A fix for back pain? Scientists test bio-synthetic discs in goats.

CHARLES FOX / Staff Photographer Of all the parts of the human body, the stubby little discs between the bones in the spine represent one of the more remarkable feats of nature’s design.

Consisting of tough, rubbery rings of collagen with jelly-like centers, they compress with every step we take. They twist. They flex. Over a lifetime of wear and tear, they replenish their supportive matrix of collagen despite having no internal blood supply.

“It is really a marvel of engineering,” said Robert L. Mauck, who as a biomedical engineer at the University of Pennsylvania, has the chops to say that. Penn scientists have come up with a synthetic disc to replace damaged discs in the spine, which so far they have tested in goats and rats. That’s because nature’s design, though impressively rugged, does not last forever. With age, nearly everyone’s spinal discs degenerate to a degree, in some cases causing terrible pain. Lower -back pain was the world’s leading cause of disability in 2017, according to the Institute for Health Metrics and Evaluation at the University of Washington. In severe cases, patients resort to having vertebrae fused together, but they lose flexibility and often are not satisfied with the result. One-third come back for repeat surgery.

So far, the researchers have implanted their discs only in rats and goats, but they appear to behave much like the real thing, said Penn Medicine orthopedic surgeon Harvey E. Smith, the clinical leader of the effort. This goat retained its normal range of motion after Penn surgeons implanted a replacement disc between two vertebrae in its neck. The results have impressed other researchers who are working on the same challenge, among them Lawrence J. Bonassar, a Cornell University biomedical engineering professor.

It has taken more than a dozen years for the Penn team to get to this point, and a lot of varied expertise. In addition to engineers and orthopedists, the group includes veterinarian Thomas P. Schaer , a research director at Penn’s New Bolton Center, who joins Smith in implanting the experimental discs in the necks of goats.

Most of the study authors also are affiliated with the Crescenz VA Medical Center in Philadelphia, such as biomedical engineer Sarah Gullbrand, the lead author of the study, and some of their funding came from the U.S. Department of Veterans Affairs. That is because members of the military suffer especially high rates of disc degeneration and back pain, whether from combat injury or operating large machinery, Mauck said.

Bus and truck drivers also may be at higher risk of disc degeneration, as are cigarette smokers — likely because smoking harms blood vessels, and therefore discs, among many other body parts.

A tough, rubbery disc is located between each pair of vertebrae in the spine, cushioning the joint and allowing it to move. Nearly everyone’s discs degenerate somewhat with age, in some cases causing terrible pain. University of Pennsylvania researchers are testing replacement discs in goats. They are made from biodegradable materials and living cells. Nearby nerves can be compressed, causing pain to shoot down the leg — a condition called sciatica. If the failed disc is in the neck, similar pain can travel down the arm.

Less clear is how disc failure causes pain in the back itself, said Smith, an associate professor at Penn’s Perelman School of Medicine. Some of the pain may be a kind of warning signal: the body’s attempt to limit motion so that an injured back can heal. Inflammatory chemicals and swelling can play a role.

For those who suffer disc-related pain, one option is fusion, in which the surgeon removes the damaged disc and inserts a piece of bone in between the vertebrae. That decompresses the nerves but the joint can no longer move, so there may be more stress on the vertebrae above and below it.

That is why the Penn team uses biodegradable materials to make its replacement discs: a sugar-like synthetic gel to mimic the collagen-based jelly inside a natural disc, and layers of a high-tech polymer to mimic the stiffer type of collagen that makes up the outer ring of a real disc. The polymer is made through a process called electrospinning, using electricity to draw out threads of fiber from a nozzle.

“Back pain is sort of like the common cold,” Smith said. “Everyone has it. We know how to treat it. But we’re still trying to get down to the root causes. In terms of the fundamental science, we have a long way to go."

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