Abnormal axial rotation of the Talus on weight-bearing computed tomography in patients with micro-instability of the ankle

Background While diagnosing mechanical chronic ankle instability (CAI) is often straightforward, identifying subtle micro-instability remains challenging. A tear of the superior bundle of the lateral ligament complex has been proposed as a contributor to micro-instability, potentially causing increased anterior translation and internal talar rotation under load. Weight-bearing computed tomography (WBCT) offers valuable insight into hindfoot alignment and load-induced deformation, making it a promising tool for assessing suspected micro-instability. This study aims to compare talar axial rotation between symptomatic patients reporting subjective micro-instability and asymptomatic controls. Methods Forty ankles from patients with osteochondral lesions of the talus (OLT) and signs of micro-instability were compared to asymptomatic controls. WBCT and image analysis software were used to generate 3D models and perform semi-automated hindfoot alignment measurements. Inter- and intra-observer reliability was also assessed. Results The OLT group showed a mean axial rotation difference of −4.5 ± 4.5 degrees compared to controls (P ' 0.001), indicating increased external rotation of the talus. Intra-observer reliability was good to excellent (ICC 0.88, 0.92), and inter-observer agreement was excellent (ICC 0.93, 0.90). Conclusion WBCT did not reveal abnormal internal rotation in OLT patients with subjective micro-instability. Instead, significant external rotation of the talus was observed. These findings suggest that external rotation may predispose patients to micro-instability.