To better understand juvenile rheumatoid arthritis, it helps to understand the anatomy of a joint.

A joint is a union between two bones. The joint allows the ends of the bones to move against one another. The surface of the bones inside a joint are covered by a slippery lining, called cartilage, which is slightly softer than bone. The cartilage is lubricated by a thick, slippery fluid, called synovial fluid. The joint capsule forms a wall around the joint by attaching to the bone above and below the joint. Ligaments prevent the bones from coming apart and tendons allow the muscles to move the bones that make up the joint.

Anatomy:

• Hand joints affected by osteoarthritis
• Hand joints affected by rheumatoid arthritis
• Major joints in the body