Why does a meniscus tear cause knee locking?

The meniscus normally follows the knee as it flexes and straightens. A flap or loose section can shift into the joint space and act like a small obstruction. This may stop the knee from fully straightening, fully bending, or moving smoothly until the tissue changes position. Swelling and muscle tightening can add to the stuck sensation. A brief feeling of stiffness is different from a true mechanical lock, and several conditions can cause either experience.

Do not forcefully twist, pull, or repeatedly bend a locked knee. Sit or lie in a safe position, keep the leg supported, and avoid putting weight through it if it feels unreliable. Cold applied through a cloth may ease swelling. Arrange a clinical assessment, particularly when locking follows a twist or is accompanied by pain, clicking, or swelling.

Get prompt medical advice if the knee remains stuck, you cannot bear weight, or movement has suddenly become very limited. Immediate assessment is sensible after a significant injury, visible deformity, severe pain, or rapidly increasing swelling. A clinician can decide whether examination, imaging, or specialist treatment is needed.

Ask whether your symptoms suggest a mechanical obstruction; whether you should use crutches temporarily; which movements are safe; and what to do if the knee locks again at home.