Study design: A systematic review of the literature.
Objective: To compare total disc replacement (TDR) with fusion, other motion-sparing devices with fusion, and motion-sparing devices with other motion-sparing devices to determine which devices may be associated with a lower risk of radiographical or clinical adjacent segment pathology (ASP).
Summary of background data: Adjacent segment pathology, also termed adjacent segment disease (ASD) or adjacent segment degeneration, is a controversial phenomenon that can occur after a spinal fusion; it is thought to be either related to the altered mechanics or loss of motion from the fusion or to be part of the natural history of progressive arthritis. Motion preservation devices theoretically may decrease or prevent ASP from occurring.
Methods: A systematic search was conducted in PubMed and the Cochrane Library for literature published between January 1990 and February 2012. For all key questions, we identified all cohort studies and randomized controlled trials, making the comparison of interest independent of the outcomes measured. We searched each full-text article to determine whether it reported any type of structural or degenerative condition specifically occurring at an adjacent segment. We included articles reporting adult lumbar patients who had degenerative disc disease, disc herniation, radiculopathy, kyphosis, scoliosis, and spondylolisthesis, and who were treated with TDR, other motion-sparing procedures, or fusion. The overall strength of the evidence for each key question was rated using the Grades of Recommendation Assessment, Development and Evaluation (GRADE) criteria.
Results: There is moderate evidence to suggest that patients who undergo fusion may be nearly 6 times more likely to be treated for ASP than those who undergo TDR. From 2 randomized trials, the pooled risk of clinical ASP treated surgically was 1.2% and 7.0% in the TDR and fusion groups, respectively (P = 0.009). The increased risk of clinical ASP treated surgically associated with fusion is 5.8%. For every 17 operations, one might expect a new clinical ASP event requiring surgery when treated with fusion in those otherwise not harmed by TDR. There was insufficient literature to answer the other key questions, resulting in low to insufficient evidence that other motion-sparing operations are superior to fusion in preventing clinical ASP.
Conclusion: There does seem to be a low rate of ASP after lumbar spinal fusion. The evidence suggests that the risk of clinical ASP following fusion is higher when compared with TDR, but there is limited evidence that fusion may increase the risk of developing clinical ASP compared with other motion-sparing procedures.
Consensus statement: 1. Evidence demonstrates that the risk of clinical ASP requiring surgery is likely greater after fusion but the risk is still quite rare. The increased risk compared to TDR could be as small as less than 1% or as great as 10%. Strength of Statement: Weak. 2. There is insufficient evidence to make a definitive statement regarding fusion versus other motion-sparing devices with respect to the risk of ASP.