Shoulder Muscles Anatomy – Simplified

Proximal humerus

Insertion of Rotato Cuffs

Mnemonic: SIT-S

a. Greater tubercle: Supraspinatus, Infraspinatus, Teres minor

b. Lesser tubercle: Subscapularis

proximal humerus muscles

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)
scapular muscles
SLR and SIT mnemonic for scapular muscle attachment

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.

clavicle muscles

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
MuscleOriginInsertionActionInnervation
Trapeziusa. Superior: Occipital protuberance, nuchal line, ligamentum nuchae

b. Middle: Spinous process of T1-T5

c. Inferior: Spinous process of T6-T12
a. Lateral calvicle


b and c. Acromion and spine of scapula
a. Elevates scapula + Upward rotation of glenoid

b. Retracts (adducts) scapula

c. Depress scapula + Upward rotation of glenoid
Cranial nerve XI; C2-C4
Levator scapulaeTransverse process of C1-C4Superior medial scapulaElevates and adducts scapulaDorsal scapular nerve; C3-C5
RhomboidsLigamentum nuchae and spinous process of C7-T5Medial scapular borderRetracts scapulaDorsal scapular nerve; C4-C5
Latissimus dorsia. Superficial: Spinous process of T7-T12 (beginning from level of inferior angle of scapula)

b. Iliac: Posterior 1/3 of iliac crest

c. Costal: Ribs 9-12

d. Scapular: Inferior angle of scapula
Biccipital grooveArm internal rotation, adduction and extensionThoracodorsal nerve; C6-C8
Serratus anteriorRibs 1-8Anterior medial scapulaProtracts and Upwardly rotates scapulaLong thoracic nerve; C5-C8
Deltoida. Clavicular: Lateral 1/3 clavicle

b. Acromial: Acromion

c. Spinal: Spine of scapula
Deltoid tuberosity of humerusa. Flexion and internal rotation of arm

b. Abduction of arm from 15-90 degrees

c. Extension and external rotation of arm
Axillary nerve; C5-C6
Pectoralis majora. Clavicular head: Anterior medial clavicle

b. Sternocostal head: Lateral border of sternum, Superior 6 costal cartilages, Fascia of external oblique muscle
Crest of greater tubercleArm adduction and internal rotationLateral and medial pectoral nerves; C5-T1
Pectoralis minorJust lateral to costal cartilage of ribs 3-5Coracoid processMedial pectoral nerve; C8, T1Stabilizes scapula
SupraspinatusSupraspinous fossa of scapulaGreater tubercle of humerusAssists deltoid and initiates arm abductionSuprascapular nerve; C4-C6
InfraspinatusInfraspinous fossa of scapulaGreater tubercle of humerusArm external rotationSuprascapular nerve; C5-C6
Teres minorLateral border of scapulaGreater tubercle of humerusArm external rotationAxillary nerve; C5-C6
SubscapularisSubscapular fossaLesser tubercle of humerusArm internal rotationUpper and lower subscapular nerves; C5-C6
Teres majorInferior angle of scapulaCrest of lesser tubercleArm internal rotation and adductionLower subscapular nerve; C5-C6

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.

triangular and quadrangular space mnemonic

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 

Leave a Reply

Your email address will not be published. Required fields are marked *