PCL Injury: Clinical Presentation, Symptoms, Diagnosis, and Grading

What is the clinical presentation of PCL injury?

A Posterior Cruciate Ligament (PCL) injury typically presents with varying degrees of pain, swelling, and a sensation of instability in the knee, often characterized by a distinctive posterior sag of the tibia, particularly after a traumatic event involving a direct blow to the flexed knee or hyperextension.

Introduction to the PCL and its Injury

The Posterior Cruciate Ligament (PCL) is one of the four major ligaments of the knee, playing a crucial role in preventing posterior displacement of the tibia relative to the femur and contributing to rotational stability. It is the strongest ligament in the knee, making isolated PCL injuries less common than Anterior Cruciate Ligament (ACL) injuries. PCL injuries typically result from high-energy trauma, such as a direct blow to the anterior tibia with the knee flexed (e.g., dashboard injury in a car accident, falling onto a flexed knee), or a hyperextension injury.

Immediate Signs and Symptoms (Acute Presentation)

The acute clinical presentation of a PCL injury can vary in severity depending on the grade of the tear (partial vs. complete) and whether other knee structures are also injured.

• Pain: Patients often report immediate or rapidly developing pain in the posterior aspect of the knee. The intensity can range from mild discomfort to severe, debilitating pain.
• Swelling (Effusion): Swelling inside the knee joint (effusion) typically develops within hours of the injury. This is due to bleeding within the joint (hemarthrosis), indicating a significant intra-articular injury.
• Instability or "Giving Way": While less dramatic than with an ACL injury, some patients may report a feeling of the knee "giving way," particularly when attempting to bear weight or with certain movements. This instability is often described as a feeling of the tibia shifting backward.
• Difficulty with Weight-Bearing and Ambulation: The pain and swelling can make it difficult and painful to put weight on the injured leg, leading to a limping gait.
• Limited Range of Motion: Swelling and pain can restrict the knee's ability to fully flex or extend.
• Feeling of a "Pop" or "Tear": While more characteristic of an ACL injury, some individuals may recall hearing or feeling a "pop" or "tear" at the time of injury, indicating a sudden and forceful ligamentous disruption.

Delayed or Chronic Presentation

In some cases, especially with lower-grade PCL injuries, the acute symptoms may be subtle or resolve quickly, leading to a delayed diagnosis. The chronic presentation often involves:

• Persistent Posterior Sag: This is a hallmark sign. Over time, the PCL-deficient knee may demonstrate a visible posterior sag of the tibia when the leg is relaxed and flexed to 90 degrees.
• Ambiguity of Symptoms: Chronic PCL insufficiency can present with vague symptoms. Patients might complain of generalized knee pain, particularly with activities that load the posterior aspect of the joint.
• Functional Limitations:
  • Difficulty or pain when descending stairs or inclines.
  • Pain with kneeling or squatting.
  • A feeling of weakness or instability during activities requiring sudden changes in direction or pushing off.
• Patellofemoral Pain: Chronic posterior laxity can lead to increased stress on the patellofemoral joint, resulting in anterior knee pain, especially with prolonged sitting, climbing stairs, or squatting.
• Early Onset Osteoarthritis: Long-term PCL insufficiency, particularly when combined with other ligamentous injuries, can alter knee kinematics, leading to accelerated degenerative changes and early onset osteoarthritis, especially in the patellofemoral and medial tibiofemoral compartments.

Physical Examination Findings

A thorough physical examination is crucial for diagnosing a PCL injury.

• Observation:
  • Effusion: Swelling around the knee joint.
  • Posterior Sag Sign (Godfrey's Test): With the patient supine and hips/knees flexed to 90 degrees, the affected tibia will sag posteriorly compared to the contralateral limb due to gravity pulling the tibia backward. This is a highly indicative sign.
• Palpation: Tenderness may be elicited over the posterior aspect of the knee joint.
• Range of Motion Assessment: Pain or mechanical block may limit flexion or extension.
• Special Tests:
  • Posterior Drawer Test: This is the primary diagnostic test. With the patient supine and the knee flexed to 90 degrees, the examiner applies a posterior force to the tibia. Excessive posterior translation of the tibia relative to the femur indicates a positive test. The amount of translation helps grade the injury.
  • Quadriceps Active Test: With the knee flexed to 90 degrees, the patient is asked to gently contract their quadriceps. In a PCL-deficient knee, the tibia will be seen to "jump" or reduce anteriorly from its posteriorly subluxed position, indicating PCL injury. This test helps differentiate PCL injury from other causes of posterior laxity.
  • Reverse Lachman Test: Performed with the knee in 30 degrees of flexion, the examiner stabilizes the femur and applies a posterior force to the tibia. Excessive posterior translation suggests PCL injury.

Diagnostic Imaging

Imaging studies help confirm the diagnosis, assess the grade of injury, and identify associated damage.

• X-rays: Primarily used to rule out associated fractures (e.g., avulsion fractures at the PCL insertion sites) and assess for signs of chronic osteoarthritis. Stress radiographs can quantify posterior laxity by measuring the amount of posterior tibial translation under stress.
• MRI (Magnetic Resonance Imaging): Considered the gold standard for evaluating soft tissue injuries of the knee. MRI provides detailed images of the PCL, allowing for assessment of the tear's location, extent, and grade, as well as identification of concomitant meniscal, collateral ligament, or articular cartilage injuries.

PCL Injury Grading

PCL injuries are graded based on the degree of posterior tibial translation relative to the femur.

• Grade I: Mild injury with minimal posterior translation (1-5 mm), where the PCL is stretched but intact.
• Grade II: Moderate injury with increased posterior translation (6-10 mm), indicating a partial or near-complete tear. The posterior drawer test shows the tibia translating to the level of the femoral condyles.
• Grade III: Severe injury with significant posterior translation (>10 mm), representing a complete PCL tear and often involving other ligamentous structures. The posterior drawer test shows the tibia translating posterior to the femoral condyles.

Conclusion and Next Steps

The clinical presentation of a PCL injury encompasses a spectrum of symptoms, from acute pain and swelling to chronic instability and functional limitations. A thorough understanding of these signs and symptoms, combined with a meticulous physical examination and appropriate diagnostic imaging, is essential for accurate diagnosis. Given the potential for long-term complications such as osteoarthritis, individuals experiencing symptoms suggestive of a PCL injury should seek prompt evaluation from a qualified healthcare professional, such as an orthopedic surgeon or sports medicine physician, to determine the appropriate management strategy.