Which ACL test involves tibial subluxation with knee extension to flexion and can produce a clunk?

Which ACL test involves tibial subluxation with knee extension to flexion and can produce a clunk?

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

Answer: (D)

This test looks for the dynamic instability that happens with ACL deficiency. In an ACL‑deficient knee, the tibia tends to sublux anteriorly when the knee is near full extension. As you move the knee into flexion, the tibia suddenly reduces back under the femur, producing a palpable and sometimes audible click or “clunk.” Practically, the maneuver combines valgus stress with tibial internal rotation while you move the knee from extension into flexion. The key feature is the two-phase behavior: a felt subluxation as the knee is extended, followed by a sudden reduction or clunk as the knee flexes to about 20–30 degrees. This dynamic relocation is characteristic of the pivot shift test and reflects the ACL’s role in preventing anterior tibial translation during movement. Static tests like the Lachman or Anterior Drawer assess anterior tibial translation at a given angle of flexion and don’t reproduce this relocation phenomenon, which is why the pivot shift is distinct for detecting ACL–related instability. Posterior Drawer tests the opposite direction and is used for the PCL.

This test looks for the dynamic instability that happens with ACL deficiency. In an ACL‑deficient knee, the tibia tends to sublux anteriorly when the knee is near full extension. As you move the knee into flexion, the tibia suddenly reduces back under the femur, producing a palpable and sometimes audible click or “clunk.”

Practically, the maneuver combines valgus stress with tibial internal rotation while you move the knee from extension into flexion. The key feature is the two-phase behavior: a felt subluxation as the knee is extended, followed by a sudden reduction or clunk as the knee flexes to about 20–30 degrees. This dynamic relocation is characteristic of the pivot shift test and reflects the ACL’s role in preventing anterior tibial translation during movement.

Static tests like the Lachman or Anterior Drawer assess anterior tibial translation at a given angle of flexion and don’t reproduce this relocation phenomenon, which is why the pivot shift is distinct for detecting ACL–related instability. Posterior Drawer tests the opposite direction and is used for the PCL.