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 natures 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.
Thats because natures design, though impressively rugged, does not last forever. With age, nearly everyones spinal discs degenerate to a degree, in some cases causing terrible pain. Lower-back pain was the worlds 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.
In late 2018, the Penn team published a promising study of what they hope is a better option: replacement discs made from a combination of synthetic materials and living cells.
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.
Its a living structure, Smith said.
Most of the study authors are affiliated with the Crescenz VA Medical Center in Philadelphia 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.
When a disc ruptures or collapses, pain can arise in several ways, though the cause is not always clear.
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 Penns Perelman School of Medicine. Some of the pain may be a kind of warning signal: the bodys attempt to limit motion so that an injured back can heal.
In some cases of disc rupture or herniation, back pain lasts for years. But in others, it goes away after a few months, though their MRIs may look similar to those patients who remain in great pain. And plenty of older people with degenerating discs never experience the pain at all.
I could have someone whos 60, and they have bone on bone, and they dont have any pain, Smith said.
(In still other cases, back pain is purely a muscular ailment, which may be alleviated with rest followed by exercise.)
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.
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.
