Annalee Yassi, Karen Lockhart

Transcription

1 Review Work-relatedness of low back pain in nursing personnel: a systematic review Annalee Yassi, Karen Lockhart Global Health Research Program (GHRP), The University of British Columbia, Vancouver, BC, Canada Background: Although non-specific low back pain (LBP) is known to be multifactorial, studies from across the globe have documented their higher prevalence in nurses. This systematic review was conducted to ascertain whether this much-documented association constitutes a causal relationship, and whether there is a discernible threshold of exposures associated with this elevated risk. Methods: PRISMA guidelines were followed and standard critical appraisal tools were applied. The outcome of interest was non-specific LBP or back injury; exposure was performing nursing duties. Applicable studies, published in English during , were identified through database searches, screened against preset inclusion/exclusion criteria. Ergonomic assessments of nursing tasks were included along with epidemiological studies. Bradford Hill considerations for causation were utilized as a framework for discussing findings. Findings: Of 987 studies identified, 89 qualified for inclusion, comprising 21 longitudinal, 36 cross-sectional analytic, 23 descriptive biomechanical/ergonomic, and 9 review studies. Overall studies showed that nursing activities conferred increased risk for, and were associated with back disorders regardless of nursing technique, personal characteristics, and non-work-related factors. Patient handling appears to confer the highest risk, but other nursing duties are also associated with elevated risk, and confound dose response assessments related to patient handling alone. Associations were strong, consistent, temporally possible, plausible, coherent, and analogous to other exposure-outcomes, with risk estimates ranging from 1.2 to 5.5 depending on definitions. A threshold of nursing activities below which the risk of back disorders is not elevated has not been established. Interpretation: Notwithstanding the bio-psycho-social nature of LBP, and complexities of studying this area, sufficient evidence exists of a causal relationship between nursing tasks and back disorders to warrant new policies. Keywords: Back disorder, Back pain, Health workers, Nurses, Nursing personnel, Nursing tasks, Occupational injury, Patient handling Introduction and Purpose While non-specific low back pain (LBP) is known to be multifactorial, 1 there is extensive literature from across the globe indicating a high prevalence of back disorders in nurses. Specifically, as stated by Hignett more than 15 years ago, based on a review of over 80 studies published over the previous three decades, it can be concluded that nurses are among the highestrisk occupations with respect to low back problems. 2 Pooling findings from published literature, Hignett determined that nurses had a point prevalence of low back problems well exceeding that of the general population; she also noted that nurses who engage in frequent patient handling have higher risks. 2 National surveys 3,4 and more recent systematic reviews 5 7 have reiterated this same conclusion. For Correspondence to: Karen Lockhart, Global Health Research Program (GHRP), The University of British Columbia, Rm. 430, 2206 East Mall, Vancouver, BC V6T 1Z3, Canada. karen.lockhart@ubc.ca example, the 2005 national survey in Canada of almost nurses confirmed that Canadian nurses do indeed incur significantly higher rates of LBP compared with the general working population. 3 The consistency of existing evidence that nurses have a higher rate of back problems when compared to the general population (e.g. Refs. 8 and 9) leads to the question is this association causal? There is a worldwide shortage of nurses; 10,11 thus, while all workers deserve decent working conditions, 12 the need to improve working conditions, and minimize work-related frustrations, is particularly important in this scarce workforce. Notwithstanding the fact that LBP, similar to other musculoskeletal conditions and indeed most diseases is multifactorial, 1,13,14 we conducted this systematic review to ascertain if the literature provides guidance to streamline the oftenlengthy adjudication process to determine workrelatedness when nurses develop back disorders. 15 ß W. S. Maney & Son Ltd 2013 DOI / Y International Journal of Occupational and Environmental Health 2013 VOL. 19 NO

2 Methodological Approach We followed standard practices for systematic reviews, and have completed the PRISMA checklist for reporting (see Appendix 1, available at dx.doi.org/ / / y S1). Given the large amount of evidence related to the hazardous nature of nursing activities (e.g. Refs. 6, 7, 16 35) and the many ergonomic standards and guidelines specifically focused on reducing the hazards involved in patient handling, we focused on the following research question: Is there sufficient evidence that the nature of nursing work substantially increases the risk of back disorders; and if so, is there is a threshold of patient handling activities that can be determined, with respect to duration of time performing these activities, or intensity of the activities performed, below which work-related back disorders are unlikely to occur? With respect to defining participants, interventions, comparisons, outcomes, and study design (PICOS) according to the PRISMA reporting guide, the participants in this systematic review were all personnel performing nursing tasks, whether as professional nurses or other categories of nursing staff; the intervention in this case is not a therapeutic intervention but is interpreted otherwise as an exposure namely performing nursing tasks; the comparisons in the various studies included in this review were comparisons to the population at large, or other occupational groups, or comparison among different subgroups within nursing, or internal comparisons according to different risk factors, and/or comparisons over time; the outcome of interest was non-specific back disorder, which, in keeping with standard search terms, we defined as back pain and/or back injuries generally manifesting as non-specific LBP and we have excluded studies that refer to back pain associated with systemic illness or major trauma. We report risk ratios or odds ratios, as provided in the studies reviewed. With respect to study design, no study design that contained systematically collected quantitative data relevant to our research question was excluded, thus both observational and experimental studies were included, according to inclusion and exclusion criteria described below. While some systematic reviews confine their assessment to epidemiological studies, other authoritative organizations include animal and other laboratory studies in assessing causal inference, as discussed recently by Verbeek. 40 We therefore adopted this more comprehensive approach and included relevant ergonomic literature; we did not systematically search for animal evidence, although alluded to animal evidence in assessing plausibility of results. Table 1 summarizes and briefly expands on the rationale for each of the PICOS decisions. Search strategy We used the search terms listed below by database searched, which included MEDLINE (1980 June 2012), EMBASE (1980 June 2012), CINAHL database, which was searched through EBSCOhost (all records until 2012), and Cochrane Library; we also searched through Google Scholar Advanced ( ). The complete search is available at /09/systematic-review-nurses-search.pdf The MEDLINE search strategy was the following: 1. nurse(s) 2. back injury 3. back pain 4. back disorder 5. patient handling 6. 1 & & & 4 9. threshold & patient tasks & 2 & & 3 & & 4 & patient lifting & 2 & & 3 & & 4 & health worker or 3 or 4 & & 5 & & 5 & & 5 & & 9 & & 11 & & 11 & & 11 & & 15 & 19 Searches in the other databases mentioned were undertaken using combinations of the following words: threshold, back injury/back pain and nurses; duration, back injury/back pain and nurses; back pain nurses transfer; cumulative load, back injury/ back pain and nurses; biomechanics, back injury/ back pain and nurses; intensity, patient-handling nurses back pain/injury. In accordance with international guidelines for conducting systematic reviews, we searched the described databases with the terms noted as well as the gray literature by visiting websites of organizations and associations of interest, such as the Association of Workers Compensation Boards of Canada, to maximize the likelihood of finding all relevant studies. We also screened reference lists of included studies for further eligible studies. 224 International Journal of Occupational and Environmental Health 2013 VOL. 19 NO. 3

3 Table 1 PICOS definitions and rationale PICOS criterion Definition Rationale Population Intervention (exposure) Comparison Outcome Study designs Nursing personnel (however defined in studies in question) Nursing activities (however defined in studies in question) General population, or other occupational groups, or subgroups within nursing, or self-comparison over time, or no comparison group. Non-specific back pain or back injury, excluding back pain associated with specific systemic conditions or major trauma. All including ergonomic (biomechanical) descriptive studies; cross-sectional and longitudinal analytic studies (including intervention studies where relevant, see Table 2); or systematic reviews. Different jurisdictions define nurses differently; we did not exclude any population of workers performing nursing duties including professional nurses, auxiliary nurses, nursing assistants regardless of subsector (acute, long-term, other), as long as the study population provided direct client/patient/resident nursing care. Nursing activities include patient-handling as well as non-patienthandling tasks associated with caring for patients. We included studies with both qualitative and quantitative assessments of this exposure. (see Table 2). Data for job descriptions that were strictly administrative were not considered nursing tasks. Different studies have different comparison groups. For national surveys, nurses were generally compared with the population at large; for many cross-sectional studies nurses were compared with people employed in other occupations or groups of nurses were compared with other groups of nurses with different work-related and/or non-work-related characteristics; for some longitudinal studies, nurses were followed over time, and outcome compared according to various work-related and/or non-work-related characteristics. The vast majority of back injuries are based on self-reports (some witnessed; others not) and whether there is a discernible incident or not, back injuries are generally closely associated with low back pain; similarly back pain is a subjective outcome. Different studies define these back disorders differently some requiring long periods without back pain prior to the onset of back pain, some required there to be time lost from work in order to include this outcome. While some reviews focus solely on low back pain, our review, to include studies with more objective outcome of relevance, we included studies with any outcome related to back pain and/or back injuries (see Table 2). This systematic review is not meant to determine the effectiveness of interventions as the success of interventions depends on many factors unrelated to the exposure of interest. Intervention studies were therefore included only if they also contained data relevant to the research questions in this study. Inclusion/exclusion criteria and study selection Relevant studies were identified using a two-step comprehensive search strategy. First, as detailed above, we conducted a computeraided search of relevant databases. Only studies published in full in English were included. We limited our search to studies published after As noted above, we included other systematic reviews, some of which went as far back as 1966; thus the results of earlier studies are adequately represented. We did not exclude studies based on methodological weaknesses if they met the criteria established for relevance, as shown in Table 2. We did, however, categorize studies by study design as is standard practice for systematic reviews 42 and explicitly assessed study weaknesses. The second step was to determine study relevance. This was conducted using a two-stage process. Studies had to meet criteria in the first stage before advancing to the next stage (see Table 2), as is customary. Stage 1 of this process resulted in 987 documents. These documents were screened by both authors Table 2 Criteria for inclusion/exclusion in the systematic review A. Stage 1 questions (Yes5inclusion; No5exclusion) 1. Is the population in the study nurses (i.e. personnel who perform nursing duties, as defined by the study s authors)? 2. Does the study meet both of the conditions below? a. Involve back injuries or back pain other than back pain associated with systemic disease or major trauma b. Involve nursing activities associated with patient care 3. Is the date of publication between 1990 and November 2010? B. Criteria for stage 2 of relevance assessment Questions (Yes5inclusion; No5exclusion) 1. Does the article/report provide primary data or a literature review of relevant data? 2. Does the study provide systematically collected data specifically regarding the risk (ergonomically and/or epidemiologically assessed) of nurses back disorders on one hand, and patient-handling tasks and/or other nursing tasks on the other? 3. Is the study published in full in English in either a peer-reviewed scientific journal or a report that has been the subject of peerreview by an external body? 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4 against the inclusion and exclusion criteria. A document was excluded when both authors were in agreement that it did not contain information pertinent to the research question. Thus, studies which focused on interventions such as training of workers, use of mechanical lifts and repositioning techniques as well as biomechanical studies were excluded unless they contained data characterizing the nature of nursing activities associated with increased risk of back disorders and/or determining a threshold of time or effort at which nurses were more likely to incur back disorders. Specifically, abstracts of all 987 documents were reviewed by both authors; where disagreements arose, a discussion ensued to resolve the issue. If there were questions as to whether or not the study qualified for the review at Stage 1, both co-authors reviewed the full text to include or exclude the study. Examples of excluded studies were secondary prevention intervention studies where the main outcome of interest was low back pain remission; we also excluded commentaries and editorials providing no new empirical evidence. Similarly, workplace intervention studies by Gundewall and colleagues, 44 and by Hartvigsen et al., 45 were originally included in the systematic review, but were deleted from the final analysis for similarly failing to meet our inclusion criteria. A total of 89 documents met the inclusion criteria for this systematic review. See Fig. 1 for the graphic representation of the study selection process. Synthesizing results and assessing causation We noted the size and definition of the population studied, research techniques used, and measurement of outcome, then assessed limitations in each study, highlighting measures taken by the researchers, if any, to mitigate biases. Additionally, to systematically assess study quality and the potential for bias, we carefully applied each of the criteria in the Critical Appraisal Skills Program. 46 These were synthesized in table form, according to study design, along with a summary of the results for each study. For longitudinal studies, as shown in Tables 3 5, we used the PICOS framework to guide the reporting of the studies, noting such factors as length of followup, and commenting on how each study added to the research question of this systematic review, followed by the critical appraisal and findings including providing risk estimates where the data provided in the article were sufficient to calculate these (see Tables 3 and 4). For the cross-sectional and ergonomic studies, we summarized the above information in Appendices 2 4 (available at / / Y S1). The Grading of Recommendations Assessment, Development and Evaluation approach to synthesizing Figure 1 Study selection process and assessing evidence has been shown to be consistent with the more generally employed Bradford Hill approach to synthesizing evidence to assess causation. 47 Given the recent debate about the appropriate use of Bradford Hill considerations in assessing work-relatedness of musculoskeletal disorders, we decided to also explicitly apply the Bradford Hill considerations 56 to the body of literature identified, carefully taking the concerns expressed by others 40,48 55,57 60 about this general approach to determining causation into account. A discussion of the strengths and limitations of the literature reviewed was then also integrated into the discussion of each of the Bradford Hill factors. In doing so, we note that experimental evidence is one of the particularly contentious considerations. Ascertaining the determinants of successful interventions to prevent back pain and back injury in nurses was definitively not part of our research questions, as the determinants of a successful intervention go well beyond the issue of causation. We note that a systematic review of the effectiveness of interventions to reduce LBP in nurses has indeed been conducted by others. 5 We therefore carefully reviewed that publication, and updated it by including further reviews of interventions to prevent back disorders in nurses conducted in the last 5 years, which met our inclusion criteria by virtue of having data relevant to our research questions. This evidence, where relevant to the questions in this systematic review, was integrated into the tables presented below and the causation assessment outlined in this article. Of note, we supplemented the systematic review with a review of the biomedical literature, informing our 226 International Journal of Occupational and Environmental Health 2013 VOL. 19 NO. 3

5 Table 3 Cohort studies with quantitative risk estimates related to low back pain (LBP) in nurses Reference Participants Exposure (and intervention, where applicable) Comparisons Outcome (and measurement techniques) 1. Eriksen et al Norwegian nurses aides were randomly selected from the Union s member list, and were mailed a questionnaire. After one reminder, 7478 (62.3%) consented to participate in the study and completed the questionnaire nurses aides fulfilled the inclusion criteria and were included in the study. Nurses aides duties performed.18 hours per week, including: patient positioning in bed; lifting or supporting patients manually between bed and chair; lifting, carrying, and pushing heavy objects. Internal comparison of injury rates by divisions defined in questionnaire responses. Intensely bothered by LBP LBP-related lost time (.3 days,.14 days,.8 weeks). Ascertained with a mailed questionnaire at baseline, 3 and 15 months. Appraisal: Strong study, with truly prospective data collection, thereby avoiding recall bias. Impact of healthy worker effect was reduced by adjusting for LBP during the 3 months prior to baseline, but not removed completely. Biases and confounders: The authors acknowledge that uncontrolled background factors, which they list as psychological traits, hostility, poor self-esteem, etc. may also have influenced the results. Quantitative risk estimates: Adjusting for baseline health complaints, demographics, lifestyle and familial factors, intense low back symptoms were predicted by frequent positioning of patients in bed (odds ratio51.63 for adjusting 5 9 patients per average shift), perceived lack of support from superiors [odds ratio (OR)51 for lowest quintile compared to OR50.6 for second lowest quintile], and perceived lack of pleasant and relaxing culture in the work unit (OR51 for not at all/very little, compared to OR50.46 for rather little). Change in work tasks increased risk of lost-time back pain by as much as an OR of 4.14 [confidence interval (CI): ]. 2. Heap nurses employed in one health district in the UK. Entrants to the survey were identified from forms completed for all accidents/incidents. Occupational activities associated with nursing, specifically patient handling. Internal comparisons by nursing categories and demographics. (Also compared trends over time in relation to multicomponent interventions) Lost-time low back injury related to patient handling. All entrants to the survey, with one exception, were seen and examined in the occupational health department within 6 weeks of the initial incident: detailed account of the incident was recorded and the back was examined. Appraisal: Prospective cohort study extending over 5 years. The study was useful in determining the prevalence of low back injuries caused by patient handling. Bias and confounders: Medical histories and risk factors (other than occupational and demographic) between injured and non-injured were not compared, and back injuries unrelated to work were excluded. Only injuries that were reported were taken into account, thus possibly lowering the actual number of back injuries as some injuries may go unreported. Quantitative risk estimates: Highest injury rate was in nursing auxiliaries (26.9 per 1000 in 1984), compared to a 7.8 per 1000 low back injury rate in staff nurses in The author hypothesized that nursing auxiliary suffered such a high injury rate because they carry a heavier lifting load, though he did not provide quantitative estimates per load category. Age, height, sex, and rank had no predictive value for injuries; except for those under 20 years old (nurses-in-training). Back injury rate fell from 13.6 per 1000 in 1981 to only 9.6 per 1000 in This decrease in injury rate is likely attributable to multicomponent workplace interventions that were implemented. International Journal of Occupational and Environmental Health 2013 VOL. 19 NO

6 Table 3 Continued Reference Participants Exposure (and intervention, where applicable) Comparisons Outcome (and measurement techniques) 3. Jansen et al workers from seven nursing geriatric homes in the Netherlands were invited to participate in the study; 769 (64%) agreed to participate. After 1 year, 523 (68%) of the subjects were observed again. Occupational activities associated with nursing, specificallyphysical load during work requiring trunk flexion between 20 and 45u, trunk flexion over 45u; and lifting or carrying loads over 10 kg Internal comparison by psycho-social work factors (physical load, age, decision authority). New episodes of LBP lasting for at least a few hours in the past 12 months; Disabling LBP. Ascertained by a quantitative assessment of physical load at baseline and a questionnaire survey at baseline and at 1 year. Appraisal: Prospective cohort followed for 1 year. Hierarchical regression analysis with a spline function was used to estimate dose response relations. Physical workload was measured quantitatively, and questionnaires at baseline for all were compared at 1 year. Hence strong prospective study with respect to quantifying the risk. Bias and confounders: Lack of information on individual characteristics of non-participants; a healthy worker effect may be decreasing actual risk levels; also difficult to predict the extent and the direction of physical load may also have biased estimates of physical load effects. Quantitative risk estimates: The risk of LBP was associated with low decision authority [relative risk (RR)51.27] and high work demands (RR51.82). The risk of disability LBP was positively associated with age (RR51.81) and not psychosocial factors. Trunk flexion over 45u was associated with disabling LBP, with a relative risk of 3.18 (95% CI: ) for 1 hour and 45 minutes of bending per week (ninetieth percentile) relative to 30 minutes per week. 4. Josephson et al. 137 Registered nurses at a hospital in Sweden. All personnel on wards with patients who required daily care participated. Nursing duties associated with patient daily care, e.g. move the patient from bed to chair, daily hygiene, etc.). Internal comparisons by job-related factors (e.g. job strain). Musculoskeletal symptoms (in the past 12 months; on-going or not) including low back pain symptoms, assessed on a 10-point scale. Ascertained by a selfadministered questionnaire completed at baseline and once a year for 3 years. Appraisal: Prospective cohort followed for 3 years. Although this was a longitudinal study, N5 565, 553, 562, and 419 nurses at the first, second, third, and fourth survey, respectively, only 50% of the initial 285 were followed through all four surveys, with the remaining consisting of new employees who joined the cohort. Biases and confounders: It is possible that a healthy worker effect was operating in this study; the authors did not comment on this. Quantitative risk estimates: Of the 285 subjects, 13% were defined as cases at all four assessments and 46% varied between cases and not cases during the study period. Almost half of the healthcare workers varied between being a case and not, over this period. The analysis indicated that job strain is a risk factor for musculoskeletal symptoms, with RR when comparing the groups with and without job strain. The risk was higher when job strain was combined with perceived high physical exertion (RR ). 5. Kim et al. 138 Workers Compensation claims related to musculoskeletal disorders filed during by employees in a large US healthcare system (n53452). Occupational activities associated with nursing (e.g. patient handling including: lifting, twisting, pushing, holding or carrying.) Internal comparisons by personal (e.g. sex and age) and job-related factors (e.g. scheduled shift, patient handling, etc.) Rates for Workers Comp claims (patient handling, demographic, work, and injury characteristics were obtained from files); relative risks for musculoskeletal disorders were ascertained from reviewing claims to determine risk factors. Appraisal: 7-year historical prospective study conducted during Strong study in analyzing risk factors across professions (patient handling). Biases and confounders: The authors also note that selection and information biases, as well as reporting biases, may have distorted results toward the null hypothesis. Some possible confounders, including psychosocial factors and co-morbidity were acknowledged by the authors as not considered. Quantitative risk estimates: About half the claims involved patient handling. In the regression model without patient handling, emergency medical workers (RR55.5), women (RR51.1), years of age (RR51.4), union members (RR51.5), evening shift workers (RR51.4), and fulltime workers (RR52.9) showed associations with musculoskeletal disorders. However, all the observed associations disappeared when patient handling was included in the regression model; patient handling was the only factor showing an association with musculoskeletal disorders (RR51.2, 95% ). 228 International Journal of Occupational and Environmental Health 2013 VOL. 19 NO. 3

7 Table 3 Continued Reference Participants Exposure (and intervention, where applicable) Comparisons Outcome (and measurement techniques) 6. Niedhammer Six hospitals in France. Female nurses were randomly et al. 139 selected from staff records: day shift and either permanent or alternating night work (n5469). Occupational activities associated with nursing: physical load (patient transfer, standing, etc.), and shift work, were considered. Internal comparisons by personal (e.g. age, smoking habits, etc.) and job-related factors (e.g. physical work-load). Chronic or recurring back pain; cervical pain; dorsal pain; lumbar pain; medical treatment for back pain. Ascertained by selfadministered questionnaire in 1980, 1985, and Appraisal: Prospective cohort followed for 10 years. Cross-sectional and longitudinal analyses were performed. Strong study in quantifying risk factors other than work-related (e.g. smoking). Biases and confounders: There was no independent assessment of physical workload or stress. Also a healthy-worker effect may be operating. Quantitative risk estimates: Factors of importance in the occurrence of back pain: age (OR51.86 for years), tobacco consumption (OR51.97), and workload (OR52.11). 7. Schoenfisch et al patient care staff in a community hospital and a medical center in the USA. Occupational exposure associated with patient-handling tasks and non-patient-handling tasks, before/ after a lift equipment policy change. Pre post at the facility before and after the implementation of a no-lift policy and the introduction of lifts. Rates of musculoskeletal injuries, days away from work, and restricted work days, ascertained by workers compensation claims data that were linked to human resources data. Appraisal: Prospective cohort followed for 13 years (intervention: introduction of lifts). Strong study in showing the high risk of patient handling. Bias and confounders: Using Workers Compensation claims data to define the injury experience among these workers limited the study to injury claims that were reported and accepted. Quantitative risk estimates: Adjusted incidence rates (IRRs) were highest for occupational/physical therapists aides, who had an adjusted IRR of 21.3 compared to managers. The risk was also very high for nursing aides (IRR58.2) and other nurses (IRR5 3.8); 72% of injuries were attributed to patient handling. No change in patient-handling injuries was observed pre versus post the introduction of lifts at the medical centre but a decrease of 44% was seen at the community hospital. At both hospitals, the rate of days away declined immediately before it was reasonable for the intervention to have been adopted, suggesting that other contextual factors such as institutional changes including a shift in the accountability of lost workday costs from the hospital to the unit managers around this time could be responsible. 8. Smedley et al hospital based nurses employed in the UK were sent a survey; 616 women completed the baseline survey; 83% agreed to take part in the longitudinal phase of the study. Of these, 961 women with no LBP in the month before the baseline questionnaire were excluded. Occupational activities associated with nursing: patient handling, manually or with a device. Internal comparisons: LBP lasting.1 day and occurring Survival analysis to explore constitutional and occupational risk factors, measured at baseline. other than in association with pregnancy, menstruation, or febrile illness; and lost-time LBP, ascertained by a baseline questionnaire and a short follow-up questionnaire sent every 3 months for 2 years. Appraisal: Prospective cohort up (every 3 months for 2 years). Strong study, with cohort consisting only of those who had been free from LBP for at least 1 month at baseline. Showed clear dose response related to nursing tasks and back disorders. Bias and confounders: The incompleteness of follow up was a potential weakness. Quantitative risk estimates: Of 838 women who provided data suitable for analysis, 322 (38%) developed LBP during follow up, including 93 (11%) whose pain led to absence from work. The strongest predictor of new LBPwas earlier history of the symptom: of 92 women who reported pain in the 12 months before answering baseline questionnaire and a history of pain for at least one month in total, 61 (66%) developed further symptoms during follow-up (91.0 new episodes per 100 woman years) and 21 (23%) required time off work as a consequence. Exposure-response trends were indeed documented for various work tasks, all of which correlated with each other. Risk factors included being tasked with patient handling. With all LBP as the outcome, exposure-response trends were observed for manual transfer of patients between bed and chair (OR51.6; 95% CI: when performed.10 times per shift); transfer of patients between bed and chair with a hoist (OR51.6; 95%CI: when performed.5 times per shift); manually moving patients around that is, repositioning them on the bed (OR51.7; 95%CI: when performed.10 times per shifts); and lifting patients in or out of the bath with a hoist (OR52.1; 95%CI: when performed.5 times per shift). Low mood was predictive of LBP leading to absence from work (OR53.4; 95%CI: ), and height was a predictor of LBP only in tallest women (OR51.7; 95%CI: for women cm tall). Other demographic variables were not predictive. International Journal of Occupational and Environmental Health 2013 VOL. 19 NO

8 Table 3 Continued Reference Participants Exposure (and intervention, where applicable) Comparisons Outcome (and measurement techniques) 9. Venning et al. 65 Rosters of nursing personnel from 10 Ontario hospitals identified 5649 subjects eligible. Completed questionnaires were returned by 4306 subjects (76%). Occupational activities associated with nursing: lifting requirement, hours and type of shift, and length of employment. Internal comparisons by personal (e.g. age) and job-related factors (e.g. amount of daily lifting) Back complaint (work-related injury or complain of discomfort), ascertained by baseline self-administered questionnaire, and a post-injury survey used only for injured personnel over the 12-month study period. Appraisal: Prospective cohort, followed for 1 year. Very strong study, as truly prospective, and with a large cohort, permitting logistic regression to assess the impact of risk adjusted for all major factors. Biases and confounders: There was no accounting for unreported injuries, lowering the actual injury count; on the other hand, neck injuries were included in the definition of back hence increasing the injury count. Additionally, the authors note that a healthy worker effect may be operating because at baseline, subjects had to be working in a facility to receive the questionnaire; a selection bias may be present in that nurses who experience unreported back pain may select out of patient care activities. Quantitative risk estimates: Significant predictors of back injury were four factors: The adjusted ORs observed were 4.26 for service areas where lifting occurs most as compared with areas where lifting occurs least; 2.19 for daily lifters versus light, occasional, and non-lifters; 1.77 for nursing aides versus registered nurses and supervisory personnel; and 1.73 for individuals who previously reported back injury versus those who had not reported previous injury. 10. Videman et al nursing students in Finland who started their training in one of the four study years. Occupational activities associated with nursing: physical workload, patient handling. One-half (control group) received traditional training in patient handling. The skills of both groups were assessed on graduation. Prevalence, severity and onset of back pain; skills in patient handling. Ascertained by questionnaires (distributed at the beginning of nursing school, every 4 months thereafter, and 1 year after nursing); and patient-handling skills assessments, respectively. Appraisal: Prospective (intervention: training on patient-handling skills) and case-referent study to assess factors associated with back injuries or back pain. The case-referent analysis of factors associated with back pain was a strong aspect of this study. The authors attribute the lack of significant difference attributed to training as possibly due to small sample size. Bias and confounders: Use of video recording for skills assessment presented problems because of loss of stereoscopic vision, and hindered application of skills. Quantitative risk estimates: In multiple regression analysis, the major risk indicators for back injuries were poor patient-handling skills (skills rating of,0.75, n586, 24% suffered back injuries during the first year as nurses, while only 2% of the nurses with skills rating.0.75), low numbers of repetitions in the sit-up test (OR of sudden back pain for nurses who scored low on the sit up test compared to OR51.0 for those who scored high on the sit-up test, when they held strenuous working postures for,3 hours daily ), and high workload scores (20% of nurses in the heavier perceived workload reported back injuries compared to 13% reported injuries in the lighter perceived workload group). For the group who scored high on handling skills but low on the sit-up test, the authors calculated an OR of 15 for nurses who held strenuous working postures for.3 hours daily, compared to an OR of 4.3 when the strenuous working posture is held for,3 hours. 230 International Journal of Occupational and Environmental Health 2013 VOL. 19 NO. 3

9 Table 3 Continued Outcome (and measurement techniques) Exposure (and intervention, where applicable) Comparisons Reference Participants Self-reported LBP defined as discomfort in the spinal area for at least one day in the 12-month follow-up period, excluding pain caused by menstruation, cancer, vascular disease or previous back surgery. Ascertained by a telephone interview at the end of the 12-month study period. Internal comparisons between the nurses who suffered LBP and those who didn t, by job-related factors (e.g. patienthandling activities) and psychological factors. Occupational activities associated with nursing: patient handling, work posture. 11.Yip nurses at six Hong Kong district hospitals. 224 participated for the initial interview. Mix of convenience and random-sampling methods. Appraisal: Prospective cohort followed for 1 year. Solid prospective study. Risk factors were assessed before the onset of symptoms, hence minimizing bias (e.g. in the reporting of nursing activities). Biases and confounders: Incompleteness of follow-up (36% lost), although the author noted no differences in demographics and job data between the participants lost to follow-up. Self-report and the lack of physical examination yields the possibility of biased recall of symptoms, posture or activity. Quantitative risk estimates: Fifty-six (38.9%) nurses reported experiencing new LBP. Sedentary leisure time activity was not associated with new LBP. Being comparatively new on a ward (adjusted RR5 2.90), working in bending postures (adjusted RR: 2.76) and poor work relationships with colleagues (adjusted RR: 2.52) were independent predictors of new LBP. analysis of causation (discussed below) by reviewing the basic science knowledge pertinent to this question, as reviewed extensively by the Institute of Medicine and National Research Council, 61 and further reviewed by other experts. 62,63 We also note that descriptive and cross-sectional studies cannot address the question of temporality (as discussed below): in other words, they cannot reliably determine whether back problems preceded the work as a nurse. Hence all the studies listed in Appendix 3 and 4 are subject to the bias inherent in all studies with such study designs. Longitudinal studies are methodologically stronger, and we confined our more detailed assessment of quality to the longitudinal studies. Given the interest in the quantitative assessment of risk, we specifically focused on the 10 longitudinal cohort studies that provided quantitative risk assessments related to LBP associated with nursing tasks, as well as the two case control studies. It is however noteworthy that the overall findings from the cross-sectional studies are consistent with the longitudinal studies. As alluded to above, where studies have taken measures to ensure that study subjects were devoid of the outcome of interest prior to the exposure in question, such measures are listed in our synthesis tables. Additionally, we note that the healthy worker effect 64 may have affected some of the studies, whereby workers leave their occupation, or are assigned less demanding work tasks, when they develop the outcome of concern (back disorders in this case), thus artificially lowering the relative risk associated with the exposure. Where this has been considered by the study in question, we have noted this in the synthesis tables as well. Results Of the 89 studies that met the inclusion criteria for our systematic review, 21 were longitudinal analyses; 36 were cross-sectional analytic studies relating the exposure to the outcome of interest; 23 were descriptive studies using biomechanical and other ergonomic techniques to assess nursing activities with respect to the predictors of risks for back pain and back injury; and 9 were review studies, compiling evidence from other published studies. As shown in Table 3, 10 of the 21 longitudinal studies were prospective studies with quantitative risk estimates relevant to our research question; two were case control studies (Table 4); and there were eight longitudinal studies that provided valuable information but lacked quantitative risk estimates for workrelated factors due to some aspect of their study design (see Appendix 2). These prospective studies are consistent in showing that work-related factors (e.g. service area, lifting, job category, organizational, and psychosocial work factors) in addition to International Journal of Occupational and Environmental Health 2013 VOL. 19 NO

10 Table 4 Case control studies with quantitative risk estimates related to low back pain in nurses Reference Participants Exposure Comparisons Outcome measures 1. Engkvist et al. 66 Cases were 240 nurses who reported work-related back injuries while employed at the Stockholm County hospitals from 1 March 1992 to 31 December Occupational exposure associated with nursing, specifically work organization (type of clinic and hours), physical exposure (patient transfer, use of device, etc.). The exposure information referred to the week before the over-exertion back injury for the cases. Randomly selected three referents for each case from the source population, matching on sex and age (N5614 referents). Cases and referents compared on work-related (e.g. schedule) and personal factors (e.g. age). Work-related over-exertion back injuries, ascertained by information on an insurance form and a posted questionnaire. Appraisal: Strong case control study, providing useful information on the relative importance of work-related versus non-work-related factors. Biases and confounders: All who reported an injury, and had been working for at least 1 week during the previous 3 months, were included in the study regardless of whether they had been on sick-leave. This inclusion might lead to the observed relative risk appearing lower than if only cases with the most severe injuries had been included. The study is limited in quantifying risks associated with specific work tasks. Quantitative risk estimates: The highest relative risks (RRs) were observed for work-related factors: working at an orthopedic clinic [RR55.2; 95% confidence interval (CI) ], greater than or equal to one patient transfer/shift (RR52.7; 95%CI ), and working full-time (RR52.4; 95%CI ). Training in the use of transfer devices, and regular use of transfer devices, was associated with a lower RR from patient transfer. Among the non-work-related factors, only body mass index of more than or equal to 25 kg/m 2 and immigrant status were associated with slightly increased risk. 2. Ryden et al. 142 Cases were 84 nurses who reported back injuries while employed at the Children s Hospital and Health Center, San Diego between 1982 and Occupational exposure associated with nursing, specifically physical load (lifting, bending, or fall), and time of shift (day or evening). 168 matched controls (2 per case) from same facilities. The cases and controls were compared on work and non-work related factors (eg. smoking). Occupational back injuries, ascertained by data obtained from the employee health records at the hospital. Additional information was obtained from Employee Health staff. Appraisal: The study design permitted analysis of a large group of factors, but most work factors could not be examined because the controls were from the same departments as the cases. Therefore this study was of minimal value with respect to understanding the role of specific nursing duties in the etiology of low back pain. Biases and confounders: Some information relevant to back injury risk factor was not available (e.g. fitness level). Possible underreporting for questions relating to cigarette smoking and alcohol consumption. Quantitative risk estimates: Significant associations were found for history of low back pain or slipped disc by self-report and for history of previous back injury. Working the day shift also was significant [odds ratio (OR)52.23; P,0.005]. Marital status (single) approached significance (OR51.65; CI ), as did low body weight (OR51.47; CI ). 232 International Journal of Occupational and Environmental Health 2013 VOL. 19 NO. 3

11 Table 5 Review studies Study Appraisal Findings 1. Buckle 113 The author reviewed seven epidemiological findings relating to the extent of the back pain problem within nursing, its distribution across nursing specialties, and the comparison with other occupational groups. The source of the studies reviewed and the inclusion/exclusion criteria were not explicit. The author gave a good overview of the methods and findings of the studies included in the review, but there were no formal quality criteria against which the studies reviewed were appraised. The author acknowledged the difficulty of quantifying exposure for certain factors. 2. Hignett 2 This study provided an overview of work-related back pain in nurses by drawing together the findings from over 80 studies published over three decades. The author did not explain the search strategy used, the inclusion/exclusion criteria or where the studies were sourced. There were also no formal quality criteria against which they were appraised. The author categorized the studies reviewed into three groups: epidemiological; testing out; and exploratory, providing a good overview of the findings within each of the categories. However, no overview was presented in tables. 3. Jensen 68 The author examined the consistency of epidemiological studies relating back pain among nurses exposed to stressful patient handling. There were clear inclusion and exclusion criteria, and six studies that included data on both patient-handling frequency and back pain prevalence were identified. The author performed a fair appraisal of the studies reviewed, although no predetermined quality criteria were mentioned. Data from each study were extracted to provide comparable information for an exposure variable and a health outcome variable. Exposure was characterized generally as less frequent versus more frequent patient handling. Results were well summarized in tables and quantitative risk assessments were presented. 4. Nelson and Baptiste 143 The authors discussed three types of controls (administrative, behavioral, and engineering) and their applicability with regard to reducing risks from patient handling. The authors did not indicate the source of the articles reviewed nor the inclusion and exclusion criteria. There is little appraisal of the studies reviewed. The authors concluded by suggesting good evidence-based strategies and recommendations to minimize back pain incidence in healthcare workers. The authors note that all seven studies reviewed comparing back pain rates of nurses with those of other occupations all show that nurses have a relatively high prevalence, although they found one study that showed an only slightly lower annual prevalence rate in a sample of retail staff (510 per 1000 at risk) compared to a sample of geriatric nurses (530 per 1000 at risk). With respect to risks within nursing, they found a lack of consistency, noting that studies cannot be easily compared because of differing methodologies and criteria for identifying those with back pain and inconsistent use of prevalence and incidence data. Nonetheless, the authors estimated a point prevalence of the order of 170 per 1000 at risk, with an annual prevalence of about per 1000 at risk, and the lifetime prevalence of back pain in nurses ranged from 350 per 1000 at risk to 810 per 1000 at risk. There was good agreement on a number of points; in particular that nursing is among the high risk occupations with respect to low back problems, with a with a point prevalence of approximately 17%, an annual prevalence of 40 50% and a lifetime prevalence ranging from 35 to 80% within the nursing profession. Generally it was agreed that more frequent patient handling correlates with increased incidence of low back pain, with one study reporting a prevalence rate of nursing staff who handled patents frequently was 3.7 times that of infrequent patent handlers, and another one reporting that 36% of all episodes of low back pain in nurses were associated with patient handling. Despite differences in specific criteria for characterizing exposure and defining health outcome, all of the studies were consistent in finding larger prevalence rates among those nursing personnel who more frequently performed physically stressful patient handling. Overall, the prevalence rate of those who more frequently handled patients was about 3.7 times that of the nursing personnel who infrequently handled patients. The authors quote the Bureau of Labor statistics 2002 and report work-related musculoskeletal disorders incidence rates in nursing of 8.8 per 100 in hospital settings and 13.5 per 100 in nursing home settings. The review found that strategies to prevent or minimize injuries associated with patient handling are often based more on tradition and personal experience rather than scientific evidence. The most common patient-handling approaches in the United States included manual patient lifting, classes in body mechanics, training in safe lifting techniques and back belts. There is strong evidence that each of these approaches in isolation is NOT effective in reducing caregiver injuries. International Journal of Occupational and Environmental Health 2013 VOL. 19 NO

12 Table 5 Continued Study Appraisal Findings 5. Pheasant and Stubbs 9 The authors assessed the level of risk inherent in a number of common patient-handling procedures based upon a new analysis of existing data sourced from over 10 studies, as well as previously unpublished data. The authors do not explicitly mention the exact number of studies reviewed. The source of the studies reviewed, the literature search criteria and the inclusion/exclusion criteria were not specified and the studies reviewed were not appraised against formal criteria or checklists. The results were well-presented in tables and the authors presented quantitative and qualitative risk assessments. 6. Roffey et al. 91 The authors examined the relationship between low back pain and awkward working positions. They summarized levels of evidence for each of what they called the Bradford Hill criteria for causality for each category of awkward occupational posture and type of low back pain. Their application of Bradford Hill criteria is quite questionable (see text) and was not acknowledged by the authors. 7. Schlossmacher and Amaral 7 The authors assessed low back disorders and the associated risks, as well as the characteristics and ergonomic factors present in nurses. A rigorous search of terms such as low back pain, professionals, hospital ergonomics, work organization, nursing found was performed in national and international databases. Sixteen studies were selected, but the authors conducted no appraisal of the studies reviewed. The main results were clearly presented in graphs. No measures of quantitative risk were put forth. 8. Waters et al. 144 The author systematically reviewed the current scientific exposure methods of cumulative spinal loading, to provide an in-depth analysis and discuss critical issues relating to their reliability and validity for estimating force distribution and practicality for field measurement. The methodologies were evaluated in terms on five defined aspects, but the quality criteria (e.g. guideline or checklist) against which the studies were evaluated were not specified. 9. Waters et al. 145 The author appraised observational studies linking cumulative spinal loading and lower back disorders then performed an in-depth appraisal of each study according to defined quality criteria (epidemiological appraisal checklist). The electronic search resulted in identification of four epidemiological studies, three of which provided sufficient information for an assessment of epidemiological quality and two of which provided sufficient data to conduct a meta-analysis. Two meta-analyses were conducted, one for exposure differences and one for differences in health outcomes. The authors report a point prevalence for back pain of 17.0% in nurses compared to 12.5% in the general population, and that nurses incurred 30% more days sickness absence per annum due to back pain than the general population. The authors identified the patient-handling maneuvers presenting the highest risk, with the two-person cradle lift the highest risk. The authors concluded that physical overload is responsible for back injuries in nurses and that while some of the features responsible for the overload can be corrected by training, many require engineering solutions, design solutions or changes in working practice. The authors identified ten studies they considered high quality that examined the relationship between bending and low back pain. Five were case control studies and five were prospective cohort studies. (Only one of the case control studies and one of the prospective studies involved nurses explicitly). The authors were not able to find high-quality studies that independently of other studies satisfied more than three of the Bradford Hill criteria for causation for either occupational bending or twisting and low back pain, and (erroneously in our opinion) rejected the association as of any causal significance. The authors concluded that the prevalence of low back injury is high among nursing professionals, with a prevalence rate between 14.7 and 72%, and its causes are related to occupational factors physical or psychological. Twenty-seven percent of low back pain in nurses is caused by the transference of the patient from bed to chair, and this task is the main cause of low back pain in nurses. There is a need for integrated spinal loading methods that are reliable, valid and practical for use in large occupational epidemiological studies. Despite considerable differences among the studies in terms of exposure assessment techniques, the findings suggest that there is an association between cumulative spinal loading and low back disability, and the meta-odds ratio for low back pain outcomes was 1.66 (95% confidence interval using quality scores 1/ ). 234 International Journal of Occupational and Environmental Health 2013 VOL. 19 NO. 3

13 previously reported back injury (which itself could be work-related), are substantial predictors of back injury in nurses. For example, Venning et al., 65 in a multicenter prospective study of 5649 nurses found that working in a service area where lifting occurred most conferred an odds ratio of 4.26 compared to working in areas where lifting occurs least. Engkvist et al. 66 found that of the non-work-related factors, only body mass index and immigrant status were associated with a slight increase in relative risk of 1.4 [95% confidence interval (CI): 0.9 2] and 1.6 (95%CI: ), respectively, in contrast to a more than a fivefold increased risk conferred by working at an orthopedic clinic, for example. Smedley and colleagues, 67 following a cohort of pain-free nurses every 3 months for 2 years, showed a clear exposureresponse relationship between nursing tasks and the development of LBP, and found that neither demographic factors (including height and weight) nor psychological factors were important predictors. The cross-sectional studies summarized in Appendix 3 also demonstrate that a large proportion of the excess risk of back orders in nurses stems from patient-handling tasks, but that patient handling is not the only nursing activity that confers risk. Of particular note, Jensen found that the prevalence rate among those who more frequently handled patients was approximately 3.7 times that of the nursing personnel who infrequently handled patients. 68 This is consistent with results from longitudinal studies. The issue of cumulative spinal loading was addressed in a number of the studies (e.g. Refs ) and was found to have an association with LBP in nurses. 72 (A possible explanation for this is provided by animal studies linking cumulative load to back tissue pathology, as discussed below.) Another finding of note was that the ratio of nurses to patients is associated with LBP; for example, according to a study by Larese and Fiorito, 73 work tasks and particularly nurse/patient ratio were more important factors than age and length of exposure. The ergonomic studies, as shown in Appendix 3, demonstrated four key points. First, patient handling is a physically demanding activity often exceeding guidelines set with respect to preventing back injuries. 22,31,70,74,75 Secondly, while loading on the back can be mitigated by assistive devices, 76 and skill in proper mechanics, 33,35,70,77 even with the use of assistive devices (some of which are better than others) and even with two patient handlers instead of one, 19,27,70 and even with skill and of use of proper body mechanics, 27,29 31,78 a measurable risk remains. Thirdly, while the personal characteristics of the nurse (e.g. sex, age, pre-existing disability, body mass index, and muscle strength) may be associated with body mechanics used, these factors do not eliminate the importance of work task in conferring risk of back injury. 65,79 And, fourthly, not only are patient lifting and transferring tasks important contributors to the physical load that confers risk of low back injury in nurses, but nurses spend considerable time in other tasks that also confer increased risk. 69,75,80,81 For example, Holmes and colleagues 69 found that in longterm care nurses, patient care, unloaded standing, walking, and miscellaneous tasks accounted for almost 80% of cumulative lumbar compression, while lifts and transfers accounted for less than 10%. Similarly, Hodder et al. 80 showed that patient-based activities, including adjusting the patients in bed, care activities (bathing and dressing), and transporting the patient in a wheelchair occurred 4.8 times as often as transfers and used 10-fold the time; they noted that both peak and cumulative strain must be considered, highlighting the high lumbar compression and shear loads known to occur with patient adjustments and handling. They showed, for example that patient care activities, especially bathing and dressing patients, required large flexion angles (over 78u) and large deviations, especially to the right, which exceeded 30u. Table 5 summarizes the review studies that were identified in our systematic review, following the search strategy outlined above. These reviews generally show that nursing results in a higher risk of back disorders and that nurses who more frequently perform physically stressful patient handling are quite elevated with one review concluding that the risk is almost four times greater than in those who infrequently handle patients. 68 Applying the Bradford Hill Considerations Bradford Hill s nine considerations for ascertaining whether an association is causal in nature have been used extensively in all medical disciplines, for conditions that range from neuropsychiatric, 82 to cardiovascular, 83 to musculoskeletal syndromes associated with malignancy. 84 While Hill used the term features to be considered, these factors have sometimes (misleadingly) been called the Bradford Hill criteria for causation. 47 The following outlines each of these considerations, commenting on limitations and biases in the evidence, and assessing the body of literature identified in this systematic review to explore if a causal relationship is more likely than not. 1. Strength: Hill noted that when risk ratios conferred by an exposure are high, the association is more likely to reflect a causative link, depending, as noted by Höfler, 58 on the index that is used. Studies in our review generally found the strength of association between patient-handling activities and back disorders to be quite strong: the studies in Tables 3 and 4 presented risk estimates for workrelated factors ranging from 1.2 to 5.2. Additionally, the comprehensive literature review International Journal of Occupational and Environmental Health 2013 VOL. 19 NO

14 conducted by Jensen 68 to examine the consistency of epidemiological studies relating LBP in nurses with patient-handling tasks, identified six studies for review, the data from which indicated that nurses who more frequently handled patients were 3.7 times more likely to have back disorders compared to those with the fewest patient-handling tasks. The multicenter prospective cohort study conducted by Venning et al. 65 identified four factors that were significant predictors of back injury, with adjusted odds ratios of 4.26 (P,0.01) for service areas where lifting occurs most as compared with areas where lifting occurs least; 2.19 (P,0.05) for daily lifters versus light, occasional, and non-lifters; 1.77 (P,0.01) for nursing aides versus registered nurses and supervisory personnel; and a risk of only 1.73 (P,0.01) for individuals who have previously reported back injury versus those who have not reported previous injury. The study conducted by Engkvist et al. 66 found that highest relative risks (RRs) were observed for work-related factors: working at an orthopedic clinic (RR5 5.2; 95%CI ), 1 patient transfer/shift (RR52.7; 95%CI ), and working full-time (RR52.4; 95%CI ); they also showed that training in the use of transfer devices, and regular use of transfer devices, reduced the RR of back disorders from patient transfer. A recent study in four occupational populations showed that the prevalence rate ratio for LBP was 4.1 for nurses compared to computer operators. 85 The prospective study of Norwegian nurses 64 found an odds ratio of 4.14 for lost-time back injuries attributed to changes in work duties. These and indeed the overall findings from all the studies as shown in Tables 3 and 4 suggest a strong association between job-related factors and back disorders in nurses, with the risk from nursing tasks increasing the risk up to more than five times, depending on the definitions of the nursing subpopulation, the exposures in question, the comparison population, and the outcome. 2. Consistency: Hill noted that if an association is observed in different settings and diverse populations, and using different study designs and techniques, the association is more likely to be causal in nature. This systematic review of 89 studies included studies from 19 countries in the Americas, Asia, Europe, and Australia, with a variety of study designs and techniques. While the extent of risk varied as discussed above, findings were consistent that nurses with a variety of differing working conditions, personal beliefs, diverse genetic make-ups, and various socioeconomic circumstances all appear to be at increased risk of back disorders. It can be concluded that the studies are remarkably consistent in showing an association between nursing activities and back disorders. 3. Specificity: As explained by Höfler, 58 echoing concerns by Rothman and Greenland, 57 as well as Cox and Wermuth, 59 the value of the consideration of specificity is limited in situations where the exposure can lead to multiple outcome and/or the outcome can be caused by multiple exposures. Due to the widely acknowledged multi-factorial nature of the causation of LBP, the multi-factorial nature of the risk factors in nursing, 14,80,86 and the fact that the same risk factors that exist in nursing exist in other settings as well (usually leading to false negative biases), this consideration must be handled with care. It is important to stress that unlike reviews that assess single risk factors, this systematic review focuses on ascertaining if a causal relationship exists between nursing tasks as a whole and back disorders, with no attempt to determine the proportion of the excess risk conferred by lifting, carrying, awkward postures, or any single physical or organizational work factor. We see no rationale in doing so for purposes of this review as combinations of physical and psychosocial risk factors are virtually always operative in the real world. 4. Temporality: As noted by others, this consideration reflects the proverb which is the cart and which is the horse? While most studies identified in this systematic review are cross-sectional in nature (see Appendix 3) and therefore not able to address the question of temporality (i.e. whether the exposure proceeded the outcome) with a high degree of certainty, there were several longitudinal studies in which temporality was addressed, as shown in Table 3. These include prospective studies to assess the predictors of new back disorders. In the prospective study by Smedley et al. 67 there was a relationship between patient handling and back injury in nurses, showing a clear increased risk in nurses who frequently assisted patients to mobilize using a walking stick, Zimmer frame, or crutches; moving patients in a wheelchair, bed, hoist, trolley, or commode; or washed and dressed patients while they were seated on a chair or commode, as well as several other activities associated with smaller increases in risk. Several case control studies, in which study populations were specifically defined based on having the outcome of interest (back disorders) or not, and the work-related risk factors of the two groups then retrospectively analyzed 65 67,95 are also longitudinal in nature, adding to the temporality consideration. In essence, in the consideration which is the cart and which is the horse clearly LBP did not lead people to choose nursing as a career. 5. Biological gradient: There are numerous studies in which a dose response relationship was indeed observed; in other words, where nursing activities involved more strenuous work, the incidence of LBP and/or back injury was higher. For example, Stobbe et al. compared nurses who were frequent patient handlers with those who infrequently handled patients and found there was a direct relationship between the number of patients lifted and the risk of a back injury. 96 In the studies that attempted to gather dose response information prospectively in a quantitative manner, Jansen and colleagues 97 found that trunk flexion over 45u was associated with disabling LBP, with a relative risk of 3.18 (95%CI: ) for 1 hour and 45 minutes of bending per week (ninetieth centile) relative to 30 minutes per week. In addition, Smedley and colleagues 67 documented exposure 236 International Journal of Occupational and Environmental Health 2013 VOL. 19 NO. 3

15 response trends for a variety of nursing tasks, all of which correlated with each other. As Höfler has noted, 58 dose response curves may take a variety of shapes. In this systematic review, the myriad of back-stressing nursing activities often confounded the assessment of a dose response relationship when patient lifting and transferring was defined as the sole exposure of interest, as described above. 69,80 This is particularly well supported by the data in the prospective study by Smedley and colleagues. 67 Moreover, basic science literature is unequivocal with respect to the existence of a biological gradient consideration, in addition to being useful with respect to the biological plausibility criterion, as noted below. Thus, in considering the existence of a biological gradient, the evidence further supports a causal relationship. 6. Plausibility: Bradford Hill noted that a biological explanation for an association supports concluding that the relationship is causal in nature. A plausible mechanism between cause and effect in this review is well established from the biomechanical and basic science literature. For example, one study calculating the compression and shear loads for 16 commonly performed patient-handling tasks found that the tasks, such as repositioning of the patient and transferring the patient from a wheelchair to the treatment table, exceeded the maximum permissible limit for the spine compressive loads set by the US National Institute of Occupational Safety and Health. 72 Other studies, including many discussed in Table 5, support the plausibility of nursing tasks conferring excessive loads. There seems to also be a growing consensus that mechanical loading plays a key role in the causation of LBP. Variants of plausible pathways have been presented. For example, Adams and colleagues 98,99 demonstrated that minor damage to a vertebral body endplate leads to progressive structural changes in the adjacent intervertebral discs. Further, in a review of the literature, van Dieen and colleagues concluded that small end-plate fractures play a key role in the etiology of LBP. They noted that in vitro studies illustrate that endplate fractures can easily remain unnoticed when using standard imaging techniques. Indeed they believe that the primary cause of LBP may be a fracture of the vertebral end-plate and the supporting trabecular bone caused by compression of the spine. They also note that in many cases these fractures will heal and the associated pain will disappear but that the end-plate fracture may lead to more severe and chronic back pain related to damage in the annulus fibrosus and facet joints. They show that this hypothesis is compatible with clinical findings and observe that this is even more likely in repeated loading, as it has been shown that spinal motion segments fail at much reduced forces in such cases. The authors also show that the assumption that compression fractures occur frequently is supported by post-mortem evidence of healed fractures of the end-plate and underlying trabecular bone. The likelihood that compression fractures could provide an explanation for the high prevalence of LBP is, as also noted by van Dieen and colleagues, consistent with the epidemiological evidence showing a relationship between tasks involving high compression forces (e.g. lifting) and back pain, although they note that exposure to compression forces will generally correlate highly with exposure to other components of mechanical load on the spine, which can cause damage directly to the annulus fibrosus, the structure implicated to back pain in discographic studies. The hypothesis advanced was shown to be compatible with the type of damage caused by repetitive loading involving a combination of compression, lateral flexion, and maximum flexion. Thus, high mechanical loads on the lower back during manual material handling are well established to be associated with low back pain, 100,101 quite plausibly due to spinal segment micro-fractures. The relationship between awkward body postures during work (e.g. trunk flexion, trunk rotation, and lifting) and LBP has been reported in several prospective studies and Coenen and colleagues recently 102 conducted a large prospective cohort study of over 1000 workers, followed for 3 years, to more definitively ascertain the influence of load magnitude as well as repetition on LBP. They again showed that cumulative low-back load is a significant risk factor for LBP. Moreover, they concluded that cumulative load appeared to reflect both the effects of working in a trunk flexed position and number of lifts during work on LBP risk. It has also been shown that physiological effects (e.g. fatigue development) often depend non-linearly on force level and endurance time. 103 The contribution of load magnitude and number of load cycles to cumulative low-back load estimations has also been studied based on in vitro compression data. 63 The evidence for an association between physical loading, such as occurs in many nursing tasks, and back pain is further supported by the excellent review by Griffith, and colleagues, 63 who overcame the traditional difficulties in assessing the relationship between mechanical exposure and LBP by developing methods that allowed for a meta-analysis of the literature. They concluded that there is indeed sufficient evidence that posture and force were independently related to LBP. 7. Coherence: As Höfler 58 also noted, laboratory evidence that is in line with an association observed epidemiologically would underline a causal conclusion. There is strong coherence between epidemiological and laboratory findings. The biomechanical studies not only from nursing studies reported here, but also from basic science and biomechanical studies in laboratories are consistent with the 43 publications identified by the Institute of Medicine National Research Council that provided quantitative information on associations between physical load at work and the occurrence of back disorders, as well as the more recent studies cited above. For lifting and/or carrying of loads, risk estimates reported varied from 1.1 to 3.5; for frequent bending and twisting, risk estimates ranged from 1.3 to 8.1; and for heavy physical work, risk estimates varied from 1.5 to 3.7. Newer animal studies are also coherent with the human evidence, as discussed above. 104 As the evidence from basic science, clinical biomechanical, and epidemiological studies, provides a coherent picture, this consideration for International Journal of Occupational and Environmental Health 2013 VOL. 19 NO

16 causality can also show that a causal relationship is likely. Thus the epidemiological literature and the basic science literature are coherent with regard to the issue of thresholds as well. 8. Experiment: There is extensive animal experimental evidence from the basic science literature. Additionally, our systematic review criteria led to the inclusion of several human studies in which an experimental intervention was successfully employed to reduce the risk of back disorders in nurses. For example, Garg and Owen 29 followed nurses prospectively to ascertain the effect of introducing an ergonomic intervention on the incidence rate of back injuries. They found that the incidence rate fell from 83/ work hours to 47/ post-intervention, adding not only evidence with respect to temporality but also evidence conforming to the requirement for an experimental design. As noted above, we also reviewed several systematic reviews that addressed the effectiveness of interventions. Dawson and colleagues, 5 authors of an excellent formal systematic review on this subject, concluded: We found consistent positive findings to support the efficacy of multidimensional strategies to prevent LBP in nurses Koppelaar and colleagues 108 recently conducted a formal systematic review of the evidence on the determinants of primary prevention interventions on patient handling in healthcare; they identified three multidimensional interventions that resulted in significant reductions in musculoskeletal disorders A larger and even more recent systematic review 109 concluded that multi-component patient-handling interventions including an organizational commitment to reducing injuries associated with patient handling, purchase of appropriate lift or transfer equipment to reduce biomechanical hazards, and a broad-based ergonomics training program that includes safe patient handling and/or equipment usage is supported by the intervention literature. This body of knowledge can be taken as supporting the experimental evidence consideration in determining a causal connection between nursing activities and LBP. 9. Analogy: This consideration asks whether for analogous exposures and outcomes an effect has already been shown. The body of ergonomic literature provides an abundance of analogies that could be called upon, including the literature that supports presumptions of work-relatedness for other musculoskeletal disorders. Armstrong and colleagues 110 presented a conceptual model for the pathogenesis of work-related upper limb and neck musculoskeletal disorders, which contained sets of cascading exposure, dose, capacity, and response variables, such that a response at one level could act as dose at the next, with responses diminishing or increasing the capacity for responding to successive doses. While their model was not directly applicable to LBP, it provides a useful analogy of how the variables factors interact. More importantly, it is noteworthy that presumptions of workrelated have indeed been established for other musculoskeletal conditions, for example for bursitis and tenosynovitis, in conjunction with various ergonomic stressors. 111 Thus the epidemiological and biomechanical literature supports the etiological importance of nursing tasks in the occurrence of low back disorders. The extensive laboratory evidence explaining the pathophysiological mechanisms related to work stressors 61,62,102,112 provides not only ample biological plausibility of this conclusion, but also assists with respect to the question of threshold. The basic science evidence, the biomechanical studies, clinical observations, and epidemiological studies suggest that it is not possible to determine a threshold below which this risk is not likely to be elevated. In other words, individual variation, work setting variation, and limitations in standardization of study design is such that science cannot discern a threshold of patient care nursing activities that could be stated to be without risk in all situations for all people. Additionally, while patient lifts and transfers confer the greatest excess risk with respect to peak load, other nursing tasks also augment the risk of back disorders. Our findings therefore confirm the results of others, for example, Waters and colleagues, who note: The risk for development of work-related musculoskeletal disorders associated with manual patient handling crosses all specialty areas of nursing. No nurse effectively is free from the risk of injury. Discussion Our findings are consistent with the findings of other reviews on this issue, 2,7,113 but add a new dimension by actually applying the Bradford Hill causal considerations to a body of knowledge to assess causation in this area. Some recent general reviews of occupational factors have suggested that occupational factors are not important in the etiology of back pain most notably the series of articles by Kwon, Roffey, Wai, and colleagues, summarized in their systematic review of their own series, 50 and cited in a recent article in The Lancet on non-specific back pain. 1 These studies, contradicting earlier reviews on this subject (e.g. Ref. 13) have been appropriately criticized, 48,49,52 54 for, among other reasons, the inappropriate application of Bradford Hill factors to individual studies rather than to the body of knowledge, which is how the Bradford Hill factors are meant to be applied, as eloquently explained by Kuijer and colleagues, 54 for example, in their critique of this series. Moreover, as Takala pointed out, 55 the Kwon, Wai, Roffey and colleagues series of articles excluded reports on basic science and biomechanics; in reference to the five considerations used in this series (statistical association, dose response relationship, experimental evidence, temporal relationships, and biological plausibility), Takala noted that there is indeed a huge amount of experimental laboratory studies that have shown evidence of short-term effects between mechanical exposures and outcomes related to LBP, when evaluated by these five aspects of causality. We agree with Takala, and have therefore 238 International Journal of Occupational and Environmental Health 2013 VOL. 19 NO. 3

17 made reference to this body of knowledge in this review. Moreover, we also echo the observation of McGill 53 in criticizing Wai et al. s conclusions regarding lack of causal association of occupational lifting and LBP, namely that everyone has different tolerance levels and the way in which lifting is conducted is important. We endorse the caution expressed by van Dieen and colleagues in their response to The Lancet Seminar on LBP, that neglect of occupational, mechanical loading as a causal factor in LBP is not based on evidence and might seriously hamper effective prevention and management. 49 The importance of mechanical loading in the causation of LBP was also recently confirmed in the meticulous meta-analysis conducted by Griffith and colleagues. 63 We are aware that the policy implications of our results may be disquieting to some. In this regard, the findings of Premji and colleagues 114 are noteworthy, in which they documented a general reluctance of scientists (or reviewers) to publish unequivocal affirmations in peer-reviewed venues to the effect that musculoskeletal disorders they are studying are work-related, even in the presence of strong, statistically-significant temporally possible associations, plausible causal mechanisms and consistency with evidence. Conversely they found that, somewhat less reluctance was seen in relation to negative results, even when no discussion of power was included. They offer various possible explanations but emphatically point out that the burden of uncertainty is currently borne disproportionately by the worker, not the workplace. 114 To begin to heed the call of Premji and colleagues for researchers to be less equivocal in presenting their results, we note that our analysis indicates that the scientific literature does indeed support a causal link between nursing duties particularly patient care tasks and the development of back pain. More importantly, our findings show that personal characteristics do not negate the importance of work-related factors in causing back disorders in those who engage in nursing duties; indeed a large multidimensional cohort study of health care workers, personal characteristics accounted for less than 12% of the new episode of LBP variance. 115 We also note that the work tasks, according to workers compensation legislation in many parts of the world and certainly in most Canadian and American jurisdictions, requires only that the work be a significant contributing factor or a substantial factor not the sole contributing factor to the injury. (The principle behind this policy is sometimes referred to as the thin skull principle, 116 or in the US eggshell skull 117 based on the idea that individuals are to be taken as they are found, frailties and all. 118 ) The literature, of course, has limitations. These include difficulties in defining the exposure in question especially given the heterogeneity of nursing activities; difficulties in defining the pertinent outcome; and great diversity in study designs and comparison populations across different studies. Some of these challenges could be overcome using methodology such as that developed by Griffith and colleagues. 63 However, as they note, it is extremely resource-intensive, and unless studies collect data in a manner that allows meta-analysis, adjusting risk estimates to take into account individual risk factors and modifiers will be impossible. Our literature review has some other limitations. For example, we only reviewed studies published in English. While we are aware that more studies have been published on this subject in other languages, we have no reason to believe that their conclusions are substantially different from what was published in English, especially given that studies from a large diversity of countries were among those included in this review. Also, we made no attempt to verify data with authors of the studies in the review: given that this review covers studies published over a 22-year period, we felt that this would likely not be fruitful. Thus, we confined our analysis to what was presented in the published articles. According to Spieler and Burton, 119 Lippel, 120 and others (e.g. Ref. 121), workers compensation adjudication can itself hinder the recovery and return-to-work process. As noted by Lippel, If a claim is only accepted in appeal, perhaps years after the original claim was filed, access to health care and rehabilitation services is not provided in a timely manner and disability may indeed be increased because of the initial refusal. It is not the litigation that leads to the disability in this case, but the unwarranted refusal of the claim. They go on to cite some of the extensive body of literature documenting that practices of social security systems can adversely affect the health of those they are meant to help and note that these issues are just as applicable to workers compensation. Others, recognizing the adverse impact on workers health associated with workers compensation adjudication practices, have called for the abolition of workers compensation systems completely, and replace these with universal systems of disability insurance in which access to care and support is not dependant on adversarial adjudication in other words, what LaDou calls the Public Health Model for workers compensation. 122,123 Indeed, since 1974 New Zealand has had a no-fault system providing compensation for all injured workers regardless of work-relatedness, allowing greater focus on prevention and rehabilitation. 124 International Journal of Occupational and Environmental Health 2013 VOL. 19 NO

18 Meanwhile, Lippel 125 has reiterated a call for workers compensation systems to reduce opportunities for adversarial interactions and better promote the dignity of claimants. Policy-makers in many jurisdictions have attempted to so this by using evidence to devise presumptions of work-relatedness to simplify adjudication where the link between an occupational exposure or occupation itself and the outcome of interest is strong. For example, healthcare workers who are diagnosed with tuberculosis are presumed to have been infected at work in many jurisdictions, including in Canada, 126,127 unless otherwise established. Five Canadian provinces have presumptions of work-relatedness for firefighters who are diagnosed with particular cancers, specifically British Columbia, 128 Alberta, 129 Saskatchewan, 130 Manitoba, 131 and Nova Scotia. 132 In many other jurisdictions worldwide such presumptions exist for a large variety of disease outcome; for example Germany and Denmark recognize bladder cancer in the metal industries where exposures to cadmium and epoxy resins may occur. 133 There are presumptions of work-relatedness not only for diseases such as tuberculosis and cancer, but also for various types of activity-related soft-tissue disorders. For example, in British Columbia, such presumptions exist for hand-wrist tendinitis and tenosynovitis as well as shoulder tendinitis. 134 As noted by LaDou, 123 while all the European countries have lists that assist in adjudication of work-relatedness, differences exist in the diagnostic and exposure criteria, with Belgium, Italy, France, and Luxembourg, having presumptions in which injured workers only need to demonstrate that they are suffering from listed diseases and that they have incurred the causal exposure or work tasks or that they have done jobs specified by the lists; whereas in Austria, Denmark, Finland, Germany, Switzerland, Portugal, Spain, and Switzerland, the lists serve merely as guides and the adjudicator may consider non-occupational factors. The precise definitions of work exposure and diagnostic criteria required for a presumption to be operative, is, of course, a matter of policy, not science alone. Conclusion Notwithstanding the methodological challenges in studying this area, and noting that science rarely produces certainty, we conclude that there is ample scientific evidence to support the creation of a presumption of work-relatedness of non-specific low back disorders in personnel who perform general nursing duties. In other words, LBP that arises in nurses who perform patient care duties should be considered to be substantially related to the risks imposed by their work, unless the contrary is shown. This does not mean that non-work-related factors play no role in creating back pain, nor does it mean that all cases of back pain in nurses should be considered work-related; it does mean, though, that there is sufficient scientific justification for reversing the burden of proof, thereby eliminating one source of frustration for injured nurses. Kwon, Roffey, Wai, and colleagues call for experimental studies in which participants are randomized into groups that do and do not receive interventions to address the ergonomic challenges identified. 91 We note, however, that most studies in this review indicated that single-factor interventions are unlikely to be effective, and that multifactor workplace interventions are those that are most likely to be successful. 5 While it is known that such studies are complex to undertake with a high degree of rigor, 135 we support these colleagues in their call for adequately powered high-quality cluster randomized controlled trials of multicomponent interventions to answer important questions about the effectiveness of specific combinations of interventions to prevent back disorders in nurses. Such high-quality studies would be very useful to guide further prevention efforts. Meanwhile, while policy decisions are not based on science alone, and good arguments can be made for abolishing workers compensation completely, in favor of universal coverage for injured workers, we believe that in the interim, policies should at least be put into place that uses the science that does exist to reduce the needless frustration of injured workers, well known to be associated with lengthy adjudication processes ,125 While more research on everything from pathophysiological mechanisms of back disorders to success of ergonomic interventions is always welcome, we believe that there is sufficient evidence to justify a presumption of work-relatedness of back disorders in nursing personnel and begin to conduct implementation research to study the barriers and facilitators to implementing such a policy to maximize the success for all parties. Acknowledgements We would like to acknowledge the assistance of Stephanie Parent in the editing and submitting of this manuscript. AY is funded by the Canada Research Council (CRC) as a Senior CRC Chair; KL is funded by a research programmatic grant from the Canadian Institutes for Health Research on the health of healthcare workers. The Canadian Federation of Nurses Unions also supported this systematic review. Disclosure There are no conflicts-of-interest to declare. 240 International Journal of Occupational and Environmental Health 2013 VOL. 19 NO. 3

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