侧方跌倒高度及髋保护器对髋部冲击影响的实验及有限元分析
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摘要
研究背景
在全球范围内,髋关节骨折越来越成为困扰老年人健康的一个重要问题,其主要发病人群是老年人,尤其是患有骨质疏松的老年女性,并且具有较高发病率、高致残率、短期内显著增加继发死亡风险和需要长期占用治疗和护理资源等特点,将给全社会带来不必要的沉重医疗及经济负担。同时,此种类型骨折的发病人群中,90%老年女性髋关节骨折是由侧方跌倒所产生的对髋部巨大的冲击作用所产生。目前对于此种类型骨折,研究者多关注于利用药物治疗骨质疏松,从而在根源上解决此问题,但相关研究结果显示此种药物干预方法效果欠佳。故此,侧方跌倒所导致的髋关节骨折目前尚无有效的预防方法。
目前,在侧方跌倒导致髋关节骨折的生物力学研究中,部分工作集中于对股骨近端骨强度相关因素的研究方面。这些因素主要包括：实验中的股骨应变速率、股骨近端各局部骨量分布情况、股骨近端拓扑学因素、股骨上段在实验加载中的不同固定角度等。这些研究可较好评价与股骨近端骨强度相关的影响因素,却无法获取侧方跌倒中不同冲击速度下髋部所受冲击力数据这一导致骨折发生的首要因素。
当前对于侧方跌倒致股骨近端骨折的跌倒冲击力方面研究主要有三类,分别为：人体跌倒模拟实验、对髋部塑料模型进行冲击实验以及对髋部及骨盆的三维数字化模型进行FEA分析并以此对冲击力进行有效预测。人体跌倒模拟实验利用人体悬吊释放的方式模拟侧方跌倒中的冲击作用,能很好地对跌倒所产生的冲击力进行量化及评价相关影响因素,但当前的人体悬吊实验存在一些不足,其中最主要的就是实验中模拟跌倒冲击的高度设置不足,仅为5cm,这主要是为了保证人体实验中受试者的人身安全,但这样也就无法获得在其他较高高度,包括真实跌倒高度下的确切髋部冲击力数据,也因此无法知道在何种高度下跌倒将有较大的致伤风险；同时,这些跌倒模拟实验中的身体姿势与真实跌倒情况中的身体姿势差别较大。由于这些原因的存在,人体侧方跌倒模拟实验中的髋部冲击力数值将远远小于真实跌倒中的数值。对髋部塑料模型进行冲击实验可获取人体实验不可能获取的髋部冲击数据,具有较好的指导作用,但这些实验仍然有一些不足：这些实验中均对髋部模型采取静态冲击方法,可在一定程度对冲击过程进行良好的模拟,但真实的跌倒冲击过程中,股骨近端以及身体姿势随冲击过程的变化将对冲击力数值有一定影响,而这些影响在静态冲击中将无法进行衡量。在进行侧方跌倒的FEA模拟研究中,利用人体全身FEA模型可以很好地预测髋部冲击力并且能较好地与已发表文献资料中的冲击结果进行有效性验证。同时这些FEA模拟研究也提供了许多生物力学实验中所无法获取的资料,譬如局部应力应变随时间的变化情况、冲击过程的细微结构变化等。但这些FEA模拟研究中也存在着一些不足,其中最重要的就是这些FEA模型未能模拟真实跌倒中的人体姿势,从而会对髋部冲击力的预测产生一定影响。
故此,为了更好模拟真实状态下的侧方跌倒冲击,就需要模拟更高跌倒高度下的冲击情况,同时对于超出人体承受范围的冲击情况,利用经有效性验证的人体全身FEA模型可较好地进行预测。
当前研究较多的用于预防侧方跌倒致股骨近端骨折的外部防护装置主要是髋关节保护器(Hip Protector, HP),它是一种主要应用于老年人的非药物干预方法,可以对跌倒所产生的对股骨大转子的直接冲击能量进行吸收和／或分流,从而降低跌倒所致的髋关节骨折的发生风险。由于HP具有较强的理论性优势,并且其成本相对于药物治疗显得更为廉价,从而受到研究者的关注。目前对于HP的研究主要集中在进行生物力学冲击防护效果的实验室研究和临床应用中的有效性研究两大方面。
Lauritzen等研究人员于1993年报道了HP的临床有效性,其结果指出：对于养老院及社区老年人群,HP可显著降低由于侧方跌倒所导致的髋关节骨折的发生风险；具有较好的临床防护效果。由此,HP开始得到研究者的广泛关注,并对其生物力学防护效果及临床应用有效性等方面都进行了进一步的深入研究。然而,对这些研究的最终结果进行归纳分析后发现,HP的有效性方面出现巨大差异：即与最初的临床研究结果不一致,并无证据显示HP具有显著的临床防护效果,尤其是最近的临床前瞻性研究及Meta分析等资料认为：并没有确切证据显示HP可降低老年人跌倒所致髋部骨折风险。相反,对HP进行的大量生物力学实验却证实,在实验室设置的相对理想状态下,HP最高可减少跌倒时股骨大转子所受冲击力的94%,并根据此实验室测试结果认为,HP可显著性降低跌倒时对髋部的直接冲击力,并可大大降低跌倒所致髋关节骨折的发生风险。
此种矛盾的出现促使研究人员进行进一步的生物力学冲击防护实验。结果表明：相对于人体在真实的滑倒后所产生的对髋部的侧方冲击力和冲击响应时间,生物力学实验室研究中所设置的有效冲击质量以及冲击高度,即模拟侧方跌倒的有效冲击能量偏小。并且认为这可能是导致生物力学实验中可获取对冲击有足够缓冲能力的最主要原因；同时,HP的临床有效性研究结果则多数认为：HP的临床有效性得不到有效证实的最主要原因可能是研究中的受试者对HP佩戴的依从性较差；研究中同时指出,改进HP的设计从而增加其临床应用依从性是证实HP临床应用有效性的首要问题。
综合以上问题,侧方跌倒致髋部骨折的预防要点在于进行较高能量跌倒模拟从而获得真实跌倒状态下的髋部冲击力,以对跌倒所致髋部骨折的相关动力性机制进行研究；然后利用高能量侧方跌倒模拟实验对佩戴HP前后的髋部冲击力进行预测,从而对HP的生物力学防护效能进行评价,为HP的临床应用及最终证实其临床有效性提供基础的生物力学有效性证据。高能量侧方跌倒模拟实验可利用经有效性验证的全身FEA模型进行预测,以避免实验中受试者受伤。
综合以上诸点,本研究中拟采用如下实验步骤：
(1)、利用压缩性能较稳定的足跟部皮肤进行皮肤及皮下软组织的压缩性能测试,然后利用FEA分析方法根据实验室测量的软组织压缩参数进行FEA模型中软组织材料参数的计算及定义,从方法学角度对软组织参数的定义进行改进,从而提高软组织在冲击压缩下的模拟精确性,为下一步的髋部有限元模型中软组织参数的精确定义提供较好的方法；
(2)、利用健康成年男性作为受试者进行侧方跌倒模拟实验研究。该实验进一步提高了跌倒高度并约束了受试者的身体姿势,使该侧方跌倒模拟实验更接近于真实跌倒情况,以尽可能降低实验误差；
(3)、建立人体全身FEA模型并进行有效性验证。利用所获取的受试者身体姿势以及冲击触地瞬间的身体下落速度等信息对人体FEA模型进行定义,以便进行不同跌倒高度下髋部的冲击力的预测,之后利用实验中所获取的髋部冲击力数据对FEA模型进行多层次验证,提高FEA模型的可信度及应用范围；
(4)、利用经多层次有效性验证的全身FEA模型进行高能量侧方跌倒髋部冲击力预测；
(5)、利用经多层次有效性验证的全身FEA模型进行高能量冲击下HP防护能力评价,以明确相关HP的防护性能并对其进行进一步的改进及测试,使其具有更好的防护性能。
研究目的
1、明确低能量侧方跌倒冲击中的跌倒高度与跌倒中产生的髋部峰冲击力、冲击力达峰时间之间的关系；
2、对人体FEA模型采用多层次验证方法进行模型有效性验证,增加人体FEA模型的模拟精确性和人体FEA模型应用的扩展性；
3、对高能量侧方跌倒产生的髋部冲击力利用FEA模拟方法进行预测；对佩戴HP前后的跌倒中产生的作用于髋部的冲击力进行预测,评估HP在高能量侧方跌倒中的缓冲防护效果。
材料和方法
1、主要材料
软组织压缩性能测试：新鲜健康人体足根部软组织标本6块；ElectroForce(?)3510材料试验机。
侧方跌倒人体实验：人体实验所需志愿者依照本研究制定的志愿者入选标准进行筛选,根据实际情况进行招募,人数不多于6名；Lunar双能X线骨密度测试仪；Motion动态运动捕捉系统、6个Eagle红外线运动捕捉摄像头及配套Cortex1.1记录及分析软件系统；AMTI三维测试力台；用于手动升降悬吊装置的手动起重器；可实现悬吊体的牢固悬吊和瞬间释放的电磁释放器；用于保护受试者髋部的中等硬度泡沫海绵缓冲材料。
侧方跌倒FEA模拟：计算机工作站,配置：双Intel Xeon E55072.66GHz4core处理器；12G1366MHz ECC内存；显存1G专业图形显卡；3.5T SATAII7200转硬盘；22寸专业显示器。ABAQUS6-10.1大型通用有限元分析软件。MIMICS14.01三维重建软件。Geomagic11.0逆向工程软件。
2、实验方法
利用压缩测试对足跟部软组织进行力学测试,对输出数据进行转换,输入ABAQUS软件中进行参数估计。将计算出的参数对FEA模型进行定义并进行同工况力学测试模拟,输出与标本实验同类型数据。将标本实验与FEA模拟所获取的力学测试输出数据进行比较,判断其是否一致。
利用人体悬吊装置进行侧方跌倒模拟实验。实验前将反光Marker球直接贴在受试者身体各个大关节及胸前等14个位置。设置受试者身体姿势以尽量与侧方跌倒中相同,并瞩受试者前臂弯曲,身体其他部位肌肉保持放松。运动捕捉系统及力台开始记录数据后即释放电磁吸引器,使受试者以初始姿势自由下落。完成跌倒模拟后停止数据记录并检查受试者髋部是否有损伤。实验中可获取受试者身体姿势随跌落变化的情况,并可根据此信息计算出各Marker点在跌倒不同时间的瞬时速度,也可获取其髋部所受冲击力情况。
利用ABAQUS通用有限元分析软件建立人体全身FEA模型,MRI三维数据来自于一名与受试者体态相似的健康成年男性志愿者的扫描数据。将侧方跌倒模拟实验中获取的身体姿势及瞬时速度等信息对FEA模型进行定义并模拟同工况下侧方跌倒所产生的冲击,输出与实验中相同类型的结果数据,将两者进行统计学分析以判断其是否一致。
全身FEA模型经验证后可进行其他工况下的冲击测试：将FEA模型的初始冲击速度定义为高能量冲击速度以模拟在较高冲击能量情况下髋部所受冲击力的情况；同时建立HP的FEA模型,将其与全身模型进行装配,然后模拟佩戴HP后在不同冲击能量下的髋部作用力情况。
3、统计学处理
对软组织抗压性能的有限元分析与实验验证中,利用各组数据点的95%可信区间衡量FEA预测数据与真实实验数据的一致性；利用双变量相关性分析对体外实验与FEA模拟所获取的软组织压缩参数进行相关性分析；利用曲线拟合方法分别获取实验及FEA预测数据的力-位移曲线的曲线方程；
在跌倒模拟实验中,利用单因素重复测量方差分析方法对跌倒高度各组的峰冲击力(Fmax)、冲击力达峰时间(Tmax)进行统计分析,不同水平间的两两比较采取LSD法。利用双变量相关性分析方法对跌倒预设高度(H)、峰冲击力(Fmax)和冲击力达峰时间(Tmax)之间的相关性进行分析,以确定各组数据之间的相关性程度,利用曲线拟合方法确定各组数据间的最佳拟合模型,以确定各组数据之间的数学表达关系。
侧方跌倒全身FE模型的实验室数据验证过程中,采用双变量相关性分析方法对实验室测量到的髋部冲击力和FE模型所模拟的髋部冲击力进行相关性分析,确定两者之间的相关性程度；利用曲线估计方法获取两组变量之间的线性关系表达式。
本研究中所有数据均采用SPSS13.0统计学软件包进行数据整理及统计学分析,所有数据资料都以均数±标准差(X±S.D.)表示,以P<0.05作为差异具有显著性的判断标准。
结果
软组织抗压性能测试中,利用体外压缩实验获取其抗压性能数据,并利用软件中相应功能进行材料参数评估。对所获材料参数赋予FEA模型中并进行模拟运算,当材料泊松比为0.497时,由FEA模拟获取的力-位移输出数据均在体外实验所获取数据的95%可信区间之内,证明这两组数据具有一致性；双变量相关性分析可知,体外实验与FEA模拟数据间有较强的线性相关关系；体外实验及FEA模拟的抗压性能数据均呈指数增长趋势。
人体侧方跌倒模拟实验中,对不同跌倒高度下的髋部峰冲击力之间利用单因素重复测量方差分析进行统计学分析,结果认为其影响在总体上具有显著性差异(F=22.228,P=0.016)。采用LSD方法进行两两比较结果：在有衬垫保护的各组中,f0.05组和f0.4组与其他各组之间均存在显著性差异(P<0.046,P<0.043),其余组之间都无显著性差异；在无衬垫保护的g0.05组,其峰冲击力为1738.88±215.66N,与其他组间的两两比较结果认为：g0.05组与f10.1、f10.15及f0.4组之间的差别具有显著性,P值分别为0.046、0.049和0.030。
对不同跌倒高度下的冲击力达峰时间之间利用单因素重复测量方差分析进行统计学分析,结果认为其影响在总体上具有显著性差异(F=40.666,P=0.010)。采用LSD方法进行两两比较结果：在有衬垫保护的各组中,f"0.05组同除f10.1组之外的其他各组间均存在显著性差异(P<0.021),f0.15-f0.4组的各组之间均无显著性差异(P>0.053)；在无衬垫保护的g0.05组,其达峰时间为22.78±2.64ms,且经两两比较后认为其与其他各组之间均有显著性差异(P<0.032)。
利用双变量相关性分析对H与Fm“及Tmax之间关系进行相关性分析,结果认为：三者之间均存在较强的线性相关关系,H与Fmax、H与Tmax之间的pearson相关系数分别为0.990(P=0.000)和-0.882(P=0.020)；Fmax与Tmax间存在较强的负线性相关关系,Spearman相关系数为-0.836(P=0.000)；利用曲线拟合方法对H与Fmax及Tmax之间关系进行分析,结果认为：H与Fmax、H与Tmax之间,最佳曲线拟合模型均为幂模型,其检验统计量分别为F=454.919,R2=0.991,P=0.000和F=185.928,R2=0.979,P=0.000；Fmax及Tmax之间的最佳曲线拟合模型为S模型,检验统计量为F=301.407,R2=0.987,P=0.000。
侧方跌倒全身FE模型的实验室数据验证中,对实验室获取髋部冲击力数据与FEA模拟获取的冲击力数据进行两变量相关性分析,采用Spearman非参数检验方法,认为两者之间有较强的线性相关关系(R2=1.000,P<0.01)。
结论
1、软组织材料参数模拟效果良好。在较低压缩率下,计算结果与体外实验结果相一致；在较高压缩率情况下,提高材料泊松比可有效增加FEA模拟的准确性。
2、侧方跌倒模拟实验可很好反映跌倒时髋部的受冲击力状态；跌倒高度与跌倒冲击力之间呈幂函数增长趋势；跌倒高度与冲击力达峰时间之间呈幂函数减小趋势；侧方跌倒高度超过0.3m,对于骨质疏松患者即有较大的导致股骨近端骨折的风险；
3、本研究中所建立的全身简化FE模型具有良好的模拟性能,可很好地反映侧方跌倒时髋部所受冲击力状况；但在模拟较低跌倒高度时模拟精确度欠佳,在模拟较高跌倒高度时模拟精确度较高；
4、当在直立位站立或行走中发生侧方跌倒时,跌倒者有较大发生股骨近端骨折的风险,即使跌倒者为股骨近端无骨质疏松等疾患的健康人；当侧方跌倒发生时,触地侧的股骨近端最先发生骨折的部位可能为股骨颈位于股骨头与大转子之间且靠近大转子一侧的部位；
5、马蹄铁形HP可以产生一定的缓冲防护效果,在较低的跌倒冲击能量下,其防护效果较好；但在较高的跌倒冲击能量下,此缓冲防护效果较为有限,髋部冲击力有可能会超出股骨近端骨折阈值而发生股骨近端骨折。
Background
Hip 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.
Objective
1. 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 methods
Instrument and apparatus
Soft 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 treatment
Experimental methods
The 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 analysis
Finite 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.
Results
Soft 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) between
Conclusions
1. 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.
在全球范围内,髋关节骨折越来越成为困扰老年人健康的一个重要问题,其主要发病人群是老年人,尤其是患有骨质疏松的老年女性,并且具有较高发病率、高致残率、短期内显著增加继发死亡风险和需要长期占用治疗和护理资源等特点,将给全社会带来不必要的沉重医疗及经济负担。同时,此种类型骨折的发病人群中,90%老年女性髋关节骨折是由侧方跌倒所产生的对髋部巨大的冲击作用所产生。目前对于此种类型骨折,研究者多关注于利用药物治疗骨质疏松,从而在根源上解决此问题,但相关研究结果显示此种药物干预方法效果欠佳。故此,侧方跌倒所导致的髋关节骨折目前尚无有效的预防方法。
目前,在侧方跌倒导致髋关节骨折的生物力学研究中,部分工作集中于对股骨近端骨强度相关因素的研究方面。这些因素主要包括：实验中的股骨应变速率、股骨近端各局部骨量分布情况、股骨近端拓扑学因素、股骨上段在实验加载中的不同固定角度等。这些研究可较好评价与股骨近端骨强度相关的影响因素,却无法获取侧方跌倒中不同冲击速度下髋部所受冲击力数据这一导致骨折发生的首要因素。
当前对于侧方跌倒致股骨近端骨折的跌倒冲击力方面研究主要有三类,分别为：人体跌倒模拟实验、对髋部塑料模型进行冲击实验以及对髋部及骨盆的三维数字化模型进行FEA分析并以此对冲击力进行有效预测。人体跌倒模拟实验利用人体悬吊释放的方式模拟侧方跌倒中的冲击作用,能很好地对跌倒所产生的冲击力进行量化及评价相关影响因素,但当前的人体悬吊实验存在一些不足,其中最主要的就是实验中模拟跌倒冲击的高度设置不足,仅为5cm,这主要是为了保证人体实验中受试者的人身安全,但这样也就无法获得在其他较高高度,包括真实跌倒高度下的确切髋部冲击力数据,也因此无法知道在何种高度下跌倒将有较大的致伤风险；同时,这些跌倒模拟实验中的身体姿势与真实跌倒情况中的身体姿势差别较大。由于这些原因的存在,人体侧方跌倒模拟实验中的髋部冲击力数值将远远小于真实跌倒中的数值。对髋部塑料模型进行冲击实验可获取人体实验不可能获取的髋部冲击数据,具有较好的指导作用,但这些实验仍然有一些不足：这些实验中均对髋部模型采取静态冲击方法,可在一定程度对冲击过程进行良好的模拟,但真实的跌倒冲击过程中,股骨近端以及身体姿势随冲击过程的变化将对冲击力数值有一定影响,而这些影响在静态冲击中将无法进行衡量。在进行侧方跌倒的FEA模拟研究中,利用人体全身FEA模型可以很好地预测髋部冲击力并且能较好地与已发表文献资料中的冲击结果进行有效性验证。同时这些FEA模拟研究也提供了许多生物力学实验中所无法获取的资料,譬如局部应力应变随时间的变化情况、冲击过程的细微结构变化等。但这些FEA模拟研究中也存在着一些不足,其中最重要的就是这些FEA模型未能模拟真实跌倒中的人体姿势,从而会对髋部冲击力的预测产生一定影响。
故此,为了更好模拟真实状态下的侧方跌倒冲击,就需要模拟更高跌倒高度下的冲击情况,同时对于超出人体承受范围的冲击情况,利用经有效性验证的人体全身FEA模型可较好地进行预测。
当前研究较多的用于预防侧方跌倒致股骨近端骨折的外部防护装置主要是髋关节保护器(Hip Protector, HP),它是一种主要应用于老年人的非药物干预方法,可以对跌倒所产生的对股骨大转子的直接冲击能量进行吸收和／或分流,从而降低跌倒所致的髋关节骨折的发生风险。由于HP具有较强的理论性优势,并且其成本相对于药物治疗显得更为廉价,从而受到研究者的关注。目前对于HP的研究主要集中在进行生物力学冲击防护效果的实验室研究和临床应用中的有效性研究两大方面。
Lauritzen等研究人员于1993年报道了HP的临床有效性,其结果指出：对于养老院及社区老年人群,HP可显著降低由于侧方跌倒所导致的髋关节骨折的发生风险；具有较好的临床防护效果。由此,HP开始得到研究者的广泛关注,并对其生物力学防护效果及临床应用有效性等方面都进行了进一步的深入研究。然而,对这些研究的最终结果进行归纳分析后发现,HP的有效性方面出现巨大差异：即与最初的临床研究结果不一致,并无证据显示HP具有显著的临床防护效果,尤其是最近的临床前瞻性研究及Meta分析等资料认为：并没有确切证据显示HP可降低老年人跌倒所致髋部骨折风险。相反,对HP进行的大量生物力学实验却证实,在实验室设置的相对理想状态下,HP最高可减少跌倒时股骨大转子所受冲击力的94%,并根据此实验室测试结果认为,HP可显著性降低跌倒时对髋部的直接冲击力,并可大大降低跌倒所致髋关节骨折的发生风险。
此种矛盾的出现促使研究人员进行进一步的生物力学冲击防护实验。结果表明：相对于人体在真实的滑倒后所产生的对髋部的侧方冲击力和冲击响应时间,生物力学实验室研究中所设置的有效冲击质量以及冲击高度,即模拟侧方跌倒的有效冲击能量偏小。并且认为这可能是导致生物力学实验中可获取对冲击有足够缓冲能力的最主要原因；同时,HP的临床有效性研究结果则多数认为：HP的临床有效性得不到有效证实的最主要原因可能是研究中的受试者对HP佩戴的依从性较差；研究中同时指出,改进HP的设计从而增加其临床应用依从性是证实HP临床应用有效性的首要问题。
综合以上问题,侧方跌倒致髋部骨折的预防要点在于进行较高能量跌倒模拟从而获得真实跌倒状态下的髋部冲击力,以对跌倒所致髋部骨折的相关动力性机制进行研究；然后利用高能量侧方跌倒模拟实验对佩戴HP前后的髋部冲击力进行预测,从而对HP的生物力学防护效能进行评价,为HP的临床应用及最终证实其临床有效性提供基础的生物力学有效性证据。高能量侧方跌倒模拟实验可利用经有效性验证的全身FEA模型进行预测,以避免实验中受试者受伤。
综合以上诸点,本研究中拟采用如下实验步骤：
(1)、利用压缩性能较稳定的足跟部皮肤进行皮肤及皮下软组织的压缩性能测试,然后利用FEA分析方法根据实验室测量的软组织压缩参数进行FEA模型中软组织材料参数的计算及定义,从方法学角度对软组织参数的定义进行改进,从而提高软组织在冲击压缩下的模拟精确性,为下一步的髋部有限元模型中软组织参数的精确定义提供较好的方法；
(2)、利用健康成年男性作为受试者进行侧方跌倒模拟实验研究。该实验进一步提高了跌倒高度并约束了受试者的身体姿势,使该侧方跌倒模拟实验更接近于真实跌倒情况,以尽可能降低实验误差；
(3)、建立人体全身FEA模型并进行有效性验证。利用所获取的受试者身体姿势以及冲击触地瞬间的身体下落速度等信息对人体FEA模型进行定义,以便进行不同跌倒高度下髋部的冲击力的预测,之后利用实验中所获取的髋部冲击力数据对FEA模型进行多层次验证,提高FEA模型的可信度及应用范围；
(4)、利用经多层次有效性验证的全身FEA模型进行高能量侧方跌倒髋部冲击力预测；
(5)、利用经多层次有效性验证的全身FEA模型进行高能量冲击下HP防护能力评价,以明确相关HP的防护性能并对其进行进一步的改进及测试,使其具有更好的防护性能。
研究目的
1、明确低能量侧方跌倒冲击中的跌倒高度与跌倒中产生的髋部峰冲击力、冲击力达峰时间之间的关系；
2、对人体FEA模型采用多层次验证方法进行模型有效性验证,增加人体FEA模型的模拟精确性和人体FEA模型应用的扩展性；
3、对高能量侧方跌倒产生的髋部冲击力利用FEA模拟方法进行预测；对佩戴HP前后的跌倒中产生的作用于髋部的冲击力进行预测,评估HP在高能量侧方跌倒中的缓冲防护效果。
材料和方法
1、主要材料
软组织压缩性能测试：新鲜健康人体足根部软组织标本6块；ElectroForce(?)3510材料试验机。
侧方跌倒人体实验：人体实验所需志愿者依照本研究制定的志愿者入选标准进行筛选,根据实际情况进行招募,人数不多于6名；Lunar双能X线骨密度测试仪；Motion动态运动捕捉系统、6个Eagle红外线运动捕捉摄像头及配套Cortex1.1记录及分析软件系统；AMTI三维测试力台；用于手动升降悬吊装置的手动起重器；可实现悬吊体的牢固悬吊和瞬间释放的电磁释放器；用于保护受试者髋部的中等硬度泡沫海绵缓冲材料。
侧方跌倒FEA模拟：计算机工作站,配置：双Intel Xeon E55072.66GHz4core处理器；12G1366MHz ECC内存；显存1G专业图形显卡；3.5T SATAII7200转硬盘；22寸专业显示器。ABAQUS6-10.1大型通用有限元分析软件。MIMICS14.01三维重建软件。Geomagic11.0逆向工程软件。
2、实验方法
利用压缩测试对足跟部软组织进行力学测试,对输出数据进行转换,输入ABAQUS软件中进行参数估计。将计算出的参数对FEA模型进行定义并进行同工况力学测试模拟,输出与标本实验同类型数据。将标本实验与FEA模拟所获取的力学测试输出数据进行比较,判断其是否一致。
利用人体悬吊装置进行侧方跌倒模拟实验。实验前将反光Marker球直接贴在受试者身体各个大关节及胸前等14个位置。设置受试者身体姿势以尽量与侧方跌倒中相同,并瞩受试者前臂弯曲,身体其他部位肌肉保持放松。运动捕捉系统及力台开始记录数据后即释放电磁吸引器,使受试者以初始姿势自由下落。完成跌倒模拟后停止数据记录并检查受试者髋部是否有损伤。实验中可获取受试者身体姿势随跌落变化的情况,并可根据此信息计算出各Marker点在跌倒不同时间的瞬时速度,也可获取其髋部所受冲击力情况。
利用ABAQUS通用有限元分析软件建立人体全身FEA模型,MRI三维数据来自于一名与受试者体态相似的健康成年男性志愿者的扫描数据。将侧方跌倒模拟实验中获取的身体姿势及瞬时速度等信息对FEA模型进行定义并模拟同工况下侧方跌倒所产生的冲击,输出与实验中相同类型的结果数据,将两者进行统计学分析以判断其是否一致。
全身FEA模型经验证后可进行其他工况下的冲击测试：将FEA模型的初始冲击速度定义为高能量冲击速度以模拟在较高冲击能量情况下髋部所受冲击力的情况；同时建立HP的FEA模型,将其与全身模型进行装配,然后模拟佩戴HP后在不同冲击能量下的髋部作用力情况。
3、统计学处理
对软组织抗压性能的有限元分析与实验验证中,利用各组数据点的95%可信区间衡量FEA预测数据与真实实验数据的一致性；利用双变量相关性分析对体外实验与FEA模拟所获取的软组织压缩参数进行相关性分析；利用曲线拟合方法分别获取实验及FEA预测数据的力-位移曲线的曲线方程；
在跌倒模拟实验中,利用单因素重复测量方差分析方法对跌倒高度各组的峰冲击力(Fmax)、冲击力达峰时间(Tmax)进行统计分析,不同水平间的两两比较采取LSD法。利用双变量相关性分析方法对跌倒预设高度(H)、峰冲击力(Fmax)和冲击力达峰时间(Tmax)之间的相关性进行分析,以确定各组数据之间的相关性程度,利用曲线拟合方法确定各组数据间的最佳拟合模型,以确定各组数据之间的数学表达关系。
侧方跌倒全身FE模型的实验室数据验证过程中,采用双变量相关性分析方法对实验室测量到的髋部冲击力和FE模型所模拟的髋部冲击力进行相关性分析,确定两者之间的相关性程度；利用曲线估计方法获取两组变量之间的线性关系表达式。
本研究中所有数据均采用SPSS13.0统计学软件包进行数据整理及统计学分析,所有数据资料都以均数±标准差(X±S.D.)表示,以P<0.05作为差异具有显著性的判断标准。
结果
软组织抗压性能测试中,利用体外压缩实验获取其抗压性能数据,并利用软件中相应功能进行材料参数评估。对所获材料参数赋予FEA模型中并进行模拟运算,当材料泊松比为0.497时,由FEA模拟获取的力-位移输出数据均在体外实验所获取数据的95%可信区间之内,证明这两组数据具有一致性；双变量相关性分析可知,体外实验与FEA模拟数据间有较强的线性相关关系；体外实验及FEA模拟的抗压性能数据均呈指数增长趋势。
人体侧方跌倒模拟实验中,对不同跌倒高度下的髋部峰冲击力之间利用单因素重复测量方差分析进行统计学分析,结果认为其影响在总体上具有显著性差异(F=22.228,P=0.016)。采用LSD方法进行两两比较结果：在有衬垫保护的各组中,f0.05组和f0.4组与其他各组之间均存在显著性差异(P<0.046,P<0.043),其余组之间都无显著性差异；在无衬垫保护的g0.05组,其峰冲击力为1738.88±215.66N,与其他组间的两两比较结果认为：g0.05组与f10.1、f10.15及f0.4组之间的差别具有显著性,P值分别为0.046、0.049和0.030。
对不同跌倒高度下的冲击力达峰时间之间利用单因素重复测量方差分析进行统计学分析,结果认为其影响在总体上具有显著性差异(F=40.666,P=0.010)。采用LSD方法进行两两比较结果：在有衬垫保护的各组中,f"0.05组同除f10.1组之外的其他各组间均存在显著性差异(P<0.021),f0.15-f0.4组的各组之间均无显著性差异(P>0.053)；在无衬垫保护的g0.05组,其达峰时间为22.78±2.64ms,且经两两比较后认为其与其他各组之间均有显著性差异(P<0.032)。
利用双变量相关性分析对H与Fm“及Tmax之间关系进行相关性分析,结果认为：三者之间均存在较强的线性相关关系,H与Fmax、H与Tmax之间的pearson相关系数分别为0.990(P=0.000)和-0.882(P=0.020)；Fmax与Tmax间存在较强的负线性相关关系,Spearman相关系数为-0.836(P=0.000)；利用曲线拟合方法对H与Fmax及Tmax之间关系进行分析,结果认为：H与Fmax、H与Tmax之间,最佳曲线拟合模型均为幂模型,其检验统计量分别为F=454.919,R2=0.991,P=0.000和F=185.928,R2=0.979,P=0.000；Fmax及Tmax之间的最佳曲线拟合模型为S模型,检验统计量为F=301.407,R2=0.987,P=0.000。
侧方跌倒全身FE模型的实验室数据验证中,对实验室获取髋部冲击力数据与FEA模拟获取的冲击力数据进行两变量相关性分析,采用Spearman非参数检验方法,认为两者之间有较强的线性相关关系(R2=1.000,P<0.01)。
结论
1、软组织材料参数模拟效果良好。在较低压缩率下,计算结果与体外实验结果相一致；在较高压缩率情况下,提高材料泊松比可有效增加FEA模拟的准确性。
2、侧方跌倒模拟实验可很好反映跌倒时髋部的受冲击力状态；跌倒高度与跌倒冲击力之间呈幂函数增长趋势；跌倒高度与冲击力达峰时间之间呈幂函数减小趋势；侧方跌倒高度超过0.3m,对于骨质疏松患者即有较大的导致股骨近端骨折的风险；
3、本研究中所建立的全身简化FE模型具有良好的模拟性能,可很好地反映侧方跌倒时髋部所受冲击力状况；但在模拟较低跌倒高度时模拟精确度欠佳,在模拟较高跌倒高度时模拟精确度较高；
4、当在直立位站立或行走中发生侧方跌倒时,跌倒者有较大发生股骨近端骨折的风险,即使跌倒者为股骨近端无骨质疏松等疾患的健康人；当侧方跌倒发生时,触地侧的股骨近端最先发生骨折的部位可能为股骨颈位于股骨头与大转子之间且靠近大转子一侧的部位；
5、马蹄铁形HP可以产生一定的缓冲防护效果,在较低的跌倒冲击能量下,其防护效果较好；但在较高的跌倒冲击能量下,此缓冲防护效果较为有限,髋部冲击力有可能会超出股骨近端骨折阈值而发生股骨近端骨折。
Background
Hip 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.
Objective
1. 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 methods
Instrument and apparatus
Soft 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 treatment
Experimental methods
The 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 analysis
Finite 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.
Results
Soft 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) between
Conclusions
1. 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.
引文
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