Which physical examination test is most sensitive for ACL integrity?

Which physical examination test is most sensitive for ACL integrity?

• A. Anterior drawer test
• B. Lachman test
• C. Pivot shift test
• D. McMurray test

Answer: (B)

The key idea is that a test which best isolates the ACL and minimizes interference from surrounding muscles will have the highest sensitivity for detecting ACL damage. The Lachman test achieves this by flexing the knee to about 20–30 degrees, then anteriorly translating the tibia relative to the femur. In this arc, the ACL is placed under tension and the tibial translation is most directly governed by the ACL’s integrity. When the ACL is torn, you typically feel increased anterior laxity with either a soft or absent endpoint, which makes the finding more consistently positive across patients, including those who guard or have partial tears. The anterior drawer test, performed at 90 degrees of flexion, is more susceptible to false negatives from quadriceps or hamstring guarding and from secondary restraints, so it tends to be less sensitive for detecting ACL injuries, especially in partial tears. The pivot shift test assesses dynamic instability and is highly specific for significant ACL deficiency when performed skillfully, but it is technically demanding and may be less reliable in some exam settings, which can affect its sensitivity. The McMurray test targets meniscal pathology, not ACL integrity, so it isn’t relevant for this question. So, the Lachman test is the best choice for sensitivity in assessing ACL integrity.

The key idea is that a test which best isolates the ACL and minimizes interference from surrounding muscles will have the highest sensitivity for detecting ACL damage. The Lachman test achieves this by flexing the knee to about 20–30 degrees, then anteriorly translating the tibia relative to the femur. In this arc, the ACL is placed under tension and the tibial translation is most directly governed by the ACL’s integrity. When the ACL is torn, you typically feel increased anterior laxity with either a soft or absent endpoint, which makes the finding more consistently positive across patients, including those who guard or have partial tears.

The anterior drawer test, performed at 90 degrees of flexion, is more susceptible to false negatives from quadriceps or hamstring guarding and from secondary restraints, so it tends to be less sensitive for detecting ACL injuries, especially in partial tears. The pivot shift test assesses dynamic instability and is highly specific for significant ACL deficiency when performed skillfully, but it is technically demanding and may be less reliable in some exam settings, which can affect its sensitivity. The McMurray test targets meniscal pathology, not ACL integrity, so it isn’t relevant for this question.

So, the Lachman test is the best choice for sensitivity in assessing ACL integrity.