Julian E Girod, MD

Joint Replacement

Summary
For advanced arthritis, joints can be replaced with synthetic materials. Metals like cobalt-chrome and titanium alloys are used in the larger joints. Polymers (long-chained molecules) such as silicone are used in the smaller joints, such as in the fingers.

The devices must be durable and must not stimulate attack by the already overactive immune system, interfere with healing, or push surrounding structures out of their normal position.

Before the advent of implants, surgeons would remove joint surfaces, hoping that the scar tissue filling in the area would allow more mobility than the arthritic joint.

This type of surgery often failed. Implants proved far more successful. They were pioneered by an army surgeon from Grand Rapids, Mich., Alfred Swanson, M.D. He fashioned the first such devices in the late 1950s out of silicone elastomers, polymers made from the element silicone, which is found in quartz.

Research to fine-tune the implants continued in the 1960s, and in 1969, the first silicone-based joint implants came on the market. These implants provided a flexible hinge for the joints of the fingers, wrists and toes. Since then, more than two dozen models have been developed, several by Swanson.

More than a million people have received joint replacements (mostly in the hip). During implant surgery, technically called "implant resection arthroplasty," the surgeon first removes the surface of the joint bones as well as excess cartilage.

The centers of the tips of abutting bones are hollowed out, and the stems of the implant are inserted there. Between the bones lies the hinge part of the implant, which both aligns the bones and allows them to bend at the joint.

The implant is "fixed," or held in place, with bone cement and, finally, the tendons, muscles and ligaments are repaired. As the site heals, the patient must exercise, but it can take a year of physical therapy to achieve maximum rehabilitation.

A new type of hand surgery replaces joints and realigns fingers at the same time. Rheumatoid arthritis patients who have a severe deviation of their fingers away from the thumb may be candidates for this procedure.

Recently introduced is an operation that repositions the tendon at the base of the little finger. Holding the finger in place forces the other fingers to align properly. Many patients who choose this surgery start moving their hands the night after the operation, and wear a splint-like support device for the next three weeks.

By six weeks after the operation, individuals are able to do most of their usual activities, especially the simple tasks that most of us take for granted, but were virtually impossible for these individuals.

Newer joint replacements use materials that resemble body components. "Recent hip implants have been coated with calcium phosphate materials, like hydroxylapatite, which interact with bone. The aim is to enhance the attachment of the implant to the bone with a biologically active material," says an expert at the FDA's Center for Devices and Radiological Health.

Rather than filling in the spaces with cement, investigators are testing a variety of porous coatings that allow "biological fixation," in which bone can grow into the implant area.

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