Before broaching this review of the research, it is worth discussing the problems and challenges associated with this topic.

Around the industrialised world, back pain is a major cause of disability. Back problems are commonly attributed to work and many in the community believe that heavy lifting contributes to back problems.

There have been thousands of studies performed on this topic. No clear answer is available.

At the heart of the problem is the type of research that has been performed. Many studies measure association between two factors. However, if we want to determine whether a component of the job, such as lifting, contributes to all causes back problems, we need to test for causation.

A commonly cited example of this may help: more drownings occur in summer. More ice cream is bought in summer. There is an association between drownings and the buying of ice creams. This does not mean buying ice cream causes drownings.

Observational studies are studies that look at a snapshot in time. They are helpful and easy to perform, but measure association. There is inherent bias in observational studies.

For example, if we asked 10,000 people across a range of occupations whether they had had back complaints in the last 10 years, a significant proportion would say yes. However, the recall of back problems may differ according to their occupation. A bricklayer, who had experienced back problems three years before the question was asked, is more likely to have needed time off work because of their back problem, compared with a bank manager who had a similar level of back pain, but was still able to do the job.

This is known as recall bias. It is a major flaw in observational studies.

In the mid-90s, a major review of the work contribution to various musculoskeletal problems was completed. The review researched a large number of studies, and essentially measured the association between health problems and work activities.

This more recent study, once again a major review of the literature, has sought to go a step beyond that review in the 90s. This review seeks to assess causation.

Causation is often determined by what is known as the Bradford Hill criteria. These criteria were developed in the 60s and include nine considerations in assessing causation, as opposed to an association. (More information can be read at Wikipedia).

The criteria addresses issues such as seeing the association consistently, that the risk factor comes before the condition, (there is a temporal relationship), there is a dose-response relationship (the higher the risk factor, the more likely the problem, e.g. a greater amount of lifting results in a greater amount of back pain), etc.

A systematic review is a structured method of summarising research. The process involves evaluating the quality of individual research studies and only including them in the review of the literature if they meet certain criteria. Systematic reviews aim to bring together the results of many studies that look at a particular topic.

Back to the current research; Canadian researchers completed this systematic review. This paper summarises eight separate systematic reviews, looking at whether various manoeuvres undertaken at work -such as twisting, lifting, sitting, etc - are contributed to, or caused by back problems.

99 studies provided information on work-related physical activity and the onset of back pain, and described evaluation of a risk factor.

Of those 99 studies, only 23 met the criteria and were rated as sufficiently high quality to be included in their systematic review. The studies came from a number of different countries.

The levels of evidence for each of the relevant Bradford Hill criteria were determined for each occupational physical activity for each of the studies.

The researchers assessed eight different occupational physical activities. These included:

• Bending/twisting;
• Awkward postures;
• Seating;
• Standing/walking;
• Carrying;
• Pushing/pulling;
• Lifting; and
• Manual handling/ assisting patients.

The research has found that there was no strong evidence to support a causal relationship between any of the individual risk factors and low back pain.

The authors found that there was conflicting evidence regarding association. Some studies identified individual factors, such as lifting or bending, being associated with higher risks of back pain. However, other studies that assessed the same risk factor found no such association. When criteria for causation were introduced, such as a dose response relationship (the risk factor preceding the onset of back problems) the authors concluded there was no strong evidence suggesting occupational physical activities caused low back pain.

If this is an area that interests you, we recommend you read the full text of the studies. The link to PubMed below provides the abstract or summary. On the right-hand side of the linked web page, you will find an icon to the Spine Journal. Click on that and it will take you to the Journal's website, where you can purchase the full text of the articles.

This issue is an important one to address. If occupational risk factors contribute to back pain, we need to identify theirs and work out ways of preventing the development of back problems. If occupational activities did not cause or contribute to back problems, this needs to be made clear.

Believing that someone is to blame for your back problem is a major source of disability. The complexities of the compensation system have been clearly shown to result in poorer outcomes. A small but significant group of people develop long-term work disability, and beliefs about how the condition developed and what might cause further harm contributes to this long-term disability.

Epidemiological studies (studies of large groups within the community) tell us that about 15 per cent of people have long-term back complaints. The back problems typically start in teenage years, will or four people in their 20s or 30s. If we look at the level of back pain around the world, there is not a significant difference between countries where there is a lot of demanding physical work and the level of back pain. These broad epidemiological factors are in line with the results of this study. This does not mean the results of this study are true and accurate.

Other researchers have questioned the validity of these systematic reviews. For example, researchers from the Netherlands indicate that the Bradford Hill criteria should not be used to assess the results of the individual study, as has been done in this review. They also indicate that the question should not be "Do occupational risk factors cause back pain", but “What is the level of risk?” That is, how much of back pain is caused by lifting (i.e. what is the attributable fraction?)

Authors

Kwon BK, Roffey DM, Bishop PB, Dagenais S, Wai EK.
 

Institution

International Collaboration on Repair Discoveries, Combined Neurosurgical and Orthopaedic Spine Program, Department of Orthopaedics, University of British Columbia, Blusson Spinal Cord Center, Vancouver General Hospital, 818 West 10th Avenue, Vancouver, British Columbia, Canada V5Z 1M9. brian.kwon@vch.ca
 

Title

Systematic review: occupational physical activity and low back pain.
 

Source

Occup Med (Lond). 2011 Dec;61(8):541-8. doi: 10.1093/occmed/kqr092. Epub 2011 Jul 4.
 

Abstract

BACKGROUND:
Although various occupational physical activities are suspected of contributing to low back pain (LBP), causal relationships have not been confirmed, complicating adjudication of work injuries, return to work instructions and preventive efforts.

AIMS:
To summarize eight systematic review (SR) reports that examined evidence supporting causal relationships between bending/twisting, awkward postures, sitting, standing/walking, carrying, pushing/pulling, lifting and manual handling/assisting patients and LBP.

METHODS:
A literature search was conducted to identify eligible studies. Methodological quality was assessed using a modified Newcastle-Ottawa Scale (NOS). Levels of evidence supporting factors for causation were examined using a Bradford Hill framework. Results were presented in eight SR reports, each focused on one or more related physical activities. This study summarizes findings from those reports and offers clinicians an overview.

RESULTS:
Collectively, the eight SR reports included 99 studies. None found strong evidence supporting a causal relationship between any occupational physical activity considered and LBP. Conflicting evidence was found between LBP and bending, twisting, lifting or pushing/pulling, but only for statistical association, not causation. Strong evidence against a causal relationship was found between LBP and manual handling/assisting patients, awkward postures, carrying, sitting, standing or walking.

CONCLUSIONS:
Although occupational physical activities are suspected of causing LBP, findings from the eight SR reports did not support this hypothesis. This may be related to insufficient or poor quality scientific literature, as well as the difficulty of establishing causation of LBP. These population-level findings do not preclude the possibility that individuals may attribute their LBP to specific occupational physical activities.
 

PubMed Link: http://www.ncbi.nlm.nih.gov/pubmed/21727180