title: Adjacent segment disease after lumbar or lumbosacral fusion: review of the literature.
abstract: METHODS
  Review of the literature.
  
  
  OBJECTIVE
  Review the definition, etiology, incidence, and risk factors associated with as well as potential treatment options.
  
  
  BACKGROUND
  The development of pathology at the mobile segment next to a lumbar or lumbosacral spinal fusion has been termed adjacent segment disease. Initially reported to occur rarely, it is now considered a potential late complication of spinal fusion that can necessitate further surgical intervention and adversely affect outcomes.
  
  
  METHODS
  MEDLINE literature search.
  
  
  RESULTS
  The most common abnormal finding at the adjacent segment is disc degeneration. Biomechanical changes consisting of increased intradiscal pressure, increased facet loading, and increased mobility occur after fusion and have been implicated in causing adjacent segment disease. Progressive spinal degeneration with age is also thought to be a major contributor. From a radiographic standpoint, reported incidence during average postoperative follow-up observation ranging from 36 to 369 months varies substantially from 5.2 to 100%. Incidence of symptomatic adjacent segment disease is lower, however, ranging from 5.2 to 18.5% during 44.8 to 164 months of follow-up observation. The rate of symptomatic adjacent segment disease is higher in patients with transpedicular instrumentation (12.2-18.5%) compared with patients fused with other forms of instrumentation or with no instrumentation (5.2-5.6%). Potential risk factors include instrumentation, fusion length, sagittal malalignment, facet injury, age, and pre-existing degenerative changes.
  
  
  CONCLUSIONS
  Biomechanical alterations likely play a primary role in causing adjacent segment disease. Radiographically apparent, asymptomatic adjacent segment disease is common but does not correlate with functional outcomes. Potentially modifiable risk factors for the development of adjacent segment disease include fusion without instrumentation, protecting the facet joint of the adjacent segment during placement of pedicle screws,fusion length, and sagittal balance. Surgical management, when indicated, consists of decompression of neural elements and extension of fusion. Outcomes after surgery, however, are modest.
authors.affiliation: Department of Neurosurgery, University of Michigan Health System, Ann Arbor, MI 48109-0338, USA. ppark@umich.edu
authors.forename: Paul
authors.initials: P
authors.lastname: Park
authors.forename: Hugh J
authors.initials: HJ
authors.lastname: Garton
authors.forename: Vishal C
authors.initials: VC
authors.lastname: Gala
authors.forename: Julian T
authors.initials: JT
authors.lastname: Hoff
authors.forename: John E
authors.initials: JE
authors.lastname: McGillicuddy
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D001696:Biomechanical Phenomena; D019299:Decompression, Surgical; D018450:Disease Progression; D005260:Female; D006801:Humans; D015994:Incidence; D016268:Internal Fixators; D017116:Low Back Pain / Q000209:etiology; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications / Q000453:epidemiology* / Q000209:etiology / Q000601:surgery; D011859:Radiography; D012189:Retrospective Studies; D012307:Risk Factors; D012447:Sacrum / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D013122:Spinal Diseases / Q000453:epidemiology* / Q000209:etiology / Q000601:surgery; D013123:Spinal Fusion; D013314:Stress, Mechanical; D016474:Weight-Bearing