The scapulothoracic joint is the articulation between the scapula and the thorax. It is not a true joint, but rather the broad contact between the inner surface of the scapula and the rib cage. The scapula is able to slide relative to the rib cage to allow for elevation and depression, along with protraction/retraction, rotation and shoulder abduction. When the arm moves relative to the body, approximately two-thirds of this motion is at the glenohumeral joint and one-third at the scapulothoracic joint. Three relatively common conditions are seen at the scapulothoracic joint. In scapular winging, the serratus anterior or trapezius fail to stabilize the scapula. (The muscle weakness is in turn caused by dysfunction of the long thoracic or spinal accessory nerves, respectively.) Snapping scapula syndrome is characterized by a grating sensation, often from overuse and scapulothoracic bursitis. With so-called scapulothoracic dyskinesis, abnormal scapula motion disrupts the normal glenohumeral joint mechanics and leads to shoulder pain. It is also possible to have a traumatic disruption of the scapulothoracic joint with high energy trauma. This is known as a scapulothoracic dissociation.
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