Aetiology and management of work-related upper extremity disorders

Best Practice & Research Clinical Rheumatology Vol. 21, No. 1, pp. 123e133, 2007 doi:10.1016/j.berh.2006.09.001 available online at http://www.sciencedirect.com

8 Aetiology and management of work-related upper extremity disorders J.B. Staal*

MSc, PhD

Senior Researcher

R.A. de Bie

MSc, PhD

Professor of Physiotherapy Research Department of Epidemiology and Caphri Research Institute, Maastricht University, Maastricht, The Netherlands

E.J.M. Hendriks

MSc, PhD

Senior Researcher Department of Epidemiology and Caphri Research Institute, Maastricht University, Maastricht, Netherlands and Dutch Institute of Allied Health Care, Amersfoort, The Netherlands

Work-related upper extremity disorders are a major cause for complaints and disability in worker populations. They may consist of a range of symptoms in the upper extremity, either clearly localised or more widespread, and are usually preceded or affected by exposure to physical activities and/or postures at work. In order to develop effective management strategies, both from a prevention and treatment perspective, more knowledge is needed with regard to the nature, pathophysiological mechanisms and risk factors of this group of disorders. This chapter reviews the clinical manifestations, mechanisms and aetiology of work-related upper extremity disorders through an exploration of the literature. We also examine and discuss the evidence for the effectiveness of several preventative and therapeutic interventions. Key words: work-related upper extremity disorders; clinical manifestations; risk factors; prevention; treatment.

Work-related upper extremity disorders (WRUED) severely hamper a majority of the working population in western countries. One third of workers’ compensation costs in private industry in the USA is estimated to be caused by WRUED1 and the direct costs, with compensation, exceeds US$ 20 billion in Washington State alone.2 In the * Corresponding author. Tel: þ31 43 3881428; Fax: þ31 43 3884128. E-mail address: [email protected] (J.B. Staal). 1521-6942/$ - see front matter ª 2006 Elsevier Ltd. All rights reserved.

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Netherlands, there has been a rise in WRUED complaints from 19% to 28% between 1997 and 20023, resulting in 8% of the whole working population taking time off work because of WRUED annually.4 The Health & Safety Executive, a British institution responsible for the regulation of occupational risks to health, estimated that self-reported WRUED resulted in 4.7 million lost working days in 2003/04.5 It is likely that the increased use of personal computers at work is associated with an accumulated incidence of WRUED.6 WRUED is an umbrella term used for a range of symptoms and disorders localised in the neck, shoulder, elbow, forearm, wrist and/or hand. These symptoms may include pain, swelling, stiffness, numbness, tingling, clumsiness, loss of co-ordination, loss of strength, skin discoloration and temperature differences, and give rise to limitations in activities either at work or during leisure time.4 By definition, the occurrence and persistence of this syndrome is considered to be affected by exposure to physical activities and/or postures at work. Throughout the literature many different diagnostic schemes, classifications and labels have been applied to describe WRUED. Examples are RSI (repetitive strain injury), forearm pain, CTD (cumulative trauma disorders), cervicobrachial fibromyalgia etc. 7 Van Eerd et al (2003), however, found in a systematic literature review that classification systems for WRUED differed in the disorders that they included, the labels used to identify the disorders and the criteria used to describe the disorders.7 They came across 27 classification systems in the literature that described disorders of the upper limb that were assumed to be caused or aggravated by work and no two systems were the same.7 In general, the literature distinguishes specific from non-specific WRUED, in which the latter is considered to be present when all specific disorders have been ruled out.8 Specific disorders may be characterised as conditions with a specific medical diagnosis such as frozen shoulder, epicondylitis, De Quervain’s syndrome, etc. The variety in terms and classification schemes for WRUED presented in the literature not only hampers direct comparisons between available studies but it also reflects the many uncertainties that still exist regarding the aetiology and nature of this syndrome. Knowledge on the aetiology and pathophysiological mechanisms involved is, however, definitely needed to gain more insight into potentially effective prevention strategies and treatments for WRUED.9 The focus of this chapter lies on the non-specific variant of WRUED. A descriptive overview is given to describe the currently available scientific knowledge regarding the aetiology and nature of WRUED. Furthermore, options for prevention and treatment will be critically reviewed and discussed. CLINICAL MANIFESTATIONS The Dutch Health Council characterises WRUED as a disturbance in the balance between load and physical capacity, preceded by activities that involve repeated movements or prolonged periods spent with one or more of the relevant body parts in a fixed position.10 The onset of complaints in WRUED is usually gradual, but in one study, it was found to be abrupt in a quarter of the patients.11 Symptoms are initially localised to one anatomical region, but may become more widespread over time. The syndrome only affects upper extremities, the neck and the other (i.e. initially uninvolved) arm may also become affected as time goes by.11 Pain, both spontaneous as well as due to activities, plays a major role in WRUED. Other symptoms may include paraesthesia, swelling, changes in colour and

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temperature, stiffness, restricted range of motion and more general symptoms such as dizziness, nausea, sleep disturbances, fatigue and headache. Paraesthesia has been found in 87e91% of patients with WRUED and subjective swelling in 73%.11e13 Changes in colour and temperature were also noted in patients with WRUED, albeit not very often.11 In one study Raynaud-like phenomena were found in 43% of the patients13, while in another study restricted range of motion was occasionally found in WRUED.11 A limited range of motion is usually the result of trauma-induced trophic changes and, hence, may not be considered a true motor sign, since it is not caused by an altered nerve or muscle function. Focal dystonia may accompany WRUED as well.14,15 We found only one study that addressed the issue of systemic signs and symptoms.13 In that study systemic complaints such as dizziness, whizzing, nausea and vertigo were noted in subgroups of patients with regional unilateral and bilateral upper limb pain, but not in patients with only local unilateral complaints.13 General stiffness and morning stiffness has been found in 52e88% of WRUED patients.11,13 Furthermore, sleep disturbances, fatigue and headaches were highly frequent among patients with WRUED.12 Besides the physical complaints, psychological complaints such as anxiety, depression and irritability were also more prevalent in patients with this syndrome when compared to healthy controls. However, it remains difficult to determine whether these complaints precede the upper extremity symptoms or are consequences of them.12 Most of the results on additional symptoms were found in cohorts of chronically disabled patients that appear to represent the more severe end of the spectrum of WRUED patients.11e13 It should be kept in mind that the distribution of pain in WRUED patients may vary from localised pain without additional physical or psychological symptoms to more widespread pain very often accompanied by one ore more of the additional symptoms summarised above. RISK FACTORS FOR WRUED Risk factors for WRUED are usually subdivided in to work-related physical risk factors, work-related psychosocial risk factors and personal risk factors.16 Many studies have been carried out on risk factors for the development of WRUED and most of them have been summarised in systematic literature studies. In a systematic review of 22 cross-sectional studies, two prospective cohort studies and one case-referent study, Arie¨ns et al (2000) concluded that there was some evidence for a positive relationship between the occurrence of neck pain and the following work-related physical risk factors: neck flexion, arm force, arm posture, duration of sitting, twisting or bending of the trunk, handearm vibration and workplace design.17 In another systematic review, including three caseecontrol studies and 26 cross-sectional studies, it was found that repetitive movements and vibration were associated with shoulder pain.18 An earlier extensive review by the National Institute for Safety and Health (NIOSH) in the USA in 1997 had already shown that there was some evidence for a relationship between occupational exposures such as repetitiveness of movements, the use of force, posture and vibration, and the development of complaints in the elbow, hand and wrist as well as neck and shoulder complaints.19 More recently, several prospective cohort studies have been published that supported the results of the earlier studies. It was shown in a Dutch prospective study in an occupational setting with 3-year follow-up that sitting at work for more than 95% of the time was a significant risk factor for

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neck pain (relative risk (RR) ¼ 2.3).20 In two other prospective cohort studies, which were carried out in populations of office workers, independent, statistically significant, relationships were established between the occurrence of WRUED and ergonomic variables such as the duration of keyboard and mouse use21e23, a smaller inner elbow angle of the keyboard arms and a greater ulnar deviation angle of the mouse wrist.24,25 Together with the physical factors, work-related psychosocial factors are also assumed to play an important role in the development of WRUED. Bongers et al (2002) performed a systematic literature study on the relationships between psychosocial factors and shoulder, elbow, hand or wrist problems.16 The review included one prospective cohort study, one caseecontrol study and 26 crosssectional studies. Consistent associations with upper limb disorders were found for perceived high work stress and non-work-related work stress and there were also some indications for an association between upper limb problems and high job demands.16 The earlier mentioned Dutch prospective study identified statistically significant adjusted associations for high quantitative job demands (RR ¼ 2.1) and low social support from co-workers (RR ¼ 2.4) as risk factors for neck pain.20 Furthermore, high job demands were identified as a risk factor for neck/shoulder symptoms (RR ¼ 2.1) and elbow/wrist/hand symptoms (RR ¼ 1.9), while low social support from co-workers was identified as a risk factor for elbow/wrist/hand symptoms (RR ¼ 2.2).26 More recent Scandinavian prospective cohort studies among computer workers showed significant associations between upper limb symptoms and high job demands, low job control and high job strain, with odds ratios varying from 1.6 to 1.9.21,23,27 In conjunction with the physical and psychosocial work-related factors, personal characteristics may also contribute to the development of WRUED. In a caseecontrol study comparing 45 computer workers with non-specific WRUED with 45 computer workers free from upper limb disorders and 42 chronic pain patients it was found that psychoneuroticism and neurotic perfectionism were risk factors for WRUED when adjusted for physical and psychosocial confounders.28 In addition, women appeared to have a higher risk of developing upper limb symptoms than men21,23,29,30, which might be explained by a difference in the effect of exposure to work-related physical and psychosocial risk factors.31 The reported results for physical, psychosocial and personal characteristics clearly indicate that WRUED have a multi-factorial origin. Since many studies were carried out on cross-sectional data more well-designed prospective cohort studies are needed to further clarify the aetiology of these types of complaints. A multi-factorial origin also implies that prevention efforts, as well as treatment, should follow a multitargeted approach. PATHOPHYSIOLOGICAL MECHANISMS A common feature of WRUED is muscle pain. The common muscle force development in many occupational activities is, however, relatively low. While the muscle as a whole will not be metabolically exhausted in these cases, the opposite might be the case for single muscle fibres. 32 According to the ‘size principle’ motor units are activated in ascending order of their size.33 Smaller motor units producing less tension are recruited at a lower level of activation and larger units are gradually recruited at a higher level of activation. Thus, with increasing force smaller low

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threshold motor units are always being recruited first. This supports the so-called ‘Cinderella’-hypothesis, which means that during low intense muscle activity, which commonly occurs during repetitive movements, some smaller motor units may become metabolically exhausted.32,34 Prolonged activation of muscles may further lead to increased muscle pressure, which hampers blood circulation thereby causing a decrease in oxygenation.35,36 Although the initial blood flow is probably sufficient during low level contractions, this might not be the case when the contraction has to be maintained for longer periods.32 This hypothesis was supported in a study by Larsson et al (1999) who compared patients with chronic trapezius myalgia with healthy controls and found that the myalgia patients had an impaired regulation of the microcirculation of the m. trapezius when compared to controls. In that study, the impaired microcirculation could not, however, be explained by changes in intramuscular pressure.37 Pritchard et al (1999) investigated the vascular responses to muscular work in the radial artery in patients with bilateral diffuse forearm and localised arm pain. They found that in diffuse forearm pain the radial artery is relatively constricted compared to healthy controls and fails to vasodilate with exercise.38 In another study, thermographic changes in the hands of keyboard operators with chronic forearm pain were investigated and compared to the changes in asymptomatic controls.39 After a task consisting of 5 minutes text typing the patient group had significantly greater reductions in temperature than the control group, which was assumed to be caused by vasomotor changes in the forearm due to sympathetic over-reactivity.39 It has also been suggested that muscle disorders may develop due to an accumulation of Ca2þ in the skeletal muscle cell as a result of prolonged motor unit activity. Accumulation of Ca2þ is supposed to have noxious and, thereby, damaging effects on the membranes of muscle fibres.32,40,41 This may increase the susceptibility of the membrane lipids to free radicals, which have a toxic effect. 32 A too high concentration of Ca2þ in the muscle cell has also been supposed to impair adenosine triphosphate formation in the mitochondria, which is a prerequisite for active force production.32 The use of force, awkward postures and repetition of movements in the upper extremities also elicit mechanical load on tendons and peripheral nerves. If certain individual physiological limits are exceeded this mechanical load may cause tissue damage. Some postulated mechanisms on the causes of tissue damage in tendons are: the exertion of a certain stretch limit, friction between the tendon and the tendon sleeve, a mechanically induced rise in local temperature and an accumulation of micro trauma.41 Biomechanical loading might also lead to the compression of peripheral nerves causing symptoms such as pain, numbness, tingling and loss of motor control. A well-known example is the carpal tunnel syndrome caused by the compression of the median nerve42, but other nerves in the upper extremities, such as the ulnar nerve and the spinal nerve roots, may be affected as well.43 Increased intra- and extra-neural pressure not only occurs as a result of confined spaces but may also be caused by nerve excursion and traction due to extreme joint positions, the use of force or repetitive movements. Elevated extraneural pressures may, in a doseeresponse manner, hinder intraneural microvascular blood flow, axonal transport and nerve function, and affect endoneurial oedema and displacement of myelin. It can also elicit the processes of nerve injury and repair leading to tissue damage.43 Rempel et al (1999) also reported, in their review of both human and animal studies, on the following cascade of biological consequences of exceeding mechanical load on peripheral nerves: endoneurial oedema, demyelination, inflammation, axonal

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degeneration, fibrosis, growth of new axons, remyelination and thickening of the perineurium and endothelium.43 Another explanation for the persistence of symptoms in WRUED patients is the psychobiological model of sensitisation.44,45 Following this model, sensitisation can be defined as an increase in response to a stimulus due to the repeated presentations of that stimulus. Contrary to sensitisation, habituation refers to a decrease in the response to repeated stimuli.46 Sensitisation processes may occur at the cellular level, the psychological level and even the interpersonal level.44,47 The degree to which sensitisation occurs might explain the individual differences in tolerance and acceptance of common subjective health complaints such as non-specific upper limb symptoms.44 A state of sustained high arousal due to, for example, high stress levels is supposed to result in sensitisation, whereas exposure to the same stimulus under conditions of low arousal would lead to habituation. Sustained arousal may interfere with activities in pain pathways, leading to sensitisation of common complaints in neural loops.44 Sensitisation at both a peripheral and central level has already been established in fibromyalgia patients.48 The mechanisms described above are more or less physiological in nature. They, in general, need further exploration, support and refinement especially with regard to the patient with persistent WRUED. Like other chronic pain disorders, prolongation of symptoms in WRUED patients may also result in a state of chronic pain, disability and work loss. Both cognitive and behavioural processes, which become more significant in chronic phases, contribute to the way patients perceive their complaints and disability and the way they cope with their problems. For obvious reasons a state of chronic, persisting pain and its accompanying behaviour should preferably be viewed from a psychological or even social standpoint, rather than purely focusing on the pathophysiological mechanisms that underly upper limb symptoms.49,50 PRIMARY PREVENTION The primary prevention of WRUED can be described as efforts that are undertaken to prevent the occurrence of symptoms in an asymptomatic population. Aetiological research aims to identify the risk factors for WRUED. Logically, these risk factors have to be modified in order to prevent the occurrence of symptoms. As explained earlier, WRUED probably have a multi-factorial origin. These factors refer to the physical, psychosocial and personal characteristics of the individual worker and his/her work environment. Since it is not easy to modify the personal characteristics of the individual worker, prevention efforts need to be targeted at both physical and psychosocial factors. Several randomised experimental studies have been undertaken to investigate the effectiveness of primary prevention efforts in this domain. Rempel et al (2006), in a randomised controlled trial (RCT) among computer operators in a call centre, recently found that the use of a forearm support in combination with ergonomics training was protective for the occurrence of neck, shoulder and upper extremity pain.51 Another randomised study showed that the use of a forearm support by call centre workers resulted in fewer reported symptoms in the neck and back when using a normal computer work station in comparison to a so-called ‘floating’ posture.52 The effect of adjustments to work stations and postures was investigated by Gerr et al (2005) in a population of keyboard workers.53 One group received adjustments based on risk factors that had been identified in a previous longitudinal cohort study24, another group received conventional adjustments as prescribed by existing standards and guidelines, while a third group was instructed to

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continue keying in their usual posture and no changes were made to their workstations. No differences in the risk for musculoskeletal symptoms were observed between participants allocated to the three groups.53 Contrary to those results, there are also randomised studies that indicate that ergonomic education and training is effective in preventing musculoskeletal symptoms in computer workers. These studies have in common that they follow a more participatory approach.54e57 Micro breaks during computer work were also found to be beneficial. They had a positive effect on reducing discomfort in the upper limb and also appeared to have no detrimental effect on worker productivity.58 In a population of aircraft manufacturing workers, which is a clearly distinct population from computer workers, ergonomic training was found to improve the ergonomics of work methods.59 The benefits of exercise in the prevention of WRUED have not been clearly supported yet by RCTs, 57,59 although it has been found to be protective for upper limb symptoms in a longitudinal cohort study consisting of workers from different occupations.60 The effects of stress management have not studied been very often. Reported results indicated that stress management following cognitive-behavioural techniques might be beneficial in reducing symptom outcomes in the short term.61 The picture that emerges from the presented results is not very clear. Specific ergonomic adjustments, such as arm supports, may be effective in specific populations, such as call centre workers, but the effectiveness of other ergonomic measures depend on their content and also on the level to which the worker participates in the decision-making process with regard to ergonomic adjustments. A number of RCTs on the primary prevention of WRUED have been published, but due to the heterogeneity in study populations and interventions it is, at this stage, difficult to summarise the reported results in clear recommendations. More methodologically sound studies are needed in order to make meaningful classifications of worker populations and interventions. Although the incidence of WRUED is generally high, for a majority of the working population upper limb symptoms are still no problem at all. This limits the possibilities of primary prevention efforts. It is highly inefficient to implement costly primary prevention strategies such as extensive ergonomic training and education while only a minority of the population is really at risk of developing WRUED. Therefore, prevention efforts should ideally be targeted at specific populations with a high risk, such as, for example, call centre workers, or at workers who present with initially mild upper limb symptoms in order to prevent these people from getting worse. TREATMENT Several treatment options have been proposed to decrease the burden of WRUED. We can also call this secondary prevention since the main objective of treatment is, besides the reductions in symptoms and disability, that people are prevented from developing chronic complaints and disability. Karjalainen et al (2000) performed a systematic literature review on the effects of biopsychosocial rehabilitation for upper limb repetitive strain injuries.49 Biopsychosocial rehabilitation was, in that review, defined as a programme of rehabilitation which included attention to medical, psychological and social issues.49 Only two RCTs studies met the inclusion criteria and the methodological quality of these studies was considered to be low. The review provided little scientific evidence for or against the effectiveness of a particular intervention.49 Verhagen et al (2004) also performed a systemic review in this domain and

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included ergonomic and physiotherapy interventions for the treatment of upper extremity work-related disorders. They found 13 RCTs and two controlled clinical trials. The content of the interventions, as reported in the studies, was variable and consisted of exercise, massage, manual therapy, ergonomic measures, multidisciplinary treatment and the use of an energised splint. According to a best-evidence synthesis the study authors concluded that there was limited evidence for the effectiveness of exercises and also for the use of keyboards with an alternative force-displacement of the keys or an alternative geometry. The methodological quality of the included studies was generally considered to be low.9 Since the publication of the review by Verhagen et al, two other randomised studies on the effects of exercise have been published. A Finnish study investigated the effects of a workplace physical exercise intervention on the intensity of headache and neck and shoulder symptoms in a population of office workers compared to no intervention. Headache and neck symptoms were significantly more reduced in the exercise group than in the control group.62 In another study, also from Finland, thoracic manipulations were compared with exercises in a population of employees from a broadcasting organisation with neck pain. Both groups improved in symptoms over a 12 month period, but the greatest improvements were reported for the manipulation group.63 In a recently published randomised study the effects of sham acupuncture were compared with placebo pills in patients with persistent arm pain due to repetitive use. Interestingly, the sham device appeared to have greater effects than the placebo pill on self-reported pain and severity of symptoms during the treatment period. The authors concluded that placebo effects seem to depend on the behaviours embedded in medical rituals.64 In general, we can conclude that among the many available treatment options both exercises and ergonomic measures may be considered as the most promising treatment alternatives for WRUED, despite the fact that the amount of evidence is still small. Since there are not many well-designed studies available, we should refrain from formulating strong statements. Methodologically sound studies are badly needed, but it can be considered as promising that during the last few years there has been a steady rise in the number of publications of epidemiological studies on the aetiology, prevention and treatment of WRUED. Practice points  Work-related upper extremity disorders can be described as a range of symptoms and disorders localised to the neck, shoulder, elbow, forearm, wrist and/ or hand  The incidence of these disorders has accumulated in Western countries over the years, possibly also due to an increased use of computers at work  The origin of work-related upper extremity disorders is multi-factorial. Physical and psychosocial characteristics of the individual worker and his/her work environment as well as personal factors contribute to the development of such complaints  Ergonomic measures, preferably following a participatory approach, are possibly effective in the prevention of these disorders although the optimum content of those interventions is still not clear  Both exercises and ergonomic measures may be considered as the most promising treatment strategies. The amount of evidence is, however, still small

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Research agenda  More well designed prospective cohort studies and randomised controlled trials are needed to extend the already existing knowledge with regard to the aetiology, prevention and treatment of work-related upper extremity disorders  When studying the effectiveness of prevention and treatment efforts, special emphasis should be given to a clear description of the characteristics of the disorder and study population and also to the content of the interventions

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