The role of EUA and MRI scans in the evaluation of chronic symptomatic ankle instability - MRI findings of intact ligament doesn’t imply functional lateral ligament complex

G Koshy, A Rajeev, K Devalia

Introduction: Chronic lateral ankle instability often follows traumatic rupture or pathological laxity of the lateral ankle ligament complex. While MRI is useful in identifying complete ligament tears, it may not reliably detect incompetence in pathologically elongated ligaments. This study aims to determine if EUA is a superior diagnostic tool compared to MRI scans in accurately diagnosing chronic lateral instability.

Methods: We conducted a prospective case analysis of 50 symptomatic patients who underwent lateral ligament reconstruction for chronic ankle instability. Each patient underwent both EUA and MRI scans prior to surgery. EUA was performed in the operating theatre under general anaesthesia, using image intensifier guidance to conduct anterior drawer stress and talar tilt tests. MRI scans were independently evaluated by two experienced musculoskeletal radiologists.

Results: EUA indicated complete insufficiency of the ankle in 49(98%) patients, as evidenced by positive anterior drawer and talar tilt tests. MRI scans reported complete ligament rupture in 17 patients (34%), thickened ATFL (Anterior Talo-Fibular Ligament) and CFL (Calcaneo-Fibular Ligament) ligaments in 18 patients (36%), and an intact lateral ligament complex in 15 patients (30%) The accuracy of MRI for intact and complete tears of the ATFL and CFL was 76% and 78%, respectively, with sensitivity and specificity of 66% and 84% for intact and 77% and 78% for complete tears, respectively. The sensitivity and specificity for thickening of ATFL and CFL were 75% and 77% respectively.

Conclusion: EUA, in conjunction with symptomatic instability, appears more reliable in assessing lateral ligament instability compared to MRI scans. While MRI is valuable for identifying additional pathologies such as osteochondral lesions, peroneal tendon subluxation or tear, and syndesmotic injuries, it is less effective for evaluating hyperlaxity and elongated lateral ligaments. Therefore, EUA should be considered a critical diagnostic tool in managing patients with chronic lateral ankle instability.