F. Lavaste

A Biplanar Reconstruction Method Based on 2D and 3D Contours: Application to the Distal Femur

A three-dimensional (3D) reconstruction algorithm based on contours identification from biplanar radiographs is presented. It requires, as technical prerequisites, a method to calibrate the biplanar radiographic environment and a surface generic object (anatomic atlas model) representing the structure to be reconstructed. The reconstruction steps consist of: the definition of anatomical regions, the identification of 2D contours associated to these regions, the calculation of 3D contours and projection onto the radiographs, the associations between points of the X-rays contours and points of the projected 3D contours, the optimization of the initial solution and the optimized object deformation to minimize the distance between X-rays contours and projected 3D contours. The evaluation was performed on 8 distal femurs comparing the 3D models obtained to CT-scan reconstructions. Mean error for each distal femur was 1 mm.

Three-Dimensional Motions of Trunk and Pelvis During Transfemoral Amputee Gait

OBJECTIVES To identify characteristics of upper-body kinematics and torque transmission to the ground during locomotion in a group of patients with transfemoral amputation as compared with a group of asymptomatic subjects; and to investigate the influence of walking velocity and residual limb length on several characteristics of upper-body motion. DESIGN Three-dimensional gait analysis with an optoelectronic device. SETTING Gait laboratory. PARTICIPANTS Twenty-seven patients with transfemoral amputation and a control group of 33 nondisabled subjects. INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Three-dimensional kinematics of the pelvis and the thorax and ground reaction force for amputees and control subjects. RESULTS For subjects with transfemoral amputation, it was observed that upper-body angular ranges of motion (ROMs) increased globally as walking velocity decreased. For these subjects, specific patterns of pelvic rotation and torque transmission by the lower limbs around the vertical axis were found. The counter-rotation between the pelvic and scapular girdles was reduced. This reduction proved to be linked with the decrease of walking velocity. Walking velocity also affected all the parameters describing the motion of upper body. Pelvic ROM increased with the length of the limb decreasing. CONCLUSIONS The huge differences found between subjects with and without amputation suggest that the motion of the upper body must be considered to enhance gait.

Experimental lumbar instability and artificial ligament

SummaryThis biomechanical study investigates the efficiency of a new procedure of destabilization at the L4/L5 spinal unit, as well as the effect of a new system to stabilize it.The instability is effective in backward-forward and in lateral bending (p < 0.05), and the neutral zone is increased in backward-forward and in axial rotation (p < 0.05).The artificial ligament and its wedge stabilize the cut spine, and is effective in backward-forward and in lateral bending (p < 0.05).

Computer-assisted assessment of spinal sagittal plane radiographs.

The sagittal shape of the spine, particularly its sagittal balance, currently is being extensively investigated. The major purpose of this study is to examine the measurement repeatability of SpineView software, which calculates 13 independent variables, to shorten and facilitate the measurement of lateral spinal radiographs; another purpose is to collect physiological data for nonpathologic spines, which can be used as a reference in future research. This article also presents two new parameters and discusses their possible role in forthcoming investigations. The interobserver repeatability study shows that most of the variables are more repeatable (less than +/-1.5 degrees ) when the operator is experienced. A less (+/-6.5 degrees ) repeatable measurement is T4-T12 kyphosis, which may be because of the poor contrast generally observed on radiographs of the upper thoracic vertebrae. The intraobserver repeatability study also demonstrates that subjective failures do not influence the results significantly, but the quality of the radiographs may have significant effect on long-term repeatability. The mean values were generally different between male and female subjects, and significant differences between the two sexes were only noticed for pelvic thickness and global spinal inclination. Normal range values and correlations between some pelvic and spinal parameters were similar to data found in the literature. The results of the current study provide evidence that the SpineView software is useful for experimental investigation of sagittal spinal alignment.

3D finite element simulation of Cotrel-Dubousset correction

The Cotrel–Dubousset (CD) scoliosis surgery was simulated for 10 patients with idiopathic scoliosis using a 3D finite element model (FEM) of the patients entire spine. The geometry of the FEM was extracted from a 3D stereo-radiographic reconstruction, and mechanical properties were personalized using lateral bending films. Finally, each step of the CD correction was simulated and results were compared with the post-operative 3D stereo-radiographic reconstruction. The whole procedure was applied for 10 patients, and quantitative comparison was performed between post-operative spine configuration and predicted configuration. For all patients, mean differences between post-operative measurements and predicted values of vertebral rotation were estimated at 5° (max: 13°) and those for linear position at 6 mm (max: 12 mm). Furthermore, intermediate steps of surgery simulation were consistent with the literature. Then, for one scoliotic patient, the model was used to investigate three alternative surgical strategies. It was found that a one-level change in the instrumentation limit may have a significant effect on spine alignment and correction.

Development of a 3D Finite Element Model of the Human Body

Even though computational techniques are now very common in automotive safety engineering, there is still a need for further development of biofidelic tools for assessing human responses in crash situations. The authors of this paper designed a 3D finite element model of the human body and constituted a large experimental database for the purpose of validation. The geometry of the seated 50th percentile adult male was chosen for the model. The number of elements used to represent the anatomy was limited to 10,000. Material laws come from existing literature and when necessary, parameter identification processes were used. Special attention was paid to the constitution of the validation database. Boundary conditions and results from most of the available cadaver and volunteer experiments were analyzed. More than 30 test configurations were selected, including sled, impactor, and belt compression tests with a wide range of energy levels and in frontal, lateral, and oblique directions. 120+ corridors were derived and integrated into the development of the validation phase. The model behavior was evaluated in the light of a set of impacts in a vehicle environment. The validation database is described in detail and correlation obtained between model responses and experimental results is shown. Uses of the model are discussed.

Development of a Finite Element Model of the Neck

Head neck responses from volunteer experiments, as obtained in various loading directions by the Naval Biodynamics Laboratory (NBDL), represent a unique set of data in the biomechanical research field. From this a set of volunteer thoracic (TI) and head responses were selected as a reference for this study. The objective of the study is to develop a finite element model (FEM) of the human neck in frontal and lateral directions. The number of elements in the model were kept low in order to reduce the processing time for simulation and to minimize damping problems. The structure of the model is as follows: the vertebrae and the head were considered as rigid bodies. The interface between vertebrae such as discs and different ligaments are modelled by brick and spring elements. The passive action of the muscles are taken into account when determining the stiffness characteristics of the ligaments. Satisfactory results were obtained in terms of kinematic responses of the head (comparison with NBDL data) in frontal and lateral directions. Further investigations are needed for modelling the muscles to allow for injury prediction. The paper describes the characteristics of this model, the rationale behind the definition of model elements, and the performance compared with the volunteer reference. For the covering abstract of the conference see IRRD 879189.

A Functional Evaluation of Prosthetic Foot Kinematics During Lower-Limb Amputee Gait

This paper reports on a functional evaluation of prosthetic feet based on gait analysis. The aim is to analyse prosthetic feet behaviour under loads applied during gait in order to quantify user benefits for each foot. Ten traumatic amputees (six trans-tibial and four trans-femoral) were tested using their own prosthetic foot. An original protocol is presented to calculate the forefoot kinematics together with the overall body kinematics and ground reaction forces during gait. In this work, sagittal motion of the prosthetic ankle and the forefoot, time-distance parameters and ground reaction forces were examined. It is shown that an analysis of not only trans-tibial but also trans-femoral amputees provides an insight in the performance of prosthetic feet. Symmetry and prosthetic propulsive force were proved to be mainly dependant on amputation level. In contrast, the flexion of the prosthetic forefoot and several time-distance parameters are highly influenced by foot design. Correlations show influential of foot and ankle kinematics on other parameters. These results suggest that prosthetic foot efficiency depends simultaneously on foot design and gait style. The evaluation, proposed in this article, associated to clinical examination should help to achieve the best prosthetic foot match to a patient.

VALIDATION STUDY OF A 3D FINITE ELEMENT HEAD MODEL AGAINST EXPERIMENTAL DATA

The basis of assumptions involved in the development of a 3D human head model by comparing its global response with cadaver tests is evaluated. Finite element model development is based on idealizations concerning the geometry, the material properties, the boundary conditions of each represented part and the interfaces between the different parts. The relevance of the model idealizations specially related to the skull and subarchnoid space modelling is assessed.

Influence of geometrical factors on the behavior of lumbar spine segments: a finite element analysis.

SummaryThe main objective of this study was the assessment of the influence of geometrical factors on the behavior of lumbar segments. To this end, a three-dimensional, parameterized, finite element model of the lumbar spine was used, and the results were compared with in-house experimental results and with the few published experimental results available concerning either the geometry of the tested samples or the differences observed at different vertebral levels. Furthermore, in order to appreciate the relative importance of the geometry, the influence of the variation of some other parameters was studied, such as the orientation of the facet joints, the gap between the articular processes, and the Youngs modulus of the disk fibers. As a first approach, a series of computations was carried out in order to evaluate the role of geometry in the mechanical behavior differences observed at different levels. It has been found that geometrical factors do exert a noticeable influence on the behavior of the spine, especially those which interfere with the dimensions of the intervertebral disk.