The shoulder girdle is made of the clavicle and the scapula on each side. It anchors the arm while giving the shoulder its wide range of motion.
The clavicle
The collarbone is an S-shaped strut between the sternum and the acromion of the scapula. It is the only bony link between the arm and the trunk and one of the most commonly broken bones.
The scapula
The shoulder blade is a flat triangle on the back of the ribs. Its acromion forms the tip of the shoulder, the coracoid process points forward, and the shallow glenoid holds the head of the humerus.
The joints
The sternoclavicular joint links the girdle to the trunk, and the acromioclavicular joint links clavicle to scapula. The glenohumeral joint trades stability for mobility, so it dislocates more than any other large joint.
Muscle attachments
The rotator cuff muscles arise from the scapula and wrap the head of the humerus. The scapula glides on the chest wall so the arm can be raised overhead.
At the bedside
The acromion is the landmark for the deltoid injection, given two to three fingerbreadths below it to avoid the axillary nerve. A fall onto the shoulder that leaves a step at the top of the shoulder suggests an acromioclavicular joint injury.
Related guides
Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).