Value of posterior cruciate ligament index in the diagnosis of anterior cruciate ligament injuries.

Assessment of the diagnostic value of the posterior cruciate ligament index (PCL index) for injuries of the anterior cruciate ligament (ACL) was done. Magnetic resonance imaging (MRI) and knee joint arthroscopy of 170 patients were evaluated. The shortest distance between the femoral and tibial attachment of PCL (x) and the distance from that line to the tip of the arc marked by the PCL (y) on the sagittal plane images were measured. The quotient of these two parameters (x/y) defined the PCL index. In 100 patients, for whom arthroscopy ruled out ACL injury, the mean PCL index was 5.01 +/- 0.76. In 30 patients in whom arthroscopy showed total ACL rupture, the mean PCL index was 2.88 +/- 0.74, and in 10 patients with ACL partial rupture, 3.09 +/- 0.23. The conclusion is that injury to the ACL changes the PCL index markedly. In diagnostically unreliable MR images, deterioration of the PCL index could help in the diagnosis of ACL injury.