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Elastic properties of osteon and trabecular bone measured by nanoindentation
A NEW METHOD FOR THE QUANTITATIVE DETERMINATION OF THE DEGREE OF MINERALIZL4TION IN THE SUBCHONDRAL BONE PLATE M. Miiller-Gerbl’, U. Linsenmeie?, R. Putz’, ‘Anatomische Anstalt Mtinchen, *Department of Radiology Miinchen INTRODUCTION: In previous studies we could show that CT osteoabsorptiometty (CT OAM. Miiller-Gerbl et al., 1989) is a suitable tool for gathering in vivo information about the stress distribution within joint surfaces. For a further analysis of adaptational processes precise quantitative data on the degree of the overall mineralization are necessary. The aim of this study was to develop a new quantitative method based on CT OAM that allows assessment of the mineralization status of the subchondral bone plate in terms of the calcium content independent of the sire of the surface so that comparisons between individuals and different joints are possible. METHODS: l.Production of sagittal CT datasets (section thickness 2 mm) of the radiocarpal joint of 9 healthy persons (aged 24 to 25 years, 7 male, 2 female) and axial CT scans (section thickness 1 mm) of the tibial plateau of 10 patients with genu varum before and 1 year after a correction osteotomy.(aged 52-73 years, 4 male, 6 female) For all CT investigations we used a reference phantom with a small cross-section, comprising two stable plastics, a water-equivalent standard and a bone-equivalent standard containing 200 mg hydroxyapatite/ml (Kalender et al., 1987). 2.Three-dimensional reconstruction of the density distribution patterns of all joint surfaces using a maximum intensity projection. In these images the number of pixels of all Hounstield values (HU) were collected. By calibration with the reference phantom the calcium content in mg /ml for each pixel was calculated. The following integration gave the calcium content of the entire joint surface. For expressing values independent of the sire of the joint surface, the amount of each HU value was expressed as a percentage of the enitre surface and integrated again. This allows direct comparisons between individuals. A graphical representation gives information in which way the HU values are distributed. RESULTS: 1. In the radiocarpal joints the relative calcium value ranked between 207 and 532 mg/ml. The right/left comparison always revealed a higher calcium content on the dominant side (differences lie between 5.47 27.12 %) 2. In patients with genu varum the medial corn-partment showed a 56 % higher mineralization than the lateral compartment. One year after osteotomy the lateral compartment showed an increase of about 28 %, the medial side a de-crease of 9 %. An analysis of the distribution of the density values revealed in the medial con-dyle a shift from high towards middle values. CONCLUSION: First applications of this new method showed that the procedure is suitable for a quantitative comparison of the overall minemlisation in the subchondral bone plate between individuals and between different joint surfaces. It can also be used to assess objectively the changes in a joint surfaces after surgical procedures REFERENCES: 1. Miiller-Gerbl et al.,Skeletal Radio1 18, 507-512, .I989 Z..Kalender et al., Med.Phys.l4,863-866,1987 CORRESPONDENCE: M.MiJller-Gerbl Anatomische Anstalt, Pettenkoferstr. 11, D-80336 Miinchen Tel: 089/5 16-4837 Fax: 089/5 160-4802
I I’” Conference
ELASTIC
PROPERTIES OF OSTEON AND TRABECULAR BONE MEASURED BY NANOINDENTATION J.Y. Rho’, T.Y. Tsu?, and G.M. Pharrr ‘Department of Biomedical Engineering, University of Memphis, Memphis, TN 381522, Department of Materials Science, Rice University, Houston, TX 77005
INTRODUCTION: Many recent investigations suggest that the elastic properties of trabecular bone tissue at the microstructural scale may be very different from those of macroscopic specimens of cortical bone [ 11. However, it is unclear whether this difference is due to the testing method or represents a true difference of the properties of the microstructural components. Thus, it would clearly be advantageous to explore the elastic properties of bone tissue with a technique which can diminish the influences of microstructural defects such as voids and inhomogeneities. One promising new technique is nanoindentation [2]. The objective of this study was to use the nanoindentation technique to determine the elastic properties of single osteons and individual trabeculae of bone tissue in the longitudinal and transverse directions. MATERIALS AND METHODS: One mate human tibia and lumbar (Ll) vertebra (age of 63) cut perpendicular and parallel to the long axis of the bone were used. The sections were dehydrated and embedded in epoxy resin. The embedded samples were metallographically polished to produce the smooth surfaces needed for nanoindentation testing. All experiments were performed using the Nano Indenter@’ JJ at the Oak Ridge National Laboratory. The OliverPharr method was used to determine the elastic modulus and hardness [2]. A total of 8.5 indentations were produced in this study. Three to five indentations were made in 5 separate trabeculae and osteons in the longitudinal and transverse directions. Significant differences in the elastic properties of trabeculae and osteons in the longitudinal and transverse direction were analyzed using ANOVA. RESULTS: Basic modulus and hardness results are summarir.ed in Table 1. The mean values of elastic moduli for the bone components were found to be statistically different @ < 0.0001). Table 1 Mean elastic properties for the osteon and trabecular bone Modulus Hardness Bone tvne g&) (Gpa) Osteons longitudinal 21.7 0.63 transverse 16.8 0.57 18.2 Tmbecular longitudinal 0.59 transverse 16.2 0.56 DISCUSSION: The results obtained in this study have bearing on the issue of whether there are significant differences in the elastic properties of cortical and trabecular bone tissue. The elastic moduli in the longitudinal direction of individual trabeculae and osteons measured in this study were 18.3 and 21.7 GPa, respectively. Thus, recent reports that the moduli of individual trabeculae and single osteons am considerably lower than those of macroscopic specimens of cortical bone, 17.1GPa [3] are inconsistent with the present study. A commonly used modulus for trabeculae, 5.4GPa [I] is nearly a factor of 4 smaller than that observed here, and the 10.7 GPa modulus observed for single osteons (fully calcified osteons) tested in tension [4] is approximately a factor of 2 smaller than the current measurements suggest. REFERENCES: [I] Choi et al., 1990, J. Biomech. 23, 1103. [2] Oliver, Pharr, 1992, J. Mater. Res. 7, 1564. [3] Reilly et al., 1974, J. Biomech 7, 271. [4] Ascenzi, Bonucci, 1967, Anat. Rec., 158,375. ACKNOWLEDGEMENTS: This research was sponsored by the Whitaker Foundation. Analytical instrumentation for the nanoindentation testing was provided by the Division of Materials Sciences, U.S. Department of Energy, under contract DE-AC05-960R22464 with Lockheed Martin Energy Research Corp. and through the SHaRE Program under contract DE-ACOS76OROOO33 between the U.S. Department of Energy and Oak Ridge Associated Universities CORRESPONDENCE: Jae-Young Rho, University of Memphis, Department of Biomedical Engineering, Memphis, TN 38152, Tel: 901-678-5485, Fax: 901-678-5281, [email protected]
of the ESB. July 8-I 1 98, Toulouse, France
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I I’” Conference
ELASTIC
PROPERTIES OF OSTEON AND TRABECULAR BONE MEASURED BY NANOINDENTATION J.Y. Rho’, T.Y. Tsu?, and G.M. Pharrr ‘Department of Biomedical Engineering, University of Memphis, Memphis, TN 381522, Department of Materials Science, Rice University, Houston, TX 77005
INTRODUCTION: Many recent investigations suggest that the elastic properties of trabecular bone tissue at the microstructural scale may be very different from those of macroscopic specimens of cortical bone [ 11. However, it is unclear whether this difference is due to the testing method or represents a true difference of the properties of the microstructural components. Thus, it would clearly be advantageous to explore the elastic properties of bone tissue with a technique which can diminish the influences of microstructural defects such as voids and inhomogeneities. One promising new technique is nanoindentation [2]. The objective of this study was to use the nanoindentation technique to determine the elastic properties of single osteons and individual trabeculae of bone tissue in the longitudinal and transverse directions. MATERIALS AND METHODS: One mate human tibia and lumbar (Ll) vertebra (age of 63) cut perpendicular and parallel to the long axis of the bone were used. The sections were dehydrated and embedded in epoxy resin. The embedded samples were metallographically polished to produce the smooth surfaces needed for nanoindentation testing. All experiments were performed using the Nano Indenter@’ JJ at the Oak Ridge National Laboratory. The OliverPharr method was used to determine the elastic modulus and hardness [2]. A total of 8.5 indentations were produced in this study. Three to five indentations were made in 5 separate trabeculae and osteons in the longitudinal and transverse directions. Significant differences in the elastic properties of trabeculae and osteons in the longitudinal and transverse direction were analyzed using ANOVA. RESULTS: Basic modulus and hardness results are summarir.ed in Table 1. The mean values of elastic moduli for the bone components were found to be statistically different @ < 0.0001). Table 1 Mean elastic properties for the osteon and trabecular bone Modulus Hardness Bone tvne g&) (Gpa) Osteons longitudinal 21.7 0.63 transverse 16.8 0.57 18.2 Tmbecular longitudinal 0.59 transverse 16.2 0.56 DISCUSSION: The results obtained in this study have bearing on the issue of whether there are significant differences in the elastic properties of cortical and trabecular bone tissue. The elastic moduli in the longitudinal direction of individual trabeculae and osteons measured in this study were 18.3 and 21.7 GPa, respectively. Thus, recent reports that the moduli of individual trabeculae and single osteons am considerably lower than those of macroscopic specimens of cortical bone, 17.1GPa [3] are inconsistent with the present study. A commonly used modulus for trabeculae, 5.4GPa [I] is nearly a factor of 4 smaller than that observed here, and the 10.7 GPa modulus observed for single osteons (fully calcified osteons) tested in tension [4] is approximately a factor of 2 smaller than the current measurements suggest. REFERENCES: [I] Choi et al., 1990, J. Biomech. 23, 1103. [2] Oliver, Pharr, 1992, J. Mater. Res. 7, 1564. [3] Reilly et al., 1974, J. Biomech 7, 271. [4] Ascenzi, Bonucci, 1967, Anat. Rec., 158,375. ACKNOWLEDGEMENTS: This research was sponsored by the Whitaker Foundation. Analytical instrumentation for the nanoindentation testing was provided by the Division of Materials Sciences, U.S. Department of Energy, under contract DE-AC05-960R22464 with Lockheed Martin Energy Research Corp. and through the SHaRE Program under contract DE-ACOS76OROOO33 between the U.S. Department of Energy and Oak Ridge Associated Universities CORRESPONDENCE: Jae-Young Rho, University of Memphis, Department of Biomedical Engineering, Memphis, TN 38152, Tel: 901-678-5485, Fax: 901-678-5281, [email protected]
of the ESB. July 8-I 1 98, Toulouse, France
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