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In other words, there is a rhythm between movements of the scapula and the humerus. Even though this term is excellent in that it expands our view of the functioning of the shoulder, it actually is not expansive enough. A better term for this coupled rhythm would be claviculoscapulohumeral rhythm because the clavicle also plays a crucial role in shoulder movement (Image 2). In fact, movement of the clavicle at the sternoclavicular joint may be the most underappreciated motion of the human body. To better understand the concept of scapulohumeral rhythm, we need to appreciate the fact that the primary purpose of the upper extremity is to place the hand in the positions necessary to work with and manipulate the world. Therefore, whatever joint motions are necessary to accomplish hand placement will work in concert toward this end. HUMERUS COUPLING WITH THE SCAPULA The best example of scapulohumeral coupling of motions is probably frontal- plane abduction of the arm. It is usually stated that the arm can abduct 180 degrees so that the arm is straight up in the air (Image 3A). However, the GH joint does not allow for 180 degrees of abduction. The GH joint itself allows only 120 degrees of humeral abduction, only two-thirds of the 180 degrees that is stated as full arm abduction. The other 60 degrees, the other one-third of this motion, is actually generated by upward rotation of the scapula relative to the rib cage of the thoracic body wall at the scapulocostal (ScC) joint (also known as the scapulothoracic joint). Upward rotation of the scapula is a movement of the scapula at the ScC joint relative to the rib cage such that the glenoid fossa of the scapula orients upward. This affords the head of the humerus the ability to continue rolling upward until the arm is vertical at 180 degrees relative to the trunk of the body (Image 3B). 52 m a s s a g e & b o d y wo r k m a rc h /a p r i l 2 0 2 1 Anterior and posterior views of the shoulder complex region. Permission Dr. Joe Muscolino. Kinesiology—The Skeletal System and Muscle Function, 3rd ed. (Elsevier, 2017). (A) 180 degrees of abduction of the arm. (B) Abduction of the arm involves humeral motion and scapular motion. Permission Dr. Joe Muscolino. Kinesiology—The Skeletal System and Muscle Function, 3rd ed. (Elsevier, 2017). ‚ Clavicle Clavicle Scapula Scapula B 180° 120° 60° A Rib cage Humerus Humerus ƒ