Scapulohumeral Rhythm

The scapulohumeral rhythm is the ratio of movement between the scapula and the humerus. This movement must be be synchronous in order to maintain optimal congruency between the glenoid fossa and humeral head. This rhythm is important clinically in order to properly measure shoulder range of motion. For every 3° of shoulder movement, there is 1° of movement at the ST joint and 2° of motion at the GH joint. This means at full 180° of motion, there will be 60° from the ST joint and 120° from the GH joint. It is important to know these ratios in order to determine the cause of the problem if a client does not have full shoulder ROM. If the scapula doesn't move, there would be decreased ROM as well as friction in the joints. This mechanism also helps to maintain the subacromial space in order to avoid impingement. With proper joint congruency, shear forces are decreased as well. Without the scapulohumeral rhythm, we would not be able to participate in many of our activities of daily living such as brushing our hair or reaching up into a high cabinet to grab something.