So-called "off-label" use of medical therapies is legal, but has triggered concerns because its risks and benefits are not well understood. What's more, the orthopedic products add more than $4,000 in hospital charges for the surgery, according to a new study published on Tuesday in Journal of the American Medical Association.

For the full study, see: bit.ly/MvXYT6

"It is expensive, we don't know if it's effective, and we don't know what the long-term implications are," said Dr. Emily Dodwell, a surgeon at the Hospital for Special Surgery in New York, who led the research.

Bone-growth proteins speed up bone formation and have been approved by the U.S. Food and Drug Administration for limited use in adults.

They have a troubled history.

Last year, a medical journal determined that doctors who were paid millions of dollars by Minneapolis-based Medtronic Inc had failed to report serious complications linked to the company's product Infuse, also known as bone morphogenetic protein-2 or BMP-2.

Those complications include increased cancer risk, sterility in men, infections, bone dissolution and worsened back and leg pain, among others.

While it's unclear whether children would experience similar side effects, a particular concern is how BMPs would interact with a still-growing skeleton, Dodwell told Reuters Health. Her study did not identify specific products.

There are also no good data on whether or not the products help youngsters, who are less likely to have healing problems than adults after spine surgeries, according to the new report.

At about 4,100 hospitals that are part of the national registry studied by the researchers, 9.2 percent of more than 8,000 spine fusions in people 18 years and younger involved BMPs.

"Most people would feel this is a high number," Dodwell noted, although she stopped short of saying BMP should never be used in minors.

In cases where BMP was used, patients' hospital bills amounted to $47,136 on average, compared to $43,126 when surgeons didn't use the product.

There was no difference in the number of complications seen during the hospital stay in the two groups, although Dodwell and her colleagues cautioned that long-term complications are the main concern. She said her team is currently analyzing data from another registry to see how kids fare after they leave the hospital.

The researchers also found that doctors more frequently used BMP in the Midwest, which is home to Medtronic. Medtronic officials could not be immediately reached for comment.

(Editing by Ivan Oransky, Michele Gershberg and Andrew Hay)

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