To analyze the ultrasonographic findings of normal and injured anterolateral ligament (ALL).

The ALLs of 20 patients with acute unilateral anterior cruciate ligament (ACL) injuries, as diagnosed by MRI, were examined by ultrasonography and MRI. The injuries were evaluated after obtaining high-resolution images. The Cohen's Kappa coefficient was used to evaluate consistency between observers. The threshold of thickness for ALL injury was obtained by receiver operating characteristic (ROC) curve analysis.

In the normal knee joints, the incidence of ALL in proximal femoral condyle attachment was 90% (18/20, Kappa=0.85) and the incidence of ALL in tibial plateau insertion was 100% (20/20, Kappa=1). The insertion of the meniscus of ALL cannot be displayed (0/20, Kappa=1). In knee joints with ACL injury, the incidence of ALL injury, as diagnosed by ultrasound, was 45% (9/20, Kappa=0.80), including nine cases with insertion tibial plateau injuries (Kappa=1) and two cases with lateral condyle of the femur attachment injuries (Kappa=0.79). The results of ROC curve analysis showed that a lateral femoral condyle attachment ALL thicker than 0.65 mm as measured by ultrasound was considered to be an injury (sensitivity: 100%; specificity: 40%), whereas an tibial plateau insertion ALL thicker than 1.25 mm was considered to be an injury (sensitivity: 88%; specificity: 93%).

ALL injury is often accompanied by ACL tear, and the injury usually occurs at the insertion of the tibial plateau. Ultrasound is a simple and rapid method for the examination of ALL.