The anterolateral ligament of the knee: MRI appearance, association with the Segond fracture, and historical perspective.

OBJECTIVE. A recent publication has drawn attention to the anterolateral ligament, a structure of the knee with which most radiologists are unfamiliar. We evaluate this structure on MRI; clarify its origin, insertion, meniscal relationship, and morphologic appearance; and identify its relationship with the Segond fracture. MATERIALS AND METHODS. A total of 53 routine knee MRI studies interpreted as normal were reviewed to characterize the anterolateral ligament. A further 20 knee MRI studies with a Segond fracture were assessed to determine a relationship between the fracture and the anterolateral ligament. RESULTS. In all 53 cases, a structure was present along the lateral knee connecting the distal femur to the proximal tibia, with meniscofemoral and meniscotibial components. This structure was somewhat ill defined and sheetlike, inseparable from the adjacent fibular collateral ligament proximally and iliotibial band distally. Aside from one case limited by anatomic distortion, all cases with a Segond fracture exhibited attachment of this structure to the fracture fragment (19/20 cases). CONCLUSION. An ill-defined sheetlike structure along the lateral knee exists attaching the distal femur, body of lateral meniscus, and proximal tibia. This structure has been referenced in the literature dating back to Paul Segond's original description of the Segond fracture in 1879. The structure is identifiable on MRI and appears to be attached to the Segond fracture fragment. For the radiologist, it may be best to forgo an attempt to separate this structure into discrete divisions, such as the anterolateral ligament, because these individual components are inseparable on routine MRI.