Rotator cuff muscles

The supraspinatus, infraspinatus, teres minor and subscapularis muscles, are collectively known as the rotator cuff muscles. Their main function is to reinforce the shoulder joint capsule to help prevent dislocation of the humerus when larger muscles contract. They also act as synergists for angular or rotational movements of the arm. For all, the origin is the scapula and insertion the humerus.

Infraspinatus

This muscle is partially covered by the deltoid and trapezius. It is named for its scapular location. It resists posterior dislocation of arm, and laterally rotates and abducts the arm.

Supraspinatus

This muscle is named for its location on the posterior (rear) aspect of the scapula. It is deep (underneath) to the trapezius. It aids the deltoid in abducting arm.

Subscapularis

This muscle forms part of the posterior (rear) wall of the axilla (arm pit). It medially rotates the arm and stabilises shoulder joint.

Teres minor

This is a small elongated muscle located below the infraspinatus  and may be inseparable from that muscle. It laterally rotates and weakly adducts the arm.

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