Temporizing cast immobilization is a safe alternative to external fixation in ankle fracture-dislocation while posterior malleolar fragment size predicts loss of reduction: a case control study

BACKGROUND: To determine if temporizing cast immobilization is a safe alternative to external fixator (ex-fix) in ankle fracture-dislocations with delayed surgery or moderate soft-tissue injury, we analysed the early complications and re-dislocation rates of cast immobilization in relation to ex-fix in patients sustaining these injuries. METHODS: All skeletally mature patients with a closed ankle fracture-dislocation and a minimum 6-months follow-up treated between 2007 and 2017 were included. Baseline demographics, comorbidities, injury description, treatment history and complications were assessed. RESULTS: In 160 patients (94 female; mean age 50 years) with 162 ankle fracture-dislocations, 35 underwent primary ex-fix and 127 temporizing cast immobilizations. Loss of reduction (LOR) was observed in 25 cases (19.7%) and 19 (15.0%) were converted to ex-fix. The rate of surgical site infections (ex-fix: 11.1% vs cast: 4.6%) and skin necrosis (ex-fix: 7.4% vs cast: 6.5%) did not differ significantly between groups (p = 0.122 and p = 0.825). Temporizing cast immobilization led to an on average 2.7 days earlier definite surgery and 5.0 days shorter hospitalization when compared to ex-fix (p < 0.001). Posterior malleolus fragment (PMF) size predicted LOR with ≥ 22.5% being the threshold for critical PMF-size (p < 0.001). CONCLUSION: Temporizing cast immobilization was a safe option for those ankle fracture-dislocations in which immediate definite treatment was not possible. Those temporized in a cast underwent definite fixation earlier than those with a fix-ex and had a complication rate no worse than the ex-fix patients. PMF-size was an important predictor for LOR. Primary ex-fix seems appropriate for those with ≥ 22.5% PMF-size. TRIAL REGISTRATION: The study does not meet the criteria of a prospective, clinical trial. There was no registration.