The Effect of Hinge Position on Posterior Tibial Slope in Medial Open-Wedge High Tibial Osteotomy

Purpose: To evaluate whether hinge position affects the change in posterior tibial slope in medial open-wedge high tibial osteotomy (HTO). Methods: We retrospectively evaluated 19 knees from 17 patients who underwent medial open-wedge HTO by 3-dimensional computed tomography scan before and after surgery. A 3-dimensional image model was constructed by applying reverse-engineering software to the computed tomography DICOM (Digital Imaging and Communications in Medicine) files. The hinge axis (i.e., the position of the hinge compared with the anteroposterior axis on an axial view), posterior tibial slope, medial-proximal tibial angle, and gap ratio (i.e., the ratio of anterior gap to posterior gap in the opened wedge) were measured. Results: The mean hinge axis was 4.92 degrees +/- 3.86 degrees. Posterior tibial slope increased from 7.29 degrees +/- 2.56 degrees preoperatively to 10.48 degrees +/- 3.01 degrees postoperatively (P = .001). The mean medial-proximal tibial angle was 85.96 degrees +/- 1.97 degrees preoperatively and 93.13 degrees +/- 3.17 degrees postoperatively (P = .001). The mean gap ratio was 62.48% +/- 7.26%. Linear regression analysis determined that the hinge axis (P = .0001) was a significant factor changing posterior tibial slope. Conclusions: Hinge position affected the change in posterior tibial slope in medial open-wedge HTO; in particular, a posterolateral hinge position led to an increase in posterior tibial slope.