BackgroundA primary goal of total hip arthroplasty is the reconstruction of the patient’s personalized kinematics. Three important factors for biomechanical reconstruction of the hip are leg length, offset and avoidance of impingement. Neck modularity improves the ability to re-create the head center to achieve these goals but also raises concerns regarding fretting debris and potential fracture. The objective of this article is to summarize the extensive in-vitro and experimental testing used to predict and therefore characterize the performance of the CLS® Brevius™ Stem with Kinectiv® Technology implant system in-vivo.

MethodsUsing finite element analysis, the worst case stem and neck constructs were identified. Fatigue per-formance bench testing was performed for ten million cycles using ISO test methods and stringent internal performance requirements used for all Zimmer GmbH monoblock stems. For the evaluation of the connection strength of the Kinectiv Technology, distraction forces were measured after implantation of the neck according to the surgical technique. Fretting wear debris was also evaluated using quanti-tative accelerated corrosion fatigue testing on Kinectiv Stem/Neck/Head construct. The influence of ante-/retroverted necks on the loading of the implant bone interface was analyzed based on a literature review while the effect of stem shortening on primary stability was tested on cadaver paired-femurs.

ResultsThe CLS Brevius Stem with Kinectiv Technology exceeds the fatigue strength performance criterion as defined by internal requirements based on ISO test methods. The Kinectiv Neck taper junction dis traction strength is stronger than the clinically used Zimmer 12/14 head/neck taper. The fretting corrosion of the stem is less than the clinically derived benchmark and is similar to the current Zimmer® M/L Taper with Kinectiv Technology. The degree of version offered by the Kinectiv necks does not exceed that found currently clinically, or values reported to result in altered femoral loading. Stem shortening does not significantly affect the torsion or axial subsidence behavior of the stem compared to the CLS Spotorno Stem.

ConclusionsThe CLS Brevius Stem with Kinectiv Technology successfully meets Zimmer’s performance strength requirements that have proven successful for many years. It demonstrates a fretting corrosion that is comparable to the mass loss of the Zimmer M/L Taper with Kinectiv Technology, both of them being less than the mass loss of the predicate Zimmer 6° taper benchmark. The CLS Brevius Stem with Kinectiv Technology provides a secure fit of the modular com-ponents.

Performance evaluation of CLS® Brevius™ Stem with Kinectiv® TechnologyDirk Weidmann, Ronja Bruhn, Susanne Frei, Daniel Hertig, Xavier Langlois, Paul Hulme, PhD

Zimmer GmbH

1

Introduction

A primary goal of total hip arthroplasty is the re-construction of the patient’s personalized kine-matics. Three important factors for biomechani-cal reconstruction of the hip are leg length, offset and avoidance of impingement. Literature has reported that leg length and dislocation are ma-jor challenges in total hip arthoplasty (THA)1–4.When introduced in the 1980’s, hip stems with modular heads and different CCD angles facili-tated a more accurate and stable biomechanical reconstruction. Although these modular designs do offer enhanced versatility, intraoperative ad-justments such as these introduce additional variables. For example, an increase in head length to improve muscle tension not only changes the femoral offset, but also increases leg length, which may not be desirable. Further-more, modular head designs, whilst a clear im-provement upon earlier designs, do not facilitate changes in femoral version, which is an impor-tant consideration when one considers the im-plications for impingement. Clinical studies report significant differences be-tween patients, and genders, in femoral head center location and the size and shape of the medullary canal. For example, women tend to have lower head centers, less offset, and greater anteversion than men5–8. When using traditional implants with very limit-ed neck-shaft angle options, these differences can make size selection and head center place-ment a challenge – especially in patients pre-senting with acute varus or valgus necks – and surgeons may be forced to compromise through: •   sacrificing  the  bone  by  making  lower  neck 

cuts to avoid leg lengthening•   seating the stem high to increase leg length•   seating  the  stem  in  varus  to  decrease  leg 

length•   seating the stem in valgus to decrease offset•   inserting a stem against  the natural antever-

sion of the femur to achieve greater prosthetic femoral anteversion.

The CLS® Brevius™ Stem with Kinectiv® Technol-ogy offers more intraoperative flexibility to re-construct personalized kinematics through mod-

ular necks which enables true independent intraoperative leg length, offset and version ad-justments. Independent version adjustments after stem implantation facilitates optimal stem positioning based on the patient’s proximal fem-oral anatomy and may reduce the risk of femoral fracture9. Its core design is based on the original CLS® Spotorno® Hip Stem with its excellent clini-cal history (survival rate of 95% at 20 years10). Optimized stem length also supports surgeons in preserving more bone and facilitates less in-vasive surgery.Kinectiv Technology addresses leg length and offset restoration by offering five length options in 4mm increments (–8mm, –4mm, +0mm, +4mm, and +8mm). This simple intraoperative flexibility is possible by offering a range of modu-lar straight, anteverted and retroverted necks (4° to 10°) to be used only in conjunction with a +0mm femoral head.Regardless of the clear advantages brought for-ward by a more bone conserving modular hip stem which offers great intra-operative freedom, Zimmer’s responsibility to the patient drives the company to perform exhaustive pre-clinical testing in order to prove the design meets both stringent internal strength requirements, but also those mandated by the relevant authorities. The objective of this paper is to summarize the extensive testing that was undertaken for the de-sign of the CLS Brevius Stem with Kinectiv Tech-nology. The paper has been divided up into five sec-tions, each of them highlighting the research activities which were undertaken to answer the following questions:•   Does the CLS Brevius Stem with Kinectiv Tech-

nology have sufficient fatigue strength to withstand in vivo loading?

•   Is the taper connection strength between the neck and stem strong enough to withstand un-wanted disassociation, and so inhibit micro-motion?

•   Is  fretting  corrosion  minimized  to  ensure  a stable connection and minimal metal ion re-lease?

•   Does  the  use  of  necks  with  version  compro-mise the anchorage of the stem body in the bone?

2

Performance evaluation of CLS® Brevius™ Stem with Kinectiv® Technology

•   What  is  the  effect  of  stem  shortening  on  the primary stability of the CLS Brevius Stem with Kinectiv Technology?

Mechanical fatigue strength of the CLS Brevius Stem with Kinectiv Technology Stem

IntroductionA hip stem must be designed to withstand the millions of load cycles that it will be subjected to during its lifetime in vivo. The majority of hip stem implants on the market today only have one mod-ular junction between the hip stem neck and the ball head. The concept of THA has been proven through extensive clinical studies, and standard designs have proved to have low fracture rates (1.5%11). The modular connection between the hip stem neck and ball head was introduced in the early 1980s12, as an initiative to allow the surgeon to make intraoperative changes, and also to facilitate the use of different ball head ma-terials for different clinical indications. Further modularity, whilst viewed as an important evolu-tion in implant design, must consider its impact regarding potentially altered fatigue strength and fretting corrosion through testing and reference to the extensive body of clinical evidence which exists.As it has been highlighted, the CLS Brevius Stem with Kinectiv Technology features an additional modular junction to incorporate the Kinectiv neck. As there have been reported fractures of other modular implant systems in literature13–15, it is critical to ensure that, similar to the standard stem with a single modular connection, the fatigue strength of the new stem can be estab-lished.

MethodsPrior to in vitro testing, a detailed Finite Element Analysis (FEA) identified the CLS Brevius Stem with Kinectiv Technology sizes 5 and 20, com-bined with Kinectiv neck DD, as being the combi-nations which resulted in the highest implant stresses, which would be the highest contribu-tors towards material fatigue.

The strength performance requirement imposed on the CLS Brevius Stem with Kinectiv Technology implants was based on ISO 7206-616 and strin-gent Zimmer internal requirements. This requirement included loading, orientation, cycles and number of test samples.ISO 7206-6 describes the test methodology for cyclic fatigue performance evaluation of the proximal, unsupported region of the femoral hip stems, while the acceptance criterion for testing was that all stems should survive the 10 million load cycles without fatigue failures (test set up shown in Fig. 1).

Fig. 1 Fatigue test setup

The requirement was the same as that for Zimmer GmbH monoblock stems, including the CLS Spotorno Stem.

ResultsAll tested stems completed the 10 millions cycles without fracture. Since all stems met the accept-ance criterion, the influence of additional load increases were evaluated, to estimate fatigue limits of the design. An increase in the safety factor of 11% and 26%, over that defined by the stringent test methodology, was found for the CLS Brevius Stem with Kinectiv Technology size 5 and 20 respectively (Fig. 2).

3

4

Design consideration for strengthThere are many factors involved in modular junc-tion design that have direct and indirect influ-ences on the fatigue strength performance of an implant. These factors affect local reaction forc-es, stress states, contact pressures and fretting motion, all of which significantly influence the strength of the construct. Grupp et al., reported that by altering the material properties of the neck from Ti to CoCr, this action increased the fa-tigue strength by 28%. However, as shown in the Zimmer study, the CLS Brevius Stem with Kinectiv Technology with titanium modular necks affords an even greater fatigue strength than the CoCr necks. The fatigue strength of any implant is not only dependent on material properties but also is heavily influenced by the design. One design aspect of the Kinectiv neck is junction length. The simplified illustration of Figure 4 shows the rela-tionship of the forces acting on the neck com-ponent.

Fig. 4

Simplified model of forces acting on a modular neck.

As the length of the neck/stem taper (LTaper) de-creases, the reaction forces at the proximal (FO) and distal (FR) regions of the taper increase for a given head center location (LNeck). This princi-ple shows that a longer neck/stem taper (LTaper) leads to lower loads in the junction. The design features embodied in the Kinectiv Technology design, including shape, size and surface finish, have been carefully engineered to meet Zim-mer’s rigorous strength requirements while maintaining minimal fretting motion (refer to section on ACF testing).

The fatigue strength of the CLS Brevius Stem with Kinectiv Technology was also compared to another modular stem design reported by Grupp et al.14.

Fatig

ue lo

ad (1

00%

=acc

epta

nce

crite

ria)

130%

120%

100%

80%

60%

40%

20%

0 CLS Brevius Kinectiv CLS Brevius Kinectiv size 5 Neck DD size 20 Neck DD

+11%

+26%

Minimum strength requirement of Zimmer monoblock stems

Fig. 2 Additional safety for the CLS Brevius Stem with Kinectiv Technology size 5 and 20.

Grupp et al. investigated the clinical failures of a titanium femoral implant successively combined with a titanium (Ti-Adapter) and cobalt chromi-um (CoCr-Adapter) neck adapter due to clinical failures of the first. The fatigue strength of the CLS Brevius Stem with Kinectiv Technology size 5 combined with the Kinectiv neck DD was 15% greater than the modular stem with a CoCr-adapter reported in literature and 43% greater than the original Ti-Adapter14 (Fig. 3).

Fig. 3 Fatigue strength comparison between another modular stem design with Ti- and CoCr necks and the CLS Brevius Stem with Kinectiv Technology size 5 combined with Neck

DD.

Performance evaluation of CLS® Brevius™ Stem with Kinectiv® Technology

5

Also, the amount of version provided by the mod-ular neck has an influence on the strength of the modular construct, since more version leads to a longer lever arms and thus to higher bending mo-ments in the stem. Kinectiv Technology offers the amount of version that successfully meets Zim-mer’s stringent strength requirements. While meeting the strength requirements, the version provided by the anteverted and retroverted necks was optimized to address a wide range of patient anatomies17. For a given head center l ocation, Ki-nectiv Technology offers the same amount of ver-sion regardless of the neck shaft angle (Fig. 5).

Fig. 5

Version provided by Kinectiv Technology.

With Zimmer’s innovative, exclusive use of the +0mm femoral head, Kinectiv Technology is able to meet the critical requirements of clinical need and implant strength without skirted femoral heads that can reduce range of motion.

Conclusion•  The CLS Brevius Stem with Kinectiv Technology

proximal fatigue strength meets and exceeds Zimmer internal standards based on ISO require ments and that are the same as used for Zimmer GmbH monoblock stems, including the CLS Spotorno Stem.

•   Even  the  sizes  showing  the  highest  implant stress exceeded the stringent acceptance cri-terion by at least 11%.

•   Compared  to  a  predicated  modular  hip  stem with a CoCr-Adapter (reported in literature14), the CLS Brevius Stem with Kinectiv Technology has 15% higher fatigue strength.

Stability of the taper junction between the stem and the Kinectiv neck

IntroductionThe connection strength between all modular junctions must be fit for purpose and meet the in-vivo requirements to be successful long term. Taper connection strength is important so as to ensure that, during loading, the taper does not disassociate and result in interface micro-mo-tions, which may lead to fretting corrosion. It should be noted that due to the oval profile of the neck taper, disassociation of the stem/neck as-sembly due to high torsional loading events, is impossible. To disassociate the neck from the stem the force must be in line with the taper axis, so as to effectively pull the neck from the stem. To evaluate the connection strength of the Kinectiv neck/stem coupling following initial assembly, the distraction forces required to separate the neck from the stem were evaluated. The Kinectiv Neck was assembled to the stem using a con-trolled compressive load, as outlined by ASTM F 200918. For assembly, the surgical technique was used whereby the neck was placed into the stem, the ball head was placed onto the neck and both together were loaded with the assembly load. The force required to distract the neck from the stem was then measured.

ResultsDistraction forces for the Kinectiv Neck/Stem junction exceeded those required to separate the head/neck taper for all specimens (Fig. 6). As suggested by research conducted by other institutions, the Kinectiv Neck/Stem junction is expected to be even more stable after initial cyclic loading via patient activities due to pro-gressive seating of the modular components under loads generated in-vivo19. Nevertheless, initial stability of the modularity is still important to ensure that it does not disassociate or allow bone chips and other debris to enter into the modularity prior to the first loadings by the im-plant recipient.

6

Conclusion•   The  Kinectiv  Neck/Stem  junction  demon-

strates distraction forces that exceed those required to separate a typical 12/14 head/neck taper.

Fig. 6 Comparison of the pull-off force between a current Zimmer 12/14 taper and the Kinectiv Necks Taper. Note: 100% is the pull-off force of a current Zimmer 12/14 titanium taper combined with a CoCr-Head.

Accellerated Corrosion Fatigue (Acf) Testing

IntroductionNumerous design and clinical factors are associ-ated with the fretting and corrosion performance of implant modularity20–23. To predict the clinical performance of modular implant designs, the corrosive boundary conditions (environmental parameters and loading) were modified to accel-erate any fretting corrosion mechanisms which might occur in the modular junction. Through analysis of retrieved specimens and laboratory testing, Zimmer has been able to refine the testing parameters to effectively induce the ob-served clinical corrosion patterns of Zimmer’s original 6 degree and newer 12/14 head-stem taper designs. Using the previously developed accelerated corrosion fatigue test, the corrosion behavior of the CLS Brevius Stem with Kinectiv Technology, with focus on the stem-neck modularity, was as-sessed and compared to the corrosion behavior of a predicate benchmark.

Method Testing was conducted using the refined test parameters, which are summarized in the table below (Figure 7).

Fig. 7 Final test parameters and accelerated corrosion fatigue test setup isolating the modularity of interest from the

testing solution.

The sample in the test chamber was placed with-in a secondary, heated bath on the test machine. The isolation of the taper junction, together with regular control of the testing parameters, such as pH and temperature, provided optimal condi-tions for test reproducibility.

Head/Neck junction Stem/neck junction

Loading Sinusoidal waveform R = 0.1 (max/min ratio)

Environment Ringer’s Solution Acidic pH Increased Temperature

Frequency 5 Hz

Orientation (M/L angle, A/P angle) Straight (10o/9o)5,6

Equipment Closed Loop Servo-hydraulic test machines in Load control

Cycles 10,000,000

Performance evaluation of CLS® Brevius™ Stem with Kinectiv® Technology

7

Quantification of fretting corrosionA mass loss approach was used to quantify the amount of fretting corrosion. Pre-test and post-test, the samples were cleaned and weighed according to a defined cleaning procedure. The difference between pre-test and post-test weight is an indicator for the amount of fretting corro-sion. The mass loss quantification consisted of the following steps:1. Precleaning and initial mass determination –

consisted of sonication, multiple cycles of manufacturing grade cleaning and analytical balance mass measurement.

2. Corrosion fatigue testing according to the pa-rameters previously outlined.

3. Post-test cleaning and final mass determina-tion – consisted of sonication, multiple cycles of manufacturing grade cleaning and analyti-cal balance mass measurement.

Accelerated corrosion fatigue testing with mass loss assessment was conducted using the Zimmer modular CLS Brevius Stem with Kinectiv Technology in combination with an extra-extend-ed offset modular neck and a +0mm offset ce-ramic head. In a first step, a ceramic head was used, in order to minimize head-neck mass loss and focus on the modularity of interest: the neck-stem modu-larity.In a second step, the CLS Brevius Stem with Kinectiv Technology system mass loss was calcu-lated adding the mass loss of a standard 12/14 head-neck (CoCr/Ti)

Data analysis and comparisonThe fretting corrosion behaviour of the CLS Brevius Stem with Kinectiv Technology was compared to the Zimmer® M/L Taper with Kinectiv® Technology and the previously tested six degree taper with a long neck length. The predicate modular Zimmer M/L Taper with Kinectiv Technology was tested previously with the same neck and head combi-nation, and tested according to the same setup. The previously tested six degree taper was intro-duced to the market more than 30 years ago24 and serves as a reasonable benchmark for mass loss.

Results and conclusions•   The  mass  loss  of  the  CLS Brevius Stem with

Kinectiv Technology was comparable to the mass loss of the Zimmer M/L Taper with Kinectiv Technology. The system mass loss for both systems is the sum of the mass loss of the tested neck-stem combination and the mass loss of a +0 mm CoCr/Titanium 12/14 taper combination (Figure 8).

Fig. 8 Accelerated corrosion fatigue mass loss results of the CLS Brevius Stem with Kinectiv Technology (left) and the Zimmer M/L Taper with Kinectiv Technology (right). Head-neck mass loss refers to the mass loss of a standard +0 12/14 taper connection (CoCr-Ti). The benchmark line refers to the mass loss results of the marketed 6° taper.

•   The system mass loss of CLS Brevius Stem with Kinectiv Technology was less than the mass loss of the predicate 6° taper benchmark (Fig. 8, red line).

•   The  mass  loss  of  the  CLS Brevius Stem with Kinectiv Technology meets Zimmer internal test requirements.

combined neck-stem mass loss

combined head-neck mass loss

mg/

10 m

illio

n cy

cles

120%

100%

80%

60%

40%

20%

0 CLS Brevius M/L Taper Kinectiv Stem Kinectiv Stem

benchmark mass loss

Effect of neck version on the loading of the implant-bone interfaceIntroductionA literature review was performed to establish whether the use of necks with implemented ver-sion compromises the anchorage of the stem body in the bone.The results of this investigation are organized into the following sections:1. Natural and post-operative version angles

are reported to demonstrate that the Kinectiv anteversion and retroversion angles are within previously reported version angles for natural and implanted femora.

2. A review of reported investigations (FEA) is presented to illustrate how changes in load-ing which is transferred to the bone may be expected with different version angles.

Results1. The version angle of the Kinectiv Technology,

allowing to address a wide range of patient anatomies5,6,8, can be altered by a maximum of ±10°. This is much smaller than the vari-ability of the natural anatomical version angle, and the observed version angle reported after total hip arthroplasty (THA)5,6,25.

2. Various authors have reported results from Finite Element Analysis (FEA) used to investi-gate the influence of version on hip contact forces and/or stem anchorage. Mathematical models have shown higher hip contact forces and moments with increasing anteversion angle26–28. In contrast, the lever arm decreas-es with increasing anteversion angle result-ing in a decrease in the torque applied to the stem29. Most papers concluded that an in-creasing anteversion angle leads to increas-ing strain in the implant/bone interface. How-ever, the degree by which the version would have to be changed in order to get a signifi-cant change in loading was greater than the maximum 10° change in version offered by the Kinectiv necks26. Thus, for situations in which stem placement would result in a change in version, the ability to correct ver-

sion using a modular neck may avoid situa-tions in which excessive version would result in changes in non-anatomical and unreason-able femoral loading.

Conclusions•   The  range  of  version  angles  made  available 

using the Kinectiv Technology already exists in the normal anatomical diversity of femurs and has been recorded post-operatively for modu-lar and non-modular implants.

•   Maximum version angles of the Kinectiv Tech-nology are less than the change in version angle required to influence the loading of the implant/bone interface and thus anchorage of the stem.

•   Modular  necks  give  the  intraoperative  flexi-biliy to avoid excessive version angles which may avoid influencing the loading of the im-plant/bone interface.

8

Performance evaluation of CLS® Brevius™ Stem with Kinectiv® Technology

The effect of distal stem shortening on primary stability

IntroductionPress-fit femoral stems rely on the strength and integrity of the interface between the stem and the cortico-cancellous bone (primary stability). A well designed implant will demonstrate a high resistance to excessive interface micro-motion and migration of the stem under load.

During the design phase of the CLS Brevius Stem with Kinectiv Technology it was hypothesized that the very distal end of the CLS Spotorno Stem may not be essential for fixation in bone and therefore the CLS Brevius Stem with Kinectiv Technology could be designed with reduced length. Shortening must not compromise the excellent fixation behavior of the original CLS Spotorno Stem. Therefore, using 3D CT scan-based femoral bone models from a database containing over 400 femoral models, the fixation principles of the CLS Spotorno Stem was investi-gated by determining the amount and type of contact with the cortical bone and evaluated with respect to different levels of stem shorten-ing (10%, 20%, 30%, 40%).

Once the possible amount of stem shortening was defined, the potential drop in primary stabil-ity, incurred through a shortening of the distal stem, has been discussed based in published literature30,31. It has been theorized that any resulting increases in micro-motion (elastic de-formation) may result in generation of fibrous tissue rather than bone, affecting secondary sta-bility32, and could compromise the long-term success of a shortened stem. Furthermore, stem migration may result in bone resorption and osteolysis, in addition to altering the intended biomechanical joint reconstruction33. Conse-quently, it was essential to undertake testing to quantify the effect that stem shortening would have on primary stability.Tests were performed using cadaveric contra-lateral femurs in which the CLS Spotorno Stem and a 30% distally shortened CLS Spotorno Stem

were implanted and then loaded cyclically, either in torsion or under loading conditions which would induce stem subsidence. During loading, the micro-motions at the interface and also the migration of the femoral stems were measured and compared between the original design and the shortened stem design, to evaluate whether the initial primary stability of the shortened CLS Spotorno Stem was significantly different (p<0.05) from that of the CLS Spotorno Stem.

MethodsTwo modes of stem micro-motion under load were analyzed in the current study: torsion and axial subsidence. Thirteen matched pairs of ca-daveric femora (26 femurs) were analysed, five pairs in torsion and eight pairs under loading conditions required for axial subsidence. Prior to stem implantation, parameters describing speci-men demographics (age and gender) and femo-ral morphology (bone quality assessed using CT as well as geometry of proximal femoral canal) were analysed to determine the suitability of a cementless implantation and ensure that femurs of a matched pair were morphologically equiva-lent. Stems were implanted by two experienced sur-geons. For a matched femoral pair, a normal CLS Spotorno and shortened CLS Spotorno Stem of equal size were implanted. Intra-operative pa-rameters describing depth of insertion, antever-sion of the femoral stem, resection cut and fit within the femoral canal (intra-operative fluoros-copy) were measured and used to ensure each matched pair was implanted in a similar manner.

Results Torsion:No statistical difference was detected between the torsional micro-motion or migration of the CLS Spotorno and shortened CLS Spotorno stems for any applied moment (Table 1). Given that the stem body was not altered between the CLS Spotorno and shortened CLS Spotorno Stems, it is not surprising that no statistical difference was observed between the torsional behaviour of the two stems.

9

Subsidence:No statistical difference was detected between the subsidence micro-motion or the migration of the CLS Spotorno Stem and 30% shortened CLS Spotorno Stems for all applied loads (Table 1). All micro-motions that were observed during all load-ing steps were less than 150µm, indicating that no formation of fibrous tissue is predicted.

Conclusion•   Shortening a stem, which has a mostly proxi-

mal fixation philosophy, by 30% (CLS Brevius Stem with Kinectiv Technology is shortened by 20% distally) did not appear to significantly affect the torsion or axial subsidence behavior of the stem.

Table 1 Results from the statistical comparison of the micro-motion and migration of the CLS Spotorno Stem compared with the shortened CLS Spotorno Stem. P values obtained from the paired t-test are reported with the number of samples per load step analysed.

Torsion Micro-motion MigrationLoad (Nm) p value p value

10Nm 0.804 (n=5) 0.332 (n=5)

20Nm 0.579 (n=4) 0.354 (n=4)

Subsidence Micro-motion MigrationLoad (N) p value p value

750 0.413 (n=8) 0.451 (n=8)

1250 0.679 (n=7) 0.322 (n=7)

1750 0.512 (n=8) 0.350 (n=8)

2500 0.948 (n=8) 0.312 (n=8)

Summary conclusion

Extensive in vitro testing of the mechanical, bio-mechanical, physicochemical and structural stability of the CLS Brevius Stem with Kinectiv Technology has been performed. The following is a summary of the conclusions which address the research questions posed at the beginning of this paper.

•   The CLS Brevius Stem with Kinectiv Technology exceeds the fatigue strength performance criterion as defined by Zimmer internal re-quirements based on ISO test methods. The strength of Kinectiv Necks is the results of a specific geometry featuring:

• – a long(er) neck taper • – a range of offset and version that success-

fully meets stringent Zimmer internal re-quirements

•   The  Kinectiv Neck/Stem junction demon-strates distraction forces that exceed those required to separate a typical 12/14 head/neck taper

•   The  fretting  corrosion  behavior  of  the  CLS Brevius Stem with Kinectiv Technology is less than the clinically derived benchmark and is similar to the current Zimmer M/L Taper with Kinectiv Technology.

•   The degree of version offered by the Kinectiv necks does not exceed that found currently clinically, or values reported to result in altered femoral loading. In addition, modular necks give the intraoperative flexibility to avoid ex-cessive version angles which may avoid influ-encing the loading of the implant/bone inter-face.

•   Through cadaveric testing, it has been estab-lished that shortening the CLS Spotorno Stem by 30% (CLS Brevius Stem with Kinectiv Tech-nology is shortened by 20% distally) did not appear to significantly affect the torsion or axial subsidence behavior of the stem com-pared to the original CLS Spotorno Stem.

10

Performance evaluation of CLS® Brevius™ Stem with Kinectiv® Technology

References

1. A.A.Hofmann and M.C.Skrzynski, Leg-length inequality

and nerve palsy in total hip arthroplasty: a lawyer

awaits!, Orthopedics., Vol. 23, no. 9, pp. 943-944,

Sep, 2000

2. J.Sanchez-Sotelo and D.J.Berry, Epidemiology of in-

stability after total hip replacement, Orthop Clin North

Am., Vol. 32, no. 4, pp. 543-52, vii, Oct, 2001

3. A.B.White, AAOS committee on professional liability:

study of 119 closed malpractice claims involving hip

replacement, AAOS bulletin,1994

4. C.B.Phillips, J.A.Barrett, E.Losina, N.N.Mahomed, E.A.

Lingard, E.Guadagnoli, J.A. Baron, W.H.Harris, R.Poss,

and J.N.Katz, Incidence rates of dislocation, pulmona-

ry embolism, and deep infection during the first six

months after elective total hip replacement, J Bone

Joint Surg Am., Vol. 85-A, no. 1, pp. 20-26 + letter to

editor, Jan, 2003

5. L.D.Dorr, MIS total hip replacement with a single pos-

terior approach, Seminars in Arthroplasty, Vol. 16, pp.

179-185, 2005

6. M.Mahfouz, Data from Femoral Bone Atlas, University

of Tennessee Center for Musculo skeletal Research,

2011

7. P.C.Noble, G.G.Box, E.Kamaric, M.J.Fink, J.W.Alexander,

and H.S.Tullos, The effect of aging on the shape of the

proximal femur, Clin Orthop Relat Res, no. 316, pp. 31-

44, Jul, 1995

8. M.Maruyama, Morphologic features of the acetabulum

and femur: anteversion angle and implant positio-

ning, Clin Orthop Relat Res, Vol. 393, pp. 52-65, 2001

9. P.J.Duwelius, M.A.Hartzband, R.Burkhart, C.Carnahan,

S.Blair, Y.Wu, and G.L.Grunkemeier, Clinical results of

a modular neck hip system: hitting the „bull’s-eye“

more accurately, Am.J.Orthop (Belle.Mead NJ), Vol. 39,

no. 10 Suppl, pp. 2-6, Oct, 2010

10. P.R.Aldinger, A.W.Jung, M.Pritsch, S. Breusch, M.

Thomsen, V.Ewerbeck, and D.Parsch, Uncemented

grit-blasted straight tapered titanium stems in pati-

ents younger than fifty-five years of age. Fifteen to

twenty-year results, J Bone Joint Surg [Am], Vol. 91, no.

6, pp. 1432-1439, Jun, 2009

11. H.Malchau, P.Herberts, T.Eisler, G.Garellick, and P.

Soderman, The Swedish Total Hip Replacement Re-

gister, J Bone Joint Surg Am., Vol. 84-A Suppl 2, pp.

2-20 + erratum + letter to editor, 2002

12. Galante, J. O.: Overview of Total Hip Arthroplasty. 829-

838. The Adult Hip Volume II; 1998

13. C.J.Dangles and C.J.Altstetter, Failure of the modular

neck in a total hip arthroplasty, J.Arthroplasty, Vol. 25,

no. 7, pp. 1169-7, Oct, 2010

14. T.M.Grupp, T.Weik, W.Bloemer, and H.P. Knaebel,

Modular titanium alloy neck adapter failures in hip

replacement--failure mode analysis and influence of

implant material, BMC.Musculoskelet.Disord., Vol. 11,

pp. 3, 2010

15. G.Wright, S.Sporer, R.Urban, and J.Jacobs, Fracture of a

modular femoral neck after total hip arthroplasty: a

case report, J Bone Joint Surg [Am], Vol. 92, no. 6, pp.

1518-1521, Jun, 2010

16. IS0 7206-6:1992(E) „Implants for surgery - Partial and

total hip joint prostheses -Part 6: Determination of en-

durance properties of head and neck region of stemmed

femoral components implants.“, 1992

17. J.S.Hertzler, PERFORMANCE EVALUATION OF KINECTIV™

TECHNOLOGY, Zimmer, Inc.,2008

18. ASTM F2009-00:2000 (2005), Standard Test Method

for Determining the Axial Disassembly Force of Taper

Connections of Modular Prostheses: 13.01:Medical

and surgical materials and devices; anesthetic and re-

spiratory equipment., 2009

19. F.Pallini, L.Cristofolini, F.Traina, and A.Toni, Modular

hip stems: determination of disassembly force of a

neck-stem coupling, Artif.Organs, Vol. 31, no. 2, pp.

166-170, Feb, 2007

20. Gilbert, J. L., Buckley, C. A., and Lautenschlager, E. P.:

Titanium oxide film fracture and repassivation: the ef-

fect of potential, pH and aeration. 199-215. In Brown,

S. A. and Lemons, J. E.: Medical applications of titani-

um and its alloys: The material and biological issues.

ASTM; 1996

21. J.R.Goldberg and J.L.Gilbert, In vitro corro sion testing of

modular hip tapers, J Biomed Mater Res B Appl Bioma-

ter, Vol. 64, no. 2, pp. 78-93, Feb 15, 2003

22. M.Viceconti, O.Ruggeri, A.Toni, and A.Giunti, Design-

related fretting wear in modular neck hip prosthesis,

J.Biomed.Mater.Res., Vol. 30, no. 2, pp. 181-186, 1996

23. M.Viceconti, M.Baleani, S.Squarzoni, and A.Toni,

Fretting wear in a modular neck hip prosthesis, J.Biomed.

Mater.Res., Vol. 35, no. 2, pp. 207-216, May, 1997

11

12

24. G.Mangan, 6 Degree and Versys 12/14 Offset Head -

Predicate Device Complaint Search, Report: Internal

Report:ZTR_WA_0012_10, 2010

25. M.Maruyama, J.R.Feinberg, W.N.Capello, and J.A.

D‘Antonio, The Frank Stinchfield Award: Morphologic

features of the acetabulum and femur: anteversion an-

gle and im plant positioning 36687, Clin Orthop Relat

Res., no. 393, pp. 52-65, Dec, 2001

26. M.O.Heller, G.Bergmann, G.Deuretzbacher, L.Claes,

N.P.Haas, and G.N.Duda, Influence of femoral antever-

sion on proximal femoral loading: measurement and

simulation in four patients, Clin.Biomech.(Bristol.,

Avon.), Vol. 16, no. 8, pp. 644-649, Oct, 2001

27. R.U.Kleemann, M.O.Heller, U.Stoeckle, W.R. Taylor,

and G.N.Duda, THA loading arising from increased fe-

moral anteversion and offset may lead to critical ce-

ment stresses, J.Orthop.Res., Vol. 21, no. 5, pp. 767-

774, Sep, 2003

28. S.W.Tohtz, M.O.Heller, W.R.Taylor, C.Perka, and G.N.

Duda, [On the biomechanics of the hip : Relevance of

femoral anteversion for hip contact force and loading

using a short-stemmed prostheses.], Orthopade, Vol.

37, no. 9, pp. 923-930, Sep, 2008

29. H.S.Gill, J.faro-Adrian, C.faro-Adrian, P. Lardy-Smith,

and D.W.Murray, The effect of anteversion on femoral

component stability assessed by radiostereometric

analysis, J.Arthroplasty, Vol. 17, no. 8, pp. 997-1005,

Dec, 2002

30. F.M.Westphal, N.Bishop, K.Püschel, and M.M.Morlock,

Biomechanics of a new short-stemmed uncemented

hip prosthesis: An in-vitro study in human bone, Hip

International, Vol. 16, no. 1 (Suppl. 3), pp. S22-S30,

2006

31. F.M.Westphal, N.Bishop, M.Honl, E.Hille, K.Puschel,

and M.M.Morlock, Migration and cyclic motion of a new

short-stemmed hip prosthesis--a biomechanical in

vitro study, Clin.Biomech.(Bristol., Avon.), Vol. 21, no.

8, pp. 834-840, Oct, 2006

32. S.Gheduzzi and A.W.Miles, A review of pre-clinical

t esting of femoral stem subsidence and comparison

with clinical data, Proc Inst Mech Eng [H]., Vol. 221, no.

1, pp. 39-46, Jan, 2007

33. S.Gheduzzi and A.W.Miles, A review of pre-clinical te-

sting of femoral stem subsidence and comparison with

clinical data, Proc Inst Mech Eng [H]., Vol. 221, no. 1,

pp. 39-46, Jan, 2007

Performance evaluation of CLS® Brevius™ Stem with Kinectiv® Technology

13

Notes:

14

Notes:

15

Lit.No. 06.02248.012 – Ed.2011-06 ZHUB

+H84406022480121/$110601F11X

Copy

righ

t 201

1 by

Zim

mer

Gm

bH

16