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DURHAM, N.C. - For more than 40 years, surgeons have been restoring pain-free normal functioning to patients whose hip joints are failing. During that time, advances in materials and refinements in surgical technique have led to success rates of greater than 90 percent after 20 years.

The hip joint itself is fairly simple. The top end of the thigh bone (femur) is shaped like a ball. This ball fits inside a socket in the hip bone, where a smooth layer of cartilage cushions the joint and allows for easy movement.

The most common site for the pain experienced by patients is the point where the ball and socket meet - either the ball itself becomes damaged, or the cartilage layer breaks down. The resulting friction during movement can create excruciating pain.

Arthritis, both osteoarthritis and rheumatoid arthritis, is the main reason for total hip joint replacement, followed by trauma (such as a fall) and necrosis (death and disintegration) of the ball portion of the joint.

Total hip joint replacement is a major surgical procedure that orthopedic surgeons typically employ when all other non-surgical treatments are unsuccessful. Severe pain and adverse effects on lifestyle are the major factors that physicians consider when deciding when and if to perform surgery, according to Duke University Medical Center orthopedic surgeon T. Parker Vail, M.D.

"The relief of pain is the number one reason to replace a hip joint," he said. "For example, if an X-ray shows damage to the joint, but the patient isn't experiencing any pain, we won't operate. There are many non-operative options we like to try before moving to surgery, and in the majority of the cases, these non-surgical remedies are satisfactory."

The following options are tried first to relieve the pain: physical therapy, individualized exercise programs, weight loss, and strategies that help reduce the shocks of day-to-day activity on the joint. Drugs, such as acetaminophen or arthritis medications, may also be prescribed for pain. The last resorts are stronger pain medications.

The operation itself, which usually lasts about two hours, begins with surgeons removing the femoral head. A new socket, which is lined with a variety of materials to reduce friction, is either screwed into the hip bone or, less frequently, cemented into place with special bone cement. After the ball is removed, a new one, which is attached to a metal stem, is inserted into the femur. The ball is inserted into the socket and the muscles and tendons that hold the entire joint together are placed back in to position. Research on the hip capsule ligaments and relevant anatomy has enabled Duke physicians to approach the hip with smaller incisions and minimal damage to surrounding muscles.

"We do most procedures under a regional block and not general anesthesia," Vail explained. "We find that patients recover much faster this way, and they can begin rehabilitation sooner, often the day after surgery. Normally, patients are discharged from the hospital within three to five days.

"Virtually every one of our patients reports a significant reduction in pain with their new hips," Vail said. "Functionally, most people can't tell the difference."

In the beginning, patients who receive new hip joints must re-learn how to do many of life's routine activities, such as walking, sitting and standing. The typical course of recovery involves physical rehabilitation to build up strength and endurance. For the first month or so, patients require crutches to get around; after that, a week or two of cane-assisted walking is normal.

"The better physical condition a patient is in prior to surgery, the less likely there will be complications after surgery," Vail explained. "Good muscle tone before surgery usually improves the effectiveness of physical therapy after surgery."

Of the common reasons for replacement joints to fail, wear and tear at the ball and socket junction occurs with the most frequency. Others causes include loosening of the stem within the femur, infection, or dislocation of the ball itself. In all cases, surgeons can replace the joint with a new one.

Vail tells his patients the rate of failure of the joint is approximately one-half percent per year, meaning that after ten years, 95 percent of the joints will be functioning as planned. Duke surgeons perform close to 700 hip and knee joint replacements each year, with Vail accounting for about half of those.

Vail and colleagues are involved in a number of clinical trials testing different materials used in making the stem, the ball, the socket, and materials that make up the crucial interface between ball and socket. Important advances in bone conservation and preservation of soft tissue structures around the hip have provided steady improvement in the success of the procedure.