3. Subjects with cervical kyphosis > 5˚, a segmental kyphotic deformity defined as 3 or more disc-osteophytes that extend dorsal to a line drawn from the dorsal caudal point of C2 to the dorsal caudal point of C7, ossification of the posterior longitudinal ligament (OPLL), or developmental spinal canal narrowing (12mm) would be excluded from the study.