Shoulder, axilla, and brachial plexus

Summary

Shoulder girdle (pectoral girdle)

The shoulder girdle is composed of the two bones (clavicle and scapula) and two joints (acromioclavicular and sternoclavicular joints) that connect the upper limb to the trunk.

Bones of the shoulder girdle

Clavicle

Scapula

Joints of the shoulder girdle

Sternoclavicular joint

Acromioclavicular joint (AC joint)

Scapulothoracic joint

Movements of the shoulder girdle

References:[1][2]

Shoulder joint (Glenohumoral joint)

Shoulder joint (Glenohumeral joint)

Bone structures associated with the glenohumeral joint differ in size. The head of the humerus is approximately four times larger than the joint socket of the scapula. The result is a greater range of motion but also joint instability!

Muscles of the shoulder joint

Rotator cuff

Muscle

Origin

All originate from the scapula

Insertion

All insert into the humerus

Function

All movements occur at the shoulder joint

Innervation
Supraspinatus
  • Abduction of the arm (from 0°–15°)
Infraspinatus
  • External rotation of the arm
Teres minor muscle
  • Axillary (lateral) border of the scapula
  • Adduction of the arm
  • External rotation of the arm

Subscapularis

  • Internal rotation of the arm
  • Subscapular nerves

Fascial slings of the pectoral girdle

  • Fascial slings are made up of several functionally antagonistic muscles.
  • There are four fascial slings in the shoulder region, which move the scapula in different directions (oblique sling, horizontal sling, anterior vertical sling, and posterior vertical sling).
  • The trapezius muscle is divided into three parts (anterior, transverse, and descending) that have different functions

Oblique sling

Name Anatomy Innervation Function Special characteristics

Rhomboid muscles

  • Scapula: elevation and retraction
  • Lateral angle of the scapula: caudal rotation

Serratus anterior

  • Origin: Ribs 1–9
  • Insertion
    • Superior angle of scapula (superior part)
    • Medial border of scapula (middle and inferior part)
    • Inferior angle of scapula (inferior part)
  • Scapula: protraction (i.e., pulls the scapulae forward as in a punching action)
  • Inferior angle of the scapula: cranial rotation
  • Maintains position of the medial border and inferior angle of the scapula in contact with the thoracic wall

Horizontal sling

Muscle Anatomy Innervation Function
Transverse part of the trapezius

The serratus anterior muscle is part of both the oblique and horizontal slings!

Anterior vertical sling

Muscle Anatomy Innervation Function
Pectoralis minor
  • Scapula: depression and protraction
  • Lateral angle of scapula: downward rotation
  • Accessory muscle of respiration
Descending part of trapezius
  • Scapula: retraction (adduction) and depression
  • Overhead abduction of the arm

Posterior vertical sling

Name Origin Innervation Function
Levator scapulae
  • Scapula: elevation (shrugging)
  • In conjunction with the rhomboid muscles: returning the elevated arm to its neutral position.

Ascending part of the trapezius

(upper fibers)

  • Scapula:
    • Adduction (pulls the scapula medially)
    • Overhead abduction of the arm

Muscles of the shoulder that insert into the arm

  • In addition to the antagonistic fascial slings, the shoulder is brought to motion by other muscles that insert into the arm.
  • The deltoid muscle primarily forms the contour of the shoulder.
Muscle Anatomy Innervation Function
Ventral muscles

Pectoralis major

(forms the anterior axillary fold)

  • Adduction, internal rotation, anteversion
  • Accessory muscle of respiration
Coracobrachialis
  • Anteversion, adduction, internal rotation
Lateral muscle Deltoid
  • Clavicular part: anteversion, internal rotation, adduction
  • Acromial part: abduction
  • Spinal part: retroversion, external rotation, adduction
Dorsal muscles

Latissimus dorsi muscle

(forms the posterior axillary fold)

  • Adduction, internal rotation, retroversion
  • Also called the “coughing muscle”
  • Accessory muscles of respiration
Teres major muscle
  • Thoracodorsal and/or subscapular nerve
  • Adduction, internal rotation, retroversion

Other muscles involved in shoulder motion

Name Anatomy Function Innervation Special characteristics
Subclavius muscle
  • Depresses the shoulder and lateral end of the clavicle
Biceps brachii
  • Long head: shoulder abduction
  • Short head: shoulder adduction
  • Both: internal rotation of the shoulder
  • None
Triceps brachii
  • Origin: infraglenoid tubercle
  • Insertion: olecranon
  • Radial nerve
  • None

References:[3]

The axilla

Axillary fossa

The anterior axillary fold is formed from the pectoralis major muscle and the posterior axillary fold from the latissimus dorsi muscle!

Axillary contents

Axillary artery

Axillary vein

Axillary lymph node groups

  • Anterior group (pectoral): drain mammary and pectoral regions
  • Posterior group (subscapular): drain the upper back and posterior neck
  • Lateral group (humeral): drain the upper limb
  • Central group (lies in axillary fat): receives lymphatics from the anterior, posterior, and lateral groups
  • Apical group (lies behind the pectoralis minor): receives lymphatics from the central group and upper outer quadrant of the breast

Brachial plexus

The main branch of the lateral cord is the musculocutaneous nerve
The main branch of the medial cord is the ulnar nerve
The main branches of the posterior cord are the radial nerve and axillary nerves
Branches from the medial and lateral cords form the median nerve

Axillary spaces

Medial axillary space

A triangular space and with a cranial, caudal, and lateral border and apex facing medially (no medial border)

Lateral axillary space

A quadrangular space

Triangular interval

A triangular space with a cranial, lateral, and medial border and apex facing caudally (no caudal border)

A simple trick for remembering the structures at the borders of the axillary spaces is to simulate them with the middle and index fingers of both hands. Form a victory sign with both hands and superimpose them at ∼ 90°. Three spaces are created that simulate the axillary spaces.

References:[4][5]

Clinical significance

  • 1. Standring S. Gray's Anatomy: The Anatomical Basis of Clinical Practice. Elsevier Health Sciences; 2016.
  • 2. Waldman SD. Atlas of Uncommon Pain Syndromes. Elsevier Health Sciences; 2013.
  • 3. Nawa S. Scapular winging secondary to apparent long thoracic nerve palsy in a young female swimmer. J Brachial Plex Peripher Nerve Inj. 2015; 10(1): pp. e57–e61. doi: 10.1055/s-0035-1567806.
  • 4. Murphy A, Hoskins A. Axillary Vein. https://radiopaedia.org/articles/axillary-vein-1. Updated January 1, 2018. Accessed November 18, 2018.
  • 5. Pacifici S. Axillary Nodes. https://radiopaedia.org/articles/axillary-nodes. Updated January 1, 2018. Accessed November 18, 2018.
last updated 12/03/2019
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