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PubMed1998

X-ray diffraction on cyclically loaded osteons.

The results of a study on the fine structural distortion due to the two previously observed types of degradation in cyclically loaded single osteons (i.e., stiffness degradation and pinching effect) are presented. Fully calcified longitudinal and alternate osteons were isolated from 350-microns-thick longitudinal sections of human femoral cortical bone. The samples were prepared from 500-microns-long central cylindrical portions of an osteon, whose two ends were penetrating into rectangular lugs for fixation to an electromechanical device that cyclically loaded the samples. This device was connected to a microwave micrometer and a recorder. The structural distortions induced by cyclic loading were investigated by high- and low-angle X-ray diffraction on conventional and synchrotron radiation sources. Cyclic loading results in a reduction in the degree of orientation of apatite crystallites, especially in longitudinal osteons, in which the most abundant longitudinal lamellae are not protected against buckling by transverse lamellae as they are in alternate osteons. In contrast, the degree of orientation of collagen fibrils does not seem to be affected by cycling loading in the two osteon types, possibly because the disorientation of collagen fibrils is, within limits, a reversible process. Finally, the contrast between the disorientation of inorganic crystallites and the apparently unaltered distribution of collagen fibrils suggests that the degradation of cyclically loaded osteons may be due to a separation of the crystallites from the fibrils.

Adult↗

PubMed1999

Computer-assisted 3D reconstruction of serial sections of cortical bone to determine the 3D structure of osteons.

The objective of this study was to create three-dimensional (3D) images for the histomorphological study of osteons. Medical imaging technology was used to register digitized 2D images of serial decalcified histological sections of bone, to segment the tissues of interest from the surrounding tissues, and to create 3D reconstructions from the segmented structures. Examination of the 3D reconstructions did not support suggestions in the literature that osteons have a spiraling organization. In contrast, the 3D reconstructions indicated that osteons have a complex pattern of organization that is dominated by branching. Examination of the reconstructions also suggested that osteons described in the literature as being dumbbell shaped are actually artifacts of the plane of sectioning. This study demonstrated the applicability of imaging and visualization technology developed for the 3D reconstruction of medical images to the reconstruction of digitized 2D images of serial sections of bone and additionally demonstrated the feasibility of using 3D reconstructions for the histomorphological study of osteons.

Animals↗

PubMed2003

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.

Adult↗

PubMed2004

Correlation study of scanning acoustic microscope reflection coefficients and image brightness intensities of micrographed osteons.

Scanning acoustic microscopy (SAM) of Haversian bone at high frequency clearly shows differences in the brightness (gray) levels of individual osteons, which were observed to correspond to the differences in reflection coefficients measured with the SAM technique: the darker the bony regions on the SAM micrographs, the lower the SAM reflection coefficient values, and vice versa. We studied the correlation between differences in brightness and the related reflection coefficients of osteons on undecalcified transverse sections of goat tibial diaphysis using a 400-MHz burst mode lens on the Olympus UH3 SAM. Results showed that there was a strong linear correlation between brightness intensities and the corresponding reflection coefficients, with a correlation coefficient r = 0.99 ( P << 0.001) using gray level 210 as cutoff. This result suggested that the image brightness intensity of osteonic bone could be measured retrospectively to provide information on the stiffness of the corresponding bone matrix.

Acoustics↗

PubMed2001

Staining intensity of individual osteons correlated with elastic properties and degrees of mineralization.

Surface staining is widely used for histological studies involving undecalcified thick bone sections. Individual osteons, particularly newly formed ones stained with toluidine blue (TB), show various color intensities. We studied the correlations between TB color intensity and the differences in stiffness and degree of mineralization of individual osteons in undecalcified histological sections of goat tibial diaphysis, measured by scanning acoustic microscopy (SAM) and contact microradiography (CMR), respectively. Results showed that all three measurements correlated significantly with each other (r = 0.567 - 0.786; all P < or = 0.01). The TB surface staining intensity of individual osteons correlated better with the reflection coefficient (stiffness index) measured by SAM (r = 0.713) than with the aluminum step-wedge equivalent thickness measured on CMR micrographs (r = 0.567). The aluminum step-wedge equivalent thickness of individual osteons on CMR correlated slightly better with the SAM reflection coefficient (r = 0.786) than with the TB surface staining intensity (r = 0.713). The results of this study suggest that TB surface staining may be used as a simple method for indicating differences in stiffness and degree of mineralization in individual osteons in comparative histological studies.

Animals↗

PubMed2002

Mechanical properties of the femur filled with calcium phosphate cement under torsional loading: a model in rabbits.

We conducted an experimental study using rabbits to determine the effect of injection of calcium phosphate cement (CPC) through a small cortical window on the torsional strength of the long bone. A drill hole created in the femoral shaft and medullary curettage before CPC injection simulates the clinical procedure for managing benign bone tumors. Torsional loading always produced a spiral fracture through the drill hole. The CPC-treated femurs, but not the polymethylmethacrylate-treated femurs, tolerated greater torsional loads and had greater energy absorption to failure at 24 h and 2 weeks postoperatively compared with the contralateral sham-operated femurs. These two parameters, however, were only 54% and 26%, respectively, of those in normal femurs at 24 h, but they were 71% and 51% of those in normal femurs at 12 weeks. Histologic sections demonstrated progressive covering of the drill hole by new bone in the CPC-treated specimens and invagination by newly formed cortical bone into the medullary cavity following sham operation. CPC increases the torsional strength of the long bones immediately after injection, although not sufficiently to preclude the need for external fixation in clinical applications. Better management of the cortical defect is needed to further improve torsional strength.

Animals↗

PubMed2004

Can the diverse elastic properties of trabecular and cortical bone be attributed to only a few tissue-independent phase properties and their interactions? Arguments from a multiscale approach.

As candidates for tissue-independent phases of cortical and trabecular bone we consider (i) hydroxyapatite, (ii) collagen, (iii) ultrastructural water and non-collagenous organic matter, and (iv) marrow (water) filling the Haversian canals and the intertrabecular space. From experiments reported in the literature, we assign stiffness properties to these phases (experimental set I). On the basis of these phase definitions, we develop, within the framework of continuum micromechanics, a two-step homogenization procedure: (i) at a length scale of 100-200 nm, hydroxyapatite (HA) crystals build up a crystal foam ("polycrystal"), and water and non-collagenous organic matter fill the intercrystalline space (homogenization step I); (ii) at the ultrastructural scale of mineralized tissues (5-10 microns), collagen assemblies composed of collagen molecules are embedded into the crystal foam, acting mechanically as cylindrical templates. At an enlarged material scale of 5-10 mm, the second homogenization step also accommodates the micropore space as cylindrical pore inclusions (Haversian and Volkmann canals, inter-trabecular space) that are suitable for both trabecular and cortical bone. The inputs for this micromechanical model are the tissue-specific volume fractions of HA, collagen, and of the micropore space. The outputs are the tissue-specific ultrastructural and microstructural (=macroscopic=apparent) elasticity tensors.A second independent experimental set (composition data and experimental stiffness values) is employed to validate the proposed model. We report a small mean prediction error for the macroscopic stiffness values. The validation suggests that hydroxyapatite, collagen, and water are tissue-independent phases, which define, through their mechanical interaction, the elasticity of all bones, whether cortical or trabecular.

Animals↗

PubMed2003

Osteocyte and bone structure.

The osteocyte is the most abundant cell type of bone. There are approximately 10 times as many osteocytes as osteoblasts in adult human bone, and the number of osteoclasts is only a fraction of the number of osteoblasts. Our current knowledge of the role of osteocytes in bone metabolism is far behind our insight into the properties and functions of the osteoblasts and osteoclasts. However, the striking structural design of bone predicts an important role for osteocytes in determining bone structure. Over the past several years, the role of osteocytes as the professional mechanosensory cells of bone, and the lacunocanalicular porosity as the structure that mediates mechanosensing have become clear. Strain-derived flow of interstitial fluid through this porosity seems to mechanically activate the osteocytes, as well as ensure transport of cell signaling molecules, nutrients, and waste products. This concept explains local bone gain and loss--as well as remodeling in response to fatigue damage--as processes supervised by mechanosensitive osteocytes. Alignment during remodeling seems to occur as a result of the osteocyte's sensing different canalicular flow patterns around the cutting cone and reversal zone during loading, therefore determining the bone's structure.

Bone Matrix↗

PubMed1972