Non-Stick Hips

Each year in the United States, more than 300,000 patients are fitted with a replacement hip or knee joint. This operation can bring a wonderful release and welcome mobility after years of pain.

Unfortunately, the life of a replacement joint is limited, on average, to 8-12 years -- even fewer years in younger, more active patients. Replacement of an artificial joint is a costly as well as a much less predictable operative procedure. Modern healthcare provisions demand more effective solutions to the problem, which is now recognized to be mechanical- and materials-related.

A major cause of artificial joint failure is the wearing away of high-density polyethylene components, such as the cup in the ball and socket of a hip joint. Adhesion between this polymer and the metal replacement ball results in the shedding of a great many (up to 10 billion) tiny particles of polyethylene. The body strives ineffectively to destroy the particles, and in so doing chemical agents are released that damage nearby bone - a process called osteolysis. Eventually, the bone may become so degraded that the joint is loosened.

Under an Institute internal research project, and in participate with the University of Texas Health Science Center at San Antonio, laboratory tests were carried out on orthopedic materials modified in various ways using ion beams. The results, recently submitted for publication, show that a coating of diamond-like carbon applied to a widely used cobalt-chrome alloy implant reduces wear of polyethylene under conditions similar to those in the body to a level where it is no longer measurable. The improvement is between one and two orders of magnitude, which could considerably extend the wear life of a hip joint.

This is just one example of the many ways ion beams can be applied to modify the surfaces of a variety of biomedical materials, including heart valves, neurological electrodes, and catheters.

Total hip replacements frequently fail because wear debris from the components (especially the acetabular polymeric cup) induces a powerful series of tissue reactions, including phagocytosis. Over the years, the chemical reactions cause osteolysis -- an attack on the bone supporting the stem of the device. Loosening occurs, and wear and mechanical failure necessitate a costly and risky replacement procedure.

Altering Material Surfaces to Prolong Service Life
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