Pivot Shift Test ACL Tear
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. o 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.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 30The 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.