Institute for Work & Health, A Case-Control Study of Biomechanical and Psychosocial Risk Factors for Occupational Low-Back Pain Michael S. Kerr, PhD Institute for Work & Health Toronto, Ontario, CANADA PREMUS 2001, Amsterdam Kerr et al. (2001) Am J Pub Health 91:

Institute for Work & Health, Study Collaborators Institute for Work & Health: Kerr MS, Frank JW, Shannon HS, Bombardier C University of Waterloo: Norman RW, Wells RW, Neumann P General Motors: Mr. Elmer Beddome CAW: Mr. John Graham The Ontario Universities Back Pain Study (OUBPS) Group Andrews D, Beaton DE, Dobbyn M, Edmonstone E, Ferrier S, Hogg-Johnson S, Ingelman P, Mondlock M, Peloso P, Smith J, Stanfield SA, Tarasuk V, Woo H

Institute for Work & Health, Why a case-control study? Uncertainty about role of physical demands necessitated concentration of effort on developing valid workplace measures Cohort model required multiple measures at multiple times to assess valid exposure Does a prospective cohort study with limited (e.g. once only) exposure assessment really provide more rigorous evidence than a case-control study with more detailed assessments?

Institute for Work & Health, Research Question After controlling for individual characteristics, what are the main work-related biomechanical and psychosocial risk factors for reported low-back pain?

Institute for Work & Health, STUDY SETTING GM-Oshawa autoplex 65 km east of Toronto Total hourly-paid work force – approx.12,000 3 Divisions:Car Assembly(7,000) Truck Assembly(3,000) FabricationsN/A Nursing stations – handle ALL WCB reports as well as most other health problems occurring at work- site Truck = 1 station; Car = 4 stations

Institute for Work & Health, The GM Study of Low-back Pain baseline questionnaire and physical exam 10,000 car and truck plant workers (hourly-paid) random selection (job-matched) accrued via workplace health stations conducted at home physical demands assessment CASES workers without LBP STUDY POPULATION workerswith LBP CONTROLS Incidence density sampling at work doing usual job video, EMG, checklists, posture (n=137) (n=179) (n2=65)

Institute for Work & Health, SUBJECT ENROLMENT (Voluntary) Random controls Cases A total of 381 subjects enrolled in the study Job-matched controls (used for proxy data)

Institute for Work & Health, CASE Definition Full-time, hourly-paid worker with “sprain- strain” LBP (reported to nursing stations) No lost-time or WCB claim requirement No previous worksite LBP report (90 days)

Institute for Work & Health, SF-36, Health-related quality of life Physical Function Role – Physical Bodily Pain Social Function VitalityRole – Emotional Mental Health General Health Were cases and controls comparable except for LBP? sd from male reference population Ref: Garrat et al. (1993) BMJ 306:1440-4

Institute for Work & Health, INDIVIDUAL Characteristics Age, height, weight, body mass index, sex education, marital status, preschool children, main wage earner, non- occupational physical activity, smoking, alcohol consumption STUDY VARIABLES - 1

Institute for Work & Health, BIOMECHANICAL Factors Peak Forces: compression; shear; hand force Cumulative Forces: average and integrated compression; Low-level (static) Forces: compression Posture and Movement: peak flexion; time non-neutral; trunk kinematics (reduced a priori to about 20 key variables, NO EMG) STUDY VARIABLES - 2

Institute for Work & Health, STUDY VARIABLES - 3 PSYCHOPHYSICAL Factors self-rated physical exertion measures distinct from "objective" measurements of physical demands analyses, but may also have additional role to play over and above the measured demands e.g. tolerance levels, "job stress", etc.

Institute for Work & Health, Karasek-Theorell Job Content Instrument "psychological demand", decision latitude, supervisor support, coworker support, workplace social environment, job self-identity - job dissatisfaction, mastery, empowerment, status inconsistency ("over-education") STUDY VARIABLES - 4 PSYCHOSOCIAL Factors

Institute for Work & Health, Summary of Key Risk Factors (after adjusting for individual characteristics)

Institute for Work & Health, Study Strengths Directly measured physical demands data combined with (basic) physical exam and interview-assisted psychosocial data for individual subjects Comprehensive workplace job demands assessments (generalizable – i.e. not specific to automobile manufacturing) Well defined study base for subject selection

Institute for Work & Health, Study Weaknesses Modest participation rate (approx 60%) Relied on workplace reporting mechanism to identify cases Self-report only for psychosocial factors Case-control design But … does a prospective cohort study with limited once only exposure assessment really provide more rigorous evidence than a case-control study with more detailed assessments?

Institute for Work & Health, How did we control for Bias? Directly measured physical demands data rather than self-report Job-matched controls used to examine potential recall bias (none observed) Used newly incident cases rather than prevalent cases Compared cases with non-participating compensation claimants (no differences) A priori reduction in variables eligible for regression modeling (multi-methods)

Institute for Work & Health, Possible Biological Mechanisms HORMONES e.g. cortisol MUSCLE TENSION PSYCHOSOCIAL LOAD INDIRECT EFFECTS PSYCHOSOCIAL LOAD e.g. job control BIOMECHANICAL LOAD e.g. cumulative compression DIRECT EFFECTS BIOMECHANICAL LOAD TOLERANCE REDUCED TOLERANCE EXCEEDED TISSUE RESPONSE

Institute for Work & Health, Main Conclusions Consistency and strength indicates biomechanical load increases LBP risk Psychosocial factors also shown to be associated with reporting LBP Job dissatisfaction not a risk factor for reporting LBP in this setting Psychosocial instruments (especially Karasek’s demands scale) may require further refinement for MSK studies

Institute for Work & Health, For additional information please contact: Mickey Kerr The Institute for Work & Health 481 University Ave., Suite 800 Toronto, ON M5G 2E9 Phone: (416) Fax: (416) Website: The Institute for Work & Health operates with the support of the Ontario Workplace Safety & Insurance Board Kerr et al. (2001) Am J Pub Health 91: