FCL and Posterolateral Corner Injuries Knee

Fibular Collateral Ligament and Posterolateral Corner Injury of the Knee

Approximately 7-16% of ligamentous knee injuries involve the posterolateral ligamentous complex of the knee. Posterolateral Corner (PLC) injuries are often combined, involving the posterior cruciate ligament (PCL) more commonly than the anterior cruciate ligament (ACL). Missed PLC injury is a frequent cause of ACL reconstruction (ACLR) failure. 

Injury can occur following a blow to the anteromedial aspect of the knee, hyperextension knee injuries and knee dislocations. Common peroneal nerve injury may be present, as can vascular injury. 

Anatomy & Function

The posterolateral corner (PLC) includes static stabilizers of the lateral knee: the fibular (lateral) collateral ligament (FCL), the popliteus tendon (PLT) and the popliteofibular ligament. Dynamically, the PLC is stabilized by the biceps femoris (hamstrings), popliteus muscle, the iliotibial band and the lateral head of the gastrocnemius muscle. The PLC functions to synergistically to control external tibial rotation, varus and posterior tibial translation along with the PCL.

Classification: Modified Hughston Classification

Grade 1Sprain, no tensile failure of capsuloligamentous structures
Grade 2Partial injuries with moderate ligament disruption
Grade 3Complete ligament disruption

Physical Examination and Work-up

On presentation, an effusion, pain and symptoms of instability may be present. Ligamentous examination is key to determine laxity relative to the uninjured knee. 

Varus Stress Test: this clinical test is used to evaluate the integrity of the fibular collateral ligament (FCL). With the patient supine, the knee is held in 20 degrees of flexion and loaded in varus distally such that the FCL is placed on stretch. The examiner assesses the amount of opening/gapping at the lateral joint space. The test is repeated with the knee in full extension.

Posterolateral Lachman Test: this clinical test is used to assess injury for to the PLC. With the patient supine, the knee is flexed to 30 degrees, and the tibia is translated posteriorly while in an externally rotated position. Excessive translation compared to the contralateral knee is consistent with a PLC injury.

Posterolateral Drawer Test: this clinical test is used to assess for to the PLC. The knee is flexed to 90 degrees and the foot is externally rotated to 15 degrees, with a posterolateral drawer is applied at the knee. Excessive posterolateral rotation compared to the contralateral knee is consistent with a PLC injury.

Dial Test: this clinical test is used to assess the integrity of the PLC, as well as to assess for a possible combined PCL tear. The patient begins in prone, and both knees are flexed to 30 degrees. The examiner cups the patient’s heels and places an external rotation force. The foot-thigh angle is measured and compared side-to-side. The knees are then flexed to 90 degrees and the test is repeated. An isolated PLC injury is consistent with > 10 degrees of external rotation in the injured knee at 30 degrees only. If there is more than 10 degrees of external rotation in the injured knee at 30 and 90 degrees, this finding is consistent with a combined PLC and PCL injury.


Stress x-rays are performed to quantify the side to side differences in ligament laxity. Standard x-rays assess for an avulsion fracture of the fibula and for degenerative changes, while long leg standing x-rays evaluate alignment. MRI assesses both the integrity of the involved ligaments and tendons, as well as the articular cartilage.

Management of Meniscus Tears

Non-operative care includes rest, short-term immobilization, and physical therapy in the setting of grade I PLC injuries. In the setting of Grade II PLC avulsion injuries and Grade III injuries surgical management may be recommended. Surgery includes posterolateral corner reconstruction utilizing two soft tissue grafts to restore stability of the knee. Rehabilitation begins immediately to reduce swelling, encourage quadriceps recruitment and to restore range of motion. A hinged knee brace is worn and patients are non-weight bearing for 6 weeks.