Third Place Award: Characterization and incidence of occult posterior malleolar fractures

Background: Occult fractures of the posterior malleolus are often missed by primary care providers and radiologists. Delayed treatment of posterior malleolar fractures can be problematic because of the potential for malunion, arthritis, or instability. The incidence and characterization of missed posterior malleolar fractures has not been reported in the literature. Methods: A retrospective review was performed of all ankle fractures with CT scans from 2005 to 2015 at a single institution. Inclusion criteria included age older than 18 yr and posterior malleolar fracture as seen on CT scan. Exclusion criteria included distal tibial shaft fractures and pilon fractures. Forty-six patients were identified with the above criteria. Data collected included whether a fracture was missed on initial radiographs by a board-certified radiologist, and the size and angle of the posterior malleolar fragment. Results: Of the 46 patients with posterior malleolar fractures, nine (19.5%) were missed on the radiology report. Seven of 46 (15.2%) were not described on all plain films prior to the CT scan. Two of seven (28.6%) radiographically occult fractures underwent open reduction and internal fixation of the posterior malleolar fragment. The average angle of occult posterior malleolar fractures relative to the transmalleolar axis was quite variable, with an average of 17 degrees (SD 11 degrees, range −20 degrees to 50 degrees). Conclusions: With a 15% incidence of occult posterior malleolar fractures, a CT scan or multiple orthogonal views can be helpful to avoid missed fractures. Given the wide variability of fracture angle, a single external rotation view is unlikely to prevent all missed fractures on initial radiographic interpretations. Level of Evidence: Level III, retrospective cohort study.