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At least 343 records · Page 19Linked to original sources
PubMed2005

Up-regulation of site-specific remodeling without accumulation of microcracking and loss of osteocytes.

Functional adaptation of bone normally protects the skeleton from fracture during daily activity. Accumulation of microcracking and loss of osteocytes have been implicated in the regulation and initiation of targeted (reparative) remodeling of bone and, in certain situations, the development of fatigue or stress fracture. We performed a histologic study of the dorsal cortex of the mid-diaphysis of the third metacarpal (Mc-III) bone of Thoroughbred racehorses after bones were bulk-stained in basic fuchsin and transverse calcified sections were prepared. The Thoroughbred racehorse is an extreme athlete whose Mc-III bone experiences particularly high cyclic strains during training and racing. A group of non-athletic horses was also included in the experiment. The following variables were quantified: activation frequency (Ac.f); bone formation rate (BFR); resorption space density (Rs.N/T.Ar); microcrack density (Cr.Dn); microcrack mean length (Cr.Le); microcrack surface density (Cr.S.Dn); osteocyte density (Ot.N/T.Ar; Ot.N/B.Ar); and bone volume fraction (B.Ar/T.Ar). Ac.f and BFR were estimated using a mathematical algorithm. Using confocal microscopy, bones were examined for fine microcracks, diffuse matrix injury, and disruption of the osteocyte syncytium. Low values for Cr.Dn (#/mm2) were found in both groups (0.022+/-0.008 and 0.013+/-0.006 for racing Thoroughbreds and non-athletic horses, respectively). There was no significant relationship between Cr.Dn and Ot.N/T.Ar; Ot.N/B.Ar, B.Ar/T.Ar, and Ot.N/T.Ar; Ot.N/B.Ar, and remodeling (Ac.f, Rs.N/T.Ar) and Ot.N/T.Ar; Ot.N/B.Ar. Intense remodeling of the Mc-III dorsal cortex was found in the racing Thoroughbreds (Ac.f 12.8+/-7.4 #/mm2/year; BFR 31.5+/-15.6%; Rs.N/T.Ar 0.19+/-0.09 #/mm2) and was significantly increased compared with non-athletic horses. Overall, remodeling was weakly correlated with Cr.Dn (r2=0.15, P<0.05). Subtle matrix injury, not detectable by bright-field microscopy, was particularly evident adjacent to resorption spaces in Thoroughbred bone. In non-athletic horses, disruption of the dendritic cell processes of osteocytes associated with cement lines and interstitial fragments was more evident. Taken together, these findings suggest that site-specific (targeted) induction of remodeling during functional adaptation of bone in a high-strain skeletal site is not dependent on accumulation of microcracking or loss of osteocytes. We hypothesize that athleticism can directly influence bone turnover in this extreme athlete through pathways that do not involve classical linear microcracks.

Age Factors↗
PubMed2005

The morphological association between microcracks and osteocyte lacunae in human cortical bone.

We studied the spatial relationship between the osteocyte lacunar-canalicular network and microdamage accumulation in bone matrix. Rib sections from 9 white women aged 50-60 were stained with basic fuchsin and examined using bright-field and fluorescence microscopy. The results showed that the numerical and length density of cracks were 5-fold higher in interstitial bone than in osteons (P<0.001). Osteocyte lacunar density was 17% lower in interstitial bone than in osteonal bone (P<0.001). In addition, the osteocyte lacunae in interstitial bone were significantly fewer (by 16%) in the area adjacent to microdamage as compared with the area remote from microdamage (P<0.001). The proportion of fields with lacunar density less than 728/mm2, the cut-off point calculated from ROC analysis, was 30% in osteonal bone, 55% in interstitial bone remote from microcracks and 83% adjacent to microcracks. The mean values of lacunar density in these bones were 10%, 22% and 27% lower than the cut-off point, respectively. The likelihood of microdamage was 3.8 times higher in bone with osteocyte lacunar density <728/mm2. About 73% of the crack profiles were spatially associated, at least partly, with bone fragments in which osteocyte lacunae were absent. We conclude that microdamage and osteocyte deficiency occur in the same bone regions; there is likely a causal relationship between them but we are unable to say which comes first.

Aging↗
PubMed2006

Intracortical remodeling during human bone development--a histomorphometric study.

Although intracortical bone remodeling is a key aspect of bone physiology, very little is known about this process during human bone development. In this study, we examined transiliac bone samples from 56 individuals between 1.5 and 22.9 years of age (31 female; tetracycline labeling present in 42 subjects) who did not have evidence of metabolic bone disease. Parameters of osteonal structure (osteon diameter, wall thickness, diameter of osteonal canals) and dynamic measures of intracortical remodeling were determined separately for the external and internal cortex. We found that measures of osteonal structure were independent of age. However, the percentage of osteons showing metabolic activity was lower in the older study subjects, corresponding to a slowdown in the turnover of cortical bone. Most dynamic parameters of bone metabolism were higher in the internal cortex than in the external cortex. Cortical porosity was negatively associated with age on the external, but not on the internal cortex. The bone forming activity that refills the remodeling cavities seemed to favor the side of the osteonal canal that faced towards the periosteum. In summary, intracortical remodeling activity varies markedly during bone development, and is slightly asymmetric between the two cortices of an iliac bone specimen. Remodeling during development is thus an age-dependent process that varies with location even within the same bone.

Adolescent↗
PubMed2006

Assessment of age at death by microscopy: unbiased quantification of secondary osteons in femoral cross sections.

The microscopic method of age at death determination was introduced by Kerley in 1965 [E.R. Kerley, The microscopic determination of age in human bone, Am. J. Phys. Anthropol, 23 (1965) 149-163.]. However, even though the method has been revised several times, there remain some fundamental issues concerning the reliability of the methods. This is because several basic histological features seen in a cross section of a bone have to be quantified according to the method, but the definition, and hence quantification, of these features leaves room for subjectivity. In a previous study we found that some of these features (osteon fragments and Haversian canals) could not be identified reliably. Only secondary osteons could be identified with a low inter and intra observer error. Furthermore, since the histological features are quantified in only parts of an entire bone cross section, the selection of these parts or areas is a potential source of bias. Finally, unless an unbiased method is used for addressing features on the borders of the selected areas, this will also introduce error. These issues have not been addressed specifically in previous studies. In this study, we used the methods of stereology to choose the regions of interest, as well as for dealing with border phenomena, and we only counted secondary osteons. Our results show a statistically significant increase in the median number of osteons per area unit with increasing age at death. However, this was after exclusion of one outlier. This result is probably due to the limited sample size (N = 24). As such, this study is preliminary, but does warrant applying the described techniques to a larger sample.

Adolescent↗
PubMed2005

Osteonal effects on elastic modulus and fatigue life in equine bone.

We hypothesized that recently formed, incompletely mineralized, and thus, relatively deformable osteons in the equine third metacarpus enhance in vitro load-controlled fatigue life in two ways. Macroscopically, there is a compliance effect, because reduced tissue elastic modulus diminishes the stress required to reach a given strain. Microscopically, there is a cement line effect, in which new osteons and their cement lines more effectively serve as barriers to crack propagation. We studied 18 4 x 10 x 100 mm beams from the medial, lateral, and dorsal cortices of metacarpal bones from 6 thoroughbred racehorses. Following load-controlled fatigue testing to fracture in 4 point bending, a transverse, 100 microm thick, basic fuchsin-stained cross-section was taken from the load-bearing region. The number and diameter of all intact (and thus recently formed/compliant) secondary osteons in a 3.8 x 3.8 mm region in the center of the section were determined. The associated area fraction and cement line length of intact osteons were calculated, and the relationships between these variables, elastic modulus (E), and the logarithm of fatigue life (logN(F)) were analyzed. As expected, logN(F) was negatively correlated with E, which was in turn negatively correlated with intact osteon area fraction and density. (LogN(F))/E increased in proportion to intact osteon density and nonlinearly with cement line density (mm/mm(2)). These results support the hypothesis that remodeling extends load-controlled fatigue life both through the creation of osteonal barriers to microdamage propagation and modulus reduction.

Animals↗
PubMed2005

Osteon interfacial strength and histomorphometry of equine cortical bone.

The interfacial strength of secondary osteons from the diaphysis of the Thoroughbred equine third metacarpal was evaluated using the fiber pushout test. The pushout was performed on 300-500 microm sections of 4x4x15 mm bone blocks machined from four anatomic regions of the cortex. Pushout strength was evaluated from proximal to distal location within the diaphysis on four osteon types classified under polarized light on adjacent histologic sections from each block. The shear strength of the interfaces were estimated from shear lag theory. Differences were found in the interfacial strength of osteons based on appearance under polarized light with bright field having the highest interfacial strength (40.3 MPa). The lowest strength was found in the dark field osteons (22.8 MPa). The dorsal region had the highest shear strength and toughness compared to all other regions. The cement line and interlamellar interfaces are similar in strength, but exhibit regional dependence--specifically, the palmar region strength is less (17.5 MPa) than the osteon interlamellar interfaces (30.4 MPa) and osteon type dependent (alternating significantly weaker than other types). Histomorphometry revealed significant regional differences (p<0.0001) in osteon area fraction among the four osteon types as well as differences in the osteon diameter (p=0.01), with dorsal regions having larger osteons (170 microm) than the palmar region (151 microm). Fatigue life and fracture toughness of Haversian bone are reported in the literature to be regionally dependent and are known to be associated with osteon pullout--an osteon interfacial phenomenon. Therefore, the results presented in this study are important to further the understanding of the mechanisms of fragility and damage accumulation in cortical bone.

Animals↗
PubMed2005

Assessment of composition and anisotropic elastic properties of secondary osteon lamellae.

Measurement of the elastic properties of single osteon lamellae is still one of the most demanding tasks in bone mechanics to be solved. By means of site-matched Raman microspectroscopy, acoustic microscopy and nanoindentation the structure, chemical composition and anisotropic elasticity of individual lamellae in secondary osteons were investigated. Acoustic impedance images (911-MHz) and two-dimensional Raman spectra were acquired in sections of human femoral bone. The samples were prepared with orientations at various observation angles theta relative to the femoral long axis. Nanoindentations provided local estimations of the elastic modulus and landmarks necessary for spatial fusion of the acoustic and spectral Raman images. Phosphate nu(1) (961 cm(-1)) and amide I (1665 cm(-1)) band images representing spatial distributions of mineral and collagen were fused with the acoustic images. Acoustic impedance was correlated with the indentation elastic modulus E(IT) (R(2)=0.61). Both parameters are sensitive to elastic tissue anisotropy. The lowest values were obtained in the direction perpendicular to the femoral long axis. Acoustic images exhibit a characteristic bimodal lamellar pattern of alternating high and low impedance values. Since this undulation was not associated with a variation of the phosphate nu(1)-band intensity in the Raman images, it was attributed to variations of the lamellar orientation. After threshold segmentation and conversion to elastic modulus the orientation and transverse isotropic elastic constants were derived for individual ensembles of apparent thin and thick lamellae. Our results suggest that this model represents the effective anisotropic properties of an asymmetric twisted plywood structure made of transverse isotropic fibrils. This is the first report that proves experimentally the ability of acoustic microscopy to map tissue elasticity in two dimensions with micrometer resolution. The combination with Raman microspectroscopy provides a unique way to study bone and mineral metabolism and the relation with mechanical function at the ultrastructural tissue level.

Anisotropy↗
PubMed2004

Reconstruction of mandibular defects with autologous tissue-engineered bone.

PURPOSE: Maxillofacial reconstructive procedures often require bone graft harvesting, which results in donor site morbidity; the use of tissue-engineered bone would eliminate this problem. In this study, a novel scaffold design and new fabrication protocol were used to produce autologous tissue-engineered constructs (scaffolds seeded with cells) to reconstruct segmental mandibular defects in a minipig model. MATERIALS AND METHODS: Porcine mesenchymal stem cells were isolated from the ilium. They were expanded in culture and seeded onto poly-dl-lactic-coglycolic acid scaffolds. The constructs were placed in a bioreactor and incubated for 10 days in medium and osteogenic supplements. Four full-thickness bony defects (2 x 2 cm) were created in the same pig's mandible. The constructs (n = 2) were placed into 2 of the defects as autologous grafts. One unseeded scaffold and 1 empty defect served as controls. At 6 weeks postimplantation, the pig was sacrificed, the mandible was harvested, and the grafted sites were evaluated by clinical, radiographic, and histologic methods. RESULTS: The construct-implanted defects appeared to be filled with hard tissue resembling bone, whereas controls were filled with fibrous tissue. Radiographically, the tissue-engineered constructs were uniformly radiodense with bone distributed throughout. The interface between native bone and constructs was indistinct. Complete bone ingrowth was not observed in control defects. Osteoblasts, osteocytes, bone trabeculae, and blood vessels were identified throughout the defects implanted with constructs. CONCLUSION: This "proof-of-principle" study indicates that porcine mandibular defects can be successfully reconstructed by in vitro cultured autologous porcine mesenchymal stem cells on a biodegradable polymer scaffold with penetration of bone and blood vessels.

Animals↗
PubMed2005

Collagen orientation patterns in human secondary osteons, quantified in the radial direction by confocal microscopy.

The composite structure of secondary osteon lamellae, key micro-mechanical components of human bone, has intrigued researchers for the last 300 years. Scanning confocal microscopy here for the first time systematically quantifies collagen orientations by location within the lamellar thickness. Fully calcified lamellar specimens, extinct or bright in cross-section under circularly polarized light, were gently flattened, and then examined along their thickness direction, the radial direction in the previously embedding osteon. Collagen orientation was measured from confocal image stacks. So-called extinct lamellae and so-called bright lamellae are found to display distinct, characteristic patterns of collagen orientation distribution. Orientations longitudinal to the osteon axis in extinct lamellae, transverse to the osteon axis in bright lamellae, and oblique to the osteon axis in both lamellar types, show parabolic distribution through specimen thickness. Longitudinal collagen in extinct lamellae, and transverse collagen in bright lamellae, peaks at middle third of lamellar thickness, while oblique collagen peaks at outer thirds of both types. Throughout the thickness, longitudinal collagen orientations characterize extinct lamellar specimens, while orientations oblique to the original osteon axis characterize bright lamellar specimens. Measured patterns complement previous indirect results by different methods and reinforce previously hypothesized differences in lamellar mechanical functions.

Adult↗
PubMed2006

Bone osteonal tissues by Raman spectral mapping: orientation-composition.

Bone is a composite material with a hierarchical structure. Its strength depends on its structural and material properties. In the present study, Raman microspectroscopic and Imaging analyses were employed to study 12 osteons in tissue sections from the femoral midshaft of a healthy human female, with a spatial resolution of approximately 1mum. Spatial changes in amount of mineral and organic matrix, as well as the variation in the mineral content were determined, imaged, and plotted as a function of the polarization of incident light. The results showed that the prominent bands, such as nu(1) PO(4) and amide I, commonly used for the determination of mineral and organic compositions, are quite sensitive to the orientation and the polarization direction of the incident light. On the other hand, bands such as amide III, nu(2) PO(4) and nu(4) PO(4) are less susceptible to the orientational effects. As a result, exclusive consideration of the nu(1) PO(4) and amide I bands for the calculation of material properties might lead to erroneous conclusions. Amide III, nu(2) PO(4) and nu(4) PO(4) Raman bands should also be taken into consideration for compositional analysis of bone structures, especially ones with unknown orientational features. Moreover, the results of the present study demonstrate the versatility of the analytical technique, and provide insights into the organization of bone tissue at the ultrastructural level.

Bone Density↗
PubMed2005

Some considerations on biomaterials and bone.

Osteoinduction is a property not traditionally attributed to Calcium Phosphate ceramics. Histologic, SEM and X-ray microanalyses of a biopsy of pulmonary alveolar microlithiasis allow to discredit this opinion. Bone, even lamellar type, was ectopically formed on microliths undergoing osteoclastic erosion. The SEM and X-ray microanalyses of coral granules implanted in humans indicate an osteoconductive property for both Calcium and Phosphorus. Analysis of in vitro allows to propose an enhancement of the osteocapability of coral. Lamellar bone formation in the near absence of loads undermines the opinion which sees a correlation between lamellar bone and mechanical loads. Analysis of the bone surrounding an uncemented titanium hip prosthesis highlights that both remodeled and newly formed bone have lamellae oriented parallel to prosthesis surfaces, i.e. orthogonal to loads, as opposed to that of lamellar bone of osteons which are oriented parallel to loads. Analysis of longitudinal sections of cortical bone under polarized light points out that lamellae are displaced parallel to the cement line surface both in the conic end of osteons and in Volkman's canals with thick wall, i.e. undergoing sloped load directions. In conclusion, there may be a relationship between lamellae formation and gravity.

Animals↗
PubMed2005

Biological fixation of endosseous implants.

Primary implant stability is ensured by a mechanical fixation of implants. However, during implant healing a biological anchorage is necessary to achieve final osseointegration. Aim of this study was to investigate the histological aspects of biological fixation around titanium screws. Forty-eight titanium screws with different surfaces (smooth, plasma sprayed, sand blasted) were inserted in tibiae and femura of sheep and analyzed by light microscope and SEM 1 hour, 14 and 90 days after implantation. One hour after implantation the implant-bone gap was filled with a blood clot and host bone chips arising from burr surgical preparation or friction during implant insertion. Fourteen days after implantation new trabecular bone and enveloped bone chips were observed in the gap: no osteogenesis developed where implant threads were in contact with host bone. Ninety days after surgery all trabecular bone and most of the bone chips were substituted by a mature lamellar bone with few marrow spaces. Our results suggest that the trabecular bone and bone chips represent a three-dimensional network ensuring a biological implant fixation in all different implant surfaces 2 weeks after surgery. Host bone chips could favour the peri-implant osteogenesis. Inter-trabecular and implant-trabecular marrow spaces of both trabecular and lamellar bone may favour the peri-implant bone turnover.

Animals↗
PubMed2005

Atomic force microscopy on human trabecular bone from an old woman with osteoporotic fractures.

AFM images were taken of the exterior surface of a single trabecula, extracted from a human femoral head removed during surgery for a hip fracture in an old women with former fractures. The images showed a dense structure of bundled collagen fibrils banded with 67 nm periodicity. Bundles were seen to run in parallel in layers confirming the collagen structure seen by other techniques. Single collagen fibrils were seen to cross the bundles, thus forming cross-links between neighboring bundles of collagen fibrils. Some of these crossing fibrils did not have the 67 nm band pattern and their dimensions were about half compared to the neighboring collagen fibrils. Very little mineral was found on the surface of the trabecula. An AFM image of a fracture plane was also displayed. The trabecula was extracted from a region close to the hip fracture. However, there were in this case no obvious features in the images that could be linked directly to osteoporosis, but altered collagen banding and collagen protrusions may alter mechanical competence. A path to extensive studies of the nanometer scale structure of bone was demonstrated.

Aged, 80 and over↗
PubMed2005

Reduced osteoblastic population and defective mineralization in osteopetrotic (op/op) mice.

Osteopetrotic (op/op) mice fail to exhibit bone remodeling because of a defective osteoclast formation due to a lack of macrophage colony-stimulating factor. In this study, we investigated the femora of op/op mice to clarify whether the osteoblastic population and bone mineralization are involved in osteoclasts or their bone resorption. The op/op mice extended the meshwork of trabecular bones from the chondro-osseous junction to the diaphyseal region. In the femoral metaphyses of op/op mice, intense alkaline phosphatase (ALPase)-positive osteoblasts were observed on the metaphyseal bone in close proximity to the erosion zone of the growth plates. Von Kossa's staining revealed scattered mineralized nodules and a fine meshwork of mineralized bone matrices while the wild-type littermates developed well-mineralized trabeculae parallel to the longitudinal axis. In contrast to the metaphysis, some op/op diaphyses showed flattened osteoblasts with weak ALPase-positivity, and the other diaphyses displayed bone surfaces without a covering by osteoblasts. It is likely, therefore, that the osteoblastic population and activity were lessened in the op/op diaphyses. Despite the osteopetrotic model, von Kossa's staining demonstrated patchy unmineralized areas in the op/op diaphyses, indicating that a lower population and/or the activity of osteoblasts resulted in defective mineralization in the bone. Transmission electron microscopy disclosed few osteoblasts on the diaphyseal bones, and instead, bone marrow cells and vascular endothelial cells were often attached to the unmineralized bone. Osteocytes were embedded in the unmineralized bone matrix. Thus, osteoclasts appear to be involved in the osteoblastic population and activity as well as subsequent bone mineralization.

Alkaline Phosphatase↗
PubMed2005

Micro- and nano-structural analyses of damage in bone.

Skeletal fractures represent a significant medical and economic burden for our society. In the US alone, age-related hip, spine, and wrist fractures accounted for more than $17 billion in direct health care costs in 2001. Moreover, skeletal fractures are not limited to the elderly; stress fractures and impact/trauma-related fractures are a significant problem in younger people also. Gaining insight into the mechanisms of fracture and how these mechanisms are modulated by intrinsic as well as extrinsic factors may improve the ability to define fracture risk and develop and assess preventative therapies for skeletal fractures. Insight into failure mechanisms of bone, particularly at the ultrastructural-level, is facilitated by the development of improved means of defining and measuring tissue quality. Included in these means are microscopic and spectroscopic techniques for the direct observation of crack initiation, crack propagation, and fracture behavior. In this review, we discuss microscopic and spectroscopic techniques, including laser scanning confocal microscopy (LSCM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopic imaging for visually observing microdamage in bone, and the current understanding of damage mechanisms derived from these techniques.

Animals↗
PubMed2005

Bone microarchitecture evaluated by histomorphometry.

The increasing use of densitometric devices for assessing bone fragility has progressively strengthened the assumption that mass is the most important property determining bone mechanical competence. Nevertheless, structure and microarchitecture are relevant aspects of bone strength. The study of microarchitecture is based on the measure of width, number, and separation of trabeculae as well as on their spatial organization. There are several methods to assess bone architecture, particularly at the trabecular level. In particular, histomorphometry, based on the use of optical microscopy and on the principles of quantitative histology and stereology, evaluates microarchitecture two-dimensionally, even if these measures appear well correlated to the three-dimensional structure and properties of bone. In addition, new computerized methods allow the acquisition of more sophisticated measurements by means of a digitizer have been introduced to integrate the use of the microscope. These methods supply information on trabecular width as well as on its distribution and on the organization of the trabeculae in the marrow space. Microarchitecture seems to be a determinant of bone fragility independent of bone density and it is important for understanding the mechanisms of bone fragility as well as the action of the drugs used to prevent osteoporotic fractures. Several in vivo studies (on animals and humans) can provide an additional interpretation for the anti-fracture effect of such drugs. For instance, bisphosphonates and parathyroid hormone seem to preserve or even improve microarchitecture. The challenge for the future will be to evaluate bone quality in vivo with the same or better resolution and accuracy than the invasive methods used today.

Animals↗
PubMed2005

The TEM characterization of the lamellar structure of osteoporotic human trabecular bone.

The lamellar structure of osteoporotic human trabecular bone was characterized experimentally by means of transmission electron microscopy (TEM). More specifically, the TEM was used to determine if trabecular bone exhibits similar lamellar structural motifs as cortical bone by analyzing unmineralized, mineralized and demineralized bone, and to study the influence of the osteocyte network on the lamellar structure of osteoporotic trabecular bone. Comparison with normal trabecular bone is included. This paper summarizes partial results of a larger study, which addressed the characterization of the hierarchical structure of normal versus osteoporotic human trabecular bone [Rubin, M.A., 2001. Multiscale characterization of the ultrastructure of trabecular bone in osteoporotic and normal humans and in two inbred strains of mice. MS Thesis, Georgia Institute of Technology.] at several structural scales.

Bone and Bones↗
PubMed2005

Unexpected ultrastructral changes in bone osteiod collagens in osteogenesis imperfecta.

Osteogenesis Imperfecta (OI) is a heterogeneous, inherited bone disorder usually resulting from a defect in collagen synthesis or function. The Sillence classification recognises four OI subtypes of which type III is the severe, progressively deforming form. Here, we report distinctive ultrastructural abnormalities of bone osteoid collagen fibrils from three patients with OI type III and compared with normal controls. Collagen biochemistry of these patients showed normal alpha1(I) and alpha2(I) chains, despite the structurally abnormal collagen fibrils. The expected lamellar organisation of normal osteoid was absent in the bone biopsies of these patients. In addition their collagen fibrils had frayed edges and no periodicity was observed in most of these fibrils. These collagen fibrils were also flower like, twisted, spiralled and sparsely distributed throughout a very thick osteoid with patchy mineralisation. These structurally abnormal collagens may not be able to provide the nucleating and scaffolding sites for normal mineralisation and may lead to the bone fragility observed in OI.

Bone Density↗