Adjacent Segment Degeneration Versus Disease After Lumbar Spine Fusion for Degenerative Pathology: A Systematic Review With Meta-Analysis of the Literature.

Study Design: A systematic review.
Objective: The purpose of this study was to review the published literature to estimate rates and identify risk factors for adjacent segment degeneration (ASDeg) and adjacent segment disease (ASDis) after lumbar fusion.
Summary of Background Data: Arthrodesis remains a common intervention for the surgical treatment of degenerative spinal disease. Clinical studies have demonstrated variability in the rates of adjacent segment pathology after lumbar fusion.
Methods: This study was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Symptoms of ASDis were distinguished and defined by the need for a revision surgery procedure to address adjacent level pathology. We searched MEDLINE, EMBASE, Cochrane Library, and CINAHL databases. Extracted data included average patient age, average time to follow-up, type of intervention, potential risk factors, and ASDeg and ASDis incidence. Funnel and forest plots were used to describe heterogeneity and meta-regression to estimate pooled incidence of ASDeg and ASDis.
Results: A total of 31 articles with 4206 patients were included for analysis. Combining all extractable data, the overall pooled incidence of ASDeg was 5.9% per year (95% CI, 4.8%, 7.2%), and ASDis was 1.8% (95% CI, 1.3%, 2.4%) per year. The incidence of ASDeg is higher with more motion segments. Sex, age, segmental sagittal alignment, fusion methods, and instrumentation were not associated with an increased risk of ASDeg or ASDis. Radiographic ASDeg did not show strong correlation with clinical outcomes.
Conclusions: The prevalence of ASDeg and ASDis has been variably reported in the literature, and fusion length is the factor most significantly associated with adjacent segment pathology. In guiding surgical strategies to avoid adjacent segment pathology, limiting the number of levels fused may have a greater impact than changes in fusion strategies.