Sharif Digital Repository

Ground reaction forces (GRFs) and their centers of pressure (CoPs) are essential inputs in musculoskeletal models of the spine that study load-lifting tasks. While GRFs and CoPs are usually measured in vivo via force-plates, they can be predicted based on motion equations, developed in AnyBody Modelling System (AMS) thus eliminating the need for laboratory equipment and in vivo measurements. This study aims to develop an easy-to-use yet accurate model that predict GRFs and CoPs during different Manual Material Handling (MMH) activities using AnyBody Modelling System and artificial neural networks. First, the accuracy of the AMS GRF prediction algorithm was evaluated for 8 normal- and 4... 

One of the most common spinal surgeries involves spinal fusion or vertebral fixation, which is used to treat various conditions such as intervertebral disc disease, scoliosis (lateral deviation of the spinal column), fractures, infections, or the presence of tumors in the spinal column. In this surgical procedure, the use of pedicle screws and titanium rods prevents motion and friction between two vertebrae. Screws may enter the vertebrae in the wrong position and angle, causing bone weakening, rupture of nerve roots or blood vessels, weakness or lack of sensation in some parts of the body, spinal cord injury, and in severe cases, paralysis of the patient. For this reason, fusion surgery is... 

We have recently designed/fabricated novel bilateral vertebra- and patient-specific drill guides for pedicle screw (PS) placements and tested their accuracy for both nondeformed and deformed thoracic spines. PS placement deviations from their preplanned positions significantly reduced when guide template were used; the success rate improved from ~72% (freehand placements) to 94% (guided placements). In the present study, we aim to use finite element (FE) analyses to evaluate the pull-out strength of these PSs inserted via either the freehand technique or our drill-guide templates. Two 3D-printed T1-T12 thoracic models of a severe scoliosis patient with a 47° thoracic dextro-scoliotic curve... 

Biomechanical models require body posture to evaluate the risk of musculoskeletal injuries during daily/occupational activities like manual material handling (MMH). The procedure to measure body posture via motion-analysis techniques is complex, time-consuming, and limited to equipped laboratories. This study aims to develop an easy-to-use yet accurate model that predict human whole-body static posture (3D body coordinates and anatomical joint angles) during different MMH activities. Twenty healthy male right-handed individuals with body mass index between 18 and 26 performed 204 symmetric and asymmetric MMH activities. Each person reached (i.e., without any load in hands) the destinations... 

Body posture is an essential input of musculoskeletal models that evaluate spinal loads in occupational activities. Posture is either measured in vivo via video-camera motion capture systems or predicted via artificial neural networks (ANNs) [1]. As video-camera measurements are impractical for use in real workstations, we have recently developed an ANN that predicts full-body posture during one- and two-handed static load-handling activities. This ANN, trained based on the posture data of 20 subjects each performing 204 static load-handling activities, uses 3D coordinates of the hand-load, body weight, and body height of the worker to predict 3D coordinates of 41 full-body skin markers. The... 

Background: Degeneration of intervertebral joints due to kinetical alterations after fusion surgery is a prevalent back disorder. While in-vivo studies are limited to medical imaging techniques, in-vitro and in-silico (passive FE modeling) investigations lack the crucial role of muscle forces. Available musculoskeletal modeling studies, not only suffer oversimplification of intervertebral joints, but have some shortcomings in incorporation of the contributing factors (that may alter postoperative kinetics). On the other hand, one of the main shortcomings in the available musculoskeletal models is their inability to account for dynamic effects and modeling transient events. Purpose: 1-... 

Objective: To assess adequacy of the National Institute for Occupational Safety and Health (NIOSH) Lifting Equation (NLE) in controlling lumbar spine loads below their recommended action limits during load-handling activities in the stoop and squat using a detailed musculoskeletal model,that is, the AnyBody Modeling System.Background: The NIOSH committee employed simplistic biomechanical models for the calculation of the spine compressive loads with no estimates of the shear loads. In addition, NLE does not include the posture of the knee during manual material handling. It is therefore unknown whether the NLE would adequately control lumbar compression and shear loads below their... 

According to epidemiological studies, low back pain is the most prevalent musculoskeletal disease thus indicating the important role of biomechanical engineers to manage risk of injury. Different quantitative (i.e., biomechanical models) and qualitative (empirical) assessment tools are used to evaluate risk of musculoskeletal injuries. The present study uses various quantitative and qualitative risk assessment tools to investigate the risk of injury among workers in Iran Khodro Automaker company (IKCO) assembly hall No. 3 (Pars Peugeot car assembly). Moreover, different engineering and administrative interventions are suggested to manage risk of musculoskeletal injuries when needed. The... 

Passive finite element (FE) models of the spine are commonly used to simulate intact and various pre- and postoperative pathological conditions. Being devoid of muscles, these traditional passive FE models are driven by simplistic loading scenarios, e.g., a constant moment and compressive follower load (FL) that do not properly mimic the complex in vivo loading condition of the spine under muscle exertions. The present works therefore aims to develop novel passive FE models that are driven by more realistic yet simple loading scenarios, i.e., in vivo measured vertebral rotations and pathological-condition dependent FLs (estimated based on detailed musculoskeletal finite element (MS-FE) spine... 

Fusion surgery or fixation of vertebrae in the spine is used to treat scoliosis, fractures, infections, tumors, spinal cord injuries, and disc herniation. In this type of surgery, two or more vertebrae are connected by special screws called pedicle screws to eliminate movement between the vertebrae. Given the serious risks of spinal fusion surgery, if the slightest mistake is made at the entry point or angle of the screw inside the vertebrae, the risk of spinal cord injury is very high, which is one of the complications of fusion surgery. Therefore, in order to increase the accuracy of screw placement, patient-specific template guides are used as drill guides in this operation. For this... 

Low back pain (LBP), the leading cause of disability worldwide, remains one of the most common and challenging occupational musculoskeletal disorders. The effective assessment of LBP injury risk, and the design of appropriate treatment modalities and rehabilitation protocols, require accurate estimation of the mechanical spinal loads during different activities. This study aimed to: 1) develop a novel 2D beam-column finite element control-based model of the lumbar spine and compare its predictions for muscle forces and spinal loads to those resulting from a geometrically-matched equilibrium-based model; 2) test, using the foregoing control-based finite element model, the validity of the... 

Spine biomechanical models suffers from either simplification in passive disc components modeling (modeling via torsional spring or beam elements) in musculoskeletal (MS) models or shortcomings in detailed muscles modeling (via a simple force and torque vector) in detailed finite element (FE) models. Considering these, that is aimed in this study to develop a hybrid MS-FE model which the calculated muscle forces by a MS model (developed based on geometrical and mechanical properties of FE model) for a desired static posture, being applied to a detailed FE model. Considering the change of discs stiffness in FE model under the applied muscles and gravity forces, the equivalent stiffness in MS... 

Investigating the influence of shoes on variables of human biomechanics is of a high importance. The purpose of this study was to examine the effect of auxetic Nike Free RN shoe on kinematics and kinetics of human body. It was asked from 11 healthy male to perform drop vertical jump in three conditions: with auxetic Nike Free RN, with conventional shoe and barefoot. 3D Cartesian positions of the markers, which were stuck to the subjects’ bodies, were recoeded using Vicon camera system. Ground reaction force and its center of pressure of each foot captured using two force plates. Moreover, activation of rectus abdominis, longissimus, iliocostalis lomburom and multifidus were recorded using... 

Continuous positive airway pressure (CPAP) is a standard treatment for patients with obstructive sleep apnea (OSA), a sleep-related breathing disorder characterized by full or partial occlusion of the upper airway during sleep. CPAP pressure adjust by a sleep technologist during attended laboratory polysomnography (PSG) to eliminate obstructive respiratory-related events (apneas, hypopneas). Because of changes in environment and lifestyle patients needed new adjustments for the device that brings discomfort and extra money for treatment. In recent, lots of methods have been proposed to replace PSG and minimized the number of biological signals to detect apnea, best results came from deep... 

Low back pain is one of the most prevalent musculoskeletal injuries in occupational activities. In order to reduce or prevent it, it is necessary to estimate the mechanical loads of body joints. Direct measurement of spinal loads is invasive and costly. Therefore, musculoskeletal modeling is a convenient tool in estimation of joints and muscles loads that often uses kinematics information as input.Marker-based motion capture systems are one of the most common ways for the estimation of body kinematics. Unfortunately, they are time consuming and expensive. Thus being marker-free and low-cost, Microsoft Kinect is a suitable alternative. Recent studies often have investigated accuracy of... 

Today, obesity, as a major global health challenge, affects more than 30 percent of the world's population. To investigate the effect of obesity on spinal function, a common method is motion analysis (kinematic method). This method is based on the claim that the abnormal mechanical function of the spine is directly related to its abnormal motions.The aim of this study is to measure and compare the range of motions (RoMs) of different segments of the spine in all anatomical plates between obese and normal individuals, as well as to calculate and compare some motion rhythms between the lumbar spine and the pelvis in these two groups. Comparing the posture of the spine between obese and normal... 

Spinal instrumentation with pedicle screws has become a widespread surgical procedure in the treatment of spinal disease. The traditional way of placing pedicle screws is to use the anatomical landmarks which at many times can be a best guess resulting in breaches of the pedicle and causing neurological injuries. Additional modalities used include the intra-operative fluoroscopy or navigation systems, which results in radiation exposure and more intra-operative time. In order to solve the technical problems, a pedicle screw navigation template that guarantees the correct implantation position and direction of vertebral pedicle screws, can be used. Compared to pedicles in the lumbar spine,... 

Manual material handling (MMH) is associated with mechanical back injuries. To manage such injuries, musculoskeletal models are employed to estimate spinal loads during MMH. These models require, as input, 3D-position of the hand-load and body posture whose measurements involve skillful and time-consuming motion analysis investigations.In order to facilitate the procedure of posture measurements and load estimations, three coupled artificial-neural-networks (ANNs) were developed. To predict whole body posture, ANN1 was trained based on our novel measurements on 15 individuals. Each individual performed several static-tasks by holding 0, 5, and 10 kg weight at 9 different anterior-left... 

pain is one of the most common musculoskeletal (MS) disorders and the most important cause of functional disability in developed and developing countries. Several studies showed that the most important factor in development of the low back pain is loads and stresses in different parts of the spine. While non-invasive measurement of these internal loads and stresses, as a tool to estimate the risk of injury, is very difficult and costly, biomechanical models of the spine are the best meansfor analyzing the risk of injury in various in-vivo activities. In order to develop a spine model, it is necessary to measure the kinematics of the vertebrae for the specified activity. In previous studies,... 

Musculoskeletal abnormalities affect joints and change their range of motion (RoM). Correcting these abnormalities thoroughly depends on the information related to the normal spine movement. Therefore, spine motion analysis can be used as an important tool to distinguish between healthy and patient individuals as well as to determine the intensity of such diseases. Additionally, existing biomechanical models need kinematics data in order to analyze spinal forces. The present study hence aims to measure 3D range of motion of thoracic and lumbar spine using inertial sensors. Their small size, portability, low weight, and relatively low cost make inertial sensors as indispensable tools in...