Anatomy of the Shoulder.
The muscles and joints of the shoulder make it the most mobile joint in the human body.
The bony anatomy of the shoulder consists of the upper arm (the proximal humerus) and the shoulder blade (the scapula). The ball of the shoulder socket is called the humeral head. The shoulder socket is called the glenoid. The roof of the shoulder originates from the scapula and forms a bony arch. This roof coming from the back of the scapula is called the acromion. The bony arch orginating from the front of the shoulder is called the coracoid process. The ligament connecting the coracoid process and the acromion is called the coracoclavicular ligament. The acromion meets the collarbone (clavicle) at a junction called the AC joint (acromioclavicular joint).
There are several other ligaments that connect the bones of the shoulder together and work to stabilize the shoulder.
The rotator cuff is a group of four muscles that originate on the shoulder blade and pass around the shoulder to where their tendons fuse to the ball of the humerus. They help with shoulder movement, and also work to keep the ball of the shoulder in the socket.
The supraspinatus is the tendon that attaches to the top of the humerus and enables outward reaching. The infraspinatus and the teres minor attach to the back of the humerus and act to externally rotate the arm. The subscapularis tendon attaches in the front of the humerus and internally rotates the arm.
The humeral head (ball) and the glenoid (socket) have a smooth white surface coating called cartilage that allows smooth gliding shoulder joint motion.
The labrum is the ring of cartilage that surounds the socket and helps with shoulder stability.
The biceps tendon at the shoulder travels in between the supraspinatus and the subscapularis tendons to attach at the top of the socket.