A knee lump can result from trauma, chronic inflammation, infection, bleeding, or tumors.
Inflammatory causes of a knee lump
A knee lump can be caused by inflammatory diseases that may also affect multiple joints within the body including:
- Ankylosing spondylitis (inflammation of joints between the vertebrae of the spine)
- Bursitis (inflammation of the protective, fluid-filled sacs around the joints)
- Gout (type of arthritis caused by a buildup of uric acid in the joints) and pseudogout
- Infectious arthritis (infection of the joint space)
- Osteoarthritis
- Psoriatic arthritis (arthritis associated with psoriasis of the skin)
- Rheumatoid arthritis (chronic autoimmune disease characterized by joint inflammation)
- Systemic lupus erythematosus (disorder in which the body attacks its own healthy cells and tissues)
Infectious causes of a knee lump
A knee lump may be caused by infectious processes including:
- Abscesses
- Boils
Traumatic causes of a knee lump
A knee lump can arise related to traumatic events. Traumatic causes include:
- Bite and sting injuries
- Fracture of bone
- Fragments of bone or cartilage
- Hematoma (collection of blood in body tissue)
- Retained foreign body
- Ruptured bursa
- Sprains and strains
Tumors that may cause a knee lump
Both benign and malignant tumors of the skin, soft tissues, or bone can cause a knee lump. Examples include:
- Fibroma (benign tumor composed of fibrous or connective tissue)
- Lipoma (benign tumor composed of fatty tissue)
- Melanoma (cancer arising in the melanocytes, or pigment-producing cells, in the skin or other parts of the body)
- Nevi (moles of the skin)
- Nonmelanoma skin cancers
- Osteosarcoma (type of bone cancer)
- Sarcoma (malignant soft-tissue tumor)
Serious or life-threatening causes of a knee lump
In some cases, a knee lump may be a symptom of a serious or life-threatening condition including:
Questions for diagnosing the cause of a knee lump
To diagnose your condition, your doctor or licensed health care practitioner will ask you several questions related to your knee lump including:
- How long have you felt your knee lump?
- Is the lump getting bigger?
- Is the lump painful?
- Is the lump stationary or mobile?
- Is the lump the result of an injury?
- Do you have any symptoms in other joints?
What are the potential complications of a knee lump?
Lumps caused by cancers may have life-threatening consequences, which depend on the type and stage (extent) of the cancer. Left untreated, lumps due to abscesses or serious infections may lead to widespread infection in the body. Knee lumps and associated symptoms can be due to serious diseases, so failure to seek treatment can result in serious complications and permanent damage.
Once the underlying cause is diagnosed, it is important for you to follow the treatment plan that you and your health care professional design specifically for you to reduce the risk of potential complications including:
