shoulder anatomy

The shoulder anatomy is made up of many different parts working together.  The Anatomy of the shoulder includes nerves, shoulder muscles, blood vessels, bursae, bones, joints, ligaments and tendons. These parts can be viewed via a shoulder exam, such as a MRI. The bones forming part of the shoulder are the humerus (upper arm bone), the clavicle (collarbone) and the scapula (shoulder blade).

The shoulder is comprised of four important joints that enable the shoulder to move in different directions.  The gliding of the shoulder blade against the rib cage ribs 2-7 forms a false joint or scapulothoracic joint. This joint is referred to as a false joint because it has no capsule or ligaments attachments. The acromioclavicular joint is located at the top of the shoulder. It is formed where the collarbone meets the acromion, shoulder blade’s part forming the highest shoulder point. Its function is to move the arm above the head. The sternoclavicular supports the arms and muscles when connecting to the main skeleton at the front of the chest. The glenohumeral joint is the main shoulder joint. It is formed when the humerus fits into the glenoid, a shallow socket, on the scapula. Glenohumeral joint is responsible for the arm rotations and being able to move away from the body.

Ligaments are soft tissues structures allowing for the connection of bones to bones. Every joint has a water sac surrounding it. This joint capsule is formed by a group of ligaments connecting the humerus to the glenoid. Shoulder dislocation is prevented by ligaments that hold the shoulder in place hence providing stability.

Tendons are soft connective tissues structures. Their function is to attach muscles to bones. Because of the presence of tendons, muscles are able to move bones by pulling on them. The shoulder also comprises of rotator cuff tendons connecting the humerus to the deepest muscle layer. What enables us to raise our arms from the side are the rotator cuff muscles and the tendons.

Shoulder muscles work together to aid in the movement and support of the shoulder.  The shoulder muscles are the deltoid muscles and the rotator cuff muscles. The deltoid muscles link the chest and the arm and give the shoulder its well rounder figure, while the rotator cuff muscles give stability rotate it in many directions.

There are three main nerves in the shoulder. These are the median nerve, the ulnar nerve and the radial nerve. Their work is carrying signals to the muscles responsible for arm movement. Axillary nerve provides motor signals to deltoid muscle and sensations to the small area of the outer shoulder skin. The shoulder has a rich supply of blood due to the blood vessels supplying the arm with blood. Bursa is a fluid filled sac that is found between the rotator cuff muscles and the larger outer layer of muscles.

Many different conditions lead to shoulder pain. These are frozen shoulder, bursitis, tendonitis, rotator cuff tear, shoulder dislocation and impingement. Other diseases causing pain are gout, arthritis and osteoarthritis. A shoulder exam is usually done to diagnose if one has any of these conditions. First is a physical exam, then for further diagnosis an MRI, an X-ray, and a CAT scan are done.