During examination of an athlete with an ACL-deficient knee, the examiner applies a valgus force with the tibia internally rotated and moves the knee slowly from full extension into flexion. At about 25 degrees of flexion a visible clunk occurs as the lateral tibial plateau relocates. The structure responsible for reducing the subluxed plateau at this point is:

• A Popliteus tendon, which actively externally rotates the femur
• B Iliotibial band, which shifts posterior to the axis of the lateral femoral condyle ✓
• C Lateral collateral ligament, which tightens progressively in flexion
• D Posteromedial capsule, which buckles and pushes the plateau forward

Explanation

In the pivot shift test, the ACL-deficient lateral tibial plateau is held subluxed anteriorly in full extension. As flexion approaches 20 to 30 degrees, the iliotibial band passes behind the axis of the lateral femoral condyle and becomes an extensor of the knee, pulling the plateau back into place and producing the characteristic clunk. The test demonstrates anterolateral rotatory instability and is considered pathognomonic of ACL deficiency, whereas the anterior drawer test measures only straight anteroposterior translation.

Reference: Campbell's Operative Orthopaedics, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.