CroweⅣ型髋关节脱位儿童髋臼有限元生物力学分析

目的:建立CroweW型发育性髋关节脱位儿童骨盆三维有限元模型,对发育性髋关节脱位儿童真性髋臼及假性髋臼的生物力学进行初步分析.方法:采用单侧发育性髋关节脱位儿童骨盆CT扫描DICOM数据,通过Mimics10.0对图像DICOM数据进行重建,经Geomagic Proe5.0进行网格优化,在Hepermesh 10.0中进行有限元网格划分后输入ANSYS12.0中,在ANSYS中根据解剖部位建立骨盆主要韧带,行单腿站立载荷加载,计算该加载方式下骨盆的应力及位移分布情况.结果:模拟患者单腿(患侧)站立状态下身体重心通过假关节的中心,骨盆极度倾斜约45°,给予生理载荷,应力主要集中在假髋臼和骶髂关节面之间,耻骨上肢内侧是应力集中区但是应力小于骶髂关节周围部分;患侧骨盆位移以髂骨翼前侧向后侧逐渐减弱.结论:建立的有限元模型在静载荷下特征部位的应力及位移能够反映CroweⅣ型髋关节脱位儿童骨盆的力学结构特性,模型的准确性高,可以成为CroweⅣ型髋关节脱位儿童骨生物力学研究的工具,满足临床研究需要.     

Dega骨盆截骨术后最佳中心边缘角的三维有限元分析

目的:应用三维有限元技术评估发育性髋关节脱位(developmental dysplasia of the hip,DDH)患儿在Dega骨盆截骨术后不同中心边缘角(center-edge angle,CEA)状态下髋臼的应力分布,为术前的手术规划提供有参考价值的生物力学结果。方法:使用已建立的DDH患者髋关节三维有限元模型,以术后CEA27°为中间值,每3°为一个变量,在Mimics誖10.0软件的模拟手术模块分别构建7组髋臼截骨术后的模型。在单腿站立和双腿站立状态下测量不同CEA状态下髋臼的应力分布。结果:单腿站立情况下,CEA为24°、27°、30°和33°的术后模型患侧髋臼的峰值应力接近正常侧。双腿站立情况下,CEA为24°时双侧髋臼的峰值应力最为接近。结论:对于该患者而言,在7组术后CEA中,24°时患侧髋臼的峰值应力与健侧最为接近,可以认为是最佳的术后CEA。有限元技术能够为Dega手术的术前规划提供个性化的指导方案。     

Performance criteria for generating predictive optimal control simulations of bicycle pedaling

The purpose of this study was to identify one or more performance-based criteria that may be used to generate predictive optimal control simulations of submaximal pedaling. Two-legged pedaling simulations were generated based on minimizing muscle activation, muscle stress, metabolic energy, time derivative of muscle force, and minimizing metabolic energy while pedaling smoothly. The simulations based on minimizing muscle activation and muscle stress most closely matched experimental pedaling data, with the activation criterion better matching experimental muscle activation timing. We conclude that predictive simulations of submaximal pedaling may be generated using a cost function based on minimizing muscle activation.     

内蒙古和林格尔土城子农业人群与林西井沟子游牧人群股骨中部的生物力学对比

肢骨的形态结构可以反映人类进化、古代人群的生存适应性活动和生存环境等重要信息。基于“骨骼功能适应”和“杠杆原理”,有学者对不同生计方式的古代人群下肢股骨开展了大量的研究工作,但是,国内外尚未有关于农业人群和游牧人群股骨之间差异性研究的报道。本文选取两个具有代表性的古代人群,即内蒙古和林格尔土城子戍边农业人群和内蒙古林西井沟子游牧人群进行对比研究。通过对股骨骨干中部横断面生物力学分析发现,农业人群股骨粗壮度与游牧人群之间具有显著差异。前者的平均粗壮度较大,后者女性组下肢骨的活动强度明显较小,这可能与游牧人群经常从事骑马活动而下肢骨活动强度相对较少有关。农业人群股骨指数的变异范围均大于游牧人群,这可能与前者男性的士兵身份有关;同时,也提示土城子男性组股骨所反映的行为活动信息并不代表真正意义上的纯农业人群下肢骨行为模式,而是一种农业和士兵行为的混合模式。在性别分工上,井沟子组的男女性均从事骑马活动,两侧股骨受力较为一致,在两侧不对称性程度和骨干横断面形状上的男女差异不大;男性股骨的粗壮度要明显大于女性,这与井沟子组男性还从事一定的狩猎行为有关。与游牧人群女性较为纤细的股骨不同,土城子组女性作为典型的农业人群代表,其下肢骨整体的活动强度较大,几乎与同组的男性和井沟子组男性相当,组内的性别差异相对较小;骨干横断面形状的显著性差异说明,土城子组内部男性和女性的行为活动方式存在明显的性别分工。本文研究结果说明农业人群女性的下肢骨活动强度较大,在行为活动方式上,戍边农业人群具有更为明显的性别分工。     

Validity and reliability of a shoe-embedded sensor module for measuring foot progression angle during over-ground walking

Wearable systems are becoming increasingly popular for gait assessment outside of laboratory settings. A single shoe-embedded sensor module can measure the foot progression angle (FPA) during walking. The FPA has important clinical utility, particularly in populations with knee osteoarthritis, as it is a target for biomechanical treatments. However, the validity and the day-to-day reliability of FPA measurement using wearable systems during over-ground walking has yet to be established. Two gait analysis sessions on 20 healthy adults were conducted. During both sessions, participants performed natural over-ground walking in a motion capture laboratory and on a 100 m linear section of outdoor athletics track. FPA was measured in the laboratory via marker trajectory data, while the sensor module measured FPA during the outdoor track walking. Validity was examined by comparing the laboratory- and sensor-measured average FPA. Day-to-day reliability was examined by comparing the sensor-measured FPA between the first and second gait analysis sessions. Average absolute error between motion capture and sensor measured FPA were 1.7° and 2.1° at session 1 and 2, respectively. A Bland and Altman plot indicated no systematic bias, with 95% limit of agreement widths of 4.2° – 5.1°. Intraclass correlation coefficient (ICC_2k) analysis resulted in good to excellent validity (ICC = 0.89 – 0.91) and reliability (ICC = 0.95). Overall, the shoe-embedded sensor module is a valid and reliable method of measuring FPA during over-ground walking without the need for laboratory equipment.     

Most marathon runners at the 2017 IAAF World Championships were rearfoot strikers,and most did not change footstrike pattern

The aim of this study was to analyze footstrike patterns in elite marathon runners at the 2017 IAAF World Championships. Seventy-one men and 78 women were analyzed in their respective races. Athletes’ footstrike patterns were recorded (120 Hz) at approximately 8.5, 19, 29.5 and 40 km (“Laps 1 – 4”) and categorized as either rearfoot (RFS), midfoot or forefoot striking; the latter two were classified together as non-rearfoot striking (NRFS). The most common footstrike pattern was RFS, with proportions never less than 54% of men or 67% of women at any distance. There were no sex-based differences for proportion of footstrike patterns, and there were no differences between footstrike proportions when comparing the top and bottom 50% of men finishers, or between women during Laps 1 and 2. A greater proportion of the top 50% of women maintained NRFS than amongst the bottom 50%. The proportion of RFS increased with distance run in the men’s race, although more than 75% of athletes across both marathons had consistent footstrike patterns between laps (79 RFS and 36 NRFS). As most athletes were RFS (including the top four finishing men), there appears to be no clear advantage to NRFS in marathon running. Coaches should note that it is normal for elite marathon runners to be either RFS or NRFS; however, forefoot striking was rare. The high proportion of athletes who maintained their footstrike pattern reflected individualized preferences for a given footstrike pattern.     

Mapping the spatial variation of mitral valve elastic properties using air-pulse optical coherence elastography

The mitral valve is a highly heterogeneous tissue composed of two leaflets, anterior and posterior, whose unique composition and regional differences in material properties are essential to overall valve function. While mitral valve mechanics have been studied for many decades, traditional testing methods limit the spatial resolution of measurements and can be destructive. Optical coherence elastography (OCE) is an emerging method for measuring viscoelastic properties of tissues in a noninvasive, nondestructive manner. In this study, we employed air-pulse OCE to measure the spatial variation in mitral valve elastic properties with micro-scale resolution at 1 mm increments along the radial length of the leaflets. We analyzed differences between the leaflets, as well as between regions of the valve. We found that the anterior leaflet has a higher elastic wave velocity, which is reported as a surrogate for stiffness, than the posterior leaflet, most notably at the annular edge of the sample. In addition, we found a spatial elastic gradient in the anterior leaflet, where the annular edge was found to have a greater elastic wave velocity than the free edge. This gradient was less pronounced in the posterior leaflet. These patterns were confirmed using established uniaxial tensile testing methods. Overall, the anterior leaflet was stiffer and had greater heterogeneity in its mechanical properties than the posterior leaflet. This study measures differences between the two mitral leaflets with greater resolution than previously feasible and demonstrates a method that may be suitable for assessing valve mechanics following repair or during the engineering of synthetic valve replacements.     

Frictional properties of contacting surfaces in the hemelytra-hindwing locking mechanism in the bug<Emphasis Type="Italic"> Coreus marginatus</Emphasis> (Heteroptera,Coreidae)

The structure and function of the hemelytra-to-hindwing locking mechanism of the bug Coreus marginatus were analysed. The system consists of a cuticular protrusion in the ventral side of the hemelytra, which locks the subcostal border of the hindwing in flight. The speed and distance slid by both surfaces against one another during flight were assessed using a combination of high-speed video recordings and a 2D geometrical model. The friction coefficient between sliding surfaces was assessed using a micromanipulator, coupled with force transducers. This was done under three experimental conditions: freshly dissected, air dried and rehydrated ethanol preserved samples. The results showed a high speed of sliding, approximately 0.18 m s^–1, with a relatively low friction coefficient (0.2 ). There was no evident difference in the friction measured under the various treatments, with the exception of the rehydrated condition, which was lower. The surface morphology of the wing locking mechanism, namely outgrowths of one part having rounded edges, and completely flat surface on the counterpart, effectively aids in the reduction of friction at the microscopic level. The structure is effective even dry, and after being preserved in ethanol, suggesting that no cuticle secreted lubrication substance is responsible for its effectiveness. The ultrastructure presumably confers mechanical stability to the system under the high load it is subjected to in flight.     

Passive hinge forces in the feeding apparatus of<Emphasis Type="Italic"> Aplysia</Emphasis> aid retraction during biting but not during swallowing

Swallowing and biting responses in the marine mollusk Aplysia are both mediated by a cyclical alternation of protraction and retraction movements of the grasping structure, the radula and underlying odontophore, within the feeding apparatus of the animal, the buccal mass. In vivo observations demonstrate that Aplysia biting is associated with strong protractions and rapid initial retractions, whereas Aplysia swallowing is associated with weaker protractions and slower initial retractions. During biting, the musculature joining the radula/odontophore to the buccal mass (termed the hinge) is stretched more than in swallowing. To test the hypothesis that stretch of the hinge might contribute to rapid retractions observed in biting, we analyzed the hinges passive properties. During biting, the hinge is stretched sufficiently to assist retraction. In contrast, during swallowing, the hinge is not stretched sufficiently for its passive forces to assist retraction, because the odontophores anterior movement is smaller than during biting. A quantitative model demonstrated that steady-state passive forces were sufficient to generate the retraction movements observed during biting. Experimental measures of the relative magnitude of the hinges active and passive forces at the protraction displacements of biting suggest that passive forces are at least a third of the total force.Abbreviations I1/I3 intrinsic buccal muscles 1 and 3 - I2 intrinsic buccal muscle 2 (nomenclature from Howells 1942)     

Reconfiguration as a Prerequisite for Survival in Highly Unstable Flow-Dominated Habitats

Unstable and mechanically demanding habitats like wind-exposed open fields or the wave-swept intertidal require rapid adaptive processes to ensure survival. The mechanism of passive reconfiguration was analyzed in two plant models exposed to irregular flow of water or air, two species of the brown seaweed Durvillaea and the giant reed Arundo donax. Irrespective of the surrounding media and the subsequent Reynolds numbers (Re ~ 10⁵ - 10⁷), reconfiguration seems to be the key strategy for streamlining to avoid overcritical drag-induced loads. This passive mechanism is also discussed in the context of the requirement of a maximized surface area for light interception, so that morphological adaptations to rapid reconfiguration represent at least a bifactorial optimization. Both tested plant models exhibited the same principles in streamlining. At a specific threshold value, the proportionality between drag forces and flow velocity can be reduced from the second power close to an almost linear relation. This empirically derived relation could be characterized by a figure of merit or Vogel number (B). A value close to B = -1, resulting in a linear increase of drag force with velocity, was found at higher velocities for both the seaweeds and the giant reed, as well as for a variety of plants described in the literature. It is therefore concluded that the ability to reduce velocity-dependent drag force to a linear relation is a potentially important adaptation for plants to survive in unstable flow-dominated habitats.