Evaluation of a cruciate ligament model: sensitivity to the parameters during drawer test simulation

The knowledge of how cruciate ligaments stabilize the knee joint could be very useful during the execution of daily living activities for the development of clinical procedures. The objective of this study was to evaluate a cruciate ligament model that could achieve this knowledge while avoiding any destructive measurements in living healthy subjects. Subject-specific geometries and kinematic data, acquired from a living subject, were the foundations of the devised model. Each cruciate ligament was modeled with 25 linear-elastic elements and their geometrical properties were subject specific. The anteroposterior drawer test was simulated, and the sensitivity to the reference length and the elastic modulus was performed. Laxity, anterior, and posterior stiffness were calculated and compared with the literature. The laxity was most sensitive to reference length but fitted the literature well considering the reference length estimated from the subject. Both stiffnesses were most sensitive to elastic modulus variations. At full extension, anterior stiffness overestimated the literature, but at 90 degrees good comparisons with the literature were obtained. Posterior stiffness showed smaller overestimations. The devised model, when properly improved, could evaluate the role of the cruciate ligaments of a living subject during the execution of daily living activities.     

Application of a rice simulation model in high temperature sensitivity study

以调试校正较高精度的ORYZA2000模型参数及高温敏感性模拟验证为目的, 为模型适应性和本地化提供依据, 利用江苏省9个试验点5个水稻(Oryza sativa)品种的田间观测数据及当地逐日气象数据, 采用ORYZA2000最新版本(V2.13)水稻生长模型, 首先挑选出5个试验点3个品种的观测数据进行模型参数适应性调试校正, 确定了水稻发育生长阶段的各项参数, 然后用该参数对独立样本的4个试验点2个水稻品种地上部分各器官生物量、叶面积指数动态变化过程及最终产量进行了动态模拟。通过t检验和质量评价指标对模拟结果进行了显著性检验。利用通过检验的模型及其参数在假设环境温度不同时间段的持续升高条件下, 开展了高温对水稻生物量及产量影响的模拟研究, 模拟结果的影响幅度与实际高温处理结果的影响幅度进行了比较。结果表明: 1)经过调试校正获得较高精度的水稻发育阶段各参数, 较准确地模拟了水稻生物量和叶面积指数的动态累积过程, 模拟值与观测值基本一致, 说明校正后参数的合理性和有效性; 2)调整参数后高温敏感性模拟结果表明, 孕穗期到开花期温度连续3天、5天、7天升高到35 ℃时, 总生物量、穗生物量和总产量与对照(CK)相比分别下降了12%-25%; 不同时间段连续升高到38 ℃时下降18%-31%; 不同时间段升高到41 ℃时, 各生物量与对照相比分别下降了20%-38%。模型模拟值与控制试验室的观测数据的下降幅度基本一致, 表明经过参数校正的ORYZA2000可以应用于水稻对气温升高响应的预测。     

水稻模拟模型在高温敏感性研究中的应用

以调试校正较高精度的ORYZA2000模型参数及高温敏感性模拟验证为目的, 为模型适应性和本地化提供依据, 利用江苏省9个试验点5个水稻(Oryza sativa)品种的田间观测数据及当地逐日气象数据, 采用ORYZA2000最新版本(V2.13)水稻生长模型, 首先挑选出5个试验点3个品种的观测数据进行模型参数适应性调试校正, 确定了水稻发育生长阶段的各项参数, 然后用该参数对独立样本的4个试验点2个水稻品种地上部分各器官生物量、叶面积指数动态变化过程及最终产量进行了动态模拟。通过t检验和质量评价指标对模拟结果进行了显著性检验。利用通过检验的模型及其参数在假设环境温度不同时间段的持续升高条件下, 开展了高温对水稻生物量及产量影响的模拟研究, 模拟结果的影响幅度与实际高温处理结果的影响幅度进行了比较。结果表明: 1)经过调试校正获得较高精度的水稻发育阶段各参数, 较准确地模拟了水稻生物量和叶面积指数的动态累积过程, 模拟值与观测值基本一致, 说明校正后参数的合理性和有效性; 2)调整参数后高温敏感性模拟结果表明, 孕穗期到开花期温度连续3天、5天、7天升高到35 ℃时, 总生物量、穗生物量和总产量与对照(CK)相比分别下降了12%-25%; 不同时间段连续升高到38 ℃时下降18%-31%; 不同时间段升高到41 ℃时, 各生物量与对照相比分别下降了20%-38%。模型模拟值与控制试验室的观测数据的下降幅度基本一致, 表明经过参数校正的ORYZA2000可以应用于水稻对气温升高响应的预测。     

Estimation of the mean waiting time of a customer subject to balking: a simulation study

To a customer, the waiting time for order processing for a product or service is important information for order placement. If the time foreseen for order fulfillment is long, the order might be lost to a competitor. In particular, modern principles of supply chain management highly suggest information sharing between entities in the chain and information technology has enabled customers to conveniently consider the waiting time for a potential balking decision. To help determine the design and operation of a manufacturing or service system in which a customer may balk based on the foreseen waiting time, this paper develops procedures to estimate the average waiting time of an order. Either the procedures allow the maximum waiting time for a balking decision to be random or do not require knowledge of the arrival process of customers before balking if the balking limit is known. For generality of the model, this paper considers general inter-arrival and service time distributions, and uses the simulation and regression approach.     

Suffocation of nerve fibers by living nanovesicles: a model simulation

A model using nanospheres to allow the simulation of the nonspecific interaction of nanobacteria (NB), one with another or with body tissues, is established. Depending primarily on their concentrations and stress levels, these apatite nanovesicles may nucleate thrombogenic conglomerates in blood, or self-assemble to dense nanoclay layers on surfaces in the body. Partial or total encapsulation of nerve fiber bundles by such mineral layers may interrupt the metabolic exchanges between the surrounded tissue and its immediate environment and may restrict signaling processes. The presented model could provide detailed insight into plaque formation triggered by NB, and the parameters encouraging it.     

A new guide and 2 new cruciate ligament anchors for securing prosthetic cruciate ligaments to the femur

A new drilling device for the correct localization of drilling holes has been developed for the fixation of cruciate ligament prostheses. We describe how the device is employed under surgical operating conditions. Its accuracy in application is demonstrated in a cadaver knee. The device has also been used clinically with success. Two new anchors for the fixation of the ligaments are proposed.     

Knee stability and muscle coordination in patients with anterior cruciate ligament injuries: An electromyographic approach

We present findings on the way in which to use electromyographic (EMG) measurements from muscles acting on the knee in planning rehabilitation of subjects after rupture of anterior cruciate ligament (ACL). ACL subjects demonstrated an earlier recruitment and a tendency to prolonged activity in muscles around the deficient knee as compared with a control group. Especially the hamstring lateralis and the gastrocnemius medialis (GM) muscles showed an earlier EMG onset and a longer EMG burst duration. The clinical relevance of the EMG findings was assessed by comparing the muscle coordination and relative levels of activity between a functionally excellent/good and a functionally poor ACL patient group. Significant differences between the two groups were noted in EMG onset and burst duration of the GM muscle. A rehabilitation program based on the EMG findings from the GM muscle was designed. In this program, the ACL subjects with poor stability were trained to change the EMG activity of the gastrocnemius muscles according to the recruitment pattern of the good/excellent ACL-group. We were able to train the subjects to change their muscle recruitment and to improve their knee stability. The stability of the knee joint depends on the stiffness of the muscles and ligaments around and within the knee. We discuss the importance of the gastrocnemius muscles with regard to knee joint stiffness.     

Investigating the primary stability of the transversal support tibial plateau concept to retain both cruciate ligaments during total knee arthroplasty

Purpose: The important roles of the anterior cruciate ligament regarding knee stability, physiologic kinematics, and proprioception are unquestioned. Thus, various efforts have been made to retain the ACL during total knee arthroplasty (TKA). Neither of the existing solutions to this problem, i.e. bicruciate retaining prostheses and implantation of two unicondylar prostheses, has been successful because of concept-specific problems as well as general difficulties with implant fixation.?The new transversal support tibial plateau concept is a prosthesis of two individual joint surfaces reinforced beneath the articular line by joint surface supports and buttressed by a single transversal support. This configuration, which enables retention of both cruciate ligaments, should provide good bone fixation and ensure long-term alignment of the individual joint surfaces. Methods: In the current study, four prototypes based on this novel concept were developed and the resulting primary stability was analyzed using adapted load testing. The test set-up, with the model-loading of specially prepared Sawbones? and a sinusoidal oscillating load transmission with 25 000 cycles over 10 increasing load levels, achieved subsidence, which enabled comparison of the four different model variants regarding primary stability in view of bone anchoring.Results: The model variant (TSmobile) that allowed transverse glide of the joint surface supports along the transversal support revealed the largest subsidence.Conclusions: A rigid attachment of the joint surface supports of the transversal support tibial plateau thus appears to offer increased primary stability regarding bone anchoring.     

GENESIS: a simulation model of phylogeny 2. A sensitivity analysis

In a former paper (Heijerman 1988) a simulation model of phylogeny, GENESIS, was presented. This paer describes the results of a sensitivity analysis of GENESIS. The analysis is performed by cganging the input parameter values and estimating the relative effects on the model's output, as summarized by several tree statistics. The results show that none of the statistics tested can be classified as an unambiguous estimator of accuracy of methods for estimating hylogenetic trees. The sensitivity analysis increases the insight into the behaviour and applicability of the model. This is a prerequisite for a correct interpretation of the results of the evaluation experiments that will be carried out using GENESIS.     

The migration of sessile organisms: a simulation model with measurable parameters

Abstract. Palaeoecologists have shown that trees migrated at rates of 100–1000 m/yr in response to post-glacial warming. In order to predict the impact of forecast anthropogenic climate changes upon forest ecosystems we need to simulate how trees may migrate in response to the changes predicted for the next 1–2 centuries. These predictions must take account of the impacts upon migration of human land-use and habitat fragmentation. We have developed a spatially-explicit mechanistic model (MIGRATE) able to simulate the migration of a single species across a realistically heterogeneous landscape. MIGRATE uses biological parameters that readily may be estimated from data in the literature or from field studies, and represents the landscape as a grid of cells, each with an associated carrying capacity. A one-dimensional version of MIGRATE has been compared both with Skellam's (1951) diffusion model and with the more recent analytical models of van den Bosch et al. (1990, 1992); despite its fundamentally different approach, MIGRATE provides comparable estimates of migration rates, given equivalent input parameters. An example is described that demonstrates the ability of the two-dimensional version of MIGRATE to simulate the likely pattern of spread of a species across a heterogeneous landscape. It is argued that MIGRATE, or models like it, will play a central role in a spatially-hierarchic modelling strategy that must be developed if we are to achieve the goal of simulating the likely response of trees, and other organisms, to both global climate change and the increasing pressures of human land-use.     

Estimation of genetical parameters for a quantitative trait subject to major gene influences

Both regression and correlation estimates of genetical variance and heritability for a quantitative trait influenced by a major gene can be obtained from the error variance-covariance matrix of MANOVA using relative-relative phenotype pairs as factors. The method is illustrated with parent-offspring data on red cell acid phosphatase phenotypes and serum acid phosphatase activity.     

A global verification study of a quasi-static knee model with multi-bundle ligaments

The ligaments of the knee consist of fiber bundles with variable orientations, lengths and mechanical properties. In concept, however, these structures were too often seen as homogeneous structures, which are either stretched or slack during knee motions. In previous studies, we proposed a new structural concept of the ligaments of the knee. In this concept, the ligaments were considered as multi-bundle structures, with nonuniform mechanical properties and zero force lengths. The purpose of the present study was to verify this new concept.

For this purpose, laxity characteristics of a human knee joint were compared as measured in an experiment and predicted in a model simulation study. In the experiment, the varus-valgus and anterior-posterior laxities of a knee-joint specimen containing the ligaments and the articular surfaces only, were determined. From this knee-joint, geometric and mechanical parameters were derived to supply the parameters for a three-dimensional quasi-static knee-joint model. These parameters included (i) the three-dimensional insertion points of bundles, defined in the four major knee ligaments, (ii) the mechanical properties of these ligament, as functions of their relative insertion orientations and (iii) three-dimensional representations of the articular surfaces. With this model the experiments were simulated. If knee-model predictions and experimental results agree, then the multi-bundle ligament models are validated, at least with respect to their functional role in anterior-posterior and varus-valgus loading of the joint.

The model described the laxity characteristics in AP-translation and VV-rotation of the cadaveric knee-joint specimen reasonably well. Both display the same patterns of laxity changes during knee flexion. Only if a varus moment of 8 N m was applied and if the tibia was posteriorly loaded, did the model predict a slightly higher laxity than that measured experimentally.

From the model-experiment comparisons it was concluded that the proposed structural representations of the ligaments and their mechanical property distributions seem to be valid for studying the anterior-posterior and varus-valgus laxity characteristics of the human knee-joint.     

Microdensitometric analysis for study of skeletal growth and aging in the living subject

Microdensitometric analysis of a radiographic image of mineralized tissue offers information on the morphologic characteristics of the specimen examined. The use of microstructure (such as individual trabecula of bone) and macrostructure (such as Harris lines of arrest) as in vivo bone markers allows for assessment of gross skeletal changes in nondestructive fashion. This technique is also applicable to the study of the interrelationship of tooth and bone. In addition, microdensitometry offers precise information on the fine structure of bone as regards the trabecular elements. This technique is applicable in determining the size and quantity of trabeculae, their persistence over long periods of time, and the factors responsible for change or lack of change in trabeculae during growth and aging.     

Estimation of descriptive parameters of overlapping chromatographic peaks: a simulation study

The characteristics of a non-linear optimization technique for resolution of overlapping chromatographic peaks are examined. A modified Meiron-Marquardt method was used. The estimates of the parameters of overlapping peaks in simulated chromatograms were investigated to indicate the limitations of present mathematical methods and, hopefully, to improve their ultimate utility. Gaussian shapes as well as exponential-Gaussian convolutes were used to simulate the chromatographic peaks. Effects on the overall performance of varying heights, widths, and separation of two peaks were determined. Random additive noise and base line drift were also simulated. For illustrative purposes, the performance of the parameter estimation techniques was expressed in terms of relative errors in estimating the second (or smaller) peak's area, height and location. The results presented indicate the relative importance of noise, skewness, height and width ratios and peak separation on the maximum resolution achievable by numerical methods in an automated chromatographic system.     

Using DL_POLY to study the sensitivity of liquid structure to potential parameters

Two case studies are presented showing the local structure in liquids and how it responds to changes in the intermolecular potential. The idea is to use realistic and unrealistic potentials in order to determine the sensitivity of local liquid structure to potential parameters. The first case study concerns two families of modified water models. In the “hybrid” family, the hydrogen bond strength is reduced, but the geometry kept constant; in the second family, the molecular geometry is changed by reducing the bond angle, keeping a constant molecular dipole moment. The local structure is measured by radial distribution functions, three-dimensional probability distribution functions and three-body angular correlations. The second case study concerns the ionic liquid dimethylimidazolium chloride ([C₁mim]Cl). The effect of reducing the hydrogen bonding potential of the cations while maintaining their charge is examined.     

Knee joint reaction force during tibial diaphyseal lengthening: a study on a rabbit model

The in vivo passive knee joint reaction force was measured in a rabbit model of tibial diaphyseal lengthening. This was based on the assumption that limb lengthening creates soft tissue tension that compresses the joint surface and generates the joint contact force. A measurement method was developed that involved the distraction of the joint and the determination of the distraction force that just separates the joint surfaces. Sixteen immature (mean+/-SD age=9+/-0.6 weeks) New Zealand White rabbits underwent 30% (left) tibial diaphyseal lengthening at a rate of two 0.4mm incremental lengthenings per day. The knee joint reaction force was measured at the end of lengthening (8 rabbits, mean+/-SD age=14+/-0.6 weeks) and five weeks after lengthening (8 rabbits, mean+/-SD age=19+/-0.7 weeks). An instrumented bilateral distractor and an extensometer were fixed cross the knee joint. The joint distraction force and distraction displacement were measured when the joint was distracted in steps and after the section of the Achilles tendon. The joint reaction force on the lengthened side was significantly higher than the control side at both time points (mean+/-SD 44.4+/-7.8 N v. 27.2+/-4.0 N at the end of lengthening, 44.3+/-S6.5 N v. 31.3+/-3.0 N at 5 weeks after lengthening). The contribution of the gastrocnemius to the joint reaction force on the lengthened side was also significantly higher than the control side at both time points (mean+/-SD 9.0+/-1.3N v. 2.8+/-0.8 N at the end of lengthening, 5.3+/-1.4N v. 2.7+/-0.5N at 5 weeks after lengthening). There were significant knee and ankle joint contractures at the end of lengthening, as evidenced by decreased range of motion (mean+/-SD 27+/-8 degrees and 36+/-13 degrees, respectively), which remained 5 weeks after lengthening (mean+/-SD 26+/-6 degrees and 35+/-8 degrees, respectively). The gastrocnemius contributed about 20% of the joint reaction force, indicating that changes in the other intra- and extra-articular structures due to joint contracture may be more important in generating the joint reaction force.     

Bayesian hierarchical models combining different study types and adjusting for covariate imbalances: a simulation study to assess model performance

Background

Bayesian hierarchical models have been proposed to combine evidence from different types of study designs. However, when combining evidence from randomised and non-randomised controlled studies, imbalances in patient characteristics between study arms may bias the results. The objective of this study was to assess the performance of a proposed Bayesian approach to adjust for imbalances in patient level covariates when combining evidence from both types of study designs.

Methodology/Principal Findings

Simulation techniques, in which the truth is known, were used to generate sets of data for randomised and non-randomised studies. Covariate imbalances between study arms were introduced in the non-randomised studies. The performance of the Bayesian hierarchical model adjusted for imbalances was assessed in terms of bias. The data were also modelled using three other Bayesian approaches for synthesising evidence from randomised and non-randomised studies. The simulations considered six scenarios aimed at assessing the sensitivity of the results to changes in the impact of the imbalances and the relative number and size of studies of each type. For all six scenarios considered, the Bayesian hierarchical model adjusted for differences within studies gave results that were unbiased and closest to the true value compared to the other models.

Conclusions/Significance

Where informed health care decision making requires the synthesis of evidence from randomised and non-randomised study designs, the proposed hierarchical Bayesian method adjusted for differences in patient characteristics between study arms may facilitate the optimal use of all available evidence leading to unbiased results compared to unadjusted analyses.