Posterior Drawer Test: Purpose, Procedure, Interpretation, and Clinical Significance

What is the Posterior Drawer Test?

The Posterior Drawer Test is a common orthopedic assessment used to evaluate the integrity of the posterior cruciate ligament (PCL) in the knee. It assesses for excessive posterior translation of the tibia relative to the femur, which is indicative of PCL laxity or rupture.

Understanding Knee Anatomy and Stability

To appreciate the significance of the Posterior Drawer Test, a basic understanding of knee anatomy is essential. The knee is a complex hinge joint, stabilized by a network of ligaments. Among these, the cruciate ligaments – the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL) – are paramount. They cross each other within the joint, forming an "X" shape, and are crucial for preventing excessive front-to-back (anterior-posterior) movement of the tibia (shin bone) relative to the femur (thigh bone).

• Posterior Cruciate Ligament (PCL): The PCL is the stronger and wider of the two cruciate ligaments. Its primary role is to prevent the tibia from sliding too far backward (posteriorly) on the femur. It also provides rotational stability.

Purpose of the Posterior Drawer Test

The primary purpose of the Posterior Drawer Test is to assess the structural integrity of the posterior cruciate ligament (PCL). Injuries to the PCL are less common than ACL injuries but can result from direct trauma to the front of the shin, such as hitting the dashboard in a car accident (dashboard injury), or falling onto a flexed knee.

A positive test result suggests a potential sprain or tear of the PCL, which can lead to knee instability, pain, and functional limitations. Early and accurate diagnosis is critical for guiding appropriate treatment, whether it involves conservative management (rest, rehabilitation) or surgical intervention.

How to Perform the Posterior Drawer Test

The Posterior Drawer Test is typically performed with the patient lying supine (on their back). Accurate positioning and technique are crucial for reliable results.

1. Patient Positioning:

   • The patient lies comfortably on their back.
   • The hip of the affected leg is flexed to 45 degrees, and the knee is flexed to 90 degrees.
   • The foot should be flat on the examination table, with the heel resting comfortably.

2. Examiner Positioning and Hand Placement:

   • The examiner sits on the patient's foot to stabilize it and prevent it from lifting off the table during the test.
   • The examiner places both hands around the patient's upper tibia, just below the knee joint line.
   • The thumbs should be placed over the anterior aspect of the tibial plateau, with the fingers wrapped around the calf.

3. Execution of the Test:

   • Ensure the hamstring muscles are relaxed. Muscle guarding can mask true instability.
   • Apply a posteriorly directed force through the tibia. This means pushing the tibia straight backward towards the patient's hip.
   • Observe the amount of posterior translation (movement) of the tibia relative to the femur.
   • Compare the movement to the unaffected knee, if possible, to establish a baseline for normal laxity.

Interpreting the Results

The interpretation of the Posterior Drawer Test relies on the degree of posterior translation observed.

• Negative Test: Little to no posterior translation of the tibia relative to the femur. The tibial plateau should feel firm and not move significantly backward.
• Positive Test: Excessive posterior translation of the tibia. This indicates laxity or rupture of the PCL. The degree of translation can be graded:
  • Grade I: 1-5 mm of posterior translation. Suggests a mild PCL sprain.
  • Grade II: 6-10 mm of posterior translation. Indicates a moderate PCL tear, with the tibia often resting posteriorly at the neutral position.
  • Grade III: Greater than 10 mm of posterior translation. Represents a severe or complete PCL tear, where the tibia can be significantly displaced posteriorly.

It's important to note that a "sag sign" (where the tibia appears to sag posteriorly when the knee is flexed to 90 degrees and unsupported) might be evident before the test is even performed, which is a strong indicator of PCL deficiency.

Clinical Significance and Next Steps

A positive Posterior Drawer Test is a significant clinical finding that warrants further investigation.

• Diagnosis: While highly indicative of PCL injury, the Posterior Drawer Test is part of a comprehensive orthopedic examination. It is usually combined with other special tests (e.g., quadriceps active test, posterior sag sign) and a thorough patient history.
• Imaging: Confirmation of a PCL injury typically requires diagnostic imaging, most commonly a Magnetic Resonance Imaging (MRI) scan. MRI provides detailed images of soft tissues, allowing for precise assessment of the ligament's condition and identification of any associated injuries (e.g., meniscal tears, cartilage damage).
• Treatment: The course of treatment for a PCL injury depends on its severity, the patient's activity level, and the presence of other knee injuries.
  • Conservative Management: Mild to moderate PCL injuries (Grade I and II) are often managed non-surgically with rest, immobilization, physical therapy focusing on strengthening the quadriceps (which can compensate for PCL weakness), and activity modification.
  • Surgical Reconstruction: Severe PCL tears (Grade III), especially those causing significant instability or combined with other ligamentous injuries, may require surgical reconstruction using a graft.

Limitations and Considerations

While valuable, the Posterior Drawer Test has certain limitations:

• Muscle Guarding: If the patient's hamstring muscles are tense, they can resist posterior translation, leading to a false-negative result, even if the PCL is injured. Ensuring complete muscle relaxation is paramount.
• Acute vs. Chronic Injuries: In acute injuries with significant swelling and pain, it may be difficult to obtain an accurate assessment. Chronic PCL deficiencies might present with less pain but noticeable instability.
• Isolated vs. Combined Injuries: PCL injuries often occur in conjunction with other ligamentous (e.g., posterolateral corner) or meniscal injuries. The Posterior Drawer Test primarily assesses the PCL but should be interpreted within the context of the entire knee examination.
• Examiner Skill: The accuracy of the test relies on the examiner's experience and ability to apply the correct force and interpret the subtle movements.

Ultimately, the Posterior Drawer Test is a crucial clinical tool for screening and evaluating PCL integrity. However, it should always be performed by a qualified healthcare professional and its results interpreted in conjunction with a full clinical picture and, when indicated, advanced imaging.