Dear Doctor:

How do I know if I need a hip replacement? My right hip gets so stiff after I’ve been sitting at work for a few hours that I can hardly walk, and then it aches for the rest of the day and night.

Dear Reader: The hip is one of the largest weight-bearing joints of the body. Its unique structure lets humans stand and walk upright and gives our legs and torso an impressively wide range of motion. It is a ball-and-socket joint, which means that the rounded head of a bone fits neatly into a cuplike hollow. In the case of the hip joint, the ball-shaped head of the femur, which is the upper leg bone, sits inside a socket within the hip, known as the acetabulum. The surfaces of the femur and the hip socket are lined with cartilage, a smooth and springy connective tissue that cushions the joint and helps reduce friction. A membrane known as the synovium produces a thick liquid that lubricates and nourishes the interior of the joint. Fluid-filled sacs known as bursae act as cushions and protect the muscles and tendons as they move over bony areas within the joint. Muscles, ligaments and tendons anchor the hip joint and provide power, stability and flexibility.

The most common reason for a hip replacement is damage to the parts of the joint that reduce pressure and eliminate friction. This often occurs due to osteoarthritis, a degenerative condition in which the tissues of the joint begin to deteriorate, and rheumatoid arthritis, a chronic inflammatory disorder. Injuries, fractures, wear-and-tear due to overuse or being overweight, and cancer, while less common, also can lead to the need for a hip replacement.

One of the main symptoms that the joint may need to be replaced is significant and persistent pain.

This occurs while walking, sitting, standing or bending over, and often is severe enough to wake you from sleep. It interferes with the ability to carry out daily activities and impairs quality of life.