Multibody dynamic simulation of knee contact mechanics

Multibody dynamic musculoskeletal models capable of predicting muscle forces and joint contact pressures simultaneously would be valuable for studying clinical issues related to knee joint degeneration and restoration. Current three-dimensional multibody knee models are either quasi-static with deformable contact or dynamic with rigid contact. This study proposes a computationally efficient methodology for combining multibody dynamic simulation methods with a deformable contact knee model. The methodology requires preparation of the articular surface geometry, development of efficient methods to calculate distances between contact surfaces, implementation of an efficient contact solver that accounts for the unique characteristics of human joints, and specification of an application programming interface for integration with any multibody dynamic simulation environment. The current implementation accommodates natural or artificial tibiofemoral joint models, small or large strain contact models, and linear or nonlinear material models. Applications are presented for static analysis (via dynamic simulation) of a natural knee model created from MRI and CT data and dynamic simulation of an artificial knee model produced from manufacturer's CAD data. Small and large strain natural knee static analyses required 1 min of CPU time and predicted similar contact conditions except for peak pressure, which was higher for the large strain model. Linear and nonlinear artificial knee dynamic simulations required 10 min of CPU time and predicted similar contact force and torque but different contact pressures, which were lower for the nonlinear model due to increased contact area. This methodology provides an important step toward the realization of dynamic musculoskeletal models that can predict in vivo knee joint motion and loading simultaneously.     

Modeling of occupant dynamics during automobile rear-end impacts

Procedures for studying the dynamic response of the occupant within a rear-end impacted vehicle are presented. Most of the researches in the impact analysis were performed by experimental approach and this costs a lot of time and money. Especially, the repeatability is very hard to produce in a destructive condition. Most of all, the analytic parameters can be investigated are limited by the experimental approach. By using numerical techniques, this research employs Kane's equation and Huston's method to develop a simulated system with visual graphic output to observe the rear-end impact response. According to the simulated results, at a constant seatback angle the maximum acceleration values of head and chest increased with the increasing of impact velocity. Furthermore, at a constant impact velocity the relative rotation angle of a passenger's head to chest decreased with the increasing of initial seatback angle.     

Heat-transfer dynamics during cryogen spray cooling of substrate at different initial temperatures

Cryogen spray cooling (CSC) is used to minimize the risk of epidermal damage during laser dermatologic therapy. However, the dominant mechanisms of heat transfer during the transient cooling process are incompletely understood. The objective of this study is to elucidate the physics of CSC by measuring the effect of initial substrate temperature (T0) on cooling dynamics. Cryogen was delivered by a straight-tube nozzle onto a skin phantom. A fast-response thermocouple was used to record the phantom temperature changes before, during and after the cryogen spray. Surface heat fluxes (q") and heat-transfer coefficients (h) were computed using an inverse heat conduction algorithm. The maximum surface heat flux (q"max) was observed to increase with T0. The surface temperature corresponding to q"max also increased with T0 but the latter has no significant effect on h. It is concluded that heat transfer between the cryogen spray and skin phantom remains in the nucleate boiling region even if T0 is 80 degrees C.     

Innocuous cooling can produce nociceptive sensations that are inhibited during dynamic mechanical contact

In a previous study of the heat grill illusion, sensations of burning and stinging were sometimes reported when the skin was cooled by as little as 2°C. Informal tests subsequently indicated that these nociceptive sensations were experienced if cooling occurred when the stimulating thermode rested on the skin, but not when the thermode was cooled and then touched to the skin. In experiment 1 subjects judged the intensity of thermal (cold/warm) and nociceptive (burning/stinging) sensations when the volar surface of the forearm was cooled to 25°C (1) via a static thermode (Static condition), or (2) via a cold thermode touched to the skin (Dynamic condition). The total area of stimulation was varied from 2.6 to 10.4 cm² to determine if the occurrence of nociceptive sensations depended upon stimulus size. Burning/stinging was rated 10.3 times stronger in the Static condition than in the Dynamic condition, and this difference did not vary significantly with stimulus size. In experiment 2, thermal and nociceptive sensations were measured during cooling to just 31°, 29° or 27°C, and data were obtained on the frequency at which different sensation qualities were experienced. Stinging was the most frequently reported nociceptive quality in the Static condition, and stinging and burning were both markedly reduced in the Dynamic condition. In experiment 3 we tested the possibility that dynamic contact might have inhibited burning and stinging not because of mechanical contact per se, but rather because dynamic contact caused higher rates of cooling. However, varying cooling rate over a tenfold range (–0.5° to –5.0°/s) had no appreciable effect on the frequency of stinging and burning. Overall, the data show that mild cooling can produce nociceptive sensations that are suppressed under conditions of dynamic mechanical contact. The latter observation suggests that cold is perceived differently during active contact with objects than during passive heat loss to the environment. Hypotheses about the physiological basis of the nociceptive sensations at mild temperatures and their possible role in the phenomena of paradoxical heat and synthetic heat are discussed. Electronic Publication     

Modeling dynamic skinfold compression

Real time compression of skinfolds was measured at three sites (triceps, abdominal medial calf), using a Slim Guide skinfold caliper adapted by the addition of a potentiometer, on eight males and eight females (age range 18–40 years). An average of eight trials for each subject at each site was used in modeling the compression curves. A mechanical model was developed, comprised of two parallel spring and viscous components in series with each other. where: Tt = thickness at time t; Tinitial = intial skinfold thickness; F = force exerted by caliper; k₁ and k₂ = coefficients of elasticity; b₁ and b₂ = coefficients of viscosity. This two-component model was the best fitting model in comparison to one or three component alternatives. The coefficients of the model were different by sex and skinfold site. Coefficients for females showed greater elasticity and less viscosity compared to those for males. Further, there appeared to be a systematic site difference with the triceps having less elasticity and viscosity in both sexes. Am. J. Hum. Biol. 11:531–537, 1999. © 1999 Wiley-Liss, Inc.     

全膝关节置换个体化患者右转步态的骨肌多体动力学仿真

目的构建个体化患者全膝关节置换(total knee replacement,TKR)的骨肌多体力学模型,模拟患者下肢右转步态时体内膝关节的生物力学行为。方法以1位具体患者的相关数据为材料,基于骨肌动力学仿真软件Any Body及其依赖于力的运动学建模方法,建立与患者相对应的TKR下肢骨肌多体动力学模型,并对患者的右转步态进行模拟。通过逆动力学分析右转步态,同时预测患者膝关节接触力、关节运动、肌肉活性和韧带力。结果模型预测的胫骨-股骨关节内、外侧接触力的均值均方根误差分别为285、164 N,相关系数分别为0.95和0.61,预测的髌骨接触力均值最大值为250 N。模型预测的接触力和肌肉活性与患者实验测量结果基本一致。此外,模型预测的胫骨-股骨的伸展弯曲、内外旋和内外翻运动的均值分布范围分别为3°~47°、-3.4°~1.5°、0.2°~-1.5°,胫骨-股骨的前后、上下和内外侧平移的运动范围分别为2.6~9.0 mm、1.6~3.2 mm、4.2~5.2 mm。模型还预测了内、外侧旁系韧带力和后交叉韧带力,其最大值分别为190、108、108 N。结论所开发的模型能够预测人工膝关节体内生物力学行为,为后续研究膝关节假体临床失效问题提供强有力的计算平台。     

The effect of corrective surgery on energy expenditure during ambulation in children with cerebral palsy

Summary Mechanical efficiency, heart rate, blood lactate, and some other variables were studied in six children with cerebral palsy who walked on a treadmill before and after corrective surgery. During each test, conducted at each child's naturally selected speed, two situations were studied: steady state level walking for 9 min, and then walking at an increasing inclination up to 20% for another 10 min. During the test the subjects were allowed to hold on to a handrail to eliminate the risk of falling off the treadmill. The corrective surgery resulted in a 5% reduction in oxygen consumption per kg body mass during level walking. The subjects' levels of physical fitness, as estimated from oxygen pulse, however, were unchanged. These results are indicative of a biomechanical improvement due to the corrective surgery. While walking at a 20% inclination the subjects off loaded themselves to different degrees on the handrail which influenced the results. Their feeling of exhaustion at this load was probably due to local factors, since heart rate was well below maximal values, and blood lactate, respiratory exchange ratio and ventilatory equivalent also indicated that they were below their anaerobic thresholds (50–60% of maximal oxygen uptake).     

一种新型膝关节假体在步态过程中接触应力的有限元仿真

目的对一种使用新方法设计的新型人工膝关节假体进行有限元模拟分析,研究改变关节假体外髁关节面的扭转角度对改善人工膝关节假体力学环境的影响。方法依据志愿者提供的膝关节CT测量数据,建立3个膝关节假体模型,内侧股骨髁在冠状面保持圆曲线,外侧股骨髁根据冠状面轮廓曲线的扭转角度不同,分为0°、10°、20°(分别命名为模型1、2、3)。将假体模型导入有限元软件,输入自然人体膝关节的运动步态信息为加载工况,模拟步态过程中膝关节假体的运动状态,并将通过模拟得到的髁间应力同使用接触力学理论公式得到的应力计算结果进行对比。结果 3组模型的最大应力出现在步态13%处,此时关节轴向力最大(2.6 kN)。模型1内、外髁最大应力分别为35.5、30.6 MPa,模型2内、外髁最大应力分别为38.4、32.6 MPa,模型3内、外髁最大应力分别为38.3、43.1 MPa。模型2、3的应力曲线相比模型1变化较为平缓。模拟得到的应力曲线与理论计算曲线的趋势相同,但个别步态时刻处有差异。结论通过增大人工膝关节假体外髁曲面的扭转角度可以改善膝关节力学环境,经过改进的膝关节假体在步态过程中对胫骨衬垫的应力突变减少,可以延长假体的使用寿命。     

The real time video vector display of ground reaction forces during ambulation

A new radiotelemetry receiver type 7060 for use with radiopills is described. Its performance under laboratory conditions was assessed and its use for clinical colonic pressure measurements evaluated. The receiver, which resembles a small microcomputer, was easy to set up and worked reasonably well under ward conditions. Difficulties were experienced with the belt aerial supplied with the receiver, which did not reliably pick up signals from a freely moving radiopill. The receiver is not suitable for ambulatory applications. Its main clinical use is in situations where frequent sampling of the radiopill's signal over a long period of time is essential (e.g. colonic pressures). The large quantity of data generated can be fed from the receiver's analogue or digital output on line to a recorder.     

Impedance control and internal model use during the initial stage of adaptation to novel dynamics in humans

This study investigated the neuromuscular mechanisms underlying the initial stage of adaptation to novel dynamics. A destabilizing velocity-dependent force field (VF) was introduced for sets of three consecutive trials. Between sets a random number of 4–8 null field trials were interposed, where the VF was inactivated. This prevented subjects from learning the novel dynamics, making it possible to repeatedly recreate the initial adaptive response. We were able to investigate detailed changes in neural control between the first, second and third VF trials. We identified two feedforward control mechanisms, which were initiated on the second VF trial and resulted in a 50% reduction in the hand path error. Responses to disturbances encountered on the first VF trial were feedback in nature, i.e. reflexes and voluntary correction of errors. However, on the second VF trial, muscle activation patterns were modified in anticipation of the effects of the force field. Feedforward cocontraction of all muscles was used to increase the viscoelastic impedance of the arm. While stiffening the arm, subjects also exerted a lateral force to counteract the perturbing effect of the force field. These anticipatory actions indicate that the central nervous system responds rapidly to counteract hitherto unfamiliar disturbances by a combination of increased viscoelastic impedance and formation of a crude internal dynamics model.     

Modeling and simulation of flexible needles

Needle insertion is performed in many clinical and therapeutic procedures. Tissue displacement and needle bending which result from needle–tissue interaction make accurate targeting difficult. For performing physicians to gain essential needle targeting skills, needle insertion simulators can be used for training. An accurate needle bending model is essential for such simulators. These bending models are also needed for needle path planning.In this paper, three different models are presented to simulate the deformations of a needle. The first two models use the finite element method and take the geometric nonlinearity into account. The third model is a series of rigid bars connected by angular springs. The models were compared to recorded deformations during experiments of applying lateral tip forces on a brachytherapy needle. The model parameters were identified and the simulation results were compared to the experimental data. The results show that the angular spring model, which is computationally the most efficient model, is also the most accurate in modeling the bending of the brachytherapy needle.     

Near infrared spectroscopy-derived interstitial hydrogen ion concentration and tissue oxygen saturation during ambulation

The objective of this study was to determine whether walking and running at different treadmill speeds resulted in different metabolic and cardiovascular responses in the vastus lateralis (VL) and lateral gastrocnemius (LG) by examining metabolite accumulation and tissue oxygen saturation. Ten healthy subjects (6 males, 4 females) completed a submaximal treadmill exercise test, beginning at 3.2 km h⁻¹ and increasing by 1.6 km h⁻¹ increments every 3 min until reaching 85% of age-predicted maximal heart rate. Muscle tissue oxygenation (SO₂), total hemoglobin (HbT) and interstitial hydrogen ion concentration ([H⁺]) were calculated from near infrared spectra collected from VL and LG. The [H⁺] threshold for each muscle was determined using a simultaneous bilinear regression. Muscle and treadmill speed effects were analyzed using a linear mixed model analysis. Paired t-tests were used to test for differences between muscles in the [H⁺] threshold. SO₂ decreased (P = 0.001) during running in the VL and LG, but the SO₂ response across treadmill speeds was different between muscles (P = 0.047). In both muscles, HbT and [H⁺] increased as treadmill speed increased (P < 0.001), but the response to exercise was not different between muscles. The [H⁺] threshold occurred at a lower whole-body VO₂ in the LG (1.22 ± 0.63 L min⁻¹) than in the VL (1.46 ± 0.58 L min⁻¹, P = 0.01). In conclusion, interstitial [H⁺] and SO₂ are aggregate measures of local metabolite production and the cardiovascular response. Inferred from simultaneous SO₂ and [H⁺] measures in the VL and LG muscles, muscle perfusion is well matched to VL and LG work during walking, but not running.     

Selective contact during TCR recognition

Recent structural analysis of the peptide-MHC complex revealsthat an antigenic peptide binds to MHC in only one conformationand that side chains anchoring in the binding pocket would notcontact TCR. The identification of all the MHC-anchoring residueson an antigenic peptide is a prerequisite to understand howa given peptide interacts with the TCR. In a combination ofbinding analysis and model simulation, model peptide repressorcl 16–26 was shown to bind to I-E^k through four anchorresidues (Leu 18, Ile21, Glu23 and Lys26), a pattern found inmany l-E^k-binding peptides. TCR reactivity analysis clearlyindicates a great variation in the interaction with cl 16–26by T cells generated from different strains of l-E^k-bearingmice. Most of the T cells generated from A/J mice reacted withthe central region of cl 16–26, while there is a greatdiversity on the recognition of cl 16–26 by T cells fromC3H and B10.BR mice. Despite the diverse interactions with antigenicpeptide by these T cells, most TCR-I-Ek contacts are limitedto the central region of the I-E^k ß-chain. T cellsrecognizing only the N-terminal part of cl 16–26 werefound to contact I-E^k at nearly the same residues as T cellsinteracting with the C-terminal of cl 16–26. TCR-I-E^krecognition was apparently independent of TCR-cl 16–26contact. The discordant TCR-peptide and TCR-MHC interactionsmay represent a unique feature of TCR recognition.     

结合呼吸运动的改进型多分支心血管系统建模与仿真

目的根据电网络模型法提出一个改进型的多分支人体心血管系统模型,以深入研究人体心血管及体循环系统。方法该模型包括心脏、肺循环、头颈循环及四肢循环,共包括48个微分方程,在此基础上建立了呼吸运动中心肺交互作用的数学模型,并应用MATLAB软件中的SIMULINK模块仿真实现得到各段血管的血压及血流量等生理信号。结果模型可模拟健康及多种心血管疾病的血压血流状态,模拟波形与Physio Bank数据库中实际生理波形相符,在健康、心力衰竭及动脉粥样硬化三种条件下,模拟波形的收缩压(SBP)、舒张压(DBP)、每搏输出量(SV)及心输出量(CO)等生理参数均符合临床测量值。将所选数据库中的呼吸信号代入模型后,可直接观察心率和血压随呼吸运动的变化规律:吸气过程经约1.5~2 s的延迟后心率代偿性加快,呼气过程则发生相反的变化趋势,与实际心肺交互过程中的呼吸性窦性心律不齐(respiratory sinus arrhythmia,RSA)现象相符。结论此改进型心血管及体循环系统模型的仿真结果与临床实际数据相符,灵活性高,对诊断和治疗心血管系统疾病具有重要意义。     

Actin dynamics during phagocytosis

Bacteria, apoptotic cells and other particulate material are taken up through phagocytosis, a conserved cellular function driven by actin polymerization. As reviewed here, small GTPases of the Rho family, their activators and effectors control the local reorganization of the actin cytoskeleton underneath bound particles. Remarkably, the molecular actors and regulatory mechanisms involved during phagocytosis through the FcR or the CR3 receptors are very similar to those underlying the cytoskeletal rearrangements that take place at the leading edge of motile cell and at adhesion sites, respectively.     

Prediction of object contact during grasping

The maximum grip aperture (MGA) during prehension is linearly related to the size of objects to be grasped and is adapted to the haptically sensed object size when there is a discrepancy between visual and haptic information. We have investigated what information is used to drive this adaptation process and how the onset of fingertip forces on the object is triggered. Subjects performed a reach-to-grasp task, where the object seen and the object grasped physically never were the same. We measured the movements of the index finger and the thumb and the contact forces between each fingertip and the object. The subjects’ adaptation of the MGA was unrelated both to different fingertip velocities at the moment of object contact, or the fingertip forces. Instead, the ‘timing’ of contact between the fingers and the object was most consistently influenced by introducing a size discrepancy. Specifically, if the object was larger than expected, the moment of contact occurred earlier, and if the object was decreased in size, then the contact occurred later. During adaptation, these timing differences were markedly reduced. Also, the motor command for applying forces on the object seemed to be released in anticipation of the predicted moment of contact. We therefore conclude that the CNS dynamically predicts when contact between the fingertips and objects occur and that aperture adaptation is primarily driven by timing prediction errors.