Anatomy of Shoulder

Functionality of Shoulder:

The complexity of the human anatomy is probably best seen in the movements of the shoulder joint. The humerus-scapula connectivity via muscle mass and tissues results in the formation of a group of structures that help in executing hand movements as well as generating the desired thrust to pick up and relocate objects in the periphery. The shoulder joints facilitate movements such as pushing and pulling, movements that are executed by everyone, throughout the day. The muscles and joints of the shoulder make the joint the most mobile in the human body. The shoulder can, not only abduct and adduct, but can also rotate clockwise and anticlockwise, along the torso.

Anatomy of Shoulder:

The shoulder anatomy comprises the collar bone or clavicle, the shoulder blade or scapula and the upper arm bone or humerus. These three main bones of the human shoulder are held in place by muscle mass, tendons and ligaments. The shoulder joints and their movements are the result of the flexibility of the tendons and articulations between the bones. Shoulder joint movements are facilitated by two kinds of cartilages. The articular cartilage is that which extends along the ends of the bones. This white cartilage facilitates the gliding movement of bones on one another. This constant friction in the region around the white cartilage causes it to wear out, initiating the onset of arthritis. Arthritis is a condition in which joints of the body, in this case the shoulder, become painful and stiff due to decreased lubrication between conjoined bones. The other cartilage in the shoulder region is the labrum. This fibrous cartilage is distinctly different from the articular cartilage. It is located only on the ends of the ball and socket shoulder joints.

The three main joints of the shoulder are acromioclavicular, glenohumeral and the sternoclavicular. The glenohumeral joint or the 'ball and socket' shoulder joint enables the arm to rotate in a circular fashion and to hinge out, away from the rest of the body alignment. This joint is the result of the articulation between the lateral scapula and the head of the humerus bone. It is characterized by the rounded anterior surface of the humerus bone and the dish shaped segment of the scapula, also referred to as the glenoid fossa. The shoulder mobility is facilitated by the fossa's shallow design and relatively loose shoulder-body connection. However, this additional mobility does not come without a drawback. The loose ball and socket shoulder joint is also the one that is most exposed to dislocation, compared to most other joints in the body. There is a soft tissue envelope that encompasses the glenohumeral joint, holding it in alignment with the scapula, humerus and biceps. The tissue is a synovial membrane that is strengthened by the coracohumeral and other glenohumeral ligaments.

The sternoclavicular shoulder joint is located at the end of the clavicle medial and the manubrium, the uppermost part of the sternum. This joint comprises a protective tissue and an intra-articular disc, both of which facilitate stability of the joint. Most shoulder movements are limited by the costoclavicular ligament, a limitation that reduces muscle damage and stabilizes the joint further. The range of shoulder movement is increased due to the flexibility of a fibrocartilaginous disc. Though sternoclavicular subluxation is rare, it is triggered by direct trauma. The serratus anterior shoulder muscle holds together the scapula and the thoracic wall, while the subclavius stabilizes the clavicle. The pectoralis minor muscle is responsible for the medial and protracting variations of the scapula. The sternocleidomastoid muscle actions flex and rotate the head, aiding respiration. The levator scapulae, rhomboid major and rhomboid minor, trapezius, rotator cuff and deltoid are other shoulder muscles that facilitate movement and functionality of the shoulder joint.