Work-Related Musculoskeletal Disorders Report, Workshop Summary, and Workshop Papers (1999) / Chapter Skim
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II Workshop Summary
II Workshop Summary
Pages 33-70
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11 Workshop Summary
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report. This is the second The workshop was clesignec3 to focus on the current state of the scientific research base pertaining to work~relatec3 musculoskeletal clisorclers, including risk factors that can contribute to such clisorclers, anc3 interventions that may alleviate or prevent such clisorclers.
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work factors, incliviclual factors, anc3 internal loacis that is, the biomechanics of work stressors; (3) the epidemiology of physical factors; (4)
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37 .o In m _ s ~ y ~ ~ 4_ o I .2 o ~5 do In o Q In o ._ Q at In E o Q E En E ._ Q E ._ Q In ._ _.
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In the boxes to the left of the central physiological pathways, Figure ~ identifies environmental factors that might affect the development of musculoskeletal disorders, including physical work, organizational factors, and social context. For example, physical work factors (such as lifting heavy boxes or equipment)
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BIOLOGICAL RESPONSES OF TISSUES TO STRESSORS Presentations Soh Tissue Responses to Physica/ Stressors: Muscles, Tenc/ons, anc/ Ligaments lames Ashton-Mi//er Reported soft tissue injuries can be the result of stresses (e.g., of posture, motion, or vibration) from a single, mechanical event or from repetitive events.
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This model is driven by theories that a muscle's ability to sustain power output is a function of its fiber composition anc3 oxiciative capacity. Recent in vivo laboratory studies of human muscle have used noninvasive spectroscopy to measure changes in tissue oxy' genation in response to varying levels anc3 duration of force.
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The studies we examined to illustrate the effects of nerve compression on periph' oral nerves incluclec3 human anc3 animal laboratory studies of the physiologic, pathos physiologic, biochemical, anc3 histologic effects of "loading." Four of these studies demonstrate the state of the evidence on peripheral nerves as well as its limitations. The first of these studies is an histological study on laboratory rats.
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Data from cadaver studies provide ranges within which such failures occur, as JO animal moclels of some soft tissues tested in laboratory studies. Even at levels clearly below these failure ranges, however, there is scientific evidence from laboratory studies that soft tissue responses include inflamma' Lion, muscle fatigue, anc3 ultrastructural degeneration that floes not heal without cessa' tion or restriction of the provoking force.
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The findings show a progressive clegeneration of nerve health uncler sustained compression, which suggests that nerve compression effects can be viewed on a spectrum cliviclec3 into early, intermediate, anc3 late categories. In clinical terms, early stages respond most favorably to conservative treatment (such as steroid injections anc3 splinting for carpal tunnel syndrome)
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Putting these clinical views on chronic nerve compression in an even broacler context, Thomas Mayer, PRIDE, Dallas, Texas, reported that even when all forms of acute nerve compression anc3 musculotenclinous sprains anc3 strains are consiclerec3, they account for a small portion of medical care anc3 medical costs (see box)
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For example, Armstrong anc3 Chaffin (1979) used a mathematical model of the mechanical relationships between belts anc3 pulleys to describe the external forces, postures, anc3 internal tendon positions that induce loacis in the carpal tunnel of the wrist.
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Discussion The relationships among external work factors, external anc3 internal loacis, anc3 soft tissue responses (as shown in Figure 1) have been stucliec3 extensively, using mod' els, human laboratory studies, anc3 workplace analyses.
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Muscle tissue, for example, is better able than nerve tissue to adapt to the types of repetitive loading that can be observed in some workplace environments. In general, the findings of these biomechanical studies, especially when combined with the earlier findings from studies of soft tissue responses, strongly support a relationship between musculoskeletal clisorclers anc3 external physical stress.
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Mark Recifern, University of Pittsburgh, observed that there is controversy over the biomechanical causation of carpal tunnel syndrome. He also noted that there are differing opinions about how biomechanical measures are related to musculoskeletal clisorclers anc3 about how such measures are used.
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The review examines the strengths and weaknesses of 600 selected studies investigating exposure to musculoskeletal disorders in the work' place. The steering committee invited a group of respected epidemiologists to discuss the NIOSH review and the epidemiological studies it covered.
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Several panelists suggested that the diagnostic definitions of carpal tunnel syndrome used in many of the studies were problematic since evidence for this diagnosis requires electrocliagnostic measures. Others suggested that some studies of questionable quality were incluclec3 in the review anc3 that the methods NIOSH used in selecting anc3 weighting studies were not repeatable.
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Peter Nathan, Portland Hand Surgery Rehabilitation Center, Oregon, maintained that NIOSH hac3 ignored studies examining the role of nonoccupational factors in the etiology of carpal tunnel syndrome. ~ believe the NIOSH document is one of social and political interest.
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These things can affect the psychological stress level of work, the degree of social support available, anc3 the satisfaction workers obtain on the job. /ncliviclual Factors The ultimate mechanism of injury in carpal tunnel syndrome anc3 cumulative trauma clisorclers is probably ischemia (or localized anemia clue to contracted blood vessels)
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have also been posed as risk factors, but the associations with carpal tunnel syndrome anc3 related clisorclers, though statistically significant, are weak, anc3 their clinical significance is low. Increasing age has consistently been associated with the slowing of the median nerve across the wrist that is thought to be critical in carpal tunnel syndrome.
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· Organizational anc3 psychosocial factors associated with work design, work social supports, and individual responses to workplace stress can be reasonably assumed as risk factors for higher rates of work-related musculoskeletal disorders. Studies have demonstrated that poorly designed jobs, highly demanding workloads and pace, and low levels of worker control on the job can be associated with higher rates of musculoskeletal disorders.
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Peter Nathan, Portland Hand Surgery Rehabilitation Center, Oregon, observed that it is essential to observe the patterns of musculoskeletal disease in the general population anc3 ask how those inclivicluals who are at risk perform when challenged at work. General health risk factors must take primacy in modeling the etiology of bodily discomfort.
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Engineering redesigns primarily involve ways to reduce biomechanical risk factors. Work methods improvements, administrative controls, and employee training can also reduce biomechanical risk factors, and they can also influence the psychosocial work environment.
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Fifteen laboratory studies, 15 field studies of injured employees, anc3 13 field studies of healthy employees were examined. All the studies involved deliberate manipulation of work conditions factors to reduce exposure anc3 risk.
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Martin Cherniack, University of Connecticut Health Center, noted that it is "a rapidly growing anc3 unruly literature that highlights essential contradictions anc3 logical inconsistencies in laboratory based anc3 applied survey methods." Many discuss sants were willing to go beyond the paper authors in considering a broacler range of studies as evidence that work~relatec3 musculoskeletal clisorclers can be reclucec3 or pre' vented with interventions. Several discussants noted the many practical ergonomic programs in place at work sites around the globe that offer evidence of results.
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Monroe Keyserling, Susan Mackinnon, Steven Moore, Peter Nathan, Barbara Silverstein, Richard Szabo, anc3 Richard Wells. Panel Comments Substantially all of the panel's major comments anc3 observations reinforced points previously macle throughout the workshop: · Musculoskeletal clisorclers are multifactorial, with work anc3 the biomechanical aspects of work being important contributing factors.
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. Donald Bloswick, for example, urged that musculoskeletal clisorclers not be clefinec3 just in terms of carpal tunnel syndrome or upper extremity cumulative trauma clisorcler.
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Armstrong, Hi., and D.B. Chaffin 1979 Some biomechanical aspects of the carpal tunnel.
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University of Michigan, Ann Arbor James Ashton Miller, University of Michigan, Ann Arbor Bruce Bernard, National Institute for Occupational Safety anc3 Health, U.S. Depart' ment of Health anc3 Human Services, Cincinnati, Ohio Sidney Blair, Loyola University Medical Center Donald Bloswick, University of Utah, Salt Lake City Paulien Bongers, TNO Prevention anc3 Health, Leiclen, Netherlands Stephen Burastero, Lawrence Livermore National Laboratory, Livermore, California Dennis Carter, Stanford University Martin Cherniack, University of Connecticut Health Center, Farmington Linda Cocchiarella, American Medical Association, Chicago, Illinois David Cochran, Occupational Safety anc3 Health Administration, U.S.
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Luke's Medical Center, Chicago, Illinois Steven Lehman, University of California, Berkeley Thomas Mayer, PRIDE, Dallas, Texas Susan Mackinnon, Washington University School of Medicine William Marras,* Ohio State University, Columbus Gary Mirka, North Carolina State University, Raleigh Samuel Moon, Duke University Medical Center Steven Moore, Texas A&M University, College Station Robert Morency, ABean, Inc., Freeport, Maine Francisco Moro, University of Wisconsin-Maclison Peter Nathan, Portland Hand Surgery Rehabilitation Center, Portland, Oregon Robert Norman, University of Waterloo, Ontario, Canada Lida Orta Anes, United Automobile Aerospace and Agricultural Implement Workers of America, UAW, Detroit, Michigan Richard Pew,*
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Chaffin, University of Michigan, Ann Arbor Harvey Checkoway, University of Washington Jerome Congleton, Texas A&M University Thomas Cook, University of Iowa Marvin I Dainoff, Miami University, Oxford, Ohio Richard Deyo, University of Washington Michael Feuerstein, Uniformed Services University of the Health Services, Bethesda Maryland, and Georgetown University School of Medicine Adam Finkel, Occupational Safety and Health Administration, U.S.
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William Colglazier, Executive Officer, National Research Council Barbara Boyle Torrey, Executive Director, Commission on Behavioral and Social Sci' ences and Education Alexandra Wigdor, Director, Division on Education, Labor, and Human Performance Anne Mavor, Study Director, Steering Committee for the Workshop on Work'Relatec3 Musculoskeletal Injuries James McGee, Senior Research Associate, Steering Committee for the Workshop on Work'Relatec3 Musculoskeletal Injuries Renae Broderick, Writer/Editor, Cornell University, Ithaca, New York Susan Coke, A`lmirlistrative Associate, Steering Committee for the Workshop on WorkRelatec3 Musculoskeletal Injuries Susan McCutchen, Senior Project Assistant, Steering Committee for the Workshop on Work'Relatec3 Musculoskeletal Injuries Nat Tipton, Sertior Project Assistant, Division on Education, Labor, and Human Perfor' mance
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BIOLOGICAL RESPONSE OF TISSUES TO STRESSES: MUSCLES. TENDONS, AND NERVES INVITED PAPER ON MUSCLES AND TENDONS: James Ashtorr'Mitler Pane} Discussion: Kai'Narl Arl, Sidrley Blair, Dennis Carter, Cario De Luck, Steven Lehman, Steven Moore, Moshe Solomorrow Questions from Invited Participants INVITED PAPER ON NERVES: David Rempet Pane} Discussion: David Florence, Steven Garfirr, Thomas Mayer, Susan Mackir~rrorr, Robert Szabo Questions from Invited Participants 67
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WORK FACTORS, INDIVIDUAL HOST FACTORS, AND INTERNAL LOADS: BIOMECHANICS OF WORK STRESSORS INVITED PAPER: Robert Rewire arid Steven Taverner Panel Discussion: Arur~ Garg, W Monroe Keysertir~g, Robert Norman, Mark Redierrt, Carolyrt Sommerich, Richard Wells Questions from Invitec3 Participants 12:30 p.m.
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Panel on the Integration of Workshop Presentations and Discussions Chair: Colic Drury Panelists: Jacqueline Agnew, Sidney Blair, Dorla1d Bloswick, Alfred Frarlzblau, Fredric Gerr, W Monroe Keysertir~g, Susan Mackir~r~orr, Steven Moore, Peter Nathan, Barbara Silversteirr, Robert Szabo, Richard Wells 2:00 p.m.
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