Scapulohumeral Rhythm

Scapulohumeral rhythm is the ratio of movement between the scapula and the humerus. It is important, especially for maximum ROM, for the joint to move in congruency with one another, meaning that the humeral head must maintain contact with the glenoid fossa. The changing position of the glenoid fossa allows for a better length-tension relationship with the muscles acting across the glenohumeral joint to produce shoulder motion. In general, for every three degrees of shoulder movement, there is a one degree of scapulothoracic (ST) joint movement (3:1 ratio) and two degrees of glenohumeral (GH) joint movement (3:2 ratio). Understanding how these movements articulate together is important in the clinical setting when considering why there are decreases in ROM, as well as shoulder complaints, such as pain, impingement, or frozen shoulder. Therefore, in order for the shoulder to abduct the full 180°, the ST joint must move 60° and the GH joint must move 120°. In order for therapists to understand the best way to treat various shoulder problems, they must be able to recognize and evaluate both the dysfunctional and correct movement patterns.