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The configuratory variation of laminas and facet joints was discussed with reference to development of degenerative spondyiolisthesis and its clinical symptoms. The authors have classified the configuration of laminas in the lower lumbar spine into three different types, (Wl, W2, and N), based on the two characteristic features of the lamina: 1) whether or not the inferior articular processes are wider than the waist part of the lamina, and 2) whether or not the facet joint spaces can be recognized on plain anteroposterior (AP) radiographs. Types W1 and W2 laminas have the laterally prominent inferior articular processes, but the facet joint spaces are not visible on AP view in Type W1. Type N lamina has narrow inferior articular processes and its facet joint spaces can be recognized on AP view. Computed tomography (CT) scanning revealed that the direction of facet joints of Types W2 and N laminas was more sagittal than that of Type W1, and that all of Type N laminas with the narrow inferior articular processes have a sagittal facet. Type N lamina was rarely seen in the 257 controls, but was quite frequent in degenerative spondyiolisthesis, 3.5% and 45.8%, respectively. Patients with Type N laminas were likely to show more severe clinical symptoms such as difficulty walking and neurologic deficits. The reasons why patients with Type N laminas are involved with symptoms of spinal stenosis have been disclosed by studies of plain radiographs and CT views as follows: the spinal canal has been encroached on, becoming a deformed triangle or trefoil with narrow lateral recesses, which might have been caused by a significantly greater slip, and the convex canal side of the inferior articular processes associated with hypertrophic osteoarthritis of the facet joints.