8.5 Work-related upper limb disorders
8.5.1 On the varieties of RSI/WRULD
The chief difficulty with generic terms like ‘RSI’ and ‘WRULD’ is the diversity of clinical conditions to which they are applied. Two main subdivisions are generally recognized, which are sometimes referred to as ‘Type I’ and ‘Type II’ RSI respectively.
The former (Type I) are relatively discrete and localized over-use injuries to specific anatomical structures. This subdivision includes conditions resulting from traumatic inflammation of soft-tissue structures, such as the various forms of peritendinitis and tenosynovitis which affect the tendons of the muscles of the forearm and their soft-tissue coverings (and also muscles at other sites in the upper limb and shoulder region), as well as lateral epicondylitis and medial epicondylitis (otherwise known as ‘tennis elbow’ and ‘golfer’s elbow’) which affect the points of origin of the extensor and flexor muscles respectively.
The Type I subdivision also includes the so-called entrapment neuropathies, although the term is not a particularly good one as the probability is that the symptoms of the condition may arise from irritation of the nerve as well as entrapment as such. The best known of these is carpal tunnel syndrome (which affects the median nerve as it passes through the confined space of the carpal tunnel at the front of the wrist). The median nerve may also be affected at other sites, as may the other nerves of the limb.
The underlying pathologies of the Type I conditions are relatively well understood (although some grey areas remain) and they are thus relatively uncontentious, except that in the medico-legal context there may be an entirely legitimate dispute as to whether the condition is caused by work in any individual case, as against being the consequence of ‘normal wear and tear’, ‘degenerative changes’, or a ‘constitutional predisposition’, etc. At law, the decision must be made in each individual case ‘on the balance of probabilities’, although for some conditions (e.g. peritendinitis and tenosynovitis) there is a stronger a priori assumption of work relatedness than for others (e.g. carpal tunnel syndrome), in that the available scientific evidence points to occupational or constitutional risk factors as being of greater or lesser relative importance in the (multifactorial) aetiology of the conditions in question.
It stands to reason that for almost any occupational or work-related condition one could name, some people will be more at risk than others—otherwise all the members of a particular work force would be affected rather than only some of them. This being so, it would seem to be fallacious to draw a distinction between a condition that is ‘caused’ by constitutional factors and merely ‘aggravated’ by work; as against being caused by work in a person who is at risk for constitutional reasons.
Over the last decade or so it has become increasingly clear, however, that very many people with RSI/WRULD cannot easily be allocated to any of the traditionally recognized clinical categories. These people—who are described as suffering from ‘Type II’ RSI—typically report symptoms of pain and dysfunction at multiple sites in the upper limb (or limbs), shoulder region and neck. These symptoms are often described as ‘diffuse’. This is an unfortunate choice of word, in that it tends to imply that the symptoms are vague and insubstantial. They are not—
at least, not always. In some cases they are crippling. A better description is
‘disseminated’. It is likewise often said that these people have no objective clinical signs. (In medical parlance, a ‘symptom’ is something reported by the patient; a
‘sign’ is something that the physician observes for herself.) This is only partly true at best—in that the principal signs that may be observed are ones in which the patient reports pain—either on the palpation of tender structures (mainly muscles) or on the performance of certain diagnostic manoeuvres (the details of which need not concern us here).
The experienced examiner will also be able to detect palpable changes in the physical quality of the muscles, which may feel ‘hard’ or ‘compacted’, etc. In some cases there will be a change in the temperature of the affected limb, indicative of a disturbance of bloodflow.
The term ‘RSI’ (or alternatively ‘repetitive strain syndrome’ [RSS]) is sometimes applied to these disseminated conditions by default, and for want of a better alternative, as if it were a diagnosis. This use of the same term in both the generic and quasi-diagnostic senses has been a source of much avoidable confusion. The practice is to be deprecated. This leaves us, however, with the problem of what else to call these conditions. My own preference is for the term disseminated over-use syndrome (DOS).
Although, in this author’s experience, the disseminated forms of RSI/WRULD are by no means unknown in manual workers on industrial assembly lines, they occur most prominently and characteristically in keyboard users. They are in fact the classic keyboard injury (see below). In contrast, assembly workers are most commonly affected by the localized varieties of RSI/WRULD. This suggests that different causative mechanisms are involved.
The disseminated over-use syndrome of the keyboard user has a characteristic natural history. The first symptoms are typically minor ones: most often a tingling in the hands or aching at the wrist; less often a dull ache in the neck or shoulder area. At first this comes on towards the end of the working day and subsides in the evenings and at weekends. The symptoms gradually become more severe, more unremitting and come to affect the person’s activities away from the workplace, interfere with her sleep, and so on. And as they do so the symptoms ‘spread’: either proximally (up the limb) or distally (down the limb), as the case may be. In due course they may ‘cross over’ to the opposite limb; or they may come to affect the upper back, the breast, or the side of the face and even occasionally the low back and lower limbs.
The underlying pathology of the syndrome remains both obscure and contentious.
There are those who take the view (often in the medico-legal context) that what is unknown is unreal. ‘If I wasn’t taught about this disease at medical school, and I don’t know how to treat it, then how can it possibly exist?’ They therefore say that people who claim to suffer from this syndrome are deluded; or they argue that the symptoms these people report are the product of ‘conversion hysteria’ or
‘somatization’ or other kinds of psychobabble. They are wrong. The syndrome
undoubtedly has a basis in organic pathology—and, complex as they are, the underlying mechanisms are slowly being unravelled.
In essence, the condition progresses from one of ordinary muscle fatigue which, when opportunities for recovery are inadequate, becomes chronic. At some point (and the mechanism is not well understood), a self-sustaining cycle of inflammation, pain and muscle spasm supervenes, involving the activation in the muscle of what are sometimes called ‘trigger points’ (see Wigley 1990, Pheasant 1991a,b etc.). At the same time (in parallel as it were) a cascade of changes is initiated in the central nervous system (CNS) mechanisms which mediate the experience of pain. This is sometimes called pain amplification or neurological sensitization (Pheasant 1991a,b,
Table 8.5 A provisional clinical classification of work-related upper limb disorders.
1992, 1994, Cohen et al. 1992, Gibson et al. 1991, Helme et al. 1992). Via various feedback loops in the CNS, disturbances of motor control and bloodflow may also ensue. The entrapment or irritation of peripheral nerves (which physiotherapists call
‘adverse neural tension’) may also be part of the picture, although how this relates to the other mechanisms is again not clear.
Psychological factors may well play a role in this process, but they are certainly not the sole causative factors involved—and there is good evidence that in many cases psychological symptoms that RSI victims report (anxiety, depression) are secondary or tertiary developments from the initial physical disorder (see below). In other words they are consequences, not causes. Sleep disturbance may be an intervening causative link.
The classification of the conditions falling into the overall RSI/WRULD category into Types I and II is a useful one—but it is something of an oversimplification. Some of the possibilities are summarized in Table 8.5 and Figure 8.15 (see also Pheasant 1994).