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Abstract:In recent years, computational fluid dynamics (CFD) has been widely used in fundamental and clinical researches of cerebral aneurysms. The research direction involves: ① the hemodynamic risk factors associated with initiation, evolution and rupture of cerebral aneurysms, ② the assessment of flow field changes in cerebral aneurysms after the implantation of coils and stent as well as the effect of such endovascular treatment by establishing the patient-specific models. This review elaborates the research progress in hemodynamics of cerebral aneurysms from 3 aspects: the development of CFD models, the morphological and hemodynamic parameters for rupture risk assessment of aneurysms and the role of CFD in the endovascular treatment of cerebral aneurysms.

Abstract:Varus deformation in knee joint is one of the common symptoms caused by unicompartment knee osteoarthritis. Currently, several operations can be used for correcting such deformation, including high tibial osteotomy, unicondylar knee arthroplasty (UKA) and fibulectomy. UKA has been developed for over 60 years, with the advantage of normal knee kinematics restored, less incision, more bony tissue preserved and larger range of motion than total knee arthroplasty (TKA). Therefore, UKA has become a reliable method for treating unicompartment knee osteoarthritis. Fibulectomy is a new kind of surgical technique for treating varus deformation in knee joint, with the advantage of simple operation, low cost and fast recovery. At present, fibulectomy has been widely applied, but its treatment mechanism is still not clear. In this review, two clinical operations UKA and fibulectomy were summarized, and the possible mechanism of fibulectomy for treating unicompartment knee osteoarthritis was proposed from the viewpoint of biomechanics. The author hypothesized that reduction in lateral muscle force after fibulectomy would cause rebalance of the resultant joint moment, therefore, the change of joint contact position and the decrease in joint contact force might be the cause of fibulectomy to release the pain for knee osteoarthritis patients.

Abstract:Objective To study the deformation and mechanical characteristics during expansion process of vascular stent in realistic stenosis model, so as to provide scientific references for interventional treatment and stent design. Methods The carotid vessel model and plaque model of patient were built by using 3D reconstruction method, and the stent model with I-shaped link was established by using Pro/E; ABAQUS/Standard was used to simulate the radial expansion (the first stage) and radial contraction (the second stage) of the stent in real stenosis model, and a realistic model of blood vessel with plaque was also established to make contrast test. Results In the first stage, radial expansion of the stent was formed. The maximum contact area was generated between the outer surface of the stent and the inner surface of the plaque/arterial wall, and the maximum stresses on the stent, plague and arterial wall were 515.000, 2.482, 1.053 MPa, respectively. In the second stage, the radial contraction of the stent resulted in “dog-bone” effect. Many gaps between the stent and vessel wall was formed, and the maximum stresses on the stent, plague and arterial wall were 464.500, 0.954, 0.316 MPa, respectively. In contrast test, the maximum stresses on stenotic vessel and stent were 0.9, 414.1 MPa in the second stage. Conclusions Compared with the model in contrast test, the stenosis model differentiating the component of vascular tissues is more consistent with the real situation of stenotic vessels, by more truly showing deformation and mechanical characteristics of the stent and blood vessel. The stent causes the maximum damage to plaque and inner wall of blood vessel in the first stage, while “dog-bone” effect of the stent is an important influencing factor that results in the gaps between the stent, plague and blood vessel. These research findings may provide significant guidance for selecting stent in interventional treatment and improving stent design.

Abstract:Biomechanical study on type I+II+III standard hemipelvic prosthesis under single-leg stance

Abstract:Objective To make comparative study on the immediate stability of intra-articular calcaneal fractures fixed by crossing screws and by plate. Methods A set of foot CT images from a normal male were collected to construct 3D finite element models of Scander-III calcaneau fracture fixed by crossing screws and by steel plate, respectively. The regular pattern of stress and displacement distributions on these two fracture models under vertical load of 700 N was analyzed. Results For the screw-fixed model, the stress was concentrated at the connecting area between screws and fracture ends, and the maximum stresses were different for screws at different places. While for the plate-fixed model, the stress was concentrated at the connecting area between plate and screw. The highest stress was concentrated in anterior segment of the plate. The maximum stresses of plate, screw and calcaneus were all lower than their shear strength. The displacements of intact calcaneus and fractures were concentrated on the posterior subtalar joints, and a larger displacement appeared on the internal part of joint facet. Conclusions Both crossing screws and steel plate can be used to fix calcaneal fractures with a preferable initial stability. Functional exercise and rehabilitation are recommended at early time after operation.

Abstract:Objective To study stress changes in forefoot intermetatarsal region when wearing high-heeled shoes, so as to provide references for quantitative analysis on inducement mechanism of intermetatarsal neuroma and corresponding treatment strategy. Methods Based on the validated foot-ankle-shoe finite element platform, changes of stress levels and tendency in intermetatarsal region were analyzed for both in balanced standing when wearing 0-3 inch (0, 2.54, 5.08, 7.62 cm) high-heeled shoes and walking when wearing 5.08 cm high-heeled shoes in a gait cycle. Results With the increase of heel height, the stresses in intermetatarsal region were significantly increased, and the stress in the third web space of toes when wearing 7.62 cm high-heeled shoes reached 312% of that when wearing flat shoes (0 cm high-heeled shoes). When walking with 5.08 cm high-heeled shoes, the third web space of toes at push-off instance had the largest stress, reaching 90 kPa, which agreed with the most commonly pathogenic site of intermetatarsal neuroma in clinic. Conclusions Wearing high-heeled shoes can obviously increase the stress in intermetatarsal region. Squeezing by upper extrusion of shoes can result in the largest stresses in the third web space of toes region, which is most likely to cause the development of intermetatarsal neuroma.

Abstract:Objective To establish a neural probe-brain tissue numerical model and investigate tissue injuries induced by probe during its insertion into brain tissues. Methods The material of brain tissue was described by a hyper-viscoelastic constitutive equation. Tissue failure and separation were simulated by the element deletion method based on a maximum principle strain failure criteria, and tissue injuries were quantified by the mean effective strain. Then effects of probe wedge angle, inserting speed and probe stiffness on the acute injury were investigated. Results Tissue strain generated by probe with wedge angle of 150° was increased by 37.1% compared with the strain induced with wedge angle of 90°. Along the insertion path, probe with a slow speed of 100 μm/s induced much higher strain value (>57%) compared to that with relatively faster speed of 500 μm/s, which generated the strain value below 25%. The probe stiffness, however, had a negligible effect on tissue injury. The strain within the tissue was only increased by 1%-2% while the stiffness decreased from 165 GPa to 5 kPa. Conclusions The established numerical model can provide references for the design of neural probe and probe inserting parameters, which will be helpful to reduce tissue injuries induced by probe insertion and thus improve the working life of neural probe to meet the long-term clinical application.

Abstract:Objective To study the influence from load strength on solute transport rate in lacunar-canalicular system (LCS) of loaded tibia using finite element method.Methods Based on micro-CT scan images of adult mice tibia, the finite element model of the tibia, which was regarded as being homogeneous biphasic-solute, was established by software of Mimics, Hypermesh and FEBio. The relationship between transport rate and solute diffusivity/load strength was obtained by setting 3 groups of different solute diffusivity (3, 15, 30 μm2/s) and load strength (0.2, 2.0, 5.0 N), respectively. By comparing the results from both fluorescence recovery after photobleaching (FRAP) experiment and finite element method, the effect of load stimulation on transport enhancement was analyzed. Results The transport rate increased with the increase of diffusion rate and load strength. The results from finite element method were basically consistent with the solute transport rules by comparing data from FRAP experiment. Conclusions The research findings can provide some basis for load response and liquidity in deep area of cortical bone, and for further revealing the mechanism of bone regeneration.

Abstract:Objective To investigate the effects from loads with different angles on morphological and biomechanical properties of trabecular bones in femoral head, so as to provide theoretical basis for studying biomechanical mechanism of necrosis and collapse of femoral head. Methods Ninety-four specimens of 12-month-old ovine trabecular bones in femoral head and forty-three specimens of human cadaver trabecular bones in femoral head were prepared. According to different angles between loading direction and principle compression direction, all the trabecular bones were divided into five groups by 10° interval (i.e. varus 10° and 0°, valgus 10°, 20° and 30°) to simulate the reduction condition under different Garden index after internal fixation of femoral neck fractures. Micro-CT scanning and calculation, compression failure test on ovine trabecular bones in femoral head and cyclic compression test on human cadaver trabecular bones in femoral head were performed to investigate morphological and mechanical indices, including BV/TV (bone volume vs. total volume), BS/BV (bone surface vs. bone volume), Tb.Th (thickness of trabecular bone), Tb.N (number of trabecular bone), Tb.Sp (trabecular separation), elastic modulus, ultimate strength, yield strength, initial secant modulus and number of cycles. Results When the angle between loading direction and principle compression direction of trabecular bones was 0°, BV/TV, Tb.Th, elastic modulus, ultimate strength, yield strength, initial secant modulus and number of cycles for trabecular bones were the maximum while BS/BV and Tb.N were the minimum, and all the formers presented decreasing tendency while BS/BV and Tb.N showed increasing tendency along with the angle increasing. ConclusionsAlong with the angle changes, the tendency of BV/TV and ultimate strength for 12-month-old ovine trabecular bones in femoral head displayed as the same as human trabecular bones in femoral head. Both the morphological and biomechanical properties of trabecular bones in femoral head will decrease when the angle between loading direction and principle compression direction of trabecular bones increases. The more the Garden index deviating from 160°, the more likely trabecular bones in femoral head to be damaged.

Abstract:Objective To study the effects by wearing high-top and low-top basketball shoes on kinematics, kinetics and sports performance of ankle joint in sagittal plane under different jumping maneuvers. Methods Twelve subjects were required to wear high-top and low-top basketball shoes to perform drop jumps(DJ) and lay-up jumps(LJ), and the parameters such as minimum/maximum joint angle, torque, power, stiffness, jumping height and dorsiflexion angle during their jumping maneuvers were simultaneously collected by the Vicon motion capture system and Kistler force plates. Results (1) The dorsiflexion angle of ankle joint was significantly decreased when wearing high-top basketball shoe (P<0.05). During DJ and LJ, no significant differences were found in jumping height, touch-down ankle angle, minimum/maximum ankle angle, and ankle range of motion (ROM) in the two shod conditions. (2) There were no significant differences in flexion/extension torque and power of ankle joint in the two shod conditions during DJ. However, during LJ, the peak value of plantarflexion torque and power from wearing high-top shoes was significantly smaller than that with low-top shoes (P<0.05). Conclusions Wearing high-top shoes do not restrict the performance of ankle plantarflexion and dorsiflexion under actual jumping situation. However, the kinetics of ankle joint in sagittal plane under different jumping maneuvers can be partly restricted. The selection and design of shoe collar height should be carefully considered to improve the mechanical effect of ankle joint in sagittal plane and optimize sports performance along with considering ankle protection.

Abstract:Objective To analyze deflection and forces of needle insertion and improve the inserting accuracy. Methods The measuring equipment was constructed with industrial camera, stepping motor and light source. The experiment of needle insertion into soft tissues was conducted with puncture needles having different diameters (1.3, 0.9, 0.6 mm), and the inserting forces at different puncture speeds (5, 10 and 15 mm/s) were measured by the force sensor. The needle deflection was obtained by digital image processing method. Based on the analysis of needle inserting forces, a projecting beam model was structured to predict the needle deflection. Results The deflections of puncture needles with diameters of 1.3 and 0.6 mm at puncture speed of 5 mm/s were predicted by using the projecting beam model. The absolute error was less than 0.5 mm, and the relative error was less than 10%. Conclusions The proposed model can predict the needle deflection effectively, which will provide references for the robot-assisted needle insertion.

Abstract:Objective To calculate joint torques and muscle forces of astronaut in spacesuit by establishing the biomechanical simulation model of upper limb interaction for human-spacesuit system, so as to assess the risk in extra-vehicular activities. Methods For spacesuit upper limb, the kinematic model of rigid body rotation and hysteresis model of joint resistant torque were built, respectively, to describe the kinematic and dynamic features of spacesuit joints. Kinematic coupling of human and spacesuit upper limb was fulfilled by restricting the displacement between spacesuit elbow and human elbow, and dynamic coupling was fulfilled by using virtual reaction element. An integrated simulation model was established in the framework of inverse sport biomechanics. With this model, the elbow flexion/extension of the astronaut under pressure-suited, unpressured-suited and unsuited condition was simulated for case study. Results The correlation coefficients of predicted muscle activation and iEMG for biceps under the three conditions were 0.86, 0.71 and 0.65, respectively; the corresponding correlation coefficients for triceps were 0.75, 0.61 and 0.60, respectively. The consistency between predicted muscle activations and surface electromyography collected in experiment qualitatively validated the accuracy of this model, and the consistency between human elbow joint torque working on muscles and spacesuit elbow joint resistant torque validated the rationality of the model. Conclusions The established biomechanical simulation model of upper limb interaction for human-spacesuit system can effectively calculate the joint torque and muscle force of astronaut in spacesuit. The simulation and experiment results indicate that joint resistant torque in pressured spacesuit has great influence on human joint torque and muscle workload, which offers methodological support for physical workload and musculoskeletal risk evaluation for astronauts in extra-vehicular activity.

Abstract:Objective To investigate the effects of vascular endothelial growth factor (VEGF) on disused bone loss. Methods Tail-suspended (TS) rat models were established and evenly divided into TS+Saline group, TS+VEGF group, CON+Saline group and CON+VEGF group. During the experiment, VEGF or equivalent amount of saline was injected into the gastrocnemius muscle of the rats’ right tibia twice a week for each rat. After four weeks, the proximal tibia of the rats was scanned by micro-CT. The bone mineral density (BMD) of the trabecular bone and cortical bone, micro-structure parameters of the trabecular bone, such as bone volume per trabecular volume (BV/TV), tabecular number (Tb.N), trabecular spacing (Tb.Sp), structure model index (SMI), and cortical thickness were used as evaluation indices to study the influence of VEGF on bone loss in the proximal tibia of tail-suspended rats. Results Compared with the control rats, in tail-suspended groups, the apparent BMD, BV/TV, Tb.N, SMI of trabecular bone and the cortical thickness all decreased significantly, while the Tb.Sp and SMI significantly increased, which showed that tail suspension would cause bone loss, while the injection of VEGF would alleviate the loss of trabecular bone in tail-suspended rats. Conclusions There might exist some relationship between the status of blood supply and bone remodeling process, and by improving the status of vascular system, the disused bone loss can be alleviated.

Abstract:Objective To investigate the effect from sequential removal of posterior ligamentous complex (PLC) on stability of injured thoracolumbar spine, and verify the role of supraspinous ligaments in maintaining stability of injured thoracolumbar spine complex. Methods Eight fresh human thoracolumbar specimens (T11-L3) were selected, and 1/3 of the L1 vertebral body was resected for "V" shape. The specimens were then mounted on the universal testing machine and subjected flexion and compression to make a fracture in L1. PLC in T12-L1 segment was then resected in a sequential manner from facet capsular ligament (FCL), interspinous ligament (ISL), supraspinous ligament (SSL) to ligamentum flavum (LF). The range of motion (ROM) and neutral zone (NZ) of the T12-L1 segment under flexion, extension, lateral bending and rotation movement were measured at each ligament removal step. Results Under flexion and extension, ROM and NZ presented a significant increase after fracture and removal of SSL. Under right lateral bending, ROM increased sharply after reduction of vertebrae and FCL, while the NZ showed a slight increase. Under left axial rotation, removal of vertebrae and FCL resulted in a significant increase in ROM, while the NZ showed no significant increase. Conclusions After removal of SSL, the stability of the T12-L1 segment decreases sharply, especially under flexion motion, and SSL is the pivotal ligament for PLC to maintain the stability of thoracolumbar spine.

Abstract:Objective To study the influence of red blood cell (RBC) deformability on blood flow, so as to make the blood flow simulation more accurately. Methods Based on analysis of rheological properties of blood and mechanical properties of RBCs, the existing two-phase flow model of blood was improved, and the effect of non-inertial lift force generated by the interaction between soft RBCs and shear flow or the vessel wall was considered in the improved model. The blood flow in vessels with different diameters was simulated by using this improved model. Results The radial motion of RBCs generated by non-inertial lift force had an obvious influence on the distribution of RBC volume fractions and blood velocity. When the vessel diameter was between 0.1-3.0 mm, the simulated relative viscosity of blood by the improved model was very close to the measured viscosity. Conclusions The non-inertial lift force is one of the main reasons leading to Fahraeus-Lindqvist effect of blood, and the improved model considering the non-inertial lift force can simulate the blood flow more accurately, which provides a more accurate method for the simulation of vascular system treatment and cell sorting.

Abstract:Objective To design an overall unloading knee brace, and analyze the relationship between the unloading force and the position of the brace as well as the thigh bracket-thigh pressure. Methods Based on biomechanical experimental platform, the mechanical and kinematic analysis on squatting down-standing upright motion was conducted to evaluate unloading capacity of the overall unloading knee brace. Results The unloading forces supplied by the brace ranged from 0 to 200 N. The forces were larger with the brace hinges installed on the front-top of the knee, and the unloading forces increased with the pressure between the thigh and thigh bracket increasing. Conclusions The proposed overall unloading knee brace can partly reduce knee force, and its unloading forces are related to the installation site of the brace as well as the elasticity of the belts.

Abstract:Traditional Chinese traumatology manipulation (TCTM) has some prominent advantage for treating cervical spine diseases in clinic, thus the biomechanical research on TCTM could possess important clinical and theoretical significance. The studies on biomechanical mechanism of TCTM for treating cervical spine diseases in recent years were reviewed from various aspects, and biomechanical issuessuch as the force measurement of TCTM, the different operation types of TCTM (i.e. tendon-soothing maneuver, bone setting manipulation), the TCTM effect on cervical tissues (i.e. vertebral body, intervertebral discs, muscles, blood vessels) were also investigated, trying to provide some biomechanics theoretical evidence and guidance for treating cervical spine diseases with TCTM in clinic.