Discovery May Lead to Longer-Lasting Artificial Hips
Researchers at the Swiss Federal Institute of Technology (Zürich, Switzerland; www.kof.ethz.ch) have made a discovery that may significantly extend the usable life of the materials used in replacement hip joints. Performed on more than 300,000 people every year, hip replacement procedures frequently use a joint consisting of a titanium alloy base with a polyethylene cup that is fitted with a ceramic ball. Even these advanced materials, however, tend to degrade after 10 to 15 years, often because of inadequate lubrication. Although replacement hips use synovial fluid, which is present in natural joints, to reduce friction, they don't receive the same level of lubrication.
Swiss researchers have focused on the polyethylene cup as the source of the problem. Natural cartilage is hydrophilic; polyethylene, on the other hand, repels water. This condition causes the protein in synovial fluid to denature, turning inside out and losing most of its lubricious properties. The team tested this assertion by treating polyethylene with oxygen plasma to reduce its water-repelling properties. Once treated, the material did indeed experience greatly reduced friction. "We would expect replacement hip joints constructed with similarly hydrophilic materials to have a longer life expectancy than current models," summarizes researcher Nicholas Spencer. Spencer goes on to say that this discovery is particularly important as "bone structure deteriorates gradually over time, making repeat transplant procedures more and more difficult." Because the polyethylene currently used only retains this increased lubricity for a matter of minutes after treatment, the research team is now working on developing derivative materials that have these traits intrinsically.