INCIDENCE OF ADJACENT SEGMENT DEGENERATION AFTER EXTENDED THORACOLUMBAR SPINAL FUSION

Abstract

Purpose: Adjacent Segment Degeneration (ASD) can occur after spinal fusion. Disc degeneration, spinal stenosis, deformity, spondylolisthesis and fracture are observed. The incidence is unknown and its occurrance 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) thoracolumbar fusions for degenerative disorders. Risk factors for ASD were to be determined.

Methods: Over 400 spinal fusions of 3 levels or greater, minimum 5 year follow-up were assessed for ASD. Radiographic data were available from a prospective data bank. The radiological incidence of ASD was distinguished from those that were clinically significant as determined by Oswestry, back and leg pain scores. |Personal and telephone interviews were conducted along with most recent plain xrays. Data was analyzed (ANOVA) from a single surgeon’s practice. Radiographic assessment was performed by the author with radiologist’s opinions available.

Results: The incidence of ASD after extended spinal fusions overall was 20%. Clinically significant ASD requiring further surgery was 12%. The incidence varied according to location of the fusion, number of levels, age and preexisting disc degeneration and or deformity at the end vertebrae. Overall it was difficult to predict risk factors but trends were noted. Long fusions(greater than or equal to 3 levels) has a significantly high risk of ASD by 5 yrs after the index operation.

Conclusions: The incidence of ASD by 5 years post spine fusion of 3 or more levels is 20% in over 400 cases.12% of these index cases needed further surgery. ASD is a clinically significant entity that deserves study to aid in its prevention.