Association of ligamentum teres thickness on MRI with femoral head extrusion in Legg–Calvé–Perthes disease

OBJECTIVE: To evaluate the association between ligamentum teres thickness measured on hip MRI and lateral femoral head extrusion in patients with Legg-Calvé-Perthes disease and to assess the intra- and interobserver reproducibility of these measurements. MATERIALS AND METHODS: This retrospective study included pelvic radiographs and hip MRI examinations of patients with Legg-Calvé-Perthes disease. Femoral head extrusion was assessed on anteroposterior pelvic radiographs using the Reimers migration index, which served as the reference standard. Two musculoskeletal radiologists independently measured ligamentum teres thickness on MRI in the mediolateral and anteroposterior planes and performed qualitative assessment of ligament morphology. Intra- and interobserver agreement was evaluated using intraclass correlation coefficients and kappa statistics. RESULTS: Sixty-four hips from 58 patients (mean age, 13.4 years) were included; femoral head extrusion was present in 24 hips (37.5%). Mediolateral ligamentum teres thickness showed excellent intraobserver and good interobserver reproducibility and was significantly greater in hips with extrusion than in those without extrusion (mean, 5.03 mm vs 3.80 mm; p = 0.008). Mediolateral thickness correlated positively with the migration index (ρ = 0.30, p = 0.016). Age was not significantly associated with ligamentum teres thickness or migration index values, and the association between mediolateral thickness and extrusion remained significant after adjustment for age (OR = 1.61; 95% CI, 1.14-2.28; p = 0.007). No significant associations were observed for anteroposterior thickness or qualitative ligament morphology. CONCLUSION: In Legg-Calvé-Perthes disease, increased mediolateral ligamentum teres thickness on MRI is associated with lateral femoral head extrusion and may represent a reproducible imaging parameter.