Which physical sign is most predictive of ligamentous knee instability?

• A. Positive Lachman test
• B. Joint line tenderness
• C. Positive ligamentous stability tests (Lachman, anterior drawer, posterior drawer) with laxity
• D. Positive McMurray sign

Answer: (C)

Ligamentous knee instability shows up when the knee demonstrates laxity across several stability tests, not just one. If the Lachman, anterior drawer, and posterior drawer tests all show laxity, it means the major ligaments—ACL, PCL, and surrounding stabilizers—are not resisting translation and rotation as they should. That pattern indicates true, global ligamentous instability rather than a localized issue.

A single positive sign like Lachman points to ACL injury, but doesn’t by itself prove instability through all the knee ligaments. Joint line tenderness and a McMurray sign point more toward meniscal problems rather than overall ligamentous laxity, so they’re less predictive of general instability.