HOW ARTHRITIS HAPPENS

To understand how arthritis develops, consider first the function and components of a typical limb joint: The ends of long bones are covered by articular cartilage, which is made up of 80 percent water. The remainder is collagen and long chains of proteins called proteoglycans, which

Inflammatory enzymes produced in response to an injury break down synovial fluid, which provides lubrication within the joint space, making it thinner and less protective.

give cartilage stiffness to withstand shearing forces as the joint moves. Areas of higher motion in the joint have higher levels of proteoglycans. Articular cartilage compresses and expands under pressure from the bones each time the joint flexes, forcing water and other fluids in and out, keeping the tissues hydrated and healthy.

Even routine activity might cause minute damage and small amounts of inflammation within a joint. Usually, the body makes the needed repairs quickly and effectively. If the insults are too severe or repetitive, however, these healing processes may be overwhelmed, starting the cascade of events that leads to arthritis.

Inflammatory enzymes produced in response to an injury break down synovial fluid, which provides lubrication within the joint space, making it thinner and less protective. Meanwhile, collagen and proteoglycans are lost, reducing the cartilage’s ability to retain water. If the process is not interrupted with rest or medical intervention, the damage mounts and the joint fills with inflammatory fluids, leading to the pressure, pain and stiffness that are the hallmarks of arthritis. Left unchecked, this cycle can tear or erode cartilage to the extent that bone ends rub painfully against each other. This is an advanced case of osteoarthritis, also called degenerative joint disease.