MRI Evaluation of Ligamentous Injury in Weightbearing-Stable Suprasyndesmotic Ankle Fractures: A Prospective Observational Study.

Background: Suprasyndesmotic ankle fractures (Weber C) account for approximately 10% of ankle fractures, and surgery is advised because of the assumed unstable nature of these injuries. Treatment of transsyndesmotic ankle fractures (Weber B) has evolved as weightbearing radiographs are employed as a modality to evaluate ankle joint stability. Joint congruency on weightbearing radiographs indicate sufficient ligamentous integrity to allow for nonoperative treatment. However, no studies have evaluated the ligamentous injury patterns in suprasyndesmotic ankle fractures with a congruent ankle joint on weightbearing radiographs. This study investigates the ligamentous injuries in patients with suprasyndesmotic fractures of uncertain stability that reduce on weightbearing radiographs, aiming to provide further insight into the ligamentous injury patterns of these injuries.

Methods: A prospective cohort study was conducted from October 2023 to August 2024, involving patients with suprasyndesmotic ankle fractures. Eligible patients underwent weightbearing radiographs, and if no medial clear space widening was noted, magnetic resonance imaging (MRI) examination was conducted. MRI results were analyzed for the integrity of the deltoid and syndesmotic ligament complexes to describe ligament injury patterns rather than guide treatment decisions. Weightbearing radiographs at 2-week, 6-week, and 6-12-month follow-up were evaluated for joint congruency and fracture healing. No clinical outcomes were assessed.

Results: Twenty patients were included in the final analysis. The majority of participants exhibited a complete rupture of the anterior inferior tibiofibular ligament and interosseous ligament. Low frequency of complete rupture of the posterior inferior syndesmotic ligament (PITFL) and the deep posterior tibiotalar ligament (dPTTL) of the deltoid complex was evident. The majority of patients demonstrated a congruent ankle joint on the 6-12-month follow-up weightbearing radiographs, with 14 of 15 showing joint congruency. One patient treated nonoperatively demonstrated widening of the medial clear space at the 6-12-month follow-up.

Conclusion: In this small observational study, suprasyndesmotic ankle fractures that demonstrated congruency on weightbearing radiographs often exhibited an intact or partially ruptured PITFL and dPTTL, when evaluated with MRI. Clinical relevance of these findings remains uncertain without outcome data.