Scapulohumeral Rhythm
The shoulder joint has the greatest range of motion in the human body. It is described as a ball and socket synovial joint. Due to its wide range of mobility, this joint lacks in stability. Both the scapula and humerus work to provide motion at this joint. The rule for scapulohumeral rhythm is as follows: for every 3 degrees of shoulder motion, approximately 1 degree occurs at the scapulothoracic (ST) joint and two degrees occurs at the glenohumeral (GH) joint. Scapulohumeral rhythm is important because it decreases the amount of sheer forces at the shoulder joint, and it allows for healthy length-tension relationships. Damage to either one of these areas greatly affects range of motion at the shoulder. Understanding scapulohumeral rhythm increases our understanding of range of motion. For example, during shoulder flexion, the GH joint contributes approximately 100-120 degrees (2/3 of a normal 0-180 range). Additionally, the ST joint contributes ...