Hinge Position Dominance Over Osteotomy Inclination in Medial Open-Wedge High Tibial Osteotomy: A Key Factor in Posterior Tibial Slope Changes.

Objective: A medial open-wedge high tibial osteotomy (MOWHTO) may increase the posterior tibial slope (PTS). The purpose of this study was to determine the effect of the osteotomy inclination angle (in the sagittal plane) in combination with different hinge positions (in the transverse plane) on the change in PTS due to a MOWHTO.

Methods: We developed a mathematical approach to determine the effect of the osteotomy inclination angle combined with different hinge positions. The change in PTS was determined for different osteotomy inclination angles, hinge positions, and intended wedge angles. Anterior-inclined, parallel, and posterior-inclined osteotomy inclination angles were simulated. Hinge positions varied between 5° anterolateral and -45° posterolateral. The wedge angles were 5°, 10°, and 15°. Moreover, 2 in silico osteotomies were performed to verify the results of the mathematical model.

Results: The PTS was maintained when the osteotomy cut was performed parallel to the tibial plateau with a lateral hinge position. The PTS changed when the osteotomy was not aligned in the sagittal plane, ranging between 0.0° and 0.6°. Different hinge positions, however, had a large effect on postoperative PTS change, ranging between 0.1° and 10.7°.

Conclusions: Our mathematical approach showed that the hinge position has a strong effect on the PTS. The sagittal osteotomy inclination angle had little effect on the PTS. An inclination angle parallel to the medial tibial plateau combined with a lateral hinge position does not change the PTS.