Tibiofemoral and patellofemoral kinematics after kinematic versus mechanical alignment in varus TKA—a dynamic knee rig study

Kinematic alignment (KA) in total knee arthroplasty (TKA) of the varus knee shows promising clinical outcomes by preserving individual joint anatomy. However, it remains unknown whether this results in knee joint kinematics that more closely resemble the native baseline condition than mechanical alignment (MA). Therefore, this study evaluated the direct influence of KA versus MA on tibiofemoral and patellofemoral kinematics and contact biomechanics in the varus knee during a standardized dynamic muscle-loaded squat. Seven fresh-frozen human cadaveric knee specimens with constitutional varus (-1.4° to -8.3°) were tested in a dynamic knee rig (30° to 130° flexion) under muscle-controlled loading. Kinematics, retropatellar contact area, peak pressure, and quadriceps force were continuously recorded across three successive states within the same specimen: native, KA TKA, and MA TKA using a medial-pivot implant design. Statistical analysis was performed using one-dimensional statistical parametric mapping, including non-parametric SnPM1D ANOVA and pairwise SnPM{F} tests for kinematics, and paired-samples SPM{t} tests for contact mechanics and quadriceps force. Between alignment techniques (KA vs. MA), no statistically significant differences emerged regarding kinematics and patellofemoral biomechanics following Holm-Bonferroni correction (all p adj > 0.05). Descriptively, KA displayed a trend toward unphysiological anterior femoral translation in deep flexion (100°–120°, p = 0.028; p adj = 0.084) and persistent patellar medialization (delta of up to 5 mm) compared to MA, though these did not retain statistical significance post-adjustment. Both TKA techniques significantly reduced patellar contact area ( p adj < 0.01), illustrating a general TKA effect rather than an alignment-specific difference. KA was not shown to restore native knee kinematics or patellofemoral mechanics more closely than MA. Descriptive kinematic variations suggest that KA does not automatically optimize functional joint mechanics when using standard implant geometries.