Anatomical basics, variations, and degenerative changes of the shoulder joint and shoulder girdle
Introduction
The upper extremity is articulated with the shoulder girdle in the shoulder joint. The only osseous connection to the trunk is the sternoclavicular articulation. Both, this joint and the acromioclavicular joint, are developmentally appositional articulations. Therefore, both joints contain a fibrocartilaginous disc and fibrocartilaginous articular surface. The shoulder joint provides the upper extremity with an almost unrestricted radius of action, but this freedom of movement makes the anatomical structures of the shoulder very vulnerable. Therefore, the shoulder joint demands close attention by orthopedic surgeons and traumatologists, and especially by radiologists, who now have the technology to image and interpret morphological details with unprecedented precision. This paper focuses on the anatomical essentials, their variations, and changes due to aging and posttraumatic events.
Section snippets
Clavicula
This short tubular bone is s-shaped. Variations on this normal shape, including extreme curvature and almost straight bones, are also within the normal range of the clavicle [1] (Fig. 1). These different ranges of curvature can produce impressions of condensations and thickening in the X-ray image. The medial end of the clavicle, the sternal extremity, has a round cross section that can become enlarged and formed like a pestil with excessive physical strain, while the acromial part is flattened
Proximal part of humerus
The hemispheric humerus head (caput humeri) is demarcated against the shaft by the anatomical neck (collum anatomicum) and bears the 20–30 cm2 articular surface. Several nutrient foramina are located in the anatomical neck, which supply the humerus head with blood. The poor healing process of fractures located medial to the anatomical neck (type II, according to Neer), which often results in pseudarthoses, is a direct result of this anatomical feature. The bicipital groove (sulcus
Acromioclavicular joint
The acromioclavicular joint, categorized as a plane joint, develops as an apposition joint and, therefore, has a rudimentary articular disc and fibrocartilaginous-covered articular facets (Fig. 12a). In rare cases, the articular disc ossifies, forming an acromioclavicular intercalate ossicle [12], [41]. The articular surfaces are normally smooth, oval in shape, and distinctly confined. Curved surfaces can sometimes be found beside the plane articular forms [12]. It is important that the
Acromioclavicular joint
The articular bodies of the acromioclavicular joint develop degenerative changes with increasing age, comparable to osteoarthrosis of the large joints. The effects of the sclerosing and grinding processes of the articular facets and the occurrence of subchondral cysts, which are responsible for the pumice-stone like aspect, are particularly apparent. More severe levels of osteoarthrosis can lead to deformations of the articular structures, which lose their normal shape and appear to be rolled
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