New angle measurement device to control the posterior tibial slope angle in medial opening wedge high tibial osteotomy.

INTRODUCTION: Medial opening wedge high tibial osteotomy has been associated with an unintentional increase in the posterior tibial slope angle. We aimed to evaluate the effectiveness of a novel bone spreader angle rod to maintain the native posterior tibial slope angle in medial opening wedge high tibial osteotomy.

MATERIALS AND METHODS: Data from 92 consecutive knees in 83 patients who underwent medial opening wedge high tibial osteotomy for knee osteoarthritis between March 2015 and June 2016 were analysed. The osteotomy was performed without the use of a bone spreader angle rod in the first 50 cases (control group) and with the use of the angle rod in the subsequent 42 cases (angle rod group). The wedge insertion angle, defined as the angle between a line drawn along the posterior aspect of the wedge spacer and a line tangential to the posterior aspect of the femoral condyles, and the posterior tibial slope angle were evaluated on pre- and postoperative lateral knee radiographs and postoperative computed tomography images.

RESULTS: Wedge insertion angle showed that wedge spacers were inserted in a more direct horizontal direction in the angle rod group than in the control group (16.0 ± 8.8° and 23.0 ± 10.0°, respectively, P < 0.001). The pre- to postoperative change in posterior tibial slope angle was significantly smaller in the angle rod group (0.6 ± 1.6°) compared to that in the control group (3.2 ± 3.2°; P < 0.0001). A change of posterior tibial slope angle > 3° (outlier) was identified in 1 case (2.4%) in the angle rod group compared to 27 cases in the control group (54.0%).

CONCLUSIONS: The direct horizontal insertion of wedge spacers with the assistance of our novel bone spreader angle rod maintains the native posterior tibial slope angle better than conventional methods.

LEVEL OF EVIDENCE: IV.