|Position of the supraspinatus muscle (red) seen from the back.|
|Posterior view of muscles connecting the upper extremity to the vertebral column. Supraspinatus muscle is labeled in red at right, while it is covered by other muscles at left.|
|Gray's||subject #123 440|
|Origin||supraspinous fossa of scapula|
|Insertion||superior facet of greater tubercle of humerus|
|Actions||abduction of arm and stabilizes humerus see part on controversy of action.|
The supraspinatus (plural supraspinati, from Latin supraspinatus) is a relatively small muscle of the upper back that runs from the supraspinatous fossa superior 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.
The supraspinatus muscle arises from the supraspinous fossa, a shallow depression in the body of the scapular 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 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 (supraspinatus, infraspinatus, and teres minor).
The supraspinatus muscle is supplied by the suprascapular nerve (C5 and C6), which arises from the superior trunk of the brachial plexus and passes laterally through the posterior triangle of the neck and through the scapular notch on the superior border of the scapula. After supplying fibers to the supraspinatus muscle, it supplies articular branches to the capsule of the shoulder joint.
Contraction of the supraspinatus muscle leads to abduction of the arm at the shoulder joint. It is the main agonist muscle for this movement during the first 10-15 degrees of its arc. Beyond 30 degrees the deltoid muscle becomes increasingly more effective at abducting the arm and becomes the main propagator of this action.
The supraspinatus muscle is one of the musculotendinous support structures called the rotator cuff that surround and enclose the shoulder. It helps to resist the inferior gravitational forces placed across the shoulder joint due to the downward pull from the weight of the upper limb.
For USMLE step 1, know that the supraspinatus initiates abduction of the shoulder. Without a functioning supraspinatus, the physician must start abducting the patient's arm and eventually the patient will be able to finish abduction if the deltoid is functional, which is common because the supraspinatus is innervated by the suprascapular nerve from the superior/upper trunk of the brachial plexus. The deltoid is innervated more distally by the axillary nerve, which arises from the posterior cord of the brachial plexus.
Controversy about Action
A 1963 study, "Function of the Supraspinatus Muscle and its Relation to the Supraspinatus syndrome - An experimental in Man" by B Van Linge and J D Mulder in Leiden, Holland showed that the supraspinatus does not cause the abduction of the first 30 degrees, as widely accepted, but rather is a synergist muscle. This means that it assists the deltoid, but is not, by itself the abducting muscle. In this study, the supraspinatus was anaesthetised, and the deltoid muscle was still able to complete a full range of abduction, however was not able to sustain an isometric contraction for more than one minute. From this study, it is suggested that the "true" action of the supraspinatus is to hold the capsule in position to allow greater functional strength and stamina of the deltoid muscle.
- Mnemonic at medicalmnemonics.com 35
- Journal of Bone and Joint Surgery, Vol 45B, No. 4, November 1963, pp 750–754
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