There are three shoulder joints: glenohumeral, acromioclavicular, and sternoclavicular. The glenohumeral joint is formed between the head of the humerus and the lateral scapula. It is a ball and socket joint that allows the arm to rotate or to hinge out and up away from the body. The acromioclavicular joint is formed between the acromion of the scapula and the clavicle. It allows a person to raise their arm above the head. The sternoclavicular joint occurs at the medial end of the clavicle with the top most portion of the sternum. Its main function is to stabilize shoulder movements.