Scapulohumeral Rhythm

The scapulothoracic rhythm is the synchronous movement between the scapula and the humerus during shoulder elevation. The scapulothoracic rhythm plays a huge role in the aligning of the humeral head with the glenoid fossa and permits an ideal length tension relationship. Due to this rhythm, the shoulder is able to move through full 180° of motion. The scapulothoracic joint contributes 60° to this motion and the glenohumeral joint contributes 120°. In other words, for every 3° of shoulder movement, the scapula contributes 1° and the humerus contributes 2°. This ratio is very helpful when it comes to measuring ROM because it can help practitioners identify which muscles and/or joints are disrupting full ROM. If a client's shoulder is incapable of full ROM, the practitioner could then measure the ROM at each joint to discover which one is not contributing as it should. If one or both of these joints is experiencing dysfunction, it results in an increase in shear forces and could cause impingement/pain. In addition to the importance of the two joints' 2:1 ratio, it is essential for the humerus to be able to laterally rotate during shoulder elevation. There are numerous reasons as to why someone might not be able to perform full shoulder ROM, but with this knowledge, the therapist might be able to discover the cause of the problem more easily. Finding the cause of the problem is essential for us as therapists so that we can help our clients restore function and help them get back to performing their meaningful activities of daily living.