Study design: A retrospective case-control study was performed using the radiographs taken at the first hospital visit in two groups; in one group, spondylolisthesis developed after the first hospital visit, and, in the other, spondylolisthesis had not developed over 10 years.

Objectives: To determine possible radiographic differences between these two groups to clarify the pathoanatomic mechanisms of anterior slipping.

Summary of background data: The etiology of degenerative spondylolisthesis, for example, underlying pathoanatomic mechanisms such as dysfunction of the disc or horizontalization of the lamina and the facets, has been difficult to resolve, because radiographs taken before the occurrence of the slip have not been available in previous investigations.

Methods: Sixty-nine patients with spondylolisthesis in whom degenerative spondylolisthesis developed after the first hospital visit and for whom radiographs taken before the slip were available were studied retrospectively. In 63 patients slipping did not develop over 10 years, with or without intervertebral instability; these patients were studied as a control group. The radiographs taken before and after the occurrence of the slip in the patients with spondylolisthesis were examined and compared with those without spondylolisthesis. Dysfunction of the disc, horizontalization of the lamina and the facets, and the sagittal alignment of the facet joints were assessed in each group.

Results: Patients in whom anterior slipping developed had signs indicating that horizontalization of the lamina and the facets had occurred before the slip. However, the patients in whom spondylolisthesis did not develop had no horizontalization of the lamina and the facets at the first hospital visit or during the follow-up period. There was no significant difference in dysfunction of the disc between the cases with and without spondylolisthesis. Sagittal alignment of the facet joints was seen more frequently in the patients in whom slipping occurred than in patients with no spondylolisthesis, but approximately 40% of the patients in whom slipping occurred did not demonstrate sagittal alignment.

Conclusion: Horizontalization of the lamina and the facets is a pathoanatomic risk factor that can predispose for the development of degenerative spondylolisthesis. If dysfunction of the disc occurs in addition to these conditions, spondylolisthesis may develop.