Adjacent segment disease after cervical spine fusion.

Anterior cervical diskectomy and fusion is one of the most common cervical spine procedures. Although it is usually successful in relieving the symptoms of radiculopathy and myelopathy, the subsequent development of clinically significant disk disease at levels adjacent to the fusion is a matter of concern. Adjacent segment cervical disease occurs in approximately 3% of patients; the incidence is expected to increase to more than 25% of patients within the first 10 years after the index fusion procedure. The disease is well described in the literature, and significant basic science and clinical research has been conducted. Nonetheless, the cause of the disease is a matter of debate. A combination of factors probably contributes to its development, including the increased biomechanical stress placed on the disk space adjacent to a fusion and the natural history of cervical spondylosis in patients known to have such pathology. Clinical and biomechanical data are available to support each of these claims. Symptomatic disk disease adjacent to a cervical fusion is a significant clinical problem, and, therefore, motion-sparing technology has been developed to reduce its incidence. Two cervical disk replacement systems are currently approved by the US Food and Drug Administration for the treatment of symptomatic cervical spondylosis.