Optimal Plate Position for Biomechanical Stability in Medial Opening-Wedge High Tibial Osteotomy: A Finite Element Analysis.

Background: Research on the ideal fixation position for plates in medial opening-wedge high tibial osteotomy (MOWHTO) directly applicable in clinical settings is scarce. Therefore, this study aimed to evaluate the biomechanical effects of different plate positions in MOWHTO through finite element analysis (FEA) to explore a potentially optimal plate position. Methods: Utilizing the computed tomography images of a 67-year-old man, a 3-dimensional model of the knee, along with an implant (TomoFix standard plate and screws), was created to simulate a virtual MOWHTO with a 10° medial opening gap. Biomechanical stability analysis of the bone-implant construct was conducted through FEA under physiologic loading simulating a 1-legged stance, with varying plate positions. Configurations for plate fixation, determined by anterior-posterior depth and height, resulted in a total of 9 fixation positions (anterior, center, and posterior in terms of depth; proximal, middle, and distal in terms of height). Criteria for assessment included inter-fragmentary micromotion at the medial opening gap, mean stress on the lateral hinge, the entire tibial bone, and the implant, stress shielding effect, and peak von Mises stress (PVMS). Results: The inter-fragmentary micromotion at the medial opening gap exhibited a tendency to decrease as the fixation position of the plate moved posteriorly and proximally, observed in both axial and shear micromotion. The mean stress on the lateral hinge of the tibia progressively decreased with more posterior or proximal plate placement, reaching its minimum in the most posterior and proximal position. In terms of the mean stress imposed on both the entire bone and implant, it decreased when the plate was positioned posteriorly and proximally, and this position was deemed favorable from the perspective of the stress shielding effect. PVMS predominantly occurred at hole 1 of the plate and its corresponding screw, and it was lower than the yield strength of the titanium alloy regardless of the plate's position. Conclusions: Placing the plate more posteriorly and proximally in MOWHTO could minimize inter-fragmentary micromotion, reduce stress on the lateral hinge and bone-implant construct, and enhance stress shielding, all without increasing the risk of implant breakage, suggesting it as a potentially optimal plate position.