Abstract:

Abstract:

Abstract:

Abstract:Total hip arthroplasty (THA) is an effective treatment for elderly femoral neck fractures, mid- to late-stage femoral head necrosis, and end-stage hip osteoarthritis. However, serious complications such as aseptic loosening of the prosthesis, peripheral fractures, and dislocation of the prosthesis still exist following THA, which makes the selection of the appropriate hip prosthesis type and placement position before THA an important challenge for surgeons. Currently, the commonly used preoperative planning methods for THA mainly rely on static images from two-dimensional (2D) X-ray or three-dimensional (3D) computed tomography (CT), which fail to adequately consider the hip joint in weight-bearing as well as motion, lumbar-hip joint changes, and prosthetic impingement during motion. Recently, the dual fluoroscopic imaging system, as a new in-vivo, dynamic radiological imaging technology, provides comprehensive and accurate dynamic 3D data for THA preoperative planning. However, the technical process and expert consensus on preoperative 3D planning of THA using a dual fluoroscopic imaging system have not yet been established, which affects the promotion and application of this technology. In light of the above, national orthopaedic experts and related professional representatives discussed and proposed seven consensus issues, and the ‘expert recommendation rate’ and ‘strong recommendation rate’ were obtained through a questionnaire survey on the recommendations of the participating experts. This consensus aims to provide guidance and reference for the standardised application of preoperative 3D planning of THA using the dual fluoroscopic imaging system.

Abstract:Injury biomechanics is an interdisciplinary field that studies the biomechanical responses and injury mechanisms of the human body under external loads. The goal is to provide scientific foundations for the prevention, diagnosis, and treatment of human injuries. This field is widely applied in clinical medicine, sports science, rehabilitation engineering, traffic safety, aerospace, and other domains. In this review, the research progress in injury biomechanics in the year 2023 is summarized, focusing on in-depth analysis of injury mechanisms, innovations in injury prediction and protective countermeasure, and the latest applications of injury diagnosis and rehabilitation technologies. By systematically reviewing the research advancements, this review aims to offer new directions and ideas to the continued development of injury biomechanics and promote interdisciplinary collaboration and technological innovation.

Abstract:Objective To study the protective effect of helmet on human head injury under continuous frontal blast shock wave. Methods A finite element head-helmet coupling model was established to analyze the effects of helmets on biomechanical response parameters such as intracranial pressure and cranial pressure under single frontal blast and continuous frontal blast shock wave. The dynamic changing law of brain tissues in the blast environment was discussed to evaluate the protective performance of helmets on human head. Results In the case of single frontal blast impact, the helmet could effectively reduce intracranial pressure in the frontal lobe, occipital lobe, and parietal lobe by 32%, 38%, and 19%, respectively, as well as peak stress at the rear of the skull. In the case of continuous frontal blast impact, the helmet could reduce intracranial pressure in the parietal lobe and occipital lobe by 36% and 21%, respectively, but its effect on intracranial pressure in the frontal lobe was limited due to the lack of facial protection. Conclusions Compared to single blast shock wave, continuous frontal blast shock wave has a more severe impact on craniocerebral injury due to its long effective effects on the head. Since the shock wave propagates from different directions and heights, the protective effect of the helmet on the face is minimal. This study can provide important references for biomechanical research of human head injury under continuous frontal blast shock wave and the design of new helmets.

Abstract:Objective To provide basic data for developing automobile crash safety standards with Chinese human body characteristics, the influence of the muscle active force on the kinematic response of an occupant's head and neck under load impact was investigated. Methods Based on computed tomography (CT) images of 50th percentile male volunteers with Chinese physical characteristics, a finite element model of the neck containing the cervical vertebrae, muscles, and fat was constructed. The validity of frontal and side impact simulation was verified, and a beam unit was added to the model to simulate the active force of neck muscles. Results The developed neck model consisted of 143 793 units and 165 077 nodes. The simulation experimental data were consistent with the trend of volunteer experimental data, which had a good consistency and verified the effectiveness of the model. A comparison of the simulation results of the activated and passive models showed that the peak motion of the activated model was lower than that of the passive model. On the side impact, the horizontal displacement of the head of the activated model in the y-direction on the coronal plane did not fully match the experimental channel of the volunteer. Conclusions The muscle active force can maintain the posture and stability of the body. The activation curves, as well as the muscle active force produced by different individuals, vary owing to the different physiological cross-sectional areas of the muscles and other factors. The finite element model of the male neck developed in this study is based on the most recent statistical data of male physiques in China. It has a detailed anatomical structure and high biological fidelity. The model can be used to study the neck injury mechanisms of medium-sized Chinese male physiques.

Abstract:Objective To evaluate the effect of helmet on biomechanical responses of pilot’s intervertebral disc under vibration environment. Methods A porous media finite element model of C5-6 segment was established based on the computed tomography (CT) images of an adult. Four loading conditions (A, B, C helmets and No helmet) were applied to the validated model with a duration of 3 600 s for vibration analysis. Considering the effects of vibration frequency, the maximum porous pressure (MPP) and maximum principal stress (MPS) of nucleus pulposus (NP) and annulus substance (AS) were obtained. Results The MPP of NP and AS decreased and became stable under the same vibration frequency. The MPS of NP and AS for B helmet was the maximum, followed by C helmet, A helmet and No helmet. The curve of MPS for B helmet was higher than that of C helmet, A helmet and No helmet. At the vibration frequency of 5 Hz and 9 Hz, the MPS of AS under four helmet conditions increased with time, and reached a constant value after 1 200 s. Under the same helmet condition, after loading for 1 200-2 400 s, the MPS of NP at 9 Hz vibration frequency was higher than that at 5 Hz and 1 Hz. The MPS of AS at 9 Hz and 5 Hz was close to each other, and both were higher than that at 1 Hz. Conclusions The helmet has an important effect on the MPP of NP and AS, and the increase of vibration frequency will lead to the increase of the MPS of AS.

Abstract:Objective To investigate the changing law of mechanical responses of herniated lumbar intervertebral disc under automobile vibration. Methods Herniated and healthy intervertebral disc specimens were made using the sheep lumbar spines. The specimens were compressed in flexion/vertical posture to simulate the stress state of the driver’s lumbar spine in different sitting positions, and then the creep experiments were carried out on this basis. The viscoelastic mechanical behaviour of lumbar intervertebral discs during dynamic creep was described using a standard linear solid model, the dynamic creep strain, strain rate, elastic modulus were calculated, and the physical significance of the constitutive equations was analyzed. Results The dynamic creep strain of the herniated lumbar disc specimen was significantly larger than that of the healthy specimen, while the amplitude was basically unchanged; the vibration acceleration had basically no effects on the dynamic creep strain, while it had a significant effect on the amplitude; the forward flexion mode had a slight effect on the dynamic creep strain, while it had a significant effect on the amplitude. The results of the present constitutive equation calculations were in agreement with the results of the experimental tests. Conclusions This study provides important theoretical guidance for the prevention of low back pain diseases in car drivers.

Abstract:Objective To evaluate the biomechanical mechanism of naso-orbito-ethmoid (NOE) combined with zygomatic fractures and weakness of the midfacial bone to provide a theoretical basis for protection against maxillofacial trauma. Methods: CT data of a young male with normal cranio-maxillofacial bones were collected. Then, a human cranio-maxillofacial finite element model was reconstructed using Mimics and other software. The nasal bone, medial suborbital margin 1/3, zygomatic bone, and frontal maxilla were impacted at a critical velocity of 16 m/s, and impact fractures were simulated. The direction of force conduction, biomechanical variations in the bones, and biomechanical mechanism of naso-orbito-ethmoid combined with zygomatic fractures at different impact velocities in the middle of the face were analyzed. Results Under different working conditions, the stresses in the NOE region with the zygomatic bone exceeded the threshold of 150 MPa when the medial side of the inferior orbital margin 1 / 3 and the intersection of the frontal maxilla were impacted at an initial velocity of 16 m/s. Under other working conditions, the stresses in the NOE region and the zygomatic bone did not exceed 150 MPa simultaneously. Conclusions NOE combined with zygomatic fractures is mostly related to high-energy impact. This occurs straightforwardly under a high-speed impact on the intersection of the frontal maxilla and the medial margin of the inferior orbit. The inferior orbital wall is a relatively weak area in the middle of the face.

Abstract:Objective To study the effects of an abnormal mechanical load in the developmental dysplasia of the hip (DDH) on the bone microstructure and blood vessels of the subchondral bone, and the correlation between bone microstructure and blood vessels. Methods A newborn rat DDH model was constructed using the swaddling method. Histological staining such as hematoxylin-eosin staining, safranin-fast green staining, and immunohistochemical staining was performed on the articular cartilage and subchondral bone of the femoral head. The microstructure of the subchondral bone was analyzed using microcomputed tomography (micro-CT). Results The DDH rats showed degeneration of the articular cartilage accompanied by deterioration of the microstructure of the subchondral bone, decreased bone formation, and increased vascular formation. The level of vascular formation in the subchondral bone was positively correlated with the degree of deterioration of the bone microstructure. Conclusions An abnormal mechanical load in the DDH causes articular cartilage degeneration, increased vascular formation in the subchondral bone, and subchondral bone microstructure deterioration. A correlation analysis revealed that the abnormal vascular formation in the subchondral bone may be an important factor causing the deterioration of bone microstructure and progression of DDH. This study has provided a new direction for the development of DDH.

Abstract:Objective The stress variations during the wear process of an artificial knee joint were studied. Then, a signal acquisition system was designed to capture the vibration signals induced by the wear of knee joint prosthesis. The aim was to provide new technical means for online wear monitoring of the artificial knee joint. Methods To effectively collect vibration signals, the optimal installation position of the vibration sensors was determined by analyzing the dynamic model of the knee joint prosthesis during motion and identifying the main distribution areas of the tibial insert contact stress. The dynamic model of the femoral prosthesis was solved using Lagrangian equations. The torque variation curve of the femoral prosthesis was obtained to validate the effectiveness of finite element analysis. The signals collected by the vibration sensors installed at different positions in the friction wear experiments and the surface morphology in different areas were compared to verify the effectiveness of the acquisition system design and finite element analysis results. Results The stress concentration regions of the tibial pad under four degrees of freedom (flexion, internal and external rotation, anterior-posterior displacement, and up-and-down displacement) were obtained based on a dynamic simulation. A stress concentration was evident in the middle and posterior regions of the tibial pad. A vibration signal with a higher amplitude was collected when the vibration sensor was installed at the rear end of the tibial pad. This aided the vibration feature extraction of the knee joint prosthesis. Conclusions The vibration signal acquisition system designed based on the dynamic simulation analysis effectively collected the vibration signals generated by the artificial knee joint during the wear process. This study provides an important means for evaluating the wear mechanisms of artificial knee joints and monitoring their full-life health status.

Abstract:Objective To analyze and compare the differences between 3D-printed patient-specific instrumentation (PSI)-assisted medial open-wedge high tibial osteotomy (OWHTO) and conventional medial OWHTO in terms of the postoperative mechanical stability, accuracy of weight-bearing alignment adjustment, and clinical outcomes. Methods: Data from patients diagnosed with knee osteoarthritis (KOA) and undergoing OWHTO from Jan. 2019 to Jan. 2022 were collected. The patients were divided into the conventional method group (23 individuals) and 3D-printed PSI-assisted group (18 individuals) based on the surgical methods. The accuracy of correction between the two methods was evaluated by comparing the preoperatively planned target correction of the hip–knee–ankle (HKA) angle with the postoperative HKA angle difference. The preoperative posterior tibial slope (PTS) and postoperative PTS angle differences were also assessed. The clinical efficacy of the two methods was assessed by collecting and analyzing the Lysholm score, visual analog scale (VAS), and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) of the patients in both the groups prior to surgery and at the 1st, 6th, 12th, and 24th month postoperatively. The occurrence of postoperative complications in both the groups was analyzed to evaluate the safety of PSI-assisted OWHTO. Results: The demographic characteristics, preoperative imaging observations, and clinical symptoms were similar between the two groups (P>0.05). With regard to the results of correction accuracy, the postoperative HKA angle difference was 2.7°±1.8° in the conventional OWHTO group and 0.8°±1.1° in the 3D-printed PSI-assisted OWHTO group (P<0.001). The postoperative PTS angle difference was 2.8°±2.2° for conventional OWHTO and 1.7°±1.9° for PSI-assisted OWHTO (P=0.003). In terms of clinical efficacy, the surgical time of the PSI-assisted group was 59.2±14.8 min. This was significantly shorter than that of the conventional method group (87.6±21.4 min) (P=0.019). The Lysholm, VAS, and WOMAC scores of the PSI-assisted group were superior to those of the conventional method group at each postoperative follow-up visit. With regard to postoperative complications, there were four cases (17.3%) in the conventional method group and three (16.7%) in the PSI-assisted group. The statistical difference between the two groups is not significant. Conclusions Compared with the conventional method, 3D-printed PSI-assisted OWHTO demonstrated superior accuracy in correcting lower limb alignment, in conjunction with favorable clinical efficacy and safety. This study has provided an effective reference for clinicians in selecting surgical treatment plans.

Abstract:Objective To investigate the effects of the patellar height and tilt angle on the long-term knee joint mobility after total knee arthroplasty (TKA). Methods Totally, 116 patients who underwent TKA without patellar replacement at Xuzhou Medical University Affiliated Hospital between January 2020 and December 2022 were included. Based on the recovery of the knee joint range of motion (ROM) within a year after surgery, the patients were divided into a normal knee ROM (knee ROM ≥ 120°) group (42 cases) and descending knee ROM (knee ROM<120°) group (74 cases). A year after the surgery, the patellar heights and tilt angles of the two groups of patients were compared. The recovery status of knee function and pain between the two groups of patients at the third month and first year after surgery were recorded. Results None of the 116 patients had nerve, vascular, or ligament injuries after surgery. Moreover, no patellar dislocation or infection occurred. The incision healed well in the first postoperative period. An year after surgery, the Insall-Salvati ratio of patellar height and patellar inclination of the patients in the normal group was lower than that of the patients in the descending group (P<0.05). Prior to surgery, at the third month and first year after surgery, the HSS scores of knee function increased gradually in both the patient groups. The HSS scores of the normal group were higher than those of the decreasing group (P<0.05), the knee pain scores of both the groups decreased gradually, and the pain scores of the normal group were lower than those of the decreasing group (P<0.05). The patellar height and inclination were risk factors for decreased knee ROM after TKA (P<0.05). Conclusions Patients who underwent TKA without patellar replacement experienced a decrease in knee ROM after surgery. This is associated with an increase in the patellar height and tilt angle.

Abstract:Objective To investigate the creep effect of ultrahigh-molecular-weight polyethylene (UHMWPE) liners on the wear of hip prostheses under different physiological activities. Methods A finite element model of a cobalt-chrome alloy (CoCr) head and UHMWPE liner was established and validated. The effects of the ISO 14242 standard gait and daily activities (standing up/sitting down, climbing stairs, and knee bending) on prosthesis wear and creep were compared and analyzed. Results Under the ISO 14242 standard gait, the maximum contact pressure of the liner decreased from 18.3 MPa to 12.2 MPa when creep was not considered, and from 15.3 MPa to 14.2 MPa when it was considered. The maximum linear penetration depths owing to wear and creep were 0.47 mm and 0.11 mm, respectively, with a wear volume of 205 mm3. The wear during different physiological activities was ranked as follows: climbing stairs > standing up/sitting down > ISO standard gait > knee flexion. The creep was ranked as follows: ISO standard gait > stair climbing > knee bending > standing up/sitting. Conclusions The wear and creep of the acetabular liner differed significantly under different physiological activities. The maximum contact pressure of the UHMWPE liner was reduced by the creep effect. This, in turn, decreased the wear volume. Both creep and wear should be considered in the design of hip prostheses to optimize their performance and extend their service life.

Abstract:Objective A simplified pelvic model of a patient was established, and periacetabular osteotomy (PAO) was simulated to investigate its effects on the stress in the sacroiliac joints in the standing position. Methods The anterior center edge angle (ACEA) and lateral center edge angle (LCEA) of the patient’s hip model were adjusted, and 27 postoperative models were obtained. Finite element calculations and analyses of each model were performed during single-leg standing and double-leg standing. Furthermore, an investigation of the stress variations and distributions on the sacroiliac cartilage was conducted in combination with a hip joint stress analysis. Results During single-leg standing, the maximum stress on the sacroiliac cartilage of a healthy individual was 18.2 MPa. With an increase in the anterior center edge angle (ACEA), the von Mises stress of the sacroiliac cartilage decreased from 34.5 MPa to 19.8 MPa. The maximum von Mises stress in the acetabular cartilage decreased from 4.767 MPa to 2.7 MPa. Before the ACEA attained 36°, the maximum von Mises stress exhibited a downward trend. After it attained 36°, the stress distribution began to increase, and the stress distribution improved significantly. During double-leg standing, the minimum and maximum von Mises stresses on the sacroiliac cartilage of the affected leg side was 2.8 and 6.5 MPa, respectively. The sacroiliac cartilage stress on the normal leg side did not vary significantly, and the stress difference between the two leg sides decreased gradually. Conclusions PAO can improve the hip joint stress and sacroiliac joint stress. Additionally, the improvement of sacroiliac joint stress is identical to that of hip joint stress. Prior to surgery, a comprehensive planning of the hip and sacroiliac joints can be used as a reference by doctors. This is of high significance for patients with developmental dysplasia of the hip (DDH) to achieve better outcomes.

Abstract:Objective To evaluate the biomechanical properties of the bilateral pedicle screw (BPS) and bilateral modified cortical bone trajectory screw (BMCS) fixation techniques in the posterior lumbar interbody fusion (PLIF) model of the L4–5 segment. Methods Finite element models of the L1–S1 lumbar spine were established using three cadaveric lumbar spine specimens. BPS-BPS (TT at the L4–5 segment), BPS-BMCS (TT at the L4 segment and MCBT at the L5 segment), BMCS-BPS (MCBT at the L4 segment and TT at the L5 segment), and BMCS-BMCS (MCBT at the L4–5 segment) were implanted into the finite element model. The range of motion (ROM) at the L4–5 segment and the peak von Mises stress on the internal fixation system, cage, and connecting rods were compared under bending, extension, flexion, and rotation conditions with a 400 N load and 7.5 N·m torque. Results The BMCS-BPS group showed lower ROM and von Mises stress on the cage, internal fixation system, and connecting rods under rotational conditions than the BPS-BPS, BPS-BMCS, and BMCS-BMCS groups. The BPS-BMCS and BMCS-BPS groups had significantly reduced ROM of the L4–5 segment under bending and rotational conditions compared with the BPS-BPS group, and significantly decreased ROM under rotational conditions compared with the BMCS-BMCS group. The BPS-BMCS and BMCS-BPS groups had a significantly reduced risk of cage subsidence under bending conditions compared with the BPS-BPS group, and under rotational conditions compared with the BMCS-BMCS group. The BPS-BMCS and BMCS-BPS groups had a significantly reduced risk of connecting rod fractures under bending and rotational conditions compared with the BPS-BPS and BMCS-BMCS groups. This enhanced the stability of the internal fixation system. Conclusions PLIF combined with the BPS-BMCS and BMCS-BPS fixation techniques can provide better stability for the internal fixation system and vertebral body as well as a lower risk of cage subsidence and connecting rod fracture during bending and rotation in the human body. This would improve the success rate of surgery and recovery effect of patients.

Abstract:Objective To evaluate the optimal traction amount for treating scoliosis using halo pelvic ring traction (HPRT) and provide theoretical references for clinical surgical assessment and rehabilitation. Methods A three-dimensional (3D) model of the thoracolumbar spine including the spinal cord was created and validated. Five traction amounts (10, 15, 20, 25, 30 mm) were applied to the model. The biomechanical responses of the spine under different traction conditions were simulated to determine the optimal amount of traction. Results As the traction increased, the Cobb angle decreased progressively. Significantly, in the range of 15–20 mm, the reduction in Cobb angle accounted for 50–70.5% of the maximum reduction. The spinal stress at the main curvature represented 47.4%–67.5% of the maximum stress. Meanwhile, the stresses in the gray and white matter of the spinal cord were 70.3%–84.5% and 68.8%–83.9% of their respective maximum stresses. Conclusions The traction amounts between 15 mm and 20 mm are optimal for treating scoliosis. This range maximizes the Cobb angle correction while maintaining lower stress levels and thereby, reduces the risk of damage to the spine and spinal cord.

Abstract:Objective To investigate the biomechanical characteristics of orthodontic tooth movement at different alveolar bone heights and provide a theoretical reference for orthodontic clinical treatment. Methods Four groups of mandibular dentition finite element models were established: the normal alveolar bone height, and 1/3, 1/2, and 2/3 reductions in height. The lingual, distal, and intrusion movements of the mandibular central incisor were simulated under different loads. The distribution and variations in periodontal stress and tooth displacement were analyzed. Results Under three movements, the degree of stress concentration in the cervical area of the tooth and the periodontal equivalent force increased as the alveolar bone height decreased and the orthodontic force increased. Meanwhile, the displacement at each observation point and the crown–root displacement difference increased, and the tendency for inclination movement of the teeth aggravated. When the alveolar bone height was reduced to 2/3, the orthodontic force under lingual and distal movement increased to 150 g and that under intrusion movement increased to 100 g. The periodontal equivalent force increased to the maximum value, and the tendency of tooth inclination movement was most significant. Conclusions　A reduction in the alveolar bone height aggravates the stress concentration at the top of the alveolar ridge and the tendency for inclination movement of the teeth. For orthodontic patients with an inferior periodontal condition, the orthodontic force should be reduced according to the alveolar bone height to ensure a safe and effective orthodontic treatment.

Abstract:Objective The progressive loading process of implants was simulated, and the influence of progressive loading methods on peri-implant bone reconstruction was evaluated. Methods Using finite element analysis combined with the ANSYS parametric design language (APDL), the average bone density of the peri-implant regions was observed using conventional loading (control group) and progressive loading (experimental group) within six months of implant placement. The biomechanical effects of bone tissues in a 1 mm3 region of interest (ROI) around the implant and variations in bone density were observed. Results Within six months after implantation, the cortical bone density of the control group decreased by 0.19 g/cm3, whereas that of the experimental group decreased by 0.15 g/cm3. The trabecular bone density of each area in the experimental group increased by 0.4 g/cm3 compared with that in the control group. The bone density in the experimental group was lower than that in the control group. The increase in cancellous bone in the experimental group was higher than that in the control group. The finite element analysis revealed that the equivalent stress distribution range and maximum value of the experimental group (8.9 MPa) were significantly higher than those of the control group (6.68 MPa). Conclusions The use of the progressive loading method within six months after implantation was conducive to the distribution of stress on the bone tissues around the implant. This reduced the variation in bone density at the edge of the implant. The peri-implant bone density increased more under progressive loading than under conventional loading. The effect is superior to that of the conventional loading method.

Abstract:Objective To predict the stress on the anterior cruciate ligament (ACL) in the left leg of a volleyball player during ball-snapping landing, using an XCM deep neural network model. Methods A complete finite element model of the knee joint was established based on magnetic resonance (MR) and CT images. The kinematic and kinetic data of the volleyball player were collected synchronously using an eight-lens Qualisys motion capture system and a Kistler three-dimensional (3D) force platform. The knee joint moments were calculated using the musculoskeletal model in OpenSim. The joint moments were used as the input to the finite element model, with ACL stresses as the output. The kinematic and kinetic data were used as the input for the neural network, with ACL stress as the output. Results The peak equivalent ACL stress of the volleyball player during ball-snapping landing was (27.7±0.36) MPa, the maximum principal stress was (8.2±0.23) MPa, the maximum shear stress was (14.7±0.32) MPa, the equivalent strain was (5.7±0.008)%, the maximum principal strain was (5.0±0.006)%, and the maximum shear strain was (7.6±0.009)%. The normalized root mean square error (NRMSE) between the predicted and calculated values ranged from 5.84% to 7.12%. The root mean square error (RMSE) ranged from 0.251 to 0.282. Conclusions The XCM model can predict the ACL stress during volleyball spikes within a certain range. This study has provided a new method to obtain biomechanical data on volleyball players as well as an effective method to help volleyball players prevent ACL injuries.

Abstract:Objective To explore the effect of transcranial direct current stimulation (tDCS) regulating the motor cortex on the performance of endurance exercise with incremental loading. Methods A randomized, double-blind, parallel control design was adopted. Forty healthy adults were randomly divided into real stimulation (lasting 20 min) or sham stimulation groups (30 s slow-rise and 30 s slow-fall stimulation provided within the 1st 1 min only). The multifocal tDCS was used, with seven small electrodes (3.14 cm2 round electrodes) placed in the primary, premotor, and supplementary motor areas to modulate motor cortex excitability. The injection current of a single electrode did not exceed 1 552 μA, and the total currents did not exceed 3 998 μA. Baseline tests on incrementally loading exercises were performed before and after the intervention, with an interval of 48 hours between the two tests. Two-way ANOVA was used to analyze the effects of this tDCS protocol on duration of cycling, power output, and revolution speed. Results All subjects completed the experiment without unexpected adverse effects. The overall accuracy rate of subjective guess was 37.5%. There was no significant difference in duration of cycling or power output between the two groups (P>0.05), and within-group statistics showed an increase in revolution speed after the real stimulation (P=0.012). Conclusions tDCS that targets and modulates the motor cortex can improve the revolution speed during cycling exercise with incremental loading in healthy adults, suggesting that this stimulation protocol may be a potential means of improving exercise efficiency in endurance sports.

Abstract:Objective To determine the acute effects of heel-to-toe drops of running shoes on the loading of the patellofemoral joint and Achilles tendon (AT) in runners with patellofemoral pain (PFP) during running. Methods Sixteen runners with PFP completed a running test while wearing running shoes with different heel-to-toe drop values. The retroreflective markers and ground reaction force were measured using an infrared motion capture system and a three-dimensional force plate. The patellofemoral joint stress (PFJS) and AT force were calculated based on biomechanical models of the patellofemoral joint and AT. Results When runners with PFP ran in negative heel shoes, the PFJS (P<0.001) during 39%–47% of the stance phase, maximum PFJS, and cumulative PFJS (P<0.05) during the stance phase were lower than those in positive heel shoes. Meanwhile, the AT force (P<0.001) and cumulative AT force (P=0.001) during 12%–46% of the stance phase were larger than those in positive heel shoes. The AT force (P<0.001) and cumulative AT force (P=0.023) in the negative-heel shoes during 12%–31% of the stance phase were higher than those in the zero-heel shoes. Conclusions Compared with runners with positive-heel shoes, runners with PFP running in negative-heel shoes had decreased PFJS and cumulative PFJS. This may potentially reduce the risk of further development of PFP. However, compared with zero- and positive-heel shoes, running in negative-heel shoes increases the AT force and cumulative AT force. This may increase the risk of AT injury. Runners with PFP are recommended to undergo acclimatization before shifting to negative-heel shoes. This would limit further progression of PFP without increasing the risk of AT injury.

Abstract:Objective To explore whether the medalists in 1 500-m freestyle swimming choose different pacing strategies from their competitors, so as to determine the most effective pacing strategy characteristics to obtain victory in swimming race. Methods The 1 500-m freestyle finalists in World Swimming Championships from 2003 to 2023 were selected as candidates of this study. According to the final ranking of the 175 elite athletes in the race, the split time, cumulative time were calculated, respectively. The differences of the main indicators in pacing strategies between medalists and their competitors were compared, and the above variables were selected Objective To explore whether the medalists in 1 500-m freestyle swimming choose different pacing strategies from their competitors, so as to determine the most effective pacing strategy characteristics to obtain victory in swimming race. Methods The 1 500-m freestyle finalists in World Swimming Championships from 2003 to 2023 were selected as candidates of this study. According to the final ranking of the 175 elite athletes in the race, the split time, cumulative time were calculated, respectively. The differences of the main indicators in pacing strategies between medalists and their competitors were compared, and the above variables were selected

Abstract:Objective To analyze the symmetry characteristics of gait dynamics, kinematics, and spatial and temporal parameters in children with mild leg length discrepancy (LLD) and evaluate the likely influence or risk of LLD on children’s growth to provide a theoretical basis for early assessment and intervention. Methods Using a modified conventional three-dimensional model, 31 markers were placed on the body surface of each subject to collect the gait parameters and calculate the symmetry index (SI). The spatial distance of the ipsilateral markers between the anterior superior iliac spine-external knee-external ankle in the standing position was recorded as the leg length. Then, 59 children with leg length difference in the range of 0.5 cm

Abstract:Objective To study the differences in dynamic stability characteristics between older and young adults during continuous turning and walking in different directions. Methods Fifteen healthy older adults and 15 healthy young adults were recruited to complete continuous clockwise and counterclockwise figure-of-8 walk. A three-dimensional motion capture system was used to collect kinematic data based on 43 bone markers. The gait and velocity of the center of mass parameters were determined using V3D software. The anterior and medial margins of stability at characteristic moments were calculated. Results Compared with clockwise turning, the step width of the inner leg increased and the anterior margin of stability of the inner leg at the toe-off instant decreased during counterclockwise turning in young adults. Meanwhile, there were no significant differences in the above parameters for older adults. Conclusions Both the age and turning direction affected the forward dynamic stability of the inner leg at the toe-off instant. Healthy older adults adopted more cautious strategies to maintain anterior and medial stability during continuous walking. It is recommended that older adults should increase turning training in daily life to improve their medial-lateral control capability and confidence in turning.

Abstract:Objective To evaluate the molecular mechanisms by which dendritic cells (DCs) detect variations in the extracellular mechanical microenvironment and dynamically adjust their migration behavior. Methods Hydrogel substrates with varied stiffness were constructed to investigate the influence of the mechanical microenvironment on the DC migration behavior. A fibrotic rat liver model was established in combination with immunohistochemistry experiments to investigate the effect of liver fibrosis on the DC migration capability. Furthermore, potential key molecules involved in the mechanical sensing cascade during DC migration were analyzed using single-cell sequencing data from human/mouse fibrotic livers. Moreover, RT-qPCR was used to examine the expression levels of these key molecules in mouse DCs on substrates of different stiffness. Results The migration capability of DCs on stiff substrates was significantly lower than that on soft substrates. The DC infiltration in fibrotic rat livers increased, and 682 differentially expressed genes (DEGs) were observed between liver-infiltrating DCs from cirrhosis patients and normal individuals. Furthermore, focusing on genes relevant to cytoskeleton regulation and migration based on KEGG and GO pathway enrichment analysis, 12 potential key molecules mediating stiffness detection during DC migration were identified. Among these, the expression levels of AIF1, GPR65, MYL12B, RAC1, and RHOG were upregulated in patients with liver cirrhosis, whereas those of ACTB, ACTG1, ARF6, CDC42, COTL1, PFN1, and TMSB10 were downregulated. Subsequently, the expression levels of ACTB and CDC42 were downregulated in mouse DCs grown on stiff substrates. This was consistent with the circumstance of liver-infiltrating DC in human cirrhotic patients. Conclusions Liver fibrosis potentially impairs DC migration and thereby, results in increased DC infiltration. ACTB and CDC42 are potential regulators of DC stiffness during migration. This study has provided a theoretical basis and an inspiring novel strategy for optimizing DC-mediated antitumor immune functions.

Abstract:Objective To investigate the mechanism and molecular structural basis of the tension-regulated interaction between ICAP1 and β1 integrin. Methods Based on the crystal structure data of the ICAP1/β1 integrin cytoplasmic tail complex (PDB ID: 4DX9), tensile molecular dynamics simulations were conducted to observe and analyze the effects of tension loading on β1 integrin on the structure and binding affinity of the ICAP1/β1 integrin complex. Results The tension modulated the dissociation of the ICAP1/β1 integrin complex bidirectionally by inducing local conformational variations at the binding interface. It initially increased and then decreased the binding affinity of β1 integrin for ICAP1. The threshold point occurred at 10 pN. The main tension-sensitive residue interactions were primarily located among ARG140-THR789, MET141-THR789, and ASP145-SER785. Conclusions As the tension applied to the cytoplasmic tail of β1 integrin increases, the conformational variations at the binding interface result in an initial enhancement followed by a reduction in the inhibitory effect of ICAP1 on β1 integrin activation. A tension threshold of 10 pN was observed. This indicated that force-induced integrin activation requires sufficient mechanical stimulus strength. This study has provided a new approach for the development of antibody drugs targeting β1 integrins.

Abstract:Objective To study the effect of a curved hollow-fiber bioreactor on the mass transfer in an artificial liver to provide references for the optimal design of new bioreactor structures and operation parameters for clinical treatment. Methods A computational fluid dynamics (CFD) model of a hollow fiber bioreactor was established using numerical simulation. The diffusion and convection mass transfer in the hollow fiber bioreactor were considered by the K-K equation and Darcy’s law. The effects of the bending count and bending amplitude on the mass transfer behavior in a hollow fiber bioreactor were analyzed. Results Dean vortices were generated in the curved hollow fiber bioreactor owing to the centrifugal force. This promoted solute remixing in the tube and thereby, diffusion mass transfer. Meanwhile, the higher transmembrane pressure in the curved hollow fiber bioreactor also promoted convection mass transfer. Consequently, the Dean vortices and high transmembrane pressure increased the solute clearance rate. When the bending counts were 0, 3, 6, 9, and 12 and the bending amplitude was 1 mm, the bilirubin clearance rates were 113.44, 117.95, 121.89, 129.89, and 140.57 mL/min respectively. When the bending amplitudes were 0, 0.5, 1, 1.5, and 2 mm and the bending count was three, the bilirubin clearance rates were 113.44, 115.45, 117.95, 120.16, and 123.14 mL/min, respectively. Conclusions The curved hollow fiber bioreactor improved the toxin removal efficiency in the artificial liver.

Abstract:Due to good biocompatibility and mechanical properties similar to those of natural biological tissues, hydrogels have been widely used in biomedical fields. With the development of biomechanics, more and more researches have found that the viscoelastic tunable composite hydrogels based on dynamic covalent bonds can better simulate the viscoelastic mechanical properties of biological tissues and natural extracellular matrix over time due to their superior biomechanical properties and stimulus responsiveness. This review summarizes in detail the applications of viscoelastic tunable composite hydrogels based on different types of dynamic covalent bonds (imide bonds, disulfide bonds, borate ester bonds, etc.) in the fields of regulating cell function, affecting tissue regeneration and repair, as well as drug delivery. The challenges and opportunities for future research are also proposed.

Abstract:In recent years, the role of temporomandibular joint (TMJ) motion in overall health of the orofacial system has increasingly captured the attention in the fields of oral medicine and rehabilitation medicine. The quantitative analysis of TMJ kinematics is crucial for understanding and treating orofacial functional disorders. This review summarizes the advancements in electronic axiography, optical motion capture, and dual-fluoroscopy technologies in clinical and research applications over the past decade. Electronic axiography and optical motion capture technologies, known for their high precision and real-time feedback, have been widely utilized in analyzing TMJ motion characteristics, evaluating treatment outcomes, and optimizing therapeutic techniques. dual fluoroscopic imaging system (DFIS) tracking technique demonstrates high accuracy and repeatability in analyzing complex joint motions. Although these technologies still face challenges regarding operational complexity, data stability, and safety, ongoing developments in motion analysis techniques and in-depth studies of orofacial system functions are expected to significantly enhance the precision and personalization of diagnostics and treatments for orofacial system diseases in the future.

Abstract:Preoperative planning, intraoperative navigation, and postoperative rehabilitation of total hip arthroplasty (THA) have been significantly enhanced by the integration of artificial intelligence (AI) technology. This review summarizes the latest advancements in AI technology for medical image segmentation and registration, with a particular focus on its application in THA. The notable differences between medical and natural images present challenges for the design of AI algorithms. Deep learning techniques, especially CNN, U-Net, and Transformer models, have demonstrated an outstanding performance in various medical image segmentation and registration tasks. The AI technology, through deep learning analysis of CT images, has significantly improved the accuracy of identifying hip pathologies. In terms of intraoperative guidance, AI systems provide real-time navigation and precise positioning for surgeries by utilizing intelligent segmentation and motion state simulation, effectively enhancing surgical efficiency. AI technology also encompasses surgical cost prediction and postoperative recovery, offering robust data support for medical decision-making through methods such as Markov models. As deep learning technology continues to advance, the analysis of medical images is progressively achieving automation and intelligence, which has significant clinical implications for improving patients’ overall surgical experiences and outcomes, suggesting potential new breakthroughs in the field of medical imaging in the future.

Abstract: