Baptiste Sandoz

Subject-specific body segment parameters' estimation using biplanar X-rays: a feasibility study

In order to improve the reliability of childrens models, the aim of this study was to determine the subject-specific masses and 3D locations of the centres of mass (CoM) of body segments using biplanar X-rays. Previous methods, validated on upper leg segments, were applied to the whole body. Six children and six adults were studied. The low-dose X-ray system EOS® was used to simultaneously get head-to-foot biplanar X-rays in the upright position. Specific methods were used to get 3D reconstructions of bones and body shape. The densities from the literature were used to define the masses. To assess the accuracy of the reconstructions, a force plate was used to compare the mass and the projection of the CoM. A mean distance of 4.5 mm between the measured and the calculated projections of the CoM was found. The mean error between the estimated and the actual body mass was 2.6%. Such a method will be useful in obtaining the body segment parameters in children, hard to obtain using direct measurement techniques.

Non-invasive assessment of human multifidus muscle stiffness using ultrasound shear wave elastography: A feasibility study.

There is a lack of numeric data for the mechanical characterization of spine muscles, especially in vivo data. The multifidus muscle is a major muscle for the stabilization of the spine and may be involved in the pathogenesis of chronic low back pain (LBP). Supersonic shear wave elastography (SWE) has not yet been used on back muscles. The purpose of this prospective study is to assess the feasibility of ultrasound SWE to measure the elastic modulus of lumbar multifidus muscle in a passive stretching posture and at rest with a repeatable and reproducible method. A total of 10 asymptotic subjects (aged 25.5 ± 2.2 years) participated, 4 females and 6 males. Three operators performed 6 measurements for each of the 2 postures on the right multifidus muscle at vertebral levels L2-L3 and L4-L5. Repeatability and reproducibility have been assessed according to ISO 5725 standard. Intra-class correlation coefficients (ICC) for intra- and inter-observer reliability were rated as both excellent [ICC=0.99 and ICC=0.95, respectively]. Reproducibility was 11% at L2-L3 level and 19% at L4-L5. In the passive stretching posture, shear modulus was significantly higher than at rest (µ < 0.05). This preliminary work enabled to validate the feasibility of measuring the shear modulus of the multifidus muscle with SWE. This kind of measurement could be easily introduces into clinical routine like for the medical follow-up of chronic LBP or scoliosis treatments.

A subject-specific biomechanical control model for the prediction of cervical spine muscle forces

Background: The aim of the present study is to propose a subject‐specific biomechanical control model for the estimation of active cervical spine muscle forces. Methods: The proprioception‐based regulation model developed by Pomero et al. (2004) for the lumbar spine was adapted to the cervical spine. The model assumption is that the control strategy drives muscular activation to maintain the spinal joint load below the physiological threshold, thus avoiding excessive intervertebral displacements. Model evaluation was based on the comparison with the results of two reference studies. The effect of the uncertainty on the main model input parameters on the predicted force pattern was assessed. The feasibility of building this subject‐specific model was illustrated with a case study of one subject. Findings: The model muscle force predictions, although independent from EMG recordings, were consistent with the available literature, with mean differences of 20%. Spinal loads generally remained below the physiological thresholds. Moreover, the model behavior was found robust against the uncertainty on the muscle orientation, with a maximum coefficient of variation (CV) of 10%. Interpretation: After full validation, this model should offer a relevant and efficient tool for the biomechanical and clinical study of the cervical spine, which might improve the understanding of cervical spine disorders. HighlightsA personalized proprioception‐based model estimating neck muscle forces is proposed.Consistent predictions are obtained independently from electromyogram‐recordings.The feasibility of building the subject‐specific model was assessed for one subject.Spine muscle response depends on the intervertebral joint load threshold.The model allows studying the effect of postural disorders or poor muscle quality.

Parametric finite element modelling of the human lower cervical spinal cord

Despite a large number of rear-end collisions on the road and a high frequency of whiplash injuries reported, the mechanism of whiplash injuries is not completely understood. One of the reasons is that the injury does not necessarily come with clear tissue damages detectable on X-ray or MRI (Chen et al.). So studying the cervical spine including the spinal cord can help to understand the injury mechanism of a whiplash. A “parametric and subject-specific modelling” (PSSM) method for the cervical spine was developed. This method enables to take geometrical parameters into account in order to generate an associated mesh (Laville et al.). The aim of the present study is to develop a parametric finite element model of the spinal cord for the lower cervical spine based on this PSSM method.

Will Automated Driving Technologies Make Today’s Effective Restraint Systems Obsolete?

The article discusses whether automobile restraint systems are obsolete in the wake of the implementation of automated driving technologies (ADTs) in vehicles as of 2017, and it mentions efforts to prevent road traffic accidents, injuries, and fatalities. According to the article, ADTs will give automobile occupants more freedom during travel. Automobile safety designs and epidemiological studies are assessed.

an attempt of early Detection of Poor Outcome after Whiplash

The main concern with whiplash is that a large proportion of whiplash patients experience disabling symptoms or whiplash-associated disorders (WAD) for months if not years following the accident. Therefore, identifying early prognostic factors of WAD development is important as WAD have widespread clinical and economic consequences. In order to tackle that question, our study was specifically aimed at combining several methods of investigation in the same WAD patients at the acute stage and 6 months later. Our longitudinal, open, prospective, multi-center study included 38 whiplash patients, and 13 healthy volunteers matched for age, gender, and socio-economic status with the whiplash group. Whiplash patients were evaluated 15–21 days after road accident, and 6 months later. At each appointment, patients underwent a neuropsychological evaluation, a full clinical neurological examination, neurophysiological and postural tests, oto-neurological tests, cervical spine cord magnetic resonance imaging (MRI) with tractography (DTI). At 6 months, whiplash patients were categorized into two subgroups based on the results of the Diagnostic and Statistical Manual of Mental Disorders as having either favorable or unfavorable progression [an unfavorable classification corresponding to the presence of post-concussion symptom (PCS)] and we searched retrospectively for early prognostic factors of WAD predicting the passage to chronicity. We found that patients displaying high level of catastrophizing at the acute stage and/or post-traumatic stress disorder associated with either abnormalities in head or trunk kinematics, abnormal test of the otolithic function and at the Equitest or a combination of these syndromes, turned to chronicity. This study suggests that low-grade whiplash patients should be submitted as early as possible after the trauma to neuropsychological and motor control tests in a specialized consultation. In addition, they should be evaluated by a neuro-otologist for a detailed examination of vestibular functions, which should include cervical vestibular evoked myogenic potential. Then, if diagnosed at risk of WAD, these patients should be subjected to an intensive preventive rehabilitation program, including vestibular rehabilitation if required.

Subject-specific mass and 3D localisation of the mass centre of child body segments using biplanar X-rays

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 cadavers (Dempster 1955), stereo-photogrammetric technique (McConville and Churchill 1980) or regression equations (Dumas et al. 2006). However, the segment mass and mass centre localisation is not yet available for children. The aim of this study is to determine the subject-specific mass, mass centre localisation and the gravity line of child body segments using 3D models from biplanar X-rays.

Evaluation of a Passive Model to Mimic Dynamic Head/Neck Movements

Whiplash has been defined as a fast motion of the head and neck without a direct force exerted onto the head. A major cause of neck injuries is car accidents, leading to whiplash associated disorders (Laporte et al. 2016). The symptoms include neck pain, fatigue, dizziness, blurred vision, painful lesions (Chalovich & Eisenberg 2005), and headaches (Panjabi et al. 1998), are non-specific and are reported up to months or years after accidents. Although, the imaging methods, such as MRI or X-Ray, are not sufficient to identify these injuries (Panjabi et al. 1998). The mechanisms of injury is not yet fully understood. It has been shown that precontracted neck muscles, acceleration level and visual inputs would influence the head motion (Eng et al. 1997; Brault et al. 2000; Kumar et al. 2005; Sandoz et al. 2016). The aim of the present study is to model the dynamic of the head/neck complex to understand muscle stabilization strategies. The boundary conditions of the model are based on previous in vivo experiments on 20 volunteers seated on an accelerated sled in frontal direction (Sandoz et al. 2016). Some of these volunteers performed EOS Xray images in order to personnalize geometrical parameters. EOS imaging system is a low dose X-rays acquisition system allowing to perform bi-planar acquisition of the subject’s cervical spine. From these X-rays, the 3D personalized geometry of each volunteer’s head neck complex can be built.

Breathing through a spirometer perturbs balance

Natural breathing is known to induce at each inspiration/ expiration, minimal perturbations of body balance that are compensated by movement of trunk and lower limb (Hodges et al. 2002). This phenomenon called posturo ventilatory synchronization may be impaired (Manor et al. 2012). Its evaluation requires simultaneous assessments of ventilation profile and postural control, using the less disruptive methods. Spirometry is the reference method to assess the ventilatory parameters. It requires however to connect the subject to the spirometer, using a mouthpiece, that is known to modify significantly the respiratory frequency (Gilbert et al. 1972) and may influence the postural control. The Optoelectronic Plethysmography (OEP) was validated as an alternative non-disruptive method to assess ventilation as it allows subjects to breathe naturally. Evidently, non-contact measure of ventilation by camera is supposed to induce no perturbation of postural control, and may be more appropriate than spirometer to assess the posturo ventilator synchronization. The objective of this study was to evaluate the postural perturbations due to the use of the spirometer, by comparing it to the OEP method, on postural control.

In Vivo Assessment of Elasticity of Child Rib Cortical Bone Using Quantitative Computed Tomography

Elasticity of the child rib cortical bone is poorly known due to the difficulties in obtaining specimens to perform conventional tests. It was shown on the femoral cortical bone that elasticity is strongly correlated with density for both children and adults through a unique relationship. Thus, it is assumed that the relationships between the elasticity and density of adult rib cortical bones could be expanded to include that of children. This study estimated in vivo the elasticity of the child rib cortical bone using quantitative computed tomography (QCT). Twenty-eight children (from 1 to 18 y.o.) were considered. Calibrated QCT images were prescribed for various thoracic pathologies. The Hounsfield units were converted to bone mineral density (BMD). A relationship between the BMD and the elasticity of the rib cortical bone was applied to estimate the elasticity of childrens ribs in vivo. The estimated elasticity increases with growth (7.1 ± 2.5 GPa at 1 y.o. up to 11.6 ± 1.9 GPa at 18 y.o.). This data is in agreement with the few previous values obtained using direct measurements. This methodology paves the way for in vivo assessment of the elasticity of the child cortical bone based on calibrated QCT images.