Mechanisms of Injuries Leading to Musculoskeletal Pathology and Behavioral Declines in an Animal Model of Repetitive Motion Injury

Details

• Personal Author:
  Barbe MF
• Description:
  There is considerable epidemiological evidence for the role of repetition and force in the onset and progression of work-related musculoskeletal disorders; however, complete understanding of these important occupational health problems requires further elucidation of the mechanisms of injuries leading to musculoskeletal pathology and behavioral declines. We have examined exposure-response relationships in upper extremity tissues and sensorimotor behaviors using an operant behavioral rat model of repetitive reaching and pulling, in which rats performed one of four different repetition and force tasks for up to 24 weeks: 1) low repetition with low force (LRLF), 2) high repetition with low force (HRLF), 3) low repetition with high force (LRHF), and 4) high repetition with high force (HRHF). Performance of the HRLF and HRHF was associated with increased incidence of myofiber kinks, tendon fibrillation, tendon collagen disorganization, and nerve axon damage. These histological signs of injury were greatest in rats performing the HRHF task. We also observed repetitive task-induced declines in bone quality in distal forelimb bones that were linked to both loading level and inflammation. These changes included a loss of bone density and trabecular bone resorption indicative of enhanced bone fragility. Anti-inflammatory drug treatment or load reduction preserved bone mass and allowed for bone adaptation. Exposure-dependent declines in grip strength and increased pain behaviors were observed that consistently correlated with task-induced inflammatory responses in forearm tissues (HRHF>HRLF=LRHF>LRLF). Initial local tissue inflammatory responses became systemic and detectable in serum as increased inflammatory cytokines, indicating that inflammatory cytokines can serve as biomarkers of the inflammatory phase of WMSDs. Unfortunately, prolonged peripheral inflammation also drove central nervous system changes, e.g. increased nociceptor-related neurotransmitters and inflammatory cytokines in the spinal cord and brain. Although traditional anti-inflammatory treatments (ibuprofen or anti- TNFalpha drugs) provided after the onset of pain behaviors reduced peripheral tissue inflammation, the spinal cord changes were not ameliorated, indicative of chronic pain related neuroplasticity. Prolonged performance of the higher demand tasks were also associated with increased fibrogenic- related proteins in the tissues, including transforming growth factor beta 1 and connective tissue growth factor. These fibrogenic changes were partially attenuated by anti-inflammatory treatments when provided early during their induction, indicating a link between the inflammatory phase and the fibrotic phase. Persistent motor declines correlated with prolonged and cyclical low-grade tissue inflammatory cytokine responses as well as progressive increases of several fibrotic proteins. Many of these fibrogenic proteins were detectable in serum, suggesting that they should be monitored in patients with WMSDs. In conclusion, we propose a model of three key interrelated pathways (peripheral tissue injury-inflammation, peripheral tissue fibrosis, and CNS reorganization) that drive persistent sensorimotor behavioral declines with performance of repetitive tasks, with the greatest effects produced by high repetition high force tasks. [Description provided by NIOSH]
• Subjects:
  Laboratories Musculoskeletal Diseases Musculoskeletal System Occupational Health Safety
• Keywords:
  Central Nervous System Laboratory Animals MSD Muscle Tissue Musculoskeletal Disorders Nerve Damage Repetitive Work Task Performance
• Publisher:
  International Commission on Occupational Health (ICOH)
• Document Type:
  Text
• Funding:
  Grant
• Genre:
  Abstract or Summary
• Place as Subject:
  OSHA Region 3 ; Pennsylvania
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  30
• NIOSHTIC Number:
  nn:20056322
• Citation:
  Eighth International Scientific Conference on Prevention of Work-Related Musculoskeletal Disorders (PREMUS 2013), July 7-11, 2013 Busan, Korea. Rome, Italy: International Commission on Occupational Health (ICOH), 2013 Jul; :30
• Federal Fiscal Year:
  2013
• Performing Organization:
  Temple University
• Peer Reviewed:
  False
• Start Date:
  20000601
• Source Full Name:
  Eighth International Scientific Conference on Prevention of Work-Related Musculoskeletal Disorders (PREMUS 2013), July 7-11, 2013 Busan, Korea
• End Date:
  20120731
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:a64c507e8a4e3d42707a5a7ddb6279d1c6082e54382f86b143f9b0a791e87140b3062b6ba633cd55b1bab41049ac1f5ae521c33f44f6d9c27e6c49ce83506a86
• Download URL:
  https://stacks.cdc.gov/view/cdc/213951/cdc_213951_DS1.pdf
• File Type:
  [PDF - 752.88 KB ]