The Relevance of Scapulohumeral Rhythm
Scapulohumeral rhythm is the ratio of movement between the scapula and humerus. The ratio is that every time the scapulothoracic joint moves 1 degree, the glenohumeral joint moves 2 degrees. Scapulohumeral rhythm affects range of motion (ROM) measurements at the shoulder because two joints are working together. Having two joints work together then increases the ROM at the shoulder joint. Scapulohumeral rhythm also results in a good length-tension relationship. This means that the muscles do not shorten as much as they normally would if the scapula was not rotated upward, which causes the muscles to maintain force longer. Scapulohumeral rhythm also causes decreased shear forces as the motion is distributed between the two joints. Scapulohumeral rhythm is clinically relevant when looking at a client who has complaints of shoulder pain or injury. Clinically, a client could come in with shoulder impingement which means their rotator cuff (RTC) muscles become weak and the humeral head elevates in the glenoid fossa, impinging the tendons of the RTC muscles. As future OT practitioners we need to know the signs and biomechanics of scapulohumeral rhythm to help our clients strengthen the precise muscles to regain correct scapulohumeral rhythm again.
