Supraspinatus muscle

At a glance

English

Supraspinatus muscle

Latin (TA2)

Musculus supraspinatus

System

Muscle

Region

Upper limb

Side

Paired, left and right

About the supraspinatus muscle

Supraspinatus is a fairly small, triangular muscle of the upper back and shoulder. It occupies the supraspinous fossa, the shallow hollow on the scapula's back, above the spine, and belongs to the rotator cuff, the group of short muscles whose tendons blend with the shoulder joint capsule and keep the humeral head centred in the glenoid cavity. The scapular spine divides it from infraspinatus below.

Its fibres arise from the medial two-thirds or so of the fossa and from the fascia covering it. They converge into a tendon that passes outwards beneath the acromion and the coracoacromial arch, crosses the top of the joint and fixes to the uppermost facet on the humerus's greater tubercle. A memory aid for the cuff tendons on the greater tubercle, from top to bottom, is SIT: supraspinatus, infraspinatus, teres minor; subscapularis on the lesser tubercle adds a final S.

The muscle starts abduction of the arm and works with deltoid throughout the movement, while pressing the humeral head into its socket so that deltoid can lift rather than simply shear the bone upwards. Once the arm is a little way from the side, deltoid takes over most of the lifting. Supraspinatus also stops the head from sliding downwards when the arm hangs with a load.

Its tendon runs in a tight space under the acromion, so it is the cuff tendon most often worn, inflamed, calcified or torn, giving pain on lifting the arm, especially in the middle of the arc. A large tear lets the humeral head ride up towards the acromion on an X-ray. The suprascapular nerve, a branch of the plexus's upper trunk, can be hurt at the suprascapular notch or with a clavicle fracture, making it hard to begin abduction.

Attachments, action and supply

Origin

Medial two-thirds of the supraspinous fossa of the scapula and the overlying supraspinous fascia.

Insertion

Highest facet on the humeral greater tubercle, plus the upper part of the shoulder joint capsule.

Action

Starts abduction of the arm and assists deltoid through the rest of it; holds the humeral head in the glenoid cavity as part of the rotator cuff.

Nerve supply

Suprascapular nerve (C5, C6), a branch of the plexus's upper trunk.

Blood supply

Suprascapular artery, with some supply from the dorsal scapular artery.