WPI Research is the research magazine of Worcester Polytechnic Institute. It contains news and features about graduate research in the arts and sciences, business, and engineering, along with notes about new grants, books, and faculty achievements.
Issue link: http://wpiresearch.epubxp.com/i/502587
notebook DEP G O WHICH ORGA IZATIO does the counting, somewhere between 300,000 and 1.2 million Americans have suf- fered spinal-cord injuries resulting in paralysis. It's long been known that such injuries leave people vulnerable to the loss of mass and strength in the leg bones. But a new study by a WPI research team has shown that bones lose mechanical strength faster and more signifcantly than previously believed, putting them at greater risk for fractures from minor stresses. "It's not just a question of how much bone mass is lost, but where that loss is occurring," notes Karen Troy, PhD, assistant professor of biomedical engineering at WPI and senior author on the paper. "We found that bone loss occurred sooner in mechanically important areas and signifcantly increased the risk of fracture." The study, "Reduction in Proximal Femoral Strength in Patients with Acute Spinal Cord Injury," was pub- lished as the featured cover story in the September 2014 issue of the Journal of Bone and Mineral Research. "Our results suggest that physicians need to begin therapies for spinal cord injur y patients sooner to maintain bone mass and strength," Troy says. "While our focus was patients with paralysis, the study also provides guidance to physicians treating patients with osteoporosis, who should now think beyond the standard bone density test when they assess the risks of hip and other fractures." Healthy bones continually adapt to mechanical forces by forming new bone and resorbing existing bone. But when bones stop car- rying loads, they begin to lose mass and weaken. In patients with spinal cord injuries, even minor impacts or stresses can result in fractures. "Their bones are so fragile that just the act of rolling over in bed can snap their knee or leg," Troy says. 8 > wpi.edu/+research In the study, Troy and her co-authors, Brent Edwards at the University of Calgary and Thomas Schnitzer at Northwestern University, studied 13 spinal cord injury patients treated at the Rehabilitation Institute of Chicago. To document the change in bone mass over time, the team took CT scans and DXA bone mineral density scans of the patients' legs at regular intervals for about four months. They fed that data into sophisticated computer models that could predict how the amount and distribution of bone loss would affect the ability of the leg bones to stand up to mechanical loads and movements. They found that the patients lost 2 percent of their leg bone mass each month, but that was equivalent to nearly a 7 percent loss in leg bone strength. "In just three and a half months, reductions in strength for some patients were on the order of that predicted for lifetime declines owing to aging," the authors wrote. The study points to the need to begin therapies early to maintain bone mass and strength, Troy says, both to prevent injuries and to assure that patients remain eligible for treatments and technolo- gies that are currently in development. "In 10 or 15 years, with ad- vances in tissue regeneration to repair the spinal cord, and with exoskeleton assist devices, many of these people will have the opportunity to get back on their feet, if their bones are strong enough to carry the load. It's very diffcult to restore bone mass once it's lost, so the better approach is to prevent the loss in the frst place." Troy says the study also has implication for the 54 million people in the United States who have low bone density or osteoporosis. With the three-fold difference the researchers observed between bone mechanical strength and bone density, physicians may want to re- consider how they evaluate bone loss and fracture risk and how they treat patients. "Bone mineral density is important, but it doesn't tell the whole story," she says. > STEMMING BONE STRENGTH LOSS IN PARALYZED PATIENTS Low Elastic Modulus High > From left, a three-dimensional reconstruction of a femur compiled from CT scans, and 3-D and 2-D planer-cut views of a femur from Karen Troy's study of mechanical strength in leg bones of individuals with paralysis. The images show the spatial distribution of elastic moduli, or the bones' resistance to mechanical loads. Red areas are stiffer and blue areas are less stiff. Troy showed that the bones in paralyzed individuals lose mechanical strength faster than previously believed. The images were featured on the cover of the Journal of Bone Mineral Research.