[MR imaging of bone bruise associated with ACL tear].

The authors reviewed 56 MR studies of the knee performed for suspected cruciate ligament tear at the Tokyo Metropolitan Hiroo Hospital from April 1990 to March 1991. There were 10 patients with abnormal signal in the subcortical bone marrow. Eight of these patients had concomitant anterior cruciate ligament (ACL) tear with no evidence of fracture on plain radiographs of the knee. The abnormal signals were all seen in the lateral compartment, almost invariably in the middle third of the lateral femoral condyle and posterolateral aspect of the tibial plateau, and were of low intensity on T1-weighted and proton density images and of high intensity on T2-weighted images. It was speculated that these abnormalities resulted from impaction of the lateral femoral condyle into the posterior lip of the tibial plateau due to rotary subluxation of the tibia. One patient had a follow-up study three months later, which revealed complete resolution of bone bruise. It was concluded that bone bruise associated with ACL tear is seen specific locations, which may be a useful secondary sign of acute ACL tear.