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Shoulder anatomy: resources

The shoulder is the most complex joint in the body with the greatest range and freedom of movement. It comprises four separate joints which form the shoulder girdle, these are:

  • Glenohumeral joint
  • Acromioclavicular (AC) joint
  • Sternoclavicular joint
  • Scapulothoracic joint

The shoulder complex requirements co-ordination of these different joints and the muscles and tendons that power them. Because of the great range of movement the shoulder is one of the most unstable joints of the body.

The picture below depicts the bone in the shoulder.

The stability of the shoulder is provided by dynamic and static factors. The static factors include the shapes of the bones, the ligaments and lining of the shoulder. The main dynamic factor is the rotator cuff. This is a group of muscles and tendons that attach to the humerus. This acts to compress the humeral head against the glenoid and assist in rotation and elevation of the arm.

The Rotator cuff muscles are:

  • Supraspinatus - attaches to greater tuberosity
  • Infraspinatus - attaches to greater tuberosity
  • Subscapularis - attaches to lesser tuberosity
  • Teres minor - attaches of greater tuberosity

please watch the video on shoulder anatomy

 

 

This image shows a scan of the supraspinatus and its insertion point.

The capsule of the shoulder is thickened to form ligaments which tighten up is certain arm positions. When a shoulder dislocates these ligaments are stretched. There is also a thickened piece of fibrocartilage 'the labrum' which deepens the socket and provides the attachments for the ligaments.

The arthroscopy pictures show a normal labrum attached to the socket and a torn labrum injured at a shoulder dislocation.

Andrew Brooksbank