Sharif Digital Repository

Background: Lower limb amputation is a major public health issue globally, and its prevalence is increasing significantly around the world. Previous studies on lower limb amputees showed analogous complexity implemented by the neurological system which does not depend on the level of amputation. Research question: What are the differences in muscle synergies between healthy subjects (HS) and transfemoral amputees (TFA) during self-selected normal transient-state walking speed? Methods: thirteen male HS and eleven male TFA participated in this study. Surface electromyography (sEMG) data were collected from HS dominant leg and TFA intact limb. Concatenated non-negative matrix factorization... 

A dynamic model of an above-knee prosthesis during the complete gait cycle was developed. The model was based on a two-dimensional multi-body mechanical system and included a hydraulic and an elastic controller for the knee and a kinematical driver controller for the prosthetic ankle. The equations of motion were driven using Lagrange method. Simulation of the foot contact was conducted using a two-point penetration contact model. The knee elastic and hydraulic controller units, the knee extension stop, and the kinematical driver controller of the ankle were represented by a spring and a dashpot, a nonlinear spring, and a torsional spring-damper within a standard prosthetic configuration.... 

Robot-mediated rehabilitation is a rapidly advancing discipline that seeks to develop improved treatment procedures using new technologies, e.g., robotics, coupled with modern theories in neuroscience and rehabilitation. A robotic device was designed and developed for rehabilitation of upper limbs of post stroke patients. A novel force feedback bimanual working mode provided real-time dynamic sensation of the paretic hand. Results of the preliminary clinical tests revealed a quantitative evaluation of the patient's level of paresis and disability  

Background and aim: Most currently-available stance control knee ankle foot orthoses (SCKAFOs) still need full knee extension to lock the knee joint, and they are still noisy, bulky, and heavy. Therefore, the aim of this study was to design, construct, and evaluate an original electromechanical SCKAFO knee joint that could feasibly solve these problems, and thus address the problems of current stance control knee joints with regards to their structure, function, cosmesis, and cost. Method: Ten able-bodied (AB) participants and two (knee ankle foot orthosis) KAFO users were recruited to participate in the study. A custom SCKAFO with the same set of components was constructed for each... 

Evaluation of spinal loads in patients with low back pain (LBP) is essential to prevent further lumbar disorders. Many studies have investigated the relationship between lifting task variables and lumbar spine loads during manual lifting activities. The nature of the external load (stable versus unstable loads) is an important variable that has received less attention. Therefore, the present study aimed to measure trunk kinematics and estimate compressive-shear loads on the lumbar spine under lifting a 120 N stable load and 120 ± 13.63 N sensual unstable load in 16 healthy and 16 non-specific LBP individuals during lifting activities. The maximal lumbar loads were estimated using a... 

Inter-segmental coordination can be influenced by chronic low back pain (CLBP). The sagittal plane lower extremities inter-segmental coordination pattern and variability, in conjunction with the pelvis and trunk, were assessed in subjects with and without non-specific CLBP during free-speed walking. Kinematic data were collected from 10 non-specific CLBP and 10 non-CLBP control volunteers while the subjects were walking at their preferred speed. Sagittal plane time-normalized segmental angles and velocities were used to calculate continuous relative phase for each data point. Mean absolute relative phase (MARP) and deviation phase (DP) were derived to quantify the trunk-pelvis and bilateral... 

Background: Studying the kinematics of the ACL deficient (ACLD) knees, during different physiological activities and muscle contraction patterns, can improve our understanding of the joint's altered biomechanics due to ACL deficiency as well as the efficacy and safety of the rehabilitations exercises. Methods: Twenty-five male volunteers, including 11 normal and 14 unilateral ACLD subjects, participated in this study. The kinematics of the injured knees of the ACLD subjects was compared with their intact knees and the healthy group during passive flexion and isometric leg press with the knees flexed from full extension to 45° flexion, with 15° intervals. An accurate registration algorithm... 

Different lifting analysis tools are commonly used to assess spinal loads and risk of injury. Distinct musculoskeletal models with various degrees of accuracy are employed in these tools affecting thus their relative accuracy in practical applications. The present study aims to compare predictions of six tools (HCBCF, LSBM, 3DSSPP, AnyBody, simple polynomial, and regression models) for the L4-L5 and L5-S1 compression and shear loads in twenty-six static activities with and without hand load. Significantly different spinal loads but relatively similar patterns for the compression (R2>0.87) were computed. Regression models and AnyBody predicted intradiscal pressures in closer agreement with... 

Background: Superior biomechanical performance of tapered interference screws, compared with non-tapered screws, with reference to the anterior cruciate ligament (ACL) reconstruction process, has been reported in the literature. However, the effect of tapered interference screw’s body slope on the initial stability of ACL is poorly understood. Thus, the main goal of this study was to investigate the effect of the interference screw’s body slope on the initial stability of the reconstructed ACL. Methods: Based on the best screw-bone tunnel diameter ratios in non-tapered screws, two different tapered interference screws were designed and fabricated. The diameters of both screws were equal to... 

Airbags are safety devices in vehicles effectively suppressing passengers’ injuries during accidents. Although there are still many cases of eye injuries reported due to eye-airbag impacts in recent years. Biomechanical approaches are now feasible and can considerably help experts to investigate the issue without ethical concerns. The eye-airbag impact–induced stresses/strains in various components of the eye were found to investigate the risk of injury in different conditions (impact velocity and airbag pressure). Three-dimensional geometry of the eyeball, fat and bony socket as well as the airbag were developed and meshed to develop a finite element model. Nonlinear material properties of... 

Adjacent segment disorders are prevalent in patients following a spinal fusion surgery. Postoperative alterations in the adjacent segment biomechanics play a role in the etiology of these conditions. While experimental approaches fail to directly quantify spinal loads, previous modeling studies have numerous shortcomings when simulating the complex structures of the spine and the pre/postoperative mechanobiology of the patient. The biomechanical effects of the L4–L5 fusion surgery on muscle forces and adjacent segment kinetics (compression, shear, and moment) were investigated using a validated musculoskeletal model. The model was driven by in vivo kinematics for both preoperative (intact or... 

This study presents a novel statistical volume element (SVE) for micromechanical modeling of the white matter structures, with histology-informed randomized distribution of axonal tracts within the extracellular matrix. The model was constructed based on the probability distribution functions obtained from the results of diffusion tensor imaging as well as the histological observations of scanning electron micrograph, at two structures of white matter susceptible to traumatic brain injury, i.e. corpus callosum and corona radiata. A simplistic representative volume element (RVE) with symmetrical arrangement of fully alligned axonal fibers was also created as a reference for comparison. A... 

In this research, the nonlinear elastic behavior of human extensor apparatus was investigated. To this goal, firstly the best material parameters of hyperelastic strain energy density functions consisting of the Mooney–Rivlin, Ogden, invariants, and general exponential models were derived for the simple tension experimental data. Due to the significance of stress response in other deformation modes of nonlinear models, the calculated parameters were used to study the pure shear and balance biaxial tension behavior of the extensor apparatus. The results indicated that the Mooney–Rivlin model predicts an unstable behavior in the balance biaxial deformation of the extensor apparatus, while the... 

The Calcium ion Ca2+ plays a critical role as an initiator and preserving agent of the cross-bridge cycle in the force generation of skeletal muscle. A new multi-scale chemo-mechanical model is presented in order to analyze the role of Ca2+ in muscle fatigue and to predict fatigue behavior. To this end, a cross-bridge kinematic model was incorporated in a continuum based mechanical model, considering a thermodynamic compatible framework. The contractile velocity and the generated active force were directly related to the force-bearing states that were considered for the cross-bridge cycle. In order to determine the values of the model parameters, the output results of an isometric simulation... 

Degenerative disc disease, associated with discrete structural changes in the peripheral annulus and vertebral endplate, is one of the most common pathological triggers of acute and chronic low back pain, significantly depreciating an individual's quality of life and instigating huge socioeconomic costs. Novel emerging therapeutic techniques are hence of great interest to both research and clinical communities alike. Exogenous crosslinking, such as Genipin, and platelet-rich plasma therapies have been recently demonstrated encouraging results for the repair and regeneration of degenerated discs, but there remains a knowledge gap regarding the quantitative degree of effectiveness and... 

Anxiety is among the most debilitating nonmotor symptoms of Parkinson's disease (PD). This study aimed to determine how PD patients with low and high levels of anxiety (LA-PD and HA-PD, respectively) compare with age- and sex-matched controls at the level of motor control of reach-to-grasp movements during single- and dual-task conditions with varying complexity. Reach-to-grasp movement kinematics were assessed in 20 LA-PD, 20 HA-PD, and 20 sex- and age-matched healthy controls under single- as well as easy and difficult dual-task conditions. Assessment of PD patients was performed during both the on- and off-drug phases. The results obtained during dual-task conditions reveal deficits in... 

Spine musculoskeletal (MS) models make simplifying assumptions on the intervertebral joint degrees-of-freedom (rotational and/or translational), representation (spherical or beam-like joints), and properties (linear or nonlinear). They also generally neglect the realistic structure of the joints with disc nuclei/annuli, facets, and ligaments. We aim to develop a novel MS model where trunk muscles are incorporated into a detailed finite element (FE) model of the ligamentous T12-S1 spine thus constructing a gold standard coupled MS-FE model. Model predictions are compared under some tasks with those of our earlier spherical joints, beam joints, and hybrid (uncoupled) MS-FE models. The coupled... 

In this study, a nonlinear poroelastic model of intervertebral disc as an infrastructure was developed. Moreover, a new element was defined consisting a disc (Viscoelastic Euler Beam Element) and a vertebra (Rigid Link) as a unit element. Using the new element, three different viscoelastic finite element models were prepared for lumbar motion segment (L4/L5). Prolonged loading (short-term and long-term creep) and cyclic loading were applied to the models and the results were compared with results of in vivo tests. Simplification of the models by using the new element leads to reduction of the runtime of the models in dynamic analyses to few minutes without losing the accuracy in the results  

This paper aims to identify an optimum bone fracture stabilizer. For this purpose, three design variables including the ratio of the screw diameter to the plate width at three levels, the ratio of the plate thickness to the plate width at three levels, and the diameter of the bone at two levels were selected for analysis. Eighteen 3D verified finite element models were developed to examine the effects of these parameters on the weight, maximum displacement and maximum von Mises stress of the fixation structure. Considering the relations between the inputs and outputs using multivariate regression, a genetic algorithm was used to find the optimal choices. Results showed that the diameter of... 

Purpose: This study exploits a novel musculoskeletal finite element (MS-FE) spine model to evaluate the post-fusion (L4–L5) alterations in adjacent segment kinetics. Methods: Unlike the existing MS models with idealized representation of spinal joints, this model predicts stress/strain distributions in all passive tissues while organically coupled to a MS model. This generic (in terms of musculature and material properties) model uses population-based in vivo vertebral sagittal rotations, gravity loads, and an optimization algorithm to calculate muscle forces. Simulations represent individuals with an intact L4–L5, a preoperative severely degenerated L4–L5 (by reducing the disc height by ~...