Rockin' to the Scapulohumeral Rhythm

What is the clinical relevance of the Scapulohumeral Rhythm? How can it affect your ROM measurements of the shoulder? Please give at least 5 reasons in your response

Scapulohumeral Rhythm is the kinematic movement or interaction between the scapula and the humerus. This movement is very important for the optimal usage of the shoulder. It helps us synchronize the movement between the scapula and the humerus, it also aligns the glenoid fossa with the head of the humerus. The scapulohumeral rhythm helps maintain a nice amount of space between the acromion and the humeral head, and helps decrease potential impingement.  In essence, when the humerus moves, it then moves the scapula and that interaction disturbs the scapulohumeral rhythm. When discussing the clinical relevancy, we know that the movement of the scapula can be described as rotations along the thorax. When the humerus adducts or abducts, the scapula moves within the frontal plane. The glenoid fossa, in response, turns upward in abduction, and turns downward in adduction. When the humerus moves (flexion or extension) in the sagittal plan, the scapula rotates posteriorly (posteriorly tilts) or anteriorly (anteriorly tilts) depending on the movement that is done. 

           When dealing with ROM in general,  for every 3° of shoulder movement there is  1° at the scapulothoracic joint (ST) and 2° at glenohumeral joint (GH). For a full 180° of motion there must be 60° coming from the ST joint and 120° coming from the GH joint. For complete ROM, the humeral head must be laterally rotated, if the humeral head is medially rotated it will have restrictions and not be able to produce full ROM. To have optimal usage, the motion should be distributed between the ST joint and the GH joint; by distributing the motion between tho joints it allows the person to have their full range of motion. This can be very helpful when trying to get the optimal usage out of the shoulder, however it can also cause ROM restrictions if one of the joints have some type of dysfunction. Since the scapulohumeral rhythm desperately depends on two joints,  if one is not working properly it can cause the person to not have optimal usage of their shoulder.