Background: The deep deltoid ligament (DDL) is a key stabilizer to the medial ankle and ankle mortise and can be disrupted in ligamentous supination external rotation type IV (LSER4) ankle fractures. The purpose of this study was to define the medial clear space (MCS) measurement on injury mortise radiographs that corresponds with complete DDL injury.
Methods: A retrospective record review at a level 1 hospital was performed identifying patients with LSER4 ankle fractures who underwent arthroscopy and open reduction internal fixation. Chart reviews provided arthroscopic images and operative reports. Complete DDL injury was defined as arthroscopic visualization of the posterior tibial tendon (PTT). Inability to completely visualize the PTT was defined as a partial DDL injury. MCS was measured on injury mortise radiographs. Eighteen subjects met inclusion criteria.
Results: Twelve subjects had complete and 6 subjects had partial DDL injury based on arthroscopic findings. Patients with complete DDL injury and those with partial DDL injury had injury radiograph MCS ranging from 5.5 to 29.9 mm and 4.0 to 5.0 mm, respectively. All patients with MCS ≥5.5 mm on injury radiographs had complete DDL injury and all patients with MCS ≤5.0 mm on injury radiographs had partial DDL injury.
Conclusion: Complete DDL injury was found on injury ankle mortise radiographs as MCS widening of ≥5.5 mm, which correlated with arthroscopic visualization of the PTT. Using this cutoff, surgeons can surmise the presence of a complete deltoid ligament injury, allowing for improved preoperative planning.
Level of evidence: Level III, retrospective comparative study.
Keywords: ankle; arthroscopy; deltoid; fracture; ligament; mortise; radiograph.