The bones of a joint are covered with a smooth, spongy material called cartilage, which cushions the bones and allows the joint to move without pain. The joint is lined by the synovium. The synovium’s lining produces a slippery fluid — called synovial fluid — that nourishes the joint and helps limit friction within. External to it is a strong fibrous casing called the joint capsule. Strong bands of tissue, called ligaments, connect the bones and help keep the joint stable. Muscles and tendons also support the joints and enable you to move. With arthritis, an area in or around a joint becomes inflamed, causing pain, stiffness and, sometimes, difficulty moving. Some types of arthritis also affect other parts of the body, such as the skin and internal organs.
There are more than 100 different types of arthritis. Some of the more common types include:
1. Osteoarthritis: This is the most common type of arthritis. It occurs when the cartilage covering the end of the bones gradually wears away. Without the protection of the cartilage, the bones begin to rub against each other and the resulting friction leads to pain and swelling. Osteoarthritis can occur in any joint, but most often affects the hands and weight-bearing joints such as the knee, hip, and facet joints (in the spine). Osteoarthritis often occurs as the cartilage breaks down, or degenerates, with age. For this reason, osteoarthritis is sometimes called degenerative joint disease.
2. Rheumatoid arthritis: RA is a long-lasting disease that can affect joints in any part of the body, but most commonly involves the hands, wrists, and knees. With rheumatoid arthritis, the immune system — the body’s defense system against disease — mistakenly attacks the body’s joints and causes the joint lining to swell. The inflammation then spreads to the surrounding tissues, and can eventually damage cartilage and bone. In more severe cases, rheumatoid arthritis can affect other areas of the body, such as the skin, eyes, and nerves.
3. Gout: It is a painful condition that occurs when the body cannot eliminate a natural substance called uric acid. The excess uric acid forms needle-like crystals in the joints that cause marked inflammation with swelling and severe pain. Gout most often affects the big toe, knee, and wrist joints.