title: ISSLS prize winner: Adaptations to the multifidus muscle in response to experimentally induced intervertebral disc degeneration.
abstract: METHODS
  Basic science study of the rabbit multifidus muscle response to intervertebral disc degeneration.
  
  
  OBJECTIVE
  To assess changes in passive mechanical properties, associated protein structure, and histology of multifidus in response to disc degeneration produced by experimental needle puncture.
  
  
  BACKGROUND
  Relationships have been reported between muscle dysfunction and low back injury; however, little is known about the cause and effect of such relationships.
  
  
  METHODS
  Twelve rabbits were studied; 4 in each of 3 groups: control, 4-weeks postintervertebral disc injury (4-week disc degeneration), and 12-weeks postintervertebral disc injury (12-week disc degeneration). Single multifidus fibers and bundles of fibers were isolated and tested for slack sarcomere length and elastic modulus. Titin isoform mass, myosin heavy chain distribution, and muscle histology were also examined.
  
  
  RESULTS
  Compared to control, individual muscle fibers were 34% stiffer and fiber bundles 107% stiffer in the 12-week disc degeneration group. No changes were detected at 4-week disc degeneration. No statistically significant change was found for MHC distribution in the 12-week disc degeneration group when compared to control, whereas titin isoforms were larger (P < 0.05) in the 12-week disc degeneration group. Histology revealed select regions of multifidus, at 12-week disc degeneration, with increased space between bundles of fibers, which in some instances was partly occupied by adipose tissue.
  
  
  CONCLUSIONS
  Multifidus becomes stiffer, both in individual fibers and fiber bundles, in response to experimentally induced intervertebral disc degeneration. This cannot be explained by change in fiber-type due to reduced muscle use, nor by the increased size of the protein titin (which would reduce stiffness). We hypothesize that fiber bundles become stiffer by proliferation and/or reorganization of collagen content within the muscle but the basis for fiber stiffening is not known.
authors.affiliation: Department of Orthopaedic Surgery, University of California San Diego, San Diego, CA 92093, USA.
authors.forename: Stephen H M
authors.initials: SH
authors.lastname: Brown
authors.forename: Diane E
authors.initials: DE
authors.lastname: Gregory
authors.forename: J Austin
authors.initials: JA
authors.lastname: Carr
authors.forename: Samuel R
authors.initials: SR
authors.lastname: Ward
authors.forename: Koichi
authors.initials: K
authors.lastname: Masuda
authors.forename: Richard L
authors.initials: RL
authors.lastname: Lieber
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D001696:Biomechanical Phenomena; D001706:Biopsy; D064211:Connectin; D004195:Disease Models, Animal; D055119:Elastic Modulus; D005260:Female; D055959:Intervertebral Disc Degeneration / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D008161:Lumbosacral Region; D008279:Magnetic Resonance Imaging; D018485:Muscle Fibers, Skeletal / Q000378:metabolism / Q000473:pathology; D009124:Muscle Proteins / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D018995:Myosin Heavy Chains / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D011817:Rabbits; D011859:Radiography; D013997:Time Factors
chemical_list: D064211:Connectin; D009124:Muscle Proteins; D011494:Protein Kinases; D018995:Myosin Heavy Chains