Do occupational factors cause hand pain?

Hand pain has been attributed to workplace exposure involving repetitive and forceful motion. There is a rich synonymy about the association of occupational factors with hand pain syndromes and it has been termed as repetitive strain injury (RSI), overuse syndrome and cumulative trauma disorder (CTD). However, the relationship between hand pain and work-related CTD has long been questioned . Workers performing similar jobs do not develop similar symptoms and, in fact, most of them do not develop any hand pain syndrome. Specific work conditions or individual differences could explain these discrepancies. Furthermore, psychological factors could play a relevant role in the development of occupational hand syndromes. In 1888, Gowers described writer’s cramp as a condition with a primarily and essentially nervous system origin and “the result of deranged action in the centres concerned in the act of writing” . Ireland described RSI not as a physical disorder but as a psychosomatic symptom complex that was a socio-political phenomenon rather than a medical condition . In fact, the Australian court system declared that RSI did not exist at all as a physical disorder. Other common features of CTD and RSI were the inclusion of umbrella diagnoses, the lack of successful therapy and, most interesting, the exclusion of self-employed in the outbreaks of RSI and CTD .

Although a clear causal relationship between work activities and pain has not been consistently demonstrated, several studies have suggested a true association. For example, repetitive work and repetitive forceful effort have been linked to higher rates of hand–wrist musculoskeletal disorders, especially CTS . The potential influence of psychological factors, including emotional response to stressful work conditions, has also been discussed .

Researchers from the Institute of Occupational Medicine in Edinburgh studied 580 cases of upper-limb soft-tissue disorders and compared them with 996 controls . The most common conditions were CTS and ganglions, both conditions being more common in females. The over represented jobs included cleaner, hairdresser, keyboard operator and music teacher. As a confounding factor, these are tasks commonly done by women. In fact, case and control groups were not well matched since 70% of the cases in the study were women, compared with 36% of controls. The report did not attempt to study the relations of particular conditions to occupations.

A study by researchers from the School of Manufacturing and Mechanical Engineering in Birmingham approached the question focussing on the workplace . Employees with self-reported upper-limb disorders from 14 industrial sites were matched with asymptomatic people doing the same task. The report described 100 matched pairs, who were examined by a research physiotherapist. The site and nature of RSI were reported as thoracic neck joint dysfunction in 48% of the cases, as wrist-joint dysfunction in 29%, wrist tendonitis or tenosynovitis in 21% and shoulder-joint dysfunction in 17%. The authors concluded that their survey could not provide reliable data on incidence or prevalence. A relevant limitation of the study was the lack of comparison between workers and general population. The authors made a questionable assumption: since a symptom was present, it was caused by the workplace. Most of the symptoms could have been secondary to established degenerative conditions of the neck and upper limbs such as osteoarthritis of the wrist and hand.

Using Bradford Hill’s nine criteria for assessing whether an association is likely to be causal (strength, consistency, specificity, time relationship, biological gradient, plausibility, coherence, experimental evidence and analogy), many of the best-designed studies could not provide conclusive evidence of a causal relationship between work practice and upper-limb disorders. Unfortunately, studies often suffer from relevant design pitfalls such as failure to account for confounding factors, the use of inadequate measures of exposure, such as job titles rather than measurements of job activity, and failure to allow for non-occupational activities, such as leisure or home activities.

Case definition: a critical issue in the study of hand pain syndromes

Hand disorders are a common cause of morbidity but their exact frequency and burden on health are difficult to determine because they comprise a heterogeneous group of disorders and non-specific regional pain syndromes. Disagreement exists about case definition and about the distinction, relation and overlap between conditions. This lack of consensus hampers comparison between studies . Thus, case definition is critical for obtaining accurate data on incidence, prevalence, outcome and response to treatment, both in general population and in individuals exposed to a putative risk factor at workplace. There is no agreement among scientific community about what constitutes a work-related musculoskeletal disease (MSD). Researchers used a variety of criteria to define MSDs and this largely limited the comparability across studies . Self-administered questionnaires and surveys have been extensively used in the identification of work-related MSDs. But it is not clear how self-reports of pain are related to physicians’ diagnoses and physical signs obtained during a structured examination, and how both of them could be best employed to define MSD cases in epidemiologic studies. Wang et al. found that self-reported pain poorly corresponded to diagnoses assigned by trained nurses for hand and wrist disorders. Substantially, more subjects reported having experienced pain than were assigned diagnoses by the nurses. The results suggest that using self-reported pain versus physical findings could result in different classifications of individuals as MSD cases. Researchers should be aware of potentially relevant discrepancies between self-reported measures and physical examination findings in the design of a study. As the correlations between these two measures were low, an intervention effective at improving one measure might be shown to be ineffective at improving the other. Thus, when evaluating the success of an intervention, screening or surveillance programme for work-related MSDs, it seems important to define clearly which measure might be most adequate and should be employed. Other potential source of discrepancy is the intermittent and episodic nature of MSD symptoms, especially in the early stages . These factors could condition that symptom reports might not correspond well to defined clinical syndromes.

According to Coggon , diagnostic criteria for occupational upper-limb disorders should be assessed depending on their practical utility in distinguishing categories of illness that differ in their risk factors or in their prognosis and response to treatment. The starting point for defining disorders could be the empirical demonstration that certain symptoms and physical signs tend to cluster abnormally within individuals exposed to an occupational factor. It is necessary to test the performance of proposed diagnostic criteria in discriminating illness with distinctive risk factors or clinical outcomes. It is also important that diagnoses be repeatable within and between observers. Ideally, methods for eliciting physical signs should be standardised. Currently, a wide range of upper-limb disorders are distinguished by clinicians; however, opinions differ both on the entities that should make-up diagnostic classifications and on the criteria by which each entity should be defined. Epidemiologists should define and evaluate possible diagnostic systems, focussing in particular on the contribution to case definition from physical examination.

After defining a diagnostic classification, to test its performance is very relevant. There are three main components to this assessment: repeatability intra- and inter-observers, associations with risk factors and association with clinical outcomes and response to therapy . A case definition may be useful in distinguishing a group of individuals with a disorder that has distinctive risk factors, offering opportunities for preventive measures. An adequate diagnostic system should distinguish groups of patients who clearly differ in their outcome or response to therapy.

To address the issue of case definition in upper-limb disorders, a workshop, convened by the United Kingdom Health and Safety Executive, developed consensus criteria for some of the most common upper-limb disorders using a Delphi technique ( Table 1 ) . These criteria provided a useful starting point for surveys of upper-limb complaints in the general population. Nevertheless, these criteria had some limitations since they did not include full details of the relevant procedures and definitions. For example, it was not clear whether two observers would agree where the boundaries of each anatomical region lie, what procedures should be adopted to elicit pain on resisted movement, where the pain should be felt and what degree of restricted movement was considered to be relevant. Regarding hand pain syndromes, criteria by Harrington et al. defined CTS, DQT and wrist tenosynovitis . Diagnostic criteria for De Quervain’s disease was defined as pain over the radial styloid and tender swelling of first extensor compartment and either pain reproduced by resisted thumb extension or positive Finkelstein’s test. Diagnostic criteria of wrist tenosynovitis were defined as pain on movement localised to the tendon sheaths in the wrist and reproduction of pain by resisted active movement. Confirming the usefulness of these criteria in epidemiological studies, Palmer et al. showed that the diagnostic criteria were reproducible and gave acceptable diagnostic accuracy in a hospital setting . Furthermore, examination could feasibly be delegated to a trained nurse and the protocol had the benefit of face and construct validity as well as consensus backing ( Fig. 1 ).

Sensitivity and specificity of the physical examination done by trained nurses vs. physicians, according to the scheme proposed by Palmer et al. (Ref. ). Abbreviations : CTS, carpal tunnel syndrome; DQT, De Quervain’s tenosynovitis; WT, wrist tenosynovitis.

Several researchers have also adopted a structured approach to the classification of soft-tissue disorders of the upper limb and neck. A systematic review by Buchbinder et al. identified four systems in which explicit criteria were proposed, intended to classify all, or a significant proportion, of soft-tissue disorders into distinct categories. Two studies were from Finland and two from North America . All four schemes were developed to investigate neck and upper-limb disorders in epidemiological surveys in the occupational health setting. However, all had limitations because of their failure to demonstrate intra- and inter-observer repeatability, or to show construct validity against alternative systems in the same domain of enquiry.

Case definition: a critical issue in the study of hand pain syndromes

Hand disorders are a common cause of morbidity but their exact frequency and burden on health are difficult to determine because they comprise a heterogeneous group of disorders and non-specific regional pain syndromes. Disagreement exists about case definition and about the distinction, relation and overlap between conditions. This lack of consensus hampers comparison between studies . Thus, case definition is critical for obtaining accurate data on incidence, prevalence, outcome and response to treatment, both in general population and in individuals exposed to a putative risk factor at workplace. There is no agreement among scientific community about what constitutes a work-related musculoskeletal disease (MSD). Researchers used a variety of criteria to define MSDs and this largely limited the comparability across studies . Self-administered questionnaires and surveys have been extensively used in the identification of work-related MSDs. But it is not clear how self-reports of pain are related to physicians’ diagnoses and physical signs obtained during a structured examination, and how both of them could be best employed to define MSD cases in epidemiologic studies. Wang et al. found that self-reported pain poorly corresponded to diagnoses assigned by trained nurses for hand and wrist disorders. Substantially, more subjects reported having experienced pain than were assigned diagnoses by the nurses. The results suggest that using self-reported pain versus physical findings could result in different classifications of individuals as MSD cases. Researchers should be aware of potentially relevant discrepancies between self-reported measures and physical examination findings in the design of a study. As the correlations between these two measures were low, an intervention effective at improving one measure might be shown to be ineffective at improving the other. Thus, when evaluating the success of an intervention, screening or surveillance programme for work-related MSDs, it seems important to define clearly which measure might be most adequate and should be employed. Other potential source of discrepancy is the intermittent and episodic nature of MSD symptoms, especially in the early stages . These factors could condition that symptom reports might not correspond well to defined clinical syndromes.

According to Coggon , diagnostic criteria for occupational upper-limb disorders should be assessed depending on their practical utility in distinguishing categories of illness that differ in their risk factors or in their prognosis and response to treatment. The starting point for defining disorders could be the empirical demonstration that certain symptoms and physical signs tend to cluster abnormally within individuals exposed to an occupational factor. It is necessary to test the performance of proposed diagnostic criteria in discriminating illness with distinctive risk factors or clinical outcomes. It is also important that diagnoses be repeatable within and between observers. Ideally, methods for eliciting physical signs should be standardised. Currently, a wide range of upper-limb disorders are distinguished by clinicians; however, opinions differ both on the entities that should make-up diagnostic classifications and on the criteria by which each entity should be defined. Epidemiologists should define and evaluate possible diagnostic systems, focussing in particular on the contribution to case definition from physical examination.

After defining a diagnostic classification, to test its performance is very relevant. There are three main components to this assessment: repeatability intra- and inter-observers, associations with risk factors and association with clinical outcomes and response to therapy . A case definition may be useful in distinguishing a group of individuals with a disorder that has distinctive risk factors, offering opportunities for preventive measures. An adequate diagnostic system should distinguish groups of patients who clearly differ in their outcome or response to therapy.

To address the issue of case definition in upper-limb disorders, a workshop, convened by the United Kingdom Health and Safety Executive, developed consensus criteria for some of the most common upper-limb disorders using a Delphi technique ( Table 1 ) . These criteria provided a useful starting point for surveys of upper-limb complaints in the general population. Nevertheless, these criteria had some limitations since they did not include full details of the relevant procedures and definitions. For example, it was not clear whether two observers would agree where the boundaries of each anatomical region lie, what procedures should be adopted to elicit pain on resisted movement, where the pain should be felt and what degree of restricted movement was considered to be relevant. Regarding hand pain syndromes, criteria by Harrington et al. defined CTS, DQT and wrist tenosynovitis . Diagnostic criteria for De Quervain’s disease was defined as pain over the radial styloid and tender swelling of first extensor compartment and either pain reproduced by resisted thumb extension or positive Finkelstein’s test. Diagnostic criteria of wrist tenosynovitis were defined as pain on movement localised to the tendon sheaths in the wrist and reproduction of pain by resisted active movement. Confirming the usefulness of these criteria in epidemiological studies, Palmer et al. showed that the diagnostic criteria were reproducible and gave acceptable diagnostic accuracy in a hospital setting . Furthermore, examination could feasibly be delegated to a trained nurse and the protocol had the benefit of face and construct validity as well as consensus backing ( Fig. 1 ).

Sensitivity and specificity of the physical examination done by trained nurses vs. physicians, according to the scheme proposed by Palmer et al. (Ref. ). Abbreviations : CTS, carpal tunnel syndrome; DQT, De Quervain’s tenosynovitis; WT, wrist tenosynovitis.

Several researchers have also adopted a structured approach to the classification of soft-tissue disorders of the upper limb and neck. A systematic review by Buchbinder et al. identified four systems in which explicit criteria were proposed, intended to classify all, or a significant proportion, of soft-tissue disorders into distinct categories. Two studies were from Finland and two from North America . All four schemes were developed to investigate neck and upper-limb disorders in epidemiological surveys in the occupational health setting. However, all had limitations because of their failure to demonstrate intra- and inter-observer repeatability, or to show construct validity against alternative systems in the same domain of enquiry.

Writer’s cramp

Writer’s cramp is a focal dystonia characterised by involuntary overactivation of muscles during handwriting. The individual pattern of writing disorder and its severity widely varies among individuals with writer’s cramp. Typical symptoms are the exertion of inadequately high pressure on pen and desk and an abnormal writing posture. Handwriting is exhausting, often even painful. The writing process is frequently slower and less fluent than in normal writers. The disease can either be restricted to handwriting (simple writer’s cramp) or involve one or more other fine motor activities such as typing, using a computer mouse, using cutlery or tools, sewing, shaving or putting on make-up. Writer’s cramp can severely handicap people in their professional performance.

The pathophysiology of writer’s cramp is not completely elucidated. Standard clinical neurologic assessment typically reveals no additional neurologic symptoms. However, a number of imaging studies point to abnormalities in the brain activity of patients with writer’s cramp. Reduced activity in the primary motor cortex parallelled by increased activity of the frontal association cortex in a Positron Emission Tomography (PET) study has been found in patients with writer’s cramp . A study showed reduced activity of the pre-motor cortex and reduced activity of the primary sensory and primary motor areas during handwriting in patients with writer’s cramp . By contrast, a newer PET approach revealed overactivity of primary motor and primary sensory areas and suggested that writer’s cramp might be caused by a major sensory problem . However, the interpretation of abnormalities in brain activity is difficult due to the discrepancy in the imaging findings. Further, abnormal brain activity in writer’s cramp can be considered as either a primary phenomenon, which is the cause for the writing disorder, or a consequence. Some authors who found an abnormal responsiveness of the motor cortex hand area to transcranial magnetic stimulation in patients with writer’s cramp , emphasise the role of impaired inhibitory mechanisms and maladaptive neuroplasticity. Electroencephalography aberrations in patients with focal dystonia suggest problems in movement preparation . Behavioural abnormalities that exceed the writing disorder were also found and some patients with writer’s cramp showed sensory dysfunctions , and a selective impairment of mental hand rotation was recently detected in patients with focal hand dystonia .

The treatment of writer’s cramp has been based on the use of botulinum toxin injections. The effects are always transient and satisfactory in only a subgroup of patients . In past years, several behavioural treatment approaches based on the pathophysiological assumption of sensory dysfunction, overuse and cortical dedifferentiation caused by maladaptive neuroplasticity have been developed and evaluated. Zeuner et al. studied sensory training by Braille reading in 10 patients with writer’s cramp. They found a clear improvement in tactile spatial acuity after 8 weeks of training, and a significant amelioration of the Fahn dystonia score, but no significant changes in objective measures of handwriting performance. Since overuse and enlargement of cortical representations could be the underlying mechanisms of writer’s cramp, Priori et al. studied the effect of limb immobilisation in seven patients with musician’s cramp and in a patient with writer’s cramp. Quality and speed of handwriting were ameliorated. Based on the aetiological hypothesis of cortical dedifferentiation, Zeuner et al. conducted a 4-week motor training programme for individualised fingers by splinting. Half of their patients showed an improvement in the Fahn dystonia score. Kinematic handwriting analyses revealed improvement of the stroke frequency in basic finger movements and in producing superimposed squiggles, whereas writing velocity and pressure while writing a test sentence were not influenced by the treatment. The direct effect of a modified pen grip between the proximal phalanges of index and middle finger was studied in 23 patients with writer’s cramp by Baur et al. They reported that the change of pen grip did not influence kinematic writing aspects but caused an immediate reduction of writing pressure in the writer’s cramp sample without the application of any other treatment. The same group showed that the combination of modified pen grip and handwriting training caused a clear reduction of writing pressure and grip force in patients with writer’s cramp, leading to a significant decrease of pain and functional impairment.