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INTRODUCTION

The nerve supply to the upper limb is an absolutely essential topic for you to nail during revision for your exams, as it is a relatively complex topic which will inevitably crop up in anatomy questions, clinical case scenarios and OSCEs. It is also very relevant once you start your clinical practice as a doctor.

This article will focus on the five terminal nerve branches of the brachial plexus which supply the upper limb. These are the musculocutaneous nerve, the axillary nerve, the radial nerve, the median nerve and the ulnar nerve. I have covered their anatomy and function, as well as the clinical features you would expect to find with a nerve injury. I have also, of course, provided a handy summary table at the end!


STRUCTURE OF THE BRACHIAL PLEXUS

The nerve supply to the upper limb is almost entirely supplied by the brachial plexus; a complex intercommunicating network of nerves formed in the neck by spinal nerve roots C5, C6, C7, C8 and T1. I have covered the brachial plexus itself in more detail in a separate article here.

The diagram below summarises the structure and branches of the brachial plexus in all its demoralising glory. You can click to make it bigger!

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brachial plexus diagram

You can see that the three cords branch to form the five terminal nerve branches which supply the upper limb:

  • the lateral cord gives the musculocutaneous nerve and the lateral root of the median nerve
  • the posterior cord gives the axillary nerve and the radial nerve
  • the medial cord gives the medial root of the median nerve and the ulnar nerve

The origins of these five nerves are distributed around the third part of the axillary artery. The musculocutaneous, median and ulnar nerves lie anteriorly and form a characteristic “M” shape around the axillary artery, which is a really easy landmark to find on a prosection. When given a diagram or prosection of the brachial plexus to label in exams, the way to stay calm and approach it like a boss is to find the “M” shape!


MUSCULOCUTANEOUS NERVE C5/C6/C7

ORIGIN

  • lateral cord of brachial plexus
  • formed from anterior divisions of superior and middle trunks

COURSE

  • it leaves the axilla by piercing coracobrachialis muscle
  • it then passes down the arm beneath biceps muscle
  • it ends as the lateral cutaneous nerve of forearm

SENSORY SUPPLY

  • skin of lateral forearm

MOTOR SUPPLY

  • anterior compartment of arm (BBC)
    • biceps – flexes elbow, supinates forearm
    • brachialis – flexes elbow
    • coracobrachialis – flexes and adducts the arm at the glenohumeral joint

COMMON INJURIES

  • musculocutaneous nerve injuries are rare, as the nerve is protected beneath the bulk of the biceps muscle
  • it may be damaged by stab wounds to the upper arm

CLINICAL FEATURES OF MUSCULOCUTANEOUS NERVE PALSY

  • SENSORY LOSS
    • numbness over lateral forearm
  • MOTOR DEFICIT
    • paralysis of anterior compartment of arm – very weak elbow flexion and weak forearm supination
    • absent biceps reflex
  • DEFORMITY
    • wasting of anterior compartment of arm
    • elbow usually held in extension with forearm pronated

AXILLARY NERVE C5/C6

ORIGIN

  • posterior cord of brachial plexus
  • formed from posterior division of upper trunk

 

COURSE

  • it passes beneath the shoulder joint through the quadrangular space with the posterior circumflex humeral artery
  • it then wraps around the surgical neck of the humerus

SENSORY SUPPLY

  • the “sergeant’s patch” of skin over the lower part of deltoid muscle

 

MOTOR SUPPLY

  • shoulder muscles
    • deltoid – abducts, flexes and extends shoulder
    • teres minor – externally rotates shoulder, forms part of rotator cuff which stabilises shoulder joint

 

COMMON INJURIES

  • fracture of surgical neck of humerus
  • stab wounds to posterior shoulder
  • anterior shoulder dislocation
  • pressure of crutches on armpits (“crutch palsy”)

 

CLINICAL FEATURES OF AXILLARY NERVE PALSY

  • SENSORY LOSS
    • numbness over “sergeant’s patch”
  • MOTOR DEFICIT
    • paralysis of deltoid – very weak shoulder abduction from 15-90°; weak shoulder flexion and extension
    • paralysis of teres minor – weak shoulder external rotation
  • DEFORMITY
    • wasting of deltoid muscle, making the bones of the shoulder joint very prominent and obvious
    • shoulder may appear adducted and internally rotated

RADIAL NERVE C5/C6/C7/C8/T1

ORIGIN

  • posterior cord
  • formed from posterior divisions of all three trunks

COURSE

  • it passes behind the axillary artery and through the triangular interval to enter the posterior compartment of the arm
  • it then winds around the spiral groove of the humerus with the profunda brachii artery, between the heads of triceps muscle
  • it enters the antecubital fossa in front of the lateral epicondyle of the humerus, between the brachialis and brachioradialis muscles
  • it then branches in the proximal forearm into two terminal branches:
    • superficial branch (mainly sensory) – descends under brachioradialis muscle to end in the dorsum of the hand
    • deep branch (mainly motor) – pierces supinator muscle and descends along the posterior interosseous membrane with the posterior interosseous artery

 

SENSORY SUPPLY

  • posterior arm and forearm
  • lateral ⅔ of dorsum of hand
  • proximal dorsal aspect of lateral 3½ fingers (thumb, index, middle and half of ring finger)

 

MOTOR SUPPLY

  • posterior compartment of arm
    • triceps – extends and adducts shoulder, extends elbow
  • posterior compartment of forearm
    • brachioradialis – flexes elbow
    • anconeus – extends elbow, stabilises elbow joint
    • supinator – supinates forearm
    • extensor carpi radialis longus and brevis – extend and abduct wrist
    • extensor carpi ulnaris – extends and adducts wrist
    • extensor digitorum, extensor pollicis longus and brevis, extensor indicis and extensor digiti minimi – extend thumb and fingers at MCPJs and IPJs
    • abductor pollicis longus – abducts thumb

 

COMMON INJURIES

  • fractures of proximal humerus, shaft of humerus or radius
  • stab wounds to antecubital fossa, forearm or wrist
    • this includes blood tests and venflons!
  • pressure of crutches on armpits (“crutch palsy“)
  • the patient falling asleep with arm hanging over the back of a chair, classically whilst drunk (“Saturday night palsy“)
  • somebody else falling asleep with their head lying on the patient’s arm (“honeymoon palsy“)
  • excessively tight plaster casts, wristbands or handcuffs
  • prolonged tourniquet use on upper arm, for example during orthopaedic or plastics procedures

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wrist drop deformity

“Wrist drop” deformity due to radial nerve palsy – the patient cannot extend their wrist or fingers

CLINICAL FEATURES OF RADIAL NERVE PALSY

  • SENSORY LOSS
    • numbness of skin over posterior arm, posterior forearm and radial distribution of dorsum of hand

 

  • MOTOR DEFICIT
    • paralysis of posterior compartment of arm – weak elbow extension
    • paralysis of posterior compartment of forearm – weak wrist extension, weak thumb extension and finger MCPJ extension
    • NB// finger IPJ extension is still possible due to intact nerve supply to the lumbrical muscles of the hand
    • absent triceps and supinator reflexes

 

  • DEFORMITY
    • wasting of triceps and posterior compartment of forearm
    • “WRIST DROP” deformity at rest and on attempted wrist extension – the patient cannot extend their wrist/fingers, resulting in unopposed wrist flexion. In the classical description of a radial nerve injury, the forearm is also pronated, the fingers are flexed and the thumb adducted.

 


MEDIAN NERVE C5/C6/C7/C8/T1

ORIGIN

  • lateral and medial cords of the brachial plexus
  • lateral root arises from anterior divisions of superior and middle trunks
  • medial root arises from anterior division of inferior trunk

COURSE

  • the median nerve runs down the arm with the brachial artery: it initially lies lateral to the artery, then crosses over to lie medial to it about halfway down the arm
  • it then passes through the medial part of the antecubital fossa between the two heads of pronator teres muscle
  • it travels through the anterior forearm between the flexor digitorum superficialis and flexor digitorum profundus muscles and gives three main branches:
    • anterior interosseous nerve – descends along anterior interosseous membrane with anterior interosseous artery
    • deep branch – enters hand through the carpal tunnel beneath flexor retinaculum of wrist, between flexor carpi radialis and flexor digitorum superficialis tendons
    • superficial/palmar cutaneous branch – arises just before the wrist and pierces the palmar carpal ligament to enter the palm over the top of the carpal tunnel – this nerve is therefore not affected by carpal tunnel syndrome

 

SENSORY SUPPLY

  • the median nerve does not supply any sensory innervation to the axilla or upper arm
  • skin over thenar eminence
  • lateral ⅔ palm of hand
  • palmar aspect of lateral 3½ fingers
  • dorsal fingertips of lateral 3½ fingers (thumb, index, middle and half of ring finger)

MOTOR SUPPLY

  • the median nerve does not supply any motor innervation to the axilla or upper arm
  • all muscles of anterior compartment of forearm EXCEPT flexor carpi ulnaris and the medial two parts of flexor digitorum profundus
    • pronator teres and pronator quadratus – pronate forearm
    • flexor carpi radialis – flexes and abducts wrist
    • palmaris longus – flexes wrist and tenses palmar aponeurosis
    • flexor digitorum superficialis – flexes fingers at PIPJs
    • lateral two parts of flexor digitorum profundus – flex index and middle fingers at DIPJs
    • flexor pollicis longus – flexes thumb at IPJ
  • intrinsic muscles of hand – LOAF muscles
    • lateral two lumbricals – flex MCPJs and extend IPJs of index and middle finger
    • opponens pollicis – opposes thumb
    • abductor pollicis brevis – abducts thumb
    • flexor pollicis brevis – flexes thumb at MCPJ

 

COMMON INJURIES

  • supracondylar fractures of humerus
  • stab wounds to antecubital fossa, forearm of wrist
    • this includes blood tests and venflons!
  • deep wrist lacerations inflicted during deliberate self harm
  • compression by carpal tunnel syndrome

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hand of benediction deformity

“Hand of benediction” due to median nerve palsy – the patient cannot flex their index or middle fingers

CLINICAL FEATURES OF MEDIAN NERVE PALSY

  • SENSORY LOSS
    • numbness of skin over thenar eminence and median distribution of hand
    • NB// in carpal tunnel syndrome, sensation to the palm is usually preserved due to an intact palmar cutaneous branch

 

  • MOTOR DEFICIT
    • paralysis of most of anterior compartment of forearm – weak forearm pronation, wrist flexion and abduction, and weak finger flexion with preservation of DIPJ flexion at ring and little fingers
    • paralysis of thenar eminenceweak pincer grip and overall grip strength, weak thumb opposition

 

  • DEFORMITY
    • wasting of anterior compartment of forearm and thenar eminence
    • “HAND OF BENEDICTION” deformity on attempted finger flexion – the patient cannot flex their index or middle fingers, resulting in unopposed extension of those two fingers. They cannot make a fist with all of their fingers.

 

 


ULNAR NERVE C8/T1

ORIGIN

  • medial cord of brachial plexus
  • formed from anterior division of inferior trunk

 

COURSE

  • the ulnar nerve runs down the arm on the medial side of the brachial artery
  • it passes behind the medial epicondyle of the humerus and enters the forearm between the two heads of flexor carpi ulnaris
  • it travels through the anterior compartment of the forearm beneath flexor carpi ulnaris with the ulnar artery
  • it then enters the palm of the hand through Guyon’s canal

 

SENSORY SUPPLY

  • the ulnar nerve does not supply any sensory innervation to the axilla or upper arm
  • skin over hypothenar eminence
  • medial ⅓ palm of hand
  • palmar aspect of lateral 1½ fingers
  • medial ⅓ dorsum of hand
  • dorsal aspect of medial 1½ fingers (little finger and half of ring finger)

 

MOTOR SUPPLY

  • two muscles of anterior compartment of forearm
    • flexor carpi ulnaris – flexes and adducts wrist
    • medial two parts of flexor digitorum profundus – flex ring and little fingers at DIPJs
  • most of the intrinsic muscles of the handHILA muscles
    • hypothenar eminence: opponens digiti minimi, flexor digiti minimi brevis and abductor digiti minimi – oppose, flex and abduct little finger
    • interossei – palmar interossei adduct, dorsal interossei abduct
    • medial two lumbricals – flex MCPJs and extend IPJs of ring and little finger
    • adductor pollicis – adducts thumb
    • NB// adductor pollicis is not part of the thenar eminence and actually lies deep beneath it as a separate structure

 

COMMON INJURIES

  • supracondylar fractures of humerus
  • fractures or soft tissue injuries to medial epicondyle of humerus
  • stab wounds to forearm or wrist
    • this include blood tests and venflons!
  • compression either at the cubital tunnel in the elbow or at Guyon’s canal in the wrist

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claw hand deformity

“Claw hand” due to ulnar nerve palsy – the patient cannot extend their ring or little fingers

CLINICAL FEATURES OF ULNAR NERVE PALSY

  • SENSORY LOSS
    • numbness over hypothenar eminence and ulnar distribution of hand

 

  • MOTOR DEFICIT
    • paralysis of flexor carpi ulnaris – weak wrist flexion and adduction
    • paralysis of medial two parts of flexor digitorum profundus – weak flexion of ring and little finger DIPJs
    • paralysis of most of the intrinsic muscles of the hand weak MCPJ flexion and IPJ extension of ring and little fingers, loss of finger abduction and adduction, loss of opposition of little finger

 

  • DEFORMITY
    • wasting of hypothenar eminence and intrinsic muscles of hand
    • “CLAW HAND” deformity at rest and on attempted finger extension – the patient cannot extend the IPJs of their ring or little fingers, resulting in fixed flexion of the IPJs and hyperextension of the MCPJs of these two fingers. The clawed appearance is most pronounced when the nerve is injured at the wrist, for example by compression in Guyon’s canal, as the function of flexor digitorum profundus will be preserved. A claw hand affecting all four fingers is much less common and is usually due to a lesion of the lower part of brachial plexus, such as Klumpke’s palsy.

 

 


 

REAL ANATOMY: PROSECTED SPECIMENS

Here is a really great little video from adivineanatomy on YouTube, which walks you through the brachial plexus and the peripheral nerves of the upper limb on a prosection:


REAL ANATOMY: SURGERY

This video from Nerve Surgery on YouTube shows a standard carpal tunnel release procedure to treat compression of the median nerve at the wrist. This is an extremely common operation, so make sure you check for a carpal tunnel scar when examining upper limb neurology in OSCEs! The surgeons have used a tourniquet to squeeze all of the blood out of the arm in order to create a nice bloodless surgical field, and it is likely the operation is being performed under local anaesthetic or using a regional Bier block. You can see that there is a lot of stuff crammed into a very small space beneath the flexor retinaculum, so it’s hardly surprising that the median nerve gets squished sometimes!

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This video from Stephen Benavides on YouTube shows an ulnar nerve transposition procedure to treat compression in the cubital tunnel at the elbow. You can see that the ulnar nerve is a fairly sizeable structure in real life – you can roll it under your fingers at your medial epicondyle quite easily if you are so inclined.


CLINICAL ANATOMY: OSCE EXAMINATION + PERIPHERAL NERVE INJURIES

If you require a refresher of how to perform a neurological examination of the upper limb, here is our super awesome (and rather sexy) Geeky Medics OSCE guide:

 

The sensory supply to the upper limb can be broken down into dermatomes (the area supplied by each spinal nerve root) and peripheral nerve territories. The best way to learn these, expecially the complicated supply to the hand, is literally to draw it on yourselves or on each other! The motor supply to the upper limb can also be broken down into myotomes (the movements which test individual spinal nerve roots) as well as peripheral nerve functions. The table below summarises how to test the function of each spinal nerve:

Upper l

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PERIPHERAL NERVE INJURIES

A thorough understanding of upper limb anatomy is absolutely essential if you want to succeed in a neurological examination OSCE station. The nerve supply to the upper limb is commonly damaged by fractures, penetrating trauma and external compression. These unfortunate events generate lots of patients with abnormal neurological examination findings who can be used in your exams! Learning the patterns of different nerve injuries can unfortunately be both complicated and tedious. I have therefore, alongside their anatomical course and functions, detailed the clinical features you would expect to see with injuries to each of the nerves in the individual sections above. I have also created a separate little summary table detailing the features of different nerve injuries below (you can click to enlarge it). To make them easier to memorise I have broken them down into three groups: sensory loss, motor deficits and deformity.

upper limb nerve injuries table

There are several different types and pathologies of nerve injuries:

  • neurapraxia – the nerve is stretched and damaged but not torn
  • rupture – the nerve is torn at a point along its length
    • axonotmesis – the nerve fibre is partially severed: the axon and myelin sheath are torn but the surrounding epineurium, perineurium and connective tissues are preserved. Natural recovery is possible through axonal regeneration, so these injuries can often be managed conservatively with support and physiotherapy.
    • neurotmesis – the nerve fibre is completely severed. There is no prospect of natural recovery, so this type of injury requires surgery to restore function.
  • avulsion – the nerve root is torn off the spinal cord at its origin. This can happen in brachial plexus injuries but would not usually cause injury to individual upper limb nerves.
  • post-traumatic neuroma – a growth of scar tissue at the site of a previous nerve injury, which leads to compression

If you want to learn about brachial plexus injuries, these are covered in detail in a separate anatomy article here.


SUMMARY

The big summary table below sums up everything we’ve just covered in what I hope is a concise and memorable fashion. Again, you can click to enlarge it and it should print out nicely onto a sheet of A4 paper. I hope you found this guide useful – good luck and may the forceps be with you!

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REFERENCES

  • International Standards for Classification of Spinal Cord Injury 2011 Revised Edition, available from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3232636/
  • Netter FH; Atlas of Human Anatomy, 5th Edition” – Elsevier Saunders 2010. This is, in my opinion, the absolute best anatomy atlas out there. The illustrations are lifelike, extremely accurate and weirdly beautiful. Plus the cover is shiny. It’s worth every penny.
  • Sinnatamby CS; Last’s Anatomy, 12th Edition” – Churchill Livingstone 2011
  • Snell RS; “Clinical Anatomy by Regions, 9th Edition” – Lippincott Williams and Wilkins 2011

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