This study is being done to prospectively collect data on subjects having posterior cervical fusion surgery using the Medtronic Infinity system. Researchers plan to collect information from patients having this type of surgery in order to learn more about patient how patients do after the surgery, including the rate of bone healing following surgery. The goal is for 250 patients to take part in the study or for 500 screws to be used, whichever comes first. Each patient will need a varying amount of screws to be used during their surgery. Because we are measuring the accuracy of each individual screw and the surgeon will likely use multiple screws during each surgery, it is likely that the study will reach its goal of 500 screws before 250 patients are enrolled in the study.