Osteoarthritis - Introduction

Introduction

Osteoarthritis, also known as degenerative joint disease, is the most common form of arthritis. In this disorder, a joint loses cartilage, the slippery material that cushions the ends of bones, over time.

As a result, the bone beneath the cartilage changes and develops bony overgrowth. The tissue that lines the joint can become inflamed, the ligaments can loosen, and the muscles around the joint can weaken. The patient feels pain and movement limitations when using the joint.

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Click the icon to see an animation about osteoarthritis.

Joints

Joints provide flexibility, support, stability, and protection. Specific parts of the joint, the synovium and cartilage, provide these functions.

Synovium. The synovium is the tissue that lines a joint. Synovial fluid is a lubricating fluid that supplies nutrients and oxygen to cartilage.

Cartilage. The cartilage is a slippery tissue that coats the ends of the bones. Cartilage is composed of four components:

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

• Water. Cartilage is composed mostly of water, which decreases with age. About 85% of cartilage is water in young people. Cartilage in older people is about 70% water.
• Chondrocytes. Chondrocytes, the basic cartilage cells, are critical for joint health.
• Proteoglycans. These large molecules bond to water, which keeps high amounts of water in cartilage.
• Collagen. This essential protein in cartilage forms a mesh to give the joint support and flexibility. Collagen is the main protein found in all connective tissues of the body, including the muscles, ligaments, and tendons.

The combination of collagen mesh and water forms a strong and slippery pad in the joint. This pad (meniscus) cushions the ends of the bones in the joint during muscle movement.