New Way to Grow Bone Gets Thumbs Up

May 16, 2001 -- It's not quite The Bionic Man; it's even better! For the first time ever, scientists have used a technique called tissue engineering to create new, living bone in a man who lost half his thumb in an accident. And there is no chance that his body will reject the new tissue, a common concern in transplants from a donor, because it grew from the man's own cells.

"We have essentially created new bone in this patient by combining his own cells, synthetic scaffolding material, and a naturally derived polysaccharide or sugar," says researcher Lawrence J. Bonassar, PhD, assistant professor at University of Massachusetts Medical School's Center for Tissue Engineering in Worcester.

In 1998, the 36-year-old man arrived at the emergency room with the entire top half of his left thumb gone, torn off at work by a machine.

"The plastic surgeon covered the top of his thumb with a [skin] graft from his stomach," says Bonassar. "This created an empty pocket where the thumb bone used to be."

Mature bones are covered with a layer of cells called the periosteum, explains Bonassar. "We knew that the periosteum contains immature cells with the potential to make bone," he says. In fact, this is how broken bones normally heal. "Periosteum cells migrate into the fracture and grow [into normal bone]."

So the team took a sample of the man's periosteum and placed it onto biodegradable scaffolding made of a synthetic material resembling coral. Not coincidentally, Bonassar tells WebMD, coral looks a lot like bone -- full of tiny holes, like a sponge. "We then placed the scaffolding seeded with the man's cells into the empty thumb pocket," he says.

As the cells continued to multiply, the new, growing bone maintained the shape of the supporting scaffold. Over time, the scaffold itself disintegrated. "That's one of the themes of tissue engineering," says Bonassar, "the scaffold degrades, and eventually you're left with just [human] tissue."

The man now has a partially functional digit where he'd had none, says Bonassar, and X-rays show it contains bone. The report is published in the May 17 issue of The New England Journal of Medicine.

In an editorial accompanying the study, Vincent R. Hentz, MD, and James Chang, MD, of Stanford University School of Medicine, argue that the man's new thumb is not as strong or as stable as it could be. In fact, they argue, he may have had better results if doctors had grafted some of his own existing bone to stump of this thumb. Yet, they write, in time, improved methods and materials are likely to bring better results.

According to Bonassar, the technology has enormous potential. Beyond helping folks who lose toes and fingers to accidents or disease, "in the near future, you'll see more and more engineering of structural tissues like cartilage, tendons, and ligaments," he says, allowing for reconstruction of noses and ears.

"Shape is very important in facial reconstruction, and we have the ability to control shape very well [with the scaffolding]. Absolutely, within a few years we'll be able to fix a nose or an ear," he tells WebMD.

Some day, the process may reduce or even eliminate the need for organ donors. "You'll see [tissue-engineered] bladders, livers, and kidneys, spinal cord, and brain," Bonassar tells WebMD.

While some of these more dramatic applications have already shown great promise in animal models, human use remains years away. For now, the restored thumb bone is proof positive that tissue engineering can work, and work safely, in human beings.