Elsevier

The Spine Journal

Volume 10, Issue 1, January 2010, Pages 76-88
The Spine Journal

Review Article
Causal assessment of occupational bending or twisting and low back pain: results of a systematic review

https://doi.org/10.1016/j.spinee.2009.06.005Get rights and content

Abstract

Background context

Low back pain (LBP) is a common musculoskeletal disorder that often occurs in the working-age population. Although numerous physical activities have been implicated in its etiology, determining causation remains challenging and requires a methodologically rigorous approach.

Purpose

To conduct a systematic review focused on establishing a causal relationship between occupational bending or twisting and LBP.

Study design

A systematic review of the literature using Medline, Embase, CINAHL, Cochrane Library, and Occupational Safety and Health database, gray literature, hand-searching occupational health journals, reference lists of included studies, and experts. Evaluation of methodological quality using a modified Newcastle-Ottawa Scale for observational studies. Summary levels of evidence for each of the Bradford-Hill criteria for causality for each category of bending or twisting and type of LBP.

Sample

Studies reporting an association between occupational bending or twisting and LBP.

Outcome measures

Numerical association between different levels of exposure to bending or twisting and the presence or severity of LBP.

Methods

A systematic review was performed to identify, evaluate, and summarize the literature related to establishing a causal relationship, according to Bradford-Hill criteria, between occupational bending or twisting and LBP.

Results

This search yielded 2,766 citations. Ten high-quality studies reported on bending and LBP. Five were case-control studies and five were prospective cohort studies. There was conflicting evidence for association, with five studies demonstrating significant associations in the majority of their risk estimates, but no evidence for consistency. Seven studies assessed dose response, with four studies demonstrating a nonsignificant dose-response trend. Four studies were able to assess temporality, but only one demonstrated significant risk estimates. Biological plausibility was discussed by two studies. There was no available evidence for experiment. Seven high-quality studies reported on twisting and LBP. Two were case-control studies and five were prospective cohort studies. Three studies reported significant associations in the majority of their risk estimates, with no evidence for consistency. Three studies demonstrated a nonsignificant dose-response trend. Two studies were able to assess temporality, but only one study was able to demonstrate significant risk estimates. Two studies discussed biological plausibility. There was no available evidence for experiment.

Conclusions

A summary of existing studies was not able to find high-quality studies that satisfied more than three of the Bradford-Hill criteria for causation for either occupational bending or twisting and LBP. Conflicting evidence in multiple criteria was identified. This suggests that specific subcategories could contribute to LBP. However, the evidence suggests that occupational bending or twisting in general is unlikely to be independently causative of LBP.

Introduction

Low back pain (LBP) is a musculoskeletal disorder involving an interaction between anatomical, psychological, socioeconomic, and occupational risk factors that may culminate in varying degrees of pain and disability. The lifetime prevalence of LBP has been estimated at 84% [1] of the general population. In the working-age population, LBP has the highest health care use among all chronic diseases, resulting in a heavy economic burden [2], [3]. Given its prevalence and consequences, LBP is a major occupational health concern. To effectuate meaningful changes in work-related LBP, it is necessary to improve our understanding of the etiology of LBP as it relates to common specific occupational physical activities.

Bending and twisting are routine physical activities performed in many different occupations, and both have been examined in various settings to determine whether they may cause LBP. Previous studies have suggested that bending or twisting is associated with increased intradiscal pressure that predisposes discs to injury (eg, degeneration or herniation) [4], [5], [6]. Despite uncertainty as to whether these activities are in fact injurious, modified duty return-to-work plans for workers with LBP often aim to reduce the performance of difficult tasks such as twisting and bending to prevent reinjury [7]. A more thorough comprehension of the causal association between bending or twisting and LBP may be beneficial to 1) establish occupational guidelines for the primary prevention of LBP, 2) identify potential work modifications for the secondary prevention of LBP, and 3) provide guidance to stakeholders involved in the adjudication process of occupational LBP claims.

Establishing causal links between specific risk factors and LBP from single studies has historically proven complex and unreliable because of the limitations imposed by specific research questions, study designs, study populations, study methodological quality, and specific types of statistical analyses. A systematic review, however, can help establish causation between isolated risk factors and LBP by summarizing all available evidence in light of the many criteria that have been proposed to determine causation [8], [9]. It can also critically appraise the methodological quality of the studies to establish the degree to which their results are subject to bias or confounding [10], [11]. To date, no systematic review has been conducted on the causality of occupational bending or twisting and LBP.

The purpose of this study was to identify, evaluate, and summarize the best available evidence regarding bending or twisting and LBP in workers, using Bradford-Hill [12] criteria for causation.

Section snippets

Methods

A systematic review was performed to identify, evaluate, and summarize the literature related to establishing a causal relationship, according to Bradford-Hill criteria, between occupational bending or twisting and LBP.

Results

Overall, the electronic and manual search strategies yielded a total of 2,766 citations, of which 275 were deemed potentially relevant. Upon review of the full-text copies of the 275 articles, 35 satisfied all of the specific study inclusion/exclusion criteria. Figure summarizes the results of the searching, Level 1 and 2 screening, data abstraction, quality appraisal, and summary evaluation of evidence for causation. A total of 23 studies were considered of low methodological quality, and 12

Discussion

Bending and/or twisting are common activities in many workplaces. Previous studies [21], [24] have indicated that performing certain bending exercises can contribute toward LBP. Twisting has been classified by Videman et al. [14] and van den Heuvel et al. [20] as a hazardous activity, which can place undue stress on the spine that may eventually culminate in LBP. The results of this study indicate that there was conflicting evidence available to support a causal relationship between bending and

Conclusions

The present study was unable to uncover evidence supporting more than three of the Bradford-Hill criteria for causation for occupational bending or twisting and LBP. Based on the results of this review, it is unlikely that occupational bending or twisting is independently causative of LBP in workers. The strength of association was often rated as weak or moderate, and none demonstrated a statistically significant dose response. This suggests that if a causal relationship exists, it may be weak.

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    FDA device/drug status: not applicable.

    Author disclosures: BKK (consulting, Medtronic); SD (consulting, Palladian Health; Scientific Advisory Board, Palladian Health).

    This study was funded by a peer-review grant provided to Drs Wai, Bishop, Kwon, and Dagenais by the Workers Compensation Board of British Columbia.

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