Posterior cortical breakage leads to posterior tibial slope change in lateral hinge fracture following opening wedge high tibial osteotomy

Purpose: This study was designed to analyze the relationship between changes in posterior tibial slope and the absence or presence of lateral hinge fracture, diagnosed in the sagittal and axial planes, as well as the coronal plane, by computed tomography (CT) following opening wedge high tibial osteotomy (HTO). Methods: This study involved 55 patients (55 knees) undergoing opening wedge HTO for primary medial osteoarthritis. Lateral hinge fractures were evaluated on CT scans according to the Takeuchi classification and were also classified as subtypes A, B, and C, depending on anterior, posterior, and both anterior and posterior cortical disruptions, respectively, as determined by the sagittal and axial planes of CT scans which corresponded to the fracture line visible on coronal CT scans. Results: Of the 55 knees, 23 were found on postoperative CT scans to have lateral hinge fractures. All 23 were classified as Type I, with 11, 12, and 0 being subtypes A, B, and C, respectively. Mean change in posterior tibial slope from 3 weeks postoperatively to last follow up in subtype B was significantly greater than in subtype A (2.5° vs 0.2°, P = 0.008) and in knees without hinge fracture (2.5° vs 0.1°, P = 0.002). Conclusion: Type I lateral hinge fractures encroached either the anterior or posterior cortex of the proximal tibia, but not both. In addition, posterior tibial slope increased over time following surgery in knees with Type I lateral hinge fracture and posterior cortex breakage, suggesting that caution should be exercised when deciding the starting time for weight bearing in such patients. Level of evidence: Case series, Level IV.