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19

A

t a recent conferencewith counsel

regarding a case of ongoing chronic pain

of four years duration arising froman

allegedly heavy-handed physiotherapy

treatment, counsel posited,‘The defence are, of

course, going to assert that a soft tissue injury

normally heals within threemonths, sowhy does

the claimant still suffer frompain?’

Among the issues that arise duringmedico-legal

work, ongoing chronic pain following soft tissue

injurymust surely be one of themost controversial.

While this is an issue that themajority of clinicians

will readily accept in their day-to-daywork (e.g. that

20 per cent of ankle sprains or whiplash injuries will

experience long-termproblems with pain and

disability), it can, of course, present considerable

problems when it comes to explaining in amedico-

legal context precisely howandwhy a claimant

continues to report ongoing pain and disability

following a soft tissue strain.

This short article aims to present a summary

in simple terms of the extant literature on the

development of chronic pain following soft tissue

trauma. It is clearly not intended to be an exhaustive

reviewbut offers the legal practitioner a snapshot of

current thinking in this burgeoning clinical field of

study, which has revealed fascinating relationships

between trauma, pain, and themind and the

cascade of events that not infrequently follow soft

tissue injuries such as whiplash or lowback strain.

Pain science

The intensity of pain a person describes following

an injury and the resulting disability rarely correlate

with the degree of soft tissue trauma. Indeed, in

early laboratory studies where subjects received

precisely the same pain stimulus (usually an

unpleasant electrical stimulus), it was found that

some subjects would rate this as only a verymild

discomfort – some not even registering the stimulus

as pain –while others would rate exactly the same

pain stimulus as the‘worst pain imaginable’.

Of course, this has entered common parlance

and in day-to-day life we now talk about people

having high or low pain thresholds, but what

causes such wide variations in pain experience?

What appears to be coming out of the research

literature is that pain thresholds, even among

healthy individuals in the laboratory setting, vary

according to that person’s fear of injury, their

previous experiences of pain, and their current

psychological state (if they are stressed or

depressed, for example). This will be discussed

further below, but one thing we can take from this

research is that clearly we can no longer regard the

intensity of pain experienced as a marker per se of

the extent of the soft tissue damage.

The stress response

A person experiencing a stress response will

describe irritability, increased sweating, and

‘jumpiness’. It has long been known that stress

delays wound healing, but there are now a

plethora of human studies demonstrating that

stress responses have a direct influence on the

way that pain is processed, and researchers have

found several important relationships between

post-traumatic stress disorder (PTSD) and pain –

for example, PTSD sufferers appear to have lower

pain thresholds and lower levels of the body’s

natural pain relieving substances (endorphins).

Indeed, a common neurobiological pathway is

shared between stress responses, negative mood,

and pain in the neurotransmitter systems of the

brain, and when we are stressed hormones are

released that make our pain nerve-endings more

sensitive. In fact, it is thought that pain can be

present – via these stress-related pathways –

even in the complete absence of physical trauma.

Interestingly, there is also evidence that a

one-off brief stressful event can make our skin

and muscles more sensitive and tender, as if the

brain has turned up the body’s sensitivity to the

environment to screen for further threats to its

survival (for a review of how this phenomenon can

be used to predict prognosis following whiplash,

see‘When range of motion is not enough: Towards

an evidence-based approach tomedico-legal

reporting in whiplash injury’,

Journal of Forensic and

Legal Medicine

, July 2014). Of course, experiencing

greater levels of pain can lead to the avoidance of

activity, be it occupation, hobbies, or socialising,

>>

FEATURE

MEDICO-LEGAL

Legal practitioners should be aware of the relationships between trauma, pain, and the

mind in injuries such as whiplash or low back strain, writes

Chris Worsfold

Explaining chronic pain

following soft tissue injury

Chris Worsfold is a neck pain

specialist and expert witness

based in Blackheath, London,

and Tonbridge, Kent

@chrisworsfold1

tonbridgeclinic.co.uk

SJ 160/6

Expert Witness Supplement Spring 2016