Biomedical subjects

T M Keaveny

Publications and source records attributed to T M Keaveny.

At least 19 recordsLinked to original sources

PubMed2002

Mechanical and chemical characteristics of mineral produced by basic fibroblast growth factor-treated bone marrow stromal cells in vitro.

It has been shown that various organ and cell cultures exhibit increased mineral formation with the addition of basic fibroblast growth factor (bFGF) and phosphate ions in the medium. However, to date there has been no attempt to relate the chemical composition of mineral formed in vitro to a measure of its mechanical properties. This information is important for understanding the in vivo mineralization process, the development of in vitro models, and the design of tissue-engineered bone substitutes. In this study we examined the reduced modulus; hardness; and mineral-to-matrix, crystallinity, carbonate-to-mineral, and calcium-to-phosphorus ratios of mineral formed by bFGF-treated rat-derived bone marrow stromal cells in vitro. The cells were treated with 1 or 3 mM beta-glycerophosphate for 3 and 4 weeks. Both mechanical parameters, reduced modulus and hardness, increased with increasing beta-glycerophosphate concentration. The only chemical measure of the mineral composition that exhibited the same dependency was the mineral-to-matrix ratio. The values of crystallinity and carbonate fraction were similar to those for intact cortical bone, but the calcium-to-phosphorus ratio was substantially lower than that of normal bone. These data indicate that the mineral formed by bFGF-treated bone cells is mechanically and chemically different from naturally formed lamellar bone tissue after 4 weeks in culture. These results can be used to improve in vitro models of mineral formation as well as enhance the design of tissue-engineered bone substitutes.

Animals↗

PubMed2001

Trabecular eccentricity and bone adaptation.

It is well established that bones functionally adapt by mechanisms that control tissue density, whole bone geometry, and trabecular orientation. In this study, we propose the existence of another such powerful mechanism, namely, trabecular eccentricity, i.e. non-central placement of trabecular bone within a cortical envelope. In the human femoral neck, trabecular eccentricity results in a thicker cortical shell on the inferior than superior aspect. In an overall context of expanding understanding of bone adaptation, the goal of this study was to demonstrate the biomechanical significance of, and provide a mechanistic explanation for, the relationship between trabecular eccentricity and stresses in the human femoral neck. Using composite beam theory, we showed that the biomechanical effects of eccentricity during a habitual loading situation were to increase the stress at the superior aspect of the neck and decrease the stress at the inferior aspect, resulting in an overall protective effect. Further, increasing eccentricity had a stress-reducing effect equivalent to that of increasing cortical thickness or increasing trabecular modulus. We conclude that an asymmetric placement of trabecular bone within a cortical bone envelope represents yet another mechanism by which whole bones can adapt to mechanical demands.

Adaptation, Physiological↗

PubMed2001

Effects of bone cement volume and distribution on vertebral stiffness after vertebroplasty.

STUDY DESIGN: The biomechanical behavior of a single lumbar vertebral body after various surgical treatments with acrylic vertebroplasty was parametrically studied using finite-element analysis. OBJECTIVES: To provide a theoretical framework for understanding and optimizing the biomechanics of vertebroplasty. Specifically, to investigate the effects of volume and distribution of bone cement on stiffness recovery of the vertebral body. SUMMARY OF BACKGROUND DATA: Vertebroplasty is a treatment that stabilizes a fractured vertebra by addition of bone cement. However, there is currently no information available on the optimal volume and distribution of the filler material in terms of stiffness recovery of the damaged vertebral body. METHODS: An experimentally calibrated, anatomically accurate finite-element model of an elderly L1 vertebral body was developed. Damage was simulated in each element based on empirical measurements in response to a uniform compressive load. After virtual vertebroplasty (bone cement filling range of 1-7 cm3) on the damaged model, the resulting compressive stiffness of the vertebral body was computed for various spatial distributions of the filling material and different loading conditions. RESULTS: Vertebral stiffness recovery after vertebroplasty was strongly influenced by the volume fraction of the implanted cement. Only a small amount of bone cement (14% fill or 3.5 cm3) was necessary to restore stiffness of the damaged vertebral body to the predamaged value. Use of a 30% fill increased stiffness by more than 50% compared with the predamaged value. Whereas the unipedicular distributions exhibited a comparative stiffness to the bipedicular or posterolateral cases, it showed a medial-lateral bending motion ("toggle") toward the untreated side when a uniform compressive pressure load was applied. CONCLUSION: Only a small amount of bone cement ( approximately 15% volume fraction) is needed to restore stiffness to predamage levels, and greater filling can result in substantial increase in stiffness well beyond the intact level. Such overfilling also renders the system more sensitive to the placement of the cement because asymmetric distributions with large fills can promote single-sided load transfer and thus toggle. These results suggest that large fill volumes may not be the most biomechanically optimal configuration, and an improvement might be achieved by use of lower cement volume with symmetric placement.

Bone Cements↗

PubMed2001

Sensitivity of damage predictions to tissue level yield properties and apparent loading conditions.

High-resolution finite element models of trabecular bone failure could be used to augment current techniques for measuring damage in trabecular bone. However, the sensitivity of such models to the assumed tissue yield properties and apparent loading conditions is unknown. The goal of this study was to assess the sensitivity of the amount and mode (tension vs. compression) of tissue level yielding in trabecular bone to these factors. Linear elastic, high-resolution finite element models of nine bovine tibial trabecular bone specimens were used to calculate the fraction of the total tissue volume that exceeded each criterion for apparent level loading to the reported elastic limit in both on-axis and transverse compression and tension, and in shear. Four candidate yield criteria were studied, based on values suggested in the literature. Both the amount and the failure mode of yielded tissue were sensitive to the magnitudes of the tissue yield strains, the degree of tension-compression asymmetry of the yield criterion, and the applied apparent loads. The amount of yielded tissue was most sensitive to the orientation of the applied apparent loading, with the most tissue yielding for loading along the principal trabecular orientation and the least for loading perpendicular to it, regardless of the assumed tissue level yield criterion. Small changes in the magnitudes and the degree of asymmetry of the tissue yield criterion resulted in much larger changes in the amount of yielded tissue in the model. The results indicate that damage predictions based on high-resolution finite element models are highly sensitive to the assumed tissue yield properties. As such, good estimates of these values are needed before high-resolution finite element models can be applied to the study of trabecular bone damage. Regardless of the assumed tissue yield properties, the amount and type of damage that occurs in trabecular bone depends on the relative orientations of the applied apparent loads to the trabecular architecture, and this parameter should be controlled for both experimental and computational damage studies.

Animals↗

PubMed2001

Dependence of yield strain of human trabecular bone on anatomic site.

Understanding the dependence of human trabecular bone strength behavior on anatomic site provides insight into structure-function relationships and is essential to the increased success of site-specific finite element models of whole bones. To investigate the hypothesis that the yield strains of human trabecular bone depend on anatomic site, the uniaxial tensile and compressive yield properties were compared for cylindrical specimens from the vertebra (n=61), proximal tibia (n=31), femoral greater trochanter (n=23), and femoral neck (n=27) taken from 61 donors (67+/-15years). Test protocols were used that minimized end artifacts and loaded specimens along the main trabecular orientation. Yield strains by site (mean+/-S.D.) ranged from 0.70+/-0.05% for the trochanter to 0.85+/-0.10% for the femoral neck in compression, from 0.61+/-0.05% for the trochanter to 0.70+/-0.05% for the vertebra in tension, and were always higher in compression than tension (p<0.001). The compressive yield strain was higher for the femoral neck than for all other sites (p<0.001), as was the tensile yield strain for the vertebra (p<0.007). Analysis of covariance, with apparent density as the covariate, indicated that inter-site differences existed in yield stress even after adjusting statistically for density (p<0.035). Coefficients of variation in yield strain within each site ranged from only 5-12%, consistent with the strong linear correlations (r(2)=0.94-0.98) found between yield stress and modulus. These results establish that the yield strains of human trabecular bone can differ across sites, but that yield strain may be considered uniform within a given site despite substantial variation in elastic modulus and yield stress.

Adult↗

PubMed2001

Relative roles of microdamage and microfracture in the mechanical behavior of trabecular bone.

Compared to trabecular microfracture, the biomechanical consequences of the morphologically more subtle trabecular microdamage are unclear but potentially important because of its higher incidence. A generic three-dimensional finite element model of the trabecular bone microstructure was used to investigate the relative biomechanical roles of these damage categories on reloading elastic modulus after simulated overloads to various strain levels. Microfractures of individual trabeculae were modeled using a maximum fracture strain criterion, for three values of fracture strain (2%, 8%, and 35%). Microdamage within the trabeculae was modeled using a strain-based modulus reduction rule based on cortical bone behavior. When combining the effects of both microdamage and microfracture, the model predicted reductions in apparent modulus upon reloading of over 60% at an applied apparent strain of 2%, in excellent agreement with previously reported experimental data. According to the model, up to 80% of the trabeculae developed microdamage at 2% apparent strain, and between 2% and 10% of the trabeculae were fractured, depending on which fracture strain was assumed. If microdamage could not occur but microfracture could, good agreement with the experimental data only resulted if the trabecular hard tissue had a fracture strain of 2%. However, a high number of fractures (10% of the trabeculae) would need to occur for this case, and this has not been observed in published damage morphology studies. We conclude therefore that if the damage behavior of trabecular hard tissue is similar to that of cortical bone, then extensive microdamage is primarily responsible for the large loss in apparent mechanical properties that can occur with overloading of trabecular bone.

Biomechanical Phenomena↗

PubMed2001

Nonlinear behavior of trabecular bone at small strains.

Study of the behavior of trabecular bone at strains below 0.40 percent is of clinical and biomechanical importance. The goal of this work was to characterize, with respect to anatomic site, loading mode, and apparent density, the subtle concave downward stress-strain nonlinearity, that has been observed recently for trabecular bone at these strains. Using protocols designed to minimize end-artifacts, 155 cylindrical cores from human vertebrae, proximal tibiae, proximal femora, and bovine proximal tibiae were mechanically tested to yield at 0.50 percent strain per second in tension or compression. The nonlinearity was quantified by the reduction in tangent modulus at 0.20 percent and 0.40 percent strain as compared to the initial modulus. For the pooled data, the mean +/- SD percentage reduction in tangent modulus at 0.20 percent strain was 9.07+/- 3.24 percent in compression and 13.8 +/- 4.79 percent in tension. At 0.40 percent strain, these values were 23.5 +/- 5.71 and 35.7+/- 7.10 percent, respectively. The magnitude of the nonlineari't depended on both anatomic site (p < 0.001) and loading mode (p < 0.001), and in tension was positively correlated with density. Calculated values of elastic modulus and yield properties depended on the strain range chosen to define modulus via a linear curve fit (p < 0.005). Mean percent differences in 0.20 percent offset yield strains were as large as 10.65 percent for some human sites. These results establish that trabecular bone exhibits nonlinearity at low strains, and that this behavior can confound intersite comparisons of mechanical properties. A nonlinear characterization of the small strain behavior of trabecular bone was introduced to characterize the initial stress-strain behavior more thoroughly.

Aged↗

PubMed2001

Biomechanics of trabecular bone.

Trabecular bone is a complex material with substantial heterogeneity. Its elastic and strength properties vary widely across anatomic sites, and with aging and disease. Although these properties depend very much on density, the role of architecture and tissue material properties remain uncertain. It is interesting that the strains at which the bone fails are almost independent of density. Current work addresses the underlying structure-function relations for such behavior, as well as more complex mechanical behavior, such as multiaxial loading, time-dependent failure, and damage accumulation. A unique tool for studying such behavior is the microstructural class of finite element models, particularly the "high-resolution" models. It is expected that with continued progress in this field, substantial insight will be gained into such important problems as osteoporosis, bone fracture, bone remodeling, and design/analysis of bone-implant systems. This article reviews the state of the art in trabecular bone biomechanics, focusing on the mechanical aspects, and attempts to identify important areas of current and future research.

Aging↗

PubMed2001

Osteoblasts respond to pulsatile fluid flow with short-term increases in PGE(2) but no change in mineralization.

Although there is no consensus as to the precise nature of the mechanostimulatory signals imparted to the bone cells during remodeling, it has been postulated that deformation-induced fluid flow plays a role in the mechanotransduction pathway. In vitro, osteoblasts respond to fluid shear stress with an increase in PGE(2) production; however, the long-term effects of fluid shear stress on cell proliferation and differentiation have not been examined. The goal of this study was to apply continuous pulsatile fluid shear stresses to osteoblasts and determine whether the initial production of PGE(2) is associated with long-term biochemical changes. The acute response of bone cells to a pulsatile fluid shear stress (0.6 +/- 0.5 Pa, 3.0 Hz) was characterized by a transient fourfold increase in PGE(2) production. After 7 days of static culture (0 dyn/cm(2)) or low (0.06 +/- 0.05 Pa, 0.3 Hz) or high (0.6 +/- 0.5 Pa, 3.0 Hz) levels of pulsatile fluid shear stress, the bone cells responded with an 83% average increase in cell number, but no statistical difference (P > 0.53) between the groups was observed. Alkaline phosphatase activity per cell decreased in the static cultures but not in the low- or high-flow groups. Mineralization was also unaffected by the different levels of applied shear stress. Our results indicate that short-term changes in PGE(2) levels caused by pulsatile fluid flow are not associated with long-term changes in proliferation or mineralization of bone cells.

Animals↗

PubMed2000

Biomechanical consequences of an isolated overload on the human vertebral body.

The biomechanical consequences of an isolated overload to the vertebral body may play a role in the etiology of vertebral fracture. In this context, we quantified residual strains and reductions in stiffness and ultimate load when vertebral bodies were loaded to various levels beyond the elastic regimen and related these properties to the externally applied strain and bone density. Twenty-three vertebral bodies (T11-L4, from 23 cadavers aged 20-90 years) were loaded once in compression to a randomized nominal strain level between 0.37 and 4.5%, unloaded, and then reloaded to 10% strain. Residual strains of up to 1.36% developed on unloading and depended on the applied strain (r2=0.85) but not on density (p = 0.25). Percentage reductions in stiffness and ultimate load of up to 83.7 and 52.5%, respectively, depended on both applied strain (r2 = 0.90 and r2 = 0.32, respectively) and density (r2 = 0.23 and r2 = 0.22, respectively). Development of residual strains is indicative of permanent deformations, whereas percentage reductions in stiffness are direct measures of effective mechanical damage. These results therefore demonstrate that substantial mechanical damage-which is not visible from radiographs-can develop in the vertebral body after isolated overloads, as well as subtle but significant permanent deformations. This behavior is similar to that observed previously for cylindrical cores of trabecular bone. Taken together, these findings indicate that the damage behavior of the lumbar and lower thoracic vertebral body is dominated by the trabecular bone and may be an important factor in the etiology of vertebral fracture.

Adult↗

PubMed2000

High-resolution finite element models with tissue strength asymmetry accurately predict failure of trabecular bone.

The ability to predict trabecular failure using microstructure-based computational models would greatly facilitate study of trabecular structure-function relations, multiaxial strength, and tissue remodeling. We hypothesized that high-resolution finite element models of trabecular bone that include cortical-like strength asymmetry at the tissue level, could predict apparent level failure of trabecular bone for multiple loading modes. A bilinear constitutive model with asymmetric tissue yield strains in tension and compression was applied to simulate failure in high-resolution finite element models of seven bovine tibial specimens. Tissue modulus was reduced by 95% when tissue principal strains exceeded the tissue yield strains. Linear models were first calibrated for effective tissue modulus against specimen-specific experimental measures of apparent modulus, producing effective tissue moduli of (mean+/-S.D.) 18.7+/-3.4GPa. Next, a parameter study was performed on a single specimen to estimate the tissue level tensile and compressive yield strains. These values, 0.60% strain in tension and 1.01% strain in compression, were then used in non-linear analyses of all seven specimens to predict failure for apparent tensile, compressive, and shear loading. When compared to apparent yield properties previously measured for the same type of bone, the model predictions of both the stresses and strains at failure were not statistically different for any loading case (p>0.15). Use of symmetric tissue strengths could not match the experimental data. These findings establish that, once effective tissue modulus is calibrated and uniform but asymmetric tissue failure strains are used, the resulting models can capture the apparent strength behavior to an outstanding level of accuracy. As such, these computational models have reached a level of fidelity that qualifies them as surrogates for destructive mechanical testing of real specimens.

Animals↗

PubMed1999

Characterization of the mechanical and ultrastructural properties of heat-treated cortical bone for use as a bone substitute.

Heat-treated bovine cortical bone has been proposed as an alternative to bone grafts and synthetic bone substitutes because it may combine the advantages of allografts (high stiffness and strength) and synthetic materials (abundant supply, reduced risk of rejection and disease transfer). Its mechanical properties and ultrastructure, however, are not well characterized. To address this, we compared the compressive (n = 20, bovine bone) and tensile (n = 26, bovine bone) mechanical properties and the ultrastructure (n = 12, human bone) of intact versus 350 degrees C heat-treated cortical bone. The 350 degrees C heat-treated bone had a mean +/- SD elastic modulus similar to the intact bone for both compression (16.3 +/- 2.2 GPa, pooled; p = 0.68) and tension (16.3 +/- 3.7 GPa, pooled; p = 0.95). It also maintained 63% of the intact strength in compression but only 9% in tension (p < 0.001). Infrared scans and X-ray diffraction patterns showed no differences between the 350 degrees C heat-treated and intact bone but large differences between ashed (700 degrees C) and intact bone. Similarly, heat-treated bone previously has been shown to be biocompatible and osteoconductive. We conclude, therefore, that 350 degrees C heat-treated cortical bone may be an excellent load-bearing bone substitute provided that it is loaded in compression only in vivo and is shown by future work to have acceptable fatigue properties.

Aged↗

PubMed1999

Structure-function relationships for coralline hydroxyapatite bone substitute.

To improve the understanding of the functional requirements of trabecular bone substitutes, the structure-function relationships of coralline hydroxyapatite were determined and compared to those of trabecular bone from a variety of anatomic sites. Mechanical properties and permeability of cylindrical coralline hydroxyapatite specimens were measured and related to various morphological parameters that were obtained from analysis of high-resolution (20 microm) computer reconstructions of each specimen. Results indicated the average (+/-SD) Young's modulus (2900 +/- 1290 MPa, n = 20) and permeability (0.50 +/- 0.19 x 10(-9) m2, n = 21) of the coralline hydroxyapatite were within the range of values exhibited by high density trabecular bone; ultimate stress (5.87 +/- 1.92 MPa, n = 13), while in the range of mid-density trabecular bone, was low considering its high volume fraction (31.3 +/- 1.9%, n = 49); and ultimate strain (0.22 +/- 0.03%, n = 13) was much lower than that of trabecular bone from any anatomic site. The only correlation found between mechanical and morphological parameters was between Young's modulus and "fabric" (a scalar measure of architecture that combined the degree of microstructural anisotropy with orientation). These results provide insight into the in vivo performance of this implant, as well as the biomechanical requirements for successful trabecular bone substitutes in general.

Animals↗

PubMed1999

Mechanical behavior of human trabecular bone after overloading.

With the etiology of osteoporotic fractures as motivation, the goal of this study was to characterize the mechanical behavior of human trabecular bone after overloading. Specifically, we quantified the reductions in modulus and strength and the development of residual deformations and determined the dependence of these parameters on the applied strain and apparent density. Forty cylindrical specimens of human L1 vertebral trabecular bone were destructively loaded in compression at 0.5% strain per second to strains of up to 3.0% and then immediately unloaded to zero stress and reloaded. (An ancillary experiment on more readily available bovine bone had been performed previously to develop this testing protocol.) In general, the reloading stress-strain curve had a short initial nonlinear region with a tangent modulus similar to Young's modulus. This was followed by an approximately linear region spanning to 0.7% strain, with a reduced residual modulus. The reloading curve always approached the extrapolated envelope of the original loading curve. Percent modulus reduction (between Young's and residual), a quantitative measure of mechanical damage, ranged from 5.2 to 91.0% across the specimens. It increased with increasing plastic strain (r2 = 0.97) but was not related to modulus or apparent density. Percent strength reduction, in the range of 3.6-63.8%, increased with increasing plastic strain (r2 = 0.61) and decreasing apparent density (r2 = 0.23). The residual strains of up to 1.05% depended strongly on applied strain (r2 = 0.96). Statistical comparisons with previous data for bovine tibial bone lend substantial generality to these trends and provide an envelope of expected behavior for other sites. In addition to providing a basis for biomechanical analysis of the effects of damage in trabecular bone at the organ level, these findings support the concept that occasional overloads may increase the risk of fracture by substantially degrading the mechanical properties of the underlying trabecular bone.

Adult↗

PubMed1999

Uniaxial yield strains for bovine trabecular bone are isotropic and asymmetric.

Although evidence suggests that yield strains for trabecular bone are isotropic, i.e., independent of loading direction, decisive support for this hypothesis has remained elusive. To explicitly test whether yield strains for trabecular bone are isotropic, compressive and tensile yield strains of 51 specimens of bovine tibial trabecular bone (0.41 +/- 0.08 g/cm3 [mean apparent density +/- SD]) were measured without end artifacts in on-axis (along the principal trabecular orientation) and off-axis (30-40 degrees oblique to on-axis) orientations. Yield strains for the on-axis and off-axis orientations were similar in tension (0.80 +/- 0.03% compared with 0.85 +/- 0.04%, p = 0.21) and compression (0.97 +/- 0.05% compared with 0.96 +/- 0.07%, p > 0.99); as expected, modulus and strength depended on loading direction. When considered with an ancillary experiment on bovine tibial trabecular bone that showed yield strains to be similar between on-axis and 90 degrees off-axis bone, these results firmly establish the isotropy of uniaxial yield strains for bovine tibial trabecular bone. This bone is of high density and has a strong, plate-type, anisotropic architecture. Therefore, yield strains for uniaxial loading are expected to be isotropic, or nearly so, for other types of dense trabecular bone, although further work is required to confirm this and to establish this behavior for bone of lower density.

Animals↗

PubMed1999

Heterogeneity of the mechanical properties of demineralized bone.

Knowledge of the mechanical properties of the collagenous component of bone is required for composite modeling of bone tissue and for understanding the age- and disease-related reductions in the ductility and strength of bone. The overall goal of this study was to investigate the heterogeneity of the mechanical properties of demineralized bone which remains unexplained and may be due to differences in the collagen structure or organization or in experimental protocols. Uniaxial tension tests were conducted to measure the elastic and failure properties of demineralized human femoral (n = 10) and tibial (n = 13) and bovine humeral (n = 8) and tibial (n = 8) cortical bone. Elastic modulus differed between groups (p = 0.02), varying from 275 +/- 94 MPa (mean +/- SD) to 450 + 50 MPa. Similarly, ultimate stress varied across groups from 15 + 4.2 to 26 + 4.7 MPa (p = 0.03). No significant differences in strain-to-failure were observed between any groups in this study (pooled mean of 8.4 +/- 1.6%; p = 0.42). However, Bowman et al. (1996) reported an average ultimate strain of 12.3 +/- 0.5% for demineralized bovine humeral bone, nearly 40% higher than our value. Taken together, it follows that all the monotonic mechanical properties of demineralized bone can display substantial heterogeneity. Future studies directed at explaining such differences may therefore provide insight into aging and disease of bone tissue.

Aged↗

PubMed1999

Biomechanical effects of intraspecimen variations in trabecular architecture: a three-dimensional finite element study.

Trabecular architecture is considered important in osteoporosis and has been quantified by a variety of mean parameters characteristic of a whole specimen. Variations within a specimen, however, have been mostly ignored. In this study, the theoretical effects of these intraspecimen variations in architecture on predicted mechanical properties were investigated through a three-dimensional finite element parameter study that simulated variations in trabecular thickness in a controlled manner. An irregularly spaced lattice of different sized rods was used to simulate trabecular bone in three distinct volume fraction ranges, representing young, middle-aged, and elderly vertebral bone. Beta distributions (a type of non-normal distribution) of trabecular thickness with coefficients of variation of either 25%, 40%, or 55% were applied to the rods in each model, and 225 simulations of uniaxial compression tests were performed to obtain modulus values. Percent modulus reductions of 22% and 43% were predicted when the intraspecimen coefficient of variation in trabecular thickness was increased from 25% to 40% and from 25% to 55%, respectively, for models of equal volume fraction. Furthermore, this trend was predicted to be independent of volume fraction. We conclude, therefore, that consideration of the intraspecimen trabecular thickness variation in conjunction with volume fraction may improve the ability to predict trabecular modulus compared with use of volume fraction alone. Further, the model suggests that if age, disease, or drug treatments increase trabecular thickness variation, this may be detrimental to mechanical properties.

Adult↗

PubMed1999

Measurement of intraspecimen variations in vertebral cancellous bone architecture.

A three-dimensional technique was developed for the quantification of the number and cross-sectional geometry of individual trabeculae oriented along a given direction. As an example application, the number of vertical and horizontal trabeculae and their respective cross-sectional geometry were determined for a set of six vertebral cancellous bone specimens (L3-L4 female vertebral bodies; age range 39-63 years). Three-dimensional optical images at a spatial resolution of 20 microm were obtained using an automated serial milling technique. The thickness distributions were generally right skewed. The mean true thickness for both the vertically and horizontally oriented trabeculae showed a strong relationship with volume fraction (vertical: r2 = 0.86; p < 0.05; horizontal: r2 = 0.80; p < 0.05), and mean trabecular thickness (Tb.Th.) (vertical: r2 = 0.81; p < 0.05; horizontal: r2 = 0.72; p < 0.05). The horizontal trabeculae were greater in number and were thinner than the vertical trabeculae. The coefficient of variation of the intraspecimen vertical trabecular thicknesses ranged from 25% to 42%, and showed a weak, albeit insignificant, positive correlation with volume fraction (r2 = 0.46). The findings demonstrated substantial intraspecimen variations exist in trabecular thickness that are not related to volume fraction. Further studies are recommended to determine the potential role of such intraspecimen variations in architecture on biomechanical properties.

Adult↗