Is it possible to avoid posterior tibial slope increase in open-wedge high tibial osteotomy?

AIM: Posterior tibial slope has shown to be increased with open-wedge high tibial osteotomy (OWHTO) which may lead to an increase in loading of the anterior cruciate ligament and causing patellofemoral problems in return. In this case series, patients with an OWHTO performed posteromedial to the medial collateral ligament (MCL), keeping it intact was investigated. The aim of this study was to evaluate the influence of this technique on the posterior tibial slope. METHODS: Thirty knees (15 right, 15 left) of 28 patients (22 women, 6 men) with a mean age of 53.57±5.9 years who had an OWHTO between January 2014 and February 2016 were included in this study. Surgical technique: A proximal tibial osteotomy is performed posteromedial to MCL keeping it intact. Following the osteotomy, distraction is also performed from the posteromedial aspect of tibia. Fixation is achieved utilizing TomoFix plate. Radiological evaluation: Preoperative and postoperative mechanical axes (MA) were measured on standard weight bearing long axis x-rays. Preoperative and postoperative posterior tibial slope angles were measured on lateral x-rays using three different Methods: the angles between medial tibial plateau and (1) posterior tibial cortex, (2) tibial proximal anatomical axis, and (3) posterior fibular cortex were measured. The correlations of three different measurement methods were analyzed. Patients were grouped according to preoperative MA deviations and postoperative MA changes (either <10º or >=10º). The posterior tibial slope changes were compared between groups. Statistical analyses: All statistical analyses were performed utilizing SPSS 18.0. RESULTS: Mean preoperative and postoperative MA deviations were 9.81°±4.94° and -2.72°± 2.69° respectively. The mean correction angle of MA of lower extremity was 12.62°±4.58°. The three methods used to measure the posterior tibial slope angles were found to be highly correlated with each other ((1) and (2) r=0.961; (1) and (3) 0.906; (2) and (3) 0.934; p values <0.0001). Preoperative mean posterior tibial slope angles were 9.50º±4.47°, 11.51º± 4.50°, and 10.80º±4.58°; postoperative angles were 6.10º±4.23°, 8.78º±4.57° and 8.11º±4.55°, respectively. Posterior tibial slope angle was significantly decreased postoperatively with respect to all three methods (p <0.0001). The changes in the posterior tibial slope was not statistically significant between the groups with preoperative <10º and >=10º deformities (p values 0.861, 0.723, 0.727, respectively). CONCLUSIONS: Posterior tibial slope was found to be decreased with this posteromedial OWHTO technique. This technique offered the advantage of preserving the posterior tibial slopes postoperatively even in highly deformed knees which necessitated higher degrees of corrections in the mechanical axes.