Posterolateral Corner Injuries

The posterolateral corner refers to a group of structures located on the outer back side of the knee. These include the lateral collateral ligament (LCL), popliteus tendon, and popliteofibular ligament, among others. Together, they stabilize the knee against forces that push it inward (varus forces) and prevent excessive rotation of the lower leg.

The PLC acts as a “check-rein” that keeps the knee stable during twisting, pivoting, and side-to-side movements. When this complex area is injured, it often occurs alongside damage to other ligaments—especially the anterior cruciate ligament (ACL) or posterior cruciate ligament (PCL). Because of its intricate anatomy and the way it interacts with other ligaments, a PLC injury can easily be overlooked unless carefully evaluated by a sports medicine specialist.

A posterolateral corner injury occurs when one or more of the stabilizing structures in this region are stretched, partially torn, or completely ruptured. These injuries are usually graded based on severity:

• Grade I: Mild stretching of the ligaments without significant instability.
• Grade II: Partial tearing, leading to mild to moderate instability.
• Grade III: Complete tearing of the ligaments, resulting in severe instability and loss of control during movement.

When a PLC injury occurs in combination with an ACL or PCL tear, it creates what is known as a multi-ligament knee injury, which requires prompt medical attention to restore stability and prevent long-term damage.

Symptoms of a posterolateral corner injury can vary depending on the extent of damage but generally include:

• Pain and tenderness along the outer and back part of the knee
• Swelling or bruising shortly after the injury
• A feeling that the knee “gives out” or cannot support weight, especially when walking downhill or turning
• Instability during twisting or side-stepping motions
• Limited range of motion or stiffness in the knee
• Occasionally, numbness or tingling due to irritation of the nearby peroneal nerve

Some patients describe a “popping” sound at the moment of injury, followed by pain and difficulty bearing weight. Because PLC injuries often occur in conjunction with other ligament tears, symptoms can overlap, making professional evaluation essential.

PLC injuries typically occur as a result of trauma or high-impact movement, particularly in contact or pivot-heavy sports. Common causes include:

• Sports injuries: Direct blows to the inside of the knee (such as in football, soccer, or basketball) can stress and tear the ligaments on the outer back corner.
• Falls or accidents: Landing awkwardly from a jump, slipping, or being involved in a motor vehicle accident can create twisting forces that injure the PLC.
• Hyperextension injuries: Overextending the knee beyond its normal range can damage multiple ligaments, including those in the posterolateral corner.

Because this area works closely with the ACL and PCL, any event that injures one of those ligaments can also damage the PLC, compounding instability and increasing the risk of long-term complications.

Athletes and active individuals who participate in contact or high-intensity sports are at the greatest risk for posterolateral corner injuries. However, these injuries can also occur in non-athletes during falls, car accidents, or sudden twisting motions. People who have previously sustained ligament injuries may also be more prone to PLC damage, as weakened surrounding structures can no longer provide optimal support.

If not properly diagnosed and treated, PLC injuries can lead to chronic instability, abnormal knee mechanics, and early arthritis due to excessive stress on the joint surfaces. That is why early recognition and evaluation by an orthopedic specialist are crucial.