Shoulder injuries – causes and solutions

In 1997, NIOSH (National Institute for Occupational Safety and Health) released a publication called Musculoskeletal Disorders and Workplace Factors, A Critical Review of Epidemiologic Evidence for Work-Related Musculoskeletal Disorders of the Neck, Upper Extremity, and Low Back http://www.cdc.gov/niosh/docs/97-141/pdfs/97-141.pdf . Although this report over 20 years old, the valuable information about what causes work-related injuries remains current.

One of the most interesting parts of the report is the evidence of work-relatedness to injuries.  From the 40 epidemiologic studies they evaluated, NIOSH judged how strong they felt the evidence was that the injury or musculoskeletal disorder (MSD) was caused by the ergonomic risk factor.   Ergonomic risk factors include:  force, repetition, awkward postures, and static postures to name a few.  The categories they used were:

  • Strong Evidence of Work-Relatedness (+++) – a causal relationship
  • Evidence of Work-Relatedness (++) – convincing epidemiologic evidence for a causal relationship
  • Insufficient Evidence of Work-Relatedness (+/0) – could not conclude the presence or absence of a causal relationship
  • Evidence of No Effect of Work Factors (-) – the specific risk factor is not related to MSDs

What they found for the shoulder area was this:

  1. Evidence of Work-Relatedness (++) between highly repetitive work and shoulder injuries. Repetitive work was defined as activities which involve continuous arm movements which affect the shoulder muscles.  It should be noted that the studies also involved awkward postures or static postures along with the repetition.
  • Hairstylists and dental hygienists are two professions where there is continuous arm and shoulder movement.  They are at risk for shoulder injuries.
  • With some professions where the job can’t be changed much, the solution is to change the way the job is done.  Proper rest breaks, alternating tasks throughout the day and stretching and strengthening of shoulder muscles will help to prevent injury.
  1. Evidence of Work-Relatedness (++) between repeated or sustained shoulder postures with greater than 60 degrees of flexion or abduction and shoulder injuries.  These are jobs that involve working with the arm above chest level.
    • Landscapers and drywallers require lifting the arms above chest level a great deal of the time.  This increases their risk for shoulder injuries.
    • This also requires a change in the way the job is done.  Proper rest breaks, alternating tasks throughout the day and stretching and strengthening of shoulder muscles will help to prevent injury.  Both professions would benefit from ergonomic tools with contoured handles and proper angles.
  1. Insufficient Evidence of Work-Relatedness (++) between both force and shoulder injuries as well as vibration and shoulder injuries.  Force means shoulder movement combined with a load and vibration means using a tool that vibrates or being on surface that vibrates.
    • It should be noted that the currently available epidemiologic studies did not provide enough evidence at that time.   Future studies may prove otherwise.
    • I could find only one other study done by the University of Waterloo “Overhead Work: Evidence-Driven Job Design and Evaluation”.  It found that by changing the direction of hand force to be in line with gravity, muscular activity lessened in the shoulder.  This decreased fatigue and in turn could reduce injuries.

I will continue with further body parts in my next post – identifying further jobs where there may be risks and providing guidelines for ergonomic intervention.

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