The relationship between isthmic and degenerative spondylolisthesis and the configuration of the lamina and facet joints.

Advanced degenerative change in the facet joints leads to displacement of the vertebral body, and the configuration of facet joints and lamina is closely related to the development of degenerative spondylolisthesis. For this study 103 patients and 25 controls were examined with respect to the configuration of the lamina, anteroposterior diameter of the vertebral canal, interarticular distance, interlaminar distance, disc degeneration, and degree of arthritic changes of facet joint, all as shown of plain radiography, and facet angle, interfacet distance, and contour of the canal side of the inferior articular process and lamina, as shown on computed axial tomography. The results of this study showed that those patients with a narrow facet angle were more likely to have developed degenerative spondylolisthesis. If the sum of both facet angles was less than 77.9 degree, the risk of development of degenerative spondylolisthesis was 2.5 times higher than if the sum was greater than 77.9 degree. Those with type N lamina, detected on plain radiographs, were especially likely to have developed degenerative spondylolisthesis. This suggested that degenerative spondylolisthesis may be due to the less effective check mechanism preventing a vertebra from slipping forward on the vertebra below. We recommend fusion of the degenerated spinal segments when operation is considered in cases of acute facet angle with symptoms.