Developmental morphological and histological studies on structures of the human fetal shoulder joint

In the present work, morphological changes in the interior structures of the developing human shoulder joint were studied at different prenatal ages (9, 12, 16, 23 and 40 weeks) and were compared with the same structures in the adult joint. It was found that the shoulder joint had gone through important developmental changes during the 12th week of the prenatal life and it is assumed that genetic factors operative during this stage of development were more important than mechanical factors. A subsequent development of the intracapsular glenohumeral ligaments was present at the 16th week. The glenoid labrum, the biceps tendon and the three glenohumeral ligaments formed a complete ring around the glenoid fossa which constituted a functional unit, which seemed to have a role in stabilizing the joint. In the present work, histological prenatal studies were done on sagittal and radial sections from the glenoid fossa and its associated structures and the results were compared with the same structures in adults. At a crown-rump length of 30 mm (9 weeks), intermingling of the collagen fibres of the superior labrum and the biceps tendon was observed and the superior labrum could be considered as an extension of the biceps tendon. While the superior and inferior parts of the labrum appeared fibrous, the posterior labrum appeared as a primitive cellular condensation. At the 12th week, it became a fibrocellular structure and changed to a fibrocartilaginous structure at the 16th week. But until full term, no definitive fibrocartilage was found due to its hypercellularity compared to the adult. It was found that at all ages, the capsule was formed of cellular and fibrous elements, its collagenous content was progressively increased with age and at full term, it became generally fibrous but was still different compared to adults. In all stages of development, the synovial tissue of different regions of the same joint exhibited marked variations in thickness, vascularity, cellular density and collagenous content. It lined the capsule, surrounded the biceps tendon and reflected on the labrum. Its cell density as well as their vascular and collagenous contents were progressively increased with age. At full term, the synovial tissue was thickest at its inferior reflection and forming large folds. The synovial tissue lining the capsule was thinner than the synovial tissue at its reflection from the labrum, many villi and processes arising from it and projecting into the joint cavity.