Institut de Biomécanique Humaine Georges Charpak (IBHGC)

Kinematic adaptations from self-selected to fast speed walking in patients with adult spinal deformity

ABI KARAM, Krystel — Mon, 01 Jan 2024 00:00:00 GMT

Kinematic adaptations from self-selected to fast speed walking in patients with adult spinal deformity ABI KARAM, Krystel; EL RACHKIDI, Rami; SEMAAN, Karl; SAAD, Eddy; FAKHOURY, Marc; SAADE, Maria; AYOUB, Elma; RTEIL, Ali; JABER, Elena; MEKHAEL, Elio; NASSIM, Nabil; MASSAAD, Abir; GHANEM, Ismat; ASSI, Ayman Purpose To investigate kinematic adaptations from self-selected to fast speed walking in ASD patients. Methods 115 primary ASD and 66 controls underwent biplanar radiographic X-rays and 3D gait analysis to calculate trunk, segmental spine and lower limb kinematics during self-selected and fast speed walking. Kinematic adaptation was calculated as the difference (Δ) between fast and self-selected speed walking. ASD with 7 or more limited kinematic adaptation parameters were classified as ASD-limited-KA, while those with less than 7 limited kinematic adaptation parameters were classified as ASD-mild-KA. Results 25 patients were classified as ASD-limited-KA and 90 as ASD-mild-KA. ASD-limited-KA patients walked with a lesser increase of pelvic rotation (Δ = 1.7 vs 5.5°), sagittal hip movement (Δ = 3.1 vs 7.4°) and shoulder–pelvis axial rotation (Δ = 3.4 vs 6.4°) compared to controls (all p < 0.05). ASD-limited-KA had an increased SVA (60.6 vs − 5.7 mm), PT (23.7 vs 11.9°), PI–LL (9.7 vs − 11.7°), knee flexion (9.2 vs − 0.4°) and a decreased LL (44.0 vs 61.4°) compared to controls (all p < 0.05). Kinematic and radiographic alterations were less pronounced in ASD-mild-KA. The limited increase of walking speed was correlated to the deteriorated physical component summary score of SF-36 (r = 0.37). Discussion Kinematic limitations during adaptation from self-selected to fast speed walking highlight an alteration of a daily life activity in ASD patients. ASD with limited kinematic adaptations showed more severe sagittal malalignment with an increased SVA, PT, PI–LL, and knee flexion, a decreased LL and the most deteriorated quality of life. This highlights the importance of 3D movement analysis in the evaluation of ASD.

Reliability of B-mode ultrasound and shear wave elastography in evaluating sacral bone and soft tissue characteristics in young adults with clinical feasibility in elderly

ABOU KARAM, Maher — Sat, 01 Jan 2022 00:00:00 GMT

Reliability of B-mode ultrasound and shear wave elastography in evaluating sacral bone and soft tissue characteristics in young adults with clinical feasibility in elderly ABOU KARAM, Maher; MUKHINA, Ekaterina; DARAS, Nils; RIVALS, ISabelle; PILLET, Helene; SKALLI, Wafa; CONNESSON, Nathanael; PAYAN, Yohan; ROHAN, Pierre-Yves Background: Physiologic aging is associated with loss of mobility, sarcopenia, skin atrophy and loss of elasticity. These factors contribute, in the elderly, to the occurrence of a pressure ulcer (PU). Brightness mode ultrasound (US) and shear wave elastography (SWE) have been proposed as a patient-specific, bedside, and predictive tool for PU. However, reliability and clinical feasibility in application to the sacral region have not been clearly established. Method: The current study aimed to propose a simple bedside protocol combining US and SWE. The protocol was first tested on a group of 19 healthy young subjects by two operators. The measurements were repeated three times. Eight parameters were evaluated at the medial sacral crest. Intraclass Correlation Coefficient (ICC) was used for reliability assessment and the modified Bland Altman plot analysis for agreement assessment. The protocol was then evaluated for clinical feasibility on a healthy older group of 11 subjects with a mean age of 65 ± 2.4 yrs. Findings: ICC showed poor to good reliability except for skin SWE and hypodermis thickness with an ICC (reported as: mean(95%CI)) of 0.78(0.50-0.91) and 0.98(0.95-0.99) respectively. No significant differences were observed between the young and older group except for the muscle Shear Wave Speed (SWS) (respectively 2.11 ± 0.27 m/s vs 1.70 ± 0.17 m/s). Interpretation: This is the first protocol combining US and SWE that can be proposed on a large scale in nursing homes. Reliability, however, was unsatisfactory for most parameters despite efforts to standardize the protocol and measurement definitions. Further studies are needed to improve reliability.

Inter-lamellar shear resistance confers compressive stiffness in the intervertebral disc: An image-based modelling study on the bovine caudal disc

ADAM, Clayton — Fri, 01 Jan 2016 00:00:00 GMT

Inter-lamellar shear resistance confers compressive stiffness in the intervertebral disc: An image-based modelling study on the bovine caudal disc ADAM, Clayton; SKALLI, Wafa; ROUCH, Philippe The intervertebral disc withstands large compressive loads (up to nine times bodyweight in humans) while providing ﬂexibility to the spinal column. At a microstructural level, the outer sheath of the disc (the annulus ﬁbrosus) comprises 12–20 annular layers of alternately crisscrossed collagen ﬁbres embedded in a soft ground matrix. The centre of the disc (the nucleus pulposus) consists of a hydrated gel rich in proteoglycans. The disc is the largest avascular structure in the body and is of much interest biomechanically due to the high societal burden of disc degeneration and back pain. Although the disc has been well characterized at the whole joint scale, it is not clear how the disc tissue microstructure confers its overall mechanical properties. In particular, there have been conﬂicting reports regarding the level of attachment between adjacent lamellae in the annulus, and the importance of these interfaces to the overall integrity of the disc is unknown. We used a polarized light micrograph of the bovine tail disc in transverse cross-section to develop an image-based ﬁnite element model incorporating sliding and separation between layers of the annulus, and subjected the model to axial compressive loading. Validation experiments were also performed on four bovine caudal discs. Interlamellar shear resistance had a strong effect on disc compressive stiffness, with a 40% drop in stiffness when the interface shear resistance was changed from fully bonded to freely sliding. By contrast, interlamellar cohesion had no appreciable effect on overall disc mechanics. We conclude that shear resistance between lamellae confers disc mechanical resistance to compression, and degradation of the interlamellar interface structure may be a precursor to macroscopic disc degeneration.

A Mechanical Descriptor of Instability in Human Locomotion: Experimental Findings in Control Subjects and People with Transfemoral Amputation

AL ABIAD, Nahime — Wed, 01 Jan 2020 00:00:00 GMT

A Mechanical Descriptor of Instability in Human Locomotion: Experimental Findings in Control Subjects and People with Transfemoral Amputation AL ABIAD, Nahime; WATIER, Bruno; PILLET, Helene While multiple criteria to quantify gait instability exist, some limitations hinder their computation during realistic walking conditions. A descriptor, computed as the distance between the center of mass of the body and the minimal moment axis ( dCOM−Δ) , has been proposed recently. This present study aims at characterizing the behavior of the mentioned descriptor in a population at a higher risk of falls. Five individuals with transfemoral amputation and 14 healthy individuals were involved in an experiment composed of motion capture and force plates acquisition during overground walking at a self-selected speed. For both groups of participants, the profile of dCOM−Δ was analyzed and descriptive parameters were calculated. The plot of dCOM−Δ was different between groups and different relative to the leading limb considered (prosthetic or contralateral). All descriptive parameters calculated, except one, were statistically different between groups. As a conclusion, amputees seem to be able to limit the average of dCOM−Δ in spite of a different evolution pattern. This is consistent with the ability of the subjects to maintain their dynamic balance. However, the extracted parameters showed the significant asymmetry of the gait profile between prosthetic and contralateral stances and highlighted the potential sources of imbalance.

Mechanical modelling of confined cell migration across constricted-curved micro-channels

ALLENA, Rachele — Wed, 01 Jan 2014 00:00:00 GMT

Mechanical modelling of confined cell migration across constricted-curved micro-channels ALLENA, Rachele Confined migration is a crucial phenomenon during embryogenesis, immune response and cancer. Here, a two-dimensional finite element model of a HeLa cell migrating across constricted-curved micro-channels is proposed. The cell is modelled as a continuum with embedded cytoplasm and nucleus, which are described by standard Maxwell viscoelastic models. The decomposition of the deformation gradient is employed to define the cyclic active strains of protrusion and contraction, which are synchronized with the adhesion forces between the cell and the substrate. The micro-channels are represented by two rigid walls and exert an additional viscous force on the cell boundaries. Five configurations have been tested: 1) top constriction, 2) top-bottom constriction, 3) shifted top-bottom constriction, 4) embedded obstacle and 5) bending micro-channel. Additionally, for the first four micro-channels both sub-cellular and sub-nuclear constrictions have been obtained, while for the fifth micro-channel three types of bending have been investigated ('curved', 'sharp' and 'sharper'). For each configuration, several parameters such as the cell behaviour, the covered distance, the migration velocity, the ratio between the cell and the nucleus area as well as the cell-substrate and cell-channel surfaces forces have been evaluated. The results show once more the fundamental role played by mechanics of both the cell and the environment.

A mechanical model to investigate the role of the nucleus during confined cell migration

ALLENA, Rachele — Thu, 01 Jan 2015 00:00:00 GMT

A mechanical model to investigate the role of the nucleus during confined cell migration ALLENA, Rachele; THIAM, Hui; PIEL, Mathieu; AUBRY, Denis 1. Introduction Cell migration in confinement plays a fundamental role in biological processes such as embryogenesis, immune response and tumorogenesis. Specifically, tumor cells continuously adapt their migratory behaviour to their environment. Therefore, it has become timely and essential for diagnostic purposes to quanti- tatively evaluate the cell deformability in confinement. Here, we propose a two-dimensional mechanical model to simulate the migration of a HeLa cell through a micro- channel. We will evaluate both the invasiveness of the cell and the mechanical forces exerted by the cell according to the surrounding microstructure.

The discriminant role of mechanics during cell migration

ALLENA, Rachele — Mon, 01 Jan 2018 00:00:00 GMT

The discriminant role of mechanics during cell migration ALLENA, Rachele Cell migration is a fundamental process involved in many mechanobiological phenomena such immune response, bone remodelling and tumorogenesis. During the last decades several numerical works have been proposed in the literature in order to unveil its main biological, chemical and mechanical principles. Here, I will show how a computational approach purely based on mechanics is able to reproduce cell migration in different configurations including migration under confinement, in presence of durotaxis and on flat substrates. A series of models will be presented each of which is based on three main ingredients: i) the active strains of the cell reproducing the cyclic protrusion-contraction movement of the cell (i.e. the polymerization and depolymerization processes), ii) the adhesion forces exerted by the cell on the surrounding and ii) the intra-synchronization between the active strains and the adhesion forces. I will show how mechanics play a critical role in determining the efficiency of the cell in terms of displacement, speed and forces.

A Cellular Potts Model of single cell migration in presence of durotaxis

ALLENA, Rachele — Fri, 01 Jan 2016 00:00:00 GMT

A Cellular Potts Model of single cell migration in presence of durotaxis ALLENA, Rachele; SCIANNA, Marco; PREZIOSI, Luigi Cell migration is a fundamental biological phenomenon during which cells sense their surroundings and respond to different types of signals. In presence of durotaxis, cells preferentially crawl from soft to stiffsubstrates by reorganizing their cytoskeleton from an isotropic to an anisotropic distribution of actin fil- aments. In the present paper, we propose a Cellular Potts Model to simulate single cell migration over flat substrates with variable stiffness. We have tested five configurations: (i) a substrate including a soft and a stiffregion, (ii) a soft substrate including two parallel stiffstripes, (iii) a substrate made of succes- sive stripes with increasing stiffness to create a gradient and (iv) a stiffsubstrate with four embedded soft squares. For each simulation, we have evaluated the morphology of the cell, the distance covered, the spreading area and the migration speed. We have then compared the numerical results to specific experimental observations showing a consistent agreement.

Heterogeneous directions of orthotropy in three-dimensional structures: finite element description based on diffusion equations

ALLENA, Rachele — Mon, 01 Jan 2018 00:00:00 GMT

Heterogeneous directions of orthotropy in three-dimensional structures: finite element description based on diffusion equations ALLENA, Rachele; CLUZEL, Christophe Heterogeneous materials such as bone or woven composites show mesostructures whose constitutive elements are all oriented locally in the same direction and channel the stress flow throughout the mechanical structure. The interfaces between such constitutive elements and the matrix are regions of potential degradations. Then, when building a numerical model, one has to take into account the local systems of orthotropic coordinates in order to properly describe the damage behavior of such materials. This can be a difficult task if the orthotropic directions constantly change across the complex three-dimensional geometry as is the case for bone structures or woven composites. In the present paper, we propose a finite element technique to estimate the continuum field of orthotropic directions based on the main hypothesis that they are mainly triggered by the external surface of the structure itself and the boundary conditions. We employ two diffusion equations, with specific boundary conditions, to build the radial and the initial longitudinal unit vectors. Then, to ensure the orthonormality of the basis, we compute the longitudinal, the circumferential, and the radial vectors via a series of vector products. To validate the numerical results, a comparison with the average directions of the experimentally observed Haversian canals is used. Our method is applied here to a human femur.

A new comprehensive approach for bone remodeling under medium and high mechanical load based on cellular activity

ALLENA, Rachele — Wed, 01 Jan 2020 00:00:00 GMT

A new comprehensive approach for bone remodeling under medium and high mechanical load based on cellular activity ALLENA, Rachele; GEORGE, Daniel; BOURZAC, Céline; PALLU, Stéphane; RÉMOND, Yves; BENSIDHOUM, Morad; PORTIER, Hugues Most of the last century, bone remodeling models have been proposed based on the observation that bone density is dependent on the intensity of the applied mechanical loads. Most of these cortical or trabecular bone remodeling models are related to the osteocyte mechanosensitivity, and they all have a direct correlation between the bone mineral density and the mechanical strain energy. However, experiments on human athletes show that high-intensity sport activity tends not to increase bone mineral density but rather has a negative impact. Therefore, it appears that the optimum bone mineral density would develop for “medium”-intensity activity (or medium mechanical loads) and not for the highest-intensity one. The authors would like to thank the CNRS for its ﬁnancial support through the Déﬁ Mécanobiologie to carry out the work.