Lachman test for ACL integrity is typically performed at what knee flexion angle?

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Multiple Choice

Lachman test for ACL integrity is typically performed at what knee flexion angle?

The Lachman test checks ACL integrity by applying anterior force to the tibia while the knee is slightly bent, so the ACL is under tension and the examiner can feel how far the tibia translates and whether there is a firm endpoint. The knee is positioned in a modest flexion range, around 30 to 40 degrees, because this angle places the ACL under peak tension while minimizing competing stabilizers and hamstring guarding. At this angle you can observe an abnormal excessive forward movement if the ACL is torn, or a solid endpoint if it is intact. Too little flexion (near full extension) can recruit other structures that blur the assessment, and too much flexion (near 90 degrees) allows the hamstrings to limit anterior translation and mask ligament laxity. Hence, 30–40 degrees provides a sensitive and specific balance for evaluating ACL integrity.

The Lachman test checks ACL integrity by applying anterior force to the tibia while the knee is slightly bent, so the ACL is under tension and the examiner can feel how far the tibia translates and whether there is a firm endpoint. The knee is positioned in a modest flexion range, around 30 to 40 degrees, because this angle places the ACL under peak tension while minimizing competing stabilizers and hamstring guarding. At this angle you can observe an abnormal excessive forward movement if the ACL is torn, or a solid endpoint if it is intact. Too little flexion (near full extension) can recruit other structures that blur the assessment, and too much flexion (near 90 degrees) allows the hamstrings to limit anterior translation and mask ligament laxity. Hence, 30–40 degrees provides a sensitive and specific balance for evaluating ACL integrity.

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