U.S. Attorney Christopher Christie is defending his decision to give special treatment to the first hip-and-knee implant manufacturer to cooperate in an investigation of an alleged industry practice of inducing doctors to use products by financial incentives.

For its cooperation, Christie’s office allowed Stryker Orthopedics Inc. of Mahwah, N.J., to sign a nonprosecution agreement. The four others signed deferred prosecution agreements, are paying a total of $310 million in fines and have agreed to abide by corporate integrity agreements for five years.