坐位骨盆的三维有限元分析

背景：由于骨盆具有复杂的结构,目前对于坐位骨盆的生物力学研究较少,有限元法日益成为骨盆生物力学研究的重要手段。 目的：以有限元法研究成人正常静态坐位骨盆应力分布。 方法：获取正常成年女性全骨盆CT扫描图像,利用CT数据通过Mimics 10.0对图像数据进行重建,利用Geomagic,Proe5.0进行实体建模,输入ANSYS。再根据解剖部位建立骨盆主要韧带。对S1椎体上终板施加600 N静载荷模拟坐位时骨盆受力环境,计算该加载方式下骨盆的应力、应变及位移的分布情况。 结果与结论：垂直加载600 N载荷于骶骨上表面时重力由骶骨经骶髂关节向下传递,到达坐骨结节。此时的坐骨结节处承受较大压应力。有限元模型在静载荷下的特征部位应力、应变值基本能够反应骨盆特有的力学结构特性,模型的准确性较高。计算结果与文献中报道的结果相近,建立的人体全骨盆三维有限元模型较客观地反映人体骨盆的解剖结构和力学特性,可作为骨盆生物力学研究的工具及满足临床研究的需要。     

基于有限元法研究顺产肛提肌损伤与盆底疾病的发生

目的 模拟阴道分娩及休息时骨盆韧带肌的生物力学特性，探讨阴道分娩时肛提肌损伤、盆腔器官脱垂及压力性尿失禁。方法 建立正常的骨盆-韧带-肌肉三维非线性有限元模型，计算不同腹压和载荷下肛提肌应力、应变分布及损伤情况；计算Ⅰ、Ⅱ、Ⅲ型压力性尿失禁以及盆腔脏器脱垂的应力、应变分布及损伤情况。结果腹压为1 kPa，载荷为3、5、8 kPa和腹压为1.5 kPa，载荷为3、5、8 kPa情况下，肛提肌最高等效应力分别为14、29、43、86、144、230 kPa；Ⅰ、Ⅱ、Ⅲ型压力性尿失禁以及盆腔脏器脱垂的应力为1.69、1.01、0.70、1.58 MPa。结论 阴道分娩造成肛提肌的耻骨直肠肌和耻骨尾骨肌中部受损，与盆底功能障碍肛提肌损伤部位一致。用科学方法找出盆底在阴道分娩时的精确损伤部位，为临床医生预防盆底疾病和制定产后康复训练提供参考依据。     

几种不同部位防压疮复合硅胶垫与人体接触的压力分布

背景：高压总是集中在骨突出部位,坐垫应能均匀分布压力,设计一种有效减压的坐垫对压疮预防有重要的作用。 目的：比较几种不同部位防压疮硅胶复合垫与人体接触的压力分布,研究减小界面压力的坐垫形式。 方法：将设计的海绵轮廓垫分为复合硅胶垫和单纯海绵垫两种,复合硅胶垫又分为整个坐面复合硅胶垫,臀部区域复合硅胶垫,坐骨区域复合硅胶垫。用X-sensor压力系统测量4种坐垫压力参数(最大压力,平均压力,压力标准差,坐骨区域压力,骶骨区域压力,大转子区域压力)和面积参数(总体接触面积,高压接触面积,低压接触面积,中压接触面积及高压百分比,中压百分比和低压百分比)。 结果与结论：与单纯海绵垫比较,复合硅胶垫有较小的压力值和高压接触面积及其占总体接触面积的百分比。与整个坐面复合硅胶垫比较,臀部区域复合硅胶垫有较小的压力值和高压接触面积及其占总体接触面积的百分比。与其他3种坐垫比较,坐骨区域复合硅胶垫有最小的压力参数值和高压接触面积及其占总体接触面积的百分比,坐骨区域压力值显著减小(P < 0.05)。表明在海绵轮廓垫上复合硅胶能起到减小界面压力的作用,硅胶垫的复合位置对界面压力值有显著影响。     

面部碰撞对行人创伤性脑损伤影响的生物力学研究

为预测和评判行人面部碰撞对创伤性脑损伤机理及生物力学响应,结合计算机断层扫描（CT）和磁共振（MRI）医学成像技术,建立符合中国人体特征的50百分位头颈部几何模型和有限元模型。有限元模型中颅骨与脑之间的相对运动采用切向滑动边界条件,摩擦系数定义为0.2,模拟鼻骨斜碰撞、鼻外侧软骨正面碰撞、牙齿正面碰撞、下颌骨碰撞和颧骨外侧斜碰撞等5种典型面部碰撞交通事故场景,探讨应力波在颅骨和脑内传播路径,得到颅内压力、von Mises等效应力和剪切应力等生物力学响应参数分布规律。结果显示,鼻骨斜碰撞颅内压力峰值为236.7 kPa,von Mises应力为25.97 kPa,超过了大脑耐受阈值;颧骨外侧斜碰撞最大横向剪切应力分别为14.56 kPa和-18.07 kPa,促使脑组织产生了较大的剪切变形,存在严重脑损伤风险。结论表明：面部碰撞的位置和方向是导致面部骨折严重程度的关键因素,面骨骨折的位置决定创伤性脑损伤的部位,面骨骨折都带有一定程度的创伤性脑损伤;头部受到冲击时,面部结构能够吸收大量的冲击能量来保护大脑,降低颅脑损伤的风险。     

辅助仰卧位侧翻过程压疮易发部位的生物力学建模与实验研究

压疮是局部组织长期受压而致组织溃烂和坏死的一种病症。通过仰卧位侧翻缓解局部压力是长期卧床患者预防压疮病症发生的有效措施之一,所以研究辅助侧翻过程中压疮典型部位的生物力学意义重大。基于解剖学理论,利用CT图像数据建立躯干部压疮易发部位的骨骼与软组织有限元模型,研究不同侧翻角度下躯干部压疮易发部位的最大应力情况,并通过美国TEKSCAN公司的压力分布测试系统对10名志愿者进行人体仰卧位侧翻实验,验证仿真分析的正确性。结果表明,在侧翻过程中人体同一部位所受的压力是不同的,在90°位置出现了应力峰值的极值点,产生了应力集中现象;在角度阈值30°～45°范围内肩部和臀部各部位应力峰值比较均衡,均在0.035～0.070 MPa,表明在此阈值内人体与辅助面多部位接触,应力较为分散,两者之间存在一个使多个压疮易发部位受压最优的接触形式。研究展示了躯干部压疮易发部位在辅助仰卧位侧翻过程中的受压变化情况,相关结果有益于仰卧位侧翻辅助器械的设计与使用,并为临床护理提供参考。     

Magic螺钉固定治疗髋臼后柱骨折的生物力学分析EI北大核心CSCD

通过有限元法分析Magic螺钉治疗髋臼后柱骨折的生物力学稳定性。基于志愿者计算机断层扫描(CT)和磁共振成像(MRI)数据建立骨盆三维有限元模型并验证其有效性,然后生成髋臼后柱骨折模型,模拟采用经坐骨结节逆行拉力螺钉、后柱单钢板、后柱双钢板和Magic螺钉进行固定,比较四种固定模型的生物力学稳定性差异。在骶骨上部施加500 N压力模拟人体重力,站位以及坐位状态下逆行拉力螺钉、后柱单钢板、双钢板以及Magic螺钉固定模型的植入物最大应力分别为:114.10、113.40 MPa;58.93、55.72 MPa;58.76、47.47 MPa;24.36、27.50 MPa;骨折端最大应力分别为:72.71、70.51 MPa;48.18、22.80 MPa;52.38、27.14 MPa;34.05、30.78 MPa。两种状态下逆行拉力螺钉固定模型骨折端位移均为最大,Magic螺钉在站立状态下位移变化量最小,但是坐位状态明显高于两种钢板固定。Magic螺钉可以满足髋臼后柱骨折的稳定性需要,与传统拉力螺钉、钢板固定方式相比具有应力分布更均匀、受力更小等优点,是一种值得推荐的内固定方法。     

个性化汽车坐垫的计算机辅助设计建模及有限元数值模拟

一个好的坐垫不仅有好的舒适性,而且还能控制臀部压力的分布,减少疾病的发生。根据不同人员臀部形状设计的个性化坐垫可提高座椅的舒适性,减少臀部压力。本文研究的目的是通过逆向工程,有效迅速地建立个性化臀部-坐垫的计算机辅助设计(CAD)模型。利用CAD建模数据,可以直接用数控机床加工个性化坐垫;可以通过有限元模拟人体臀部与坐垫界面的压力分布,分析座椅舒适性的影响因素。     

基于磁共振图像的人体骨盆三维重建及有效性验证

目的：利用磁共振图像重建人体骨盆,并利用有限元方法验证建立该模型的有效性,为临床上不适合CT扫描的患者,提供了从MRI图像重建人体模型和骨盆生物力学研究的另一种方法。方法：采用1.5T的核磁成像仪扫描获取正常骨盆MRI图像,利用Hypermesh进行网格划分和韧带添加,采用Mimics和Geomagic对图像数据进行重建。对模型施加适当的界条件,运用有限元分析方法,分析该模型的应力应变和位移结果,同实验测量文献和CT重建的模型有限元模型结果对比。结果：骨盆上关键点的应力应变和位移数值基本吻合引用的参考文献对应点数值,趋势基本相似。坐位时,垂直加载600 N载荷于骶骨上表面,应力由骶骨经骶髂关节向下传递,经坐骨上支、到达坐骨结节;应力主要集中在坐骨大切迹和坐骨结节。站位时,垂直加载600 N载荷于骶骨上表面,应力分别经骶骨翼、骶髂关节,坐骨大切迹,弓状线,至髋臼;应力主要集中在骶髂关节和坐骨大切迹。结论：成功利用MRI建立的有限元模型,其基本可以反应骨盆的力学结构特点,准确性较高,可以作为用于研究骨盆及其植入物生物力学的基础。站立位时,骨盆的主要负重和稳定结构位于后方;坐位时,骨盆承载人体重量并在上下应力传导中起着非常重要的作用。     

大腿残肢步态过程的非线性有限元分析

目的利用三维有限元分析方法研究大腿截肢患者在行走过程中3个不同时相下残肢的生物力学特性,为建立完整的大腿接受腔测量、设计与评估系统提供研究基础。方法首先根据CT图像三维重建大腿截肢患者的骨骼、肌肉软组织和接受腔的三维几何模型;定义软组织为超弹性和线弹性材料属性,并相应建立两个有限元仿真模型;定义残端与接受腔之间的接触关系,约束残肢近端,对模型的远端施加膝关节载荷,模拟步态周期中足跟着地时期、站立相中期、脚尖离地3个时相下大腿残肢-接受腔系统所受载荷;计算分析接触界面上的应力,并对比分析超弹性和线弹性软组织力学特性对接触界面力学行为特性的影响。结果无论线弹性还是超弹性模型,3个时相下大腿残肢-接受腔界面的最大接触压力均在残肢末端达到最大值。超弹性模型3个时相下接触压力峰值分别为55.80、47.63和50.44 kPa;而线弹性模型接触压力的最大值都增加2倍以上,其值分别为149.86、118.55和139.68 kPa。同时通过分析接触面间的径向剪切应力和轴向剪切应力发现,3个时相下接触界面间的应力在残肢末端较集中,在足跟着地到脚尖离地过程中,有部分力通过接受腔后侧缘传递转向接受腔前缘传递。结论不同时相下残肢与接受腔接触界面的压力和剪切应力分布情况不同,在设计接受腔时需要充分考虑其受力特点。     

小腿残肢与接受腔的非线性有限元分析

目的研究残肢与接受腔生机界面力学特性及残端应力情况,为设计和优化小腿接受腔结构、提高其佩戴舒适性提供理论依据。方法针对释压稳定(compression-release stabilization,CRS)接受腔,采用有限元软件ABAQUS分析残肢与CRS接受腔界面应力分布情况,软组织采用非线性超弹性材料Mooney-Rivlin本构模型,得到静止站立中期残肢与CRS接受腔接触界面正应力和剪切应力分布情况,并相应建立髌韧带承重(patellar tendon bearing,PTB)小腿接受腔三维有限元模型,将两者结果进行比较。结果残肢与CRS接受腔界面应力主要分布在胫骨内侧、胫骨外侧和后肌群等承重区,与PTB接受腔模型主要受力区域相似,CRS接受腔残肢末端平均界面应力较PTB接受腔高19 kPa。结论 CRS接受腔具有较好的透气性且应力分布较合理,接受腔形状的不同可改变残肢与接受腔生机界面应力分布,优化其设计有助于提高假肢穿戴舒适性。     

Evaluation of a new sitting concept designed for prevention of pressure ulcer on the buttock using finite element analysis

Excessive compressive load induces pressure related soft tissue damage, i.e. pressure ulcer (PU), in buttock area in wheelchair users. In solving this problem, our previous study has introduced a concept of Off-Loading sitting, which partially removes the ischial support to reduce pressure under buttocks. However, the effect of this sitting concept has only been evaluated using the interface pressure and tissue perfusion measurements. The objective of this investigation was to evaluate the Off-Loading posture for its ability to reduce internal pressure and stress in deep buttock tissues. This evaluation was performed on a 3D finite element (FE) model which was established and validated in a sitting posture and has realistic material properties and boundary conditions. FE analysis in this study confirmed that the pressure relief provided by Off-Loading posture created profound effect in reducing the mechanical stress within deep tissues. It was concluded that Off-Loading posture may prove beneficial in preventing sitting related PU.     

Clinically oriented real-time monitoring of the individual’s risk for deep tissue injury

Spinal cord injury patients are under daily risk for developing deep tissue injury which is a severe pressure ulcer that initiates in soft tissues at the bones’ proximity. We aimed to formulate a patient-specific biomechanical model that can continuously monitor internal tissue stresses in real time. We adopted a formulation solving an axisymmetric contact problem of a finite-thickness, elastic layer (soft tissue), and a rigid spherical indentor (ischial tuberosity). We utilized finite element analyses to expand the formulation for large deformations. Sensitivity analyses showed that the soft tissue mechanical properties are the most influential factors in this modeling. We then used synthetic surface pressure data and actual surface pressures recorded under the buttocks of five paraplegic wheelchair users to demonstrate clinical feasibility. Output parameters were designed to be simple so that they can be easily interpreted by the user. Specifically, we calculated peak and average internal von Mises stress and stress dose, under each buttock, and also a time-dependent stress asymmetry index, to account for frequency of posture adjustments. Inter-subject variability was higher than the intra-subject variability. The heaviest subject had the highest maximal and average peak internal soft tissue stress. We believe that this method holds a high potential for clinical applications.     

冲击波强度与幼年大鼠肺冲击伤程度的量效关系

目的:探索冲击波强度与幼年大鼠肺冲击伤程度的量效关系,为儿童冲击伤研究提供动物模型和基础。方法:选取20天龄幼年健康SD雄鼠40只,随机分为4组:BIG1、BIG2、BIG3和BIG4,每组各10只,采用BST-Ⅰ型生物激波管以4.8~5.8 MPa驱动压致伤,观察各组动物伤后生命体征、肺大体解剖和光镜病理等,并进行肺冲击伤严重程度评分。结果:幼鼠在驱动压致伤后均出现了不同程度的呼吸急促、心率加快的表现,外耳道出血发生率为57.5%（46/80）。肺大体解剖表现为不同程度的肺出血、水肿和肺不张等。光镜下病理主要表现为不同程度的肺出血、渗出、炎症细胞的浸润、肺间质水肿增厚、肺泡内水肿和肺泡壁的断裂等。4.8 MPa驱动压时,动物所受超压峰值为433 kPa,正向冲量14 226.4 kPa[?m,肺器官损伤定级（OIS）集中在Ⅱ、Ⅲ级（40%、30%）,肺冲击伤简明损伤定级（AIS）评分为0.90±0.57,损伤程度为轻度;5.0 MPa驱动压时,超压峰值为447.7 kPa,正向冲量14 463.5 kPa[?m,OIS多集中在Ⅲ级（60%）,AIS评分为1.60±0.69,损伤程度为中度;5.5 MPa驱动压时,超压峰值为484.7 kPa,正向冲量15 017.0 kPa[?m,OIS多集中在Ⅳ级（70%）,AIS评分为3.10±0.56,损伤程度为较重;5.8 MPa驱动压时,超压峰值为506.8 kPa, 正向冲量15 325.5 kPa[?m,OIS集中在Ⅴ级（40%）附近,AIS评分为4.00±0.67,肺损伤程度为重度。各组间损伤严重程度有明显统计学差异（P<0.05）。结论:利用BST-I型生物激波管,采用4.8~5.8 MPa高压段的驱动压可建立稳定的幼年SD鼠轻~重度肺冲击伤模型。幼年大鼠肺组织对冲击波损伤的耐受性强于成年大鼠肺组织,也强于幼年兔肺组织,其机制尚不太清楚,值得进一步深入研究。     

The false premise in measuring body-support interface pressures for preventing serious pressure ulcers

Presently, commercial cushioning products for pressure ulcer prevention are being evaluated for their protective effect exclusively based on interfacial pressures between the cushion/mattress and the patient. However, interface pressures cannot predict elevated mechanical stresses in deep tissues adjacent to bony prominences. Such deep tissue stress concentrations are associated with local ischaemia and hypoxia, which over time result in deep tissue necrosis, particularly of muscle tissue. In order to demonstrate this phenomenon, a physical phantom of the mechanical interaction between the ischial tuberosities (IT) and gluteus muscles of the buttocks was built, incorporating geometric replica of the human IT and real (bovine) muscle tissue. Internal muscle stresses directly under the IT were five to 11-fold greater than stresses at more distal locations, and a Pearson correlation test showed that they could not have been predicted from the interface pressures in the phantom. Accordingly, though pressure ulcer prevention clinics which utilize routine sitting pressure measurements report effective outcomes, the present results highlight a problem in using body-support pressure measurements to predict the risk for pressure-related deep tissue injury.     

高频超声对坐骨结节周围疾病的诊断价值

目的探讨坐骨结节周围病变的高频超声声像图特点及高频超声检查特异性。方法 41例坐骨结节周围病变患者,均经临床确诊,其中男性18例,女性23例;年龄8个月～67岁,平均年龄40岁(标准差1.2岁)。采用高频探头进行纵、横、斜切扫查,回顾性分析临床及高频超声影像资料,将资料分为坐骨结节滑膜囊肿、感染性病变、肿瘤性及肿瘤样病变、软组织损伤4大类,分析各类疾病的声像图特点及超声检查特异度。结果高频超声对坐骨结节周围病变的显示率100.0%(41/41),诊断符合率为82.9%(34/41),其中高频超声对坐骨结节滑膜囊肿诊断符合率为87.5%(7/8),对感染性病变诊断符合率为91.3%(21/23),对肿瘤性及肿瘤样病变诊断符合率为55.6%(5/9)。结论高频超声对坐骨结节滑膜囊肿及感染性病变具有较高的特异性,对肿瘤性及肿瘤样病变特异性较低。因坐骨结节周围软组织损伤病例少,对其特异性有待观察。高频超声对坐骨结节周围疾病的检查具有很高的临床应用价值,可作为首选的影像学检查方法。     

Use of MRI images to measure tissue thickness over the ischial tuberosity at different hip flexion

The goal of this experiment was to investigate changes in the thickness of the soft tissue overlying the ischial tuberosity (IT) due to changes in hip flexion angle and the addition of a sitting load. Eleven healthy subjects were tested. An apparatus constructed from foam blocks and an air bladder was used to position the subjects in different postures within an MRI tube. MRI images of the buttocks and thigh were obtained for four postures: Supine, 45° Hip Flexion, Non-Weight-Bearing 90° Hip-Flexion, and Weight-Bearing 90° Hip-Flexion. The thickness of muscle, adipose tissue, and skin was measured between the IT tip and skin surface, perpendicular to the cushion placed beneath the thighs. The tissue overlying the IT was found to be significantly (P < 0.001) thinner in 90° Hip-Flexion (73.8 ± 9.0 mm) than in the supine position (135.9 ± 8.1 mm). Muscle thickness decreased significantly from Supine to Non-Weight-Bearing 90° Hip-Flexion (59.1 ± 8.5%, P < 0.001), and further decreased from Non-Weight-Bearing to Weight-Bearing 90° Hip-Flexion (46.2 ± 7.9%, P < 0.001). Under Weight-Bearing 90° Hip-Flexion, the muscle tissue deformed significantly (P < 0.001) more than the adipose tissue and skin. We concluded that the tissue thickness covering the IT significantly decreased with hip flexion, and further decreased by nearly half during loading caused by sitting. In addition, the muscle tissue experienced the largest deformation during sitting. The results of this study may improve our understanding of risk factors for pressure ulcer development due to changes in tissue padding over the IT in different postures.     

Finding the optimal setting of inflated air pressure for a multi-cell air cushion for wheelchair patients with spinal cord injury

Pressure distribution patterns of the seating interface on the multi-cell air cushion (ROHO High Profile) of 36 adults with spinal cord injury (SCI) (Neurological level Th3 -L1) were measured at different air pressure levels by a pressure mat measurement system. Stress distribution relative to the inflated air pressure in the air cushion on the patients' wheelchairs was analyzed to determine the appropriate inflated air pressure of the cushion for patients. The maximum pressure points in all subjects were at the areas of the ischial tuberosities (82 to 347 mmHg). The optimal reduction in interface pressure at the ischial tuberosities was obtained just before bottoming out. The cushion air pressure at that point was between 17 and 42 mmHg, and correlated well to body weight (r = 0.495, P = 0.0021). In contrast, the maximum pressure levels did not correlate to body weight or the Body Mass Index (BMI). Pressure at the ischial area could be reduced, but not eliminated, by adjusting the air pressure. The maximum pressure levels seemed to be related to the shape of the buttocks, especially the amount of soft tissue, and exceeded the defined threshold for pressure ulcers (> 80 g/cm2).