Adjacent Segment Disease Following Spinal Fusion
Invited lecture given at the Neurosurgical Society of Australasia
73rd Annual Scientific Meeting
Adelaide, September 1st 2017
73rd Annual Scientific Meeting
Adelaide, September 1st 2017
Abstract
Lumbar spinal fusion may be followed by degeneration at motion segments adjacent to the fusion. Systematic reviews of adjacent segment pathology (ASP) publications have noted wide variations in reported prevalence. A review by Harrop et al in 2008, calculated that 34% of patients (340/926) had developed radiological signs of degeneration (ASDegen) and 14% (173/1216) developed symptomatic disease (ASDis). A 2011 retrospective study by Sears et al, of further surgery for ASDis following 1000 consecutive PLIF procedures, noted an annual incidence of 2.5% and observed a substantial rise in incidence with increasing age and with the number of levels fused, at the time of index surgery.
The pathophysiology of Adjacent Segment Pathology (ASP) is complex and current evidence suggests that it is most likely, multifactorial. It remains controversial as to whether the rigid fused segment(s) predisposes to adjacent segment degeneration or whether ASP is solely the result of the natural history. Identical twin and epidemiological studies have provided strong evidence that genetic factors play a substantial role in the evolution of degenerative spine disease.
Numerous in vitro biomechanical studies have reported increased range-of-motion or intra-discal pressures at levels adjacent to a simulated fusion but the results of these studies have varied and the validity of test methodologies has been challenged; consequently, the conclusions remain in doubt. Aspects of fusion procedures such as damage to adjacent structures (e.g. muscles, ligaments, facet joints, etc.) may be as important as any rigid immobilisation.
The medium to longer term results of high-level clinical studies are beginning to emerge and suggest a contribution from the fusion procedure. A 2014 systematic review and meta-analysis by Ren et al of studies of ASDeg or ASDis following lumbar fusion vs. motion-preserving devices, analysed the results of 1,270 patients from 13 studies, including randomized controlled trials (RCTs) and cohort studies. Overall, the prevalence of clinical ASDis was not significantly different between fusion and motion-preserving procedures (P = 0.10) in studies reporting less than 5 years of follow-up but significant differences appeared when follow-up exceeded 5 years (P = 0.001). Regarding posterior motion preserving devices vs. fusion, several cohort studies and three RCTs have been conducted. While the results trend towards a reduction in ASP, study numbers are small. Further and larger randomized trials are required.
The controversy regarding the role fusion plays in the pathophysiology of ASP will hopefully soon be resolved and perhaps provide surgeons with ways to mitigate its development.
Lumbar spinal fusion may be followed by degeneration at motion segments adjacent to the fusion. Systematic reviews of adjacent segment pathology (ASP) publications have noted wide variations in reported prevalence. A review by Harrop et al in 2008, calculated that 34% of patients (340/926) had developed radiological signs of degeneration (ASDegen) and 14% (173/1216) developed symptomatic disease (ASDis). A 2011 retrospective study by Sears et al, of further surgery for ASDis following 1000 consecutive PLIF procedures, noted an annual incidence of 2.5% and observed a substantial rise in incidence with increasing age and with the number of levels fused, at the time of index surgery.
The pathophysiology of Adjacent Segment Pathology (ASP) is complex and current evidence suggests that it is most likely, multifactorial. It remains controversial as to whether the rigid fused segment(s) predisposes to adjacent segment degeneration or whether ASP is solely the result of the natural history. Identical twin and epidemiological studies have provided strong evidence that genetic factors play a substantial role in the evolution of degenerative spine disease.
Numerous in vitro biomechanical studies have reported increased range-of-motion or intra-discal pressures at levels adjacent to a simulated fusion but the results of these studies have varied and the validity of test methodologies has been challenged; consequently, the conclusions remain in doubt. Aspects of fusion procedures such as damage to adjacent structures (e.g. muscles, ligaments, facet joints, etc.) may be as important as any rigid immobilisation.
The medium to longer term results of high-level clinical studies are beginning to emerge and suggest a contribution from the fusion procedure. A 2014 systematic review and meta-analysis by Ren et al of studies of ASDeg or ASDis following lumbar fusion vs. motion-preserving devices, analysed the results of 1,270 patients from 13 studies, including randomized controlled trials (RCTs) and cohort studies. Overall, the prevalence of clinical ASDis was not significantly different between fusion and motion-preserving procedures (P = 0.10) in studies reporting less than 5 years of follow-up but significant differences appeared when follow-up exceeded 5 years (P = 0.001). Regarding posterior motion preserving devices vs. fusion, several cohort studies and three RCTs have been conducted. While the results trend towards a reduction in ASP, study numbers are small. Further and larger randomized trials are required.
The controversy regarding the role fusion plays in the pathophysiology of ASP will hopefully soon be resolved and perhaps provide surgeons with ways to mitigate its development.
