title: Does spinal instrumentation influence the healing process of posterolateral spinal fusion? An in vivo animal model.
abstract: METHODS
  An in vivo sheep model was used to investigate the effect of spinal instrumentation on the healing process of posterolateral spinal fusion.
  
  
  OBJECTIVE
  To examine the role of spinal instrumentation during the healing process of posterolateral fusion.
  
  
  BACKGROUND
  In long bone fractures, internal fixation improves the union rate but does not accelerate the healing process. Spinal instrumentation also improves the fusion rate in spinal arthrodesis. However, it remains unclear whether the use of spinal instrumentation expedites the healing process of spinal fusion.
  
  
  METHODS
  Sixteen sheep underwent posterolateral spinal arthrodeses at L2-L3 and L4-L5 using equal amounts of autologous bone. One of those segments was selected randomly to be augmented with transpedicular screw fixation (Texas Scottish Rite Hospital spinal system). The animals were killed at 8 weeks or 16 weeks after surgery. Fusion status was evaluated by biomechanical testing, manual palpation, plain radiography, computed tomography, and histology.
  
  
  RESULTS
  Instrumented fusion segments demonstrated significantly higher stiffness than did uninstrumented fusions at 8 weeks after surgery. Radiographic assessment and manual palpation showed that the use of spinal instrumentation improved the fusion rate at 8 weeks (47% versus 38% in radiographs, 86% versus 57% in manual palpation). Histologically, the instrumented fusions consisted of more woven bone than the uninstrumented fusions at 8 weeks after surgery. The 16-week-old fusion mass was diagnosed biomechanically, radiographically, and histologically as solid, regardless of pedicle screw augmentation.
  
  
  CONCLUSIONS
  The current study's results demonstrated that spinal instrumentation creates a stable mechanical environment to enhance the early bone healing of spinal fusion.
authors.affiliation: Department of Orthopaedic Surgery, Hokkaido University School of Medicine, Sapporo, Japan. mkanayama@aol.com
authors.forename: M
authors.initials: M
authors.lastname: Kanayama
authors.forename: B W
authors.initials: BW
authors.lastname: Cunningham
authors.forename: J C
authors.initials: JC
authors.lastname: Sefter
authors.forename: J A
authors.initials: JA
authors.lastname: Goldstein
authors.forename: G
authors.initials: G
authors.lastname: Stewart
authors.forename: K
authors.initials: K
authors.lastname: Kaneda
authors.forename: P C
authors.initials: PC
authors.lastname: McAfee
mesh_terms: D000818:Animals; D001863:Bone Screws; D016025:Bone Transplantation / Q000000981:diagnostic imaging / Q000473:pathology / Q000502:physiology; D004195:Disease Models, Animal; D004548:Elasticity; D017102:Fracture Healing / Q000502:physiology*; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology / Q000601:surgery*; D016348:Osseointegration / Q000502:physiology*; D012756:Sheep; D013123:Spinal Fusion / Q000295:instrumentation; D013314:Stress, Mechanical; D014057:Tomography, X-Ray Computed; D016474:Weight-Bearing / Q000502:physiology