Deep posterior tibiotalar ligament in Weber B ankle fractures: An observational study correlating arthroscopic and stress radiographic findings

Research Type: Level 4 – Case series Introduction/Purpose: Weber B fractures often show unstable gravity stress tests but stable weightbearing radiographs (classified SER4a), suggesting partial deltoid ligament injury with an intact deep posterior tibiotalar ligament (dPTTL). Conversely, a dPTTL rupture is assumed if both radiographs are unstable (classified SER4b). However, the state of the dPTTL in SER4a vs. SER4b has not been well studied. This study assessed the prevalence of dPTTL injury using direct visualization during arthroscopy of SER4a and SER4b fractures. Methods: We conducted a prospective study on 20 patients with Weber B/SER4a-b ankle fractures having unstable gravity stress tests or unstable weightbearing radiographs (medial clear space ≥ 4.0 millimeters). Blinded assessors evaluated the dPTTL using minimally invasive arthroscopy under local anesthesia. Intact dPTTL was defined by normal ligament visualization with tensioning and medial joint space closing with dorsiflexion. Results: Based on radiographic criteria, 15 patients were classified as SER4a and five as SER4b. Arthroscopy showed an intact dPTTL in 14 SER4a injuries. One patient with a 3.9 mm medial clear space had a torn dPTTL. All SER4b injuries revealed dPTTL disruptions with arthroscopic assessment. Conclusion: In Weber B fractures evaluated arthroscopically, the dPTTL is typically intact in cases where weightbearing radiographs are stable despite unstable gravity stress tests. Conversely, complete dPTTL disruption was consistently observed in cases where both tests were unstable. These findings support the hypothesis that a stable weightbearing radiograph indicates an intact dPTTL.