(1) 48 patients with ante-position type instability (AP group), were followed-up for an average of 4.2 years (range: 8.7 to 1.2 years) to clarify the special features of the AP group.
(2) 6 patients were diagnosed as degenerative spondylolisthesis, with their anterior slip shown in all postures by motion X-ray.
In 42 patients (87.5%), the anterior slip was only recognized in the flexion position, thus many of the AP group have kept their situation unchanged.
(3) In all 6 degenerative spondylolisthesis patients, their lamina (Facet joints) in the A-P view of X-P were shown to be W, M or XM type. There were no X or U types.
(4) Comparing the changed and unchange group, we found the following resulls: The changed group had statishcally larger (more than 5 degrees) negative disc-angles in flexion (P<0.01), larger facer angles (P<0.05), smaller lordotic curves in their lumbar spine (P<0.01), bigger facet angles (P<0.05) than the unchanged group.
There were no significant differrences in age, range of motion, or lumbo-sacral angle between the two groups.