Infraspinatus

The infraspinatus (Latin: musculus infraspinatus) is a flat triangular-shaped muscle of the upper limb. It extends between the scapula and humerus. As the infraspinatus acts at the shoulder joint, it belongs to the muscles of the shoulder girdle. Together with the supraspinatus, teres minor and subscapularis, the infraspinatus muscle is classified as one of the rotator cuff muscles that provide stability to the shoulder joint.

Origin

The infraspinatus muscle originates from the infraspinous fossa located on the posterior surface of the scapula.

Insertion

The muscle fibers of the infraspinatus pass laterally from the infraspinous fossa and insert on the greater tubercle of the humerus.

Action

The infraspinatus muscle stabilizes the glenohumeral (shoulder) joint and provides external (lateral) rotation of the arm.

Innervation

The infraspinatus is innervated by the suprascapular nerve that arises from the fifth and sixth cervical (C5, C6) nerve roots of the brachial plexus.

Blood supply

The arterial blood supply to the infraspinatus muscle is primarily provided by the suprascapular and circumflex scapular arteries.