PAPER 136: THE INCIDENCE OF ADJACENT SEGMENT DEGENERATION IN EXTENDED THORACOLUMBAR FUSIONS

Abstract

Purpose: Adjacent Segment Degeneration (ASD) can occur after spinal fusion, disc degeneration, spinal stenosis, deformity, spondylolisthesis and fracture. The incidence is unknown and its occurence difficult to predict. Further major surgery is required to correct the clinical problem that exists although not all cases of ASD are symptomatic. The primary purpose of this study was to identify the incidence of ASD after multilevel (> /= 3 level) thoracolumbar fusions for degenerative disorders at a minimum 5 year followup. Risk factors for ASD were to be determined.

Method: 405 spinal fusions of three levels or greater, performed between 1988 and 2001, minimum five year followup were assessed for ASD. Radiographic data was available from a prospective data bank. The radiological incidence of ASD was distinguished from those that were clinically significant as determined by Oswestry Disability Index, back and leg pain visual analog scales.

Results: The incidence of ASD after extended spinal fusions overall was 28%, based on radiological evaluation. There was an 18% incidence of clinically significant ASD. 10% of the entire group required surgery to address ASD. The incidence varied according to the location of the fusion, number of levels, age and pre-existing disc degeneration and/or deformity at the end vertebrae. Overall it was difficult to predict risk factors but trends were noted. Long fusion (> /= 3 levels) have a significantly high risk of ASD by five years after the index operation. Adjacent level degenerative disc disease and spinal stenosis were the most common type of ASD.

Conclusion: The incidence of ASD by five years post spine fusion of three or more levels is 28% in over 405 cases. 10% of these cases needed further surgery. ASD is a clinically significant entity that deserves further study to aid in its prevention.