Posterolateral Corner (PLC) Injury: Symptoms, Causes, and Complications

What are the Symptoms of a PLC Injury?

A Posterolateral Corner (PLC) injury of the knee is a complex and often debilitating condition affecting the stability of the knee joint, typically presenting with pain, swelling, and a distinct feeling of instability or "giving way," particularly during activities that involve pivoting or cutting.

Understanding the Posterolateral Corner (PLC)

The Posterolateral Corner (PLC) is a critical anatomical region of the knee that provides a significant portion of its stability, particularly against varus (bow-legged) forces, external rotation, and posterior translation of the tibia relative to the femur. It is not a single structure but a complex functional unit comprising several key ligaments, tendons, and capsular structures.

Key structures of the PLC include:

• Lateral Collateral Ligament (LCL): A cord-like structure that resists varus stress.
• Popliteus Tendon: A muscle-tendon unit that acts as a dynamic stabilizer and an internal rotator of the tibia.
• Popliteofibular Ligament: A strong ligament connecting the popliteus tendon to the fibular head, providing crucial stability.
• Fibular Collateral Ligament (FCL): Another term for the LCL, emphasizing its connection to the fibula.
• Posterolateral Capsule: The thickened portion of the joint capsule on the posterior-lateral aspect.
• Biceps Femoris Tendon: While primarily a hamstring muscle, its attachment to the fibular head contributes to posterolateral stability.

These structures work synergistically to prevent excessive external rotation of the tibia, limit varus angulation, and resist posterior displacement of the lateral tibial plateau, especially when the knee is in extension or slight flexion.

Common Mechanisms of PLC Injury

PLC injuries typically result from high-energy trauma, often involving a combination of forces. Understanding the mechanism can help in recognizing the potential for this injury. Common scenarios include:

• Direct Blow to the Anteromedial Knee: This can drive the tibia posteriorly and create a varus (bowing out) force, stressing the PLC structures.
• Hyperextension with External Rotation: A common mechanism in sports, where the knee is forced into hyperextension while the foot is planted and externally rotated.
• Varus Stress: A force applied to the medial side of the knee, pushing the knee outward and stretching the lateral structures.
• Dashboard Injury: In motor vehicle accidents, the tibia can be driven posteriorly and externally rotated, often leading to combined PCL and PLC injuries.

Acute Symptoms of a PLC Injury

When a PLC injury occurs, the symptoms can range from subtle to severe, depending on the grade of the tear (Grade I: mild, Grade II: moderate, Grade III: severe/complete rupture).

Typical acute symptoms include:

• Immediate Pain: Sharp, localized pain on the outside (lateral aspect) and back of the knee. The pain may worsen with attempts to straighten the leg or bear weight.
• Swelling (Effusion): Rapid onset of swelling around the knee joint, indicating internal bleeding and fluid accumulation. This may be more noticeable on the lateral side.
• Instability or "Giving Way": A profound feeling that the knee is unstable, loose, or wants to buckle, particularly when trying to pivot, turn, or bear weight on the affected leg. This sensation is often more pronounced when walking downhill or descending stairs.
• Difficulty with Weight-Bearing: Due to pain and instability, putting full weight on the injured leg can be challenging or impossible.
• Limited Range of Motion (ROM): Pain and swelling can restrict the ability to fully extend or flex the knee.
• Bruising (Ecchymosis): Discoloration may appear around the lateral knee, indicating bleeding into the soft tissues. This may develop hours to days after the injury.
• Audible Pop or Tear: Some individuals may report hearing or feeling a distinct "pop" at the time of injury.
• Foot Drop/Numbness (Peroneal Nerve Involvement): In severe injuries, the common peroneal nerve, which runs close to the fibular head, can be stretched or damaged. This can result in weakness in lifting the foot (foot drop), numbness, or tingling along the top of the foot and outer calf. This is a critical symptom requiring immediate medical attention.

Chronic Symptoms and Long-Term Implications

If a PLC injury is not diagnosed and treated appropriately, chronic symptoms and long-term complications can develop, leading to persistent functional limitations:

• Persistent Instability: The most common chronic complaint. The knee continues to feel loose or "give way" during activities, especially those involving pivoting, cutting, or rapid changes in direction. This can significantly impact participation in sports and daily activities.
• Recurrent Effusions: Episodes of swelling may recur, particularly after activity, due to ongoing instability and irritation within the joint.
• Feeling of "Looseness": A subjective sensation that the knee is not securely held together.
• Difficulty with Activities of Daily Living: Challenges with walking on uneven ground, going up or down stairs, or performing tasks that require knee stability.
• Gait Abnormalities: A characteristic "varus thrust" or "lateral thrust" may be observed during walking, where the knee bows outward excessively during the stance phase, indicating instability.
• Progressive Degeneration and Osteoarthritis: Chronic instability places abnormal stresses on the articular cartilage of the knee, significantly increasing the risk of early-onset osteoarthritis and meniscal tears.

Associated Injuries

It is crucial to recognize that PLC injuries rarely occur in isolation. Due to the high-energy mechanisms typically involved, they are frequently accompanied by other significant ligamentous injuries, making diagnosis and treatment more complex.

Common associated injuries include:

• Posterior Cruciate Ligament (PCL) Injury: This is the most common associated injury, with a high percentage of PLC injuries occurring alongside a PCL tear. This combination leads to profound posterior and rotational instability.
• Anterior Cruciate Ligament (ACL) Injury: While less common than PCL co-injury, ACL tears can also occur with PLC injuries, leading to multi-ligamentous instability.
• Meniscus Tears: Especially lateral meniscus tears, can occur due to the forces involved.
• Peroneal Nerve Palsy: As mentioned, damage to the common peroneal nerve can lead to motor and sensory deficits in the lower leg and foot.

When to Seek Medical Attention

Due to the complexity of the PLC and the high likelihood of associated injuries, it is imperative to seek prompt medical attention if you suspect a PLC injury. Early and accurate diagnosis by an orthopedic surgeon or sports medicine physician is critical for optimal outcomes. A thorough physical examination, specialized stress tests, and imaging studies (such as MRI) are typically required to confirm the diagnosis and assess the extent of the damage. Ignoring these symptoms can lead to chronic instability, further knee damage, and long-term functional impairment.

Conclusion

A Posterolateral Corner injury is a significant orthopedic condition characterized by pain, swelling, and a profound sensation of knee instability. Recognizing the acute symptoms and understanding the potential for chronic complications and associated injuries is vital for anyone experiencing a knee injury, especially following high-impact trauma. Prompt medical evaluation and appropriate management are essential to restore knee stability, prevent further damage, and ensure a return to function.