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

3D shape reconstruction of the femur from planar X-ray images using statistical shape and appearance models

Major trauma is a condition that can result in severe bone damage. Customised orthopaedic reconstruction allows for limb salvage surgery and helps to restore joint alignment. For the best possible outcome three dimensional (3D) medical imaging is necessary, but its availability and access, especially in developing countries, can be challenging. In this study, 3D bone shapes of the femur reconstructed from planar radiographs representing bone defects were evaluated for use in orthopaedic surgery. Statistical shape and appearance models generated from 40 cadaveric X-ray computed tomography (CT) images were used to reconstruct 3D bone shapes. The reconstruction simulated bone defects of between 0% and 50% of the whole bone, and the prediction accuracy using anterior–posterior (AP) and anterior–posterior/medial–lateral (AP/ML) X-rays were compared. As error metrics for the comparison, measures evaluating the distance between contour lines of the projections as well as a measure comparing similarities in image intensities were used. The results were evaluated using the root-mean-square distance for surface error as well as differences in commonly used anatomical measures, including bow, femoral neck, diaphyseal–condylar and version angles between reconstructed surfaces from the shape model and the intact shape reconstructed from the CT image. The reconstructions had average surface errors between 1.59 and 3.59 mm with reconstructions using the contour error metric from the AP/ML directions being the most accurate. Predictions of bow and femoral neck angles were well below the clinical threshold accuracy of 3°, diaphyseal–condylar angles were around the threshold of 3° and only version angle predictions of between 5.3° and 9.3° were above the clinical threshold, but below the range reported in clinical practice using computer navigation (i.e., 17° internal to 15° external rotation). This study shows that the reconstructions from partly available planar images using statistical shape and appearance models had an accuracy which would support their potential use in orthopaedic reconstruction

FEMUR KEMİĞİNİN KLİNİK VE SONLU ELEMANLAR YÖNTEMİYLE ANALİZİ: LİTERATÜR ARAŞTIRMASI

Yaşlılarda görülen kırıklar birçok ülkede giderek artan bir tıbbi endişe kaynağı haline gelmiştir (Roth ve ark., 2010). Düşük KMY (Kemik Mineral Yoğunluğu) ile ilişkili kırıklar, ayrıca 50 yaş üzerinde görülme sıklığı artan kırıklar osteoporotik kırıklar olarak bilinmektedir (Kanis ve ark., t.y.)

Generation of a statistical model of the anatomy of human pelvises

Osteoarthritis and osteoporosis are two medical conditions involving the hip which affect the life quality of many people worldwide. These two diseases are diagnosed with 2D imaging by analysis of radiological measures, bone mineral density and joint space. Computed Tomography (CT) can provide 3D images of the hip, but has higher cost and imposes a higher radiation dose to the patient. Another option (which the Biomechanics group in Lund is working on) is to utilize statistical models to construct a 3D model from a 2D image. The Biomechanics group has developed a statistical model of the anatomical variability of the human femur. Adding an equivalent model for the pelvis would then allow to fully represent the hip joint. In this study, CT scans from 26 male and 21 female patients scheduled for hip replacement surgery were used to create a Statistical Shape Model (SSM) to describe the shape of pelvis. To be able to generate the SSM, the shapes of all bones were defined by identical meshes. A template mesh was created based on one of the available anatomies and it was then registered to each hip bone. The registered bones were then used to create the SSM. The registration method was evaluated by a point-to-surface distance difference. For the SSM, the shape variation and the reconstruction of the hip bones were evaluated for the whole group and for the male and female patient cohorts within the group. The SSM created during the study was able to represent the shape variation of both male and female bones. Visually, the gender variance was associated to the width and thickness of the bone, corresponding with the known differences of the pelvic bone between the genders. The results indicate that the model can represent the shape of the bone accurately, independent of gender. Combined with a statistical model for the femur, the SSM created in this study can be used to provide a 2D to 3D reconstruction of the hip from clinical diagnostic images.3D-modell av höftbenet kan hjälpa till att förutspå artros Det är viktigt att förebygga sjukdomar innan de bryter ut. Vanliga 2D-röntgenbilder är inte alltid tillräckligt noggranna men med 3D-modeller kan tidiga tecken på artros lättare identifieras. Vi strävar för att få fram 3D-bilder av höften från vanliga röntgenbilder

Bone strain change as a result of a long distance run modeled on a finite element tibia

Stress injuries typically develop as a result of overuse and lack of recovery. However, despite a 7-year stress fracture incidence rate of approximately 40%, in vivo bone stresses and strains do not approach levels of ultimate strength. Therefore, there must be outside factors such as muscle fatigue which lead to increased strain and injury risks. PURPOSE: Muscle fatigue during a long distance run may lead to increased bone strain in the tibia, and result in increased injury risk. METHODS: Sixteen runners did a graded treadmill test to determine max heart rate and VO2,max, which were then used to set the fatiguing speed for the long distance run. Before and after the fatiguing run, participants completed 10 trials over the force platform and through the field of view of an eight camera system within 5% of the fatiguing speed and with the right foot hitting the platform. Stance phase was analyzed for joint, muscle and contact forces. These forces were then distributed on an individually scaled finite element model (FEM) tibia and the peak principal strain location and magnitude were determined. The magnitude and location of pre- and post-principal strain and von Mises equivalent strain were compared using a repeated measures t-test. RESULTS: Peak principal strains in both compression and tension were significantly reduced at the point of peak contact forces (P \u3c 0.001). In addition, von Mises equivalent strains decreased significantly at the 95th percentile and median values (P\u3c 0.001). CONCLUSION: The hypothesis that strain magnitude would increase as a result of fatigue was not supported. Several variables such as triceps surae muscle force, vertical stiffness, and step width were altered by the run but none of these changes reached statistical significance. Model inputs were slightly decreased, and perhaps may have been the reason for the decrease. Further research is necessary to determine the exact reason. Limitations for this study included not including a fibula in the model, maintaining bone properties from pre- to post-fatigue, and a lack of quantification of fatigue

Association of incident hip fracture with the estimated femoral strength by finite element analysis of DXA scans in the Osteoporotic Fractures in Men (MrOS) study

Finite element model can estimate bone strength better than BMD. This study used such a model to determine its association with hip fracture risk and found that the strength estimate provided limited improvement over the hip BMDs in predicting femoral neck (FN) fracture risk only. INTRODUCTION: Bone fractures occur only when it is loaded beyond its ultimate strength. The goal of this study was to determine the association of femoral strength, as estimated by finite element (FE) analysis of DXA scans, with incident hip fracture as a single condition or with femoral neck (FN) and trochanter (TR) fractures separately in older men. METHODS: This prospective case-cohort study included 91 FN and 64 TR fracture cases and a random sample of 500 men (14 had a hip fracture) from the Osteoporotic Fractures in Men study during a mean ± SD follow-up of 7.7 ± 2.2 years. We analysed the baseline DXA scans of the hip using a validated plane-stress, linear-elastic FE model of the proximal femur and estimated the femoral strength during a sideways fall. RESULTS: The estimated strength was significantly (P < 0.05) associated with hip fracture independent of the TR and total hip (TH) BMDs but not FN BMD, and combining the strength with BMD did not improve the hip fracture prediction. The strength estimate was associated with FN fractures independent of the FN, TR and TH BMDs; the age-BMI-BMD adjusted hazard ratio (95% CI) per SD decrease of the strength was 1.68 (1.07-2.64), 2.38 (1.57, 3.61) and 2.04 (1.34, 3.11), respectively. This association with FN fracture was as strong as FN BMD (Harrell's C index for the strength 0.81 vs. FN BMD 0.81) and stronger than TR and TH BMDs (0.8 vs. 0.78 and 0.81 vs. 0.79). The strength's association with TR fracture was not independent of hip BMD. CONCLUSIONS: Although the strength estimate provided additional information over the hip BMDs, its improvement in predictive ability over the hip BMDs was confined to FN fracture only and limited

Validated respiratory drug deposition predictions from 2D and 3D medical images with statistical shape models and convolutional neural networks

For the one billion sufferers of respiratory disease, managing their disease with inhalers crucially influences their quality of life. Generic treatment plans could be improved with the aid of computational models that account for patient-specific features such as breathing pattern, lung pathology and morphology. Therefore, we aim to develop and validate an automated computational framework for patient-specific deposition modelling. To that end, an image processing approach is proposed that could produce 3D patient respiratory geometries from 2D chest X-rays and 3D CT images. We evaluated the airway and lung morphology produced by our image processing framework, and assessed deposition compared to in vivo data. The 2D-to-3D image processing reproduces airway diameter to 9% median error compared to ground truth segmentations, but is sensitive to outliers of up to 33% due to lung outline noise. Predicted regional deposition gave 5% median error compared to in vivo measurements. The proposed framework is capable of providing patient-specific deposition measurements for varying treatments, to determine which treatment would best satisfy the needs imposed by each patient (such as disease and lung/airway morphology). Integration of patient-specific modelling into clinical practice as an additional decision-making tool could optimise treatment plans and lower the burden of respiratory diseases.</p

Injury Risk Assessment of the Femur in Children with Osteogenesis Imperfecta

Osteogenesis imperfecta (OI) is a genetic disorder characterized by increased bone fragility and decreased bone mass, which leads to high rates of bone fracture. OI has a prevalence of 1/5,000 to 1/10,000 in the United States. About 90% of persons with OI have a genetic mutation in the coding for collagen type I, which is the major protein of connective tissues, including bone. While its prevalence classifies it as a rare disease, it is the most common disorder of bone etiology. Until recently, little was known about the mechanics and materials of OI bone or their impact on fracture risk. Fracture risk is typically characterized by clinical type and radiographs. Finite element (FE) models have recently been developed to examine fracture risk during ambulation and various daily activities of the femur and tibia in children and adolescents with OI. This research aims to provide further information about the impact of OI in children and adolescents during loading conditions. FE models of the femur with normal bone, OI type I (mild) bone and OI type III (severe) bone material properties were developed and analyzed. These models showed the effects of lateral bowing versus increased gluteus medius and gluteus maximus force production on bone injury risk. Lateral bowing and muscle force increase permutations to the standard model of no bowing and normal muscle forces during ambulation showed significant changes to stress levels. Along with FE models, quantitative gait analyses were performed on 10 children with mild OI and ten age- and gender-matched controls to analyze the firing patterns of the gluteus medius and gluteus maximus muscles during normal ambulation. The OI population exhibited a delay in gluteus maximus activation. Additional FE models examined the impact of creating the model directly from a CT scan of a child with severe OI versus scaling a standard model to match the size and shape of and OI femur based on x-ray images alone. Comparison of these two model geometry development techniques resulted in a significant difference in femoral stresses and strains