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23. 9. 2012.

Movements of the pectoral(shoulder) girdle

The pectoral girdle consists of the scapula and the clavicle, articulating with each other at the acromioclavicular joint. It provides the link between the upper limb and the axial skeleton via the shoulder(glenohumeral) joint and the sternoclavicular joint respectively. The flattened triangular scapula provides attachment for many muscles, some of which anchor the pectoral girdle to the thorax and others which control the position of the upper limb. The clavicle, however, acts primarily as a strut holding the upper limb away from the trunk. Because of the connections(both muscular and ligamentous) between the scapula and clavicle, movements of the pectoral girdle, either independently or in association with the upper limb, mean that both bones are always involved. The position and movement of the scapula are determined by the activity of the muscles attached to it. An individual muscle when acting in concert with various combinations of other muscles may be involved in producing several different movements of the pectoral girdle. Consequently, in the following account individual muscles will be described in detail according to their major action. Movements between the scapula and thorax are allowed because the fascia covering adjacent layers of muscles facilitates gliding and sliding movements.
The movements of the shoulder girdle are described as taking place from the anatomical position where the scapula lies obliquely over the second to seventh ribs on the posterior wall of the thorax with the coracoid process pointing anteriorly. The movements described are:
  1. Retraction – movement of the scapula, whilst maintaining its vertical position, such that its medial border approaches the vertebral column, as in bracing the shoulder. The glenoid fossa thus comes to face more directly lateral.
  2. Protraction – movement of the scapula forwards around the chest wall, as in rounding the shoulders. There may be some associated lateral rotation in this movement. The glenoid fossa comes to face more directly forwards.
  3. Elevation – where the pectoral girdle is lifted upwards as in shrugging the shoulders.
  4. Depression – where the pectoral girdle is pulled downwards.
  5. Lateral (forwards) rotation of the pectoral girdle is a complex movement whereby the inferior angle of the scapula moves laterally around the chest wall, while the strut-like action of the clavicle results in a concomitant upward movement of the scapula, thus causing the glenoid fossa to be turned increasingly upwards.
  6. Medial (backward) rotation of the pectoral girdle returns the scapula to its resting position from lateral rotation. 

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