A navigation-based analysis of native knee collateral ligament length change patterns in function of CPAK classification.

Introduction: Introduction This study investigates the elongation patterns of native knee collateral ligaments across various coronal plane alignment phenotypes (CPAK classification), aiming to refine soft tissue balancing in Total Knee Arthroplasty (TKA).

Materials and methods: Materials and methods In this cross-sectional study, 84 patients were analyzed prior to undergoing TKA using a computer-assisted surgery (CAS) system. CPAK types were determined using pre-operative standing full-leg radiographs. The CAS system facilitated real-time tracking of the native medial (MCL) and lateral (LCL) collateral ligament elongation throughout passive knee motion. Data were normalized and analyzed using a linear mixed model to assess the impact of knee alignment on ligament elongation, with ANOVA and Fisher's LSD method applied at a 95% confidence level.

Results: Results A significant correlation was observed between aHKA and MCL length changes during deep flexion (90°-110°), with the MCL shortening in valgus-aligned knees and lengthening in varus/neutral knees. CPAK III (valgus knees with high JLO) showed significantly more MCL shortening than CPAK I, II, and IV at 90° flexion (p < 0.05). Knees with similar aHKA values exhibited comparable MCL behavior. Across all CPAK types, the LCL displayed a consistent pattern of progressive loosening with flexion. Valgus knees, particularly CPAK III, demonstrated a significantly tighter LCL in full extension compared to other types (p < 0.05). No significant effect of aHKA or JLO on LCL behavior was found.

Conclusion: Conclusion This study demonstrates that MCL and LCL elongation patterns are phenotype-dependent. While the LCL consistently loosens with flexion across types, MCL behavior varies significantly with coronal alignment. These findings suggest that alignment-based ligament behavior must be considered for optimal soft tissue balance and support a shift toward personalized TKA strategies aimed at replicating native knee kinematics.