Lateral Distance From the Osteotomy Hinge Point to the Tibial Cortex Is Associated With Lateral Hinge Fracture Type and Fracture Occurrence Time After Medial Open-Wedge High Tibial Osteotomy

Purpose: To verify whether the distance from the hinge point to the tibial cortex affects the occurrence time and characteristics of the lateral hinge fracture (LHF) in medial open-wedge high tibial osteotomy. Methods: We retrospectively reviewed 171 knees in 171 patients (121 women, 50 men; mean age, 53.9 years; range, 36-67 years) who had undergone medial open-wedge high tibial osteotomy with locking plate fixation between January 2011 and December 2020. Osteotomy hinge point and LHFs were identified on intraoperative fluoroscopy and immediate postoperative radiographs. LHF type was classified as suggested by Takeuchi et al. Acute fracture was defined as a fracture that occurred during surgery, and delayed fracture was defined as a fracture observed after 1 month postoperatively. The nearest distances from osteotomy hinge point to lateral, distal, and proximal cortex were measured on postoperative radiographs. We compared the distance between the different types and between acute and delayed LHFs. Results: There were 55 LHFs (32%) (type I, 40 knees; type II, 14 knees; type III, 1 knee) that occurred acutely in 41 knees and were found as delayed fractures in 14 knees. The patient demographics were not significantly different between non-LHFs and each type of LHFs. Proximal and distal distances were not statistically different among fracture types and between occurrence times. However, lateral distances were significantly shorter in type I LHFs (6.2 +/- 1.8 mm) and longer in type II LHFs (9.3 +/- 2.3 mm) than in non-LHFs (7.1 +/- 2.7 mm) (P = .020 and .004, respectively). The lateral cortical distances were also different between acute LHFs (6.4 +/- 1.9 mm) and delayed LHF (9.0 +/- 2.7 mm) (P < .001). In the case of fracture type, the frequency of type I decreases with increase in the lateral distance, whereas that of type II increases with increase in the lateral cortical distance. In acute fracture, type I was dominant (85.4%), whereas in delayed fracture, type II was dominant (57.2%). Conclusions: The lateral cortical distance from the hinge point was significantly associated with LHF occurrence. Shorter distance increased the risk for acute type I LHF, whereas longer distance increased the risk for delayed type II LHFs.