Fortnightly review: work factors and upper limb disordersBMJ 1997; 315 doi: https://doi.org/10.1136/bmj.315.7119.1360 (Published 22 November 1997) Cite this as: BMJ 1997;315:1360
- Peter W Buckle, reader in ergonomics ()a
- Accepted 24 July 1997
In 1713, Ramazzini wrote of upper limb problems in professional writers (box).1 His observations of causative factors (prolonged static postures, highly repetitive work, psychological attributes of the work) and difficulties in treatment and management are still debated today.
The diseases of persons incident to this craft arise from three causes: first constant sitting, second the perpetual motion of the hand in the same manner, and thirdly the attention and application of the mind …. Constant writing also considerably fatigues the hand and whole arm on account of the continual and almost tense tension of the muscles and tendons. I knew a man who, by perpetual writing, began first to complain of an excessive weariness of his whole right arm, which could be removed by no medicines, and which was at last succeeded by a perfect palsy of the whole arm.
Classification and diagnosis
Precise identification of the tissue(s) responsible may be difficult in symptom based conditions. The non-specific soft tissue disorders may involve loss of grip and pinch strength, and nerve dysfunction, and are the source of concern, debate, and, often, litigation. Other disorders of the upper limb may allow a definite diagnosis. The diagnostic criteria used may depend on the setting—for example, sensitive criteria (low false negative rate) may be needed in an occupational setting and more highly specific criteria used in secondary or tertiary care to avoid overdiagnosis. Prospective studies support the relation between physical exposures in the work system and upper limb disorders.2 Some studies show a relation between increased exposure and increased response.3 4 There is some conflict between the epidemiological findings and current theory relating to underlying disease and possible mechanisms for the disorders under investigation.5
Current epidemiological evidence is often based on studies with weak designs.6 7 The consistency in the results, however, strongly supports a relation with factors arising from work. Here, I review evidence on selected disorders that provide insights into the associations and aetiology of this group of disorders.3
Occupational and work associations with pain in the shoulder, arm, and hand have been recognised for almost 300 years
The most important work system factors are prolonged static muscle load; highly repetitive and monotonous work; high force exertions or mechanical compression of tissues, especially at the hands; use of vibrating equipment and tools; and work with many deadlines and little control
Surprisingly few objective data or epidemiological studies exist on the importance of individual factors (such as age), systemic conditions, and activities outside work
Management of the conditions is enhanced through early reporting or presentation and liaison in the workplace
The importance of active surveillance to identify people with symptoms and those at risk should be emphasised to employers
All studies are hampered by the difficulty in defining diagnostic criteria and the problems of obtaining valid measurements of exposure to risk
Articles were selected for this review from an extensive search of the current literature and computerised searches of Medline and Ergonomic Abstracts (keywords: upper limb, neck, shoulder disorders, work related) along with key review papers published in high quality peer reviewed journals over the past five years.
Carpal tunnel syndrome
Carpal tunnel syndrome has been studied widely. Workers in the garment industry had a threefold increase in risk compared with hospital workers,8 and oyster and crab packers had a relative risk of 14.8 and meat and poultry industries 13.8 compared with industry wide levels.9 More specific studies have found odds ratios of 15.5 for workers in jobs requiring high force and high repetition compared with those in low exposure groups; high repetition on its own had an odds ratio of 5.5.10 People working with flexed wrists and those working with extended wrists had odds ratios of 8.7 and 5.4 respectively,11 whereas industrial workers exposed to jobs requiring high force and high repetition had an odds ratio of 4.0 compared with those doing light work.12 Others have also reported significant findings.13 Using hand held vibrating tools also increases the risk (different studies have found odds ratios of 4.8 and 7.0), as does repetition of wrist movements (odds ratios 4.6 and 2.0).14 15 Most of these studies have controlled for age and sex, where feasible.
Although some studies have considered the potential protective effect of work,16 there is considerable evidence that carpal tunnel syndrome is strongly associated with several factors in the work system. This is consistent with the probable mechanisms leading to the syndrome—namely, the stretching or compression of the median nerve at the wrist, and ischaemia.3 This, coupled with the increase in pressure in the carpal tunnel when the wrist is in extreme postures, helps clarify the process leading to the syndrome. Individual factors associated with this condition, such as obesity,17 are considered further below.
In two studies of lateral epicondylitis, risk was sixfold greater in exposed groups than controls.2 18 Exposure in the groups was defined as strenuous work requiring use of the muscle tendon structures of the upper limb. In another study, more strenuous work led to the reporting of more symptoms, but clinical examination showed a similar prevalence in groups doing strenuous and non-strenuous work.19 Other research, however, did not support a work related aetiology.20 Unfortunately, none of these studies considered exposure with regard to the extensor muscles of the forearm or cumulative exposure. Though this condition is often known as tennis elbow, there are few studies of the role of tennis in such disorders.3
High risks for hand-wrist tendinitis have been found in groups such as meat processing workers and workers in other manufacturing industries. Large increases in risk (odd ratios 36,2 29,21 7,22 and 820) strongly support the association between work exposure and hand-wrist tendinitis. A meta-analysis found the adjusted odds ratio for hand-wrist tendinitis to be 9.1 (95% confidence interval 4.9 to 16.2).23
Neck and shoulder disorders
Though lacking specificity in outcome measures, many studies have found associations between factors within the work system and disorders of the neck and shoulder.3 5 Both physical and psychosocial work system factors show significant associations,24 25 but the strongest associations have been found with physical factors at work.26 Cumulative exposure also seems to have an effect.4
Hand-arm vibration syndrome
Vibration applied to the hand is associated with serious disturbance of the vascular system (Raynaud's disease or vibration white finger). It seems probable that vibration impairs muscle strength, and it may lead to osteoarthritis of the wrist and elbow.3 Vibration is thought to alter the feedback from the mechanoreceptors in the hand, which may lead to overlarge forces being exerted to operate the tool, and the tonic vibration reflex leads to further muscle load.3 The use of vibrating tools often requires high forces at the hand because of the intrinsic design of the tools (their weight and size) and the tasks being performed.
Studies of non-specific conditions tend not to have specific outcome measures. Many have used symptom questionnaires, and then used symptoms of pain and discomfort at specific body sites to assess the strength of association to work related factors.3 Some studies have reflected on the lack of an identifiable pathological basis for these disorders coupled with the uncharacteristic pain patterns.6 The reported pain may arise from muscle or tendons, and psychological events may be contributing to patterns of pain reporting and subsequent chronic pain.3
High relative risks for butchers (11.5), food industry workers (8.8), and packers (7.9) have been recorded.27 Risk factors reported for these disorders show consistency for highly repetitive work, static or constrained neck and shoulder postures, and high physical loads or forces at the hand as well as for the duration and intensity of exposure. A study of sewing machine operators found that those working only a few hours a day had fewer problems, but this shorter exposure postponed the onset of symptoms only by about six months.28 Mechanisms for muscle disorders are consistent with this reporting pattern. However, in the absence of detailed clinical histories of these disorders it may be some time before the true underlying pathology is understood. That said, those who currently suggest a predominantly psychological or psychosomatic origin do so with little, if any, supporting evidence. Although personal characteristics and other environmental and psychosocial factors may contribute, most evidence shows that there are several important work related risk factors.3
Most epidemiological studies consider age and sex, but it is less clear which additional factors should, or could, be considered. For example, significant increases in risk for carpal tunnel syndrome associated with obesity (body mass index) have been reported,17 but few studies have paid equal attention to details of work systems and individual factors. Age has been recognised as having an effect, but findings are not consistent. Other factors such as time in the job and reproductive status (in women) require control before conclusions can be reached.
The 1 provides an overview of studies that have shown an association between individual factors and various conditions. Though consistent or strong associations have been found,12 the 1 is dominated by conflicting results and lack of information. Thus, sex differences may be due to genetic differences or to gender differences in exposures at and away from work. For example, although the incidence of carpal tunnel syndrome seems to be more common in women (male:female ratio of 1:3),29 studies that have controlled for exposure show no evidence of greater susceptibility to work related carpal tunnel syndrome in women.9 Differences may be due to differences in anthropometric variables, physical strength, or the tasks performed rather than to sex differences. Studies of physical dimensions (of the carpal canal, for example) have produced conflicting results,3 and there is little to support the belief that previous trauma increases susceptibility. Although the importance of individual factors must be recognised, and should be studied further, current evidence indicates that exposure to hazards in the work system is important.
Behaviour of the worker is an additional factor in determining the modification of exposure. For example, some workers may feel more able to take short rest pauses and thus alleviate potential fatigue than do others. Similarly, highly motivated workers may exceed normal thresholds and cause “damage” in much the same way that people participating in active sports may injure themselves through overexertion.
Factors outside work
Little is known of the contribution of factors outside of work to the development of disorders of the upper limbs. Some sporting activities are commonly thought to have an association, but there is little epidemiological evidence to support these beliefs. The same is true of hobbies such as knitting. The role of soft tissue mechanisms of trauma and injury to the soft tissues of the upper limbs has been reviewed extensively elsewhere.3
Developments in the understanding of muscle pain and injury would seem to be particularly relevant to the non-specific disorders.30 If the pattern of pain and resultant behaviour is to be fully understood the mechanisms by which skeletal muscle can become damaged (physical trauma, eccentric exercise, metabolic depletion, etc) must be seen in the context of the system as a whole (pressure on nerve tracts, stresses on articulating surfaces, etc) rather than as discrete entities. Low level continuous contractions and static load on the musculoskeletal system may produce changes in the muscle that lead to chronic muscle pain.3 The role of intramuscular pressure is important but has yet to be fully explained.31 Small amounts of shoulder abduction or flexion can cause large increases in intramuscular pressure. The occluded and impaired blood flow may lead to chronic muscle damage.32
Although most reports of muscle disorders seem to be of those in the shoulder and neck, other examination procedures enable reporting of muscle disorders of the wrist, and in particular the extensors.33 Static load on nerve tissue (for example, constant hydrostatic pressure) may be critical at relatively low pressure, for example 4000–8000 Pa34; pressure in the carpal tunnel with the wrist flexed and extended may approach these values.35 The recruitment patterns of motor units in specific muscles suggest that units may become overloaded even at very low levels of static loading during contractions of long duration.36 Changes in slow motor units in patients with chronic muscle pain have been shown.32 37 Pain may increase muscle activation, which in turn contributes to the chronicity of muscle pain in the neck and shoulder muscles. The relation between acute and chronic pain is important in understanding the course of these disorders and the relation between specific activities and the reoccurrence of pain.38 The relation between fatigue, pain, and disorder requires further research.
Cold may affect the development of upper limb disorders directly and also indirectly from the use of protective equipment (gloves). The muscles must exert greater force to overcome the restrictions of the protective clothing and as a result of difficulties in coordinating and applying the appropriate strength at the hand.
Preventing and managing disorders
The need for early intervention in the workplace is well recognised.3 Prevention of upper limb disorders may be facilitated by surveillance of hazardous exposures, people at risk, and early symptoms (box). Experience from other musculoskeletal disorders (back pain, for example) suggests that the mislabelling of patients and mismanagement at the early stage of presentation may well have an effect on the subsequent course of the disorder. On the basis of the current evidence, treatment and management must consider whether the condition might be related to work. General treatment regimens have been reviewed and summarised elsewhere.26 39
Checklist for surveillance of risk factors
Awkward postures (eg deviated wrist)
High static muscle load (eg neck, shoulder girdle)
High force exertion at hands
Sudden applications of force
Work with short cycle times
Little task variety
Frequent tight deadlines
Inadequate rest or recovery periods
High cognitive demands
Little scope for control over work
Cold work environment
Exposed to vibrating equipment
Localised mechanical stresses on tissues
Poor social support
Conflict of interest: None.
I thank Drs B Silverstein, E Viikari-Juntura, and J Devereux for their helpful comments in the preparation of this review.