Insufficient blood supply of fovea capitis femoris, a risk factor of femoral head osteonecrosis.

BACKGROUND: A defective nutrient foramen in the fovea capitis femoris was hypothesized to reflect the blood circulation pattern of the femoral head, leading to insufficient blood supply and causing osteonecrosis of the femoral head. METHODS: Normal and necrotic femoral head specimens were collected. The necrotic femoral head group was divided into a non-traumatic and traumatic subgroup. 3D scanning was applied to read the number, the diameter, and the total cross-sectional area of the nutrient foramina in the fovea capitis femoris. Chi-squared tests and independent t-tests were used to detect any differences in the categorical and continuous demographic variables. Logistic regression models were used to estimate the odds ratio (OR) for non-traumatic and traumatic osteonecrosis in different characteristic comparisons. RESULTS: A total of 249 femoral head specimens were collected, including 100 normal femoral heads and 149 necrotic femoral heads. The necrotic femoral head group revealed a significantly higher percentage of no nutrient foramen (p < 0.001), a smaller total area of nutrient foramina (p < 0.001), a smaller mean area of nutrient foramina (p = 0.014), a lower maximum diameter of the nutrient foramen (p < 0.001), and a lower minimum diameter of the nutrient foramen (p < 0.001) than the normal femoral head group. The logistic regression model demonstrated an increasing number of nutrient foramina (crude OR, 0.51; p < 0.001), a larger total area of nutrient foramina (crude OR, 0.58; p < 0.001), a larger mean area of nutrient foramina (crude OR, 0.52; p = 0.023), a greater maximum diameter of the nutrient foramen (crude OR, 0.26; p < 0.001), and greater minimum diameter of the nutrient foramen (crude OR, 0.20; p < 0.001) significantly associated with reduced odds of osteonecrosis of the femoral head (ONFH). The necrotic femoral head group was further divided into 118 non-traumatic and 31 traumatic necrotic subgroups, and no significant difference was observed in any characteristics between them. CONCLUSIONS: Characteristics of the nutrient foramen in the fovea capitis femoris showed a significant defect of necrotic than normal femoral heads, and significantly reduced odds were associated with the higher abundance of the nutrient foramen in ONFH. Therefore, the condition of the nutrient foramen might be the indicator of ONFH.

An extraction socket classification developed using analysis of bone type and blood supply to the buccal bone in monkeys.

Bone modeling and remodeling following tooth extraction has been studied extensively. The reason for bone loss during the remodeling process is multifactorial, and the primary reason for this loss is still yet to be determined. The aim of this study was to examine the type of bone and the blood supply to the buccal bone in monkeys. Six maxillary arches from six monkeys were used. The arches were divided into three sections: right posterior, anterior from canine to canine, and left posterior. Blocks were decalcified and prepared for histologic processing and examination. Modified Masson trichrome and retic staining were used. Histologic sectioning demonstrated that the blood supply to the buccal bone came from the inner (socket) side of the alveolus, the periodontal ligament, the adjacent interdental bone, and the supraperiosteal vessels emanating from the covering gingiva or mucosa. Histologic examination showed that the buccal bone was composed of bundle and cortical bone. The thickness of the buccal bone was not uniform coronoapically, and the thinnest area of buccal bone was the coronal portion.

Characterization of the spatial arrangement of secondary osteons in the diaphysis of equine and canine long bones.

The blood supply of bone cells in compact bone is provided primarily by blood vessels located within Haversian canals forming the centre of osteons. Mid-diaphysial cross-sections of radii and third metacarpal bones from two horses and radii from two mature dogs were studied using reflective light microscopy to quantify the spatial ordering of canals and compared to a computational model. The distributions of canals were analyzed using: 1) the autocorrelation function (ACF), which describes the probability of finding two canals separated by a given distance and 2) the shortest distance distribution (SDD), which describes the probability that a site within bone is located at a given distance from the nearest canal. The order in the investigated horse radii, as characterized by the oscillations of the ACF, was found to be independent of the anatomical location although, in the metacarpal bone the order was higher in the lateral than in the cranial location. Among the dogs, marked differences were only found in the ACF. An analysis of the SDD demonstrates that ordering of canals minimizes the distance of osteocytes from a blood vessel. This suggests that the efficiency of the blood supply can be adapted through differences in the order of the Haversian canals. In our model, the ordering of canals is achieved via an exclusion zone around each canal, imposed upon newly formed osteons. Simulations demonstrate that differences in the observed order can be explained by either a larger size or a larger variability of this exclusion zone.

Effects of basic fibroblast growth factor administration on vascular changes in wound healing of rat palates.

OBJECTIVE: The purpose of this study was to investigate the vascular changes induced by mucoperiosteal denudation of rat palate and to elucidate the effects of basic fibroblast growth factor (bFGF) administration on the palatal vascular network in wound healing. METHODS: A total of 117 male Wistar rats were used for the study on their 20th postnatal day. The animals were divided into three groups: a scar formation group, a basic fibroblast growth factor group, and a control group. The scar formation and basic fibroblast growth factor groups had lateral mucoperiosteum excised from the palate. In the basic fibroblast growth factor group, a solution of basic fibroblast growth factor was injected into the operated area 1 week after excision. At 6, 8, and 10 weeks postoperatively, palatal vascular changes were investigated by immunohistochemical staining and corrosion cast techniques. RESULTS: Throughout the experimental period, there were significantly fewer vessels in the scar formation group than in the control and basic fibroblast growth factor groups. In the basic fibroblast growth factor group, the elongation of new vessels and capillary proliferation proceeded, and after 10 weeks a highly organized vascular network was established. The scar formation group showed few Volkmann's canals that were shrunken or closed, whereas the basic fibroblast growth factor group evidenced Volkmann's canals with arterioles or venules, as seen in the control. CONCLUSIONS: The results suggested that injection of basic fibroblast growth factor into palatal wounds improves the vascular supply to the operated mucosa and underlying bone during and after palatal wound healing, which may contribute to tissue remodeling of the palate during growth.

A model of the intracortical vascular system of long bones and of its organization: an experimental study in rabbit femur and tibia.

The vascular anatomy of the cortical bone and the canal system are highly correlated, and the former has an important bearing on shape and microscopic lamellar structure, as it is established in the progression of the remodelling process. The classical description of a longitudinal system of canals (Havers') connected by the transversal Volkmann's canals is the generally acknowledged model of the structural organization of the cortex. However, it is remarkably difficult to study the circulation inside the compact bone in detail owing to its hard, calcified matrix, and the methods thus far applied have represented either the bone morphology and the architecture of the canal system or the injected vessel network. In the present study, the intracortical vessel network was injected with black China ink and evidenced by transillumination of full-thickness, decalcified hemicortices. By making use of the depth of field of the microscope objective, the three-dimensional architecture of the network was highlighted and the morphometry of vessel size measurements and a classification of the network nodes according to the number of arms was made possible. These observations were integrated with data obtained by routine histology on decalcified sections relevant to the connections of the intracortical canal system with the outer environment, with regard to the direction of advancement of new canals and with regard to the mode of formation of the system nodes. The formation of the intracortical vessels network involved two processes: the incorporation of the periosteal network and osteonal remodelling, the latter occurring through the advancement of cutting cones followed by their own vascular loop and by concentric lamellar apposition. The two systems could be distinguished by the diameter of the vessels (the former were significantly larger) and by the network architecture (the former convoluted, and the latter longitudinally orientated and straight). Longitudinal vessels could form branches or create connections with the periosteal derived vessels that occasionally meet on the line of their advancement. They were observed entering from either inside the cortex from the metaphyses or from the endosteal surface of the marrow cavity. The combined observations from different methods of study documented a model of intracortical canal and vessel networks formed by two initially independent systems: one derived from the external, periosteal vessels, and one from metaphyseal and marrow vessels. Connections between the two were established with the advancing of cutting cones from the extremities of the diaphysis. Analysis of the system architecture and the modalities of its progressive organization suggested that the direction of advancement of a forming canal does not necessarily correspond to the final blood flow direction of its central vessel.

Aberrant bony vasculature associated with activating fibroblast growth factor receptor mutations accompanying Crouzon syndrome.

Fibroblast growth factor receptor mutations are associated with and, in fact, cause most syndromes presenting with craniosynostosis. This knowledge has resulted in a shift in the paradigm of suture fusion causation; it was thought previously that abnormal tensional forces arising in the cranial base caused fusion of the vault sutures, but it is now understood that aberrant intercellular signaling in the developing skull leads to abnormal suture morphogenesis. Although the mutations associated with these syndromes are known and the phenotypic consequences are well documented, the pathway from mutation to phenotype has yet to be elucidated. Surgical reconstruction is the primary treatment of craniofacial abnormalities associated with craniosynostotic syndromes such as Crouzon syndrome. In many cases, calvarial vault reshaping is dependent on the quality of the autologous bone available; however, the bone of patients with craniosynostosis syndrome is often more brittle, thinner, and less robust than cranial bone from nonaffected donors. The relation between syndromic craniosynostoses and this bone has not been previously described. In this study, the osteon and blood vessel diameters of calvarial bone from patients with Crouzon syndrome and age- and sex-matched normal calvarial bone are measured. Statistical analysis demonstrates a quantitative and significant difference in the blood vessel diameter but not in the osteon diameter. This finding could be a result of abnormal blood vessel development caused by the fibroblast growth factor receptor mutation occurring before and coincident with bone formation and leading to weakened and fragile bone tissue.

Understanding stress concentration about a nutrient foramen.

We investigated the microstructural basis of a reduced stress concentration around the primary nutrient foramen of the equine third metacarpus. We quantified the spatial variations of compositional parameters (mineral content, volume fraction, histological architecture, and osteonal trajectories) from microradiographs and polarizing microscopic images of thin sections. These variations in composition and organization in turn cause variations in mechanical properties of cortical bone. We modeled the spatially inhomogeneous anisotropic elastic properties based on the measured compositional parameters and used the properties as inputs to a finite element model of the bone containing the foramen. This model, spatially constructed solely from the microscopic images, was subsequently validated by our mechanical test results. We found that: (1) a primary mechanism for stress concentration reduction appears to be due to an increased compliance near the foramen: the sharp discontinuity represented by the hole is softened by embedding it in a compliant region; (2) a reinforcing ring of increased stiffness exists at some distance from the foramen; and (3) a ring of lamellar bone exists along the foramen inside edge, which might serve to reduce the chance of cracks forming there. Our work is allowing us to design biomimetic structures with holes by mimicking the microstructure near the nutrient foramen.

Effect of lacunocanalicular architecture on hydraulic conductance in bone tissue: implications for bone health and evolution.

Bone tissue health depends largely on efficient fluid and solute transport between the blood supply and cells that are the living component of the tissue. We hypothesized that the lacunocanalicular hydraulic network, which is defined by the pericellular fluid space that is common to all bone tissue, is optimized to transport fluid and solutes between the blood supply and bone cells. An analytical study was carried out to evaluate the effect of osteonal architecture, including the osteon diameter, number of annular lamellar regions, and number and length of canalicular channels, on fluid transport between the blood supply and bone cells. On the basis of this analysis, we conclude that osteon size is limited to the distance over which fluid and solutes can be transported efficiently between the blood supply and cells. This analytic model suggests that hydraulic conductivity is highest in lamellar regions closest to the Haversian canal (HC) and decreases with increasing distance from the blood supply, reaching a plateau after the fifth lamella (169 micro m radius). Furthermore, an increase in the diameter of the HC, or a decrease in the length of canaliculi, reduces the hydraulic conductivity within the lacunocanalicular network. Applying the principle of minimal expenditure of energy to this analysis, the path distance comprising five or six lamellar regions represents an effective limit for fluid and solute transport between the blood supply and cells; beyond this threshold, hydraulic resistance in the network increases and additional energy expenditure is necessary for further transportation. This suggests that transport is optimized to meet metabolic demands concomitant with a minimal expenditure of energy. This fundamental new insight into bone structure and physiology may provide a new basis of understanding for tissue engineering, bone physiology in health and disease, and evolutionary biology.

Diaphyseal nutrient foramina in the first metatarsals in normal and hallux valgus feet: location and surgical implications.

We examined 47 first metatarsals from amputated lower limbs to determine the situation of the main diaphyseal nutrient foramina (NFs) in normal and hallux valgus feet. All the NFs, excepting one, were in a plantar-fibular location. The NF situation was analyzed by means of the foraminal index and three minimum distances: from NF to proximal extremity, from NF to the shaft dorsal face (NFDS) and from NF to the border of the cartilaginous coating of the metatarsal head. We found a constant location of the NF in the middle of the total metatarsal length and sexual dimorphism in NFDS (lower in females); there were no differences by side, neither by digital or metatarsal types, nor between normal and hallux valgus types. Vascular complications in some osteotomies are discussed. In the surgical design, the NF situation can be estimated from either the total or physiological metatarsal length by means of the corresponding equations as reported here.

Estimation of the poroelastic parameters of cortical bone.

Cortical bone has two systems of interconnected channels. The largest of these is the vascular porosity consisting of Haversian and Volkmann's canals, with a diameter of about 50 microm, which contains a.o. blood vessels and nerves. The smaller is the system consisting of the canaliculi and lacunae: the canaliculi are at the submicron level and house the protrusions of the osteocytes. When bone is differentially loaded, fluids within the solid matrix sustain a pressure gradient that drives a flow. It is generally assumed that the flow of extracellular fluid around osteocytes plays an important role not only in the nutrition of these cells, but also in the bone's mechanosensory system. The interaction between the deformation of the bone matrix and the flow of fluid can be modelled using Biot's theory of poroelasticity. However, due to the inhomogeneity of the bone matrix and the scale of the porosities, it is not possible to experimentally determine all the parameters that are needed for numerical implementation. The purpose of this paper is to derive these parameters using composite modelling and experimental data from literature. A full set of constants is estimated for a linear isotropic description of cortical bone as a two-level porous medium. Bone, however, has a wide variety of mechanical and structural properties; with the theoretical relationships described in this note, poroelastic parameters can be derived for other bone types using their specific experimental data sets.

Microvessel density in alveolar ridge regeneration with autologous and alloplastic bone.

PURPOSE: The purpose of this study was to conduct a comparative immunohistochemical evaluation of microvessel density (MVD) in alveolar sites augmented with autologous bone or Bio-Oss. MATERIALS AND METHODS: Eighteen patients participated in this study. All patients presented maxillary ridge defects. These defects were filled in a random fashion with autologous bone or Bio-Oss. Endosseous implants were inserted after a mean of 3 months in the sites augmented with autologous bone and after a mean of 6 months in the sites augmented with Bio-Oss. As part of the implant site preparation, a trephine was used to harvest bone cores. As control, bone cores retrieved in nonaugmented sites were used. The mean value of MVD in control bone was 25.6 +/- 3.425. In the sites augmented with autologous bone, the MVD was 29.8 +/- 4.4, while in the sites regenerated with Bio-Oss, the MVD was 29.7 +/- 2.4. The statistical analysis showed that the difference in MVD between control bone and autologous bone (P = 0.057) and between control bone and Bio-Oss (P = 0.023) was statistically significant. The difference between the sites regenerated with autologous bone and those regenerated with Bio-Oss was not significant (P = 0.6889). CONCLUSIONS: Our results show that both sites augmented with autologous bone and Bio-Oss presented a higher and statistically significant quantity of microvessels compared with control specimens. No significant differences were found when comparing the MVD of the sites regenerated with autologous bone and those regenerated with Bio-Oss. The retrieval time was, however, a mean of 3 months for the autologous bone sites and a mean of 6 months for the Bio-Oss sites. These data could support the hypothesis of faster healing for the sites augmented with autologous bone.

A first estimation of prestress in so-called circularly fibered osteonic lamellae.

The existence and role of prestress in the various hierarchical structures of long bone are long standing questions. In this study, the prestress and associated strain that exist in a component of human bone microstructure, circularly fibered osteonic lamella, are estimated. Such estimates allow the formulation of hypotheses on prestress formation and lamellar stiffness. Dimensional measurements were obtained for eight fully calcified lamellae. These dimensions, before isolation from the surrounding alternate osteon and after strain relief by isolation and axial sectioning, furnish data upon which a geometric lamellar model is constructed. A material model is based on the most likely hypothesis as to lamellar structure. This geometric-material model allows estimation of the preexisting strain. The largest strains occur in shear circumferential-axial and normal axial strain directions, averaging 0.08 and 0.05, respectively. The geometric-material model expresses prestress in terms of as yet unknown elastic moduli. The average prestress magnitude is the largest in shear circumferential-axial direction, compensating for alternate osteon weakness in this direction. The estimated axial prestress confirms long hypothesized alternate osteon precompression, which impedes fractures of areas of collagen bundles transverse to the osteon axis at low stresses. The results of the model support the formulation of the following biological hypotheses: (a) lamellar prestress occurs at a supra-molecular level, namely through collagen bundles which are themselves likely to be prestressed; (b) collagen bundles oblique to the lamellar axis are responsible for shear prestress; (c) prestress ranges up to 0.11 GPa; and (d) the lamella is less stiff than alternate osteon.

Histomorphological study on pattern of fluid movement in cortical bone in goats.

Streaming potential is considered one of the most important mechanisms to moderate the function of osteoblasts and osteocytes in bone growth, remodeling and fracture repair. The present study was designed to demonstrate the fluid flow pattern in the cortical bone matrix in an animal model using undecalcified histological techniques. Immediately after injection of ferritin into the tibia nutrient artery of four adult goats, the animals were euthanized. Undecalcified transverse and longitudinal blocks of cortical bone obtained from the tibial diaphysis were immersed in Perl's reagent and embedded in methyl methacrylate. Sections were cut and ground to 30-50 microm thickness for histomorphological evaluation at different magnifications and focusing levels. A serial grinding technique was used to validate the observations made at different focusing levels. As expected, ferritin was observed in the interstitial compartment in both transverse and longitudinal sections. In osteons sectioned transversely, the pattern of centrifugal movement of ferritin marker was demonstrated as single or multiple halos around the Haversian canal. The most apparent halo in osteons with multiple halos was the one found closest to the Haversian canal. The total number of identifiable single or multiple halos increased or was altered when counting was made with higher magnification or at different focusing levels, respectively. Irregular and incomplete ferritin halos indicated structural complexity of the osteons. Overall, the pattern of ferritin movement was consistent with bulk interstitial fluid flow influenced by both hydrostatic pressure and transudation. This study demonstrated for the first time multiple concentric halos of the fluid flow marker ferritin around Haversian canals in the cortical interstitial compartment. The results suggest that the undecalcified technique might be a useful method for qualitative and quantitative studies on cortical fluid flow.

The multipoint contact plate in fracture treatment of the atrophied mandible: animal study and clinical application.

Rapid consolidation of osseous fractures requires stable immobilization of the fragments. In the atrophied mandible, the nutrient supply should be ensured by protecting the periosseous soft tissue, i.e., the periosteum. In the conventional placement of osteosynthesis plates, however, the subimplant nutrition is restricted because of the high surface pressure between the osteosynthesis plate and bone. In order to improve the subimplant nutrient supply, we designed a new osteosynthesis plate with a "knobbed" underside enabling multipoint contact. Histomorphologic comparative studies were conducted on 16 Göttingen minipigs with an average weight of 47.5 +/- 8 kg. In each minipig, one side of the mandible was fractured and one side was left intact. One side of each mandible was plated with a six-hole dynamic multipoint contact plate and the other side with a conventional plate. The plates were applied, either epiosseous or epiperiosteal, with bicortical screws under defined torque. The results demonstrate the advantages of multipoint contact plates over the conventional ones and create the clinical basis for a "bio-logical" plate design that allows callus to grow between the knobs and therefore provide adequate nutritional and vascular supply. The plate's knobbed profile also promotes extraosseous venous drainage without impeding intraosseous fluid flow. This plate is the logical choice for rapid fracture consolidation in the high-grade atrophied mandible.

Ultrastructural features in the structure of blood capillaries of the Haversian canal.

Electron microscopy was used to study osteon capillaries of the compact tissue of human growing long bones. The capillaries were found to be of the continuous type. On the lumenal surface of endothelial cells of the arterial capillaries there were a great number of micropinocytotic vesicles as well as a lot of branching cytoplasmic processes forming a characteristic spongioid layer. Vesicles and filopodia were considerably fewer on the basal surface of the cells. The endothelial cells of the venous capillaries had a small number of micropinocytotic vesicles and single cytoplasmic projections on their lumenal and basal surfaces. The capillary wall contained a great amount of pericytes. There were a lot of micropinocytotic vesicles in the cytoplasm.

Morphology of the Haversian canal. An electron microscopic study.

Electron microscopic study of the Haversian canal and its content was performed. Four types of wall lining cells were identified: undifferentiated lining cells, resting mature osteoblasts, active osteoblasts, osteoblast-osteocytes which represented different stages in the differentiation process of the fibrilogenetic cell population. The narrow space between the lining cells and the mineralized bone tissue contained randomly oriented collagen fibrils arranged in layers. Such arrangement of the fibrils determined the lamellar model of the osteons prior to their mineralization. The perivascular space contained both poorly differentiated and mature fibrilogenetic cells with numerous cytoplasmic processes as well as collagen fibrils with different orientation. The cells and the fibrils formed networks which were the sites of the metabolic exchange between the blood vessels and the bone tissue. This process was realised in the medium of the interstitial fluid which filled the perivascular space. All these make the perivascular space an important link of the osteon microcirculation.

A distributed model of exchange processes within the osteon.

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.

Vascular canals in bovine cortical bone studied by corrosion casting.

The architecture of vascular canals in cortical bovine bone was studied by a corrosion casting method. Prior to perfusion of the casting polymer, both cellular and nonmineralized components were removed to ensure proper impregnation into vascular canals--haversian and Volkmann's canals within secondary osteons and the vascular canals of periosteal circumferential lamellae. The resulting castings revealed an anastomotic system of canals within and between these two regions of cortical bone. The nature of these arborizations, their varying degrees of interconnectiveness, and their spatial, three-dimensional ordering are clearly demonstrated in this study.

The blood and lymph bed in Haversian bone.

The structure of the components of the Haversian canals of the osseous tissue of the adult human mandible was studied in celloidin sections stained with haematoxylin and eosin. Fine blood vessels - mostly profiles of postcapillary venules, precapillaries and occasional capillaries - were demonstrated in osteons with Haversian canals 60-80 microns in diameter. Neither lymph capillaries nor vessels were observed, even in wider Haversian canals with larger blood vessels. The intraosseal spaces with rich blood vessel plexuses likewise did not contain any lymphatics with a characteristic form.