Experimentally based numerical models and numerical simulation with parameter identification of human lumbar FSUs in traction

Numerical simulation of the behaviour of human lumbar spine segments, moreover, parameter-identification of the component organs of human lumbar FSUs are presented in traction therapies, by using FEM analysis. First, a simple 2D model, than a refined 2D model, and finally a refined 3D model were applied for modeling lumbar FSUs. For global numerical simulation of traction therapies the material constants of component organs have been obtained from the international literature. For local parameter identification of the component organs, an interval of the possible material moduli has been considered for each organ, and the possible combinations of real moduli were obtained, controlling the process by the measured global deformations. In this way, the efficiency of conservative traction therapies can be improved by offering new experimental tensile material parameters for the international spine research

Intervertebral disc characterization by shear wave elastography: an in-vitro preliminary study

Patient-specific numerical simulation of the spine is a useful tool both in clinic and research. While geometrical personalization of the spine is no more an issue, thanks to recent technological advances, non-invasive personalization of soft tissue’s mechanical properties remains a challenge. Ultrasound elastography is a relatively recent measurement technique allowing the evaluation of soft tissue’s elastic modulus through the measurement of shear wave speed (SWS). The aim of this study was to determine the feasibility of elastographic measurements in intervertebral disc (IVD). An in-vitro approach was chosen to test the hypothesis that SWS can be used to evaluate IVD mechanical properties and to assess measurement repeatability. Eleven oxtail IVDs were tested in compression to determine their stiffness and apparent elastic modulus at rest and at 400 N. Elastographic measurements were performed in these two conditions and compared to these mechanical parameters. The protocol was repeated six times to determine elastographic measurement repeatability. Average SWS over all samples was 5.3 ± 1.0 m/s, with a repeatability of 7 % at rest and 4.6 % at 400 N; stiffness and apparent elastic modulus were 266.3 ± 70.5 N/mm and 5.4 ± 1.1 MPa at rest, respectively, while at 400 N they were 781.0 ± 153.8 N/mm and 13.2 ± 2.4 MPa. Correlations were found between elastographic measurements and IVD mechanical properties; these preliminary results are promising for further in-vivo application.The authors are grateful to the ParisTech BiomecAM chair program on subject-specific musculoskeletal modelling for funding (with the support of Proteor, ParisTech and Yves Cotrel Foundations)

Reverse engineering applied to a lumbar vertebra

Bone studies can be made in vivo or in vitro. However, disadvantages of both traditional techniques call for a compromise between the two. Reverse engineering allows in vitro bone samples to be simulated and analysed in a virtual in vivo environment thus offering a middle ground solution and a sound foundation on which biomechanical studies of bone could develop.peer-reviewe

Basics of Multibody Systems: Presented by Practical Simulation Examples of Spine Models

Computer modeling is a widely used method to determine the biomechanical behavior of a system. The aim of our biomechanical multibody simulation computer modeling is to consider the characteristics of a musculoskeletal system through the use of knowledge from the fields of mechanics, anatomy, and physiology in the model in an appropriate manner, in order to obtain as accurately as possible a realistic simulation of the biomechanical behavior of the system. Various application examples of a lumbar spine model that takes the spinal structures with their specific material properties into account are presented: effects of different spine alignments in standing position, effects of overweight on the spinal biomechanics, and application possibilities of biomechanical computer models in medicine

Finite element modeling and simulation of degeneration and hydrotraction therapy of human lumbar spine segments

A large percent of population is affected by low back pain problems all over the world, starting from the degeneration of the lumbar spinal structure, caused generally by ageing and mechanical overloading. If the degeneration is not too advanced, surgical treatments can be avoid, by applying conservative treatments, like traction therapies. Dry traction is a well-known method, however, often happens that instead of the traction effect and stress relaxation, the compression increases in the discs due to muscle activities. This verifies the importance of the suspension hydro-traction therapy, where the muscles are completely relaxed. The aim of this study was doubled: to model and simulate numerically the age-related and accidental degenerations of lumbar functional spinal units (FSU) and to simulate the mechanical answer of the more or less degenerated lumbar segments for the hydro-traction treatment, by using FE method. The basic question was: how to unload the disc to regain or improve its functional and metabolic ability. FE simulations of the mechanical behaviour of human lumbar FSUs with life-long agerelated and sudden accidental degenerations are presented for tension and compression. Compressive material constants were obtained from the literature, tensional material moduli were determined by parameter identification, using in vivo measured global elongations of segments as control parameters. 3D FE models of a typical FSU of lumbar part L3-S1 were developed extended to several nonlinear and nonsmooth unilateral features of intervertebral discs, ligaments, articular facet joints and attachments. The FE model was validated both for compression and tension, by comparing the numerical calculations with experimental results. The weightbath hydrotraction therapy decreases pain, increases joint flexibility, and improves the quality of life of patients with cervical or lumbar discopathy. Numerical simulations were investigated to clear the biomechanical effects of hydrotraction treatment of more or less degenerated segments to improve the efficiency of the non-invasive conservative treatment

Design of a Passive Exoskeleton Spine

In this thesis, a passive exoskeleton spine was designed and evaluated by a series of biomechanics simulations. The design objectives were to reduce the human operator’s back muscle efforts and the intervertebral reaction torques during a full range sagittal plane spine flexion/extension. The biomechanics simulations were performed using the OpenSim modeling environment. To manipulate the simulations, a full body musculoskeletal model was created based on the OpenSim gait2354 and “lumbar spine” models. To support flexion and extension of the torso a “push-pull” strategy was proposed by applying external pushing and pulling forces on different locations on the torso. The external forces were optimized via simulations and then a physical exoskeleton prototype was built to evaluate the “push-pull” strategy in vivo. The prototype was tested on three different subjects where the sEMG and inertial data were collected to estimate the muscle force reduction and intervertebral torque reduction. The prototype assisted the users in sagittal plane flexion/extension and reduced the average muscle force and intervertebral reaction torque by an average of 371 N and 29 Nm, respectively

Multi-Scale Vertebral-Kinematics Based Simulation Pipeline of the Human Spine With Application to Spine Tissues Analysis

This study developed an analytical tool for understanding spine tissues’ behavior in response to vertebral kinematics and spine pathology over a range of body postures. It proposed a novel pipeline of computational models based on predicting individual vertebral kinematics from measurable body-level motions, using musculoskeletal dynamics simulations to drive the vertebrae in corresponding spine FEMs. A reformulated elastic surface node (ESN) lumbar model was developed for use in MSD simulations. The ESN model modifies the lumbar spine within an existing MSD model by removing non-physiological kinematic constraints and including elastic IVD behavior. The model was scaled using subject-specific anthropometrics and validated to predict in vivo vertebral kinematics and IVD pressures during trunk flexion/extension. The ESN model was integrated into a novel simulation pipeline that automatically maps it to a kinematics-driven FEM (KD-FEM). The KD-FEM consisted of lumbar vertebrae scaled to subject-specific geometries and actuated by subject-specific vertebral kinematics from the ESN model for different activities. The pipeline was validated for its ability to predict in vivo IVD pressures at L4-L5 level during flexion and load carrying postures. A detailed multi-layered multi-phase lumbar canal FE model was integrated into the KD-FEM to quantify risks to canal tissues due to vertebral kinematics and progressive canal narrowing (stenosis). This enabled distinct computation of proposed stenosis measures, including cerebrospinal fluid pressure, cauda equina deformation and related stresses/pressure/strains, among others. Model outputs included measures during flexion and comparison of three clinically relevant degrees of progressive stenosis of the bony vertebral foramen at L4 level

Finite Element Analysis of Human Lumbar Vertebrae in Pedicle Screw Fixation

In totality of 100%, near about 85% of adult’s falls back pain, which directly related to their daily assignments and activities and 25% of people, reported lower back pain,which is associated with the vertebral compression. Spinal de-generation is also a medical situation which directly affecting men and women of different age groups.Spine injury is mostly found on vertebrae L1– L5 and corresponding intervertebral disk and in this analysis, the purposes of the present research are conclude the appropriate dimensions of pedicle screw (diameter and length) for its fixation in L2–L3-L4 vertebral region. In this analysis pedicle screw of Titanium with different diameters 5, 5.5, 6.0, 6.5 mm. and length 45, 50 mm have been considered. Further to this Finite element analysis (FEA) with boundary condition, i.e. fixed bottom surface of the L4 vertebrae and loads were applied on top surface of L2 vertebrae. The different loading condition has been considered for various body weights. Results were analyzed to provide appropriate pedicle screw size