The Lachman test primarily assesses the integrity of which knee ligament?

• A. ACL
• B. PCL
• C. MCL
• D. LCL

Answer: (B)

The Lachman test evaluates the anterior cruciate ligament because it directly tests the ACL’s job of preventing the tibia from moving forward relative to the femur. With the knee flexed about 20–30 degrees, the examiner stabilizes the thigh and gently pulls the tibia forward. If the ACL is intact, the tibia shows only a small amount of forward movement and a firm endpoint is felt. If the ACL is torn, there is excessive anterior translation of the tibia and the endpoint is soft or absent, signaling laxity.

This position isolates the ACL better than other tests and is particularly sensitive in acute injuries because hamstring guarding is minimized. By contrast, the posterior cruciate ligament would influence backward movement of the tibia, not forward movement; collateral ligaments (MCL and LCL) are assessed with varus/valgus stress tests rather than this forward translation maneuver.