Anatomical Frame Research Articles

Intra-protocol repeatability and inter-protocol agreement for the analysis of scapulo-humeral coordination

Multi-center clinical trials incorporating shoulder kinematics are currently uncommon. The absence of repeatability and limits of agreement (LoA) studies between different centers employing different motion analysis protocols has led to a lack dataset compatibility. Therefore, the aim of this work was to determine the repeatability and LoA between two shoulder kinematic protocols. The first one uses a scapula tracker (ST), the International Society of Biomechanics anatomical frames and an optoelectronic measurement system, and the second uses a spine tracker, the INAIL Shoulder and Elbow Outpatient protocol (ISEO) and an inertial and magnetic measurement system. First within-protocol repeatability for each approach was assessed on a group of 23 healthy subjects and compared with the literature. Then, the between-protocol agreement was evaluated. The within-protocol repeatability was similar for the ST ([Formula: see text] = 2.35°, [Formula: see text] = 0.97°, SEM = 2.5°) and ISEO ([Formula: see text] = 2.24°, [Formula: see text] = 0.97°, SEM = 2.3°) protocols and comparable with data from published literature. The between-protocol agreement analysis showed comparable scapula medio-lateral rotation measurements for up to 120° of flexion-extension and up to 100° of scapula plane ab-adduction. Scapula protraction-retraction measurements were in agreement for a smaller range of humeral elevation. The results of this study suggest comparable repeatability for the ST and ISEO protocols and between-protocol agreement for two scapula rotations. Different thresholds for repeatability and LoA may be adapted to suit different clinical hypotheses.

Concurrent validation of Xsens MVN measurement of lower limb joint angular kinematics

This study aims to validate a commercially available inertial sensor based motion capture system, Xsens MVN BIOMECH using its native protocols, against a camera-based motion capture system for the measurement of joint angular kinematics. Performance was evaluated by comparing waveform similarity using range of motion, mean error and a new formulation of the coefficient of multiple correlation (CMC). Three dimensional joint angles of the lower limbs were determined for ten healthy subjects while they performed three daily activities: level walking, stair ascent, and stair descent. Under all three walking conditions, the Xsens system most accurately determined the flexion/extension joint angle (CMC > 0.96) for all joints. The joint angle measurements associated with the other two joint axes had lower correlation including complex CMC values. The poor correlation in the other two joint axes is most likely due to differences in the anatomical frame definition of limb segments used by the Xsens and Optotrak systems. Implementation of a protocol to align these two systems is necessary when comparing joint angle waveforms measured by the Xsens and other motion capture systems.

The electrophysiological time course of somatosensory spatial remapping: vision of the hands modulates effects of posture on somatosensory evoked potentials

We investigated the electrophysiological correlates of somatosensory processing under different arm postures by recording event-related potentials at frontal, central and centroparietal sites during tactile stimulation of the hands. Short series of 200ms vibrotactile stimuli were presented to the palms of the participants' hands, one hand at a time, in either uncrossed- or crossed-hands postures. The manipulation of posture allowed us to investigate the electrophysiological processes underlying the spatial remapping of somatosensory stimuli from anatomical into external frames of reference. To examine somatosensory spatial remapping independently of its effects on attentional processes, the stimuli were presented unpredictably in terms of location, and in temporal onset. We also examined how vision of the limbs affects the process of remapping. When participants had sight of their hands (Experiment 1) the effect of posture was observed over regions contralateral to the stimulated hand from 128ms, whereas when their limbs were covered (Experiment 2) effects of posture influenced the ipsilateral regions from 150ms. These findings add to an increasing body of evidence which indicates that sight of the hand modulates the way in which information in other modalities is processed. We argue that in this case, sight of the hand biases spatial encoding of touch towards an anatomical frame of reference.

Soft Tissue Artifact Assessment During Treadmill Walking in Subjects With Total Knee Arthroplasty

Accurate measurement of knee kinematics during functional activities suffers mainly from soft tissue artifact (STA): the combination of local surface deformations and rigid movement of markers relative to the underlying bone (also called rigid STA movement: RSTAM). This study proposes to assess RSTAM on the thigh, shank, and knee joint and to observe possible features between subjects. Nineteen subjects with knee arthroplasty were asked to walk on a treadmill while a biplane fluoroscopic system (X-rays) and a stereophotogrammetric system (skin markers) recorded their knee movement. The RSTAM was defined as the rigid movement of the cluster of skin markers relative to the prosthesis. The results showed that RSTAM amplitude represents approximately 80-100% of the STA. The vertical axis of the anatomical frame of the femur was influenced the most by RSTAM. Combined with tibial error, internal/external rotation angle and distraction-compression were the knee kinematics parameters most affected by RSTAM during the gait cycle, with average rms values of 3.8° and 11.1 mm. This study highlighted higher RSTAM during the swing phase particularly in the thigh segment and suggests new features for RSTAM such as the particular shape of some RSTAM waveforms and the absence of RSTAM in certain kinematics during the gait phases. The comparison of coefficient of multiple correlations showed some similarities of RSTAM between subjects, while some correlations were found with gait speed and BMI. These new insights could potentially allow the development of new methods of compensation to avoid STA.

Visibility-driven PET-CT visualisation with region of interest (ROI) segmentation

Multi-modality (MM) positron emission tomography-computed tomography (PET-CT) visualises biological and physiological functions (from PET) as region of interests (ROIs) within a higher resolution anatomical reference frame (from CT). The need to efficiently assess and assimilate the information from these co-aligned volumes simultaneously has stimulated new visualisation techniques that combine 3D volume rendering with interactive transfer functions to enable efficient manipulation of these volumes. However, in typical MM volume rendering visualisation, the transfer functions for the volumes are manipulated in isolation with the resulting volumes being fused, thus failing to exploit the spatial correlation that exists between the aligned volumes. Such lack of feedback makes MM transfer function manipulation complex and time consuming. Further, transfer function alone is often insufficient to select the ROIs when they have similar voxel properties to those of non-relevant regions. In this study, we propose a new ROI-based MM visibility-driven transfer function (m 2-vtf) for PET-CT visualisation. We present a novel `visibility' metric, a fundamental optical property that represents how much of the ROIs are visible to the users, and use it to measure the visibility of the ROIs in PET in relation to how it is affected by transfer function manipulations to its counterpart CT. To overcome the difficulty in ROI selection, we provide an intuitive ROI selection tool based on automated PET segmentation. We further present a MM transfer function automation where the visibility metrics from the PET ROIs are used to automate its CT's transfer function. Our GPU implementation achieved an interactive visualisation of PET-CT with efficient and intuitive transfer function manipulations.

The Test-Retest Reliability of Anatomical Co-Ordinate Axes Definition for the Quantification of Lower Extremity Kinematics During Running

Three-dimensional (3-D) kinematic analyses are used widely in both sport and clinical examinations. However, this procedure depends on reliable palpation of anatomical landmarks and mal-positioning of markers between sessions may result in improperly defined segment co-ordinate system axes which will produce in-consistent joint rotations. This had led some to question the efficacy of this technique. The aim of the current investigation was to assess the reliability of the anatomical frame definition when quantifying 3-D kinematics of the lower extremities during running. Ten participants completed five successful running trials at 4.0 m·s−1 ± 5%. 3-D angular joint kinematics parameters from the hip, knee and ankle were collected using an eight camera motion analysis system. Two static calibration trials were captured. The first (test) was conducted prior to the running trials following which anatomical landmarks were removed. The second was obtained following completion of the running trials where anatomical landmarks were re-positioned (retest). Paired samples t-tests were used to compare 3-D kinematic parameters quantified using the two static trials, and intraclass correlations were employed to examine the similarities between the sagittal, coronal and transverse plane waveforms. The results indicate that no significant (p>0.05) differences were found between test and retest 3-D kinematic parameters and strong (R2≥0.87) correlations were observed between test and retest waveforms. Based on the results obtained from this investigation, it appears that the anatomical co-ordinate axes of the lower extremities can be defined reliably thus confirming the efficacy of studies using this technique.

A hip joint kinematics driven model for the generation of realistic thigh soft tissue artefacts

In human movement analysis, accuracy and robustness of the algorithms used to determine the location of centres of rotation from stereophotogrametric data depend mainly on their capacity to deal with the artefacts due to soft tissue deformation (STA). While evaluating these algorithms using a mathematical simulation approach, effectual realizations of STAs are needed. This study aimed at accomplishing this objective by modelling STAs, in twelve selected areas of the thigh, as a linear function of the hip angles, assuming no knee joint movement. The proposed model was calibrated and assessed using ex-vivo experiments. This entailed that only the component of the STA due to skin stretching was accounted for. Photogrammetric data of markers placed on the skin and on hip-bone and femur pins were recorded during passive flexion-extension, ab-adduction, rotation and circumduction of the hip joint. Artefact skin marker displacements were represented in a femur embedded anatomical frame. Model parameters were estimated by minimizing the least squares difference between measured and modelled STAs. The STA affecting a skin marker placed in a given thigh location of a given subject could be modelled with a high accuracy (median root mean square difference over 4 subjects×3 trials×12 markers×3 coordinates: 0.8mm—inter quartile range 1.0mm). This was also true for a hip joint movement different from the one used to calibrate the model. High inter-subject variability of the model parameters confirmed the subject-dependency of the phenomenon.

Motion analysis of front crawl swimming applying CAST technique by means of automatic tracking

Kinematic analysis of swimming is of interest to improve swimming performances. Although the video recordings of underwater swimmers are commonly used, the available methodologies are rarely precise enough to adequately estimate the three dimensional (3D) joint kinematics. This is mainly due to difficulties in obtaining the required kinematic parameters (anatomical landmarks, joint centres and reference frames) in the swimming environment. In this paper we propose a procedure to investigate the right upper limb’s 3D kinematics during front crawl swimming in terms of all elbow and shoulder degrees of freedom (three rotations of the shoulder, two of the elbow). The method is based upon the Calibrated Anatomical Systems Technique (CAST), a technique widely used in clinics, which allows estimation of anatomical landmarks of interest even when they are not directly visible. An automatic tracking technique was adopted. The intra-operator repeatability of the manual tracking was also assessed. The root mean squared difference of three anatomical landmarks, processed five times, is always lower than 8 mm. The mean of the root mean squared difference between trajectories obtained with the different methodologies was found to be lower than 20 mm. Results showed that complete 3D kinematics of at least twice as many frames than without CAST can be reconstructed faster and more precisely.

An evaluation of anatomical and functional knee axis definition in the context of side-cutting

Side-cutting is commonly used to evaluate knee joint kinematics and kinetics in the context of anterior cruciate ligament injury risk. Many existing side-cutting studies fail to clearly define the orientation of the femoral frame and the knee axis, making comparisons between studies difficult. A femoral frame constructed using the ISB or existing functional methods does not necessarily have a medial-lateral axis that is aligned with the axis of the knee. A functional frame that directly aligns with the medial-lateral knee axis was compared to the ISB anatomical frame and the Besier functional frame (Besier et al., 2003) to determine whether the chosen frame would affect the interpretation of side-cutting data. Kinematic and kinetic variables were calculated during three side-cutting manoeuvres of 28 subjects. Differences in mean frame orientation were correlated with the differences in mean knee angle during side-cutting. The differences between the ISB anatomical frame and the functional frames were significantly correlated with the differences in superior-inferior and medial-lateral axis orientations. Coefficients of multiple correlation showed a good to high (CMCs≥0.74) similarity between frames for knee angles and moments. Using a femoral anatomical frame rather than a functional frame most significantly affected offset rather than cross talk in knee angles and moments measured during side-cutting. There were no significant differences in offset or cross talk between the two functional methods. Maximum differences of <4° for frontal plane knee angle requires cautious interpretation but differences <8Nm for knee joint moment were not thought to affect the interpretation of side-cutting data when comparing between studies.

A linear soft tissue artefact model for human movement analysis: Proof of concept using in vivo data

We investigated the accuracy of a linear soft tissue artefact (STA) model in human movement analysis. Simultaneously recorded bone-mounted pin and skin marker data for the thigh and shank during walking, cutting and hopping were used to measure and model the motion of the skin marker clusters within anatomical reference frames (ARFs). This linear model allows skin marker movements relative to the underlying bone contrary to a rigid-body assumption. The linear model parameters were computed through a principal component analysis, which revealed that 95% of the variance of the STA motion for the thigh was contained in the first four principal components for all three tasks and all subjects. For the shank, 95% of the variance was contained in the first four principal components during walking and cutting and first five during hopping. For the thigh, the maximum residual artefact was reduced from 27.0mm to 5.1mm (walking), 22.7mm to 3.0mm (cutting) and 16.2mm to 3.5mm (hopping) compared to a rigid-body assumption. Similar reductions were observed for the shank: 24.2mm to 1.9mm (walking), 20.3mm to 1.9mm (cutting) and 14.7mm to 1.8mm (hopping). A geometric analysis of the first four principal components revealed that, within the ARFs, marker cluster STA is governed by rigid-body translations and rotations rather than deformations. The challenge remains, however, in finding the linear model parameters without bone pin data, but this investigation shows that relatively few parameters in a linear model are required to model the vast majority of the STA movements.

4 year olds localize tactile stimuli using an external frame of reference

Adults show a deficit in their ability to localize tactile stimuli to their hands when their arms are in the less familiar, crossed posture (e.g., Overvliet et al., 2011; Shore et al., 2002). It is thought that this ‘crossed-hands effect’ arises due to conflict (when the hands are crossed) between the anatomical and external frames of reference within which touches can be perceived. Pagel et al. (2009) studied this effect in young children and observed that the crossed-hands effect first emerges after 5.5-years. In their task, children were asked to judge the temporal order of stimuli presented across their hands in quick succession. Here, we present the findings of a simpler task in which children were asked to localize a single vibrotactile stimulus presented to either hand. We also compared the effect of posture under conditions in which children either did, or did not, have visual information about current hand posture. With this method, we observed a crossed-hands effect in the youngest age-group testable; 4-year-olds. We conclude that young children localize tactile stimuli with respect to an external frame of reference from early in childhood or before (cf. Bremner et al., 2008). Additionally, when visual information about posture was made available, 4- to 5-year-olds’ tactile localization accuracy in the uncrossed-hands posture deteriorated and the crossed-hands effect disappeared. We discuss these findings with respect to visual–tactile-proprioceptive integration abilities of young children and examine potential sources of the discrepancies between our findings and those of Pagel et al. (2009).

Restricted recovery of external remapping of tactile stimuli after restoring vision in a congenitally blind man

People with surgically removed congenital dense bilateral cataracts offer a natural model of visual deprivation and reafferentation in humans to investigate sensitive periods of multisensory development, for example regarding the recruitment of external or anatomical frames of reference for spatial representation. Here we present a single case (HS; male; 33 years; right-handed), born with congenital dense bilateral cataracts. His lenses were removed at the age of two years, but he received optical aids only at age six. At time of testing, his visual acuity was 30% in the best eye. We performed two tasks, a tactile temporal order judgment task (TOJ) in which two tactile stimuli were presented successively to the index fingers located in the two hemifields, adopting a crossed and uncrossed hand posture. The participant judged as precisely as possible which side was stimulated first. Moreover, we used a crossmodal-congruency task in which a tactile stimulus and an irrelevant visual distracter were presented simultaneously but independently to one of four positions. The participant judged the location (index or thumb) of the tactile stimulus with hands crossed or uncrossed. Speed was emphasized. In contrast to sighted controls, HS did not show a decrement of TOJ performance with hands crossed. Moreover, while the congruency gain was equivalent to sighted controls with uncrossed hands, this effect was significantly reduced with hands crossed. Thus, an external remapping of tactile stimuli still develops after a long phase of visual deprivation. However, remapping seems to be less efficient and to only take place in the context of visual stimuli.

Comparative Assessment of Bone Pose Estimation Using Point Cluster Technique and OpenSim

Estimating the position of the bones from optical motion capture data is a challenge associated with human movement analysis. Bone pose estimation techniques such as the Point Cluster Technique (PCT) and simulations of movement through software packages such as OpenSim are used to minimize soft tissue artifact and estimate skeletal position; however, using different methods for analysis may produce differing kinematic results which could lead to differences in clinical interpretation such as a misclassification of normal or pathological gait. This study evaluated the differences present in knee joint kinematics as a result of calculating joint angles using various techniques. We calculated knee joint kinematics from experimental gait data using the standard PCT, the least squares approach in OpenSim applied to experimental marker data, and the least squares approach in OpenSim applied to the results of the PCT algorithm. Maximum and resultant RMS differences in knee angles were calculated between all techniques. We observed differences in flexion/extension, varus/valgus, and internal/external rotation angles between all approaches. The largest differences were between the PCT results and all results calculated using OpenSim. The RMS differences averaged nearly 5° for flexion/extension angles with maximum differences exceeding 15°. Average RMS differences were relatively small (< 1.08°) between results calculated within OpenSim, suggesting that the choice of marker weighting is not critical to the results of the least squares inverse kinematics calculations. The largest difference between techniques appeared to be a constant offset between the PCT and all OpenSim results, which may be due to differences in the definition of anatomical reference frames, scaling of musculoskeletal models, and/or placement of virtual markers within OpenSim. Different methods for data analysis can produce largely different kinematic results, which could lead to the misclassification of normal or pathological gait. Improved techniques to allow non-uniform scaling of generic models to more accurately reflect subject-specific bone geometries and anatomical reference frames may reduce differences between bone pose estimation techniques and allow for comparison across gait analysis platforms.

Assessment of anatomical frame variation effect on joint angles: A linear perturbation approach

Although the interpretability and reliability of joint kinematics depends strongly on the accuracy and precision of determining the anatomical frame (AF) orientation, the exact dependency of joint angle error on AF misalignment is still not clear. To fully understand the behavior, this study uses linear perturbations to quantify joint angle error due to known modifications of the AFs, where the joint angles are calculated according to the Cardanic convention. The result is a functional representation of joint angle error with dependence on nominal joint angles and on the orientations of the alternative AFs relative to the nominal AFs. The results are validated using numerical analysis on knee joint angle data during walking. The derived relationship elucidates results from previous work studying this effect and allows AF differences to be inferred by joint angle curves when multiple sets of joint angle curves are collected simultaneously.

What decision-making models can tell us about tactile remapping

To locate an object by touch, for example when fumbling around in the dark, or to react to a tactile event on the skin, somatosensory information must be quickly combined with the current position of the hand relative to the rest of the body. Not much is know yet about the time course of this integration between touch and body posture (e.g., proprioception), called tactile remapping. A tactile localization task in which there is a spatial conflict between the somatotopic and the external spatial representations can provide some constraints on the timing of the proprioceptive signal (necessary for the remapping) relative to the tactile input. Here, we construe this localization task as a perceptual discrimination problem. By making use of established models of decision-making, we aim to shed light on the internal processes during tactile remapping. In the experiment, participants had to make a speeded saccade towards a brief somatosensory stimulus applied to the finger of one hand, while their arms were either crossed or uncrossed about the body midline. The eye movement trajectories were recorded and revealed that especially in the crossed condition fast saccades occasionally started toward the incorrect (anatomically congruent) side and were corrected in-flight, resulting in a turn-around saccade (about 250 ms after tactile onset, which might reflect the completion of tactile remapping). Similar curved traces have been observed recently in a random-dot motion (RDM) discrimination task were subjects had to report their decision by moving a handle to a left or right target [1]. While in the RDM task the curved traces were interpreted as a change of mind, direction-reversal here is thought to be induced by the (delayed) proprioceptive signal. With crossed hands, the current body posture needs to be taken into account and the representation of touch changes through time due to the remapping [2]. In the uncrossed posture remapping is trivial as the anatomical and external reference frames are aligned. In the framework of decision-making and in line with [1], we treat the initial direction of a saccade as a first choice, caused by crossing a decision-threshold. Accordingly, we apply two computational models able to account for changes of mind, a simple drift-diffusion model [1] and a biophysically-realistic nonlinear attractor model [3], to fit experimental reaction-time distributions and performance. In the models, turn-around saccades originate from a second threshold crossing if the accumulated evidence of the initially losing alternative overtakes the first choice. Remapping only the outcome of the decision to a different motor response in the crossed-hand condition proved insufficient to explain the differences in reaction times and performance to the uncrossed case. This suggests that internal differences between the two conditions are already present prior to the decision-making stage. From the modeling perspective the proprioceptive signal thus changes the input (evidence) for deciding on a saccade to the left or right. Allowing only the model inputs to vary between crossed and uncrossed conditions, we gain predictions on the relative size and timing of the internal proprioceptive signal for tactile remapping.

Articular surface remodeling of the hip after periacetabular osteotomy

Periacetabular osteotomies are a family of surgical procedures used to treat hip dysplasia. In a periacetabular osteotomy, the operating surgeon aims to increase acetabular coverage of the femoral head. The surgical correction has mechanical goals of increasing the stability of the joint and to improving the pressure distribution across the acetabulum. Although it is known that bone will remodel under changing load at the microstructural level, it is unclear whether there is any gross remodeling of the acetabulum or the femoral head in response to the change in loading following a periacetabular osteotomy. This observational study aims to quantify the shape of operative and contralateral hip joint surfaces pre and postoperatively to determine whether there are gross morphological changes in the shape of any of the bony articular surfaces of the joint. Preoperative and postoperative computed tomography (CT) scans were segmented as triangulated meshes. The bony articular surfaces of these meshes were then isolated. The vertices of these surfaces were fit to spheres and to general ellipsoids and, in the case of the acetabulum, examined in anatomical coordinate frames to look for changes between pre and postoperative segmentations. Spherical fit results were consistent preoperatively and postoperatively, with small changes in the radii of the spheres of best fit for both operative and nonoperative hips. Ellipsoid fitting showed variations between preoperative and postoperative scans in both eccentricity and orientation. Because there is no clear evidence of gross articular surface remodeling, periacetabular osteotomy for an adult should be planned with the expectation that the patient's existing articular structure will be preserved.

SU‐E‐J‐85: A New Approach to Evaluating the Impact of Organ Sub‐Volume Sensitivity to Irradiation by Deforming Cohort Dose Data Onto a Single ‘reference Human’

Purpose: We propose a new approach to normal tissue complication probability (NTCP) investigations by deforming doses from a patient cohort onto a single anatomic frame of reference in order to identify crucial anatomic features. Methods: To perform this study, IMRT treatment plans of seven different prostate cancer patients were used. Organs of interest (rectum, prostate) were delineated manually by an expert physician. CT scans, structures, and prescription dose distributions were exported into DICOM and then imported into the Computational Environment for Radiotherapy Research (CERR). The contrast of the organ of interest was enhanced at the surface boundary using the contour lines and overwriting the Hounsfield Unit (HU) of the CT scan. CTscans [2,7] were deformed onto reference scan CT1 using B‐spline method for deformable image registration available in Plastimatch. The warping of doses [2,7] was then performed utilizing the corresponding B‐spline transformation files. Results: Examination of the Dose Volume Histograms (DVHs) of the prostate reveals a substantial agreement in the mean dose within 1% between the initial prescribed dose and warped dose. However, for organs with large irregularity and heterogeneous dose distribution such as rectum, the DVHs of the warped dose showed larger deviation from the initial prescribed dose. Dose variance shows a significant variation along the rectum anterior wall. Conclusions: This study shows the feasibility of deforming a patient cohort onto a standard anatomy while retaining the dosimetric and volumetric information. This technique works better with organs which have simple geometry that can be indentified on the CT scan. Discrepancies between the initial and warped dose can be attributed to the low resolution CT scans and the choice of the DIR algorithm. This might be improved by mapping onto a reference anatomy with a high resolution CT scan such as the one provided by the Visible Human Project.NIH R01 CA85181

Event-related potential evidence for the use of external coordinates in the preparation of tactile attention by the early blind

Recent studies have suggested that visual experience in childhood is crucial for the automatic activation of an external spatial reference frame in tactile perception. These findings are largely based on behavioural work, with limited exploration using event-related potentials (ERPs). The present study examined the role of external spatial frameworks on tactile perception by recording ERP correlates of both preparatory processes and somatosensory processing during a tactile attention task for a group of early blind participants and age-matched sighted controls who carried out the task in darkness. Participants had to shift attention to one hand or the other as indicated by an auditory cue presented at the start of each trial, in order to detect infrequent tactile targets delivered to the attended hand. Spatial information about the external environment was acquired in advance during tactile exploration of the testing booth. ERPs measured during the cue-target interval indicated a conflict between anatomical and external spatial reference frames for both early blind and sighted participants, as marked by the delayed onset of the anterior directing attention negativity, although the delay was more pronounced in the sighted. A delay was also observed, irrespective of visual experience, on the onset of attentional modulations of somatosensory ERPs elicited by tactile stimuli. Although these results confirm that neither concurrent nor developmental vision is necessary for the default use of an external spatial framework in tactile attention, they suggest that the relative impact of an external vs. an anatomical spatial coordinate system may be affected by visual experience.

Kinematic performance of a six degree-of-freedom hand model (6DHand) for use in occupational biomechanics

Upper extremity musculoskeletal disorders represent an important health issue across all industry sectors; as such, the need exists to develop models of the hand that provide comprehensive biomechanics during occupational tasks. Previous optical motion capture studies used a single marker on the dorsal aspect of finger joints, allowing calculation of one and two degree-of-freedom (DOF) joint angles; additional algorithms were needed to define joint centers and the palmar surface of fingers. We developed a 6DOF model (6DHand) to obtain unconstrained kinematics of finger segments, modeled as frusta of right circular cones that approximate the palmar surface. To evaluate kinematic performance, twenty subjects gripped a cylindrical handle as a surrogate for a powered hand tool. We hypothesized that accessory motions (metacarpophalangeal pronation/supination; proximal and distal interphalangeal radial/ulnar deviation and pronation/supination; all joint translations) would be small (less than 5° rotations, less than 2mm translations) if segment anatomical reference frames were aligned correctly, and skin movement artifacts were negligible. For the gripping task, 93 of 112 accessory motions were small by our definition, suggesting this 6DOF approach appropriately models joints of the fingers. Metacarpophalangeal supination was larger than expected (approximately 10°), and may be adjusted through local reference frame optimization procedures previously developed for knee kinematics in gait analysis. Proximal translations at the metacarpophalangeal joints (approximately 10mm) were explained by skin movement across the metacarpals, but would not corrupt inverse dynamics calculated for the phalanges. We assessed performance in this study; a more rigorous validation would likely require medical imaging.

Anatomical reference frame versus planar analysis: implications for the kinematics of the rat hindlimb during locomotion

Functional recovery is the primary goal of therapeutic intervention in neuromuscular rehabilitation. The purpose of this study was to perform a segmental kinematic analysis using both planar angles computation and a tridimensional (3D) reconstruction of the rat hindlimb, regarding the morphology and the movement of each segment. Seven rats were evaluated for natural overground walking, and motion capture of the right hindlimb was collected with an optoeletronic system while the animals walked in the track. 3D biomechanical analyses were carried out and hip, knee, ankle, and metatarsophalangeal joint angular displacements were calculated. For flexion/extension, the knee joint and toe segment were statistically different between planar and 3D analysis, with the toe segment performing less extension at initial contact (IC) and the amplitude during swing phase for the knee being larger. During abduction/adduction, all hip joint parameters were statistically different except at IC and toe-off (TO) instants, the planar angles being higher than the 3D angles. In the horizontal plane, significant differences were found for ankle peaks of rotation, with increased results for the planar angles. In conclusion, a comparison between planar and 3D segmental kinematic analysis using a tridimensional reconstruction of the rat hindlimb demonstrated that different joints have different motion patterns within motion planes, probably related with physiological constraints and muscle actions. A major indication of the need for an anatomical reference frame kinematic analysis is supported by the knowledge that neuromuscular diseases are related to important clinical signs or motor deficits that should be observed, qualified, and quantified.