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Anatomy of the Shoulder


Lt Col Jerman
The anatomy of the shoulder allows it to have the greatest flexibility and range of motion of any joint in the body. Unfortunately, that anatomy can also allow the shoulder to become unstable or vulnerable to injury because the ball of the upper arm is larger than the shoulder socket that holds it. Dr. Patel, what else can you tell us about the anatomy of the shoulder?

Dr. Patel
Well, Dr. Jerman, muscles, tendons, and ligaments serve to hold the shoulder in a stable position by supporting the bones. The three bones of the shoulder are the upper arm bone, called the humerus; the shoulder blade, called the scapula; and the collarbone, called the clavicle.

Four joints in the shoulder connect these bones and provide the shoulder’s range of motion. Each of these joints can be injured and cause discomfort or pain.

The glenohumeral joint is the ball-and-socket that links the head of the humerus to the glenoid of the scapula. The acromioclavicular, or AC, joint is where the clavicle meets the acromion of the scapula. The sternoclavicular, or SC, joint connects the clavicle to the chest bone, or sternum. Where the scapula meets with the ribs at the back of the chest is called the scapulothoracic joint.

Ligaments are tough, fibrous tissues that connect bone to bone and provide stability for the joints. For example, the glenohumeral ligaments, or GHL, surround the glenohumeral joint and connect the humerus to the glenoid. Coracoclavicular ligaments, or CCL, attach the clavicle to the scapula. Both the GHL and the CCL help to keep the shoulder in place.

The rotator cuff in the shoulder is formed by a group of four muscles and tendons that connect the scapula to the humerus, providing support for the glenohumeral joint and initiating movement of the ball in the socket. The rotator cuff can be vulnerable to tears and weakening due to a number of causes, including trauma, strain, and overuse.

The shoulder also contains structures called bursal sacs, which are fluid-filled membranes within and around the shoulder. Bursal sacs cushion the joints and help minimize friction between the bones and muscles.