1 The Axilla and Brachial plexus Prof. AO Ihunwo, PhD School of Anatomical Sciences
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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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