The effect of preoperative diagnosis on the incidence of adjacent segment disease after lumbar fusion

BACKGROUND: The aim of this study was to determine the incidence of adjacent segment disease (ASD) requiring reoperation after lumbar fusion and to compare survivorship of adjacent levels according to preoperative diagnosis. METHODS: Two hundred and seventy five patients who underwent instrumented posterolateral fusion of the lumbar spine without an interbody device were included. Patients were stratified by preoperative diagnoses (lumbar spinal stenosis, spondylolisthesis, or postlaminectomy revision) and were followed for an average time of 59 months. The incidence of ASD requiring reoperation was calculated via Kaplan-Meier survivorship analysis. A Cox-proportional hazards regression analysis was performed to identify the independent impact of preoperative diagnosis, age, sex, and number of segments fused on ASD development. RESULTS: A total of 59 (21.5%) patients required reoperation for ASD. Following Kaplan-Meier analysis, the predicted ASD-free survival was 79.7% (95% CI, 72.3-85.3) at 5 years and 53.4% (95% CI, 40.0-65.0) at 10 years. Moreover, the incidence was not significantly different between diagnostic subgroups by the log-rank test (P=0.144). Following risk factor analysis, the only significant factor associated with ASD was increasing age (RR 1.02; 95% CI, 1.00-1.05). Male sex, preoperative diagnosis, and the numbers of segments fused were not significantly associated with ASD. CONCLUSIONS: Few studies to date have specifically investigated the influence of pre-operative diagnosis on lumbar fusion outcomes. The incidence of ASD requiring reoperation was estimated at 20.3% and 45.7% at 5 and 10 years, respectively. In this study, the incidences of ASD based on preoperative diagnosis were not significantly different between groups; the only significant risk factor was increasing age.