A New Intraoperative Syndesmosis Instability Classification System: Utility and Medium-term Results in Closed Displaced Ankle Fractures.

OBJECTIVE: To investigate the utility and medium-term results of a new intra-operative classification system for distal tibiofibular syndesmosis injury in ankle fractures.

METHODS: Between January 2010 and January 2015, 116 patients diagnosed with displaced closed Weber B and C ankle fractures were treated in our department. The etiology of injury was 56 cases of fall-sprain, 36 of traffic injury, 14 of fall from a height, and 10 of multiple injuries. After fixation of the fibular fracture, we classify syndesmosis stability as either normal or one of three grades of instability using the fibular hook traction test. This determined further fixation selection and final syndesmosis treatment.

RESULTS: Of 116 cases, 82 (71%) demonstrated a tibiofibular syndesmosis injury and 52 (45%) were unstable. Twenty-six cases were type I injuries (<4 mm displacement), 41% cases were type II injuries (4-7 mm displacement), and 3% of cases were type III injuries (>7 mm displacement). Types II and III are defined as unstable and require stabilization. Type III injuries have multiplanar instability and require two screws at the syndesmosis. Weber C fractures demonstrate significantly greater degrees of instability than Weber B fractures (χ2 = 15.50, P = 0.0014). All patients were followed up for 12-24 months, with no cases of non-union or broken screws. Good and excellent results were achieved in 93% of cases (according to the American Orthopaedic Foot and Ankle Society scoring system).

CONCLUSION: The syndesmosis instability classification system provides a rational and efficient basis for managing syndesmosis instability. Our results from application of the algorithm justify its further evaluation in the treatment of patients with closed displaced Weber B and C ankle fractures.