Scapula

The scapula, commonly called the shoulder blade, is a flat, triangular bone located on the posterior thoracic wall. Along with the clavicle, it forms the pectoral girdle, which supports and positions the upper limb. The scapula articulates with the humerus at the glenohumeral joint and with the clavicle at the acromioclavicular joint .^1,2

The scapula has three borders, three angles, and several prominent landmarks. On its lateral side, the shallow glenoid cavity receives the head of the humerus to form the glenohumeral joint. A prominent ridge on the posterior surface, called the scapular spine, expands laterally into the acromion, which articulates with the clavicle. Another projection, the coracoid process, extends anteriorly and provides attachment for several muscles and ligaments .^1,2

The broad surfaces and borders of the scapula provide attachment sites for numerous muscles that move or stabilize the shoulder and upper limb. These include the rotator cuff muscles as well as muscles that position the scapula relative to the thorax. Movements of the scapula, including elevation, depression, protraction, retraction, and rotation, contribute substantially to the overall mobility of the shoulder girdle and upper limb .^1,2

The scapula does not form a conventional synovial joint directly with the ribs. Instead, it moves over the posterior thoracic wall through an interface of muscles and connective tissues commonly called the scapulothoracic articulation. This is a functional articulation rather than a true anatomical joint and is distinct from the scapula's joints with the clavicle and humerus .^1,2