The posterior drawer test is the most accurate test for a posterior cruciate ligament (PCL) injury. The PCL is located in the back of the knee and is the primary restraint in posterior tibial translation. Injuries to the posterior cruciate ligament are not as common as ACL injuries.
A physician will want to perform the Posterior Drawer Test during a routine exam for a knee injury or if they suspect a tear of the PCL. If the physician finds laxity anteriorly and posteriorly while evaluating for an ACL tear with the Lachman’s test, they will want to perform a Posterior Drawer Test as well. It is important to test for PCL tears because a PCL tear may give a false positive Lachman’s test due to posterior subluxation.
The test is performed with the patient lying supine and the knee flexed to 90°. The examiner will stabilize the foot. Next, the examiner will push backwards on the tibia, looking for the tibia to sag posteriorly. The examiner will want to observe the amount of translation in relationship to the femur. The test is considered positive if excessive posterior translation of the tibia is demonstrated. The physician will move the thumb from the femoral condyle to the tibial plateau. The medial tibial plateau is normally 10mm anterior to the medial femoral condyle. If the PCL is intact, a step-off between the medial femoral condyle and medial tibial plateau is maintained when posterior force is applied to the proximal tibia.
Other PCL tests include the Posterior Sag Test, Quadriceps Active Test, and Dial Test. When performing the Posterior Sag Test, both knees are flexed to 90° and the knee is viewed from the side to compare the positions of the anterior tibia. To perform the Quadriceps Active Test, the patient’s knee is flexed to 90° and the patient is then asked to actively contract the quadriceps muscle with the leg stabilized. The tibia should be actively reduced from the posterior subluxed position.
The Dial Test is performed with the patient in the supine or prone position with both knees in 90° and 30° of flexion. An external rotational force is then applied to both feet. The amount of external rotation to both lower extremities is measured at each ankle. Flexion at the 90° angle will test the posterior cruciate ligament. More than 10° of external rotation indicates a significant injury. Testing the injured extremity in 30° of flexion is done to determine an injury to the posterolateral corner. More than 10° of external rotation indicates a significant injury.
A common cause of injury to the PCL is due to a bent knee hitting a dashboard during a car accident. The injury is caused by a direct blow to the proximal tibia with the knee flexed. A PCL injury may also occur due to non-contact hyperflexion of the knee with the foot in plantar flexion.
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