ABSTRACT
For as long as spinal fusions have been performed, there have been questions regarding the fate of the segments adjacent to the fusion. The term “adjacent segment degeneration” is loosely defined as degenerative changes that occur at the mobile spinal segment immediately above or below a previously fused segment or segments. The first published report of adjacent segment degeneration was in 1956 (1). Since that time, there have been more than 300 articles published pertaining to the definition, diagnosis, outcomes, and treatment of adjacent segment degeneration. There are several reports that have described degeneration adjacent to noninstrumented fusions (2,3,4), but the large majority of the descriptions refer to segments adjacent to an instrumented fusion (5,6,7,8). Recent advances in motion-sparing surgery have spurned even more interest in risk factors for and treatment of adjacent segment degeneration. The industry for disc arthroplasty has described motion preservation as a primary advantage of the artificial disc over fusion for degenerative conditions. Data exists both supporting and refuting this claim, but a question remains. Does fusion truly increase the rate of adjacent segment degeneration, or is it just a passive player present in a patient that is “preprogrammed” to degenerate at those levels regardless?
