THREE-DIMENSIONAL FINITE ELEMENT ANALYSIS OF HUMAN FOOT DURING HEEL RISE: ROLE OF THE GASTROCNEMIUS-SOLEUS (G-S) MUSCLE

Geometric positioning of the foot and transfer of plantar loads can be adversely affected when muscular control in gastrocnemius-soleus (G-S) complex is abnormal. This study aims to develop a 3-D musculoskeletal finite element (FE) model of the foot to quantify the precise role of the G-S complex in biomechanical behavior of the foot. Movements of the ankle and metatarsophlageal joints, as well as forefoot plantar pressure peaks and pressure distribution under the metatarsal heads (MTHs) were all found to be extremely sensitive to reduction in the muscle load in the G-S complex. The findings may provide clinicians with knowledge to understand the underlying mechanism for relieving pain, injury or other structural deformities under metatarsal areas in patients who suffer from GS muscle contracture

OSTEOCHONDRAL INJURY DURING SIMULATED DROP LANDING COMPRESSION: PRE AND POST IMPACT MICRO-COMPUTED TOMOGRAPHY

The purpose of this study was to investigate osteochondral injuries due to impact load. Average nominal strain of 34%±5% was applied to equine osteochondral plugs. The deformation of cartilage and bone on one plane was measured using real-time imaging during the impact. High resolution micro-computed tomography prior to and following the loading was used to investigate the extent of the damage to the specimens. The average peak strain in bone and cartilage was 0.11±0.01 and 0.20±0.08, respectively. Microfractures were found in the µCT images in the subchondral bone, ranging from 200µm to 30µm wide. The 3D images of micro-fractures, obtained here, can be used for future studies of bone remodeling as a result of such impact-induced damages. The strain in the bone was significantly large indicating the ability of bone to absorb the impact energy

DEVELOPMENT AND VALIDATION OF A HEAD-NECK FINITE ELEMENT MODEL FOR INJURY ANALYSIS

In this study, the digitized geometrical data of the embalmed skull and vertebrae (C1-C7) of a 68 year-old male cadaver were processed to develop a comprehensive, geometrically accurate, nonlinear CO-C7 FE model. The biomechanical response of human neck under near vertex drop impact conditions were investigated and compared with the published experimental data. The results show that the predicted resultant head impact force history and corresponding motions of each motion segment all agree well with pUblished data. The stress variation histories in the neck were found to be consistent with the rotational motions of the motion segments under dynamic loading. The current model may offer potential to effectively reflect the behavior of human cervical spine suitable for further biomechanics and traumatic studies

ANKLE PLANTARFLEXOR CONTRIBUTIONS TO KNEE JOINT LOADING AND ANTERIOR CRUCIATE LIAGAMENT FORCE DURING SINGLE-LEG LANDING

The purpose of this study was to identify the effects of height on ankle plantarflexor contributions to the knee joint loading and the anterior cruciate ligament (ACL) force during single leg landing. Eight healthy subjects performed landing from 30 and 60 cm heights. Subject-specific musculoskeletal models, based on single-leg landing, were developed in OpenSim using kinematics and kinetics data. Predicted muscle forces and knee joint reaction forces were input into another knee model to estimate ACL forces during landing. Large Soleus muscle forces (~5B.W.) were found to act on the tibia at the same time when peak ACL forces occurred. The Gastrocnemius muscles, which acted as an ACL antagonist peaked earlier than the Soleus with a lower magnitude (~3BW). The Gastrocnemius-Soleus complex acted to stabilize the knee joint during single leg landing

The role of the ankle plantar flexor muscles in trip recovery during walking: a computational modeling study

BackgroundReactive lower limb muscle function during walking plays a role in balance, stability, and ultimately fall prevention. The objective of this study was to evaluate muscle and joint function used to regain balance after trip-based perturbations during walking.Research questionHow are lower limb muscles used to recover from external tripping during walking?MethodThe dominant legs of 20 healthy adult participants with similar athletic backgrounds were tripped using a split-belt instrumented treadmill. High- and medium-intensity trips were simulated by deceleration of the dominant leg at initial contact from the speed of 1.1 m/s to 0 m/s and back to 1.1 m/s in 0.4 s and 0.8 s, respectively. Lower limb kinematics, kinetics, and muscle forces following perturbations were computed to pre-perturbation values using statistical parametric mapping (SPM) paired t-test.ResultsA greater ankle dorsiflexion angle (mean difference: 5.3°), ankle plantar flexion moment (mean difference: 0.6Nm/kg), and gastrocnemius and soleus muscle forces (mean difference: 4.27N/kg and 13.56N/kg for GAS and SOL, respectively) were observed post-perturbation step despite the magnitude of the perturbation.SignificanceThis study concludes that adequate timely response of ankle function during a compensatory step is required for a successful recovery after tripping during walking in young healthy adults. Weakness in plantar flexors suggests insufficient ankle moments, which ultimately can result in falls. The findings of this paper can be used as a reference for the joint moments and range of motion needed to recover trips in the design of assistive devices. In addition to that, clinicians can use the estimated values of muscle forces and the pattern of muscle activities to design targeted training in fall prevention among the elderly

EFFECT OF TIBIAL ROTATION INHIBITION ON ACL INJURY AT DIFFERENT FLEXION ANGLES

This study investigates the damages to the knee joint due to impact load and inhibition of tibia rotation. A rig was manufactured to test fifteen fresh porcine knee specimens replicating single leg landing. Three knee flexion angles (22.5o, 37.5o and 52.5o) were tested. For each angle, 5 specimens were fixed and consecutive displacement control loads with increments of 0.5 mm were applied to tibia until catastrophic failure happened. Anterior cruciate ligament avulsions were found in greater flexion angles but not at low flexion angles. No significant difference was observed in the following parameters in different knee flexion angles; peak compressive force, internal tibia torque, and posterior femoral displacement. Our results also suggest that an optimum tibia rotation may be needed to avoid ACL injury while its inhibition could lead to intrachondral fracture

Lumbar Model Generator:a tool for the automated generation of a parametric scalable model of the lumbar spine

Low back pain is a major cause of disability and requires the development of new devices to treat pathologies and improve prognosis following surgery. Understanding the effects of new devices on the biomechanics of the spine is crucial in the development of new effective and functional devices. The aim of this study was to develop a preliminary parametric, scalable and anatomically accurate finite-element model of the lumbar spine allowing for the evaluation of the performance of spinal devices. The principal anatomical surfaces of the lumbar spine were first identified, and then accurately fitted from a previous model supplied by S14 Implants (Bordeaux, France). Finally, the reconstructed model was defined according to 17 parameters which are used to scale the model according to patient dimensions. The developed model, available as a toolbox named the lumbar model generator, enables generating a population of models using subject-specific dimensions obtained from data scans or averaged dimensions evaluated from the correlation analysis. This toolbox allows patient-specific assessment, taking into account individual morphological variation. The models have applications in the design process of new devices, evaluating the biomechanics of the spine and helping clinicians when deciding on treatment strategies.</jats:p

Development of a biomechanical model of the interface between the residual limb and prosthesis for trans-femoral amputees

Prosthetic socket fitting is achieved by the prosthetist applying artisan techniques which are skill dependent and of subjective nature.This study investigates the use of finite element (FE) modelling techniques to predict the biomechanical behaviour at the residual limb / socket interface for the purpose of obtaining a quantitative evaluation of socket fit. Three dimensional FE models of the residual limb of trans-femoral amputees were generated based on geometrical data obtained using a mechanical digitizer and magnetic resonance (MR) imaging techniques. The inter-segmental loadings at the amputee's hip during standing and walking were applied to the FE models. These were measured with the aid of force platforms and infrared cameras. The material characteristic is introduced to the FE models were obtained by testing the residual limb's soft tissue with a computer controlled mechanical indentor. The FE models were validated by comparing predicted and measured pressures at the interface between the residual limb and the socket. The majority of the FE prediction erred within 70% of the measured values. Detailed internal geometry of two trans-femoral amputees' residual limb in its natural shape and wearing quadrilateral and ischial containment type sockets was studied using MR imaging techniques. At the ischial level, the maximum difference in cross sectional area between the muscles of the sound limb and the residual limb was approximately 62%. The difference in muscles' size can be attributed to muscle atrophy in the residual limb or an increase in the muscle bulk in the sound limb. At similar level, the cross sectional area of the rectus femoris in the residual limb was reduced by as much as 68% from its natural shape when wearing the quadrilateral socket. Based on the acquired MR images,a two dimensional FE model of a transverse section 30 mm below the ischium was modelled. The model incorporated the interface characteristics between the muscles and intermuscular tissues. The maximum stress was recorded inside the residual limb near muscles / intermuscular tissue interface and at muscles/ bone interface. The FE models generated have shown the potential of predicting stresses and deformation at the residual limb.Prosthetic socket fitting is achieved by the prosthetist applying artisan techniques which are skill dependent and of subjective nature.This study investigates the use of finite element (FE) modelling techniques to predict the biomechanical behaviour at the residual limb / socket interface for the purpose of obtaining a quantitative evaluation of socket fit. Three dimensional FE models of the residual limb of trans-femoral amputees were generated based on geometrical data obtained using a mechanical digitizer and magnetic resonance (MR) imaging techniques. The inter-segmental loadings at the amputee's hip during standing and walking were applied to the FE models. These were measured with the aid of force platforms and infrared cameras. The material characteristic is introduced to the FE models were obtained by testing the residual limb's soft tissue with a computer controlled mechanical indentor. The FE models were validated by comparing predicted and measured pressures at the interface between the residual limb and the socket. The majority of the FE prediction erred within 70% of the measured values. Detailed internal geometry of two trans-femoral amputees' residual limb in its natural shape and wearing quadrilateral and ischial containment type sockets was studied using MR imaging techniques. At the ischial level, the maximum difference in cross sectional area between the muscles of the sound limb and the residual limb was approximately 62%. The difference in muscles' size can be attributed to muscle atrophy in the residual limb or an increase in the muscle bulk in the sound limb. At similar level, the cross sectional area of the rectus femoris in the residual limb was reduced by as much as 68% from its natural shape when wearing the quadrilateral socket. Based on the acquired MR images,a two dimensional FE model of a transverse section 30 mm below the ischium was modelled. The model incorporated the interface characteristics between the muscles and intermuscular tissues. The maximum stress was recorded inside the residual limb near muscles / intermuscular tissue interface and at muscles/ bone interface. The FE models generated have shown the potential of predicting stresses and deformation at the residual limb

Side-to-side comparison of knee kinematics and kinetics during a single-leg drop landing from two heights in female athletes

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Complications of Reverse Total Shoulder Arthroplasty: A Computational Modelling Perspective

Reverse total shoulder arthroplasty (RTSA) is an established treatment for elderly patients with irreparable rotator cuff tears, complex proximal humerus fractures, and revision arthroplasty; however, with the increasing indications for RTSA over the last decade and younger implant recipients, post-operative complications have become more frequent, which has driven advances in computational modeling and simulation of reverse shoulder biomechanics. The objective of this study was to provide a review of previously published studies that employed computational modeling to investigate complications associated with RTSA. Models and applications were reviewed and categorized into four possible complications that included scapular notching, component loosening, glenohumeral joint instability, and acromial and scapular spine fracture, all of which remain a common cause of significant functional impairment and revision surgery. The computational shoulder modeling studies reviewed were primarily used to investigate the effects of implant design, intraoperative component placement, and surgical technique on postoperative shoulder biomechanics after RTSA, with the findings ultimately used to elucidate and mitigate complications. The most significant challenge associated with the development of computational models is in the encapsulation of patient-specific anatomy and surgical planning. The findings of this review provide a basis for future direction in computational modeling of the reverse shoulder