Orthopedic surgeons have devised operations to repair or replace knees, elbows and hips of people becoming crippled by arthritis. Wear and tear arthritis of the knee, typically triggered by an injury years earlier, can cause knock-knees or bowleg deformities. Rheumatoid arthritis can also destroy the knee. Surgeons may be able to correct the allignment of the knee or replace the diseased knee with an artificial one made of plastic and metal.

It is the most common metabolic disease affecting the elderly. One common sign of the disease is the so-called Dowagers hump. Vertebrae in the spine are typicaly affected the most, sometimes collapsing and disappearing. Men get osteoporosis, too, but because on average their bones are bigger and denser it's not as obvious as soon. Yet astronauts in space, where they are not putting weight on their bones, rapidly lose bone. Normally bone is constantly being renewed in response to the pull of gravity and of muscles.

Doctors don't know the cause of osteoporosis but they do know that a person's calcium balance is a key factor. In the normal person the amount of bone being lost and the amount being formed are equal, as is the amount of calcium lost and the amount of new calcium absorbed. If there is not enough calcium available from your diet, you body will take calcium from the bones to supply it to your heart and nerve cells.