Scapulohumeral Rhythm

What is the clinical relevance of the scapulohumeral rhythm? How can it affect your ROM measurements of the shoulder? Please give at least 5 reasons in your response

Scapulohumeral Rhythm is defined as a kinematic interaction between the scapula and the humerus. The ratio of movement among the shoulder movement, scapula, and humerus is 3:2:1. For example: if there is full range of motion for shoulder abduction (180 degrees), 120 degrees of movement should happen at the glenohumeral joint and 60 degrees of movement should happen at the Scapulothoracic joint. Because of this, it is important to stabilize the scapula when measuring true glenohumeral abduction or flexion ROM so that the ROM measurements are not skewed. (For example: the seemingly full range of motion measurements may be coming from an unstable scapula that exceeds its 60 degrees of movement while the humerus has less than 120 degrees of movement) 

In order to have full ROM for should abduction, scapulohumeral rhythm has to work to distribute the motion between the two joints and the humerus has to rotate laterally so that the scapula can upwardly rotate and posteriorly tilt. ROM at the shoulder can also be affected by other problems with scapulohumeral rhythm. The scapulohumeral rhythm distributes the motion between two joints, prevents impingement in the subacromial space and tearing of the supraspinatus muscle, permits good length-tension relationship, and helps with the alignment of the humeral head on the glenoid fossa.  It also provides joint congruency, which results in a decrease of shear forces. It is important for clinicians to understand scapulohumeral rhythm because dysfunction in the scapulohumeral rhythm can result in pain, instability, impingement, and decreased range of motion. It is also important to recognize when the client may be compensating due to scapulohumeral dysfunction and therefore may be causing more damage to their body. In addition, it is important to check for compensations when measuring range of motion so that measurements are not skewed.