb et al which they believed was accurate

from what multiple studies have reported. Aligning the OTS

tibial components toward the medial 1/3 of the tubercle has

been shown in multiple studies to be the most reproducible

clinical landmark in terms of tibial tray rotation and was used

by the majority of surgeons in the United States for tibial

alignment. The authors only evaluated 3 OTS implant designs

for this study although there were many more different types

on the market. Nonetheless, based on these findings and

similarities between the OTS brands, the authors felt these

results were likely highly translatable to other OTS brands. In

this study, only symmetrical implant designs were compared

with the CIM TKA, despite the fact that implant manufacturers

had introduced other asymmetrical designs on the market.

However, as Jin et al emphasized in their study, although

leading to better results in tibial fit, there were still cases with

both over- and under-hang on the same tibial trial with the

asymmetrical design. Moreover, these investigators stated

that it has to be noted that no precise definitions for absolute

tibial component under-hang or overhang can be found in the

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literature. However, Mahoney and Kinsey's observations

indicated that the presence of an overhang of greater than or

equal to 3 mm in at least 1 zone increased the odds of patients

reporting knee pain which was why the authors chose this

threshold to be of importance. Jin et al suggested under-hang

is more acceptable during surgery than over-hang as the

surgeon can remove uncovered bone during the procedure

and correct rotation. To the authors’ knowledge, no studies

investigating a possible correlation between tibial under-

coverage and implant failure exist. However, it has been

hypothesized that tibial under-coverage may be a causal factor

in increased osteolysis, tibial subsidence and implant

loosening, and led to pain and early implant failure.

Additionally, studies have shown that blood exudation from

exposed bone sections not covered by prostheses were an

important source of blood loss and that the control of bleeding

was not amenable to methods such as electrocautery, ligature

control, or the use of bone wax. The authors suggested that

further research should be made in this field.

Shroeder et al (2019) examined implant survivorship, patient

satisfaction, and patient-reported functional outcomes at 2

years for patients implanted with a customized, posterior

stabilized (PS) total knee replacement (TKR) system. A total

of 93 patients (100 knees) with the customized PS TKR were

enrolled at 2 centers. Patients’ length of hospitalization and pre

operative pain intensity were assessed. At a single time- point

follow-up, these researchers evaluated patient reported

outcomes utilizing the KOOS Jr., satisfaction rates, implant

survivorship, patients’ perception of their knee and their overall

preference between the 2 knees, if they had their contralateral

knee replaced with an off-the-shelf (OTS) implant. At an

average of 1.9 years, implant survivorship was found to be 100

%. From pre-op until time of follow-up, these investigators

observed an average decrease of 5.4 on the numeric pain

rating scale. Satisfaction rate was found to be high with 90 %

of patients being satisfied or very satisfied, and 88 % of

patients reporting a “natural” perception of their knee some or

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all the time. Patients with bilateral implants mostly (12/15)

stated that they preferred their customized implant over the

standard TKR. The evaluation of KOOS Jr. showed an

average score of 90 at the time of the follow-up. The authors

concluded that based on these findings, they believed that the

customized PS implant provided patients with excellent

outcomes post-surgery.

Reimann et al (2019) stated that despite recent innovations in

TKA, 20 % of the patients are not completely satisfied with the

clinical results. Regarding patient-specific implants (PSI),

these investigators compared individual and off-the-shelf

implant (OSI) TKA concerning the post-operative outcome like

function and global patient satisfaction. Between 2013 and

2014, a total of 228 patients received a TKA due to primary

OA with an indication for a bicondylar, cruciate retaining

prosthesis; 125 patients received a PSI and 103 an OSI TKA.

The outcome after surgery was evaluated retrospectively by 2

questionnaires and a clinical follow-up examination. The Knee

Society Score (KSS) was used to evaluate function. To

compare the satisfaction the Knee Injury and Osteoarthrosis

Outcome Score (KOOS) and a modified EuroQol (EQ)

including 5 additional questions were used. Finally, 84

patients with PSI and 57 with OSI completed follow-up.

Concerning demographic data, the PSI group showed a

significantly younger age, 5 years on average. The ROM was

comparable in both groups. The KSS and the separate

function score achieved significantly better results in the PSI

group. For subjects with PSI TKA, the global satisfaction

showed significant better values. The authors concluded that

significantly higher values in KSS and its function score led to

a better basic daily function in PSI group. In addition, the PSI

TKA achieved a higher global patient satisfaction.

Nevertheless, both should mainly be assessed in the context

of average younger age and the influence of expectations.

The reason why patients with PSI TKA were more satisfied

remained unclear because of study design. These data

cannot reveal whether it was because of prosthetic design or

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of other parameters like expectations and awareness of

receiving an individual implant. They stated that further

studies that examine expectations, patient reported outcome

measures (PROMs) and kinematics, in particular, are needed.

The authors stated that this study had some limitations.

Besides the retrospective design, there was no randomization

and blinding. In addition, the rate of drop-outs was quite high.

Hence, a selection bias cannot be certainly excluded.

Satisfied patients might be more willing to take part in a study

with an examination compared to unsatisfied. To the authors'

knowledge, the study was one of the first to compare PROMs

and objective clinical data in subjects with PSI TKA and

conventional TKA on a larger scale.

Buch et al (2019) stated that “Fast-Track” protocols have been

introduced in total knee arthroplasty (TKA) with the intention to

increase health care savings while maintaining or improving

patient outcomes. The influence of the implant design in a

“Fast-Track” setting has not been described yet. These

investigators compared a customized implant with standard

off-the-shelf (OTS) devices when utilizing a “Fast-Track”

protocol. A total of 62 patients were prospectively enrolled at

a single-center and implanted with either a customized or a

standard OTS implant resulting in 30 patients being treated

with an OTS design (Columbus Total Knee System) and 32

with the customized design (iTotal®G2, Cruciate Retaining

TKA, ConforMIS, Inc.,). The same institutional fast-track

protocol was utilized on all patients and included pre-, intra-,

and post-operative medical treatment. These researchers

evaluated total length of stay (LOS), discharge destination and

range of motion (ROM) at 6 to 8 weeks post-op and at an

average of 16 months post-op follow-up to compare the OTS

implant with the customized device. Implant survivorship was

assessed at a minimum of 25 months post-op. Using the fast

track protocol these researchers were able to decrease overall

LOS to 2.1 days versus 3.6 days prior to introduction of the

protocol. The use of the customized implant further reduced

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LOS significantly to 1.6 days. Significantly higher number of

patients who got implanted with the customized device (66 %)

were discharged within 24 hours than in the OTS group (30

%). Patients treated with the customized implant were found

to be discharged home more often than patients treated with

the OTS implants (97 % versus 80 %) and achieved higher

ROM both at 6-8 weeks (114° versus 101°) and at an average

of 16 months (122° versus 114°) than patients who got treated

with the OTS device. At an average follow-up of 28 months,

there was 1 implant revision in the customized group (due to

tibial fracture resulting from patient fall). For the OTS group

there was 1 implant revision (late infection) and 1 poly swap

(due to instability). The authors stated that based on this

analysis they observed a positive influence of the customized

device on patient outcomes and hospital metrics and

concluded that the implant choice is an important factor for

TKA in a “fast-track” setting.

The authors believed this was the 1st study to compare the

effect of the knee implant design on LOS and hospital metrics

in a defined fast-track program. They stated that this study

was not without limitations that have to be taken into

consideration when interpreting the results. This study was

performed prospectively with patients selecting the implant

design. Including blind randomization of the patient /

component matching may have eliminated potential selection

bias between the 2 study groups. Thus, these researchers

had little influence on the composition of the study cohorts that

might have led to inequalities between the study groups.

However, since patient demographics and co-morbid

conditions were similar and no statistically significant

difference was detected between the 2 groups these

investigators considered their findings to be valid. With a total

of 62 patients participated in this study the patient cohort was

relatively small (n = 32 in the ConforMIS group).

Nevertheless, the differences observed between the groups

were large enough to be of significance and the authors

believed they would be similar for a larger study population.

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These researchers suggested that further research with a

larger study population should be carried out in the future. For

this study all TKAs were performed by a single surgeon who is

experienced with all devices used. Experience and a high

expertise in performing TKA has been shown to result in better

outcomes and additional studies at different sites should be

conducted to verify if the implant design does have an impact

on a faster discharge. Lastly, fast track surgery can be

implemented in multiple ways with the same guidelines but

different protocols. The authors noted that these findings only

reflected the fast-track protocol they utilized in this study. As

there is no single definition of the “fast track protocol” in

literature these investigators proposed that their protocol

should be used in future research in order to validate their

findings.

O'Connor et al (2019) noted that the amount of TKA

procedures performed in the United States has been

increasing steadily and is projected to reach 3 million

procedures annually by 2030 in patients aged greater than or

equal to 65 years. A rise in TKA procedures will increase

spending on osteoarthritis (OA) treatments, which is currently

the 2nd highest category of spending for Medicare patients.

Because TKA procedures account for a substantial amount of

total OA spending, payers and providers are examining

methods to reduce spending on the procedure while improving

clinical outcomes. Customized individually made implants

have been shown to improve clinical outcomes, such as

physical function and limb alignment, compared with OTS

implants; however, the economic impact of customized

implants has yet to be established. These investigators

analyzed TKA episode expenditures among Medicare fee-for

service (FFS) members who received a customized or an OTS

implant. Members undergoing a TKA procedure using the

customized implant technology were identified in the Medicare

FFS database and were propensity matched (1:5) to a cohort

of members who received OTS implants. Reimbursement for

the initial procedure (i.e., customized and OTS procedure), a

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pre-operative computed tomography (CT) scan, and 12-month

post-operative healthcare utilization were analyzed. The

overall episode expenditures were used to construct a budget

impact model to calculate the per-member per-month (PMPM)

spending for Medicare FFS beneficiaries. The average total

episode spending was significantly lower among the

customized implant cohort ($18,585) compared with the OTS

implant cohort ($20,280; a $1,695 difference; p < 0.0001).

This savings resulted in $0.08 PMPM savings for the

Medicare FFS program when a portion (10 %) of eligible

members received the customized implant technology. A

sensitivity analysis, which varied with the customized implant

market penetration and the percent of customized implant-

eligible procedures, indicated that the savings could be as

great as $0.28 PMPM. The authors concluded that the

findings of this study suggested that compared with OTS

implants, customized knee implants can reduce healthcare

spending among patients undergoing TKA. These findings

may help to determine the economic impact of customized

knee implant technology on specific health plan populations.

In addition, the results may be of benefit for providers who are

taking on financial risk for patients undergoing TKA

procedures, such as those participating in accountable care

organizations or bundled payment programs. Moreover, these

researchers stated that this study did not examine the financial

impact of receiving a customized implant in a commercial

population with TKA. Given the positive findings in the

Medicare population, a similar review is recommended to be

completed in a commercial population among younger patients

aged less than 65 years, because the findings may indicate

that customized implants could also result in substantial

savings for a commercial health plan. It is also suggested that

future studies conduct sub-analyses by sex, race, and co-

morbidities to understand the economic impact on these

specific populations. (Funding for this study was provided by

Conformis Inc., Billerica, MA; Dr. O'Connor is principal

investigator of a clinical trial sponsored by Conformis and her

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institution receives research support from Conformis for that;

Ms. Blau was a consultant to Conformis at the time of this

study).


Because medical coding does not distinguish between

customized and OTS implants in administrative claims data,

the customized implant cohort was identified through matching

health plan members to multiple demographic and procedural

characteristics of customized implant order numbers provided

by the manufacturer to ensure that members who were

identified as having a customized implant actually received the

implant. The coding methodology used could have limited

impact on study findings. The study selection criteria only

allowed for exact matches; thus, there was an extremely low

chance that a patient who did not receive a customized

implant was included in the customized implant cohort.

However, it was possible for a patient who received a

customized implant to be included in the OTS implant cohort if

the patient did not receive a pre-operative CT scan in the out

patient setting, which was therefore not listed in the Medicare

database. Because the OTS implant cohort was selected from

a large population (i.e., 228,697 procedures), the chance of

incorrect categorization was low and was unlikely to have any

impact on the study's results. In addition, as a result of the

conservative nature of patient selection used in the study, not

all customized implant order numbers were identified in the

Medicare FFS database and/or were included in the analysis.

Finally, the driving factor of the index procedure pay amount

differences between the 2 cohorts was not identified during the

analysis. These researchers examined multiple factors that

could potentially increase or decrease a hospital's diagnosis-

relayed group (DRG) pay amount. The factors examined by

the authors included the percent of patients with a short stay

(which reduced DRG payments in some instances), the outlier

payments (made when hospital costs exceed a certain

threshold), and the percent of patients whose index visit was

classified with DRG code 469 (reimbursed at a higher rate

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than DRG code 470). Although the results of these analyses

suggested that each factor may slightly contribute to the index

differences observed between the 2 cohorts, no one factor

made a meaningful impact that fully explained these

differences.

Namin et al (2019) examined the impact of insurance

coverage on the adoption of customized individually made

(CIM) knee implants and compared patient outcomes and

cost-effectiveness of OTS and CIM implants. A system

dynamics simulation model was developed to study adoption

dynamics of CIM and meet the research objectives. The

model reproduced the historical data on primary and revision

knee replacement implants obtained from the literature and the

Nationwide Inpatient Sample. Then the dynamics of adoption

of CIM implants were simulated from 2018 to 2026. The rate

of 90-day re-admission, 3-year revision surgery, recovery

period, time savings in operating rooms, and the associated

cost within 3 years of primary knee replacement implants were

used as performance metrics. The simulation results indicated

that by 2026, an adoption rate of 90 % for CIM implants can

reduce the number of re-admissions and revision surgeries by

62 % and 39 %, respectively, and can save hospitals and

surgeons 6 % on procedure time and cut down cumulative

healthcare costs by approximately $38 billion. The authors

concluded that CIM implants have the potential to deliver high-

quality care while decreasing overall healthcare costs, but their

adoption requires the expansion of current insurance

coverage. This work presented the 1st systematic study to

understand the dynamics of adoption of CIM knee implants

and instrumentation. More broadly, the current modeling

approach and systems thinking perspective could be used to

consider the adoption of any emerging customized therapies

for personalized medicine.

The authors noted that this dynamics simulation model has

several limitations. First, the current simulation model, like

most models, cannot portray full reality, but the validated

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model can potentially help uncover complexities in the

healthcare system around TKAs. The analyses compared the

relative potential of different insurance policies rather than

predicting precisely the long-term effect of these policies.

Second, the simulation model did not consider indirect costs

and delays associated with administrative processes. Indirect

costs may include lost wages due to patients’ disability from

the procedures. Administrative processes may include delays

due to the FDA approval process and bureaucratic burdens of

ordering system. All hospital entities have to use FDA-

approved medical devices; however, FDA regulations for 3-D

printed medical devices are expected to increase in the near

future, which could put increased pressure on the adoption of

these products. In this model, these researchers assumed

that the FDA would approve new CIM implant manufacturers

and their products within a period of 4 months. Complexity of

ordering system may include selection of implant (partial, total,

cruciate retaining, etc.) and transferring the CT data to a

manufacturer that could cause bureaucratic burdens and limit

the adoption. These investigators considered performance

improvements of CIM implants, the design phase and the use

phase during surgery, as a “moving target” since the

evaluation process takes time and may not reflect the latest

effects of product modifications on performance. OTS

implants have been on the market for a long time, and 3-D

printed patient-specific surgical guidance for OTS implants and

robotically assisted surgery have enhanced their

improvements up to the present; CIM implants were introduced

only a few years ago. For this reason, these researchers

considered the potentials for improvements of CIM implants in

the design phase and the use phase during surgery to be 5 %

per year: 2.5 % higher than OTS. However, to increase the

confidence in the model, sensitivity analyses were done on the

performance improvement assumptions for each type of

implant. According to the sensitivity analysis results

presented, the model is relatively robust to changes in

performance improvements. In addition, the online simulator

platform provides decision-makers with the flexibility to

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incorporate various performance improvement rates for either

type of implant (OTS or CIM), initially or midway through the

simulation run, and observe the results. Out-patient total joint

arthroplasty has become more popular in recent years

because of the economic benefits due to lower costs

associated with reduced LOS; CMS removed TKA from

inpatient-only list beginning January 2018. However,

according to the American Association of Hip and Knee

Surgeons (AAHKS), outpatient TKA should only be utilized for

patients who are healthy enough to have a procedure in such

settings. The patient should also have an appropriate home

support for being discharged with no hospitalization. Similar to

any other episode of care, there are advantages and

disadvantages associated with outpatient TKA, i.e., reduced

costs and discharge on the day of surgery that could lead to

either patient satisfaction or dissatisfaction if it causes more

complications such as implant failure, stiffness, more re

admissions and potentially revision surgeries. In this generic

model, these researchers considered that OTS and CIM

implants can be used in either inpatient or outpatient setting

uniformly, however, if the dynamic changes and more patients

become interested in outpatient procedures, the model can be

expanded to distinguish between inpatient and outpatient

settings.

Prophylactic Radiation Therapy Following Total Knee Arthroplasty

Chidel and colleagues (2001) stated that heterotopic

ossification (HO) occurs in 42 % of patients who have

undergone total knee arthroplasty (TKA). Bone formation

usually is found in the quadriceps expansion and causes

minimal to no symptoms. Specific therapy usually is

unnecessary, but cases have been reported in which

manipulation under anesthesia (MUA) or revision arthroplasty

has been required. These investigators reported a small

series of 5 patients (6 knees) who have undergone surgical

intervention for HO of the knee with radiotherapy given post-

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operatively for prophylaxis against future HO. The authors

concluded that although this series was small, it appeared that

the use of prophylactic radiation may reduce recurrence after

resection of symptomatic HO after TKA. Moreover, they stated

that further investigation is needed to confirm these

preliminary findings.

Farid and associates (2013) noted that therapeutic options for

arthrofibrosis following TKA include MUA, open or arthroscopic

arthrolysis, and revision surgery to correct identifiable

problems. These investigators proposed pre-operative low-

dose irradiation and Constrained Condylar or Rotating-hinge

revision for severe, idiopathic arthrofibrosis. Irradiation may

decrease fibro-osseous proliferation while constrained

implants allow femoral shortening and release of contracted

collateral ligaments. A total of 14 patients underwent 15

procedures for a mean overall motion of 46° and flexion

contracture of 30°; 1 patient had worsening range of motion

(ROM) while 13 patients had 57° mean gain in ROM (range of

5° to 90°). Flexion contractures decreased by a mean of 28°.

There were no significant complications at a mean follow-up of

34 months (range of 24 to 74 months).

Furthermore, an UpToDate review on “Total knee

arthroplasty” (Martin and Crowley, 2018) does not mention

radiation therapy/radiotherapy for post-operative management.

Patient-Specific Cutting Guides

Huijbregts et al (2016) noted that patient-specific

instrumentation (PSI) for TKA has been introduced to improve

alignment and reduce outliers, increase efficiency, and reduce

operation time. In order to improve the understanding of the

outcomes of PSI, these researchers conducted a meta-

analysis. They identified randomized and quasi-randomized

controlled trials (RCTs) comparing patient-specific and

conventional instrumentation in TKA. Weighted mean

differences (WMDs) and risk ratios (RRs) were determined for

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radiographic accuracy, operation time, hospital stay, blood

loss, number of surgical trays required, and patient-reported

outcome measures. A total of 21 RCTs involving 1,587 TKAs

were included. Patient-specific instrumentation resulted in

slightly more accurate hip-knee-ankle axis (0.3°), coronal

femoral alignment (0.3°, femoral flexion (0.9°), tibial slope

(0.7°), and femoral component rotation (0.5°). The RR of a

coronal plane outlier (greater than 3° deviation of chosen

target) for the tibial component was statistically significantly

increased in the PSI group (RR =1.64). No significance was

found for other radiographic measures. Operation time, blood

loss, and transfusion rate were similar. Hospital stay was

significantly shortened, by approximately 8 hours, and the

number of surgical trays used decreased by 4 in the PSI

group. Knee Society scores and Oxford knee scores were

similar. The authors concluded that PSI did not result in

clinically meaningful improvement in alignment, fewer outliers,

or better early patient-reported outcome measures. Efficiency

is improved by reducing the number of trays used, but PSI did

not reduce operation time.

Patient-Specific Implants

Schwarzkopf and colleagues (2015) stated that TKA

instrumentation and implant designs have been evolving, with

one of the current innovations being patient-specific implants

(PSIs). In a retrospective, cohort study, these researchers

examined if there is a significant difference in surgical time,

intra-operative blood loss, post-operative ROM, and LOS

between PSI and conventional TKA. A consecutive series of

621 TKA patients, 307 with PSIs and 314 with conventional

implants, was reviewed. Differences in estimated blood loss,

LOS, ROM, and surgical time/tourniquet time between the 2

cohorts were analyzed. Linear regression analysis

demonstrated that PSI decreased estimated blood loss by

44.72 ml (p < 0.01), decreased LOS by 0.39 days (p < 0.01),

decreased post-operative ROM by 3.90° (p < 0.01), and had a

negligible difference on surgical and tourniquet time. The

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authors concluded that the use of PSI was associated with

decreased estimated blood loss, decreased LOS, decreased

ROM, and no discernible difference in surgical or tourniquet

time, all of which were unlikely to be clinically significant.

These researchers stated that future studies need to address

quality of life (QOL) and patient-reported functional outcome

measurements between the 2 cohorts. Level of Evidence = III.


First, the retrospective nature of this study limited their ability

to uniform the measurement criteria of the different evaluated

variables, thus leading to possible bias. This study used data

for the 2 cohorts from different time periods. The conventional

implants were performed between January 2008 and

December 2010, while the PSIs were performed between

January 2011 and June 2013. This could allow for possible

bias due to factors such as improved pain management and

improved protocols. This study focused on interpreting the

differences in ROM as a measure of difference between the

PSI and conventional implants. Because of the retrospective

nature of the study, there was no standardized approach for

documenting both pre- and post-surgical ROM

measurements. By not following a specific protocol for

collecting ROM values, there was possibly a variability in

measurements based on how ROM was measured and by

whom. For future studies, it would be more meaningful to

address these issues in a prospective study to lessen the

amount of variation. In the future, it would be important to

address factors such as QOL and patient-reported outcome

measures. Ideally, a follow-up study should address these

measurements in a prospective, randomized controlled

fashion. These investigators noted that the findings of this trial

demonstrated statistically significant differences in estimated

blood loss and LOS; however, it appeared that these

differences may not represent any clinically significant

differences. This was best explained by the negligible change

in estimated blood loss (44.72 ml) and LOS (0.39 days)

between cohorts. Nonetheless, whether these intra-operative

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and post-operative benefits of individualized implants were

truly associated with long-term favorable outcomes for patients

remains to be evaluated. That post-operative increase in ROM

was less in the patient-specific group compared with the

conventional group suggested that further analysis of other

parameters such as post-operative knee score, pain score,

and alignment will be useful in determining any long-term

advantage of customized instruments and implants. Of note,

conventional instrumentation may be associated with

increased operative times and intra-operative blood loss due

to its reliance on manual intra-medullary alignment guides.

Furthermore, patient-specific implants provided greater bone

coverage, thus eliminating exposed bone, and may contribute

to decreased post-operative blood loss compared with

conventional implants.

Meier and colleagues (2019) noted that previous studies

analyzing femoral components of TKAs have demonstrated

the limited ability of these components to accommodate size

variations observed in the patient population, especially width

and femoral offset. These investigators used a large data set

of knee CT scans to determine the variations in the distal and

posterior femoral geometries and to examine if there is a

correlation between distal condylar offset and posterior

femoral offset as a potential parameter for

symmetry/asymmetry; and to evaluate what proportion of

knees would have a substantial mismatch between the

implant's size or shape and the patient's anatomy if a femoral

component of a modern standard TKA of symmetric (sTKA) or

asymmetric (asTKA) designs were to be used. These

researchers carried out a retrospective study on 24,042 data

sets that were generated during the design phase for a

customized TKA implant. These data set were drawn from

European and US-American patients. Measurements

recorded for the femur included the overall AP and medio

lateral (ML) widths, widths of the lateral condyle and the

medial condyle, the distal condylar offset (DCO) between the

lateral and medial condyles in the supero-inferior direction,

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and the posterior femoral offset (PFO) as the difference

between the medial and lateral posterior condylar offset (PCO)

measured in the AP direction. A consecutively collected

subset of 2,367 data sets was further evaluated to determine

the difference between the individual AP and ML dimensions

of the femur with that of modern TKA designs using two

commercially available implants from different vendors. These

investigators observed a high degree of variability in AP and

ML widths as well as in DCO and PFO. Furthermore, they

found no correlation between DCO and PCO of the knees

studied. Instances of a patient having a small DCO and higher

PCO were commonly seen. Analysis of the DFOs revealed

that overall, 62 % (14,906 of 24,042) of knees exhibited DCO

of greater than 1 mm and 83 % (19,955 of 24,042) of femurs

exhibited a greater than 2-mm difference between the lateral

and medial PCO. Concerning AP and ML measurements, 23

% (544 of 2,367) and 25 % (592 of 2,367) would have a

mismatch between the patient's bony anatomy and the

dimensions of the femoral component of ± 3 mm if they would

have undergone a modern standard sTKA or asTKA design,

respectively. The authors concluded that analysis of a large

number of CT scans of the knee showed that a high degree of

variability exists in AP and ML widths as well as in DCO and

PFO. The investigators stated that these findings suggested

that it is possible that a greater degree of customization could

result in surgeons performing fewer soft tissue releases and

medial resections than now are being done to fit a fixed-

geometry implant into a highly variable patient population.

However, as an imaging study, it could not support one

approach to TKA over another; comparative studies that

assess patient-reported outcomes and survivorship are

needed to help surgeons decide among sTKA, asTKA, and

customized TKA (cTKA).


First and most important was the virtual nature of

measurements, which could not be directly transferred to the

intra-operative situation and may not be associated with

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differences in pain or function after TKAs performed in clinical

practice. Another drawback of the present study was that CT

did not display cartilage thickness, which varied between 0

and 5 mm; Clarke reported a mean of 2 mm for the posterior

condyle, therefore making pre-operative measurement of the

PCO inaccurate. Furthermore, when the posterior condyles in

knees with varus alignment are considered, the cartilage

thickness of the medial condyle is usually found to be less

than the cartilage thickness of the lateral condyle. As a

consequence, over-resection of the medial posterior condyle

and under-resection of the lateral posterior condyle may

occur. A further consequence may be additional rotational

requirements and balancing. However, no standard TKA

instrumentation allowed for cartilage estimation but focused on

bony landmarks, cuts, and ligament balance. That being so,

the authors believed that although their measurement

approach may have shortcomings, those shortcomings directly

parallel those that are in common use in clinical practice in that

their measurement approaches based on cartilage were

similar to the alignment guides used during TKA. Even so, this

issue should be considered -- and the authors hope remedied

-- by future studies and perhaps future instrument systems.

Furthermore, cartilage and bone loss could influence ligament

balance and laxity, and these factors differ between patients;

likewise, surgeons may differ in terms of how they achieve

ligament balance, making this even more complicated. To try

to mitigate this, given that these differences were likely to be

more severe in knees with large deformities, the authors

excluded knees with varus or valgus deformities of greater

than 15°. The authors also noted that these data set included

implant dimensions that were generated from the design

process of a cTKA but did not include patient demographic

information; that being so, they could not assume that these

findings applied equally to men and women or different

ethnicities. Furthermore, because mapping the entire

database of implant dimensions was prohibitive when

comparing sTKA and asTKA, a large consecutive series was

selected to limit the effect of selection bias. Because the

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conclusions drawn were limited to cases that fell into the range

of sizes supported by the collected data, the conclusions

should apply to patients having knees with dimensions falling

into the FDA clearance range of cTKA. Thus, these

conclusions did not apply to small knees with dimensions that

did not fall in the clearance range, thereby probably excluding

parts of the Asian population. However, to the authors’ best

knowledge, this was the largest data set evaluated so far

depicting a large cross-section of European and US-American

patients and highlighting that surgeons intra-operatively had to

deal with individual anatomic geometries. Finally, the

comparisons were done using 3 modern TKA designs,

including symmetric and asymmetric designs; therefore, these

findings may not apply to every available commercial implant.

However, said modern standard TKA designs are of particular

interest because they are commonly used worldwide.

Namin et al (2019) stated that more than 6 million people were

living with knee replacement implants in the U.S. as of 2017.

This number is expected to increase to more than 3.5

million/year by 2030. The cost-effectiveness of total joint

replacement procedures has been broadly studied; however,

there is a compelling need to improve beyond the value

afforded by off-the-shelf knee implants. These investigators

examined the impact of insurance coverage on the adoption of

customized individually made (CIM) knee implants, and

compared patient outcomes and cost-effectiveness of off-the

shelf and CIM implants. The drawbacks of CIM implants

include (typically) expensive than OTS implant, lack of long

term evidence for clinical outcomes, need for customized

instrumentation, higher exposure to radiation in the process of

axial imaging such as computed tomography (CT) scanning,

and increased complexity of the implant ordering system.

These researchers developed a system dynamics model to

reproduce the historical data on primary and revision knee

replacement implants obtained from the literature and the

Nationwide Inpatient Sample. In simulation analyses, rate of

90-day re-admission, 3-year revision surgery, hospitalization

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and recovery period, time savings in operating rooms (ORs),

and the associated cost within 3 years of primary knee

replacement implants were used as comparison indicators.

The results compared the adoption of CIM and its economic

and patient outcome impacts to off-the-shelf implants under

different insurance coverage for CIM implants. The simulation

results indicated that, by 2025, an adoption rate of 90 % for

CIM implants will reduce the number of re-admissions and

revision surgeries by 62 % and 39 %, respectively, and save

hospitals and surgeons 6 % on procedure time, resulting in

cumulative savings of approximately $40 billion in healthcare

costs. The authors concluded that CIM implants have the

potential to deliver high-quality care while decreasing total

costs, but their adoption requires the expansion of current

insurance coverage.

The authors stated that the objective of the present study was

to take a systematic look at the adoption of CIM knee

implants. The goal was not to explore how to improve

treatment, but rather to perform what-if analyses. The flexible

nature of the model lends itself to extending it to study

innovative policies and interventions focused on economic

burden and patient outcomes when new information becomes

available. The model allows decision and policy makers to test

different coverage policies on the basis of their preference.

For instance, they can consider a dynamic scenario for their

coverage rate for CIM procedures on the basis of their initial

investment and savings throughout the simulation time. They

can also test the effect of time delays on the preparation of the

infrastructure. These investigators stated that these findings

may help policy makers consider CIM implants as an attractive

option for improving patient outcomes while reducing the total

costs of healthcare associated with TKA. The result could

inform decision-making among the Centers for Medicare &

Medicaid Services, private insurance providers, and hospitals,

spurring them to consider adoption of CIM implants and to

offer alternative payment methodologies that would encourage

widespread use of CIM knee implants.

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Wheatley et al (2019) noted that patient-specific implants have

been linked to stiffness. These researchers evaluated

outcomes in patient-specific implants. They performed a

retrospective review with a primary outcome of manipulation

under anesthesia (MUA); secondary outcomes included Knee

Society Scores (KSS), Knee Society Functional Scores

(KSFS), range of motion (ROM), and Forgotten Joint Scores

(FJS). Pre-operative measurements were similar in both

groups. There was 1 MUA in the custom patient specific

(CPS) and 2 in the off-the-shelf (OTS) groups. There was no

difference in post-operative scores. The authors concluded

that the findings of this study suggested that patient-specific

implants had comparable rates of MUA and functional

outcomes as conventional implants. These researchers stated

that future studies should take into account the inclusion of

additional outcome measures and longer term follow-up.


First, its retrospective nature has inherent potential for

selection bias with potentially more motivated patients

requesting the CPS TKA. Furthermore, as the primary

surgeon also noticed an increase in the manipulation rate of

his custom CR implants, a decrease in stiffness may represent

a learning curve in the implantation of the CPS knee

arthroplasty. However, the CPS group included his first CPS

implantation, so the authors believed the lack of difference

found in manipulation rates was likely a true finding. Another

drawback was that due to the relatively high Knee Society

Scores in the off-the-shelf group, it would be difficult to

demonstrate a significant increase in the functional scores of

the CPS group. Additionally, less than 50 % of the patients

included in the original cohort completed the FJS survey once

contacted. The relatively low response rate, 43 %, could be

considered a potential source of bias. With the low response

and relatively good functional scores in both groups, the study

was under-powered to detect a small, but potentially significant

difference in FJS scores. Furthermore, 3 months was a short

time period for follow-up to examine outcomes after knee

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arthroplasty. However, the authors felt that this was sufficient

length of follow-up to address the primary outcome of

manipulation rates as the majority of manipulations were

typically performed within the first 6 to 12 weeks following

surgery. However, since the principal objective of this study

was to compare manipulation rates, they believed the results

were still valuable.

Unicompartmental Versus Total Knee Replacement

In a systematic review and meta-analysis, Wilson and

colleagues (2019) presented a comprehensive summary of the

published data on UKA or TKA, comparing domains of

outcome that have been shown to be important to patients and

clinicians to allow informed decision-making. These

investigators carried out the c review using data from RCTs,

nationwide databases or joint registries, and large cohort

studies. Medline, Embase, Cochrane Controlled Register of

Trials (CENTRAL), and Clinical Trials.gov, were searched

between January 1, 1997 and December 31, 2018. Studies

published in the past 20 years, comparing outcomes of

primary UKA with TKA in adult patients. Studies were

excluded if they involved fewer than 50 subjects, or if

translation into English was not available. A total of 60 eligible

studies were separated into 3 methodological groups: 7

publications from 6 RCTs, 17 national joint registries and

national database studies, and 36 cohort studies. Results for

each domain of outcome varied depending on the level of

data, and findings were not always significant. Analysis of the

3 groups of studies showed significantly shorter hospital stays

after UKA than after TKA (-1.20 days (95 % CI: -1.67 to -0.73),

-1.43 (-1.53 to -1.33), and -1.73 (-2.30 to -1.16), respectively).

There was no significant difference in pain, based on patient

reported outcome measures (PROMs), but significantly better

functional PROM scores for UKA than for TKA in both non-trial

groups (MD -0.58 (-0.88 to -0.27) and -0.32 (-0.48 to -0.15),

respectively). Regarding major complications, trials and cohort

studies had non-significant results, but mortality after TKA was

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significantly higher in registry and large database studies (RR

0.27 (0.16 to 0.45)), as were venous thromboembolic events

(VTE; 0.39 (0.27 to 0.57)) and major cardiac events (0.22

(0.06 to 0.86)). Early re-operation for any reason was higher

after TKA than after UKA, but revision rates at 5 years

remained higher for UKA in all 3 study groups (RR 5.95 (1.29

to 27.59), 2.50 (1.77 to 3.54), and 3.13 (1.89 to 5.17),

respectively). The authors concluded that TKA and UKA are

both viable options for the treatment of isolated

unicompartmental osteoarthritis. By directly comparing the 2

treatments, this study demonstrated better results for UKA in

several outcome domains. However, the risk of revision

surgery was lower for TKA. This information should be

available to patients as part of the shared decision-making

process in choosing treatment options.

Ceramic Femoral Prosthesis in Total Knee Arthroplasty

In a prospective, comparative study, Bergschmidt and co

workers (2016) examined the clinical and radiological

outcomes of a TKA system, comparing a ceramic (BIOLOX

delta) and metallic (Co28Cr6Mo) femoral component over a

5- year follow-up period. A total of 43 TKA patients (17 metallic

and 26 ceramic femoral components) were enrolled in the

study. Clinical and radiological evaluations were performed pre

operatively and at 3, 12, 24 and 60 months post- operatively,

using the Hospital for Special Surgery (HSS) Knee Score,

WOMAC function scale and Short Form-36 (SF-36) score, in

addition to standardized X-rays. The HSS-Score improved

significantly from 58.7 ± 12.7 points pre-operatively to 88.5 ±

12.3 points at 5-years post-operative in the ceramic group, and

60.8 ± 7.7 to 86.2 ± 9.4 points in the metallic group. WOMAC-

and SF-36-Scores showed significant improvement over time in

both groups. There were no significant differences between

groups for HSS-, WOMAC- and SF-36- Scores, nor for ROM (p

≤ 0.897) at any follow-up evaluation.

Furthermore, radiological evaluation showed no implant

loosening or migration in either group. The authors concluded

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that mid-term outcomes for the ceramic femoral components

demonstrated good clinical and radiological results, as well as

comparable survivorship to the metallic femoral component of

the same total knee system, and to other commonly used

metallic total knee systems. Thus, ceramic knee implants may

be a promising solution for the population of patients with

osteoarthritis and metal sensitivity. These researchers stated

that long-term studies are needed to confirm the positive mid

term results, and to follow the implant survival rate in regard to

the enhanced wear resistance of ceramic implants.

Nakamura and associates (2017) stated that ceramic bearings

are not commonly used in TKA. Currently, little information is

available regarding if long-term survivorship and good clinical

outcomes can be ensured with ceramic knee implants. These

researchers examined the clinical and radiological outcomes,

and evaluated the long-term durability of a ceramic tri-condylar

implant. A total of 507 consecutive TKAs were performed

using a ceramic tri-condylar femoral implant. The posterior

cruciate ligament was sacrificed, and all components were

fixed with bone cement. Clinical outcomes were assessed

retrospectively with the Knee Society scoring system. Kaplan-

Meier survivorship was calculated to determine the cumulative

survival rate. A total of 167 knees (114 patients) were

available for clinical outcomes. The average range of flexion

improved from 118.1° pre-operatively to 123.7° at a minimum

15-year follow-up (p < 0.001). The average Knee Society

knee score improved from 39.1 to 92.8 (p < 0.001). The

functional score also improved from 36.0 to 47.0 (p < 0.001).

With revision for any surgery or radiographic failure as the end

point, Kaplan-Meier survivorship at 15 years was 94.0 %. With

revision of any component as the end-point, the corresponding

survivorship was 96.2 %. The authors concluded that clinically,

the post-operative knee flexion range and Knee Society scores

were good after long-term follow-up. The survivorship of the

ceramic knee implant was excellent

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over the 15-year follow-up, and long-term durability was

achieved, making ceramic a promising alternative material for

the femoral component in TKA.

Xiang and colleagues (2019) noted that ceramic bearings have

been widely used in total hip arthroplasty (THA), which

resulted in satisfactory clinical outcomes due to the excellent

tribological characteristics of the implants. However, ceramic

components are not commonly used in TKA because of

brittleness. These researchers analyzed information regarding

the clinical outcomes (including survival without revision,

causes of revision, functional outcome, and incidence of

loosening) and reached a definitive conclusion about the use

of ceramic femoral components in TKA. Medline, Embase,

Cochrane, and ClinicalTrials.gov databases were searched for

studies that reported the clinical and/or radiological outcomes

with or without survival data of ceramic TKA implants and that

included more than 10 patients with a minimum of 1 year follow-

up. From an initial sample of 147, there were 14 studies that met

the inclusion criteria. Overall, there was a notable enhancement

of joint function after the procedure, with a satisfactory mid- and

long-term survival of the ceramic components, which is

comparable to that of the conventional alloy components

reported previously. In addition, the revision rate was reported to

be between 0 % and 14.37 % according to the included

studies. However, revision due to aseptic loosening, wear, and

component fracture appeared to be rare, demonstrating the

safety of in-vivo use of ceramic bearings in the TKA procedure.

The authors concluded that ceramic TKA implants showed

similar post-operative clinical results and survival rate compared

to their conventional metallic counterparts. These findings

confirmed the safety of in-vivo use of ceramic bearings in TKA,

with rare implant breakage and aseptic loosening. They stated

that considering the excellent characteristics of the tribology of

ceramics, the clinical use of ceramic prostheses in TKA could

be promising.

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http://ClinicalTrials.gov


The authors stated that by systematically reviewing these

single-armed studies, they found that ceramic components

could be used in the TKA procedure, with excellent long-term

joint function and survival. However, because of the limited

use of ceramic TKA components worldwide, RCTs and cohort

studies comparing the long-term clinical results and survival

between ceramic TKA components and conventional cobalt-

chromium prostheses were not available. This may jeopardize

the strength of this conclusion. These researchers stated that

more research on ceramic TKA components, especially

comparative studies with a higher level of evidence, are

needed to support the use of ceramic components in the TKA

procedure.

MAKOplasty of the Knee

Kouk et al (2018) stated that total patellectomies are

uncommon procedures that are reserved as salvage treatment

for severely comminuted fractures of the patella. Due to the

alteration of normal joint mechanics, these patients presented

later on in life with degenerative cartilage damage to the

femoro-tibial joint and altered extensor mechanism. There are

very few reports of unicondylar knee arthroplasties following

previous patellectomy and none that specifically address

robot-assisted unicompartmental knee arthroplasty (UKA). A

recent case report by Pang et al described the use of

minimally invasive fixed-bearing unicondylar knee arthroplasty

in a patellectomized patient with moderate medial

compartment osteoarthritis (OA). This report detailed a case

with more significant chondral loss along with patellar tendon

subluxation. This was a case report of a patient with severe

medial compartment OA after a patellectomy following a motor

vehicle collision. After failing conservative treatment, the

patient underwent a medial MAKOplasty with complete

resolution of arthritic pain. The authors concluded that

significant pain relief and improved knee function could be

achieved with MAKOPlasty partial knee resurfacing system in

a previously patellectomized patient with severe medial

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compartment OA. Moreover, this case report was limited by its

length of follow-up (5 weeks) and its subsequent evaluation on

the efficacy of the treatment. To fully evaluate the treatment,

the patient should be followed longitudinally and additional

patients should be added. These researchers stated that robot-

assisted unicondylar arthroplasty may be a potential therapeutic

option in a patient with severe, isolated medial compartment OA

status after remote patellectomy.

Deese et al (2018) stated that UKA originated in the 1950's.

There have been many enhancements to the implants and the

technique, improving the precision and accuracy of this

challenging operation. Specifically for Robotic Arm Interactive

Orthopedic System (Rio; Mako Stryker, Fort Lauderdale, FL),

there are many studies reporting clinical outcomes, but this

search offered nothing regarding patient reported outcomes

using validated surveys. Patients with onlay tibial components

presenting for routine follow-up of robotic-arm assisted UKA

performed between May 2009 and September 2013 were

invited to participate; 4 joints had simultaneous patella femoral

resurfacing. Knee Injury and Osteoarthritis Outcomes Score

(KOOS) and the 2011 Knee Society Scores were collected.

Radiographic evidence of OA in the non-operative knee

compartments was documented. A total of 81 patients

presented for follow-up and consented to participate. Mean

follow-up was 54 months; mean patient reported KOOS

activities of daily living (ADL) and pain scores were each 90.

Knee Society 2011 mean objective score was 96 and mean

function score 81. There was 1 revision to total knee at 40

months post-op for pain after injury; 77 % reported their knee

always felt "normal", 20 % sometimes, and only 3 % reported

that it never felt normal. The authors concluded that the

literature on UKA failure rates suggested that UKA may be a

less forgiving procedure than total knee arthroplasty (TKA).

Robotic-arm assisted surgery has been reported to improve

the accuracy of implant placement. Based on the authors’

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prospectively collected positive patient outcomes, they have

achieved good results from performing robotic-arm assisted

UKA on select patients.


One was the number of subjects – only 54 % of the possible

participants presented for follow-up consented to participate.

Patients were consented and enrolled at the time of routine

annual follow-up and therefore the authors could not enroll any

patients that did not show up and did not reschedule their

appointment; 46 % were of working age 65 and under, which

these researchers agreed contributed to poor follow-up

compliance. Close proximity to military base may explain the

high number lost to follow-up as this population tended to

move frequently making it difficult to keep up with contact

information. The authors’ institution was the first facility in the

region to offer this technique and many patients came from

out-of-state, hence making it difficult for them to return to

clinic. Unfortunately, these investigators did not have a

consecutive series and therefore introduced selection bias.

There were no outcome scores collected or consistency in the

documented pain or function levels pre-operatively; thus, these

researchers had no baseline for comparison to the follow-up

scores.

Appendix

Kellgren-Lawrence Classification System

The Kellgren-Lawrence classification system uses a 0 to 4

grading method for classifying the severity of osteoarthritis

(OA) based on radiographs.

Table: Kellgren-Lawrence Classification System for

Osteoarthritis

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Grade

Grade 0

(none)

Definite absence of x-ray changes of

osteoarthritis.

Grade 1

(doubtful)

Doubtful narrowing of the joint space with

possible osteophytic lipping.

Grade 2

(minimal)

Definite osteophyte formation and possible

joint space narrowing.

Grade 3

(moderate)

Moderate multiple osteophytes formation,

definite narrowing of joint space, some

sclerosis, and possible deformity of bone

ends.

Grade 4

(severe)

Large osteophytes formation, severe

narrowing of joint space with marked

sclerosis and definite deformity of bone

ends.

Source: Kohn, Sassoon, Fernando (2016) and Knipe et al.

(2020)

CPT Codes / HCPCS Codes / ICD-10 Codes

Information in the [brackets] below has been added for clarification purposes. Codes requiring a 7th character are represented by "+":

Code Code Description

CPT codes not covered for indications listed in the CPB:

+0396T Intra-operative use of kinetic balance sensor for

implant stability during knee replacement

arthroplasty (List separately in addition to code

for primary procedure)

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0054T Computer-assisted musculoskeletal surgical

navigation orthopedic procedure, with image-

guidance based on fluoroscopic images

0055T Computer-assisted musculoskeletal surgical

navigation orthopedic procedure with image-

guidance based on CT/MRI images

20985 Computer-assisted surgical navigation

procedure for musculoskeletal procedures,

image-less

77401 -

77412

Radiation treatment delivery [following total

knee arthroplasty]

Other CPT codes related to the CPB:

27440 Arthroplasty, knee, tibial plateau

27441 with debridement and partial synovectomy

27442 Arthroplasty, femoral condyles or tibial plateau

(s), knee

27443 with debridement and partial synovectomy

27445 Arthroplasty, knee, hinge prosthesis (eg,

Walldius type)

Total knee arthroplasty (TKA):

CPT codes covered if selection criteria are met:

27447 Arthroplasty, knee, condyle and plateau; medial

AND lateral compartments with or without

patella resurfacing (total knee arthroplasty)

HCPCS codes covered if selection criteria are met:

C1776 Joint device (implantable) [FDA approved

device]

ICD-10 codes covered if selection criteria are met:

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M17.0 -

M17.9

Osteoarthritis of knee [with radiographic

evidence]

ICD-10 codes not covered if selection criteria are met:

A00.0 -

B99.9

Infectious and parasitic diseases

I87.2 Venous insufficiency (chronic) (peripheral)

L08.0,

L08.81,

L88

Pyoderma

M00.861

-

M00.869

Arthritis due to other bacteria, knee

M01.X61

-

M01.X69

Direct infection of knee in infectious and

parasitic diseases classified elsewhere

M62.551

-

M62.559

Muscle wasting and atrophy, not elsewhere

classified, thigh [muscle atrophy of the leg]

M62.561

-

M62.569


classified, lower leg [muscle atrophy of the leg]

M89.711

- M89.79

Major osseous defect [osseous abnormalities]

S81.001+

- S81.859

Open wound of knee and lower leg

T78.40x+ Allergy, unspecified, NEC [allergy to

components of the implant]

Revision or replacement of total knee arthroplasty:


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27486 -

27487

Revision of total knee arthroplasty, with or

without allograft

27488 Removal of prosthesis, including total knee

prosthesis, methylmethacrylate with or without

insertion of spacer, knee


C1776 Joint device (implantable) [not covered for

customized total knee implant]


M89.9 Disorder of bone, unspecified [confirmed by

imaging]

M94.9 Disorder of cartilage, unspecified [confirmed by

imaging]

M97.11x+

-

M97.12x+

Periprosthetic fracture around internal

prosthetic, knee joint [confirmed by imaging]

T84.012+

-

T84.013+

Broken internal knee prosthesis [confirmed by

imaging]

T84.022+

-

T84.023+

Instability of internal knee prosthesis

T84.032+

-

T84.033+

Mechanical loosening of prosthetic joint

[confirmed by imaging]

T84.062+

-

T84.063+

Wear of articular bearing surface of internal

prosthetic knee joint [confirmed by imaging]

Proprietary



T84.092+

-

T84.093+

Other mechanical complication of internal knee

prosthesis [confirmed by imaging]

Z96.651 -

Z96.659

Presence of artificial knee joint

Unicompartmental knee arthroplasty:


27437 Arthroplasty, patella; without prosthesis

27438 with prosthesis

27446 Arthroplasty, knee, condyle and plateau; medial

OR lateral compartment


C1776 Joint device (implantable) [not covered for

customized total knee implant]


M17.0 -

M17.9

Osteoarthritis of knee [with radiographic

evidence]

ICD-10 codes not covered if selection criteria are met:

I87.2 Venous insufficiency (chronic) (peripheral)

M62.551

-

M62.559


classified, thigh [muscle atrophy of the leg]

M62.561

-

M62.569


classified, lower leg [muscle atrophy of the leg]

M89.711

- M89.79

Major osseous defect [osseous abnormalities]

UniSpacer interpositional spacer:

Proprietary



No specific code

ICD-10 codes not covered if selection criteria are met (not all inclusive):

M17.0 -

M17.9

Osteoarthritis of knee

Bicompartmental, bi-unicompartmental knee and staged bicompartmental arthroplasty:

No specific code

ICD-10 codes not covered if selection criteria are met (not all inclusive):

M17.0 -

M17.9

Osteoarthritis of knee

The above policy is based on the following references:

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1915.

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Proprietary


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Copyright Aetna Inc. All rights reserved. Clinical Policy Bulletins are developed by Aetna to assist in administering plan

benefits and constitute neither offers of coverage nor medical advice. This Clinical Policy Bulletin contains only a partial,

general description of plan or program benefits and does not constitute a contract. Aetna does not provide health care

services and, therefore, cannot guarantee any results or outcomes. Participating providers are independent contractors

in private practice and are neither employees nor agents of Aetna or its affiliates. Treating providers are solely

responsible for medical advice and treatment of members. This Clinical Policy Bulletin may be updated and therefore is

subject to change.

Copyright © 2001-2020 Aetna Inc.

Proprietary

AETNA BETTER HEALTH® OF PENNSYLVANIA

Amendment to Aetna Clinical Policy Bulletin Number: 0660 Knee

Arthroplasty

There are no amendments for Medicaid.

www.aetnabetterhealth.com/pennsylvania revised 08/18/2020

Proprietary

http://www.aetnabetterhealth.com/pennsylvania

0660 knee arthroplasty - aetna better health

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