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The infraspinatus is the main external rotator of the shoulder. When the arm is fixed, it adducts the inferior angle of the scapula. Its synergists are teres minor and the deltoid. [4] The infraspinatus and teres minor rotate the head of the humerus outward (external, or lateral, rotation); they also assist in carrying the arm backward. [1]
Infraspinatus, 14. Teres minor), 15. Biceps muscle. The rotator cuff is a group of muscles and their tendons that act to stabilize the human shoulder and allow for its extensive range of motion. Of the seven scapulohumeral muscles, four make up the rotator cuff. The four muscles are: supraspinatus muscle; infraspinatus muscle; teres minor muscle
The infraspinous fossa (infraspinatus fossa or infraspinatous fossa) of the scapula is much larger than the supraspinatous fossa; toward its vertebral margin a shallow concavity is seen at its upper part; its center presents a prominent convexity, while near the axillary border is a deep groove which runs from the upper toward the lower part.
The infraspinatous fascia is a dense fibrous membrane, covering the infraspinatous muscle and fixed to the circumference of the infraspinatous fossa; it affords attachment, by its deep surface, to some fibers of that muscle.
Animation of the shoulder joint. The muscles shown are subscapularis muscle (at right), infraspinatus muscle (at top left), teres minor muscle (at bottom left) The movement of the scapula across the rib cage in relation to the humerus is known as the scapulohumeral rhythm, and this helps to achieve a further range of movement. This range can be ...
The muscle which can 'cancel' or to some degree reverse the action of the muscle. Muscle synergies are noted in parentheses when relevant. O (Occurrences) Number of times that the named muscle row occurs in a standard human body. Here it may also be denoted when a given muscles only occurs in a male or a female body.
Together, these keep the humeral head in the glenoid cavity, preventing upward migration of the humeral head caused by the pull of the deltoid muscle at the beginning of arm elevation. The infraspinatus and the teres minor, along with the anterior fibers of the deltoid muscle, are responsible for external rotation of the arm. [6]
The medial two-thirds of the fossa give origin to the Infraspinatus; the lateral third is covered by this muscle. There is a ridge on the outer part of the back of the scapula. This runs from the lower part of the glenoid cavity, downward and backward to the vertebral border, about 2.5 cm above the inferior angle.