Normal Joint* In a normal joint (where two bones come together), the muscle, bursa (sacs of fluid that protect moving muscles, skin and tendons) and tendons (tissue that attaches muscle to bone) support the bone and help the joint to move. The synovial membrane releases a slippery fluid into the joint space. Cartilage covers the ends of the bone to absorb shocks and to keep the bones from rubbing together when the joint moves.

Joint with Osteoarthritis* With osteoarthritis, cartilage breaks down and the bones rub together. The joint then loses shape and moves. The ends of the bone become thick, forming spurs (bony growths). Bits of cartilage or bone float in the joint space.

Joint with Rheumatoid Arthritis* With rheumatoid arthritis, the joint becomes inflamed and the synovial membrane becomes thicker. This causes the joint to swell, causing damage to bone and cartilage. Over time, the bone and cartilage gets destroyed. Space between the joint gets smaller, and the joint loses shape and moves.