Medial hinge fracture after closing wedge high tibial osteotomy: Proposing a new classification and risk factor analysis of a neglected complication

Purpose: Contralateral hinge fracture is one of the most common complications of medial opening wedge high tibial osteotomy (HTO), however, this complication has been poorly investigated after closing-wedge HTO (CW-HTO). The primary aim of this study was to describe the incidence and characteristics and propose a classification system of medial hinge fracture (MHF) after CW-HTO. The secondary aim was to identify demographic and surgical factors that predispose to MHF. Methods: Consecutive patients who underwent CW-HTO for varus malalignment performed at a single institution were retrospectively screened for eligibility. Preoperative data were retrieved from medical charts, while incidence and type of MHF were evaluated on postoperative X-rays. To determine risk factors for MHF, a series of univariate logistic regression were performed using demographic and radiological data as independent variables, using a generalised linear mixed model (GLMM). Variables that demonstrated a significant difference (p < 0.1) in univariate analyses were defined as independent variables and were used as covariates in a multivariate analysis with the same dependent variables RESULTS: A total of 137 knees were included in the study. The incidence MHF fractures was 57% and three distinct types of fractures were identified. The most common fracture type was the two fragment one, with its subtypes "linear" (31%), "distal" (9%) and "proximal" (8%). A "third fragment" MHF was identified in 7% of cases, while "intra-articular" pattern was observed in 2%. Multivariate analysis showed that increased distance between the end of the osteotomy line up until the medial tibial plateau and decreased length of the osteotomy line were significantly associated with higher probability of MHF: respectively OR (odds ratio) 2.8 [1.20-6.78] (p = 0.018) for the former and OR of 0.35 [0.16-0.77] (p = 0.009) for the latter. Conclusion: MHF is a common complication after CW-HTO, and all the risk factors appear to be related to the osteotomy line: higher MHF incidence was associated with an increased distance from the medial plateau and reduced depth of the cut. Both these parameters are clinically relevant as they are modifiable. Level of evidence: Level IV.