Diagnostic Value of Computed Tomography and Risk Factors for Lateral Hinge Fracture in the Open Wedge High Tibial Osteotomy

PURPOSE: The purposes of this study were to evaluate (1) the disparity of detection of lateral hinge fracture (LHF) between postoperative simple radiography and high-resolution computed tomography (CT) and affecting factors of LHF and (2) whether generally recommended postoperative rehabilitation protocols are appropriate according to the type of LHF. METHODS: From 2014 to 2015, patients who underwent primary open wedge high tibial osteotomy (OWHTO) for isolated medial compartment osteoarthritis of the knee joint were retrospectively enrolled. The patients with minimum 1-year follow-up were included. The incidence of LHF after OWHTO based on simple radiographs was compared with its incidence based on CT scans. In the stable type of LHF and the non-LHF group, early weight bearing was encouraged immediately after OWHTO. In unstable LHF (types II and III), weight bearing was delayed until 2 weeks postoperatively. RESULTS: Twenty-three cases (24.5%) of LHF after 94 OWHTOs were detected (15 cases on simple radiographs, 8 cases on CT scan). The coronal osteotomy slope and the osteotomy gap were significantly larger in the LHF group than in the non-LHF group (coronal osteotomy slope, 20.3° ± 5.1° vs 16.7° ± 4.2°, P = .001; anterior osteotomy gap, 7.9 mm ± 2.1 mm vs 6.7 mm ± 1.8 mm, P = .008; posterior osteotomy gap, 12.7 mm ± 3.7 mm vs 11.2 mm ± 3.2 mm, P = .048). The correction loss of the hip-knee-ankle angle and the medial proximal tibial angle in the LHF group was significantly larger than those in the non-LHF group (1.3° ± 1.8° vs 0.4° ± 1.4°, P < .001; 1.3° ± 1.1° vs 0.7° ± 0.9°, P = .009, respectively). CONCLUSIONS: Further evaluation with CT scanning is highly valuable immediately after all OWHTO because of its higher detection rate (24.5%) of LHF compared with simple radiographs (16%). In addition, the coronal osteotomy slope was steeper and the opening gap was larger in the LHF group than in the non-LHF group. Finally, the LHF should be managed conservatively in order to prevent postoperative correction loss. LEVEL OF EVIDENCE: Level III, case-control study.