Biomechanics Blog Post #3: Shoulder

 Scapulo-humeral Rhythm (SR) is the kinematic interaction with the humerus and scapula. It is a description of shoulder elevation, which is a crucial osteo-kinematic movement to allow an individual to be considered independent. It contains two major joints: scapulothoracic (1 degree) and glenohumeral (2 degrees) joints, which result in a 1:2 ratio. The main clinical relevance of this rhythm consists two major factors: prevents impingement between the humerus and the acromion, and it preserves the length-tension relationship of the glenohumeral muscles. This means it can sustain force production through a larger range of motion. It can affect range of motion in many ways. In one way, if the SR was not present in the shoulder, then it would become rigid and limit ROM. If the scapula does not upwardly rotate, then it will lead to shoulder impingement, which limits ROM. Since SR is considered to have joint congruency, then if one joint is injured then it will negatively affect ROM. SR keeps the length for the deltoids, and it saves it from active insufficiency, which positively affects ROM to reach the full 180 degrees.