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Work-related Musculoskeletal Disorders.doc.doc

  1. 1. Work-Related Musculoskeletal Disorders Work-Related Musculoskeletal Disorders of the Upper Limb Thomas J. Armstrong, Ph.D. The University of Michigan, Ann Arbor, MI 48109-2117 Work Related Musculoskeletal Disorders: Characteristics • Work Related Musculoskeletal Disorders, WMSDs: Disorders of the muscles, tendons and nerves that are caused, precipitated or aggravated by repeated exertions or movements • Primary cause may be work related or non-work related • Work exposure is an important consideration in determining work-relatedness and in return to work • Names for Musculoskeletal Disorders o Cumulative trauma disorders o Repetitive trauma disorders o Repetitive strain injuries o Occupational cervicobrachial disorders o Overuse syndromes o Work related disorders o Musculoskeletal Pain/Symptoms Tendons • The major force producing muscles of the hand are located in the forearm • Forces and movements are transferred from the muscles to the fingers by tendons • Tendon Sheaths • In places where tendons rub on adjacent anatomical structures, they are surrounded by tendon sheaths called synovial or bursa membranes • Tendon sheath secrete synovial fluid that lubricates and nourishes the tendons Nerves • Nerve carry electrical impulses that control exertions, movements, subconscious functions (blood flow, sweating) and provide information about touch, position and hot and cold) • The fingers are one of the most sensitive parts of the body • Properties of Musculoskeletal Disorders o mechanical and physiological process o related to work intensity and duration o require periods of weeks, months or years to develop o require periods of weeks, months or years for recovery o poorly localized, nonspecific and episodic o often unreported o multiple work and personal causes Localized Fatigue o mechanical and physiological process o pain and impaired work performance o develops in seconds, minutes or hours o recovery should be complete within minutes or hours after cessation of work o symptoms may be hard to distinguish from those of other disorders o workers should seek help if symptoms persist from one day to next or interfere with activities of work or daily living. MSD morbidity patterns: see: Bureau of Labor Statistics: Personal MSD Factors • Rheumatoid arthritis • Endocrinological disorders, e.g., diabetes • Acute trauma, e.g., bruises, burns, lacerations • Vitamin B-6 deficiency 1
  2. 2. Work-Related Musculoskeletal Disorders Work-Related Musculoskeletal Disorders of the Upper Limb • Wrist size and shape • Obesity • Gender • Pregnancy • Oral contraceptives • Gynecological surgery, e.g., oophorectomy, hysterectomy Screening & Diagnostic Tests Disease Test Positive Test Negative Total Present A B A+B Absent C D C+D Total A+C B+D A+B+C+D Sensitivity = A / (A+B) Specificity = D / (C+D) Positive Predictive Value = A / (A+C) Negative Predictive Value = D / (B+D) Katz JN, Larson MG, Fossel AH, Liang MH. Validation of a surveillance case definition of carpal tunnel syndrome. American Journal of Public Health 81(2):189-193, 1991. Given a screening test: Psen=0.90 & Pspec=0.90 For n=100 applicants of which 10% have or will develop a given condition we find: Test Test Positive Negative Total Present 9 1 10 Absent 9 81 90 Total 18 82 100 Work Factors of Musculoskeletal Disorders • Repeated or sustained exertions • Forceful exertions • Localized mechanical stresses • Posture stresses • Low temperatures • Vibration • Work schedule & duration • Psychosocial stresses Exposure – Response Work, Force and Posture Each work element of a “standardized job” involves a prescribed pattern of forces and postures for a given individual. Example 1: Case Packing Objective: Pack boxes of bottles into a cardboard case Production: 150 cases / hour Materials cartons boxes of bottles (15N or 3 lb per pair) Work elements, exertions and postures 2
  3. 3. Work-Related Musculoskeletal Disorders Work-Related Musculoskeletal Disorders of the Upper Limb a b Figure 2: Plots of right hand force (a) and right wrist flexion/extension postures (b) versus time. Job Analysis Tools: • Posture targeting (Corlett and Madeley 1979) • Force & posture tracking (Armstrong & Chaffin 1979) • Checklist (Keyserling and Stetson 1993) • RULA (McAtamney & Corlett 1993) • REBA (Hignett and McAtamney 2000) • Strain Index (Moore & Garg 1995) • ACGIH (ACGIH 2002) • Washing State (Washington State 2000) • Open ended inspection (Keyserling et al 1991) • OWAS (Karhu et al. 1977; 1981) • EMG probability distribution (Jonsson 1988) • Wrist velocity/acceleration (Marras and Schonmarklin 1993) • Portable Posture Exposure, PEO (Fransson-Hall & Gloria 1995) • OCRA (Colombini 1998) • Many similarities between job analysis tools, e.g., repetition Analysis of exertion patterns for control of fatigue: Bystrom and Fransson-Hall (1994) studied fatigue in intermittent work (work cycles varied from 5s work: 2.4s rest to 5s work: 15s rest) using multiple indices: heart rate, blood pressure, muscle blood flow, electromyography, muscle potassium and lactate efflux, perceived exertion, and grip force. Unacceptable fatigue occurred for combinations of work-rest cycles with a mean contraction intensity, %MVCmean, of 17%MVC or a continuous handgrip contraction greater than 10%. Thus we can write for intermittent work: %MVCmean x Ttot = %MVCrest x Trest + %MVCwork x Twork and Ttot=Twork + Trest Substituting Twork into the first equations enables us to calculate: Trest/Ttot = (%MVCwork-%MVCmean)/((%MVCwork-%MVCrest) Table:Assessment of MSD Risk Factors: Instrument Body Part Repetition Force UAW-GM RFC Upper limb RFC I: Low >30s; Hi <30s Selected factors: yes/no Keyserling & Stetson & back RFCII: Low, Medium, High 1993 (Latko et al1997) RULA McAtamney & Upper limb Muscle use score Loads Corlett 1993 & torso Exertions > 1 min <2kg, 2-10Kg, >10Kg > 4X / min Strain Index (generic) Hand, wrist, Efforts / min: Light, somewhat hard, Moore & Garg 1995 forearm < 4, 4-8; 9-14; 15-19; > 19 hard, very hard, near max Duty cycle: <10; 10-29; 30-59; 60-79; >80% ACGIH TLV Hand Wrist None to maximum (0-10) None to maximum, 3
  4. 4. Work-Related Musculoskeletal Disorders Work-Related Musculoskeletal Disorders of the Upper Limb ACGIH 2002 Includes, frequency, speed of continuous scale motion, duty cycle Washington State Upper limb, same motions >2hr/day intense Exertion of fixed force Washington State 2000 trunk keying >4hr/day holding unsupported objects of specified weights Wrist Velocity Marras Hand, wrist, Angular velocity & acceleration &Schonmarklin 1993 forearm of wrist (continuous scale) References ACGIH (2002). Hand Activity Level. Two Thousand Two Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Limits. cincinnati, American Conference of Governmental Industrial Hygienists: 109-119. Armstrong T, Buckle P, Fine L, Hagberg M, Jonsson B, Kilbom A, KourinkaI , Silverstein B, Sjogaard G, Viikari-Juntura E. A conceptual model for work-related neck and upper limb disorders, Scand. J. Work, Environment and Health, 19(2):74-84, 1993. Armstrong T, Lakey E. An Ergonomics Guide to Cumulative Trauma Disorders of the Hand and Wrist. Fairfax, VA: American Industrial Hygiene Association, 1994. Armstrong, T. J., D. B. Chaffin, et al. (1979). "A methodology for documenting hand positions and forces during manual work." J Biomech 12(2): 131-3. Armstrong, T. J., J. A. Foulke, et al. (1982). "Investigation of cumulative trauma disorders in a poultry processing plant." Am Ind Hyg Assoc J 43(2): 103-16. Bjorksten M Jonsson B, Endurance limit of force in long-term intermittent static contractions, Scand. J. Work Environ. Hlth. (1977 Mar) 3(1):23-7 Borg G. Psychophysical scaling with applications in physical work and the perception of exertion. Scand. J. Work Environ. Hlth. 1990;16(Suppl 1):55-58 Brandt E, Pope A (ed). Enabling America: Assessing the Role of Rehabilitation Science and Engineering. Committee on Assessing Rehabilitation Sciences., Washington, DC: National Academy Press, 1997. Bystrom, S. and Fransson-Hall, C. Acceptability of intermittent handgrip contractions based on physiological response. Human Factors 1994. 36(1), 158-171. Colombini, D. (1998). "An observational method for classifying exposure to repetitive movements of the upper limbs." Ergonomics 41(9): 1261-89. Corlett, E., S. Madeley, et al. (1979). "Posture targeting: a technique for recording working postures." Ergonomics 22(3): 357-366. Fransson-Hall, C., R. Gloria, et al. (1995). "A portable ergonomic observation method (PEO) for computerized on-line recording of postures and manual handling." Appl Ergon 26: 93-100. Health and Safety, Case Studies in Successful Occupational Health and Safety Practice. North Ryde, NSW: CCH International, 1991 Hignett, S. and L. McAtamney (2000). "Rapid entire body assessment (REBA)." Appl Ergon 31(2): 201-5. Karhu, O., P. Kansi, et al. (1977). "Correcting working postures in industry: A practical method for analysis." Applied Ergonomics 8: 199-201. Keyserling, W. M., D. S. Stetson, et al. (1993). "A checklist for evaluating ergonomic risk factors associated with upper extremity cumulative trauma disorders." Ergonomics 36(7): 807-31. – contact UAW Safety and Health Office for latest version. Marras, W. S. and R. W. Schoenmarklin (1993). "Wrist motions in industry." Ergonomics 36(4): 341-51. McAtamney, L. and E. Corlett (1993). "RULA: a survey method for the investigation of work-related upper limb disorders." Applied Ergonomics 24(2): 91-99. Moore, J. S. and A. Garg (1995). "The Strain Index: a proposed method to analyze jobs for risk of distal upper extremity disorders." Am Ind Hyg Assoc J 56(5): 443-58. NRC and IOM (2001). Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC, National Academy Press. Http:// Washington-State (2000). WAC 296-62-051 Ergonomics. 2002. Work-Related Musculoskeletal Disorders: A Review of the Evidence. National Research Council, National Academy Press, 2101 Constitution Avenue N.W., Washington, D.C. 20418, 1998. Http:// 4