Definition

Juvenile arthritis (JA) refers to a number of different conditions with two characteristics in common. First, they all strike children. Second, they all involve inflammation of the joints.

Description

Humans can move their head, arms, legs, fingers, and toes because of joints. A joint is a structure where two or more bones come together. The elbow, for example, is a joint at which bones in the upper and lower arm come together.

The space between the bones in a joint is occupied by a variety of other structures and fluids. These structures and fluids help the bones move more smoothly. One of the structures in a joint is the articular capsule. The articular capsule surrounds the bones that come together at a joint and the space between the joint. The articular capsule contains a thin covering called the synovial (pronounced si-NO-vee-uhl) membrane. The synovial membrane...