Pivot Shift Test


 

The anterior cruciate ligament is located in the front of the knee. Rupture of the anterior cruciate ligament (ACL) is a condition commonly seen in sports usually due to a non-contact pivoting injury. 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 a chronic setting. Lachman’s test is the most sensitive examination test for ACL injury. 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 tibia moves anterolaterally in extension; however, when you flex the knee, the IT band becomes a flexor of the knee. The IT band pulls back and reduces the tibia. The pivot shift test goes from extension (tibia subluxed) to flexion, with the tibia reduced by the iliotibial band. Both the Lachman’s tests 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. For the Lachman’s test, the femur is stabilized with one hand and the other hand pulls the tibia anteriorly and posteriorly against the femur. The tibia can be pulled forward more than normal (anterior translation). The examiner will have a sense of increased movement and lack of a solid end point. For the pivot shift test, the patient should be lying supine and 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. To perform, 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 ACL prevents anterior translation of the tibia. It is a secondary restraint to tibial rotation and varus and valgus stress. The ACL consists of two bundles: the posterolateral bundle and the anteromedial bundle. The posterolateral bundle prevents pivot shift, contributes to rotational stability, prevents internal rotation of the tibia with the knee in near extension, and increases the anterior translation and tibial rotation at 30o of flexion. The anteromedial bundle is tight in flexion, and it increases anterior translation at 90o of flexion. The Lachman’s test is the most sensitive test especially in acute settings, and the examiner will find no end point with anterior translation of the tibia. In an acute setting, physical examination can be difficult or limited due to pain. With the Pivot shift test, the patient must be completely relaxed, and the test is helpful in chronic situations especially if the patient complains of the knee giving way. In the Pivot shift, the knee subluxes in extension and reduces at 20-30 degrees of flexion. The Pivot shift correlates closely with patient satisfaction of their reconstructed knee. It is a measure of functional instability following ACL reconstruction. Vertical femoral tunnel placement will cause rotational instability seen as a positive pivot shift, and the malposition of the bone tunnel will be seen in an AP view x-ray of the knee. The 9 or 10 o’clock position is better than the 12 o’clock position; the vertical position is bad. The patient with an ACL injury usually has a non-contact pivoting injury event with an awkward landing, feeling a “pop” sensation, or immediate swelling. Aspiration usually shows blood in the knee which proves a 75% chance of ACL tear when you aspirate blood from the knee. Patients will also exhibit a positive Lachman’s test which may be hard to examine because of the pain. Aspiration of the knee may make the examination easier. MRI of the knee joint will show the hematoma, and it may show bone lesions or bruising in the typical location which is characteristic with tears of the ACL. These injuries are typically located at the middle of the femoral condyle and posterior part of the tibia laterally. You may find a triple injury within the MRI (O’Donoghue’s Unhappy Triad). The O’Donoghue’s Unhappy Triad include an anterior cruciate ligament (ACL) injury, a medial cruciate ligament (MCL) injury, and a lateral meniscus injury. In chronic ACL tears, the posterior horn of the medial meniscus is the most commonly injured structure. In acute ACL tear, send the patient for therapy for range of motion, brace the patient and allow the MCL to heal and reconstruct the ACL later if needed. Patients should do stress hamstring therapy in ACL tears. The patient will probably complain of instability immediately or later on.
 
 
 

Author
Nabil Ebraheim, MD

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