I.

Introduction

Arthritis, any of more than 100 different diseases causing pain, stiffness, and in most cases, swelling in the joints. According to the National Arthritis Foundation, arthritis is the number-one cause of physical disability, affecting more than 20 percent of all Americans and about 50 percent of those over 65. Arthritis affects people of both sexes and of all races, socioeconomic levels, and geographic areas. Although most forms of arthritis are more common in adults, about 300,000 children in the United States suffer from some type of arthritis-related disease.

Arthritis affects movable joints, that is, those joints where bones meet and move relative to one another. Movable joints cushion the bones and prevent them from rubbing against each other during movement. These joints are composed of cartilage—smooth, elastic tissue—surrounded by a casing called the joint capsule. The joint capsule is lined with a synovial membrane that secretes synovial fluid, a liquid that fills the joint cavity and further reduces friction between the bones. Although all arthritic conditions involve joint pain, the severity, duration, and effects of this pain vary considerably from one condition to another.