No difference in patellar tracking between symmetrical and asymmetrical femoral component designs in TKA
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Poor knee extension function after total knee arthroplasty (TKA) is associated with factors including articular geometry and alignment. Femoral trochlear geometry has evolved from symmetrical to become more prominent proximal–laterally, with the groove aligned proximal–lateral to distal–medial. This study in vitro tested the hypothesis that a modern asymmetrical prosthesis would restore patellar tracking and stability to more natural behaviour than an older symmetrical prosthesis.
Six knees had their patellar tracking measured optically during active knee extension. Medial–lateral force versus displacement stability was measured at fixed angles of knee flexion. The measurements were repeated after inserting each of the symmetrical and asymmetrical TKAs.
Significant differences of patellar lateral displacement stability, compared to normal, were not found at any angle of knee flexion. The patella tracked medial–laterally within 2.5 mm of the natural path with both TKAs. However, for both TKAs near knee extension, the patella was tilted laterally by approximately 6° and was also flexed approximately 8° more than in the natural knee.
The hypothesis was not supported: The more anatomical component design did not provide more anatomical patellar kinematics and stability.
KeywordsTotal knee arthroplasty (TKA) Patellofemoral joint Stability Kinematics Trochlear groove
We thank Stryker (UK) Ltd for donating the prostheses used in this study. J. Stoddard was supported by a grant from the orthopaedic Surgery Department of the University of Newcastle.
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