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Biomechanics

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Articles 1 - 30 of 140

Full-Text Articles in Biomedical Engineering and Bioengineering

The Effect Of Implant Conformity On Muscle Force Requirements In The Implanted Knee, Grace Mcconnochie Aug 2019

The Effect Of Implant Conformity On Muscle Force Requirements In The Implanted Knee, Grace Mcconnochie

Boise State University Theses and Dissertations

Implant geometry is a significant factor in determining knee stability and patient satisfaction following total knee replacement (TKR). Ineffective muscle recruitment, impaired joint functionality and increased implant wear are consequences of an unstable knee replacement. Current knee laxity evaluation techniques are limited in their ability to account for the muscular response to knee instability. This study utilizes a subject specific lower-body musculoskeletal finite element (FE) model with dynamic muscle loading to evaluate implant laxity during activities of daily living. The effect of varying implant conformity on the muscle forces required to maintain a target kinematic profile during simulated laxity testing ...


Kinematics During Knee Extension, Lunge, And Chair Rise, Center For Orthopaedic Biomechanics, Kevin Shelburne, Phd, Michael D. Harris, Phd, Vasiliki Kefala, Donald R. Hume, Bradley S. Davidson, A. J. Cyr, R. H. Kim, A. A. Ali, E. M. Mannen Apr 2019

Kinematics During Knee Extension, Lunge, And Chair Rise, Center For Orthopaedic Biomechanics, Kevin Shelburne, Phd, Michael D. Harris, Phd, Vasiliki Kefala, Donald R. Hume, Bradley S. Davidson, A. J. Cyr, R. H. Kim, A. A. Ali, E. M. Mannen

Living Kinematics of the Knee

No abstract provided.


Impact In Practice, Maria Garman Jan 2019

Impact In Practice, Maria Garman

ENGS 88 Honors Thesis (AB Students)

Medial Tibial Stress Syndrome (Shin splits) is an overuse injury caused by repetitive impact. If ignored it can lead to stress reactions and then stress fractures in the shins. This nagging injury is something that plagues many track athletes especially as they start to wear their competition shoes more frequently at practice to work on technical aspects of their events.

This paper investigates the relationship between ground reaction forces experienced by the athletes in each stride and what shoes they are wearing on their feet. Due to the fact that repetitive impact is a cause for shin splints, the conclusion ...


Development And Exploration Of A Z-Shaped Foot And Ankle Internal Fixation Plate, Rhaz Shaghaghi Paul, Ian Hames, Sean Rich Jan 2019

Development And Exploration Of A Z-Shaped Foot And Ankle Internal Fixation Plate, Rhaz Shaghaghi Paul, Ian Hames, Sean Rich

Williams Honors College, Honors Research Projects

This paper will detail the design process of developing a Z-shaped foot and ankle internal fixation plating system. Group 6: Plates for the Sole was made up of 5 team members, who worked together to accommodate their client’s request to complete a biomechanical analysis of a Z-Plate design and a construct a prototype. The Z-Plate’s purpose is to provide podiatrists with a new solution that can fit nicely on the small, irregular bones of the foot, while also remaining strong enough to withstand the forces and torques of the foot.


Thenar Muscle And Transverse Carpal Ligament Relationship, Jeremy Granieri Loss Jan 2019

Thenar Muscle And Transverse Carpal Ligament Relationship, Jeremy Granieri Loss

ETD Archive

The transverse carpal ligament (TCL) acts as a partial origin for the thenar muscles (abductor pollicis brevis (APB), flexor pollicis brevis (FPB), opponens pollicis (OPP)). The attachment between the thenar muscles and TCL implies a relationship between the tissues. The thenar muscles rely on their origins for thumb motion and force production. However, individual thenar origin information is lacking. Further information regarding the anatomical relationship between the individual thenar muscles and TCL may provide insight into thenar muscle function. In addition, the TCL responds to thenar muscle contraction as shown by volar migration of the TCL during various thumb movements ...


Hip And Knee Biomechanics For Transtibial Amputees In Gait, Cycling, And Elliptical Training, Greg Orekhov Dec 2018

Hip And Knee Biomechanics For Transtibial Amputees In Gait, Cycling, And Elliptical Training, Greg Orekhov

Master's Theses and Project Reports

Transtibial amputees are at increased risk of contralateral hip and knee joint osteoarthritis, likely due to abnormal biomechanics. Biomechanical challenges exist for transtibial amputees in gait and cycling; particularly, asymmetry in ground/pedal reaction forces and joint kinetics is well documented and state-of-the-art passive and powered prostheses do not fully restore natural biomechanics. Elliptical training has not been studied as a potential exercise for rehabilitation, nor have any studies been published that compare joint kinematics and kinetics and ground/pedal reaction forces for the same group of transtibial amputees in gait, cycling, and elliptical training. The hypothesis was that hip ...


Hypothesis Paper: Mechanism For Primary Blast Induced Traumatic Brain Injury With Minimal Head Motion, Charles F. Babbs Oct 2018

Hypothesis Paper: Mechanism For Primary Blast Induced Traumatic Brain Injury With Minimal Head Motion, Charles F. Babbs

Weldon School of Biomedical Engineering Faculty Working Papers

Transit of the human skull by blast waves produces diffuse brain injury. The exact mechanisms are unknown. This paper describes plausible mechanisms in which steep intracranial pressure gradients, demonstrated in prior computational models of blast-skull interaction, produce subsequent deformation and motion of the whole brain within the skull, without obvious movement of the head. Equations of motion are derived to describe the acceleration, velocity, and relative position of both the skull and the brain in response to known extracranial and intracranial pressures both during and several hundred milliseconds after blast wave passage. A finite element model is solved to visualize ...


Characterization And Quantification Of Fibrin Gel Mechanics With Fibroblast Invasion, Nicklaus Iavagnilio, Sarah Calve, Adrian Buganza-Tepole Aug 2018

Characterization And Quantification Of Fibrin Gel Mechanics With Fibroblast Invasion, Nicklaus Iavagnilio, Sarah Calve, Adrian Buganza-Tepole

The Summer Undergraduate Research Fellowship (SURF) Symposium

Cutaneous wounds undergo an intricate healing process stimulated by a variety of local mechanical and biological stimuli that lead to patterns of growth and remodeling. Despite significant research in dermal wound healing, pathological scarring is still common particularly in wounds closed under mechanical stress, or large wounds left to heal by secondary intention. The purpose of this study is to utilize previously established wound healing models using fibrin gels and fibroblasts to better understand the functional relationships of the biological processes of normal compared to abnormal wound healing. Increases in uni-axial strain and transforming growth factor beta-1 concentration have been ...


Inverse Dynamic Analysis Of Acl Reconstructed Knee Joint Biomechanics During Gait And Cycling Using Opensim, Megan V. Pottinger Aug 2018

Inverse Dynamic Analysis Of Acl Reconstructed Knee Joint Biomechanics During Gait And Cycling Using Opensim, Megan V. Pottinger

Master's Theses and Project Reports

ACL (anterior cruciate ligament) injuries of the knee joint alter biomechanics and may cause abnormal loading conditions that place patients at a higher risk of developing osteoarthritis (OA). There are multiple types of ACL reconstruction (ACLR), but all types aim to restore anterior tibial translation and internal tibial rotation following surgery. Analyzing knee joint contact loads provide insight into the loading conditions following ACLR that may contribute to the long-term development of OA. Ten ACLR subjects, who underwent the same reconstruction, performed gait and cycling experiments while kinematic and kinetic data were collected. Inverse dynamic analyses were performed on processed ...


The Development Of A Temporomandibular Force Simulator To Study Craniofacial Strain In-Vitro, Kenneth Kc Ip Jun 2018

The Development Of A Temporomandibular Force Simulator To Study Craniofacial Strain In-Vitro, Kenneth Kc Ip

Electronic Thesis and Dissertation Repository

An in-vitro musculoskeletal loading simulator was developed to replicate the internal forces of mastication, and then employed in a comparison of clinically relevant facial fracture repairs. Muscle forces are simulated by pneumatic pistons via 3D printed mounts that are reverse-engineered from CT scan to match muscle attachment sites, which are adhered to bone in order to simulate native stress distributions. Bite force and bone strain pattern of the craniofacial structure under load were measured using a force sensor and strain gauges respectively. In a series of five fresh-frozen cadaveric heads, it was found that strain patterns of the craniofacial structure ...


Validation Of Computational Methods For Fracture Assessment Of Metastatic Disease To The Proximal Femur, Palani Taver Permeswaran May 2018

Validation Of Computational Methods For Fracture Assessment Of Metastatic Disease To The Proximal Femur, Palani Taver Permeswaran

Theses and Dissertations

Stage IV cancer is characterized by a cancer’s ability to metastasize, or spread throughout the body. Metastatic disease in bone is a devastating condition affecting hundreds of thousands of people each year. Stage IV cancer patients suffering from metastatic disease in the proximal femur are at high risk of catastrophic pathologic fracture, an event which severely impacts patient health. Although metrics have been created to assess the risk of impending fracture, they lack specificity in the proximal femoral region. Shortcomings of these metrics further complicate clinical decision making related to prophylactic fixation in these medically compromised individuals.

Fortunately, by ...


Walking Speed Differentially Alters Spinal Loads In Persons With Traumatic Lower Limb Amputation, Brad D. Hendershot, Iman Shojaei, Julian C. Acasio, Christopher L. Dearth, Babak Bazrgari Mar 2018

Walking Speed Differentially Alters Spinal Loads In Persons With Traumatic Lower Limb Amputation, Brad D. Hendershot, Iman Shojaei, Julian C. Acasio, Christopher L. Dearth, Babak Bazrgari

Biomedical Engineering Faculty Publications

Persons with lower limb amputation (LLA) perceive altered motions of the trunk/pelvis during activities of daily living as contributing factors for low back pain. When walking (at a singular speed), larger trunk motions among persons with vs. without LLA are associated with larger spinal loads; however, modulating walking speed is necessary in daily life and thus understanding the influences of walking speed on spinal loads in persons with LLA is of particular interest here. Three-dimensional trunk-pelvic kinematics, collected during level-ground walking at self-selected (SSW) and two controlled speeds (~1.0 and ~1.4 m/s), were obtained for seventy-eight ...


Examining Reverse Total Shoulder Arthroplasty Baseplate Fixation In Patients With E2-Type Glenoid Erosion, Matthew D. Mahaffy Feb 2018

Examining Reverse Total Shoulder Arthroplasty Baseplate Fixation In Patients With E2-Type Glenoid Erosion, Matthew D. Mahaffy

Electronic Thesis and Dissertation Repository

Superior glenoid erosion of the shoulder joint is a result of humeral subluxation caused by rotator cuff tears, and can be addressed using implants, specifically reverse total shoulder arthroplasty. This thesis examined the regional variations of bone present in superiorly eroded glenoids, established a baseline for regular RTSA baseplate fixation in patients with this defect, and compared the effect of geometric baseplate differences on implant fixation. The superiorly eroded glenoids demonstrated similar regional bone density variations as normal glenoids, and the superior and inferior regions of the glenoid demonstrated the densest and least dense cancellous bone, respectively. These regions also ...


Design And Analysis Of A 3d-Printed, Thermoplastic Elastomer (Tpe) Spring Element For Use In Corrective Hand Orthotics, Kevin Thomas Richardson Jan 2018

Design And Analysis Of A 3d-Printed, Thermoplastic Elastomer (Tpe) Spring Element For Use In Corrective Hand Orthotics, Kevin Thomas Richardson

Theses and Dissertations--Mechanical Engineering

This thesis proposes an algorithm that determine the geometry of 3D-printed, custom-designed spring element bands made of thermoplastic elastomer (TPE) for use in a wearable orthotic device to aid in the physical therapy of a human hand exhibiting spasticity after stroke. Each finger of the hand is modeled as a mechanical system consisting of a triple-rod pendulum with nonlinear stiffness at each joint and forces applied at the attachment point of each flexor muscle. The system is assumed quasi-static, which leads to a torque balance between the flexor tendons in the hand, joint stiffness and the design force applied to ...


Predictive Modeling Of Hip Dislocation: Assessment Of Surgical And Patient Factors To Reduce The Occurrence Of Hip Instability And Adverse Clinical Outcomes, Daniel N. Huff Jan 2018

Predictive Modeling Of Hip Dislocation: Assessment Of Surgical And Patient Factors To Reduce The Occurrence Of Hip Instability And Adverse Clinical Outcomes, Daniel N. Huff

Electronic Theses and Dissertations

Instability and dislocation remain leading indications for revision of primary Total Hip Arthroplasty (THA). Many studies have addressed the links between implant design and propensity for dislocation, however a comprehensive review of the ability of modern THA constructs to protect against joint instability is needed.

Accordingly, the objective of this study is to provide objective data about THA risks to be considered in the treatment algorithm to protect against adverse joint loading conditions and joint instability. Adverse loading conditions were assessed in a population of activities of daily living using data from telemetric hip implant representation in an FE simulation ...


Predictive Simulations Of Gait And Their Application In Prosthesis Design, Anne D. Koelewijin Jan 2018

Predictive Simulations Of Gait And Their Application In Prosthesis Design, Anne D. Koelewijin

ETD Archive

Predictive simulations predict human gait by solving a trajectory optimization problem by minimizing energy expenditure. These simulations could predict the effect of a prosthesis on gait before its use. This dissertation has four aims, to show the application of predictive simulations in prosthesis design and to improve the quality of predictive simulations. Aim 1 was to explain joint moment asymmetry in the knee and hip in gait of persons with a transtibial amputation (TTA gait). Predictive simulations showed that an asymmetric gait required less effort. However, a small effort increase yielded a gait with increased joint moment symmetry and reduced ...


Brain Motion, Deformation, And Potential Injury During Soccer Heading, Charles F. Babbs Dec 2017

Brain Motion, Deformation, And Potential Injury During Soccer Heading, Charles F. Babbs

Weldon School of Biomedical Engineering Faculty Working Papers

This paper addresses the problem of what is happening physically inside the skull during head-ball contact. Mathematical models based upon Newton’s laws of motion and numerical methods are used to create animations of brain motion and deformation inside the skull.

Initially a 1 cm gap filled with cerebrospinal fluid (CSF) separates the brain from the rigid skull in adults and older children. Whole head acceleration induces a pulse of artificial gravity within the skull. Because brain density differs slightly from that of CSF, the brain accelerates and strikes the inner aspect of the skull, undergoing viscoelastic deformation, ranging from ...


Characterizing Anisotropy In Fibrous Soft Materials By Mr Elastography Of Slow And Fast Shear Waves, John Larson Schmidt Dec 2017

Characterizing Anisotropy In Fibrous Soft Materials By Mr Elastography Of Slow And Fast Shear Waves, John Larson Schmidt

Engineering and Applied Science Theses & Dissertations

The general objective of this work was to develop experimental methods based on magnetic resonance elastography (MRE) to characterize fibrous soft materials. Mathematical models of tissue biomechanics capable of predicting injury, such as traumatic brain injury (TBI), are of great interest and potential. However, the accuracy of predictions from such models depends on accuracy of the underlying material parameters. This dissertation describes work toward three aims. First, experimental methods were designed to characterize fibrous materials based on a transversely isotropic material model. Second, these methods are applied to characterize the anisotropic properties of white matter brain tissue ex vivo. Third ...


Rehabilitating Asymmetric Gait Using Asymmetry, Tyagi Ramakrishnan Nov 2017

Rehabilitating Asymmetric Gait Using Asymmetry, Tyagi Ramakrishnan

Graduate Theses and Dissertations

Human gait is a complex process that involves the coordination of the central nervous and muscular systems. A disruption to the either system results in the impairment of a person’s ability to walk. Impairments can be caused by neurological disorders such as stroke and physical conditions like amputation. There is not a standardized method to quantitatively assess the gait asymmetry of affected subjects. The purpose of this research is to understand the fundamental aspects of asymmetrical effects on the human body and improve rehabilitation techniques and devices. This research takes an interdisciplinary approach to address the limitations with current ...


Sagittal Subtalar And Talocrural Joint Assessment During Ambulation With Controlled Ankle Movement (Cam) Boots, Ben Mchenry, Emily L. Exten, Janelle A. Cross, Karen M. Kruger, Brian Law, Jessica M. Fritz, Gerald F. Harris Nov 2017

Sagittal Subtalar And Talocrural Joint Assessment During Ambulation With Controlled Ankle Movement (Cam) Boots, Ben Mchenry, Emily L. Exten, Janelle A. Cross, Karen M. Kruger, Brian Law, Jessica M. Fritz, Gerald F. Harris

Biomedical Engineering Faculty Research and Publications

Background: The purpose of the current study was to determine sagittal plane talocrural and subtalar kinematic differences between barefoot and controlled ankle movement (CAM) boot walking. This study used fluoroscopic images to determine talar motion relative to tibia and calcaneal motion relative to talus.

Methods: Fourteen male subjects (mean age 24.1 ± 3.5 years) screened for normal gait were tested. A fluoroscopy unit was used to collect images at 200 Hz during stance. Sagittal motion of the talocrural and subtalar joints were analyzed barefoot and within short and tall CAM boots.

Results: Barefoot talocrural mean maximum plantar and dorsiflexion ...


The Effect Of Radial And Ulnar Length Change On Distal Forearm Loading, Ahaoiza D. Isa Aug 2017

The Effect Of Radial And Ulnar Length Change On Distal Forearm Loading, Ahaoiza D. Isa

Electronic Thesis and Dissertation Repository

The effect of distal radial and ulnar length change on forearm bone loading is not well understood during simulated dynamic wrist loading. This thesis presents two studies which investigate the effect of these length changes on distal forearm loading under simulated dynamic wrist motion. The first study investigates the effect of radial length change on axial loading at the distal radius and ulna and relationship between ulnar variance and distal forearm loading. The complex variation in axial loads in the distal radius and during length change and dynamic wrist motion were studied and discussed. There was no correlation between native ...


Biomechanical Testing Of An Exercise For Strengthening The Proximal Femur., Alyssa Osbourne Aug 2017

Biomechanical Testing Of An Exercise For Strengthening The Proximal Femur., Alyssa Osbourne

Electronic Theses and Dissertations

Based on the principles of cutting edge bone remodeling research, a unique therapeutic exercise device was designed specifically to improve bone quality at the most critical location of the proximal femur prone to fracture: the superior-lateral femoral neck where the fracture first initiates during a fall. The exercise/device is intended to work by inducing enough strain in the bone to stimulate the body’s natural bone remodeling mechanisms to increase bone density in the proximal femur and consequently prevent a fracture from arising if a fall to the side does occur.

In order to test the proposed exercise, experiments ...


Biomechanics Of Snoring And Sleep Apnea, Charles F. Babbs Jul 2017

Biomechanics Of Snoring And Sleep Apnea, Charles F. Babbs

Weldon School of Biomedical Engineering Faculty Working Papers

To understand the mechanisms of snoring and sleep apnea a first-principles biomechanical analysis was done for airflow through branched parallel channels, separated by a freely movable soft palate, and converging to a common channel at the base of the tongue in a “Y-shaped” configuration. Branches of the Y describe slit-like passages on the nasal and oral sides of the soft palate, when the palate is pushed by backward movement of the tongue to form a wedge between the tongue surface and the posterior pharyngeal wall. The common channel of the Y describes the oropharyngeal passage between the base of the ...


The Development Of A Platform Interface With The Use Of Virtual Reality To Enhance Upper-Extremity Prosthetic Training And Rehabilitation, Ashley D. Knight Jun 2017

The Development Of A Platform Interface With The Use Of Virtual Reality To Enhance Upper-Extremity Prosthetic Training And Rehabilitation, Ashley D. Knight

Graduate Theses and Dissertations

This dissertation focuses on the investigation and development of an effective prosthetic training and rehabilitation platform with the use of virtual reality to facilitate an effective process to return amputees to the highest level of independence and functioning possible.

It has been reported that approximately 10 million people live with a limb loss worldwide, with around 30% being an upper-extremity amputee. The sudden loss of a hand or arm causes the loss of fine, coordinated movements, reduced joint range of motion (ROM), proprioceptive feedback and aesthetic appearance, all which can be improved with the use of a prosthesis and proper ...


The Biomechanics Of Music Performance, Rachel F. Bellisle, Jessika Decker May 2017

The Biomechanics Of Music Performance, Rachel F. Bellisle, Jessika Decker

Senior Honors Projects

When first learning to play a wind instrument, beginner musicians are taught how to hold their instrument and correctly position their body. They are taught how to sit, where to put their hands and fingers on the keys, and how to hold their arms. This initial lesson on posture and hand positioning is often short, as one quickly moves on to learn the embouchure and breathing techniques that allow sound to be produced. As a musician progresses in skill, positioning is emphasized more, and they learn that it can affect their risk of strain or injury and improve their sound ...


Anthropometric Shape Parameters In Obese Subjects: Implications For Obese Total Joint Arthroplasty Patients, Kevin James Simoens May 2017

Anthropometric Shape Parameters In Obese Subjects: Implications For Obese Total Joint Arthroplasty Patients, Kevin James Simoens

Theses and Dissertations

Obesity is a severe concern worldwide and its prevalence is expected to continue to increase. Linked to diabetes, kidney disease, heart disease, and high blood pressure among other things, obesity has been identified as the forthcoming, largest preventable cause of mortality. Osteoarthritis, surgical consequences, distribution of subcutaneous adipose tissue, and alteration of joint biomechanics have vast implications in total joint repair (TJR). Previous studies have linked obesity to increased forces through weight-bearing lower extremities, alterations in gait, and risk of implant failure. The objectives of this study were to (1) provide a tool to predict lower extremity dimensions and shape ...


Multimodal Evaluation Of Local And Whole-Joint Cartilage Changes In An In Vivo Animal Model, David James Heckelsmiller May 2017

Multimodal Evaluation Of Local And Whole-Joint Cartilage Changes In An In Vivo Animal Model, David James Heckelsmiller

Theses and Dissertations

Osteoarthritis is a chronic, deleterious disease of the joints. It currently affects nearly 25 million Americans. Clinically, osteoarthritis presents as joint pain and verified by radiographic evidence of joint space narrowing. Unfortunately, symptomatic osteoarthritis describes the later stages of disease, at which point irreversible cartilage and bone damage has occurred. Cross-sectional imaging modalities offer the promise of visualizing early features of disease, enabling the development and evaluation of interventions to forestall or prevent degenerative change. Modalities of clinical interest include magnetic resonance imaging (MRI) and multi-detector computed tomography (MDCT).

The following work describes the efficacy of MRI-derived measures for the ...


Biplane Fluoroscopy For Hindfoot Motion Analysis During Gait: A Model-Based Evaluation, Janelle A. Cross, Ben Mchenry, Robert C. Molthen, Emily Exten, Taly Gilat-Schmidt, Gerald F. Harris May 2017

Biplane Fluoroscopy For Hindfoot Motion Analysis During Gait: A Model-Based Evaluation, Janelle A. Cross, Ben Mchenry, Robert C. Molthen, Emily Exten, Taly Gilat-Schmidt, Gerald F. Harris

Biomedical Engineering Faculty Research and Publications

The purpose of this study was to quantify the accuracy and precision of a biplane fluoroscopy system for model-based tracking of in vivo hindfoot motion during over-ground gait. Gait was simulated by manually manipulating a cadaver foot specimen through a biplane fluoroscopy system attached to a walkway. Three 1.6-mm diameter steel beads were implanted into the specimen to provide marker-based tracking measurements for comparison to model-based tracking. A CT scan was acquired to define a gold standard of implanted bead positions and to create 3D models for model-based tracking. Static and dynamic trials manipulating the specimen through the capture ...


Specimen-Specific Natural, Pathological, And Implanted Knee Mechanics Using Finite Element Modeling, Azhar Akber Ali Jan 2017

Specimen-Specific Natural, Pathological, And Implanted Knee Mechanics Using Finite Element Modeling, Azhar Akber Ali

Electronic Theses and Dissertations

There is an increasing incidence of knee pain and injury among the population, and increasing demand for higher knee function in total knee replacement designs. As a result, clinicians and implant manufacturers are interested in improving patient outcomes, and evaluation of knee mechanics is essential for better diagnosis and repair of knee pathologies. Common knee pathologies include osteoarthritis (degradation of the articulating surfaces), patellofemoral pain, and cruciate ligament injury and/or rupture. The complex behavior of knee motion presents unique challenges in the diagnosis of knee pathology and restoration of healthy knee function. Quantifying knee mechanics is essential for developing ...


The Effect Of Twist On The Mechanical Properties Of The Intervertebral Disc, Maxine Harvey-Burgess Jan 2017

The Effect Of Twist On The Mechanical Properties Of The Intervertebral Disc, Maxine Harvey-Burgess

Theses and Dissertations (Comprehensive)

Introduction: Intervertebral disc (IVD) herniation is a common injury to the IVD and a frequent source of low back pain. IVD herniation occurs when the nucleus pulposus migrates through both the inter- and intralamellar matrices of the annulus fibrosus (AF). There are a number of mechanical risk factors associated with herniation, including repetitive flexion and twist. In vivo, twist combined with repetitive flexion has been associated with increased experience of low back pain and herniation. Additionally, in vitro, when repetitive flexion is combined with twist, IVD herniation occurs more easily than repetitive flexion alone. However, the mechanisms behind this relationship ...