Objective To explore the influence of child head injury under different impact angles by applying the finite element model of six-year-old child pedestrian as specified in the European New Car Assessment Programme (Euro NCAP). Methods Based on the finite element model of 6-year-old pedestrian with detailed anatomical structure as specified by the Euro NCAP (TB024), four groups of simulation experiments were set up to explore the mechanism of head injury in children under different impact angles. The initial position for head mass center was on the longitudinal center line of the car. The initial speed of the car was 40 km/h. The car contacted with the model from the direction of the right (0°), the front (90°), the left (180°) and the back (270°). The kinematics differences and head impact responses were compared, and injuries of the facial bone and skull were analyzed. Results Through the analysis of head contact force, acceleration of head mass center, resultant velocity of head mass center with the vehicle, head injury criterion (HIC15), facial bone fracture and skull stress distribution, it was found that the risk of head fracture and brain contusion under back impact and front impact was higher than that under side impact. The risk of head fracture and brain contusion was highest under back impact, while the lowest under side impact. Conclusions Child pedestrian head injury was the largest under back impact. The results have important application values for the assessment and development of car-pedestrian collision protection device.

Objective To study the influence of the distance of displaced fragment on the union of diaphysis fracture. Methods A wedge-shaped bone fragment was taken from central radial of the right forelimb of 120 New Zealand white rabbits for estabhshment of experimental animal model. The bone fragment was fixed to the main bone with two Kirschner wires, with certain space between bone fragment and the main bone. Then, the rabbits were divided into five groups, ie, Group A (in situ fixation),Group B (the space was 1/5 diameter of the radial shaft), Group C (the space was 2/5 diameter of the radial shaft), Group D (the space was 3/5 diameter of the radial shaft), Group E (the space was 4/5 diameter of the radial shaft). The animals were killed at 2, 4, 6, 8 weeks after operation. X-ray photos were taken to observe the fracture healing and the improved Gary X-ray used for scoring. HE staining after tissue section was employed to observe the histomorphological changes of fracture healing. Immunohistochemical method was used to determine expression of BMP-2. Results X-ray findings showed insignificant statistical difference between Group A and Group B, delayed union in Groups C and D and nonunion of bone absorption in Group E. Morphological observation showed same change in fracture site in Groups A and B lout significant late in emergence, formation and remodeling of the callus in the other groups compared with Group A, mainly with delayed fracture union or nonunion. There was no statistical difference in expression of BMP-2 between Group B and Group A (P ＞ 0. 05), but there was statistical significance in Groups C, D and E compared with Group A at 2 weeks (P ＜0.01). There was statistical difference between Group E and Group A at 4 weeks (P ＜0. 01) but no statistical difference at 6 and 8 weeks between either two groups (P ＞ 0. 05). Conclusions The distance of displaced fragment will influence fracture healing. The larger distance of the displaced fragment will beget more obvious influence on fracture healing. When the distance is more than 2/5 diameter of the bone shaft, the fracture will present union disorder.

Objective To explore the imaging findings and diagnostic values of X-ray, CT, MR,and ultrasonography in traumatic knee joints hemarthrosis and lipohemarthrosis. Methods Traumatic knee joints hemarthrosis (12 knees) and lipohemarthrosis (18 knees) proved by operation (27 knees) or puncturation (3 knees) were included in the study. Horizontal-beam plain radiographs (16 knees), CT (30 knees), MRI (30 knees) and ultrasonography (24 knees) in supine position were investigated. Results (1)supine position horizontal-beam plain radiographs: Fat-liquid layer was found in 8 cases of lipohemarthrosis. Dense supragenual bursa was found in 1 case of lipohemarthrosis and 7 cases of hemarthrosis. Fracture (13 knees) was diagnosed correctly. (2) CT findings: double fluid-fluid layer was found in 11 of all 18 cases, and single fluid-fluid layer was found in 7 of 11 cases of lipohemarthrosis. Single fluid-fluid layer was found in 3 of 12 cases of hemarthrosis. Isodensity was detected in 9 cases, and high-density blood clot was found in 4 cases. Fracture (30 knees) was diagnosed correctly. (3) MRI findings: in 12 of 18 cases of lipohemarthrosis, double fluid-fluid layer was shown including supernatant layer as short T1, long T2signal and low signal after fat-suppression, middle layer as long T1, long T2 signal and high signal after fat-suppression, and dependent layer as iso-T1, iso-T2 and slight high signal after fat-suppression. Single fluid-fluid layer was seen in 6 cases, only had aforementioned upper and under layer.Only aforementioned supernatant layer and dependent layer were seen in 12 cases of hemarthrosis. 4 cases showed entire blood clot in fluid, T1WI showed middle signal or center iso-signal accompanied with peripheral high signal ring, and fat-suppression imaging showed high signal. T2WI and fat-suppressionimaging showed middling or high signal accompanied with peripheral low signal ring. Fracture (30 knees) was diagnosed correctly. (4) Ultrasound findings: In 10 of 14 cases of lipohemarthrosis, double fluid-fluid level was shown, supernatant layer as equal echo, middle layer as echoless, and dependent layer as cloudy echo. Four cases with single fluid-fluid level only showed aforementioned upper and under layer. Three of 10 cases of hemarthrosis showed single fluid-fluid level, only showing aforementioned upper and under layer,and 7 cases showed cloudy echo and float. In 3 cases the fluid blood clot showed irregular shape low-equal echo bolus. No fracture hne was found. Conclusions CT can clearly detect fracture line, hemarthrosis and lipohemarthresis, and can substitute plain radiography. MRI is the best way to diagnose hemarthresis and lipohemarthrosis. Ultrasonography can be used in diagnosing hemarthresis and lipohemarthrosis but not helpful in the diagnosis of fracture.

Senile dementia is a disease that gradually develops with age. At present, the etiology, pathogenesis and treatment of senile dementia cannot be completely determined clinically. Therefore, it is extremely necessary to prevent and treat senile dementia from prevention and disease management. For the non-ill people, this article analyzed the susceptible groups of senile dementia from the perspective of TCM constitution, combined with the current prevention plan of Alzheimer's disease, from the aspects of examination, nutritional supplementation, adjustment of work and rest, exercise, etc., early physical fitness prevention targeting populations at different stages was conducted; the early onset of senile dementia is not obvious, and the early prevention of senile dementia can be carried out from various aspects in combination with constitution identification and inspection of senile dementia; for the exact sick population, disease management guidance can be added on the basis of the above aspects to provide definite and feasible recommendations for disease prevention and management of the elderly.

Objective To explore the effects of different skull-brain interfaces and mesh density of the cerebrospinal fluid (CSF) on dynamic responses of the brain. Methods The impact kinematics on cadaver head under rotation and translation impacts were reconstructed based on the 50th percentile adult head finite element model. The interfaces between skull and CSF, CSF and brain were modeled with different types of interfaces, which were set as sharing nodes, tied, frictionless sliding, so as to investigate the effect of different interface types on dynamic responses of the brain. Then, the interfaces between CSF, skull and brain were set as sharing nodes, while CSF was divided into single-layer and tri-layer of hexahedral element with the constant thickness of CSF, to study influences of CSF with different mesh density layers on dynamic responses of the brain. Results The intracranial pressure was highly sensitive to the interface types, while the brain response seemed to be relatively insensitive to the variation in CSF layers. Conclusions The research findings provide theoretical references for the construction of CSF and the selection of skull-brain contact interface of the head finite element model.

Objective To study the influence of skull thickness on intracranial biomechanical parameters by finite element method. Methods The female head at 5th percentile was selected for CT scanning to construct finite element model of the head with high biofidelity,and the model was verified by reconstructed cadaver test. The finite element model of the head with different skull thickness was established, and multiple groups of tests were carried out to compare the intracranial mechanical parameters. Results The negative value of intracranial pressure was significantly affected by the decrease in skull thickness under the same head size, while the negative value of intracranial pressure was slightly affected, with an increasing trend. The shear stress and von Mises stress of brain tissues were significantly increased with skull thickness increasing. Conclusions Under the same head size, the skull thickness will affect head injury to a certain extent, and people with small skull thickness are more likely to be injured than those with large skull thickness.

Objective To compare and analyze the effect of membrane element and spring element on biomechanical responses of cervical ligaments. Methods Based on the existing 6-year-old pediatric neck finite element model, the ligaments were simulated by membrane element and spring element, respectively. Then dynamic tensile test of C4-5 vertebrae and tensile test of full cervical spine were conducted. The membrane element model was also used to simulate the bending test, and the simulation results were analyzed. Results In dynamic tensile test of C4-5 vertebral segment, the final failure force of membrane element simulation test and spring element simulation test was 1 207 N and 842 N, respectively, and their difference from the cadaver experiment was 0.6% and 30.6%, respectively. In full cervical tensile test, the difference of peak force from membrane element simulation test and cadaver experiment was 1.8%. The peak force of spring element simulation test was 484 N, and the difference from simulation test and cadaver experiment was large. The simulation result of membrane element bending test was good. Conclusions The spring element had some limitations in force simulation. The membrane element had higher biofidelity and could reflect the biomechanical response of the ligaments.

Objective:To investigate the distribution characteristics and clinical significance of aeroallergen sensitization in children with airway allergic diseases.Methods:The information of children who were diagnosed with airway allergic diseases and performed with skin prick test(SPT)of aeroallergens was collected and retrospectively analyzed from Beijing Children′s Hospital from January to December, 2019.A total of 2557 patients were divided into ≤5 years of age group, 6-11 years of age group and ≥12 years of age group according to age, and allergic rhinitis group, asthma group, allergic rhinitis combined with asthma group according to diseases.The differences in the distribution of positive rates of 18 kinds of aeroallergens in age group and disease group were compared.Results:The positive rates of SPT in 2557 children from high to low were weeds pollens in summer and autumn, molds, trees pollens in spring, dust mites, etc..The top five strong positive rates from high to low were Artemisia pollen, Humulus pollen, Dermatophagoides farina, Betula pollen and Fraxinus pennsylvanica pollen.The positive rate was 71.5%(539/754)in the ≤5 years of age group, 78.5%(1241/1581)in 6-11 years of age group, and 81.1%(180/222)in ≥12 years of age group.The difference in positive rates of SPT among different age groups was statistically significant( χ2=16.825, P<0.05). In the group of ≤5 years of age group, the main aeroallergens were Chenopodium pollen(310/754, 41.1%), Alternaria alternate(307/754, 40.7%), Humulus pollen(295/754, 39.1%), Artemisia pollen(293/754, 38.9%)and Fraxinus pennsylvanica pollen(258/754, 34.2%). The main aeroallergens in the 6-11 years of age group were Chenopodium pollen(853/1581, 54.0%), Humulus pollen(769/1581, 48.6%), Artemisia pollen(768/1581, 48.6%), Alternaria alternate(751/1581, 47.5%)and Fraxinus pennsylvanica pollen(724/1581, 45.8%). The main aeroallergens in the ≥12 years of age group were Chenopodium pollen(131/222, 59.0%), Humulus pollen(119/222, 53.6%), Artemisia pollen(113/222, 50.9%), Alternaria alternate(112/222, 50.5%)and Dermatophagoides farina(103/222, 46.4%). The positive rate of allergic rhinitis group was 73.6%(1164/1582), asthma group was 72.4%(234/323), allergic rhinitis combined with asthma group was 86.0%(561/652). The positive rate of SPT was significantly different among different disease groups( χ2=43.408, P<0.05). The main aeroallergen of allergic rhinitis, asthma and allergic rhinitis combined with asthma was Chenopodium pollen.The positive rates of 18 kinds of aeroallergens were significantly different among the three disease groups(all P<0.05). The positive rate of each aeroallergen in allergic rhinitis combined with asthma was higher than that in single airway allergic disease. Conclusion:In children with airway allergic disease, the sensitization spectrum of aeroallergen varies among different age groups and disease groups.Clinicians should monitor allergens regularly and give preventive treatment to children with airway allergic disease.

Objective To study the constitutive model of adipose tissue at medium strain rate and its parameter inversion. Methods Based on experiments of adipose tissue mechanical properties, the compression experiment of adipose tissues was reconstructed by finite element method, and the parameters for characterizing constitutive models of adipose tissues were screened. Combined with the method of feasible direction (MFD) in optimization method, the reverse calculation for parameters of fat tissue constitutive model at medium strain rate was conducted. ResultsCompared with Ogden constitutive model, the viscoelastic constitutive model was more suitable for characterizing the mechanical response at medium strain rate (260 s-1). The parameters of the constitutive model suitable for simulation were obtained using the reverse method. Conclusions The viscoelastic constitutive model was more suitable for characterizing the mechanical response at medium strain rate. The results provide references for studying the influence of human adipose tissues on body injury in finite element simulation of vehicle collisions.

Objective To study influencing factors of renal blunt impact injury by using finite element (FE) method. Methods Based on CT images of the kidney, the kidney FE models for different age groups were constructed. The renal blunt impact test was reconstructed, and the influence of kidney material constitutive parameters, kidney tissue structure, kidney size, impact position and impact velocity on injury severity were analyzed. Results Under the same impact condition, the stress of renal cortex decreased with the kidney mass increasing, and increased with the impact velocity of the hammer increasing. The renal capsule had a certain energy absorption effect, so as to reduce the kidney stress. When the kidney was impacted, the stress of renal cortex under side impact was significantly higher than that under frontal impact. Conclusions Compared with viscoelastic constitutive model, Mooney Rivlin material constitutive model is more suitable for FE evaluation on renal injury severity. The renal injury decreases with the kidney mass increasing. The increase of impact velocity will intensify the renal injury severity. Renal capsule will reduce renal injury to a certain extent, so the existence of renal capsule structure must be considered in FE modeling of the kidney. Compared with frontal and rear impact, the renal injury severity is greater when the kidney is impacted from the lateral side.