Advances in osteoporosis imaging

Using Anisotropic 3D Minkowski Functionals for Trabecular Bone Characterization and Biomechanical Strength Prediction in Proximal Femur Specimens

The ability of Anisotropic Minkowski Functionals (AMFs) to capture local anisotropy while evaluating topological properties of the underlying gray-level structures has been previously demonstrated. We evaluate the ability of this approach to characterize local structure properties of trabecular bone micro-architecture in ex vivo proximal femur specimens, as visualized on multi-detector CT, for purposes of biomechanical bone strength prediction. To this end, volumetric AMFs were computed locally for each voxel of volumes of interest (VOI) extracted from the femoral head of 146 specimens. The local anisotropy captured by such AMFs was quantified using a fractional anisotropy measure; the magnitude and direction of anisotropy at every pixel was stored in histograms that served as a feature vectors that characterized the VOIs. A linear multi-regression analysis algorithm was used to predict the failure load (FL) from the feature sets; the predicted FL was compared to the true FL determined through biomechanical testing. The prediction performance was measured by the root mean square error (RMSE) for each feature set. The best prediction performance was obtained from the fractional anisotropy histogram of AMF Euler Characteristic (RMSE = 1.01 ± 0.13), which was significantly better than MDCT-derived mean BMD (RMSE = 1.12 ± 0.16, p<0.05). We conclude that such anisotropic Minkowski Functionals can capture valuable information regarding regional trabecular bone quality and contribute to improved bone strength prediction, which is important for improving the clinical assessment of osteoporotic fracture risk.

Bone mineral density values derived from routine lumbar spine multidetector row CT predict osteoporotic vertebral fractures and screw loosening

BACKGROUND AND PURPOSE

Established methods of assessing bone mineral density are associated with additional radiation exposure to the patient. In this study, we aimed to validate a method of assessing bone mineral density in routine multidetector row CT of the lumbar spine.

MATERIALS AND METHODS

In 38 patients, bone mineral density was assessed in quantitative CT as a standard of reference and in sagittal reformations derived from standard multidetector row CT studies without IV contrast. MDCT-to-quantitative CT conversion equations were calculated and then applied to baseline multidetector row scans of another 62 patients. After a mean follow-up of 15 ± 6 months, patients were re-assessed for incidental fractures and screw loosening after spondylodesis (n = 49).

RESULTS

We observed conversion equations bone mineral densityMDCT = 0.78 × Hounsfield unitMDCTmg/mL (correlation with bone mineral densityquantitative CT, R(2) = 0.92, P < .001) for 120 kV(peak) tube voltage and bone mineral densityMDCT = 0.86 × Hounsfield unitMDCTmg/mL (R(2) = 0.81, P < .001) for 140 kVp, respectively. Seven patients (11.3%) had existing osteoporotic vertebral fractures at baseline, while 8 patients (12.9%) showed incidental osteoporotic vertebral fractures. Screw loosening was detected in 28 patients (57.1% of patients with spondylodesis). Patients with existing vertebral fractures showed significantly lower bone mineral densityMDCT than patients without fractures (P < .01). At follow-up, patients with incidental fractures and screw loosening after spondylodesis, respectively, showed significantly lower baseline bone mineral densityMDCT (P < .001 each).

CONCLUSIONS

This longitudinal study demonstrated that converted bone mineral density values derived from routine lumbar spine multidetector row CT adequately differentiated patients with and without osteoporotic fractures and could predict incidental fractures and screw loosening after spondylodesis.

Predicting the Biomechanical Strength of Proximal Femur Specimens with Minkowski Functionals and Support Vector Regression

Regional trabecular bone quality estimation for purposes of femoral bone strength prediction is important for improving the clinical assessment of osteoporotic fracture risk. In this study, we explore the ability of 3D Minkowski Functionals derived from multi-detector computed tomography (MDCT) images of proximal femur specimens in predicting their corresponding biomechanical strength. MDCT scans were acquired for 50 proximal femur specimens harvested from human cadavers. An automated volume of interest (VOI)-fitting algorithm was used to define a consistent volume in the femoral head of each specimen. In these VOIs, the trabecular bone micro-architecture was characterized by statistical moments of its BMD distribution and by topological features derived from Minkowski Functionals. A linear multi-regression analysis and a support vector regression (SVR) algorithm with a linear kernel were used to predict the failure load (FL) from the feature sets; the predicted FL was compared to the true FL determined through biomechanical testing. The prediction performance was measured by the root mean square error (RMSE) for each feature set. The best prediction result was obtained from the Minkowski Functional surface used in combination with SVR, which had the lowest prediction error (RMSE = 0.939 ± 0.345) and which was significantly lower than mean BMD (RMSE = 1.075 ± 0.279, p<0.005). Our results indicate that the biomechanical strength prediction can be significantly improved in proximal femur specimens with Minkowski Functionals extracted from on MDCT images used in conjunction with support vector regression.

Trabecular bone structure parameters from 3D image processing of clinical multi-slice and cone-beam computed tomography data

OBJECTIVE

Bone strength depends on both mineral content and bone structure. The aim of this in vitro study was to develop a method of quantitatively assessing trabecular bone structure by applying three-dimensional image processing to data acquired with multi-slice and cone-beam computed tomography using micro-computed tomography as a reference.

MATERIALS AND METHODS

Fifteen bone samples from the radius were examined. After segmentation, quantitative measures of bone volume, trabecular thickness, trabecular separation, trabecular number, trabecular nodes, and trabecular termini were obtained.

RESULTS

The clinical machines overestimated bone volume and trabecular thickness and underestimated trabecular nodes and number, but cone-beam CT to a lesser extent. Parameters obtained from cone beam CT were strongly correlated with μCT, with correlation coefficients between 0.93 and 0.98 for all parameters except trabecular termini.

CONCLUSIONS

The high correlation between cone-beam CT and micro-CT suggest the possibility of quantifying and monitoring changes of trabecular bone microarchitecture in vivo using cone beam CT.

Trabecular bone structure analysis of the spine using clinical MDCT: can it predict vertebral bone strength?

Recent technical improvements have made it possible to determine trabecular bone structure parameters of the spine using clinical multi-detector computed tomography (MDCT). Therefore, the purpose of this study was to analyze trabecular bone structure parameters obtained from clinical MDCT in relation to high resolution peripheral quantitative computed tomography (HR-pQCT) as a standard of reference and to investigate whether clinical MDCT can predict vertebral bone strength. Fourteen functional spinal segment units between T7 and L3 were harvested from 14 formalin-fixed human cadavers (11 women and 3 men; age 84 ± 10 years). All functional spinal segment units were examined using HR-pQCT (isotropic voxel size of 41 μm(3)) and a clinical whole-body MDCT (interpolated voxel size of 146 × 146 × 300 μm(3)). Trabecular bone structure analyses (histomorphometric and texture measures) were performed in the HR-pQCT as well as MDCT images. Vertebral failure load (FL) of the functional spinal segment units was determined in an uniaxial biomechanical test. The HR-pQCT and MDCT derived trabecular bone structure parameters showed correlations ranging from r = 0.60 to r = 0.90 (p < 0.05). Correlations between trabecular bone structure parameters and FL amounted up to r = 0.86 (p < 0.05) using the HR-pQCT images, and up to r = 0.79 (p < 0.05) using the MDCT images. Correlation coefficients of FL versus trabecular bone structure parameters obtained with HR-pQCT and MDCT were not significantly different (p > 0.05). In this cadaver model, the spatial resolution of clinically available whole-body MDCT scanners was suitable for trabecular bone structure analysis of the spine and to predict vertebral bone strength.

Prediction of bone strength by μCT and MDCT-based finite-element-models: how much spatial resolution is needed?

OBJECTIVES

Finite-element-models (FEM) are a promising technology to predict bone strength and fracture risk. Usually, the highest spatial resolution technically available is used, but this requires excessive computation time and memory in numerical simulations of large volumes. Thus, FEM were compared at decreasing resolutions with respect to local strain distribution and prediction of failure load to (1) validate MDCT-based FEM and to (2) optimize spatial resolution to save computation time.

MATERIALS AND METHODS

20 cylindrical trabecular bone specimens (diameter 12 mm, length 15-20mm) were harvested from elderly formalin-fixed human thoracic spines. All specimens were examined by micro-CT (isotropic resolution 30 μm) and whole-body multi-row-detector computed tomography (MDCT, 250 μm × 250 μm × 500 μm). The resolution of all datasets was lowered in eight steps to ~ 2,000 μm × 2000 μm × 500 μm and FEM were calculated at all resolutions. Failure load was determined by biomechanical testing. Probability density functions of local micro-strains were compared in all datasets and correlations between FEM-based and biomechanically measured failure loads were determined.

RESULTS

The distribution of local micro-strains was similar for micro-CT and MDCT at comparable resolutions and showed a shift toward higher average values with decreasing resolution, corresponding to the increasing apparent trabecular thickness. Small micro-strains (εeff<0.005) could be calculated down to 250 μm × 250 μm × 500 μm. Biomechanically determined failure load showed significant correlations with all FEM, up to r=0.85 and did not significantly change with lower resolution but decreased with high thresholds, due to loss of trabecular connectivity.

CONCLUSION

When choosing connectivity-preserving thresholds, both micro-CT- and MDCT-based finite-element-models well predicted failure load and still accurately revealed the distribution of local micro-strains in spatial resolutions, available in vivo (250 μm × 250 μm × 500 μm), that thus seemed to be the optimal compromise between high accuracy and low computation time.

Cylinders or walls? A new computational model to estimate the MR transverse relaxation rate dependence on trabecular bone architecture

OBJECTIVE

Bone density is distributed in a complex network of interconnecting trabecular plates and rods that are interspersed with bone marrow. A computational model to assess the dependence of the relaxation rate on the geometry of bone can consider the distribution of bone material in the form of two components: cylinders and open walls (walls with gaps). We investigate whether the experimentally known dependence of the transverse relaxation rate on the trabecular bone structure can be usefully interpreted in terms of these two components.

MATERIALS AND METHODS

We established a computer model based on an elementary computational cell. The model includes a variable number of open walls and infinitely long cylinders as well as multiple geometric parameters. The transverse relaxation rate is computed as a function of these parameters. Within the model, increasing the trabecular spacing with a fixed trabecular radius is equivalent to thinning the trabeculae while maintaining constant spacing.

RESULTS

Increasing the number of cylinder and wall gap elements beyond their nearest neighbors does not change the transverse relaxation rate. Although the absolute contribution to the relaxation due to open walls is on average more important than that due to cylinders, the latter drops off rapidly. The change on transverse relaxation rate is larger for changing cylinder geometry than for changing wall geometry, as it can be seen from the effect on the relaxation rate when trabecular spacing is varied, compared to varying the size of wall gaps.

CONCLUSION

Our results provide strong evidence that trabecular thinning, which is associated with increasing age, decreases the relaxation rates. The effect of thinning plates and rods on the transverse relaxation can be understood in terms of simple cylinders and open walls. A reduction in the relaxation rate can be seen as an indication of thinning cylinders, corresponding to reduced bone stability and ultimately, osteoporosis.

In vitro ceramic scaffold mineralization: comparison between histological and micro-computed tomographical analysis

The porous structure of beta-tricalcium phosphate (β-TCP) scaffolds was assessed by conventional histomorphometry and micro-computed tomography (micro-CT) to evaluate the substitutability of time-consuming histomorphometry by rapid micro-CT. Extracellular matrix mineralization on human mesenchymal stem cell seeded β-TCP scaffolds was scanned by means of micro-CT after 6 weeks in cultivation and evaluated morphometrically. For the histomorphometric analysis, undecalcified sections were prepared in the mediosagittal plane of the cylindrical tissue-engineered constructs. The sections were scanned at a nominal resolution of 8 μm and stained with von Kossa and Toluidine Blue. Pores were analyzed with both methods for morphometrical parameters such as horizontal/vertical diameter and pore/mineralized tissue area. Results showed highly significant correlations between histomorphometry and micro-CT for pore horizontal length (r = 0.95), pore vertical length (r = 0.96), pore area (r = 0.97), and mineralized tissue area (r = 0.82). Mean percentage differences between histomorphometry and micro-CT measurements ranged from 1.4% (pore vertical diameter) to 14.0% (area of mineralized tissue). With its high image precision, micro-CT qualifies as an additional tool for endpoint evaluation measurements of mineralized tissue development within tissue-engineered constructs also in ceramic scaffolds.

Bone marrow fat composition as a novel imaging biomarker in postmenopausal women with prevalent fragility fractures

The goal of this magnetic resonance (MR) imaging study was to quantify vertebral bone marrow fat content and composition in diabetic and nondiabetic postmenopausal women with fragility fractures and to compare them with nonfracture controls with and without type 2 diabetes mellitus. Sixty-nine postmenopausal women (mean age 63 ± 5 years) were recruited. Thirty-six patients (47.8%) had spinal and/or peripheral fragility fractures. Seventeen fracture patients were diabetic. Thirty-three women (52.2%) were nonfracture controls. Sixteen women were diabetic nonfracture controls. To quantify vertebral bone marrow fat content and composition, patients underwent MR spectroscopy (MRS) of the lumbar spine at 3 Tesla. Bone mineral density (BMD) was determined by dual-energy X-ray absorptiometry (DXA) of the hip and lumbar spine (LS) and quantitative computed tomography (QCT) of the LS. To evaluate associations of vertebral marrow fat content and composition with spinal and/or peripheral fragility fractures and diabetes, we used linear regression models adjusted for age, race, and spine volumetric bone mineral density (vBMD) by QCT. At the LS, nondiabetic and diabetic fracture patients had lower vBMD than controls and diabetics without fractures (p = 0.018; p = 0.005). However, areal bone mineral density (aBMD) by DXA did not differ between fracture and nonfracture patients. After adjustment for age, race, and spinal vBMD, the prevalence of fragility fractures was associated with -1.7% lower unsaturation levels (confidence interval [CI] -2.8% to -0.5%, p = 0.005) and +2.9% higher saturation levels (CI 0.5% to 5.3%, p = 0.017). Diabetes was associated with -1.3% (CI -2.3% to -0.2%, p = 0.018) lower unsaturation and +3.3% (CI 1.1% to 5.4%, p = 0.004) higher saturation levels. Diabetics with fractures had the lowest marrow unsaturation and highest saturation. There were no associations of marrow fat content with diabetes or fracture. Our results suggest that altered bone marrow fat composition is linked with fragility fractures and diabetes. MRS of spinal bone marrow fat may therefore serve as a novel tool for BMD-independent fracture risk assessment.

Update on the female athlete triad

Updated prevalence estimates of all 3 components of the Female Athlete Triad, a syndrome characterized by low energy availability, functional hypothalamic amenorrhea, and osteoporosis, is low (0 %-16 %), however, estimates of 1 or 2 concurrent components approach 50 %-60 % among certain athlete groups. Recent research identifies components of the Triad among female adolescent athletes, particularly those participating in leanness sports, such as endurance running. This is alarming, as adolescents require adequate nutrition and normal hormone function to optimize bone mineral gains during this critical developmental period. Current literature highlights new assessments, such as measurements of bone microarchitecture and hormone levels to better evaluate bone strength and the hormonal and metabolic profile of athletes with and at risk for the Triad. Recent data also provides support for additional potential consequences of the Triad, such as endothelial dysfunction and related cardiovascular effects, stress fractures, and musculoskeletal injuries. Additional prospective research is needed to evaluate long-term indicators and consequences of the Triad and identify effective behavioral treatment strategies.

Assessment of bone fragility with clinical imaging modalities

INTRODUCTION

Osteoporotic fractures are a vital public health concern and have created a great economic burden to our society. Therefore, early diagnosis of patients with high risk of osteoporotic fractures is essential. The current gold standard for assessment of fracture risk is the measurement of bone mineral density using dual-energy X-ray absorptiometry. However, such techniques are not very effective in the diagnosis of patients with osteopaenia. Doctors are usually unable to make an informed decision regarding the treatment plan of these patients. In addition to bone mineral density, advanced imaging modalities have been explored in recent years to assess bone quality in other contributing factors, such as microarchitecture of trabecular bone, mineralisation, microdamage and bone remodelling rates. Currently, the microarchitecture of trabecular bone can be evaluated in vivo by high-resolution peripheral quantitative computed tomography techniques, which have a resolution of 80 µm. However, such imaging techniques still remain a high-end research tool rather than a diagnostic tool for clinical applications. Thus, the limited accessibility and affordability of high-resolution peripheral quantitative computed tomography have become major concerns for the general public. Alternatively, combining bone mineral density measurements with stochastic assessments of spatial bone mineral density distribution from dual-energy X-ray absorptiometry images may offer an economic and efficient approach to non-invasively evaluate skeletal integrity and identify the at-risk population for osteoporotic fractures. The aim of this critical review is to assess bone fragility with clinical imaging modalities.

CONCLUSION

High-resolution quantitative computed tomography imaging technique may provide direct measurements of microarchitectures of trabecular bone in vivo. However, it is an expensive method of imaging modality.

Advances in bone imaging for osteoporosis

The diagnosis and management of osteoporosis have been improved by the development of new quantitative methods of skeletal assessment and by the availability of an increasing number of therapeutic options, respectively. A number of imaging methods exist and all have advantages and disadvantages. Dual-energy X-ray absorptiometry (DXA) is the most widely available and commonly utilized method for clinical diagnosis of osteoporosis and will remain so for the foreseeable future. The WHO 10-year fracture risk assessment tool (FRAX(®)) will improve clinical use of DXA and the cost-effectiveness of therapeutic intervention. Improved reporting of radiographic features that suggest osteoporosis and the presence of vertebral fracture, which are powerful predictors of future fractures, could increase the frequency of appropriate DXA referrals. Quantitative CT remains predominantly a research tool, but has advantages over DXA--allowing measurement of volumetric density, separate measures of cortical and trabecular bone density, and evaluation of bone shape and size. High resolution imaging, using both CT and MRI, has been introduced to measure trabecular and cortical bone microstructure. Although these methods provide detailed insights into the effects of disease and therapies on bone, they are technically challenging and not widely available, so they are unlikely to be used in clinical practice.

Bone texture analysis is correlated with three-dimensional microarchitecture and mechanical properties of trabecular bone in osteoporotic femurs

Fracture of the proximal femur is a major public health problem in elderly persons. It has recently been suggested that combining texture analysis and bone mineral density measurement improves the failure load prediction in human femurs. In this study, we aimed to compare bone texture analysis with three-dimensional (3D) microarchitecture and mechanical properties of trabecular bone in osteoporotic femurs. Eight femoral heads from osteoporotic patients who fractured their femoral neck provided 31 bone cores. Bone samples were studied using a new high-resolution digital X-ray device (BMA™, D3A Medical Systems) allowing for texture analysis with fractal parameter H (mean), and were examined using micro-computed tomography (microCT) for 3D microarchitecture. Finally, uniaxial compression tests to failure were performed to estimate failure load and apparent modulus of bone samples. The fractal parameter H (mean) was strongly correlated with bone volume fraction (BV/TV) (r = 0.84) and trabecular thickness (Tb.Th) (r = 0.91) (p < 0.01). H (mean) was also markedly correlated with failure load (r = 0.84) and apparent modulus (r = 0.71) of core samples (p < 0.01). Bone volume fraction (BV/TV) and trabecular thickness (Tb.Th) demonstrated significant correlations with failure load (r = 0.85 and 0.72, respectively) and apparent modulus (r = 0.72 and 0.64, respectively) (p < 0.01). Overall, the best predictors of failure load were H (mean), bone volume fraction, and trabecular thickness, with r (2) coefficients of 0.83, 0.76, and 0.80 respectively. This study shows that the fractal parameter H (mean) is correlated with 3D microCT parameters and mechanical properties of femoral head bone samples, which suggests that radiographic texture analysis is a suitable approach for trabecular bone microarchitecture assessment in osteoporotic femurs.

Reproducibility of trabecular bone structure measurements of the distal radius at 1.5 and 3.0 T magnetic resonance imaging

The purpose of this study was to assess and compare the reproducibility of trabecular bone structure measurements of the distal radius at 1.5 and 3.0 T magnetic resonance imaging (MRI). Root mean square reproducibility errors ranged from 0.69% to 4.94% at 1.5 T MRI and from 0.38% to 5.80% at 3.0 T MRI. Thus, reproducibility errors of trabecular bone structure measurements are overall in an acceptable range and similar at 1.5 and 3.0 T MRI.

Quality assurance of imaging techniques used in the clinical management of osteoporosis

Recent advances in the densitometric and imaging techniques involved in the management of osteoporosis are associated with increasing accuracy and precision as well as with higher exposure to ionising radiation. Therefore, special attention to quality assurance (QA) procedures is needed in this field. The development of effective and efficient QA programmes is mandatory to guarantee optimal image quality while reducing radiation exposure levels to the ALARA principle (as low as reasonably achievable). In this review article, the basic QA procedures are discussed for the techniques applied to everyday clinical practice.

Understanding the burden of osteoporosis and use of the World Health Organization FRAX

Fracture prevention is a critical component of managing osteoporosis, which is not longer defined by T-score alone. The internationally validated World Health Organization Fracture Risk Assessment Tool (FRAX) provides the clinician a state-of-the-art tool for predicting patients at greatest risk for fracture. The FRAX tool takes into account country, bone mineral density of the hip (when available), age, sex, and 8 clinical risk factors to calculate the 10-year probability of a major osteoporotic fracture and the 10-year probability of a hip fracture. From this tool, an absolute fracture risk is generated, aiding clinicians in determining which patients with low bone mass and osteoporosis to treat.

Estimation of an early meaningful time point of bone parameter changes in application to an osteoporotic rat model with in vivo microcomputed tomography measurements

The commonly used preclinical animal model of postmenopausal osteoporosis is the mature ovariectomized rat, whereby cessation of ovarian oestrogen production consequently results in bone volume reduction. The study aim was to precisely define the time course of structural changes resulting from ovariectomy and thereby reduce the time animals have to be treated to judge the effects of osteoporosis treatment. For this purpose, we assessed architectural changes by microcomputed tomography ( μCT) during 10 weeks following ovariectomy or sham surgery at two-week intervals. Moreover, the trabecular microarchitecture of the lumbar vertebrae was assessed after necropsy. Besides this, serum biomarkers of bone turnover were determined. These data were in a new approach additionally correlated to femur mRNA expression profiles. We selected the osteoblast marker genes osteocalcin and type I collagen as well as the two osteoclast marker genes cathepsin k and tartrate-resistant acid phosphatase 5. The gene expression analysis suggested an activation of osteoblasts as well as octeoclasts. The significantly induced serum levels of osteocalcin and collagen degradation fragments also revealed this higher rate of bone turnover. Our results indicate that as soon as four weeks after ovariectomy the bone volume fraction exhibited a decline of 30% and 50% of the connectivity density. In addition, significant decreases of trabecular number and thickness as well as of the bone volume fraction were only observed in vertebrae of ovariectomized animals. Interestingly, changes of trabecular morphology were also found in the sham animals as a consequence of senescence.

Measurement of subregional vertebral bone mineral density in vitro using lateral projection dual-energy X-ray absorptiometry: validation with peripheral quantitative computed tomography

Although a strong relationship exists between areal bone mineral density (aBMD) derived from dual-energy X-ray absorptiometry (DXA) and bone strength, the predictive validity of aBMD for osteoporotic vertebral fractures remains suboptimal. The diagnostic sensitivity of DXA may be improved by assessing aBMD within vertebral subregions, rather than relying on an estimate derived from the total area of the vertebra. The objective of this study was to validate a method of measuring subregional vertebral aBMD in vitro using lateral-projection DXA against subregional volumetric BMD (vBMD) measured with peripheral quantitative computed tomography (pQCT). A mixed set of 49 lumbar and thoracic vertebrae from 25 donors were scanned using lateral-projection DXA and pQCT. aBMD and apparent vBMD were measured in 7 vertebral regions (1 total area and 6 subregions) from the lateral DXA scan. vBMD was calculated in anatomically equivalent regions from pQCT scan data, using a customised software program designed to increase efficiency of the analysis process. Significant differences in densitometric parameters between subregions were observed by DXA and pQCT (P < 0.01). Subregional vBMD derived from pQCT was explained by a significant proportion of the variance in DXA-derived aBMD (R (2) = 0.51-0.67, P < 0.05) and apparent vBMD (R (2) = 0.64-0.75, P < 0.05). These results confirm the validity of measuring aBMD in vertebral subregions using lateral-projection DXA. The clinical significance should now be explored.

Dual energy X-ray absorptimetry: fundamentals, methodology, and clinical applications

Dual-energy X-ray absorptiometry (DXA; DEXA) is the technique of choice to diagnose osteoporosis and to monitor the response to treatment. It is also useful for measuring body composition. In recent years, new applications have been developed, including vertebral morphometry through the study of the lateral spine, prosthesis integration in orthopedics, and lipodystrophy in HIV+ patients, although its use in these cases is not well established. DXA densitometry is accurate and precise. It is essential to optimize each step of the diagnostic process, taking care to ensure the best acquisition, image analysis, and interpretation of the results. Thus, to obtain the greatest utility from DXA, radiologists need to know the technique, its indications, and its pitfalls. This article reviews the fundamentals, modalities, methods, and clinical applications of DXA.

Combination of texture analysis and bone mineral density improves the prediction of fracture load in human femurs

Twenty-one excised femurs were studied using (1) a high-resolution digital X-ray device to estimate three textural parameters, (2) dual-energy X-ray absorptiometry (DXA) to measure bone mineral density (BMD), and (3) mechanical tests to failure. Textural parameters significantly correlated with BMD (p < 0.05) and bone strength (p < 0.05). Combining texture parameters and BMD significantly improved the fracture load prediction from adjusted r(2) = 0.74 to adjusted r(2) =0.82 (p < 0.05).

INTRODUCTION

The purpose of this study is to determine if the combination of bone texture parameters using a new high-resolution X-ray device and BMD measurement by DXA provided a better prediction of femoral failure load than BMD evaluation alone.

METHODS

The proximal ends of 21 excised femurs were studied using (1) a high-resolution digital X-ray device (BMA, D3A Medical Systems) to estimate three textural parameters: fractal parameter Hmean, co-occurrence, and run-length matrices, (2) DXA to measure BMD, and (3) mechanical tests to failure in a side-impact configuration. Regions of interest in the femoral neck, intertrochanteric region, and greater trochanter were selected for DXA and bone texture analysis. Every specimen was scanned twice with repositioning before mechanical testing to assess reproducibility using intraclass correlation coefficient (ICC) with 95% confidence interval. The prediction of femoral failure load was evaluated using multiple regression analysis.

RESULTS

Thirteen femoral neck and 8 intertrochanteric fractures were observed with a mean failure load of 2,612 N (SD, 1,382 N). Fractal parameter Hmean, co-occurrence, and run-length matrices each significantly correlated with site-matched BMD (p < 0.05) and bone strength (p < 0.05). The ICC of the textural parameters varied between 0.65 and 0.90. Combining bone texture parameters and BMD significantly improved the fracture load prediction from adjusted r(2) =0.74 to adjusted r(2) = 0.82 (p < 0.05).

CONCLUSION

In these excised femurs, the combination of bone texture parameters with BMD demonstrated a better performance in the failure load prediction than that of BMD alone.

Validated finite element models of the proximal femur using two-dimensional projected geometry and bone density

Two-dimensional finite element models of cadaveric femoral stiffness were developed to study their suitability as surrogates of bone stiffness and strength, using two-dimensional representations of femoral geometry and bone mineral density distributions. If successfully validated, such methods could be clinically applied to estimate patient bone stiffness and strength using simpler and less costly radiographs. Two-dimensional femur images were derived by projection of quantitative computed tomography scans of 22 human cadaveric femurs. The same femurs were fractured in a fall on the hip configuration. Femoral stiffness and fracture load were measured, and high speed video was recorded. Digital image correlation analysis was used to calculate the strain distribution from the high speed video recordings. Two-dimensional projection images were segmented and meshed with second-order triangular elements for finite element analysis. Elastic moduli of the finite elements were calculated based on the projected mineral density values inside the elements. The mapping of projection density values to elastic modulus was obtained using optimal parameter identification in a set of nine of the 22 specimens, and validated on the remaining 13 specimens. Finite element calculated proximal stiffness and strength correlated much better with experimental data than areal bone mineral density alone. In addition, finite element calculated strain distributions compared very well with strains obtained from digital image processing of the high speed video recordings, further validating the two-dimensional projected subject-specific finite element models.

A preliminary dual-energy X-ray absorptiometry-based finite element model for assessing osteoporotic hip fracture risk

To more accurately assess osteoporotic hip fracture risk in a specific patient, a dual-energy X-ray absorptiometry (DXA)-based finite element model was constructed from the patient’s femur DXA image. The outermost contour of the femur bone segmented from the DXA image was used to generate a finite element mesh. Bone mechanical properties, such as Young’s modulus, are correlated with areal bone mineral density (BMD) captured in the DXA image. A quasi-static loading condition representing a sideway fall was applied to the finite element model. Three fracture risk indices were introduced and expressed as ratios of internal forces caused by impact forces occurring in sideway fall to bone ultimate cross-section strength at the three critical locations, i.e. the femoral neck, the intertrochanteric region, and the subtrochanteric region. The proposed finite element modelling procedure was validated against six representative clinical cases extracted from the Manitoba BMD database, where initial and follow-up DXA images have been taken to monitor longitudinal variation of areal BMD in individual patients. It was found from the clinical validation that variations in the proposed fracture risk indices have the same trends as those indicated by the conventional areal BMD and T-score. In addition, by the three proposed fracture risk indices it is possible to further identify the specific fracture location. It was also found that for the same subject, the variations in the three fracture risk indices have quite different magnitudes, with intertrochanteric region the largest and subtrochanteric region the smallest, which is probably owing to the different content of trabecular and cortical bones in the three regions. With further development, it is promising that the proposed DXA-based finite element model will be a useful tool for accurate assessment of osteoporosis development and for treatment monitoring.

The combination of structural parameters and areal bone mineral density improves relation to proximal femur strength: an in vitro study with high-resolution peripheral quantitative computed tomography

The aim of this study was to assess structural indices from high-resolution peripheral quantitative computed tomography (HR-pQCT) images of the human proximal femur along with areal bone mineral density (aBMD) and compare the relationship of these parameters to bone strength in vitro. Thirty-one human proximal femur specimens (8 men and 23 women, median age 74 years, range 50-89) were examined with HR-pQCT at four regions of interest (femoral head, neck, major and minor trochanter) with 82 μm and in a subgroup (n = 17) with 41 μm resolution. Separate analyses of cortical and trabecular geometry, volumetric BMD (vBMD), and microarchitectural parameters were obtained. In addition, aBMD by dual-energy X-ray absorptiometry (DXA) was performed at conventional hip regions and maximal compressive strength (MCS) was determined in a side-impact biomechanical test. Twelve cervical and 19 trochanteric fractures were confirmed. Geometry, vBMD, microarchitecture, and aBMD correlated significantly with MCS, with Spearman's correlation coefficients up to 0.77, 0.89, 0.90, and 0.85 (P < 0.001), respectively. No differences in these correlations were found using 41 μm compared to 82 μm resolution. In multiple regression analysis of MCS, a combined model (age- and sex-adjusted) with aBMD and structural parameters significantly increased R (2) values (up to 0.90) compared to a model holding aBMD alone (R (2) up to 0.78) (P < 0.05). Structural parameters and aBMD are equally related to MCS, and both cortical and trabecular structural parameters obtained from HR-pQCT images hold information on bone strength complementary to that of aBMD.

MRI texture analysis of femoral neck: Detection of exercise load-associated differences in trabecular bone

PURPOSE

To assess the ability of co-occurrence matrix-based texture parameters to detect exercise load-associated differences in MRI texture at the femoral neck cross-section.

MATERIALS AND METHODS

A total of 91 top-level female athletes representing five differently loading sports and 20 referents participated in this cross-sectional study. Axial T1-weighted FLASH and T2*-weighted MEDIC sequence images of the proximal femur were obtained with a 1.5T MRI. The femoral neck trabecular bone at the level of the insertion of articular capsule was divided manually into regions of interest representing four anatomical sectors (anterior, posterior, superior, and inferior). Selected co-occurrence matrix-based texture parameters were used to evaluate differences in apparent trabecular structure between the exercise loading groups and anatomical sectors of the femoral neck.

RESULTS

Significant differences in the trabecular bone texture, particularly at the superior femoral neck, were observed between athletes representing odd-impact (soccer and squash) and high-magnitude exercise loading (power-lifting) groups and the nonathletic reference group.

CONCLUSION

MRI texture analysis provides a quantitative method for detecting and classifying apparent structural differences in trabecular bone that are associated with specific exercise loading.

Gender aspects of osteoporosis and bone strength

Although postmenopausal and elderly women are more frequently affected by osteoporosis, men are not protected from the disease. Age-related osteoporosis involves several gender-specific clinical aspects such as disease onset time and different dynamics of bone loss. Men benefit from larger bones and a time-delay of age-related changes in bone density and quality. Moreover, secondary osteoporosis is more common in males than in females. High-resolution peripheral quantitative computed tomography (HR-pQCT) and high-resolution magnetic resonance imaging (HR-MRI) represent novel research tools for a noninvasive quantification of bone microstructure which is of interest for musculoskeletal gender studies. For optimal design of such studies, researchers should be aware of technical pitfalls and site-specificity of bone microstructure.

A fully automated trabecular bone structural analysis tool based on T2* -weighted magnetic resonance imaging

One major source affecting the precision of bone structure analysis in quantitative magnetic resonance imaging (qMRI) is inter- and intraoperator variability, inherent in delineating and tracing regions of interest along longitudinal studies. In this paper an automated analysis tool, featuring bone marrow segmentation, region of interest generation, and characterization of cancellous bone of articular joints is presented. In evaluation studies conducted at the knee joint the novel analysis tool significantly decreased the standard error of measurement and improved the sensitivity in detecting minor structural changes. It further eliminated the need of time-consuming user interaction, and thereby increasing reproducibility.

Transplantation of mesenchymal stem cells from young donors delays aging in mice

Increasing evidence suggests that the loss of functional stem cells may be important in the aging process. Our experiments were originally aimed at testing the idea that, in the specific case of age-related osteoporosis, declining function of osteogenic precursor cells might be at least partially responsible. To test this, aging female mice were transplanted with mesenchymal stem cells from aged or young male donors. We find that transplantation of young mesenchymal stem cells significantly slows the loss of bone density and, surprisingly, prolongs the life span of old mice. These observations lend further support to the idea that age-related diminution of stem cell number or function may play a critical role in age-related loss of bone density in aging animals and may be one determinant of overall longevity.

Methods for assessing bone quality: a review

BACKGROUND

Bone mass, geometry, and tissue material properties contribute to bone structural integrity. Thus, bone strength arises from both bone quantity and quality. Bone quality encompasses the geometric and material factors that contribute to fracture resistance.

QUESTIONS/PURPOSES

This review presents an overview of the methods for assessing bone quality across multiple length scales, their outcomes, and their relative advantages and disadvantages.

METHODS

A PubMed search was conducted to identify methods related to bone mechanical testing, imaging, and compositional analysis. Using various exclusion criteria, articles were selected for inclusion.

RESULTS

Methods for assessing mechanical properties include whole-bone, bulk tissue, microbeam, and micro- and nanoindentation testing techniques. Outcomes include structural strength and material modulus. Advantages include direct assessment of bone strength; disadvantages include specimen destruction during testing. Methods for characterizing bone geometry and microarchitecture include quantitative CT, high-resolution peripheral quantitative CT, high-resolution MRI, and micro-CT. Outcomes include three-dimensional whole-bone geometry, trabecular morphology, and tissue mineral density. The primary advantage is the ability to image noninvasively; disadvantages include the lack of a direct measure of bone strength. Methods for measuring tissue composition include scanning electron microscopy, vibrational spectroscopy, nuclear magnetic resonance imaging, and chemical and physical analytical techniques. Outcomes include mineral density and crystallinity, elemental composition, and collagen crosslink composition. Advantages include the detailed material characterization; disadvantages include the need for a biopsy.

CONCLUSIONS

Although no single method can completely characterize bone quality, current noninvasive imaging techniques can be combined with ex vivo mechanical and compositional techniques to provide a comprehensive understanding of bone quality.

Qualitative and quantitative evaluation of bony structures based on DICOM dataset

PURPOSE

The aim of this study was to investigate bone mass using different cone-beam computed tomographies (CBCTs) combined with image analysis and to determine whether bone quantity or quality was detected.

MATERIALS AND METHODS

Different measurements recorded on mandible bones of pigs in the retromolar region were evaluated on ProMax 3D (Planmeca Oy, Finland) and the ILUMA™CT (IMTEC™ Imaging, Ardmore, OK) to calculate a calibration curve. The spatial relationships of pig mandible halves relative to adjacent defined anatomical structures were assessed by means of 3D visualization software. In addition to the screenshot, their bone quality was evaluated in accordance with the Lenkholm and Zarb classification.

RESULTS

The CBCT calibration curves based on the measurements taken from the ProMax and ILUMA CT showed linear correlation. Huge Hounsfield units intervals were found between the 2 CBCTs and there was no correlation with the computed tomography. Exact information on the micromorphology of the bone cylinders was not available. A subjective correlation according to Lenkholm and Zarb showed overlapping in all groups.

CONCLUSIONS

CBCT is a good choice for analyzing bone mass. However, it does not provide any information on bone quality. To obtain information on the microarchitecture of the spongiosa, it is necessary to use a computed tomography with finite element analysis.

High resolution 3D imaging of ex-vivo biological samples by micro CT

Non-destructive volume visualization can be achieved only by tomographic techniques, of which the most efficient is the x-ray micro computerized tomography (μCT).

High resolution μCT is a very versatile yet accurate (1-2 microns of resolution) technique for 3D examination of ex-vivo biological samples^{1, 2}. As opposed to electron tomography, the μCT allows the examination of up to 4 cm thick samples. This technique requires only few hours of measurement as compared to weeks in histology. In addition, μCT does not rely on 2D stereologic models, thus it may complement and in some cases can even replace histological methods^{3, 4}, which are both time consuming and destructive. Sample conditioning and positioning in μCT is straightforward and does not require high vacuum or low temperatures, which may adversely affect the structure. The sample is positioned and rotated 180° or 360°between a microfocused x-ray source and a detector, which includes a scintillator and an accurate CCD camera, For each angle a 2D image is taken, and then the entire volume is reconstructed using one of the different available algorithms^5-7. The 3D resolution increases with the decrease of the rotation step. The present video protocol shows the main steps in preparation, immobilization and positioning of the sample followed by imaging at high resolution.

Advanced imaging assessment of bone fragility in glucocorticoid-induced osteoporosis

Advanced bone imaging techniques provide structural information, beyond bone mineral density (BMD), and growing evidence indicates that BMD only partially explains bone strength and fracture resistance. Assessing glucocorticoid-induced osteoporosis (GIO) is important, especially the documentation of glucocorticoid (GC) impact on trabecular and cortical bone and on macro and microstructural features. Advanced methods for assessing macrostructure of bone include volumetric quantitative computed tomography (vQCT), high-resolution computed tomography (hrCT), and high-resolution magnetic resonance imaging (hrMRI). The methods for assessing bone microstructure include micro computed tomography (μCT) and micro magnetic resonance imaging (μMRI). Many advanced imaging techniques have been used in vitro and in vivo to examine structural effects of GIO in animals and in humans, and these applications are explored in this review. In human in vitro studies, investigators have used standard bone histomorphometry and μCT to compare trabecular microarchitecture and bone remodeling in postmenopausal women and in males with GIO, and have found that high-dose GC produces dramatic bone loss, accompanied by major reduction in trabecular connectivity and increases in trabecular perforations. In animal studies, investigators have used standard histomorphometry along with pQCT, vQCT, hrMRI or μCT to examine GIO in a variety of animal models including rats, minipigs and sheep. They generally have found excellent relationships between treatment-induced structural changes assessed by these advanced imaging techniques and changes in BMD and biomechanical properties. They also have examined various therapeutic interventions in animals and monitored their efficacy using quantitative imaging methods. In human in vivo studies, investigators have serially examined postmenopausal women and males with GIO in order to assess the extent of skeletal deterioration and to determine the best advanced measures of BMD and structure, with which to monitor disease activity and therapeutic response, and to predict fracture risk. They generally have found that bone density and structural measures obtained by pQCT, vQCT and hrMRI contributed substantially to understanding the skeletal effects of glucocorticoids and to predicting the risk of fracture in human GIO. These animal and human applications, illustrating advanced imaging in GIO, are still in early stages of development. However, as discussed in this review, the novelty and power of the imaging approaches are compelling, and their utility is promising.

Performance of μMRI-Based virtual bone biopsy for structural and mechanical analysis at the distal tibia at 7T field strength

PURPOSE

To assess the performance of a 3D fast spin echo (FSE) pulse sequence utilizing out-of-slab cancellation through phase alternation and micro-magnetic resonance imaging (μMRI)-based virtual bone biopsy processing methods to probe the serial reproducibility and sensitivity of structural and mechanical parameters of the distal tibia at 7.0T.

MATERIALS AND METHODS

The distal tibia of five healthy subjects was imaged at three timepoints with a 3D FSE sequence at 137 × 137 × 410 μm(3) voxel size. Follow-up images were retrospectively 3D registered to baseline images. Coefficients of variation (CV) and intraclass correlation coefficients (ICCs) for measures of scale and topology of the whole tibial trabecular bone (TB) cross-section as well as finite-element-derived Young's and shear moduli of central cuboidal TB subvolumes (8 × 8 × 5 mm(3) ) were evaluated as measures of reproducibility and reliability. Four additional cubic TB subregions (anterior, medial, lateral, and posterior) of similar dimensions were extracted and analyzed to determine associations between whole cross-section and subregional structural parameters.

RESULTS

The mean signal-to-noise ratio (SNR) over the 15 image acquisitions was 27.5 ± 2.1. Retrospective registration yielded an average common analysis volume of 67% across the three exams per subject. Reproducibility (mean CV = 3.6%; range, 1.5%-5%) and reliability (ICCs, 0.95-0.99) of all parameters permitted parameter-based discrimination of the five subjects in spite of the narrow age range (26-36 years) covered. Parameters characterizing topology were better able to distinguish two individuals who demonstrated similar values for scalar measurements (≈ 34% difference, P < 0.001). Whole-section axial stiffness encompassing the cortex was superior at distinguishing two individuals relative to its central subregional TB counterpart (≈ 8% difference; P < 0.05). Interregion comparisons showed that although all parameters were correlated (mean R(2) = 0.78; range 0.57-0.99), the strongest associations observed were those for the erosion index (mean R(2) = 0.95, P ≤ 0.01).

CONCLUSION

The reproducibility and structural and mechanical parameter-based discriminative ability achieved in five healthy subjects suggests that 7T-derived μMRI of TB can be applied towards serial patient studies of osteoporosis and may enable earlier detection of disease or treatment-based effects.

The osseous endplates in lumbar vertebrae: thickness, bone mineral density and their associations with age and disk degeneration

INTRODUCTION

As the gateway of nutrient supply, the vertebral endplate is essential to maintain the integrity and function of the avascular intervertebral disk. While a link between calcium deposition in the endplate and disk degeneration is well established from histological studies, findings on the association between endplate thickness and age and disk degeneration are conflicting. Moreover, the association between endplate bone mineral density (BMD) and disk degeneration remains unexplored in humans.

OBJECTIVES

To determine the thickness and BMD of lumbar spine osseous endplates in men and explore their associations with age and disk degeneration.

METHODS

From a spine archive, 150 cadaveric lumbar vertebrae (L1-L5) from 48 male human spines (mean age 50 years, range 21-64) were scanned using micro-CT (μCT). The osseous endplates were extracted from the vertebral body to measure the mean thickness and volumetric BMD. The difference between cranial and caudal endplates, associations of endplate thickness and BMD with age and discographic degeneration pathology were examined.

RESULTS

Overall, the mean thickness was 1.03±0.24 mm for cranial (to disk) endplates and 0.78±0.16 mm for caudal endplates. For lumbar intervertebral disks, the cranial endplate was significantly thicker and denser than the caudal endplate (p<0.001-0.05). Thickness and BMD of endplates were independent of age. Based on discography, a trend of more severe disk degeneration associated with greater thickness in both the cranial and caudal endplates was observed, and was most marked in severely degenerated disks (p<0.05). However, no evidence was detected for a link between more severe disk degeneration and elevated endplate BMD (p>0.05).

CONCLUSIONS

In the lumbar spine, both the thickness and BMD of endplates were independent of age, which ranged from 21 to 64 years. The endplates cranial to intervertebral disks were thicker and had higher BMD than the corresponding caudal endplates. Judged from discography, more degeneration in the adjacent intervertebral disk was associated with greater endplate thickness, but not higher endplate BMD. Thus, endplate sclerosis, reflecting elevated endplate BMD, may not be a risk factor for disk pathology in men.

Tibial tunnel aperture irregularity after drilling with 5 reamer designs: a qualitative micro-computed tomography analysis

BACKGROUND

There is limited information in the literature on comparisons of antegrade versus retrograde reaming techniques and the effect on the creation of anterior cruciate ligament (ACL) tibial tunnel entry and exit apertures.

HYPOTHESIS

Proximal and distal apertures of ACL tibial tunnels, as created with different reamers, will be affected by type of reamer design.

STUDY DESIGN

Controlled laboratory study.

METHODS

Forty skeletally mature porcine tibias with bone mineral density values comparable with a young athletic population were included in this study. Five 9-mm reamer models were used (3 antegrade: A1, smooth-bore reamer; A2, acorn-head reamer; A3, flat-head reamer; 2 retrograde: R1, retrograde acorn reamer; R2, single-blade retrograde reamer), and a new reamer was used for each tibia (8 reamer-tibia pairs per reamer model). All specimens underwent micro-computed tomography scanning, and images were reconstructed and analyzed using 3-dimensional image analysis software. Aperture rim fractures were graded on a 0-IV scale that described the proportion of the fractured aperture circumference. Specimens with incomplete apertures were also recorded. Because of the unique characteristics of various tunnels, intratunnel characteristics were observed and recorded.

RESULTS

In sum, 1 proximal and 7 distal aperture rim fractures were found; 3, 0, and 4 distal aperture rim fractures were found with groups A1, A2, and A3, respectively. Incomplete apertures were more commonly found at the distal aperture (n = 15) than the proximal aperture (n = 8); there were no tibias with this finding at both apertures. All incomplete distal apertures occurred with the retrograde technique, and all incomplete proximal apertures occurred with the antegrade technique, most commonly with reamer design A3. An added finding of tunnel curvature at the distal aspect of the tunnel was observed in all 8 tibias with R1 reamers and 5 tibias with R2 reamers. This phenomenon was not observed in any of the tibias reamed with the antegrade technique.

CONCLUSION

Anterior cruciate ligament tibial tunnel aperture characteristics were highly dependent on reamer design. Optimal proximal aperture characteristics were produced by the retrograde reamers, whereas optimal distal aperture characteristics were obtained with the antegrade reamers. In addition, a phenomenon of tunnel curvature in retrograde-type reamers was found, which may have effects on ACL graft or screw fixation.

CLINICAL RELEVANCE

Differences in tunnel aperture shapes and fractures depend on reamer design. This information is important for the creation of ACL reconstruction tunnels with different reamer designs.

The neuroendocrine basis of anorexia nervosa and its impact on bone metabolism

Anorexia nervosa (AN) is a condition of profound undernutrition associated with alterations in various neuroendocrine axes, many of which contribute to a marked impairment in bone accrual and low bone mineral density. This review focuses on changes in the hypothalamo-pituitary-gonadal axis, the growth hormone insulin-like growth factor-1 axis, and the hypothalamo-pituitary-adrenal axis in AN, as well as alterations in various appetite-regulating hormones. In addition, the review discusses low bone mineral density and altered bone microarchitecture in AN, the pathophysiology underlying impaired bone metabolism, and possible therapeutic strategies to optimize bone health.

Morphometric analysis - Cone beam computed tomography to predict bone quality and quantity

AIM

Modified quantitative computed tomography is a method used to predict bone quality and quantify the bone mass of the jaw. The aim of this study was to determine whether bone quantity or quality was detected by cone beam computed tomography (CBCT) combined with image analysis. MATERIALS AND PROCEDURES: Different measurements recorded on two phantoms (Siemens phantom, Comac phantom) were evaluated on images taken with the Somatom VolumeZoom (Siemens Medical Solutions, Erlangen, Germany) and the NewTom 9000 (NIM s.r.l., Verona, Italy) in order to calculate a calibration curve. The spatial relationships of six sample cylinders and the repositioning from four pig skull halves relative to adjacent defined anatomical structures were assessed by means of three-dimensional visualization software.

RESULTS

The calibration curves for computer tomography (CT) and cone beam computer tomography (CBCT) using the Siemens phantom showed linear correlation in both modalities between the Hounsfield Units (HU) and bone morphology. A correction factor for CBCT was calculated. Exact information about the micromorphology of the bone cylinders was only available using of micro computer tomography.

CONCLUSION

Cone-beam computer tomography is a suitable choice for analysing bone mass, but, it does not give any information about bone quality.

A comparison of conventional maximum intensity projection with a new depth-specific topographic mapping technique in the CT analysis of proximal tibial subchondral bone density

OBJECTIVE

The objective was to identify subchondral bone density differences between normal and osteoarthritic (OA) proximal tibiae using computed tomography osteoabsorptiometry (CT-OAM) and computed tomography topographic mapping of subchondral density (CT-TOMASD).

MATERIALS AND METHODS

Sixteen intact cadaver knees from ten donors (8 male:2 female; mean age:77.8, SD:7.4 years) were categorized as normal (n = 10) or OA (n = 6) based upon CT reconstructions. CT-OAM assessed maximum subchondral bone mineral density (BMD). CT-TOMASD assessed average subchondral BMD across three layers (0-2.5, 2.5-5 and 5-10 mm) measured in relation to depth from the subchondral surface. Regional analyses of CT-OAM and CT-TOMASD included: medial BMD, lateral BMD, and average BMD of a 10-mm diameter area that searched each medial and lateral plateau for the highest "focal" density present within each knee.

RESULTS

Compared with normal knees, both CT-OAM and CT-TOMASD demonstrated an average of 17% greater whole medial compartment density in OA knees (p < 0.016). CT-OAM did not distinguish focal density differences between OA and normal knees (p > 0.05). CT-TOMASD focal region analyses revealed an average of 24% greater density in the 0- to 2.5-mm layer (p = 0.003) and 36% greater density in the 2.5- to 5-mm layer (p = 0.034) in OA knees.

CONCLUSIONS

Both CT-OAM and TOMASD identified higher medial compartment density in OA tibiae compared with normal tibiae. In addition, CT-TOMASD indicated greater focal density differences between normal and OA knees with increased depth from the subchondral surface. Depth-specific density analyses may help identify and quantify small changes in subchondral BMD associated with OA disease onset and progression.

A Study of Mechanical Properties of Human Femoral Heads Using Nanoindentation

Human bone fracture associated with osteoporosis was hypothesized to be related to the alteration of mechanical properties in bones. In this work, cortical and trabecular bones from human femoral heads were studied. Bone samples of eight female and four male patients, with ages varying from 37 to 93 years, were collected from total hip replacement surgery. Reduced modulus (Er) and hardness (H) of osteons, interstitial lamellae and trabeculae were characterized by nanoindentation. The results showed both the reduced modulus and hardness of the interstitial lamellae were significant higher than those of osteons and trabeculae. Though there was no significant difference in microstructures in the Group A (age < 60 years) and B (age > 60 years), the Group B bones demonstrated to be stiffer.

Superparamagnetic bifunctional bisphosphonates nanoparticles: a potential MRI contrast agent for osteoporosis therapy and diagnostic

A bone targeting nanosystem is reported here which combined magnetic contrast agent for Magnetic Resonance Imaging (MRI) and a therapeutic agent (bisphosphonates) into one drug delivery system. This new targeting nanoplatform consists of superparamagnetic γFe(2)O(3) nanoparticles conjugated to 1,5-dihydroxy-1,5,5-tris-phosphono-pentyl-phosphonic acid (di-HMBPs) molecules with a bisphosphonate function at the outer of the nanoparticle surface for bone targeting. The as-synthesized nanoparticles were evaluated as a specific MRI contrast agent by adsorption study onto hydroxyapatite and MRI measurment. The strong adsorption of the bisphosphonates nanoparticles to hydroxyapatite and their use as MRI T2(∗) contrast agent were demonstrated. Cellular tests performed on human osteosarcoma cells (MG63) show that γFe(2)O(3)@di-HMBP hybrid nanomaterial has no citoxity effect in cell viability and may act as a diagnostic and therapeutic system.