Introduction

The combination of the collagen meshwork and the high water content, tightly bound by proteoglycans, creates a resilient and slippery pad in the joint, which resists the compression between bones during muscle movement. The synovial fluid lubricates and provides oxygen and nutrients to the bloodless cartilage.

Osteoarthritis: The Disease Process

Deterioration of Cartilage. Osteoarthritis develops when cartilage in a joint deteriorates. The process is usually slow.

• In the early stages of the disease the surface of the cartilage, or even the synovium in some people, becomes inflamed and swollen. There is a loss of proteoglycan molecules and other tissue components that cause water loss. Fissures and pits appear in the cartilage.
• As the disease progresses and more tissue is lost, the cartilage loses elasticity and fluid. It becomes increasingly prone to damage due to repetitive use and injury.
• Eventually large amounts of cartilage are destroyed, leaving the ends of the bone within the joint unprotected.

To compound the process, bone around arthritic joints is not structurally normal. As the body tries to repair damage to the cartilage, problems can develop:

• Clusters of damaged cells or fluid-filled cysts may form around the bony areas or near the fissures.
• Fluid pockets may also form within the bone marrow itself, causing swelling. The marrow, which runs up through the center of bone, is rich in nerve fibers, and such injuries may be an important source of pain in many patients with osteoarthritis.
• Bone cells may respond to damage by multiplying, growing ,and forming dense, misshapen plates around exposed areas.
• At the margins of the joint, the bone may produce outcroppings, on which new cartilage cells (chondrocytes) proliferate and grow abnormally.

Location of Osteoarthritis

Unlike some other types of arthritis, such as rheumatoid arthritis, osteoarthritis does not spread through the entire body. (In other words, it is not systemic.) Rather, it affects one or several joints. Osteoarthritis affects joints differently depending on their location in the body.

• Osteoarthritis is commonly found in joints of the fingers, feet, knees, hips, and spine.
• It sometimes occurs in the wrist, elbows, shoulders, and jaw, but is not common in these locations.