Biomechanical Properties Of Trabecular Bone Research Articles

Comparison of HR-pQCT- and microCT-based finite element models for the estimation of the mechanical properties of the calcaneus trabecular bone

The calcaneus bone is formed of extensive trabecular bone and is therefore well suited to be used as an example of loaded bone to establish the ability of combining microfinite element (microFE) technique with high-resolution peripheral quantitative computed tomography (HR-pQCT) in determining its mechanical properties. HR-pQCT is increasingly used as a tool for in vivo bone clinical research, but its use has been limited to the distal radius and tibia. The goal of this study was to determine the applicability of HR-pQCT-derived microFE models of the calcaneus trabecular bone with 82 μm voxel size with reference to higher-resolution microCT-based models taken as gold standard. By comparing the outputs of microFE models generated from both HR-pQCT and microCT images of the trabecular bone of five calcaneus cadaveric specimens, it was found that the HR-pQCT-based models predicted mechanical properties for fracture load, total reaction force and von Mises stress are considerably different from microCT-based counterparts by 33, 64 and 70%, respectively. Also, the morphological analysis showed a comprehensive geometrical difference between HR-pQCT-based microFE models and their microCT-based equivalents. The results of the HR-pQCT-based models were found to have strong dependency on the threshold value chosen to binarise the images prior to finite element modelling. In addition, it was found that the voxel size has a strong impact on accuracy of imaged-based microFE models compared to other factors such as the presence of soft tissue and image scanning integration time. Therefore, although HR-pQCT has shown to be useful to predict overall structural and biomechanical changes, it is limited in providing local accurate biomechanical properties of trabecular bone and therefore should be used with caution when assessing bone remodelling through local changes of trabecular bone apposition and resorption in disease treatment monitoring.

Direct estimation of human trabecular bone stiffness using cone beam computed tomography

The aim of this study was to evaluate the possibility of estimating the biomechanical properties of trabecular bone through finite element simulations by using dental cone beam computed tomography data. Fourteen human radius specimens were scanned in 3 cone beam computed tomography devices: 3-D Accuitomo 80 (J. Morita MFG., Kyoto, Japan), NewTom 5 G (QR Verona, Verona, Italy), and Verity (Planmed, Helsinki, Finland). The imaging data were segmented by using 2 different methods. Stiffness (Young modulus), shear moduli, and the size and shape of the stiffness tensor were studied. Corresponding evaluations by using micro-CT were regarded as the reference standard. The 3-D Accuitomo 80 (J. Morita MFG., Kyoto, Japan) showed good performance in estimating stiffness and shear moduli but was sensitive to the choice of segmentation method. NewTom 5 G (QR Verona, Verona, Italy) and Verity (Planmed, Helsinki, Finland) yielded good correlations, but they were not as strong as Accuitomo 80 (J. Morita MFG., Kyoto, Japan). The cone beam computed tomography devices overestimated both stiffness and shear compared with the micro-CT estimations. Finite element-based calculations of biomechanics from cone beam computed tomography data are feasible, with strong correlations for the Accuitomo 80 scanner (J. Morita MFG., Kyoto, Japan) combined with an appropriate segmentation method. Such measurements might be useful for predicting implant survival by in vivo estimations of bone properties.

Increased calcium uptake and improved trabecular bone properties in intestinal alkaline phosphatase knockout mice.

Previous studies have demonstrated a negative correlation between intestinal alkaline phosphatase (IAP) activity and calcium (Ca) absorption in the gut, as IAP acts as a protective mechanism inhibiting high Ca entry into enterocytes, preventing Ca overload. Here we evaluated Ca absorption and bone properties in knockout mice (KO) completely devoid of duodenal IAP (Akp3 -/- mice). Female C57BL/6 control mice (WT, n=7) and KO mice (n=10) were used to determine Ca absorption in vivo and by in situ isolated duodenal loops followed by histomorphometric analysis of duodenal villi and crypts. Bone mineral density, morphometry, histomorphometry and trabecular connectivity and biomechanical properties were measured on bones. We observed mild atrophy of the villi with lower absorption surface and a significantly higher Ca uptake in KO mice. While no changes were seen in cortical bone, we found better trabecular connectivity and biomechanical properties in the femurs of KO mice compared to WT mice. Our data indicate that IAP KO mice display higher intestinal Ca uptake, which over time appears to correlate with a positive effect on the biomechanical properties of trabecular bone.

Influence of the shape of the micro-finite element model on the mechanical properties calculated from micro-finite element analysis.

Assessing the biomechanical properties of trabecular bone is of major biological and clinical significance for the research of bone diseases, fractures and their treatments. Micro-finite element (µFE) models are becoming increasingly popular for investigating the biomechanical properties of trabecular bone. The shapes of µFE models typically include cube and cylinder. Whether there are differences between cubic and cylindrical µFE models has not yet been studied. In the present study, cubic and cylindrical µFE models of human vertebral trabecular bone were constructed. A 1% strain was prescribed to the model along the superior-inferior direction. E values were calculated from these models, and paired t-tests were performed to determine whether these were any differences between E values obtained from cubic and cylindrical models. The results demonstrated that there were no statistically significant differences in the E values between cubic and cylindrical models, and there were no significant differences in Von Mises stress distributions between the two models. These findings indicated that, to construct µFE models of vertebral trabecular bone, cubic or cylindrical models were both feasible. Choosing between the cubic or cylindrical µFE model is dependent upon the specific study design.

Relationship between sample volumes and modulus of human vertebral trabecular bone in micro-finite element analysis

Micro-finite element (μFE) models have been widely used to assess the biomechanical properties of trabecular bone. How to choose a proper sample volume of trabecular bone, which could predict the real bone biomechanical properties and reduce the calculation time, was an interesting problem. Therefore, the purpose of this study was to investigate the relationship between different sample volumes and apparent elastic modulus (E) calculated from μFE model. 5 Human lumbar vertebral bodies (L1–L5) were scanned by micro-CT. Cubic concentric samples of different lengths were constructed as the experimental groups and the largest possible volumes of interest (VOI) were constructed as the control group. A direct voxel-to-element approach was used to generate μFE models and steel layers were added to the superior and inferior surface to mimic axial compression tests. A 1% axial strain was prescribed to the top surface of the model to obtain the E values. ANOVA tests were performed to compare the E values from the different VOIs against that of the control group. Nonlinear function curve fitting was performed to study the relationship between volumes and E values. The larger cubic VOI included more nodes and elements, and more CPU times were needed for calculations. E values showed a descending tendency as the length of cubic VOI decreased. When the volume of VOI was smaller than (7.34mm3), E values were significantly different from the control group. The fit function showed that E values approached an asymptotic values with increasing length of VOI. Our study demonstrated that apparent elastic modulus calculated from μFE models were affected by the sample volumes. There was a descending tendency of E values as the length of cubic VOI decreased. Sample volume which was not smaller than (7.34mm3) was efficient enough and timesaving for the calculation of E.

Inhibition of CaMKK2 reverses age-associated decline in bone mass

Decline in bone formation is a major contributing factor to the loss of bone mass associated with aging. We previously showed that the genetic ablation of the tissue-restricted and multifunctional Ca2+/calmodulin (CaM)-dependent protein kinase kinase 2 (CaMKK2) stimulates trabecular bone mass accrual, mainly by promoting anabolic pathways and inhibiting catabolic pathways of bone remodeling. In this study, we investigated whether inhibition of this kinase using its selective cell-permeable inhibitor STO-609 will stimulate bone formation in 32week old male WT mice and reverse age-associated of decline in bone volume and strength. Tri-weekly intraperitoneal injections of saline or STO-609 (10μM) were performed for six weeks followed by metabolic labeling with calcein and alizarin red. New bone formation was assessed by dynamic histomorphometry whereas micro-computed tomography was employed to measure trabecular bone volume, microarchitecture and femoral mid-shaft geometry. Cortical and trabecular bone biomechanical properties were assessed using three-point bending and punch compression methods respectively. Our results reveal that as they progress from 12 to 32weeks of age, WT mice sustain a significant decline in trabecular bone volume, microarchitecture and strength as well as cortical bone strength. However, treatment of the 32week old WT mice with STO-609 stimulated apposition of new bone and completely reversed the age-associated decrease in bone volume, quality, as well as trabecular and cortical bone strength. We also observed that regardless of age, male Camkk2−/− mice possessed significantly elevated trabecular bone volume, microarchitecture and compressive strength as well as cortical bone strength compared to age-matched WT mice, implying that the chronic loss of this kinase attenuates age-associated decline in bone mass. Further, whereas STO-609 treatment and/or the absence of CaMKK2 significantly enhanced the femoral mid-shaft geometry, the mid-shaft cortical wall thickness and material bending stress remained similar among the cohorts, implying that regardless of treatment, the material properties of the bone remain similar. Thus, our cumulative results provide evidence for the pharmacological inhibition of CaMKK2 as a bone anabolic strategy in combating age-associated osteoporosis.

Intervention timing of strontium treatment on estrogen depletion-induced osteoporosis in rats: Bone microstructure and mechanics

To evaluate the effect of intervention timing of Sr treatment on trabecular bone microstructure and mechanics. Ninety female rats were randomly divided into three batches with three groups in each batch. Each group was divided according to the initiation timing of vehicle or strontium compound (SrC), which was at week 0 (early), 4 (mid-term) and 8 (late) after the ovariectomy, respectively. The treatment lasted for 12 weeks. The trabecular bone biomechanical properties, trabecular bone tissue mechanical properties, trabecular bone microstructure, and bone remodeling were analyzed with mechanical testing, nanoindentation, microCT, and histomorphometry, respectively. The osteoblast and osteoclast phenotypic genes were analyzed with real-time polymerase chain reaction (PCR). Early and mid-term Sr treatment significantly increased biomechanical properties of trabecular bone, which was associated with increased microarchitecture parameters, increased bone formation parameters and up-regulation of osteoblast-related gene expression. Late Sr treatment failed to exert a beneficial effect on any of those parameters. The beneficial effect of Sr was dependent on the intervention timing in ovariectomized rats.

Prediction of Biomechanical Properties of Trabecular Bone in MR Images With Geometric Features and Support Vector Regression

Whole knee joint MR image datasets were used to compare the performance of geometric trabecular bone features and advanced machine learning techniques in predicting biomechanical strength properties measured on the corresponding ex vivo specimens. Changes of trabecular bone structure throughout the proximal tibia are indicative of several musculoskeletal disorders involving changes in the bone quality and the surrounding soft tissue. Recent studies have shown that MR imaging also allows non-invasive 3-D characterization of bone microstructure. Sophisticated features like the scaling index method (SIM) can estimate local structural and geometric properties of the trabecular bone and may improve the ability of MR imaging to determine local bone quality in vivo. A set of 67 bone cubes was extracted from knee specimens and their biomechanical strength estimated by the yield stress (YS) [in MPa] was determined through mechanical testing. The regional apparent bone volume fraction (BVF) and SIM derived features were calculated for each bone cube. A linear multiregression analysis (MultiReg) and a optimized support vector regression (SVR) algorithm were used to predict the YS from the image features. The prediction accuracy was measured by the root mean square error (RMSE) for each image feature on independent test sets. The best prediction result with the lowest prediction error of RMSE = 1.021 MPa was obtained with a combination of BVF and SIM features and by using SVR. The prediction accuracy with only SIM features and SVR (RMSE = 1.023 MPa) was still significantly better than BVF alone and MultiReg (RMSE = 1.073 MPa). The current study demonstrates that the combination of sophisticated bone structure features and supervised learning techniques can improve MR-based determination of trabecular bone quality.

Biomechanical properties across trabeculae from the proximal femur of normal and ovariectomised sheep

The elastic behaviour of trabecular bone is a function not only of bone volume and architecture, but also of tissue material properties. Variation in tissue modulus can have a substantial effect on the biomechanical properties of trabecular bone. However, the nature of tissue property variation within a single trabecula is poorly understood. This study uses nanoindentation to determine the mechanical properties of bone tissue in individual trabeculae. Using an ovariectomised ovine model, the modulus and hardness distribution across trabeculae were measured. In both normal and ovariectomised bone, the modulus and hardness were found to increase towards the core of the trabeculae. Across the width of the trabeculae, the modulus was significantly less in the ovariectomised bone than in the control bone. However, in contrast to this hardness was found not to differ significantly between the two groups. This study provides valuable information on the variation of mechanical material properties in healthy and diseased trabecular bone tissue. The results of the current study will be useful in finite element modelling where more accurate values of trabecular bone modulus will enable the prediction of the macroscale behaviour of trabecular bone.

Biomechanical effect of mineral heterogeneity in trabecular bone

Due to daily loading, trabecular bone is subjected to deformations (i.e., strain), which lead to stress in the bone tissue. When stress and/or strain deviate from the normal range, the remodeling process leads to adaptation of the bone architecture and its degree of mineralization to effectively withstand the sustained altered loading. As the apparent mechanical properties of bone are assumed to depend on the degree and distribution of mineralization, the goal of the present study was examine the influences of mineral heterogeneity on the biomechanical properties of trabecular bone in the human mandibular condyle. For this purpose nine right condyles from human dentate mandibles were scanned and evaluated with a microCT system. Cubic regional volumes of interest were defined, and each was transformed into two different types of finite element (FE) models, one homogeneous and one heterogeneous. In the heterogeneous models the element tissue moduli were scaled to the local degree of mineralization, which was determined using microCT. Compression and shear tests were simulated to determine the apparent elastic moduli in both model types. The incorporation of mineralization variation decreased the apparent Young's and shear moduli by maximally 21% in comparison to the homogeneous models. The heterogeneous model apparent moduli correlated significantly with bone volume fraction and degree of mineralization. It was concluded that disregarding mineral heterogeneity may lead to considerable overestimation of apparent elastic moduli in FE models.

Effects of Treatment with Parathyroid Hormone 1–84 on Quantity and Biomechanical Properties of Thoracic Vertebral Trabecular Bone in Ovariectomized Rhesus Monkeys

Osteoporosis is characterized by impaired bone quality leading to increased susceptibility to fracture, particularly of the thoracic spine. However, the lumbar spine is studied most commonly. We investigated the effects of 16 months of treatment with full-length parathyroid hormone (PTH) 1-84 (5, 10, or 25 microg/kg) on bone mineral density (BMD) and on architecture and biomechanical properties of trabecular bone at the thoracic spine of ovariectomized (OVX) adult rhesus monkeys and compared the results with those from the lumbar spine. At baseline, 9 months after surgery, dual-energy X-ray absorptiometric BMD at T9-T12 was 7% lower in OVX than in sham animals. All PTH(1-84) doses increased BMD to sham levels within 7 months. Micro-computed tomography of T10 vertebrae showed that trabecular bone volume and connectivity were higher in PTH(1-84)-treated animals than in sham controls, primarily through a significantly greater trabecular number. Peripheral quantitative computed tomography of trabecular bone cores from T11 and T12 confirmed that PTH(1-84) increased BMD. Compression testing of the cores showed that PTH(1-84) treatment increased stiffness, modulus, yield load, and yield stress to levels significantly greater than in sham animals, with the largest effect in the 10 microg/kg group (35-54% greater than in OVX controls). Thus, PTH(1-84) treatment increased BMD and the biomechanical properties of trabecular bone at the thoracic spine of OVX rhesus monkeys. The 10 microg/kg dose produced the greatest effect on trabecular strength, possibly because the highest dose stimulated bone remodeling excessively. Importantly, the changes observed were similar to those in lumbar vertebrae, thereby validating extrapolation of results from the lumbar to the thoracic spine.

Non-Invasive Analysis of the Micro-Structural and Biomechanical Properties of Trabecular Bone in Human Femoral Head

This study investigates micro-structural and mechanical properties of trabecular bone in human femoral head with and without osteoporosis using a micro-CT and a finite element model. 15 cored trabecular bone specimens with 20 of diameter were obtained from femoral heads with osteoporosis resected for total hip arthroplasty, and 5 specimens were removed from femoral head of cadavers, which has no history of musculoskeletal diseases. A high-resolution micro-CT system was used to scan each specimen to obtain histomorphometry indexes. Based on the micro-images, a FE-model was created to determine mechanical property indexes. While the non-osteoporosis group had increases the trabecular thickness, the bone volume, the bone volume fraction, the degree of anisotropy and the trabecular number compared with those of osteoporotic group, the non-osteoporotic group showed decreases in trabecular separation and structure model index. Regarding the mechanical property indexes, the reaction force and the Young's modulus were lower in the osteoporotic group than in non-osteoporotic group. Our data shows salient deteriorations in trabecular micro-structural and mechanical properties in human femoral head with osteoporosis.

Propriétés mécaniques de greffons humains provenant de têtes fémorales et traitées par un procédé d’épuration physico-chimique (Ostéopure™)

Purpose of the study Bone grafts and bone substitutes must be biocompatible osteoconductors with satisfactory mechanical properties similar to native bone. When the bone treatment is conducted under specific conditions, the elasticity module under infra-maximal loading can be optimized to achieve reproducible values. The purpose of this work was to determine the effect of the cleaning and sterilization process using Osteopure™ on the biomechanical properties of trabecular bone harvested from human femoral heads. Material and method Seventy trabecular bone samples were tested: group 1F (fresh samples); group 1N (after application of Osteopure™ cleaning); group 1S (after Osteopure® cleaning and sterilization). Non-destructive and destructive tests (group 1D) were performed. Two fresh femoral heads were used as controls for the destructive test (group 2). The first non-destructive test was applied directly after section (group 1F). Other samples were then purified with Osteopure™ treatment and a second non-destructive test was conducted (group 1N). A third non-destructive test was conducted after sterlization with 25kgray radiation (group 1S). Treatments 1 and 2 were performed by OST Developpement SA (Clermont-Ferrand). Finally a destruction test was applied along the directional axis (group 1D). For the 31 samples in group 2 (control) the destructive test was applied along the directional axis immediately after section. Compression tests were performed at a deformation speed of 3 mm/min for 0.3% deformation. Results The Young module did not exhibit any significant difference between the three steps of the testing in the three orthogonal directions. The Young module was not significantly different between group 1F and group 2 (controls). Maximal force of compression was significantly different (P<0.01). There was a linear relationship between maximal force at rupture and the Young module obtained during destructive tests, for groups 1D and 2 respectively. The compression curves obtained from sterilized samples (group 1D) were not significantly different from those observed for fresh trabecular bone in group 2 (controls). Discussion The Young module values measured from 70 - 673 MPa. For non-destructive tests, the module values were to the order of 64% of those obtained for destructive tests. Decreased maximal force of rupture observed for treated samples in comparison with fresh samples can be explained by the extraction of most of the lipids. Conclusion The Osteopure™ method does not alter stiffness of bone allografts. The elasticity module observed in treated bones is close to that observed in fresh bones. Mechanical resistance to compression is however only half the force of compression observed in the hip joint for daily activities. The linear relationship between the elasticity mode and loading required for rupture is not affected by treatment with Osteopure™. The advantages related to elimination of prions or viral contamination appear by far to be more important than the minor changes observed in the mechanical characteristis of allografts.

Relationships between young modulus of elasticity, ash density, and MRI derived effective transverse relaxation T2* in tibial specimens.

It has been hypothesized that the MR relaxation time T2* of bone marrow present in the intertrabecular spaces may be related to the density of the trabecular network and may be a predictor of trabecular bone properties. To derive a relationship between the marrow relaxation time T2* and biomechanical properties of trabecular bone, we studied two sets of trabecular bone specimens from human tibiae. The first set consisted of 12 specimens that were defatted and immersed in saline; the second set consisted of 18 specimens with marrow in the trabecular spaces. The MR studies were conducted on a 1.5 T imaging system. In the first set of specimens, a GE sequence (TR = 70 ms; TE = 5, 10, 15, 20, 25 ms) was used to obtain images in the axial plane. In the second set, a water suppression pulse was used prior to an asymmetric SE sequence (TR = 300 ms; TE = 4, 8, 12, 16, 20, 24 ms) to obtain images in the axial, coronal, and sagittal planes. The T2* of the intertrabecular saline of the marrow fat was calculated assuming a monoexponential decay. In both sets, the elastic moduli were measured in three orthogonal directions (superoinferior, anteroposterior, and mediolateral). The ash density was determined after the completion of the experiments. Our results indicate a moderate significant negative correlation between T2* and ash density or elastic modulus (E) in both sets of specimens. The correlation coefficients were slightly improved between the transverse relaxation rate 1/T2* and bone density or E. We found a good correlation between T2* and the reciprocal ash density (r = 0.88) and between T2* and the reciprocal elastic modulus 1/E (r = 0.87 to r = 0.95) in the first set, while in the second set the correlation remained moderate. With use of a multiple linear regression model (1/E = a x T2* + b x 1/T2* + n), the reciprocal elastic moduli 1/E were predicted to > 90% by T2* and 1/T2* in the first set of specimens. This finding was not replicated with the second set of specimens. In the second set of specimens, we found poor to moderate correlation coefficients between the T2* times in the three orthogonal planes (r = 0.45 to r = 0.71). Trabecular bone properties such as density and strength may potentially be assessed with quantitative MR techniques. However, especially for in vitro studies, specimen preparation, acquisition parameters, and specimen geometry may have a significant impact on the obtained results.