The shoulder is a ball-and-socket joint that allows the arm to rotate with a circular movement with the ability to hinge out, up and away from the body. It is made up of two joints, the acromioclavicular joint and the glenohumeral joint.
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.
The rotator cuff connects the humerus to the scapula and is made up of the tendons of four muscles, the supraspinatus, infraspinatus, teres minor and the subscapularis. Tendons attach muscle to bone and muscles in turn move bones by pulling on the tendons.
