Baker's cyst

A Baker's cyst is a swelling that develops behind the knee due to excess fluid buildup in the joint capsule. It often results from knee joint problems like arthritis or a tear in the cartilage, which cause increased fluid production. The excess fluid causes the bursa—small fluid-filled sacs—to enlarge, forming a noticeable lump. While it may cause discomfort or swelling, some people experience no symptoms. Treatment typically focuses on addressing the underlying knee issues and may include rest, anti-inflammatory medications, or physical therapy. In some cases, fluid drainage or surgery might be necessary if symptoms persist.