At the joints, the ends of bones are covered with articular cartilage, which normally reduces friction. When a person has osteoarthritis (OA), the articular cartilage softens, cracks, and wears away entirely in some areas. If diseased cartilage wears away, the joint becomes swollen and warm to the touch as body enzymes break down the debris. As the disease progresses, the exposed bone thickens and forms spurs that cause the bone ends to enlarge and joint movement to be restricted. The fingers, spine, hips, and knees are most often affected.
The cause of OA is not known, but a combination of genetic and mechanical factors is believed to be involved. It appears that arthritis begins in joints that have been overworked. Compression and abrasion may repeatedly damage the articular cartilage, which then must be broken down and replaced more often. Apparently, in persons with OA, cartilage breakdown occurs at a faster rate than replacement.
Weight loss is one recommendation for combating OA.Taking off 3 pounds can reduce the load on a hip or knee jointby 9-15 pounds. In addition, activities that cause finger pain should be avoided by using such items as lightweight pots and pans, Velcro fasteners, and electric can openers. A sensible ex-
ercise program can be designed to build up muscles and stabilize joints; low-impact activities like biking and swimming are best. Recently, acetaminophen (present in Tylenol) has been found to be as effective in controlling pain as a nonsteroidal anti-inflammatory drug such as ibuprofen, which is in Advil, poly Nuprin, and Motrin. Proper use of crutches or a cane can also assist mobility.
If all else fails, joint surgery may be recommended. During arthroscopy, surgeons use an arthroscope, a tiny tubular instrument that not only bears a lens and light source but also a camera to view the diseased joint on a television screen. Probes and surgical instruments can then be guided into the joint to remove debris and smooth the ends of bones. A diseased knee or hip can be replaced with a prosthesis (pros-the'sis) (artificial substitute). Figure 6A shows that half of the artificial joint is anchored by a metal shank driven into the marrow of the femur, and the other half is attached to the coxal bone (hip) or tibia (knee). Previously, the metal was always fastened to the bone with cement, but now, an alternative method is available. Some metal implants have a porous surface, and bone tissue can grow into the crevices to fasten the prosthesis. Since it takes time for bone to grow, patients are on their feet and can walk faster when cement is used. Artificial knees and hips do not have the flexibility and durability of natural ones; jumping, twisting, and heavy lifting are discouraged, as is excessive walking.
