title: Posterolateral lumbar fusions in athymic rats: characterization of a model.
abstract: BACKGROUND
  The athymic rat has been used to study the role of osteoinductive products in spinal fusions. This small animal model has been advocated to minimize potential inflammatory responses to allogeneic or xenogenic proteins. Despite past experience, this model has not yet been well characterized.
  
  
  OBJECTIVE
  To further define and validate a posterolateral lumbar fusion model in the athymic rat.
  
  
  METHODS
  Comparison of fusions after animal survival surgery.
  
  
  METHODS
  Forty athymic and 20 normothymic rats.
  
  
  METHODS
  Manual palpation, radiography and histology at 3 and 6 weeks.
  
  
  METHODS
  Single-level intertransverse fusions were performed at the L4-L5 level of 40 athymic rats. Twenty rats were implanted with autograft (athymic/autograft), and 20 had no graft placed (athymic/no graft). An additional 20 autograft fusions were performed on normothymic rats (normothymic/autograft). Half were sacrificed at 3 weeks; half were sacrificed at 6 weeks.
  
  
  RESULTS
  At 3 weeks, 0% of the athymic/no graft rats fused, 20% of the athymic/autograft rats fused and 20% of the normothymic/autograft rats fused by manual palpation. At 6 weeks, 0% of the athymic/no graft rats fused, 30% of the athymic/autograft rats fused and 40% of the normothymic/autograft rats fused by manual palpation. Radiographs were of limited utility in determining fusion, and histology results were roughly concordant with those of manual palpation.
  
  
  CONCLUSIONS
  This work further characterizes the athymic rat posterolateral lumbar fusion model. The absence of a thymus does not appear to affect autograft fusion rates, and no spontaneous fusions were seen when no graft was placed.
authors.affiliation: Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, PO Box 208071, New Haven, CT 06520-8071, USA. jonathan.grauer@yale.edu
authors.forename: Jonathan N
authors.initials: JN
authors.lastname: Grauer
authors.forename: David A
authors.initials: DA
authors.lastname: Bomback
authors.forename: Roberto
authors.initials: R
authors.lastname: Lugo
authors.forename: Nancy W
authors.initials: NW
authors.lastname: Troiano
authors.forename: Tushar C
authors.initials: TC
authors.lastname: Patel
authors.forename: Gary E
authors.initials: GE
authors.lastname: Friedlaender
mesh_terms: D000818:Animals; D016025:Bone Transplantation; D005260:Female; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D023421:Models, Animal; D010173:Palpation / Q000379:methods; D011859:Radiography; D051381:Rats; D011923:Rats, Nude; D013123:Spinal Fusion