MR imaging of the posterior cruciate ligament: normal, abnormal, and associated injury patterns.

The posterior cruciate ligament (PCL) of the knee has received little attention in the radiology literature, but its importance in knee stability has come under close scrutiny in recent years. Unrepaired injury of the PCL can lead to chronic instability and early joint degeneration. Three major mechanisms of trauma that involves the PCL are posterior displacement of the tibia in a flexed knee, hyperextension, and rotation combined with an adduction or abduction force. The spectrum of PCL injuries includes partial tear or intrasubstance injury, complete ligamentous rupture, and avulsion of the PCL insertion site on the posterior tibia. Associated injuries include injury of other ligaments, meniscal tear, bone injury, and joint effusion. PCL rupture is easily identified with magnetic resonance (MR) imaging by using simple signal intensity and structural characteristics. Because clinical and arthroscopic assessment of the PCL can be difficult, MR imaging can be valuable for evaluating the acutely injured knee when operative repair of the PCL is being considered.