For the first time, U.S. regulators have cleared Medtronic’s controversial Infuse Bone Graft biologic product for lower-back surgery for use with plastic — rather than titanium — spinal components.

Doctors have long legally used Infuse on their patients in ways not approved by U.S. regulators. The Minnesota-run device company studied the published reports of those experiments and, based on the results, convinced the Food and Drug Administration to approve three new Infuse uses as safe, a company spokesman said Monday.

Infuse’s active ingredient is a synthetic human protein called rhBMP-2 that causes bones to grow together after surgery. Previously the bone-forming biologic was only approved for spinal-fusion surgery if it was placed inside a hollow titanium “cage” in the spine bone; the new approval allows Medtronic to market Infuse inside of implants made of PEEK, a common plastic used in medical devices.

Medtronic said in a news release that the FDA clearance gives doctors three more FDA-approved procedures — for surgery from a frontal approach using a PEEK implant to fuse two of five bones in the lower back; and two other fusion procedures involving the same bones and PEEK implants, but where the doctor uses a surgical approach from the side of the body.

Infuse has never been approved in the U.S. for spine surgeries that approach from the back, and the FDA has said rhBMP-2 may cause life-threatening complications if used to fuse bones in the neck. In January the FDA advised doctors to avoid using rhBMP-2 in patients under 18 because their bones may still be growing.

Used in more than 1 million people worldwide since 2002, Infuse is Medtronic’s largest product liability headache, accounting for more than 6,000 actual and threatened personal-injury lawsuits. As of Dec. 1, Medtronic reached agreements to settle about 3,900 of the cases for an undisclosed sum, according to securities filings published Monday.

The company continues to cooperate with ongoing investigations into the sales and marketing of Infuse by attorneys general in five states, the Monday filing with the Securities and Exchange Commission said. (Minnesota is not among the states investigating.)

In a Dec. 3 quarterly earnings report, Medtronic Chief Financial Officer Gary Ellis said rhBMP-2 is expected to be off the market in Europe until next summer — an unexpected development that will reduce international Infuse revenue by $7 million per quarter.

European sales stopped in October after inspectors from Dutch and Spanish authorities toured the factory in New Jersey where an outside contractor makes the collagen sponge that soaks up the rhBMP-2 solution inside the cage. The European inspectors found the contractor lacked adequate measures to prevent “particle contamination” of the sponges for Infuse, which is called “Inductos” in Europe.

Medtronic officials said the finding turned up in a routine audit and the issue has not caused any patient-safety problems.

The changes do not affect availability of Infuse collage sponges in the U.S., which are manufactured in Puerto Rico, the company spokesman said.