Predicting Hip Fracture Type With Cortical Bone Mapping (CBM) in the Osteoporotic Fractures in Men (MrOS) Study

A Correspondence-Based Network Approach for Groupwise Analysis of Patient-Specific Spatiotemporal Data

Methods for statistically analyzing patient-specific data that vary both spatially and over time are currently either limited to summary statistics or require elaborate surface registration. We propose a new method, called correspondence-based network analysis, which leverages particle-based shape modeling to establish correspondence across a population and preserve patient-specific measurements and predictions through statistical analysis. Herein, we evaluated this method using three published datasets of the hip describing cortical bone thickness of the proximal femur, cartilage contact stress, and dynamic joint space between control and patient cohorts to evaluate activity- and group-based differences, as applicable, using traditional statistical parametric mapping (SPM) and our proposed spatially considerate correspondence-based network analysis approach. The network approach was insensitive to correspondence density, while the traditional application of SPM showed decreasing area of the region of significance with increasing correspondence density. In comparison to SPM, the network approach identified broader and more connected regions of significance for all three datasets. The correspondence-based network analysis approach identified differences between groups and activities without loss of subject and spatial specificity which could improve clinical interpretation of results.

Cortical and Trabecular Bone Deficit in Middle-Aged Men Living with HIV

A significant increase in the risk of hip fracture was observed in middle-aged men living with human immunodeficiency virus (MLWH), almost a decade earlier than those without infection. Data regarding cortical and trabecular bone deficit of hip, an important determinant of bone strength, in MLWH are limited. Quantitative CT was performed in consecutive MLWH aged ≥30 years between November 2017 and October 2018 at Severance Hospital, Seoul, Korea. Volumetric bone mineral density (vBMD) and cortical bone mapping parameters of hip (cortical thickness [CTh], cortical bone vBMD [CBMD], cortical mass surface density [CMSD], endocortical trabecular density [ECTD]) were compared to age-matched and body mass index (BMI)-matched controls (1:2) using a community-based healthy adults cohort. Among 83 MLWH and 166 controls (mean age: 47.2 years; BMI: 23.6 kg/m2 ), MLWH had lower total hip vBMD (280 ± 41 versus 296 ± 41 mg/cm3 ), CMSD (155 versus 160 mg/cm2 ), and ECTD (158 versus 175 mg/cm3 ) than controls that remained robust after adjustment for covariates (adjusted β: total hip vBMD, -18.8; CMSD, -7.3; ECTD, -18.0; p < 0.05 for all). Cortical bone mapping revealed localized deficit of CTh, CBMD, and CMSD in the anterolateral trochanteric region and femoral neck in MLWH compared to controls, with a more extensive ECTD deficit. In MLWH, lower CD4 T-cell count (/100 cells/mm3 decrement) and protease inhibitor (PI)-based regimen (versus non-PI regimen) at the time of antiretroviral treatment initiation were associated with lower total hip vBMD (adjusted β -7.5 for lower CD4 count; -28.3 for PI-based regimen) and CMSD (adjusted β -2.6 for lower CD4 count; -12.7 for PI-based regimen; p < 0.05 for all) after adjustment for covariates including age, BMI, smoking, alcohol use, hepatitis C virus co-infection, tenofovir exposure, and CT scanner types. MLWH had lower hip bone density with cortical and trabecular bone deficit compared to community-dwelling controls. © 2023 American Society for Bone and Mineral Research (ASBMR).

Strategies to reduce the onset of sleeve gastrectomy associated bone loss (STRONG BONES): Trial design and methods

Background

Despite recognized improvements in obesity-related comorbidities, mounting evidence implicates surgical weight loss in the onset of skeletal fragility. Sleeve gastrectomy (SG) is the most commonly performed bariatric procedure and is associated with 3-7% axial bone loss in the year following surgery. Bisphosphonates are FDA-approved medications for the prevention and treatment of age-related bone loss and may represent a strategy to reduce bone loss following SG surgery.

Methods

The Strategies to Reduce the Onset of Sleeve Gastrectomy Associated Bone Loss (STRONG BONES) trial (NCT04922333) is designed to definitively test whether monthly administration of the bisphosphonate, risedronate, for six months can effectively counter SG-associated bone loss. Approximately 120 middle-aged and older (≥40 years) SG patients will be randomized to six months of risedronate or placebo treatment, with skeletal outcomes assessed at baseline, six, and 12-months post-surgery. The primary outcome of the trial is 12-month change in total hip areal bone mineral density (aBMD), measured by dual energy x-ray absorptiometry (DXA). This will be complemented by DXA-acquired aBMD assessment at other skeletal sites and quantitative computed tomography (QCT) derived changes in bone quality. Change in muscle mass and function will also be assessed, as well as biomarkers of bone health, turnover, and crosstalk, providing mechanistic insight into intervention-related changes to the bone-muscle unit.

Discussion

Results from the STRONG BONES trial have the potential to influence current clinical practice by determining the ability of bisphosphonate use to mitigate bone loss and concomitant fracture risk in middle-aged and older SG patients.

Risk assessment of femoral pathological fracture in prostate cancer patients by computed tomography analysis

INTRODUCTION

Prostate cancer often forms osteoblastic lesions that appear as a high-dense shadow upon X-ray. Although the lesions may seem to increase bone strength, pathological fracture occurs in one in four patients with prostate cancer. The aim of this study is to elucidate the factors that may increase the risk of pathological fracture in patients with prostate cancer metastases in the proximal femur by analyzing computed tomography data.

MATERIALS AND METHODS

Computed tomography data of the femur of 62 prostate cancer patients were retrospectively analyzed. The patients were divided into three groups based on the presence or absence of femoral metastatic lesions and pathological fracture. Surgical specimens of the proximal femur collected from patients who had a pathological fracture were histologically analyzed.

RESULTS

Bone density in the marrow area was increased in all cases with metastases compared with those with no metastases. Contrarily, the cortical bone density at the medial trochanter region was significantly lower in patients who had pathological fractures in the proximal femur than those who did not. Accordingly, histological analysis of the surgical specimens revealed that the affected cortical bone was osteopenic without any apparent new bone formation.

CONCLUSION

These results indicate that prostate cancer is less effective in inducing bone formation in the cortex than in the marrow and that the decrease in the cortical bone density at the medial trochanter region leads to an increased risk of pathological fracture. Therefore, a previously undocumented risk factor for pathological fracture in prostate cancer patients is presented.

Spatial assessment of femoral neck bone density and microstructure in hip osteoarthritis

Osteoarthritis (OA) is known to involve profound changes in bone density and microstructure near to, and even distal to, the joint. Critically, however, a full, spatial picture of these abnormalities has not been well documented in a quantitative fashion in hip OA. Here, micro-computed tomography (44.8 μm/voxel) and data-driven computational anatomy were used to generate 3-D maps of the distribution of bone density and microstructure in human femoral neck samples with early (6F/4M, mean age = 51.3 years), moderate (14F/8M, mean age = 60 years), and severe (16F/6M, mean age = 63.3 years) radiographic OA. With increasing severity of radiographic OA, there was decreased cortical bone mineral density (BMD) (p=0.003), increased cortical thickness (p=0.001), increased cortical porosity (p=0.0028), and increased cortical cross-sectional area (p=0.0012, due to an increase in periosteal radius (p=0.018)), with no differences detected in the total femoral neck or trabecular compartment measures. No OA-related region-specific differences were detected through Statistical Parametric Mapping, but there were trends towards decreased tissue mineral density (TMD) in the inferior femoral neck with increasing OA severity (0.050 < p ≤ 0.091), possibly due to osteophytes. Overall, the lack of differences in cortical TMD among radiographic OA groups indicated that the decrease in cortical BMD with increasing OA severity was largely due to the increased cortical porosity rather than decreased tissue mineralization. As porosity is inversely associated with stiffness and strength in cortical bone, increased porosity may offset the effect that increased cortical cross-sectional area would be expected to have on reducing stresses within the femoral neck. The use of high-resolution imaging and quantitative spatial assessment in this study provide insight into the heterogeneous and multi-faceted changes in density and microstructure in hip OA, which have implications for OA progression and fracture risk.

Protective effect of bisphosphonate on the cortical bone at key locations of the femur in aromatase inhibitor-associated bone loss: A three-dimensional cortical bone mapping study

•

Aromatase inhibitor use was associated with cortical bone loss in the hip.

•

Bisphosphonate protected hip cortical bone against aromatase inhibitor use.

•

The effect was prominent at the superior femoral neck and greater trochanter.

Aromatase inhibitor treatment in breast cancer is associated with accelerated bone loss and an increased risk of fracture. Bisphosphonates (BPs) are the mainstay treatment of aromatase inhibitor-associated bone loss (AIBL), which might improve femoral bone at key locations prone to fracture. To test this hypothesis, we performed three-dimensional cortical bone mapping based on quantitative computed tomography (QCT) scans in postmenopausal women with early breast cancer who were receiving aromatase inhibitors. Data of subjects who had both baseline and at least one follow-up QCT at Severance Hospital (South Korea) between 2005 and 2015 were analyzed (BP users, n = 93; BP non-users, n = 203). After exclusion of BP users with low medication persistence (proportion of days covered: <50%), BP users and non-users were 1:1 matched (n = 54 for each group) in terms of age, lumbar spine volumetric bone mineral density (LSvBMD), femoral neck areal BMD (FNaBMD), and total hip areal BMD (THaBMD). During a median follow-up of 2.1 years, BP use attenuated bone loss in LSvBMD (+7.2% vs. −3.8%, p < 0.001), FNaBMD (+1.3% vs. −2.7%, p < 0.001), and THaBMD (-0.3% vs. −2.5%, p = 0.024). BP had a protective effect on cortical parameters of femoral bone: estimated cortical thickness (CTh) (+3.3% vs. + 0.1%, p = 0.007) and cortical mass surface density (CMSD, cortical mass per unit surface area was calculated by multiplying cortical BMD with CTh) (+3.4% vs. −0.3%, p < 0.001). CMSD increased by up to 15% at key locations such as the superior part of the femoral neck and greater trochanter. BP prevented the thinning of average CTh of the femoral neck (-1.4% vs. −6.1%, p < 0.001), particularly at the superior anterior quadrant of femoral neck (absolute difference: +12.8% point vs. non-users). Compared to BP non-users, BP users had improved cross-sectional moment of inertia (+4.4% vs. −0.7%, p = 0.001) and less increase in buckling ratio (+1.3% vs. + 7.5%, p < 0.001). In summary, BP use prevented cortical bone deficits observed in AIBL at key locations of the proximal femur.

Augmenting Osteoporosis Imaging with Machine Learning

PURPOSE OF REVIEW

In this paper, we discuss how recent advancements in image processing and machine learning (ML) are shaping a new and exciting era for the osteoporosis imaging field. With this paper, we want to give the reader a basic exposure to the ML concepts that are necessary to build effective solutions for image processing and interpretation, while presenting an overview of the state of the art in the application of machine learning techniques for the assessment of bone structure, osteoporosis diagnosis, fracture detection, and risk prediction.

RECENT FINDINGS

ML effort in the osteoporosis imaging field is largely characterized by "low-cost" bone quality estimation and osteoporosis diagnosis, fracture detection, and risk prediction, but also automatized and standardized large-scale data analysis and data-driven imaging biomarker discovery. Our effort is not intended to be a systematic review, but an opportunity to review key studies in the recent osteoporosis imaging research landscape with the ultimate goal of discussing specific design choices, giving the reader pointers to possible solutions of regression, segmentation, and classification tasks as well as discussing common mistakes.

Spatial distribution of hip cortical thickness in postmenopausal women with different osteoporotic fractures

Few studies h ave discussed the association between cortical bone outside the fracture site and the fracture itself. Focusing on hip cortical thickness, this study revealed distinct distributions of the parameters for hip (trochanteric or femoral neck), vertebral, and peripheral osteoporotic fractures and suggested that the spatial distribution of hip cortical thickness was fracture-specific.

PURPOSE

Cortical bone is critical for bone strength. Hip cortical thickness is reported to be closely associated with the incidence of hip fractures, but its relationship with nonhip fractures is rarely studied. As the hip is a major site for fracture risk assessment, it would be of great benefit to investigate the association between hip cortical thickness and different osteoporotic fractures.

METHODS

One hundred age-matched postmenopausal women were equally assigned to 4 osteoporotic fracture groups (trochanteric, femoral neck, vertebral, and peripheral fractures) and a nonfracture group. Each subject had a clinical quantitative computed tomography scan of the bilateral hips and the lumbar spine. A cortical bone mapping algorithm was adopted to calculate hip cortical thickness. Hip and lumbar trabecular density and the hip cortical thickness distribution were compared among the groups.

RESULTS

All the fracture groups presented lower lumbar trabecular density. Compared with nonfracture controls, patients with hip or vertebral fractures but not peripheral fractures showed decreased cortical thickness and trabecular density of the hip. Fracture-specific distributions of cortical thickness were revealed, including zonal defects on the neck-intertrochanter junction, greater trochanter, and the periphery of the lesser trochanter for trochanteric fractures, a focal defect on the anterosuperior neck for femoral neck fractures, a moderate and average distribution for vertebral fractures, and focally thicker cortices on the anterosuperior greater trochanter and the periphery of the lesser trochanter for peripheral fractures.

CONCLUSION

The spatial distribution of hip cortical thickness was different for each type of osteoporotic fracture, and patients with centrally located fractures demonstrated more severe cortical deterioration. This finding needs to be validated in a larger sample.

Physical activity induced adaptation can increase proximal femur strength under loading from a fall onto the greater trochanter

Physical activity enhances proximal femur bone mass, but it remains unclear whether the benefits translate into an enhanced ability to resist fracture related loading. We recently used baseball pitchers as a within-subject controlled model to demonstrate physical activity induced proximal femur adaptation in regions associated with weight bearing and increased strength under single-leg stance loading. However, there was no measurable benefit to resisting common injurious loading (e.g. a fall onto the greater trochanter). A lack of power and a small physical activity effect size may have contributed to the latter null finding. Softball pitchers represent an alternative within-subject controlled model to explore adaptation of the proximal femur to physical activity, exhibiting greater dominant-to-nondominant (D-to-ND) leg differences than baseball pitchers. The current study used quantitative computed tomography, statistical parametric mapping, and subject-specific finite element (FE) modeling to explore adaptation of the proximal femur to physical activity in female softball pitchers (n = 25). Female cross-country runners (n = 15) were included as symmetrically loaded controls, showing very limited D-to-ND leg differences. Softball pitchers had D-to-ND leg differences in proximal femur, femoral neck, and trochanteric volumetric bone mineral density and content, and femoral neck volume. Voxel-based morphometry analyses and cortical bone mapping showed D-to-ND leg differences within a large region connecting the superior femoral head, inferior femoral neck and medial intertrochanteric region, and within the greater trochanter. FE modeling revealed pitchers had 19.4% (95%CI, 15.0 to 23.9%) and 4.9% (95%CI, 1.7 to 8.2%) D-to-ND leg differences in predicted ultimate strength under single-leg stance loading and a fall onto the greater trochanter, respectively. These data affirm the spatial and strength adaptation of the proximal femur to weight bearing directed loading and demonstrate that the changes can also have benefits, albeit smaller, on resisting loads associated with a sideways fall onto the greater trochanter.

Finite element analysis informed variable selection for femoral fracture risk prediction

Logistic regression classification (LRC) is widely used to develop models to predict the risk of femoral fracture. LRC models based on areal bone mineral density (aBMD) alone are poor, with area under the receiver operator curve (AUROC) scores reported to be as low as 0.63. This has led to researchers investigating methods to extract further information from the image to increase performance. Recently, the use of active shape (ASM) and appearance models (AAM) have resulted in moderate improvements, but there is a risk that inclusion of too many modes will lead to overfitting. In addition, there are concerns that the effort required to extract the additional information does not justify the modest improvement in fracture risk prediction. This raises the question, are we reaching the limits of the information that can be extracted from an image? Finite element analysis was used in combination with active shape and appearance modelling to select variables to develop LRC models of fracture risk. Active shape and active appearance models were constructed based on a previously reported cohort of 94 post-menopausal Caucasian women (47 with and 47 without a fracture). T-tests were used to identify differences between the two groups for each mode of variation. Femur strength was predicted for two load cases, stance and a fall. Stepwise multi-variate linear regression was used to identify shape and appearance modes that were predictors of strength for the femurs in the training set. Femurs were also synthetically generated to explore the influence of the first 10 modes of the shape and appearance models. Identified modes of variation were then used to generate LRC models to predict fracture risk. Only 6 modes, 4 active appearance and 2 active shape modes, were identified that had a significant influence on predicted fracture strength. Of these, only two active appearance modes were needed to substantially improve the predictive mode performance (ΔAUROC = 0.080). The addition of 3 more modes (1 AAM and two ASM) further improved the performance of the classifier (ΔAUROC = 0.123). Further addition of modes did not result in any further substantial improvements. Based on these findings, it is suggested that we are reaching the limits of the information that can be extracted from an image to predict fracture risk.

DXA-Based 3D Analysis of the Cortical and Trabecular Bone of Hip Fracture Postmenopausal Women: A Case-Control Study

Methods using statistical shape and appearance models have been proposed to analyze bone mineral density (BMD) in 3D from dual energy X-ray absorptiometry (DXA) scans. This paper presents a retrospective case-control study assessing the association of DXA-derived 3D measurements with osteoporotic hip fracture in postmenopausal women. Patients who experienced a hip fracture between 1 and 6 years from baseline and age-matched controls were included in this study. The 3D-SHAPER software (version 2.7, Galgo Medical, Barcelona, Spain) was used to derive 3D analysis from hip DXA scans at baseline. DXA and 3D measurements were compared between groups. Total hip areal BMD of hip fracture group as measured by DXA was 10.7% lower compared to control group. Differences in volumetric BMD (total hip) as measured by 3D-SHAPER were more pronounced in the trabecular compartment (-23.3%) than in the cortex (-8.2%). The area under the receiver operating curve was 0.742 for trabecular volumetric BMD, 0.706 for cortical volumetric BMD, and 0.712 for total hip areal BMD. Differences in the cortex were locally more pronounced at the medial aspect of the shaft, the lateral aspect of the greater trochanter, and the superolateral aspect of the neck. Marked differences in volumetric BMD were observed in the greater trochanter. This case-control study showed the association of DXA-derived 3D measurements with hip fracture. Analysis of large cohorts will be performed in future work to determine if DXA-derived 3D measurements could improve fracture risk prediction in clinical practice.

Cortical bone mapping improves finite element strain prediction accuracy at the proximal femur

Despite evidence of the biomechanical role of cortical bone, current state of the art finite element models of the proximal femur built from clinical CT data lack a subject-specific representation of the bone cortex. Our main research hypothesis is that the subject-specific modelling of cortical bone layer from CT images, through a deconvolution procedure known as Cortical Bone Mapping (CBM, validated for cortical thickness and density estimates) can improve the accuracy of CT-based FE models of the proximal femur, currently limited by partial volume artefacts. Our secondary hypothesis is that a careful choice of cortical-specific density-elasticity relationship may improve model accuracy. We therefore: (i) implemented a procedure to include subject-specific CBM estimates of both cortical thickness and density in CT-based FE models. (ii) defined alternative models that included CBM estimates and featured a cortical-specific or an independently optimised density-elasticity relationship. (iii) tested our hypotheses in terms of elastic strain estimates and failure load and location prediction, by comparing with a published cohort of 14 femurs, where strain and strength in stance and fall loading configuration were experimentally measured, and estimated through reference FE models that did not explicitly model the cortical compartment. Our findings support the main hypothesis: an explicit modelling of the proximal femur cortical bone layer including CBM estimates of cortical bone thickness and density increased the FE strains prediction, mostly by reducing peak errors (average error reduced by 30%, maximum error and 95th percentile of error distribution halved) and especially when focusing on the femoral neck locations (all error metrics at least halved). We instead rejected the secondary hypothesis: changes in cortical density-elasticity relationship could not improve validation performances. From these improved baseline strain estimates, further work is needed to achieve accurate strength predictions, as models incorporating cortical thickness and density produced worse estimates of failure load and equivalent estimates of failure location when compared to reference models. In summary, we recommend including local estimates of cortical thickness and density in FE models to estimate bone strains in physiological conditions, and especially when designing exercise studies to promote bone strength.

Heterogeneous Spatial and Strength Adaptation of the Proximal Femur to Physical Activity: A Within-Subject Controlled Cross-Sectional Study

Physical activity (PA) enhances proximal femur bone mass, as assessed using projectional imaging techniques. However, these techniques average data over large volumes, obscuring spatially heterogeneous adaptations. The current study used quantitative computed tomography, statistical parameter mapping, and subject-specific finite element (FE) modeling to explore spatial adaptation of the proximal femur to PA. In particular, we were interested in adaptation occurring at the superior femoral neck and improving strength under loading from a fall onto the greater trochanter. High/long jump athletes (n = 16) and baseball pitchers (n = 16) were utilized as within-subject controlled models as they preferentially load their take-off leg and leg contralateral to their throwing arm, respectively. Controls (n = 15) were included but did not show any dominant-to-nondominant (D-to-ND) leg differences. Jumping athletes showed some D-to-ND leg differences but less than pitchers. Pitchers had 5.8% (95% confidence interval [CI] 3.9%-7.6%) D-to-ND leg differences in total hip volumetric bone mineral density (vBMD), with increased vBMD in the cortical compartment of the femoral neck and trochanteric cortical and trabecular compartments. Voxel-based morphometry analyses and cortical bone mapping showed pitchers had D-to-ND leg differences within the regions of the primary compressive trabeculae, inferior femoral neck, and greater trochanter but not the superior femoral neck. FE modeling revealed pitchers had 4.1% (95% CI 1.4%-6.7%) D-to-ND leg differences in ultimate strength under single-leg stance loading but no differences in ultimate strength to a fall onto the greater trochanter. These data indicate the asymmetrical loading associated with baseball pitching induces proximal femur adaptation in regions associated with weight bearing and muscle contractile forces and increases strength under single-leg stance loading. However, there were no benefits evident at the superior femoral neck and no measurable improvement in ultimate strength to common injurious loading during aging (ie, fall onto the greater trochanter), raising questions as to how to better target these variables with PA. © 2019 American Society for Bone and Mineral Research.

Association between osteoporotic femoral neck fractures and DXA-derived 3D measurements at lumbar spine: a case-control study

A case-control study assessing the association of DXA-derived 3D measurements at lumbar spine with osteoporotic hip fractures was performed. Stronger association was found between transcervical hip fractures and integral (AUC = 0.726), and cortical (AUC = 0.696) measurements at the lumbar spine compared with measurements at the trabecular bone (AUC = 0.617); although femur areal bone mineral density (aBMD) remains the referent measurement for hip fracture risk evaluation (AUC = 0.838).

PURPOSE

The aim of the present study was to evaluate the association between DXA-derived 3D measurements at lumbar spine and osteoporotic hip fractures.

METHODS

We analyzed a case-control database composed by 61 women with transcervical hip fractures and 61 age-matched women without any type of fracture. DXA scans at lumbar spine were acquired, and areal bone mineral density (aBMD) was measured. Integral, trabecular and cortical volumetric BMD (vBMD), cortical thickness, and cortical surface BMD (sBMD) at different regions of interest were assessed using a DXA-based 3D modeling software. Descriptive statistics, tests of difference, odds ratio (OR), and area under the receiver operating curve (AUC) were used to compare hip fracture and control groups.

RESULTS

Integral vBMD, cortical vBMD, cortical sBMD, and cortical thickness were the DXA-derived 3D measurements at lumbar spine that showed the stronger association with transcervical hip fractures, with AUCs in the range of 0.685-0.726, against 0.670 for aBMD. The highest AUC (0.726) and OR (2.610) at the lumbar spine were found for integral vBMD at the posterior vertebral elements. Significantly, lower AUC (0.617) and OR (1.607) were found for trabecular vBMD at the vertebral body. Overall, total femur aBMD remains the DXA-derived measurement showing the highest AUC (0.838) and OR (6.240).

CONCLUSION

This study showed the association of DXA-derived measurements at lumbar spine with transcervical hip fractures. A strong association between vBMD at the posterior vertebral elements and transcervical hip fractures was observed, probably because of global deterioration of the cortical bone. Further studies should be carried out to investigate on the relative risk of transcervical fracture in patients with long-term cortical structural deterioration.

The spatial differences in bone mineral density and hip structure between low-energy femoral neck and trochanteric fractures in elderly Chinese using quantitative computed tomography

The purpose of this study was to investigate the differences in bone mineral density (BMD) and hip structure between femoral neck and trochanteric fractures in elderly Chinese individuals using quantitative computed tomography (QCT). A total of 625 Chinese patients (mean age 75.8 years) who sustained low-energy hip fractures (female: 293 femoral neck, 175 trochanteric; male: 82 femoral neck, 75 trochanteric) were recruited. Each patient underwent a hip QCT scan. The areal BMD (aBMD) of the contralateral normal hip was obtained using a computed tomography X-ray absorptiometry module. Using the bone investigation toolkit (BIT) module, the femoral neck was divided into four quadrants: supero-anterior (SA), infero-anterior (IA), infero-posterior (IP), and supero-posterior (SP). Estimated cortical thickness, cortical BMD, and trabecular BMD were measured in each quadrant. Using the hip structure analysis (HSA) function, several parameters were calculated. Stratified by sex, covariance analyses were applied to compare the femoral neck fractures group with trochanteric fractures group after adjustments for age, height, and weight. In women, trochanteric fractures exhibited lower trabecular BMD and estimated cortical thickness at three quadrants of the femoral neck (IA: P = 0.02, P < 0.01; IP: P < 0.01, P = 0.01; SP: P = 0.01, P < 0.01), and lower aBMD at the trochanter area (P < 0.01); femoral neck fractures exhibited lower cortical BMD and estimated cortical thickness at the SA quadrant (P = 0.04, P = 0.01). Differences in HSA parameters were not statistically significant. Among all parameters, the most valuable ones to discrimination of hip fracture type are estimated cortical thickness of the SA quadrant of femoral neck and the aBMD of the trochanter area. In men, only lower cortical BMD at the SP quadrant and aBMD at the trochanter were found in the trochanteric fractures (P = 0.02, P < 0.01). QCT outcomes indicate that spatial differences are helpful to explore the pathogenesis of different type of hip fractures. In women, trochanteric fractures are related to severer osteoporosis, whereas cortical fragility in the SA region of the femoral neck predominates in cases of femoral neck fractures. In men, trochanteric fractures are related to more bone loss of trochanter.

Ultrashort echo time magnetic resonance imaging (UTE-MRI) of cortical bone correlates well with histomorphometric assessment of bone microstructure

Ultrashort echo time magnetic resonance imaging (UTE-MRI) techniques have been increasingly used to assess cortical bone microstructure. High resolution micro computed tomography (μCT) is routinely employed for validating the MRI-based assessments. However, water protons in cortical bone may reside in micropores smaller than the detectable size ranges by μCT. The goal of this study was to evaluate the upper limit of UTE-MRI and compare its efficacy to μCT at determining bone porosity ex vivo. This study investigated the correlations between UTE-MRI based quantifications and histomorphometric measures of bone porosity that cover all pores larger than 1 μm. Anterior tibial midshaft specimens from eleven donors (51 ± 16 years old, 6 males, 5 females) were scanned on a clinical 3 T-MRI using UTE magnetization transfer (UTE-MT, three power levels and five frequency offsets) and UTE-T2* sequences. Two-pool MT modeling and bi-component exponential T2* fitting were performed on the MRI datasets. Specimens were then scanned by μCT at 9 μm voxel size. Histomorphometry was performed on hematoxylin and eosin (H&E) stained slides imaged at submicron resolution. Macromolecular fraction from MT modeling, bi-component T2* fractions, and short component T2* showed strong correlations (R > 0.7, p < 0.01) with histomorphometric total and large-pores (>40 μm) porosities as well as with μCT-based porosity. UTE-MRI could also assess small pores variations with moderate correlations (R > 0.5, p < 0.01). The UTE-MRI techniques can detect variations of bone porosity comprised of pores below the range detectable by μCT. Such fine pore variations can contribute differently to the development of bone diseases or to the bone remodeling process, however, this needs to be investigated. In scanned specimens, major porosity changes were from large pores, therefore the μCT employment was likely adequate to validate UTE-MRI biomarkers.

Hip Fracture Discrimination Based on Statistical Multi-parametric Modeling (SMPM)

Studies using quantitative computed tomography (QCT) and data-driven image analysis techniques have shown that trabecular and cortical volumetric bone mineral density (vBMD) can improve the hip fracture prediction of dual-energy X-ray absorptiometry areal BMD (aBMD). Here, we hypothesize that (1) QCT imaging features of shape, density and structure derived from data-driven image analysis techniques can improve the hip fracture discrimination of classification models based on mean femoral neck aBMD (Neck.aBMD), and (2) that data-driven cortical bone thickness (Ct.Th) features can improve the hip fracture discrimination of vBMD models. We tested our hypotheses using statistical multi-parametric modeling (SMPM) in a QCT study of acute hip fracture of 50 controls and 93 fragility fracture cases. SMPM was used to extract features of shape, vBMD, Ct.Th, cortical vBMD, and vBMD in a layer adjacent to the endosteal surface to develop hip fracture classification models with machine learning logistic LASSO. The performance of these classification models was evaluated in two aspects: (1) their hip fracture classification capability without Neck.aBMD, and (2) their capability to improve the hip fracture classification of the Neck.aBMD model. Assessments were done with 10-fold cross-validation, areas under the receiver operating characteristic curve (AUCs), differences of AUCs, and the integrated discrimination improvement (IDI) index. All LASSO models including SMPM-vBMD features, and the majority of models including SMPM-Ct.Th features performed significantly better than the Neck.aBMD model; and all SMPM features significantly improved the hip fracture discrimination of the Neck.aBMD model (Hypothesis 1). An interesting finding was that SMPM-features of vBMD also captured Ct.Th patterns, potentially explaining the superior classification performance of models based on SMPM-vBMD features (Hypothesis 2). Age, height and weight had a small impact on model performances, and the model of shape, vBMD and Ct.Th consistently yielded better performances than the Neck.aBMD models. Results of this study clearly support the relevance of bone density and quality on the assessment of hip fracture, and demonstrate their potential on patient and healthcare cost benefits.

An Automatic Personalized Internal Fixation Plate Modeling Framework for Minimally Invasive Curved Bone Fracture Surgery Based on Preregistration With Capsule Projection Model

OBJECTIVE

In this paper, a framework to visualize and model internal fixation plates is presented for computer-aided personalized and minimally invasive curved bone fracture surgery.

METHODS

We focus on personalized reverse reconstruction of the bone fracture plate based on three-dimensional (3-D) mesh models obtained from a 3-D optical scanner. The steps of the method are as follows. First, principal component analysis and the K-means method are used to reconstruct a Bezier curve (ridge line) of broken bones. Second, based on the geometric shape of the curved broken bones, a capsule projection model of the broken bones is proposed to obtain the feature information of the broken bone sections. Third, the ordering points to identify the clustering structure (OPTICS) method is utilized for preregistration (rough registration). Fourth, a regional self-growth strategy is designed to extract the cross-section points. Fifth, the iterative closest point method is applied for the accurate registration of the fracture surface models. Finally, a personalized internal fixation plate model is reconstructed based on several user points.

RESULTS

The internal fixation plate model can be reconstructed according to the patient's bone parameters.

CONCLUSION

Clinicians can use this framework to obtain personalized and accurate internal fixation plate models that effectively represent the broken bones of patients. Via X-ray navigation, the personalized forged plate can be fixed on the target area through a small incision.

SIGNIFICANCE

This framework provides a reasonable and practicable technical approach for computer-aided minimally invasive curved bone fracture surgery.

Adaptation of the proximal humerus to physical activity: A within-subject controlled study in baseball players

The proximal humerus is a common, yet understudied site for osteoporotic fracture. The current study explored the impact of prolonged physical activity on proximal humerus bone health by comparing bone properties between the throwing and nonthrowing arms within professional baseball players. The proximal humerus in throwing arms had 28.1% (95% CI, 17.8 to 38.3%) greater bone mass compared to nonthrowing arms, as assessed using dual-energy x-ray absorptiometry. At the level of the surgical neck, computed tomography revealed 12.0% (95% CI, 8.2 to 15.8%) greater total cross-sectional area and 31.0% (95% CI, 17.8 to 44.2%) greater cortical thickness within throwing arms, which contributed to 56.8% (95% CI, 44.9 to 68.8%) greater polar moment of inertia (i.e., estimated ability to resist torsional forces) compared to nonthrowing arms. Within the humeral head and greater tubercle regions, throwing arms had 3.1% (95% CI, 1.1 to 5.1%) more trabecular bone, as assessed using high-resolution magnetic resonance imaging. Three-dimensional mapping of voxel- and vertex-wise differences between arms using statistical parametric mapping techniques revealed throwing arms had adaptation within much of the proximal diaphysis, especially the posterolateral cortex. The pattern of proximal diaphysis adaptation approximated the pattern of strain energy distribution within the proximal humerus during a fastball pitch derived from a musculoskeletal and finite element model in a representative player. These data demonstrate the adaptive ability of the proximal humerus to physical activity-related mechanical loads. It remains to be established how they translate to exercise prescription to improve bone health within the proximal humerus; however, they provide unique insight into the relationship between prolonged loading and skeletal adaptation at a clinically relevant osteoporotic site.

Collagen proton fraction from ultrashort echo time magnetization transfer (UTE-MT) MRI modelling correlates significantly with cortical bone porosity measured with micro-computed tomography (μCT)

Intracortical bone porosity is a key microstructural parameter that determines bone mechanical properties. While clinical MRI visualizes the cortical bone with a signal void, ultrashort echo time (UTE) MRI can acquire high signal from cortical bone, thus enabling quantitative assessments. Magnetization transfer (MT) imaging combined with UTE-MRI can indirectly assess protons in the bone collagenous matrix, which are inversely related to porosity. This study aimed to examine UTE-MT MRI techniques to evaluate intracortical bone porosity. Eighteen human cortical bone specimens from the tibial and fibular midshafts were scanned using UTE-MT sequences on a clinical 3 T MRI scanner and on a high-resolution micro-computed tomography (μCT) scanner. A series of MT pulse saturation powers (500°, 1000°, 1500°) and frequency offsets (2, 5, 10, 20, 50 kHz) were used to measure the macromolecular fraction (MMF) and macromolecular T2 (T2MM ) using a two-pool MT model. The measurements were made on 136 different regions of interest (ROIs). ROIs were selected at three cortical bone layers (from endosteum to periosteum) and four anatomical sites (anterior, mid-medial, mid-lateral, and posterior) to provide a wide range of porosity. MMF showed moderate to strong correlations with intracortical bone porosity (R = -0.67 to -0.73, p < 0.01) and bone mineral density (BMD) (R = +0.46 to +0.70, p < 0.01). Comparing the average MMF between cortical bone layers revealed a significant increase from the endosteum towards the periosteum. Such a pattern was in agreement with porosity reduction and BMD increase towards the periosteum. These results suggest that the two-pool UTE-MT technique can potentially serve as a novel and accurate tool to assess intracortical bone porosity.

Micro-Finite Element Analysis of the Proximal Femur on the Basis of High-Resolution Magnetic Resonance Images

PURPOSE OF REVIEW

Hip fractures have catastrophic consequences. The purpose of this article is to review recent developments in high-resolution magnetic resonance imaging (MRI)-guided finite element analysis (FEA) of the hip as a means to determine subject-specific bone strength.

RECENT FINDINGS

Despite the ability of DXA to predict hip fracture, the majority of fractures occur in patients who do not have BMD T scores less than - 2.5. Therefore, without other detection methods, these individuals go undetected and untreated. Of methods available to image the hip, MRI is currently the only one capable of depicting bone microstructure in vivo. Availability of microstructural MRI allows generation of patient-specific micro-finite element models that can be used to simulate real-life loading conditions and determine bone strength. MRI-based FEA enables radiation-free approach to assess hip fracture strength. With further validation, this technique could become a potential clinical tool in managing hip fracture risk.

Cortical Bone Mapping: Measurement and Statistical Analysis of Localised Skeletal Changes

PURPOSE OF REVIEW

Cortical bone mapping (CBM) is a technique for measuring localised skeletal changes from computed tomography (CT) images. It can provide measurements with accuracy surpassing the underlying imaging resolution. CBM can detect changes in several properties of the cortex, with no prior assumptions about the likely location of said changes. This paper summarises the theory behind CBM, discusses its strengths and limitations, and reviews some studies in which it has been applied.

RECENT FINDINGS

CBM has revealed associations between fracture risk and cortical properties in specific regions of the proximal femur which present feasible therapeutic targets. Analyses of several pharmaceutical and exercise interventions quantify effects that are distinct both in location and in the nature of the micro-architectural changes. CBM has illuminated age-related changes in the proximal femur and has recently been applied to other bones, as well as to the assessment of cartilage. The CBM processing pipeline is designed primarily for large cohort studies. Its main impact thus far has not been in the realm of clinical practice, but rather to improve our fundamental understanding of localised bone structure and changes.

Cortical and Trabecular Bone Analysis of Patients With High Bone Mass From the Barcelona Osteoporosis Cohort Using 3-Dimensional Dual-Energy X-ray Absorptiometry: A Case-Control Study

High bone mass (HBM), a rare phenotype, can be detected by dual-energy X-ray absorptiometry (DXA) scanning. Measurements with peripheral quantitative computed tomography at the tibia have found increased trabecular bone mineral density and changes in cortical bone density and structure, all of which lead to increased bone strength. However, no studies on cortical and trabecular bone have been performed at the femur. The recently developed 3-dimensional (3D)-DXA software algorithm quantifies the trabecular and cortical volumetric bone mineral density (vBMD) and the anatomical distribution of cortical thickness using routine hip DXA scans. We analyzed the femurs of 15 women with HBM and 15 controls from the Barcelona Osteoporosis (BARCOS) cohort using the 3D-DXA technique. The mean vBMD of proximal femur was 29.7% higher in HBM cases than in controls for the integral bone, 41.3% higher for the trabecular bone, and 7.3% higher for the cortical bone (p < 0.001). No differences in bone size were detected between cases and controls. Patients with HBM had a thicker cortex and higher trabecular and cortical vBMDs, as measured by 3D-DXA at the femur and compared to controls; bone size was similar in both groups. To the best of our knowledge, this is the first description of trabecular and cortical characteristics of the hip in patients with HBM.

Sex differences in the spatial distribution of bone in relation to incident hip fracture: Findings from the AGES-Reykjavik study

In this case-cohort study, we used data-driven computational anatomy approaches to assess within and between sex spatial differences in proximal femoral bone characteristics in relation to incident hip fracture. One hundred male and 234 female incident hip fracture cases, and 1047 randomly selected noncase subcohort participants (562 female) were chosen from the population-based AGES-Reykjavik study (mean age of 77 years). The baseline -i.e. before hip fracture- hip quantitative computed tomography scans of these subjects were analyzed using voxel-based morphometry, tensor-based morphometry, and surface-based statistical parametric mapping to assess the spatial distribution of volumetric bone mineral density (vBMD), internal structure, and cortical bone properties (thickness, vBMD and trabecular vBMD adjacent to the endosteal surface) of the proximal femur, respectively, in relation to incident hip fracture. Results showed that in both men and women: 1) the superior aspect of the femoral neck and the trochanteric region (except for cortical bone thickness) were consistently identified as being associated with incident hip fracture, and 2) differences in bone properties between noncases and incident hip fracture cases followed similar trends, were located at compatible regions, and manifested heterogeneity in the spatial distribution of their magnitude with focal regions showing larger differences. With respect to sex differences, most of the regions with a significant interaction between fracture group and sex showed: 1) differences of greater magnitude in men between noncases and incident hip fracture cases with different spatial distributions for all bone properties with the exception of cortical bone thickness, and 2) that while most of these regions showed better bone quality in male cases than in female cases, female cases showed higher vBMD in the principal compressive group and higher endotrabecular vBMD at several regions including the anterior, posterior, and lateral aspects of the proximal femur. These findings indicate the value of these image analysis techniques by providing unique information about the specific patterns of bone deterioration associated with incident hip fracture and their sex differences, highlighting the importance of looking to men and women separately in the assessment of hip fracture risk.

Fracture Prediction by Computed Tomography and Finite Element Analysis: Current and Future Perspectives

PURPOSE OF REVIEW

This review critiques the ability of CT-based methods to predict incident hip and vertebral fractures.

RECENT FINDINGS

CT-based techniques with concurrent calibration all show strong associations with incident hip and vertebral fracture, predicting hip and vertebral fractures as well as, and sometimes better than, dual-energy X-ray absorptiometry areal biomass density (DXA aBMD). There is growing evidence for use of routine CT scans for bone health assessment. CT-based techniques provide a robust approach for osteoporosis diagnosis and fracture prediction. It remains to be seen if further technical advances will improve fracture prediction compared to DXA aBMD. Future work should include more standardization in CT analyses, establishment of treatment intervention thresholds, and more studies to determine whether routine CT scans can be efficiently used to expand the number of individuals who undergo evaluation for fracture risk.

A new quantitative 3D approach to imaging of structural joint disease

Imaging of joints with 2D radiography has not been able to detect therapeutic success in research trials while 3D imaging, used regularly in the clinic, has not been approved for this purpose. We present a new 3D approach to this challenge called joint space mapping (JSM) that measures joint space width in 3D from standard clinical computed tomography (CT) data, demonstrating its analysis steps, technical validation, and reproducibility. Using high resolution peripheral quantitative CT as gold standard, we show a marginal over-estimation in accuracy of +0.13 mm and precision of ±0.32 mm. Inter-operator reproducibility bias was near-zero at −0.03 mm with limits of agreement ±0.29 mm and a root mean square coefficient of variation 7.5%. In a technical advance, we present results from across the hip joint in 3D with optimum validation and reproducibility metrics shown at inner joint regions. We also show JSM versatility using different imaging data sets and discuss potential applications. This 3D mapping approach provides information with greater sensitivity than reported for current radiographic methods that could result in improved patient stratification and treatment monitoring.

Development of Subject-Specific Proximal Femur Finite Element Models Of Older Adults with Obesity to Evaluate the Effects of Weight Loss on Bone Strength

Study background

Recommendation of intentional weight loss in older adults remains controversial, due in part to the loss of bone mineral density (BMD) known to accompany weight loss. While finite element (FE) models have been used to assess bone strength, these methods have not been used to study the effects of weight loss. The purpose of this study is to develop subject-specific FE models of the proximal femur and study the effect of intentional weight loss on bone strength.

Methods

Computed tomography (CT) scans of the proximal femur of 25 overweight and obese (mean BMI=29.7 ± 4.0 kg/m²), older adults (mean age=65.6 ± 4.1 years) undergoing an 18-month intentional weight loss intervention were obtained at baseline and post-intervention. Measures of volumetric BMD (vBMD) and variable cortical thickness were derived from each subject CT scan and directly mapped to baseline and post-intervention models. Subject-specific FE models were developed using morphing techniques. Bone strength was estimated through simulation of a single-limb stance and sideways fall configuration.

Results

After weight loss intervention, there were significant decreases from baseline to 18 months in vBMD (total hip: -0.024 ± 0.013 g/cm³; femoral neck: -0.012 ± 0.014 g/cm³), cortical thickness (total hip: -0.044 ± 0.032 mm; femoral neck: -0.026 ± 0.039 mm), and estimated strength (stance: -0.15 ± 0.12 kN; fall: -0.04 ± 0.06 kN). Adjusting for baseline bone measures, body mass, and gender, correlations were found between weight change and change in total hip and femoral neck cortical thickness (all p<0.05). For every 1 kilogram of body mass lost cortical thickness in the total hip and femoral neck decreased by 0.003 mm and 0.004 mm, respectively. No significant correlations were present for the vBMD or strength data.

Conclusion

The developed subject-specific FE models could be used to better understand the effects of intentional weight loss on bone health.

How does the femoral cortex depend on bone shape? A methodology for the joint analysis of surface texture and shape

In humans, there is clear evidence of an association between hip fracture risk and femoral neck bone mineral density, and some evidence of an association between fracture risk and the shape of the proximal femur. Here, we investigate whether the femoral cortex plays a role in these associations: do particular morphologies predispose to weaker cortices? To answer this question, we used cortical bone mapping to measure the distribution of cortical mass surface density (CMSD, mg/cm2) in a cohort of 125 females. Principal component analysis of the femoral surfaces identified three modes of shape variation accounting for 65% of the population variance. We then used statistical parametric mapping (SPM) to locate regions of the cortex where CMSD depends on shape, allowing for age. Our principal findings were increased CMSD with increased gracility over much of the proximal femur; and decreased CMSD at the superior femoral neck, coupled with increased CMSD at the calcar femorale, with increasing neck-shaft angle. In obtaining these results, we studied the role of spatial normalization in SPM, identifying systematic misregistration as a major impediment to the joint analysis of CMSD and shape. Through a series of experiments on synthetic data, we evaluated a number of registration methods for spatial normalization, concluding that only those predicated on an explicit set of homologous landmarks are suitable for this kind of analysis. The emergent methodology amounts to an extension of Geometric Morphometric Image Analysis to the domain of textured surfaces, alongside a protocol for labelling homologous landmarks in clinical CT scans of the human proximal femur.

Ricci-flow based conformal mapping of the proximal femur to identify exercise loading effects

The causal relationship between habitual loading and adaptive response in bone morphology is commonly explored by analysing the spatial distribution of mechanically relevant features. In this study, 3D distribution of features in the proximal femur of 91 female athletes (5 exercise loading groups representing habitual loading) is contrasted with 20 controls. A femur specific Ricci-flow based conformal mapping procedure was developed for establishing correspondence among the periosteal surfaces. The procedure leverages the invariance of the conformal mapping method to isometric shape differences to align surfaces in the 2D parametric domain, to produce dense correspondences across an isotopological set of surfaces. This is implemented through a multi-parametrisation approach to detect surface features and to overcome the issue of inconsistency in the anatomical extent present in the data. Subsequently, the group-wise distribution of two mechanically relevant features was studied – cortical thickness and surface principal strains (simulation results of a sideways fall). Statistical inferences over the surfaces were made by contrasting the athlete groups with the controls through statistical parametric mapping. With the aid of group-wise and composite-group maps, proximal femur regions affected by specific loading groups were identified with a high degree of spatial localisation.

Measurement of the bone endocortical region using clinical CT

The extent of the endocortical region and cortical bone mineral density (cBMD) throughout the proximal femur are of interest as both have been linked to fracture risk and osteoporosis treatment response. Non-invasive in-vivo clinical CT-based techniques capable of measuring the cortical bone attributes of thickness, density and mass over a bone surface have already been proposed. Several studies have robustly shown these methods to be capable of producing cortical thickness measurements to a sub-millimetre accuracy. Unfortunately, these methods are unable to provide high quality cBMD estimates, and are not designed to measure any attributes over the endocortical region of cortical bone. In this paper, we develop a cortical bone mapping based technique capable of providing an improved cBMD estimate and a measure of the endocortical width, while maintaining similar quality cortical thickness and trabecular bone mineral density (tBMD) estimates. The performance of the technique was assessed using a paired dataset of ex-vivo QCT and HR-pQCT scans across 72 proximal femurs. The HR-pQCT scans were analysed using a new method developed for this study: high resolution tissue classification (HRTC). In HRTC the cortical, endocortical and sub-surface trabecular bone features are extracted from the partially resolvable microarchitectural details in the HR-pQCT scan. We demonstrate that measurement of the endocortical extent from QCT is possible with an accuracy of -0.15±0.71mm, and that local cBMD can be measured down to densities of 300 mg/cm³.

Regional analysis of age-related local bone loss in the spine of a healthy population using 3D voxel-based modeling

Local variations in bone loss may be of great importance to individually predict osteoporotic fractures but are neglected by current densitometry techniques. The purpose of this study was to evaluate regional variations of normal bone loss at the spine among different age groups using voxel-based morphometry. Non-contrast MDCT scans of 16 patients under the age of 40 (mean age 26years) without spinal pathology were identified as a reference cohort, where each thoracolumbar vertebra was assessed individually. For comparison, 38 patients >40years were grouped by decades in 4 cohorts of 10 patients each, except the youngest, including 8 patients only. All spines were automatically detected, segmented and non-rigidly registered for spatially normalized vertebral bodies. Afterwards, statistical and T-score mapping was performed to highlight local density differences in comparison to the reference cohort. The calculated statistical maps of significantly affected density regions (ADR) started to highlight small local changes of volumetric bone mineral density (vBMD) distribution within the vertebra of L5 (ADR: 7.9%) in the fifties cohort. Regions near the endplates were most affected. The effect dramatically increased in the sixties cohort, where bone loss was most prominent from T12 to L2. In the seventies cohort, around 50% of voxels in T10 to L5 showed significantly decreased vBMD. In conclusion, ADR and local T-score maps of the spine showed age-related local variations in a healthy population, corresponding to known areas of fracture origination and increased fracture incidence. It thus might provide a powerful tool in diagnosis of osteoporosis.

Spatial Differences in the Distribution of Bone Between Femoral Neck and Trochanteric Fractures

There is little knowledge about the spatial distribution differences in volumetric bone mineral density and cortical bone structure at the proximal femur between femoral neck fractures and trochanteric fractures. In this case-control study, a total of 93 women with fragility hip fractures, 72 with femoral neck fractures (mean ± SD age: 70.6 ± 12.7 years) and 21 with trochanteric fractures (75.6 ± 9.3 years), and 50 control subjects (63.7 ± 7.0 years) were included for the comparisons. Differences in the spatial distributions of volumetric bone mineral density, cortical bone thickness, cortical volumetric bone mineral density, and volumetric bone mineral density in a layer adjacent to the endosteal surface were investigated using voxel-based morphometry (VBM) and surface-based statistical parametric mapping (SPM). We compared these spatial distributions between controls and both types of fracture, and between the two types of fracture. Using VBM, we found spatially heterogeneous volumetric bone mineral density differences between control subjects and subjects with hip fracture that varied by fracture type. Interestingly, femoral neck fracture subjects, but not subjects with trochanteric fracture, showed significantly lower volumetric bone mineral density in the superior aspect of the femoral neck compared with controls. Using surface-based SPM, we found that compared with controls, both fracture types showed thinner cortices in regions in agreement with the type of fracture. Most outcomes of cortical and endocortical volumetric bone mineral density comparisons were consistent with VBM results. Our results suggest: 1) that the spatial distribution of trabecular volumetric bone mineral density might play a significant role in hip fracture; 2) that focal cortical bone thinning might be more relevant in femoral neck fractures; and 3) that areas of reduced cortical and endocortical volumetric bone mineral density might be more relevant for trochanteric fractures in Chinese women. © 2017 American Society for Bone and Mineral Research.

Sex-related variations in cortical and trabecular bone of the femoral neck in an elderly Chinese population

Quantitative computed tomography (QCT) was used to investigate sex-related variations in cortical and trabecular bone of the femoral neck. Cortical bone thickness of women in the superior quadrant was thinner than that of men, and the cortex in all four quadrants was negatively associated with age in women.

INTRODUCTION

This cross-sectional study aimed to investigate sex-related similarities and differences in femoral neck structure in an elderly Chinese population by QCT bone investigational toolkit (BIT) analysis.

METHODS

This study included 207 male (67.9 ± 7.7 years; range, 55-87 years) and 400 female subjects (68.0 ± 8.7 years; range, 55-96 years). BIT module was used to measure cortical and trabecular bone in anatomic quadrants of the femoral neck. Measurements of cortical thickness (Ct.Th), cortical vBMD (Ct.vBMD), trabecular vBMD (Tb.vBMD), and integral vBMD (It.vBMD) at the femoral neck were determined in four anatomical sectors.

RESULTS

The greatest difference between sexes, after adjusting for age, height, and weight, was in Ct.Th of Quadrant Supero-anterior (SA), which was 27.4% lower in women (p<0.001). Ct.Th of Quadrant Supero-posterior (SP) was 15.1% lower in women (p = 0.027). Ct.Th and Tb.vBMD in all four quadrants appeared to be negatively associated with age in females, whereas no significant relationship was observed in males, except Ct.Th of Quadrant SP.

CONCLUSIONS

The superior femoral neck geometry between males and females was significantly different, even after adjustment for body size and age, and the sub-regional cortical and trabecular bone negatively age-related changes in women indicated that women apparently have a more vulnerable geometrical outcome with age for fractures than men.

Three-dimensional adiabatic inversion recovery prepared ultrashort echo time cones (3D IR-UTE-Cones) imaging of cortical bone in the hip

PURPOSE

We present three-dimensional adiabatic inversion recovery prepared ultrashort echo time Cones (3D IR-UTE-Cones) imaging of cortical bone in the hip of healthy volunteers using a clinical 3T scanner.

METHODS

A 3D IR-UTE-Cones sequence, based on a short pulse excitation followed by a 3D Cones trajectory, with a nominal TE of 32μs, was employed for high contrast morphological imaging of cortical bone in the hip of heathy volunteers. Signals from soft tissues such as muscle and marrow fat were suppressed via adiabatic inversion and signal nulling. T₂^⁎ value of the cortical bone was also calculated based on 3D IR-UTE-Cones acquisitions with a series of TEs ranging from 0.032 to 0.8ms. A total of four healthy volunteers were recruited for this study. Average T₂^⁎ values and the standard deviation for four regions of interests (ROIs) at the greater trochanter, the femoral neck, the femoral head and the lesser trochanter were calculated.

RESULTS

The 3D IR-UTE-Cones sequence provided efficient suppression of soft tissues with excellent image contrast for cortical bone visualization in all volunteer hips. Exponential single component decay was observed for all ROIs, with averaged T₂^⁎ values ranging from 0.33 to 0.45ms, largely consistent with previously reported T₂^⁎ values of cortical bone in the tibial midshaft.

CONCLUSIONS

The 3D IR-UTE-Cones sequence allows in vivo volumetric imaging and quantitative T₂^⁎ measurement of cortical bone in the hip using a clinical 3T scanner.

Physical Activity for Strengthening Fracture Prone Regions of the Proximal Femur

PURPOSE OF REVIEW

Physical activity improves proximal femoral bone health; however, it remains unclear whether changes translate into a reduction in fracture risk. To enhance any fracture-protective effects of physical activity, fracture prone regions within the proximal femur need to be targeted.

RECENT FINDINGS

The proximal femur is designed to withstand forces in the weight-bearing direction, but less so forces associated with falls in a sideways direction. Sideways falls heighten femoral neck fracture risk by loading the relatively weak superolateral region of femoral neck. Recent studies exploring regional adaptation of the femoral neck to physical activity have identified heterogeneous adaptation, with adaptation principally occurring within inferomedial weight-bearing regions and little to no adaptation occurring in the superolateral femoral neck. There is a need to develop novel physical activities that better target and strengthen the superolateral femoral neck within the proximal femur. Design of these activities may be guided by subject-specific musculoskeletal modeling and finite-element modeling approaches.

Focal osteoporosis defects play a key role in hip fracture

BACKGROUND

Hip fractures are mainly caused by accidental falls and trips, which magnify forces in well-defined areas of the proximal femur. Unfortunately, the same areas are at risk of rapid bone loss with ageing, since they are relatively stress-shielded during walking and sitting. Focal osteoporosis in those areas may contribute to fracture, and targeted 3D measurements might enhance hip fracture prediction. In the FEMCO case-control clinical study, Cortical Bone Mapping (CBM) was applied to clinical computed tomography (CT) scans to define 3D cortical and trabecular bone defects in patients with acute hip fracture compared to controls. Direct measurements of trabecular bone volume were then made in biopsies of target regions removed at operation.

METHODS

The sample consisted of CT scans from 313 female and 40 male volunteers (158 with proximal femoral fracture, 145 age-matched controls and 50 fallers without hip fracture). Detailed Cortical Bone Maps (c.5580 measurement points on the unfractured hip) were created before registering each hip to an average femur shape to facilitate statistical parametric mapping (SPM). Areas where cortical and trabecular bone differed from controls were visualised in 3D for location, magnitude and statistical significance. Measures from the novel regions created by the SPM process were then tested for their ability to classify fracture versus control by comparison with traditional CT measures of areal Bone Mineral Density (aBMD). In women we used the surgical classification of fracture location ('femoral neck' or 'trochanteric') to discover whether focal osteoporosis was specific to fracture type. To explore whether the focal areas were osteoporotic by histological criteria, we used micro CT to measure trabecular bone parameters in targeted biopsies taken from the femoral heads of 14 cases.

RESULTS

Hip fracture patients had distinct patterns of focal osteoporosis that determined fracture type, and CBM measures classified fracture type better than aBMD parameters. CBM measures however improved only minimally on aBMD for predicting any hip fracture and depended on the inclusion of trabecular bone measures alongside cortical regions. Focal osteoporosis was confirmed on biopsy as reduced sub-cortical trabecular bone volume.

CONCLUSION

Using 3D imaging methods and targeted bone biopsy, we discovered focal osteoporosis affecting trabecular and cortical bone of the proximal femur, among men and women with hip fracture.

Statistical Parametric Mapping of HR-pQCT Images: A Tool for Population-Based Local Comparisons of Micro-Scale Bone Features

HR-pQCT enables in vivo multi-parametric assessments of bone microstructure in the distal radius and distal tibia. Conventional HR-pQCT image analysis approaches summarize bone parameters into global scalars, discarding relevant spatial information. In this work, we demonstrate the feasibility and reliability of statistical parametric mapping (SPM) techniques for HR-pQCT studies, which enable population-based local comparisons of bone properties. We present voxel-based morphometry (VBM) to assess trabecular and cortical bone voxel-based features, and a surface-based framework to assess cortical bone features both in cross-sectional and longitudinal studies. In addition, we present tensor-based morphometry (TBM) to assess trabecular and cortical bone structural changes. The SPM techniques were evaluated based on scan-rescan HR-pQCT acquisitions with repositioning of the distal radius and distal tibia of 30 subjects. For VBM and surface-based SPM purposes, all scans were spatially normalized to common radial and tibial templates, while for TBM purposes, rescans (follow-up) were spatially normalized to their corresponding scans (baseline). VBM was evaluated based on maps of local bone volume fraction (BV/TV), homogenized volumetric bone mineral density (vBMD), and homogenized strain energy density (SED) derived from micro-finite element analysis; while the cortical bone framework was evaluated based on surface maps of cortical bone thickness, vBMD, and SED. Voxel-wise and vertex-wise comparisons of bone features were done between the groups of baseline and follow-up scans. TBM was evaluated based on mean square errors of determinants of Jacobians at baseline bone voxels. In both anatomical sites, voxel- and vertex-wise uni- and multi-parametric comparisons yielded non-significant differences, and TBM showed no artefactual bone loss or apposition. The presented SPM techniques demonstrated robust specificity thus warranting their application in future clinical HR-pQCT studies.

Can CT image deblurring improve finite element predictions at the proximal femur?

The aim of this study was to determine if a CT image deblurring algorithm can improve CT-based FE modelling accuracy at the proximal femur. Experimental data (CT scans of fourteen proximal fresh-frozen cadaveric femurs, non-destructive surface strain measurements in stance and sideways fall loading configurations on all femurs, and failure loads obtained in stance for seven specimens, in sideways fall for the other seven) were taken from a recent study (Schileo et al., 2014). An estimate of the 3D Point Spread Function for each CT scan was used within a deconvolution solver to perform the deblurring. The most proximal regions of three specimens were scanned using an HRpQCT scanner and compared to the original and deblurred CT images to quantify errors in bone contour estimates and determine correlation of intensity values within the bone contours. Subject-specific FE models of the proximal femur were generated. The accuracy of deblurred FE predictions against experimental measurements was compared to the published (non-deblurred) FE results. When compared to HRpQCT, CT deblurring led to lower mean surface distances (0.31 vs. 0.49mm) and higher CT intensity correlations with respect to the original CT. All indicators of strain prediction accuracy were significantly improved in deblurred FE models, more markedly at the femoral neck (peak error reduced by 38%). Failure load prediction, based on a simple elastic limit model, was also improved in deblurred FE models, although differently for stance and sideways fall loading conditions. In stance, correlation was unchanged, but specimen-wise errors were reduced (mean error 10% vs. 15%). In sideways fall, correlation notably increased (R(2)=0.95 vs. 0.81), despite a general overestimation of failure load. In summary, the proposed CT deblurring technique yielded moderate but significant improvements in FE predictions, and may thus be considered a first step toward the improvement of CT-based FE models of the human femur.

The Effects on the Femoral Cortex of a 24 Month Treatment Compared to an 18 Month Treatment with Teriparatide: A Multi-Trial Retrospective Analysis

BACKGROUND

Teriparatide (TPTD) is an anabolic agent indicated for the treatment of severely osteoporotic patients who are at high risk of fragility fractures. The originally approved duration of TPTD treatment in several regions, including Europe, was 18 months. However, studies of areal bone mineral density (aBMD) showed additional benefit when treatment is continued beyond 18 months, and the drug is currently licenced for 24 months. Improvements in cortical structure at the proximal femur have already been shown in patients given TPTD for 24 months using quantitative computed tomography (QCT). Here, we investigate whether cortical and endocortical trabecular changes differ between an 18- and 24-month treatment.

METHODS

Since an 18- versus 24-month TPTD study using QCT has not been conducted, we studied combined QCT data from four previous clinical trials. Combined femoral QCT data from three 18-month TPTD studies ('18-month group') were compared with data from a fourth 24-month trial ('24-month group'). Cortical parameters were measured over the entire proximal femur which allowed for a comparison of the mean changes as well as a visual comparison of the colour maps of changes after 18 and 24 months TPTD.

RESULTS

For both the combined 18-month group and the 24-month group, overall cortical thickness and endocortical trabecular density increased, while overall cortical bone mineral density decreased. While the changes in the 24-month group were of greater magnitude compared to the 18-month group, the differences were only significant for the endocortical trabecular density (ECTD), corrected for age, weight, femoral neck T-score, total hip T-score and the baseline mean ECTD.

CONCLUSION

Although the combination of data from different clinical trials is not optimal, these data support the concept that the duration of TPTD in the 18-24 month phase is of clinical relevance when considering improvement in hip structure.

Quantitative 3D analysis of bone in hip osteoarthritis using clinical computed tomography

Objective

To assess the relationship between proximal femoral cortical bone thickness and radiological hip osteoarthritis using quantitative 3D analysis of clinical computed tomography (CT) data.

Methods

Image analysis was performed on clinical CT imaging data from 203 female volunteers with a technique called cortical bone mapping (CBM). Colour thickness maps were created for each proximal femur. Statistical parametric mapping was performed to identify statistically significant differences in cortical bone thickness that corresponded with the severity of radiological hip osteoarthritis. Kellgren and Lawrence (K&L) grade, minimum joint space width (JSW) and a novel CT-based osteophyte score were also blindly assessed from the CT data.

Results

For each increase in K&L grade, cortical thickness increased by up to 25 % in distinct areas of the superolateral femoral head–neck junction and superior subchondral bone plate. For increasing severity of CT osteophytes, the increase in cortical thickness was more circumferential, involving a wider portion of the head–neck junction, with up to a 7 % increase in cortical thickness per increment in score. Results were not significant for minimum JSW.

Conclusions

These findings indicate that quantitative 3D analysis of the proximal femur can identify changes in cortical bone thickness relevant to structural hip osteoarthritis.

Key Points

• CT is being increasingly used to assess bony involvement in osteoarthritis

• CBM provides accurate and reliable quantitative analysis of cortical bone thickness

• Cortical bone is thicker at the superior femoral head–neck with worse osteoarthritis

• Regions of increased thickness co-locate with impingement and osteophyte formation

• Quantitative 3D bone analysis could enable clinical disease prediction and therapy development

Electronic supplementary material

The online version of this article (doi:10.1007/s00330-015-4048-x) contains supplementary material, which is available to authorized users.