Posterior ankle soft tissue echo intensity is associated with anterior ankle pain and dorsiflexion limitation following ankle fracture surgery

Background: Limited ankle dorsiflexion range of motion (ROM) and anterior ankle pain are common sequelae following ankle fracture surgery. While anterior ankle impingement syndrome (AAIS) is traditionally linked to anterior structural changes, the role of posterior soft tissues, such as the flexor hallucis longus (FHL) and Kager's fat pad (KFP), is unclear. This study aimed to investigate the association between the echo intensity (EI) of posterior ankle soft tissues and the clinical signs suggestive of AAIS after ankle fracture surgery. Methods: This cross-sectional study included 40 patients who underwent open reduction and internal fixation for ankle fractures. Anterior ankle pain intensity was assessed using a visual analogue scale during forced dorsiflexion as part of the Molloy-Bendall test in a non-weight-bearing position to capture pain provoked under conditions characteristic of anterior ankle impingement. Ankle dorsiflexion ROM was measured under both weight-bearing and non-weight-bearing conditions. The EI of the FHL and KFP was quantified from greyscale B-mode ultrasound images. Multiple regression analyses were conducted to identify independent predictors of anterior ankle pain and dorsiflexion ROM. Participants were further classified based on FHL stretch test results. Higher FHL EI also predicted reduced dorsiflexion ROM. Participants with a positive FHL stretch test exhibited significantly greater EI values in the FHL and KFP, higher pain intensity, and more restricted dorsiflexion than those with a negative test. Conclusion: Higher EI of the posterior ankle soft tissues, especially the FHL, was associated with greater anterior ankle pain and reduced dorsiflexion ROM following ankle fracture surgery. These findings suggest that posterior soft tissue assessment using B-mode ultrasound may provide additional clinical information in patients with anterior ankle pain and dorsiflexion limitation after ankle fracture surgery. Longitudinal and interventional studies are needed to determine whether posterior soft tissue alterations contribute to the development or persistence of AAIS-related symptoms.