title: Adjacent segment degeneration: observations in a goat spinal fusion study.
abstract: METHODS
  The adjacent discs of 13 goats, originally used in a lumbar spinal fusion model study, were analyzed for symptoms of intervertebral disc degeneration by means of magnetic resonance imaging (MRI), macroscopy, and histology. These goats were followed for 6 months and the results were compared with 6 control goats.
  
  
  OBJECTIVE
  To evaluate the development of adjacent segment disc degeneration in vivo in a goat lumbar spinal fusion model.
  
  
  BACKGROUND
  There is ongoing debate on whether adjacent segment degeneration (ASD) develops through increased biomechanical load on discs adjacent to fusion sites, or by the natural process of pre-existing degenerative disease. Animal models offer an opportunity to separate these factors by evaluating the development of ASD in nondegenerated animal spines.
  
  
  METHODS
  In a spinal fusion model study 2 segments (L3-L4 and L1-L2) were fixated and followed for 3 months (n = 6) and 6 months (n = 7) in 13 skeletally mature goats. Two adjacent discs (T13-L1 and L4-L5), 1 interjacent disc (L2-L3) and a control disc (L5-L6) were analyzed by means of magnetic resonance imaging, macroscopy, and histology. These results were compared with the discs of 6, nonoperated "normal" goats.
  
  
  RESULTS
  No differences were observed in the adjacent and interjacent intervertebral discs after both follow-up periods. However, severe degenerative changes were observed in the L5-L6 level, originally included as controls.
  
  
  CONCLUSIONS
  Large animal fusion models offer an excellent opportunity to study ASD in vivo, as pre-existing degenerative disc disease is not present and biomechanical effects of the fusion can be studied more isolated. Our results suggest that adjacent disc degeneration does not develop in our spinal goat fusion model. There is, however, an increased risk of disc degeneration in the L5-L6 level through an unclear mechanism.
authors.affiliation: Department of Orthopaedic Surgery, VU University Medical Center (VUmc), Amsterdam, The Netherlands.
authors.forename: Roel J W
authors.initials: RJ
authors.lastname: Hoogendoorn
authors.forename: Macro N
authors.initials: MN
authors.lastname: Helder
authors.forename: Paul I J M
authors.initials: PI
authors.lastname: Wuisman
authors.forename: Ruud A
authors.initials: RA
authors.lastname: Bank
authors.forename: Vincent E
authors.initials: VE
authors.lastname: Everts
authors.forename: Theo H
authors.initials: TH
authors.lastname: Smit
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D006041:Goats; D007403:Intervertebral Disc / Q000473:pathology* / Q000601:surgery; D008159:Lumbar Vertebrae / Q000473:pathology* / Q000601:surgery; D008279:Magnetic Resonance Imaging; D023421:Models, Animal; D015588:Observer Variation; D015203:Reproducibility of Results; D013122:Spinal Diseases / Q000209:etiology / Q000473:pathology*; D013123:Spinal Fusion / Q000009:adverse effects*; D013997:Time Factors