Medical Dictionary: Arthritis

Arthritis affects nearly 1 in 3 Americans. It can appear in various forms, from arthritis of various joints to rheumatoid arthritis, osteoarthritis, and beyond. Every form has one thing in common: It causes pain. This medical dictionary covers the terms used in the report, Arthritis: Keeping your joints healthy, and includes details on arthritis and its symptoms, treatments, medications, causes, and its forms, such as arthritis of the knee or hip, rheumatoid arthritis, and osteoarthritis.

antibodies: Proteins produced by white blood cells to fight viruses, bacteria, and other foreign invaders.

antigen: A foreign protein or carbohydrate complex that causes an immune response.

articular cartilage: Tough, rubbery tissue that forms the surface of bones within joints.

autoimmune disease: A condition caused when an individual’s immune system reacts against his or her own organs and tissues.

bursitis: Inflammation of the bursae, fluid-filled sacs that ease friction between tendons and bones (and tendons and ligaments), causing swelling and pain.

cartilaginous joint: A joint that contains a tough cartilage plate that permits slight movement.

collagen: The main structural protein in connective tissue.

connective tissue: The material that holds various body structures together; cartilage, tendons, ligaments, and blood vessels are composed entirely of connective tissue.

cytokines: Messenger molecules that allow cells to communicate and alter one another’s function.

diathermy: Physical therapy using high-frequency electric current, ultrasound, or microwaves to deliver heat to muscles and ligaments.

elastin: Stretchable protein found in connective tissue.

enthesis: A site where ligaments or tendons attach to bone; plural is entheses.

enzyme: A protein that regulates chemical changes in other substances.

fixed joint: Fibrous tissue connecting the plates of the skull.

gout: Arthritis caused by uric acid crystals.

Heberden’s node: A bony growth on the joint nearest the fingertip, caused by osteoarthritis.

human leukocyte antigen (HLA) complex: A type of receptor on cells involved in recognizing foreign antigens; these receptors are genetically determined, and some are associated with different types of arthritis.

inflammation: A response to injury or foreign invasion designed to protect the body; the symptoms are heat, redness, swelling, and pain.

ligament: Fibrous tissue connecting bones and cartilage.

Lyme disease: An infectious disease transmitted by a tick bite; characterized by rash, flulike symptoms, and inflammation of the heart, nerves, and joints.

lymphocyte: A type of white blood cell. B lymphocytes produce antibodies. T lymphocytes destroy abnormal cells and interact with B lymphocytes.

psoriasis: A common skin disease characterized by thickened patches of inflamed red skin; sometimes accompanied by painful joint swelling and stiffness.

reactive arthritis: Joint problems triggered by bacterial or viral infection elsewhere in the body.

rheumatic disease: Any one of over 100 disorders that cause inflammation in connective tissues.

rheumatoid factor: An antibody found in about 85% of people with rheumatoid arthritis; also appears in other diseases and sometimes in healthy people.

rheumatology: The branch of medicine devoted to the study and treatment of connective tissue diseases.

scleroderma: An autoimmune disease in which the skin thickens and hardens; sometimes other parts of the body are affected, and joint pain may result.

synovial joint: The most mobile type of joint; found in the shoulders, wrists, fingers, hips, etc.

synovitis: Inflammation of the synovium.

synovium: A thin membrane lining joint capsules that produces synovial fluid.

tendon: A tough, fibrous band of tissue that attaches muscle to bone.

tendonitis: Inflammation of a tendon, usually caused by injury, which may restrict movement of the muscle attached to the tendon.

urethritis: Inflammation of the urethra.

vasculitis: Inflammation of blood vessels.