title: Flexibility and distraction after monosegmental and bisegmental lumbosacral fixation with angular stable fixators.
abstract: METHODS
  In human lumbosacral spines, the flexibility and intersegmental distraction allowed by four monosegmental and bisegmental intrapedicular devices during compression and flexion/compression loading were investigated.
  
  
  OBJECTIVE
  To compare the flexibility and intersegmental distraction allowed by four monosegmental and bisegmental intrapedicular, lumbosacral fixation devices applied to destabilized cadaveric spines, and to determine the effect of each device on the flexibility and intersegmental distraction of the motion segment above each fused segment.
  
  
  BACKGROUND
  The lumbosacral segment is the most mobile region in the lumbar spine, exhibiting the highest range of motion in both flexion and extension. Therefore, the fixation of this and the adjacent segment is of special clinical interest.
  
  
  METHODS
  L5-S1 facetectomy or L5 laminectomy procedures were performed on cadaveric human lumbosacral spines. Fixation devices then were applied across one or two levels, and intersegmental motion under flexion/compression or under pure compression loads was monitored.
  
  
  RESULTS
  The flexibility and posterior strain allowed by the four implants did not differ significantly between implants. The strain across the stabilized site (monosegmental and bisegmental) was below 10% for all devices tested. The flexibility and distraction were reduced to levels below intact after the fixators were applied. The distraction across the segment above the fusion was not increased because of fixation with these four fixators.
  
  
  CONCLUSIONS
  Angular stable fixation devices, such as those described here, provide adequate stabilization of the posteriorly destabilized spine.
authors.affiliation: Department of Orthopedic Surgery, Charles A. Dana Research Institute, Harvard-Thorndike Laboratory, Beth Israel Hospital, Boston, Massachusetts, USA.
authors.forename: R H
authors.initials: RH
authors.lastname: Wittenberg
authors.forename: M
authors.initials: M
authors.lastname: Shea
authors.forename: W C
authors.initials: WC
authors.lastname: Hayes
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004867:Equipment Design; D006801:Humans; D016268:Internal Fixators; D007796:Laminectomy; D008159:Lumbar Vertebrae / Q000503:physiopathology / Q000601:surgery*; D008875:Middle Aged; D012447:Sacrum / Q000503:physiopathology / Q000601:surgery*; D013123:Spinal Fusion / Q000295:instrumentation*; D013314:Stress, Mechanical