What clinical sign is indicative of an ACL injury during a physical exam?

• A. Joint effusion
• B. Positive McMurray test
• C. Positive Lachman test
• D. Visible bruise

Answer: (C)

The presence of a positive Lachman test during a physical examination is a key clinical sign indicative of an ACL (anterior cruciate ligament) injury. The Lachman test specifically assesses the integrity of the ACL by evaluating the anterior translation of the tibia relative to the femur. When the ACL is intact, there should be a firm endpoint limiting this anterior translation; however, if the ligament is injured or torn, there will be increased anterior movement of the tibia, often described as a "soft" or " mushy" endpoint, which is characteristic of a positive Lachman test.

This test is particularly effective because it is performed with the knee in a position that best isolates the ACL while minimizing the influence of other stabilizing structures. Therefore, a positive result provides strong evidence of ACL compromise and is often used in the clinical assessment of potential ACL injuries.