Causes / typical injury mechanism / pathophysiology: The posterolateral corner (PLC) of the knee consists of a relatively complex set of structures whose fundamental role is to provide varus support for the knee joint and prevent external rotation or posterior translation of the lower leg. Structures of the PLC include the lateral collateral ligament (LCL, also known as fibular collateral ligament), iliotibial (IT) band, popliteus tendon complex, biceps femoris short and long head, fabellofibular ligament, arcuate ligament complex, lateral gastrocnemius tendon, and mid-third lateral capsular ligament. The major biomechanical components of the PLC are the LCL, popliteus tendon, and popliteofibular ligament. The LCL provides most of the varus support in the PLC, although LCL lesions are typically defined as a separate diagnostic entity. Important associated neurovascular structures are the peroneal nerve and the inferior lateral genicular artery.

PLC injuries typically result from hyperextension of the knee, occasionally in conjunction with varus or external rotational force of the lower leg. The most common causes are athletic injuries, motor vehicle accidents, and falls.

Classic history and presentation: Patients typically present with a history of knee trauma related to athletics or a motor vehicle accident involving hyperextension of the knee or varus force on the knee. Patients often present acutely, reporting pain in the posterolateral knee and around the fibular head. There may be visible soft tissue swelling and varying degrees of joint effusion. Associated neurovascular injury may result in numbness, tingling, weakness, or pallor in the lower leg. Chronic injuries are more likely to present with instability in the absence of swelling or effusion. Isolated PLC lesions may not present with varus joint laxity, particularly if the LCL is still intact.

Prevalence: PLC lesions are relatively rare, implicated in approximately 10% of knee injuries, less than half of which are isolated PLC injuries. They are thought to be widely underreported, which can have adverse effects on the surgical repair of other knee structures.

• Sex / gender – This condition predominantly affects men over women. 

Risk factors:

• Motor vehicle accidents
• Athletic knee twisting injuries
• There has been some evidence to suggest that obese patients are at an increased risk of injury due to low-energy mechanisms.