What is the shoulder?

The shoulder is a complex joint that connects the arm to the trunk. It is made up of three bones and four ligaments that work together to allow the arm and hand to be positioned as desired by an individual. A wider range of movements are made by the shoulders that require a greater freedom of action, which also responds to greater instability. In order to cope with these types of situations, the shoulders’ complex tendons and muscles come into play.

The shoulder is a more complex and sophisticated joint that enables more movement possibilities of the whole organism. The bones that form the shoulder joint are known as the humerus (upper arm bone), the scapula (shoulder blade) and the clavicle (collarbone). In order to be fully functional, it is associated with a number of ligaments, tendons, muscles and nerves that allow movement, and blood vessels that allow the survival of tissues that compose it. The upper part of the shoulder is articulated between the scapula and the clavicle, while the lower part is articulated with the sternum. The shoulder joint is also comprised of the part of the body where the humerus attaches to the scapula, the head sitting in the glenoid cavity. The so-called humerus tubercles allow the muscles of the rotator cuff to attach securely to the shoulder joint. 

The four ligaments associated with the bones of the shoulder include the following: the glenohumeral ligaments (upper, middle and lower), which connect the humerus to the glenoid cavity and are responsible for most of the shoulder’s stability;  the coracoacromial ligament, which connects the scapula to the clavicle; the coracoacromial clavicle ligaments (conoid and trapezoid), which combine the clavicle to the scapula by allowing them to remain attached bearing heavy loads; and finally, the transverse humeral ligament, which keeps the tendon of the long head of the biceps in motion between the two tubercles of the humerus.

Common conditions associated with the shoulder include rotator cuff tear and bone fractures of one or more of the bones of the shoulder. Due to the fact that it is the most movable joint in the body, shoulder problems (including pain) are more likely to occur because of the range of motion allowed. Shoulder instability, whether from a degenerative process or possible injury, requires medical attention. Seeking the most appropriate form of treatment is essential in order to prevent symptoms from worsening. 


What function does the shoulder serve? 

The shoulder connects the arm and hand to the trunk and allows them to be positioned and moved about as desired. By sliding along the rear part of the chest, the scapula allows broad based movements to be made with the arm. Coming into play are also the articulation between the scapula and humerous, as well as the scapulothoracic articulation i.e. that between the shoulder blade and ribs, located at the back of the chest.

The muscles and joints of the shoulder permit flexion and extension of the arm, making it one of the most mobile joints in the human body. It can also abduct and adduct (move away or move toward the side), rotate externally and internally (outward and inward), as well as rotate anterior and posterior (frontwards and backwards).