Originally Published MDDI October 2005
Spine simulators developed at Purdue University (West Lafayette, IN) should help device companies design more-durable implants. Firms can use the hydraulic machines, which reproduce the motions and stresses put on the spine, to find design flaws.
Implants are attached to a cadaver and are then tested in the simulators. This could potentially solve problems before the devices reach the market.
Another potential application is to use the machines as a training tool for clinicians. Such a tool would allow them to observe device function and the effect of small changes in implantation methods. Test results could shed light on long-term implant performance.
Physicians can also use the simulators to practice procedures. “So far, that seems to be one of the best ways to use the devices,” says Eric Nauman, assistant professor of mechanical engineering at Purdue. “We can practice surgical techniques, test implants, and look at the effects of different loading conditions.”
Purdue graduate student Jeremy Wade works with the polyurethane spine model.
There are two types of simulators—one tests implants for the cervical spine and the other tests those for the lumbar region. Researchers are using software called a finite-element model to determine whether the simulators are working correctly. It provides data about the implant, including its strength.
In the cervical spine simulator, a switch from hydraulic actuators to ones driven by electricity should downsize the machine and make it run faster. It will take 3–5 months before this change is completed, according to Ben Hillberry, professor of biomedical and mechanical engineering at Purdue.
Hillberry designed the machines with the help of graduate students Beth Galle and Shreekant Gayakar. They got input from orthopedic surgeon John Gorup when designing the lumbar simulator.
The lumbar simulator is larger and runs slower than its cervical counterpart, but it is versatile. It can be converted into a knee simulator in about 30 minutes. Although that adaptability is on the back burner right now, it could come in handy in the future.
The next step is to start running a test for 10 million cycles, Hillberry says. Implants need to withstand 10 million cycles, which equals 10 years of life. This process will take about 4 months.
“Two cycles per second at 10 million cycles takes a considerable amount of time,” says Nauman. Since it takes so long to get data for a single implant, the researchers have a goal of setting up the machines to handle six stations. This would allow more implants to be tested at once.
Researchers are also adding muscle to a model, opening the door to applications that examine spinal disorders such as osteoporosis and scoliosis.
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