Biomedical subjects

D Testi

Publications and source records attributed to D Testi.

11 recordsLinked to original sources

PubMed2004

Differences in proximal femur geometry distinguish vertebral from femoral neck fractures in osteoporotic women.

Bone mineral density (BMD) is generally used to predict the risk of fracture in osteoporotic subjects. However, femoral neck BMD and spine BMD have been reported not to be significantly different among patients with hip or vertebral fractures, suggesting that other risk factors are needed to determine the different fracture types. Proximal femur geometry (PFG) parameters, such as hip axis length (HAL), femoral neck-shaft angle (NSA) and femoral neck diameter (FND) have also been shown to predict the risk of hip fracture. These parameters are statistically different in spine fractures compared with both types of hip fractures (trochanteric and femoral neck) when considered together. We wanted to assess the difference in these parameters by comparing spine fractures with a homogeneous group of hip fractures, i.e. femoral neck fractures. 807 post-menopausal women were divided into three groups; those with vertebral fractures (182), those with femoral neck fractures (134) and a control group without fractures (491). Dual X-ray absorptiometry (DXA) scans of the spine and hip were carried out to measure BMD and define the PFG parameters of the hip. Data were statistically analysed. In agreement with other authors, we found that women with femoral neck fractures had longer HAL, wider FND and larger NSA than controls, whereas there were no statistically significant differences in PFG between women with spine fractures and controls. Logistic regression showed HAL and NSA could predict the risk of femoral neck but not vertebral fracture. These data indicate specificity of some PFG parameters for hip fracture risk.

Aged↗

PubMed2003

A method for assessment of the shape of the proximal femur and its relationship to osteoporotic hip fracture.

The shape of the proximal femur has been demonstrated to be important in the occurrence of fractures of the femoral neck. Unfortunately, multiple geometric measurements frequently used to describe this shape are highly correlated. A new method, active shape modeling (ASM) has been developed to quantify the morphology of the femur. This describes the shape in terms of orthogonal modes of variation that, consequently, are all independent. To test this method, digitized standard pelvic radiographs were obtained from 26 women who had suffered a hip fracture and compared with images from 24 age-matched controls with no fracture. All subjects also had their bone mineral density (BMD) measured at five sites using dual-energy X-ray absorptiometry. An ASM was developed and principal components analysis used to identify the modes which best described the shape. Discriminant analysis was used to determine which variable, or combination of variables, was best able to discriminate between the groups. ASM alone correctly identified 74% of the individuals and placed them in the appropriate group. Only one of the BMD values (Ward's triangle) achieved a higher value (82%). A combination of Ward's triangle BMD and ASM improved the accuracy to 90%. Geometric variables used in this study were weaker, correctly classifying less than 60% of the study group. Logistic regression showed that after adjustment for age, body mass index, and BMD, the ASM data was still independently associated with hip fracture (odds ratio (OR)=1.83, 95% confidence interval 1.08 to 3.11). The odds ratio was calculated relative to a 10% increase in the probability of belonging to the fracture group. Though these initial results were obtained from a limited data set, this study shows that ASM may be a powerful method to help identify individuals at risk of a hip fracture in the future.

Aged↗

PubMed2001

Comparison of logistic and Bayesian classifiers for evaluating the risk of femoral neck fracture in osteoporotic patients.

Femoral neck fracture prediction is an important social and economic issue. The research compares two statistical methods for the classification of patients at risk for femoral neck fracture: multiple logistic regression and Bayes linear classifier. The two approaches are evaluated for their ability to separate femoral neck fractured patients from osteoporotic controls. In total, 272 Italian women are studied. Densitometric and geometric measurements are obtained from the proximal femur by dual energy X-ray absorptiometry. The performances of the two methods are evaluated by accuracy in the classification and receiver operating characteristic curves. The Bayes classifier achieves an accuracy approximately 1% higher than that of the multiple logistic regression. However, the performances of the two methods, evaluated by the area under the curves, are not statistically different. The study demonstrates that the Bayes linear classifier can be a valid alternative to multiple logistic regression in the classification of osteoporotic patients.

Aged↗

PubMed2001

HIDE: a new hybrid environment for the design of custom-made hip prosthesis.

This technical note describes a new software environment (HIPCOM design environment, HIDE) for the design of custom-made total hip replacements. These devices are frequently designed using general-purpose mechanical computer-aided design (CAD) programs using a set of bone contours extracted from the computer tomography (CT) images as anatomical reference. On the contrary, the HIDE system was developed to let the operator directly design the stem shape onto the CT images in a single-step operation. The operator can directly import CT data in DICOM format or use special functions to reconvert to a digital stack, the CT images printed on a radiological film. Once the stack of CT images is loaded, the operator can design the implant shape by imposing control sections directly on the CT images. The interpolation of these control sections produces the basic 3D shape of the custom-made stem. The shape is then exported to the CAD-computer-aided manufacturing (CAM) program to refine the design and to generate the part program to manufacture the implant with a CNC tooling machine. Using HIDE, the duration of design steps it affected was reduced by more than 50% with respect to the standard method in use at the manufacturer site. HIDE also improved the accuracy and the repeatability of the whole procedure. The learning curve became flat after only ten cases. These good results were achieved because of the integration of the vectorial description of the prosthetic component with the raster description of the CT data that allowed the designer to use all details available in the CT images.

Computer-Aided Design↗

PubMed2001

Border-tracing algorithm implementation for the femoral geometry reconstruction.

In some orthopaedic applications such as the design of custom-made hip prostheses, reconstruction of the bone morphology is a fundamental step. Different methods are available to extract the geometry of the femoral medullary canal from computed tomography (CT) images. In this research, an automatic procedure (border-tracing method) for the extraction of bone contours was implemented and validated. A composite replica of the human femur was scanned and the CT images processed using three different methods, a manual procedure; the border-tracing algorithm; and a threshold-based method. The resulting contours were used to estimate the accuracy of the implemented procedure. The two software techniques were more accurate than the manual procedure. Then, these two procedures were applied to an in vivo CT data set in order to determine to most critical region for repeatability. Only for the images located in this region, the repeatability measurement was carried out for six in vivo CT data sets to evaluate the inter-femur repeatability. The border-tracing method was found to achieve the highest repeatability.

Algorithms↗

PubMed1999

CT data sets surface extraction for biomechanical modeling of long bones.

In modelling applications such as custom-made implants design is useful to have a surface representation of the anatomy of bones rather than the voxel-based representation generated by tomography systems. A voxel-to-surface conversion process is usually done by a 2D segmentation of the images stack. However, other methods allow a direct 3D segmentation of the CT or MRI data set. In the present work, two of these methods, namely the Standard Marching Cube (SMC) and the Discretized Marching Cube (DMC) algorithms, were compared in terms of local accuracy when used to reconstruct the geometry of a human femur. The SMC method was found to be more accurate than the DMC method. The SMC method was capable of reconstructing the inner and outer geometry of a human femur with a peak error lower than 0.9 mm and an average error comparable to the pixel size (0.3 mm). However, the large number of triangles generated by the algorithm may limit its adoption in many modelling applications. The peak error of the DMC algorithm was 1.6 mm but it produced approximately 70% less triangles than the SMC method. From the results of this study, it may be concluded that three dimensional segmentation algorithms are useful not only in visualisation applications but also in the creation of geometry models.

Algorithms↗

PubMed1999

Risk of fracture in elderly patients: a new predictive index based on bone mineral density and finite element analysis.

Hip fracture is more and more frequent in elderly population. For this reason, an increasing attention has been focused on the development of a non-invasive method to predict femoral neck fracture. A conventional approach to fracture diagnosis is the measurement of bone mass by dual-energy X-ray absorptiometry in some regions of interest. The aim of this work is to assess a method that accounts for the structural details of the bone providing a more direct determination of strength properties, and improving the diagnostic power of the current densitometric systems. A 2D finite element model of the proximal femur is derived from dual-energy X-ray absorptiometry data. Initially, the method is validated in vitro using a replica of the human femur. The predicted results are compared to strain-gauge measurements and to a 3D finite element model, with good agreement being observed. Then, an in vivo preliminary study on a limited group of patients is carried out. The loading condition that simulates a fall to the side onto the greater trochanter from standing height is employed. All simulations show a peak strain at the femoral neck region with a strain distribution typical of a fall on the side. The proposed method seems to supply a useful tool for the in vivo analysis of the risk of hip fracture.

Aged↗

PubMedDate not supplied

A new method for the automatic mesh generation of bone segments from CT data.

A new procedure for the automatic generation of finite element meshes of bone segments from computed tomography (CT) data sets is described. The new method allows a direct automatic generation from the CT data and produces a very accurate unstructured hexahedral mesh. The accuracy of the method was established using the CT images of an artificial femur showing range of attenuation values comparable to those of a human femur. To establish the optimal values for the parameters controlling the mesh a sensitivity analysis was carried out using mesh-conditioning indicators. Some of the best meshes, with increasing levels of refinement, were used to analyse the stresses induced in the proximal femur by single leg stance posture. The accuracy of the meshes was evaluated using an implicit a posteriori residual-based error estimates. The number of elements with stress residuals larger than 10% of the peak stress was 7.8% using the coarsest mesh and only 1.8% with the finest mesh. The proposed method has been proved able to conjugate full automation with high-quality finite element meshes. The stress predictions obtained using these hexahedral-only meshes have been more accurate than those obtained by any other automatic mesh generation algorithm. Once properly integrated in an easy-to-use application, the described method could finally make feasible many clinical applications of finite element analysis.

Bone and Bones↗

PubMedDate not supplied

Development of a software for the design of custom-made hip prostheses using an open-source rapid application development environment.

The present work describes a technology transfer project called HIPCOM devoted to the re-engineering of the process used by a medical devices manufacturer to design custom-made hip prostheses. Although it started with insufficient support from the end-user management, a very tight scheduling and a moderate budget, the project developed into what is considered by all partners a success story. In particular, the development of the design software, called HIPCOM Interactive Design Environment (HIDE) was completed in a time shorter than any optimistic expectation. The software was quite stable since its first beta version, and once introduced at the user site it fully replaced the original procedure in less than two months. One year after the early adoption, more than 80 custom-made prostheses had been designed with HIDE and the user had reported only two bugs, both cosmetics. The scope of the present work was to report the development experience and to investigate the reasons for these positive results, with particular reference to the development procedure and the software architecture. The choice of TCL/TK as development language and the adoption of well-defined software architecture were found to be the success key factors. Other important determinants were found to be the adoption of an incremental software engineering strategy, well suited for small to medium projects and the presence in the development staff of a technology transfer expert.

Computer-Aided Design↗

PubMedDate not supplied

CCD film digitizers in clinical practice: evaluation of the main properties.

Until hospitals convert to 'filmless' radiology departments, computerized display and archival of x-ray images will necessitate devices to transform conventional X-ray films into digital images. Current methods for digitizing x-ray films include laser based and Charged Couple Device (CCD) based scanners. There is now much interest in the use of CCD devices for demanding applications, with the lower cost of ownership contributing towards the diffusion of CCD scanners. We report a study comparing the performance of three CCD based systems (an x-ray film digitizer, and two low cost flatbed scanners), looking at characteristic curve, useful optical range with respect the noise, repeatability, Modulation Transfer Function (MTF), and geometric distortion. In addition, we evaluated the potential and limitations of these devices in the clinical assessment of x-ray films. The most important weakness of CCD devices derived from the stability and the noise of CCD detectors, mostly affecting the useful optical range in the darker regions of x-ray films. Spatial resolution and geometric distortion were confirmed be the real points of strength of CCD technology. Therefore, the most appropriate system for each user depends on what type of clinical decision will be made following inspection of the digitised images.

Computer Simulation↗

PubMedDate not supplied

Fracture prediction for the femoral neck using finite element models.

Fracture of the femoral neck is an important clinical, social and economic topic. Prediction in subjects who are at risk for this type of fracture has been the object of numerous studies. Nonetheless, the methods of classification based on densitometric indicators alone have shown poor accuracy. It is the purpose of this study to propose a method to obtain an estimate of the resistance of the proximal femur, and to improve accuracy in prediction in subjects who are at risk for fracture. Based on the densitometric dataset alone, a bidimensional finite element model was developed that takes into account the distribution of density together with the femoral anatomy and the typical conditions of trauma. The model was applied to a group of preliminary osteoporotic patients. The statistical classification showed an increase in accuracy by 13%, as compared to a classification based on densitometric indicators alone.

Adult↗