Purpose or Case Report: Bassett's ligament is an accessory fascicle of the anterior tibiofibular ligament that is not well addressed in pediatric patients. In the adult literature, it is known that the ligament is not present in some patients, but may be thickened in the setting of talar dome osteoarthritis. The purpose of our study was to determine the prevalence of Bassett’s ligament and measure its thickness in pediatric patients with MRI findings of lateral talar osteochondral lesions (OCLs), medial talar OCLs, and posterior ankle impingement and compare these measurements with patients with a normal ankle MRI.
Methods & Materials: Retrospective review of pediatric ankle MRI studies obtained through our electronic medical record was performed identifying 21 lateral talar dome OCLs (13.5±2.9 years; 33% female). Matched 1:1 controls of patients with medial talar OCLs (14.1±2.5; 62% female), posterior ankle impingement (12.5±2.4; 52% female), and those with normal ankle MRIs (13.8±2.5 years; 67% female) were obtained. All examinations were retrospectively reviewed by consensus by both a pediatric musculoskeletal radiologist and a pediatric radiology fellow for the presence of Bassett's ligament and its axial plane maximal thickness. Prevalence of the ligament and average thickness were calculated per subgroup and analyzed between subgroups for significant differences.
Results: Twenty-one MRI examinations were obtained in each subgroup, for a total of 84 MRI examinations. The prevalence of Bassett’s ligament and its thickness in patients with lateral talar OCLs, medial talar OCLs, posterior impingement, and in normal ankle examinations was 71% (15/21) 1.88 ± 0.45 mm, 52% (11/21) 1.38 ± 0.22 mm, 52% (11/21) 1.33 ± 0.19 mm, and 71% (15/21) 1.52 ± 0.35 mm, respectively. Ligament thickness was significantly increased between the lateral talar OCL group when compared with the medial talar OCL, posterior impingement and normal groups with p-values of <0.01, <0.01, and 0.02, respectively. Comparison of ligament thickness between the control subgroups did not reach significance (p<0.05).
Conclusions: Bassett’s ligament is a common and normal anatomic structure in the anterolateral compartment and is not a sign of ankle pathology. However, thickening of Bassett’s ligament is seen with lateral talar dome OCLs and is not appreciated with other talar abnormalities or with a normal ankle MRI. Thickening of Bassett's ligament in the setting of a lateral talar dome OCL may be an indirect sign of anterolateral tibiotalar capsule injury.