Full-flexion gap balancing-driven personalized preoperative planning for TKA: biomechanical evidence of improved load symmetry in an in vitro model

Purpose Conventional morphology-based planning (MB) in total knee arthroplasty (TKA) often results in imbalanced medial–lateral loading, which is a major risk factor for prosthesis loosening. This study aimed to evaluate a full-flexion gap balance planning (GB) approach and compare its biomechanical performance with MB planning. Methods TKA surgical planning was performed on eight subjects. In vivo knee kinematics were obtained using a dual X-ray imaging system. The implant position was optimized within an in silico surgical-planning framework by minimizing medial–lateral gap differences across the full flexion range using in vivo dynamic kinematics. Using 3D-printed in vitro models, joint contact forces were measured at various flexion angles to compare medial–lateral load distribution between GB and MB planning. Results GB planning optimized femoral varus/valgus by approximately 4° within anatomical constraints, significantly reducing the medial–lateral gap difference to a mean of < 1 mm across the entire flexion range ( p < 0.05). In contrast, the medial–lateral gap difference exceeded 2 mm with MB planning. Furthermore, at mid-to-high flexion angles (30°–100°), GB planning reduced the medial–lateral load imbalance by approximately 38%–67% compared with MB planning ( p < 0.05). Conclusion GB planning significantly improves medial–lateral load balance across the full range of flexion compared to conventional MB planning. This personalized planning optimizes joint loading patterns in vitro, which may theoretically align with principles aimed at reducing flexion-related adverse outcomes.