Axilla and Brachial Plexus

Learning Objectives

After reading this post you will know:

  • Boundaries of axilla.
  • Contents of axilla.
  •  Groups of Axillary lymph nodes
  • Formation, parts and brancjes of brachial plexus.
  • Erb’s and Klumpke’s palsy.
  • Branches of axillary artery
  • Axillary lymph nodes and area drained by them.

 BOUNDARIES AND CONTENTS OF AXILLA

  Q. Which structures form  the boundaries of axilla?

   Ans. Axilla is a four sided pyramidal space situated  between the upper part of the arm and  upper  part of lateral thoracic  wall.

 Boundaries:Boundaries and contents of axilla

  1. Apex ; Is directed upwards and medially and is formed by cervicoaxillary  canal via which it communicates with the posterior triangle of neck .
    • Boundaries of cervicoaxillary canal are:
      • Anteriorly: middle third of clavicle.
      • Posteriorly: superior border of scapula.
      • Medially: outer border of 1st rib.
  2. Base: Skin , superficial fascia and dome shaped axillary fascia
  3. Anterior wall : Is formed by pectoralis major, clavipectoral fascia enclosing pectoralis minor and subclavius muscles.
  4. Posterior wall : Is formed by subclavius, teres major and latissimus dorsi..
  5. Medial wall : Is formed by upper four ribes and intercostals muscles, upper  four digitations of serratus anterior.
  6. Lateral wall: Is formed by upper part of humerus ( intertubercular sulcus)  with long head of biceps brachii and short head of biceps brachii and coracobrachialis muscle.

  Q. Enumerate the contents of axilla. 

Ans. Contents of axilla

  1. Axillary artery & its branches
  2. Axillary vein & its tributaries
  3. Axillary lymph nodes
  4. Axillary tail of mammary gland ( tail of Spence)
  5. Cords of brachial plexus
  6. Long thoracic nerve
  7. Intercostobrachial nerve
  8. Axillary fat & areolar tissue.

Q. Draw a labelled diagram to show the various groups of axillary lymph nodes.

axillary lymph nodes

Q. Where should the incision be placed to drain axillary abcess.

A. The safe site to place incision is midway between the anterior and posterior  margins of base of axilla, close to the  medial wall.

BRACHIAL PLEXUS

Q. Describe brachial plexus under the  following  headings:

  1. Formation
  2. Parts
  3. Location  of parts of brachial plexus
  4. Branches
  5. Structures supplied by branches of brachial plexus

     A. a. Formation : Is formed by the ventral ramii of C5- C8 and T1 spinal nerves.

  • Prefixed plexus : if there is contribution from C4 spinal nerve
  • Postfixed plexus : if there is contribution from T2 spinal nerv

b. Components:

  1. Roots – ventral ramii of C5-C8 & T1 spinal nerves
  2. Trunks – Three
  • Upper trunk – C5 & C6 roots join to form upper trunk
  • Middle trunk – C7 root forms middle trunk
  • Lower trunk – C8 & T1 roots join to form lower trunk

iii. Divisions : Each trunk divides into anterior (ventral)  and posterior (dorsal)  divisions.

iv. Cords : Three

  • Lateral cord – anterior divisions of upper and middle trunk join to form lateral cord.
  • Medial cord – anterior division of lower trunk forms medial cord.
  • Posterior cord – posterior divisions of all the three trunks join to form posterior cord..

c. Location: Brachial plexus is divided into two parts:

  • Supraclavicular Part lies in the posterior triangle of neck. It comproses of roots and trunks of brachial plexus.
  • Infraclvicular  Part lies in the axilla. It comprises of cords of brachial plexus.

*Divisions are located behind the clavicle.

Formation and Branches of Brachial Plexus                                   brachial plexus

    d. Branches of brachial plexus

From the roots :

  • Dorsal scapular nerve (C5)
  • Long thoracic nerve ( C5,C6,C7)

From the upper trunk:

  • Suprascapular nerve ( C5, C6)
  • Nerve to subclavius (C5,C6)

 From the three cords of brachial plexus.

  Branches of lateral cord – Three

  • Lateral pectoral nerve ( C5-7)
  • Lateral root of median nerve (C5-7)
  • Musculocutaneius nerve (C5-7)

   Branches of medial cord –  Five

  • Medial pectoral nerve (C8,T1)
  • Medial cutaneous nerve of arm (C8,T1)
  • . Medial cutaneous nerve of forearm (C8,T1)
  • Medial root of median nerve (C8,T1)
  • Ulnar nerve (C8,T1)

Branches of posterior cord – Five

  • Upper subscapular nerve (C5,C6)
  • Lower subscapular nerve (C5,C6)
  • Thoracodorsal nerve (C6-8)
  • Axillary nerve (C5,C6)
  • Radial nerve (C5-8, T1)

Structures Supplied by Branches of Brachial Plexus.

Part of brachial plexusNerveStructures supplied/Distribution
Roots Dorsal Scapular Rhomboidus mjor and minor and levator scapulae muscles
Roots Long thoracic Serratus anteriormuscle
Upper trunkNerve to subclavius subclavius muscle
Upper trunkSuprascapularSupraspinatus, infraspinatus, muscle and glenohumeral joint
Lateral cordLateral pectoral pectoralis major & pectoralis minor
Lateral cordMusculocutaneousa.Muscles of anterior /flexor compartment of arm : cobrachialis biceps brachii, and brachialis,
b. Continues as l ateral cutaneous nerve of forearm.
Medial cordMedial pectoral Pectoralis minor and pectoralis major
Medial cordMedian6 ½ flexor muscles in forearm (except ), and five hand muscles and skin of lateral 1/3 rd of palm & lateral 1 ½ digits
Medial cordMedian cutaneous nerve of armSupplies skin on medial side of arm
Medial cordMedian cutaneous nerve of forearmSupplies skin over medial side of forearm
Medial cordUlnar1 ½ flexor muscles in forearm(flexor carpi ulnaris, ulnar half of flexor digitorum profundus), 15 muscles in hand ( adductor pollicis, all hypothenar muscles, all dorsal and palmar interrossei) and skin of medial 1/3 rd of palm and palmar surface of medial 1 ½ digits.
Posterior cordUpper subscapular Upper part of subscapularis
Posterior cordThoracodorsalLatissimus dorsi
Posterior cordLower subscapular Inferior part of subscapularis and teres major
Posterior cordAxillary Deltoid & teres minor , Shoulder joint joint, and skin over inferior part of deltoid
Posterior cordRadialAll the muscles of extensor compartment of arm and forearm: triceps brachii, anconeus, brachioradialis, extensor muscles of forearm; supplies skin on posterior aspect of arm and forearm via posterior cutaneous nerves of arm and forearm, lateral 2/3d of dorsum of hand and lateral 3 1/2 digits till bed..

Q. Describe briefly:

  1. Erb’s point and Erb’s paralysis
  2. Klumpke’s paralysis

Brachial plexus Erb's point

A  Erb’s point : Is the region on upper trunk of  brachial plexus where :

  • It is formed by union two roots – Ventral rami of C5&C6
  • It divides into two divisions – anterior and posterior divisions
  • It providesorigin to two nerves – suprascapular and nerve to subclavius.

 

Erb’s paralysis (Erb-Duchenne Palsy) Erb's paralysis

i. Site of lesion – Erb’s point i.e. upper trunk of  brachial plexus(C5,C6).

ii. Cause:  Undue separation of head from the shoulder which may occur in the  following conditions.

  • The most common cause is an abnormal or difficult childbirth ( forceps delivery).
  • When a person falls on shoulder.

iii. Position of  the upper limb:  appears like a Policeman’s or Waiter taking tip.

  • The arm is adducted and medially rotated.
  • The forearm is extended and pronated.
  • Motor loss : muscles paralyzed are biceps brachii, brachialis, brachioradialis and  supinator.
    • supraspinatus and deltoid  (loss of  abduction of arm)
    • infraspinatus and teres minor ( loss of lateral rotation of arm).
    • biceps brachii, brachialis, brachioradialis ( loss of flexion of  forearm).
    • biceps brachii and supinator ( loss of supination of forearm).
  • Sensory loss : loss of sensations from the skin over the lower part of the deltoid (supplied by axillary nerve). 

Klumpke’s paralysis :

i. Site of lesion : Lower trunk of brachial plexus (C8,T1)Klumpke's paralysis

ii.Cause : Undue separation of arm from the  trunk ( abduction injury) which may occur  in the following  conditions.

  • Birth injury
  • Clutching something while falling from the height.

iii. Position of the hand : complete claw hand

  • hyperextension at metacarpophalangeal joints
  • flexion at interphalangeal joints.
  • Motor loss : Intrinsic muscles of the hand are paralyzed.
  • Sensory loss: Loss of sensations from a  narrow zone along the medial side of  hand  and forearm.
  • Horner’s syndrome : due to involvement of sympathetic fibers of T1 spinal nerve. Following are the clinical signs in Horner’s syndrome:
    • Partial Ptosis – drooping of eylied ( due to paralysis of a part of  levator palpabrae superioris that is supplied by sympathetic fibers).
    • Miosis – constiction of pupil ( due to paralysis of dilator pupillae that is supplied by sympathetic fibers).
    • Anhydrosis –  decreased sweating.
    • Enophthalmos – posterior displacement of the eye.

Characteristic features of Horner syndrome are:

  • Partial ptosis ( drooping of upper eyelid)
  • Miosis ( constriction of pupil)
  • Anhydrosis ( absence of sweat)

AXILLARY ARTERY

Q. Enumerate the branches of axillary artery.Axillary arter and its branches

A. Axillary artery extends from outer border of 1st rib to the lower border of teres   major. It is divided into three parts by   pectoralis minor muscle. Branches of  the three parts are as follows :

  1. First part ( proximal to pectoralis minor) :
  • Superior thoracic artery

     b. Second part( deep to pectoralis minor);

  • Thoracoacromial artery
  • Lateral thoracic artery

     c. Third part (distal to pectoralis minor):

  • Anterior circumflex humeral artery
  • Posterior circumflex humeral artery
  •  Scapular artery

 

 

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