Shoulder Girdle: Structure, Function & Diseases

The shoulder girdle is probably one of the most elegant regions of the human body: by cleverly combining bones and muscles, nature has extracted the truly maximum range of motion from the joint here. The main role, however, is played by the muscles.

What is the shoulder girdle?

Schematic diagram showing the anatomy of the shoulder. Click to enlarge. In the human body, the shoulder girdle refers to that part that connects the upper extremity to the trunk. It basically includes two bones, scapula (shoulder blade) and clavicle (collarbone), three joints, the sternoclavicular joint, the acromioclavicular joint, and the shoulder joint, and lots of muscles.

Anatomy and structure

The anatomy of the shoulder girdle is quite flowery to describe in words, but usually difficult to understand without a corresponding illustration. The scapula is actually very loosely integrated into the rest of the skeleton as a triangular, planar bone with a base at the top and apex at the bottom:

The only bony connection to the trunk is actually that anterior one via the narrow clavicle, which in turn is connected only to the sternum. Of course, this connection is not particularly load-bearing, especially considering that the scapula on the other side is the only connection to our arms, which are not only constantly used for heavy labor, but also have a considerable weight of their own. Therefore, the main load is borne by the muscles of the shoulder girdle, which clamp, secure, and at the same time always make the shoulder blade move forward to the chest, upward, toward the spine, toward the back muscles, and of course toward the arm. In the end, the scapula, pulled by these muscles, slides along the ribs of the posterior rib cage without any real cartilaginous articular surface between them. From this it is already clear that tensing the arm without tensing the shoulder girdle would make no sense at all: it would practically tear the scapula from its suspension. The muscles are roughly divided into anterior and posterior trunk-shoulder girdle muscles, the enumeration of which would lead too far at this point. The best-known representative is perhaps the trapezius muscle, which connects the thoracic and cervical vertebrae to the scapula and clavicle in a diamond shape on the back and is thus responsible for pulling the scapula towards the spine, for example when lifting objects. Important vascular and nerve pathways pass through the region of the shoulder girdle, especially below the collarbone. If they are damaged by accidents or other space-occupying lesions, there is a risk of defined failures or supply bottlenecks in the shoulder region or in the arms and hands.

Functions and tasks

The function of the shoulder girdle, in summary, is to provide stability between the trunk and upper extremity. Because this is done primarily through muscular action, the shoulder girdle is an incredibly flexible part of the body. The individual bony joints between the clavicle and the scapula or sternum have little movement in relation to each other, but in combination with the shoulder joint and muscle plate, this results in an incredibly large range of motion for the arm. This should be about 180 degrees of abduction, 40 degrees of tightening, 170 degrees of leading, 40 degrees of returning, and about 70 degrees of rotation in both directions in a healthy young person.

Diseases and ailments

If the degrees of shoulder motion are limited and at the same time there is pain at rest or during certain movements, this may indicate various diseases or injuries of the shoulder. With regard to the shoulder girdle in the narrower sense (i.e., leaving out the acromioclavicular joint), clavicle fractures are of particular importance. It is the most common fracture in humans at all. It usually occurs during a fall onto the outstretched arm, since the greatest stresses occur at the clavicle (and at the radius of the forearm). The clavicle usually breaks in the middle third, the fracture pieces then usually stand bent, by pulling the powerful neck muscle with the long name (Musculus sternocleidomastoideus). Thus, the clavicle fracture is often easily visible from the outside. A backpack bandage is the conservative method of treatment.Stabilization with a plate is sometimes indicated and, in principle, is not a major procedure since the bone is readily accessible.