What is the overall ratio of glenohumeral to scapulothoracic motion in scapulohumeral rhythm?

In scapulohumeral rhythm, the overall ratio of glenohumeral motion (movement at the shoulder joint) to scapulothoracic motion (movement of the scapula on the thoracic wall) is established as 2:1. This means that for every two degrees of movement that occur at the glenohumeral joint, there is one degree of movement at the scapulothoracic joint.

This 2:1 ratio is crucial for the overall function of the shoulder complex, allowing for optimal range of motion and stability. During shoulder abduction and flexion, both the humerus and scapula must work in concert. The glenohumeral joint provides the majority of the motion, while the scapula provides the necessary support and positioning to facilitate that movement, as well as to maintain the optimal positioning of the glenoid fossa in relation to the moving humeral head.

As a result, this rhythmic interplay between glenohumeral and scapulothoracic motion is vital in preventing shoulder dysfunction and maximizing the effectiveness of upper limb activities. Understanding this ratio is fundamental for physical therapists when assessing and treating shoulder conditions, ensuring that both components are functioning harmoniously.