CT measurement of Segond fracture fragment distance to the Gerdy tubercle predicts combined anterolateral ligament and iliotibial band capsulo-osseous layer involvement on MRI.

OBJECTIVE: Segond fractures are avulsion fractures of the anterolateral tibial plateau, but the ligamentous structures involved remain debated. This study aimed to determine whether CT-measured fragment distance to the Gerdy tubercle predicts combined involvement of the anterolateral ligament (ALL) and the capsulo-osseous layer of the iliotibial band (ITB) as defined by MRI. MATERIALS AND METHODS: We retrospectively analyzed 86 patients (58 male, 28 female; mean age 30.9 ± 11.4 years) with acute Segond fractures on CT and MRI. CT measured fragment dimensions and distance to the Gerdy tubercle. MRI assessed the ALL, ITB, and its capsulo-osseous layer, classifying patients into ALL-only (n = 48) vs combined ALL + ITB involvement (n = 38). ROC analysis evaluated CT parameters. RESULTS: Anterior cruciate ligament(ACL) injury occurred in all 86 patients (100%). MRI showed ALL attachment in 100% and combined involvement in 44.2%. Fragment dimensions did not differ between groups (all p > 0.05). CT distance to Gerdy tubercle was shorter in the combined group (9.2 ± 1.6 mm vs 11.2 ± 3.1 mm, p = 0.029). A cutoff < 10 mm predicted combined involvement (sensitivity 78.9%, specificity 62.5%; AUC = 0.72, 95% CI 0.60-0.84). CONCLUSION: Segond fractures consistently involve the ALL. Combined involvement of the capsulo-osseous layer adjacent to the ITB occurs in a substantial subset and is associated with a fragment distance of < 10 mm from the Gerdy tubercle on preoperative CT, as identified on MRI. This simple, reproducible CT marker may assist in surgical planning for anterolateral complex injuries when interpreted alongside MRI findings.