Biomechanics - Scapulohumeral Rhythm

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The shoulder complex is just like the name suggests-- complex! Functional movements of the arm and shoulder require the clavicle, scapula, and humerus to work together in a kinetic chain. If dysfunction occurs in one joint or body structure in the complex, the function and movement of the whole complex will suffer. This relationship is known as the "scapulohumeral rhythm" and specifically refers to the collaboration of the scapulothoracic and glenohumeral joints. For full range of motion to occur, the humeral head must remain in optimal alignment with the glenoid fossa (1). When reaching above the head, the scapula rotates upward to permit this alignment, as well as to maintain an optimal length-tension relationship among the abductor muscles (2). As the glenoid and humeral head remain in alignment, shear forces are decreased, reducing the risk of friction and associated pain (3). If the scapula does not upwardly rotate adequately, the subacromial space is limited, and the structures inside the space can become impinged (4). Dysfunction of the scapulohumeral rhythm can also result in changes to ROM measurements. For full 180° of shoulder abduction, 60° of motion occurs at the scapulothoracic joint and 120° at the glenohumeral joint. Thus, problems with either joint will severely affect the ROM of the client (5).

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