Axial Load Weightbearing Radiography in Determining Lateral Malleolus Fracture Stability: A Cadaveric Study

BACKGROUND: Ankle fractures are the most common fracture treated by orthopaedic surgeons in the United States. Isolated lateral malleolus fractures are treated nonoperatively, while associated deltoid disruption injuries are unstable and usually treated by fixation of the fracture. Various stress radiographs and MRI have been used to determine deltoid competency and the subsequent need for operative stabilization of lateral malleolus fractures. To date, no standardization of stress radiography has been performed. The aim of this study was to evaluate the ability of weightbearing ankle X-rays to determine stability and their reliability. METHODS: This study sought to utilize simulated weightbearing radiography as a potential method to determine the need for lateral malleolus fixation. Twelve cadaveric ankle specimens were tested by obtaining ankle mortise radiographs for interpretation of medial clear space. Each ankle was tested with 0, 25, 36, and 50 kg of axially applied weight. The groups of measurements obtained were: intact ankles (Group A), ankles with an isolated oblique fibular osteotomy (Group B), and osteotomized ankles after complete deltoid ligament transaction (Group C). Three authors measured the medial clear space for every ankle using PACSR software. Instability of the ankle mortise was defined as medial clear space widening of greater than 2 mm from the intact ankle. RESULTS: An isolated lateral malleolus fracture (Group B) and a lateral malleolus fracture with an incompetent deltoid ligament (Group C) showed no statistical medial clear space widening with simulated axial weightbearing radiography when compared to intact ankles (Group A). ANOVA's between Group A and B had p < 0.001, and between Group A and C of p < 0.001. CONCLUSION: Our model did not find instability with an osteotomized fibula and a disrupted deltoid. CLINICAL RELEVANCE: This study suggests a weightbearing radiograph of an isolated lateral malleolus fracture cannot determine deltoid ligament integrity and thus need for fibular operative fixation.