Shoulder

Explanation

Here you will find the most important anatomical fundamentals of a healthy shoulder joint and an overview of all essential shoulder injuries with short definitions of the respective maladies.

The healthy shoulder joint

Anatomy

The shoulder is primarily a joint that is controlled by muscles. That means that the linkage of the joint is stabilized extensively by the musculature. The hip joint can be regarded as a contrast thereto; a significant portion of hip joint stability is guaranteed via a large-scale, bony surface contact of the joint partners and stable ligaments, which are very durable under pressure and can withstand enormous forces.

The muscular control of the shoulder joint has proven to be a great advantage, if one considers the degree of movement that has been gained thereby. However, a significant disadvantage also arises from the minimal contact surface between the head of the humerus and the glenoid cavity of the shoulder blade (glenohumeral joint). In comparison to the hip joint, the stability is much less; thus the shoulder joint is significantly more vulnerable to injury. .

1. Head of the upper arm (Humerus)
2. Shoulder acromion (Acromion)
3. Shoulder joint
4. Collar bone (Clavicle)
5. Coracoid process (Coracoid)
6. Shoulder joint (Glenohumeral joint)

Regarding types of maladies or injuries, three special diagnoses are especially conspicuous due to their frequency. These are shoulder pain upon moving the arm (impingement syndrome), a torn ligament in the interior level of the shoulder musculature (rotator cuff rupture), as well as a dislocation of the shoulder (shoulder dislocation). Without appropriate expertise, no conclusions can be drawn about the causes of these maladies. Therefore, an explanation is given here.

At first, consideration will be given to the components of the shoulder joint. Thereby, it will be easier to understand the injuries and their respective therapies.

In the graph, the upper arm is shown from the front with its upper arm head and the shoulder blade. One can recognize the relatively small surface of the joint, which links both bones together. In addition to the musculature, the upper arm has another support, among others, for stabilizing the shoulder joint. This consists of a cartilage lip (Labrum), which sustains the rounded form of the upper arm head in the same manner as the indentation of a saucer prevents a cup from sliding. The cartilage lip is called the Labrum glenoidale. If a portion of this cartilage lip is torn off, then a dislocation of the shoulder always occurs, even if no violent action has taken place, because the stability is impaired.

In the second graph, the interior shoulder musculature is shown (red arrow). These muscles, which originate, among others, from the interior and exterior sides of the shoulder blade, run through the bony channel (foramen) that is created by the shoulder blade (here the anterior view), and encompass the head of the upper arm from above as if a ball would be grasped by a hand. According to the portion of this musculature that runs like a type of cuff, the arm can be twisted inward or outward ("rotated") or brought into a horizontal position. Therefore, these muscles have been compiled into a group and designated "rotator cuffs". If one now observes the bony channel through which these muscles run (shoulder acromial cap), then one can well understand, that damage to muscular tissue is unavoidable upon stress or with constricted modifications in this region. As hemp twine unravels if it is continuously pulled over a sharp edge, the musculature can also suffer minor injuries. The body tries to degrade and to reuse these damaged fibers; this is accompanied by swelling and pain in the shoulder region. In turn, the bony channel that already is narrow anyway becomes even more constricted for the musculature due to this swelling. Consequently, pain occurs upon rotating the arm inward and outward, upon lifting the arm and especially when lying on the affected shoulder during the night. These symptoms describe the so-called "impingement syndrome". Additional causes of this symptom are, e.g. an arthrosis of the joint between collar bone / clavicle and shoulder blade (shoulder joint arthrosis) or an inflammation of the bursa in the muscular channel, i.e. beneath the shoulder acromion (Bursitis subacromialis).

If an additional injury of the musculature has occurred with advanced degeneration of muscle fibers, then the rotating cuffs are finally severed ("rotator cuff rupture").

This process can (seldom) be accompanied with a loud noise and sudden occurrence of severe pain - but the "tearing" nearly always occurs over an interval of several months or years, since always only a small portion of the fibers of the entire rotating cuff muscle group are affected simultaneously.

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