Required force for distraction during medial opening wedge high tibial osteotomy may serve as a predictive indicator for lateral hinge fracture.

Introduction: Medial open wedge high tibial osteotomy is a biological procedure for treating unicompartmental knee osteoarthritis. The literature repeatedly highlights the significance of preserving an intact lateral hinge during this procedure. We investigated the temporal course of distraction forces during distraction at the osteotomy site, aiming to quantitatively measure and analyse temporal changes in distraction forces at different distraction points for intact and fractured lateral hinges. Materials and Methods: This biomechanical study was conducted on 10 human cadavers, which were divided into two groups: one with preserved 1 cm intact lateral cortexes (ILCs) and the other with completely osteotomised fractured lateral cortexes (FLCs). An experimental setup was custom designed to facilitate the required force measurement during distraction. The distraction forces were recorded with a force gauge at 0.5-mm intervals throughout the distraction. Results: There was a significant difference between the ILC and FLC groups in distraction forces at all points (8-15 mm). The ILC group consistently exhibited higher distraction force values, with FLC recording values ranging from 8.8% to 13.2% of ILC's. Lateral hinge fractures caused an 86.7% reduction in the initial required force for distraction, significantly impacting the force required for distraction. The ILC group displayed a linear increase in the required distraction force up to 12.5 mm of distraction, which reached 3.7 times the initial value at 12.5 mm of distraction. The FLC group had lower baseline required distraction forces, following a relatively linear trend with more limited increases. Conclusion: FLCs in medial opening wedge osteotomy are associated with significant reductions in the force required for distraction, and a sudden decrease in distraction force during distraction may indicate a lateral hinge fracture. Force measurement devices for use during distraction could offer valuable insights and provide surgeons with immediate warnings for LHFs. Level of Evidence: Level IV.