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INTRODUCTION

The brachial plexus is widely renowned as one of the most horribly fiddly and complicated pieces of anatomy you’ll ever have to learn. This of course means that examiners absolutely LOVE testing you on it! I always found the most difficult part was to grasp which bits of tiny stringy nerve fibres went where and how they joined together. I have therefore tried to create the clearest possible summary diagram to help you make sense of this, and have provided lots of images and videos to show you what it looks like in real life. I have also summarised the key aspects of proximal brachial plexus injuries like Erb’s and Klumpke’s palsy.

The best way to memorise the brachial plexus is by drawing it – you are of course welcome to print out my diagram, but I would suggest getting some paper and drawing out the plexus yourself as well to help it stick in your mind. Enjoy!

THE BRACHIAL PLEXUS IN A NUTSHELL

  • the brachial plexus is a complex intercommunicating network of nerves formed by spinal nerves C5, C6, C7, C8 and T1
  • it supplies all sensory innervation to the upper limb and most of the axilla, with the exception of an area of the medial upper arm and axilla, which is supplied by the intercostobrachial nerve T2
  • it supplies all motor innervation to the muscles of the upper limb and shoulder girdle, with the exception of trapezius, which is supplied by the spinal accessory nerve IX
  • it also supplies autonomic innervation to the upper limb by intercommunicating with the stellate ganglion of the sympathetic trunk at the level of T1, where it gains sympathetic fibres which supply specialist functions:
    • vasomotor – stimulates vasoconstriction of arteries, arterioles and capillaries resulting in skin pallor and coldness
    • pilomotor – stimulates contraction of arrector pili muscles within hair follicles, making hairs stand on end
    • sudomotor or secretomotor – stimulates production of sweat from sweat glands
  • the brachial plexus begins as the anterior rami of five spinal nerve roots C5-T1, which emerge from the intervertebral foramen of their respective vertebrae to lie in the posterior triangle of the neck between the anterior and medial scalene muscles
  • the five spinal nerves quickly unite to form superior, middle and inferior trunks, which continue to pass laterally between the anterior and medial scalene muscles and cross the base of the posterior triangle of the neck, where they can be found behind the subclavian artery. They pass over the apex of the lung and the first rib towards the clavicle.
  • behind the middle third of the clavicle, each trunk splits into an anterior division and a posterior division. These continue to pass downwards behind the clavicle to enter the axilla.
  • the six divisions combine to form lateral, posterior and medial cords. These are distributed around and named according to their relationship with the second part of the axillary artery, which is located behind the pectoralis minor muscle. The cords travel laterally with the axillary artery towards the arm. The artery and cords are ensheathed by an extension of the prevertebral fascia known as the axillary sheath – this is a target for brachial plexus nerve blocks.
  • the cords divide around the third part of the axillary artery into their five terminal branches: the musculocutaneous, axillary, radial, median and ulnar nerves. These are summarised below and described in detail in a separate article here.
  • the brachial plexus gets its blood supply from various branches of the subclavian artery along its length, including:
    • ROOTS – vertebral artery, anterior and posterior spinal arteries
    • TRUNKS + DIVISIONS  ascending and deep cervical arteries, superior intercostal artery
    • CORDS  axillary artery

 

STRUCTURE OF THE BRACHIAL PLEXUS

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

The structure of the brachial plexus

 

Some key points to take away from this diagram are:

  • the brachial plexus is easier to learn if you break it down into its component segments and tackle them one at a time: these are roots, trunks, divisions, cords and terminal branches
  • ROOTS: there are five nerve roots from C5-T1, which give three nerve branches: the dorsal scapular nerve, the long thoracic nerve and the first intercostal nerve. It is important to remember that C5 also gives fibres which join fibres from C3 and C4 to form the phrenic nerve, which is not shown on the diagram.
  • TRUNKS: the five nerve roots combine to form three trunks. The superior trunk is formed from C5 and C6. The middle trunk is formed from C7. The inferior trunk is formed from C8 and T1. The superior trunk gives two nerve branches: the suprascapular nerve and the nerve to subclavius. The middle and inferior trunks do not give off any extra branches.
  • DIVISIONS: there are six divisions in total, comprising an anterior division and a posterior division from each of the three trunks. Anterior division fibres usually supply flexor muscles, and posterior division fibres usually supply extensors. There are no extra nerve branches arising from the divisions.

 

  • CORDS: the divisions combine to form three cords, which are distributed around the axillary artery:
    • the lateral cord is formed from the anterior divisions of the superior and middle trunks. It gives one extra nerve branch: the lateral pectoral nerve.
    • the posterior cord is formed from the posterior divisions of the superior, middle and inferior trunks. It gives three nerve branches: the upper subscapular nerve, the thoracodorsal nerve and the lower subscapular nerve.
    • the medial cord is formed from the anterior division of the inferior trunk. It gives three nerve branches: the medial pectoral nerve, the medial cutaneous nerve of the arm (also known as the medial brachial cutaneous nerve) and the medial cutaneous nerve of the forearm (also known as the medial antebrachial cutaneous nerve).

 

  • TERMINAL BRANCHES: the three cords branch to form 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.

 

  • it is very easy to panic when given a diagram or prosection of the brachial plexus to label in exams. The way to stay calm is to look for the “M” shape formed around the axillary artery by the musculocutaneous, median and ulnar nerves. This is a really easy landmark to find and will give you your bearings. Once you have found this, you should be able to confidently identify those three nerves. You will then be able to identify the small axillary nerve and large radial nerve originating from the posterior cord behind the axillary artery. The medial cutaneous nerves of the arm and forearm can be found travelling down the arm below the ulnar nerve. The three branches from the posterior cord should also be easy to spot – you will see the two small subscapular nerves and the large thoracodorsal nerve between them, which forms a bundle with the thoracodorsal artery and vein to supply latissimus dorsi. Any extra branches you can spot after that will definitely be merit points!

 

  • there are many recognised anatomical variations to this structure, which may affect over 50% of people! The most significant ones include:
    • pre-fixed brachial plexus – contributing nerve roots all moved up one, therefore the plexus is derived from C4-C8
    • post-fixed brachial plexus – contributing nerve roots all moved down one, therefore the plexus is derived from C6-T2
    • individual nerves may also helpfully decide to arise from different cords, intercommunicate with others or be completely absent. Thankfully, while this is probably totally fascinating to neurologists and plastic surgeons, you should never be given an atypical brachial plexus in your exams!

You will be expected to know what each of the nerves of the brachial plexus actually does. I have provided a brief outline of the origin and function of each of the nerve branches below. I have also covered the five terminal branches to the upper limb in lots more detail in a separate article here.

NERVES OF THE BRACHIAL PLEXUS: BRANCHES FROM THE NERVE ROOTS

DORSAL SCAPULAR NERVE C5

  • ORIGIN: C5 nerve root of the brachial plexus
  • SENSORY SUPPLY: none
  • MOTOR SUPPLY: levator scapulae (elevates scapula), rhomboid major and rhomboid minor (stabilise, retract and medially rotate scapula)

 

LONG THORACIC NERVE (OF BELL) C5/C6/C7

  • ORIGIN: C5, C6 and C7 nerve roots of the brachial plexus
  • SENSORY SUPPLY: none
  • MOTOR SUPPLY: serratus anterior (protracts and stabilises scapula)
  • CLINICAL SIGNIFICANCE: the long thoracic nerve often crops up in exam questions. An injury to the long thoracic nerve, for example as a result of a sports injury or damage during axillary surgery, results in “winging” of the scapula on examination. The deformity may be visible at rest, and a classic way to elicit or exaggerate it in an OSCE is by asking the patient to push against a wall and looking for abnormal posterior protrusion of the scapula on the affected side.

 

FIRST INTERCOSTAL NERVE T1

  • ORIGIN: T1 nerve root of the brachial plexus
  • SENSORY SUPPLY: narrow strip of skin over first intercostal space
  • MOTOR SUPPLY: first intercostal muscles (elevate and depress ribcage during inspiration and expiration)

NERVES OF THE BRACHIAL PLEXUS: BRANCHES FROM THE TRUNKS

SUPRASCAPULAR NERVE C5/C6

  • ORIGIN: superior trunk of the brachial plexus
  • SENSORY SUPPLY: glenohumeral and acromioclavicular joints
  • MOTOR SUPPLY: supraspinatus (stabilises and abducts shoulder) and infraspinatus (stabilises and externally rotates shoulder)

NERVE TO SUBCLAVIUS C6

  • ORIGIN: superior trunk of the brachial plexus
  • SENSORY SUPPLY: none
  • MOTOR SUPPLY: subclavius (depresses clavicle and elevates first rib)

NERVES OF THE BRACHIAL PLEXUS: BRANCHES FROM THE CORDS

LATERAL PECTORAL NERVE C5/C6/C7

  • ORIGIN: lateral cord of the brachial plexus
  • SENSORY SUPPLY: none to skin, but it is thought to play an important role in the sensation of chest wall pain, for example after mastectomy or breast implant insertion, and is therefore a target for regional nerve blocks
  • MOTOR SUPPLY: upper clavicular part of pectoralis major (flexes, adducts and internally rotates shoulder)

 

UPPER SUBSCAPULAR NERVE C5/C6

  • ORIGIN: posterior cord of the brachial plexus
  • SENSORY SUPPLY: none
  • MOTOR SUPPLY: subscapularis (stabilises and internally rotates shoulder)

 

LOWER SUBSCAPULAR NERVE C5/C6

  • ORIGIN: posterior cord of the brachial plexus
  • SENSORY SUPPLY: none
  • MOTOR SUPPLY: subscapularis (stabilises and internally rotates shoulder) and teres major (adducts and internally rotates shoulder, protracts and depresses scapula)

 

THORACODORSAL NERVE C6/C7/C8

  • ORIGIN: posterior cord of the brachial plexus
  • SENSORY SUPPLY: none
  • MOTOR SUPPLY: latissimus dorsi (extends, adducts and internally rotates shoulder, externally rotates trunk)
  • CLINICAL SIGNIFICANCE: the thoracodorsal nerve is vulnerable to injury during axillary dissection, for example during lymph node clearance for breast cancer. This results in shoulder movement weakness, which is best elicited on examination by asking the patient to place the dorsum of their hand on the opposite buttock to test extension, adduction and internal rotation. Thankfully, most patients do not suffer from significant loss of function in terms of day-to-day activities, but elderly people may struggle to pull themselves up from a sitting position, and young climbers or bodybuilders are likely to notice significantly reduced performance on the affected side.

 

MEDIAL PECTORAL NERVE C8/T1

  • ORIGIN: medial cord of the brachial plexus
  • SENSORY SUPPLY: none to skin, may have a role in sensation of chest wall pain following breast surgery
  • MOTOR SUPPLY: pectoralis minor (stabilises scapula, raises ribs during inspiration) and lower sternocostal part of pectoralis major (extends, adducts and internally rotates shoulder)

 

MEDIAL CUTANEOUS NERVE OF ARM T1

  • ORIGIN: medial cord of the brachial plexus
  • SENSORY SUPPLY: skin of lower third of medial arm
  • MOTOR SUPPLY: none

 

MEDIAL CUTANEOUS NERVE OF FOREARM C8

  • ORIGIN: medial cord of the brachial plexus
  • SENSORY SUPPLY: skin over biceps muscle, antecubital fossa and medial forearm
  • MOTOR SUPPLY: none

NERVES OF THE BRACHIAL PLEXUS: THE TERMINAL BRANCHES

These are the five most important ones for your exams! I’ve summarised them here and also provided a separate, more detailed article on the nerve supply to the upper limb (with its own summary diagram!) here.

MUSCULOCUTANEOUS NERVE C5/C6/C7

  • ORIGIN: lateral cord of the brachial plexus
  • SENSORY SUPPLY: lateral forearm
  • MOTOR SUPPLY: anterior compartment of arm: biceps (flexes elbow, supinates forearm), brachialis (flexes elbow) and coracobrachialis (adducts shoulder, flexes elbow)
  • CLINICAL SIGNIFICANCE: musculocutaneous nerve injuries are rare, but result in very weak elbow flexion and weak forearm supination which can be very disabling.

 

AXILLARY NERVE C5/C6

  • ORIGIN: posterior cord of the brachial plexus
  • SENSORY SUPPLY: “sergeant’s patch” over lower deltoid
  • MOTOR SUPPLY: deltoid (abducts, flexes and extends shoulder) and teres minor (stabilises and externally rotates shoulder)
  • CLINICAL SIGNIFICANCE: the axillary nerve may be injury by shoulder dislocations or proximal humeral fractures, resulting in numbness over the sergeant’s patch and profound weakness of shoulder abduction from 15-90°. Other examination findings include deltoid wasting and weakness of shoulder flexion, extension and external rotation.

 

RADIAL NERVE C5/C6/C7/C8/T1

  • ORIGIN: posterior cord of the brachial plexus
  • SENSORY SUPPLY: posterior arm and forearm, lateral ⅔ of dorsum of hand and proximal dorsal aspect of lateral 3½ fingers
  • MOTOR SUPPLY: the radial nerve supplies the posterior compartment of arm, which contains triceps (extends and adducts shoulder, extends elbow). It also supplies the entirety of the posterior compartment of the forearm. This consists of 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 (extend and adduct wrist), extensor digitorum, extensor pollicis longus and brevis, extensor indicis and extensor digiti minimi (extend thumb and fingers at MCPJs and IPJs) and abductor pollicis longus (abducts thumb).
  • CLINICAL SIGNIFICANCE: radial nerve injuries are commonly due to compression, for example by leaning or lying on the arm for extended periods, excessively tight plaster casts or prolonged tourniquet use. It can also be damaged by fractures of the humerus or radius, or by stab wounds. Radial nerve injury results in loss of innervation to the muscles of the posterior compartments of the arm and forearm. This manifests as numbness in the radial nerve distribution and a “wrist drop” deformity with very weak extension of the elbow, wrist and fingers.

 

MEDIAN NERVE C5/C6/C7/C8/T1

  • ORIGIN: lateral and medial cords of the brachial plexus
  • SENSORY SUPPLY: thenar eminence, lateral ⅔ palm of hand, palmar aspect of lateral 3½ fingers, and dorsal fingertips of lateral 3½ fingers
  • MOTOR SUPPLY: all muscles of anterior compartment of forearm EXCEPT flexor carpi ulnaris and the medial two parts of flexor digitorum profundus. The median nerve therefore supplies pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum superficialis, the lateral two parts of flexor digitorum profundus, flexor pollicis longus and pronator quadratus. These forearm muscles flex the wrist, the proximal interphalangeal joints of all four fingers and the distal interphalangeal joints of the index and middle fingers. They also pronate the forearm and abduct the wrist. The median nerve also supplies the LOAF muscles of the hand: the lateral two lumbricals, opponens pollicis,  abductor pollicis brevis and flexor pollicis brevis. The lumbricals flex the MCPJs and extend the IPJs of the index and middle finger. The muscles of the thenar eminence flex, abduct and oppose the thumb.
  • CLINICAL SIGNIFICANCE: the median nerve is most commonly damaged by compression within the carpal tunnel at the wrist, resulting in numbness of the median nerve distribution to the hand, wasting of the thenar eminence, weak grip strength and a “hand of benediction” deformity due to an inability to flex the index or middle fingers. It can also be injured by supracondylar fractures of the humerus and stab wounds or lacerations to the forearm or wrist.

 

ULNAR NERVE C8/T1

  • ORIGIN: medial cord of the brachial plexus
  • SENSORY SUPPLY: hypothenar eminence, medial ⅓ palm of hand, palmar aspect of lateral 1½ fingers, medial ⅓ dorsum of hand and dorsal aspect of medial 1½ fingers
  • MOTOR SUPPLY: the ulnar nerve supplies just two muscles in the anterior compartment of the forearm: flexor carpi ulnaris, which flexes and adducts the wrist, and the medial two parts of flexor digitorum profundus, which flex the DIPJs of the ring and little fingers. It also supplies all of the intrinsic muscles of the hand EXCEPT the LOAF muscles supplied by the median nerve. These can be remembered as the HILA muscles: hypothenar eminence, interossei, medial two lumbricals and adductor pollicis. The hypothenar eminence consists of opponens digiti minimi, flexor digiti minimi brevis and abductor digiti minimi, which oppose, flex and abduct the little finger respectively. The palmar interossei adduct the fingers, whilst the dorsal interossei abduct them. The medial two lumbricals flex the MCPJs and extend the IPJs of the ring and little fingers. Adductor pollicis adducts the thumb – it is worth noting that this muscle does not form part of the thenar eminence and actually lies deep beneath it as a separate structure.
  • CLINICAL SIGNIFICANCE: the ulnar nerve may be injured by supracondylar fractures of the humerus, medial epicondylar fractures, stab wounds to the forearm or wrist, or compression at either the cubital tunnel in the elbow or Guyon’s canal in the wrist. This results in numbness in the ulnar distribution to the hand, wasting of the hypothenar eminence and intrinsic muscles of the hand, a “claw hand” deformity due to an inability to extend the ring and little fingers, and weak finger abduction and adduction.

REAL ANATOMY: PROSECTED SPECIMENS

This labelled prosection specimen really nicely sums up all the parts of the brachial plexus:

brachial plexus

Labelled prosection showing the parts of the brachial plexus
(
image from http://tinyurl.com/ojluc8n)

Here is an awesome in-depth video review of the anatomy of the axilla from jono03 on YouTube, which begins with a thorough breakdown of the brachial plexus and a systematic approach to finding all the branches. It really is a fabulously thorough bit of teaching, and its creator has lots of other dissection videos available on his channel that would be great to bookmark for revision purposes. Remember, the “M” shape is the key to unlocking which nerves are which!

 

Here is another wonderfully concise video from RocketdoggyVT on YouTube, which walks you through a good quality prosection of the brachial plexus and shows you pretty much all of the nerve branches. As an added bonus, he also shows you the axillary artery and its branches.

REAL ANATOMY: RADIOLOGY

The brachial plexus is usually assessed using an MRI scan, which is the best imaging method for looking at soft tissues. Here are some images of a normal brachial plexus, and some interesting pathological cases. See how many of the parts you can identify on the scans!

This coronal MRI scan shows the normal appearance of the brachial plexus – you can see the C5, C6 and C7 nerve roots emerging from the vertebrae and converging further down into the trunks, divisions and roots.
(image from Chhabra et al 2012 – full article available at http://tinyurl.com/nmf3bbk)

This MRI shows a patient who recently underwent neck surgery. The C5 and C6 nerve roots have been completely severed (neurotmesis) and there is evidence of post-traumatic neuroma formation at their ends. The patient was treated with nerve transfer surgery.
(image from Chhabra et al 2012 – full article available at http://tinyurl.com/nmf3bbk)

MRI plexiform neurofibromas of brachial plexus

This MRI of a patient with neurofibromatosis type 1 (NF1) shows large plexiform neurofibromas of both brachial plexuses, affecting nerve roots C5, C6, C8, T1 and T2.
(image from Paradowski et al 2005 – available from http://tinyurl.com/p3q6vwe)

MRI peripheral nerve sheath tumour of upper trunk

This MRI shows a malignant peripheral nerve sheath tumour (neurosarcoma) of the upper trunk of the brachial plexus.
(image from Chhabra et al 2012 – full article available at http://tinyurl.com/nmf3bbk)

CT pancoast tumour right lung apex

This coronal CT scan shows a Pancoast tumour in the apex of the right lung, invading the lower brachial plexus. These tumours classically cause Horner’s syndrome and hand muscle wasting.
(image from Mohammad Niknejad on Radiopaedia.org – available from http://tinyurl.com/npyptdl)

REAL ANATOMY: SURGICAL

Severe brachial plexus injuries can be treated successfully with nerve grafts or nerve transfers. This video from NEUROSURGERY Journal on YouTube shows a double fascicular nerve transfer for a patient who sustained a severe upper brachial plexus injury during a car accident. The video outlines the procedure and shows the preoperative examination findings, including wasting of deltoid and biceps muscles, inability to flex the elbow, and preservation of wrist and hand movements. It then shows a clear dissection of the distal brachial plexus with isolation of the musculocutaneous, median and ulnar nerves – the fibres look so much nicer in real life than they do in prosections! The surgeons demonstrate stimulation of nerve fibres to produce different wrist and hand movements. Appropriate fibres from the median and ulnar nerves are then selected and used to reconstruct the musculocutaneous nerve supply to the biceps and brachialis muscles using microsurgical techniques.

 

CLINICAL ANATOMY: OSCE EXAMINATION + BRACHIAL PLEXUS INJURIES

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

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BRACHIAL PLEXUS INJURIES

It is possible for the brachial plexus to be injured at the level of the cervical nerve roots or trunks in the neck, causing a syndrome of neurological deficits and clinical features. The most common three you’ll need to know about are Erb’s palsy, Klumpke’s palsy and Horner’s syndrome. Brachial plexus injuries are rare, but are often used in exams to test your anatomical knowledge! I will just summarise the key features below so you don’t lose the will to live entirely.

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.
    • neurotmesis – the nerve fibre 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
  • post-traumatic neuroma – a growth of scar tissue at the site of a previous nerve injury, which leads to compression

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UPPER BRACHIAL PLEXUS INJURY: ERB’S PALSY

  • SITE OF INJURY: superior trunk of the brachial plexus (C5/C6) – occasionally the middle trunk (C7) is also involved
  • MECHANISM: traction injury due to excessive lateral neck flexion towards the contralateral side, or excessive shoulder depression, resulting in violent stretching +/- tearing of the upper portion of the brachial plexus
  • CAUSES: the classical cause is a traction injury during difficult or obstructed childbirth, such as shoulder dystocia requiring emergency forceps delivery, or breech presentations with the arms raised above the head. The stretching mechanism can also be caused by falls onto the neck/shoulder or excessive traction on the arm, for example during sports (often known as “burner syndrome”), motorbiking accidents or attempts to reduce a shoulder dislocation. It can also result from direct trauma by clavicle fractures, gunshot wounds or stab injuries.
  • NERVES INJURED: musculocutaneous, axillary and suprascapular nerves, and nerve to subclavius
  • CLINICAL FEATURES: Erb’s palsy results in loss of sensation to the skin over the “sergeant’s patch”, lateral arm and lateral forearm. There is wasting of the deltoid, supraspinatus and infraspinatus muscles and the anterior compartment of the arm, with loss of shoulder abduction and external rotation, elbow flexion and wrist supination. This results in a “waiter’s tip” deformity characterised by a limp, adducted, internally rotated shoulder, an extended elbow and a pronated wrist. Biceps reflex is absent. Wrist flexion, wrist extension and finger movements are usually preserved. If C7 is involved, elbow and wrist extension will also be diminished and the wrist may be held in fixed flexion. Severely affected untreated babies may be left with stunted arm growth, joint contractures and circulatory problems.

Clinical photographs showing Erb’s palsy in a baby and an adult. You can clearly see the waiter’s tip deformity, and in the adult the wasting of the deltoid and biceps muscles is much more prominent.
(images from Heise et al 2015 http://tinyurl.com/pewjkxr and www.with-trauma.com)

LOWER BRACHIAL PLEXUS INJURY: KLUMPKE’S PALSY

  • SITE OF INJURY: inferior trunk of the brachial plexus (C8/T1)
  • MECHANISM: traction injury due to excessive force placed on an abducted shoulder results in violent stretching +/- tearing of the lower portion of the brachial plexus
  • CAUSES: Klumpke’s palsy is the rarest brachial plexus syndrome. The most common cause is a traction injury during difficult childbirth, such as an arm presentation requiring force on the arm to successfully deliver the rest of the baby. The same mechanism can also be caused by a falling person grabbing onto something, e.g. grabbing a branch when falling from a tree, or by other causes of excessive abduction such as motorbiking accidents. Direct trauma can result from clavicle fractures, gunshot wounds or stabbings. It can also be caused by compression of the lower plexus by a mass in the root of the neck, such as lymphoma or lung cancer.
  • NERVES INJURED: median and ulnar nerves
  • CLINICAL FEATURES: Klumpke’s palsy results in loss of skin sensation in the median and ulnar distributions of the hand – the sensory supply to the lateral dorsum of the hand is preserved as this comes from the radial nerve. There is also loss of sensation in medial forearm and arm. The injury affects the motor nerve fibres to all small intrinsic muscles of the hand. There is therefore generalised wasting of hand muscles with a loss of MCPJ flexion, IPJ extension, finger abduction and adduction, and opposition. The anterior compartment of the forearm is also affected, resulting in loss of wrist flexion. This results in a “claw hand” deformity affecting all four fingers, characterised by IPJ flexion and MCPJ hyperextension at rest, and an inability to extend the fingers. The wrist is classically held supinated. Shoulder and movements are usually preserved. T1 injuries may be associated with Horner’s syndrome, and there may be associated superior/middle trunk injuries. Interestingly, the godmother of British baking Mary Berry has a claw hand deformity of her left hand due to childhood polio – clearly it doesn’t stop her making awesome cakes!
Mary Berry (the nation's grandma) has a claw hand deformity due to childhood polio - you would also see this with Klumpke's palsy

Mary Berry, the nation’s grandma, has a left claw hand deformity due to childhood polio – you would also see this with Klumpke’s palsy (image from Marie Claire)

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TOTAL/COMPLETE BRACHIAL PLEXUS INJURY

  • SITE OF INJURY: entire brachial plexus C5/C6/C7/C8/T1
  • MECHANISM: usually severe or complex traction injuries sustained during difficult childbirth or high speed road traffic accidents, resulting in violent stretching +/- tearing of all nerve roots
  • NERVES INJURED: entire brachial plexus
  • CLINICAL FEATURES: totally limp, dangling, atrophied and numb upper limb with associated Horner’s syndrome

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HORNER’S SYNDROME

  • SITE OF INJURY: T1 nerve root
  • MECHANISM: any injury to the T1 nerve root associated with loss of sympathetic function
  • CAUSES: acquired Horner’s syndrome may be due to a traction injury, direct trauma, cerebral pathology or extrinsic compression. The classical cause in exams is usually a Pancoast tumour in the apex of the lung.
  • NERVES INJURED: T1 nerve root, sympathetic trunk or stellate ganglion
  • CLINICAL FEATURES: Horner’s syndrome causes loss of sympathetic nerve supply to the face and neck. The key features are ipsilateral partial ptosis (drooping eyelid), miosis (constricted pupil), anhidrosis (loss of sweating on affected side of face), dilatation lag (slowly dilating pupil) and enophthalmos (eye appears sunken). With traction injuries there may be associated Klumpke’s palsy. With nerve root compression there may be associated hand/arm pain and wasting of the intrinsic muscles of the hand – this should trigger alarm bells for an underlying malignancy!

 

THORACIC OUTLET SYNDROME

  • SITE OF INJURY: trunks of brachial plexus, classically the inferior trunk but can affect any or all of the trunks
  • MECHANISM: compression of neurovascular structures at the level of the thoracic outlet between the root of the neck and the upper thorax. The thoracic outlet is bounded by the scalene muscles, the first rib, and the clavicle.
  • CAUSES: may be due to a congenital fibrous tissue band, cervical rib or musculoskeletal abnormality, or an acquired pathology such as whiplash trauma, repetitive strain/sports injury, malunion of a clavicular fracture, or an underlying malignancy such as lymphoma or lung cancer.
  • NERVES INJURED: classically the ulnar nerve, but may affect any combination of nerves supplying the upper limb. In about 5% of cases, compression may also affect the subclavian artery and/or vein which run with the trunks through the thoracic outlet.
  • CLINICAL FEATURES: thoracic outlet syndrome leads to a combination of neurological and vascular symptoms. Neurological features include wasting of the intrinsic muscles of the hand with reduced grip strength, and some patients may experience numbness or paraesthesia. Some patients report neuropathic pain affecting the arm, shoulder and neck. Vascular symptoms tend to be brought on or exacerbated by vigorous overhead activities, such as lifting or throwing. Subclavian artery compression causes aching or painful claudication of the arm, pallor and extreme cold; severe cases may lead to ischaemia with ulceration and gangrene. Subclavian vein compression can result in diffuse arm pain and swelling, venous distension and cyanosis. Venous obstruction may lead to thrombosis of the subclavian or axillary veins, which is known as Paget-Schroetter syndrome.

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BRACHIAL NEURITIS/PLEXITIS

  • SITE OF INJURY: any part of brachial plexus – may affect individual nerves/cords or entire plexus
  • MECHANISM: inflammatory reaction against the nerves of the brachial plexus
  • CAUSES: brachial neuritis may be idiopathic (Parsonage-Turner syndrome). Commonly recognised triggers include bacterial, viral or parasitic infections, immunisations, trauma, childbirth, recent surgery or radiotherapy, and systemic inflammatory disorders such as lupus, polyarteritis nodosa or other types of vasculitis. It may also occur as part of a polyneuropathy, such as Guillain-Barre syndrome or motor neurone disease, or as a paraneoplastic syndrome associated with lymphoma.
  • NERVES INJURED: any component of brachial plexus
  • CLINICAL FEATURES: brachial neuritis classically starts with sudden onset of excruciating shoulder and arm pain on the affected side, followed by the development of paralysis and atrophy of affected muscle groups within a couple of weeks. The onset of symptoms may be preceded by prodromal symptoms of a systemic infection, or another immunological trigger such as trauma, surgery or immunisation. The syndrome is particularly associated with hepatitis E virus infection – occurring bilaterally in up to 10% of cases. Patients usually present acutely due to the severity of the pain, and tend to support the affected arm in an adducted, internally rotated position. The phrenic nerve or lower cranial nerves may also be affected in a minority of cases.

SUMMARY

I hope you found this guide helpful and now feel able to approach this nightmarish subject with confidence. As long as you remember to look for the “M” shape, you should be totally fine. Once you have triumphed over the brachial plexus, you have officially won at anatomy forever. Good luck, and may the forceps be with you!

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brachial plexus diagram

REFERENCES

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