title: Innervation of anulus tears: an experimental animal study.
abstract: METHODS
  A prospective immunohistological study in an animal model.
  
  
  OBJECTIVE
  To identify and describe the phenotype of neoinnervation in experimental anular tears.
  
  
  BACKGROUND
  Controversy surrounds neoinnervation of degenerate discs which has been proposed as the anatomic basis for discogenic pain. Ablation of neoinnervation has been postulated as the theoretical basis for the claimed successes of procedures such as intradiscal electrotherapy. The animal model of disc degeneration previously developed in our research center provides an opportunity to investigate the innervation of anular tears in an extensively characterized lesion.
  
  
  METHODS
  A surgical anular tear was created in 5 lumbar discs in 11 sheep which were killed at 1, 2, 3, and 12 months. Each spine was x-rayed and divided into motion segments for histologic analysis. Serial sections through the tear were immunostained for protein gene product 9.5, tyrosine hydroxylase, and calcitonin gene receptor protein.
  
  
  RESULTS
  Neoinnervation of the periphery of the anular tear was observed. Ingrowing nerves penetrated marginally deeper than the normal anular innervation but no nerves were identified in the inner anulus or nucleus. A minority of the new axons were calcitonin gene receptor protein or tyrosine hydroxylase positive.
  
  
  CONCLUSIONS
  The anulus tears in this model are innervated only peripherally to a depth only marginally greater than that of the normal anulus.
authors.affiliation: Spine Unit, Royal Adelaide Hospital, The University of Adelaide, Adelaide, South Australia. andrew.fagan@adelaide.edu.au
authors.forename: Andrew B
authors.initials: AB
authors.lastname: Fagan
authors.forename: Ghafar
authors.initials: G
authors.lastname: Sarvestani
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Moore
authors.forename: Robert D
authors.initials: RD
authors.lastname: Fraser
authors.forename: Barrie
authors.initials: B
authors.lastname: Vernon-Roberts
authors.forename: Peter C
authors.initials: PC
authors.lastname: Blumbergs
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D007403:Intervertebral Disc / Q000294:innervation* / Q000473:pathology; D055959:Intervertebral Disc Degeneration / Q000473:pathology; D008159:Lumbar Vertebrae / Q000294:innervation* / Q000473:pathology; D009416:Nerve Regeneration / Q000502:physiology; D010146:Pain / Q000473:pathology; D011446:Prospective Studies; D012756:Sheep; D013122:Spinal Diseases / Q000473:pathology