title: Disc degeneration reduces the delamination strength of the annulus fibrosus in the rabbit annular disc puncture model.
abstract: BACKGROUND
  Degenerative disc disease is a common pathologic disorder accompanied by both structural and biochemical changes. Changes in stress distribution across the disc can lead to annulus fibrosus (AF) damage that can affect the strength and integrity of the disc. Given that some present degeneration therapies incorporate biological regrowth of the nucleus pulposus (NP), it is crucial that the AF remains capable of containing this newly grown material.
  
  
  OBJECTIVE
  To examine the resistance of AF to delamination using an adhesive peel test in experimentally degenerated rabbit discs.
  
  
  METHODS
  Experimentally induced disc degeneration; excised AF tissue study.
  
  
  METHODS
  Disc degeneration was induced in eight New Zealand white rabbits by annular puncture; four additional rabbits served as controls. In experimental rabbits, an 18-gauge needle was inserted into the anterolateral AF region of levels L2-L3 and L4-L5, and disc height was monitored by X-ray. Animals were sacrificed at 4 and 12 weeks postsurgery and magnetic resonance images and X-rays were taken. Four discs were excised from the experimental animals; two punctured (L2-L3 and L4-L5) and two controls (L3-L4 and L6-L7). The same four discs were also excised from the age-matched control animals and served as nonpunctured control discs. To determine resistance to delamination, AF samples were dissected from each disc and subjected to a mechanical peel test at 0.5 mm/s.
  
  
  RESULTS
  Magnetic resonance imaging and X-ray images confirmed dehydration of the NP and reduced disc height, similar to that found in clinical degeneration. Resistance to delamination was significantly lower in punctured/degenerated discs compared with both the nonpunctured discs from the same animal (27% lower) and the nonpunctured control discs (30% lower) (p=.024).
  
  
  CONCLUSIONS
  The findings of this study suggest that degeneration increases the potential for delamination between AF layers. Given this substantial change to the integrity of the AF after degeneration, clinical treatments should not only target rehydration or regrowth of the NP, but should also target repair and strengthening of the AF to confine the NP.
authors.affiliation: Department of Kinesiology and Physical Education, Wilfrid Laurier University, Waterloo, 75 University Ave West, Waterloo, Ontario, Canada, N2L 3C5; Department of Orthopaedic Surgery, University of California San Diego, 9500 Gilman Dr., La Jolla, CA 92093, USA.
authors.forename: Diane E
authors.initials: DE
authors.lastname: Gregory
authors.affiliation: Department of Orthopaedic Surgery, University of California San Diego, 9500 Gilman Dr., La Jolla, CA 92093, USA.
authors.forename: Won C
authors.initials: WC
authors.lastname: Bae
authors.affiliation: Department of Bioengineering, University of California San Diego, 9500 Gilman Dr., La Jolla, CA 92093, USA; Department of Radiology, University of California San Diego, 200 West Arbor Drive, San Diego, CA, 92103, USA.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Sah
authors.affiliation: Department of Radiology, University of California San Diego, 200 West Arbor Drive, San Diego, CA, 92103, USA. Electronic address: koichimasuda@ucsd.edu.
authors.forename: Koichi
authors.initials: K
authors.lastname: Masuda
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D007403:Intervertebral Disc / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology*; D055959:Intervertebral Disc Degeneration / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology*; D008279:Magnetic Resonance Imaging; D011677:Punctures; D011817:Rabbits; D011859:Radiography; D013718:Tensile Strength
keywords: Animal model; Annulus fibrosus; Disc herniation; Disc therapy; Lamellae; Puncture