The effect of the sagittal plane osteotomy inclination on the posterior tibial slope in medial open wedge HTO: experimental study with a square column model

BACKGROUND: Medial open-wedge high tibial osteotomy (HTO) is an effective and safe treatment method for medial osteoarthritis of the knee. However, unintended changes in the posterior tibial slope (PTS) may occur. Several factors cause PTS alterations after medial open-wedge HTO; however, research on sagittal-plane osteotomy inclination (SPOI) in relation to the PTS is sparse. The purpose of this study was to evaluate whether the SPOI affects changes in the PTS after medial open-wedge HTO. The hypothesis was that an SPOI parallel to the PTS causes no change in the PTS after medial open-wedge HTO. METHODS: A square column model with a 10° posterior slope was produced using two three-dimensional (3D) programs and a 3D printer. Then, a series of medial open-wedge HTO procedures was performed on the square column model through virtual simulation using the two 3D programs, and an actual simulation was conducted using a 3D printer, a testing machine and a measurement system. The SPOI was divided into four types: ① SPOI 20° (posterior-inclined 10° osteotomy), ② SPOI 10° (osteotomy parallel to posterior slope), ③ SPOI 0° (anterior-inclined 10° osteotomy), and ④ SPOI − 10° (anterior-inclined 20° osteotomy). The correction angle was increased at intervals of 5° from 0° to 30°. The change in posterior slope was measured in the sagittal plane. RESULTS: The posterior slope was increased in SPOI 20° (posterior-inclined 10° osteotomy), maintained in SPOI 10° (osteotomy parallel to posterior slope), and decreased in SPOI 0° (anterior-inclined 10° osteotomy) and SPOI − 10° (anterior-inclined 20° osteotomy) based on the correction angle. CONCLUSIONS: In this study using a square column model, the SPOI affected the change in the PTS, and an SPOI parallel to the PTS caused no change in the PTS after medial open-wedge HTO.