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The Axilla and

Brachial plexus

Prof. AO Ihunwo, PhD School of Anatomical Sciences

Lecture Outline

Axilla

Introduction

Boundaries

Contents

Brachial Plexus

Spinal Nerves – formation &

Importance

Brachial Plexus

Formation & Components

Relations

Branches

Clinical Implications/Injuries

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Introduction

Pyramidal space between

upper limb & thorax

Communicates with

posterior triangle of neck

Transmits neurovascular

structures & lymph

vessels/nodes

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Boundaries

Anterior: Pectoralis major & minor,

subclavius & clavipectoral fascia

Posterior: Teres major,

subscapularis, Latissmus dorsi

Lateral: Humerus: upper part of shaft

with intertubercular groove

Medial: Serratus anterior (4-5

digitations), intercostal muscle at 4th

intercostal space

Floor (Base): Axillary fascia and skin

Apex: Bounded by clavicle, scapula,

outer border of 1st rib; directed

towards root of neck

Contents of Axilla

Medial wall: Lateral thoracic vessels, lateral

branches of 2-4 intercostal Nn, Long thoracic N

Posterior Wall: Subscapular vessels, posterior

circumflex humeral vessels, Axillary N, Upper & Lower Subscapular Nn, Thoracodorsal N.

Lateral wall: Medial cut. N of arm, axillary vein,

medial cut. N of forearm, Ulnar N, 3rd part of axillary artery, medial root of median N, median N, musculocutaneous N, posterior cord

Other structures: Axillary lymph nodes, fat

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Principles of Limb Plexuses - Introduction

Nerves that form Limb plexuses arise from

spinal cord

Spinal Cord

Long cylindrical structure.

Av. Length in adults – 45 cm

Extent:

Foramen magnum to lower border of L1 vertebra.

Diameter varies at different levels

Presents 2 enlargements

Cervical (C3 to T2) innervates upper limb &

Lumbar (L1 to S3) innervates lower limb

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Spinal Nerves

Spinal nerves consist of

8 Cervical (C1 – C8)

12 Thoracic (T1 – T12)

5 Lumbar (L1 – L5)

5 Sacral (S1 – S5)

1 Coccygeal (Co1)

Note that there is a connection

between all ventral rami of spinal

nerves

C1

C5

T1

T12

L5

Co1

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Formation of spinal nerve from

dorsal & ventral roots

Dorsal ramus: –

innervates skin

muscles &

connectives tissue of

back

Ventral ramus:–

Form nerve plexuses

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Importance of spinal nerves Dermatomes are areas of sensory innervation

on skin for each spinal nerve

Dorsal

Ventral

c7 c6

c8

c3

T1 T3

c3

c5

c6

c8 T1

T3

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Importance of spinal nerves

Myotome refers to muscle(s) that one particular spinal root supplies

Importance

Diagnosis of neurological disorders

lesions of nerve roots result in typical patterns of neurologic defects (muscle weakness, loss of sensation) that allow localisation of causating lesion

Referred pain, especially dermatomes

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Brachial Plexus

Network of nerves from

spinal cord that controls

muscle movements &

sensation in Upper limb

Components

Roots

Trunks

Divisions

Cords

Branches

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Formation of Brachial Plexus

Roots (5): Ventral rami of C5

C6

C7

C8

T1

Prefixed brachial plexus: C4 – C8.

Large contribution from C4 with T2 absent & T1 reduced in size

Postfixed brachial plexus: C6 – T2.

Large contribution from T2 with C4 absent & C5 reduced in size

C1

C5

T1

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Trunks & Divisions

Trunks (3)

Superior trunk: C5 & C6

Middle trunk:

continuation of C7

Inferior trunk: C8 & T1

Divisions (6)

Each trunk splits into

anterior (3) & posterior (3)

divisions

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Cords (3)

Lateral cord: anterior

divisions of upper &

middle trunks

Medial cord: anterior

division of lower trunk

Posterior cord: posterior

divisions of upper, middle

& lower trunks

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Relations of components

Roots: Between anterior &

middle scalene muscles

Trunks: Cross posterior

triangle of neck

Divisions: Behind the

clavicle

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Relations of components…

Cords:

Lie in axilla

Named according to their

relation with 2nd part of axillary

artery

Lateral

Medial

Posterior

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Supraclavicular Branches

Roots:

Muscular (scalene &

longus colli muscles)

Dorsal scapular nerve

Long thoracic nerve

Contribution from C3 to

Phrenic nerve (C3-C5)

Trunks:

Nerve to subclavius

Suprascapular nerve

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Infraclavicular Branches (13)

Lateral cord (3)

lateral pectoral

musculocutaneous

lateral head of medial nerve

Posterior cord (5)

axillary nerve

upper subscapular

middle subscapular

(thoracodorsal)

lower subscapular

radial nerve

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Infraclavicular Branches…

Medial cord (5)

medial cutaneous nerve

of arm

medial cutaneous nerve

of forearm

medial pectoral

medial head of median

nerve

ulnar nerve

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From Nerve Roots Muscles Cutaneous

Roots Dorsal scapular C5 rhomboid muscles &

levator scapulae -

Long thoracic

C5,

C6,

C7

Serratus anterior -

superior

trunk

Nerve to

subclavius

C5,

C6 subclavius -

Suprascapular C5,

C6

Supraspinatus &

Infraspinatus -

Distribution of Supraclavicular Branches

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Distribution of Infraclavicular Branches

From Nerve Roots Muscles Cutaneous

Lateral

cord

lateral

pectoral

C5, C6,

C7

pectoralis major &

pectoralis minor (by

communicating with

medial pectoral nerve)

-

Musculo-

Cutaneous

C5, C6,

C7

coracobrachialis,

brachialis & biceps

brachii

lateral cutaneous

nerve of forearm

Lateral head

(root) of

median nerve

C5, C6,

C7 fibres to median nerve -

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Medial

cord

Medial

pectoral C8, T1

Pectoralis minor &

pectoralis major -

Medial head

(root) of

median nerve

C8, T1 fibres to median nerve portions of hand not served

by ulnar or radial

Medial

cutaneous

nerve of arm

C8, T1 - front & medial skin

of arm

Medial

cutaneous

nerve of

forearm

C8, T1 - medial skin of forearm

Ulnar C8, T1

flexor carpi ulnaris,

medial 2 bellies of

flexor digitorum

profundus,

most of small muscles

of hand

skin of medial side of hand,

medial 1½ fingers on

palmar side

medial 1½ fingers on

dorsal side

Distribution of Infraclavicular Branches…

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Posterior

cord

Upper

subscapular C5, C6 Subscapularis (upper part) -

Middle

subscapular

(thoracodorsal)

C6, C7,

C8 Latissimus dorsi -

Lower

subscapular C5, C6

lower part of subscapularis

& teres major -

Axillary C5, C6

anterior branch: deltoid & a

small area of overlying skin

posterior branch: teres

minor & deltoid muscles

posterior branch

becomes upper lateral

cutaneous nerve of

arm

Radial

C5, C6,

C7, C8,

T1

Triceps brachii, anconeus,

extensor muscles of forearm

& brachioradialis

skin of posterior arm

as posterior cutaneous

nerve of the arm

Distribution of Infraclavicular Branches…

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Clinical Implications

Brachial plexus injuries falls on side of head/shoulders

(violent stretching of nerves)

traction (forceps delivery)

pressures leading to incomplete injuries.

Cords rarely damaged by direct injury

except gunshots & stab wounds.

Efforts to reduce a shoulder joint dislocation could also produce brachial nerve injuries.

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Brachial Plexus Injuries

Superior trunk Injury

(Erb-Duchenne paralysis)

Upper trunk stretches or

tears

Erb’s point

Waiter’s tip position

hanging extended (flexors

paralyzed), in medial rotation

(lateral rotators paralyzed)

Brachial Plexus Injuries…

Inferior trunk injury

Klumpke’s paralysis

‘clawed hand’ deformity

Anesthesia on medial

surface of arm & hand

& paralysis/atrophy of

muscles innervated by

ulnar nerve

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Brachial Plexus Injuries …

Crutch Paralysis

Pressure from usage of

crutches

Mostly affects radial & Ulnar

‘Wrist drop’ deformity

Sleep palsy:

Pressure on radial nerve with

subject asleep under influence

of alcohol or some narcotics.

‘Saturday night palsy’

Usually temporary 27

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Brachial Plexus Injuries …

Winging of the scapula

Long thoracic nerve.

A ‘winged’ appearance on the back.

Inability to raise arm or carry out pushing movements

Cervical rib syndrome

Presence of a cervical rib (C7) may put pressure on lower trunk

Questions

What structures form the boundaries of the axilla.

List the contents of the axilla

Draw a well labelled diagram of the brachial plexus (No

description required)

Describe the formation of the brachial plexus from the

roots to the cords.

Describe the origin and distribution of the ulnar nerve.

What are the effect of injury to the nerve at the

epicondyle. [Could also be median or radial nerves]

Describe the brachial nerve injuries

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