Nervous reactions

Work-Related Upper Limb Disorders have been recorded ever since the early
18th Century. So what is the modern approach to solving problems with soft
tissues relating to repetitive work-based use? 
By Steve Milanese

Work-Related Upper Limb Disorders (WRULD) is a term used to describe
disorders of the body’s soft tissue generated by activities related to
occupational tasks. Most commonly, the soft tissues involved are found in the
upper limbs, reflecting the increased exposure to repetitive stress of this
part of the body during modern industrial activities. However, no area of the
body is safe from these disorders.

The term WRULD describes a clinical condition that has resulted from
occupational overload, but not the specific structures at fault. The site of
application, direction and magnitude of the forces encountered in the workplace
will have a significant effect on the soft tissue involved. Occupations or
pastimes involving particular types of stress often trigger a unique form,
affecting specific areas of the body.

All soft tissues of the body are at risk during the development of a WRULD,
including tendons, muscles, ligaments, cartilage, nerves, and even blood
vessels. Unlike sporting injuries which are often traumatic and result from a
single overload situation, WRULD are often the result of weeks, months or even
years of cumulative stresses, which affect more than one area.

The body will attempt to adapt to this cumulative stress and it is only when
the body’s adaptive capacity is exceeded that the symptoms develop. The injured
structures will display the main signs of injury, such as pain, swelling etc.
while the ‘secondary affected’ structures may often appear to be normal under
casual observation. But we often treat the main symptomatic soft tissue without
dealing with the ‘secondary affected’ structures that may be at fault.

The worker with shoulder tendonitis, for example, may also exhibit weak
muscles around the shoulder girdle caused by poor work posture, increased
muscle tension and/or recreational activities. Treating the ‘injured’ tendon
may settle the immediate symptoms, but failure to deal with the ‘secondary
affected’ structures risks the symptoms returning. Changing the person’s
workstation may not solve the problem, therefore, as they take their secondary
muscle imbalances with them.

Before considering the specific soft tissues at fault, the risk factors that
may predispose the worker to developing WRULD should be examined.

Risk factors

A risk factor is any attribute, experience or exposure that significantly
increases the risk of occurrence of a disorder, though it may not be a causal
factor in itself. Writing in 1717, Bernard Ramazzinni1 in what was effectively
one of the first recorded risk assessments, said: "Various and manifold is
the harvest of diseases reaped by workers from the crafts and trades they
pursue. All the profit they get is fatal injury to their health mostly from two
causes. The first I ascribe to the harmful character of the materials they
handle.

"The second I ascribe to certain violent and irregular motions and
unnatural postures of the body, by reason of which the natural structure of the
vital machine is so impaired serious diseases gradually develop there
from."

So has much changed in the past 290 years? Common risk factors reported for
the development of WRULD in the workplace include:

– Dynamic and static muscle load: excessive loading of the muscles in
either static or dynamic situations leads to an increased risk of damage to the
muscle/tendon units directly, or may lead to structural changes in the muscles
that predispose other soft tissue to injury. Even small forces repetitively
applied to the body may lead to injury due to the visco-elastic nature of the
soft tissues of the body (Carlstedt and Nordin 1989).2

– Uncomfortable work postures: Postures that place the joints of the
body in awkward positions, particularly if sustained for long periods, will
lead to excess stress across the soft tissues. Shortened soft tissues will
tighten up over a period of time, and lengthened tissues will stretch and weaken.
Alteration in the muscle balance around the joints will affect the
biomechanical efficiency. Prolonged sitting with rounded shoulders will lead to
weakness of the muscles around the scapulae, affecting the ability to move and
position the scapulae when using the arms. This biomechanical inefficiency
places excess stress through the muscles of the shoulder joint, leading to
greater risk of rotator cuff tendonitis and impingement.

– Mental stress, tension: Increased work stress will lead to the
increased risk of WRULD through two main mechanisms. When in a state of tension
people tend to overwork muscles, leading to increased tension across the muscle
tendon units. This excess stress over the muscles/tendons may adversely affect
the visco-elastic properties of the tissue, affecting the capacity to withstand
increased external forces. People also tend to adopt a protective posture when
under stress. This is reflected in a forward head posture with rounded
shoulders. This protective posture will affect the biomechanics of the upper
body, increasing the risk of WRULD in the neck, shoulder, elbows and wrists or
hands.

– Adverse environmental factors: Poor lighting, increased noise
levels and adverse thermal environments (generally too cold) have been shown to
increase the risk. This may occur through increased muscle tension or another
mechanism as yet undefined.

– Poor work organisation: A poor work set-up will lead to increased
tension, increased dynamic or static muscle workload and often, poor postures.

– Personal factors: A number of personal risk factors for the
development of WRULD have also been reported.

– Gender: Many studies report an increased incidence among female
workers (Cohen et al 1992),3 although this may reflect the gender ratio in the
relevant workforce (Hutson 1997)4. Gender-based hormonal influences, such as
use of oral contraception (Sabour and Fadel 1979),5 pregnancy, gynaecological
surgery and meno-pause (Cannon et al 1981)6 have all been reportedly linked
with an increased risk of developing WRULD.

– General health: Employees who are physically unable to withstand
the physical nature of the task are at risk of developing WRULD. The inability
to cope with the work demands may be due to a state of physical deconditioning,
or due to rheumatological conditions, which render the connective tissue
susceptible to injury when placed under a repetitive load.

– Socio-economic status: A lower socio-economic status has been
linked to a higher risk of WRULD. This may be secondary to increased employment
in tasks involving repetitive and physically strenuous demands, deficient diet
along with little or no exercise and the increased likelihood of these
individuals being exposed to stress at home (Ayoub and Wittells 1989).7

– Job tenure: The first few months on the job is the most critical
period for the development of WRULD and it has been demonstrated that
increasing numbers of years on the job do not significantly increase the risks,
possibly indicating the effect of training and technique on reducing the risk
of injury. As time passes, work techniques may change to become more effective,
reducing the stress on the body. Potential risk factors in the development of
over-use injuries in a group of patients I have seen in industry are those
workers who are ‘trying too hard’. In this scenario, it appears that the muscle
action used to perform a movement is above normal, resulting in co-contraction
of both agonists and antagonists during performance of a task. This type of
inefficient motor usage is most likely to be seen in the performance of new
motor skills. A Kilbom (1994)8 also identified the role of factors such as
skill and training on the level of WRULD in repetitive work tasks. A second
cause for the decreased risk of WRULD with increasing work history is the
effect of survivor bias. Workers susceptible to the effects of WRULD self
select out of the potentially injurious work tasks by leaving the job (Sorock
and Courteney 1996).9 Those working on the job the longest are therefore less
susceptible to the effects of WRULD.

The neural system

The influence of neural tissue on the incidence of WRULD is often
overlooked. When we talk about neural tissue we are referring to the nerve
(axon) and the soft tissue around the nerve. In the body, the nerves are
surrounded by connective tissue from when they leave the spinal column through
to their final destination. This connective tissue acts to protect the nerves
from undesired forces and chemicals (Butler 2000).10 When people move, they
affect not only the muscles and joints, but also the neural tissue. When moving
from full trunk extension to flexion, the spinal canal elongates up to 90mm
(Louis 1981).11

When lifting the arm above the head, brachial nerves lengthen by up to 20
per cent (Zoech et al 1991).12 As the brachial nerves pass along the arm from
the neck they pass through, around and over muscles, around bony prominences,
over the front of joints, and under/over ligaments. Where the nerve lies in
close contact with other soft tissue, it forms an interface. When a
muscle/tendon/ ligament at these interfaces is affected by occupational
stresses either directly with local inflammation, or indirectly through
increased tension, the adjacent nerves may also be affected.

Potential sites of compromise include the lateral part of the elbow
(mimicking tennis elbow), along the front of the forearm (under the
finger/wrist flexor muscles), along the medial border of the elbow, over the
first rib at the base of the neck and along the side of the neck, where the
nerves emerge from between the scaleni muscles.

Another common example of this interfacing occurs in Carpal Tunnel Syndrome
(CTS), where the median nerve is affected through the carpal tunnel at the
front of the wrist. This tunnel is formed by the wrist bones posteriorly and
carpal tissue anteriorly and contains tendons, blood vessels and the median
nerve. If there is inflammation within the carpal tunnel, secondary to overuse
etc. then the median nerve is affected and the worker reports the classic
symptoms of CTS – pins and needles in the hand. Compression of the nerves can
occur at any of the previously described interface sites.

A second mechanism is due to repetitive stress over the neural tissue,
leading to adaptive shortening of the connective tissues. If during normal
movement people stretch neural tissue that lacks full range (remember in the
arm it may be expected to extend up to 20 per cent) this appears to result in
increased tension in the muscles that protect the nerve. These workers will
often report a recurrent history of overused muscle/tendon injuries despite
repeated rehabilitation.

Treating the injured tissue (in this case the tendons and muscles) may
settle the symptoms, but unless the cause for the overactivity in the muscles
(ie, to protect the nerves) is dealt with, the symptoms will return. They will
only fully heal when the secondary affected tissue (i.e. the nerve tissue) is
dealt with.

J Byng (1997)13 found a high incidence of abnormal sensations during nerve mobility
tests in a group of WRULD patients and a group of asymptomatic keyboard
operators, compared to non-process type workers. This suggested that
‘asymptomatic keyboard workers are demonstrating changes in neural tissues.
Some form of intervention may be necessary to prevent these individuals from
becoming the next cohort of patients’.

Treatment

The stretching of symptomatic nerve tissue should only be performed by a
trained practitioner. Physiotherapists are trained to gauge the correct
strength, duration and direction of stretching in symptomatic conditions. Do
not attempt to stretch the tissue except under their guidance. Clinically, I
have found that stretching the nerve tissue in symptomatic cases of WRULD is a
potential minefield, and requires a lot of care and control. The potential for
an adverse reaction to the stretching is higher in this type of soft tissue
than with muscles, tendons and ligaments.

Preventive strategies

People can’t stretch symptomatic nerve tissue themselves, except under guidance,
but why wait until the horse has bolted before doing something. Like all other
areas of the body subject to secondary changes associated with
sustained/repetitive work activities, we can help to prevent symptoms
developing.

I believe that stretching the neural tissue should form part of a normal
stretching programme warm-up in tasks involving repetitive sustained
activities.

There has been some controversy in the press lately about the benefits of
stretching during sporting activities. Sport sessions generally last for one or
two hours, while work activities often last for eight hours. The potential for
maladaptive changes to soft tissue are far greater during work activities where
the risk of sudden traumatic injury is higher. It makes good sense then that we
should stretch the tissues at risk of tightening due to our work activities.

An exercise for stretching neural soft tissues is described below. One
warning, though – nerves do not like stretching as much as the other soft
tissues of the body. Do not push the stretch. It is designed to take the body
through a ‘normal’ range of motion and all the usual rules of stretching apply.
Don’t bounce the stretch, listen to your body, and if it causes pain or any
pins and needles STOP, and seek professional help. As with any stretch, all
that should be felt is a comfortable stretching sensation along the arm. This
stretch is designed to stretch the Median nerve, the most common nerve involved
in WRULD.

It can also help prevent injury to the neural tissue by ensuring that the
tissue which the nerves pass through are free from external pressures. Work
garments that cause increased pressure around the arms, such as tight sleeves
rolled up to the elbow/forearm, may inadvertently lead to increased pressure on
the nerves. I have also seen neural based WRULDs resulting from workers resting
their forearms on the edges of work surfaces, resulting in a concentration of
pressure on the medial forearms.

Heavy backpacks with narrow shoulder straps may also lead to increased
pressure over the tops of the shoulders, affecting the nerves passing over the
first rib. Review the safety/protective equipment used in the workplace to make
sure it does not place too much pressure over the nerves and blood vessels in
the arms/neck.

Good rehabilitation is one of the best preventative strategies. The high
incidence of re-aggravation of WRULDs in the community suggests that current
rehabilitation programmes need to be reviewed. Making sure the injured worker
is fully rehabilitated and the stresses through the soft tissues are balanced,
is vital. However, this does not mean that an injured worker should be kept off
the job for extended periods of time. We should follow the model of sports
medicine where the worker should return to the task as soon as safely possible
in a graduated fashion.

We should make more use of increased task rotations, pause exercise
programmes, ergonomic interventions and work strengthening programmes to ensure
the task is safe and the worker can develop an adequate level of ‘fitness for
the job’. Programmes aimed at redressing the maladaptive changes resulting from
repeated exposure to occupational stresses should be developed and implemented.
This model of correcting tissue imbalance as a routine part of an activity is
commonplace in sport. Swimmers routinely do strengthening exercises for the
muscles stretched and weakened during swimming strokes and stretching
programmes for those tissues shortened.

Conclusion

It is time to reconsider the role of secondary structures such as the
nervous tissue on the incidence and recalcitrant nature of WRULD in the
workplace. Giant leaps have been made in this area of musculoskeletal medicine,
and physiotherapists and medical practitioners are developing a better
understanding and appreciation of the role of these tissues. It is important to
extend this concept into the preventative area of occupational health. The
introduction of pause exercise programmes, tied in with production schedules
aimed at reducing the adaptive changes in secondary tissues, will assist in
reducing the incidence.

Steve Milanese, B.App.Sc (Physio), Grad.Cert. (Sports Physio), Grad. Dip.
(Ergonomics). M.App.Sc. (Manipulative Therapy) Senior Researcher, Centre for
Allied Health Research, University of South Australia, Clinical specialist –
Musculoskeletal Physiotherapy, St. Mary’s Hospital, London

References

1. Bernard Ramazinni (1713): DeMorbis Artificum Distraba

2: Carlstedt CA and Nordin M (1989) : Biomechanics of tendons and ligaments
in : Nordin M., Frankel VH (eds) Basic Biomechanics of the Musculoskeletal
System Lea & Febiger. London Chapter 3. p.698-738

3: Cohen ML, Arroyo JF, Champion GD and Browne CD (1992): In search of the
pathogenesis of refractory cervicobrachial pain syndrome In: Medical Journal of
Australia 156: 432-436

4: Hutson MA (1997): Work Related Upper Limb Disorders Butterworth
Heinemann: Oxford

5: Sabour M and Fadel H: The carpal tunnel syndrome – a new complication
ascribed to the "pill", American Obstet. Gynecol 1970; 107: 1265-1267

6: Cannon L, Bernacki E and Walter S (1981): Personal and occupational
factors associated with carpal tunnel syndrome, Journal of Occupational
Medicine 23: 255-258

7: Ayoub MA and Wittels NE (1989): Cumulative trauma disorders,
International Review of Ergonomics 3: 217-272

8: Kilbom, A. 1994. Repetitive work of the upper extremity, International
Journal of Industrial Ergonomics

9: Sorock GS and Courteney TK (1996): Epidemiologic concerns for
ergonomists: illustrations from the musculoskeletal disorder literature.
Ergonomics 39:4: 562-578

10: Butler D. (2000): The Sensitive Nervous System, NOI Group Publications,
Australia.

11: Louis R (1981): Vertebroradicular and vertebromedullar dynamics.
Anatomica Clinica 3: 1-11

12: Zoech G., Reihsner R., Beer R. et al (1991): Stress and strain in
peripheral nerves, Neuro-Orthopedics 10: 73-82

13: Byng J (1997): Overuse syndromes of the upper limb and the upper limb
tension test: a comparison between patients, asymptomatic keyboard workers and
asymptomatic non-keyboard workers, Manual Therapy 2(3) 157-164

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