Kinematic alignment reduces tibial internal rotation and maintains a larger retropatellar contact area than mechanical alignment in early flexion in valgus knees

PURPOSE: Alignment effects after total knee arthroplasty (TKA) may be particularly relevant in valgus phenotypes. This study compared kinematic alignment (KA) and mechanical alignment (MA) in valgus cadaveric knees during active, muscle-loaded flexion, using the native knee as reference. METHODS: Ten fresh-frozen valgus knees (arithmetic hip-knee-ankle angle [aHKA] 0.8°-6.4°) were tested in a dynamic knee rig from 30° to 130° of flexion. Each specimen was assessed sequentially in its native state and after TKA with KA and MA. Tibiofemoral and patellofemoral kinematics were analyzed using one-dimensional statistical non-parametric mapping (SnPM1D) with post hoc paired F-tests, and retropatellar contact mechanics and quadriceps force using paired SPM1D t-tests. RESULTS: Compared with MA, KA showed less tibial internal rotation during early flexion (p = 0.011) and less dynamic valgus deviation in deep flexion (p = 0.017), as well as a larger early-flexion retropatellar contact area (p < 0.001). Neither condition restored the native anteroposterior translation pattern. Patellar tilt differed between KA and MA (p < 0.001); KA showed greater internal tilt early in flexion and subsequently shifted toward external tilt. No significant differences between KA and MA were detected for patellar shift, peak pressure or quadriceps force. CONCLUSION: Under these experimental conditions, KA and MA produced distinct rotational, coronal and patellofemoral responses. Similarity to the native reference was outcome- and flexion-dependent. The mild-to-moderate valgus range and the simulated muscle loading preclude conclusions about clinical superiority or the optimal alignment for valgus TKA. LEVEL OF EVIDENCE: N/A.