title: Magnetic resonance imaging and biological changes in injured intervertebral discs under normal and increased mechanical demands.
abstract: METHODS
  An animal model was used to examine the short-term tissue response to changes in the mechanical environment after the structure (disc) is mechanically injured.
  
  
  OBJECTIVE
  To observe changes in an injured intervertebral disc and the corresponding motion segment when the mechanical demands of the disc were increased by fusion of the adjacent motion segments.
  
  
  BACKGROUND
  Disc degeneration has been modeled in animals by producing a tear in the anulus via laminectomy, laparotomy, or posterolaterally. Methods of altering and quantifying the mechanics of the intervertebral joint by use of internal fixation and fusion in the canine have been developed.
  
  
  METHODS
  Eight dogs divided into two groups (a study and a control group) had anular stab wounds (L2-L3). The study group was surgically instrumented posteriorly from L3 to L7. Magnetic resonance imaging studies were conducted for all animals before and periodically after the surgical procedures. At the end of the study, the segments were processed histologically and biochemically.
  
  
  RESULTS
  Anular bulging was seen on magnetic resonance imaging in all control animals 4 months after injury and did not progress out until 6 months after injury. Similar changes were seen in study animals, but 75% were herniated by 6 months. Histologic changes correlated with magnetic resonance imaging changes. No significant difference in water or proteoglycan content of the disc tissue between groups was found.
  
  
  CONCLUSIONS
  Progression from the bulging of the anulus to herniation was not evident in damaged discs not subjected to adjacent fusions. No change in water or proteoglycan content as a function of altered mechanical state was found, suggesting the short-term effect of the altered mechanics is on the mechanical structure and not on the cells or extracellular matrix.
authors.affiliation: Department of Orthopaedic Surgery, Montefiore Medical Center, Bronx, New York.
authors.forename: J M
authors.initials: JM
authors.lastname: Olsewski
authors.forename: M J
authors.initials: MJ
authors.lastname: Schendel
authors.forename: L J
authors.initials: LJ
authors.lastname: Wallace
authors.forename: J W
authors.initials: JW
authors.lastname: Ogilvie
authors.forename: C R
authors.initials: CR
authors.lastname: Gundry
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D004285:Dogs; D007403:Intervertebral Disc / Q000293:injuries* / Q000473:pathology / Q000503:physiopathology*; D008159:Lumbar Vertebrae / Q000293:injuries* / Q000473:pathology / Q000503:physiopathology*; D008161:Lumbosacral Region; D008279:Magnetic Resonance Imaging; D012016:Reference Values; D013123:Spinal Fusion; D014951:Wounds, Stab / Q000175:diagnosis* / Q000473:pathology / Q000503:physiopathology*