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Squeaky Hip Implants
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With the growing success of joint replacement surgeries, patients have become accustomed to certain indignities related to having a metal replacement part in a hip, knee or shoulder. For example, they tend to set off airport metal detectors and attract attention of security personnel. Now, there's more. The Mayo Clinic Biomechanics Laboratory report released at an annual meeting of the American Academy of Orthopedic Surgeons sheds light on the potential causes of the squeak, thus guiding means of eliminating it. The sound is associated with implants made of a material known as alumina ceramic-on-ceramic — and is audible to the person with the implant and those nearby. After 11,000 cycles of tests in a mechanical simulator that reproduced the flexion and extension motions of the hip, Mayo Clinic investigators concluded that: • Squeaking occurred when the film fluid between the two moving surfaces was disrupted. • Disruption could be caused by the presence of particles that originate from wear and tear, or from imperfect alignment or positioning of implant surfaces. • Squeaking occured especially quickly under highest pressure on the artificial joint. • Once squeaking started, it didnt stop — and was constant at all frequencies tested. According to Robert Trousdale, M.D., the lead Mayo investigator: Adding a small amount of lubricant solved the problem in the lab. Our research is helpful because it can be applied to devising a solution to the squeak problem. Most likely that will consist of improving the design of implants so they have less chance of material transfer and disruption, which appears to be an important aspect in the basis of the squeak. In addition to Dr. Trousdale, the Mayo research team included Drs. Kai-Nan An and Christophe Chevillotte.
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