Muscles - Shoulder (intrinsic)

Question 1

What are the non-rotator cuff muscles?

Answer 1

These are the deltoid and the teres major.

Question 2

Deltoid

Answer 2

Shaped like an inverted triangle. Can be sub-divided into anterior, posterior and middle fibres.

Origin - lateral 1/3 of clavicle, acromion and spine of scapula

Insertion - deltoid tuberosity on the lateral aspect of the humerus.

Innervation - Axillary nerve

Actions:

Anterior fibres - flexion and medial rotation

Middle fibres - major abductor (takes over from supraspinatus after 15 degrees).

Posterior fibres - extension and lateral rotation

Question 3

Teres major

Answer 3

Forms the inferior border of the ‘quadrangular space’ from which the axillary nerve and posterior circumflex humeral artery pass through to reach the posterior scaupula region.

Origin - posterior surface of inferior angle of the scapula

Insertion - intertubercular groove.

Innervation - lower subscapular nerve

Functions:

1) Adducts and extends at the shoulder
2) Medially rotates the arm

Question 4

What are the four muscles of the rotator cuff?

Function?

Answer 4

There is the supraspinatus, infraspinus, subscapularis and teres minor.

Provides stability to the glenohumeral joint.

Question 5

Supraspinatus

Answer 5

Origin - supraspinous fossa of scapula

Insertion - greater tubercle of humerus

Innervation - suprascapular nerve

Function - Abduction of arm (first 15 degrees)

Question 6

Infraspinatus

Answer 6

Origin - infraspinous fossa

Insertion - greater tubercle of the humerus

Innervation - suprascapular nerve

Function - laterally rotates the arm

Question 7

Subscapularis

Answer 7

Origin - subscapularis fossa of the costal fossa

Insertion - lesser tubercle of the humerus

Innervation - upper and lower subscapular nerves

Action - medially rotates the arm

Question 8

Teres minor

Answer 8

Origin - posterior surface of the scapula, adjacent to the lateral border.

Insertion - lesser tubercle of the humerus

Innervation - axillary nerve

Function - laterally rotates the arm

Question 9

Clinical relevance: rotator cuff tendonitis

Answer 9

Refers to the inflammation of the tendons of the rotator cuff muscles.

Occurs secondary to repetitive movements of the shoulder joint.

The muscle most commonly affected is the supraspinatus. During abduction it rubs against the coracoacromial arch. This cause inflamation and degenerative changes to the tendon itself.

Treatment - conservation - rest, analgesia, physiotherapy. In more severe cases, steroid injections and surgery can be considered.