The shoulder is a mobile joint that allows the arm to move in many different directions. It is a ball and socket joint but, unlike the hip joint, which has a deep socket for the ball of the hip to fit into, the shoulder socket is very shallow. It has been compared to a “golf ball” on a tee.” The surrounding muscles and ligaments provide stability to keep the shoulder in the socket and allows for a removable range of motion.
The glenoid is the socket of the shoulder joint. It is made of bone and its surface has a smooth layer, called articular cartilage.
The humeral head, or the head of the humerus, fits into the glenoid. The humeral head also has articular cartilage. The glenoid and the humeral head make up the shoulder joint, also know as the glenohumeral joint.
The labrum is a piece of fibrous tissue made of a different sort of cartilage, called fibrocartilage, which surrounds the glenoid. It forms a rim like structure which aid in stabilizing the joint and provides an attachment for the ligament of the shoulder. The labrum can tear which can lead to the shoulder being unstable, or dislocating out of the socket.
The acromion is a bone located on the top of the shoulder joint. It can have a hook of bone in front which can pinch the rotator cuff and the bursa leading to impingement or bursitis.
The bursa is a fluid-filled sac that helps cushion the rotator cuff so the muscles and tendons can move smoothly. The bursa can become inflamed and lead to bursitis (Impingement).
The rotator cuff muscles surround the shoulder joint and act to move and stabilize it. There are four different rotator cuff muscles. They attach are four different rotator cuff muscles. They attach to the humeral head by way of tendons. When these tendons get irritated, it is tendinitis. When these tendons actually tear, either partially or completely, from the humeral head, this is what is known as the rotator cuff tear. Unfortunately, complete rotator cuff tears do not heal and must be reattached surgically.
The ligaments of the shoulder are thickenings of the shoulder capsule or sac that surrounds the shoulder joint. The ligaments are cord-like and help to stabilize the shoulder joint and keep the ball within the socket.
The clavicle, or collarbone, is the main bone that connects the shoulder to the rest of the body. The acromioclavicular joint is made up of where the acromion meets the clavicle. It is stabilized by ligaments. When these ligaments become damaged, sprained, or torn, it is called shoulder separation.
To see more information about the shoulder, including video animations of shoulder anatomy and other shoulder injuries and ways to treat them, please click here.