title: Effects of static compression with different loading magnitudes and durations on the intervertebral disc: an in vivo rat-tail study.
abstract: METHODS
  An in vivo rat-tail model was used to study the effects of static compression with different loading magnitudes and durations on the intervertebral disc.
  
  
  OBJECTIVE
  To investigate the effects of static compression with different loading magnitudes and durations on the intervertebral disc over a period of time.
  
  
  BACKGROUND
  A disc degeneration model is essential for studying therapeutic effects on degenerated disc. Static compression can induce degenerative-like changes in the intervertebral disc. However, the consequences of the simulation model over a period of resting have not been clearly documented, which may have confounding effects on the experimental outcome.
  
  
  METHODS
  Thirty-five rats were used. Static compressions with different loads (11 or 17 N) and durations (1 hour daily or continuous) were applied to the rat-tail caudal 8-9 disc for 2 weeks, and followed with 3 weeks of rest. The disc height was quantified in vivo on days 4, 18, and 39. The rats were killed and the discs were harvested for morphologic examination on day 39 after the disc height measurement.
  
  
  RESULTS
  Significant decrease in disc height was observed after continuous static compression for both 11 and 17 N, and continued during the resting period. The morphologic evaluation of the continuous compressed disc showed a decreased nuclear size, reduced number of nuclear cells, and irregular nuclear shape with inward bulging of disorganized annular collagen lamellas. Daily compression of 1 hour was found to induce a transient increase in disc height, but restored after the 3-week resting period. Favorable morphologic changes, including vacuolated nuclear cells and oval nuclear shape with well-organized annular collagen lamellas, were seen in the rat disc specimens with daily compression of 1 hour.
  
  
  CONCLUSIONS
  Disc degenerative-like changes without recovery were demonstrated in the rat caudal disc after continuous compression. The changes in disc height and disc morphology were found to be dependent on the duration of load application and may have clinical implication.
authors.affiliation: Department of Health Technology and Informatics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR, People's Republic of China.
authors.forename: Alon
authors.initials: A
authors.lastname: Lai
authors.forename: Daniel H K
authors.initials: DH
authors.lastname: Chow
authors.forename: Sammy W
authors.initials: SW
authors.lastname: Siu
authors.forename: S S
authors.initials: SS
authors.lastname: Leung
authors.forename: Emily F L
authors.initials: EF
authors.lastname: Lau
authors.forename: F H
authors.initials: FH
authors.lastname: Tang
authors.forename: Malcolm H
authors.initials: MH
authors.lastname: Pope
mesh_terms: D000818:Animals; D019245:Compressive Strength / Q000502:physiology*; D004195:Disease Models, Animal; D007403:Intervertebral Disc / Q000502:physiology*; D007405:Intervertebral Disc Displacement / Q000503:physiopathology; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D013623:Tail / Q000502:physiology*; D013997:Time Factors; D016474:Weight-Bearing / Q000502:physiology