Long term outcome of adjacent levels of posterolateral lumbar fusion

Posterolateral lumbar fusion is commonly recognized to have a significant effect upon the more proximal unfused segments. Wether these effects are clinically significant remains unclear. Long term studies with standardized follow-up are scarce. The purpose of this study was to examine the long term roentgenographic and clinical effects of posterolateral fusion upon the 3 cephalad unfused segments. The levels below a floating fusion were also examined. The factors promoting the occurrence of degenerative changes on standard or dynamic x rays were also investigated with a multivariate analysis model. 102 patients who underwent a posterolateral fusion were retrospectively reviewed with an average follow-up of 8.9 years. 39 patients (group I) were fused for low back pain caused by isthmic lysis spondylolisthesis, 15 (group II) for degenerative disc disease and 48 (group III) in addition to a posterior decompression for a lumbar spinal stenosis. Pre and postoperative standard and dynamic roentgenograms were compared in order to study : evolution of the disc space height, modifications in the angular and antero-posterior mobility, modifications in the antero-posterior displacement of the vertebral bodies. Degenerative changes were frequent. 49 per cent of the patients demonstrated a severe disc space narrowing, 30 per cent developed a degenerative spondylolisthesis, 32 per cent an angular hypermobility and 35 per cent an antero-posterior hypermobility. Only one factor was found to increase significantly the occurrence of degenerative changes: the indication of lumbar fusion. Degenerative changes were significantly more frequent in group III's patients. However, no significant correlation was found between the roentgenographic findings and the final functional results and only 8 patients required a new surgery. These results may suggest that posterolateral fusion accelerates the development of degenerative changes in adjacent discs if the fusion is performed on a degenerative spine.