HISTOCHEMISTRY AND DEVELOPMENT OF THE HUMAN SHOULDER AND ACROMIO-CLAVICULAR JOINTS WITH PARTICULAR REFERENCE TO THE EARLY DEVELOPMENT OF THE CLAVICLE

Abstract

Histochemical studies on the development of the shoulder joint and acromioclavicular joint as well as of the early development of the clavicle were carried out on 49 human embryos and fetuses. From a dense, homogeneous interzone a central joint cavity appears in the shoulder joint at a crown-rump length of 28 mm, the interzone first passing through a typical 3-layered appearance. During the development, large quantities of chondroitin sulphate (A or C or possibly both) accumulate in the layers of the interzone. From the central cavity the joint cavity extends, during the subsequent stages, to the peripheral parts of the joint, this extension being preceded by a loosening of the peripheral areas of the interzone by accumulation of large quantities of acid mucopolysaccharides. During this extension the joint cavity completely encircles the long tendon of the biceps brachii which from the very outset manifests itself in situ as part of the interzone. The glenoid labrum develops from the skeletal blastema as the most peripheral area of the glenoid fossa. In the acromino-clavicular joint a distinct 3-layered interzone could not be seen, the articular disc being formed as a fibrous, vascular strand extending through the joint and dividing it into two parts. A joint cavity appears first between the disc and the acromion (at 45 mm), while a cavity formation between the disc and the clavicle does not appear until later (in the present study at 68 mm). By the histochemical reactions the development of the clavicle may be divided into 2 phases: (1) the phase of desmal ossification, and (2) the chondral phase including peri- and endochondral ossification. The articular ends of the clavicle are lined by fibrocartilage, there being in the early stages of development avascular perichondria and not chondrogenous layers which, as part of the interzone, line the subsequent articular cartilages in other limb joints. The 2 growth cartilages at the ends of the desmal bony center in the clavicle are ordinary hyaline cartilages. It is only in their rapid proliferation and rapid hypertrophy, with subsequent regressive changes, that they differ from the cartilages forming the primordia of the long bones.