Why does knee cartilage injury cause knee locking?

Cartilage helps the joint surfaces move smoothly and distributes force. An injury may create a loose or displaced flap, rough surface, or swelling that occupies space inside the joint. As the knee bends or straightens, that tissue can catch between moving surfaces. Some people describe a true block, while others feel clicking, catching, or a momentary hesitation that releases after changing position. Pain and swelling can also limit movement and create a locked feeling without a physical obstruction.

A clinician will ask whether the knee can fully straighten, how the injury occurred, and whether swelling followed. Examination helps separate cartilage symptoms from ligament, tendon, or kneecap problems.

Stop the movement that caused the knee to catch and avoid twisting, deep squats, or impact exercise until it is assessed. Do not forcefully jerk the knee straight. Gentle movement within a pain-free range may prevent stiffness, while a wrapped cold pack can help after activity. If the knee repeatedly locks, arrange an appointment with an orthopaedic clinician or physiotherapist for an examination and a safe rehabilitation plan.

Seek urgent assessment if the knee remains physically locked and cannot straighten, you cannot bear weight, or a major injury caused immediate swelling or deformity. Prompt review is also sensible when locking recurs, gives way, or is accompanied by substantial swelling. Do not drive if the knee cannot bend or straighten safely.

Does my description suggest a true mechanical block or pain-limited movement? Which activities are safe while healing? Do I need imaging or a referral? What should I do if the knee locks again?