Teng Y, Mizu-uchi H, Xia Y, et al. - Via performing this three-dimensional (3D) surgical simulation study, researchers sought to determine how axial and sagittal hinge axes (hinge axes in the axial and sagittal planes) influence medial and lateral posterior tibial slope (PTS) in medial open-wedge high tibial osteotomy (OWHTO). In addition, they examined the quantitative correlation between hinge axis and PTS change. They retrieved preoperative computed tomography data from patients with varus knee deformity. In a 3D surgical simulation of OWHTO, a standard hinge axis (0°) and 12 different hinge axes (6 axial hinge axes and 6 sagittal hinge axes: ±10°, ±20° and ±30°) were defined utilizing a bone model. Included were a total of 93 varus knees in 93 patients. The differences between before and after simulation surgery in medial and lateral PTS, medial proximal tibial angle, opening gap, and opening wedge angle were determined. Findings of 3D OWHTO simulation suggest significant influence of axial hinge axis on medial and lateral PTS in OWHTO, but there appeared no effect of sagittal hinge axis on change in PTS. Every 10° change of axial hinge axis with a 10° coronal valgus correction resulted in nearly 1.6° change of PTS.