Diagnostic Value of Calcaneofibular Ligament Tortuosity on Oblique Coronal MRI in Chronic Ankle Instability.

BACKGROUND: Lateral ankle sprains are common injuries that may progress to chronic ankle instability (CAI). Although stress radiographs are widely used to assess mechanical instability, magnetic resonance imaging (MRI)-based parameters for evaluating calcaneofibular ligament (CFL) instability remain limited. The purpose of this study was to evaluate the diagnostic value of the CFL tortuosity angle (C angle) measured on oblique coronal MRI in patients with CAI and to examine its relationship with clinical and radiographic measures. METHODS: A retrospective analysis of 120 patients (82 CAI, 38 controls) was performed. The C angle was measured on oblique coronal T2-weighted MRI. Talar tilt angle was assessed using stress radiography in the CAI group. Functional outcomes and ankle eversion strength were also evaluated. RESULTS: A total of 120 patients were included, comprising 82 patients with CAI and 38 controls without a history of ankle sprain. The C angle was significantly greater in the CAI group compared with controls (76.5° ± 18.3° vs 31.9° ± 5.4°, P < .001). Receiver operating characteristic analysis demonstrated excellent diagnostic performance (area under the curve, 0.97), with an optimal cutoff of 40.9° (sensitivity, 97.6%; specificity, 100%). The C angle showed a moderate correlation with talar tilt angle (r = 0.327, P = .003) but limited association with functional scores and muscle strength. CONCLUSION: The CFL tortuosity angle on oblique coronal T2-weighted MRI demonstrated high diagnostic accuracy for CAI and may serve as a useful adjunctive parameter in evaluating ligament instability. LEVEL OF EVIDENCE: Level IV, retrospective comparative study.