Which joint contributes more to shoulder elevation between 90-180 degrees?

The acromioclavicular (AC) joint plays a crucial role in shoulder elevation, especially between 90 and 180 degrees of arm movement. This range of motion is primarily accomplished through a combination of scapular motion and glenohumeral motion.

When the arm is elevated above 90 degrees, proper scapular motion is essential for full range of motion at the shoulder. The AC joint facilitates the necessary upward rotation of the scapula, which allows for the glenohumeral joint to have a greater range of motion without impingement. This upward rotation of the scapula at the AC joint is vital for stabilizing the shoulder complex and maintaining efficient mechanics during overhead activities.

In contrast, while the sternoclavicular (SC) joint helps with the overall mobility of the shoulder girdle, and the glenohumeral (GH) joint provides the primary movement for arm elevation, the AC joint's mechanics specifically contribute to the higher stages of shoulder elevation by enabling the scapula to move effectively.

The scapulothoracic (ST) joint, although it includes the movements of the scapula against the thoracic wall, does not account for a specific joint action, making its contribution less direct in terms of joint