Specific components of the posterolateral corner that can be identified on MRI, albeit with some variability, are the biceps femoris tendon, the fibular collateral ligament, the popliteus musculotendinous complex including the popliteofibular ligament, the fabellofibular ligament, and the arcuate ligament. In general, these normally low-signal-intensity structures are defined as "sprain" when there is thickening and intermediate signal intensity within the structure on fatsuppressed fast spin-echo T2-weighted images and as torn when the structure is discontinuous with a visible gap. Some researchers support the use of a coronal oblique plane of imaging to improve visualization of some of the finer, obliquely oriented structures of the posterolateral corner, including the popliteofibular, arcuate, and fabellofibular ligaments, although this has not become routine. Recognition of bone marrow changes in thefibular head, including the so called “arcuate” fracture that may also be seen on radiographs is also helpful in diagnosing posterolateral corner injury. Being aware of the normal and abnormal MRI appearances of the structures of the posterolateral corner of the knee and of the patterns of injury often seen in patients with posterolateral corner rotatory instability will help radiologists suggest the diagnosis of posterolateral corner injury even when not clinically suspected. This diagnosis is especially important in the setting of combined injuries because unrecognized and unaddressed posterolateral corner injuries may contribute significantly to ACL and PCL graft failure.

posterolateral corner, Knee,MRI