LCL and PLC Injuries
The lateral collateral ligament (LCL), also known as the fibular collateral ligament, is a crucial structure on the outer side of the knee. It connects the femur (thighbone) to the fibula, the smaller bone on the outside of the lower leg, providing stability to the knee. The primary role of the LCL is to prevent the knee from gapping open on the outer side, especially when force is applied to the inner knee. This ligament plays a vital role in stabilizing the knee during lateral movements.
The posterolateral corner (PLC) of the knee, once referred to as the “dark side of the knee” due to limited understanding, is now recognized as a critical component in knee stability. This complex area includes three main structures: the LCL, the popliteus tendon, and the popliteofibular ligament. These structures work in tandem to stabilize the outer knee and prevent excessive outward (external) rotation of the shinbone (tibia) in relation to the thighbone (femur).
Due to advancements in anatomical and biomechanical research, new surgical techniques have been developed to reconstruct torn ligaments in their precise anatomical locations. These improvements have significantly enhanced surgical outcomes for posterolateral corner injuries.
The posterolateral corner structures collaborate to stabilize the knee, especially during rotational movements. The LCL acts like a rope, preventing the knee from opening up on the outside, while the popliteus tendon and the popliteofibular ligament limit excessive external rotation of the tibia. Without proper function of these structures, the knee becomes unstable, making it prone to further injury.
Posterolateral corner injuries can occur through both contact and non-contact mechanisms. Common causes include:
- Contact injuries: A direct blow to the inside of the knee, such as during a car accident or a sports collision.
- Non-contact injuries: These often occur when the knee is hyperextended, bending backward under pressure. This is common in athletes like gymnasts or in individuals with excess weight.
When the posterolateral corner is injured, the outer side of the knee may gap open, leading to increased external rotation of the lower leg. In severe cases, the nearby common peroneal nerve may be affected, resulting in debilitating symptoms like foot drop (inability to lift the foot upward). Immediate assessment by an experienced surgeon is crucial in such cases to prevent long-term nerve damage.
LCL injuries typically present with the following symptoms:
- Pain and swelling on the outside of the knee.
- Instability: Difficulty stopping or cutting during sports, especially when shifting side-to-side.
- Knee buckling: A feeling that the knee is giving out, particularly when moving laterally.
- Difficulty performing specific movements: Athletes often notice they can’t stop or change direction towards the affected side due to the instability caused by the LCL tear.
Unfortunately, most injuries to the posterolateral corner do not heal without medical intervention. The lateral side of the knee is naturally unstable because both the lateral femoral condyle of the femur and the lateral tibial plateau are convex (rounded). When the ligaments and tendons in this area are damaged, the knee becomes even more unstable.
Moreover, posterolateral corner injuries are often accompanied by damage to other knee ligaments. For instance, complete LCL tears frequently occur in combination with other ligament injuries, necessitating surgical reconstruction to restore knee function. Timely treatment is crucial. If treatment is delayed for more than six weeks, and the patient is bowlegged (a common condition in many men), an osteotomy (surgical correction of the bowleggedness) may be required before ligament reconstruction to ensure the best long-term outcome.
Accurate diagnosis of a posterolateral corner injury requires a combination of a detailed physical examination, specialized X-rays, and magnetic resonance imaging (MRI). One key diagnostic tool is the varus stress X-ray, which can help quantify the severity of the injury with millimeter precision. This stress test allows orthopedic surgeons to objectively assess the extent of the damage and confirm the diagnosis of a posterolateral corner injury.
A global consensus has been reached regarding the optimal timing for treating posterolateral corner injuries. According to this consensus, Grade 1 and 2 tears (partial injuries) can often be treated non-surgically with physical therapy. In contrast, Grade 3 tears (complete ligament ruptures) almost always require surgery.
The best time to surgically treat a complete LCL tear or other posterolateral corner structures is within the first two weeks after the injury. By addressing the injury promptly, surgeons can prevent scar tissue formation and weakened tissue, ensuring the knee can be restored to its normal anatomical position. Delaying surgery increases the risk of long-term instability and poor outcomes.
At a Glance
Mark Cinque, MD
- Board-certified, fellowship-trained orthopedic surgeon
- Orthopedic Residency: Stanford University, Fellowship: The Steadman Clinic
- Authored over 100 peer-reviewed publications
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