| BackgroundHip fractures more and more become an big health issue of the elderly in the world, especially elderly women suffering from osteoporosis. Hip fracture has a high incidence of high disability rate in the short term; a significant increase in the characteristics of secondary risk of death and long-term occupation of treatment and care resource will bring the heavy medical and economic burden to the society. Otherwise,90%of older women hip fractures caused by sideways fall. For the hip fracture, researchers pay more attention to the use of the drug treatment of osteoporosis, which address the root causes of this problem, but the results show that such drug intervention ineffective. Therefore, the hip fracture caused by sideways fall is currently no effective methods to preventing.At present, in biomechanics research of hip fracture caused by sideways fall, some work has focused on bone strength of the proximal femoral bone. These factors include:the femur in the experimental strain rate, local proximal femur bone mass distribution, proximal femur topology factors, and proximal femur in the experiment in a fixed angle. These studies evaluated the related factors about proximal femur bone strength, but can not access the impact velocities in the sideways fall.Three type of research method of sideways fall:the human fall impact test simulation experiments, the impact experiment of femur plastic models and three-dimensional FEA model of the hip and pelvis. The human body release experiments simulate the sideways fall, to quantify and evaluate the relevant factors fall simulation. There are some shortcomings of current body release experiments: the height of simulation fall was set in experiment, only5cm, in order to ensure the personal safety of subjects in human experimentation, but it will not be able to access other higher altitudes, including the real fall height of the exact hip impact force data, and therefore can not know what the height of the fall will have a greater risk of injury. On the other side, the body posture of the fall simulation was different from the real fall situation. Due to the existence of these reasons, the human side falls simulation of hip impact force values will be far less than the value in the real fall. Impact test impact data available human trials are unlikely to get hip hip plastic model, better guiding role, but these experiments are still some deficiencies take the static impact on the hip model:in these experiments can be to some extent, a good simulation of the impact process and have a certain influence, but the real impact falls, proximal femur, and body posture with the value of the impact of process changes will impact these effects can not be measured in a static impact will. FEA simulation of the side of the falls, the use of human body FEA model can be a good predictor of the impact of hip and good results have been published in the literature the impact of validation. This FEA simulation of the data can not be obtained in many biomechanics experiments, such as local stress and strain changes over time, subtle structural changes of the impact process. This FEA simulation of a number of shortcomings, one of the most important of these FEA model can not simulate the real fall in body posture, which will have a certain impact on the hip, impact prediction.Therefore, in order to better simulate the real state of the side fall impact, you need to simulate the higher fall height, impact, beyond the scope of the human body to withstand the impact of the human body FEA model validation can be better to carry out the forecast.Studied for the prevention side of the falls caused the external shield of proximal femoral fractures a hip protector (Hip Protector, HP), it is one of the main non-pharmaceutical interventions used in the elderly, can falls arising from the greater trochanter of the femur directly impact energy absorption and/or shunt, thereby reducing the risk of hip fractures caused by falls. HP has a strong theoretical advantage, and its cost relative to the drug treatment is even more inexpensive, and thus subject to the attention of the researchers. The researches of HP focus during the two major aspects of the validity of research in the laboratory research and clinical application of the protective effect of the impact of biomechanics.Lauritzen has been reported the clinical efficacy of HP in1993, the results pointed out:for nursing homes and elderly in the HP can significantly reduce the risk of side of the falls, hip fractures, with better clinical protection effect. A result, HP began extensive attention from researchers; biomechanics protective effect and clinical application of validity have carried out further in-depth study. However, summarized and analyzed the final results of these studies found that the effectiveness of HP’s a huge difference:the results are inconsistent with the initial clinical studies, there is no evidence to show that HP has a significant clinical protective effect, especially the most recent clinical prospective research and Meta-analysis data suggest that:there is no conclusive evidence to show that HP can reduce falls in older people due to hip fracture risk. On the contrary, a large number of biomechanical experiments carried out on HP, but confirmed in laboratory settings, the relatively good condition, HP can be reduced to94%of the greater trochanter impact suffered in the fall, and in accordance with this laboratory test results that the HP can significantly reduce the direct impact of the fall on the hip, can greatly reduce the fall due to the occurrence of hip fracture risk.The emergence of such contradictions prompted the researchers to further biomechanical impact protection experiments. The results showed that:the impact of real slip relative to the body on the side of the hip and the impact of response time, set in the biomechanics laboratory studies the impact of quality and impact height, the analog side of the falls the effective impact energy is too small. And think that this may lead to biomechanical experiments have sufficient buffering capacity available on the impact of the most important reason; the same time, the clinical efficacy results in the HP most think the most important reason:HP’s clinical efficacy is not proven effective may be worn by poor compliance of subjects in the study of HP; study also pointed out that to improve the design of HP thus increasing the compliance of its clinical application is to confirm the effectiveness of the most important issue of the clinical application of HP.Based on the above problem, the side of the falls caused by hip fracture prevention points to higher energy fall simulation to obtain the real fall under the state of hip impact on fall-induced hip fractures related to the dynamic mechanism; high-energy side fall simulation to predict the impact of the hip before and after wearing HP, HP biomechanical protection performance evaluation, the clinical application of the HP and ultimately confirmed the validity of its clinical efficacy based on biomechanics evidence. The high-energy side falls simulation experiments can be used the validation systemic FEA model predicted that in order to avoid the experiment, subjects were injured.Integrated the above point, this study intends using the following experimental steps:(1), Compress performance than the stable of heel skin to skin and subcutaneous soft-organization of the compression performance test, then the use of FEA analysis method based on laboratory measurements of the soft Organization compression parameters for the FEA model soft-organization of material parameters of the calculation and the definition from methodological point of view to improve the definition of parameters of the soft tissue, thereby improving the simulation accuracy of the soft tissue under shock compression, for the precise definition of the soft tissue parameters in the next finite element model of the hip to provide a better method;(2), the side of healthy adult males as subjects fall simulation study. Fall height of the experiment to further improve and to restrain the body posture of the subjects, so that the side of the falls simulations closer to the real fall situation, in order to minimize the experimental error;(3), the establishment of the human body FEA model validation. Subjects body posture and the impact of the physical whereabouts of the moment of touchdown speed of access to information on the human body FEA model is defined, for the prediction of the impact of different fall height of hip, hip obtained in the experiments impact data on the FEA model multi-level verification, and improve the credibility of the FEA model and the scope of application;(4), validated by the effectiveness of multi-level systemic FEA model of high-energy side impact forecast fall hip;(5), validated by the effectiveness of multi-level systemic FEA model HP protection capability in the high-energy impact evaluation, a clear protective performance of HP and its further improvement and testing, it has better protection performance.Objective1. A clear low-energy side of falls the hip impact in the fall height and fall in the peak impact force, the relationship between the peak time of impact:2, the FEA model to the human body using the authentication method of the multi-level model validation, increase the scalability of human FEA model simulation accuracy and human FEA model application;3, right side of the high-energy fall hip impact using FEA simulation method to predict to predict the impact of the hip; the role of wear HP before and after the fall to assess the fall of the high-energy side, HP buffering protective effects.Material and methodsInstrument and apparatusSoft tissue compression performance tests:fresh healthy human foot roots of soft tissue6; ElectroForce (?)3510materials testing machine.Sideway falling experiment:human experiments required volunteers selected according to the volunteers of this study and formulate standards for screening, recruitment in accordance with the actual situation, not more than six; the Lunar dual-energy X-ray absorptiometry tester; Motion dynamic motion capture system,6Eagle infrared movement to capture the camera and supporting the Cortex1.1recording and analysis software system; AMTI force plates of three-dimensional test; manual lifting device used to manually lift suspension device; can achieve suspension of solid suspension and instantaneous release of the electromagnetic release; medium hardness foam sponge cushioning material used to protect subjects hip.FEA simulation:computer workstations, Configuration:CPU:Dual Intel Xeon E55072.66GHz4-core processor;12G1366MHz ECC memory; Memory the1G professional graphics card;3.5T SATAII7200RPM hard drive;22-inch professional display. ABAQUS6-10.1:large-scale general purpose finite element analysis software. MIMICS14.01. Geomagic11.0reverse.Specimen and treatmentExperimental methodsThe use of compression test of the soft tissue of the heel mechanical testing, the output data conversion, input parameters in the ABAQUS software estimates. The calculated parameters of the FEA model is defined and the mechanical test simulation of the same conditions, the output and specimen experiment with the types of data. The specimens of experimental and FEA simulation of the mechanical test output data to determine whether consistent.Body suspension device side of the fall simulation. Reflective Marker ball before the experiment is directly attached to the14position of the large joints of the subjects’body and chest. Set the receiver body posture to fall to the side as far as possible, and visions subjects forearm bent, and the rest of the body muscles stay relaxed. Motions capture system and force Taiwan to start recording data after the release of electromagnetic suction, so that the subjects to free fall to the initial position. Complete stop after the fall simulation data logging and check the subjects with hip injury. Available subjects posture with the drop changes, according to this information to calculate the Marker point in the fall at different times of the instantaneous velocity, is also available hip suffered the impact of the experiment.ABAQUS finite element analysis software to establish the human body FEA model of MRI3D data from a subjects body scan data of healthy adult male volunteers. Side of the falling body posture and the instantaneous velocity information on the FEA model to define and simulate the same conditions the side of the falls the same types of results arising from the impact of output and experimental data obtained in the simulation, the two statistics analysis to determine whether consistent.Can be systemic FEA model proven impact testing of other conditions:the definition of the initial impact velocity of the FEA model to simulate the impact velocity of the high-energy hip suffered from the impact force in case of a higher impact energy; established HP FEA model and systemic model for assembly, and then simulate the hip forces in different impact energy wear HP.Statistical analysisFinite element analysis and experimental verification of soft tissue compression performance, the95%confidence interval of each set of data points to measure the FEA prediction data and real experimental data consistency; bivariate correlation analysis of the in vitro experiments and FEA simulation soft tissue compression parameters obtained correlation analysis; curve fitting method to obtain the data of experimental and FEA prediction curve equation of the force-displacement curve;In the fall simulation experiments, using single factor repeated measures analysis of variance on the fall height of each peak impact force (Fmax), the impact of peak time (Tmax) for statistical analysis, pairwise comparisons of the different levels to take LSD method. The correlation between bivariate correlation analysis of the fall of the default height (H), the peak impact force (Fmax) and the impact of peak time (Tmax) were analyzed to determine the degree of correlation between each set of data using curve fitting method to determine the best fitting model in each set of data to determine the mathematical expression of the relationship between each set of data.Side of the falling body FE model laboratory data validation process using bivariate correlation analysis to the laboratory measurements of hip impact force and FE model to simulate the impact of hip correlation analysis, to determine boththe correlation between the degree; curve estimation method to obtain a linear relationship between the two sets of variable expression.All data in this study using SPSS13.0statistical package for data processing and statistical analysis, all data are presented as mean+standard deviation (X±SD) said that the difference was significant (P<0.05) as of criteria.ResultsSoft tissue compression performance testing, in vitro compression tests to obtain their compression performance data, and use the software function of the material parameters assessment. Obtained material parameters given in the FEA model and the simulation operation, when the material Poisson’s ratio is0.497, obtained by the FEA simulation force-displacement output data are in vitro experiments to obtain the95%confidence interval of the data to prove that these two sets of data consistency; bivariate correlation analysis shows that there is a strong linear correlation between the in vitro experiments and FEA simulation data; compression performance of the in vitro experiments and FEA simulation data showed exponential growth trend.Human side falls in the simulation, the fall height of the peak hip impact force between a single-factor repeated measures analysis of variance for statistical analysis, concluded that its impact in the overall significant difference (F=22.228, P=0.016). LSD method for pairwise comparison results:In the liner protection groups, between f0.05and f0.4group and other groups there were significant differences (P<0.046, P <0.043), and the remaining between groups without significant differences; no liner protection g0.05-peak impact force is1738.88±215.66N, and any two of the other groups concluded that:g0.05group and f0.1between f0.15and f0.4group difference was significant, P values were0.046,0.049and0.030.Fall height of the peak time of impact between a single-factor repeated measures ANOVA for statistical analysis, concluded that its impact in the overall significant difference (F=40.666, P=0.010). LSD method for pairwise comparison results:in the liner to protect each group, the f0.05group than fO.1group outside the other groups there are significant differences (P<0.021), f0.15f0.4group had no significant difference (P>0.053); no liner protection g0.05-peak time was22.78±2.64ms, and by the pairwise comparisons that and among the other groups were significant differences (P<0.032). Bivariate correlation analysis, correlation analysis on the relationship between H and Fmax and Tmax concluded that:there is a strong linear relationship among the pearson correlation coefficient between H and Fmax, H and Tmax were0.990(P=0.000) and-0.882(P=0.020); there is a strong negative linear correlation between Fmax and Tmax, the Spearman correlation coefficient was-0.836(P=0.000); curve fitting method of H with the relationship between Fmax and Tmax:H and Fmax. H and Tmax between the best curve fitting model are the power model, the test statistic F=454.919, R2=0.991, P=0.000and F=185.928, R2=0.979, P=0.000; between Fmax and Tmax is the best curve fitting model for the S model, test statistic is F=301.407, R2=0.987, P=0.000.Side of the falling body FE model laboratory data validation, and impact data obtained by the hip impact force data and FEA simulation laboratory to obtain the two-variable correlation analysis, using non-parametric method of Spearman test methods, and concluded that the two strong strong linear correlation (Spearman’s Rz=1.000, P<0.01) betweenConclusions1. A soft tissue material parameter simulation to good effect. Lower compression ratio, calculated results and the in vitro results; the case of higher compression ratio to improve the material Poisson than can effectively increase the accuracy of the FEA simulation.2, the side of the falls simulation experiments may well reflect the fall by the impact of state of the hip; the power function between the growth trend in the fall height and fall impact; fall height and impact of peak time between the power function decreases trends; side fall to a height exceeding0.3m, that is, have a greater risk of proximal femoral fractures in patients with osteoporosis;3, this study established body to simplify the FE model has a good analog performance may well reflect the hip side of the falls suffered by the impact of conditions; simulation accuracy of the poor but in the simulation of a lower fall height, simulation of higher fall height of analog high accuracy;4, when the side of the falls occurred in the upright position to stand or walk, falls the larger the risk of proximal femur fractures occur even if the fall of the proximal femur osteoporosis and other disorders of healthy people:the side of the fallsoccurs. the touchdown side of the proximal femur is the first occurrence of the fracture site may be located in the femoral neck between the femoral head and greater trochanter, and close to the large rotor side of the site:5, horseshoe-shaped HP buffer protective effect in the low impact energy falls under the protection is better:but in the high impact energy falls, this buffer is more limited protective effect, the impact of the hip proximal femoral fracture threshold may exceed the occurrence of proximal femoral fractures. |
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