Anatomy
In keeping with the scope of this site, our descriptions of anatomy will cover bone and muscle structures and articulations.
Bone Anatomy
Shoulder complex bones are the clavicle, scapula and humerus.
The scapula, an irregular bone, is located dorsal to the thorax. Major features include the spine of the scapula, the acromion process and coracoid process. The clavicle, also known as the collar bone is oriented horizontally. Clavicles medially connect, via ligaments, to the opposite clavicle, the sternum, and superior ribs. The lateral portion connects to the coracoid and acromion processes of the scapula. The humerus is a long bone articulating proximaly with the glenoid fossa of the scapula to make the glenohumeral joint. JointsAcromioclavicular - acromion process of scapula articulates with the distal clavicle
Coracoclavicular - coracoid process of scapula articulates with the distal clavicle Scapulothoracic - not a typical joint but is a "physiological" articulation of scapula and thoracic wall Sternoclavicular - articulation of sternum and clavicle Glenohumeral - glenoid fossa of the scapula articulates with the humeral head of the proximal humerus |
Muscle Anatomy
Shoulder complex muscles provide a wide range of motion in which, at various points, each of the three bones may be displaced greatly from anatomical position. Some muscles both originate and insert on shoulder complex bones, while some originate from the thorax or cervical region.
Pectoralis major, latissimus dorsi, trapezius, and deltoid muscles each have long lines of origin that allow wide angles of action.
Differences in moment arms and muscular attachment and strength provide a general trend in strength of shoulder complex movements. Movements from strongest to weakest: adduction, extension, flexion, abduction, internal rotation, and external rotation.
Pectoralis major, latissimus dorsi, trapezius, and deltoid muscles each have long lines of origin that allow wide angles of action.
Differences in moment arms and muscular attachment and strength provide a general trend in strength of shoulder complex movements. Movements from strongest to weakest: adduction, extension, flexion, abduction, internal rotation, and external rotation.