Posterior Cruciate Ligament (PCL): Tests, Injury Grades, and Diagnosis

What is the test for PCL stress?

Assessing stress on the Posterior Cruciate Ligament (PCL) primarily involves a series of specific clinical examination maneuvers designed to evaluate the ligament's integrity and the degree of posterior tibial translation, with the Posterior Drawer Test being the most definitive and widely utilized.

Understanding the Posterior Cruciate Ligament (PCL)

The Posterior Cruciate Ligament (PCL) is one of the four major ligaments of the knee, located deep within the joint. Its primary function is to prevent the tibia (shin bone) from moving too far backward (posteriorly) relative to the femur (thigh bone). Unlike the Anterior Cruciate Ligament (ACL), PCL injuries are less common but often result from direct trauma to the front of the shin, such as a dashboard injury in a car accident, or a fall onto a flexed knee. Understanding its role is crucial for appreciating the diagnostic tests.

Clinical Assessment of PCL Integrity

When a PCL injury is suspected, a thorough clinical examination is paramount. This involves a series of provocative tests performed by a trained healthcare professional, such as a physician, physical therapist, or athletic trainer. These tests aim to identify abnormal posterior translation of the tibia, which indicates PCL laxity or rupture.

Key Diagnostic Tests for PCL Stress

Several clinical tests are employed to assess PCL integrity, often used in combination to confirm findings.

• Posterior Drawer Test

  • Purpose: This is considered the gold standard for assessing PCL integrity. It directly evaluates the amount of posterior translation of the tibia on the femur.
  • Procedure: The patient lies supine (on their back) with the hip flexed to 45 degrees and the knee flexed to 90 degrees. The examiner sits on the patient's foot to stabilize it and grasps the tibia just below the joint line, placing their thumbs on the tibial tuberosity. The examiner then applies a firm, consistent posterior force to the tibia.
  • Positive Sign: A positive test is indicated by excessive posterior translation of the tibia relative to the femur, often with a soft or absent end-feel. The degree of posterior sag or translation is noted.
  • Interpretation: Significant posterior translation (greater than 6-8mm compared to the uninjured side) suggests a PCL tear.

• Posterior Sag Sign (Godfrey's Test)

  • Purpose: This test identifies gross posterior displacement of the tibia due to gravity when the PCL is compromised.
  • Procedure: The patient lies supine with both hips and knees flexed to 90 degrees. The examiner supports the patient's heels, allowing the lower legs to relax.
  • Positive Sign: A positive sign is observed when the tibia on the injured side appears to "sag" posteriorly compared to the uninjured side, creating a visible step-off or depression just below the patella.
  • Interpretation: A visible posterior sag indicates a significant PCL injury, often a complete tear. This is a good initial screening test before the Posterior Drawer.

• Quadriceps Active Test (Active Drawer Test)

  • Purpose: This test differentiates between a PCL tear and a posterior subluxation that might be masked by other injuries. It utilizes the quadriceps muscle to pull the tibia anteriorly.
  • Procedure: The patient lies supine with the hip flexed to 45 degrees and the knee flexed to 90 degrees, similar to the Posterior Drawer position. The examiner stabilizes the foot and observes for a posterior sag. The patient is then asked to actively contract their quadriceps muscles (as if trying to slide their foot forward on the table).
  • Positive Sign: A positive test occurs if the tibia, which was posteriorly subluxed (sagging), translates anteriorly with quadriceps contraction, indicating that the PCL was indeed torn and allowing the initial posterior sag.
  • Interpretation: Anterior translation of the tibia upon quadriceps contraction confirms PCL insufficiency, as the quadriceps is effectively pulling the tibia forward from its abnormally posterior position.

• Reverse Lachman Test

  • Purpose: This test is a variation of the Lachman test for ACL, adapted for the PCL, particularly useful for detecting PCL laxity in less-flexed positions.
  • Procedure: The patient lies supine with the knee flexed to 30 degrees. The examiner stabilizes the femur with one hand and grasps the tibia with the other, applying a posterior force to the tibia.
  • Positive Sign: Excessive posterior translation of the tibia relative to the femur at 30 degrees of flexion.
  • Interpretation: Indicates PCL laxity, especially in cases where the Posterior Drawer might be less clear.

• Dial Test

  • Purpose: While not solely for PCL, the Dial Test helps identify associated posterolateral corner (PLC) injuries, which often accompany PCL tears, by assessing external tibial rotation.
  • Procedure: The patient lies supine with knees flexed to 30 degrees, then to 90 degrees. The examiner externally rotates both feet and lower legs simultaneously.
  • Positive Sign: Increased external rotation (greater than 10-15 degrees compared to the uninjured side) at 30 degrees of flexion suggests an isolated PLC injury. Increased external rotation at both 30 and 90 degrees suggests combined PCL and PLC injury.
  • Interpretation: Helps determine the extent of the injury and if other structures besides the PCL are involved, which significantly impacts treatment planning.

Grades of PCL Injury

The findings from these clinical tests help classify the severity of a PCL injury:

• Grade I: Mild sprain, with a firm end-point on the posterior drawer test, but slight increased posterior translation (1-5 mm).
• Grade II: Moderate injury, with increased posterior translation (6-10 mm) and a soft end-point, but still some integrity.
• Grade III: Complete tear, significant posterior translation (over 10 mm), often with an absent end-point and a positive posterior sag sign. This grade may also involve other structures like the posterolateral corner.

Beyond Clinical Tests: Imaging and Diagnostics

While clinical tests are crucial for initial assessment, they are often complemented by imaging studies to confirm the diagnosis, assess the extent of the injury, and rule out other pathologies:

• X-rays: Primarily used to rule out fractures or avulsion injuries (where the ligament pulls a piece of bone away). Stress X-rays can quantify the amount of posterior translation.
• Magnetic Resonance Imaging (MRI): The gold standard for visualizing soft tissue structures like ligaments. An MRI can directly show the integrity of the PCL, the presence of edema, and any associated injuries to cartilage, menisci, or other ligaments.

Importance of Professional Diagnosis

It is critical to emphasize that these tests are performed by skilled healthcare professionals. Self-diagnosis based solely on symptoms or self-performance of these tests is unreliable and not recommended. An accurate diagnosis by an expert is essential for developing an appropriate and effective treatment plan, whether it involves conservative management (rehabilitation) or surgical intervention.

Conclusion

Assessing PCL stress involves a systematic clinical examination utilizing specific provocative tests like the Posterior Drawer, Posterior Sag Sign, and Quadriceps Active Test. These tests, combined with a thorough patient history and often supplemented by imaging, allow healthcare professionals to accurately diagnose PCL injuries and grade their severity. A precise diagnosis is the foundation for effective management, guiding patients through appropriate rehabilitation or surgical pathways to restore knee stability and function.