Iit is important to differentiate between radiographical adjacent segment disease (ASD), which is radiographical evidence of degeneration at the levels adjacent to a previous fusion, and clinical ASD, which is the development of clinically relevant symptoms (i.e., radiculopathy and/ or myelopathy) that correlate with radiographical evidence of degeneration that is adjacent to a previous fusion 1).
Adjacent segment cervical disease occurs in approximately 3% of patients per year, with an expected incidence of 25% within the first 10 years following fusion. Nonfusion procedures such as anterior discectomy and posterior foraminotomy do not decrease the rate of adjacent segment disease compared with Anterior cervical discectomy and fusion (ACDF).
Future prospective studies should continue to focus on excellent patient follow-up and accurate assessment of patient symptoms that are attributable to an adjacent level as this has been an under-reported finding in prospective studies 9).
Lawrence et al. 13) performed a systematic review to determine the risk factors for the development of ASD after cervical fusion surgery. They concluded that the factors contributing to the development include age of less than 60 years, fusing adjacent to the C5-C6 and/or C6-C7 levels, a pre-existing cervical disc herniation, and/or dural compression secondary to spinal stenosis.
Enthusiasm has developed for artificial disk replacement as a motion-sparing alternative to fusion. To date, however, multiple clinical trials and subsequent follow-up studies have failed to demonstrate significant reduction of adjacent segment disease when artificial disk replacement is performed instead of fusion 14).
Concerns with adjacent segment disease and the desire to preserve physiological motion have led to technological and clinical efforts for cervical arthroplasty.
The suggested move to cervical disc replacement has led to this latter procedure being one of the most scrutinised surgical treatments in the twenty-first century.
Short- and medium-term prospective randomised clinical trials and systematic reviews show cervical disc replacement to be at least as good as ACDF as regards the clinical outcomes in the management of degenerative cervical spondylosis. This is logical since the neural decompression procedure is essentially the same. However, the rationale for arthroplasty over arthrodesis has been built on two main proposed roles: the preservation of segmental motion and the prevention of adjacent segment disease. Whilst results thus far show that this first role seems to be achieved, its clinical significance is as yet unproven; the second is so far not proven. In addition, the long-term fate of the implants is also unknown. Long-term safety and efficacy, therefore, still await further clinical studies 15).
From a meta-analysis of prospective studies, there is no difference in the rate of ASD for Anterior cervical discectomy and fusion (ACDF) versus total disc arthroplasty (TDA).
There is also an overall lower rate of follow-up for patients with ACDF than for those with TDA. Future prospective studies should continue to focus on excellent patient follow-up and accurate assessment of patient symptoms that are attributable to an adjacent level as this has been an under-reported finding in prospective studies 16) 17)