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Original article
Assessment of the impact of lifting device use on low back pain and musculoskeletal injury claims among nurses
  1. Alex Burdorf1,
  2. Elin Koppelaar1,
  3. Bradley Evanoff2
  1. 1Department of Public Health, Erasmus MC, Rotterdam, The Netherlands
  2. 2Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, USA
  1. Correspondence to Dr Alex Burdorf, Department of Public Health, Erasmus MC, PO Box 2040, Rotterdam 3000 CA, The Netherlands; a.burdorf{at}erasmusmc.nl

Abstract

Objectives The aims of this study were: (1) to evaluate the effect of manually lifting patients on the occurrence of low back pain (LBP) among nurses, and (2) to estimate the impact of lifting device use on the prevention of LBP and musculoskeletal disorder (MSD) injury claims.

Methods A literature search of PubMed, Embase and Web of Science identified studies with a quantitative assessment of the effect of manually lifting patients on LBP occurrence and studies on the impact of introducing lifting devices on LBP and MSD injury claims. A Markov decision analysis model was constructed for a health impact assessment of patient lifting device use in healthcare settings.

Results The best scenario, based on observational and experimental studies, showed a maximum reduction in LBP prevalence from 41.9% to 40.5% and in MSD injury claims from 5.8 to 5.6 per 100 work-years. Complete elimination of manually lifting patients would reduce the LBP prevalence to 31.4% and MSD injury claims to 4.3 per 100 work-years. These results were sensitive to the strengths of the association between manually patient lifting and LBP as well as the prevalence of manual lifting of patients. A realistic variant of the baseline scenario requires well over 25 000 healthcare workers to demonstrate effectiveness.

Conclusions This study indicates that good implementation of lifting devices is required to noticeably reduce LBP and injury claims. This health impact assessment may guide intervention studies as well as implementation of programmes to reduce manual lifting of patients in healthcare settings.

https://doi.org/10.1136/oemed-2012-101210

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    What this paper adds

    • This study indicates that a reduction in the occurrence of low back pain in healthcare settings can only be achieved by interventions which result in a big decrease in mechanical load and a high level of implementation in the population at risk.

    • Most intervention studies on lifting devices in healthcare settings are too small to be able to demonstrate their effectiveness.

    • A health impact assessment is a valuable technique for designing and carrying out primary preventive interventions in the workplace.

    Introduction

    The most common musculoskeletal disorder (MSD) among nurses is low back pain (LBP).1 A significant proportion of back pain episodes can be attributed to events that occur during patient handling activities, such as pushing and/or pulling, awkward back postures, and lifting. It has been well documented that manual lifting is a risk factor for the occurrence of LBP.2–5

    Lifting devices have been developed to reduce the mechanical load related to manual lifting in order to decrease the occurrence of LBP. The efficacy of lifting devices has been assessed in a number of laboratory studies6 ,7 and some observational studies.8 ,9 However, the timely and integrated implementation of lifting device use into the actual work situation remains difficult. A number of design limitations and logistical barriers have hampered workplace studies of the effectiveness of lifting devices for reducing the occurrence of LBP.10 A crucial issue is the need for sufficiently long follow-up periods for intervention studies. While lifting devices can reduce mechanical load during lifting activities with patients, an important risk factor for LBP, a reduction in the occurrence of LBP may result in a delayed response.11 However, when intervention studies with sufficiently long follow-up periods are not available, quantitative health impact assessment is a powerful method to assess the potential effects of an intervention.12

    In a health impact assessment, information from observational and experimental studies with limited time horizons may be used to predict the effect of introducing lifting aids in healthcare settings on the long-term course of LBP in nursing personnel. In this regard, a particularly useful technique is a Markov model of disease, which can be used for discrete health events that occur more than once over time.13 A Markov model assumes that the subject is always in one of a finite number of health states, for example, having symptoms or not having symptoms of LBP. The course of disease is modelled by transitions from one state to another during a specified period of time. Under the assumption that the transition probabilities are constant over time, a Markov chain may be created by repeating multiple cycles to represent a meaningful time interval, for example, employment in the same job for 30 years or more. The impact of introducing lifting aids on the occurrence of LBP in a hypothetical cohort of nurses can be modelled by adjusting the transition probabilities for the estimated effect of lifting aids on the occurrence of LBP.

    The aims of this study were: (1) to evaluate the effect of manually lifting patients on the occurrence of LBP among nurses, and (2) to estimate the impact of using lifting devices as an intervention to prevent LBP and MSD.

    Methods

    Available evidence

    The health impact assessment simulates a cohort of nurses with a 10-year follow-up period for the occurrence of LBP in the presence or absence of lifting devices for patient transfers. This model requires knowledge concerning (1) the course over time of the occurrence of LBP among nurses, (2) the effect of manually lifting patients on the occurrence of LBP, and (3) the impact of the introduction of patient lifting devices on reducing the occurrence of LBP. Model parameters were based on reviews of published studies in PubMed, Embase and Web of Science. First, a literature search was conducted for original studies on the effect of manual lifting of patients on LBP among nurses. Table 1 presents the nine studies found: six cross-sectional studies, two longitudinal studies and one case-referent study, all with a quantitative measure of association between manual lifting of patients and the occurrence of LBP.14–22 The measure of association between manual lifting of patients and LBP ranged from 1.1 to 7.5. In two out of three studies with an ordinal expression of exposure, no clear trend of increased occurrence of LBP with higher frequency of daily lifting of patients was observed. The fraction of LBP attributed to manual lifting of patients varied between 0.01 and 0.60 in these study populations (table 1).

    View this table:
    Table 1

    Associations between manually lifting patients and the occurrence of back pain among nursing personnel in nine observational studies

    Second, a literature search was conducted for observational and experimental studies that describe the impact of introducing lifting devices in healthcare organisations on the occurrence of LBP or MSD. Studies were only selected if information was presented on the uptake of the intervention, either by availability of lifting devices or by actual use of these devices. Table 2 summarises the main findings of eight studies with a quantitative expression of the impact of lifting device use on the occurrence of LBP or other measures of musculoskeletal problems.9 ,23–29 The uptake of the intervention varied considerably, as well as the reported influence of equipment on health outcomes. Two studies clearly showed the complexity of evaluating the effects of this intervention, with a substantial decrease in MSD injury claims in one intervention hospital but no decrease in a second intervention hospital.9 ,28

    View this table:
    Table 2

    Experimental and longitudinal studies on the impact of lifting device use on the occurrence of back pain among nursing personnel

    Disease model and parameters

    The health measure LBP in the past 12 months was chosen, since it is a frequently used health outcome in observational studies on associations between mechanical load and LBP.30 The second health measure was an MSD injury claim caused by patient handling activities, since several authors have suggested that a reduction in manually lifting patients will have a greater impact on lost work days as a primary cause for filing an injury claim than on the occurrence of episodes of LBP.23 ,24

    The disease model consisted of a Markov chain approach with 1-year increments of time during which a subject may make a transition from one health state to another.13 In the first step, the occurrence of LBP in the past 12 months was simulated, whereby the events modelled over each cycle of 1 year include the annual probabilities that a nurse has a new episode of LBP after having been free from LBP for at least 1 year (incidence), has a repeated episode of LBP from 1 year to another year (recurrence), recovers from LBP by having at least 1 year free of LBP (recovery), or leaves work due to becoming permanently work disabled due to LBP. The latter health state was considered an absorbing state, that is, transition to another state from within this state is regarded as impossible. These LBP states were enumerated in such a way that, in any given year, an individual was in one health state only and that the probabilities of the three non-absorbing states sum up to 1. Subsequently, among those nurses with LBP in a given year, the likelihood of a patient-handling related injury claim in that same year was incorporated in the model. In the second step, the impact of lifting devices was introduced by the assumption that the use of lifting devices will result in a decreased incidence of LBP, reflected in a reduced probability of an incident episode of LBP. The probabilities for recurrence and recovery were not changed. All transition probabilities were assumed to be constant over time, that is, the transition from one health state to another health state in a given year is independent of the health status in earlier 1-year cycles (see online supplementary appendix A for details of model assumptions).

    Model parameters were derived from the available evidence presented in tables 1 and 2. The prevalence of LBP was 45% in a large cross-sectional study among nurses,19 and from the subsequent longitudinal follow-up an annual incidence of 25%, recurrence of 66% and recovery of 34% were estimated.21 The annual transitional probability from LBP to becoming permanently work disabled due to LBP was set at 1.37 out of 1000 workers with LBP, based on disability statistics in the Netherlands. From table 1, four studies with comparable definitions were pooled to estimate an exposure prevalence for manually lifting at least one patient per shift of 57% (95% CI 56% to 58%) and an OR of 2.07 (95% CI 1.65 to 2.50).15 ,16 ,19 ,22 Based on six studies in table 2, a pooled estimate of MSD injury claims prior to the intervention was calculated, resulting in 6.2 claims per 100 worker-years (95% CI 5.8 to 6.6).9 ,23 ,24 ,26 ,28 ,29 In the Markov model this parameter was regarded as a utility linked to the proportion of workers with LBP, thereby assuming that among those workers with LBP in a given year, a specific proportion will file an MSD injury claim in that same year.

    In order to estimate the proportional reduction in the annual incidence of LBP due to a specific reduction in the exposure, the potential impact fraction (PIF) was calculated with the formulaEmbedded Image

    where P indicates the prevalence of exposure in the study population before the intervention, P′ the prevalence of exposure after the introduction of lifting devices, and OR the association between manually lifting patients and LBP.31 Note that the OR was used as an approximation of the relative risk. The PIF will equal the population attributable fraction, presented in table 1, when the exposure to lifting patients manually is completely eliminated. If this formula is applied to the model parameters described above, complete elimination would result in a PIF of 0.38 and a consequent decrease in the annual incidence of LBP from 25.0% to 15.5%. However, studies in real life situations have found the reduction in manual lifting of patients to be substantially less, as shown by studies listed in table 2. Three studies with comparable definitions of exposure showed a pooled reduction in the prevalence for manually lifting at least one patient per shift of 16% (95% CI 13.5% to 17.6%).25 ,27 ,28 In the health impact assessment model, this relates to a PIF of 0.06, indicating that approximately 6% of all LBP cases will be prevented by implementing lifting devices.

    Simulations and sensitivity

    A simulation was carried out with two hypothetical cohorts of nurses. In the first cohort nurses enter their job without a history of LBP. The second cohort consists of nurses already working in healthcare settings (ie, ‘current’ nurses) with an overall prevalence of LBP of 45%. Both cohorts will be followed up for a period of 10 years.

    Three intervention scenarios were evaluated for their impact on LBP and MSD injury claims (see table 3). For each scenario the realistic variant reflects the evidence available from observational and experimental studies, and the maximum variant provides the maximum gain to be achieved with complete elimination of manual lifting of patients. The baseline scenario assumes an annual incidence of LBP of 25%, recurrence of 66% and recovery of 34%, about 57% of all nurses involved in manually lifting patients at least once a day, and an OR of 2.07 for patient lifting and incident LBP. In the second scenario, the annual incidence of LBP is changed by 5 percentage points. In the third scenario, the association between patient lifting and LBP is varied according to the CIs of the pooled estimate, thus using OR values of 1.65 and 2.50. As a consequence, the PIFs in the realistic variant will be 0.04 and 0.07, respectively, and PIFs in the maximum variant 0.27 and 0.46, respectively.

    View this table:
    Table 3

    Sensitivity of different scenarios for the impact of lifting devices in healthcare settings on the annual prevalence of LBP and MSD injury claims in a hypothetical cohort of newly hired nursing staff during a 10-year follow-up period

    The sensitivity analysis determined to what extent the assumptions underlying these scenarios influenced the outcome of the health impact assessment. For all 10 possible combinations, the impact on LBP and MSD injury claims about 10 years after the start of the intervention was estimated. In addition, for those combinations with the highest change in LBP prevalence, a power analysis was conducted to illustrate the required number of nurses in the intervention population in order to detect the estimated reduction in the prevalence of LBP.32

    Results

    Figure 1 depicts the simulation of the natural course of LBP among nurses entering their job without a history of LBP and among nurses already working in healthcare. In the cohort of newly hired workers, the prevalence of LBP quickly increased in the first 4 years and after 6 years remained stable at approximately 42%. In the cohort of current workers, the prevalence dropped slightly in the first few years and after 6 years was similar to the prevalence among newly hired workers. The baseline scenario with a realistic representation of evidence showed a maximum reduction in LBP prevalence from 41.9% to 40.5% after 10 years. The maximum variant of this scenario with complete elimination of manually lifting patients reduced the LBP prevalence from 41.9% to 31.4%. It is of interest to note that the impact of the intervention attenuated over time to a maximum influence after 6 years.

    Figure 1
    Figure 1

    Simulation of the natural course of low back pain (LBP) among nursing personnel entering their job without a history of LBP and among nursing personnel already working in healthcare settings with an assumed prevalence of LBP of 45% and the potential effects of implementation of lifting devices.

    Table 3 summarises the impact of different scenarios and assumptions on LBP and MSD injury claims. Since both cohorts had very similar results, only information pertaining to newly hired nurses is presented. Changes in the annual incidence of LBP had a substantial influence on the estimated burden of disease, but did not influence the impact of the intervention. For example, the change in the annual incidence of LBP from 20% to 30% resulted in a similar increase in the annual prevalence of LBP from 36.7% to 46.2%, and an increase in annual MSD injury claims from 5.1 to 6.4. However, the estimated impact of the lifting devices on reduction in the prevalence of LBP varied between 9.9% and 10.8%, while the corresponding figures for MSD injury claims were 1.4 and 1.5.

    A change in the magnitude of the association between patient lifting and LBP had a considerable influence. A higher OR implied a higher PIF and, as illustrated in table 3, larger health gains. With a change in OR from 1.65 to 2.50, the maximum reduction in the prevalence of LBP rose from 7.1% to 13.4% and the reduction in MSD injury claims from 1.0 to 1.9.

    Figure 2 presents the power analysis for the combinations with the highest PIFs for the required number of newly hired nurses in the intervention population to be able to demonstrate a statistically significant effect of introducing lifting devices on the annual prevalence of LBP. In the best scenario with a PIF of 0.46, about 350 nurses need to be included to demonstrate an impact in a longitudinal study with 1-year follow-up. Longer follow-up periods will decrease the required sample size, but after 4 years there are no gains to be made. In the realistic variant of the baseline scenario with a PIF of 0.06, these numbers were 42 100 and 25 700, respectively. For MSD injury claims, the best scenario would require over 10 000 newly hired nurses. Among nursing personnel already working in healthcare settings, the best scenario would require approximately 1000 subjects in a study with sufficient power to demonstrate a change in LBP (not shown).

    Figure 2
    Figure 2

    Required number of newly hired nurses in the intervention population to demonstrate a statistically significant effect on the prevalence of low back pain for three different estimates of the potential impact fraction (PIF) of the implementation of lifting devices.

    Discussion

    This health impact assessment on the effect of lifting device use for patient transfers in healthcare settings demonstrates that the impact of this intervention depends strongly on the proportion of LBP that is attributable to manual lifting of patients (how much can be avoided) and on the success of strategies to reduce the proportion of nurses involved in manually lifting patients (how much exposure reduction can be achieved). The synthesised evidence from observational and experimental studies suggests that implementation of patient handling devices in healthcare settings will not result in a noticeable reduction in LBP or MSD injury claims unless such implementation results in a substantial decrease in manual lifting of patients. Given the reported change in exposure to manually lifting patients, several intervention studies were severely underpowered to demonstrate the effectiveness of lifting devices in healthcare settings. Likewise, those studies that have reported a substantial decrease in MSD injury claims have most likely succeeded in eliminating most manual patient lifting by nurses.

    The results of this health impact assessment seem to mirror findings reported in the literature. The intervention studies in table 2 showed large differences in impact on the occurrence of LBP or MSD injury claims, varying from 0%9 to almost 60%.24 An important explanation for these strongly varying findings is the integrity of the intervention, especially incomplete uptake of the intervention. Three intervention studies have suggested that limited use of the available lifting equipment is a possible reason for a lack of reduction in musculoskeletal injury claims9 ,28 or prevalence of LBP.27 Recent studies on primary preventive interventions on manual patient handling in healthcare settings have identified many barriers at an individual and organisational level that hampered appropriate implementation.33 ,34

    A second reason for the large differences in the effects of interventions is the uncertainty regarding the proportion of LBP that is caused by manually lifting patients. In the observational studies presented in table 1, the fraction of LBP attributed to manual lifting of patients varied between 1% and 60%. In the disease model, a population attributable fraction of 38% was used, which seems reasonable in light of the population attributable fractions of between 27% and 34% in the two longitudinal studies included in table 1.21 ,22 In a meta-analysis, lifting as an occupational risk factor for LBP accounted for approximately 33–39% of all LBP episodes in the workforce.3

    This health impact assessment shows that programmes to reduce patient lifting in healthcare settings will only be effective when manual patient lifting is almost completely phased out. This requires careful development and implementation of such programmes with ample attention to frequently mentioned barriers, such as employee motivation, the convenience and easy accessibility of devices, a supportive management climate, and workers’ involvement in decision making.24 ,33 The scenario with the highest effects due to the elimination of manual lifting predicted a relative reduction of approximately 33% in the prevalence of LBP and MSD injury claims. Our model could not distinguish well between onset of LBP, aggravation of LBP in terms of chronicity and recurrence, and consequences for productivity loss due to work days lost and modified work. In a cost–benefit analysis the indirect costs will be of paramount importance. A recent study in two large hospitals in the USA reported that patient handling activities contributed to 72% of all MSD injuries and 53% of compensation costs among patient care staff.35 Another study on the long-term impact of a programme including the use of several patient handling devices reported a 60% decrease in MSD injury claims and an even a steeper drop of 86% in work days lost and 79% in work days on modified duties. The return-on-investment period was less than 15 months.24 Both studies demonstrate that the indirect costs of LBP and other musculoskeletal complaints caused by patient handling activities may provide a strong impetus for the implementation of ergonomic devices.

    Our health impact assessment has several limitations that must be borne in mind. First, the Markov chain used in the current analysis was completely defined by the transitions from health to LBP and vice versa, which were held constant over time. There are only few longitudinal studies available to evaluate the dynamic course of LBP over a prolonged period of many years. Good consistency was found between the prevalence, incidence and recurrence used in our disease model and reported in several occupational cohorts. The annual incidence of 25% was consistent with other occupational populations.21 ,36 ,37 The high yearly recurrence of LBP reflects the finding that a history of LBP is a strong predictor of future episodes.19 ,36 ,38 A study among nurses with 8 years of follow-up concluded that LBP has a more recurrent than progressive nature.39 The sensitivity analysis showed that the estimated impact of the intervention on the occurrence of LBP and MSD injury claims was not sensitive to substantial changes in the incidence of LBP and, thus, it is expected that the assumptions on transition probabilities between health and incident and recurrent LBP will not have biased the evaluation. However, the simple dichotomy between health and having LBP does not take into account the severity and aggravation of LBP and it has recently been suggested that mechanical load is related more to the persistence of multi-site pain than its onset.40

    A second important limitation is the uncertainty in the association between manual lifting of patients and the occurrence of LBP. The majority of studies in table 1 were of cross-sectional design and, as a consequence, causality cannot be determined. The two longitudinal studies showed comparable results and had the highest weights in the meta-analysis with a pooled OR of 2.07. Since most studies did not adjust for awkward back postures and strenuous movements, and the number of studies in the meta-analysis was limited, it is difficult to ascertain whether this OR is a accurate reflection of the true association between manual patient lifting and LBP. A similar remark can be made for the estimated prevalence of exposure of 57% to manually lifting patients and to the proportion with MSD injury claims in exposed populations. In addition, the review of the literature could not provide an exposure–response relationship between increased frequency of patient lifting and higher occurrence of LBP. A few studies presented exposure–response trends, but the evidence was too heterogeneous to be used in a meta-analysis. Information was also lacking for considering a cumulative effect of mechanical load on transition probabilities, whereby the likelihood of incidence and recurrence would increase over time with prolonged exposure.

    A third limitation of the health impact assessment is that the parameters in the model are held constant for a period of 10 cycles over a 10-year period. Although the Markov model may be expanded with cycle-specific variables that reflect ageing of the workforce, turnover among nursing staff, and expected changes in patient characteristics, in the absence of suitable information the transition probabilities were considered constant over time.

    This health impact assessment clearly indicates that a substantial reduction in the occurrence of LBP and MSD injury claims can only be achieved with good to excellent implementation of lifting devices for patient lifting in healthcare settings. As stated in several studies, the introduction of interventions in a dynamic work environment causes many problems. The fact that only one randomised controlled trial was included in this review underlines the opinion that a true experimental design in studies on the implementation of lifting devices in the workplace is difficult to realise. Workplaces and work organisations are continuously liable to changes that may interfere with the effects of the intervention. It is recommended that intervention studies, whether observational or experimental, not only measure changes in health outcome, but also changes in mechanical exposure along the pathway of the intervention during a sufficiently long follow-up period. It is of interest to note that intervention programmes in healthcare organisations are not limited to lifting devices. Other ergonomic improvements related to patient handling activities, such as electric adjustable beds, slide sheets and compression stocking slides, may also reduce mechanical load among nursing personnel.8

    The modelling of the dynamic pattern of LBP over time demonstrated that large intervention studies with a follow-up period of 3–4 years are required in order to demonstrate the effectiveness of lifting devices. This may not be feasible and, thus, a health impact assessment can be used to estimate the potential gains in burden of disease that may go unnoticed in cohort and intervention studies with few years of follow-up. The health impact assessment also presents guidance for the design of powerful intervention studies. For example, the pattern in the prevalence of LBP following the implementation of the intervention as presented in figure 1 clearly suggests that the likelihood of demonstrating the effectiveness of lifting devices will be substantially higher in newly hired than in an existing workforce.

    In conclusion, this assessment of the impact of lifting device use on LBP prevalence and injury claims among nurses clearly indicates the complexities of demonstrating a noticeable reduction in LBP due to this intervention. Health impact assessment may guide intervention studies as well as implementation of programmes to reduce manual lifting of patients in healthcare settings.

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    Supplementary materials

    • Supplementary Data

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    Footnotes

    • ▸ Additional material is published online only. To view please visit the journal online (http://dx.doi.org/10.1136/oemed-2012-101210).

    • Contributors AB is guarantor. AB was involved in planning of the study, data collection, statistical analyses and interpretation of data, and drafted the manuscript; EK contributed to data collection, interpretation of data, and critical review of the manuscript; BE had critical input into data interpretation and writing manuscript. All authors read and approved the final manuscript.

    • Funding This work was supported by a grant from the Netherlands Organization for Health Research and Development (ZonMW) (Grant 63200014).

    • Competing interests None.

    • Provenance and peer review Not commissioned; externally peer reviewed.