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Biomedical subjects

P Augat

Publications and source records attributed to P Augat.

At least 37 records · Page 2Linked to original sources
PubMed2000

Prediction of bone strength of distal forearm using radius bone mineral density and phalangeal speed of sound.

This investigation compares quantitative ultrasound (QUS) measurement of the phalanges with peripheral quantitative computed tomography (pQCT) and dual X-ray absorptiometry (DXA) measurement of the forearm, to estimate the strength of the distal radius in 13 cadaveric forearms. The cadavers were scanned at the distal radius by pQCT and DXA for bone mineral density (BMD) and at the approximate phalanges by QUS for speed of sound (SOS). The distal radii were subjected to a simulated Colles fracture produced with a materials testing machine. The load at which the distal radius was fractured was considered as a representation of bone strength. The bone strength correlated significantly with SOS at different phalanges (r = 0.63-0.72), BMD at different regions of interest by DXA (r = 0.67-0.75), and cortical BMD at different sites by pQCT (r = 0.61-0.67). Standard stepwise regression analysis showed that adding phalangeal SOS into forearm densitometric variables significantly enhanced the statistical power for prediction of the strength of the distal radius. Our results suggest that, for assessment of site-specific distal forearm strength, QUS measurement of the phalanges is comparable to forearm densitometry. Phalangeal QUS may add clinical value if distal forearm strength has a high priority.

Aged↗
PubMed2000

In vivo assessment of trabecular bone structure using fractal analysis of distal radius radiographs.

Our purpose in this study was (i) to measure trabecular bone structure using fractal analysis of distal radius radiographs in subjects with and without osteoporotic hip fractures, and (ii) to compare these measures with bone mineral density (BMD) as well as with measures of trabecular bone structure derived from high resolution magnetic resonance (MR) images. Distal radius radiographs were obtained using semi-industrial films (55 kVp, 400 mAs) in 30 postmenopausal patients, who had suffered osteoporotic hip fractures (74.8+/-8.2 years) in the last 24 months and 27 postmenopausal age-matched (74.6+/-6.6 yr) normal volunteers. Radiographs were digitized at 50 microm. A Fourier power spectrum-based fractal dimension (FD) characterizing the trabecular pattern was measured in a region of interest proximal to the joint line. The fractal dimension was calculated over two spatial frequency (f) ranges: FD1 was calculated over 0.5<log(f)<l.0, FD2 over the higher range 1.0<log(f)<1.5. Trabecular BMD in the radius was obtained using peripheral quantitative computed tomography (pQCT) (Stratec GmbH, Germany). In addition BMD of the proximal femur was determined using dual x-ray absorptiometry (DXA) (QDR 2000, Hologic, MA). In a subset of patients (16 controls and 18 with hip fractures), high resolution MR imaging of the distal radius (spatial resolution of 156 x 156 x 500 microm) was used to obtain measures analogous to bone histomorphometry. There were significant differences (p<0.05) between the fracture and nonfracture groups in the total femur BMD (13%), trabecular BMD in the distal radius (4%), and the fractal dimension in the radiographs (FD2) (3%). The correlations between FD2 and the total femur BMD as well as trabecular bone BMD in the distal radius were -0.48 (p<0.006) and -0.22 (p<0.33); respectively; FD1 increased with BMD and showed lower correlations. FD2 showed good correlations with App. Tb.N (-0.71) and App. Tb.Sp (0.69) (p<0.01), moderate correlation with App BV/TV (-0.53) (p<0.05), and no significant correlation with App. Tb.Th. The correlations between structural measures and FD1 showed the inverse trend and were typically lower. The odds ratios for a hip fracture were 2.44 for total femur BMD, 1.5 for trabecular BMD (radius), and 1.5 for FD2, respectively. In summary, the fractal measures derived from radiographs of the radius show differences between subjects with and without hip fractures, the predictive power of measures in the distal radius are comparable to radial trabecular BMD but lower than that of total hip BMD.

Aged↗
PubMed1999

Trabecular bone architecture in the distal radius using magnetic resonance imaging in subjects with fractures of the proximal femur. Magnetic Resonance Science Center and Osteoporosis and Arthritis Research Group.

To determine whether magnetic resonance (MR)-derived measures of trabecular bone architecture in the distal radius are predictive for prevalent hip fractures, 20 subjects with hip fractures and 19 age-matched postmenopausal controls were studied. Bone mineral density (BMD) measures at the hip (dual-energy X-ray absorptiometry, DXA) and the distal radius (peripheral quantitative computed tomography, pQCT) were also obtained. We compared the MR-based structural measures derived in the radius with those in the calcaneus of the same patients. In the radius, images were acquired at an in-plane resolution of 156 microm and a slice thickness of 0.5 mm. Stereologic measures such as the apparent trabecular thickness (app. Tb.Th), fractional trabecular bone volume (app. BV/TV), trabecular spacing (app. Tb.Sp) and trabecular number (app. Tb.N) were derived from the images. Measures of app. Tb.Sp and app. Tb.N in the distal radius showed significant (p<0.05) differences between the two groups, as did hip BMD measures. However, radial trabecular BMD measures showed only a marginal difference (p = 0.05). Receiver operating curve analysis was used to determine the diagnostic efficacy of BMD, structural measures and a combination of the two. The area under the curve (AUC) for total hip BMD was 0.73, and for radial trabecular BMD was 0.69. AUC for most of the measures of trabecular bone structure at the distal radius was lower than for hip BMD measures; however, AUC for app. Tb.N at the radius was 0.69, comparable to trabecular BMD using pQCT. The AUC for combined BMD (hip) and structure measures was higher (0.87) when radius and calcaneus structure was included. Measures of trabecular architecture derived from MR images combined with BMD measures improve the discrimination between subjects with hip fractures and normal age-matched controls.

Aged↗
PubMed1999

Ultrasound velocity of trabecular cubes reflects mainly bone density and elasticity.

Studies have indicated that quantitative ultrasound (QUS) variables may be influenced by the mechanical properties of bone which in turn are determined by bone's material and structural properties. However, from these studies it is unclear what role density, elasticity, and structure play in determining velocity. Eighteen defatted, 12-mm cubic trabecular bone specimens were cut from cadaveric specimens. Amplitude-dependent speed of sound (SOS) using a single point QUS system was assessed in three orthogonal axes. Magnetic resonance images were obtained, from which measures of apparent trabeuclar structure were derived. The specimens were nondestructively tested in compression along three orthogonal axes defined by the sides of the cubes. The elastic modulus (in the three directions) and the strength (in one direction) were determined. Trabecular BMD was measured by quantitative computed tomography. SOS varied significantly with direction of measurement, with the highest value in the axial direction (axial:1715 m/s, sagittal: 1662 m/second, and coronal: 1676 m/s). SOS of each of the three axes was generally associated with the various mechanical (r = 0.30-0.87), density (r = 0.81-0.93), and bone structural variables (0.3-0.8). However, after adjusting the SOS correlations by density, only the correlation with elasticity remained significant in the coronal direction. BMD alone explained 88-93% of variance in SOS whereas in the multivariate model, BMD plus elasticity and/or anisotropic variables explained 96-98% of the variance in SOS. Variability of SOS is explained mostly by density and to a small extent by elasticity or anisotropy. Since only 2-6% of the variance of the QUS measurement is not explained by density and elasticity, one could conclude that the remaining variance reflects other properties of bone or perhaps simply measurement error. Evidence that these other properties may be structure related is only found in the anisotropy of QUS parameter.

Adult↗
PubMed1999

Predictive value of bone mineral density and Singh index for the in vitro mechanical properties of cancellous bone in the femoral head.

OBJECTIVE: The purpose of this study was to assess the validity of two methodically different radiological parameters, bone mineral density and Singh Index, for the prediction of mechanical properties in femoral cancellous bone. DESIGN: Coherence between in vitro evaluation of mechanical properties and bone mineral density on a femoral bone slice, combined with clinical determination of Singh Index on ordinary X-rays. BACKGROUND: It is accepted that bone densitometry yields excellent prediction of mechanical bone quality, but is considered to be an expensive and not widely available method for routine diagnostics in clinical practice. In contrast, determination of Singh Index is an inexpensive and simple technique, but its predictive value for bone mechanics is still controversially discussed. METHODS: We used cortically confined bone slices from 33 femoral heads. Bone mineral density was measured using quantitative computed tomography. Strength and elastic modulus were assessed by mechanical testing in up to 39 circular positions on each slice. Singh Index was evaluated on ordinary X-rays of the hip by two independent readers. RESULTS: Bone mineral density showed strong correlations with strength (r=0.86) and good correlations with elastic modulus (r=0.68). Singh Index correlated well with strength (r=0.70), but only moderately with elastic modulus (r=0.52). CONCLUSIONS: The strong validity of bone mineral density in predicting mechanical bone quality was confirmed. Singh Index assessment permits a rough estimation of mechanical strength in particular and can therefore be used for first estimations of mechanical bone quality, provided that readings were performed by experienced clinicians. RELEVANCE: Reduced mechanical bone quality induces an increase in fracture risk. Whenever performed, bone mineral density measurement allows an excellent evaluation of the mechanical properties of cancellous bone in the hip and can be recommended for screening evaluations. The assessment of Singh Index on ordinary X-rays of the hip is an inexpensive and simple method, and allows a rough estimation of the mechanical quality of the femur. However, due to its subjective character, its predictive value for the mechanical quality of bone in individual patients remains uncertain.

Aged↗
PubMed1999

Fractal analysis of radiographs: assessment of trabecular bone structure and prediction of elastic modulus and strength.

The purpose of this study was to determine whether fractal dimension of radiographs provide measures of trabecular bone structure which correlate with bone mineral density (BMD) and bone biomechanics, and whether these relationships depend on the technique used to calculate the fractal dimension. Eighty seven cubic specimen of human trabecular bone were obtained from the vertebrae and femur. The cubes were radiographed along all three orientations--superior-inferior (SI), medial-lateral (ML), and anterior-posterior (AP), digitized, corrected for background variations, and fractal based techniques were applied to quantify trabecular structure. Three different techniques namely, semivariance, surface area, and power spectral methods were used. The specimens were tested in compression along three orientations and the Young's modulus (YM) was determined. Compressive strength was measured along the SI direction. Quantitative computed tomography was used to measure trabecular BMD. High-resolution magnetic-resonance images were used to obtain three-dimensional measures of trabecular architecture such as the apparent bone volume fraction, trabecular thickness, spacing, and number. The measures of trabecular structure computed in the different directions showed significant differences (p<0.05). The correlation between BMD, YM, strength, and the fractal dimension were direction and technique dependent. The trends of variation of the fractal dimension with BMD and biomechanical properties also depended on the technique and the range of resolutions over which the data was analyzed. The fractal dimension showed varying trends with bone mineral density changes, and these trends also depended on the range of frequencies over which the fractal dimension was measured. For example, using the power spectral method the fractal dimension increased with BMD when computed over a lower range of spatial frequencies and decreased for higher ranges. However, for the surface area technique the fractal dimension increased with increasing BMD. Fractal measures showed better correlation with trabecular spacing and number, compared to trabecular thickness. In a multivariate regression model inclusion of some of the fractal measures in addition to BMD improved the prediction of strength and elastic modulus. Thus, fractal based texture analysis of radiographs are technique dependent, but may be used to quantify trabecular structure and have a potentially valuable impact in the study of osteoporosis.

Biomechanical Phenomena↗
PubMed1998

Local tissue properties in bone healing: influence of size and stability of the osteotomy gap.

To characterize the site-specific mechanical and histological properties in fracture repair and to relate these properties to the initial mechanical situation, an experimental fracture model was used in the metatarsus of 42 sheep. The mechanical situation of a transverse osteotomy was described by three gap sizes (1, 2, or 6 mm) and two amounts of strain (7 or 31%). An external fixator that allowed a defined axial movement provided control of these settings. Nine weeks following surgery, the healing area was dissected and tensile and compressive properties were measured in subregions of the fracture gap and the periosteal callus. The central, sagittal section was used for quantitative histology. We found the quality of the tissue along the osteotomy line to be most important for regaining mechanical stability. Increasing the size of osteotomy gaps resulted in poorer mechanical and histological qualities, and the repair process was less complete. Interfragmentary strain did not significantly influence the repair process. The smaller strain levels had already stimulated the secondary repair process, and this stimulatory effect could not be further enhanced by increasing the amount of strain. Our finding that large gaps between bone segments were not as well healed as were smaller gaps suggests that it is advantageous to avoid large gaps in fracture treatment.

Animals↗
PubMed1998

Distal radius fractures: mechanisms of injury and strength prediction by bone mineral assessment.

The strength of the radius depends on the mechanical properties of cancellous and cortical bone. By assessing both compartments quantitatively with bone densitometry, we tried to identify the specificity of each in predicting the load at which the distal radius will fracture. Twenty human cadaver forearms were scanned for bone mineral and geometric properties with quantitative computed tomography and dual x-ray absorptiometry. In both a neutral loading situation and one in which the wrist was extended 45 degrees, the load distribution was determined with pressure-sensitive films, and a fracture simulating a fall on the hand was produced with a material testing machine. Fractures that occur with the wrist in extension were produced by a central impact of the scaphoid onto the radiocarpal joint, and those that occur under neutral loading conditions were produced by a more commonly distributed loading pattern. The load at fracture was most specifically predicted (r2=0.74) by bone mineral and geometric measures of the cortex at the shaft of the radius. Bone mineral density measures of trabecular (r2=0.64) and total (r2=0.66) bone were less successful in predicting the fracture load. After adjustment for bone size, the geometric and density measures revealed similar specificity. Cortical bone, therefore, contributes significantly to the strength of the distal radius and may play an important role in the prediction of osteoporotic wrist fractures.

Absorptiometry, Photon↗
PubMed1998

Quantitative bone mineral assessment at the forearm: a review.

Bone mineral density and geometric properties of the human forearm can be measured to determine the amount of bone or bone loss at the scanning site and to predict the risk of forearm fractures. These forearm measurements are also used to estimate bone mass at remote anatomical locations and thereby estimate the risk for spine, hip and other fractures. The peripheral location of the human forearm, with its relatively small amount of surrounding soft tissue, improves the accuracy and the precision of bone mass measurement and has made this site an early choice for the assessment of a subject's bone mineral status. Furthermore, the anatomy of the human radius enables the examination of both cortical and cancellous bone. This review describes the procedures for non-invasive bone assessment at peripheral sites including some of the more recently developed systems dedicated to assessment of the distal radius. The accuracy, precision and normative values they provide are presented. Responses to different forms of therapies as well as the ability to discriminate or predict osteoporotic fractures are also assessed. Low radiation dose, comfortable and fast handling, moderate cost, and a strong association with the risk of non-spine fractures, promote the use of forearm scanning as a widely applied screening procedure for the detection of generalised osteoporotic bone loss. However, a higher accuracy of fracture risk prediction at the spine or at the hip can be achieved by a direct bone density measurement at these sites. The monitoring of treatment at the distal forearm appears to require a longer follow-up time due to its decreased responsiveness compared with such highly trabecular load-bearing sites as the spine and the proximal femur.

Absorptiometry, Photon↗
PubMed1998

Image-based assessment of spinal trabecular bone structure from high-resolution CT images.

The goal of this study was to assess whether a high-resolution CT measure of trabecular bone structure can enhance the discrimination between subjects with or without a vertebral fracture and having overall low hip or spine bone mineral density (BMD) by dual-energy X-ray absorptiometry (DXA). Sixty-one women with low BMD by DXA (T-score < -2.5 at hip or spine) were examined. Twenty women had sustained a vertebral fracture. Quantitative CT (QCT) BMD and high-resolution CT spinal scans were performed on a whole-body CT scanner. For the high-resolution images (0.31 mm pixel, 1.5 mm thick slice), trabecular bone was segmented from marrow using an adaptive threshold, region growth and skeletonization step. From the processed image we measured the apparent trabecular bone fraction (BV/TV), apparent trabecular thickness (I.Th) and apparent trabecular spacing (I.Sp). We also assessed the connectivity of the marrow space using region growing to derive a mean (HA) and maximum (HM) hole size. Despite the fact that the study population was preselected to have a low BMD by DXA, QCT BMD was highly associated with (p < 0.005) with fracture status. All structural parameters were correlated (r approximately 0.64 to 0.79) with BMD with p < 0.003 and showed significant differences between the fracture and non-fracture group. However, except for HA, this difference did not remain significant after adjustment for BMD. When BMD and then HA was entered into a paired linear regression model to predict fracture outcome, HA contributed with p = 0.03 and BMD with p = 0.86. ROC analysis was applied and showed that HA, BMD, I.Th and I.Sp discriminated the two groups with areas of 0.76, 0.75, 0.71 and 0.68, respectively. These findings suggest that an assessment of vertebral trabecular structure from high-resolution CT images is useful in discriminating subjects with vertebral fractures and potentially useful for predicting future fractures.

Aged↗
PubMed1998

Power spectral analysis of vertebral trabecular bone structure from radiographs: orientation dependence and correlation with bone mineral density and mechanical properties.

Trabecular bone structure and bone density contribute to the strength of bone and are potentially important in the study of osteoporosis. Fourier transforms of the textural patterns in radiographs of trabecular bone have previously been used for the measurement of trabecular bone structure in subjects, however, the relationship between these measures and biomechanical properties of bone have not previously been established. In this study radiographs were acquired of 28 cubic specimens of spinal trabecular bone along each of the three anatomic axes: cranio-caudal or superior-inferior (SI), medial-lateral (ML), and anterior-posterior (AP). The radiographs were digitized, background corrected, and uniformly aligned. The Fast Fourier transform (FFT) was performed on a region comprised solely of trabecular bone for each image. The zero (DC), first (FMO), and second moments (SMO) of the Fourier power spectrum and the fractal dimension (FD) as determined from the Fourier power spectrum were correlated with stereology measures, with bone mineral density (BMD) as well as with measured biomechanical properties [Young's elastic modulus (YM) and ultimate strength] of the cubes. The results show that the power spectra-based measures, when compared with structural parameters determined using 3D stereology, show good correlations with bone volume fraction, trabecular spacing, thickness, and number. These power spectral measures showed fair to good correlations with BMD and the biomechanical properties. Moreover, the correlations between the power spectral measures of trabecular structure and the BMD, YM, and stereology measures of structure depend on the orientation of the radiographic image. Specifically, these were significant differences in the measured biomechanical properties and the power spectral measures of the trabecular structure between the SI and ML and the SI and AP directions. In addition, depending on the spatial frequency range for analysis, the fractal dimension showed opposite trends with changes in BMD and biomechanical properties. Multivariate regression models showed the correlation coefficients increasing with the inclusion of some of the power spectral measures, suggesting that FFT-based texture analysis may play a potential role in studies of osteoporosis.

Biomechanical Phenomena↗
PubMed1998

Anisotropy of the elastic modulus of trabecular bone specimens from different anatomical locations.

To associate the mechanical anisotropy of trabecular bone with the relationship between bone mineral density (BMD) and mechanical properties, 97 cubic specimens of human trabecular bone were imaged with computed tomography. Bone cubes from the spine, the calcaneus, the distal, and the proximal femur were tested multidirectionally to measure their compressive stiffness and to calculate their ratios of mechanical anisotropy. The ultimate strength was determined in a destructive test in cephalo-caudal (c-c) direction. Compressive stiffness was largest in the c-c direction for the specimens from the spine, as well as the distal and the proximal femur, but not the calcaneus. Anisotropy ratios in c-c direction were larger at the distal femur and the spine than in the proximal femur. The predictive power of BMD for the mechanical properties varied with anatomical location and strongly depended on the loading direction. While at the spine the c-c stiffness was highly correlated to BMD (r2 = 0.73), the perpendicular directions showed only modest correlations (r2 < 0.53). The correlations of mechanical properties with BMD were greatest at locations where the anisotropy was less pronounced (proximal femur) or rather uniform (spine). The data suggest that BMD can be most successfully applied to determine the mechanical properties in the principal loading direction, which from a clinical perspective may be most relevant.

Adult↗
PubMed1998

Assessment of bone mineral at appendicular sites in females with fractures of the proximal femur.

The prediction of hip fractures by measurements at remote sites or the improvement of predictive power by measurements at multiple sites could potentially increase the success of osteoporosis screening programs. In a cross-sectional study on 137 postmenopausal women, we tested the hypothesis that bone assessment at the hip, the forearm, and the tibia are independently associated with osteoporotic fractures of the hip. Bone mineral densities, geometric features, and ultrasound properties were determined with hip dual X-ray absorptiometry, forearm peripheral quantitative computed tomography (QCT), and tibia speed of sound measurement. While the odds ratios for fracture discrimination per standard deviation decrease ranged between 3 and 4 for measurements at the hip, they were only 1.8 at the forearm and 1.4 at the tibia. Measurements at the tibia or the forearm were neither independently associated with osteoporotic hip fractures (p > 0.05) nor could any combination of measurements significantly increase the power for the identification of fractures as measured with receiver operating curves. Women who sustained trochanteric fractures were characterized by a generalized loss of bone mineral. Cervical fractures were associated with a decrease of bone mineral density at the hip, but no significant alterations in bone mass or geometric properties were observed at the tibia or at the forearm. Fracture risk prediction at the hip is therefore preferably performed by measurements at the hip itself. Peripheral QCT at the distal radius and tibial ultrasound seem capable of depicting women with an increased risk for trochanteric but not for cervical fractures. The risk assessment appears not to be improved by including information of cortical or geometric properties of the forearm.

Absorptiometry, Photon↗
PubMed1998

Noninvasive assessment of bone density and structure using computed tomography and magnetic resonance.

For several reasons, including low cost and radiation dose, simplicity, and the ability to image several skeletal sites, dual X-ray absoptiometry (DXA) is the most widely employed technique for diagnostic and serial assessment of integral bone mass in osteoporosis and other metabolic bone diseases. However, three-dimensional imaging modalities such as quantitative computed tomography (QCT) and magnetic resonance (MR) imaging offer the ability to separately examine different factors that may play independent and important roles in osteoporosis. These factors include the density of the trabecular and cortical compartments as well as the pattern of trabecular microarchitecture. New developments in QCT include volumetric approaches for precise compartmental assessment of the spine and proximal femur as well as thin-slice tomography of the vertebral body for assessment of trabecular texture. In addition, ultrahigh resolution CT scanners (spatial resolution ë50-150(i)i) have been developed for imaging of trabecular structure in specimens and in some cases for the peripheral skeleton (distal radius and phalanges). High resolution MR measurements may be employed for assessment of the trabecular texture at a range of peripheral sites, including the calcaneus, distal radius, and phalanges.

Adult↗
PubMed1998

High-resolution magnetic resonance imaging: three-dimensional trabecular bone architecture and biomechanical properties.

The purpose of this study was to use high-resolution magnetic resonance (MR) imaging combined with image analysis to investigate the three-dimensional (3D) trabecular structure, anisotropy, and connectivity of human vertebral, femoral, and calcaneal specimens. The goal was to determine whether: (a) MR-derived measures depict known skeletal-site-specific differences in architecture and orientation of trabeculae; (b) 3D architectural parameters combined with bone mineral density (BMD) improve the prediction of the elastic modulus using a fabric tensor formulation; (c) MR-derived 3D architectural parameters combined with BMD improve the prediction of strength using a multiple regression model, and whether these results corresponded to the results obtained using higher resolution depictions of trabecular architecture. A total of 94 specimens (12 x 12 x 12 mm cubes) consisting of trabecular bone only were obtained, of which there were 7 from the calcaneus, 15 from distal femur, 47 from the proximal femur, and 25 from the vertebral bodies. MR images were obtained using a 1.5 Tesla MR scanner at a spatial resolution of 117 x 117 x 300 microm. Additionally, BMD was determined using quantitative computed tomography (QCT), and the specimens were nondestructively tested and the elastic modulus (YM) was measured along three orthogonal axes corresponding to the anatomic superior-inferior (axial), medial-lateral (sagittal), and anterior-posterior (coronal) directions. A subset of the specimens (n=67) was then destructively tested in the superior-inferior (axial) direction to measure the ultimate compressive strength. The MR images were segmented into bone and marrow phases and then analyzed in 3D. Ellipsoids were fitted to the mean intercept lengths, using single value decomposition and the primary orientation of the trabeculae and used to calculate the anisotropy of trabecular architecture. Stereological measures were derived using a previously developed model and measures such as mean trabecular width, spacing, and number were derived. Because the spatial resolution of MR images is comparable to trabecular bone dimensions, these measures may be subject to partial volume effects and were thus treated as apparent measures, such as BV/TV, Tb.Sp, Tb.N, and Tb.Th rather than absolute measures, as would be derived from histomorphometry. In addition, in a subset of specimens, the Euler number per unit volume was determined to characterize the connectivity of the trabecular network. There were significant differences in the BMD, trabecular architectural measures, elastic modulus, and strength at the different skeletal sites. The primary orientation axes for most of the specimens was the anatomic superior-inferior (axial) direction. Using the fabric tensor formulation, in addition to BMD, improved the prediction of YM (SI), while including some of the architectural parameters significantly improved the prediction of strength. In comparing MR-derived 3D measures with those obtained from 20 microm optical images (n=18; 9 vertebrae, 9 femur specimens), good correlations were found for the apparent Tb.Sp and Tb.N, moderate correlation was seen for the apparent BV/TV, and poor correlation was found for the apparent Tb.Th. Using these higher resolution images, the fabric tensor formulation for predicting the elastic modulus also showed improved correlation between the measured and calculated modulus in the axial (SI) direction. In summary, high-resolution MR images may be used to assess 3D architecture of trabecular bone, and the inclusion of some of the 3D architectural measures provides an improved assessment of biomechanical properties. Further studies are clearly warranted to establish the role of architecture in predicting overall bone quality, and the role of trabecular architecture measures in clinical practice. (ABSTRACT TRUNCATED)

Anatomy, Cross-Sectional↗
PubMed1998

Accuracy of cortical and trabecular bone measurements with peripheral quantitative computed tomography (pQCT).

In order to assess the accuracy of peripheral QCT (Stratec XCT 960) we analysed scans of the European Forearm Phantom and another phantom consisting of K2HPO4 encased in aluminium tubes to simulate cortical walls. Additionally 14 cadaveric forearm specimen scans were compared to CT scans acquired on a GE9800Q. The accuracy for density assessment of the European Forearm Phantom was better than 3%. A small increase in density was observed with increasing thickness of the aluminium wall (10% for each mm). Density measurements within the wall were confounded by limited spatial resolution. For a thickness of less than 4 mm, the density within the wall was underestimated by up to 40%. The measurement of mineral content was not influenced by this effect and showed an accuracy error of less than 6%. The agreement of density measurements on the different CT systems was very strong (R2 > 0.96; RMSE < 6.2%). Our findings suggest that the Stratec pQCT scanner very accurately measures volumetric trabecular and total bone mineral densities at the distal radius while the assessment of cortical density is associated with considerable inaccuracies due to limited spatial resolution.

Aluminum↗
PubMed1998

Effects of mechanical factors on the fracture healing process.

An interdisciplinary study based on animal experiments, cell culture studies, and finite element models is presented. In a sheep model, the influence of the osteotomy gap size and interfragmentary motion on the healing success was investigated. Increasing gap sizes delayed the healing process. Increasing movement stimulated callus formation but not tissue quality. Typical distributions of intramembranous bone, endochondral ossification, and connective tissue in the fracture gap are quantified. The comparison of the mechanical data determined by a finite element model with the histologic images allowed the attribution of certain mechanical conditions to the type of tissue differentiation. Intramembranous bone formation was found for strains smaller than approximately 5% and small hydrostatic pressure (< 0.15 MPa). Strains less than 15% and hydrostatic pressure more than 0.15 MPa stimulated endochondral ossification. Larger strains led to connective tissue. Cell culture studies on the influence of strain on osteoblasts supported these findings. Proliferation and transforming growth factor beta production was increased for strains up to 5% but decreased for larger strains. Osteoblasts under larger strains (> 4%) turned away from the principal strain axis and avoided larger deformations. It is hypothesized that gap size and the amount of strain and hydrostatic pressure along the calcified surface in the fracture gap are the fundamental mechanical factors involved in bone healing.

Animals↗