Avulsion fracture of the lateral ankle ligament complex in severe inversion injury: incidence and clinical outcome.

Background: Avulsion fracture of the lateral ankle ligaments is often undetected on early radiographs. The epidemiology and treatment of such avulsion fractures have received much less attention than the epidemiology and treatment of rupture of these ligaments.

Hypothesis: The clinical characteristics of avulsion fracture are different from those of ligament rupture. Unlike nonoperative treatment of lateral ligament rupture, nonoperative treatment of avulsion fracture does not yield satisfactory results.

Study Design: Cohort study; Level of evidence, 2.

Methods: A total of 169 consecutive patients with severe inversion injury were classified into a ligament rupture group or avulsion fracture group on the basis of physical examination findings and anterior talofibular ligament and calcaneofibular ligament radiographic views. Age, sex, activity level, and the mechanism of injury were analyzed. Patients in both groups were treated by casting. Follow-up examination of 152 patients included clinical assessment and functional evaluation based on the Karlsson system.

Results: Avulsion fracture was diagnosed in 44 (26%) of the 169 patients and was most common among children and patients over 40 years of age. Sedentary level activity and low-energy injury were more common in the avulsion fracture group than in the ligament rupture group (77% vs 37%, respectively, P = .001; 68% vs 43%, respectively, P =.004). Nonoperative treatment of avulsion fracture (mean Karlsson score, 89.1 points) yielded satisfactory results that were comparable with those of nonoperative treatment of ligament rupture (mean Karlsson score, 88.4 points) (P = .123). Osseous union was achieved in 65% of the patients with avulsion fracture.

Conclusion: Avulsion fracture of the lateral ankle ligaments in cases of severe inversion injury is more common than previously believed. Because of the high incidence and difficulty of detection in children, a high level of suspicion is necessary in order to obtain an accurate diagnosis of avulsion fracture in cases of severe inversion injury and to achieve adequate stability.