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International audience; Subject-specific tensioning of ligaments is essential for the stability of the knee joint and represents a challenging aspect in the development of finite element models. We aimed to introduce and evaluate a new procedure for the quantification of ligament prestrains from biplanar X-ray and CT data. Subject-specific model evaluation was performed by comparing predicted femorotibial kinematics with the in vitro response of six cadaveric specimens. The differences obtained using personalized models were comparable to those reported in similar studies in the literature. This study is the first step toward the use of simplified, personalized knee FE models in clinical context such as ligament balancing.

This work presents an accurate method to measure gleno-humeral translations in a controlled pseudo-kinematic environment. Low-dose biplanar X-rays were acquired from nine healthy subjects at three elevations of the arm in the scapular plane. On each set of images, shoulder bony landmarks were manually located in 3D using a dedicated software. Intra-observer and inter-observer repeatability of landmark identification, as well as humeral head center (GH) translations, were studied. Repeatability for the identification of GH in the global coordinate system (CS) was good with 95% confidence intervals (CIs) ranging from 0.57 to 2.25 mm. Scapular landmark CIs ranged from 0.80 to 12 mm. Gleno-humeral translations of small amplitude (

International audience; Adolescent idiopathic scoliosis (AIS) is a threedimensional deformity of the spine, often progressing rapidly during the growth spurt. Severe scoliosis can lead to significant degradation of quality of life and functional impairment; the aim of early orthotic treatment is to slow down curvature progression until skeletal maturity. Efficacy of bracing has often been questioned (Negrini et al., 2010; Weinstein et al., 2013), and often relies on the orthotist’s experience since objective methods to design and predict brace action are still in development (Cobetto et al., 2014). A clinically-relevant method for the evaluation of brace simulation in AIS was recently presented (Vergari et al., 2015) and applied to preliminarily validate a finite element model (FEM) of the trunk.The aim of this work was to improve the simulation of brace action on scoliotic trunks and to validate the model on a larger cohort

Detailed knowledge about subject-specific knee ligament length variation during knee flexion is crucial for musculoskel- etal modeling in human movement analysis and in clinical con- texts (Ascani et al. 2014). In this respect, accurate estimation of ligament origin and insertion locations is needed. Although extensive literature exists describing the ligament attachment site position ex vivo (Kopf et al. 2009), this information is hardly obtainable in vivo unless using medical imaging tech- niques (magnetic resonance, MRI, or computed tomography, CT) that are time- onsuming, expensive and, when radiation is involved, risky for the subjects. Furthermore, the identifica- tion of the ligament attachment site location using MRI may be characterized by significant inter- and intra-observer variabil- ity thus leading to errors that are too large to generate reliable subject-specific knee models (Rachmat et al. 2014). Therefore, the aim of the present study is to propose and validate a method for the accurate in vivo estimation of the subject-specific length of the major knee ligaments (anterior and posterior cruciate, ACL and PCL, medial and collateral ligaments, MCL and LCL) which does not necessarily require the use of medical imaging techniques to identify the ligament attachment sites.

3D personalized models are more and more requested for clinical and biomechanical studies. Techniques based on bi-planar X-rays present the advantage of a low radiation dose for the patient. However, up to now, such techniques have shown limited accuracy in the case of pelvis reconstruction. This study proposes and validates a method providing accurate 3D personalized model of the pelvis from bi-planar X-rays. The algorithm is based on the fast computation of an initial solution followed by local deformations based on 2D anatomical points and contours that are digitized in both radiographs. Results were close to CT-scan reconstructions (mean difference 1.6 mm and differences under 4.3 mm for 95% of the points). Moreover, 3D morphometry of the pelvis could be obtained with an accuracy of 5%. This technique provides 3D patient specific model with a low radiation dose.

Biomechanical models have been proposed in order to simulate the surgical correction of spinal deformities. With these models, different surgical correction techniques have been examined: distraction and rod rotation. The purpose of this study was to simulate another surgical correction technique: the in situ contouring technique. In this way, a comprehensive three-dimensional Finite Element (FE) model with patient-specific geometry and patient-specific mechanical properties was used. The simulation of the surgery took into account elasto-plastic behavior of the rod and multiple moments loading and unloading representing the surgical maneuvers. The simulations of two clinical cases of hyperkyphosis and scoliosis were coherent with the surgeon's experience. Moreover, the results of simulation were compared to post-operative 3D measurements. The mean differences were under 5 degrees for vertebral rotations and 5 mm for spinal lines. These simulations open the way for future predictive tools for surgical planning.

1. Introduction The EOS imaging system produces two simultaneous X-rays of a subject. Both views are used for the generation of a sub- ject-specific 3D skeletal model. This model then allows to obtain quantitative parameters concerning the morphology and the positioning of bones. Furthermore, thanks to the low dose of the EOS imaging, it is possible to take several stereoradiographies of the same subjects in order to study different positions of the fem- oro-patellar joint (Dagneaux et al. 2014) or to analyze different positions of the subjects. Also, it can be a way to compare tibia and femur relative positions without and with an orthotic device such as a brace for example. For that, the 3D model, obtained from the reference standing position, is registered across the different pairs of X-rays for the other positions. The goals of this study are 1/ to evaluate the reproducibility of the registration of both in vitro and in vivo and 2/ to a o assess the accuracy of this manual method using in vitro data.

39ème Congrès de la Société de Biomécanique, VALENCIENNES, FRANCE, 27-/08/2014 - 29/08/2014; Digital human models (DHM) are used for ergonomics assessment of a product or a workplace in its early phase of development. Differently sized manikins are simulated to provide designs that accommodate with a large range of a target population (Chaffin 2005 ). They are also used in ergonomics research for posture/movement analysis, and personalised manikins should be defined. The geometric model of a DHM consists of two distinguished parts: an external body shape and an internal articulated linkage representing the skeleton. To build a subject-specific manikin, a set of anthropometric measurements are first collected from a volunteer under study. The manikin's external shape and internal linkage are estimated as a function of these external inputs. For instance, Human Builder, one of the most widely used DHMs, requires up to 70 anthropometric measurements such as stature, sitting height, and weight for creating a manikin. In practice, not all required anthropometric measures are available. The missing parameters necessary for manikin generation are automatically estimated from a chosen anthropometric database. A similar module can be found in RAMSIS, another DHM widely used in automotive packaging. However, few studies have been published for verifying the realism of these personalised manikins, in particular their internal skeleton linkage (Zhang et al. 2004 ). Thanks to recent advances in medical imaging, data of both external body shape and internal skeleton are becoming available. Therefore, this study aimed to verify how good these personalised manikins are, especially in terms of the joint location

Considering the increasing development of three dimensional (3D) imaging, the 3D assessment of the acetabular coverage is to become the most interesting tool for the detection of acetabular pathologies. Biplanar X-rays based methods allow a 3D reconstruction of the hip with a reduced radiation dose. This study proposes a 3D assessment method of the acetabular coverage from biplanar X-rays or from an anteroposterior X-ray (conventional clinical imaging). An in vitro evaluation of the method was performed on six hip joints in comparison with computed tomography. The global coverage, the local coverage and the acetabular rim orientation were estimated in 3D. The mean global acetabular coverage was 40% with an estimated mean accuracy of 1.3% for the biplanar X-rays based method. This study evaluated a 3D assessment method of the acetabular coverage from biplanar X-rays or anteroposterior X-ray and open the way for clinical in vivo applications.

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.

Reconstruction methods from biplanar radiography allow a 3D clinical analysis, for patients in standing position, with a low radiation dose. This low-dose and postural imaging modality is thus very...

The mechanisms of idiopathic scoliosis progression are still not fully understood. The aim of this study is to explore, using finite element simulation, effect of the combination of gravity and anterior spinal overgrowth on scoliosis progression. 14 adolescents (10 girls, 4 boys) with an average age of 10.8 years [range 9; 13] were divided in three groups: thoraco-lumbar scoliosis (TL), lumbar scoliosis (L), asymptomatic patients (A). Accurate 3D reconstructions of the spine have been built using bi-planar X-rays. A patient specific validated finite element model has been used. Simulations have been launched with simulation of the combined effect of gravity and growth. The progression during the simulation was defined by a maximal axial rotation movement greater or equal than 4 degrees and a maximal lateral displacement greater or equal than 5 mm ("first order progression" for one criterion, "second order" for the both criteria). In the group TL, we notice an aggravation for 4 patients (Cobb angle increase at least by 4 degrees , mean at 5.9 degrees ). Only three patients of the group L show a progression with a smaller Cobb angle increase (mean 3.9 degrees ). For the group A, no progression is found for 3 and a progression is found for 1. An anterior spinal overgrowth combined with gravity and a pre-existent curve in the spine could lead to a progression of scoliosis. It seems necessary to consider differently lumbar curves from other curves. Numerical simulation with a patient specific model appears as a useful tool to investigate mechanisms of scoliosis aggravation.

Neck range of motion (RoM) tests are useful to understand cervical motions. Cervical RoM assessment is now a necessary step in clinical evaluation of patient's spine pathologies. However, clinical ...

The design of child dummies models for impact biomechanics needs description of the child body segments. Geometric characteristics of adult body segments are obtained by direct measurement on cadav...

Geometrical measurements of the rib cage were performed in vitro by Roberts and Chen (Roberts and Chen 1972) for finite element modelling. Few authors propose in vivo tools for the 3D geometrical d...