Clinical Relevance of the Scapulohumeral Rhythm

Blog Post #3

Your scapulohumeral rhythm consists of muscle contractions and motions that occur between your scapula and humerus. Scapulohumeral rhythm is needed for a person to have efficient arm movement. Without proper scapulohumeral rhythm, a multitude of problems can occur including shoulder impingement syndrome, which is when bursa or tendons in the shoulder have parts of the shoulder bone pressed into them. For full range of motion in the shoulder the humeral head has to rotate laterally in the body. This particular motion comes through the assistance of the scapulohumeral rhythm and is distributed between two joints: the glenohumeral joint and the scapulothoracic joint.

 The scapulohumeral rhythm is based off a ratio, the ratio of movement between the scapula and humerus. This ratio needs to be kept in mind while measuring ROM in the shoulder. It is a general rule that for every 3 degrees of shoulder movement there is one degree at the scapulothoracic joint and 2 degrees at the glenohumeral joint. In a full 180 degrees of motion, there are 60 degrees of motion from the scapulothoracic joint and 120 degrees from the glenohumeral joint. So for example, is your scapulohumeral rhythm is working correctly, and you have your body at about 120 degrees abduction, then based off the 2:1 ratio your glenohumeral joint should be at 80 degrees and the scapula at 40 degrees.

Images from: 

http://hometraininguae.com/yoga-straps-for-scapular-strength

https://www.academyofclinicalmassage.com/the-scapulohumeral-rhythm/

https://www.local-physio.co.uk/articles/shoulder-pain/shoulder-impingement-syndrome/