Locking of the knee during walking most strongly suggests which of the following injuries?

• A. Anterior cruciate ligament rupture
• B. Medial collateral ligament sprain
• C. Patellar dislocation
• D. Medial meniscus tear

Answer: (D)

Locking of the knee during walking points to a mechanical block inside the joint, most often from a torn meniscus with a fragment catching between the femur and tibia. The medial meniscus is the more commonly injured one because it is more firmly attached to the joint capsule and the MCL, making it less mobile and more susceptible to tearing with twisting and weight-bearing. When a piece of torn meniscal tissue becomes interposed in the joint, it can prevent full extension or flexion, producing a locked sensation. Other injuries like ACL rupture tend to cause instability or giving way, MCL sprain causes medial pain and laxity, and patellar dislocation causes displacement of the patella—none of which classically produce a true locking in the joint.