Peripheral Nerves

So many ways to injure a peripheral nerve – The upper limb

Traditional nerve injury classifications
Most clinicians would have learnt about grades of peripheral nerve injury ranging from the more minor neurapraxia, (conduction block with eventual reversal) to axonotmesis (axon severed, but connective tissues OK) and neurotmeses (neurones severed and connective tissue cut or badly scarred). These categories emerged post WW2 from the work of Sunderland and Seddon. Although we learned them, we rarely used them, unless perhaps you were working in peripheral nerve surgery. Sunderland and other peripheral nerve experts always talked about pre-neurapraxias (Sunderland called them perverted nerves). The pre-neurapraxis need a revisit.

A new look at nerve injury classification
Molecular biology has shown us that genetic and environmental forces combine to produce altered kinds and numbers of ion channels at mid axon sites along nerves, creating ectopic discharge – the basis of many syndromes such as carpal tunnel syndrome, tarsal tunnel syndrome and neurogenic tennis elbow. They may react to mechanical, temperature and emotional forces, but still not be picked up on a nerve conduction test. If Sunderland were alive today, I think he would be delighted to see his “perverted nerves” exposed.

A new view of peripheral nerve injury
Of course, nerves can be severely injured by traction, pinch and rubbing forces. The literature is full of exotic ways of injuring peripheral nerves, including grenade throwing practice (long thoracic), ‘love bites’ (accessory), handcuffs (radial sensory), cycling, taxi driving (ulnar), biceps exercise (musculocutaneous), injections (radial) and simple repetitive wrist flexion and extension (median). A whole range of familial and systemic states will also intervene. Some spider bites can be particularly mean on nerves too.

But a modern view is that it is not only the injuring movements which are critical, but the nerve owner’s responses and perceptions of the injury. Recent studies showing increased nerve adrenosensitivity (eg. more sensitive when stressed) and immunoreactivity (eg worse with the flu) with injury suggest the brain plays a big part in the clinical manifestations.

Your turn
Can you let us know a novel and exotic way of injuring an upper limb nerve, from your patient or personal experiences? This month’s prize to the most novel (and educational) nerve injury story is a new NOI Mirror Box!

Thanks for the beautiful poems on the anterior cingulate cortex from last month. The winner, Lorna Fox (NZ), sent us a lovely long poem, more of an ode really! – the first two paragraphs are here, but read the rest of the poem and the other anterior cingulate contributors.

Congratulations Lorna, a set of the New Explain Pain Posters are on their way over to you!

There’s a multi-use part of my brain,
involved in expressing my pain.
Examine my neck,
it’ll light up like heck,
and dim when distracted again.

My brain does this without thinking.
I guess it’s a little like blinking.
I wish I were dead,
I’m not swinging the lead,
I’m gonna go out and get drinking.

It’s actions are entirely unplanned…

NOI mirror box update
The mirror box has got a new slant to it! We recruited Pythagoras to help with the design and came up with a triangular mirror box that is sturdier, easier to set up, more durable and easier to post, while still using the same hygienic corflute material and quality perspex mirror. The original classic square box design still works well and some may prefer its more spacious box.

Mirror therapy forms a part of an evidence based graded motor imagery programme involving laterality recognition and motor imagery. It has become trendy recently, with claims for great successes in the literature. Lorimer Moseley’s recent article in Scientific American is a reminder that while initial results are encouraging, we need to be careful. Here at NOI, we would like to remind readers that the mirror is only a part of the management of complex pain states. Tailormade programmes, uses of other parts of the imagery programme, hard work, compliance, education and graded programmes are all a part of this exciting but embryonic therapy.

 

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