Hip replacement surgeries are often a result of a variety of arthritis-related conditions or of a secondary condition developed from diabetes or long-term steroid use. As the baby-boomer generation approaches retirement, the number of cases involving total hip joint replacement is expected to rise significantly.
Stephen Boedo, associate professor of mechanical engineering, is working with a team from Cornell University to better meet the needs of this growing population through the development of a novel hip joint design that will more directly utilize the human gait cycle and reduce overall wear on the device. “Current designs involve a spherical ball and cup geometry composed of ceramic, metal, and plastic materials, and synovial fluid produced in a membrane surrounding the artificial joint provides lubrication,” Boedo says. “Unfortunately, this design tends to increase the potential for excessive wear of the articulating surfaces and can often require revision surgery seven to 10 years after replacement.”
Boedo’s design, developed in partnership with John Booker, professor of mechanical engineering at Cornell, utilizes ellipsoidal cup geometry and elastic spring elements. The ellipsoidal cup geometry distributes the synovial fluid pressure more evenly over the surface of the joint during the load-carrying (stance) phase of the gait cycle. The spring elements separate ball and cup surfaces during the load-free (swing) phase of the gait cycle. Initial analysis indicates a substantial improvement in lubricant film thickness and reduction in lubricant film pressure, both of which are indicators of reduced wear. The team is now planning initial prototyping and has filed a provisional patent.
The research results were recently presented at the 2012 International Joint Tribology Conference sponsored by the American Society of Mechanical Engineers and the Society of Tribologists and Lubrication Engineers. “It is our hope this design will increase the longevity of artificial hips and improve the quality of life for individuals with joint-related illnesses,” Boedo adds.