HIGH TIBIAL OSTEOTOMY SHIFTS TIBIOFEMORAL LOADING TO THE LATERAL COMPARTMENT WITHOUT ALTERING KINEMATICS: A 3D FLUOROSCOPIC STUDY OF SIT-TO-STAND

Purpose: High tibial osteotomy (HTO) is a widely used joint-preserving surgery for medial compartment knee osteoarthritis (OA). While its static realignment effects are well documented, the in vivo dynamic biomechanical alterations remain unclear. This study aimed to quantify the 3D rigid-body kinematics and tibiofemoral contact mechanics of the knee in HTO patients during a sit-to-stand (STS) task. Methods: Twelve patients with medial knee OA (Kellgren–Lawrence grade 2–3) were recruited. Participants performed an STS task under dual-plane fluoroscopy before and approximately 6 months after medial opening-wedge HTO. A model-based 2D/3D registration method was used to determine 3D kinematics, and geometry-based virtual cartilage models were employed to calculate contact metrics. Results: HTO significantly shifted the mechanical axis from varus to valgus. Dynamically, the medial compartment exhibited a significant increase in inter-articular distance and a reduction in contact area throughout the STS cycle, confirming effective unloading. Notably, no significant differences were detected in the 3D kinematic patterns, including the screw-home mechanism, between pre- and post-operative conditions. Conclusion: This study provides novel in vivo evidence that the static realignment from HTO translates into robust dynamic unloading during high-demand functional activities with no significant kinematic changes detected. The procedure successfully restores a favorable mechanical environment while maintaining the knee’s physiological motion patterns.