What does a positive Lachman's test typically indicate?

A positive Lachman's test is a specific clinical examination maneuver used to assess the integrity of the anterior cruciate ligament (ACL) in the knee. When performing this test, the examiner stabilizes the femur with one hand while the other hand pulls the tibia forward. A significant amount of forward movement or "laxity" indicates that the ACL may be torn or compromised.

The ACL plays a crucial role in stabilizing the knee, preventing anterior translation of the tibia relative to the femur. When this ligament is injured—often due to sudden stops, changes in direction, or direct blows—a positive Lachman's test result is expected. This diagnostic tool is particularly valued for its reliability and sensitivity in detecting ACL injuries compared to other tests.

Understanding this context helps clarify that a positive result specifically relates to the ACL's condition and not to injuries of other structures such as the patellar tendon, quadriceps muscle, or meniscus.