Supraspinatus

What is the Supraspinatus

Supraspinatus is a small triangular muscle in the upper shoulder region. It is the smallest of the 4 rotator cuff muscle, the other three being the infraspinatus, subscapularis, and teres minor.

Anatomy

Location and Attachments

Origin	Supraspinous fossa of scapula
Insertion	The upper surface of the greater tubercle of humerus

It originates from the middle two-thirds of the supraspinous fossa, the concave depression at the upper back aspect of the scapula above its spine.

The muscle fibers merge and form a single tendon which runs laterally, from underneath the acromion, crosses the shoulder joint, and reaches the humerus to insert into the greater tubercle. It inserts into the highest of the three facades on the greater tubercle, the lower two occupied by the infraspinatus and teres minor.

These three attachments are sometimes abbreviated as SIT from top to bottom, standing for Supraspinatus, Infraspinatus, and Teres minor.

Relations to Other Muscular Structures

The supraspinatus is deep to the spine muscle trapezius. It is the uppermost rotator cuff muscle, with the infraspinatus inferior to it.

The subacromial bursa that interacts with the rotator cuff keeps the supraspinatus ligament separate from the coracoacromial ligament, the deltoid muscle, and the acromion.

Functions

Action

Initiating abduction of arm, stabilizing the shoulder joint

Abducting the arm: The supraspinatus contracts to abduct the humerus at the shoulder joint. It is the primary agonist for abducting the arm for the first 15 degrees approximately, beyond which the deltoids take over the action. The supraspinatus then assists the deltoid with further abduction.

Stabilizing the shoulder: Along with the other rotator cuff muscles, it plays a vital role in keeping the humeral head centered in the glenoid cavity when the shoulder moves. The supraspinatus holds the humerus in place, resisting the downward pull of gravity on the shoulder joint due to the arm’s weight.

The primary antagonists of supraspinatus are infraspinatus, teres minor, latissimus dorsi and pectoralis major.

Innervation

Nerve

Suprascapular nerve (C5 and C6)

Blood Supply

Artery

Suprascapular artery

The suprascapular artery is a branch of the subclavian artery — the thyrocervical trunk to be exact. Apart from this, the supraspinatus may also receive additional blood supply from the dorsal scapular artery.