Why does a meniscus tear cause knee swelling?

A meniscus tear can disturb the tissues that help the knee move smoothly. The joint lining may respond to this irritation by producing extra fluid, causing puffiness or a deeper feeling of fullness. Swelling may appear soon after a twisting injury or build gradually after repeated activity. It can make bending difficult and may be accompanied by pain, clicking, or stiffness. Swelling by itself does not establish the cause, because injuries and inflammatory conditions can affect the knee in similar ways.

Scale back activities that increase the swelling, especially running, jumping, deep squats, and twisting. Rest the knee in a supported position and use a cold pack wrapped in cloth for short periods if it feels soothing. Gentle movement within comfort can help prevent stiffness. Arrange an evaluation if the swelling does not settle, keeps returning, or interferes with walking or sleep.

Seek prompt care for rapidly increasing swelling, a knee that becomes locked, inability to bear weight, or a major injury. A hot, red, swollen knee with fever also needs urgent medical attention. A clinician can examine the joint and decide whether further testing is appropriate.

Ask whether the swelling feels like fluid inside the joint; how to measure improvement; which exercises and activities are suitable; and what symptoms should lead you to return sooner.