Coronal Plane Alignment Of The Knee (CPAK) Type III Valgus Knee Exhibits Lateral Pivot Motion During Squatting

Medial pivoting motion has been identified as the primary kinematic pattern throughout flexion of the native knee joint. The recently introduced coronal plane alignment of the knee (CPAK) classification categorizes knees into nine alignment-based phenotypes, yet the relationship between these phenotypes and their respective kinematic behavior remains poorly documented, particularly in less common valgus phenotypes. Therefore, this study aimed to perform a detailed analysis of the pivoting motion of the CPAK type III knees during ex vivo simulated squatting. Considering the more lateral weight-bearing axis in the valgus phenotype, we hypothesized that weight-bearing motion is associated with lateral pivot motion.We retrospectively analysed a previously collected dataset of sixty-nine native fresh-frozen cadaveric knees subjected to squatting motion (35°-100°) on a physiological knee joint simulator. Seventeen CPAK Type III knees were identified based on full-leg computed tomography scans. Next, we discerned between medial and lateral pivoting throughout the range of motion based on the location of the instantaneous center of rotation (ICOR) to the center of the tibial plateau. Furthermore, we screened for possible associations between CPAK’s coronal lower limb alignment features and lateral pivoting. All 17 CPAK type III knees exhibited a lateral center of rotation during squatting, with 8 demonstrating lateral pivoting as the predominant pattern over more than half of the flexion range. This study showed that a lateral pivot motion pattern occurred during squatting in approximately half of the CPAK type III specimens, from mid to deep flexion (58.5°-100°) when tested in a loaded knee simulator. The current study offers essential data and insights to be considered for subsequent research on the role of native valgus knee kinematics in optimizing TKA outcomes.