Biomedical subjects

R D Bloebaum

Publications and source records attributed to R D Bloebaum.

At least 19 recordsLinked to original sources

PubMed2001

Modeling and remodeling in a developing artiodactyl calcaneus: a model for evaluating Frost's Mechanostat hypothesis and its corollaries.

The artiodactyl (mule deer) calcaneus was examined for structural and material features that represent regional differences in cortical bone modeling and remodeling activities. Cortical thickness, resorption and formation surfaces, mineral content (percent ash), and microstructure were quantified between and within skeletally immature and mature bones. These features were examined to see if they are consistent with predictions of Frost's Mechanostat paradigm of mechanically induced bone adaptation in a maturing "tension/compression" bone (Frost, 1990a,b, Anat Rec 226:403-413, 414-422). Consistent with Frost's hypothesis that surface modeling activities differ between the "compression" (cranial) and "tension" (caudal) cortices, the elliptical cross-section of the calcaneal diaphysis becomes more elongated in the direction of bending as a result of preferential (> 95%) increase in thickness of the compression cortex. Regional differences in mineral content and population densities of new remodeling events (NREs = resorption spaces plus newly forming secondary osteons) support Frost's hypothesis that intracortical remodeling activities differ between the opposing cortices: 1.) in immature and mature bones, the compression cortex had attained a level of mineralization averaging 8.9 and 6.8% greater (P < 0.001), respectively, than that of the tension cortex, and 2.) there are on average 350 to 400% greater population densities of NREs in the tension cortices of both age groups (P < 0.0003). No significant differences in cortical thickness, mineral content, porosity, or NREs were found between medial and lateral cortices of the skeletally mature bones, suggesting that no modeling or remodeling differences exist along a theoretical neutral axis. However, in mature bones these cortices differed considerably in secondary osteon cross-sectional area and population density. Consistent with Frost's hypothesis, remodeling in the compression cortex produced bone with microstructural organization that differs from the tension cortex. However, the increased remodeling activity of the tension cortex does not appear to be related to a postulated low-strain environment. Although most findings are consistent with predictions of Frost's Mechanostat paradigm, there are several notable inconsistencies. Additional studies are needed to elucidate the nature of the mechanisms that govern the modeling and remodeling activities that produce and maintain normal bone. It is proposed that the artiodactyl calcaneus will provide a useful experimental model for these studies.

Animals↗

PubMed2001

The contribution of cortical and cancellous bone to dual-energy X-ray absorptiometry measurements in the female proximal femur.

Dual-energy X-ray absorptiometry (DXA) is the most common method for determining bone mineral density (BMD) in the proximal femur. However, there remain questions concerning the contribution of cortical and cancellous bone to this technology in the proximal femur. The purpose of this investigation was to identify structural and compositional characteristics of human bone in the proximal femur that significantly influence DXA BMD measurements. Twenty-four femora were obtained at autopsy from Caucasian females ranging in age from 17 to 92 years (mean +/- SD, 61 +/- 25 years). DXA scans were performed on each specimen with a Hologic QDR-2000 densitometer. Direct measurements were determined from proximal femoral sections for cancellous bone (volume fraction, ash fraction, cancellous cross-sectional area and percent cancellous cross-sectional area), cortical bone (thickness, ash fraction, porosity, cortical cross-sectional area and percent cortical cross-sectional area) and anteroposterior thickness. These parameters were compared with the associated DXA measurements by means of simple and multiple regressions. Cancellous volume fraction was the best predictor of variability of DXA measurements for both the neck and trochanter, with an R2 of 0.87 and 0.76, respectively (p < 0.0001). There was only a minor influence of cortical factors such as thickness (neck and trochanter R2 = 0.51 and 0.42, respectively, p < 0.001) and trochanteric cross-sectional area (R2 = 0.21, p < 0.05). Although the accuracy for determining specific components of the proximal femur was low, the DXA BMD measurement was a strong predictor of cancellous bone factors, but not cortical bone factors that have been shown to change significantly with age.

Absorptiometry, Photon↗

PubMed2001

Evidence of a hypermineralised calcified fibrocartilage on the human femoral neck and lesser trochanter.

Femoral neck fractures are a major cause of morbidity and mortality in elderly humans. In addition to the age-related loss of cancellous bone, changes to the microstructure and morphology of the metaphyseal cortex may be a contributing factor in osteoporotic hip fractures. Recent investigations have identified a hypermineralised tissue on the neck of the femur and trochanteric region that increases in fractional area with advancing age in both males (Boyce & Bloebaum, 1993) and females (Vajda & Bloebaum, 1999). The aim of this study was to determine if the hypermineralised tissue previously observed on the proximal femur is calcified fibrocartilage. Regional variations in the fractional area of hypermineralised tissue, cortical bone, and porosity of the cortical bone along the neck of the femur and lesser trochanter were also quantified. Comparison of back scattered electron and light microscope images of the same area show that regions of hypermineralised tissue correlate with the regions of calcified fibrocartilage from tendon and capsular insertions. The hypermineralised tissue and calcified fibrocartilage had similar morphological features such as the interdigitations of the calcified fibrocartilage into the bone, lacunar spaces, and distinctly shaped pores adjacent to the 2 tissues. Regions of the neck that did not contain insertions were covered with periosteum. There were no regional differences (P > 0.05) on the superior and inferior femoral neck in terms of the percentage area of hypermineralised calcified fibrocartilage, cortical bone, or cortical bone porosity. The lesser trochanter exhibited regional differences in the fractional area of hypermineralised calcified fibrocartilage (P = 0.007) and cortical bone (P = 0.007) but not porosity of the cortical bone (P > 0.05). The effects of calcified fibrocartilage on femoral neck periosteal expansion, repair, and mechanics are unknown, but may play a role in osteoporotic fractures and intracapsular fracture healing.

Cartilage↗

PubMed2000

Possible explanation for the white band artifact seen in clinically retrieved polyethylene tibial components.

Studies have focused attention on the appearance of a subsurface white band in clinically retrieved polyethylene components and the possible contribution of this phenomenon to early polyethylene delamination. Unconsolidated polyethylene particles and oxidation have been suggested as possible reasons for the appearance of the white band. Calcium stearate and other additives used in processing ultra-high molecular weight polyethylene may also contribute to formation of the white band. A quantitative investigation was conducted on 11 retrieved tibial components that exhibited a subsurface white band to determine whether the amount of calcium stearate particles and additives were greater in the white band region when compared with the mid-portion of the same section of polyethylene. Calcium stearate particles and other additives were quantified using backscattered electron imaging with correlated elemental analysis. The particles were identified based on morphology and elemental patterns similar to reference calcium stearate particles and known additives. Significantly more (p < 0. 0001) calcium stearate particles and additives were present in the white band region (4578 +/- 418 particles/mm(2); mean +/- standard error) than the mid-portion region (1250 +/- 147 particles/mm(2)) of the sectioned tibial inserts. The percent area occupied by calcium stearate particles and additives was five times higher (p < 0.0001) within the white band region (0.81 +/- 0.10%) than the mid-portion region (0.16 +/- 0.03%). The increased presence of calcium stearate and other additives in the white band region suggests that they may play a role in the formation of the white band. In future investigations it may be important to consider how calcium stearate and other additives in polyethylene resins affect white band formation and the possible contribution to crazing, early delamination, and osteolysis in total joint replacement.

Adult↗

PubMed2000

Elemental and morphological identification of third-body particulate and calcium stearate inclusions in polyethylene components.

Third-body particulate such as human bone chips, hydroxyapatite, and bone cement are considered contributing factors in accelerated wear in total joint replacement. Particulate wear debris is now considered the major contributing factor in aseptic loosening of total joint replacements. The ability to distinguish between different third-body particulate is necessary to better understand wear mechanisms when conducting implant retrieval analysis. The objective of this investigation is to demonstrate that backscattered electron imaging with correlated energy dispersive X-ray analysis can accurately identify third-body particulate in retrieved polyethylene components. It is important that this technique can also distinguish between third-body particulate and normal inclusions in the polyethylene such as calcium stearate, based on the distinct morphology and elemental composition of each material. Therefore, the ability to distinguish third-body particulate from calcium stearate inclusions is essential in gaining a better understanding of the contributing factors associated with coating separation and accelerated wear observed in clinically retrieved polyethylene components.

Biocompatible Materials↗

PubMed2000

Age-related cancellous bone loss in the proximal femur of caucasian females.

The purpose of this investigation was to directly define the age-related intrafemoral variations in cancellous bone density, bone mineralization and rate of bone loss in a cadaveric population of Caucasian female femoral necks and trochanters. Forty-three Caucasian female femora were obtained and divided into premenopausal, postmenopausal and elderly age groups. The neck and trochanter were removed, and cores of cancellous bone were taken from the superior, middle and inferior regions; volume fraction and ash fraction were determined for each core. The cancellous bone volume fraction of the neck was significantly greater than that of the trochanter, as was that of the inferior region of the neck compared with the superior and middle regions at all age groups (p<0.05). The mean neck/trochanter and neck inferior/superior volume fraction ratios did not change with age; however, the variance increased with age (p<0.001). This increasing variability with age suggests that there may be a subpopulation of individuals within the elderly Caucasian population with a significantly different intrafemoral bone density distribution than was present prior to menopause. This study identified no mineralization changes with age in the cancellous bone of the proximal femur (p>0.05). The influence of increased neck/trochanter and neck inferior/superior ratios on femoral neck integrity and fracture prediction is of interest and requires further investigation.

Adolescent↗

PubMed1999

Age-related hypermineralization in the female proximal human femur.

Hip fracture incidence increases exponentially with age in virtually every human population that has been studied. In spite of this, relatively few studies have examined age-related changes in the metaphyseal cortex of the proximal femur. The present study investigates cortical aging changes in the female proximal femur, with particular reference to regions of hypermineralization. Thirty-three femora from Caucasian females were obtained at autopsy and analyzed using backscattered electron imaging. Variations in hypermineralized tissue area, cortical bone area, and porosity were quantified with standard stereological methods. Cortical width was quantified with digital calipers. Gender differences were examined by statistical comparison with previously published results. Hypermineralized tissue volume was significantly (P < 0.001) greater in elderly individuals. Hypermineralized tissue preferentially appeared near ligamentous or tendinous insertion sites, suggesting the hypermineralized tissue may be a calcified fibrocartilage. Cortical width significantly (P < 0.001) decreased with age and porosity significantly (P < 0.001) increased with age, however the changes were site-specific. The femoral neck and intertrochanteric cortices had a smaller change in cortical width and porosity with age than the diaphysis, but the femoral neck and intertrochanteric cortices had a larger increase in hypermineralized tissue. Comparison with previous data suggests that cortical aging in the proximal femur is similar between males and females and is unlikely to explain the higher incidence of fracture in females. However, the data strongly indicates that age-related changes in the femoral diaphysis cannot be directly extrapolated to either the femoral neck or intertrochanteric cortices.

Adolescent↗

PubMed1999

Comparative micromotion of fully and proximally cemented femoral stems.

This investigation studied the differences of in vitro micromotion between two stem designs. The two stem types investigated were a proximally cemented stem with distal press fit and a fully cemented stem. After initial micromotion testing to 2250 N in simulated single leg stance and stair climb, six of each stem type were loaded dynamically for 1 million cycles at 950 N at 1 Hz. Micromotion studies were repeated. The two stem types had similar micromotion. For the single leg stance, fully cemented implant motion averaged (+/- 95% confidence) 18 +/- 8 microns toggle, 41 +/- 5 microns axial, and 59 +/- 22 microns rotation. Proximally cemented implant motion averaged 20 +/- 6 microns toggle, 42 +/- 6 microns axial, and 31 +/- 15 microns rotation. For the simulated stair climb, fully cemented implant motion averaged 24 +/- 10 microns toggle, 45 +/- 8 microns axial, and 92 +/- 32 microns rotation. Proximally cemented implant motion averaged 19 +/- 10 microns toggle, 42 +/- 9 microns axial, and 87 +/- 53 microns rotation. For both loading conditions, there were no significant differences measurable between the two systems. After dynamic testing of the fully cemented implants, there were no significant changes in the micromotion of either the toggle or the rotation, but an average of 18 microns increase of axial motion was measured in the fully cemented stem. For the proximally cemented implants, there were no significant changes after dynamic testing. This differences was not considered clinically significant because roentgen stereophotogrammetric analysis studies have shown that more than 4 mm of migration is required before clinical symptoms manifest. The protocol developed in this study may help provide a screening process to determine the stability of femoral stem designs before these devices are used clinically.

Adult↗

PubMed1999

Loading conditions and cortical bone construction of an artiodactyl calcaneus.

Customary nonuniform distributions of physiological bone strains are thought to evoke heterogeneous material adaptation in diaphyseal cortices of some limb bones. Recent studies of artiodactyl calcanei have suggested that the regional prevalence of specific mechanical strain features such as mode and magnitude correlate with specific variations in cortical bone ultrastructure, microstructure and mineralization. These data are also consistent with predictions of current algorithms of mechanically induced bone adaptation. However, detailed characterization of the customary functional strain environment of these bones is needed to understand better the mechanisms of these adaptations. An in vitro loading method and rosette strain gauges were used to record principal strains, maximum shear strains and principal strain angles at multiple locations on ten calcanei of adult male mule deer (Odocoileus hemionus hemionus). Each hind limb was fixed in an apparatus to mimic the mid-support phase of the gait and loaded via the Achilles tendon over a broad range of functional loads (0 to 2943 N). Strains were recorded on the craniolateral, craniomedial, caudal, medial and lateral cortices at mid-diaphysis. Loading variations included the progressive elimination of the ligament and tendon along the caudal calcaneus. The results showed that the cranial cortex experiences longitudinal compressive strains that are nearly equal to the principal minimum strains and that the caudal cortex receives longitudinal tensile strains that are nearly equal to the principal maximum strains. With a 981 N load, the mean principal compressive strain on the cranial cortex was -636+/-344 micro(&egr;) (mean +/- s.d., N=9) and the mean principal tensile strain on the caudal cortex was 1112+/-68 micro;(&egr;)x (N=9). In contrast to the cranial and caudal cortices, principal strains in the medial and lateral cortices displayed relatively large deviations from the longitudinal axis (medial, 24 degrees cranial; lateral, 27 degrees caudal). Although shear strains predominated at all gauge sites, variations in maximum shear strains showed no apparent regional pattern or consistent regional predominance. The plantar ligament and tendon of the superficial digital flexor muscle were shown to have important load-sharing functions. These results demonstrate that the functionally loaded artiodactyl calcaneus generally behaves like a cantilevered beam with longitudinal compression and tension strains predominating in opposing cranial and caudal cortices, respectively. Differences in osteon remodeling rates, osteon morphology and mineral content reported previously between the cranial and caudal cortices correlate, in part, with the magnitudes of the principal compressive and tensile strains, respectively. However, material differences that distinguish the medial and lateral cortices from the cranial and caudal cortices could not be primarily attributed to locally increased shear strains as previously suggested. Variations in osteon and/or collagen fiber orientation may correlate more strongly with principal strain direction.

Animals↗

PubMed1998

Comparison of human, primate, and canine femora: implications for biomaterials testing in total hip replacement.

The canine model remains an animal of choice for determining the efficacy and safety of various materials and designs used in human total hip replacement (THR). The primate also is used in orthopedic-related research for studying limb anatomy, gait, and age-related bone loss. In order to better understand the appropriateness of these animal models for human THR, external morphologies of thirty-three adult Caucasian human, sixteen adult chimpanzee, and forty-two adult greyhound femora were compared using osteometric methods. Measured parameters included anteversion angle, cervico-diaphyseal angle, femoral head offset in the frontal plane, and anterior bow profiles along the femoral diaphysis. Although some of the measured parameters were approximately similar between species (e.g., mean cervico-diaphyseal angle of humans and chimpanzees), the majority demonstrated morphologic differences that may be biomechanically significant for interpreting stress transfer across the hip (e.g., mean anteversion angle and mean normalized femoral head offset between species). Additionally, age-related changes in proximal femoral morphology and gait pattern, as well as species-related differences in local muscle and inertial forces, may result in notably different loading conditions across the hip joint of each species. Therefore, discretion must be exercised when evaluating canine or primate THR materials and designs for potential use in the human hip.

Adolescent↗

PubMed1998

Dissolution of particulate hydroxyapatite in a macrophage organelle model.

It is controversial as to whether debris from hydroxyapatite (HA)-coated implants jeopardizes the long-term success of total joint replacements. It has been hypothesized that liberated HA particles are engulfed by macrophages and through normal cellular digestion prevent osteolysis and third-body wear. HA particulates, however, have been observed at the interface and on polyethylene articulating surfaces. There is limited data demonstrating the ability of HA to dissolve at the acidity levels associated with macrophage organelle digestion. The objective of this study was to determine if particulate HA could dissolve at the pH levels found in macrophage organelles. Characterized HA particles were placed into buffered solutions corresponding to phagosomal organelle pH levels: cytoplasmic (pH 7), phagosomal (pH 6), and lysosomal (pH 5). Flasks were under continuous agitation in a shaker chamber at 37 degrees C. Calcium and phosphate ions were measured beyond the maximum life span of an activated macrophage. The data showed that calcium ions rose within the first 24 h and then remained constant throughout the experiment for all pH groups. Phosphate ion concentration showed a similar pattern at the lysosomal pH but remained undetected at the other organelle pH levels. The saturation point was highest at the lysosomal pH level and lowest at the cytoplasmic pH level. The results of this experiment leave the potential for HA particles to dissolve following macrophage digestion. However, caution must be exercised when interpreting the macrophage organelle digestion hypothesis; the size of the HA particle, the length of time required to completely dissolve the particle, and potential cellular toxicity all are factors that have yet to be determined before this hypothesis can be validated.

Calcium↗

PubMed1998

Technique for identification of submicron metal particulate from implants in histological specimens.

Metal implants are being used with increasing frequency for the treatment of many diseases in the field of orthopedics, cardiology, cardiovascular surgery, and otolaryngology. Unfortunately, metals can be a source of submicron particles, which may have adverse effects on tissues. This article describes a technique that uses backscattered electron imaging and energy dispersive X-ray microanalysis, which have the capacity to perform both quantitative and qualitative analysis. The particles can be characterized by size, shape, amount, and composition. Although this technique can be used near the implant interface, it is particularly helpful in tissues a great distance from the implant site with a low concentration of metal debris. In addition, the sensitivity and specificity of this technique can be adjusted to the investigator's needs.

Electron Probe Microanalysis↗

PubMed1998

Errors in quantitative backscattered electron analysis of bone standardized by energy-dispersive x-ray spectrometry.

Backscattered electron (BSE) imaging has proven to be a useful method for analyzing the mineral distribution in microscopic regions of bone. However, an accepted method of standardization has not been developed, limiting the utility of BSE imaging for truly quantitative analysis. Previous work has suggested that BSE images can be standardized by energy-dispersive x-ray spectrometry (EDX). Unfortunately, EDX-standardized BSE images tend to underestimate the mineral content of bone when compared with traditional ash measurements. The goal of this study is to investigate the nature of the deficit between EDX-standardized BSE images and ash measurements. A series of analytical standards, ashed bone specimens, and unembedded bone specimens were investigated to determine the source of the deficit previously reported. The primary source of error was found to be inaccurate ZAF corrections to account for the organic phase of the bone matrix. Conductive coatings, methylmethacrylate embedding media, and minor elemental constituents in bone mineral introduced negligible errors. It is suggested that the errors would remain constant and an empirical correction could be used to account for the deficit. However, extensive preliminary testing of the analysis equipment is essential.

Animals↗

PubMed1998

Porous-coated metal-backed patellar components in total knee replacement. A postmortem retrieval analysis.

The use of porous-coated metal-backed patellar components to achieve consistent fixation by bone ingrowth and to provide relief of pain warrants serious scrutiny. We conducted a quantitative postmortem investigation of eleven consecutively retrieved components with use of high-resolution contact radiographs, electron microscopy, and histological analysis. The implants had been in situ for a mean (and standard deviation) of 45+/-36 months (range, one to eighty-four months). Analysis of the high-resolution contact radiographs revealed that a mean of 86+/-12 per cent (range, 61 to 100 per cent) of the porous coating was in contact with the host bone. Backscattered electron imaging showed that the mean volume fraction of bone ingrowth was 13+/-9 per cent (range, 0 to 30 per cent). No significant difference was detected, with the numbers available, between the volume fraction of the bone ingrowth measured in the porous coating and that of the host cancellous bone in the patellae.

Aged↗

PubMed1997

Biomechanical implications of mineral content and microstructural variations in cortical bone of horse, elk, and sheep calcanei.

BACKGROUND: Artiodactyl and perissodactyl calcanei have been recently introduced as models for examining bone for mechanically mediated adaptation. We have reported substantial regional variations in cortical bone microstructure and mineral content within the same cross-section of mule deer calcanei. In part, these variations may be adaptations accommodating the customary presence of predominantly tension, compression, and shear strain modes in mutually exclusive cortical locations. Calcanei from skeletally mature horses, elk, and sheep were examined in order to corroborate these previous findings. METHODS: From each species, one calcaneus was obtained from each of 13 animals. Each bone was cut transversely near mid-shaft into two segments and examined for mineral (ash) content. From each species, an additional segment obtained from each of 7 of the original 13 bones was examined for microstructure using 50x backscattered electron images. Regions examined included the compression (cranial), tension (caudal), and medial and lateral (shear) cortices. Periosteal (P), middle (M), and endosteal (E) regions were also examined separately within the compression and tension cortices. Quantified microstructural parameters included: (1) secondary osteon population density (OPD), (2) fractional area of secondary bone (FASB), (3) porosity, (4) population density of new remodeling events (NRE = resorption spaces and newly forming secondary osteons), and (5) secondary osteon diameter and minimum-to-maximum chord ratio. RESULTS: Results in each species showed variations that are considered to be mechanically important and are similar to those reported in mule deer calcanei. Mineral content data suggest that remodeling activity in the compression, medial, and lateral cortices was occurring at a slower rate than remodeling in the tension cortex. In comparison to the tension cortices, the compression cortices have approximately 6.0% higher mineral content (P < 0.007) and 35% higher OPD (P < 0.01). Additionally, the compression cortices have more nearly perfectly round osteons and lower FASB, porosity, NRE, and osteon diameter (P < 0.05; except for FASB in horse where P = 0.087 and NRE in sheep where P = 0.520). However, patterns of microstructural variations between intracortical regions (P, M, E) are inconsistent when compared to data reported in mule deer calcanei. Microstructural characteristics between the medial and lateral cortices were similar although some significant differences were identified. In general, the microstructure of the medial and lateral cortices differ from the neighboring compression and tension cortices. CONCLUSIONS: Differences in mineral content and microstructure between opposing compression and tension cortices of these three species resemble differences previously reported in mule deer calcanei. The majority of the microstructural variations can be explained in the context of strain-magnitude-based rules of Frost's Mechanostat Theory of mechanically induced bone adaptation. These variations may also be strongly influenced by the strain mode predominating in each cortical location. The hypothesis that intracortical material adaptations are correlated with progressive transcortical strain magnitude variations is not supported by the inconsistent transcortical variations in material organization. These interpretations do not preclude the possibility that other specific strain features may contribute to a complex adaptive signal.

Animals↗

PubMed1997

Postmortem analysis of consecutively retrieved asymmetric porous-coated tibial components.

The objective of this investigation was to conduct a postmortem analysis of 8 porous-coated asymmetric tibial components to measure the extent of radiolucencies and bone ingrowth. With the use of radiographic, electron microscope, and histologic analysis techniques, a quantitative postmortem study of 8 consecutively retrieved porous-coated tibial components was conducted. Time in situ averaged 47+/-36 months. The components were secured with 4 pegs and 2 screws. Autograft bone chips were applied to the resected tibia during implantation. Contact radiographs of an average of 8 3-mm sections from each implant revealed that 73%+/-17% of the porous coating had no apparent radiolucencies present between the host bone and porous coating for the series. Backscattered electron imaging showed that the bone ingrowth averaged 6%+/-2%. Histologic analysis was unable to demonstrate any adverse cellular response. The analysis suggested that this asymmetric implant design is stable and biocompatible and has potential for long-term clinical durability.

Aged↗

PubMed1997

Reproducibility of techniques using Archimedes' principle in measuring cancellous bone volume.

Researchers have been interested in developing techniques to accurately and reproducibly measure the volume fraction of cancellous bone. Historically bone researchers have used Archimedes' principle with water to measure the volume fraction of cancellous bone. Preliminary results in our lab suggested that the calibrated water technique did not provide reproducible results. Because of this difficulty, it was decided to compare the conventional water method to a water with surfactant and a helium method using a micropycnometer. The water/surfactant and the helium methods were attempts to improve the fluid penetration into the small voids present in the cancellous bone structure. In order to compare the reproducibility of the new methods with the conventional water method, 16 cancellous bone specimens were obtained from femoral condyles of human and greyhound dog femora. The volume fraction measurements on each specimen were repeated three times with all three techniques. The results showed that the helium displacement method was more than an order of magnitudes more reproducible than the two other water methods (p < 0.05). Statistical analysis also showed that the conventional water method produced the lowest reproducibility (p < 0.05). The data from this study indicate that the helium displacement technique is a very useful, rapid and reproducible tool for quantitatively characterizing anisotropic porous tissue structures such as cancellous bone.

Animals↗

PubMed1997

Determining mineral content variations in bone using backscattered electron imaging.

The mechanical properties of bones are greatly influenced by the ratio of organic constituents to mineral. Determination of bone mineral content on a macroscopic scale is straightforward, but microscopic variations, which can yield new insights into remodelling activities, mechanical strength, and integrity, are profoundly more difficult to measure. Measurement of microscopic mineral content variations in bone material has traditionally been performed using microradiography. Backscattered electron (BSE) imaging is a technique with significantly better resolution than microradiography with demonstrated consistency, and it does not suffer from projection-effect errors. We report results demonstrating the applicability of quantitative BSE imaging as a tool for measuring microscopic mineral content variations in bones representing a broad range of mineralization. Bones from ten species were analyzed with Fourier-transformed infrared spectroscopy, X-ray diffraction, energy dispersive X-ray spectrometry, ash measurements, and BSE imaging. BSE image intensity (graylevel) had a very strong positive correlation to mineral (ash) content. Compositional and crystallographic variations among bones had negligible influence on backscattered electron graylevels. The present study confirms the use of BSE imaging as a tool to measure the microscopic mineral variability in a broad range of mineralized tissues.

Animals↗