The supraspinatus (plural supraspinati) is a relatively small muscle of the upper back that runs from the supraspinous fossa superior portion of the scapula (shoulder blade) to the greater tubercle of the humerus. It is one of the four rotator cuff muscles and also abducts the arm at the shoulder. The spine of the scapula separates the supraspinatus muscle from the infraspinatus muscle, which originates below the spine. Structure The supraspinatus muscle arises from the supraspinous fossa, a shallow depression in the body of the scapula above its spine. The supraspinatus muscle tendon passes laterally beneath the cover of the acromion. Research in 1996 showed that the postero-lateral origin was more lateral than classically described. The supraspinatus tendon is inserted into the superior facet of the greater tubercle of the humerus. The distal attachments of the three rotator cuff muscles that insert into the greater tubercle of the humerus can be abbreviated as SIT when viewed from superior to inferior (for supraspinatus, infraspinatus, and teres minor), or SITS when the subscapularis muscle, which attaches to the lesser tubercle of the humerus, is included. Nerve supply The suprascapular nerve (C5) innervates the supraspinatus muscle as well as the infraspinatus muscle. It comes from the upper trunk of the brachial plexus. This nerve can be damaged along its course in fractures of the overlying clavicle, which can reduce the person's ability to initiate the abduction. Function The supraspinatus muscle performs abduction of the arm, and pulls the head of the humerus medially towards the glenoid cavity. It independently prevents the head of the humerus from slipping inferiorly. The supraspinatus works in cooperation with the deltoid muscle to perform abduction, including when the arm is in an adducted position. Beyond 15 degrees the deltoid muscle becomes increasingly more effective at abducting the arm and becomes the main propagator of this action. Clinical significance The supraspinatus forms part of the rotator cuff and is one of its most frequently damaged components, whether from acute injury or gradual degeneration. Bad posture and age are leading risk factors, with a high prevalence of unsymptomatic partial and full tears, as well as symptomatic syndromes with chronic pain. Connected pathologies include acromial impingement, frozen shoulder, and poor sleep, especially on the side. Both ultrasound and MRI are now effective methods of diagnosis. Tear Diagnosis Antero-posterior projectional radiography of the shoulder may demonstrate a high-riding humeral head, with an