The upper limb bones and shoulder girdle form the superior . Four joints (glenohumeral, sternoclavicular, acromioclavicular, and scapulothoracic) and two bones (the clavicle and scapula) form the shoulder girdle. The glenohumeral joint (i.e., shoulder joint) is one of the most flexible joints in the body and relies on a complex system of muscles, including the rotator cuff, to keep it in shape and enable mobility. Branches of the subclavian and axillary arteries supply the entire upper extremity. Veins of the upper extremity drain into the axillary vein, and lymphatics of the upper extremity drain into the . The branches of the brachial plexus supply the motor and sensory innervation of the upper extremity. The axilla is a three-dimensional pyramid-shaped area at the junction of the arm and thorax, inferior to the shoulder joint, through which important vessels and nerves pass from the trunk to the arm.
For more information, see “” and “ .”
- Definition: a bony ring that connects the upper limb to the axial skeleton
- Bones 
- Joints 
Bones of the shoulder girdle
- Definition: an S-shaped bone that connects the scapula to the sternum, located above and anterior to the first rib
- Muscle attachments
- Subclavian groove
- Impression for costoclavicular ligament (medial)
- Tuberosity for coracoclavicular ligament (lateral)
- Definition: a flat and triangular-shaped bone that overlies the 2nd–7thposterior ribs.
- Borders: medial, lateral/axillary, and superior
- Angles: superior, inferior, and lateral
- Spine of scapula
- Supraspinous fossa
- Infraspinous fossa
- Costal (anterior) surface
- Subscapular fossa
- Coracoid process
- Suprascapular notch
- Glenoid fossa
- Posterior surface
Joints of the shoulder girdle
Sternoclavicular joint 
- Anterior sternoclavicular ligament and posterior sternoclavicular ligament
- Unites the sternal ends of both clavicles
- Strengthens the joint capsule superiorly
- Costoclavicular ligament
Acromioclavicular joint (AC joint) 
- Definition: : a synovial plane joint between the lateral end of the clavicle and the acromion of the scapula
- Acromioclavicular ligament
- Coracoclavicular ligament
Scapulothoracic joint 
- Type of joint
Movements of the scapula (scapulothoracic joint)
- Elevation: trapezius (upper part), levator scapulae, and the rhomboid muscles
- Depression: gravity, trapezius (lower fibers), pectoralis minor, and serratus anterior
- Protraction (scapular abduction): serratus anterior, pectoralis major, and pectoralis minor
- Retraction (scapular adduction): trapezius (middle part), latissimus dorsi, and the rhomboid muscles
- Lateral (upward) rotation: serratus anterior, trapezius (upper and lower part)
- Medial (downward) rotation: latissimus dorsi, levator scapulae, pectoralis minor, and rhomboid muscles
Shoulder joint (glenohumeral joint) 
- Type of joint: ball-and-socket joint between the head of the humerus and the glenoid cavity of the scapula
- Glenoid labrum: a fibrocartilaginous rim surrounding the glenoid fossa
- Joint capsule
- Coracoacromial arch
- Coracoacromial ligament
- Coracohumeral ligament
- Glenohumeral ligament
- Transverse humeral ligament
- Synovial fluid-filled sac
- Lies between the acromion, coracoacromial ligament, and deltoid muscle superiorly, and between the shoulder joint capsule and supraspinatus tendon inferiorly
- Does not communicate with the shoulder joint cavity
- Facilitates smooth gliding movement of the supraspinatus tendon and deltoid muscle
- Other bursae are the subscapular, subcoracoid, subscapular recess, coracoclavicular and supraacromial bursae.
- Subacromial bursa
- Movements of the shoulder joint
Muscles of the shoulder girdle
The muscles of the proximal upper limb can be distinguished according to their attachments:
- Scapulohumeral muscles
- Axioappendicular muscles
Scapulohumeral (intrinsic shoulder) muscles 
- Six muscles originate from the scapula and insert into the humerus:
Rotator cuff muscles
- The rotator cuff muscles are responsible for providing the glenohumeral joint with stability and mobility.
- The tendons of the rotator cuff muscles surround the head of the humerus from all sides and hold the humeral head to the articular surface of the scapula.
- The deltoid muscle rests on the rotator cuff.
- The contour of the shoulder is formed mainly by the deltoid muscle.
- See “ .”
- Teres major muscle: forms the inferior border of the quadrangular space
- Rotator cuff muscles
|Rotator cuff||Supraspinatus muscle|
|Teres minor muscle|
|Teres major muscle|
“roTISSerie:” Teres minor, Infraspinatus, Supraspinatus, and Subscapularis are the muscles of the rotator cuff.
Anterior axioappendicular muscles 
- lateral end of the clavicle : depresses the shoulder and
- Stabilizes scapula (draws it anteriorly and inferiorly against the thoracic wall)
- Accessory muscle of respiration
- See “ .”
SALT: The Serratus Anterior muscle is innervated by the Long Thoracic nerve.
Posterior axioappendicular (extrinsic shoulder) muscles 
Superficial extrinsic shoulder muscles
- Trapezius muscle
- Latissimus dorsi muscle
- Deep extrinsic shoulder muscles
- A three-dimensional, pyramid-shaped area at the junction of the arm and thorax
- Inferior to the shoulder joint, through which important vessels and nerves pass from the trunk to the arm
- Anterior wall: pectoralis major and pectoralis minor muscles
- Posterior wall: latissimus dorsi, teres major, and subscapularis muscles, and the scapula
- Lateral wall: coracobrachialis muscle and the humerus
- Medial wall: serratus anterior, the 1st–4thribs, and the intercostal muscles
Axillary spaces 
- Definition: anatomical spaces (2 triangular, 1 quadrangular) bound by the teres minor muscle (cranially) and the teres major muscle (caudally), through which structures leave the axilla
Medial triangular space (upper triangular space)
- Shape: a triangular space with a cranial, caudal, and lateral border and apex inferomedially (i.e., no medial border)
- Structures within: circumflex scapular artery and vein
Triangular interval (lower triangular space)
- Shape: a triangular space with a cranial, lateral, and medial border and apex inferiorly (i.e., no caudal border)
- Structures within
- Shape: a quadrangular space that allows access to the posterior arm and shoulder area
- Structures within
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 peace sign with both hands and superimpose them at ∼ 90°. Three spaces are created. These represent the axillary spaces.
Vascular supply and lymphatic drainage
Arterial supply 
Axillary artery 
- Origin: continuation of the subclavian artery at the outer border of the 1strib
- In the axilla, it lies lateral to the axillary vein.
- Continues as the brachial artery at the outer border of the teres major
- Divided into 3 parts by the overlying pectoralis minor muscle
|Branches of the axillary artery|
|Superior thoracic artery|| |
|Thoracoacromial artery (thoracoacromial trunk)|| |
|Lateral thoracic artery|| || |
|Anterior humeral circumflex artery|| |
|Posterior humeral circumflex artery|
Scapular anastomosis 
- Definition: an anastomosis between the branches of the first part of the subclavian artery and the third part of the axillary artery that provides collateral circulation to the arm in case of occlusion or injury to the axillary or subclavian arteries
|Overview of scapular arteries|
|Dorsal scapular artery|
|Circumflex scapular artery|
|Subscapular artery|| |
Venous drainage 
- Origin: formed at the outer border of the teres major muscle by the union of the basilic vein and the accompanying veins of the brachial artery
- Drains: upper limb, axilla, lateral chest wall
Lymphatic drainage 
- Description: a network of nerves derived from the C5–T1 spinal nerves that give rise to the peripheral nerves of the upper limb and shoulder
- Anterior rami of C5–T1 spinal nerves (i.e., five roots)
The roots form three trunks that are located in the neck.
- C5 and C6 form the upper trunk of the brachial plexus: The suprascapular nerve (innervates the infraspinatus and supraspinatus muscles) and nerve to subclavius (innervates the subclavius muscle) originate here.
- C7 forms the middle trunk of the brachial plexus.
- C8 and T1 form the lower trunk of the brachial plexus.
- The roots form three trunks that are located in the neck.
- Divisions: All three trunks separate into an anterior and posterior division that enters into the axillary fossa.
- Only the cords and proximal portions of their branches lie in the axilla.
- There are three cords, which are named according to their position in relation to the axillary artery.
- Functional significance
|The brachial plexus|
|Branches of the brachial plexus||Spinal roots||Motor innervation||Sensory innervation|
|Lateral cord||Musculocutaneous nerve|| || |
|Lateral pectoral nerve|| || |
|Lateral root of median nerve|| |
|Medial cord||Medial root of median nerve|| |
|Medial pectoral nerve|| |
|Medial cutaneous nerve of arm|| || |
|Posterior cord||Upper subscapular nerve|| || |
|Lower subscapular nerve|| || |
|Thoracodorsal nerve|| || |
|Radial nerve|| |
“Rugby Teams Drink Cool Beer!” (Roots, Trunks, Divisions, Cords, Branches is the order of the brachial plexus divisions)