LONG-TERM OUTCOME OF ADJACENT LEVELS OF P OSTEROLATERAL LUMBAR FUSION

Posterolateral lumbar fusion is commonly recognized to have a signific ant effect upon the more proximal unfused segments. Wether these effec ts are clinically significant remains unclear. Long term studies with standardized follow-up are scarce. The purpose of this study was to ex amine the long term roentgenographic and clinical effects of posterola teral fusion upon the 3 cephalad unfused segments. The levels below a floating fusion were also examined. The factors promoting the occurren ce of degenerative changes on standard or dynamic x rays were also inv estigated with a multivariate analysis model. 102 patients who underwe nt a posterolateral fusion were retrospectively reviewed with an avera ge follow-up of 8.9 years. 39 patients (group I) were fused for low ba ck pain caused by isthmic lysis spondylolisthesis, 15 (group II) for d egenerative disc disease and 48 (group III) in addition to a posterior decompression for a lumbar spinal stenosis. Pre and postoperative sta ndard and dynamic roentgenograms were compared in order to study : evo lution of the disc space height, modifications in the angular and ante ro-posterior mobility, modifications in the antero-posterior displacem ent of the vertebral bodies. Degenerative changes were frequent. 49 pe r cent of the patients demonstrated a severe disc space narrowing, 30 per cent developed a degenerative spondylolisthesis, 32 per cent an an gular 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 c hanges were significantly more frequent in group III's patients. Howev er, 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 a ccelerates the development of degenerative changes in adjacent discs i f the fusion is performed on a degenerative spine.