• Michael J Lee, Joseph R Dettori, Christopher J Standaert, Erika D Brodt, and Jens R Chapman.
• Department of Orthopaedic Surgery, University of Washington Medical Center, Seattle, WA 98195, USA. mjl3000@u.washington.edu
• Spine. 2012 Oct 15; 37 (22 Suppl): S18S30S18-30.

Study DesignSystematic review.ObjectiveTo determine the population risk of radiographical degeneration in the lumbar and cervical spine as well as the risk of adjacent segment pathology (ASP) among patients who receive and do not receive (but were eligible for) fusion for lumbar or cervical degeneration.Summary Of Background DataThe etiology of ASP remains unclear. It has been suggested that ASP results because of a biomechanical stress transfer from the fusion. It has also been suggested that ASP is a continuation of natural arthritic disease. We sought to examine the literature and compare the rates of spinal degeneration without fusion and the rates of adjacent segment degeneration. Similarities or differences may yield insight into the etiology of ASP.MethodsA systematic review of the English language literature was undertaken for articles published between 1990 and March 15, 2012. Electronic databases and reference lists of key articles were searched to identify articles reporting prevalence and/or incidence of radiographical spinal degeneration (de novo degeneration) or radiographical adjacent segment pathology (RASP) (degeneration after fusion). Two independent reviewers assessed the level of evidence and the overall quality of the literature using the Grades of Recommendation Assessment, Development and Evaluation criteria. Disagreements were resolved by consensus.ResultsWe identified 15 studies from our search strategy that met the inclusion criteria from a total of 235 possible studies. Various definitions of radiographical spinal degeneration were used across the studies. For the population risk of radiographical lumbar and cervical spine degeneration, the cumulative incidence ranged from 12.7% to 51.5% during a 5- to 25-year period across 3 studies. One study of the cervical spine reported that there was a baseline prevalence of disc degeneration of 21.7% and, in their follow-up study, reported that 47.9% of individuals had evidence of progression of degeneration during a mean 5.8-year follow-up. The rate of progression per 100 person-years showed an age- and sex-specific trend, with females progressing at a faster rate than males through the 50s, males progressing faster than females during the 60s and 70s, with rates becoming identical in the 80s. Regarding age-specific risk, the prevalence of lumbar degeneration increased with age across 2 studies. For RASP following fusion, the cumulative incidence ranged from 6.3% to 44.4% during 6 to 12.6 years of follow-up across the 7 studies; the risk of cervical RASP was higher than that of lumbar despite the shorter mean follow-up periods.ConclusionRASP may occur at a higher rate than natural history and suggests that another factor (such as biomechanical effect of fusion) may accelerate pathologic changes.Consensus StatementASP may occur at a higher rate than natural spinal degeneration and suggests that another factor (such as biomechanical effect of fusion) may accelerate pathologic changes. Strength of Statement: Weak.

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