Adjacent segment disease: Current evidence and the role of motion preservation technologies

Spinal fusion is gold-standard treatment for degenerative disc disease (DDD) both at cervical and lumbar spine, and it is time tested. Perhaps it has its bundle of complications. Elimination of motion results in accentuated degeneration of adjacent segments leading to adjacent segment degeneration radiographically and, if symptomatic, leads to adjacent segment disease. There is still a debate on whether there is such an entity or whether it is a manifestation of natural history or an iatrogenic phenomenon. Motion preservation surgeries were developed to address the same issue, which includes total disc replacement, nucleus replacement, interspinous implants, and dynamic posterior stabilization systems. The primary goal of motion preservation surgery is to maintain normal or near-normal motion in an attempt to prevent adverse outcomes, which are commonly seen with conventional spinal fusion, most notably the development of adjacent-level DDD. A search was conducted in PubMed using the terms (“adjacent segment”) AND (“disease” OR “degeneration” or “pathology”). Then the articles were shortlisted based on time of publication (2005 onward), publication in English and inclusion of human subjects. This resulted in 253 articles. Another search for ((“Motion preservation”) AND (“Spine”)) OR (“Adjacent segment disease”) OR (“Adjacent segment pathology”) OR (“Adjacent segment degeneration”) yielded 76 articles. This narrative review discusses various issues pertaining to the current evidence regarding adjacent segment disease (ASD), including the controversy on whether ASD is actually an entity, its etiopathogenesis, clinical features, as well as the role of motion preservation technologies to reduce its incidence. There is still enthusiasm and concerns regarding the benefits of motion preservation surgery since it is still an area of ongoing research.