The Effect of Sagittal Plane Inclination on Posterior Tibial Slope in Medial Open Wedge HTO – Experimental Study With a Square Column Model-

Background: Medial open-wedge high tibial osteotomy (MOWHTO) is an effective and safe treatment method in medial osteoarthritis of knee. However, it may accompany unintended change of posterior tibial slope (PTS). Several factors are known to cause PTS change after MOWHTO. However, there is a lack of research on the sagittal plane osteotomy inclination (SPOI). The purpose of this study was to evaluate that SPOI affected the change in PTS. The hypothesis was that parallel SPOI causes no PTS change after MOWHTO. Methods:A square column model with a 10° posterior slope was produced by two 3D programs and a 3D printer. A series of MOWHTO was performed on a square column model through virtual simulation using two 3D programs and an actual simulation using a 3D printer, a testing machine and a measurement system. The SPOI was divided into 4 types: ① parallel SPOI plus 10° (SPOI: 20°), ② parallel SPOI (SPOI: 10°), ③ perpendicular SPOI (SPOI: 0°), and ④ perpendicular SPOI minus 10° (SPOI: -10°). The correction angle was increased by 5° from 0° to 30°. The change of the posterior slope was measured in sagittal plane.Results: The posterior slope was increased in the parallel SPOI plus 10° (SPOI: 20°). It was maintained in the parallel SPOI (SPOI: 10°) and decreased in the perpendicular SPOI (SPOI: 0°) and perpendicular SPOI minus 10° (SPOI: -10°).Conclusion: SPOI affected the change in PTS. Parallel SPOI causes no PTS change after MOWHTO.