Predicting Syndesmotic Injury in Weber B Ankle Fractures

CATEGORY: Trauma; Ankle INTRODUCTION/PURPOSE: Accurate pre-operative diagnosis of syndesmotic injuries can be difficult in the setting of AO 44-B1 fractures. Ankle fractures with syndesmotic injuries have worse reported outcomes. No study has investigated the relative fracture height in determining potential syndesmotic injury. The goal of this study was to establish if pre-operative radiographs could accurately predict syndesmotic injury. METHODS: Patients treated for an isolated AO 44-B1 fracture over a ten-year period (2007-2017) were reviewed. Anteroposterior and mortise views of the ankle were used to determine the zone of distal extent of the proximal fracture fragment (Figure 1). Syndesmotic injury was defined as positive intraoperative stress exam that required syndesmotic fixation. Relative risks were determined between zones with a statistical significance set at 0.05. Ten randomly selected radiographs were reviewed by two authors and assessed by intra-class correlation (ICC) for inter- and intra-observer reliability. RESULTS: There were 548 AO 44-B1 fractures that were reviewed; and 287 patients were included in the study. There were 191 zone 1 injuries, 57 zone 2 injuries, and 39 zone 3 injuries. Of these, 17% (33 patients) of zone 1, 42% (24) of zone 2, and 74% (29) of zone 3 fractures had syndesmotic injuries. The relative risk of syndesmotic injury of Zone 1 compared to Zone 2 was 2.4 (p<0.001), Zone 1 to Zone 3 was 4.3 (p<0.001), Zone 2 to Zone 3 was 1.8 (p=0.002). The ICC for inter- and intra-observer reliability was perfect (ICC=1). CONCLUSION: AO 44-B1 fractures have a varying rate of syndesmotic injury. Weber B fractures that end between the level of the plafond and the physeal scar (Zone 2) are 2.6 times more likely to have a syndesmotic injury compared to those that end below the plafond (Zone 1). This is magnified in those injuries ending above the scar (Zone 3). This simple classification of AO 44-B1 fractures is predictive of syndesmotic injury and may aid in preoperative counseling and planning.