No abstract

We investigated the development of cartilage canals to clarify their function in the process of bone formation.Cartilage canals are tubes containing vessels that are found in the hyaline cartilage prior to the formation of a secondary ossification centre (SOC). Their exact role is still controversial and it is unclear whether they contribute to endochondral bone formation when an SOC appears. We examined the cartilage canals of the chicken femur in different developmental stages (E20, D2, 5, 7, 8, 10 and 13). To obtain a detailed picture of the cellular and molecular events within and around the canals the femur was investigated by means of three-dimensional reconstruction, light microscopy, electron microscopy, histochemistry and immunohistochemistry [vascular endothelial growth factor (VEGF), type I and II collagen]. An SOC was visible for the first time on the last embryonic day (E20). Cartilage canals were an extension of the vascularized perichondrium and its mesenchymal stem cell layers into the hyaline cartilage. The canals formed a complex network within the epiphysis and some of them penetrated into the SOC were they ended blind. The growth of the canals into the SOC was promoted by VEGF. As the development progressed the SOC increased in size and adjacent canals were incorporated into it. The canals contained chondroclasts, which opened the lacunae of hypertrophic chondrocytes, and this was followed by invasion of mesenchymal cells into the empty lacunae and formation of an osteoid layer. In older stages this layer mineralized and increased in thickness by addition of further cells. Outside the SOC cartilage canals are surrounded by osteoid, which is formed by the process of perichondral bone formation. We conclude that cartilage canals contribute to both perichondral and endochondral bone formation and that osteoblasts have the same origin in both processes.

In the past, interpretations of anorectal development were mainly based on analysis of serially sectioned embryos of various nonhuman species as well as some human specimens. A four-dimensional view of the developmental situation in the human has never been established nor connected to recent findings obtained from newer molecular techniques. We, therefore, investigated human embryonic and fetal pelves by means of immunohistochemistry and in situ hybridization to elucidate differentiation and interaction of epithelial and mesenchymal layers of the anorectum. To emphasize spatial as well as sequential morphological development, we produced three-dimensional reconstructions of the specimens at hand. Research conducted proved that the decisive steps of epithelial and muscular differentiation occur between the 7th and 9th week after conception. This study elucidates a biphasic epithelial ''closure'' in the anal canal and interactions between epithelium, smooth musculature, and skeletal musculature. Based on the results presented here, it is possible to describe the pathogenesis of two anorectal malformations: the imperforate anal membrane and the anal membrane stenosis. This study will now provide the basis for further research into developmental processes occurring before the ones examined.

No abstract

The "bare spot" of the glenoid cavity has recently been described as a constant reference point to quantify the amount of bone loss from the inferior portion of the glenoid cavity. In shoulder surgery this spot should help the surgeon to determine the width of the inferior portion of the glenoid cavity arthroscopically. The aim of this study was to determine the localization of the bare spot within the glenoid cavity and to prove its usefulness in shoulder surgery by means of a macroscopic study using embalmed glenohumeral joints ( n=20; 12 left, 8 right). Each glenoid cavity was photographed and transferred to a commercial AutoCAD software program. The bare spot was marked and the mean distances between the center of the bare spot and the inferior ( a), anterior ( b(1)) and posterior ( b(2)) inner margins of the glenoid labrum as well as its relationship ( c) to the mid-point of a virtual circle formed by the inferior portion of the glenoid cavity were measured (mean values : a=9.70, b(1)=10.88, b(2)=13.71, c=3.2 mm). In most cases, the bare spot showed a significantly excentric position within the inferior part of the glenoid cavity ( p<0.05). Due to the great variability in the shape of the glenoid cavity, an inferior circle according to previous descriptions could only be observed in half the specimens. From the results of our study the bare spot seems to be an unreliable landmark for the determination of the center of the inferior portion of the glenoid cavity, although it has a constant appearance and is probably expressed as the result of cartilaginous distribution due to dynamic shoulder activity.

In mammals, the exact role of cartilage canals is still under discussion. Therefore, we studied their development in the distal femoral epiphysis of mice to define the importance of these canals. Various approaches were performed to examine the histological, cellular, and molecular events leading to bone formation. Cartilage canals started off as invaginations of the perichondrium at day (D) 5 after birth. At D 10, several small ossification nuclei originated around the canal branched endings. Finally, these nuclei coalesced and at D 18 a large secondary ossification centre (SOC) occupied the whole epiphysis. Cartilage canal cells expressed type I collagen, a major bone-relevant protein. During canal formation, several resting chondrocytes immediately around the canals were active caspase 3 positive but others were freed into the canal cavity and appeared to remain viable. We suggest that cartilage canal cells belong to the bone lineage and, hence, they contribute to the formation of the bony epiphysis. Several resting chondrocytes are assigned to die but others, after freeing into the canal cavity, may differentiate into osteoblasts.

Compression syndromes of the common fibular nerve and its branches frequently occur primarily as well as secondarily to trauma and surgery. A keen knowledge of the course and the relationship of the deep fibular nerve to adjacent anatomical structures in the proximal leg is mandatory. Previous literature often lacks detailed information on the course of the deep fibular nerve and is based on a limited number of observations. The aim of this study was to investigate the common fibular nerve and its branching pattern with special regard to the relationship between the deep fibular nerve and the anterior intermuscular septum of the leg. Variations in the course of the fibular nerve were demonstrated. The fibular compartments of the leg (n = 111) were dissected in 57 embalmed cadavers and included: 1) investigation of the number of muscular branches; 2) entering passages to the respective compartments of the leg; and 3) the relationship between the fibularis longus muscle and the deep fibular nerve. The most proximal muscular branch of the deep fibular nerve directly "pierced" the anterior intermuscular septum of the leg. Narrow passages within the fibular compartment and, in consequence, areas of possible higher incidence of nerve compression were suggested at the level of the intermuscular septa of the leg, between the two distinct portions of the fibularis longus muscle and the crossing of the supplying vessels. There were hardly ever statistically significant differences between the two sides or male and female gender. According to our results, the anterior intermuscular septum of the leg may be regarded as an important landmark for the surgeon when dissecting the muscular branches of the deep fibular nerve. The variable branching pattern of the deep fibular nerve within the fibular compartment of the leg should be taken into account.

A detailed study of so-called communicating cartilage canals, which penetrate deeply up into the lower hypertrophic zone of the epiphyseal growth plate in the embryonic chicken femur (E20), was carried out with the aim to clarify whether or not these canals are involved in the boneforming process. In addition, we examined the manner in which cartilage canals are formed and compare the present data with our previous data. The canals were investigated by means of light microscopy, electron microscopy, immunohistochemistry (VEGF, VEGFR2/Flk1, type I collagen), and 3D reconstruction. Some communicating canals deeply penetrate into the upper hypertrophic zone where they terminate, showing electron-dense cells at their end. Subcellular characteristics of these cells are hardly detectable and we suppose that they undergo cell death. Other canals pass down deeper into the lower hypertrophic zone. The upper segment of these canals is composed of capillaries, mesenchymal cells, and macrophage-like cells. Precursors of osteoblasts are adjacent to the canals. The lower segment of communicating canals is composed of bone matrix or osteoid, which contains type I collagen fibrils and cells having the typical subcellular features of osteoblasts. No vessels are found in these segments. Immunohistochemistry shows that the matrix of the canals labels positively for type I collagen. In addition, staining with sirius red demonstrates that bone matrix is formed in these parts. We assume that the osteoblast-like cells of the lower segments of communicating canals originate either from mesenchymal cells or even from hypertrophic chondrocytes. Our immunohistochemical data also reveal that vascular endothelial growth factor (VEGF) and the corresponding receptor VEGFR2/Flk1 (VEGF receptor 2/Flk1) are localized in cartilage canals of the reserve zone, the proliferative zone, and the hypertrophic zone. The receptor is found in the endothelial cells of the vessels. Furthermore, VEGF is present in hypertrophic chondrocytes. The results of our study suggest that cartilage canals penetrate actively into the cartilage anlage and that bone is formed in the lower segments of the communicating canals where no vessels are detectable.