Additional anteromedial staple fixation prevents changes in the posterior tibial slope in retrotuberosity bi-planar open-wedge high tibial osteotomy

Purpose To compare the changes in posterior tibial slope (PTS) between retrotuberosity biplane open-wedge high tibial osteotomies (RT-OWHTOs) with and without additional anteromedial staple fixation. Methods Seventy-nine and 77 cases of RT-OWHTOs without (Group N) and with (Group S) additional staple fixation, respectively, were retrospectively reviewed. All procedures were performed using a locking spacer plate. Demographics and preoperative knee condition were similar between the groups. Clinically, the Western Ontario and McMaster Universities Arthritis Index and range of motion were evaluated preoperatively and 2 years postoperatively. Radiographically, the mechanical axis (MA), medial proximal tibial angle (MPTA), and PTS were evaluated preoperatively and within 2 years postoperatively. Hinge fractures were investigated using computed tomography at 2 weeks postoperatively. PTS loss was defined as the difference between the corresponding values at 2 weeks and 2 years postoperatively. The incidence of PTS failure (PTS loss ≥ ± 3°) was also investigated. Results The clinical results were not significantly different between groups N and S preoperatively and 2 years postoperatively. There were no significant differences in the MA, MPTA, and PTS between the groups preoperatively and 2 weeks postoperatively; changes in these variables did not differ significantly between the groups. The incidence of hinge fractures, all of which were categorized as Takeuchi type 1, did not differ significantly. PTS loss within 2 years postoperatively was significantly greater in group N than in group S (1.0° vs. 0.1°; p < 0.01). The incidence of the PTS failure was 16.5% (13/79) and 2.6% (2/77) in groups N and S, respectively ( p < 0.01). Conclusion Additional anteromedial staple fixation could prevent changes in the PTS in RT-OWHTO. It is a simple method for preventing an increase in the PTS after RT-OWHTO. Level of evidence III.