The acromioclavicular joint is where the acromion, part of the shoulder blade (scapula), and the collar bone (clavicle) meet. The glenohumeral joint is where the ball (humeral head) and the socket (the glenoid) meet.
Rotator cuff anatomy
The rotator cuff connects the upper arm bone to the shoulder blade. It is made up of the tendons of four muscles:
The deltoid muscle forms the rounded curve of the shoulder. Tendons attach muscle to bone. Muscles move bones by pulling on the tendons.
The deltoid and the rotator cuff are important for shoulder movement. The deltoid is a strong muscle that moves the arm away from the body and allows overhead motion. The rotator cuff helps with that movement and keeps the ball tightly in the socket during shoulder motion. The reverse shoulder replacement is special because the parts are made differently so the deltoid can raise the arm without the rotator cuff.