Infraspinatus Muscle

Origin

The infraspinatus muscle originates from the:

- medial two thirds of the infraspinous fossa of the scapula;

- internal surface of the infraspinous fascia.

Insertion

The fibers of the infraspinatus muscle travel superolaterally and insert, via a flat tendon, onto the middle facet of the greater tubercle of the humerus. Part of this tendon also merges with the capsule of the glenohumeral (shoulder) joint.

Key Features & Anatomical Relations

The infraspinatus muscle is one of the rotator cuff muscles. It is a thick bipennate type of skeletal muscle. It is located:

- anterior (deep) to the trapezius and deltoid muscles, and the infraspinous fascia;

- posterior (superficial) to the scapula, and the subtendinous bursa of infraspinatus muscle;

- superior to the teres major and minor muscles;

- lateral to the rhomboid major and minor muscles.

Actions & Testing

The infraspinatus muscle is involved in multiple actions:

- laterally rotates the arm at the glenohumeral (shoulder) joint;

- transversely abducts the arm at the glenohumeral joint (i.e., it abducts the flexed arm along the transverse plane).

It is one of the four rotator cuff (SITS) muscles, the other three being the supraspinatus, teres minor and subscapularis muscles. These muscles work together to stabilize the glenohumeral joint, by holding the head of the humerus in the glenoid fossa of the scapula, during its movements (Standring, 2016).

The infraspinatus muscle can be tested by laterally rotating the arm at the glenohumeral joint against resistance, while the forearm is held in the flexed position and the arm is in the adducted position (Moore, Dalley and Agur, 2009).

List of Clinical Correlates

- Injury or rupture of rotator cuff

References

Moore, K. L., Dalley, A. F. and Agur, A. M. R. (2009) Clinically Oriented Anatomy. Lippincott Williams & Wilkins.

Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice. Gray's Anatomy Series 41st edn.: Elsevier Limited.