Shoulder anatomy

The shoulder girdle, also called the pectoral girdle, is an incomplete bony ring formed by the clavicle and scapula on each side of the body, joined anteriorly by the manubrium of the sternum. The bones of the shoulder girdle articulate with each other and partake in the formation of 4 joints that include:
The sternoclavicular joint - formed between the sternum and clavicle.
The acromioclavicular (AC) joint - formed between the scapula and the clavicle.
The glenohumeral (shoulder) joint - formed between the scapula and humerus.
The scapulothoracic joint - formed between the scapula and the posterior thoracic cage.
The shoulder girdle functions as the anchor that attaches the upper limbs to the axial skeleton. Additionally, the shoulder girdle allows for a large range of motion, mainly in the highly mobile scapulothoracic joint.

The muscles of the shoulder support and produce the movements of the shoulder girdle. They attach the appendicular skeleton of the upper limb to the axial skeleton of the trunk. Four of them are found on the anterior aspect of the shoulder, whereas the rest are located on the shoulder’s posterior aspect and in the back.
Anterior axio-appendicular muscles: Pectoralis major, pectoralis minor, subclavius and serratus anterior.