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Abstract: Vascular canals in cortical bone during growth and development typically show an anisotropic pattern with canals falling into three main categories: circumferential, radial, and longitudinal. Two major hypotheses attempt to explain the preferred orientations in bone: that vascular canal orientation is optimized to resist a predominant strain direction from functional loading, or that it reflects growth requirements and velocity. We use a controlled growth experiment in broiler chickens to investigate the effect of growth rate on vascular canal orientation. Using feed restriction we set up a fast growing control group and a slow growing restricted group. We compared the microstructure in the humerus and the femur at 42 days of age using synchrotron micro‐computed tomography (micro‐CT), a three‐dimensional (3D) method that visualizes the full canal network. We measured the 3D orientation of each canal in the whole cross‐section of the bone cortex using a set of custom ImageJ scripts. Using these orientations we compute laminar, radial, and longitudinal indices that measure the proportion of circumferential, radial, and longitudinal canals, by unit of length, in the cortex. Following previous studies we hypothesized that vascular canal orientation is related to growth, with radial canals linked to a faster growth rate and related to functional loading through a high laminar index in flight bones which reflects torsional loading resulting from active flight. The control group had final body weights that were nearly twice the final weights of the restricted group and higher absolute growth rates. We found consistent patterns in the comparison between the humerus and the femur in both groups, with the humerus having higher laminar and longitudinal indices, and a lower radial index than the femur. The control group had higher radial indices and lower laminar and longitudinal indices in both the humerus and the femur than the restricted group. The higher radial indices in our control group point to a link between radial canals and faster growth, and between laminar canals and slower growth, while the higher laminar indices in the humerus point to a link between circumferential canals and torsional loading. Overall, our results indicate that the orientation of the cortical canal network in a bone is the consequence of a complex interaction between the growth rate of that bone and functional loading environment. [ABSTRACT FROM AUTHOR]

Abstract: Cortical bone porosity and specifically the orientation of vascular canals is an area of growing interest in biomedical research and comparative/paleontological anatomy. The potential to explain microstructural adaptation is of great interest. However, the determinants of the development of canal orientation remain unclear. Previous studies of birds have shown higher proportions of circumferential canals (called laminarity) in flight bones than in hindlimb bones, and interpreted this as a sign that circumferential canals are a feature for resistance to the torsional loading created by flight. We defined the laminarity index as the percentage of circumferential canal length out of the total canal length. In this study we examined the vascular canal network in the humerus and femur of a sample of 31 bird and 24 bat species using synchrotron micro‐computed tomography (micro‐CT) to look for a connection between canal orientation and functional loading. The use of micro‐CT provides a full three‐dimensional (3D) map of the vascular canal network and provides measurements of the 3D orientation of each canal in the whole cross‐section of the bone cortex. We measured several cross‐sectional geometric parameters and strength indices including principal and polar area moments of inertia, principal and polar section moduli, circularity, buckling ratio, and a weighted cortical thickness index. We found that bat cortices are relatively thicker and poorly vascularized, whereas those of birds are thinner and more highly vascularized, and that according to our cross‐sectional geometric parameters, bird bones have a greater resistance to torsional stress than the bats; in particular, the humerus in birds is more adapted to resist torsional stresses than the femur. Our results show that birds have a significantly (P = 0.031) higher laminarity index than bats, with birds having a mean laminarity index of 0.183 in the humerus and 0.232 in the femur, and bats having a mean laminarity index of 0.118 in the humerus and 0.119 in the femur. Counter to our expectation, the birds had a significantly higher laminarity index in the femur than in the humerus (P = 0.035). To evaluate whether this discrepancy was a consequence of methodology we conducted a comparison between our 3D method and an analogue to two‐dimensional (2D) histological measurements. This comparison revealed that 2D methods significantly underestimate (P < 0.001) the amount of longitudinal canals by an average of 20% and significantly overestimate (P < 0.001) the laminarity index by an average of 7.7%, systematically mis‐estimating indices of vascular canal orientations. In comparison with our 3D results, our approximated 2D measurement had the same results for comparisons between the birds and bats but found significant differences only in the longitudinal index between the humerus and the femur for both groups. The differences between our 3D and pseudo‐2D results indicate that differences between our findings and the literature may be partially based in methodology. Overall, our results do not support the hypothesis that the bones of flight are more laminar, suggesting a complex relation between functional loading and microstructural adaptation. [ABSTRACT FROM AUTHOR]

The aim of this paper is to remove speckle noise and enhance the laminar bone structure in ultrasound images in order to aid the anesthesiologist during an epidural anesthesia needle insertion. In this regard, a direction and scale sensitive anisotropic diffusion (AD) algorithm called the complex wavelet diffusion algorithm is proposed. The proposed algorithm is tested on synthetic and real ultrasound images of the laminar bone and the results are compared with the speckle-reducing AD method. Results indicate that the proposed method can better highlight the diagonal-shaped laminar bones while removing speckle noise. Furthermore, the proposed despeckling algorithm is very fast providing the anesthesiologist with real-time information while an epidural injection is performed. [ABSTRACT FROM AUTHOR]

Laminar bone tissue is commonly found in Dinosauria (including birds) and Mammalia. The tissue emerged convergently several times, and its frequent occurrence among amniotes has stimulated researchers to study some of its geometric features. One such feature is lamina thickness or lamina density (LD, expressed as number of laminae per mm). We measured LD in a sample of sauropodomorph dinosaur taxa (basal sauropodomorphs, basal sauropods and Neosauropoda) and compared it with LD of a selection of mammals. LD is relatively constrained within the groups; nonetheless mean sauropodomorph LD differs significantly from mean mammal LD. However, increasing sample size with other dinosaur groups and more perissodactyls and artiodactyls may alter this result. Among sauropods, LD does not change drastically with increasing femur length although a slight tendency to decrease may be perceived. We conclude that the laminar vascular architecture is most likely determined by a combination of structural and functional as well as vascular supply and physiological causes. [ABSTRACT FROM AUTHOR]

Abstract: This study uses a nanoindentation technique to examine variations in the local mechanical properties of porcine femoral cortical bone under hydrated conditions. Bone specimens from three age groups (6, 12 and 42 months), representing developing bone, ranging from young to mature animals, were tested on the longitudinal and transverse cross-sectional surfaces. Elastic modulus and hardness of individual lamellae within bone''s microstructure: laminar bone, interstitial bone, and osteons, were measured. Both the elastic modulus and hardness increased with age. However, the magnitudes of these increases were different for each microstructural component. The longitudinal moduli were higher than the transverse moduli. Dehydrated samples were also tested to allow a comparison with hydrated samples and these resulted in higher moduli and hardness than the hydrated samples. Again, the degree of variation was different for each microstructural component. These results indicate that the developmental changes in bone have different rates of mechanical change within each microstructural component. [Copyright &y& Elsevier]

There are many reports on laminar bone in various young animals during their growth periods. One of the concentric laminar bone units around the long-bone marrow periphery consists of three components: bright line, woven bone, and lamellar bone in the long-bone cortex of young calves and pigs. However, the fine structure, especially the uniform bright line or ‘hypercalcified line’ present in the unit-center, has not been elucidated as yet. The laminar bone of young calves was found to be initially formed from the hypercalcified lines; that is, ‘hypercalcified primear’ reported previously by the other authors. Such primear lines containing collagen fibrils scattered deposits of rod-like structures containing fine non-collagenous fibrils and globular structures showing no fibrils and some remnants. Osteocytes occasionally existed in the lines as well as adjacent to the lines, although no cells have been reported in the line. The cell lacunae were larger than those of woven bone and lamellar bone. The hypercalcified primear lines contained higher Ca and P content, and the molar ratio (1.78) was similar to 1.75 in the woven bone and lamellar bone. However, the physical and chemical resistances were significantly lower than that of the surrounding bone. Therefore, the hypercalcified primear lines are strongly suggested to show a lower crystallization. Further, fine structural observations of the primear-line forming cells and histochemical and immuno-histochemical investigations of the primear lines will be necessary. [ABSTRACT FROM AUTHOR]

de Margerie hypothesized that preferred orientations of primary vascular canals in avian primary cortical bone mediate important mechanical adaptations. Specifically, bones that receive habitual compression, tension or bending stresses typically have cortices with a low laminarity index (LI) (i.e. relatively lower cross-sectional areas of circularly (C) orientated primary vascular canals, and relatively higher areas of canals with radial (R), oblique (O) or longitudinal (L) orientations. By contrast, bones subject to habitual torsion have a high LI (i.e. relatively higher C-orientated canal area) [LI, based on percentage vascular canal area, = C/(C + R + O + L)]. Regional variations in predominant collagen fibre orientation (CFO) may be the adaptive characteristic mediated by LI. Using turkey ulnae, we tested the hypothesis that site-specific variations in predominant CFO and LI are strongly correlated. Mid-diaphyseal cross-sections (100 ± 5 µm) from subadult and adult bones were evaluated for CFO and LI using circularly polarized light images of cortical octants. Results showing significant differences between mean LI of subadult (40.0% ± 10.7%) and adult (50.9% ± 10.4%) ( P < 0.01) bones suggest that adult bones experience more prevalent/predominant torsion. Alternatively, this relationship may reflect differences in growth rates. High positive correlations between LI and predominant CFO (subadults: r = 0.735; adults: r = 0.866; P < 0.001) suggest that primary bone can exhibit potentially adaptive material variations that are independent of secondary osteon formation. [ABSTRACT FROM AUTHOR]

Laminar bone or primary plexiform tissue, not Haversian bone, shows an alternative concentric pattern of laminar-bone units or plates around the bone marrow periphery of long bones, although the laminar bone is gradually replaced by osteons during the growth period. One laminar-bone unit is constructed with a hypercalcified line in the center, woven bone on both sides of the line, and lamellar bone with laminated appositional lines. Such a laminar bone showing a homogeneous calcification has been reported in young calves and some young large animals, but it has not been reported in foals although a previous report proposed that the bone structure was distinguishable from plexiform tissue. In this study, we compared young calves with foals by backscattered electron imaging mainly of transverse ground sections of mid-diaphysis. Foals had many hypercalcified lines arranged concentrically around the bone marrow periphery, which were similar to those of young calves. However, rows of cylindrical osteon-like structures with Haversian canal-like canals running along the long-bone axis were arranged between the concentric hypercalcified lines. Each Haversian canal-like structure was enclosed with laminated appositional rings of lamellar bone deposited on the woven bone. In the developing period, the bone units containing the concentric hypercalcified lines were basically equal to the laminar-bone units. The osteon-like structures or ‘pseudo-osteons’ were gradually replaced by ‘true osteons’ during the growth period. The blood vessels in the Haversian canal-like canals of foals ran along the long-bone axis, whereas the blood vessels in the concentrically prolonged bone cavities of young calves ran transversely to obliquely against the long-bone axis. Thus, the long-bone cortex of foals showing an alternative concentric pattern of a row of the osteon-like structures arranged between the hypercalcified lines will be histologically classified into a variety of laminar bone caused by the different arrangement of blood vessels. Such a laminar bone may have a biomechanical structure against physical stress, especially the modified laminar bone of foals with osteon-like structures, when compared with the typical concentric laminar bone of young calves and also Haversian bone possessing variously calcified numerous osteons caused by bone remodeling.Copyright © 2003 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

This study was designed to compare the regenerative potential at dehisced implant sites of the resorbable demineralized laminar bone sheets and non resorbable GTAM membranes. Twenty-six standard screw-type fixtures showing buccal dehiscences in 7 patients were treated using the GBR principles and received either laminar bone sheets (experimental) or GTAM (control) membranes. Twelve experimental and 10 control sites were available for evaluation at second stage surgery carried out 8 months following implant placement. Height and maximum width of the dchiscence defects were measured at the time of implant insertion and at second-stage procedure. Mean percentage of defect fill was 75.11% in the experimental dehiscences vwsus 86.70% in the control defects. A statistically significant difference in the percentage of defect fill could not be evidenced between the two treatment modalities. Complete till was observed in 25% of the experimental versus 70% of the control sites. A significant difference was found in the median Density Index with the GTAM group showing a consistency similar lo bone in a larger number of sites. Histologically, material with the same staining features of bone was evidenced inside the GTAM membranes in 3 cases while newly-formed bone was present in all instances under the control GTAM barriers. In ihe laminar bone-treated sites, the membrane maintained its integrity in almost all cases. Newly formed bone was found underlying the membrane in cases with a Density index of 5 with no evidence of bony tissue adhering to the laminar sheets. [ABSTRACT FROM AUTHOR]