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PubMed2001

In vivo histological changes occurring in hydroxyapatite cranial reconstruction--case report.

Histological changes were observed in a hydroxyapatite plate and hydroxyapatite granules used to repair a craniotomy defect and removed after 2 years and 9 months of use. The hydroxyapatite plates and granules had completely fused to the cranium, with new bone formation on the dural side extending in a three-dimensional matrix along the pores with the Haversian system in the center. New bone formation was less extensive under the artificial dura than under normal dura. This finding suggests that the dura has the ability to promote bone formation. A new vessel was found along the interconnecting pores. The interconnecting pores allow osteoconduction in the hydroxyapatite plate, so new bone formation can progress. Hydroxyapatite has osteoconduction properties and is biocompatible, so gains strength in vivo through new bone formation, and is the ideal material for artificial bones. Factors important to achieving good bone formation after cranial reconstruction surgery include presence of the dura, and pore size approximate to the Haversian system (100-500 microns) and interconnecting pores in the hydroxyapatite plate.

Adult↗
PubMed1977

The effect of chronic low level lead intoxication on the Haversian remodeling system in dogs.

The greatest portion of lead ingested by human beings or experimental animals is stored in bone. Once in bone, lead is difficult to remove. It may have a half-life of 20 years or more and could interfere with bone metabolism. The effects of lead intoxication on the production of intercellular matrix have been reported previously but the effects of lead on bone turnovers rates were not reported. In this paper we reported the results of a study of the effects of lead on bone turnover in dogs. Differences between experimental and control dogs were found when measuring appositional rates, radial closure rates, activation frequencies, osteon formation times, and bone formation rates. We found that dogs subjected to a low dose (1.3 mg. per kg. per day) of lead over a long period of time (201 days) showed a statistically significant decrease in bone formation activity at the cell (90 per cent), tissue (85 per cent), and organ (78 per cent) levels when compared to controls. Although these observations were made on a small experimental and control sample (four dogs), they suggest that chronic low dose lead intoxication does alter normal bone physiology.

Animals↗
PubMed1984

Lamellar bone turnover system and its effector organ.

Juxtaposition of cell kinetics in the asymmetric, self-renewing osteoclast and osteoblast populations in the evolving secondary Haversian systems, which are in neutral balance, disclosed their genetically determined fixed and flexible or variable properties, the latter controllable. These jointly controlled cell populations (coupling) at local and organ level, constitute the Effector Organ of Lamellar Bone Turnover Systems (EO LBTS). In part genetically preprogrammed, this system also responds during growth and maturity to environmental (mainly biomechanical) factors that adjust structure to function. Since the pattern of signals and stimuli generated within the bones under the conditions of mechanical loads differs during growth and maturity, the two major expressions of the LBTS (i.e., modeling of bones during growth and their remodeling during growth and maturity) can be explained by the appropriate response of its EO to those patterns. Since normal physical activity has a limited range and bones sustain more or less predictable deforming forces, the signals and stimuli so generated must preserve more or less similar patterns. Considering also the constraints on the system (constants of the EO LBTS), modeling and remodeling patterns, as well as the gross and microscopic organization of bones, would vary little from one individual to another under normal circumstances. For its proper function, the EO LBTS requires the presence in the cell environment of specific and nonspecific permissive factors (as any cell or tissue in the organism) and it may be influenced further by modulatory factors which link it with the system maintaining calcium ion homeostasis in the body fluids. Mechanical failure of the skeleton in metabolic bone disease can be explained by the alterations in the biochemical or biomechanical milieu due to disorders of other organs and systems which interfere with the primary (structural) function of the EO LBTS.

Adaptation, Physiological↗
PubMed2000

A histomorphometric observation of flows in cortical bone under dynamic loading.

Ferritin was used as a histological marker for interstitial fluid flows in four goats. Two transcortical pins were inserted into each tibia mediolaterally-one at the proximal side and one at the distal side of the diaphysis. For the experimental limb, dynamic loading was applied to the pins on the lateral side. The contralateral limb was used as control. Ferritin was injected into the nutrient arteries feeding the two tibiae. The goat was then euthanized immediately. Undecalcified slides of the tibial cortical bone from both the experimental and the control limbs were studied histologically. Percentages of Haversian systems marked with ferritin halos and the average radial distance of ferritin transudation away from the Haversian canals were assessed. Results for the medial and lateral sides of both the experimental and control tibiae were reported. Significant differences in the ferritin transudation distance were found between the experimental and the control tibia (P < 0.005) and between the medial and the lateral sectors (P < 0.05). The approach documented in this paper could be used to address systematically how external loading might affect the transport phenomena in cortical bone.

Animals↗
PubMed1981

Micromechanical oscillators and techniques for determining the dynamic moduli of microsamples of human cortical bone at microstrains.

Two micromechanical oscillators are described along with methods and techniques which have been successfully used to determine the elastic, dynamic, shear and Young's moduli at microstrain levels, and which with proper design modifications might, under restricted experimental conditions, also be employed to determine viscous moduli. Although these systems can be used with any microsamples, they were designed originally for dynamic studies of the unit microstructural element of human cortical bone, the secondary osteon (Haversian system).

Biomechanical Phenomena↗
PubMed2005

Modeling deformation-induced fluid flow in cortical bone's canalicular-lacunar system.

To explore the potential role that load-induced fluid flow plays as a mechano-transduction mechanism in bone adaptation, a lacunar-canalicular scale bone poroelasticity model is developed and implemented. The model uses micromechanics to homogenize the pericanalicular bone matrix, a system of straight circular cylinders in the bone matrix through which bone fluids can flow, as a locally anisotropic poroelastic medium. In this work, a simplified two-dimensional model of a periodic array of lacunae and their surrounding systems of canaliculi is used to quantify local fluid flow characteristics in the vicinity of a single lacuna. When the cortical bone model is loaded, microscale stress, and strain concentrations occur in the vicinity of individual lacunae and give rise to microscale spatial variations in the pore fluid pressure field. Furthermore, loading of the bone matrix containing canaliculi generates fluid pressures in the contained fluids. Consequently, loading of cortical bone induces fluid flow in the canaliculi and exchange of fluid between canaliculi and lacunae. For realistic bone morphology parameters, and a range of loading frequencies, fluid pressures and fluid-solid drag forces in the canalicular bone are computed and the associated energy dissipation in the models compared to that measured in physical in vitro experiments on human cortical bone. The proposed model indicates that deformation-induced fluid pressures in the lacunar-canalicular system have relaxation times on the order of milliseconds as opposed to the much shorter times (hundredths of milliseconds) associated with deformation-induced pressures in the Haversian system.

Animals↗
PubMed1979

Cortical circulation of long bones.

Intravascular injections of India ink in the femora of adult dogs revealed the existence of two distinct vascular systems in the cortex. One courses through the entire thickness of the cortex and is a regular, longitudinal network of uniform capillaries which is in continuity with the periosteal and endosteal networks. Once the haversian systems form a second network appears, radiating from the bone marrow. That system, primarily transverse, anastomoses in the haversian canals with the capillaries of the first system. Therefore, the merging of the two networks occurs primarily in the middle layer of the cortex. The direction of the arterial blood flow in the mature animal is predominantly centrifugal, while the venous drainage is centripetal. In the immature animal, the contribution of the periosteal network is much greater. Because the two cortical systems are profusely anastomosed with each other and with the periosteal and endosteal circulatory networks, the blood can flow in either direction, depending on physiological conditions.

Animals↗
PubMed1994

Scanning electron microscopy of collagen fiber orientation in the bone lamellar system in non-decalcified human samples.

Previous studies on collagen fiber orientation have led to different interpretations and theories about the fiber arrangement in the lamellar compact bone. The purpose of this investigation was to provide new and more in-depth data on fiber arrangement in the lamellar bone system in order to explain the orientation of the fiber bundles. This was carried out by applying a simple method of preparation which permitted observation of non-decalcified samples. A previously isolated Haversian system was subjected to slow bending up to reaching the fracture point. Hence, the fracture surface was observed by SEM. The same samples were also observed by polarized light microscopy. A significant alternation of fiber orientation in the adjacent lamellae was observed. Different domains of differently oriented fibers were present within the same lamella; conjugating fibers connecting adjacent lamellae were also shown. This method avoided most of the artifacts due to chemical treatment of bone samples. The results can be easily interpreted by means of the same criteria applied in mechanics for the studying of composite materials.

Adult↗
PubMed1979

[Bone perfusion after plate osteosynthesis. A study of the intact rabbit tibia with disulfin blue vital staining].

After operative fracture treatment an interference with blood supply has to be expected. The fixation of a plate to an intact rabbit tibia lead to extended areas where circulation is disturbed. These disturbances were partially reversible within one week without structural changes visible in the recovering bone. Only the zones remaining without vascular supply after one week started to recover in the 4th week, when intracanalicular remodelling and the formation of new Haversian systems became visible at the borders of the avascular regions.

Animals↗
PubMed1997

Incorporation of devitalised autografts in dogs.

Segments of the tibial diaphysis from 24 adult dogs were reimplanted after extracorporeal autoclaving or gamma-irradiation. Fixation was by interlocking intramedullary nailing, or plating. The dogs were killed after 36 weeks and the tibias examined. Bony union was seen in 46 of the 48 contact areas. Microangiography and Tc-perfusion scans demonstrated complete revascularisation of all the grafts. Biomechanical tests showed defective union with increased bending and decreased stiffness compared to normal controls. Fluorescent microscopy confirmed restitution of Haversian systems and slow replacement of the graft by lamellar bone containing viable osteocytes.

Angiography↗
PubMed1980

Levels of antimony, arsenic, cadmium, copper, lead, mercury, selenium, silver, tin and zinc in bone tissue of industrially exposed workers.

The contents of the elements antimony, arsenic, cadmium, copper, lead, mercury, selenium, silver, tin and zinc in bone tissue from autopsy specimens of the femur of workers who had been exposed to a large number of metals in a smeltery and refinery in Northern Sweden as well as of a control group have been quantitatively assayed. The analytical techniques used were atomic absorption spectrophotometry, neutron activation analysis and particle induced X-ray emission analysis (PIXE) in a proton microprobe. Increased levels of lead in the bone tissue of exposed workers compared to a non-exposed control group were observed. The median level of lead in the group of exposed workers exceeded the corresponding value of the control group about 5 times. Using the proton microprobe in the PIXE-mode, concentration profiles of copper, lead and zinc were examined within the Haversian system of the bone samples.

Aged↗
PubMed1992

Micromechanics modeling of Haversian cortical bone properties.

A finite-element micromechanics model for Haversian cortical bone tissue has been developed and studied. The model is an extension of two-dimensional micromechanics techniques for fiber-reinforced composite materials. Haversian systems, or secondary osteons, are considered to be the fiber component, and interstitial lamellar bone the matrix material. The cement line is included as an 'interphase' component along the fiber/matrix interface. The model assumes a regular repeatable spacing of the longitudinally aligned continuous fibers and is, therefore, restricted to approximating Haversian cortical bone in its present form. Haversian porosity is modeled explicitly by incorporating a hollow fiber to represent the Haversian canal. Solutions have been obtained by applying uniform macroscopic stresses to the boundaries of the repeating unit cell model. Macroscopic mechanical property predictions correspond reasonably well with the experimental data for cortical bone, but are necessarily dependent on the input properties for each constituent, which are not well established. The predicted variation in the elastic modulus with porosity is not as sensitive as that observed experimentally. Stresses within the constituents can also be modeled with this method and are demonstrated to deviate from the macroscopic applied stress levels.

Biomechanical Phenomena↗
PubMed1982

Fluid flow in bone in vitro.

Recent dielectric measurements suggest that the electromechanical effect in wet (fluid saturated) bone is not due to a piezoelectric effect. This would imply that the electromechanical effect observed in wet bone is due to a streaming potential and is therefore dependent on fluid flow in stressed bone. A model for fluid flow in bone in vitro is presented. This model predicts a rapid decay (of the order of a millisecond or less) for the fluid flow in Haversian systems. The implications of this result for the interpretation of the electromechanical effect in wet bone are discussed.

Biomechanical Phenomena↗
PubMed1979

Gross and microscopic anatomical studies of palate structure and osteotomy site.

A normal 1-year-old infant palate and a newborn cleft palate were studied grossly, radiographically, and microscopically for histological structure in hard palate osteotomy sites. A correlated study of biopsies from an osteotomy site seven days postoperatively and another at twelve months following osteotomy was also made. The findings showed that successful osteotomy in infant cleft palate surgery translocates autogenous fibrous bone and osteogenic cells into a cleft-bridging position. Woven fibrous bone rapidly forms across the cleft, and then matures by lamellar bone replacement and haversian system remodeling. Both normal and cleft palates have a rich anastomosis of microscopic blood supply that is vitally important in the remodeling process. These factors may help to explain successful long-term results in early cleft palate osteotomy surgery.

Cartilage↗
PubMed2003

Micromechanically based poroelastic modeling of fluid flow in Haversian bone.

To explore the hypothesis that load-induced fluid flow in bone is a mechano-transduction mechanism in bone adaptation, unit cell micro-mechanical techniques are used to relate the microstructure of Haversian cortical bone to its effective poroelastic properties. Computational poroelastic models are then applied to compute in vitro Haversian fluid flows in a prismatic specimen of cortical bone during harmonic bending excitations over the frequency range of 10(0) to 10(6) Hz. At each frequency considered, the steady state harmonic response of the poroelastic bone specimen is computed using complex frequency-domain finite element analysis. At the higher frequencies considered, the breakdown of Poisueille flow in Haversian canals is modeled by introduction of a complex fluid viscosity. Peak bone fluid pressures are found to increase linearly with loading frequency in proportion to peak bone stress up to frequencies of approximately 10 kHz. Haversian fluid shear stresses are found to increase linearly with excitation frequency and loading magnitude up until the breakdown of Poisueille flow. Tan delta values associated with the energy dissipated by load-induced fluid flow are also compared with values measured experimentally in a concurrent broadband spectral analysis of bone. The computational models indicate that fluid shear stresses and fluid pressures in the Haversian system could, under physiologically realistic loading, easily reach the level of a few Pascals, which have been shown in other works to elicit cell responses in vitro.

Adaptation, Physiological↗
PubMed1984

[Osteon patterns in the diaphysis of the human femur].

25 bone cylinders from 5 human femora were examined with respect to the direction of osteons, visualizing the Haversian systems. These canal systems, infiltrated with indian ink showed characteristic patterns. The osteons of the femur shaft run from proximally anterior to distally posterior, forming a double diagonal architecture. From these results it is derived, that the architecture of osteons may be looked at as a functional adaptation to mechanical stresses in the femur diaphysis.

Aged↗
PubMed1985

The structure of the trabeculae of cancellous bone. 1. The calcaneus.

87 either cylindroid or laminar trabeculae, isolated from the perpendicular or inferior bundles of the human calcaneus, were embedded in methylmatecrylate and serially cut along longitudinal and transversal planes with a rotatory-blade saw. The microscopical study of the sections showed that in 83% of the samples secondary osteons run along the longitudinal axis of the trabeculae and their lumina either form a continuous channel network throughout each trabecula (37% of cases) or are restricted to discrete segments (46% of cases). The trabeculae entirely devoid of osteons (17%) are the thinnest, never exceeding 400 microns in thickness. This value is not even exceeded by the segments devoid of osteons in the trabeculae in which the Haversian canals occur only intermittently; conversely, the segments containing Haversian canals can reach and exceed 600 microns in thickness. The maximum distance of the osteocytic lacunae from filtering surfaces--i.e. outer surface of the trabeculae or inner surface of the Haversian canals--was found to be almost the same in the segments of the trabeculae that enclose or not osteons, even though the average trabecular thickness is greater in the former than in the latter regions. On the basis of these findings the formation of endotrabecular osteons may be viewed as a device that indirectly favours the metabolic exchange of deep-seated osteocytes while increasing the free surface area available for bone tissue reconstruction. It remains doubtful whether the Haversian systems may also contribute to improve the mechanical properties of the trabeculae. The arrangement of the collagen fibrils, which differs between cylindroid and laminar trabeculae, is apparently well suited to ensure the resistance of the trabeculae to mechanical loading through the use of the least amount of building material, in accordance with Wolff's law.

Adult↗