KSSTA - 2026-08-03 - Journal Article
Reduced patella medialization in valgus and varus knees using a KA-optimized femoral component in kinematically aligned TKA.
Simon JM, Siedow TM, Thorwächter C, Traxler H, Kirchhoff K, Endres F, Holzapfel BM, Müller PE, Niethammer TR
Topics
Key Takeaway
A KA-optimized femoral component (PTA 20°) reduced patellar medialization by 2.0–2.5 mm versus a standard design (PTA 6°) in both valgus and varus cadaveric knees, but did not improve contact area, peak pressure, or quadriceps force.
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Summary
This cadaveric study compared a KA-optimized femoral component (PTA 20°) versus a standard component (PTA 6°) on patellofemoral kinematics and contact mechanics in 17 fresh-frozen knees tested dynamically from 30°–130° flexion. The KA-optimized design reduced patellar medialization by 2.5 mm (varus) and 2.0 mm (valgus) between 30°–70° flexion, but contact area decreased after TKA regardless of component design, and peak pressure was slightly higher with the KA-optimized component up to mid-flexion (+1.1 MPa at 90° in valgus knees). Quadriceps force was equivalent between designs, indicating that trochlear geometry optimization alone does not restore native patellofemoral load distribution.
Key Limitation
Cadaveric testing eliminates dynamic neuromuscular contributions (VMO activation, IT band tension) that critically govern in vivo patellar tracking, limiting direct translation of these contact pressure findings to clinical outcomes.
Original Abstract
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.