Scapulothoracic anatomy and snapping scapula syndrome
The scapula is essential for load transfer from the trunk to the upper extremity – it has various muscular insertions that allow positioning of the scapula and thereby the glenoid fossa relative to the trunk. Other muscles, originating from the scapula, help positioning the arm in space.
As a result of its flexibility, the absence of osseous constraints and finely-tuned movements in the sternoclavicular, acromioclavicular, glenohumeral and scapulothoracic articulations, the shoulder joint is the most mobile joint in the body. The scapulothoracic articulation differs from the other articulations in the sense, that no joint capsule, synovium or cartilage is present.
In the scapulothoracic articulation, three layers of muscles and bursae have been described, that facilitate sliding movements to adjust the position of the scapula: the superficial plane consists of the trapezius and latissimus dorsi muscles, the intermediate level includes the rhomboid muscles and the levator scapulae and the deep layer is formed by the subscapularis and serratus anterior muscles and additional bursae: the infraserratus and supraserratus bursae.