Adjacent segment disease after fusion for cervical spondylosis; myth or reality?

Cervical spondylosis is a common cause of radiculopathy and myelopathy, often treated by discectomy and interbody fusion. However, there has been a recent vogue for the use of artificial disc prostheses to decrease the risk of accelerated degenerative disease at adjacent levels. The short-term results of artificial disc replacements have been encouraging, but the long-term justification for using this new technology hinges on whether the incidence of adjacent segment disease decreases. It will also be necessary to demonstrate that movement at the operated levels is maintained and the incidence of device failure is low. We review the radiological, biomechanical and clinical evidence for adjacent segment disease, and the rationale for using artificial cervical disc replacements. There is presently insufficient evidence to justify the widespread use of artificial disc replacements in the treatment of cervical spondylosis, but neither is there sufficient evidence to criticize their use. Present evidence suggests that adjacent segment disease is partly due to the natural history of spondylotic disease and partly due to cervical fusion. Randomized trials are required to ascertain whether the incidence of adjacent segment disease changes with the use of artificial disc replacements in the long term. Indications for the use of artificial discs are presently unclear, but disc replacements might be recommended for 'young' patients who require an anterior cervical discectomy, with good ranges of neck movements, and an awareness of the satisfactory short-term results, but lack of long-term outcome data, preferably within the limits of a clinical trial.