Transformation methods for estimation of subject-specific scapular muscle attachment sites

The parameters that describe the soft tissue structures are among the most important anatomical parameters for subject-specific biomechanical modelling. In this paper, we study one of the soft tissue parameters, namely muscle attachment sites. Two new methods are proposed for transformation of the muscle attachment sites of any reference scapula to any destination scapula based on four palpable bony landmarks. The proposed methods as well as one previously proposed method have been applied for transformation of muscle attachment sites of one reference scapula to seven other scapulae. The transformation errors are compared among the three methods. Both proposed methods yield significantly less (p < 0.05) prediction error as compared to the currently available method. Furthermore, we investigate whether there exists a reference scapula that performs significantly better than other scapulae when used for transformation of muscle attachment sites. Seven different scapulae were used as reference scapula and their resulting transformation errors were compared with each other. In the considered statistical population, no such a thing as an ideal scapula was found. There was, however, one outlier scapula that performed significantly worse than the other scapulae when used as a reference. The effect of perturbations in both muscle attachment sites and other muscle properties is studied by comparing muscle force predictions of a musculoskeletal model between perturbed and non-perturbed versions of the model. It is found that 10 mm variations in muscle attachments have more significant effect on muscle force predictions than 10% variations in any of the other four analysed muscle properties.     

Evaluation of regression-based 3-D shoulder rhythms

The movements of the humerus, the clavicle, and the scapula are not completely independent. The coupled pattern of movement of these bones is called the shoulder rhythm. To date, multiple studies have focused on providing regression-based 3-D shoulder rhythms, in which the orientations of the clavicle and the scapula are estimated by the orientation of the humerus. In this study, six existing regression-based shoulder rhythms were evaluated by an independent dataset in terms of their predictability. The datasets include the measured orientations of the humerus, the clavicle, and the scapula of 14 participants over 118 different upper arm postures. The predicted orientations of the clavicle and the scapula were derived from applying those regression-based shoulder rhythms to the humerus orientation. The results indicated that none of those regression-based shoulder rhythms provides consistently more accurate results than the others. For all the joint angles and all the shoulder rhythms, the RMSE are all greater than 5°. Among those shoulder rhythms, the scapula lateral/medial rotation has the strongest correlation between the predicted and the measured angles, while the other thoracoclavicular and thoracoscapular bone orientation angles only showed a weak to moderate correlation. Since the regression-based shoulder rhythm has been adopted for shoulder biomechanical models to estimate shoulder muscle activities and structure loads, there needs to be further investigation on how the predicted error from the shoulder rhythm affects the output of the biomechanical model.     

Algorithms to determine event timing during normal walking using kinematic data

Algorithms to predict heelstrike and toeoff times during normal walking using only kinematic data are presented. The accuracy of these methods was compared with the results obtained using synchronized force platform recordings of two subjects walking at a variety of speeds for a total of 12 trials. Using a 60Hz data collection system, the absolute value errors (AVE) in predicting heelstrike averaged 4.7ms, while the AVE in predicting toeoff times averaged 5.6ms. True average errors (negative for an early prediction) were +1.2ms for both heelstrike and toeoff, indicating that no systematic errors occurred. It was concluded that the proposed algorithms provide an easy and reliable method of determining event times during walking when kinematic data are collected, with a considerable improvement in resolution over visual inspection of video records, and could be utilized in conjunction with any 2-D or 3-D kinematic data collection system.     

Evaluation and calibration of an electromagnetic tracking device for biomechanical analysis of lifting tasks.

Electromagnetic motion tracking devices are increasingly used as a kinematic measuring tool. The aim of this study was to evaluate a long-range transmitter in an environment with a conventional force plate present in order to assess its suitability for further biomechanical applications. Using a calibration apparatus developed in our lab and Optotrack measurements, the performances of the Motion Star were evaluated. Positions and orientations were measured in a 140 x 80 x 120 cm(3) space centered on the force plate. Using a mathematical model developed at Queen's University, these data were calibrated. Errors on position and orientation were less than 150 mm and 10 degrees before calibration of the Motion Star, and less than 20mm and 2 degrees after calibration, with no differences between data collected with the force plate switched on/off. These errors did not depend on sensor orientation. Variability of the signal was small indicating minimal noise. Field distortion was the largest source of measurement error, which increased with the distance between the transmitter and the sensor and the proximity of the sensor to the force plate. Before its use for biomechanical analysis of lifting tasks and validation of dynamic models using force plate data, the data from electromagnetic motion tracking devices must be calibrated to decrease the errors due to electromagnetic field distortion.     

Estimating muscle attachment contours by transforming geometrical bone models

For individualization of a biomechanical model, it is necessary to estimate the muscle attachments of the person to whom it is to be adapted. One of the methods to estimate muscle attachments is to use model transformations to transform a model with known muscle attachments to the bones of a person. We hypothesize that the location and shape of muscle attachment sites correlate with the shape of the bones they are attached to. If this hypothesis holds, it is possible to predict the location of muscle attachments when the shape of the bones is known. To validate this hypothesis, geometric models of three sets of shoulder bones were built. These models consist of 3-D surface models of the scapula, clavicle, and humerus, with the muscle attachment contours connected to them. By means of geometric transformations, the models were transformed, so the muscle attachments of the different data sets could be compared. Using these techniques, 50 per cent of the muscle attachment contours could be predicted with high accuracy. The muscle attachment contours that could not be predicted were all influenced by measurement errors. For 30 per cent of the muscle attachment contours, it was not possible to distinguish the interindividual differences from the inaccuracies of the method used. From this study, we concluded that most muscle attachment contours can be predicted by means of geometric models of the bones.     

Animation of in vitro biomechanical tests.

Interdisciplinary communication of three-dimensional kinematic data arising from in vitro biomechanical tests is challenging. Complex kinematic representations such as the helical axes of motion (HAM) add to the challenge. The difficulty increases further when other quantities (i.e. load or tissue strain data) are combined with the kinematic data. The objectives of this study were to develop a method to graphically replay and animate in vitro biomechanical tests including HAM data. This will allow intuitive interpretation of kinematic and other data independent of the viewer's area of expertise. The value of this method was verified with a biomechanical test investigating load-sharing of the cervical spine. Three 3.0 mm aluminium spheres were glued to each of the two vertebrae from a C2-3 segment of a human cervical spine. Before the biomechanical tests, CT scans were made of the specimen (slice thickness=1.0 mm and slice spacing=1.5 mm). The specimens were subjected to right axial torsion moments (2.0 Nm). Strain rosettes mounted to the anterior surface of the C3 vertebral body and bilaterally beneath the facet joints on C3 were used to estimate the force flow through the specimen. The locations of the aluminium spheres were digitised using a space pointer and the motion analysis system. Kinematics were measured using an optoelectronic motion analysis system. HAMs were calculated to describe the specimen kinematics. The digitised aluminium sphere locations were used to match the CT and biomechanical test data (RMS errors between the CT and experimental points were less than 1.0 mm). The biomechanical tests were "replayed" by animating reconstructed CT models in accordance with the recorded experimental kinematics, using custom software. The animated test replays allowed intuitive analysis of the kinematic data in relation to the strain data. This technique improves the ability of experts from disparate backgrounds to interpret and discuss this type of biomechanical data.     

Objective classification of scapular kinematics in participants with movement faults of the scapula on clinical assessment

The aim of this study was to assess the potential of employing a classification tool to objectively classify participants with clinically assessed movement faults (MFs) of the scapula. Six participants with a history of shoulder pain with MFs of the scapula and 12 healthy participants with no movement faults (NMFs) performed a flexion movement control test of the scapula, while scapular kinematic data were collected. Principal component scores and discrete kinematic variables were used as input into a classifier. Five out of the six participants with a history of pain were successfully classified as having scapular MFs with an accuracy of 72%. Variables related to the upward rotation of the scapula had the most influence on the classification. The results of the study demonstrate the potential of adopting a multivariate approach in objective classification of participants with altered scapular kinematics in pathological groups.     

Whole body inverse dynamics over a complete gait cycle based only on measured kinematics

This paper presents a three-dimensional (3D) whole body multi-segment model for inverse dynamics analysis over a complete gait cycle, based only on measured kinematic data. The sequence of inverse dynamics calculations differs significantly from the conventional application of inverse dynamics using force plate data. A new validated "Smooth Transition Assumption" was used to solve the indeterminacy problem in the double support phase. Kinematic data is required for all major body segments and, hence, a whole body gait measurement protocol is presented. Finally, sensitivity analyses were conducted to evaluate the effects of digital filtering and body segment parameters on the accuracy of the prediction results. The model gave reasonably good estimates of sagittal plane ground forces and moment; however, the estimates in the other planes were less good, which we believe is largely due to their small magnitudes in comparison to the sagittal forces and moment. The errors observed are most likely caused by errors in the kinematic data resulting from skin movement artefact and by errors in the estimated body segment parameters. A digital filtering cut-off frequency of 4.5Hz was found to produce the best results. It was also shown that errors in the mass properties of body segments can play a crucial role, with changes in properties sometimes having a disproportionate effect on the calculated ground reactions. The implication of these results is that, even when force plate data is available, the estimated joint forces are likely to suffer from similar errors.     

The macromolecular structure of human cervical-mucus glycoproteins. Studies on fragments obtained after reduction of disulphide bridges and after subsequent trypsin digestion.

Human cervical-mucus glycoproteins (mucins) were extracted with 6 M-guanidinium chloride in the presence of proteinase inhibitors and purified by isopycnic density-gradient centrifugation. The whole mucins (Mr approx. 10 X 10(6] were degraded into 'subunits' (Mr approx. 2 X 10(6] by reduction of disulphide bonds. Trypsin digestion of the 'subunits' produced glycopeptides with Mr approx. 380000, which appear to be rod-like with a length of approx. 105 nm. The relationship between the radius of gyration and the Mr value obtained by light-scattering for whole mucins, 'subunits' and 'domains' suggest that cervical-mucus glycoproteins are linear flexible macromolecules composed of, on the average, four or five 'domains'/subunit and four subunits/whole mucin macromolecule. The shape-dependent particle scattering function for the whole mucins and the 'subunits' are in accordance with that of a linear flexible chain. No evidence for a branched or a star-like structure was found. A tentative model for cervical mucins is proposed.     

Comparative biomechanical analysis of the rotational shot put technique

The study aimed to establish the modalities of the rotational shot put technique of two elite shot putters with substantially different constitutional characteristics. A biomechanical analysis of the technique was carried out using the APAS 3-D kinematic system, whereby a 15-segment model of shot putters was defined by 18 reference points. To enable the calculation of the kinematic and dynamic parameters, independent routines were programmed by the Matlab software. Anthropometric characteristics were established on the basis of 15 variables measured by the International Biological Programme (IBP) procedure. The results of the study revealed some differences between the athletes in terms of their mesomorphic constitutional component, body mass index, circular measures of the lower and upper extremities and the muscular, fat and bone mass. The technique models of both shot putters differ mostly in terms of the following kinematic and dynamic parameters: absolute release velocity, height of release, maximum angular velocity of the elbow of the throwing arm, trajectory of the centre of gravity of the body and the shot, torsional rotation of the shoulder axis relative to the hip axis, maximum force applied to the shot, kinetic energy and the kinetic energy differential of the shot.     

Kinematic models of the upper limb joints for multibody kinematics optimisation: An overview

Soft tissue artefact (STA), i.e. the motion of the skin, fat and muscles gliding on the underlying bone, may lead to a marker position error reaching up to 8.7 cm for the particular case of the scapula. Multibody kinematics optimisation (MKO) is one of the most efficient approaches used to reduce STA. It consists in minimising the distance between the positions of experimental markers on a subject skin and the simulated positions of the same markers embedded on a kinematic model. However, the efficiency of MKO directly relies on the chosen kinematic model. This paper proposes an overview of the different upper limb models available in the literature and a discussion about their applicability to MKO.The advantages of each joint model with respect to its biofidelity to functional anatomy are detailed both for the shoulder and the forearm areas. Models capabilities of personalisation and of adaptation to pathological cases are also discussed. Concerning model efficiency in terms of STA reduction in MKO algorithms, a lack of quantitative assessment in the literature is noted. In priority, future studies should concern the evaluation and quantification of STA reduction depending on upper limb joint constraints.     

An alternative definition of the scapular coordinate system for use with RSA

When performing radiostereometric analysis (RSA), computed tomography scans are often taken to obtain the landmarks used to create anatomical coordinate systems (CSs) for quantifying joint kinematics. Different conventions for defining CSs lead to an inability to compare results among studies. The International Society of Biomechanics (ISB) has proposed a set of CSs; however, the landmarks needed to create the recommended scapular CS require the entire scapula to be scanned, thereby also exposing breast and other tissues to radiation. The main purpose of this work was to investigate an alternate definition of the CS that has repeatably attainable landmarks and axes as close as possible to those recommended by the ISB, while limiting the portion of the scapula requiring scanning. Intra- and inter-investigator variabilities of landmark digitization were quantified in one model of a scapula and one cadaveric specimen. Based on the variability of the digitizations, an alternative CS was defined. The differences between the ISB and alternative CSs were evaluated on 11 cadaveric specimens. Beaded biplanar RSA was performed on the glenohumeral joint model in 15 different configurations and the resulting kinematics were calculated for each set of landmark digitizations using both sets of coordinate systems. While the kinematic angles obtained using the alternative CS were statistically different from those obtained using the ISB standard, these differences were small (on the order of 5°) and therefore considered to be of little clinical significance. In all likelihood, the benefits of decreasing radiation exposure outweigh these differences in angles.     

Validation of imaging-based quantification of glenohumeral joint kinematics using an unmodified clinical biplane fluoroscopy system

Model-based tracking, using CT and biplane fluoroscopy, allows highly accurate quantification of glenohumeral motion and changes in the subacromial space. Previous investigators have used custom-built biplane fluoroscopes designed specifically for kinematic applications, which are available at few institutions and require FDA approval prior to clinical use. The aim of this study was to demonstrate the utility of an off-the-shelf clinical biplane fluoroscope for kinematic applications by validating model-based tracking for measurement of glenohumeral motion using an unmodified clinical system. Biplane images of each shoulder of a cadaver torso were acquired at various joint positions and during simulated movements along anatomical planes of motion. The pose of each humerus and scapula was determined using model-based tracking and compared to a bead-based gold standard. Error due to a temporal-offset between corresponding biplane images, characteristic of clinical biplane systems, was determined by comparison of measured and known relative position of 2 bead clusters of a phantom that was imaged while moved throughout the fluoroscopy image volume. Model-based tracking had global kinematic mean absolute errors of 0.27 mm and 0.29° (static), and 0.22–0.32 mm and 0.12–0.45° (dynamic). Glenohumeral mean absolute errors were 0.39 mm and 0.45° (static), and 0.36–0.42 mm and 0.41–0.48° (dynamic). The temporal-offset was predicted to add errors of 0.06–0.85 mm and 0.05–0.28° for cadaveric trials for the speeds examined. For defined speeds, sub-millimeter and sub-degree kinematic accuracy and precision were achieved using an unmodified clinical biplane fluoroscope for quantification of glenohumeral motion.     

广义Rothermel模型预测平地无风条件下红松-蒙古栎林地表混合可燃物的火行为

以帽儿山地区红松-蒙古栎林下地表混合可燃物为材料,进行不同含水率、载量和混合比例的室内点烧试验,观测得到蔓延速率、驻留时间、反应强度、火线强度和火焰长度,并与采用表面积加权法和载量加权法的广义Rothermel模型预测值进行比较.结果表明:广义Rothermel模型对红松-蒙古栎林下地表混合可燃物的林火蔓延速率、反应强度的预测平均绝对误差分别为0.04 m·min-1、77 kW·m-2,预测平均相对误差分别为16％、22％;对驻留时间、火线强度和火焰长度的预测偏低,预测平均绝对误差分别为15.5 s、17.3 kW·m-1和9.7 cm,预测平均相对误差分别为55.5％、48.7％和24％.这些误差可以看成是用该模型预测同类可燃物相应火行为的误差下限.两种加权算法对模型预测精度影响差异不大,当红松可燃物所占比重较小时,表面积加权法得到的蔓延速率和反应强度预测值精度较高,载量加权法得到的火线强度和火焰长度预测值精度较高;当红松可燃物所占比重较大时,结果则相反.     

Error in the description of foot kinematics due to violation of rigid body assumptions

Kinematic data from rigid segment foot models inevitably includes errors because the bones within each segment move relative to each other. This study sought to define error in foot kinematic data due to violation of the rigid segment assumption. The research compared kinematic data from 17 different mid and forefoot rigid segment models to kinematic data of the individual bones comprising these segments. Kinematic data from a previous dynamic cadaver model study was used to derive individual bone as well as foot segment kinematics.Mean and maximum errors due to violation of the rigid body assumption varied greatly between models. The model with least error was the combination of navicular and cuboid (mean errors <=1.3°, average maximum error <=2.4°). Greatest error was seen for the model combining all the ten bones (mean errors <=4.4°, average maximum errors <=6.9°). Based on the errors reported a three segment mid and forefoot model is proposed: (1) Navicular and cuboid, (2) cuneiforms and metatarsals 1, 2 and 3, and (3) metatarsals 4 and 5. However the utility of this model will depend on the precise purpose of the in vivo foot kinematics research study being undertaken.     

广义Rothermel模型预测平地无风条件下红松蒙古栎林地表混合可燃物的火行为

以帽儿山地区红松-蒙古栎林下地表混合可燃物为材料,进行不同含水率、载量和混合比例的室内点烧试验,观测得到蔓延速率、驻留时间、反应强度、火线强度和火焰长度,并与采用表面积加权法和载量加权法的广义Rothermel模型预测值进行比较.结果表明： 广义Rothermel模型对红松 蒙古栎林下地表混合可燃物的林火蔓延速率、反应强度的预测平均绝对误差分别为0.04 m·min^-1、77 kW·m^-2,预测平均相对误差分别为16%、22%;对驻留时间、火线强度和火焰长度的预测偏低,预测平均绝对误差分别为15.5 s、17.3 kW·m^-1和9.7 cm,预测平均相对误差分别为55.5%、48.7%和24%.这些误差可以看成是用该模型预测同类可燃物相应火行为的误差下限.两种加权算法对模型预测精度影响差异不大,当红松可燃物所占比重较小时,表面积加权法得到的蔓延速率和反应强度预测值精度较高,载量加权法得到的火线强度和火焰长度预测值精度较高;当红松可燃物所占比重较大时,结果则相反.     

Estimation of carcass composition and cut composition from computed tomography images of live growing pigs of different genotypes

The aim of the present work was (1) to study the relationship between cross-sectional computed tomography (CT) images obtained in live growing pigs of different genotypes and dissection measurements and (2) to estimate carcass composition and cut composition from CT measurements. Sixty gilts from three genotypes (Duroc×(Landrace×Large White), Pietrain×(Landrace×Large White), and Landrace×Large White) were CT scanned and slaughtered at 30 kg (n=15), 70 kg (n=15), 100 kg (n=12) or 120 kg (n=18). Carcasses were cut and the four main cuts were dissected. The distribution of density volumes on the Hounsfield scale (HU) were obtained from CT images and classified into fat (HU between −149 and −1), muscle (HU between 0 and 140) or bone (HU between 141 and 1400). Moreover, physical measurements were obtained on an image of the loin and an image of the ham. Four different regression approaches were studied to predict carcass and cut composition: linear regression, quadratic regression and allometric equations using volumes as predictors, and linear regression using volumes and physical measurements as predictors. Results show that measurements from whole animal taken in vivo with CT allow accurate estimation of carcass and cut composition. The prediction accuracy varied across genotypes, BW and variable to be predicted. In general, linear models, allometric models and linear models, which included also physical measurements at the loin and the ham, produced the lowest prediction errors.