Shoulder Muscles Anatomy – Simplified

Proximal humerus

Insertion of Rotato Cuffs

Mnemonic: SIT-S

a. Greater tubercle: Supraspinatus, Infraspinatus, Teres minor

b. Lesser tubercle: Subscapularis

Attachment of Other muscles

Anteriorly and posteriorly the muscles attach on each side of the depressions (groove and sulcus).

a. Anteriorly: Insertion of 3 muscles

Mnemonic: Lady between 2 Majors

• Crest of greater tubercle: Pectoralis major
• Intertubercular sulcus or Bicipital groove (between greater and lesser tubercle): Lattisimus dorsi (Tendon of long head of biceps passes through this grrove)
• Crest of lesser tubercle: Teres major

b. Posteriorly: Origin of 2 muscles

Mnemonic: Red between 2 Heads

• Radial groove: Radial nerve
• Superior to radial groove: Lateral head of triceps
• Inferior to radial groove: Medial head of triceps

c. On Proximal Shaft:

Mnemonic: CD

• Medial side: Coracobrachialis
• Lateral side: Deltoid

Scapula

a. Medial border: Insertion of 3 muscles

Mnemonic: SLR – all supplied by nerves from ROOT of brachial plexus

• Anteriorly: Serratus anterior (Long thoracic nerve)
• Posteriorly:
  • Superiorly: Levator scapulae (Dorsal scapular nerve)
  • Inferiorly: Rhomboids – minor superior to major (Dorsal scapular nerve)

b. Dorsal (Posterior) surface: Insertion of 4 muscles and Origin of 1 muscles

Mnemonic: SIT (remember the greater tubercle muscles)

Muscles on medial aspect of dorsal surface is supplied by nerves from trunk of brachial plexus.

• Above spine of scapula (supraspinous fossa): Supraspinatus (Suprascapular nerve)
• Below spine of scapula (infraspinous fossa): Infraspinatus (Suprascapular nerve)
• On lateral border: 3 Ts
  • Teres minor
  • Below Teres minor: Teres major (minor superior to major)
  • Above Teres minor (Infraglenoid tubercle): Origin of Triceps long head

Lattisimus dorsi also originates on inferior angle of scapula dorsally.

c. Anterior (Ventral) surface: Subscapular fossa (Subscapularis)

d. Around Glenoid fossa: 2 long heads

• Supraglenoid tubercle: Long head of biceps
• Infraglenoid tubercle: Long head of tricpes

e. Coracoid process:

• Tip: Coracobrachialis, Biceps short head
• Superior surface: Pectoralis minor

f. Spine of scapula and Acromion:

• Upper lip of spine of scapula and medial margin of acromion: Trapezius insertion
• Inferior lip of spine of scapula and lateral margin of acromion: Deltoid origin

Clavicle

Acromion continues with lateral clavicle through acromioclavicular joint. Spine of scapula, Acromion and Clavicle forms an arc.

a. Lateral 1/3 of clavicle:

• Anterior border: Deltoid origin
• Posterior border: Trapezius insertion

b. Medial 1/3 of clavicle:

• Anterior surface: Pectoralis major
• Superior surface: Sternocleidomastoid
• Inferior surface: Subclavius

Internal rotators of arm are supplied by nerves from the CORDS of the brachial plexus.
a. Pectoralis major: Lateral and medial pectoral nerves (from lateral and medial cords)
b. Latissimus dorsi: Thoracodorsal nerve (from posterior cord)
c. Teres major: Lower subscapular nerve (from posterior cord)
d. Subscapularis: Upper and lower subscapular nerve (from posterior cord)

Learn the Anatomy of Brachial Plexus: https://epomedicine.com/medical-students/brachial-plexus-simplified/

Shoulder Muscles by Action

a. Forward flexion: Deltoid (anterior fibers), Pectoralis major (clavicular fibers), Coracobrachialis, Biceps

b. Extension: Deltoid (posterior fibers), Teres major, Teres minor, Latissimus dorsi, Pectoralis major (sternocostal fibers), Triceps (long head)

c. Horizontal adduction: Pectoralis major, Deltoid (anterior fibers)

d. Horizontal abduction: Deltoid (posterior fibers), Teres major, Teres minor, Infraspinatus

e. Abduction: Deltoid, Supraspinatus, Infraspinatus, Subscapularis, Teres minor, Long head of biceps (if arm laterally rotated first – trick movement)

f. Adduction: Pectoralis major, Latissimus dorsi, Teres major, Subscapularis

g. Internal rotation: Pectoralis major, Deltoid (anterior fibers), Latissimus dorsi, Teres major, Subscapularis

h. External rotation: Infraspinatus, Deltoid (posterior fibers), Teres minor

i. Elevation of scapula: Trapezius (upper fibers), Levator scapulae, Rhomboids (major and minor)

j. Depression of scapula: Serratus anterior, Pectoralis major, Pectoralis minor, Latissimus dorsi, Trapezius (lower fibers)

k. Protraction (forward movement) of scapula: Serratus anterior, Pectoralis major, Pectoralis minor, Latissimus dorsi

l. Retraction (backward movement) of scapula: Trapezius, Rhomboid major, Rhomboid minor

m. Scapular upward rotation: Trapezius (upper fibers), Serratus anterior

n. Scapular downward rotation: Levator scapulae, Rhomboids, Pectoralis minor

Important Muscular Spaces of Shoulder

The 3 important spaces – triangular space, quadrangular space and triangular interval exists between the 3 “T” muscles attaching on lateral border of dorsal scapula and the humerus.

Mnemonic: Interlock the 2 fingers of both hands as shown in the fingure above. 2 fingers oriented upwards represent Humerus and Triceps long head. 2 fingers oriented laterally represent Teres minor and Teres major. Remember that all these 3 muscles attach on the lateral border of dorsal scapula. Also remember ‘minor superior to major’.

a. Quadrangular space:

• Borders
  • medial: long head of triceps
  • lateral: humeral shaft
  • superior: teres minor
  • inferior: teres major
• Contents 
  • axillary nerve 
  • posterior humeral circumflex artery

b. Triagnular space:

• Borders
  • inferior: teres major
  • lateral: long head of triceps
  • superior: lower border of teres minor
• Contents
  • scapular circumflex artery

c. Triagnular interval (Lower triangular space):

• Borders
  • superior: teres major
  • lateral: shaft of humerus
  • medial: long head of the triceps
• Contents
  • profunda brachii artery
  • radial nerve