Introduction: The characteristics of cervical spondylolisthesis are not currently fully understood, because of the shortage of reports covering the large population of patients with cervical spondylolisthesis. The purpose of this study was to elucidate the characteristics of cervical spondylolisthesis by examining a relatively large number of cases. Methods: We analyzed 101 cases with more than 2 mm of vertebral listhesis as determined from X-ray or computed tomography (CT) images among 731 patients who underwent surgery at a single institute. We considered the C2-7 angle, range of motion, and C2-7 sagittal vertical axis on lateral X-ray images. From sagittal CT images, classifications into five grades based on the slipped disc and adjacent caudal levels were made. We examined the orientation of facet joints at the slipped level using axial CT images. Results: Spondylolisthesis was recognized in 101 cases at 124 levels. Anterior and posterior spondylolisthesis were detected in 68 and 40 cases, respectively. Anterior spondylolisthesis developed predominantly at C3 or C4, usually at the level adjacent to the narrowed disc, or at C7, adjacent to the stiffened thoracic spine. The disc height was relatively preserved at the anterior slipped level. Posterior spondylolisthesis developed predominantly at the level of the significantly narrowed disc associated with advanced intervertebral osteoarthritis. At the segment with listhesis in the lower cervical spine, the direction of the facet joint in the axial plane tended to be posteromedial. Conclusions: Cervical degenerative spondylolisthesis was classified into two types. The first and more common listhesis occurred adjacent to stiffened levels, and anterior slippage was common in this type. The second and less common listhesis occurred within progressively degenerated segments, and posterior slippage was prominent. We have uniquely described the morphological changes in orientation of the cervical facet joints at the slipped level in the transverse plane.
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