Object: The authors compared the incidence of radiologically documented changes and symptomatic adjacent-level cervical disc disease after single-level discectomy and subsequent cervical fusion or arthroplasty in two independent prospective clinical studies.
Methods: The patients were treated with the Affinity Anterior Cervical Cage System or the Bryan Artificial Cervical Disc. In each study the patients were required to undergo serial cervical radiography preoperatively and 24 months postoperatively, as well as serial clinical evaluations including documentation of adverse events, neurological status, and results of the 36-item Short Form Health Survey. All serial radiographs were reviewed prior to evaluating the clinical symptoms for development of increasing or new adjacent degenerative disc disease (DDD). Subsequently, the clinical data were analyzed. For various reasons of exclusion, the cases analyzed in the Bryan disc-treated cohort consisted of 74 patients and in the Affinity system-treated cohort there were 158 patients. New anterior osteophyte formation or enlargement, increased narrowing of an interspace, new DDD, and calcification of the anterior longitudinal ligament were the radiological findings indicative of adjacent-level disease. Fusion was associated with a significant increase in x-ray film-based changes of adjacent-disc disease (p = 0.009, odds ratio [OR] 2.44). In the cage fusion series, the incidence of symptomatic adjacent-level DDD was statistically greater than that in the group treated with the artificial disc (p = 0.018), and the patients required a statistically greater number of medical treatments related to episodic symptoms of neck, shoulder, and arm pain attributed to new disc disease (p = 0.001, OR 35.8).
Conclusions: In comparing these prospective studies the authors demonstrated that maintaining motion rather than fusion will prevent symptomatic adjacent-disc disease and will decrease adjacent-level radiological indicators of disease at a 24-month postoperative interval.