Posterior Plate Positioning Without Distal Placement in Medial Closing-Wedge Distal Femoral Osteotomy.

Background: Despite efforts to improve mechanical stability and reduce complications after medial closed-wedge distal femoral osteotomy (MCDFO), the role of plate positioning in determining mechanical stability remains unclear. Purpose: To determine the biomechanically optimal plate position during MCDFO using finite element analysis (FEA). Study Design: Descriptive laboratory study. Methods: Five distinct 3-dimensional finite element models of the distal femur and implant (TomoFix Medial Distal Femur Plate and screws) were developed from computed tomography data, and a virtual MCDFO was performed. To identify the biomechanically optimal implant positioning, nine unique configurations were created by systematically varying the plate height (proximal-distal) and depth (anterior-posterior) in 5 mm increments. Physiological loading conditions were simulated by applying joint loads at 0°, 30°, and 90° of knee flexion. Biomechanical stability of the bone-implant construct, including the osteotomy site, was evaluated based on the following parameters: (1) micromotion at the osteotomy site, (2) mean stress applied to the bone and implant, (3) mean stress in the lateral hinge of the distal femur, and (4) peak von Mises stress (PVMS) on the plate and each screw. Results: A total of 30 analyses were conducted by performing 6 simulations for each model to meet the sample size requirement determined by a priori power analysis. Micromotion at the osteotomy site was significantly reduced with posterior and proximal plate positioning, a trend consistent across all knee flexion angles. The mean stress in the bone and implant showed no clear directional trend with plate position, whereas stress at the lateral hinge of the distal femur was lowest with posterior-middle placement and remained consistent across all flexion angles. PVMS revealed that anterior-distal placement tended to produce the highest stresses across the plate and screws-occasionally exceeding the titanium alloy's yield strength-while posterior-proximal repositioning progressively reduced them. Conclusion: Posterior plate positioning without distal placement was associated with improved biomechanical stability of the bone-implant construct during MCDFO in this FEA. Clinical Relevance: Because plate position can be readily adjusted during MCDFO, the present findings provide practical biomechanical guidance for implant placement and may help reduce mechanical complications associated with the procedure.