Study design: Systematic review.
Objective: To perform a systematic review to define the incidence of clinical adjacent segment pathology (CASP) after lumbar fusion surgery and define potential risk factors for the development of CASP.
Summary of background data: Concerns for the longevity of current arthrodesis constructs and the effects of arthrodesis on adjacent segments have received increasing attention during the past decade. There is a lack of precision regarding the terminology used to describe the pathologies of adjacent segment disease. The term ASP is proposed as an umbrella term to refer to the breadth of clinical and/or radiographical changes at adjacent motion segments that developed subsequent to a previous spinal intervention.
Methods: A systematic search was performed in Medline and the Cochrane Collaboration Library for literature published through January 2012. Level of evidence ratings were assigned to each article independently by 2 reviewers. Extracted were the percentage risks of CASP during 5- and 10-year time periods, risk factors, the effect estimates (relative risks and odds ratios), and corresponding confidence intervals reported from each study's multivariate analyses. Forest plots of odds ratios or relative risks with their 95% confidence intervals evaluating patient, disease, and surical risk factors were constructed using the data provided by the individual studies.
Results: We identified 162 total citations from our literature search. Of these, 31 full- text articles were evaluated for meeting inclusion criteria. From these 31 studies, 5 studies met inclusion criteria. The mean patient ages ranged from 50 to 64 years. The mean annual incidence of CASP ranged from 0.6% to 3.9%. With respect to patient factors, age more than 60 years was associated with an increased risk of developing CASP. Other factors that may increase the risk of developing CASP are pre-existing facet degeneration, degenerative disc disease, performing a multilevel fusion, stopping a construct at L5, performing a laminectomy adjacent to a fusion, and excessive disc height distraction during posterior interbody fusion.
Conclusion: This systematic review was limited to higher-quality studies that evaluated risk factors using multivariate analyses. Identified were key patient, disease, surgical, and radiographical factors that may be considered when counseling and treating patients with degenerative conditions. Further high-quality studies are required before any concrete conclusions can be made about this controversial topic.
Consensus statements: 1. The risk of developing CASP after lumbar fusion occurs at a mean annual incidence of 0.6% to 3.9%. Strength of Statement: Strong. 2. Patients older than 60 years or who have pre-existing facet/disc degeneration may have an increased risk of developing CASP. Strength of Statement: Strong. 3. The risk of developing CASP may be greater after multilevel fusions and fusions adjacent to but not including the L5–S1 level, and may increase when performing a laminectomy adjacent to a fusion. Strength of Statement: Strong.