In 1994, a National Institutes of Health Consensus Panel declared that total hip replacement is one of the most successful surgical procedures, providing immediate and substantial improvement in a patient's pain, mobility, and quality of life.

More than 168,000 total hip replacements are performed each year in the United States, according to the American Academy of Orthopaedic Surgeons.

The primary symptoms for total hip replacement (THR) are pain and disability, usually accompanied by X-ray evidence of joint disease. There is a broad span of ages among today's THR patients, but it is most common in men age 65 to 74 and women age 75 to 84.

THR involves removing diseased or damaged bone in the upper end of the thigh bone (femur) and the section of the lower pelvis into which the femur fits. The bone is then replaced with a prosthesis, usually made of a metal alloy or polyethelene (plastic) components. Successful replacement of deteriorated, arthritic, and severely injured hips has contributed to enhanced mobility and comfortable, independent living for many people who would otherwise be substantially disabled.

Hip arthroplasty has been recorded as early as the 1890s and total hip replacement in the 1930s, but the procedures were mostly unsuccessful in providing long-term relief of pain and restoring mobility to the patient. Infection, poor fit and too much wear on surrounding bone were problems that plagued both patient and surgeon.

Then in the early 1960s, John Charnley, M.D., developed low-friction arthroplasty. He overcame the problem of loosening of the prosthesis by reducing the diameter of the ball on the femoral prosthesis, thereby reducing friction between the metal prosthesis and the socket of the hip replacement. He fixed the prosthesis in the femur with a specially designed mixture of the self-curing acrylic cement, polymethylmethacrylate, which was used primarily by dentists at the time.

Despite the technological advances, other hurdles remained. Originally the head of the femur prosthesis was seated in a cup of Teflon, but soon it was apparent that Teflon degraded and caused adverse tissue reactions. Better materials were needed.

Then one day, a young man selling gears made of high molecular-weight polyethylene stopped at the hospital where Charnley worked. The plastic intrigued an engineer who worked with Charnley, but Charnley dismissed it. However, when tests in his biomechanical laboratory showed that the plastic was highly resistant to wear, Charnley began working with the manufacturer to make it suitable to use in the hip replacement procedure.

Today, engineering research in biological, mechanical and material science has made implants very durable. New technology involving prosthetic devices, along with advances in surgical techniques, has diminished the risks associated with the operation and improved the immediate and long-term outcome of hip replacement surgery.

Current research, like that of biomedical engineer Douglas Robertson, M.D., Ph.D., of the Washington University School of Medicine, may provide options for a more tailored fit to the patient and reduce the need to maintain a large inventory of implants.

Newer cementing techniques have achieved a more secure fit of the prosthesis, and the addition of a porous coating to the implant has improved prosthesis fixing in a cementless procedure. Coatings, such as calcium phosphate (hydroxyapatite), applied to implant surfaces to enhance fixation is a new technology still under investigation.