Planning orthodontic surgery with the Hexapod system]

Treatment of maxillofacial dysgnathia using a combined surgical/orthodontic approach requires careful orthodontic and orthognathic diagnosis and treatment planning. In the present study, a system enabling on-line presentation of the necessary displacements of the jaw during surgery, while improving the accuracy of the planning, is described. Using the hexapod principle, it is possible to plan operations with six degrees of freedom and to measure the three-dimensional movements of jaws and jaw segments within the planning stage. Routinely prepared casts are employed for simulation of the operation. The displacements of the jaw are presented in a manner familiar to the orthodontic surgeon, namely in a surgical record. The accuracy achieved with the hexapod is superior to that achievable intra-operatively.     

Three-dimensional video analysis of facial movements: a new method to assess the quantity and quality of the smile

The results of neuromuscular reconstructions of the paralyzed face are difficult to assess. Very sophisticated methods are necessary to measure the motor deficits of facial paralysis or the functional recovery in the face. The aim of this development was a relatively simple system for data acquisition, which is easy to handle and which makes it relatively cheap to delegate data acquisition to centers all over the world, which will not be able to derive a data analysis on their own, but will send their data to a center with specialized equipment. A complex mirror system was developed to get three different views of the face at the same time on the video screen. At each investigation, a digital video is taken from a calibration grid and from standardized facial movements of the patient. Secondary analysis of the digital videofilm is made possible at any time later on by the support of a computer program, which calculates distances and movements three-dimensionally from the frontal image and the right and left mirror images. Pathologies of the mimic movements can be identified as well as improvements after surgical procedures by this system. The significant advantage is the possibility to watch the same movement on the video which is under study and to apply any kind of study later on. Taking the video needs only a few minutes, and fatigue of the patient's mimic system is prevented. Measurements usually at the endpoints of the movements give excellent information on the quantity of the movement or the degree of the facial palsy, whereas the video itself is very informative regarding the quality of the smile. Specific computer software was developed for standardized three-dimensional analysis of the video-documented facial movements and for data presentation. There are options like two-dimensional graphs of single moving points in the face or three-dimensional graphs of the movements of all measured points at the same time during a standardized facial movement. By a comparison of the right- and left-sided alterations of specific distances between two points during the facial movements, the degree of normal symmetry or pathologic asymmetry is quantified. This system is more suitable for detailed scientific multicenter studies than any other system previously established. A very sensitive instrument for exact evaluation of mimic function is now available.     

A behavior-based inverse kinematics algorithm to predict arm prehension postures for computer-aided ergonomic evaluation.

In this paper, the computational problem of inverse kinematics of arm prehension movements was investigated. How motions of each joint involved in arm movements can be used to control the end-effector (hand) position and orientation was first examined. It is shown that the inverse kinematics problem due to the kinematic redundancy in joint space is ill-posed only at the control of hand orientation but not at the control of hand position. Based upon this analysis, a previously proposed inverse kinematics algorithm (Wang et Verriest, 1998a) to predict arm reach postures was extended to a seven-DOF arm model to predict arm prehension postures using a separate control of hand position and orientation. The algorithm can be either in rule-based form or by optimization through appropriate choice of weight coefficients. Compared to the algebraic inverse kinematics algorithm, the proposed algorithm can handle the non-linearity of joint limits in a straightforward way. In addition, no matrix inverse calculation is needed, thus avoiding the stability and convergence problems often occurring near a singularity of the Jacobian. Since an end-effector motion-oriented method is used to describe joint movements, observed behaviors of arm movements can be easily implemented in the algorithm. The proposed algorithm provides a general frame for arm postural control and can be used as an efficient postural manipulation tool for computer-aided ergonomic evaluation.     

A gearing mechanism with 4 degrees of freedom for robotic applications in medicine]

Applications in robot-aided surgery are currently based on modifications of manipulators used in industrial manufacturing processes. In this paper we describe novel rotatory kinematics for a manipulator, specially developed for deployment in robot-aided surgery. The construction of the gearing mechanism used for the positioning and orientation of a linkage point is described. Forward and inverse kinematics were calculated, and a constructive solution proposed. The gearing mechanism is based on two disk systems, each of which consists of two opposing rotatable discs. The construction was designed in such a way that the linkage point can be positioned freely anywhere within the mechanism's range of motion. The kinematics thus permits an x-y-positioning via rotating movements only. The spatial arrangement of two of such disc systems permits movements in four degrees of freedom (DOF). The construction is compact, but can be further miniaturized, is flexible and manufacturing costs are low. On the basis of this mechanical concept a new, small automated manipulator for surgical application will be developed.     

Kinematics estimation of straddled movements on high bar from a limited number of skin markers using a chain model

To reduce the effects of skin movement artefacts and apparent joint dislocations in the kinematics of whole body movement derived from marker locations, global optimisation procedures with a chain model have been developed. These procedures can also be used to reduce the number of markers when self-occlusions are hard to avoid. This paper assesses the kinematics precision of three marker sets: 16, 11 and 7 markers, for movements on high bar with straddled piked posture. A three-dimensional person-specific chain model was defined with 9 parameters and 12 degrees of freedom and an iterative procedure optimised the gymnast posture for each frame of the three marker sets. The time histories of joint angles obtained from the reduced marker sets were compared with those from the 16 marker set by means of a root mean square difference measure. Occlusions of medial markers fixed on the lower limb occurred when the legs were together and the pelvis markers disappeared primarily during the piked posture. Despite these occlusions, reconstruction was possible with 16, 11 and 7 markers. The time histories of joint angles were similar; the main differences were for the thigh mediolateral rotation and the knee flexion because the knee was close to full extension. When five markers were removed, the average angles difference was about 3 degrees . This difference increased to 9 degrees for the seven marker set. It is concluded that kinematics of sports movement can be reconstructed using a chain model and a global optimisation procedure for a reduced number of markers.     

Helical motion analysis of the knee--I. Methodology for studying kinematics during locomotion

A technique for investigating the three-dimensional kinematics of knee motion during dynamic functional tasks has been developed. It involves the combined usage of a six degree of freedom goniometer and helical motion analysis. A detailed procedure for coordinate system alignment and calibration must be followed. Once established this entire procedure is routinely implementable. Ensemble averages from multiple walking strides reveal that this technique is sensitive enough to differentiate between the kinematics of an uninjured and injured knee.     

Effect of hip flexibility on optimal stalder performances on high bar

In the optimisation of sports movements using computer simulation models, the joint actuators must be constrained in order to obtain realistic results. In models of a gymnast, the main constraint used in previous studies was maximum voluntary active joint torque. In the stalder, gymnasts reach their maximal hip flexion under the bar. The purpose of this study was to introduce a model of passive torque to assess the effect of the gymnast's flexibility on the technique of the straddled stalder. A three-dimensional kinematics driven simulation model was developed. The kinematics of the shoulder flexion, hip flexion and hip abduction were optimised to minimise torques for four hip flexion flexibilities: 100°, 110°, 120° and 130°. With decreased flexibility, the piked posture period is shorter and occurs later. Moreover the peaks of shoulder and hip torques increase. Gymnasts with low hip flexibility need to be stronger to achieve a stalder; hip flexibility should be considered by coaches before teaching this skill.     

Shoulder movements during quadrupedal locomotion in arboreal primates

The kinematics of scapula and shoulder joint movements were analyzed in three species of arboreal quadrupedal primates using cineradiography. Our findings indicate that scapular movement is highly important for forelimb movement in primates with this ancestral mode of locomotion. Retroversion of the scapula (syn. caudal rotation or extension) during the stance phase contributes more than 40% to the stride length of the forelimb. Lateral forelimb excursions, a general feature for arboreal primates, are based on complex three-dimensional scapular movements guided by the clavicle. Humeral abduction is achieved by scapular abduction and transversal rotation of the scapula about its longitudinal axis, and is therefore strikingly different from humeral abduction in humans. At the same time, the movements of the shoulder joint are limited to flexion and extension only.     

Trajectory formation and speed-accuracy trade-off in aiming movements

The trade-off between speed and accuracy and the patterning of movement kinematics have been central issues for theories of human movement for almost a century. In the present contribution experimentally obtained kinematics of reciprocal aiming movements, performed under different task conditions, are modelled as resulting from a single non-linear dynamical system whose parameters vary so as to respond to the task demands. Providing a unified account of speed-accuracy trade-off and trajectory formation phenomena, the model offers a theoretical framework in which both discrete and continuous movements, performed along one or more dimensions can be understood.     

Ergonomic Risk Assessment of Developing Musculoskeletal Disorders in Workers with the Microsoft Kinect: TRACK TMS

Background

Routine ergonomic assessment of postures and gestures in the workplace are mostly conducted by visual observations, either direct or based on video recordings. Nowadays, low-cost three-dimensional cameras like Microsoft Kinect offers the possibility of recording the full kinematics of workers in a non-intrusive way, providing a more precise, and reliable assessment of their motor strategies.

Grasping kinematics from the perspective of the individual digits: a modelling study

Grasping is a prototype of human motor coordination. Nevertheless, it is not known what determines the typical movement patterns of grasping. One way to approach this issue is by building models. We developed a model based on the movements of the individual digits. In our model the following objectives were taken into account for each digit: move smoothly to the preselected goal position on the object without hitting other surfaces, arrive at about the same time as the other digit and never move too far from the other digit. These objectives were implemented by regarding the tips of the digits as point masses with a spring between them, each attracted to its goal position and repelled from objects' surfaces. Their movements were damped. Using a single set of parameters, our model can reproduce a wider variety of experimental findings than any previous model of grasping. Apart from reproducing known effects (even the angles under which digits approach trapezoidal objects' surfaces, which no other model can explain), our model predicted that the increase in maximum grip aperture with object size should be greater for blocks than for cylinders. A survey of the literature shows that this is indeed how humans behave. The model can also adequately predict how single digit pointing movements are made. This supports the idea that grasping kinematics follow from the movements of the individual digits.     

Direct comparison of kinematic data collected using an electromagnetic tracking system versus a digital optical system

The purpose of this study was to quantify the dynamic accuracy of kinematics measured by a digital optical motion analysis system in a gait analysis laboratory (capture volume approximately 20m(3)) compared to a standard range direct-current electromagnetic (EM) tracking device (capture volume approximately 1m(3)). This is a subset of a larger effort to establish an appropriate marker set for the optical system to quantify upperlimb kinematics simultaneously with gait, in comparison to previous studies of isolated upperlimb movements that have employed EM tracking devices. Rigid clusters of spherical reflective markers and EM sensors were attached to a mechanical articulator that mimicked three-dimensional joint rotations, similar to the elbow. As the articulator was moved through known ranges of motion (i.e. gold standard), kinematic data were collected simultaneously using both tracking systems. Both systems were tended to underestimate the range of motion; however, the application of post hoc smoothing and least-squares correction algorithms reduced these effects. When smoothing and correction algorithms were used, the magnitude of the mean difference between the gold standard and either the EM or optical system did not exceed 2 degrees for any of the compound motions performed. This level of agreement suggests that the measurements obtained from either system are clinically comparable, provided appropriate smoothing and correction algorithms are employed.     

Carpal bone kinematics and ligament lengthening studied for the full range of joint movement

Present data on carpal kinematics and carpal ligament behaviour are limited to flexion and deviation movements of the hand. These motions do not represent all the wrist-joint motions which are important for the activities of daily living. The goal of this project was to obtain insight into carpal kinematics and carpal ligament behaviour during motions of the hand covering the full range of motion of the wrist joint.

The carpals and the ligaments of four wrist-joint specimens were provided with radiopaque markers. These joints were subjected to Röntgenstereophotogrammetric experimentation in a large number of hand positions to determine carpal positions and ligament lengths. The movements of the carpal bones were described by means of finite helical axes (FHA).

It was found that the movements of the carpals in the distal row closely resemble those of the hand. Conversely, the motions of the carpals of the proximal row appeared not to be directly proportional to the hand motions and exhibited clear out-of-plane movements. Furthermore, it could be shown that movements of the hand into the ulnodorsal quadrant of the full range of hand motion corresponds to larger helical rotations and translations for most of the carpals than when the hand was moved into any other quadrant. The maximal ligament length changes determined did not exceed the length changes reported for pure flexion and pure deviation movements of the hand.     

Study of different kinds of locomotor movements in rats

The kinematics and electromyographic activity of the hind limb muscles of intact rats fixed in a special frame were investigated during locomotor movements of different kinds. A change in the external conditions determining the degree of limb loading (the presence or absence of support, and so on) was shown to lead to changes in the pattern and (or) amplitude of the movements. Six types of locomotion were distinguished, and in accordance with the kinematics of the hind limb movements these can be divided into two types: swimming and stepping. The analysis showed marked variability of the parameters (frequency, duration of the swing phase and of the support phase) of the different locomotor movements.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 2, pp. 183–189, March–April, 1985.     

Properties of 3D rotations and their relation to eye movement control

Rotations of the eye are generated by the torques that the eye muscles apply to the eye. The relationship between eye orientation and the direction of the torques generated by the extraocular muscles is therefore central to any understanding of the control of three-dimensional eye movements of any type. We review the geometrical properties that dictate the relationship between muscle pulling direction and 3D eye orientation. We then show how this relation can be used to test the validity of oculomotor control hypotheses. We test the common modeling assumption that the extraocular muscle pairs can be treated as single bidirectional muscles. Finally, we investigate the consequences of assuming fixed muscle pulley locations when modeling the control of eye movements.     

A method for measuring joint kinematics designed for accurate registration of kinematic data to models constructed from CT data

A method for measuring three-dimensional kinematics that incorporates the direct cross-registration of experimental kinematics with anatomic geometry from Computed Tomography (CT) data has been developed. Plexiglas registration blocks were attached to the bones of interest and the specimen was CT scanned. Computer models of the bone surface were developed from the CT image data. Determination of discrete kinematics was accomplished by digitizing three pre-selected contiguous surfaces of each registration block using a three-dimensional point digitization system. Cross-registration of bone surface models from the CT data was accomplished by identifying the registration block surfaces within the CT images. Kinematics measured during a biomechanical experiment were applied to the computer models of the bone surface. The overall accuracy of the method was shown to be at or below the accuracy of the digitization system used. For this experimental application, the accuracy was better than +/-0.1mm for position and 0.1 degrees for orientation for linkage digitization and better than +/-0.2mm and +/-0.2 degrees for CT digitization. Surface models of the radius and ulna were constructed from CT data, as an example application. Kinematics of the bones were measured for simulated forearm rotation. Screw-displacement axis analysis showed 0.1mm (proximal) translation of the radius (with respect to the ulna) from supination to neutral (85.2 degrees rotation) and 1.4mm (proximal) translation from neutral to pronation (65.3 degrees rotation). The motion of the radius with respect to the ulna was displayed using the surface models. This methodology is a useful tool for the measurement and application of rigid-body kinematics to computer models.     

Ensemble averaging and multiple statistical testing of EMG activities of cyclically repeated body motions. A tool for muscle function analysis in experimental and clinical orthopaedics.

Coupled with suitable computerized signal recording and processing methods surface electromyography can be a powerful tool for the analysis of muscle activity in specific body movements. It can be used for this purpose in experimental and in clinical diagnostic orthopaedics as well as in physiotherapy. We describe in this paper a motion analysis system comprising this feature. It has been employed for the diagnosis of the basic angular kinematics and muscle function in human gait and other cyclically repeatable movements of the human locomotive system. Changes in the temporal characteristics of the movements and the muscle activity due to changed physical or experimental conditions can be systematically investigated this way. Such changes can be the result of surgical and/or conservative orthopaedic therapy, a long term physiotherapeutic program, or modified walking conditions as in experimental orthopaedics. They are displayed and validated by signal ensemble averaging and subsequent multiple statistical testing (e.g. by a suitably adapted Bonferroni criterion). The efficiency of the system is demonstrated by an exemplary gait analysis of selected kinematic and muscular effects caused by an experimental simulation of a leg length inequality.     

In-vivo three-dimensional carpal bone kinematics during flexion–extension and radio–ulnar deviation of the wrist: Dynamic motion versus step-wise static wrist positions

An in-vivo approach to the measurement of three-dimensional motion patterns of carpal bones in the wrist may have future diagnostic applications, particularly for ligament injuries of the wrist. Static methods to measure carpal kinematics in-vivo only provide an approximation of the true kinematics of the carpal bones. This study is aimed at finding the difference between dynamically and statically acquired carpal kinematics.For eight healthy subjects, static and a dynamic measurements of the carpal kinematics were performed for a flexion–extension and a radio–ulnar deviation movement. Dynamic scans were acquired by using a four-dimensional X-ray imaging system during an imposed cyclic motion. To assess static kinematics of the wrists, three-dimensional rotational X-ray scans were acquired during step-wise flexion–extension and radio–ulnar deviation. The helical axis rotations and the rotation components. i.e. flexion–extension, radio–ulnar deviation and pro–supination were the primary parameters. Linear mixed model statistical analysis was used to determine the significance of the difference between the dynamically and statically acquired rotations of the carpal bones.Small and in most cases negligible differences were observed between the dynamic motion and the step-wise static motion of the carpal bones. The conclusion is that in the case of individuals without any pathology of the wrist, carpal kinematics can be studied either dynamically or statically. Further research is required to investigate the dynamic in-vivo carpal kinematics in patients with dynamic wrist problems.     

The Relation between Geometry and Time in Mental Actions

Mental imagery is a cognitive tool that helps humans take decisions by simulating past and future events. The hypothesis has been advanced that there is a functional equivalence between actual and mental movements. Yet, we do not know whether there are any limitations to its validity even in terms of some fundamental features of actual movements, such as the relationship between space and time. Although it is impossible to directly measure the spatiotemporal features of mental actions, an indirect investigation can be conducted by taking advantage of the constraints existing in planar drawing movements and described by the two-thirds power law (2/3PL). This kinematic law describes one of the most impressive regularities observed in biological movements: movement speed decreases when curvature increases. Here, we compared the duration of identical actual and mental arm movements by changing the constraints imposed by the 2/3PL. In the first two experiments, the length of the trajectory remained constant, while its curvature (Experiment 1) or its number of inflexions (Experiment 2) was manipulated. The results showed that curvature, but not the number of inflexions, proportionally and similarly affected actual and mental movement duration, as expected from the 2/3PL. Two other control experiments confirmed that the results of Experiment 1 were not attributable to eye movements (Experiment 3) or to the perceived length of the displayed trajectory (Experiment 4). Altogether, our findings suggest that mental movement simulation is tuned to the kinematic laws characterizing actions and that kinematics of actual and mental movements is completely specified by the representation of their geometry.