title: High magnitude cyclic load triggers inflammatory response in lumbar ligaments.
abstract: BACKGROUND
  Cumulative trauma disorder is commonly reported by workers engaged in prolonged repetitive/cyclic occupational activities. Recent experimental evidence confirms that relatively short periods of cyclic lumbar flexion at high loads result in substantial creep of viscoelastic tissues, prolonged periods of its recovery to baseline together with a neuromuscular disorder and exposure to instability. The biochemical process associated with the creep and neuromuscular disorder are not well explored. The purpose of the study is to identify the ligaments as one of the organs of failure and an acute inflammation as the result of failure as a preliminary step in the development of chronic inflammation that might lead to cumulative trauma disorder elicited by high magnitude cyclic loads.
  
  
  METHODS
  The lumbar spine of anaesthetized cats was subjected to cyclic flexion loading at high magnitudes for six periods of 10 min each with 10 min rest in between followed by 7h rest. Lumbar displacement was monitored throughout. Supraspinous ligaments from L-3/4, L-4/5, L-5/6 and unloaded T-10/11 were removed at the end of testing and assessed using mRNA expression for cytokine (IL-1beta, IL-6, IL-8, TNFalpha, TGFbeta). Cytokines expression in the lumbar ligaments were statistically compared to their self control in the unloaded thoracic ligament. The creep developed during the loading and its recovery during the 7h rest was calculated.
  
  
  RESULTS
  The mean creep developed during the loading period reached 57.3% recovering to a residual value of 25.5% at the end of the 7h rest. Increase in cytokine expression was seen in all lumbar ligaments with statistical significance in the L-4/5 and L-5/6 levels.
  
  
  CONCLUSIONS
  The results confirm that prolonged high magnitude cyclic loading of the lumbar spine in flexion-extension elicits substantial residual creep together with significant increases in cytokines expression, consistent with an acute inflammation, several hours post loading. Further exposure to cyclic loading over time may result in conversion to chronic inflammation.
authors.affiliation: Musculoskeletal Disorders Research Laboratory, Bioengineering Division, Department of Orthopedic Surgery, Health Sciences Center, University of Colorado, Denver, Aurora, CO 80045, USA.
authors.forename: Karen
authors.initials: K
authors.lastname: King
authors.forename: Bradley
authors.initials: B
authors.lastname: Davidson
authors.forename: Bing He
authors.initials: BH
authors.lastname: Zhou
authors.forename: Yun
authors.initials: Y
authors.lastname: Lu
authors.forename: Moshe
authors.initials: M
authors.lastname: Solomonow
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002415:Cats; D012090:Cumulative Trauma Disorders; D016207:Cytokines / Q000378:metabolism; D004548:Elasticity; D004576:Electromyography; D007249:Inflammation; D008022:Ligaments / Q000293:injuries; D008159:Lumbar Vertebrae / Q000473:pathology*; D008161:Lumbosacral Region / Q000293:injuries; D013314:Stress, Mechanical; D013997:Time Factors; D016474:Weight-Bearing
chemical_list: D016207:Cytokines