Biomechanics- Scapulohumeral Rhythm

Scapulohumeral rhythm is referring to the collaborative movements of the head of the humerus and the scapula. When the shoulder moves it must be a sychnonus movement between scapula and humerus so any minor issue can lead to loss of function of the entire shoulder. This rhythm is what allows for full ROM so when working on ADLs the shoulder will be a common target area, as it allows for a great range of hand placement. This rhythm allows the abductors to maintain an optimal length-tension relationship. It also help to maintain the subacromion space, which if not being maintained could impinge the suprapinatus tendon, subacromial bursa, long head of the biceps, and the shoulder joint capsule. Scapulohumeral rhythm is important to note when understanding shoulder movement measurements. The rule is that for every 3 degrees of shoulder movement there is 1 degree of movement at the scapulothoracic(ST) joint and 2 degree as the glenohumeral(GH) joint. This means if there is 150° of shoulder movement, 50° is from the ST joint and 100° from the GH joint. If the measurement is not reaching full ROM this rule will help the therapist to target which joint needs to be further assessed. In scapulohumeral rhythm the humeral head should laterally rotate so if full ROM is not met the therapist should assess lateral rotation of the humerus.