Apparent Bone Volume Fraction Research Articles

Investigating the subchondral trabecular bone microstructure in patients with osteonecrosis of the femoral head using multi-detector row computed tomography.

To analyse the microstructural changes of subchondral trabecular bone in patients with osteonecrosis of the femoral head (ONFH) using multi-detector row computed tomography (MDCT). We retrospectively investigated 76 hips in 50 patients diagnosed with ONFH between 2017 and 2021. Groups 1, 2, 3, and 4 comprised hips without ONFH, ONFH without femoral head collapse (FHC), ONFH with mild collapse (<2 mm), and ONFH with severe collapse (>2 mm), respectively. All patients underwent MDCT, and the subchondral trabecular bone microstructure was assessed. Regions of interests were set at the lateral boundary of the femoral head necrotic lesion and centre of the acetabular weight-bearing portion. In both the femoral head and the acetabular regions, there were significant differences in Groups 2 and 3 compared to Group 1, with increased volumetric bone mineral density and apparent bone volume fraction, and more plate-like with increased connectivity, indicating that osteosclerotic changes were occurring. In both the femoral head and the acetabular regions, osteosclerotic changes of subchondral trabecular bone microstructure were present before FHC.

MR imaging pattern of tibial subchondral bone structure: considerations of meniscal coverage and integrity

To compare regional differences in subchondral trabecular structure using high-resolution MRI in meniscus-covered/meniscus-uncovered tibia in cadaveric knees with intact/torn menisci. 3D proton density CUBE MRI of 6 cadaveric knees without significant osteoarthritis (OA) was acquired, 0.25-mm resolution. Menisci were evaluated and classified intact or torn. MR data were transferred to ImageJ program to segment tibial 3D volume of interest (VOI). Data was subdivided into meniscus-covered/meniscus-uncovered regions. Segmented VOI was classified into binary data, trabeculae/bone marrow. The trabecular bone data was used to measure MR biomarkers (apparent subchondral plate-connected bone density (adapted from spine MR), apparent trabecular bone volume fraction, apparent mean trabecular thickness, apparent connectivity density, and structure model index (SMI)). Mean value of parameters was analyzed for the effects of meniscal tear/tibial coverage. Nine torn menisci and 3 intact menisci were present. MR measures of bone varied significantly due to meniscal coverage/tear. Subchondral plate-connected bone density under covered meniscus regions increased from 10.9 to 23.5% with meniscal tear. Values increased in uncovered regions, 19.3% (intact) and 32.4% (torn). This reflects higher density when uncovered (p = 0.048) with meniscal tear (p = 0.007). Similar patterns were found for trabecular bone fraction (coverage p < 0.001, tear p = 0.047), trabecular thickness (coverage p = 0.03), connectivity density (coverage p = 0.002), and SMI (coverage p = 0.015). Quantitative trabecular bone evaluation emphasizes intrinsic structural differences between meniscus-covered/meniscus-uncovered tibias. Results offer insight into bone adaptation with meniscal tear and support the hypothesis that subchondral bone plate-connected bone density could be important in early subchondral bone adaptation.

Effect of local zoledronic acid administration in a rat model of posterolateral spinal fusion

Study designRandomized animal model study. PurposePosterolateral spinal fusion represents a common surgical procedure in the United States. The effect of bisphosphonate administration in these patients is poorly understood. The purpose of this study is to determine whether local administration of bisphosphonate by soaking bone autograft would affect the apparent bone density or structural properties of the fusion mass in a rat model of posterolateral spinal fusion. Methods36 Spring Dawley rats underwent L4-5 posterolateral spinal fusion with bone autograft. These rats were divided into three groups, two experimental groups and one control group. Each of the experimental groups underwent spinal fusion with morselized vertebral cortical and cancellous autograft soaked in zoledronic acid solution; one group 20 mcg/mL, another 200 mcg/mL. The control group underwent L4-5 spinal fusion with cancellous allograft soaked with saline. At 8 weeks, the rats were euthanized for analysis. Evaluations consisted of micro-CT scanning, four-point bending biomechanical testing, histology, and radiographs. ResultsBoth of the experimental groups showed statistically significant increase in apparent bone density and bone volume fraction at the fusion mass. Biomechanical measures revealed a trend for improvement in the experimental groups, but these did not reach statistical significance. ConclusionsThis data suggest that locally administered bisphosphonate medications result in increased apparent bone density and bone volume fraction at the fusion mass in posterolateral spinal fusion, and that there appear to be no deleterious consequences with regards to the stiffness or maximum load to failure of the fusion mass under flexion bending evaluation.

Periarticular bone predicts knee osteoarthritis progression: Data from the Osteoarthritis Initiative.

Osteoarthritis (OA) is a disease with a substantial public health burden. Quantitative assessments of periarticular bone may be a biomarker capable of monitoring early disease progression. The purpose of this study was to evaluate whether measures of periarticular bone associate with longitudinal structural progression. We conducted a 12-18 months longitudinal study using the Osteoarthritis Initiative (OAI). Participants received knee dual-energy x-ray absorptiometry (DXA), trabecular magnetic resonance (MR) imaging, and x-rays. Knee DXAs generated proximal tibial medial:lateral periarticular bone mineral density (paBMD) measures. Proximal tibial trabecular MR images were assessed for trabecular morphometry: apparent bone volume fraction (BVF), trabecular number, thickness, and spacing. Weight-bearing x-rays were assessed for medial tibiofemoral joint space narrowing (JSN). Chi-squared analyses assessed whether periarticular bone measures were predictive of worsening medial tibiofemoral JSN, adjusted for age, sex, and BMI. In all, 444 participants, mean age 64.2 ± 9.2 years, BMI 29.5 ± 4.6kg/m2, and 52% male at baseline. Medial JSN (radiographic progression) occurred in 40 participants (9%). Higher baseline medial:lateral paBMD, apparent BVF, trabecular number and thickness, and lower baseline and decreased trabecular spacing were all associated with more progression of JSN in the medial compartment. From lowest to highest baseline medial:lateral paBMD quartile groups, 2%, 5%, 11%, and 18% had medial JSN progression, respectively, between the 36- and 48-month visits, p-values = 0.001 and 0.002 unadjusted and adjusted. The rate of change in medial:lateral paBMD, apparent BVF, and spacing were associated with more medial JSN. For rate of medial:lateral paBMD change from lowest to highest quartile, the proportion of each group that experienced medial JSN progression were 5%, 5%, 11%, and 18%, with an unadjusted and adjusted p-value of 0.005. Baseline and most rates of periarticular bone change associate with knee OA structural progression, highlighting the close relationship between subchondral bone and JSN. Future studies should focus on developing these measures as predictive and pathophysiological biomarkers, and evaluating their deployment in clinical trials testing bone-targeted therapeutics.

Knee Alignment Is Quantitatively Related to Periarticular Bone Morphometry and Density, Especially in Patients With Osteoarthritis.

Static alignment influences knee loading and predicts osteoarthritis (OA) progression. Periarticular bone is important in dispersing forces across the knee, and there is substantial evidence for molecular crosstalk between cartilage and subchondral bone. The aim of this study was to evaluate the relationship between periarticular trabecular bone morphology and bone mineral density (BMD) and knee alignment in OA. This was a cross-sectional analysis of participants in the Osteoarthritis Initiative Bone Ancillary Study. Dual x-ray absorptiometry (DXA) was performed to measure tibial periarticular bone mineral density (paBMD). Magnetic resonance imaging of knee trabecular bone was performed to calculate the apparent bone volume fraction (aBVF), apparent trabecular number (aTbN), apparent trabecular spacing (aTbSp), and apparent trabecular thickness (aTbTh). Static alignment was assessed by measuring the hip-knee-ankle (HKA) angle on long-limb films. The study group comprised 436 participants (mean ± SD age 65.4 ± 9.2 years, 46% female, mean ± SD body mass index 29.6 ± 4.6 kg/m2 ), 71% of whom had OA. Correlations between the HKA angle and medial:lateral paBMD, medial paBMD, aBVF, aTbN, aTbTh, and aTbSp were -0.63, -0.34, -0.29, -0.32, -0.22, and 0.30, respectively. More varus alignment was associated with higher medial:lateral paBMD, medial paBMD, aBVF, aTbN, aTbTh, and lower aTbSp. In OA knees, the results were more pronounced. In non-OA knees, the most consistent association was with medial:lateral paBMD. Static alignment was associated with medial:lateral paBMD in all knees and with medial paBMD and trabecular morphometry in OA knees only. Aberrant knee loading may lead to increased relative subchondral bone density, which is partly related to a higher aBVF and a greater number of thicker trabeculae with smaller intertrabecular spacing. Knee DXA may be a useful early biomarker of knee OA.

Validation of quantitative magnetic resonance imaging-based apparent bone volume fraction in peri-articular tibial bone of cadaveric knees.

BackgroundIn the knee, high-resolution magnetic resonance (MR) imaging has demonstrated that increased apparent bone volume fraction (trabecular bone volume per total volume; BV/TV) in the peri-articular proximal medial tibia is associated with joint space narrowing and the presence of bone marrow lesions. However, despite evidence of construct validity, MR-based apparent BV/TV has not yet been cross-validated in the proximal medial tibia by comparison with a gold standard (e.g., micro-computed tomography [microCT]). In this cadaveric validation study we explored the association between MR-based apparent BV/TV and microCT-based BV/TV in the proximal peri-articular medial tibia.MethodsFresh cadaveric whole knee specimens were obtained from individuals 51 to 80 years of age with no knee pathology other than osteoarthritis. Ten knees were collected from five cadavers within 10 hours of death and underwent a 3-Tesla MR exam including a coronal-oblique 3-dimensional fast imaging with steady state precession (3D FISP) sequence within 36 hours of death. The specimens were placed in a 4% paraformaldehyde in phosphate buffer within 58 hours of death. After preservation, a subchondral region from the tibial plateau was collected and underwent microCT imaging with a voxel size of 9 μm x 9 μm x 9 μm. A single reader analyzed the microCT images in a similar volume of interest as selected in the MR measures. A different reader analyzed the MR-based trabecular morphometry using a custom analysis tool. To analyze the MR-based trabecular morphometry, a rectangular region of interest (ROI) was positioned on the 20 central images in the proximal medial tibial subchondral bone. The primary outcome measures were MR-based and microCT-based trabecular BV/TV in the proximal medial tibia.ResultsThe MR-based apparent BV/TV was strongly correlated with microCT-based BV/TV (r = 0.83, confidence interval = 0.42 to 0.96), despite the MR-based apparent BV/TV being systematically lower than measured using microCT.ConclusionsMR-based apparent BV/TV in the proximal peri-articular medial tibia has good construct validity and may represent an alternative for CT-based BV/TV.

C-arm CT for histomorphometric evaluation of lumbar spine trabecular microarchitecture: a study on anorexia nervosa patients

Bone histomorphometry measurements require high spatial resolution that may not be feasible using multidetector CT (MDCT). This study evaluated the trabecular microarchitecture of lumbar spine using MDCT and C-arm CT in a series of young adult patients with anorexia nervosa (AN). 11 young females with AN underwent MDCT (anisotropic resolution with a slice thickness of ~626 μm) and C-arm CT (isotropic resolution of ~200 µm). Standard histomorphometric parameters the of L1 vertebral body, namely the apparent trabecular bone volume fraction (BV/TV), trabecular thickness (TbTh), trabecular number (TbN) and trabecular separation (TbSp), were analysed using MicroView software (GE Healthcare, Piscataway, NJ). Bone mineral density (BMD) was measured using dual-energy X-ray absorptiometry. Trabecular parameters derived from MDCT and C-arm CT were compared, and their association with BMD parameters was evaluated. Histomorphometric parameters derived from C-arm CT, namely TbTh, TbN and TbSp, were significantly different from the corresponding MDCT parameters. There were no significant correlations between C-arm CT-derived parameters and the corresponding MDCT-derived parameters. C-arm CT-derived parameters were significantly (p<0.001) correlated with anteroposterior L1 spine BMD and Z-scores: TbTh (r=0.723, r=0.744, respectively), TbN (r=-0.720, r=-0.712, respectively) and TbSp (r=0.656, r=0.648, respectively). BV/TV, derived from C-arm CT, was significantly associated with body mass index (r=0.636) and ideal body weight (r=0.730) (p<0.05). These associations were not present in MDCT-derived parameters. This study suggests that the spatial resolution offered by C-arm CT more accurately captures the histomorphometric parameters of trabecular morphology than MDCT in patients with AN.

Postmenopausal women with osteoporosis and osteoarthritis show different microstructural characteristics of trabecular bone in proximal tibia using high-resolution magnetic resonance imaging at 3 tesla

BackgroundOsteoporosis (OP) and osteoarthritis (OA) are two common musculoskeletal disorders that affect the quality of life in aged people. An inverse relationship between OP and OA was proposed four decades ago. However, the difference in microstructure of the trabecular bone of these two disorders by high-resolution MRI (HR-MRI) has not been compared. The primary objective of the study is to explain the actual relationship between OA and OP based on differences between bone microstructure of these two diseases. The secondary objectives are to find out the significance of Euler number and its relationship with other structural parameters, and important role of HR-MRI to reveal the microstructure of trabecular bone directly.MethodsTotally, 30 women with OP and 30 women with OA (n = 60) were included in this study. Primary OA of hip, knee, as well as spinal arthrosis were diagnosed according to plain X-ray film findings. Osteoporosis was defined based on the latest criteria of World Health Organization (WHO). Structural and textural parameters derived from HR-MRI images of proximal tibia were calculated and compared with special software.ResultsThere were significant differences in apparent bone volume fraction, trabecular thickness, mean roundness, Euler number, entropy and inverse different moment between OP and OA patients. In OP group, apparent trabecular separation (Tb.Sp), inertia, absolute value and contrast were positively correlated with Euler number, whereas apparent trabecular number (Tb.N), mean trabecular area, inverse difference and inverse different moment were negatively correlated. Apparent trabecular bone volume fraction (BV/TV), mean trabecular area, mean trabecular perimeter and mean skeleton length negatively correlated with Euler number in OA group. Inverse different moment was the texture parameter, which influenced bone mineral density (BMD) of femoral neck, meanwhile contrast influenced BMD of both great trochanter and Ward’s triangle in OP group. While in OA group, Euler number was the exclusive parameter, which affected BMD of femoral neck and Ward’s triangle.ConclusionsWe found significant differences in microstructure parameters derived from HR-MRI images between postmenopausal women with OP and OA. It convincingly supports the hypothesis that there might be an inverse relationship between OP and OA.

High resolution quantitative computed tomography-based assessment of trabecular microstructure and strength estimates by finite-element analysis of the spine, but not DXA, reflects vertebral fracture status in men with glucocorticoid-induced osteoporosis

High-resolution quantitative computed tomography (HRQCT)-based analysis of spinal bone density and microstructure, finite element analysis (FEA), and DXA were used to investigate the vertebral bone status of men with glucocorticoid-induced osteoporosis (GIO). DXA of L1–L3 and total hip, QCT of L1–L3, and HRQCT of T12 were available for 73 men (54.6±14.0years) with GIO. Prevalent vertebral fracture status was evaluated on radiographs using a semi-quantitative (SQ) score (normal=0 to severe fracture=3), and the spinal deformity index (SDI) score (sum of SQ scores of T4 to L4 vertebrae). Thirty-one (42.4%) subjects had prevalent vertebral fractures. Cortical BMD (Ct.BMD) and thickness (Ct.Th), trabecular BMD (Tb.BMD), apparent trabecular bone volume fraction (app.BV/TV), and apparent trabecular separation (app.Tb.Sp) were analyzed by HRQCT. Stiffness and strength of T12 were computed by HRQCT-based nonlinear FEA for axial compression, anterior bending and axial torsion. In logistic regressions adjusted for age, glucocorticoid dose and osteoporosis treatment, Tb.BMD was most closely associated with vertebral fracture status (standardized odds ratio [sOR]: Tb.BMD T12: 4.05 [95% CI: 1.8–9.0], Tb.BMD L1–L3: 3.95 [1.8–8.9]). Strength divided by cross-sectional area for axial compression showed the most significant association with spine fracture status among FEA variables (2.56 [1.29–5.07]). SDI was best predicted by a microstructural model using Ct.Th and app.Tb.Sp (r2=0.57, p<0.001). Spinal or hip DXA measurements did not show significant associations with fracture status or severity.In this cross-sectional study of males with GIO, QCT, HRQCT-based measurements and FEA variables were superior to DXA in discriminating between patients of differing prevalent vertebral fracture status. A microstructural model combining aspects of cortical and trabecular bone reflected fracture severity most accurately.

Bone marrow lesions are associated with altered trabecular morphometry

Bone marrow lesions (BMLs) are a common magnetic resonance (MR) feature in patients with osteoarthritis, however their pathological basis remains poorly understood and has not been evaluated invivo. Our aim was to evaluate the trabecular structure associated with the presence and size of BMLs present in the same regions of interest (ROI) using quantitative MR-based trabecular morphometry. 158 participants in the Osteoarthritis Initiative (OAI) were imaged with a coronal 3D fast imaging with steady state precession (FISP) sequence for trabecular morphometry in the same session as the OAI 3T MR knee evaluation. The proximal medial tibial subchondral bone in the central weight-bearing ROI on these knee 3D FISP images were quantitatively evaluated for apparent bone volume fraction, trabecular number, spacing, and thickness. BMLs were also evaluated in the subchondral bone immediately adjacent to the articular cartilage. BML volume was also evaluated within the same trabecular morphometry ROI and semi-quantitatively classified as none, small, or large. Kruskal-Wallis test was used to determine if mean apparent bone volume fraction, trabecular number, spacing, or thickness differed by BML score. Compared to knees with ROIs containing no BMLs, knees with small or large BMLs had statistically higher apparent bone volume fraction (P<0.01), trabecular number (P<0.01), and thickness (P=0.02), and lower trabecular spacing (P<0.01). Compared to knees with ROIs containing no BMLs, knees with ROIs containing small or large BMLs had higher apparent bone volume fraction, trabecular number and thickness, but lower trabecular spacing. These findings may represent areas of locally increased bone remodeling or compression.

Cross-sectional DXA and MR measures of tibial periarticular bone associate with radiographic knee osteoarthritis severity

We evaluated the relationship of medial proximal tibial periarticular areal bone mineral density (paBMD) and trabecular morphometry and determined whether these bone measures differed across radiographic medial joint space narrowing (JSN) scores. 482 participants of the Osteoarthritis Initiative (OAI) Bone Ancillary Study had knee dual X-ray absorptiometry (DXA) and trabecular bone 3T magnetic resonance imaging (MRI) exams assessed at the same visit. Medial proximal tibial paBMD was measured on DXA and apparent trabecular bone volume fraction (aBV/TV), thickness (aTb.Th), number (aTb.N), and spacing (aTb.Sp) were determined from MR images. Radiographs were assessed for medial JSN scores (0-3). We evaluated associations between medial paBMD and trabecular morphometry. Whisker plots with notches of these measures versus medial JSN scores were generated and presented. Mean age was 63.9 (9.2) years, BMI 29.6 (4.8) kg/m(2), and 53% were male. The Spearman correlation coefficients between DXA-measured medial paBMD and aBV/TV was 0.61 [95% confidence interval (CI) 0.55-0.66]; between paBMD and aTb.Th was 0.38 (95%CI 0.30-0.46); paBMD and aTb.N was 0.65 (95%CI 0.60-0.70); paBMD and aTb.Sp was -0.65 (95%CI -0.70 to -0.59). paBMD and the trabecular metrics were associated with medial JSN scores. The moderate associations between periarticular trabecular bone density and morphometry and their relationship with greater severity of knee OA support hypotheses of remodeling and/or microscopic compression fractures in the natural history of OA. Longitudinal studies are needed to assess whether knee DXA will be a predictor of OA progression. Further characterization of the periarticular bone in OA utilizing complementary imaging modalities will help clarify OA pathophysiology.

Prediction of Biomechanical Properties of Trabecular Bone in MR Images With Geometric Features and Support Vector Regression

Whole knee joint MR image datasets were used to compare the performance of geometric trabecular bone features and advanced machine learning techniques in predicting biomechanical strength properties measured on the corresponding ex vivo specimens. Changes of trabecular bone structure throughout the proximal tibia are indicative of several musculoskeletal disorders involving changes in the bone quality and the surrounding soft tissue. Recent studies have shown that MR imaging also allows non-invasive 3-D characterization of bone microstructure. Sophisticated features like the scaling index method (SIM) can estimate local structural and geometric properties of the trabecular bone and may improve the ability of MR imaging to determine local bone quality in vivo. A set of 67 bone cubes was extracted from knee specimens and their biomechanical strength estimated by the yield stress (YS) [in MPa] was determined through mechanical testing. The regional apparent bone volume fraction (BVF) and SIM derived features were calculated for each bone cube. A linear multiregression analysis (MultiReg) and a optimized support vector regression (SVR) algorithm were used to predict the YS from the image features. The prediction accuracy was measured by the root mean square error (RMSE) for each image feature on independent test sets. The best prediction result with the lowest prediction error of RMSE = 1.021 MPa was obtained with a combination of BVF and SIM features and by using SVR. The prediction accuracy with only SIM features and SVR (RMSE = 1.023 MPa) was still significantly better than BVF alone and MultiReg (RMSE = 1.073 MPa). The current study demonstrates that the combination of sophisticated bone structure features and supervised learning techniques can improve MR-based determination of trabecular bone quality.

Women with Anorexia Nervosa: Finite Element and Trabecular Structure Analysis by Using Flat-Panel Volume CT

To use finite element modeling based on flat-panel volume computed tomography (CT) and bone mineral density (BMD) provided by dual-energy x-ray absorptiometry (DXA) to compare bone failure load, stiffness, and trabecular structure in women with anorexia nervosa (AN) and age-matched normal-weight control subjects. The study was approved by the institutional review board and complied with HIPAA guidelines. Informed consent was obtained. Fourteen women, eight with AN (mean age, 26.6 years) and six control subjects (mean age, 26.3 years), underwent flat-panel volume CT of the distal radius to determine apparent trabecular bone volume fraction (BV/TV), apparent trabecular number (TbN), apparent trabecular thickness (TbTh), and apparent trabecular separation (TbSp). Bone strength and stiffness were calculated from uniaxial compression tests by using finite element models created from flat-panel volume CT. DXA was used to determine BMD of the radius, lumbar spine, and hip. Means ± standard deviations of all variables were calculated for both groups and compared (Student t test). Univariate regression analysis and stepwise regression modeling were performed. Patients with AN had lower values for stiffness (284.77 kN/mm ± 76.14 vs 389.97 kN/mm ± 84.90, P = .04), failure load (4.98 kN ± 1.23 vs 7.01 kN ± 1.52, P = .02), BV/TV (0.32% ± 0.09 vs 0.44% ± 0.02, P = .007), and TbN (1.15 mm(-3) ± 0.20 vs 1.43 mm(-3) ± 0.13, P = .008) and higher values for TbSp (0.62 mm ± 0.20 vs 0.40 mm ± 0.04, P = .02) compared with normal-weight control subjects. TbTh was lower in women with AN (P = .1). BMD measurements were significantly lower for the AN group. BMD measurements and trabecular parameters (except TbTh) correlated with stiffness and failure load (r = 0.58 to 0.83). Failure load and stiffness are abnormal in women with AN compared with those in normal-weight control subjects and correlate with BMD and trabecular parameters.

Improvements in Vertebral Body Strength Under Teriparatide Treatment Assessed In Vivo by Finite Element Analysis: Results From the EUROFORS Study

Monitoring of osteoporosis therapy based solely on DXA is insufficient to assess antifracture efficacy. Estimating bone strength as a variable closely linked to fracture risk is therefore of importance. Finite element (FE) analysis-based strength measures were used to monitor a teriparatide therapy and the associated effects on whole bone and local fracture risk. In 44 postmenopausal women with established osteoporosis participating in the EUROFORS study, FE models based on high-resolution CT (HRCT) of T(12) were evaluated after 0, 6, 12, and 24 mo of teriparatide treatment (20 microg/d). FE-based strength and stiffness calculations for three different load cases (compression, bending, and combined compression and bending) were compared with volumetric BMD (vBMD) and apparent bone volume fraction (app. BV/TV), as well as DXA-based areal BMD of the lumbar spine. Local damage of the bone tissue was also modeled. Highly significant improvements in all analyzed variables as early as 6 mo after starting teriparatide were found. After 24 mo, bone strength in compression was increased by 28.1 +/- 4.7% (SE), in bending by 28.3 +/- 4.9%, whereas app. BV/TV was increased by 54.7 +/- 8.8%, vBMD by 19.1 +/- 4.0%, and areal BMD of L(1)-L(4) by 10.2 +/- 1.2%. When comparing standardized increases, FE changes were significantly larger than those of densitometry and not significantly different from app. BV/TV. The size of regions at high risk for local failure was significantly reduced under teriparatide treatment. Treatment with teriparatide leads to bone strength increases for different loading conditions of close to 30%. FE is a suitable tool for monitoring bone anabolic treatment in groups or individual patients and offers additional information about local failure modes. FE variables showed a higher standardized response to changes than BMD measurements, but further studies are needed to show that the higher response represents a more accurate estimate of treatment-induced fracture risk reduction.

Implications of noise and resolution on mechanical properties of trabecular bone estimated by image‐based finite‐element analysis

Recent advances in micro-magnetic resonance imaging (microMRI) now allow noninvasive assessment of mechanical properties of trabecular bone (TB) in vivo by micro finite-element analysis. The first aim of this work was to address the implications of limited resolution and signal-to-noise ratio on elastic properties of TB derived under conditions of in vivo imaging via simulation at various resolutions and noise levels on the basis of models derived from microCT images at 21 microm isotropic voxel size from cores of cadaveric human TB (n = 13) from three anatomic sites. The second aim was to compare how elastic constants derived from actual MR images at 9.4 Tesla at 50 microm isotropic voxel size compare with those from high-resolution microCT. Elastic moduli computed from simulated in vivo microMR images were highly correlated with those obtained from microCT (R(2) = 0.99) and the data were relatively immune to noise. Correlations of similar strength were obtained between estimated moduli from microCT and acquired high-field MR images. Systematic errors manifesting in significant deviations of the slopes from unity are caused by higher apparent bone-volume fraction of the MR images but can potentially be corrected with appropriate histogram-standardization techniques.

Distal Radius in Adolescent Girls with Anorexia Nervosa: Trabecular Structure Analysis with High-Resolution Flat-Panel Volume CT

To examine trabecular microarchitecture with high-resolution flat-panel volume computed tomography (CT) and bone mineral density (BMD) with dual-energy x-ray absorptiometry (DXA) in adolescent girls with anorexia nervosa (AN) and to compare these results with those in normal-weight control subjects. The study was approved by the institutional review board and complied with HIPAA guidelines. Informed consent was obtained. Twenty adolescent girls, 10 with mild AN (mean age, 15.9 years; range, 13-18 years) and 10 age- and sex-matched normal-weight control subjects (mean age, 15.9 years; range, 12-18 years) underwent flat-panel volume CT of distal radius to determine apparent trabecular bone volume fraction (BV/TV), apparent trabecular number (TbN), apparent trabecular thickness (TbTh), and apparent trabecular separation (TbSp). All subjects underwent DXA of spine, hip, and whole body to determine BMD and body composition. The means and standard deviations (SDs) of structure parameters were calculated for AN and control groups. Groups were compared (Student t test). Linear regression analysis was performed. AN subjects compared with control subjects, respectively, showed significantly lower mean values for BV/TV (0.37% +/- 0.05 [SD] vs 0.46% +/- 0.03, P = .0002) and TbTh (0.31 mm +/- 0.03 vs 0.39 mm +/- 0.03, P < .0001) and higher mean values for TbSp (0.54 mm +/- 0.13 vs 0.44 mm +/- 0.04, P = .02). TbN was lower in AN subjects than in control subjects, but the difference was not significant (1.17 mm(-3) +/- 0.15 vs 1.22 mm(-3) +/- 0.07, P = .43). There was no significant difference in BMD between AN and control subjects. BMD parameters showed positive correlation with BV/TV and TbTh in the control group (r = 0.55-0.84, P = .05-.01) but not in AN patients. Flat-panel volume CT is effective in evaluation of trabecular structure in adolescent girls with AN and demonstrates that bone structure is abnormal in these patients compared with that in normal-weight control subjects despite normal BMD. http://radiology.rsnajnls.org/cgi/content/full/249/3/938/DC1.

Age- and direction-related adaptations of lumbar vertebral trabecular bone with respect to apparent stiffness and tissue level stress distribution

The objective of this study was to study the age-related adaptation of lumbar vertebral trabecular bone at the apparent level, as well as the tissue level in three orthogonal directions. Ninety trabecular specimens were obtained from six normal L4 vertebral bodies of six male cadavers in two age groups, three aged 62 years and three aged 69 years, and were scanned using a high-resolution micro-computed tomography (micro-CT) system, then converted to micro-finite element models to do micro-finite element analyses. The relationship between apparent stiffness and bone volume fraction, and the tissue level von Mises stress distribution for each trabecular specimen when compressed separately in the longitudinal direction, medial–lateral and anterior–posterior directions (transverse directions) were derived and compared between two age groups. The results showed that at the apparent level, trabecular bones from 69-year group had stiffer bone structure relative to their volume fractions in all three directions, and in both age groups, changes in bone volume fraction could explain more variations in apparent stiffness in the longitudinal direction than the transverse directions; at the tissue level, aging had little effect on the tissue von Mises stress distributions for the compressions in all the three directions. The novelty of the present study was that it provided quantitative assessments on the age and direction-related adaptation of Chinese male lumbar vertebral trabecular bone from two different levels: stiffness at the apparent level and stress distribution at the tissue level. It may help to understand the failure mechanisms and fracture risks of vertebral body associated with aging and direction for the prevention of fracture risks in elder individuals.

Predicting regional variations in trabecular bone mechanical properties within the human proximal tibia using MR imaging

Trabecular bone density changes throughout the proximal tibia are indicative of several musculoskeletal disorders of the knee joint. Many of these disorders involve not only changes in the amount of bone, but also in the surrounding soft tissue. Osteoarthritis, for instance, involves bone density changes below the subchondral bone and throughout the proximal tibia, along with degradation evident in the articular cartilage. Osteoporosis, characterized by low bone density may also involve changes in bone size, structure or microarchitecture, each of which may contribute to fracture risk. Recent studies have shown that magnetic resonance (MR) imaging, most frequently applied for soft tissue imaging, also allows non-invasive 3-dimensional characterization of bone microstructure. The purpose of the current study is to use whole joint MR images to acquire regional apparent bone volume fraction (appBVF) throughout the proximal tibia and correlate with mechanical properties measured on the corresponding ex vivo specimens. To compare our method to a high-resolution imaging modality, micro-CT analysis was performed in a subset of specimens. Using linear mixed-effects models, significant correlations ( p < 0.05) were determined between MR appBVF and Young's modulus ( r 2 = 0.58, MPSE = 3633 MPa 2), yield stress ( r 2 = 0.73, MPSE = 1.53 MPa 2) and ultimate stress ( r 2 = 0.72, MPSE = 2.29 MPa 2). Comparable significant correlations ( p < 0.05) were also determined between micro-CT BVF and Young's modulus ( r 2 = 0.47, MPSE = 5179 MPa 2), yield stress ( r 2 = 0.80, MPSE = 1.23 MPa 2) and ultimate stress ( r 2 = 0.83, MPSE = 1.76 MPa 2). The current study demonstrates that MR imaging may be used as an in vivo imaging tool to determine differences in bone strength between subjects and regional variations within a single tibia.

Monitoring Teriparatide-Associated Changes in Vertebral Microstructure by High-Resolution CT In Vivo: Results From the EUROFORS Study

We introduce a method for microstructural analysis of vertebral trabecular bone in vivo based on HRCT. When applied to monitor teriparatide treatment, changes in structural variables exceeded and were partially independent of changes in volumetric BMD. Monitoring of osteoporosis therapy based solely on bone densitometry is insufficient to assess anti-fracture efficacy. Assessing bone microstructure in vivo is therefore of importance. We studied whether it is possible to monitor effects of teriparatide on vertebral trabecular microstructure independent of BMD by high-resolution CT (HRCT). In a subset of 65 postmenopausal women with established osteoporosis who participated in the EUROFORS study, HRCT scans of T(12), quantitative CT of L(1)-L(3), and DXA of L(1)-L(4) were performed after 0, 6, and 12 mo of teriparatide treatment (20 microg/d). We compared BMD and 3D microstructural variables in three groups of women, based on prior antiresorptive treatment: treatment-naïve; pretreated; and pretreated women showing inadequate response to treatment. We found statistically highly significant increases in most microstructural variables and BMD 6 mo after starting teriparatide. After 12 mo, apparent bone volume fraction (app. BV/TV) increased by 30.6 +/- 4.4% (SE), and apparent trabecular number (app. Tb.N.) increased by 19.0 +/- 3.2% compared with 6.4 +/- 0.7% for areal and 19.3 +/- 2.6% for volumetric BMD. The structural changes were partially independent of BMD as shown by a significantly larger standardized increase and a standardized long-term precision at least as good as DXA. Patients who had shown inadequate response to prior osteoporosis treatment did show improvements in BMD and structural measures comparable to treatment-naïve patients. HRCT is a feasible method for longitudinal microstructural analysis of human vertebrae in vivo, offers information beyond BMD, and is sufficiently precise to show profound effects of teriparatide after 12 mo.

Prediction of mechanical properties of trabecular bone using quantitative MRI

Techniques for quantitative magnetic resonance imaging (MRI) have been developed for non-invasive estimation of the mineral density and structure of trabecular bone. The R*2 relaxation rate (i.e. 1/T*2) is sensitive to bone mineral density (BMD) via susceptibility differences between trabeculae and bone marrow, and by binarizing MRI images, structural variables, such as apparent bone volume fraction, can be assessed. In the present study, trabecular bone samples of human patellae were investigated in vitro at 1.5 T to determine the ability of MRI-derived variables (R*2 and bone volume fraction) to predict the mechanical properties (Young's modulus, yield stress and ultimate strength). Further, the MRI variables were correlated with reference measurements of volumetric BMD and bone area fraction as determined with a clinical pQCT system. The MRI variables correlated significantly (p < 0.01) with the mechanical variables (r = 0.32–0.46), BMD (r = 0.56) and bone structure (r = 0.51). A combination of R*2 and MRI-derived bone volume fraction further improved the prediction of yield stress and ultimate strength. Although pQCT showed a trend towards better prediction of the mechanical properties, current results demonstrate the feasibility of combined MR imaging of marrow susceptibility and bone volume fraction in predicting the mechanical strength of trabecular bone and bone mineral density.