Which special test is most appropriate to assess anterolateral knee instability in a suspected ACL injury?

• A. Lateral pivot shift test
• B. Bounce home test
• C. Varus stress test
• D. Lachman test

Answer: (A)

The key idea is detecting anterolateral rotatory instability, a pattern you see when the ACL is injured and the anterolateral structures (like the IT band complex) fail to control tibial rotation. The lateral pivot shift test reproduces this instability most directly. With the knee starting near extension, you apply a valgus stress and internally rotate the tibia while guiding the knee into flexion. In an ACL-deficient knee, the lateral tibial plateau subluxates anteriorly and TIM, and as the knee flexes to about 20–30 degrees the tibia suddenly reduces back under the femur, producing a palpable clunk or shift. That clunk is the hallmark of anterolateral rotatory instability and confirms ACL deficiency with involvement of the anterolateral structures.

Other tests target different issues. The bounce home test is more indicative of a meniscal tear, not rotary instability. The varus stress test assesses the lateral collateral ligament and posterolateral corner structures, not the ACL-related anterolateral instability. The Lachman test focuses on pure anterior translation of the tibia to evaluate ACL laxity, but it does not reproduce the rotary component seen with anterolateral instability.