The infraspinatus muscle is a thick, triangular muscle.
As one of the four muscles of the rotator cuff, the main function of the infraspinatus is to externally rotate the arm and stabilise the shoulder joint.
The infraspinatus performs a number of actions on the shoulder and humerus:
- It is the major external rotator of the shoulder.
- Working with the teres minor, subscapularis, and the deltoids, the primary function of the infraspinatus is extension, horizontal (transverse) extension and external rotation of the humerus at the shoulder joint.
- When the arm is fixed, it abducts] the inferior angle of the scapula.
- The infraspinatus and teres minor rotate the head of the humerus outward (external, or lateral, rotation); they also assist in carrying the arm backward (extension of the glenohumeral joint).
- It also helps to stabilise the shoulder joint by keeping the head of the humerus firmly pressed medially against the scapula.
- Additionally, the infraspinatus reinforces the capsule of the shoulder joint.
Figure 1. Infraspinatus muscle.
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