Rhythm In Motion

Scapulohumeral rhythm is a term used to describe the relationship between the movement of the scapula and the movement of the humerus. In general, the movement of the glenohumeral joint compared to the movement of the scapulothoracic functional joint has a ratio of 2:1. This means that during full 180° arm elevation, 120° will be movement at the glenohumeral joint while the remaining 60° is movement at the scapulothoracic joint. 

Clinically, scapula movement is necessary to help maintain the subacromial space and avoid shoulder impingement. Also, scapulohumeral rhythm distributes the motion between two joints and allows for optimal length-tension relationship of the muscles involved. This joint congruency decreases the shear forces by keeping the glenoid fossa of the scapula in a position where it can hold onto the humeral head. This also helps prevent active insufficiency of the muscles around the glenohumeral joint.