Deltoid incompetence in association with an isolated fibular fracture is assumed to be present if there is medial tenderness, ecchymosis, or substantial swelling. We sought to determine whether these soft-tissue indicators predict deltoid incompetence by comparing such findings with the findings on stress radiographs.

Over a thirty-two-month period, 138 patients who presented acutely with a Weber type-B supination-external rotation (SE) fibular fracture were evaluated for tenderness (in nine locations), ecchymosis, and swelling. Patients who presented with an apparently isolated fibular fracture and an intact ankle mortise (with a medial clear space of < or =4 mm and no talar subluxation) were evaluated with a stress radiograph to determine deltoid competence. Four groups of patients were identified: those who had an SE2 fracture (defined as those who had a stable ankle on the stress radiograph), those who had a stress (+) SE4 fracture (defined as those who had an unstable ankle on the stress radiograph), those who had an SE4 fracture (defined as those who presented with a wide medial clear space), and those who had a bimalleolar fracture. These four groups were compared with regard to tenderness, swelling, and ecchymosis at the time of initial presentation. Patients with SE2 injuries were allowed immediate weight-bearing.

Of the ninety-seven patients who presented with an isolated fibular fracture and an intact mortise, sixty-one had a stable SE2 injury and thirty-six had an unstable stress (+) SE4 injury. All stable SE2 injuries healed with an intact mortise. Medial tenderness, ecchymosis, and swelling were not predictive of deltoid incompetence (instability).

Stress radiographs allow for the accurate diagnosis of deltoid incompetence in patients with Weber type-B SE fibular fractures and no other osseous injury. Soft-tissue indicators are not accurate predictors of instability. If medial tenderness, ecchymosis, and swelling are used as operative indications, in some cases surgery may be performed on stable ankles.