The pivot shift test is most specific for injury to which structure?

• A. ACL
• B. MCL
• C. PCL
• D. Meniscus

Answer: (D)

The pivot shift test is most specific for an ACL tear because it reproduces the characteristic rotary instability caused when the ACL is deficient. In a knee with an intact ACL, anterior translation and internal rotation are restrained, and the tibia remains stable as you move from extension into flexion. When the ACL is torn, the tibia can sublux anteriorly around 20–30 degrees of flexion and then reduce back as you continue to flex, producing a distinct clunk. This specific pattern of anterior subluxation with sudden reduction is highly indicative of ACL injury.

Other structures don’t produce this same reproducible clunk. The medial collateral ligament (MCL) injury mainly causes valgus laxity, detectable with a valgus stress test. The Posterior Cruciate Ligament (PCL) injury leads to a posterior tibial sag or positive posterior drawer test. Meniscal injuries typically cause joint-line pain, catching, or locking, and are diagnosed with tests like McMurray or Thessaly rather than the pivot shift clunk.