The Relevance of Scapulohumeral Rhythm and How it Affects Range of Motion

The scapulohumeral rhythm is very important in movement. The scapula must move in order to maintain contact with the humerus. As the scapula rotates, the glenoid fossa also rotates to maintain contact with the head of the humerus to allow full abduction of the shoulder. As the scapula rotates upward, the optimal length-tension relationship develops from the abductor muscles. The scapulohumeral rhythm maintains the subacromial space in the shoulder and prevents impingement of the structures that pass beneath it. Scapulohumeral rhythm allows for the scapula and humerus to move together and can greatly affect the range of motion (ROM) measurements of the shoulder. This rhythm influences how these structures interact to produce movement at the shoulder. The collaborative movement between the scapula and humerus allows the movement of the shoulder to be distributed between two joints. The ratio for movement between the scapula and humerus is 2:1; for every 3 degrees of movement in the shoulder, 1 degree comes from the scapulothoracic (ST) joint and 3 degrees come from the glenohumeral (GH) joint. In order for the shoulder to move the full 180 degrees, 60 degrees of movement comes from the ST joint and 120 degrees comes from the GH joint. Without adequate scapulohumeral rhythm, ROM can be impaired and impingement of the subacromial space can occur.