The posterior drawer test is a physical examination technique used to assess knee stability. It evaluates a specific knee ligament to identify potential injuries and is one of several methods used to determine the integrity of knee structures.
The Knee’s Components
The knee joint is a complex structure supported by ligaments, which connect bones and provide stability and movement. The posterior cruciate ligament (PCL) is located at the back of the knee, connecting the shin bone (tibia) to the thigh bone (femur).
The PCL’s role is to prevent the tibia from sliding too far backward relative to the femur. It also helps control excessive knee rotation, especially when the knee is bent. The PCL is comprised of two functional bundles, the anterolateral and posteromedial bundles, which work together to maintain knee stability.
What a Positive Result Signifies
A positive posterior drawer test indicates an injury or tear to the posterior cruciate ligament (PCL). During this test, an examiner applies a backward force to the shin bone while the knee is bent. Excessive backward movement of the tibia or a “soft” or “mushy” feeling at the end of this movement suggests damage to the PCL.
PCL injuries are graded based on the degree of instability observed. A Grade I injury involves microscopic tears or an overstretch, resulting in minimal posterior translation of the tibia, 1-5 millimeters. A Grade II injury signifies a partial tear where the tibia moves further back, sometimes becoming flush with the femoral condyles, showing 6-10 millimeters of posterior translation. A Grade III injury indicates a complete tear or rupture of the PCL, where the tibia falls significantly posterior to the femoral condyles, often exceeding 10 millimeters of translation, and frequently involves other damaged ligaments.
Common Causes and Symptoms
PCL tears result from significant force applied to the knee. A common mechanism is a direct blow to the front of the bent shin, such as hitting the dashboard in a car accident, often referred to as a “dashboard injury.” Falling hard onto a bent knee with the foot pointed downward can also cause this injury. Hyperextension of the knee, where the joint is forced beyond its normal range of motion, can also lead to a PCL tear.
Individuals with a PCL injury experience symptoms. Pain, which can be sharp or dull, may develop immediately or within hours to days, often localized around the back of the knee. Swelling and inflammation occur quickly after the injury, sometimes leading to stiffness and difficulty bending the knee. A feeling of instability or the knee “giving out” is common, and people may find it difficult to bear weight, walk, or go down stairs.
Confirming the Injury and Treatment Options
While a positive posterior drawer test suggests a PCL injury, further diagnostic steps are necessary for confirmation and to assess the full extent of the damage. Magnetic Resonance Imaging (MRI) is the preferred imaging method to confirm a PCL tear and identify any associated injuries to other ligaments, cartilage, or bone. X-rays may also be used to rule out fractures or avulsion injuries, though they cannot directly visualize a PCL tear.
Treatment approaches for PCL injuries vary depending on the tear’s severity and the patient’s activity level. Conservative management, often recommended for Grade I and II tears or isolated injuries, involves rest, applying ice, compression, and elevation (RICE) to reduce swelling and pain. Physical therapy is an important part of conservative care, focusing on quadriceps strengthening and proprioceptive training to improve knee stability and function. Bracing, particularly dynamic PCL braces that apply an anterior force to the tibia, can also be used to reduce posterior translation and support healing, often worn for several months.
Surgical intervention, primarily PCL reconstruction, is generally reserved for higher-grade tears, particularly Grade III injuries with significant instability, or when conservative treatments fail to alleviate symptoms. Surgery is also frequently recommended for PCL tears that occur in combination with other knee ligament injuries, due to the increased instability. Reconstruction often involves using grafts, such as Achilles tendon or hamstring tendon allografts, to replace the torn ligament. The double-bundle technique, which reconstructs both parts of the PCL, is often preferred for its ability to replicate the knee’s natural biomechanics and improve stability.
Following surgery, a structured rehabilitation program is initiated to restore range of motion, strengthen surrounding muscles, and gradually return to activities. Full recovery can take 6 to 18 months, depending on the injury’s severity and if surgery was performed.