In this article we bring you some of the evidence on the connection between work and shoulder problems.

In the most basic descriptive format, the shoulder consists of the shoulder girdle and the shoulder joint.

The shoulder joint is where the humerus meets the glenoid section of the blade bone. The joint allows a large level of mobility. This occurs at the expense of stability, with only a small amount of contact between the two bones. 

The shoulder girdle encompasses muscles and ligaments that act to stabilise the shoulder joint, such as the four muscles that make up the rotator cuff. These shoulder girdle structures enable the muscles of the shoulder joint to perform more effectively in moving the arm in such an exercise as throwing a ball.
 

The Rotator Cuff – Normal Anatomy (a) and Post-Injury with a tear (bursa not shown) (b)

From: Clinical Practice Guidelines for the Management of Rotator Cuff Syndrome in the Workplace The University of New South Wales, Medicine, Rural Clinical School, Port Macquarie Campus 2013

The two main divisions of the shoulder must work together for effective and efficient movement.

When considering the relationship between shoulder pain and a person’s occupation, it is important to recognise that most research on work relatedness will focus on degenerative conditions rather than acute injuries. Acute injuries can of course be a direct result of an occupational accident and can be the precursor to the degenerative process. But conditions that develop over time more commonly result in extended period of time off and incur the greatest claims costs.

Shoulder tendonitis describes a condition of inflammation of a tendon or tendons of the shoulder joint or shoulder girdle. This is the most commonly categorised shoulder pathology in research. Reported shoulder pain may also come from inflammation of other structures within the joint that aid movement, such as bursitis. A bursa is a small fluid filled sac that acts to enhance the ease of tendon movement at a joint. Shoulder pain may also come from nerve damage or nerve impingement which can also cause a weakening of movement and a tingling sensation down the arm in addition to pain.

Work relatedness

Shoulder disorders are common in the workplace. They mostly involve muscle, tendon or other soft tissue damage as opposed to arthritic causes.

Of work characteristics that are debated as being risk factors for development of shoulder pain, the top three are: repetition of tasks performed, loaded or forceful movement and posture of the shoulder during movement.

The mechanism of injury is thought to be internal and external to the soft tissues involved.

For instance, with sustained internal force of the rotator cuff muscles through repetitive and loaded shoulder movement above head height, inflammation and degeneration over time can occur through a lack of microcirculation within the muscle.

Externally, elevated shoulder movement that is repetitive and loaded can squeeze or tear the tendons between the bony structures that surround them causing pain and accelerating the degenerative process.

Unless a specific shoulder condition is targeted by a study, research will try to group shoulder pathologies under the heading of shoulder pain. Therefore, the way in which this is quantified is important as it will likely incorporate different types of conditions with differing symptoms. Some studies may use different criteria for classifying a person as having or not having shoulder pain. This can be a key point to note initially as it can affect the validity of comparing results between studies or interest groups.  

We start with two tables from Clinical Practice Guidelines for the Management of Rotator Cuff Syndrome in the Workplace - The University of New South Wales, Medicine, Rural Clinical School, Port Macquarie Campus.

Environmental Factors that may Influence the Development of Shoulder Pain

Personal Factors that may Influence the Development of Shoulder Pain

Below are a series of research articles, with a summary of the article followed by the abstract. 

Van der Windt, D. A., Thomas, E., Pope, D. P., de Winter, A. F., Macfarlane, G. J., Bouter, L. M. and Silman, A. J.,
Occupational risk factors for shoulder pain: a systematic review.
Occupational & Environmental Medicine, 2000. 57(7): p. 433-42.

Summary

This article is a review, which seeks to bring together the information from relevant research studies undertaken in this area.  The review looked at 29 studies on the topic described.

Studies included had to pass a basic screening process for methodology to be included in this review.  The review looked at how job tasks were analysed, the types of risk factors included, how shoulder pathology was assessed and the statistical analyses used. The authors also included studies which measured psychosocial influences on shoulder pain, such as autonomy, stress, support and job satisfaction.

Due to the differences between many of the studies in terms of the methods they used, strong associations and trends could not be clearly defined, but a link was found between physical load, psychosocial work environment and shoulder pain.

When the researchers isolated the studies of high quality methodology, they found there was a consistent positive associations between shoulder pain and

• repetitive movements
• vibration
• duration of employment
• job dissatisfaction. 

The authors of this review noted that the majority of the studies did not consider each person’s previous work history or non-work related activities.  They felt that these conditions may impact on shoulder pathology and therefore should be included in any assessment of the condition.

Abstract

Abstract: OBJECTIVES: To systematically evaluate the available evidence on occupational risk factors of shoulder pain. METHODS: Relevant reports were identified by a systematic search of Medline, Embase, Psychlit, Cinahl, and Current Contents. The quality of the methods of all selected publications was assessed by two independent reviewers using a standardised checklist. Details were extracted on the study population, exposures (physical load and psychosocial work environment), and results for the association between exposure variables and shoulder pain. RESULTS: 29 Studies were included in the review; three case-control studies and 26 cross sectional designs. The median method score was 60% of the maximum attainable score. Potential risk factors related to physical load and included heavy work load, awkward postures, repetitive movements, vibration, and duration of employment. Consistent findings were found for repetitive movements, vibration, and duration of employment (odds ratio (OR) 1.4 - 4.6 in studies with method scores >/= 60%). Nearly all studies that assessed psychosocial risk factors reported at least one positive association with shoulder pain, but the results were not consistent across studies for either high psychological demands, poor control at work, poor social support, or job dissatisfaction. Studies with a method score >/=60% reported ORs between 1.3 and 4.0. Substantial heterogeneity across studies for methods used for exposure assessment and data analysis impeded statistical pooling of results. CONCLUSIONS: It seems likely that shoulder pain is the result of many factors, including physical load and the psychosocial work environment. The available evidence was not consistent across studies, however, and the associations were generally not strong. Future longitudinal research should evaluate the relative importance of each individual risk factor and the role of potential confounding variables-such as exposure during leisure time-to set priorities for the prevention of shoulder pain in occupational settings.

Svendsen, S.W., Gelineck, J., Mathiassen, S. E., Bonde, J. P., Frich, L. H., Stengaard-Pedersen, K. and Egund, N.,

Work above shoulder level and degenerative alterations of the rotator cuff tendons: a magnetic resonance imaging study.

Arthritis & Rheumatism, 2004. 50(10): p. 3314-22.

Summary

This article aims to show how working with the shoulder in an elevated position (above 90 degrees) for an extended period of time can produce pathological changes to the rotator cuff muscles. This was measured by way of Magnetic Resonance Imaging (MRI) technology by fully qualified radiologists. Direct measurements of arm use were used,   as well as self reported work histories from questionnaires. These allowed the researchers to estimate the time spent with the arm in an elevated position above 90 degrees, over each person’s entire working life.

They found that if a person spent a total of 5 months over their working life with their arm in an elevated position above 90 degrees, the risk of rotator cuff pathology was increased. It was also found that the risk of a having abnormalities on MRI scans increased by 15% for every 5-month increment in lifetime shoulder elevation.

Abstract

Abstract: OBJECTIVE: To determine whether work performed with the arms in a highly elevated position is associated with alterations in the rotator cuff tendons as assessed by magnetic resonance imaging (MRI). METHODS: A cross-sectional study was performed in a historical cohort of male machinists, car mechanics, and house painters. The participants were right-handed, ages 40-50 years, and had been employed in their trades for not less than 10 years. Seventy-one percent of invited subjects participated (136 of 192). Lifetime upper arm elevation was assessed by direct measurements combined with individual work histories obtained by questionnaire and from registry data. Supraspinatus tendinopathy was evidenced by MRI signal intensity changes and morphologic alterations. Infraspinatus and subscapularis tendinopathy were also assessed. Additional outcomes were acromioclavicular joint degeneration and humeral head cysts. The MRI findings were evaluated by radiologists who were blinded to exposure status and symptoms. RESULTS: An exposure-response relationship was found between lifetime upper arm elevation and supraspinatus tendinopathy, with an age-adjusted odds ratio of 1.27 (95% confidence interval 1.02-1.60) for a 5-month increase in the total number of full-time working months spent with the arm elevated >90 degrees . CONCLUSION: Work with the arms in a highly elevated position is associated with MRI-diagnosed alterations in the supraspinatus tendon. By demonstrating the first part of a possible biologic pathway, the study corroborates the work-relatedness of rotator cuff disorders.

Frost, P., Bonde, J. P., Mikkelsen, S., Andersen, J. H., Fallentin, N., Kaergaard, A. and Thomsen, J. F.,
Risk of shoulder tendonitis in relation to shoulder loads in monotonous repetitive work.
American Journal of Industrial Medicine, 2002. 41(1): p. 11-8.

Summary

The risk of shoulder tendonitis as a result of repetitive, loaded movement was examined here. Workers from a variety of factory type work were assessed in terms of both their job tasks and also their shoulder problems. A team of ergonomists visited the worksites and analysed the movements of different jobs and categorised each as either repetitive and/or forceful or not.

The groups of workers in each job category that were classified as not having repetitive or forceful jobs were used as a reference group for comparative purposes. The researchers used a 12 point scale to assess each person’s shoulder symptoms, which helped the authors used a standard method to determine who had a shoulder tendonitis problem.

The results showed that workers involved with repetitive tasks were two to three times more likely to suffer shoulder tendonitis.

Furthermore, workers who also had an element of force to their job, (10% of maximal voluntary contraction and above) had a 40% increase in the prevalence rate of shoulder tendonitis.

Abstract

Abstract: BACKGROUND: Few studies relate the occurrence of shoulder disorders to quantified ergonomic exposures. This study evaluates the hypothesis that shoulder loads in repetitive work might contribute to the occurrence of shoulder tendonitis. METHODS: This is a cross-sectional study of 1961 workers in repetitive work and 782 referents. Shoulder loads were quantified at task level and measures of exposures were assigned based on task distribution. Symptoms in combination with clinical criteria defined shoulder tendonitis. RESULTS: The prevalence of shoulder tendonitis was higher among exposed workers (adjusted OR 3.1, 95% CI 1.3-3). Neither frequency of movements (ranging 1-36/min) nor lack of micro-pauses in shoulder flexion (ranging 0-100% of cyclus time) was related to disease prevalence. Increasing force requirements (categorized as light = 1, somewhat hard = 2, hard = 3 or very hard = 4) increased risk slightly (OR 1.6, 95% CI 1.0-2.6 per unit). CONCLUSIONS: The results indicate that workers with repetitive tasks have increased risk of shoulder tendonitis, which partially can be attributed to force requirements.

Kaergaard, A. and J.H. Andersen.
Musculoskeletal disorders of the neck and shoulders in female sewing machine operators: prevalence, incidence, and prognosis.
Occupational & Environmental Medicine, 2000. 57(8): p. 528-34.

Summary

These researchers assess the risk factors that contribute to the development of myofascial pain syndrome and rotator cuff tendonitis in female sewing machine operators. Out of 243 women, 178 were followed up over a period of 2 years in which they completed a questionnaire and underwent a clinical examination. The findings were compared to 357 female industrial workers that were not involved with repetitive tasks.

2.2% of the comparison group and 5.8% of the sewing machine operators had rotator cuff tendonitis at the baseline examination.  15.2% and 9.0% respectively had myofascial pain syndrome.

Of those affected, the 2 year follow-up showed that 11 of the 15 women with myofascial pain were no longer classed as sufferers, whereas only 1 of the 13 with rotator cuff tendonitis could say the same.

In examining for factors that may show why rotator cuff tendonitis is a more persistent disorder.  It was revealed that years of employment was the main difference between the development of the conditions. Rotator cuff tendonitis was more prevalent as years of employment increased, unlike myofascial syndrome which showed a U shaped prevalence rate against time.

Other factors that were found to be associated with either condition were a self rating of general health as fair or poor (43% of respondents). High stress levels, smoking, being a single mother, job strain and lack of support at work were also linked to of development of shoulder conditions.

Abstract

Abstract: OBJECTIVES: To assess the occurrence and persistence of two restrictively defined neck-shoulder disorders among sewing machine operators. To assess factors associated with the development of neck-shoulder disorder and prognostic factors for remaining a case, when disorders were already present. METHODS: In an initial group of 243 sewing machine operators, 178 were followed up for 2 years. At baseline and at 1 and 2 years follow up the participants underwent a clinical examination of the neck and arms and filled in a questionnaire about current musculoskeletal complaints. Clinical criteria for two main neck-shoulder disorders were defined: rotator cuff tendonitis and myofascial pain syndrome. A baseline control group consisted of 357 women with varied non-repetitive work. RESULTS: At baseline the overall prevalence of myofascial pain syndrome and rotator cuff tendonitis was 15.2% and 5.8% among sewing machine operators compared with 9.0% and 2.2%, respectively, among controls. The presence of the disorders was strongly associated with a self perception of poor general health. Although myofascial pain syndrome showed a U shaped association with years as a sewing machine operator, rotator cuff tendonitis was absent among the newest recruits and present among 15% of the women with more than 20 years as a sewing machine operator. Besides years as a sewing machine operator, the risk of having a neck-shoulder disorder at baseline was significantly associated with high stress (prevalence ratio (PR)=2.54; 95% confidence interval (95% CI) 1.28 to 5.05) when adjusted for age, body mass index, smoking, living alone with children, job strain, and social support from colleagues and supervisors. Only one of 13 participants with rotator cuff tendonitis at baseline recovered during follow up. Myofascial pain syndrome showed a much more fluctuating tendency. Low social support (RR 3.72; 95% CI 1.22 to 11.30) and smoking (RR 3.93; 95% CI 1.33 to 11.58) were associated with the development of neck-shoulder disorders, which was also associated with neck-shoulder pain score and living alone with children. CONCLUSION: Rotator cuff tendonitis showed a higher degree of persistence than myofascial pain syndrome. Both disorders highly influenced the perception of general health. Women who lived alone with children, were smokers, or experienced low support from colleagues and supervisors had a higher risk of contracting a neck-shoulder disorder.

Pope, D. P., Croft, P. R., Pritchard, C. M., Silman, A. J. and Macfarlane, G. J.,
Occupational factors related to shoulder pain and disability.
Occupational & Environmental Medicine, 1997. 54(5): p. 316-21.

Summary

This study obtained information about shoulder pain and occupation, both previous and present, via questionnaires and interviews. 232 people took part in the interview and answered questions relating to repetition, weights lifted and postures adopted at work, as well as questions on the duration of shoulder pain and whether such symptoms caused any disability in activities of daily living. Information was also collected that related to the working environment, be it wet or cold for example, and if it generated any stress. The data from those who reported shoulder pain was compared to the data of those who did not.

It was found that for men carrying weights on one shoulder,  there was  5.5 times the likelihood of shoulder pain.  This this increased further if the weight was 25lb or over.

Men needing to take constant rest breaks due to aching muscles and the ongoing aching of joints and muscles after a shift was associated with 2 and 3 times the likelihood of  shoulder pain. Of the work environment, damp and cold conditions lead to a 5-6 times greater risk for shoulder pain. Interestingly, this was not a significant risk for women.

Those men and women who reported their jobs to be monotonous or stressful were found to have a 2.7 and 1.9 times higher chance respectively, of developing some form of shoulder pain or disability.

Abstract

Abstract: OBJECTIVES: To determine, in a population based study, the influence of occupational factors on the occurrence of shoulder pain and disability. METHODS: A random sample of patients was selected from the register of a general practice in the Greater Manchester area of the United Kingdom. Information was collected by a posted questionnaire with specific enquiries about symptoms in the shoulder region and related disability. A lifetime occupational history was obtained including physical exposures, working conditions, and psychosocial aspects of each workplace. Analysis has been conducted as a case-control study, comparing occupational exposures at the time of onset of symptoms in those with shoulder pain and disability with corresponding occupational exposures in those without shoulder pain and disability. RESULTS: An increased risk of shoulder pai