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Abstract:The study of spine biomechanics is an important foundation for understanding spine function, spine pathogenesis as well as selection of spinal therapeutic approaches. This review summarizes the basic research progress and results of spine biomechanics from five aspects, including the individual components of spine (such as spinal vertebrae), intervertebral discs, ligaments and functional spinal units and the whole spine. All these studies include the in vitro and in vivo experiments on human spinal specimens and animal spinal specimens, and the results of different research methods such as the mathematical model. This review also summarizes some of the poorly understood biomechanical data, which would become an important research direction in the future.

Abstract:Objective Aiming at the clinical problem of the low matching degree with the patient’s anatomical morphology for traditional cervical fusion cage, a cervical fusion cage with the function of adjustable height and the shape matched with the vertebral body was established, and its biomechanical properties were evaluated. Methods A cervical C4-5 segment fusion model was established according to anterior cervical discectomy and fusion (ACDF), so as to simulate different motion conditions, i.e. anterior flexion, posterior extension, left/right lateral flexion, left/right rotation, and stress of the fusion cage and vertebral endplate was calculated. After three-dimensional (3D) printing of the fusion cage, an in vitro mechanical experiment was conducted to explore safety and stability of the fusion cage. ResultsThe fusion cage could keep the range of motion (ROM) of cervical vertebrae at the fusion segment with 1°-2.8° and reduce the ROM to 40%-80% of the natural segment. In the in vitro compression test, the yield load of the fusion cage was (2 721.67±209) N, which met the maximum demand of the physiological load in service state. Conclusions The designed fusion device with adjustable height shows better biomechanical properties and can reduce the selection step in operation.

Abstract:Objective To evaluate the biomechanical properties of lumbar interbody fusion with NiTi memory alloy stent-autogenous bone granule-absorbable bone cement. Methods The normal L3-5 segment finite element model (M0), L4-5 intervertebral fusion model with box fusion cage (M1), L4-5 intervertebral fusion model with NiTi memory alloy stent (M2) and L4-5 interbody fusion model with bone granule-absorbable bone cement for casting bone graft (M3) were constructed, respectively. The models were applied with mechanical loading to analyze the mechanical stability and the peak stress of L4 interior endplate. Results The range of motion (ROM) of L4-5 segment in M1 and M2 models was significantly lower than that of M0 model under flexion, extension, lateral flexion and axial rotation. In M3 model, the stability of the surgical segment was further improved and the peak stress of L4 interior endplate was much smaller than that of M1 and M2 models. Conclusions NiTi memory alloy stent and traditional box fusion cage have biomechanical equivalence when used alone in lumbar interbody fusion, and application of bone granule-absorbable bone cement for casting bone graft can further improve the stability and reduce the stress of endplate.

Abstract:Objective To evaluate the influence of dynamic fixation (rotating and sliding pedicle screws) on stability of the atlantoaxial joint. Methods A series of in vitro biomechanical tests were performed using six fresh adult cervical spines (occipital bone-C4 segment) to simulate different conditions in surgery， including the intact state, the injury state, rigid fixation, rotating pedicle screw fixation, sliding pedicle screw fixation. The repeated measurement design was employed, and under intact, injury and different fixation states, the pure moment of 1.5 N·m in flexion-extension, left-right lateral bending, left-right axial rotation directions were applied using the spinal testing machine. The movement of atlantoaxial spine was measured consecutively by three-dimensional （3D） measurement system in order to analyze the range of motion (ROM) and neutral zone (NZ) of atlantoaxial joints. Results Under injury state, ROM of atlantoaxial joints was significantly larger than that under intact state during flexion, extension, lateral bending and rotation, leading to the instability of atlantoaxial joints. ROM of fixation segments was significantly reduced during flexion, extension, lateral bending and rotation after rigid and dynamic fixation. Compared with rigid fixation, dynamic fixation showed a significant ROM increase during lateral bending. NZs of fixation segments after dynamic fixation were significantly reduced. There were no significant ROM differences between rigid fixation and dynamic fixation. Conclusions The stability of atlantoaxial joints by dynamic fixation during flexion, extension and rotation was comparable to that by rigid fixation, but weaker during lateral bending. Dynamic screw fixation can maintain the relative stability of atlantoaxial joints.

Abstract:Objective To analyze factors that affect axial mechanical performance of the posterior pedicle fixation system. Methods The mechanical model for axial mechanical properties of the posterior pedicle fixation system was established to perform mechanical analysis. By referring to the Standard YY/T 0961-2014, tests on axial ejection force and axial clamping torque of JHL-I multi-axis components, JHL-I single-axis components, JHL-V multi-axis components and JHL-V single-axis components were performed by using Instron E3000 and Instron E10000 mechanical testing machines. Results The ejection rigidity of the single-axis component of vertebral nail system was significantly higher than that of the multi-axis component of vertebral nail system; the torsion rigidity of JHL-V was higher than that of JHL-I. The type and size of the locking bolt as well as its locking torque were the main factors affecting axial ejection force of the posterior spinal pedicle fixation system; the size of the locking bolt and the diameter of the connection rod were the main factors affecting axial clamping torque of the system; axial mechanical properties of the system could be improved by increasing the diameter of the connecting rod, the coefficient of friction between each connecting element, and the pitch diameter of the locking bolt. Conclusions The research findings provide references for optimizing and improving axial mechanical properties of the posterior pedicle fixation system.

Abstract:Objective To study the stability of lumbar spine after transforaminal lumbar interbody fusion (TLIF) surgery combined with a novel articular process fixation system (APFS). Methods Based on the validated finite element model of L3-S1 intact segment (Model A), TLIF surgery was simulated to establish bilateral pedicle screw TLIF model (Model B), right unilateral pedicle screw TLIF model (Model C), APFS combined with right pedicle screw fixation TLIF model (Model D). The range of motion (ROM) of the lumbar spine model and stress distributions on pedicle screws, APFS and interbody fusion cages under different working conditions were observed. Results The overall ROMs of Models B, C, and D under different working conditions were comparable, which were all smaller than those of the physiological model. Compared with Models B and C, the maximum compressive stress of the right pedicle screw and the interbody fusion cage in Model D was the smallest or between Models B and C under different working conditions. Model D had the largest peak stress of APFS and right pedicle screw during anterior flexion. Conclusions APFS combined with contralateral pedicle screw fixation can be used as a novel fixation method for TLIF surgery of lumbar spine.

Abstract:Objective To analyze the biomechanical characteristics of lumbar fusion by 3 internal fixation methods using three-dimensional (3D) finite element (FE) method. Methods The FE fixation models of physiological L4-5, unfixed fusion L4-5, translaminar facet screw (TLFS), lumbar pedical screw+translaminar facet screw (LPS+TLFS), bilateral pedical screw (BPS) with complete osteotomy or partial osteotomy of facet joint were established, respectively. The biomechanical characteristics of L4 centrum and implants under six motion states (spinal flexion, extension, lateral bending and axial rotation) in L4-5 fusion model and three fixation models were compared by FE analysis. Results The average maximal displacements of L4 centrum in L4-5 unfixed fusion model, TLFS model, TLFS+LPS model, BPS model were 1.410 8, 0.629 8, 0.336 9, 0.252 8 mm (complete osteotomy of facet joint) and 1.296 7, 0.844 9, 0.340 9, 0.273 8 mm (partial osteotomy of facet joint); the average maximal displacements of cage were 0.479 9, 0.319 5, 0.167 6, 0.126 4 mm (complete osteotomy of facet joint) and 0.378 7, 0.348 4, 0.183 5, 0.137 2 mm (partial osteotomy of facet joint)；the average maximum stresses of screws and rods during 6 motions in TLFS model, TLFS+LPS model, BPS model were 178.34, 79.55, 56.33 MPa (complete osteotomy of facet joint) and 142.29, 103.02, 59.69 MPa (partial osteotomy of facet joint). Conclusions In percutaneous transforaminal lumbar interbody fusion, the fixation effect of BPS model was similar to that of LPS+TLFS model. BPS model could achieve the best spinal stability, and LPS+TLFS model was also a good fixation method. The stability of TLFS model alone was relatively poor, but it was still better than that of cage bone graft without internal fixation. In the absence of internal fixation, preservation of the articular process significantly increased stability of the spine.

Abstract:Objective To investigate the feasibility of absorbable magnesium alloy screws in atlantoaxial dislocation fixation. Methods Four kinds of screws with triangular, rectangular, trapezoidal and zigzag thread were designed with WE43 magnesium alloy. The finite element simulation analyses were performed on the screw- polyurethane model and atlantoaxial fixation system model. The stress and displacement distributions on the models were obtained. Results The pull-out force simulations were carried out on four kinds of magnesium alloy screws according to ASTM F543 standard specification. The stresses of screws with triangular, rectangular, trapezoidal and zigzag thread were 146.20, 185.22,194.98, 264.55 MPa, respectively. The pull-out strength of the screw with triangular thread was the largest, and the peak stress was the smallest. The magnesium alloy screw with triangular thread used for atlantoaxial fixation could meet the strength requirements of flexion/extension, rotation and bending of the neck. The peak stress of the screw was reduced by 17.16 MPa after adding hydroxyapatite (HA) coating on the surface, and the stress on the screw was within the range of bonding strength between coating and magnesium alloy substrate. Conclusions Under the same loading condition, the screw with triangular thread has good stability and the best pull-out force performance. After heat treatment, the strength of magnesium alloy screw with triangular thread meets the load-bearing requirements for atlantoaxial dislocation fixation. HA coating on screw surface can optimize mechanical properties of the screw, and there exits good bonding strength between the coating and the screw.

Abstract:Objective To establish the model of goat intervertebral disc degeneration （IDD） induced by controllable axial compressive stress and evaluate its imaging and pathological characteristics. Methods Twenty goats were randomly divided into 4 groups (control group, 4-week pressure group, 8-week pressure group, 12-week pressure group, n=5, 40 N pressure). Disc height index (DHI) was used to evaluate the change of intervertebral disc height by X-ray, Pfirrmann classification method was used to observe the degree of intervertebral disc degeneration by magnetic resonance imaging (MRI), and histopathological observation and evaluation for intervertebral disc were conducted by HE staining and immunohistochemistry. Results DHI in control group showed no significant changes with the extension of pressure time, while DHI in the experimental group gradually decreased. There was no significant change in Pfirrmann classification in control group. In experimental group, with the extension of time, the higher the degeneration aggravated with the Pfirrmann classification increasing. In experimental group, HE staining showed that the disc nucleus pulposus decreased in volume and nucleus pulposus cells, which were gradually replaced by fibrous tissues. Immunohistochemical staining showed that type I collagen in the nucleus pulposus gradually increased, type Ⅱ collagen gradually decreased, and intervertebral disc degeneration occurred. Conclusions A certain axial compressive stress can lead to degeneration of goat lumbar intervertebral disc, and the degree of degeneration is gradually increased with the extension of time.

Abstract:Objective To establish the finite element model of upper cervical vertebrae C0-3 with Jefferson fracture, and to analyze the influence of posterior atlantoaxial fusion (PSF) and occipitocervical fusion (OCF) on biomechanical properties of the vertebral body and mechanical conduction of the screw-rod system. Methods Based on CT images, the C0-3 segment Jefferson fracture model of human upper cervical spine was established. PSF, OCF1 and OCF2 internal fixation were performed according to surgical plan in clinic, and 50 N concentrated force and 1.5 N·m torque were applied to bottom of the occipital bone. The stress distribution and range of motion (ROM) of the cervical vertebral body, the maximum stress of the screw-rod system and the stress distribution of the intervertebral disc for C0-3 segment during flexion, extension, bending and rotation of the upper cervical spine were studied. Results Compared with PSF, the ROM of OCF1 and OCF2 vertebral bodies increased, and the stress of the nail rod decreased. OCF had a better fixation effect. Conclusions PSF, OCF1 and OCF2 fixation method can reduce the upper cervical ROM and restore stability of the upper cervical spine, which make stress distributions of the vertebral body and intervertebral disc tend to be at normal level. The research result can provide a theoretical basis for clinical surgery plan.

Abstract:Objective Taking pig kidney as an example, through a series of comparative and analogical experiments, the influencing factors of compressive stress at relaxation stage of biological tissues were analyzed, and a more accurate and widely applicable biomechanical model at relaxation stage was established. Methods The compressive stress relaxation experiments of pig kidney under different conditions were carried out by using the self-built mechanical experiment platform. The collected data were analyzed and mapped, and various factors affecting the relaxation force changes were summarized. Based on the conclusion, the neural network learning algorithm was used to model the force change process at relaxation stage of pig kidney. Results The pre-extrusion pressure and relaxation time were the main influencing factors for compressive stress changes of biological tissues at relaxation stage. The average error of test sample validation experiment was 6.4 mN, and the average prediction error of generalization sample validation experiment was 34.9 mN, so the modeling effect was good. Conclusions Neural network modeling algorithm has the advantages of strong generalization ability and good fault tolerance, which contributes to providing more realistic force tactile feedback prediction for virtual surgery system. It is also a new idea for mechanical modeling of nonlinear biological tissues.

Abstract:Objective To study the effect of plaque eccentricity on stent performance and stress distributions of artery and plaque during stent implantation in stenotic vessels. Methods The stent and idealized stenotic vessels were constructed, and 4 different eccentricities (0%, 20%, 40%, 60%) were attributed to the plaque. Then the stent recoil, stent foreshortening, and stress distributions of artery and plaque when the stent was expanded to the target displacement were analyzed by the finite element method. Results Along with the increase of plaque eccentricity, both stent recoil and stent foreshortening gradually grew. At the same time, the stress of artery and plaque also showed an increasing tread, and high-stress areas gradually approached the narrow side. The maximum von Mises stress of the plaque was much greater than that of the artery. Conclusions Plaque eccentricity had a certain effect on performance of the stent and stress distributions of stenotic vessels. In stent design, the geometry of the plaque should be considered to improve clinical effect of the stent in interventional treatment.

Abstract:Objective To analyze stress distributions on mandible bone and periodontal ligaments during acceleration of orthodontic tooth movement by mechanical vibration, and investigate the mechanism of static-vibration coupled loading to accelerate orthodontic tooth movement. MethodsThe finite element model including tooth, periodontal ligament, cancellous bone and cortical bone was established by Mimics，SolidWorks，Geomagic and ANSYS Workbench software. Conventional static orthodontic force and low-magnitude high-frequency mechanical vibration loads were applied to the finite element model for dynamic analysis. ResultsThe compression and tension zones of alveolar bone and periodontal tissues were identified based on Y-normal stress distribution of alveolar bone and periodontal tissues, which was periodic with the same frequency as the applied low-magnitude high-frequency vibration. The von Mises stress of alveolar bone and periodontal tissues also showed periodic changes, but the compression and tension zones of alveolar bone and periodontal tissues could not be identified based on von Mises stress distribution of alveolar bone and periodontal tissues. Conclusions In the field of orthodontics, Y-normal stress is a reasonable mechanical stimulus, and static-vibration coupled loading is an effective method for accelerating orthodontic treatment. The research findings can provide guidance for low-magnitude high-frequency mechanical vibration to accelerate orthodontic tooth movement.

Abstract:Objective To study the effects of different root control attachment on root control and periodontal ligament （PDL） stress during canine distal translation in plastic aligner-based orthodontic treatment. Methods Through three-dimensional (3D) finite element technology, 11 models composed of 4 attachments and 3 kinds of loading were established. Namely, attachment A: no attachments; attachment B: traditional vertical rectangular attachment; attachment C: 1/4 spherical double optimized attachment; attachment D: double optimized door arch attachment; load a: 0.15 mm distal translation of the canine; b: load a+ application of 30 N·mm counterclockwise torque to stress surface of the attachment; load c: load a+ application of 30 N·mm counterclockwise torque to the entire crown. The root control effect of distal translation of the right maxillary canine was simulated with plastic aligner under different loads. Results Displacement modes of all models were distally tipped translation. The double optimized door arch attachment showed the optimal root control effect during canine distal translation. The root control effect for two groups of double optimized attachment was better than that of traditional rectangular attachment. The effect of adding attachments on root control of the canine was better than that of applying only counterclockwise couple. The PDL stress mainly appeared in distal alveolar ridge and root apex without attachment, while the PDL stress mainly appeared in distal alveolar ridge with attachment. Conclusions The most suitable measure to improve the effect of root control during canine distal translation is to use the double optimized door arch attachment in clinic.

Abstract:Objective To make finite element analysis and compressive performance test on three-dimensional (3D) printed personalized poly-ether-ether-ketone (PEEK) condyle prosthesis, so as to analyze stress distribution characteristics and mechanical properties of the prosthesis, and to evaluate its clinical value and prospect. Methods The finite element models of PEEK condyle prosthesis, mandible and fixation screw were established by software such as CBCT, Mimics, Geomagic Studio, SolidWorks and ANSYS Workbench. The maximum mastication force was applied, and the maximum stress of the condyle prosthesis and screw, as well as the stress and strain of the mandible were recorded. In order to simulate the actual clinical situation, a special fixture was designed to test compression performance of the condyle prosthesis prepared by the fused deposition modeling (FDM) and selective laser sintering (SLS) at the rate of 1 mm/min. Results The peak stress of the PEEK condyle prosthesis was 10.733 MPa, which was located at the back of the condyle neck. The peak stress of 5 fixing screws was 9.707 5 MPa, which appeared on the 2# and 5# screws near the trailing edge of the mandibular ascending branch. The peak stress of both the prosthesis and the screw was smaller than its yield strength. The maximum pressure of the condyle prosthesis prepared by FDM and SLS was (3 814.7±442.6) N and (1 193.970±260.350) N, respectively. Compared with the SLS preparation, the FDM prepared prosthesis not only had higher compression strength but also better toughness. Conclusions The 3D printed personalized PEEK condyle prosthesis shows uniform stress distributions and good mechanical properties, which can provide the theoretical basis for PEEK as reconstruction material for repairing temporomandibular joint.

Abstract:Objective To study the effects of excitation source, intraocular pressure and material parameters on frequency response of human eye under acoustic excitation. Methods Based on the three-dimensional (3D) finite element model of the whole eye, as well as the deformation and stress distribution of human eye, the effects of various parameters on frequency response of human eye were quantitatively analyzed. Results When other parameters were fixed and only the position and size of the excitation source changed, the amplitude at resonance of human eye (the acoustic excitation source was placed directly above the cornea, at an offset of 45°, and at larger excitation) at 134 Hz was 35, 48 and 133 μm, respectively. When only the intraocular pressure changed, the first-order resonance frequency was almost unaffected by the intraocular pressure, and the resonance frequencies of other orders would shift slightly to the left as the intraocular pressure increased. When only the scleral elastic parameters changed, the resonance frequency of eye tissues increased with the increase of the scleral elasticity. Conclusions The position and size of the excitation source have no effects on resonance frequency of human eye, but they have a greater effect on the resonance amplitude. The material parameters of human eye tissues have a greater effect on the frequency response, and there is a linear relationship between the intraocular pressure and resonance frequency. The results provide the theoretical basis for clinical development of high-performance intraocular pressure monitoring technology.

Abstract:Objective Comprehensively considering the effectiveness and safety of massage, a method for evaluating the pros and cons of oscillation excitation and pulse excitation for lumbar oblique-pulling manipulation was proposed, and lumbar oblique-pulling manipulation under oscillation excitation was optimized. Methods A multi-rigid body biomechanical model of thoracolumbar spine was established. The manipulation force was used as the input force of the model. Using MATLAB/Simulink, variation of the displacement and acceleration of each lumbar segment with time was simulated. For the optimization of lumbar massage manipulation, the core elements of massage force, namely, frequency (f) and operand (n) were changed, and then the maximum relative displacement and maximum acceleration of each lumbar segment were compared. A new index z was proposed to comprehensively evaluate effectiveness and safety of the manipulation. Results The maximum relative displacement of each lumbar segment was almost equal when lumbar oblique-pulling manipulation under two kinds of excitation was applied. For lumbar oblique-pulling manipulation, the maximum acceleration of each lumbar segment under oscillation excitation was significantly smaller than that under pulse excitation. When the frequency of massage was 1-2.5 Hz, the overall effect of massage was better, and the overall effect had no relation with the operands, and the force of massage lasted for one operand; when the frequency of message was 3.33 Hz and the operands were more than 5, the massage had the best effect, meanwhile the strength of each lumbar segment was relatively large; when the frequency of massage exceeded 5 Hz, and the overall performance of massage was not good. Conclusions Lumbar oblique-pulling manipulation under oscillation excitation is safer than that under pulse excitation. The research findings provide doctors with a reasonable range of operating parameters for lumbar oblique-pulling manipulation under pulse excitation.

Abstract:Objective To investigate biomechanical characteristics of femoral neck fracture with different reduction qualities. Methods Three cases of Sawbones artificial femoral models were selected, and two cases of Pauwel III femoral neck fracture were modeled. Three cannulated screws were inserted into the models in the form of inverted triangle to fix the fracture. Two cases maintained different reduction qualities (defined as Model 1 and Model 2). In the 3 third case, no modeling operation was performed (defined as intact model). Then the strain gauges were respectively pasted on regions of interest of the 3 femoral models. Finally, the femur model was applied with the vertical load on mechanical testing machine. Results When the displacement of femoral head reached 4 mm, the average load of intact model, Model 1 and Model 2 was (236.30±5.35), (196.57±3.56), (69.50±2.95) N, showing significant differences. When the displacement of femoral head reached 5 mm, the average load of intact model, Model 1 and Model 2 was (276.7±3.40)，(232.93±2.64)，(80.83±4.54) N, showing significant differences. Conclusions The lower the reduction quality of the femoral neck fracture, the weaker the ability of the femur to bear stress, the higher the probability of nonunion, re-fracture and femoral head necrosis in the process of postoperative rehabilitation.

Abstract:Objective Based on the existing clinical drainage device, two novel mechanisms were designed for the connection between the drainage tube of the patient and the drainage tube of the drainage bag, so as to compare such two mechanisms and validate whether the mechanisms can meet the design requirements for clinical use. Methods Mechanism 1 used the method of electromagnetic drive to pull in and Mechanism 2 used the magnetization method of permanent magnet to pull in. The finite element model of static electromagnetic field was established. The force of the two mechanisms under different currents was compared, and the distribution of magnetic field lines and magnetic induction intensity was analyzed. Simulation experiments were designed for preliminary experimental research. Results Under the pull-in state, the maximum magnetic induction of Mechanism 1 and Mechanism 2 at the closed end surface was found in contact area of the two iron cores. The suction force of Mechanism 1 could be adjusted by the current. When the current was 1 A, the maximum magnetic induction intensity at the closed end was 0.76 T, the electromagnetic force measured by the experiment was 6.08 N, the magnetic force of Mechanism 2 was 6.68 N, which was smaller than the 8 N suture tension. Mechanism 2 was separated by supplying the driving coil with a reverse magnetic field. Conclusions When the current was 1 A, Mechanism 1 could meet the magnetic attraction requirements, and Mechanism 2 could be separated when the current reached 1.8 A. Both mechanisms met the requirements of clinical design, but Mechanism 2 was more secure in the process of application. The feasibility of the mechanism structure was verified by finite element analysis and experimental test.

Abstract:Objective To analyze characteristics of muscle activity and changes of corresponding kinematic parameters of the lower limbs for the elderly carrying heavy objects under synchronous stop modes, and explore the effects of hand weight-bearing and stop modes on gait stability and body balance of the elderly. Methods The ankle, knee, hip joint angles and surface electromyography (EMG) signals of bilateral lower limbs were collected under the condition of emergency stop and planned stop by loading 0 kg, 2.5 kg on both hands and 5 kg on right hand. Results Under different weight-bearing modes, the ankle and hip angles of bilateral lower limbs were significantly different (P<0.05), while the knee angles did not change significantly, and different stop modes significantly affected the angle changes in each joint (P <0.001); the average EMG of tibia anterior muscle, lateral femoral muscle, and biceps femoris in braking leg showed higher muscle activity during emergency stop. Conclusions In order to cope with the instability caused by weight-bearing and emergency stop, the elderly will have a corresponding balance mechanism in the lower limbs. During an emergency stop, braking the tibialis anterior muscle of the leg requires a higher muscle activity level to control flexion angle of the ankle joint, thereby reducing amplitude of the ankle joint fluctuation. The single-handed load increases the muscle performance differences between the braking leg and trailing leg, resulting in the lateral instability.

Abstract:Objective To compare the differences in plantar kinetics between older male adults and young male adults during walking, and to explore the influences of aging on plantar kinetics. Methods The in-shoe plantar sensory measurement system was used to collect and compare left foot parameters of 13 older men and 14 young men during tandem walk, including contact time, beginning of contact in percentage of roll over process (%ROP), and end of contact in %ROP, peak pressure, instant of peak pressure in %ROP, maximum mean pressure, pressure-time integral, maximum force, instant of maximum force in %ROP, mean force and force-time integral. Results Beside media arch, the contact time on all regions of older men was longer, whereas, the beginning of contact in %ROP on lateral heel, lateral arch was greater, and the end of contact in %ROP on medial heel and 2nd-3rd metatarsal head was smaller compared with young men. The maximum force and mean force on the whole foot region, and the maximum mean pressure and maximum force on 2nd-3rd metatarsal head of older people were significantly lower; the pressure-time integral on the whole foot region, the 4th-5th metatarsal head, the 2nd -5th toes, and the force-time integral on the whole foot region, medial heel, lateral heel and 2nd -5th toes were significantly higher compared with young men. Conclusions During tandem walking, plantar fascia dysfunction might be one of the main reasons for the decline of postural control ability, and the contraction enhancement of flexor digitorum longus and flexor digitorum brevis could compensate for postural stability improvement in older men.

Abstract:Objective To study the effect of gender and maneuvers on anterior cruciate ligament (ACL) injury risk factors for volleyball players. Methods Sports biomechanics data of volleyball players during stop-jump, drop landing and sidestep cutting were collected. The ACL injury rate and biomechanical parameters of simulated injured jumps were obtained with Monte Carlo simulation. The influence of gender and maneuvers on ACL injury risk factors was validated by 2×3 mixed designed two-way ANOVA. Results Sidestep cutting was the highest risk maneuver of ACL injury for both genders (P＜0.001). Compared with male players, female players had a greater risk of ACL injury during sidestep cutting and stop-jump (P＜0.001), while male players were more prone to have ACL injury than female players during drop landing (P＜0.001). The risk factors of ACL injury obtained by simulation were significantly influenced by gender and maneuvers (P＜0.001). Conclusions Male players were more likely to increase ACL load due to smaller knee flexion, forward leg tilt and heel landing than female players during sidestep cutting, while female players owned larger ground reaction force (GRF) and knee extension moment. Smaller knee flexion angle during stop jump was the major risk factor for both genders, however more characteristics contributed to the males. Female players with large GRF, knee valgus and extension moment, and heel-landing were likely to have ACL injury, while the small knee flexion angle was the key risk factor for male players. The results can provide evidences for evaluation of volleyball players’ ACL injury risk, individualized injury prevention protocols, and clinical treatment and rehabilitation directions.

Abstract:The most serious problem facing the implantation of vascular graft in the body is the formation of blood clots. In order to solve this problem, various attempts have been made by the scientific community for many years. However, endothelialization is the fundamental method to solve thrombosis and keep vascular graft open for a long time. Poly （ε-caprolactone） (PCL) has the advantages of biodegradability, low cost and good mechanical properties. In recent years, it has been widely used as tissue engineering scaffolds, drug deliverys and so on. This article mainly reviews the endothelialization of small-caliber vascular graft based on PCL after implanted in different animal models, as well as the endothelialization of the same animal model but under different implantation conditions, and trying to find the reasons why small-caliber vascular grafts are still not ideal in clinical applications at different angles such as the different animal models and the different way about endothelialization, and provide references for future animal model selection.

Abstract:Due to the effect of structural characteristics and service environment of esophageal stent, fatigue damage of esophageal stent is developed easily, which may lead to serious complications. At present, the researches on fatigue performance of esophageal stent involve load spectrum, stress-strain relationship, fatigue crack and fatigue life prediction, and there are three main research method: theoretical analysis, numerical simulation and experimental research. In this paper, various analysis methods and limitations for measuring fatigue performance of esophageal stent are elaborated and summarized in detail, and the future research of esophageal stent is prospected.

Abstract:Pelvic floor dysfunction disease has a high incidence in women after pregnancy. During this special physiological period of women pregnancy, posture of woman pelvis will change, and the pelvic biomechanics will change as well. Such mechanical changes will bring corresponding diseases. The relationship between dynamic changes and occurrence of functional disorders were discussed, the influences of changes in abdominal pelvic mechanics on the pelvic floor after pregnancy were summarized, and the high risk factors of pelvic floor dysfunction （PFD） were investigated, so as to provide the optimal treatment plans and method for pelvic floor rehabilitation treatment.