Osteoarthritis is the most common type of arthritis in the United States, with nearly 27 million people affected by it. In fact, osteoarthritis of the knee and hips is the leading cause of arthritis-related disability in the nation. The disease affects people of all races and occupational backgrounds. It most commonly affects middle-aged and older people, with most people affected after age 45. Men under age 55 are more likely to have osteoarthritis than women under 55. After age 55, women are more commonly affected, and, overall, more women have osteoarthritis than men. It is thought that this is because the broader female hips put more long-term stress on the knees. However, age increases the risk for osteoarthritis in both men and women.
Osteoarthritis is a chronic condition characterized by the breakdown of the joint’s cartilage. Cartilage is the part of the joint that cushions the ends of the bones and allows easy movement of joints. The breakdown of cartilage causes the bones to rub against each other, causing stiffness, pain and loss of movement in the joint. Osteoarthritis is thought to date back to ancient humans, as evidence of osteoarthritis has been found in ice-aged skeletons. Despite the longevity and frequency of the disease, the cause is still not completely known and there is no cure. In fact, many different factors can play a role in whether or not you get osteoarthritis, including age, obesity, injury or overuse and genetics. Any one of these factors, or a combination of them, can contribute to the development of osteoarthritis.
There are several stages of osteoarthritis:
- Cartilage loses elasticity and is more easily damaged by injury or use.
- Wear of cartilage causes changes to underlying bone. The bone thickens and cysts may occur under the cartilage. Bony growths, called spurs or osteophytes, develop near the end of the bone at the affected joint.
- Bits of bone or cartilage float loosely in the joint space.
- The joint lining, or the synovium, becomes inflamed due to cartilage breakdown causing cytokines (inflammation proteins) and enzymes that damage cartilage further.
- Changes in the cartilage and bones of the joint can lead to pain, stiffness and limited mobility.
Deterioration of cartilage can:
- Affect the shape and makeup of the joint so it doesn’t function smoothly. This can mean that you limp when you walk or have trouble going up and down stairs.
- Cause fragments of bone and cartilage to float in joint fluid causing irritation and pain.
- Cause bony spurs, called osteophytes, to develop near the ends of bones.
- Affect the joint’s hyaluronan, a lubricating component of cartilage, which hinders the joint’s ability to absorb shock.