Scapulohumeral muscles

The scapulohumeral muscles, also referred to as the intrinsic muscles of the shoulder, originate from the scapula and/or clavicle and attach to the humerus. These muscles are integral to shoulder movement and provide dynamic stability by ensuring the humeral head remains centered within the glenoid cavity during arm motions. The group comprises six muscles: the deltoid, teres major, and the four rotator cuff muscles (supraspinatus, infraspinatus, teres minor, and subscapularis).

1. Deltoid

Deltoid is a multipennate muscle vital for various shoulder movements, including arm abduction, flexion, extension, and internal/external rotations.

• The anterior fibers contribute to flexion and medial rotation, while the posterior fibers facilitate extension and lateral rotation. The middle fibers are primarily responsible for abduction, assuming this role after the supraspinatus initiates the movement.

2. Rotator Cuff Muscles

These muscles stabilize the shoulder joint and perform specific functions:

• Supraspinatus: Initiates abduction of the arm, managing the first 0-15 degrees of motion.

• Infraspinatus and Teres Minor: These muscles act as external rotators of the arm, aiding lateral rotation and contributing to joint stability.

• Subscapularis: Performs medial (internal) rotation of the arm.

3. Teres Major

Teres major is positioned inferiorly to the rotator cuff. It assists in internal rotation and adduction of the arm, complementing the actions of the subscapularis.