Joint replacement surgery has revolutionized the treatment of late-stage arthritis for most patients. Enhanced surgical techniques and modern care during and after the hospital stay have helped speed patients to quick recoveries back to near-normal function.

Designing engineers and orthopedic surgeons hope improvements of implants will allow longer lasting function of the replacements. These improvements may allow the replacement of joints in younger patients and provide an alternative to patients who fail to get adequate relief from more conservative treatments.

The hip is a good example of a large weight-bearing joint that is frequently replaced. It is made of two main parts: The ball at the top of the thighbone that fits perfectly into the round socket in the pelvis; and the shape of the bones and “ropes” of tissue between the bones, called ligaments that provide stability to the joint. The ball and socket are both covered with a smooth durable layer of cartilage that cushions the ends of the bones and enables them to move easily. It is this layer that “goes bad” in most forms of arthritis. Doctors and researchers continually try to find a way to replace healthy living cartilage effectively, but success is likely many years away.

Varied designs
At this time, the best medical science has to offer is to replace the entire joint. Many different designs and materials are currently used in artificial hip joints. All of them consist of two basic components: the ball component (usually made of polished metal) and the socket component (usually made of strong plastic). Both components are attached to the normal bone with either a rough surface (into which bone will grow) or bone cement.

The “weak link,” according to most studies of joint replacement, is the contact surface between the ball and socket. Just as the surface that nature makes can wear out with time (arthritis), the plastic surface of the joint slowly wears away with time and can eventually cause the metal parts to loosen from the bone. Even the most polished ball’s surface has tiny scratches that scrape against the plastic cup and cause the loss of tiny pieces of polyethylene plastic. These tiny pieces are recognized as foreign and stimulate the formation of cells that clean up the body. The cleanup cells in bone dissolve the bone (osteolysis) near the metal pieces of a joint replacement and can cause them to become completely loose and in need of rereplacement.

The second operation, or revision, is much more difficult and has higher risks of complications and lower rates of patient satisfaction.

It used to be that total hip replacement (arthroplasty) was the only option for these patients. Although the traditional surgery offers pain relief, it is often accompanied with limitations. Many patients are prevented from maintaining a more active lifestyle.

A new pain-relieving procedure known as hip resurfacing can be benefi cial for younger hip arthritis patients. Current studies show that after 10 years, 95 percent of patients with a resurfaced hip are functioning well.

Pluses and minuses
Compared with conventional total hip arthroplasty, hip resurfacing off ers distinctive advantages in the appropriate patient with end-stage hip arthritis. Th e most obvious advantage is bone preservation, because bone on the upper femur is maintained rather than resected, or removed. Another advantage is a more physiologic transfer of stress to the proximal thigh with activity.

These two advantages may make revision surgery at a later date less difficult because more femoral bone remains.

Another advantage is that with hip resurfacing the incidence of dislocation is lower. The larger diameter femoral head used reduces the dislocation rate when compared tothe smaller 28mm and 32mm heads used in a conventional total hip arthroplasty. For younger patients, the larger head also offers a greater range motion, which is essential for physical activities.

The risks of resurfacing are similar to those of total hip arthroplasty. They include infection, venothrombolic disease, neurovascular damage, wear, loosening, limb length inequality, and the physiologic stresses associated with surgical intervention. Hip resurfacing patients are also at risk for fractures of the femoral neck below the resurfacing, which occurs in roughly 2 to 3 percent of the procedures.

Dramatic changes
Hip resurfacing can produce dramatic changes in patients’ lives and activity levels. Several TCO patients have returned to skating, skiing, and bike riding. Some physicians will also allow patients to return to running and contact activities after the first year. There is hope for high activity and mobility after hip replacement surgery, even though patients might not feel as if they have returned to their athletic prime.