Trabecular Network Research Articles

Microarchitectural Abnormalities Are More Severe in Postmenopausal Women with Vertebral Compared to Nonvertebral Fractures

Abnormal bone microarchitecture predisposes postmenopausal women to fragility fractures. Whether women with vertebral fractures have worse microarchitecture than those with nonvertebral fractures is unknown. Postmenopausal women with a history of low trauma vertebral fracture (n=30) and nonvertebral fracture (n=73) and controls (n=120) had areal bone mineral density of lumbar spine, total hip, femoral neck, 1/3 radius, and ultradistal radius measured by dual-energy x-ray absorptiometry. Trabecular and cortical volumetric bone mineral density and microarchitecture were measured by high-resolution peripheral quantitative computed tomography of the distal radius and tibia. Finite element analysis estimated whole bone stiffness. Mean age of subjects was 68±7 yr. Groups were similar with respect to age, race, and body mass index. Mean T-scores did not differ from controls at any site except the ultradistal radius (vertebral fracture, 0.6 sd lower; nonvertebral fracture, 0.4 sd lower). Compared to controls, women with vertebral fractures had lower total, cortical, and trabecular volumetric density, lower cortical thickness, trabecular number and thickness, greater trabecular separation and network heterogeneity, and lower stiffness at both radius and tibia. Differences between women with nonvertebral fractures and controls were similar but less pronounced. Compared to women with nonvertebral fractures, women with vertebral fractures had lower total and trabecular density, lower cortical thickness and trabecular number, and greater trabecular separation and heterogeneity at the tibia. Whole bone stiffness tended to be lower (P=0.06). Differences between fracture groups at the radius were not statistically significant. Women with vertebral fractures have more severe trabecular and cortical microarchitectural deterioration than those with nonvertebral fractures, particularly at the tibia.

Effect of Subchondral Drilling on the Microarchitecture of Subchondral Bone

Background: Marrow stimulation techniques such as subchondral drilling are clinically important treatment options for symptomatic small cartilage defects. Little is known about whether they induce deleterious changes in the subchondral bone. Hypothesis: Subchondral drilling induces substantial alterations of the microarchitecture of the subchondral bone that persist for a clinically relevant postoperative period in a preclinical large animal model. Study Design: Controlled laboratory study. Methods: Standardized full-thickness chondral defects in the medial femoral condyles of 19 sheep were treated by subchondral drilling. Six months postoperatively, the formation of cysts and intralesional osteophytes was evaluated. A standardized methodology was developed to segment the ovine subchondral unit into reproducible volumes of interest (VOIs). Indices of bone structure were determined by micro–computed tomography (micro-CT). Results: Analysis of the microarchitecture revealed the absence of zonal stratification in the ovine subarticular spongiosa, permitting an unimpeded and simultaneous analysis of the entire subchondral trabecular network. Subchondral drilling led to the formation of subchondral bone cysts (63%) and intralesional osteophytes (26%). Compared with the adjacent unaffected subchondral bone, drilling induced significant alterations in nearly all parameters for the microarchitecture of the subchondral bone plate and the subarticular spongiosa, most importantly in bone volume, bone surface/volume ratio, trabecular thickness, separation, pattern factor, and bone mineral density (BMD) (all P ≤ .01). Conclusion: The data show that the ovine subchondral bone can be reliably evaluated using micro-CT with standardized VOIs. We report that subchondral drilling deteriorates the microarchitecture both of the subchondral bone plate and subarticular spongiosa and decreases BMD. These results suggest that the entire osteochondral unit is altered after drilling for an extended postoperative period. Clinical Relevance: The subchondral bone remains fragile after subchondral drilling for longer durations than previously expected. Further evaluations of structural subchondral bone parameters of patients undergoing marrow stimulation are warranted.

Tortuosidade e conectividade da rede trabecular do rádio distal a partir de imagens microtomográficas

A osteoporose e uma doenca que causa perda de massa ossea e deterioracao da estrutura trabecular. A rede formada pelo osso trabecular e muito importante para estabelecer a competencia mecânica do esqueleto. Estudos mostram que a microarquitetura trabecular pode elevar a predicao do risco de fratura para cerca de 90%, por isso a sua investigacao e de grande interesse da comunidade cientifica. Varios parâmetros estao relacionados a competencia mecânica da estrutura ossea, entretanto, a tortuosidade trabecular ainda nao foi seriamente levada em consideracao e sua contribuicao e desconhecida. Neste trabalho, o enfoque esta direcionado a estimativa da tortuosidade trabecular e sua correlacao com a conectividade, atraves da caracteristica de Euler-Poincare, para amostras do osso radio distal in vitro, a partir de imagens de microtomografia computadorizada. Um metodo para estimar a tortuosidade do volume trabecular e apresentado e a tortuosidade e computada para os dois sentidos das tres direcoes do volume. Os resultados apresentam valores distintos da tortuosidade dependendo da qualidade da rede trabecular e uma correlacao positiva (r = 0,64) com a caracteristica de Euler-Poincare; alem disso, observa-se que a tortuosidade busca alinhar-se nas direcoes de maiores tensoes e compressoes imprimidas a rede trabecular. Tais resultados evidenciam a importância da tortuosidade como parâmetro estrutural da rede trabecular.

Association of larger holes in the trabecular bone at the distal radius in postmenopausal women with type 2 diabetes mellitus compared to controls.

Adults with type 2 diabetes mellitus (DM) have an elevated fracture risk despite normal areal bone mineral density (aBMD). The study objective was to compare trabecular bone microarchitecture of postmenopausal women with type 2 DM and women without type 2 DM. An extremity 1T magnetic resonance imaging system was used to acquire axial images (195 × 195 × 1,000 μm(3) voxel size) of the distal radius of women recruited from outpatient clinics or by community advertisement. Image segmentation yielded geometric, topologic, and stereologic outcomes, i.e., number and size of trabecular bone network holes (marrow spaces), endosteal area, trabecular bone volume fraction, nodal and branch density, and apparent trabecular thickness, separation, and number. Lumbar spine (LS) and proximal femur BMD were measured with dual x-ray absorptiometry. Microarchitectural differences were assessed using linear regression and adjusted for percent body fat, ethnicity, timed up-and-go test, Charlson Index, and calcium and vitamin D intake; aBMD differences were adjusted for body mass index (BMI). Women with type 2 DM (n = 30, mean ± SD age 71.0 ± 4.8 years) had larger holes (+13.3%; P = 0.001) within the trabecular bone network than women without type 2 DM (n = 30, mean ± SD age 70.7 ± 4.9 years). LS aBMD was greater in women with type 2 DM; however, after adjustment for BMI, LS aBMD did not differ between groups. In women with type 2 DM, the average hole size within the trabecular bone network at the distal radius is greater compared to controls. This may explain the elevated fracture risk in this population.

Individual trabecula segmentation (ITS)-based morphological analyses and microfinite element analysis of HR-pQCT images discriminate postmenopausal fragility fractures independent of DXA measurements.

Osteoporosis is typically diagnosed by dual-energy X-ray absorptiometry (DXA) measurements of areal bone mineral density (aBMD). Emerging technologies, such as high-resolution peripheral quantitative computed tomography (HR-pQCT), may increase the diagnostic accuracy of DXA and enhance our mechanistic understanding of decreased bone strength in osteoporosis. Women with (n = 68) and without (n = 101) a history of postmenopausal fragility fracture had aBMD measured by DXA, trabecular plate and rod microarchitecture measured by HR-pQCT image-based individual trabecula segmentation (ITS) analysis, and whole bone and trabecular bone stiffness by microfinite element analysis (µFEA) of HR-pQCT images at the radius and tibia. DXA T-scores were similar in women with and without fractures at the spine, hip, and 1/3 radius, but lower in fracture subjects at the ultradistal radius. Trabecular microarchitecture of fracture subjects was characterized by preferential reductions in trabecular plate bone volume, number, and connectivity over rod trabecular parameters, loss of axially aligned trabeculae, and a more rod-like trabecular network. In addition, decreased thickness and size of trabecular plates were observed at the tibia. The differences between groups were greater at the radius than the tibia for plate number, rod bone volume fraction and number, and plate-rod and rod-rod junction densities. Most differences between groups remained after adjustment for T-score by DXA. At a fixed bone volume fraction, trabecular plate volume, number, and connectivity were directly associated with bone stiffness. In contrast, rod volume, number, and connectivity were inversely associated with bone stiffness. In summary, HR-pQCT-based ITS and µFEA measurements discriminate fracture status in postmenopausal women independent of DXA measurements. Moreover, these results suggest that preferential loss of plate-like trabeculae contribute to lower trabecular bone and whole bone stiffness in women with fractures. We conclude that HR-pQCT-based ITS and µFEA measurements increase our understanding of the microstructural pathogenesis of fragility fracture in postmenopausal women.

On the effect of marrow in the mechanical behavior and crush response of trabecular bone

The present paper focuses on the mechanical behavior analysis of bones at mesoscopic scale, paying a special attention to the trabecular bone and the bone marrow filling the porosities. Uni-axial quasi-static compression tests under unconfined conditions have been performed to identify the mechanical behavior of 46 trabecular bone samples. The bone marrow for 22 samples has been preserved to analyze the fluid flow effects on the crushing response. Although deformation patterns do not differ significantly, the average crush behavior of the trabecular bone shows an unexpected decrease of the mechanical properties when the marrow is kept in the sample (26% for the elastic modulus ( E a ), 38% for the maximum compressive stress ( σ m a x ) and 33% for the average stress ( σ m e a n )). An explanation is given by analyzing the contribution of the bone marrow viscosity which smooths the mechanical response. A numerical analysis on an idealized trabecula confirms that the marrow induces transverse pressure and extra local stress on trabeculae during its flow, causing the premature collapse of the trabecular network.

Long range node‐strut analysis of trabecular bone microarchitecture

We present a new morphometric measure of trabecular bone microarchitecture, called mean node strength (NdStr), which is part of a newly developed approach called long range node-strut analysis. Our general aim is to describe and quantify the apparent "latticelike" microarchitecture of the trabecular bone network. Similar in some ways to the topological node-strut analysis introduced by Garrahan et al. [J. Microsc. 142, 341-349 (1986)], our method is distinguished by an emphasis on long-range trabecular connectivity. Thus, while the topological classification of a pixel (after skeletonization) as a node, strut, or terminus, can be determined from the 3 × 3 neighborhood of that pixel, our method, which does not involve skeletonization, takes into account a much larger neighborhood. In addition, rather than giving a discrete classification of each pixel as a node, strut, or terminus, our method produces a continuous variable, node strength. The node strength is averaged over a region of interest to produce the mean node strength of the region. We have applied our long range node-strut analysis to a set of 26 high-resolution peripheral quantitative computed tomography (pQCT) axial images of human proximal tibiae acquired 17 mm below the tibial plateau. We found that NdStr has a strong positive correlation with trabecular volumetric bone mineral density (BMD). After an exponential transformation, we obtain a Pearson's correlation coefficient of r = 0.97. Qualitative comparison of images with similar BMD but with very different NdStr values suggests that the latter measure has successfully quantified the prevalence of the "latticelike" microarchitecture apparent in the image. Moreover, we found a strong correlation (r = 0.62) between NdStr and the conventional node-terminus ratio (Nd∕Tm) of Garrahan et al. The Nd∕Tm ratios were computed using traditional histomorphometry performed on bone biopsies obtained at the same location as the pQCT scans. The newly introduced morphometric measure allows a quantitative assessment of the long-range connectivity of trabecular bone. One advantage of this method is that it is based on pQCT images that can be obtained noninvasively from patients, i.e., without having to obtain a bone biopsy from the patient.

Assessing Methods for Characterising Local and Global Structural and Biomechanical Properties of the Trabecular Bone Network

We apply noval techniques, the Scaling Index Method (SIM), which reveals local topology of the structure, and the Minkowski Functionals (MF), which provide four global topological characteristics, to assess strength of the trabecular network of the human bone. We compare capabilities of these methods with the standard analysis, biomechanical Finite Element Method (FEM) and morphological parameters, in prediction of bone strength and fracture risk. Our study is based on a sample of 151 specimens taken from the trabecular part of human thoracic and lumbar vertebrae in vitro, visualised using µCT imaging (isotropic resolution 26µm) and tested by uniaxial compression. The sample of donors is heterogeneous, consisting of 58 male and 54 female cadavers with a mean age of 80 ±10 years. To estimate the predictive power of the methods, we correlate texture measures derived from µCT images with the maximum compressive strength (MCS) as obtained in biomechanical tests. A linear regression analysis reveals that the failure load estimated by FEM shows the highest correlation with MCS (Pearson's correlation coefficient r=0.76). None of the methods in current study is superior to the FEM: morphometric parameters give r<0.5, global topological characteristics show r=0.73 for the first Minkowski Functional MF₁, which coincides with bone volume fraction BV/TV and r=0.61 for the second Minkowski functional MF₂, which coincides with bone surface BS. Although scaling indices provided by SIM correlate only moderately with MCS (r=0.55), texture measures based on the nonlinear combination of local (SIM) and global (MF) topological characteristics demonstrate high correlation with experimental MCS (r=0.74) and with failure load estimated by FEM (r=0.95). Additional advantage of the proposed texture measures is possibility to reveal the role of the topologically different trabecular structure elements for the bone strength.

Poor Trabecular Microarchitecture in Male Current Smokers: The Cross-Sectional STRAMBO Study

Current smoking (but not past smoking) is associated with higher risk of fracture independent of areal bone mineral density (aBMD); however, the pathophysiologic mechanism underlying this association is not clear. In 810 men aged 60-87, aBMD was measured by dual-energy X-ray absorptiometry. Bone microarchitecture at the distal radius and distal tibia was assessed by high-resolution peripheral quantitative computed tomography using the Xtreme CT Scanco device. Current smokers (n=47) had lower trabecular volumetric density (Dtrab), lower trabecular number (TbN), more heterogenous trabecular network (higher trabecular spacing standard deviation [TbSpSD]), as well as higher urinary deoxypyridinoline and higher C-reactive protein levels in comparison with 261 men who never smoked (adjusted for age, weight, height, time spent outdoors, physical activity, and intake of alcohol, caffeine, and calcium). Abnormal values (lower Dtrab and TbN, higher TbSpSD, deoxypyridinoline, and C-reactive protein) were found mainly in 21 current smokers who smoked eight or more cigarettes per day. Cortical parameters and aBMD did not differ from the never-smokers. In 502 former smokers, aBMD and all bone microarchitectural parameters did not differ from the never-smokers. At the tibia (not radius), Dtrab decreased, whereas TbSpSD slightly increased across quartiles of smoking intensity (number of pack-years). In conclusion, older men who are moderate current smokers have poor trabecular (but not cortical) microarchitecture, which is not reflected by a decrease in aBMD.

Numerical investigation of ultrasound refraction caused by oblique orientation of trabecular network in cancellous bone

Ultrasound propagation through cancellous bone can be greatly affected by the trabecular structure. In the present study, the ultrasound propagation for the oblique orientation of the trabecular network was numerically investigated using 3-D finite-difference time-domain (FDTD) simulations. The models of cancellous bone were reconstructed from X-ray microcomputed tomographic (μCT) images of a bovine bone. Cancellous bone models with various orientations of the trabecular network were realized by cutting the μCT images rotated from 0 to 90°. Ultrasound waveforms propagating through these cancellous bone models were simulated while changing the receiving position. The refraction of the ultrasound wave for the oblique angle of the main orientation was investigated on the basis of the variation in the arrival time and peak amplitude. As the propagation direction approached the direction parallel to the main orientation, the arrival time of the first peak became less and the peak amplitude became smaller. This means that the wave of the first peak, which corresponded to a fast wave, propagated in the direction perpendicular to the main orientation. In addition, a strong correlation between the first-peak amplitude and the arrival time was observed in the porosity range of 0.68 to 0.85, in which the slope of the amplitude with respect to time increased linearly with porosity.

MICRO-FINITE ELEMENT ANALYSIS OF TRABECULAR BONE YIELD BEHAVIOR — EFFECTS OF TISSUE NONLINEAR MATERIAL PROPERTIES

Bone tissue material nonlinearity and large deformations within the trabecular network are important for the characterization of failure behavior of trabecular bone at both the apparent and tissue levels. Micro-finite element analysis (μFEA) is a useful tool for determining the mechanical properties of trabecular bone due to certain experimental difficulties. The aim of this study was to determine the effects of bone tissue nonlinear material properties on the apparent- and tissue-level mechanical parameters of trabecular bone using μFEA. A bilinear tissue constitutive model was proposed to describe the bone tissue material nonlinearity. Two trabecular specimens with different micro-architectures were taken as examples. The effects of four parameters, i.e., tissue Young's modulus, tissue yield strain in tension, tissue yield strain in compression, and post-yield modulus on the apparent yield stress/strain, tissue von Mises stress distribution, the amount of tissue elements yielded in compression and tension under compressive and tensile loading conditions were obtained using nine cases for different values of those parameters by totally 36 nonlinear μFEA. These data may provide a reference for more sophisticated evaluations of bone strength and the related fracture risk.

Individual trabecula segmentation (ITS)–based morphological analysis of microscale images of human tibial trabecular bone at limited spatial resolution

Individual trabecula segmentation (ITS), a rigorous model-independent 3D morphological analysis, has been developed to assess trabecular plate and rod microstructure separately based on micro-computed tomographic (µCT) images. We examined the influence of the limited spatial resolution, noise, and artifact of high-resolution peripheral quantitative CT (HR-pQCT) on ITS measurements of human tibial trabecular bone. In comparison with measurements from "gold standard" µCT images (25 µm), decreased spatial resolution (40, 60, and 80 µm) of µCT had minimal influence on the correlations of the scale of trabecular plates (ie, plate bone volume fraction, thickness, and surface area) and the orientation (ie, axial bone volume fraction) and structural type (ie, plate tissue fraction) of the trabecular network. ITS measurements of HR-pQCT images correlated significantly with those of µCT images at a similar voxel size (80 µm, r = 0.71-0.94); correlations were stronger for plate-related parameters, suggesting that measurements of trabecular rods are more subject to noise and artifact associated with HR-pQCT imaging technology. In comparison with measurements of "gold standard" µCT images, the percent absolute errors of HR-pQCT measurements such as axial and plate bone volume fraction, plate number and tissue fraction, and plate and rod thickness (3.5% to 10.3%) were comparable with those of bone volume fraction (9.3%). For both HR-pQCT and µCT images, measurements of the scale and junction densities of trabecular plates and orientation and structural type were strong and positive indicators of the elastic modulus of trabecular bone (r = 0.59-0.95). We conclude that ITS measurements of HR-pQCT images are highly reflective of trabecular bone microarchitecture from a biomechanical perspective.

A new device and method for measuring the elastic modulus of single trabeculae

The smallest functional unit of cancellous bone is the single trabecula. To investigate its influence at the macroscopic level, a mechanical characterization is required. The aim of this work is to present a new procedure for measuring the elastic behavior of a single trabecula, assumed as an isotropic material, by means of a bending protocol. Our experimental setup permits the measurement of the bending force and deflection of a single trabecula within the natural network. The exact geometry of the trabecula is attained by using a laser scanning microscopy of the labeled sample and subsequently using it as the input for FE simulation. The results between the FE analysis and experimental data are compared in order to determine an isotropic elastic modulus of the trabecula. The system uncertainty has been estimated using the propagation of uncertainty method based on the analytical bending function for a fixed beam. Variables are force, deflection, radius and length and their relative uncertainties. It results in a total uncertainty of 13%, dominated by the influence of radius uncertainty, which is related to the exact determination of the real geometry of the trabecula. The system has been subsequently validated using samples with known geometry and elastic modulus. Finally, the proposed new method consists of sample preparation, a newly designed sample positioning system, an experimental bending test on a single trabecula within the trabecular network, labeling of the bone with a fluorescent marker, 3D imaging of the trabecula and FE analysis of the bending test.

Trabecular bone scales allometrically in mammals and birds

Many bones are supported internally by a latticework of trabeculae. Scaling of whole bone length and diameter has been extensively investigated, but scaling of the trabecular network is not well characterized. We analysed trabecular geometry in the femora of 90 terrestrial mammalian and avian species with body masses ranging from 3 g to 3400 kg. We found that bone volume fraction does not scale substantially with animal size, while trabeculae in larger animals' femora are thicker, further apart and fewer per unit volume than in smaller animals. Finite element modelling indicates that trabecular scaling does not alter the bulk stiffness of trabecular bone, but does alter strain within trabeculae under equal applied loads. Allometry of bone's trabecular tissue may contribute to the skeleton's ability to withstand load, without incurring the physiological or mechanical costs of increasing bone mass.

Better skeletal microstructure confers greater mechanical advantages in Chinese-American women versus white women

Despite lower areal bone mineral density (aBMD), Chinese-American women have fewer fractures than white women. We hypothesized that better skeletal microstructure in Chinese-American women in part could account for this paradox. Individual trabecula segmentation (ITS), a novel image-analysis technique, and micro-finite-element analysis (µFEA) were applied to high-resolution peripheral quantitative computed tomography (HR-pQCT) images to determine bone microarchitecture and strength in premenopausal Chinese-American and white women. Chinese-American women had 95% and 80% higher plate bone volume fraction at the distal radius and tibia, respectively, as well as 20% and 18% higher plate number density compared with white women (p < .001). With similar rodlike characteristics, the plate-to-rod ratio was twice as high in the Chinese-American than in white trabecular bone (p < .001). Plate-rod junction density, a parameter indicating trabecular network connections, was 37% and 29% greater at the distal radius and tibia, respectively, in Chinese-American women (p < .002). Moreover, the orientation of the trabecular bone network was more axially aligned in Chinese-American women because axial bone volume fraction was 51% and 32% higher at the distal radius and tibia, respectively, than in white women (p < .001). These striking differences in trabecular bone microstructure translated into 55% to 68% (distal radius, p < .001) and 29% to 43% (distal tibia, p < .01) greater trabecular bone strength, as assessed by Young's moduli, in the Chinese-American versus the white group. The observation that Chinese-American women have a major microstructural advantage over white women may help to explain why their risk of fracture is lower despite their lower BMD.

Assessment of Trabecular Bone Architecture and Intrinsic Properties of Cortical bone Tissue in a Mouse Model of Chronic Kidney Disease

Chronic kidney disease (CKD) is often associated with increased fracture risk; however, the CKD-effects on bone microstructure and intrinsic material properties have not been fully elucidated. This study was undertaken to evaluate the time course of trabecular architectural changes and material properties of cortical bone in the tibia of a mouse model of high-turnover CKD. Male mice subjected to 5/6 nephrectomy (Nx, n=8) and those sham-operated (Sham, n=8) were used. Starting at 8 weeks of age (2 weeks after surgery), Nx mice were fed with high phosphate diet. The tibial metaphysis was scanned by in vivo micro-computed tomography (μCT) for trabecular architecture analysis from 10 to 26 weeks of age with 4-week interval. Then, the animal was blood-sampled before sacrifice, and the scanned tibia was harvested. The midlayer of a cortical cross-section was evaluated for mineral-to-matrix ratio, mineral maturity, and collagen maturity by Fourier transform infrared microspectroscopy and for stiffness and hardness by the nanoindentation test. Serum chemicals showed the successful induction of high-turnover CKD in Nx. The age-related regression of trabecular network was observed in both groups but to the higher degree in Nx. In vivo μCT revealed significant interactions between age and CKD in trabecular number, thickness, and separation. On the other hand, the chemical and mechanical properties of cortical bone did not differ significantly between Nx and Sham. Thus, the compromised trabecular architecture will be contributory to bone fragility in high-turnover CKD.

Numerical Study on the Morphology and Mechanical Role of Healthy and Osteoporotic Vertebral Trabecular Bone

This study presents a numerical methodology to clarify the morphology of complex trabecular network architecture in human lumbar vertebra by means of the new post-processing technique for calculated microscopic stress by the homogenization method. Micro-CT image-based modeling technique is used and careful but intuitive and easy-to-use method for microstructure model, in other words region of interest (ROI), is also presented. The macroscopic homogenized properties that include not only the Young’s moduli but also shear moduli could explain the difference of morphology between healthy and osteoporotic bones. This paper focuses on the change of degree of anisotropy. Then, the microscopic stress under three basis load cases was analyzed. In this analysis, the homogenization method has a merit in the computational cost. The trabeculae are classified into eight groups from the viewpoint of load bearing function against three loading conditions in the proposed post-processing of numerical results. It contributes to the understanding of the mechanical role of trabecular bone in vertebra. The primary trabecular bone that has been supposed to support the self-weight and secondary bone that connects the primary bone are successfully visualized. The discussion on the mechanical role of plate-like trabecular bone in the load path network system is also highlighted.

Wound healing and blastema formation in regenerating digit tips of adult mice

Amputation of the distal region of the terminal phalanx of mice causes an initial wound healing response followed by blastema formation and the regeneration of the digit tip. Thus far, most regeneration studies have focused in embryonic or neonatal models and few studies have examined adult digit regeneration. Here we report on studies that include morphological, immunohistological, and volumetric analyses of adult digit regeneration stages. The regenerated digit is grossly similar to the original, but is not a perfect replacement. Re-differentiation of the digit tip occurs by intramembranous ossification forming a trabecular bone network that replaces the amputated cortical bone. The digit blastema is comprised of proliferating cells that express vimentin, a general mesenchymal marker, and by comparison to mature tissues, contains fewer endothelial cells indicative of reduced vascularity. The majority of blastemal cells expressing the stem cell marker SCA-1, also co-express the endothelial marker CD31, suggesting the presence of endothelial progenitor cells. Epidermal closure during wound healing is very slow and is characterized by a failure of the wound epidermis to close across amputated bone. Instead, the wound healing phase is associated with an osteoclast response that degrades the stump bone allowing the wound epidermis to undercut the distal bone resulting in a novel re-amputation response. Thus, the regeneration process initiates from a level that is proximal to the original plane of amputation.

Abnormal microarchitecture and reduced stiffness at the radius and tibia in postmenopausal women with fractures

Measurement of areal bone mineral density (aBMD) by dual-energy x-ray absorptiometry (DXA) has been shown to predict fracture risk. High-resolution peripheral quantitative computed tomography (HR-pQCT) yields additional information about volumetric BMD (vBMD), microarchitecture, and strength that may increase understanding of fracture susceptibility. Women with (n = 68) and without (n = 101) a history of postmenopausal fragility fracture had aBMD measured by DXA and trabecular and cortical vBMD and trabecular microarchitecture of the radius and tibia measured by HR-pQCT. Finite-element analysis (FEA) of HR-pQCT scans was performed to estimate bone stiffness. DXA T-scores were similar in women with and without fracture at the spine, hip, and one-third radius but lower in patients with fracture at the ultradistal radius (p < .01). At the radius fracture, patients had lower total density, cortical thickness, trabecular density, number, thickness, higher trabecular separation and network heterogeneity (p < .0001 to .04). At the tibia, total, cortical, and trabecular density and cortical and trabecular thickness were lower in fracture patients (p < .0001 to .03). The differences between groups were greater at the radius than at the tibia for inner trabecular density, number, trabecular separation, and network heterogeneity (p < .01 to .05). Stiffness was reduced in fracture patients, more markedly at the radius (41% to 44%) than at the tibia (15% to 20%). Women with fractures had reduced vBMD, microarchitectural deterioration, and decreased strength. These differences were more prominent at the radius than at the tibia. HR-pQCT and FEA measurements of peripheral sites are associated with fracture prevalence and may increase understanding of the role of microarchitectural deterioration in fracture susceptibility. © 2010 American Society for Bone and Mineral Research.

In vitro and in vivo MR evaluation of internal gradient to assess trabecular bone density

Here we propose a new magnetic resonance (MR) strategy based on the evaluation of internal gradient (Gi) to assess the trabecular bone (TB) density in spongy bone. Spongy bone is a porous system characterized by a solid trabecular network immersed in bone marrow and characterized by a different relative percentage of water and fats. Using a 9.4 T MR micro-imaging system, we first evaluated the relative water and fat Gi as extracted from the Spin-Echo decay function in vitro of femoral head samples from calves. Indeed, the differential effects of fat and water diffusion result in different types of Gi behavior. Using a clinical MR 3T scanner, we then investigated in vivo the calcanei of individuals characterized by different known TB densities. We demonstrate, on these samples, that water is more prevalent in the boundary zone, while fats are rearranged primarily in the central zone of each pore. In vitro experiments showed that water Gi magnitude from the samples was directly proportional to their TB density. Similar behavior was also observed in the clinical measures. Conversely, fat Gi did not provide any information on spongy-bone density. Our results suggest that water Gi may be a reliable marker to assess the status of spongy bone.