Pediatric Bassett’s ligament: pathology or normal anatomy?

Background: Bassett’s ligament is an accessory fascicle of the anterior inferior tibiofibular ligament. The prevalence, normal thickness and clinical implications of a thickened ligament have not been described in the pediatric radiology literature. Objective: The purpose of this study was to determine the prevalence and thickness of Bassett’s ligament in pediatric patients with magnetic resonance imaging (MRI) findings of lateral talar osteochondral lesions, medial talar osteochondral lesions and posterior ankle impingement, to compare these measurements with normal MRIs, and to compare the reproducibility of these measurements. Materials and methods: This is a retrospective study of pediatric ankle MRIs with four cohorts containing 21 patients each. All MRIs were retrospectively reviewed by a pediatric musculoskeletal radiologist and a pediatric radiology fellow. The prevalence of Bassett’s ligament and its axial thickness were obtained for each cohort with repeat measurements for intra-observer and interobserver variability. Average thickness and standard deviation of Bassett’s ligament were calculated. Results: The prevalence of Bassett’s ligament and its thickness in each cohort were (mean±standard deviation): lateral osteochondral lesions, 71% (15/21), 1.9±0.5 mm; medial osteochondral lesions, 52% (11/21), 1.4±0.2 mm; posterior impingement, 52% (11/21), 1.3±0.2 mm; and normal ankle examinations, 71% (15/21), 1.5±0.4 mm. The thickness of Bassett’s ligament was increased in the lateral talar osteochondral lesion group when compared to normal (P=0.02), while thickness in the medial osteochondral lesion and posterior impingement groups was not significant when compared to normal. The repeat measurements showed no significant difference in intra-observer and interobserver variability. Conclusion: Bassett’s ligament is a normal structure in children. Thickening of Bassett’s ligament is seen with lateral osteochondral lesions and may be an indirect sign of anterolateral tibiotalar capsule injury.