A Practitioner’s Guide

www.asse.org NOVEMBER 2006 PROFESSIONAL SAFETY 27 WORK-RELATED MUSCULOSKELETAL disorders (WRMSDs) constitute a major problem in many industries in terms of frequency, cost to employers and impact on the daily lives of those injured. In 2004, WRMSDs accounted for one-third of the 1.3 million injury and illness cases resulting in days away from work (U.S. Bureau of Labor Statistics [BLS], 2005). They also are associated with a substantially higher number of days away from work than other types of injury and illness (BLS, 2005). WRMSDs are impairments generally characterized by chronic pain and discomfort that may originate in nerves, tendons, tendon sheaths, muscles or blood vessels. These disorders include nerve compression disorders such as cubital tunnel syndrome, carpal tunnel syndrome and thoracic outlet syndrome, as well as inflammations of the tendons and sheaths such as tendonitis and tenosynovitus. However, a large proportion of WRMSDs cannot be associated with damage to specific tissues as identified by, for example, X-ray or ultrasound. Thus, while it is generally agreed that musculoskeletal disorders can be the result of adverse occupational loads, the mechanisms behind their causation and persistence are still largely obscure. The contributing work-related factors for musculoskeletal disorders are fairly well established. In an analysis of the epidemiologic evidence, Bernard (1997) concludes that substantial evidence exists for an association between exposure to awkward postures and neck/shoulder disorders, for a combination of physical work factors leading to disorders of the elbow, hand/wrist and tendonitis, and for heavy lifting being connected with low back disorders. In an evaluation and discussion of a broader set of studies, members of the National Research Council Steering Committee for the Workshop on Work-Related Musculoskeletal Injuries (1999) concludes that for “those studies involving the highest levels of exposure to biomechanical stressors of the upper extremity, neck and back, and for those with the sharpest contrast among the study groups, the positive relationship between the occurrence of musculoskeletal disorders and the conduct of work is clear.” Therefore, the prevention of musculoskeletal disorders in the workplace often focuses on the evaluation of jobs in terms of the physical job requirements and the development of solutions to reduce the frequency, duration and/or intensity of the biomechanical stressors during work. Ergonomics job analysis (EJA) is performed to systematically: •identify hazardous work situations that present peak exposures (e.g., extremely heavy lifting); •determine whether exposure is beyond conventionally recommended levels (e.g., working in kneeling postures for more than 2 hours per 8-hour shift); •rank order jobs for intervention; •evaluate whether interventions actually reduce exposures associated with jobs. Common questions that arise in ergonomics practice include: •Is greater than 50 lb ever handled during a job? •Do workers in a job spend more than 25% of the work time in trunk flexion? •Which tasks or jobs are the most hazardous?