SEARCH · Search PubMed
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Explore the source record for details and available documents.
Bone is a very dynamic tissue capable of modiA,fing its composition, microstructure, and overall geometry in response to the changing biomechanical needs. Streaming potential has been hypothesized as a mechanotransduction mechanism that may allow osteocytes to sense their biomechanical environment. A correct understanding of the mechanism for streaming potential will illuminate our understanding of bone remodeling, such as the remodeling associated with exercise hypertrophy, disuse atrophy, and the bone remodeling arounid implants. In the current research, a numerical model based on the finite element discretization is proposed to simulate the fluid flows through the complicated hierarchical flow system and to calculate the concomitant stress generated potential (SGP) as a result of applied mechanical loading. The lacunae-canaliculi and the matrix microporosity are modeled together as discrete one-dimensional flow channels superposed in a biphasic poroelastic matrix. The cusplike electric potential distribution surrounding the Haversian canal that was experimentallv observed and reported in the literature earlier was successfully reproduced by the current numerical calculation.
The routes of venous drainage from the diaphyseal marrow of the human tibia have been investigated by roentgenologic techniques following perfusion with an aqueous barium sulphate suspension. Plain roentgenographs immediately after perfusion revealed that the dye promptly escaped from the marrow into the general systemic circulation through a number of large transcortical routes. The periosteal veins were shown as a delicate network of venules lying on the external surface of the shaft. The perfused dye appeared diffusely scattered throughout the whole width of the medullary canal and extended from metaphysis to metaphysis suggesting the marrow to be an open circulatory system with ill-defined boundaries. A central venous sinus, as commonly perceived, was not demonstrated. Microradiographs revealed an extensive network of cortical sinusoids and venules that were continuous with similar vessels within the marrow and on the external surface of the bone. The injected dye also perfused the haversian venules. Intersinusoidal shunts, fine efferent vessels that did not combine to form larger venules, were observed within the marrow. The principal nutrient veins and their radicles were not demonstrated by this technique.
This study concerns the histologic examination of apatite-titanium complex dental implants (two-piece, cylindrical type) in dogs. There was no plaque control. One to 3 months after implantation, the surface of the apatite root was directly bound to newly formed, woven bone. Seven-and-a-half months to 1 year after implantation, the apatite root was directly bound to the newly formed lamellar bone, which provided strong bone bonding (apatite-bone bonding). There appear to be two types of mechanisms for the resorption of apatite ceramics: first, cellular-type resorption by both multinuclear and mononuclear macrophages; and second, a noncellular, fluid mechanism (dissolution). The gingival sulcus around implants and downward growth of the epithelial cells could be observed in almost all of the implants. There was no cellular inflammation in the tissue around the implants, in the nasal cavity, or in the maxillary sinus. From this study we concluded that clinical application of this dental implant system would be practical.
An area of nonlamellar new bone formation was observed in the anterior epitympanic region of 27 randomly chosen human temporal bones. The donors ranged in age from 9 to 80 years and had no evidence of ear disease or systemic skeletal or metabolic abnormalities. The frequency of this finding suggests that it is a normal feather of the human anterior attic recess.
Structure and relationships of stromal cells were studied by light (LM) and transmission electron microscopy (TEM) in the perimedullary spaces that form the growing cortex of the chick embryo tibia. Observation under LM showed that in all perimedullary spaces the interstices between the cells carpeting the bone surface and the endothelial lining contain stromal cells surrounded by an amorphous matrix. Two types of stromal cells were distinguished: stellate and spindle-shaped. All stromal cells are alkaline phosphatase-positive. TEM showed that both types of stromal cells have cytoplasmic processes of various length and calibre, coming into contact with each other as well as with endothelial cells and osteoblasts or bone lining cells. Capillaries were found to have a continuous endothelial lining; occasionally endothelial cells radiate cytoplasmic processes towards stromal cells. Along all the above-mentioned cellular contacts adherens and/or gap junctions were often observed. The results of the present study, together with our previous findings on osteoblast-osteocyte relationships, show that the cells of the osteogenic lineage form a continuous protoplasmic network that extends from the osteocytes to the vascular endothelium, passing through osteoblasts (or bone lining cells) and stromal cells. The occurrence of gap junctions among this cytoplasmic network, namely of junctions enabling metabolic and electric coupling, indicates that it forms a functional syncytium, suggesting the hypothesis that the activity of the cells pertaining to the osteogenic lineage might be regulated not only by diffusion (volume transmission) through the intercellular fluids of systemic (hormones) and local factors (cytokines, etc.) but also by signals issued through the cytoplasmic network of the osteogenic cells (wiring transmission).
Scanning acoustic microscopy (SAM) provides the means for studying the elastic properties of a material at a comparable level of resolution to that obtained by optical microscopy for structural studies. SAM is nondestructive and permits observation of properties in the interior of materials which are optically opaque. Two modes of ultrasonic signals have been used in a Model UH3 Scanning Acoustic Microscope (Olympus Co., Tokyo, Japan) as part of a continuing study of the microstructural properties of bone. The pulse mode, using a single narrow pulse in the range of 30 MHz to 100 MHz, has been used to survey the surface and interior of specimens of human and canine femoral compact cortical bone at resolutions down to approximately 30 microns. To obtain more detailed information at significantly higher resolution, the burst mode, comprised of tens of sinusoids, has been used at frequencies from 200 MHz to 600 MHz. This has provided details of both human and canine single osteons (or haversion systems) and ostenoic lamellae at resolutions down to approximately 1.7 microns, well within the thickness of a lamella as viewed in a specimen cut transverse to the femoral axis.
A model is developed whereby the secondary osteon--the dominant microstructural component of the cortical bone tissue--is considered as an n-layered cylinder with internal stresses in linear isotropic elasticity. An exact solution is obtained for a loading condition represented by a tensile-compressive force. The lengthening, the side deformation, and the strain energy of the system are explicitly calculated. The behavior of the main elastic quantities is illustrated by graphs. In particular, the important role played by the parity of the number of lamellae is revealed.
The pathway for intracortical fluid flow response to a step-load was identified in vivo using intramedullary pressure (ImP) and streaming potential (SP) measurements, and allowed the development of a load-induced flow mechanism which considers mechanotransduction and mechanoelectrotransduction phenomena. An avian model was used for monitoring, simultaneously, ImP and SP under axial loading which generated peak strains of approximately 600 microstrain (microepsilon). ImP response to step-load decayed more quickly than SP relaxation, in which multiple time constants were observed during the relaxations. While the initial relaxation of SP showed a decay on the order of 200 ms, ImP decayed on the order of approximately 100 ms. After the initial decay (approximately 200 ms after loading), ImP quickly relaxed to base line, while SP continued to dominate relaxation. It appears that the decay of ImP is indicative of resistive fluid flow occurring primarily in the vasculature and other intraosseous channels such as lacunar-canalicular pores, and that SP represents the fluid flow in the smaller porosities, i.e., lacunar-canalicular system or even microspores. These results suggest that SP and ImP decays are determined by a hierarchical interdependent system of multiple porosities, and that the temporal dynamics of load-bearing define the manner in which the fluid patterns and pressures are distributed.
Mineral transport to bone is dependent on an adequate blood supply. Thus, the role of vasoactive agents merits orthopaedic interest. This paper outlines the morphology of osteons and capillaries in cortical bone and discusses the possible morphological effects of systemic phenylephrine on mice tibiae. The frequency of dilated capillaries on histological serial sections did not significantly change. Hence, a postcapillary mechanism is likely to explain previous EM findings: i.e., an adrenaline-induced increase of the lumen diameter and perivascular cell edema.
14 femoral heads with late stage avascular necrosis of different etiologies were histologically examined, with special attention to vascular structures. Decalcified slices were stained with hematoxylin-eosin, safranin-O, van Gieson stain, and Martius Scarlet Blue. Immunohistochemical techniques with antibodies against Factor VIII, and Ulex Europeus Lectin were used to visualize the endothelium of the blood vessels. 5 distinct zones of the necrotic femoral head could be identified. The necrotic zone contained areas with richly vascularized connective tissue. In the transitional zone, several areas with intravascular aggregations of newly formed and older fibrin clots were noticed, mainly on the venous side of the vascular system. Other small vessels were collapsed, with a few endothelial cells clumped together in the center of a concentric fibrous tissue. We suggest that obstruction to the venous outflow due to intravascular thrombosis as well as to perivascular fibrosis is important in the pathogenesis of non-traumatic avascular necrosis of the femoral head.
A mathematical model was developed to study stress-induced fluid flow in the canaliculi-lacunae system in an osteon. The effect of canaliculi diameters on the magnitude and depth of penetration of squeeze flow through the canaliculi system was investigated. An optimal canaliculus diameter (which would maximize the fluid velocity through the canaliculi) was determined. For canaliculi diameters of 0.2 micron, squeeze flow can nourish four to five concentric layers of osteocytes in an osteon. It is possible that such stress-induced flow may be important in bone remodeling, and that lack of such flow may be one cause for producing osteoporosis due to immobilization.
In order to understand various exchange processes within the osteon, a mathematical model to describe the system has been developed which allows for concentration gradients in the axial and radial directions as well as cellular consumption and binding to bone surface. The normal values for the model parameter are discussed and the effects of the model parameters on the behaviour of the model are investigated. This model supports the idea that diffusion alone may be an inefficient mechanism in transport between blood and osteocytes.
One hundred twenty titanium and ceramic root-form and titanium blade implants were placed into 30 dog mandibles. Twenty-four implants in six control dogs (in situ for 5 months) did not receive prostheses. Ninety-six implants in 24 dogs supported prostheses for 6, 12, 18, or 24 months. Computerized morphometry data presented the percent of the implant surface apposed directly by bone. A three-way factorial analysis of variance was used to assess significance. Individual implant means ranged from 0% (mobile implant) to 71% bone adaptation. From these data, two-stage titanium root-form implants were shown to be apposed by more bone than the other five systems, and overall, titanium implant systems were apposed by more bone than ceramic systems. Between 41% and 50% of the surface of integrated ceramic implants were apposed by bone, whereas between 50% and 65% of the surfaces of titanium implants were apposed by bone. Also, two-stage surgery for blade implants appears important for implant success. Furthermore, the use of Nomarski differential illumination appears to be useful for examining the quality of interfacial bone to correlate with the amount of bone quantified by morphometric protocols.
Drifting osteons were followed longitudinally through the cortex of human and baboon long bones using serial sections. Direction of transverse drift was recorded at different cross-sectional levels of the same systems, and maximum angular change in drift direction was measured for each system. Most drifting osteons exhibit: (1) substantial ( approximately 90 degrees ) variation in the direction of transverse drift along their longitudinal axes, (2) intermittent regions of concentric (type I) morphology, and (3) change in drift direction over time, evident at single cross-sectional levels. Additionally, 3-dimensional reconstruction reveals that the basic multicellular units (BMUs) responsible for creating drifting osteons are morphologically distinct from the cutting-cone-closing-cone model BMUs that produce other types of osteons. The stimulus involved in the activation and guidance of drifting BMUs is unclear, but it is likely that the complex strain environment experienced by long bone cortices exerts a significant influence on their morphology.
Long-term clinical success of endosseous dental implants is critically related to a wide bone-to-implant direct contact. This condition is called osseointegration and is achieved ensuring a mechanical primary stability to the implant immediately after implantation. Both primary stability and osseointegration are favoured by micro-rough implant surfaces which are obtained by different techniques from titanium implants or coating the titanium with different materials. Host bone drilled cavity is comparable to a common bone wound. In the early bone response to the implant, the first tissue which comes into contact with the implant surface is the blood clot, with particular attention to platelets and fibrin. Peri-implant tissue healing starts with an inflammatory response as the implant is inserted in the bone cavity, but an early afibrillar calcified layer comparable to the lamina limitans or incremental lines in bone is just observable at the implant surface both in vitro than in vivo conditions. Just within the first day from implantation, mesenchymal cells, pre-osteoblasts and osteoblasts adhere to the implant surface covered by the afibrillar calcified layer to produce collagen fibrils of osteoid tissue. Within few days from implantation a woven bone and then a reparative trabecular bone with bone trabeculae delimiting large marrow spaces rich in blood vessels and mesenchymal cells are present at the gap between the implant and the host bone. The peri-implant osteogenesis can proceed from the host bone to the implant surface (distant osteogenesis) and from the implant surface to the host bone (contact osteogenesis) in the so called de novo bone formation. This early bone response to the implant gradually develops into a biological fixation of the device and consists in an early deposition of a newly formed reparative bone just in direct contact with the implant surface. Nowadays, senile and post-menopausal osteoporosis are extremely diffuse in the population and have important consequences on the clinical success of endosseous dental implants. In particular the systemic methabolic and site morphological conditions are not favorable to primary stability, biological fixation and final osseointegration. An early good biological fixation may allow the shortening of time before loading the implant, favouring the clinical procedure of early or immediate implant loading. Trabecular bone in implant biological fixation is gradually substituted by a mature lamellar bone which characterizes the implant ossoeintegration. As a final consideration, the mature lamellar bone observed in osseointegrated implants is not always the same as a biological turnover occurs in the peri-implant bone up to 1mm from the implant surface, with both osteogenesis and bone reabsorption processes.
Blood formation by pluripotent stem cells and their progeny is thought to be regulated by receptor-ligand interactions between cell-substrate, cell-cell and cell-matrix in the bone marrow. Primitive stem cells form progenitors and, in their turn, these give rise to haemopoietic progeny which are more specifically committed in that they can form progressively fewer types of blood cells. Recently we have established that direct cell-cell communication via gap junctions may be part of this regulatory system. Connexin43 gap junctions metabolically couple the three dimensional meshwork of bone marrow stromal cells to form a functional syncytium in which some blood-forming cells are also coupled. The expression of gap junctions in the bone marrow is markedly upregulated when there is an urgent and substantial demand for blood-formation; for example, following cytotoxic injury after 5-fluorouracil or irradiation; or during neonatal blood-formation and in the epiphysis of growing bones. Chemical blockade of gap junctions blocks blood-formation in long-term cultures but is reversible after the blockade has been relieved. This short review highlights briefly the known regulatory mechanisms of blood-formation with especial attention to gap junctional communication.
Besides rigid fixation, lag screws have distinct advantages compared with plates in appropriate indications in mandibular fractures. However, in current lag screw systems, the relatively small area of the screw head has to transfer the tensile force which can exceed 1000 N in the symphysis, to the thin cortical bone plate. Countersinking, which is obligatory in most systems, will weaken the cortical plate. Finite element analysis (FEA) revealed that load in this situation can exceed the normal tensile strength of metal and bone. Consequently, a new washer was constructed which both increased the supporting surface and did not require countersinking. The washer is self adapting (SAW) to the cortical plate in a defined position, forming a ball and socket joint with the screw head. Using the FEA model, a ten-fold reduction in load on bone and metal was observed with the new washer. In a miniature pig mandibular symphysis fracture model, the clinical applicability and a favourable histological reaction were demonstrated, compared with conventional lag screw designs.