Recently, the Food and Drug Administration turned down the company’s application to sell a new spinal fusion device that is essentially a high-strength version of an approved one called Infuse. An agency review of clinical studies raised questions about a higher rate of cancers in patients treated with the new product, which is called Amplify, compared with those who did not get it.

Meanwhile, a long-running investigation by the Justice Department into the marketing of Infuse is apparently widening. In recent years, a number of physicians were contacted by prosecutors in connection with that inquiry, but just a few weeks ago, another doctor said he had also been contacted by Justice Department officials. He asked not to be identified because the inquiry is under way.

Prosecutors have also sought records from United States Army researchers involved in studies of Infuse, a bioengineered bone growth product that has also been used to treat severely wounded American soldiers, according to people who have been contacted as part of the inquiry.

Medtronic has said it plans to discuss the rejection of Amplify with regulators to try to allay their concerns, and the company has not been charged with any wrongdoing in the criminal inquiry. But the developments could pose significant future problems for Medtronic, a medical device giant whose other products include heart pacemakers and defibrillators.

A Wall Street analyst, Larry Biegelsen of Wells Fargo Securities, said Infuse accounts for the vast majority of Medtronic’s sales of biologic products, which he projected would reach $897 million in the company’s current fiscal year.

Mr. Biegelsen said the continuing federal investigation of Infuse, along with the F.D.A.’s rejection of Amplify, could lead to a slowdown of Infuse sales over the next year. He estimated that off-label use by doctors of the bone-growth protein made up 70 to 80 percent of Infuse sales.

The extent of the federal criminal inquiry involving Infuse is not clear. But the doctor who was recently contacted by Justice Department officials also said that it was his understanding that prosecutors had contacted other physicians in recent months.

One military surgeon testified before a federal grand jury in Boston investigating the Infuse issue about a year ago, said people with knowledge of the inquiry who also requested anonymity because it was continuing.

Army officials have also provided the Justice Department with the results of a military investigation into the experimental use of Infuse on dozens of soldiers at Walter Reed Army Medical Center in Washington, said Col. Norvell V. Coots, commander of the Walter Reed Health Care System. The Army’s 2008 report on that investigation found that a former military doctor, Dr. Timothy R. Kuklo, had overstated Infuse’s benefit in a medical journal study that examined its use in the treatment of solders whose shin bones had been severely shattered by explosive devices in Iraq.

Dr. Kuklo, who became a Medtronic consultant, also forged the signatures of that study’s co-authors in a journal submittal, the Army said. Medtronic later broke its ties to him, and the medical journal that published the article retracted it.

Medtronic has previously disclosed both the existence of a federal inquiry into its marketing of Infuse as well as the Justice Department’s interest into research it underwrote at Walter Reed.

In response to an inquiry from The New York Times, the company released a statement noting its previous disclosures. It declined to say whether federal officials were examining specific issues like company-sponsored research.

“Medtronic does not comment on what precise topics the government may or may not be examining at any point in the investigation,” the company said.

Henry J. Dane, who represented Dr. Kuklo in the Walter Reed investigation, said the Justice Department had subpoenaed the doctor’s records. Mr. Dane said he understood that prosecutors had also sought records from academic researchers and doctors outside the military who worked on other studies about Infuse that had been financed by Medtronic.

“He’s far from the only one,” to get a subpoena, said Mr. Dane, referring to Dr. Kuklo.

Mr. Dane said that a lawyer in Boston, Thomas C. Frongillo, has represented Dr. Kuklo and other physicians contacted by the Justice Department in the Infuse investigation. Reached by telephone, Mr. Frongillo declined comment. Several academic researchers involved in Medtronic-financed studies about Infuse did not respond to inquiries or declined to comment.

A spokeswoman for the United States attorney’s office in Boston, Christina DiIorio-Sterling, cited Justice Department policy in declining to confirm or deny the existence of an investigation.

In 2002, the Food and Drug Administration approved the use of Infuse for a certain type of spinal fusion procedure, in which problem spinal vertebrae are joined in an effort to stop severe back pain. Doctors are free to use an approved product in any way they choose, and many surgeons began using Infuse for other types of spinal fusion operations.

Some of the doctors who performed research studies into such so-called off-label uses of Infuse received millions of dollars in consulting fees from Medtronic, Congressional investigations have found.

In 2008, the F.D.A. issued a warning about the use of bone-growth proteins like Infuse in one off-label fusion procedure used to treat neck pain, citing reports of life-threatening injuries.

Article source: http://feeds.nytimes.com/click.phdo?i=37afb8e7001c28a201826e18162dc225