Probable causes of a knee lump include chronic inflammatory conditions, local infections and bone or soft tissue tumors, according to Healthgrades. Lumps can be single or multiple, and they can quickly grow or stay the same size. They can exist as soft or hard bumps that are painful or pain-free.
Chronic inflammatory conditions, such as arthritis, may lead to a joint deformity that feels like a knee lump, states Healthgrades. An injury to the joint also sometimes causes a deformity that appears like a lump. Knee lumps caused by local infections grow as boils or abscesses. Insect bites and serious injuries, such as bone fractures, are traumatic causes of knee lumps that lead to blood accumulation in the tissues, a condition also known as hematoma.
Some lumps are benign or malignant tumors of the knee bones, skin or soft tissues, says Healthgrades. A biopsy or surgical procedure may be necessary to find out if the lumps are cancerous. Other lumps are sac-like cysts full of fluid that appear in various areas of the body. Fluid build-up from the knee joint that grows behind the knee is known as a Baker’s cyst.
Some knee lumps indicate an injury that requires urgent medical care, notes Healthgrades. Individuals should seek medical attention if they experience other symptoms, such as an immobile knee joint, loss of sensation or paralysis.