Which test is considered the best for diagnosing an ACL tear?

Which test is considered the best for diagnosing an ACL tear?

• A. Lachman Test
• B. Anterior Drawer Test
• C. Posterior Sag Sign
• D. Patellar Apprehension Test

Answer: (A)

The most reliable way to detect an ACL tear is to assess anterior translation of the tibia when the knee is in a modest bend, because that position isolates the ACL as the main restraint. The Lachman test does exactly this: the knee is flexed about 20–30 degrees, which tightens the ACL and makes any abnormal laxity more apparent. A positive finding is increased anterior movement of the tibia with a softer or absent end point compared to the other knee. This combination of sensitivity and specificity is why the Lachman test is considered the best single test for an ACL rupture, especially in the acute setting where swelling and muscle guarding can obscure other tests. By contrast, the anterior drawer test is performed with the knee at 90 degrees and can be more affected by hamstring guarding and swelling, making it less reliable on its own in acute injuries. The posterior sag sign targets the posterior cruciate ligament, not the ACL, and the patellar apprehension test assesses patellofemoral stability rather than cruciate integrity.

The most reliable way to detect an ACL tear is to assess anterior translation of the tibia when the knee is in a modest bend, because that position isolates the ACL as the main restraint. The Lachman test does exactly this: the knee is flexed about 20–30 degrees, which tightens the ACL and makes any abnormal laxity more apparent. A positive finding is increased anterior movement of the tibia with a softer or absent end point compared to the other knee. This combination of sensitivity and specificity is why the Lachman test is considered the best single test for an ACL rupture, especially in the acute setting where swelling and muscle guarding can obscure other tests.

By contrast, the anterior drawer test is performed with the knee at 90 degrees and can be more affected by hamstring guarding and swelling, making it less reliable on its own in acute injuries. The posterior sag sign targets the posterior cruciate ligament, not the ACL, and the patellar apprehension test assesses patellofemoral stability rather than cruciate integrity.