Last month, Senate finance committee chairman Max Baucus (D-Mont.) launched an investigation into Medtronic over its walkout on contracts with a group purchasing organization.

Now, he's looking into the Minneapolis-based device giant again.

A Senate committee led by Baucus is investigating whether doctors with financial links to Medtronic were aware of complications with a bone-growth spinal product when they wrote about it in articles published in peer-reviewed journals.

Baucus and senior committee member Chuck Grassley (R-Iowa) said Wednesday they sent a letter to the company requesting documents related to the bone-growth product, called Infuse.

The senators said their investigation was prompted by newspaper reports that argued studies conducted by doctors with financial ties to Medtronic either downplayed or didn't report side effects later discovered in research led by doctors without links to the company.

"These reports that doctors conducting medical trials while on Medtronic's payroll may have hidden serious side effects for patients are deeply troubling," Baucus said in a statement.

A 2010 Journal Sentinel report said that a 2004 study, funded by Medtronic, found three-quarters of bone morphogenetic protein 2 patients experienced ectopic bone growth, where the bone grows outside of the fusion area, the senators said. The authors, with financial ties to Medtronic, said the growth "did not appear to have an ill effect on the patients."

However, an independent study, in 2008, found five patients with ectopic bone formation had suffered neurological impairment.

Also, a recent study found that men receiving Infuse suffered temporary or permanent sterility at higher rates than men getting a bone graft, according to the New York Times - a fact not reported in the original Medtronic-funded study, the senators said.

The senators also said reports have surfaced of a link between the product and potentially fatal swelling of the neck, severe leg pain and even cancer.

The senators requested Medtronic give a detailed list of payments to clinical investigators and communications with medical journal editors and the Food and Drug Administration about the product. The senators want the files no later than July 11.

In a statement sent to ABC News, Medtronic said it would respond to the senators' requests.

The company also said the sterility, neck swelling and ectopic bone formation risks mentioned in the senators' letter were already listed on the drug's FDA warning label. The company also said in 44 clinical trials, no statistically significant differences in cancer risk emerged for patients using Infuse.

Medtronic also said it provided all adverse event data to the FDA, regardless of financial relationships with investigators.

Infuse was approved by the FDA in 2002.

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