The Type of Lateral Hinge Fracture in Medial Open-Wedge High Tibial Osteotomy Determines Its Stability: A Biomechanical Study.

Abstract

BACKGROUND Lateral hinge fractures (LHFs) are considered risk factors for delayed union or nonunion after medial open-wedge high tibial osteotomies (MOWHTOs). However, there is limited evidence on the extent to which the morphology of the hinge fracture influences the stability of a MOWHTO. PURPOSE/HYPOTHESIS The purpose of this study was to validate the Takeuchi classification under axial and torsional loading to identify the LHF types requiring surgical treatment. It was hypothesized that (1) LHFs would reduce construct stiffness and increase interfragmentary instability across the osteotomy gap, and (2) shear displacement associated with impaired bone healing of >2 mm would be observed in Takeuchi type 2 and 3 fractures. STUDY DESIGN Descriptive laboratory study. METHODS A total of 24 fresh-frozen human cadaveric proximal tibiae underwent MOWHTO fixed with a locking compression plate. The specimens were assigned to 3 different groups so that the mean bone mineral density values were similar between the groups. Each group simulated a different type of LHF according to the Takeuchi classification: (1) type 1 fracture, extension along the osteotomy plane; (2) type 2 fracture, extension distal to the proximal tibiofibular joint; and (3) type 3 fracture, proximal extension into the lateral tibial plateau. Each specimen was subjected to 10 quasi-static cycles of axial compression up to 720 N, followed by internal and external torsional loading up to 10 N·m, while the interfragmentary movements were captured with a motion tracking system. RESULTS Compared with a MOWHTO with a preserved lateral hinge, Takeuchi type 2 and 3 fractures significantly increased shear displacement and hinge rotation by 2.2 mm and 2.3°, respectively, resulting in at least 80% reduction in torsional stiffness (P < .001). In contrast, Takeuchi type 1 fractures did not significantly alter the torsional stability of a MOWHTO. Takeuchi type 2 and 3 fractures significantly increased axial displacement at the hinge site by 0.2 mm (P < .01) compared with an intact hinge MOWHTO, while axial displacement of the medial osteotomy gap remained unchanged. All Takeuchi types significantly reduced axial construct stiffness by at least 28% (P < .01). CONCLUSION From a biomechanical perspective, Takeuchi type 1 LHFs did not affect the torsional stability of MOWHTO, whereas Takeuchi type 2 and 3 fractures resulted in significantly reduced torsional stiffness, increased shear displacement, and hinge rotation across the osteotomy gap. All Takeuchi fracture types resulted in reduced axial construct stiffness, while axial displacement was not significantly affected by the type of hinge fracture. CLINICAL RELEVANCE The observed shear displacement of >2 mm for Takeuchi type 2 and 3 fractures may be indicative of impaired bone healing and may therefore qualify these fractures for hinge fixation to potentially reduce the risk of delayed union and nonunion.