Surgeons have used stem cells (search) from fat to help repair skull damage in a 7-year-old girl in Germany, in what's apparently the first time such fat-derived cells have been exploited to grow bone in a human.

The girl had been injured two years before in a fall, which destroyed several areas of her skull totaling nearly 19 square inches, the German researchers reported.

Other surgeons had failed to correct the defects, and the girl wore a protective helmet. Her brain could sometimes be seen pulsating through the missing areas of her skull.

But several weeks after the stem-cell surgery, she was able to leave her helmet behind, the researchers report in the December issue of the Journal of Cranio-Maxillofacial Surgery. The skull is now smooth to the touch, the missing parts replaced by thin but solid bone, said Dr. Hans-Peter Howaldt (search) of the Justus-Liebig-University Medical School in Giessen, Germany. The child was not identified.

Howaldt, who performed the surgery last year, said the damage was too extensive to be repaired with bone grafts from her body. He said the hope was that if bits of the child's bone were mixed with stem cells, the cells would turn into bone-building cells that would create additional bone.

That appears to have happened, Howaldt said in a telephone interview Thursday.

"I cannot prove that our success comes from the stem cells alone," he said, "but the combination of the two things simply worked."

In August, other German doctors reported growing a jaw bone in a man's back muscle and transplanting it to his mouth to fill a gap left by cancer surgery. The researchers used bone marrow, which also contains stem cells, to help grow the bone. But it's not clear whether the stem cells were responsible for the bone growth.

So Roy C. Ogle of the University of Virginia, an expert in skull reconstructive surgery who has been studying bone regeneration from fat-derived cells, said he considered the new report to be the first indicating that any kind of stem cell had been used to grow bone in a human.

"It is a very big deal," said Ogle, who called the study a landmark.

He agreed that the study didn't prove that stem cells provided the new bone. But it also indicates that the implanted cells did no harm, which has been a concern with using stem cells in people, he said.

Ogle said many surgeons would have augmented the child's bone with a mineral paste or collagen instead of stem cells. Howaldt said he believes it's better to use the body's own tissue.

Howaldt and his colleagues treated the skull in the same operation that recovered bone from the girl's pelvis and about 1.5 ounces of fat tissue from her buttocks. The bone was milled into chips about one-tenth of an inch long and placed in the missing areas of the skull. Then surgeons added the stem cells to the bone chips. The cells had been extracted from the girl's fat in a laboratory while surgeons prepared the girl's skull.

Howaldt said the bone chips appeared to instruct the stem cells to make more bone. While the new bone should grow as the child grows, she's old enough that her skull won't grow much more anyway, he said.