Introduction

Introduction

Osteoarthritis, also known as degenerative joint disease, is the most common form of arthritis. Scientists now believe osteoarthritis results from a combination of genetic abnormalities and joint injuries. In this disorder, an affected joint experiences a progressive loss of cartilage, the slippery material that cushions the ends of bones.

As a result, the bone beneath the cartilage undergoes changes that lead to bony overgrowth. The tissue that lines the joint can become inflamed, the ligaments can loosen, and the associated muscles can weaken. The patient experiences pain when using the joint. In addition to humans, nearly all vertebrates suffer from osteoarthritis, including porpoises and whales, as did long-extinct terrestrial travelers such as dinosaurs.

Click the icon to see an animation about osteoarthritis.

Joints

Joints are designed to provide flexibility, support, stability, and protection. These functions, essential for normal and painless movement, are primarily supplied by specific parts of the joint: the synovium and cartilage.

Synovium. The synovium is a membrane that surrounds the entire joint. It is filled with synovial fluid, a lubricating liquid that supplies nutrients and oxygen to cartilage.

Cartilage. The cartilage is a slippery tissue that coats the ends of the bones. Cartilage is one of the few tissues in the body that does not have its own blood supply. It has a number of essential components:

Click the icon to see an image of the synovial membrane and cartilage in the knee joint.

• Chondrocytes. Chondrocytes, the basic cartilage cells, are critical for balance and function.
• Water. Cartilage contains a high percentage of water, although it decreases with age. About 85% of cartilage is water in young people, and about 70% is water in older individuals.
• Proteoglycans. These are large molecules that help make up cartilage. Their important value is their capacity to bond to water, which ensures the high-fluid content in cartilage.
• Collagen. This is the critical protein in cartilage. It forms a mesh to give support and flexibility to the joint. Collagen is the main protein found in all the connective tissues of the body, including the muscles, ligaments, and tendons.