Improving hip replacements

Mar 24, 2006

Kettering researchers offer real insight into component wear to help extend the life of hip replacements.

A research project conducted by Kettering University in partnership with McLaren Hospital in Flint and William Beaumont Hospital in Royal Oak, Mich., examines how real human behaviors impact total hip replacement components. The results of this project could help component manufacturers produce materials that last longer, fit more aptly into the human body and provide greater movement for patients.

Some people walk with bowed legs. Others walk with a hunch, as if they're carrying a weight on their back. And some walk with a noticeable limp, perhaps the result from years of playing sport or working a job that exerts constant pressure on certain joints such as the hip.

Over time, those with discomfort in their hip region may undergo hip replacement surgery, a prospect that for years would cause many to grown in dismay. After all, if one had a hip replacement before 1990, they could expect the hip materials in their body to last perhaps 10, maybe 15 years at best.

But with increased research into component wear and material production, this period of time has improved considerably over the last 10 years, and hope for a longer period of time under which hip replacement components could last might be on the horizon.

Since January 2005, Kettering Graduate Student Assistant Jake Short '06 of Montrose, Mich., Dr. Trevor Harding, associate professor of Manufacturing and Industrial Engineering at Kettering, and doctors from McLaren and William Beaumont Hospital, have worked on a project that measures wear generated by transitioning between different human behaviors on total hip replacement implants.

The project, funded through a grant from The McLaren Foundation and overseen by Harding, debunks previous hip replacement component research, which relied on tests conducted using unrealistic representations of total hip arthroplasty patient behaviors.

The ultimate goal of this project is to show the extent to which real patients with hip implants live with the replacement parts, and how their everyday activities-walking, biking, climbing stairs and resting-wear these materials. The results of this project could help manufacturers better understand how actual human behavior impacts hip components.

Unfortunately, many people don't have a full understanding of what a hip replacement means. Based on research by the National Institute of Arthritis and Musculoskeletal and Skin Disease (an arm of the National Institute of Health), people typically require hip replacement surgery because the joint wears down due to a number of issues, such as osteoarthritis, rheumatoid arthritis, bone tumors and avascular necrosis (loss of bone caused by inefficient supply of blood). In some cases, severe trauma to the hip area and infrastructure from, say, a devastating hip check during a hockey game, can also cause deterioration over time.

This new project will employ Kettering's 12-Station Hip Simulator manufactured by MTS Inc. The device helps researchers study the articulation, or movement and operation, of the hip components using the simulator to replicate walking motions and other common activities. During tests, researchers manipulate loadings on the hip joint using an intricate computer-controlled hydraulic system.

Raj Israel, director of the Implant Retention Laboratory at William Beaumont Hospital, provides data to Shorez and Harding on the wear of actual hip replacements removed from patients. Researchers then evaluate the data in terms of actual wear patterns in comparison to standardized tests that use continuous loads under laboratory-controlled test environments and those created by the researchers that better represent actual human behavior.

"The current testing standards do not seem to correspond to the actual wear of components removed from patients," Israel explained, adding that this research project could in essence "help manufacturers of these components to better help patients with materials that wear more efficiently in the human body."

Dr. Otto Wickstrom, an orthopedic surgical resident at McLaren who provides general knowledge on the function of hips for this project, echoed Israel's comments. "This could lead to the development of a new standard for how wear in hip components is tested," he said. He also added that this is a different sort of project for him, because they are dealing with materials that were used by real patients.

One important aspect of this project is the ability to generate computer models to predict "wear damage produced by real patients," Harding said. Jake Shorez, who works directly with Wickstrom and Israel on this project, will be able to take data collected from gait analysis, input it into the new controller provided by MTS Inc., and model different human activities, which he can then simulate in the 12-Station Hip Simulator.

The results from this modeling and simulation exercise will hopefully yield information about how real human activities wear hip replacement components to give researchers, doctors and manufacturers a better idea of material integrity under actual conditions.

Shorez, who graduated from Kettering in 2005 with a BS/MS degree in Mechanical Engineering, believes this project is an exceptional compliment to his career. "I like that this project can help people in a direct way," he said. "Some day I would like to continue working in this area and perhaps find a position where I can work with manufacturers of implants to make the parts better," he added.

Harding feels that involving Shorez in this research partnership between the two hospitals and University represents an example of what Kettering students and graduates can accomplish on a professional level. "Jake represents what is best about our students at Kettering," he said. "He is self-motivated, professional and naturally inquisitive about technology and its application to real-world problems. We're fortunate to have such a terrific student working with us on this project and I know he will benefit tremendously from his interactions with engineers, scientists and medical personnel," Harding added.

He also said that Dr. Patrick Atkinson '91, associate professor of Mechanical Engineering at Kettering, adjunct assistant professor of Surgery, Michigan State University, and director of Orthopedic Research at McLaren Regional Medical Center, helped establish this project through his ongoing work with McLaren.

To learn more about this project, contact Dr. Trevor Harding at (810) 762-9811.

Written by Gary J. Erwin