A surgeon at Stanford University, in a study released Wednesday, suggests that one of Medtronic's best-selling spinal products poses a risk of male sterility. That finding is in stark contrast to earlier research by doctors paid by Medtronic, who found no connection between the product, Infuse, and a condition that causes sterility. 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, Eugene J. Carragee, MD, 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.