Scapulothoracic Articulation

The shoulder complex consists of four distinct articulations the glenohumeral joint, the acromioclavicular joint, the sternoclavicular joint, and the scapulothoracic articulation. The wide range of motion of the shoulder (exceeding a hemisphere) is the result of synchronous, simultaneous contributions from each joint The most important function of the shoulder is arm elevation. Several investigators have attempted to relate glenohumeral and scapulothoracic motion during arm elevation in various planes... 

Table 49.13). About two-thirds of the motion takes place in the glenohumeral joint and about one-third in the scapulothoracic articulation, resulting in a 2 1 ratio. 

The scapulothoracic plane separates the body of the scapula and the subscapularis muscle from the thoracic surface, consisting of the superficial aspect of the serratus anterior muscle which overlies the ribs. This gliding plane allows the scapula and the glenoid cavity to tilt anteriorly and posteriorly around the rib cage during shoulder movements. In addition, the scapulothoracic articulation has an important role in shoulder abduction. 

The shoulder represents the group of structures connecting the arm to the thorax. The combined movements of four distinct articulations — glenohumeral, acromioclavicular, sternoclavicular, and scapulothoracic — allow the arm to be positioned in space. 

The two functional joints in the shoulder girdle are the suprahumeral joint and the scapulothoracic joint. As mentioned, both figure prominently in shoulder biomechanics and pathology. The suprahumeral joint is formed by the articulation of the head of the humerus with the coracoacromial arch, composed of the acromion, the coracoid process, and the ligament between them. Articulation occurs during abduction. 

The second functional joint is the scapulothoracic joint. This is formed by the scapula and the posterior thorax (ribs). Because muscle and fascia lie between the articulating surfaces, it is not a true joint with approximated articular surfaces and is also lacking a capsule. 

---