The supraspinatus (plural supraspinati) is a relatively small muscle of the upper arm that runs from the scapula (shoulder blade) to the humerus (upper arm).
It is one of the four rotator cuff muscles that surround and enclose the shoulder.
The spine of the scapula separates the supraspinatus muscle from the infraspinatus muscle, which originates below the spine.
The supraspinatus performs a number of actions on the shoulder and humerus:
- Contraction of the supraspinatus muscle leads to abduction of the arm at the shoulder joint — see Figure 2. 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.
- It helps to resist the gravitational forces pulling the shoulder joint due to the downward pull from the weight of the arm.
- It also helps to stabilise the shoulder joint by keeping the head of the humerus firmly pressed medially against the scapula.
- It assists in external rotation when shoulder is abducted and internal rotation when shoulder is flexed.
Figure 1. Supraspinatus muscle.
Figure 2. Supraspinatus shoulder motion with rotator cuff.
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