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Predicting 1-year flexion results in Predicting 1-year flexion results in Total Knee Replacement patientsTotal Knee Replacement patients

Negus JJ Negus JJ MSc MSc 1,21,2

Parker DA Parker DA FRACSFRACS11

Coolican MRJ Coolican MRJ FRACSFRACS11

Galea A Galea A MRCSMRCS11

Ogut M Ogut M 22

11 Sydney Orthopaedic Research Institute Sydney Orthopaedic Research Institute22 University of Sydney University of Sydney

Australian Orthopaedic AssociationAustralian Orthopaedic Association7070thth Annual Scientific Meeting Annual Scientific Meeting

Adelaide, 2010Adelaide, 2010

www.sori.com.auwww.sori.com.au

DeclarationsDeclarations

No conflicts of interest to declareNo conflicts of interest to declare


IntroductionIntroduction

A knee with poor flexion can be clinically restrictive.A knee with poor flexion can be clinically restrictive. ≤≤90˚ often a clinical cut-off90˚ often a clinical cut-off

It is unclear whether a knee with poor flexion at It is unclear whether a knee with poor flexion at

6-weeks will benefit from a manipulation6-weeks will benefit from a manipulation

Postoperative flexion has been shown to correlate Postoperative flexion has been shown to correlate to preoperative flexion, but not as a quantitative to preoperative flexion, but not as a quantitative predictor.*predictor.*

* Anouchi * Anouchi et al et al `96, Lingard `96, Lingard et al et al ‘04, Ritter ‘04, Ritter et al et al ’03’03


Aims of StudyAims of Study

1.1. To identify the value of early postoperative To identify the value of early postoperative flexion measurements as predictors of 1-year flexion measurements as predictors of 1-year flexion.flexion.

2.2. To identify which knees might benefit from To identify which knees might benefit from manipulation in the early postoperative phase.manipulation in the early postoperative phase.


MethodsMethods Prospective series of Prospective series of 104 knees in 100 patients104 knees in 100 patients

2 specialist knee surgeons2 specialist knee surgeons Age, BMI, Surgeon (implant)Age, BMI, Surgeon (implant) ROM measured ROM measured

Pre-op, intra-op, day 2, day 6, 6 weeks, 1 yearPre-op, intra-op, day 2, day 6, 6 weeks, 1 year Functional scores (WOMAC, Oxford)Functional scores (WOMAC, Oxford)

Pre-operativePre-operative 1 year1 year

Discharge 6 days postoperativelyDischarge 6 days postoperatively Most commonly to inpatient rehabilitationMost commonly to inpatient rehabilitation

Physiotherapy and rehabilitation not standardisedPhysiotherapy and rehabilitation not standardised


Patients and MethodsPatients and Methods

Knee flexion measured with a goniometerKnee flexion measured with a goniometer Reproducible technique *Reproducible technique *

Spinal or general anaestheticSpinal or general anaesthetic

Medial parapatellar approachMedial parapatellar approach

Fixed bearing prosthesis; patella Fixed bearing prosthesis; patella resurfacedresurfaced

Peri-articular soft tissue infiltration of local Peri-articular soft tissue infiltration of local anaestheticanaesthetic

Closure with knee flexed between 60 – Closure with knee flexed between 60 – 90˚90˚

* Edwards * Edwards et al et al ‘04‘04


DemographicsDemographics

Group Male Female

Number 104 33 67

Pre-op flexion

113 (50-135)

Age 70 (52-86) 71 (47-94)

BMI 28.9 28.9


RESULTSRESULTS


Arc of motionArc of motion


Correlations with flexion at 1 yearCorrelations with flexion at 1 year

Significant correlations between –Significant correlations between – Preoperative flexion Preoperative flexion & 1 year flexion & 1 year flexion p= p=

0.0040.004 Week 6 flexion Week 6 flexion & 1 year flexion& 1 year flexion p=<0.001p=<0.001

Preoperative flexion Week 6 flexion


Predictive equation at 6 Predictive equation at 6 weeksweeks

6/52 Flexion Multiply by

<100˚ 1.27

100-109˚ 1.122

110-119˚ 1.068

≥120˚ 1.035

Mean accuracy of 0.22˚ (0.04˚ if 6 week flexion is >100˚)

If 6 week flexion >100˚ 4 knees overestimated by >10˚Only 1 had 1 year flexion <110˚


Clinical courseClinical course

• ≤≤90˚ at 6 weeks90˚ at 6 weeks

• Only 15% of these still had ≤90˚ at 1-yearOnly 15% of these still had ≤90˚ at 1-year

• ≤ ≤90˚ at 1 year90˚ at 1 year

• 75% had ≥110˚preoperative flexion75% had ≥110˚preoperative flexion


Pre-op ≤90˚ vs. >90˚Pre-op ≤90˚ vs. >90˚

*


6 week ≤90˚ vs. >90˚6 week ≤90˚ vs. >90˚


Statistical modelStatistical model

A regression analysis model taking into account all A regression analysis model taking into account all variablesvariables

It explains 54% of the variance in the results *It explains 54% of the variance in the results *

Mean predictive accuracy 1.0˚ Mean predictive accuracy 1.0˚ (SD 8.0, CI 1.9)(SD 8.0, CI 1.9)

Only 8 predictions were overestimated by >10˚ Only 8 predictions were overestimated by >10˚

* * Anouchi Anouchi et al et al 19961996


EquationEquation

1 year flexion 1 year flexion = =

-29753306 -29753306

+ ( 137000000 + ( 137000000 * * BMI BMI -0.5 -0.5 ) )

+ ( 6.18 + ( 6.18 * * Pre-op flexion Pre-op flexion 3 3 ) )

+ ( 2983 * + ( 2983 * 6 week flexion 6 week flexion 2 2 ))


ConclusionsConclusions

1.1. 54% of the variance of final flexion accounted for 54% of the variance of final flexion accounted for byby

Preoperative flexion, 6 week flexion and BMI.Preoperative flexion, 6 week flexion and BMI. No effect of age, gender, surgeon and flexion at other time pointsNo effect of age, gender, surgeon and flexion at other time points

1.1. Flexion at 6 weeks can guide our predictions of Flexion at 6 weeks can guide our predictions of final flexion.final flexion.

1.1. A statistical model is needed to predict poor A statistical model is needed to predict poor flexion results.flexion results.

2.2. This study suggests caution before manipulating This study suggests caution before manipulating knees, based on a single postoperative flexion knees, based on a single postoperative flexion measurement alone.measurement alone.


DiscussionDiscussion

The ability to predict which knees are likely to The ability to predict which knees are likely to end up with a poor result would benefit end up with a poor result would benefit surgeons and patients.surgeons and patients.

Further work before the model can be used as Further work before the model can be used as a clinical tool.a clinical tool.

Retrospective data analysis of extensive database.Retrospective data analysis of extensive database. Regression analysis for all variables.Regression analysis for all variables. Refine predictive equation.Refine predictive equation.


Thank YouThank You

Many thanks to Dr Corey Scholes 1 PhD for his help with the statistical analysis

1 – Sydney Orthopaedic research Institute


BibliographyBibliography

Anouchi YS Anouchi YS et alet al. Range of motion in total knee . Range of motion in total knee replacement. COOR 1996;331:87-92replacement. COOR 1996;331:87-92

Ritter MA Ritter MA et alet al. Predicting ROM after total knee . Predicting ROM after total knee arthroplasty. JBJS Am 2003;85:1278-1285arthroplasty. JBJS Am 2003;85:1278-1285

Edwards JZ Edwards JZ et alet al. Measuring flexion in knee . Measuring flexion in knee arthroplasty patients. J Arthroplasty;19:3:369-372arthroplasty patients. J Arthroplasty;19:3:369-372

Lingard EA Lingard EA et alet al. Predicting the outcome of total knee . Predicting the outcome of total knee arthroplasty. JBJS Am. 2004;86:2179-2186arthroplasty. JBJS Am. 2004;86:2179-2186

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