Scapula

The scapula is a flat, triangular bone on the back of the shoulder that articulates with the humerus and clavicle and helps form the shoulder joint.

Glenoid cavity: A shallow socket on the scapula that articulates with the head of the humerus. This socket forms the scapular side of the shoulder’s main ball-and-socket joint.
Scapulohumeral rhythm: The coordinated movement of the scapula and humerus during arm elevation. The scapula rotates as the humerus rises, preserving joint alignment and range.
Scapular fracture: A break in the scapula, usually caused by substantial trauma. Its protected position makes fractures uncommon and often signals serious associated injury.
Glenohumeral joint: The shoulder joint formed by the humeral head and the glenoid cavity of the scapula. This is the scapula’s principal articulation with the upper arm.
Acromion: A projection of the scapula that extends over the shoulder joint and articulates with the clavicle. Its joint with the clavicle anchors the scapula to the collarbone.
Rotator cuff: A group of four muscles and tendons that stabilizes and moves the shoulder joint. Its muscles act on the scapula and humerus to center the joint during movement.
Winged scapula: A condition in which the medial border of the scapula protrudes from the back. Damage to muscles or nerves that stabilize the scapula can produce this visible sign.
Acromioclavicular joint: The joint between the acromion of the scapula and the clavicle. It contrasts with the glenohumeral joint by linking the scapula to the collarbone.
Coracoid process: A hook-shaped projection of the scapula that provides attachment for muscles and ligaments. This projection anchors structures that stabilize and move the shoulder.
Serratus anterior: A muscle that attaches the ribs to the medial border of the scapula and protracts and rotates it. It holds the scapula against the rib cage and helps rotate it upward.

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