Infuse is a bioengineered bone growth protein that has been widely used in spinal fusion procedures since 2002. The Infuse label notes the sterility-related complication as a possible side effect, but the Medtronic-sponsored researchers in published reports attributed that complication to surgical technique, not the product itself.

The Stanford surgeon, Dr. Eugene J. Carragee, found that men treated with Infuse developed a condition that causes temporary or permanent sterility at a far higher rate than men who received a bone graft, another material that is used to fuse spinal vertebrae. He urged doctors to counsel men about Infuse’s risks. The study was posted Wednesday on the Web site of The Spine Journal, which he edits.

“It is important that men who are considering having children have the opportunity to weigh the risks of the various available procedures,” said Dr. Carragee, who based his study on 240 patients he treated several years ago with Infuse or a bone graft.

The type of spinal fusion at issue is known as an anterior lumbar fusion, a procedure performed on about 80,000 patients a year in this country. Infuse is used in about half of those procedures, and men make up about half of the patients who undergo spinal fusions. The sterility complication at issue in Dr. Carragee’s study affects only men, not women.

Among the 69 patients treated by Dr. Carragee who received Infuse, five men developed the complication related to sterility, in contrast to one patient among the 174 men who received a bone graft. The condition resolved itself in half of those six patients.

Two surgeons who were involved in the original Infuse trial defended their findings in statements, saying that not enough men had experienced sterility-related complications in their study to statistically link the problem to Infuse. The surgeons, Dr. J. Kenneth Burkus and Dr. Thomas A. Zdeblick, noted the complication in a medical journal article published soon after Infuse was approved by the Food and Drug Administration in 2002, but they divided those patients by the surgical technique used, not by whether or not the men had received Infuse.

In his Web article, Dr. Carragee questioned why the researchers had not broken out the patients in their study between those who had received Infuse and those who had not, a method that he said was a standard way to present clinical trial results.

In an e-mail, Dr. Zdeblick said Dr. Carragee’s study was of limited value because it reflected the results of a retrospective look at patients rather than a clinical trial. Such reports “are notorious for being misleading,” he wrote.

The new study is likely to intensify a debate over whether industry-financed researchers present study findings in ways that favor the interests of corporate sponsors. Dr. Burkus, who practices in Columbus, Ga., and Dr. Zdeblick, a professor at the University of Wisconsin, have each received millions of dollars from Medtronic in consulting fees or royalty payments.

Both men have adamantly insisted that those financial relationships have not affected their scientific judgment.

Nevertheless, in a commentary accompanying the new study, Dr. James D. Kang of the University of Pittsburgh wrote that industry support was one way to explain the different conclusions reached by Dr. Carragee and the Medtronic-sponsored researchers.

“There does not seem to be any rational explanation for these observational differences,” Dr. Kang wrote.

Dr. Dan M. Spengler, a professor and former chairman of orthopedic surgery at Vanderbilt University, who was not involved with the study, said it added to growing evidence about various risks from Infuse. “It’s just startling to me,” he said.

Marybeth Thorsgaard, a spokeswoman for Medtronic, based in Minneapolis, said the company believed that it had provided the F.D.A. and doctors with all available medical information about Infuse. Analysts have estimated that sales of Infuse reached about $900 million in Medtronic’s most recent fiscal year; overall company sales hit $16 billion during that period.

“You have to consider the totality of the data that has been presented, not how one study was reported,” said Ms. Thorsgaard.

Dr. Carragee’s report is not the first time doctors have challenged how Medtronic-sponsored researchers characterized the risks of Infuse in medical articles.

Since 2006, an orthopedic surgeon in Croatia, Dr. Tomislav Smoljanovic, has written more than 35 letters to medical journals questioning the claims. In their 2002 report, Dr. Burkus and Dr. Zdeblick reported that a major clinical study involving Infuse had found no adverse effects with the product, including the sterility-related complication.

Among other things, Dr. Smoljanovic and colleagues pointed out in letters that the Medtronic-sponsored researchers, while identifying that six men in their study had developed the sterility-related complication, had not identified how many of those men had received Infuse as opposed to a bone graft.

Last year, Dr. Burkus and his colleagues publicly disclosed in response to the Croatian physicians’ letters that five of the six men affected in their study had received Infuse. However, they have insisted that the figure was not statistically significant to link the problem with Infuse.

Dr. Carragee, the Stanford surgeon, said his Infuse study was prompted by a complaint he received from Dr. Smoljanovic about an Infuse-related article in The Spine Journal.

Dr. Carragee said he and his colleagues had posted their study online, ahead of the publication’s print edition, because of the public health implications of the findings. He said that forthcoming edition of The Spine Journal would be dedicated to complications involving bioengineered bone growth products like Infuse.

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