A twinge in the shoulder girdle during a particular movement or the sudden inability to raise the arm above horizontal – these are just two of the many complaints that occur when the complex shoulder joint wears down. Here, you can learn more about the causes of degenerative shoulder disease and find out what types of conditions exist and how to treat them.
Structure of the shoulder: bony structures
When people talk about the “shoulder,” they rarely realize how complex the shoulder girdle is and how intricately the individual bones, muscles, and tendons are connected by joints, bursae, and gliding layers.
In terms of bony structures, in addition to the scapula with the acromion and the coracoid process, the clavicle and the spherical humeral head are also involved in the shoulder joint. Although the actual shoulder joint is formed only by the humeral head and the small glenoid cavity on the side of the scapula, the acromion, clavicle, and coracoid process form the roof and lateral boundary of this joint.
Shoulder joint: extremely mobile
Unlike the hip joint, the shoulder joint does not have a large socket enclosing the condyle; instead, the articular surface of the scapula is an almost straight surface. This has the advantage that movement in almost all directions is possible in the shoulder joint – unlike in the hip joint, where the large acetabulum provides stability but also restricts mobility.
However, the disadvantage of this design is that many structures surrounding the shoulder joint are used to stabilize it. If any of these structures fail, shoulder mobility is compromised.
Shoulder muscles, tendons, and bursa.
In addition to the bones, the muscles with their tendons play an essential role in the structure and function of the shoulder.
Of particular note are the rotator cuff muscles – muscles responsible for rotational movements of the shoulder – namely the supra- and infraspinatus muscles, the subscapularis muscle, and the teres minor muscle. The rotator cuff presses the humeral head against the glenoid cavity, ensuring contact between the joint surfaces.
In addition, the following components play a role:
- Between the muscles, the bones and the ligamentous attachments lie several bursae to ensure the mobility of the structures in relation to each other.
- In addition, the deltoid muscle (Musculus deltoideus), located above the rotator cuff and shoulder level, is significantly involved in the shape of the shoulder and gives it its typical roundness.
- Furthermore, the two-headed biceps muscle (biceps derives from Latin and means “two-headed”) has a special task. Each of its two muscle bellies has a tendon with which it is attached to the bone.
- The so-called long biceps tendon runs like a rope through the shoulder joint and maintains contact between the humeral head and the joint surface, especially during lateral movements of the arm.
How do degenerative shoulder diseases develop?
The structures involved in the construction of the shoulder joint are stressed with every shoulder-arm movement – day in, day out, throughout our lives. However, a trouble-free sequence of movements, especially those that take place with the arm away from the body, the abduction movements, is only possible if the individual joints do not show signs of wear and tear such as osteoarthritis. In addition, the long biceps tendon must run well lubricated through its guide channel, and the bursae between the muscles must allow smooth muscle action.
Because shoulder motion requires the interplay of so many structures, it is not surprising that different degrees of wear and tear can lead to a variety of medical conditions.
