Reduced patella medialization in valgus and varus knees using a KA‐optimized femoral component in kinematically aligned TKA
Johanna‐Maria Simon, Tara Mauritia Siedow, Christoph Thorwächter, Hannes Traxler, Katharina Kirchhoff, Felix Endres, Boris Michael Holzapfel, Peter Ernst Müller, Thomas Richard NiethammerAbstract
Purpose
Patellofemoral complications after total knee arthroplasty (TKA) are linked to femoral component design and trochlear alignment. This study compared the effects of a kinematically aligned (KA)‐optimized femoral component versus a standard design on patellofemoral kinematics, contact mechanics and quadriceps function, using native knee biomechanics as reference.
Methods
Seventeen fresh‐frozen cadaveric knees (10 valgus, 7 varus) were tested in a dynamic knee rig (30°–130° flexion) under controlled loading, divided into a valgus and a varus group. Patellofemoral kinematics, contact area and peak pressure patterns were recorded in the native state and after KA TKA using either a standard component (prosthetic trochlear angle [PTA] 6°) or a KA‐optimized design (PTA 20°). One‐dimensional statistical parametric mapping (SPM1D) independent two‐sample t tests were applied ( α = 0.05).
Results
The KA‐optimized component reduced medialization between 30° and 70° in both groups (varus: 2.5 mm; valgus 2.0 mm). Patellar tilt remained unchanged. Contact area decreased after TKA without consistent differences between components (valgus: p < 0.001 until 80°; varus: p < 0.001 at 60°–80°). Peak pressure was not reduced with the KA‐optimized design; slightly higher values occurred up to mid‐flexion (+1.1 MPa at 90°), normalizing at higher flexion angles in valgus knees. In varus knees, both designs increased peak pressure at high flexion (+1.5 MPa at 120°). Quadriceps force showed no significant differences.
Conclusion
The KA‐optimized femoral component reduces patellar medialization but does not improve patellofemoral loads or quadriceps efficiency, suggesting that isolated geometric optimization may be insufficient to restore physiological biomechanics after KA TKA.
Level of Evidence
N/A.