What are the intrinsic shoulder muscles?

The intrinsic shoulder muscles are six short muscles that connect the scapula to the humerus, primarily acting on the glenohumeral joint. They include deltoid, supraspinatus, infraspinatus, teres minor, teres major, and subscapularis. Four of these (supraspinatus, infraspinatus, teres minor, and subscapularis) form the rotator cuff, which stabilizes the shoulder.

Which muscles make up the rotator cuff?

The rotator cuff consists of four intrinsic shoulder muscles: supraspinatus, infraspinatus, teres minor, and subscapularis. They work together to stabilize the humeral head in the glenoid cavity during arm movements.

What is the main function of the deltoid muscle?

The deltoid is the chief abductor of the arm, responsible for abduction from 15° to 90°. Its anterior fibers flex and medially rotate the arm, middle fibers abduct the arm, and posterior fibers extend and laterally rotate the arm.

Why is the supraspinatus muscle clinically important?

The supraspinatus is prone to degeneration and tearing, a common rotator cuff injury. This often results in difficulty initiating arm abduction, with patients needing to assist using the opposite hand.

What actions do the infraspinatus and teres minor perform?

Both the infraspinatus and teres minor primarily laterally rotate the arm and help stabilize the humeral head in the glenoid cavity.

How does the teres major differ from the teres minor?

The teres major adducts and medially rotates the arm and extends it from a flexed position, while the teres minor laterally rotates the arm and stabilizes the shoulder. They have different nerve supplies: teres major is innervated by the lower subscapular nerve, and teres minor by the axillary nerve.

What is the role of the subscapularis in shoulder movement?

The subscapularis medially rotates and adducts the arm and stabilizes the shoulder joint by holding the humeral head in the glenoid cavity.

Why are intramuscular injections given in the lower half of the deltoid?

Injections are given in the lower half of the deltoid to avoid injury to the axillary nerve, which winds around the surgical neck of the humerus in the upper part of the muscle.

Intrinsic Shoulder Muscles – Anatomy & Function

❓ Frequently Asked Questions