SPINAL FUSION AND THE RISK OF SYMPTOMATIC ADJACENT LEVEL DISC DEGENERATION – A SYSTEMATIC REVIEW

Abstract

Introduction Disc replacement surgery is being investigated as an alternative to spinal fusion surgery in the hope that maintaining segment spinal motion will not only relieve pain, but also prevent or reduce the likelihood of symptomatic adjacent segment degeneration that is believed to be a consequence of fusion surgery. The aim of this study was to identify evidence in the medical literature that indicates whether or not spinal fusion surgery increases the likelihood of symptomatic adjacent segment degeneration compared to disc replacement surgery or natural history.

Methods A search of the Cochrane Controlled Trials Register, Medline and reference lists of retrieved articles was performed. Search terms included arthroplasty replacement, spinal fusion, prognosis, controlled clinical trials and cohort studies, Studies were included if abstracts were available electronically, were published in the English language before1/3/2005 and involved humans. Levels of evidence were determined using the Oxford Centre for Evidence-Based Medicine criteria (http://www.cebm.net/levels of evidence.asp).

Discussion The majority of identified studies were case series of patients presenting with adjacent level disc degeneration following spinal fusion surgery (Level 4) and whilst indicating patients can develop adjacent level disc degeneration following fusion surgery, do not indicate the likelihood of doing so. Uncontrolled prospective cohort studies (Level 4) provide conflicting evidence. One retrospective cohort (Level 2b) studying comparing the incidence of adjacent disc degeneration following spinal fusion and discectomy or decompressive surgery alone found that the incidence of degeneration in the superior adjacent disc was increased in the fusion group, but was not associated with differences in functional outcome. No systematic reviews of inception cohort studies (Level 1) were identified.

Conclusions Only poor quality evidence has been published to support the proposition that spinal fusion surgery is associated with an increased likelihood of developing symptomatic adjacent level disc degeneration. Long term follow-up of patients enrolled in prospective randomised controlled trials comparing outcomes of spinal fusion and disc replacement surgery is necessary to determine whether or not disc replacement surgery decreases the likelihood of any symptomatic adjacent level disc degeneration that can be attributed to spinal fusion surgery.