Axilla

Axilla is the area that lies underneath the glenohumeral joint. It is significant because it contains the axillary artery and the neurovascular bundle known as brachial plexus.

Borders

  • Pyramid shaped (with apex & 5 other borders)
  • Apex (axillary inlet) – lateral border of 1st rib, superior border of scapula & posterior border of clavicle
  • Lateral wall – intertubercular groove of humerus
  • Medial wall – serratus anterior & thoracic wall
  • Anterior wall – pectoralis major, pectoralis minor & subclavius muscles
  • Posterior wall – subscapularis, teres major, latissimus dorsi
    Screenshot 2018-12-14 at 19.50.23.png
    Fig 1. Anterior view of the axilla

    Screenshot 2018-12-14 at 19.50.32.png
    Fig 2. Transverse view of the axilla

Deltoid

  • Has anterior, middle and posterior parts
  • Origin – scapula & clavicle
  • Insertion – deltoid tuberosity on lateral surface of humerus
  • Innervation – axillary nerve (C5-C6)
  • Action
    • anterior fibres – flexion & medial rotation
    • middle fibres – major ABDuctor of arm (15-90 degrees with the help of supraspinatus)
    • posterior fibres – extension & lateral rotation

Teres major

  • Origin – dorsal surface of inferior angle of scapula
  • Insertion – medial lip of intertubercular groove of humerus
  • Innervation – lower subscapular nerve (C5-C6)
  • Action – extension, ADDuction & medial rotation of arm
Screenshot 2018-12-14 at 20.02.37.png
Fig 3. Deltoid & teres major muscles

Axillary artery

  • Become axillary artery from subclavian artery when it emerges from beneath the clavicle & crosses the 1st rib.
  • Continues as brachial artery once reaches inferior border of teres major muscle.
  • Provides blood to all shoulder muscles
Screenshot 2018-12-14 at 20.08.42.png
Fig 4. The axillary artery

Brachial plexus

IMG_3652.JPG
Fig 5. Brachial plexus

Two good mnemonic I use are “Rugby Teams Drink Cold Beer” – to remember the roots, trunks, divisions, cords and branches!

Another good mnemonic is “Most Alcoholics Must Really Urinate” – to remember the order of the nerve branches

  • Musculocutaneous nerve
    • Supplies anterior flexor compartment of arm
    • Injury = inability to flex elbow
  • Axillary nerve
    • Behind surgical neck of humerus
    • Supplies deltoid & teres minor
    • Injury = usually surgical neck fracture, loss of ABDuction of shoulder from 15-90 degrees
  • Median nerve
    • Anterior to the elbow, runs between two heads of the pronator teres
    • Supplies lateral flexors of the wrist, 2 lateral lumbricals & thenar eminence (via recurrent branch)
    • Injury = usually carpal tunnel syndrome, supracondylar fractur or lunate dislocation; common signs are resulting in “hand of benediction”, thenar eminence atrophy
  • Radial
    • Runs in radial groove in posterior humerus
    • Supplies triceps, brachioradialis & extensors of the wrist
    • Injury = fracture to body of humerus, Saturday night palsy, resulting in “wrist drop”
  • Ulnar
    • Posterior to medial epicondyle, superficial to flexor retinaculum
    • Supplies medial flexors of wrist, 3rd & 4th lumbricals, interosseous muscles, hypothenar eminence
    • Injury = medial epicondyle fracture or fracture of hook of hamate; results in inability to ABD/ADDuct fingers, hypothenar atrophy or “ulnar claw hand”
Screenshot 2018-12-14 at 21.09.41.png
Fig 6. Common clinical signs of brachial plexus nerve injuries

This video is a great quick resource that summarises everything.

Although this is a paediatric EM resource, I find this is still helpful to use in adults & an easy way to remember!

Screenshot 2018-12-14 at 21.05.39.png
Fig 7. Easy ways to test brachial plexus nerves

Erb’s palsy

  • C5/C6 injury
  • Usually resulting from trauma or traumatic birth
  • Limb handing by the side, medially rotated with pronated forearm

Klumpke’s palsy

  • C8-T1
  • Usually pancoast tumour, traumatic birth
  • Radial, ulnar and median nerves affected – all fingers clawed, loss of all lumbricals

References

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