Posterior malleolar fragments contributing to syndesmotic stability: Clinical significance of lateral displacement.

Abstract

The indications for fixation of posterior malleolar fragments in ankle fractures remain controversial, and the correct interpretation of the pathology underlying fracture morphology is still unclear. This study focused on the anatomical characteristics of the posterior inferior tibiofibular ligament (PITFL) and the fracture pattern and displacement of posterior malleolar fragments, to determine which types of posterior malleolar fragments contribute to syndesmotic stability. Seventy patients with Weber type B ankle fractures associated with posterior malleolar fragments involving ≤25 % of the articular surface were included. Following fibular fixation, syndesmotic stability was assessed using the Cotton test. The relationship between Mason and Molloy fracture classification, the presence of lateral displacement (LD), and syndesmotic instability were all investigated. Syndesmotic instability was observed in 7/70 cases (10 %), including in 27.3 % of Mason and Molloy type 1 fractures and 55.6 % of LD-type fractures. Conversely, only 1 of the 54 cases that were neither Mason and Molloy type 1 nor LD-type demonstrated syndesmotic instability. PITFL function is likely preserved in most Weber type B fractures with Mason and Molloy type 2 posterior malleolar fragments caused by external rotation injury. In contrast, LD-type fragments suggest complete disruption of the PITFL, including the deep layer, and require treatment strategies that take this into account.