During phase II of scapulohumeral rhythm (90-180 degrees), how much movement comes from the glenohumeral joint?

In phase II of scapulohumeral rhythm, which occurs between 90 to 180 degrees of shoulder abduction, the movement of the glenohumeral joint contributes significantly to the overall motion. The total range of motion during this phase involves both glenohumeral and scapular movements. Specifically, the glenohumeral joint allows for about 60 degrees of abduction, while the scapula contributes about 30 degrees of upward rotation.

This understanding is critical because scapulohumeral rhythm refers to the coordinated movement of the shoulder girdle and the arm, which optimally distributes movement across the joints involved. By knowing that the glenohumeral joint contributes specifically 60 degrees in this phase, it highlights the relationship between the two joints during arm elevation. This rhythm is vital for ensuring full range of motion and functional use of the upper extremities while preventing excessive stress on the shoulder structures.

In conclusion, during the phase II of scapulohumeral rhythm, the glenohumeral joint's contribution of 60 degrees is essential for achieving the complex movements required for raising the arm above the head, while ensuring stability and efficiency in the shoulder complex.