Does fusion increase the incidence of adjacent segment disease in patients with symptomatic lumbar degenerative disk disease?

This is a retrospective cohort study. It was conducted to compare the incidence of adjacent segment disease (ASD) in patients who have undergone fusion for treatment of lumbar degenerative disk disease and patients who were treated conservatively to determine if fusion increases the risk of adjacent segment disease. Previous case series have indicated that fusion increases the risk of ASD. The eligible population included patients without previous spinal surgery who were evaluated for symptomatic lumbar degenerative disk disease. The study population underwent lumbar fusion with instrumentation. The control population consisted of patients with the same diagnosis who were managed conservatively. ASD was defined as new symptoms of radiculopathy, referable to a different anatomical level of the spine. There were 83 patients with a mean follow-up of 4.3 years including 42 males and 41 females. There were 24 patients who underwent fusion (“fusion”) and 59 patients who were managed nonoperatively (“nonsurgery”). A total of 22 patients reported new symptoms of radiculopathy after a mean 6.5 years. There was no statistically significant difference in the incidence of new radiculopathy between the groups (fusion 17% vs. nonsurgery 30%, P = 0.27). Six patients underwent surgery for symptoms different than their initial complaint after a mean disease-free interval of 7.5 years. There was no statistically significant difference in the incidence of additional surgery between the groups (fusion 4% vs. nonsurgery 8%, P = 0.67). There was no statistically significant difference in mean period before reoperation in patients who underwent fusion (7.8 years) vs. nonsurgery (7.5 years). In conclusion, among a population of patients with symptomatic lumbar degenerative disk disease, there was no difference in incidence of new spinal symptoms (according to a newly-created questionnaire to define ASD) or rates of operation in patients who underwent fusion compared to nonoperative treatment. These findings challenge the commonly held observation that adjacent segment disease is directly attributable to fusion. Further study is warranted to determine whether fusion increases the incidence of degeneration at adjacent spinal segments.