San Diego-based NuVasive, a manufacturer of products used in the surgical treatment of spine disorders, announced Wednesday that it has agreed to acquire Cervitech, a New Jersey-based firm developing a cervical disc replacement device. NuVasive said it will initially pay some $47 million for Cervitech, plus an additional $33 million contingent upon FDA approval of Cervitech's PCM cervical disc system. As much as half of the payment will be made in NuVasive stock, the San Diego-based company said. NuVasive added that Cervitech's PCM investigational device is currently undergoing a clinical trial in the United States that should be complete by the fourth quarter of this year.