Osteoarthritis (OA) is a joint disease that causes the cartilage to break down and the bone to overgrow or form cysts. Cartilage is a smooth, shiny material that lines the joints - allowing them to glide easily as you move. It is a type of resilient connective tissue that covers and protects the ends of bones in joints. Although OA can affect any joint in the body, it most frequently affects the hips, knees, hands, feet, and spine.
Arthritis is the leading cause of disability in the United States. OA is the most common form of arthritis. It affects almost 14% of adults in this country. Statistics show that men and women are affected in equal numbers. OA usually occurs after the age of 45, but it can occur earlier in life, and even be seen in the spines of teenagers. It occurs in all people of either gender. After menopause, women tend to get more severe and complicated problems.
Risk factors for developing OA include:
- being overweight
- having a family member with the condition
- having another form of arthritis
- increasing age
- repeated injury to the joint through sports or work
There's no cure for OA, though research is beginning to unravel the mechanisms of the disease, which should lead to new treatments. Treatments currently focus on managing pain, reducing the load on the joints, and improving the strength of the muscles supporting the joints. Experimental therapies try to slow the progression of the disease and increase the mobility and flexibility of the joints.
As you move or put pressure on a joint, cartilage allows bones to slide over one another and acts as a shock absorber. Cartilage itself does not have any nerve cells and therefore cannot sense pain. OA results when the cartilage becomes worn out, allowing the bones underneath to rub against each other and cause pain and swelling. It is not simple wear-and-tear but an actual disease process involving the cells and proteins of the bone and cartilage.
As the condition progresses, the joint may become disfigured and small growths called osteophytes begin to grow inside the joints. Osteophytes are small, irregular, bony growths that are also called bone spurs. Bits of broken-off cartilage or bone are also found floating inside the joint. This causes even more pain, swelling, and immobility of the joint.
The exact cause of these changes is unknown. Scientists believe that the following factors play a role:
- being overweight: Excess weight puts stress on weight-bearing joints such as hips and knees, and increases the risk of cartilage breakdown. This is the most important risk factor for OA affecting hips, and leg and foot joints.
- family genes: Scientists believe that OA may be passed on through families, with the symptoms appearing in middle age.
- injury: Trauma to the joint, such as overuse, can damage the cartilage and lead to OA. This is often the cause of OA in younger people.
- increasing age: The cartilage wears down with time. By age 65, 80% to 90% of people have OA, as shown on X-ray, though a much smaller percentage have symptoms.
- other types of arthritis: For example, rheumatoid arthritis can also damage joints and lead to OA.