Which ACL test is associated with a clunk as the tibia reduces during knee flexion?

Which ACL test is associated with a clunk as the tibia reduces during knee flexion?

• A. Lachman
• B. Anterior Drawer
• C. Pivot Shift
• D. Posterior Drawer

Answer: (C)

The key idea is a dynamic test that captures a tibial subluxation and then a sudden reduction (a clunk) as the knee moves into flexion, which is characteristic of ACL deficiency. In this maneuver, the knee is held to apply valgus stress with internal rotation while you begin with the leg extended and then flex it. In an ACL-injured knee, the tibia sits anteriorly and outward relative to the femur. As you push the knee into flexion, the iliotibial band and surrounding structures pull the tibia back into place, producing a palpable or audible clunk as it reduces. That clunk during reduction is the hallmark sign of this test. This test is different from the others because it combines a sense of instability with a clear reduction event during knee flexion, not just a static amount of anterior or posterior translation measured at a single angle. Lachman, Anterior Drawer, and Posterior Drawer all assess translation at particular knee positions without the dynamic reduction that creates the clunk. The presence of that clunk strongly suggests ACL incompetence and rotational instability, which the pivot shift maneuver is designed to reveal.

The key idea is a dynamic test that captures a tibial subluxation and then a sudden reduction (a clunk) as the knee moves into flexion, which is characteristic of ACL deficiency. In this maneuver, the knee is held to apply valgus stress with internal rotation while you begin with the leg extended and then flex it. In an ACL-injured knee, the tibia sits anteriorly and outward relative to the femur. As you push the knee into flexion, the iliotibial band and surrounding structures pull the tibia back into place, producing a palpable or audible clunk as it reduces. That clunk during reduction is the hallmark sign of this test.

This test is different from the others because it combines a sense of instability with a clear reduction event during knee flexion, not just a static amount of anterior or posterior translation measured at a single angle. Lachman, Anterior Drawer, and Posterior Drawer all assess translation at particular knee positions without the dynamic reduction that creates the clunk. The presence of that clunk strongly suggests ACL incompetence and rotational instability, which the pivot shift maneuver is designed to reveal.