Trajectory architecture of the trabecular bone between the body and the neural arch in human vertebrae

The cancellous structure of vertebrae has been studied to investigate the direction of trabeculae and thus the lines of stress. The trabecular bone of the pedicle, connecting the body to the lamina, differed in different regions of the vertebral column. At C2 level, it was found that trabeculae are involved in transfer of th column. At C2 level, it was found that trabeculae are involved in transfer of the compressive forces from the superior articular surface to the inferior articular process and body. Throughout the thoracic region, trabeculae in the pedicle were inclined anteriorly towards the body, indicating that compressive forces in the thoracic spine are transferred from the neural arch to the body. In the lower lumbar region, trabeculae run from the body towards the neural arch. Trabeculae in the thoracic transverse processes extend from the costal facet to the lamina, suggesting that weight brought by the ribs to the costotransverse articulations is transmitted to laminae through transverse processes.     

Architecture of the cancellous bone of the human talus

The trabeculae of the cancellous bone are formed along the direction of the lines of stresses to which a bone is subjected. The talus sustains the weight of the body and transmits the weight in different directions (i.e., the calcaneus and navicular). The aim of the present study was to investigate the architecture of the cancellous bone of the talus to understand the mechanism of transmission of force within the bone. Twenty-five dry, macerated tali of adult male humans were used to study the trabecular architecture. In a few bones, serial longitudinal (parasagittal), transverse (coronal), and horizontal sections were cut; in other bones, the trabecular bone was exposed by removal of cortical bone. Trabecular architecture was studied by dissection microscope and by taking radiographs of the slices. The body of the talus consisted of vertical, parallel plates arranged posteroanteriorly. This kind of orientation of the plates facilitates the transmission of weight, when the tibia rolls posteroanteriorly on the trochlear surface during walking. The trabecular architecture in the head of talus consisted of semiarched plates running parallel to each other. The vertical limb of these semiarched plates were situated above the middle and anterior calcaneal facets on the plantar surface of the head, whereas the horizontal limbs of the arches were deep to the navicular articular surface of the head. The vertical plates of the body and semiarched plates of the head were interconnected by a meshwork of irregularly arranged trabecular bone of the neck. The architecture of this meshwork was such that it could facilitate the change in the direction and nature of force. In conclusion, the part of compressive force, acting vertically downward on the body of the talus during standing, was converted to tensile force in the neck, and its direction was made perpendicular to enable this force to go toward the head of the talus. In a similar manner, the semiarched pattern of plates in the head facilitated the change in the direction of the force, at the end of the stance phase, from the downward (toward calcaneus) to the forward (toward navicular) direction. Anat. Rec. 252:185–193, 1998. © 1998 Wiley-Liss, Inc.     

Stress in the human elbow joint

Summary The proximal radio-ulnar joint has two different types of articular surfaces. The contact area between the articulating surfaces is at its greatest when the joint is in a middle position. The highest density of osseous material is found on the ulnar side of the head of the radius. The subchondral bone beneath the radial notch of the ulna has a higher density at the edges than in the middle. In photoelastic experiments the intensity and configuration of isochromatics correspond to the material density of the osseous tissue of ulna and radius. The analysis of spongiosa near the joint shows bands of compressive cancellous trabeculae radiating axially into the subchondral cortex, crossed at right angles by bands of tensile cancellous trabeculae. These findings are in agreement with the course of the trajectories found in photoelastic experiments. The composition of the annular ligament is variable. The palmar and dorsal parts are made up of firm connective tissue; opposite the radial notch of the ulna, however, cartilage cells are embedded in the ligament.The histological composition of the annular ligament and the cancellous architecture in the radius and the ulna are in agreement with Pauwels' (1963) hypothesis that part of the compressive force in the elbow joint is transferred to the proximal radio-ulnar joint via the annular ligament. The distribution of the material in the subchondral bony tissue indicates that there is only partial contact between he radial head circumference and the radial notch of the alnal in all positions of the joint.Supported by the Deutsche Forschungsgemeinschaft (Ti 121/2; Zi 192/1 and Zi 192/3)Dedicated to Professor Dr. Benno Kummer in honor of his 60. birthday     

Fourier analysis methodology of trabecular orientation measurement in the human tibial epiphysis

Methods to quantify trabecular orientation are crucial in order to assess the exact trajectory of trabeculae in anatomical and histological sections. Specific methods for evaluating trabecular orientation include the 'point counting' technique (Whitehouse, 1974), manual tracing of trabecular outlines on a digitising board (Whitehouse, 1980), textural analysis (Veenland et al. 1998), graphic representation of vectors (Shimizu et al. 1993; Kamibayashi et al. 1995) and both mathematical (Geraets, 1998) and fractal analysis (Millard et al. 1998). Optical and computer-assisted methods to detect trabecular orientation of bone using the Fourier transform were introduced by Oxnard (1982) later refined by Kuo & Carter (1991) (see also Oxnard, 1993, for a review), in the analysis of planar sections of vertebral bodies as well as in planar radiographs of cancellous bone in the distal radius (Wigderowitz et al. 1997). At present no studies have applied this technique to 2-D images or to the study of dried bones. We report a universal computer-automated technique for assessing the preferential orientation of the tibial subarticular trabeculae based on Fourier analysis, emphasis being placed on the search for improvements in accuracy over previous methods and applied to large stereoscopic (2-D) fields of anatomical sections of dried human tibiae. Previous studies on the trajectorial architecture of the tibial epiphysis (Takechi, 1977; Maquet, 1984) and research data about trabecular orientation (Kamibayashi et al. 1995) have not employed Fourier analysis.     

Development of the trabecular structure within the ulnar medial coronoid process of young dogs

This study describes the timing of development of the trabecular structure of the ulnar medial coronoid process (MCP) in the dog. The right MCPs of nine healthy golden retrievers, aged 4 to 24 weeks, without signs of secondary joint disease were dissected and scanned with microcomputed tomography (micro-CT) at a voxel size of 34 microm to determine histomorphometric parameters. Bone volume fraction and mean trabecular separation show a reciprocal pattern in time, reflecting an initial high bone density (and low trabecular separation), and then a sharp drop in density at 8-10 weeks, followed by a gradual increase to high values at 24 weeks. With a similar bone volume fraction as in young bone, the older bone shows thicker trabeculae and a more plate-like structure. This is reflected in the much smaller number of trabeculae and the lower surface/volume ratio at higher age. An anisotropic structure of the trabeculae with an orientation in the direction of the proximodistal axis of the ulna is already present at 6 weeks after birth. This primary alignment was perpendicular to the humeroulnar articular surface, matching the direction of the compressive forces applied to the MCP by the humeral trochlea. The secondary alignment appeared at 13 weeks after birth and was directed along the craniocaudal axis of the MCP, toward the attachment of the anular ligament. In comparison with data from long bones and vertebrae, the findings of a high bone volume fraction and a well-defined trabecular alignment at a very early age are remarkable. The high bone volume fraction is possibly a remnant of the fetal trabecular structure, as dogs are relatively immature at birth compared to other animals. Soon after the start of steady locomotion, the trabecular structure changes into a more mature-like structure. The early trabecular alignment is possibly a reflection of the early load-bearing function of the MCP in the elbow joint.     

Comparison of the trabecular architecture and the isostatic stress flow in the human calcaneus

It is a common theory that the architecture of trabecular bone follows the principal stress trajectories, as suggested by Wolff's pioneering studies of the proximal femur. Since first published in the late 19th-century, this observation (popularized as "Wolff's law") has been supported by numerous studies, but nearly all of them have been focused on the femoral head and neck. In this study, the manifestation of Wolff's law in the human calcaneus has been analyzed. For this purpose, finite element (FE) analysis of the entire complex of the foot during standing was undertaken. Orientation of the principal stress flow through the calcaneus was compared with the trabecular alignment in a single cadaveric calcaneal specimen, by fitting second-order polynomials to real trabecular paths and FE-predicted isostatics and calculating their angle of inclination with the calcaneal cortex at their insertion points. Four dominant trabecular patterns were identified in the cadaveric sagittal section of the specimen of the calcaneus: one directed primarily in the dorsal-plantar direction, one aligned anteriorly-posteriorly, and two that are strongly oblique. Subsequent numerical simulations showed that the dorsal-plantar oriented and posterior oblique trabecular paths are aimed to support compressive stresses, while the antero-posteriorly directed and anterior oblique groups act to bear tension. Insertion angles of real trabecular paths into the calcaneal cortex were similar to those of the isostatics that were computed under musculoskeletal loading conditions of standing (maximum absolute local difference 13 degrees, maximum local error 60%). This suggests that the trabecular patterns of the calcaneus are mainly shaped by isostatics (static principal stress flow) that are characteristic of the standing posture. The present modeling approach can be utilized to explore effects of abnormal alterations in the isostatic flow on the microarchitecture of the calcaneal trabeculae, as well as for better understanding of the mechanisms of calcaneal fractures.     

Age-related changes in the articular cartilage of human sacroiliac joint

 Iliac and sacral articular cartilage of 25 human sacroiliac joints (1–93 years) are examined by light microscopy and immunohistochemistry in order to gain further insight into the nature and progress of degenerative changes appearing during aging. These changes can already be seen in younger adults as compared to cartilage degeneration known in other diarthrodial joints. Structural differences between sacral and iliac cartilage can already be observed in the infant: the sacral auricular facet is covered with a hyaline articular cartilage, reaching 4 mm in thickness in the adult and staining intensely blue with alcian blue at pH1. Iliac cartilage of the newborn is composed of a dense fibrillar network of thick collagen bundles, crossing each other at approximately right angles. A faint staining with alcian blue suggests a low content of acidic glycosaminoglycans. In the adult, iliac cartilage becomes hyaline and its maximal thickness reaches 1–2 mm. Both articular facets exhibit morphological changes during aging that are more pronounced in the iliac cartilage and resemble osteoarthritic degeneration; the staining pattern of the extracellular matrix becomes inhomogenous, chondrocytes are arranged in clusters and the articular surface develops superficial irregularities and fissures. Sometimes fibrous tissue fills up these defects. Nevertheless, large areas of iliac cartilage remain hyaline in nature. Sacral articular cartilage often remains largely unaltered until old age. The sacral subchondral bone plate is usually thin and shows spongiosa trabeculae inserted at right angles, suggesting a perpendicular load on the articular facet. Iliac subchondral spongiosa shows no definite alignment and joins the thickened subchondral bone plate in an oblique direction. The iliac cartilage therefore seems to be stressed predominantly by shearing forces, arising from the changing monopodal support of the pelvis during locomotion. The subchondral bone plate on both the iliac and sacral auricular facet is penetrated by blood vessels that come into close contact with the overlying articular cartilage. These vessels may contribute to the high incidence of rheumatoid and inflammatory diseases in the human sacroiliac joint. Immunolabelling with an antibody against type II collagen reveals a diminished immunoreactivity in the upper half of adult sacral cartilage and only a faint and irregular labelling in the iliac cartilage. Type I collagen can be detected in a superficial layer on the sacral articular surface and around chondrocyte clusters in iliac cartilage, as in dedifferentiating chondrocytes during the development of osteoarthritis. Accepted: 22 April 1998     

Trabecular generation de novo. A morphological and immunohistochemical study of primary ossification in the human femoral anlagen.

An understanding of trabecular formation in early skeletal development may provide insight into the problem of trabecular replacement in the aging skeleton. In an optical and scanning electron microscope study of the processes of de novo trabecular generation, the immunohistochemical distribution of collagen Types I, II and III, together with the matrix organising proteins fibronectin and tenascin, has been examined in the ossifying human femoral anlage. In the region of the developing spongiosa, the primary osseous trabeculae that arose by endochondral ossification were assembled around calcified cartilage remnants, consisting almost entirely of aggregates of mineralised microspheres. These structures were specifically recognised by antibodies raised against collagen Type II and fibronectin. In contrast, the primary osseous trabeculae that arose by subperiosteal intramembranous processes, were assembled around a framework of prominent coarse fibres that were recognised by antibodies raised against collagen Type III and tenascin. Irrespective of their origin, all the new trabeculae were similar in their general staining character for collagen Type I and fibronectin. However, throughout the developmental stages examined here endochondral trabeculae were separated from intramembranous trabeculae by a discrete boundary of compressed cells and mineralised cartilage.     

A study of intercellular relationships between trabecular bone and marrow stromal cells in the murine femoral metaphysis

The cellular relationship between the substantia spongiosa of bone (cancellous or trabecular bone) and the haematopoietic bone marrow in the femoral metaphysis of C57BL/6NJCL mice was studied by transmission electron microscopy (TEM). Special attention was directed to intercellular junctions between osteocytes, osteoblasts, and bone marrow reticular cells. These were gap junctions and adhesive devices of simple architecture referred to as primitive junctions or zonula adherens-like junctions. Gap junctions were observed between osteocytes (within the trabeculae) and osteoblasts (at the trabecular surface) and between osteoblasts and marrow reticular cells. Gap junctions were also observed between the same cell type within each of these categories. These junctions involved the plasmalemmal membranes of adjacent cell bodies and of processes. Primitive cell junctions had a similar cellular distribution. Quantitative analysis of the cell types covering or positioned around the trabecular bones and of gap junctions between these and other cells was carried out by TEM. It was found that osteoblasts were the most numerous cell type, occupying 31% of the total of each cell type positively identified around the trabeculae (31%), while pre-osteoblasts, (flattened bone marrow reticular cells) took up 26%. These data emphasise the intimate relationship of the various mesenchymal cells based on processes and intercellular junctions, and point to an anatomical and probably functional integration of trabeculae and marrow. The functional significance and putative regulatory activity of this unit are discussed.     

Trabecular generation de novo

Summary An understanding of trabecular formation in early skeletal development may provide insight into the problem of trabecular replacement in the aging skeleton. In an optical and scanning electron microscope study of the processes of de novo trabecular generation, the immunohistochemical distribution of collagen Types I, II and III, together with the matrix organising proteins fibronectin and tenascin, has been examined in the ossifying human femoral anlage. In the region of the developing spongiosa, the primary osseous trabeculae that arose by endochondral ossification were assembled around calcified cartilage remnants, consisting almost entirely of aggregates of mineralised microspheres. These structures were specifically recognised by antibodies raised against collagen Type II and fibronectin. In contrast, the primary osseous trabeculae that arose by subperiosteal intramembranous processes, were assembled around a framework of prominent coarse fibres that were recognised by antibodies raised against collagen Type III and tenascin. Irrespective of their origin, all the new trabeculae were similar in their general staining character for collagen Type I and fibronectin. However, throughout the developmental stages examined here endochondral trabeculae were separated from intramembranous trabeculae by a discrete boundary of compressed cells and mineralised cartilage.     

Belastung und Beanspruchung des Humerus bei Quadrupeden

Zusammenfassung Die schematisierte Vorderextremität eines Rindes wird in verschiedenen Stellungen betrachtet und die Biegemomente, die im Humerus auftreten, dargestellt. Gleichzeitig werden die funktionell günstigste Achsenform und die auftretenden Randspannungen berechnet. Die spannungsoptischen Versuche ergeben ein Bild der Spannungstrajektorien, das eine weitgehende Ähnlichkeit mit der Spongiosaarchitektur des Humerus hat. Ferner werden die im Bereich der Vorderextremität und des Schultergelenks zur Geltung kommenden Kräfte betrachtet. Abschließend wird die Statik der Vorderextremität der Quadrupeden im Sagittalschnitt mit der des menschlichen Beines im Frontalschnitt verglichen.

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Stress and load of the humerus of quadrupeds

Summary The schematically shown forelimb of a bovine is studied in different positions, and the bending stresses observable in the humerus are demonstrated. At the same time the functionally optimal axial direction and the marginal tension are calculated. The photoelastic investigations result in a picture of the stress trajectories which resembles extensively the spongiosa architecture of the humerus. Then the forces are shown which are relevant in the region of the forelimb and the shoulder joint. Finally the statics of the forelimb of quadrupeds in sagittal section is compared to the human pelvic limb in frontal section.

     

Sesamoid bones also show functional adaptation in their microanatomy—The example of the patella in Perissodactyla

The patella is the largest sesamoid bone of the skeleton. It is strongly involved in the knee, improving output force and velocity of the knee extensors, and thus plays a major role in locomotion and limb stability. However, the relationships between its structure and functional constraints, that would enable a better understanding of limb bone functional adaptations, are poorly known. This contribution proposes a comparative analysis, both qualitative and quantitative, of the microanatomy of the whole patella in perissodactyls, which show a wide range of morphologies, masses, and locomotor abilities, in order to investigate how the microanatomy of the patella adapts to evolutionary constraints. The inner structure of the patella consists of a spongiosa surrounded by a compact cortex. Contrary to our expectations, there is no increase in compactness with bone size, and thus body size and weight, but only an increase in the tightness of the spongiosa. No particular thickening of the cortex associated with muscle insertions is noticed but a strong thickening is observed anteriorly at about mid-length, where the strong intermediate patellar ligament inserts. The trabeculae are mainly oriented perpendicularly to the posterior articular surface, which highlights that the main stress is anteroposteriorly directed, maintaining the patella against the femoral trochlea. Conversely, anteriorly, trabeculae are rather circumferentially oriented, following the insertion of the patellar ligament and, possibly also, of the quadriceps tendon. A strong variation is observed among perissodactyl families but also intraspecifically, which is in accordance with previous studies suggesting a higher variability in sesamoid bones. Clear trends are nevertheless observed between the three families. Equids have a much thinner cortex than ceratomorphs. Rhinos and equids, both characterized by a development of the medial border, show an increase in trabecular density laterally suggesting stronger stresses laterally. The inner structure in tapirs is more homogeneous despite the absence of medial development of the medial border with no “compensation” of the inner structure, which suggests different stresses on their knees associated with a different morphology of their patellofemoral joint.     

Elastic strains in antler trabecular bone determined by synchrotron X-ray diffraction

The microstructure and associated mechanical properties of antler trabecular bone have been studied using a variety of techniques. The local trabeculae properties, as well as the three-dimensional architecture were characterized using nanoindentation and X-ray microtomography, respectively. An elastic modulus of 10.9+/-1.1 GPa is reported for dry bone, compared with 5.4+/-0.9 GPa for fully hydrated bone. Trabeculae thickness and separation were found to be comparable to those of bovine trabecular bone. Uniaxial compression conducted in situ during X-ray microtomography showed that antler can undergo significant architectural rearrangement, dominated by trabeculae bending and buckling, due to its low mineral content. High-energy synchrotron X-ray diffraction was used to measure elastic strains in the apatite crystals of the trabeculae, also under in situ uniaxial compression. During elastic loading, strain was found to be accommodated largely by trabeculae aligned parallel to the loading direction. Prior to the macroscopic yield point, internal strains increased as trabeculae deformed by bending, and load was also found to be redistributed to trabeculae aligned non-parallel to the loading direction. Significant bending of trabecular walls resulted in tensile strains developing in trabeculae aligned along the loading direction.     

Morphometric study of the equine navicular bone: variations with breeds and types of horse and influence of exercise

Navicular bones from the 4 limbs of 95 horses, classified in 9 categories, were studied. The anatomical bases were established for the morphometry of the navicular bone and its variations according to the category of horse, after corrections were made for front or rear limb, sex, weight, size and age. In ponies, navicular bone measurements were smallest for light ponies and regularly increased with body size, but in horses, navicular bone dimensions were smallest for the athletic halfbred, intermediate for draft horse, thoroughbreds and sedentary halfbreds and largest for heavy halfbreds. The athletic halfbred thus showed reduced bone dimensions when compared with other horse types. Navicular bones from 61 horses were studied histomorphometrically. Light horses and ponies possessed larger amounts of cancellous bone and less cortical bone. Draft horses and heavy ponies showed marked thickening of cortical bone with minimum intracortical porosity, and a decrease in marrow spaces associated with more trabecular bone. Two distinct zones were observed for the flexor surface cortex: an external zone composed mainly of poorly remodelled lamellar bone, disposed in a distoproximal oblique direction, and an internal zone composed mainly of secondary bone, with a lateromedial direction for haversian canals. Flexor cortex external zone tended to be smaller for heavy ponies than for the light ponies. It was the opposite for horses, with the largest amount of external zone registered for draft horses. In athletic horses, we observed an increase in the amount of cortical bone at the expense of cancellous bone which could be the result of reduced resorption and increased formation at the corticoendosteal junction. Cancellous bone was reduced for the athletic horses but the number of trabeculae and their specific surfaces were larger. Increased bone formation and reduced resorption could also account for these differences.     

Age-related changes in the lumbar facet joints

The normal appearance of the lumbar facet joints has been related to the age of the subject. We classified the changes in the menisci, articular cartilage, and subarticular cortical bone with respect to age in 24 cadavers. Normally the meniscus diminishes in size, the articular cartilage thins, and subarticular cortical bone thickens with age. Determination of normality must be made with respect to age.     

Relations between radiograph texture analysis and microcomputed tomography in two rat models of bone metastases

AIMS: Osteolytic (Walker 256, W256) and osteoblastic (MatLyLu, MLL) metastases were induced to investigate their effect on bone architecture by microcomputed tomography (microCT) and texture analysis of radiographs. METHODS: Fischer and Copenhagen rats received an intracardiac injection with W256/MLL cells, respectively. Femur and tibia radiographs were analyzed by texture analysis with run lengths and fractal algorithms. Microarchitecture was analyzed on primary and secondary spongiosa by microCT. RESULTS: W256 and MLL induced a decrease of trabecular bone mass, a disconnection of trabeculae and an increased conversion of plates into pillars. On radiographs and 3-dimensional models of W256 rats, a disappearance of the primary spongiosa was observed. On radiographs and 3-dimensional models of MLL rats, osteolytic lesions were observed as disseminated dark areas. Run length and fractal analyses were altered in both metastases. CONCLUSION: W256 and MLL cells induced two different patterns of osteolysis. Texture analysis of radiographs is a useful technique to explore trabecular bone changes.     

Accounting for beta-particle energy loss to cortical bone via paired-image radiation transport (PIRT)

Current methods of skeletal dose assessment in both medical physics (radionuclide therapy) and health physics (dose reconstruction and risk assessment) rely heavily on a single set of bone and marrow cavity chord-length distributions in which particle energy deposition is tracked within an infinite extent of trabecular spongiosa, with no allowance for particle escape to cortical bone. In the present study, we introduce a paired-image radiation transport (PIRT) model which provides a more realistic three-dimensional (3D) geometry for particle transport in the skeletal site at both microscopic and macroscopic levels of its histology. Ex vivo CT scans were acquired of the pelvis, cranial cap, and individual ribs excised from a 66-year male cadaver (BMI of 22.7 kg m(-2)). For the three skeletal sites, regions of trabecular spongiosa and cortical bone were identified and segmented. Physical sections of interior spongiosa were taken and subjected to microCT imaging. Voxels within the resulting microCT images were then segmented and labeled as regions of bone trabeculae, endosteum, active marrow, and inactive marrow through application of image processing algorithms. The PIRT methodology was then implemented within the EGSNRC radiation transport code whereby electrons of various initial energies are simultaneously tracked within both the ex vivo CT macroimage and the CT microimage of the skeletal site. At initial electron energies greater than 50-200 keV, a divergence in absorbed fractions to active marrow are noted between PIRT model simulations and those estimated under existing techniques of infinite spongiosa transport. Calculations of radionuclide S values under both methodologies imply that current chord-based models may overestimate the absorbed dose to active bone marrow in these skeletal sites by 0% to 27% for low-energy beta emitters (33P, 169Er, and 177Lu), by approximately 4% to 49% for intermediate-energy beta emitters (153Sm, 186Re, and 89Sr), and by approximately 14% to 76% for high-energy beta emitters (32p, 188Re, and 90Y). The PIRT methodology allows for detailed modeling of the 3D macrostructure of individual marrow-containing bones within the skeleton thus permitting improved estimates of absorbed fractions and radionuclide S values for intermediate-to-high energy beta emitters.     

Cortical bone development under the growth plate is regulated by mechanical load transfer

Longitudinal growth of long bones takes place at the growth plates. The growth plate produces new bone trabeculae, which are later resorbed or merged into the cortical shell. This process implies transition of trabecular metaphyseal sections into diaphyseal sections. We hypothesize that the development of cortical bone is governed by mechanical stimuli. We also hypothesize that trabecular and cortical bone share the same regulatory mechanisms for adaptation to mechanical loads. To test these hypotheses, we monitored the development of the tibial cortex in growing pigs, using micro-computer tomography and histology. We then tested the concept that regulatory mechanisms for trabecular bone adaptation can also explain cortical bone development using our mechanical stimulation theory, which could explain trabecular bone (re)modelling. The main results showed that, from the growth plate towards the diaphysis, the pores of the trabecular structure were gradually filled in with bone, which resulted in increased density and cortical bone. The computer model largely predicted this morphological development. We conclude that merging of metaphyseal trabeculae into cortex is likely to be governed by mechanical stimuli. Furthermore, cortex development of growing long bones can be explained as a form of trabecular bone adaptation, without the need for different regulatory mechanisms for cortical and trabecular bone.     

Expression of alkaline phosphatase in the mature mouse placenta visualized by in situ hybridization and enzyme histochemistry

Alkaline phosphatases (APs) are a family of cell surface glycoproteins that are expressed in a variety of tissues. Their physiologcial functions are still unclear. Three different AP genes have been found to be expressed in mice, and AP cloned from the placenta is of the tissue non-specific (TNAP) type. We have in investigated the location of TNAP mRNA and active AP in mature mouse placenta, using in situ hybridization and enzyme histochemistry on serial sections. Digital image analysis was used to estimate relative amounts of TNAP mRNA. Tissue non-specific alkaline phosphatase messenger was detected only in the placental labyrinth, whereas active AP was present both in the labyrinth and in a zone of cells at the margin of the decidua basalis, bordering the myometrium and the metrial gland. This latter location of AP activity has not been described previously. The AP-positive zone of the decidua had a condensed appearance and a central defect in the zone was visible on sections taken from the middle of the placenta. No TNAP messenger was found in the zone of AP-positive decidual cells.