Q: Why are so many people having their joints replaced?

A: Americans are living longer and staying active, and aging baby boomers don't want to stop participating in sports because of pain.

Another reason is replacement joints last a long time and work well. With better managing of chronic conditions such as heart disease and cancer come higher expectations for a comfortable, functional life.

Modern-day joint- replacement surgery has been done in the United States since the 1970s, with more than one million hip and knee replacements in 2010. Demand is expected to increase dramatically.

Many people turn to joint replacement when pain is no longer treatable and interferes with their lives.

Issues such as obesity lead to more stress on the joints, premature deterioration, and earlier joint replacements.

The goal of surgery is to relieve the pain in the joint caused by damage to the cartilage. The pain may be so severe the person avoids using the joint, weakening surrounding muscles and making movement even more difficult. A physical exam, lab tests, and X-rays will show the extent of the damage. Total joint replacement is considered if other options no longer relieve the pain and disability.

During hip or knee replacement, the surgeon removes the damaged surfaces of the joint and replaces them with plastic or metal implants. Today's implants are more durable and last longer. After surgery, many people walk more easily; some ride a bike or play golf. Joint replacement is one of the great advances for improving quality of life.

Menachem M. Meller, M.D., Ph.D., an orthopedic surgeon at Mercy Philadelphia Hospital.