Scapulohumeral Rhythm

     The scapulohumeral rhythm is important in movement and to obtain  full ROM at the shoulder. This rhythm is present in shoulder elevation, flexion and abduction and really whenever you are reaching to grab something in a tall cabinet at work or for a snack on the top shelf of the pantry. In order to perform this movement the scapula, humerus and glenoid fossa must move and work together. As the scapula moves upward, the glenoid fossa will tilt up to maintain contact with the humerus that is rolling superiorly. It is imperative that they all work together because each part  contributes to total ROM and if one part of this chain is not functioning properly, there will be a decrease in ROM. The scapulohumeral rhythm also helps maintain the subacromial space which will result in impingement and pain if not maintained. This impingement can also lead to rotator cuff muscle weakness and scapulthoracic muscle weakness which will negatively effect the dynamic stabilization of the shoulder. The scapulohumeral rhythm collaborative motion is caused by the shoulder being classified into two joints: scapulothoracic (ST) and the glenohumeral (GH) joints. These joints have a 1:2 ratio for shoulder movement. This means that for every 3° of shoulder movement there will be 1° at the ST joint and 2° at the GH joint. So for a full ROM at the shoulder of 180°, 60° will come from the ST joint and 120° will come from the GH joint. These joints working together will allow for joint congruency which will result in decrease shear forces and will permit optimal length tension relationships for the abductors muscles. Without scapulohumeral rhythm, full shoulder ROM will not be achieved and pain and impingement are likely to occur.