Work Related Upper Limb Disorders

Thomas J. Armstrong
The University of Michigan
Ann Arbor, MI 48109

Copyright 2002, Thomas J. Armstrong


Background, morbidity patterns, regulatory issues, risk factors and programs

I. Background
1.1 Work related musculoskeletal disorders- a Definition
1.2 Examples
1.3 AKA:
1.4 Characteristics of Work Related Disorders
1.5 Localized Fatigue
II. Morbidity Patterns, Work Trends & Risk Factors
2.1 Morbidity Patterns
2.2 Work Trends
2.3 Personal Factors
2.4 Work Factors
2.5 Pathomechanics and Pathophysiology
III. Regulatory Issues
IV. Program for Control of work related disorders
4.1 Goals
4.2 The Process
4.3 Ergonomics Team
4.4 Health Surveillance
4.5 Analysis of Jobs
4.6 Control Measures
V. References

Job Analysis

1. Documentation
2. Hand activity/repetition level
3. Hand Force
4. Contact stress
5. Posture

I. Background

1.1 Work-Related Musculoskeletal Disorders, WMSDs - a Definition

Disorders of the musculo-tendinous-osseous-nervous system that are caused, precipitated or aggravated by repeated exertions or movements of the body. This definition reflects the philosophy of workers' compensation laws in most western countries.

1.2 Examples

'WMSD' is NOT a diagnosis, it refers to a group of disorders with similar characteristics. Some examples include:
  • myalgia
  • myofacial pain syndrome
  • tendinitis
  • peritendinitis
  • teosynovitis
  • gamekeepers thumb
  • de Quervain's disease
  • epicondylitis
  • trigger finger
  • carpal tunnel syndrome
  • cubital tunnel syndrome
  • thoracic outliet syndrome
  • Guyon's canal syndrome
  • hypothenar hammer syndrome
  • vibration hand-arm syndrome
  • Examples of these often can be found in plant medical records, workers' compensation reports, OSHA logs and personnel medical records.

    1.3 WMSDs AKA:

    1. Occupational cervicobrachial disorders, Scandinavia, Japan
    2. Repetitive trauma disorders, U. S. A. - OSHA
    3. Repetitive strain injuries, British Commonwealth countries
    4. Overuse syndromes, Sports medicine
    5. Regional musculoskeletal disorders, Rheumatologists
    6. Work related disorders, (WHO)

    1.4 Characteristics WMSDs

    There is not unanimous agreement about which of these terms is best and arguments can be made for all of them. Some of the common characteristics of these disorders include:
    1. mechanical and physiological processes
    2. related to work intensity and duration
    3. development requires weeks, months and years
    4. recovery requires weeks, months and years
    5. symptoms often poorly localized, nonspecific and episodic
    6. often unreported
    7. multifactorial (more than one causal factor)
    As a result, these disorders often are under-reported and epidemiological methods usually are required to identify jobs, tools, areas, plants or industries with excessive risk.

    Side view of hand holding tool box in hook grip posture
    Figure 1a: Fingers supporting weight of tool box
    anatomical view of the hand-wrist showing how weight of tool box is supported by muscles in forearm
    Figure 1b: Mucles in forearm contract to flex fingers against weight of tool box
    anatomical view of the wrist showing how tendons slide against internal structures of the wrist with wrist and finger motion
    Figure 1c: Contraction of muscles in forearm cause tendons to rub against sides of carpal tunnel

    1.5 Localized Fatigue

    There are similarities and important differences between chronic muscle, tendon and nerve disorders and localized fatigue. There may be confusion between fatigue and cumulative trauma disorders. Fatigue can be defined as a physiological and biomechanical process that results in discomfort and impaired performance. Some of the

    Characteristics of fatigue include:
    1. mechanical and physiological processes (Basmajian 1978)
    2. results in pain and impairs work performance (Corlett and Bishop 1978, Harms-Ringdahl 1986)
    3. related to the intensity and duration of work (Rohmert 1973)
    4. occurs within seconds, minutes or hours (Rohmert 1973)
    5. recovery occurs within minutes, hours or, in extreme cases, a few days (Rohmert 1973)
    6. Time to exhaustion and discomforat increases significantly as exertion force drops below 15% of maximum, but physiological changes and pain may result from prolonged or repeated exertions at lower levels.
    7. fatigue may be a precursor to chronic muscle-tendon-nerve disorders. It is often assummed that if we control fatigue, we will control WMSDs.
    Hand gripping force gauge Graph showing Grip endurance, time to forearm Pain and time to hand pain as a function of percent grip strength
    Figure 2: Grip endurance, time to forearm pain and time to hand pain as a function of percent grip strength

    As a general rule, workers should not be experiencing symptoms from the previous days at the beginning of their work shift. Persistence of such symptoms indicates that there may be something more seriously wrong than fatigue from an "honest day of work."

    References:

    1. Basmajian JV. Muscles spared when ligaments suffice. Muscles Alive: Their Functions Revealed by Electromyography. Fourth ed. Baltimore, MD: The WIlliams & Wilkins Company; 1978.
    2. Brandt E, Pope A (ed). Enabling America: Assessing the Role of Rehabilitation Science and Engineering. Committee on Assessing Rehabilitation Sciences. http://www.nap.edu, Washington, DC: National Academy Press, 1997.
    3. Bystrom, S. and Fransson-Hall, C. Acceptability of intermittent handgrip contractions based on physiological response. Human Factors 1994. 36(1), 158-171.
    4. Corlett EN, Bishop RP. A technique for assessing postural discomfort. Ergonomics 1976;19(2):175-182
    5. National Research Council (U.S.). Committee on Human Factors. and NetLibrary Inc. (1999). Work-related musculoskeletal disorders report, workshop summary, and workshop papers. Washington, D.C., National Academy Press.
    6. National Research Council (U.S.). Panel on Musculoskeletal Disorders and the Workplace. and Institute of Medicine (U.S.) (2001). Musculoskeletal disorders and the workplace : low back and upper extremities. Washington, D.C., National Academy Press.
    7. Rohmert, W. 1973. Problems in Determining Rest Allowances, Part I. Use of Modern Methods to Evaluate Stress and Strain in Static Muscular Work. Applied Ergonomics4:91-95.
    8. Saldana, N., Herrin, G. and Armstrong, T. Automated assessment of musculoskeletal discomfort in the workforce: a tool for surveillance. Ergonomics 37(6):1097-112, 1994.
    9. Violante, F., T. J. Armstrong, et al. (2000). Occupational ergonomics : work related musculoskeletal disorders of the upper limb and back. London, Taylor & Francis.