Anterior cervical decompression and fusion (ACDF) is one of the standard surgical techniques for the treatment of cervical spinal disorders including degenerative diseases, trauma, infection, and tumor. However, the surgical outcomes of ACDF can be deteriorated by the development of adjacent segment degeneration or disease in the postoperative time course. In this article, the biomechanical background, incidence, risk factors, prevention, and management of this disorder are discussed. The incidence rate of adjacent segment degeneration or disease varies according to different reports. The risk factors are reported to be a level of fusion, the number of fusion levels, the preexistence of degenerative changes at the adjacent segments, and the alignment of the entire cervical spine and the fused segments. Although adjacent segment disease can be a sequel of the natural aging of the patients, a comparative study with control population revealed that patients who underwent ACDF had significantly higher incidence of disc degeneration at the adjacent segments than the control population. Adjacent segment diseases can be prevented by the use of motion preservation techniques including artificial disc replacement and decompression surgery without fusion. It can be managed by repeated ACDF, expansive laminoplasty, and artificial disc replacement, although the efficacies of these revision surgical procedures remain to be tested in the larger case series.
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