Prediction of femoral strength using 3D finite element models reconstructed from DXA images: validation against experiments

Computed tomography (CT)-based finite element (FE) models may improve the current osteoporosis diagnostics and prediction of fracture risk by providing an estimate for femoral strength. However, the need for a CT scan, as opposed to the conventional use of dual-energy X-ray absorptiometry (DXA) for osteoporosis diagnostics, is considered a major obstacle. The 3D shape and bone mineral density (BMD) distribution of a femur can be reconstructed using a statistical shape and appearance model (SSAM) and the DXA image of the femur. Then, the reconstructed shape and BMD could be used to build FE models to predict bone strength. Since high accuracy is needed in all steps of the analysis, this study aimed at evaluating the ability of a 3D FE model built from one 2D DXA image to predict the strains and fracture load of human femora. Three cadaver femora were retrieved, for which experimental measurements from ex vivo mechanical tests were available. FE models were built using the SSAM-based reconstructions: using only the SSAM-reconstructed shape, only the SSAM-reconstructed BMD distribution, and the full SSAM-based reconstruction (including both shape and BMD distribution). When compared with experimental data, the SSAM-based models predicted accurately principal strains (coefficient of determination >0.83, normalized root-mean-square error <16%) and femoral strength (standard error of the estimate 1215 N). These results were only slightly inferior to those obtained with CT-based FE models, but with the considerable advantage of the models being built from DXA images. In summary, the results support the feasibility of SSAM-based models as a practical tool to introduce FE-based bone strength estimation in the current fracture risk diagnostics

How accurately can subject-specific finite element models predict strains and strength of human femora? Investigation using full-field measurements

Subject-specific finite element models have been proposed as a tool to improve fracture risk assessment in individuals. A thorough laboratory validation against experimental data is required before introducing such models in clinical practice. Results from digital image correlation can provide full-field strain distribution over the specimen surface during in vitro test, instead of at a few pre-defined locations as with strain gauges. The aim of this study was to validate finite element models of human femora against experimental data from three cadaver femora, both in terms of femoral strength and of the full-field strain distribution collected with digital image correlation. The results showed a high accuracy between predicted and measured principal strains (R2=0.93, RMSE=10%, 1600 validated data points per specimen). Femoral strength was predicted using a rate dependent material model with specific strain limit values for yield and failure. This provided an accurate prediction (<2% error) for two out of three specimens. In the third specimen, an accidental change in the boundary conditions occurred during the experiment, which compromised the femoral strength validation. The achieved strain accuracy was comparable to that obtained in state-of-the-art studies which validated their prediction accuracy against 10–16 strain gauge measurements. Fracture force was accurately predicted, with the predicted failure location being very close to the experimental fracture rim. Despite the low sample size and the single loading condition tested, the present combined numerical-experimental method showed that finite element models can predict femoral strength by providing a thorough description of the local bone mechanical response

Generation of 3D shape, density, cortical thickness and finite element mesh of proximal femur from a DXA image

Areal bone mineral density (aBMD), as measured by dual-energy X-ray absorptiometry (DXA), predicts hip fracture risk only moderately. Simulation of bone mechanics based on DXA imaging of the proximal femur, may help to improve the prediction accuracy. Therefore, we collected three (1-3) image sets, including CT images and DXA images of 34 proximal cadaver femurs (set1, including 30 males, 4 females), 35 clinical patient CT images of the hip (set 2, including 27 males, 8 females) and both CT and DXA images of clinical patients (set 3, including 12 female patients). All CT images were segmented manually and landmarks were placed on both femurs and pelvises. Two separate statistical appearance models (SAMs) were built using the CT images of the femurs and pelvises in sets 1 and 2, respectively. The 3D shape of the femur was reconstructed from the DXA image by matching the SAMs with the DXA images. The orientation and modes of variation of the SAMs were adjusted to minimize the sum of the absolute differences between the projection of the SAMs and a DXA image. The mesh quality and the location of the SAMs with respect to the manually placed control points on the DXA image were used as additional constraints. Then, finite element (FE) models were built from the reconstructed shapes. Mean point-to-surface distance between the reconstructed shape and CT image was 1.0mm for cadaver femurs in set 1 (leave-one-out test) and 1.4mm for clinical subjects in set 3. The reconstructed volumetric BMD showed a mean absolute difference of 140 and 185mg/cm3 for set 1 and set 3 respectively. The generation of the SAM and the limitation of using only one 2D image were found to be the most significant sources of errors in the shape reconstruction. The noise in the DXA images had only small effect on the accuracy of the shape reconstruction. DXA-based FE simulation was able to explain 85% of the CT-predicted strength of the femur in stance loading. The present method can be used to accurately reconstruct the 3D shape and internal density of the femur from 2D DXA images. This may help to derive new information from clinical DXA images by producing patient-specific FE models for mechanical simulation of femoral bone mechanics

Evaluation of composition and mineral structure of callus tissue in rat femoral fracture.

ABSTRACT. Callus formation is a critical step for successful fracture healing. Little is known about the molecular composition and mineral structure of the newly formed tissue in the callus. The aim was to evaluate the feasibility of small angle x-ray scattering (SAXS) to assess mineral structure of callus and cortical bone and if it could provide complementary information with the compositional analyses from Fourier transform infrared (FTIR) microspectroscopy. Femurs of 12 male Sprague-Dawley rats at 9 weeks of age were fractured and fixed with an intramedullary 1.1 mm K-wire. Fractures were treated with the combinations of bone morphogenetic protein-7 and/or zoledronate. Rats were sacrificed after 6 weeks and both femurs were prepared for FTIR and SAXS analysis. Significant differences were found in the molecular composition and mineral structure between the fracture callus, fracture cortex, and control cortex. The degree of mineralization, collagen maturity, and degree of orientation of the mineral plates were lower in the callus tissue than in the cortices. The results indicate the feasibility of SAXS in the investigation of mineral structure of bone fracture callus and provide complementary information with the composition analyzed with FTIR. Moreover, this study contributes to the limited FTIR and SAXS data in the field

Bone Loss Rate May Interact with Other Risk Factors for Fractures among Elderly Women: A 15-Year Population-Based Study

Aim was to investigate fracture risk (FR) according to bone loss (BL) rate. A random sample of 1652 women aged 53.5 years was measured with dual X-ray absorptiometry in femoral neck in 1989 and 1994 and divided into tertiles of annual BL rate: high >0.84%, moderate 0.13%–0.84%, and low <0.13%. Low trauma energy fractures during following 10 years were recorded. There were no differences in FR between BL tertiles in Cox regression model. Factors predicting lower FR in Cox model were in high tertile: high T-score (HR 0.71; 95% CI 0.54–0.93, P = .012), no sister's fracture (HR 0.35; 0.19–0.64, P = .001), no mother's fracture (HR 0.52; 0.31–0.88, P = .015), in moderate tertile: high T-score (HR 0.69;0.53–0.91, P = .008) and good grip strength (HR 0.98; 0.97–0.99, P = .022). In low tertile there were no predictors for FR. BL predicted FR in women with mother's fracture in univariate and multivariate model (OR 2.6; 1.15–5.7, P = .021) but with sister's fracture this was observed only in multivariate model (OR 2.66; 1.09–6.7, P = .039). Accordingly, the risk factors for postmenopausal fractures, especially mother's fracture, may interact with BL

Factors affecting structural properties and in vitro starch digestibility of extruded starchy foams containing bran

Article title: Factors affecting structural properties and in vitro starch digestibility of extruded starchy foams containing bran Article reference: YJCRS2207 Journal title: Journal of Cereal Science First author: Syed Ariful Alam Final version published online: 7-SEP-2016 Full bibliographic details: Journal of Cereal Science (2016), pp. 190-197 DOI information: 10.1016/j.jcs.2016.08.018Rye bran of two different particle sizes (coarse: 440 mm and fine: 28 mm) were prepared by milling of commercial rye bran. Coarse and fine rye bran was added into a blend of rye endosperm flour and corn starch (70:30) to achieve two bran levels, 15 or 30%, to produce directly puffed extrudates. A co-rotating twin screw extruder was used with a screw speed of 500 rpm, barrel temperature profile: 40-70-75-90- 95-110-110 C and constant feed rate of 67 g/min. Feed moisture content of 17% was used either as in barrel-water feed or as preconditioning. Fine bran addition effectively improved macrostructural properties as compared to coarse bran through increasing expansion by 3.3e11.7% and piece density by 3.8 e10.5%. Reduction of bran particle size significantly (P < 0.05) increased crispiness by 66.7e203.3%. Particle size reduction of bran had only minor influences on cell wall thickness, cell area and hydrolysis index of the extrudates. Extrudates made with 30% fine bran at in barrel-water feed provided the crispiest extrudates with lower in vitro hydrolysis index. The results demonstrated that the macrostructural and mechanical properties of extrudates containing rye bran can be improved by reducing bran particle size.Peer reviewe

In Vivo Evaluation of the Potential of High-Frequency Ultrasound for Arthroscopic Examination of the Shoulder Joint

Objective. Accurate arthroscopic evaluation of cartilage lesions could significantly improve the outcome of repair surgery. In this study, we investigated for the first time the potential of intra-articular ultrasound as an arthroscopic tool for grading cartilage defects in the human shoulder joint in vivo and compared the outcome to results from arthroscopic evaluation and magnetic resonance imaging findings. Design. A total of 26 sites from 9 patients undergoing routine shoulder arthroscopy were quantitatively evaluated with a clinical intravascular (40MHz) ultrasound imaging system, using the regular arthroscopy portals. Reflection coefficient (R), integrated reflection coefficient (IRC), apparent integrated backscattering (AIB), and ultrasound roughness index (URI) were calculated, and high-resolution ultrasound images were obtained per site. Each site was visually graded according to the International Cartilage Repair Society (ICRS) system. "Ultrasound scores" corresponding to the ICRS system were determined from the ultrasound images. Magnetic resonance imaging was conducted and cartilage integrity at each site was classified into 5 grades (0 = normal, 4 = severely abnormal) by a radiologist. Results. R and IRC were lower at sites with damaged cartilage surface (P = 0.033 and P = 0.043, respectively) and correlated with arthroscopic ICRS grades (r (s) = -0.444, P = 0.023 and r (s) = -0.426, P = 0.03, respectively). Arthroscopic ICRS grades and ultrasound scores were significantly correlated (rs = 0.472, P = 0.015), but no significant correlation was found between magnetic resonance imaging data and other parameters. Conclusion. The results suggest that ultrasound arthroscopy could facilitate quantitative clinical appraisal of articular cartilage integrity in the shoulder joint and provide information on cartilage lesion depth and severity for quantitative diagnostics in surgery.Peer reviewe

Bone mineral density of the proximal femur after hip resurfacing arthroplasty: : 1-year follow-up study

Peer reviewe

Magnetic Resonance Imaging of Cartilage Repair: A Review

Articular cartilage lesions are a common pathology of the knee joint, and many patients may benefit from cartilage repair surgeries that offer the chance to avoid the development of osteoarthritis or delay its progression. Cartilage repair surgery, no matter the technique, requires a noninvasive, standardized, and high-quality longitudinal method to assess the structure of the repair tissue. This goal is best fulfilled by magnetic resonance imaging (MRI). The present article provides an overview of the current state of the art of MRI of cartilage repair. In the first 2 sections, preclinical and clinical MRI of cartilage repair tissue are described with a focus on morphological depiction of cartilage and the use of functional (biochemical) MR methodologies for the visualization of the ultrastructure of cartilage repair. In the third section, a short overview is provided on the regulatory issues of the United States Food and Drug Administration (FDA) and the European Medicines Agency (EMEA) regarding MR follow-up studies of patients after cartilage repair surgeries