The Lachman test is a physical examination maneuver that asseses anterior cruciate ligament (ACL) integrity, which is an essential component of knee stability. The Lachman test is best conducted on a supine patient with the knee flexed at 20 to 30 degrees. Physiologically, when the femur is stabilized and the tibia is pulled anteriorly, a well-defined "end-point" that limits anterior movement of the tibia can be felt. In a positive Lachman test, however, there is excessive unrestricted anterior movement of the tibia, with no "hard" end point. This indicates an ACL injury or tear. Video Index: 0:06 - Purpose of the test 0:17 - Performing the test 1:04 - Logical basis and interpretation of the test outcome