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

Abstract 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.