Scapulohumeral rhythm (also called as glenohumeral rhythm) is the kinematic interaction between the scapula and the humerus, given by Codman in the year 1930.
This coordinated interaction is important for the optimal function of the shoulder. When there is a change in the normal position of the scapula relative to the humerus, can this can cause a dysfunction of the scapulohumeral rhythm. The change of the normal position is also called scapular dyskinesia.
The purpose of the scapulohumeral rhythm is two-fold. First, it allows the glenoid fossa to maintain a good position for the various movements of the head of the humerus. Second, the changing position of the glenoid fossa allows for a better length-tension relationship in the muscles acting across the glenohumeral joint to produce shoulder motion
There are two key motion components of the scapulohumeral rhythm. The first is abduction of the glenohumeral joint. Abduction of the glenohumeral joint is produced primarily by the supraspinatus and deltoid muscles. The second part of the scapulothoracic rhythm is upward rotation of the scapula. Upward rotation of the scapula is produced primarily by the upper and lower fibers of the trapezius as well as the serratus anterior muscle.
FEATURES OF ABNORMAL SCAPULOHUMERAL RHYTHM
Typically signs of abnormal scapulohumeral rhythm includes :
Studies have shown abnormal scapulohumeral rhythm as a major cause of rotator cuff impingement.
Scapulohumeral rhythm is a common metric for assessing muscle function and shoulder joint motion. There is a three dimensional scapular kinematic pattern during normal arm elevation that include upward rotation, posterior tilting and varying internal/external rotation dependent on the plane and angle of elevation. When there is a change in the normal position of the scapula related to the humerus, the scapulohumeral rhythm is disturbed.
CAUSES OF ABNORMAL SCAPULOHUMERAL RHYTHM
Alterations in scapular position and control afforded by the scapula stabilizing muscles are believed to disrupt stability and function of the glenohumeral joint, thereby contributing to shoulder impingement, rotator cuff pathology and shoulder instability
Joint causes include high grade AC instability, AC arthrosis and instability and GH joint.
Bony Causes include Thoracic Kyphosis, Clavicle Fracture.
EXERCISES TO IMPROVE SCAPULOHUMERAL RHYTHM