The infraspinatus muscle

(M. infraspinatus)

The M. infraspinatus is a skeletal muscle of the shoulder. Together with the M. supraspinatus, the M. teres minor, and the M. subscapularis, it forms the muscle-tendon-cap. The main task of the infraspinatus muscle is the outside rotation in the shoulder joint as well as in abduction and adduction of the arm.
Because the shoulder joint is not hold by bones and the ligaments are weak, saving is mainly done by muscles of the muscle-tendon-cap. The humerus is hold by these four muscles in the very flat joint cup of the shoulder blade. The functional result is an extreme flexibility but a certain instability and sensitivity as well. Luxations caused by extrenal effects while exercising or falling on arm and shoulder are very common. Injuries of muscles as well as breaks of bones on the basis of muscles are often combined with luxation.

The muscle originates on the hollow of the shoulder blade (Fossa infraspinata), on the edge of the rear part. Its triangular shape covers almost the whole shoulder blade and is based with its tendon on the tuberosity (Tuberculum majus).
 

The M. infraspinatus