Elsevier

The Journal of Arthroplasty

Volume 27, Issue 8, September 2012, Pages 1452-1459
The Journal of Arthroplasty

In Vitro Comparison of Fixed- and Mobile Meniscal–Bearing Unicondylar Knee Arthroplasties: Effect of Design, Kinematics, and Condylar Liftoff

https://doi.org/10.1016/j.arth.2012.02.011Get rights and content

Abstract

Unicondylar knee arthroplasty (UKA) has become a popular alternative to total knee arthroplasty or high tibial osteotomy for unicompartmental knee conditions. This study investigated the effects of kinematics and femoral liftoff on the wear of fixed and mobile versions of a UKA design. The fixed bearing had lower wear than the mobile bearing under all conditions. Wear was higher in lateral bearings than medial bearings, indicating that the increased sliding distance laterally had a greater effect than the greater loading medially. Femoral condylar liftoff resulted in increased wear in the medial UKAs but reduced wear in the lateral UKAs for both the bearing designs. The reduced wear rates observed for the fixed UKA bearings highlight the potential for a longer osteolysis-free clinical outcome for these devices.

Section snippets

Materials

Six medial and 6 lateral Preservation mobile-bearing UKAs and 6 medial and 6 lateral Preservation fixed-bearing UKAs (DePuy International Ltd) were tested. All UKAs investigated were size 3 systems with Co-Cr-Mo alloy femoral and tibial components interposed by PE inserts of 9.5 mm in designated thickness. Both medial and lateral system PE inserts had been manufactured from GUR 1020 ram extruded bar (DePuy, Leeds, UK), sterilized by gas plasma. In addition, 2 of each PE insert type were used as

Mobile UKA System

Wear of the meniscal system increased as the study progressed. This study consisted of 3 stages: high kinematics (0-5 Mc), intermediate kinematics (5-7 Mc), and intermediate kinematics with induced lateral femoral condylar liftoff (7-9 Mc). Wear of the lateral system was consistently greater than the medial system (Fig. 2); however, this only became significant (ANOVA and Mann-Whitney, P < .05) from 5 Mc onward (during testing under intermediate kinematics). During high-kinematic conditions,

Discussion

Two 9-Mc knee simulator studies were conducted to investigate the mobile- and fixed-bearing variations of a unicompartmental knee device (the Preservation UKA). By assessing the individual and combined UKA systems, the influences of design and the effects of kinematic inputs and femoral condylar liftoff on the in vitro wear and wear performance were assessed.

Conclusion

This study demonstrated that substantially reduced in vitro wear rates can be achieved by mobile- and fixed-bearing UKA devices when compared with clinically successful TKA devices. This study also demonstrated the effects of design, kinematic input, and femoral condylar liftoff on in vitro wear:

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    Wear was reduced with the fixed-bearing UKA compared with the mobile-bearing UKA.

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    Wear was consistently increased in the lateral side in both UKA designs, indicating that the increased sliding distance

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    The Conflict of Interest statement associated with this article can be found at doi:10.1016/j.arth.2012.02.011.

    This study was supported by the EPSRC, and the components tested within this study were supplied by DePuy International, Leeds, UK.

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