Myology of the Shoulder

Question 1

Rotator Cuff Muscles

Answer 1

Supraspinatus, Infraspinatus, Subscapularis, Teres Minor

Question 2

Glenohumeral joint dynamic stability

Answer 2

Achieved by the rotator cuff muscles. They contract in synchronously to keep the head of humerus near the glenoid fossa at all time.

Question 3

Supraspinatus

Answer 3

Sits underneath acromion.
O- Supraspinous fossa of scapula
I- Upper facet of greater tubercle
N- Suprascapula nerve C4-C6
A- Initiates abduction, stabilizes head of humerus 
Prevents shearing of the deltoid.

Question 4

Infraspinatus

Answer 4

O- Infraspinatus fossa of scapula
I- Middle facet of greater tubercle
N- Suprascapula C4-C6
A- Laterally rotates arm at glenohumeral joint, abducts and stabilizes head of humerus.

Question 5

Teres Minor

Answer 5

Smallest muscles of rotator cuff.
O- Upper 2/3rds of lateral border of scapula.
I- Inferior facet of greater tubercle.
N- Axillary Nerve C5-C6
A- Laterally rotates arm at glenohumeral joint, abducts and stabilizes humeral head in glenoid fossa.

Question 6

Teres Major

Answer 6

Synergist for Latissimus Dorsi.
O- Inferior angle and lower 1/3 of lateral border of scapula.
I- Crest of lesser tubercle on humerus
N- Lower subscapular Nerve C6-C7
A- Extend shoulder, Abduct and medially rotates.

Question 7

Subscapularis

Answer 7

O- Subscapularis fossa
I- Lesser tubercle of humerus
N- Upper and lower subscapula nerve (C5-C7)
A- Medially rotates arm at glenohumeral joint
Stabilises head of humerus.

Question 8

Extrinsic Musculature of Shoulder

Answer 8

Deltoid, trapezius, latissimus dorsi, levator scapula and rhomboid major/minor.

Question 9

Deltoid

Answer 9

O- Lateral 1/3 of clavicle, acromion and spine of scapula (inferior aspect).
I- Deltiod tuberosity of humerus.
N- Axillary (C5-6)
A- All fibers: Abduct
Anterior: Flex and medially rotate
Middle: Abduct with anterior and posterior fibers
Posterior: Extend and laterally rotate.

Question 10

Pectoralis Major

Answer 10

O- Clavicular head: medial 1/2 of clavicle
Sternal head: anterior surface of sternum, the first 6 costal cartialedge and the 6th rib
I- Lateral lip of sulcus (bicipital groove)
N- Upper fibers: Lateral pectoral C5-C7
Lower fibers: Lateral and medial pectoral C5-C7
A- Tilts scapula anteriorly
Depress, abduct and downwardly rotate scapula

Pulls corocoid process, pulling scapula anteriorly

Question 11

Latissimus Dorsi

Answer 11

O- Inferior angle of scapula, spinous processes of last 6 thoracic vertebrae, posterior iliac crest
I- Floor of sulcus/ bicipital groove
N- Thoracodorsal C6-C8
A- Extends shoulder, abducts and medially rotates.

Climbing muscle- Pull ups, brings O to I rather than I to O.

Question 12

Serratus Anterior

Answer 12

O- External surface of upper 8/9 ribs
I- Anterior surface of medial border of scapula
N- Long thoracic nerve C5-C8
A- Abduct scapula, holds medial border against thorax
Depresses scapula

Dysfunction of serratus anterioir can cause scapular ‘winging’, as nothing is maintaining the scapula against the thorax.
‘Superman’ muscle

Question 13

The Axilla

Answer 13

Area underneath glenohumeral joint- junction between upper limb and thorax.

Anterior wall: Pectoralis major, pectoralis minor and subclavius muscles.
Medial border: Serratus anterior, thorax.
Posterior wall: Subscapularis, teres major, latissimus dorsi.

Neurovascular bundle passes through axilla.
Pulse point from axillary artery, accessible in abduction.