Sharif Digital Repository

A novel optimisation algorithm is developed to predict coactivity of abdominal muscles while accounting for both trunk stability via the lowest buckling load (Pcr) and tissue loading via the axial compression (Fc). A nonlinear multi-joint kinematics-driven model of the spine along with the response surface methodology are used to establish empirical expressions for Pcr and Fc as functions of abdominal muscle coactivities and external load magnitude during lifting in upright standing posture. A two-component objective function involving Fc and Pcr is defined. Due to opposite demands, abdominal coactivities that simultaneously maximise Pcr and minimise Fc cannot exist. Optimal solutions are... 

Objective: This study aimed to present and evaluate a new deep learning model for determining cervical vertebral maturation (CVM) degree and growth spurts by analyzing lateral cephalometric radiographs. Methods: The study sample included 890 cephalograms. The images were classified into six cervical stages independently by two orthodontists. The images were also categorized into three degrees on the basis of the growth spurt: pre-pubertal, growth spurt, and post-pubertal. Subsequently, the samples were fed to a transfer learning model implemented using the Python programming language and PyTorch library. In the last step, the test set of cephalograms was randomly coded and provided to two... 

The present study examined the effects of auxetic shoes on the biomechanics of the spine, as compared to barefoot and conventional shoe conditions, during gait and drop vertical jump (DVJ) activities using a combined in vivo and musculoskeletal modeling approach. Motion and force-plate data as well as electromyographic (EMG) activities of select trunk muscles of 11 individuals were collected during foregoing activities. In DVJ activity, two main phases of first landing (FL) and second landing (SL) were studied. In the FL phase of DVJ noticeable alternations were observed when auxetic shoes were used. That is, compared to the conventional footwear condition, smaller EMG activities in extensor... 

Using an iterative kinematics-driven nonlinear finite element model, relative efficiency of individual abdominal muscles in spinal stability in upright standing posture was investigated. Effect of load height on stability and muscle activities was also computed under different coactivity levels in abdominal muscles. The internal oblique was the most efficient muscle (compared with the external oblique and rectus abdominus) in providing stability while generating smaller spinal loads with lower fatigue rate of muscles. As the weight was held higher, stability deteriorated requiring additional flexor-extensor activities. The stabilising efficacy of abdominal muscles diminished at higher... 

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... 

Scoliosis, kyphosis, and bone fracture are health problems, especially of the elderly throughout the world. The vertebra protects the spinal cord. Any impairment to the vertebra can lead to pain and nervousness. NiTi alloy (Nitinol) helps to resolve the problem by fulfilling such requirements as for strength, durability, resistance to wear, and shockwave damping which is due to the shape memory effect. Nitinol medical applications have so far been restricted to surgical devices and orthopaedics. Little has been said about Nitinol use for medication of the spinal vertebra disorder. This article appraises the potential features of Nitinol for vertebral implantation and therapeutic prescription... 

Epidemiological studies are divided over the causative role of body weight (BW) in low back pain. Biomechanical modeling is a valuable approach to examine the effect of changes in BW on spinal loads and risk of back pain. Changes in BW have not been properly simulated by previous models as associated alterations in model inputs on the musculature and moment arm of gravity loads have been neglected. A detailed, multi-joint, scalable model of the thoracolumbar spine is used to study the effect of BW (varying at five levels, i.e., 51, 68, 85, 102, and 119kg) on the L5-S1 spinal loads during various static symmetric activities while scaling moment arms and physiological cross-sectional areas of... 

Workplace safety assessment, personalized treatment design and back pain prevention programs require accurate subject-specific estimation of spinal loads. Since no noninvasive method can directly estimate spinal loads, easy-to-use regression equations that are constructed based on the results of complex musculoskeletal models appear as viable alternatives. Thus, we aim to develop subject-specific regression equations of L4-L5 and L5-S1 shear and compression forces during various symmetric/asymmetric tasks using a nonlinear personalized finite element musculoskeletal trunk model. Kinematics and electromyography (EMG) activities of 19 young healthy subjects were collected during 64 different... 

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  

Nowadays, cervical disorders are common due to human lifestyles. Accordingly, the cage design should be optimized as an essential issue. For an optimal design, an objective function is utilized to calculate the proper geometrical parameters. Additionally, the base material of the cage plays a key role in its functionality and final cost. Novel materials are currently introduced with more compatibility with the bone in terms of mechanical and chemical properties. In this study, a cervical cage was modeled based on PEEK material with three types of tooth designs on its surface. The cervical cage is assumed to be implanted between C6 and C7 vertebrae. The geometric parameters of the cage were... 

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 ~... 

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... 

Motor abundance allows reliability of motor performance despite its variability. The nature of this variability provides important information on the flexibility of control strategies. This feature of control may be affected by low back pain (LPB) and trunk flexion/extension conditions. Goal equivalent manifold (GEM) analysis was used to quantify the ability to exploit motor abundance during repeated trunk flexion/extension in healthy individuals and people with chronic non-specific LBP (CNSLBP). Kinematic data were collected from 22 healthy volunteers and 22 CNSLBP patients during metronomically timed, repeated trunk flexion/extension in three conditions of symmetry, velocity, and loading;... 

Traditional load-control musculoskeletal and finite element (FE) models of the spine fail to accurately predict in vivo intervertebral joint loads due mainly to the simplifications and assumptions when estimating redundant trunk muscle forces. An alternative powerful protocol that bypasses the calculation of muscle forces is to drive the detailed FE models by image-based in vivo displacements. Development of subject-specific models, however, both involves the risk of extensive radiation exposures while imaging in supine and upright postures and is time consuming in terms of the reconstruction of the vertebrae, discs, ligaments, and facets geometries. This study therefore aimed to introduce a... 

Measurements of spinal segment ranges of motion (RoMs), movement coordination, and three-dimensional kinematics during occupational activities have implications in occupational/clinical biomechanics. Due to the large amount of adipose tissues, obese individuals may have different RoMs, lumbopelvic coordination, and kinematics than normal-weight ones. We aimed to measure/compare trunk, lumbar, and pelvis primary RoMs in all anatomical planes/directions, lumbopelvic ratios (lumbar to pelvis rotations at different trunk angles) in all anatomical planes/directions and three-dimensional spine kinematics during twelve symmetric/asymmetric statics load-handling activities in healthy normal-weight... 

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... 

Spinal fusion surgery is usually followed by accelerated degenerative changes in the unfused segments above and below the treated segment(s), i.e., adjacent segment disease (ASD). While a number of risk factors for ASD have been suggested, its exact pathogenesis remains to be identified. Finite element (FE) models are indispensable tools to investigate mechanical effects of fusion surgeries on post-fusion changes in the adjacent segment kinematics and kinetics. Existing modeling studies validate only their intact FE model against in vitro data and subsequently simulate post-fusion in vivo conditions. The present study provides a novel approach for the comprehensive validation of a lumbar... 

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 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 under muscle exertions. We aim to develop novel passive FE models that are driven by more realistic yet simple loading scenarios, i.e., in vivo vertebral rotations and pathological-condition dependent FLs (estimated based on detailed musculoskeletal finite element (MS-FE) models). In these novel force–displacement control FE models,... 

Body posture measurement approaches, required in biomechanical models to assess risk of musculoskeletal injuries, are usually costly and/or impractical for use in real workplaces. Therefore, we recently developed three artificial neural networks (ANNs), based on measured posture data on several individuals, to predict whole body 3D posture (coordinates of 15 markers located on body's main joints), segmental orientations (Euler angles of 14 body segments), and lumbosacral (L5-S1) moments during static manual material handling (MMH) activities (ANNPosture, ANNAngle, and ANNMoment, respectively). These ANNs require worker's body height, body weight (only for ANNMoment), hand-load 3D position,...