title: Electrochemical measurement of transport into scoliotic intervertebral discs in vivo using nitrous oxide as a tracer.
abstract: METHODS
  An in vivo study measuring nitrous oxide concentrations in scoliotic intervertebral discs during surgery.
  
  
  OBJECTIVE
  To determine pathways for nutrient transport into scoliotic human discs in vivo.
  
  
  BACKGROUND
  The intervertebral disc is the largest avascular structure in the body. Disc cells in the nucleus rely on the blood supply from the vertebral bodies for supply of nutrients and removal of waste. Loss of nutrient supply is thought to lead to disc degeneration, but solute transport has not been measured in vivo in humans.
  
  
  METHODS
  We measured solute transport into the disc using N2O as a tracer, in 19 human discs from five patients with neuromuscular scoliosis (6-19 years of age) during surgery for correction of scoliotic deformities. During anesthesia N2O diffuses into the disc at a rate governed by effective permeability of the vertebral body-disc interface. Intradiscal N2O concentrations were measured amperometrically using silver needle microelectrodes, which were inserted into the discs once they were exposed by an anterior approach.
  
  
  RESULTS
  For all spines N2O concentrations were very low in the disc at the curve apex (6% those expected from unimpeded diffusion) and, although still low, were significantly higher 2 discs below or above the apex.
  
  
  CONCLUSIONS
  Because flux into the apical disc is most restricted, the decrease in solute transport is possibly induced by changes in mechanical stress on the disc; microfocal radiographs of a scoliotic spine suggest that increased endplate calcification could be partly responsible for limiting solute diffusion.
authors.affiliation: Nuffield Department of Orthopaedic Surgery, Oxford University, Oxford, England.
authors.forename: M R
authors.initials: MR
authors.lastname: Urban
authors.forename: J C
authors.initials: JC
authors.lastname: Fairbank
authors.forename: P J
authors.initials: PJ
authors.lastname: Etherington
authors.forename: L
authors.initials: L
authors.lastname: Loh FRCA
authors.forename: C P
authors.initials: CP
authors.lastname: Winlove
authors.forename: J P
authors.initials: JP
authors.lastname: Urban
mesh_terms: D000293:Adolescent; D000328:Adult; D018685:Anesthetics, Inhalation / Q000493:pharmacokinetics*; D002648:Child; D002675:Child, Preschool; D006801:Humans; D007403:Intervertebral Disc / Q000098:blood supply* / Q000378:metabolism*; D007432:Intraoperative Period; D008839:Microelectrodes; D009609:Nitrous Oxide / Q000493:pharmacokinetics*; D012600:Scoliosis / Q000378:metabolism* / Q000601:surgery
chemical_list: D018685:Anesthetics, Inhalation; D009609:Nitrous Oxide