Tests for Examination of the Knee

There are multiple tests for examination of the knee. Tests include the McMurray’s test, the Lachman’s test, the pivot shift test, the reverse pivot shift test, the posterior drawer test, the dial test, the valgus stress test, and the Varus stress test. The McMurray’s test is a knee examination test that elicits pain or a painful click as the knee is brought from flexion to extension with either internal or external rotation. The McMurray’s test uses the tibia to trap the meniscus between the femoral condyle and the tibia.


 When performing the McMurray’s test, the patient should be lying supine with the knee flexed. The examiner then grasps the patient’s heel with one hand and places the other hand over the knee joint. To test the medial meniscus, the knee is fully flexed, and the examiner then passively externally rotate the tibia and places a valgus force. The knee is then extended in order to test the medial meniscus. To test the lateral meniscus, the examiner passively internally rotates the tibia and places a Varus force. The knee is then extended in order to test the lateral meniscus. A positive test is indicated by pain, clicking, or popping within the joint and may signal a tear of either the medial or lateral meniscus when the knee is brought from flexion to extension. The Lachman’s test is the most sensitive examination test for ACL injury. The anterior cruciate ligament is located in the front of the knee.


 The ACL keeps the tibia from sliding out in front of the femur and provides rotational stability to the knee. To perform the Lachman’s test, the patient should be lying supine and completely relaxed. Make sure that the patient’s hip muscles, quadriceps, and hamstring muscles are all relaxed. Bend the knee to about 20-30 degrees. Stabilize the femur with one hand and with the other hand, pull the tibia anteriorly and posteriorly against the femur. With an intact ACL, as the tibia is pulled forward, the examiner should feel an endpoint. If the ACL is ruptured, the ACL will be lax and the examination will feel softer with no endpoint. The tibia can be pulled forward more than normal (anterior translation). Lachman’s test is the best examination test to diagnose a tear of the ACL.


 The Pivot shift test is a specific test for ACL deficient knee (ACL injury). Pivot shift is pathognomonic for an ACL tear and is best demonstrated in the chronic setting when there is a chronic ACL tear. On the other hand, the Lachman’s test is the most sensitive examination test for ACL injury, acute and chronic. The ACL keeps the tibia from sliding out in front of the femur and provides rotational stability to the knee. Rupture of the ACL causes anterolateral rotatory instability. The pivot shift test goes from extension (tibia subluxed) to flexion, with the tibia reduced by the iliotibial band. Both the Lachman’s test and the pivot shift test are associated with 20-30 degrees of knee flexion. The Lachman’s test starts at 20-30 degrees of flexion. With the pivot shift test, you feel the clunk at 20-30 degrees of flexion. 20-30 degrees of flexion is important for examination of the ACL. The patient should be lying supine. Make sure the patient is totally relaxed. With pivot shift, the knee is in the subluxed position when the knee is in full extension. The pivot shift starts with extension of the knee and you can feel a “clunk” at 20-30 degrees of flexion. Hold the knee in full extension then add valgus force plus internal rotation of the tibia to increase the rotational instability of the knee. Then take the knee into flexion. A palpable clunk is very specific of an ACL tear. The iliotibial band will reduce the tibia and create the clunk on the outside of the knee. Always compare with the other side.


 The reverse pivot shift test helps to diagnose acute or chronic posterolateral instability of the knee. A significantly positive reverse pivot shift test suggests that the PCL, the LCL, the arcuate complex, and the popliteofibular ligament are all torn. The reverse pivot shift test begins with the patient supine with the knee in 90o of flexion. Valgus stress is then applied to the knee with an external rotation force. Bring the knee from 90o of flexion to full extension. The tibia reduces from a posterior subluxed position at about 20o of flexion. A shift and reduction of the lateral tibial plateau can be felt as it moves anteriorly from a posteriorly subluxed position. A “clunk” occurs as the knee is extended. This is called reverse pivot shift because shift of the lateral tibial plateau occurs in the opposite direction of the true pivot shift (seen in ACL tears). If the tibia is posterolaterally subluxed, the iliotibial band will reduce the knee as the IT band transitions from a flexor to extensor of the knee. It is very important to compare this test to the contralateral knee. Posterolateral corner injury includes the LCL, popliteofibular ligament, arcuate complex, and the lateral capsule.


 The posterior drawer test is the most accurate test for PCL injury. The posterior cruciate ligament is located in the back of the knee. The PCL is the primary restraint to posterior tibial translation. The PCL is larger than the ACL. Injuries to the posterior cruciate ligament (PCL) are not as common as other ACL injuries. This should be performed as part of the routine exam of the injured knee, if you suspect a tear of the PCL, or if you find laxity anteriorly and posteriorly while evaluating for ACL tear with the Lachman’s test. The PCL tear may give a false Lachman’s test due to posterior subluxation. Test is done with the patient in supine position and the knee is flexed to 90o. The examiner stabilizes the foot. Next, the examiner pushes backwards on the tibia, looking for the tibia to sag posteriorly. Observe the sag that develops due to tear of the posterior cruciate ligament (PCL). The amount of translation in relationship to the femur is observed. The test is considered positive if excessive posterior translation of the tibia is demonstrated.


 The dial test is performed to diagnose posterolateral instability due to posterolateral corner injury with or without PCL injury. Isolated injuries of the posterolateral corner are rare and often cause instability and Varus thrust. By performing the dial test, you can detect if there is an isolated or combined injury of the posterolateral corner of the knee. Dial test is performed with the patient in the supine or prone position with both knees in 30o and 90o of flexion. It is preferable to perform the test in the prone position. Support the thigh in position if you are going to perform the test in the supine position. An external rotational force is then applied to both feet. The amount of external rotation to both lower extremity is measured at both ankles. Testing the injured extremity in 30o of flexion is done to determine injury to the posterolateral corner. Flexion at the 90o angle will test the posterior cruciate ligament (PCL) for injury. More than 10o of external rotation compared to the other side indicates a significant injury. More than 10o of external rotation asymmetry at 30o and 90o is consistent with PLC and PCL injury (combined injury). To perform the valgus stress test, palpate around the knee in order to check for injury to the MCL. Usually the site of tenderness and pain is above the level of the knee joint and rarely below the knee joint. Place valgus force on the nee (force from the outside). The best way to test the superficial part of the MCL is to place the knee in about 30o of flexion.


 With the MCL isolated and the knee flexed to 30o, move the knee from side to side to assess for stability of the knee. Check for opening on the medial side when valgus force is applied. Next place the knee back into 0o of full extension and test the stability of the MCL in the same way. If the MCL appears to be loose in full extension, this will signal a complete injury to the posterior capsule or cruciate ligaments in addition to injury of the MCL (it is a combined injury). Valgus force at 30o of knee flexion will test the superficial part of the MCL, which is the strongest part of the MCL. The Varus stress test checks for joint laxity on the outside of the knee, which usually represents an injury to the lateral collateral ligament (LCL). Palpate around the knee in order to check for injury to the LCL. Apply a Varus force to the knee. The LCL needs to be checked for an endpoint. Isolated tear of the LCL is tested at 30 degrees of flexion.


 With the LCL isolated and the knee flexed to 30o, move the knee from side to side to assess for stability of the knee. Next place the knee back into 0o of full extension and test the stability of the LCL in the same way. A positive test demonstrates lateral joint laxity compared to the unaffected side when a Varus force is applied to the knee. Varus instability at 0 degrees and 30 degrees of flexion indicates a combined injury of the LCL and the cruciate ligaments. An isolated injury to the LCL will give you Varus instability at 30 degrees of flexion.

Author
Nabil Ebraheim, MD

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