Reduced patella medialization in valgus and varus knees using a KA-optimized femoral component in kinematically aligned TKA.

Abstract

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. 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). 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. 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. N/A.