Which ligament's integrity is assessed by the Lachman test?

• A. Posterior cruciate ligament
• B. Medial collateral ligament
• C. Anterior cruciate ligament
• D. Lateral collateral ligament

Answer: (C)

The Lachman test is used to assess anterior tibial translation when the knee is placed in about 20–30 degrees of flexion, and it specifically targets the structure that resists that forward motion—the anterior cruciate ligament. If the ACL is intact, forward movement of the tibia is limited and a definite end feel is felt. If the ACL is torn or deficient, there is marked anterior translation of the tibia with a soft or absent end feel. This makes the Lachman test the most reliable single test for ACL integrity, especially in acute injuries where swelling or hamstring guarding can mask other signs. In contrast, tests for other ligaments—posterior translation for the posterior cruciate ligament, valgus stress for the medial collateral ligament, and varus stress for the lateral collateral ligament—focus on those distinct stabilizers.