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| Journal of the New Zealand Medical Association,
20-June-2003, Vol 116 No 1176
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OOS or MUD? Time for a cleanup
Peter Dodwell
Use of the term ‘occupational overuse syndrome’
(OOS) in New Zealand confuses the diagnosis of disorders of the upper limbs,
since it has come to encompass both a classification and a specific disorder and
also both an effect and its supposed cause. We need to adopt a more logical
approach and use more precise
terminology.1
Although New Zealand’s ACC law was intended to
eliminate the concept of fault, this persists in the area of work-related,
gradual-process injuries. As a major grey area, OOS is the focus of fierce
debate over whether or not a person’s work has caused a gradual-process
injury. It is not the proper role of doctors to take sides and prejudge such
matters but to determine the effect of work in causing injury and illness so
that problems can be prevented.
Historical review of gradual-process terminologyA succession of misleading terms has
arisen, describing symptoms of workers in occupations with intensive hand use.
‘Telegrapher’s cramp’ was described in 1875, and an editorial
in the Lancet that year indicated its
most frequent occurrence in writers, telegraph operators and
musicians.2,3 Descriptions then emphasized the
‘spasm (cramp) and pain in groups of muscles in consequence of overuse or
frequently repeated muscular acts’.4 In
musicians, the dominant symptoms were summarised in a review by Fry as pain,
weakness and loss of response and control, and he noted that the terms of spasm,
cramp, paresis and palsy were an overstatement and it was more a question of
‘loss of accuracy and agility’.5
Vague initial symptoms were often noted by musicians or writers, such as a
feeling of weight, tightness, numbness or coldness. Swelling was noted in some
severe cases and more than half the major authors documenting these conditions
noted areas of tenderness in the affected limbs. Most authors emphasized that
these conditions were quite separate from tenosynovitis. Poore observed that
‘Fatigue of a muscle is much more easily brought about by prolonged
contraction than by a succession of intermitting contractions, no matter how
forcible these may be,’ and that in violinists it was therefore generally
a problem of ‘the left hand which grasps the instrument and fingers the
strings’.6,7 Others noted the process
spreading from one muscle group to another and to the non-involved side quite
frequently (arguing for a more central element to the nervous system aspect of
the lesion). Although there were a number of less popular terms, the two main
ones used during the late 19th century were ‘occupational cramp’ and
‘occupational neurosis’ (meaning a neurological disorder of
occupational origin, without the modern implication of a psychiatric
condition).5
After 1910, terminology became divided in three directions:
the use of ‘occupational cramp’ continued in parts of Europe; Brain
described ‘occupational neurosis’ (but, ignoring previous
literature, he compared it with hysterical paralysis); and the third and most
substantial line of literature introduced an emphasis on the term
‘tenosynovitis’.5,8
The last term has persisted in many countries as a
favourite. And yet Howard, studying peritendonitis crepitans, demonstrated that
‘the site and distribution of swelling, of tenderness, and of crepitation
never coincided with the extent and boundaries of normal tendon sheaths’
and showed histologically that tendon sheaths were not
involved.9 He asserted that
‘tenosynovitis’ was a misnomer and that ‘The primary change is
without doubt in the muscle, the other factors developing secondary to muscle
exhaustion...’ Yet this particular confusion was to linger for decades to
come, so that Semple described ‘tenosynovitis’ as ‘the second
commonest industrial disease in the United
Kingdom’.10 That same year tenosynovitis
was called ‘the terminological hoax’ by Fry, and this diagnosis
continues to cause concern.11,12
1986 marked the ascendancy of ‘repetition strain
injury’ (RSI) as well as OOS, and a paper by Fry demonstrated the
proliferation of confusing terminology.13 In
this he used the terms ‘overuse injury (RSI) of the upper limb,’
‘overuse injury,’ and ‘overuse injury syndrome,’ and
went on to state categorically that ‘overuse injury is incorrectly termed
tenosynovitis and inappropriately called Repetition Strain Injury,’
despite using the term RSI as synonymous with ‘overuse injury’ in
his own abstract. Yet Fry described all these variously-named conditions as
being ‘a common and distinct clinical entity’. His view was that
‘Tenderness of intrinsic muscles of the hand and ligaments of the wrist
joints and carpometacarpal joint of the thumb are virtually diagnostic of
overuse injury.’
In contrast, Semple in 1991 noted that few compensation
claims during the Australian ‘RSI epidemic’ came from heavy industry
(implying a dubious dose-response relationship for biomechanical
factors).14 He concluded that ‘a careful
study of the available literature strongly suggests that this particular Emperor
has few, if any, clothes.’
Quintner summarized the RSI epidemic in Australia in
similarly ambiguous terms: ‘There was general agreement that RSI included
conditions with a known pathological basis, such as tenosynovitis, elbow
epicondylitis, shoulder rotator cuff degeneration, and carpal tunnel syndrome.
More difficult to understand [were] those syndromes characterised by poorly
localised pain where the underlying pathology was difficult to define –
for example, tension neck, cervical syndrome, and thoracic outlet syndrome. The
most commonly encountered RSI condition was a diffuse pain syndrome, termed
repetitive (or repetition) strain injury
(RSI).’15
Here, within a single sentence, was the
‘doublethink’ that allowed professionals to use the same term (in
this case RSI) to describe both a particular condition and also the group of
conditions of which it was a part. Others to this day have been indulging the
same doublethink with the terms ‘the overuse syndrome’ and
‘occupational overuse syndrome’.
In New Zealand, ACC and OSH published a guideline book on
OOS.16 The three-page-long section entitled
‘Definition’ fails to provide a succinct and unambiguous definition
of OOS and it concedes ‘not all practitoners agree with this
definition’. A ‘classification’ is offered that is more in the
nature of a differential diagnosis, listing conditions that might or might not
involve occupational overuse in a particular case. There are a number of
explanatory notes (including the statement that this ‘syndrome’ is
not a clinical entity or a diagnosis on its own but is a general or
‘umbrella’ term – thus refuting the earlier belief of
Fry.
There followed two major efforts at clarification of causes
and terminology: Hagberg et al and the NIOSH
review.17,18 Both saw the importance of not
prejudging causes and both used the generic term ‘musculoskeletal
disorder’ (MSD) in a classification of conditions that are potentially
work related. The major difference between the classifications in the two books
was that the former included a section on more non-specific disorders whereas
NIOSH deliberately excluded these (emphasizing clarity of biomechanics). Both
publications stressed first reaching a non-judgmental diagnosis, thus permitting
a separate logical analysis of evidence of a causal relationship with work.
Hagberg summarised this well in a flow diagram, in which the list of potential
conditions caused by work, which are termed in this document ‘work-related
musculoskeletal disorders’ (WMSDs), was similar to the ACC-OSH
classification, but was more comprehensive, and focused on a functional
organ/tissue classification ie, the site of presumed pathology.
Credibility of diagnosis: separating cause from effectThe problems with the term OOS are
twofold. First is uncertainty about causes; ‘tennis elbow’ (lateral
epicondylitis, but with the added implication of a known cause) may be a
tempting diagnosis, but often has nothing to do with tennis. Other causes of
epicondylitis than the merely mechanical are possible. Of all the specific
musculoskeletal disorders none is exclusively caused by employment. The
individual circumstances must be weighed very carefully.
Often, a person with a particular syndrome (eg, carpal
tunnel syndrome, CTS) may prove to have multiple factors involved, or the cause
may remain unknown.19
Uncertainty should be even greater where the apparent site
of injury is widespread and objective findings scant, yet some echo Fry by
claiming that such patients with no objective signs have symptoms and history
‘typical of the overuse syndrome’. Uncertainty generates a
paradoxical certainty.13
The credibility of experts who claim to diagnose
fibromyalgia reliably (another disorder based entirely on subjective evidence)
came into question in 2000 when the Journal of
Rheumatology featured two case histories (one involving a family of six)
where experts swore fibromyalgia was the problem until this was clearly refuted
by videotape evidence confirming fraud.20,21 A
finding of the US Supreme Court was that it is not good law for courts to accept
the firm belief of an expert without adequate
explanation.21 In August 2000, the District
Court, in its role as an appeal forum for ACC decisions in New Zealand, rejected
the sole diagnosis of OOS (without objective evidence) as insufficient
foundation for conclusions about work as the cause of
pain.22 In 2002 it was similarly ruled that a
diagnosis of fibromyalgia is not evidence in itself of physical
injury.23
The second problem is unnecessary obscurity; there is a
conflict in using OOS as both a ‘single’ diagnosis and as a
classification. In the Oxford English Dictionary the term ‘syndrome’
is defined as ‘A group of symptoms or pathological signs which
consistently occur together, esp. with an (originally) unknown cause; a
condition characterized by such a set of associated symptoms.’
It makes sense to have a general descriptive term for a
group of conditions caused by work. But the OSH/ACC handbook on OOS is
self-contradictory in calling this group ‘occupational overuse
syndrome’. An umbrella term for a group of conditions cannot at the same
time be used to describe a syndrome.
Those who use the term OOS as though describing a specific
entity tend to speak of ‘it’ or ‘the overuse syndrome’
rather than using the plural (as though disorders of occupational overuse might
be a single disease process).
Some doctors will claim that a single patient has a
combination of, for example, epicondylitis, writer’s cramp and rotator
cuff disorder. It stretches credibility to claim that this protean mixture is a
single ‘entity’ of
‘the overuse syndrome’ with
a single mechanism of injury. In these circumstances, if pain alone (in multiple
sites) has been identified, the diagnosis of OOS is no clearer than MUD: a
Musculoskeletal Undiagnosed Disorder or a Muddled Unscientific
Diagnosis.
Determining causesThe multifactorial nature of many
MSDs was emphasised by Hagberg.17 Macfarlane,
reporting on both physical and non-physical predictors of the development of
forearm pain, found evidence that the non-physical stressor of
‘dissatisfaction with support from
supervisors and colleagues’ is a stronger predictor than the physical
stressor of repetitive movement of forearm or
wrist.24
In the NIOSH review, evidence for physical work as the
substantial cause was found for a number of the more clear-cut clinical
syndromes – but only for specific work tasks. For example, these might be
neck/shoulder conditions such as rotator cuff disorder in tasks involving
extreme use of the shoulder (forceful or repetitive flexion beyond 60 degrees),
or carpal tunnel syndrome in those involving forceful or repetitive
gripping/twisting actions with hand/wrist movement.
A review of biomechanical research by Keyserling considered
the plausibility of CTS arising from keyboard
work.25 It emphasized that the muscle activity
during keying and mouse work was ‘relatively low (less than 10% of Maximum
Voluntary Contraction)’. This undermines arguments that depend for their
logic on anaerobic changes that occur only during maximal contraction. A more
persuasive finding was that ‘Peak wrist acceleration was found to be the
best discriminator between high- and low-risk jobs.’ A Mayo Clinic study
also found no evidence of increased incidence of CTS in those making heavy use
of keyboards.26
It has been ruled in court that ACC legislation requires
reasonable proof (on the balance of probabilities) regarding the cause of a
supposed injury.27 This requires a plausible
biomechanical mechanism of injury from a specific work task, and evidence of
effects of exposure to that task consistent with a dose-response curve. It is
more convincing to see not only onset but offset of symptoms in a time sequence
plausibly matching the period of exposure and of its cessation. Terms such as
‘occupational overuse’ have a legitimate place as a cause (a
stressor) rather than as a diagnosis. Non-physical stressors as causes are
specifically excluded by ACC law (but not by OSH law).
Terminology to separate cause from effect
Author
information: Peter Dodwell, Occupational Physician, Wellington
Correspondence: Dr
Peter Dodwell, P O Box 14666, Wellington. Fax: (04) 386 3878; email: dodwellassoc@paradise.net.nz
References:
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