PATHOANATOMIC MECHANISMS OF DEGENERATIVE SPONDYLOLISTHESIS - A RADIOGRAPHIC STUDY

Study Design. A retrospective case-control study was performed using t he radiographs taken at the first hospital visit in two groups; in one group, spondylolisthesis developed after the first hospital visit, an d, in the other, spondylolisthesis had not developed over 10 years. Ob jectives. To determine possible radiographic differences between these two groups to clarify the pathoanatomic mechanisms of anterior slippi ng. Summary of Background Data. The etiology of degenerative spondylol isthesis, for example, underlying pathoanatomic mechanisms such as dys function 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 investigati ons. Methods. Sixty-nine patients with spondylolisthesis in whom degen erative spondylolisthesis developed after the first hospital visit and for whom radiographs taken before the slip were available were studie d retrospectively. In 63 patients slipping did not develop over 10 yea rs, with or without intervertebral instability; these patients were st udied as a control group. The radiographs taken before and after the o ccurrence of the slip in the patients with spondylolisthesis were exam ined and compared with those without spondylolisthesis. Dysfunction of the disc, horizontalization of the lamina: and the facets, and the sa gittal alignment of the facet joints were assessed in each group. Resu lts. Patients in whom anterior slipping developed had signs indicating that horizontalization of the lamina and the facets had occurred befo re the slip. However, the patients in whom spondylolisthesis did not d evelop had no horizontalization of the lamina and the facets at the fi rst hospital visit or during the follow-up period. There was no signif icant 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 p atients in whom slipping occurred did not demonstrate sagittal alignme nt. Conclusion. Horizontalization of the lamina and the facets is a pa thoanatomic risk factor that can predispose for the development of deg enerative spondylolisthesis. If dysfunction.of,the disc,occurs in addi tion to these conditions, spondylolisthesis may develop.