IMU-based joint axis identification method for arbitrary joints in OpenSim - a simulation study

The relation between the instantaneous center of rotation and facet joint forces – A finite element analysis

Biomechanical analyses of jaw movement suggest that considerable differences in mechanical advantage may exist for individual masticatory muscles as a function of the inferior-superior position of the jaw. These variations in mechanical advantage have been hypothesized from the knowledge that the jaw opening and closing muscles apply force around a center of rotation that moves with variations in the magnitude of jaw depression. The influence of these peripheral mechanical properties would appear significant for models of lip-jaw motor control. In the present study, to verify empirlcally the influence of a moving, instantaneous center of rotation for the jaw, changes in mechanical advantage were analyzed by recording EMG from the medial pterygoid, masseter, and anterior and posterior heads of the temporalis during isometric jaw closing manuevers. lntramuscular comparisons of EMG level for each closing muscle were obtained for a range of positions of the jaw while it was acting against a static load. Relative changes in EMG level for each muscle, as a function of jaw position, were interpreted in relation to variations in mechanical advantage predicted from an analysis of the instantaneous center of jaw rotation. These data will be discussed in relation to the motor control of the jaw in speech production.

Instantaneous centers of rotation for lumbar segmental extension in vivo

Understanding the kinematics of the spine provides paramount knowledge for many aspects of the clinical analysis of back pain. More specifically, visualisation of the instantaneous centre of rotation (ICR) enables clinicians to quantify joint laxity in the segments, avoiding a dependence on more inconclusive measurements based on the range of motion and excessive translations, which vary in every individual. Alternatively, it provides motion preserving designers with an insight into where a physiological ICR of a motion preserving prosthesis can be situated in order to restore proper load distribution across the passive and active elements of the lumbar region. Prior to the use of an unconstrained dynamic musculoskeletal model system, based on multi-body models capable of transient analysis, to estimate segmental loads, the model must be kinematically evaluated for all possible sensitivity due to ligament properties and the initial locus of intervertebral disc (IVD). A previously calibrated osseoligamentous model of lumbar spine was used to evaluate the changes in ICR under variation of the ligament stiffness and initial locus of IVD, when subjected to pure moments from 0 to 15 Nm. The ICR was quantified based on the closed solution of unit quaternion that improves accuracy and prevents coordinate singularities, which is often observed in Euler-based methods and least squares principles. The calculation of the ICR during flexion/extension revealed complexity and intrinsic nonlinearity between flexion and extension. This study revealed that, to accommodate a good agreement between in vitro data and the multi-body model predictions, in flexion more laxity is required than in extension. The results showed that the ICR location is concentrated in the posterior region of the disc, in agreement with previous experimental studies. However, the current multi-body model demonstrates a sensitivity to the initial definition of the ICR, which should be recognised as a limitation of the method. Nevertheless, the current simulations suggest that, due to the constantly evolving path of the ICR across the IVD during flexion–extension, a movable ICR is a necessary condition in multi-body modelling of the spine, in the context of whole body simulation, to accurately capture segmental kinematics and kinetics.

When under influence of an incident wave system, any floating body presents a general motion with all six degrees of freedom, unless it presents some kind of restrains on it. For a free moving body, the center of rotation will depend on the force distribution and might not coincide with its center of gravity. For long and slender floating structures, such as FPSO platforms, a small change in the center of Pitch rotation would result in significant change in the overall motions in its fore and aft regions. Therefore, it is of high importance to obtain a better understating of the instantaneous position of the body center of rotation in Heave and Pitch response. This paper investigates the position of the Instantaneous Center of Rotation in Pitch Response of a scaled down model of a FPSO platform under different regular wave conditions. The investigation uses basic kinematics equations for rigid body, defining the 6 degrees of freedom of the rigid body motion from a finite number of markers installed in the model. A high quality tracking system captures the markers positions in order to define the rigid body at each instant of time. For an initial approach, the study considers the response due to head waves seas with experimental validation.

Analyzing center of rotation during opening and closing movements of the mandible using computer simulations

Metacarpophalangeal Joint Mechanics After 3 Different Silicone Arthroplasties

The location of the center of rotation (COR) of joints is a key parameter in multiple applications of human motion analysis. The aim of this work was to propose a novel real-time estimator of the center of fixed joints using an inertial measurement unit (IMU). Since the distance to this center commonly varies during the joint motion due to soft tissue artifacts (STAs), our approach is aimed at adapting to these small variations when the COR is fixed. Our proposal, called ArVE ${_{d}}$ , to the best of our knowledge, is the first real-time estimator of the IMU-joint center vector based on one IMU. Previous works are off-line and require a complete measurement batch to be solved, and most of them are not tested in the real scenario. The algorithm is based on an extended Kalman filter (EKF) that provides an adaptive vector to STA motion variations at each time instant, without requiring a preprocessing stage to reduce the level of noise. ArVE ${_{d}}$ has been tested through different experiments, including synthetic and real data. The synthetic data are obtained from a simulated spherical pendulum whose COR is fixed, considering both a constant and a variable IMU-joint vector, which simulates translational IMU motions due to STA. The results prove that ArVE ${_{d}}$ is adapted to obtain a vector per sample with an accuracy of 6.8 ± 3.9 mm on the synthetic data, which means an error of lower than 3.5% of the simulated IMU-joint vector. Its accuracy is also tested on the real scenario estimating the COR of the hip of five volunteers using as reference the results from an optical system. In this case, ArVE ${_{d}}$ gets an average error of 9.5% of the real vector value. In all the experiments, ArVE ${_{d}}$ outperforms the published results of the reference algorithms.

Mandibular condyles translate back and forth during mouth closing and opening in primates and most other mammals. To account for the functional significance of this phenomenon, several hypotheses have been proposed. The sarcomere-length hypothesis holds that condylar translation provides a mechanical advantage by minimizing sarcomere-length changes in the masseter-medial pterygoid complex throughout a wide range of jaw openings. As the hypothesis is inherently associated with the locations of the instantaneous centers of rotation (ICRs) of the mandible, a more accurate determination of this variable would help test this hypothesis. This study investigated ICRs in the sagittal plane during human symmetrical mandibular opening based on a recently developed analytical method. The results confirmed that, with inter- and intraindividual variation, the natural opening was a simultaneous rotational and translational motion. In addition, the ICR was found to lie closer to the condyle during the first 10 degrees than during the rest of the rotation. This suggests that for the condyles the rotational component is somewhat more significant at the early phase than at the late phase of the opening stroke. For the whole range of the natural opening, the grossly approximated centers of rotation (CRs) scattered below the palpable lateral condylar poles in the superior half of the ramus. This study supports neither the ICR path determined by Grant ([1973], J. Biomech. 6:109-113) nor the conclusions reached by recording manually operated jaw movements in human cadavers (Rees [1954] Br. Dent. J. 6:125-133). Moss's suggestion ([1960] Disorders of the Temporomandibular Joint (Philadelphia: W.B. Saunders), pp. 73-88) that the center of rotation lies at the lingula is also not confirmed. Although the new data cannot reject the sarcomere-length hypothesis, they do not strongly support it either. Another hypothesis is proposed in this study as plausible. With this hypothesis, translation is regarded as an adaptation to the use of the inferior head of the lateral pterygoid as a jaw depressor in noncarnivorous mammals. Potential functional advantages of this portion of the muscle are also discussed.

BackgroundPrevious research has identified separate sagittal plane instantaneous centers of rotation for the metatarso-phalangeal and metatarso-sesamoid joints, but surprisingly, it does not appear that any have integrated the distinctive morphological characteristics of all three joints and their respective axes into a model that collectively unifies their functional motions. Since all joint motion is defined by its centers of rotation, establishing this in a complicated multi-dimensional structure such as the metatarso-phalangeal-sesamoid joint complex is fundamental to understanding its functionality and subsequent structural failures such as hallux abducto valgus and hallux rigidus.MethodsBased on a hypothesis that it is possible to develop an instantaneous center of rotation common to all four osseous structures, specific morphometrics were selected from a sequential series of 0.5-mm sagittal plane C-T sections in one representative cadaver specimen randomly selected from a cohort of nine, seven which were obtained from the Body Donation Program, Department of Anatomy, University of California, San Diego School of Medicine, and two which were in the possession of one author (MD). All mature skeletal specimens appeared grossly normal, shared similar morphological features, and displayed no evidence of prior trauma, deformity, or surgery. Specific C-T sections isolated the sagittal plane characteristics of the inter-sesamoidal ridge and each sesamoid groove, and criteria for establishing theoretical sesamoid contact points were established. From these data, a geometric model was developed which, to be accurate, had to closely mimic all physical and spatial characteristics specific to each bone, account for individual variations and pathological states, and be consistent with previously established metatarso-phalangeal joint functional motion.ResultsSequential sagittal plane C-T sections dissected the metatarsal head from medial to lateral and, at approximately midway through the metatarsal head, the circular nature of the inter-sesamoidal ridge (crista) was isolated; other C-T sections defined, respectively, the elliptical characteristics of the tibial (medial) and fibular (lateral) sesamoid grooves in each specimen. A general plane model representing the most basic form of the joint was developed, and its center of rotation was established with a series of tangential and normal lines. Simplified tibial sesamoid and fibular plane models were developed next which, when combined, permitted the development of a spherical model with three separate contact points. Based on the morphometrics of each sesamoid groove and a more distally positioned tibial sesamoid, the model was modified to accurately define the center of rotation and one distinctive sagittal plane geometric and functional characteristic of each groove.ConclusionConsistent with our hypothesis, this theoretical geometric model illustrates how it is possible to define an instantaneous center of rotation common to all three joints while simultaneously accounting for morphometric and spatial variability. This should provide additional insight into metatarso-phalangeal-sesamoid joint complex functionality and the physical characteristics that contribute to its failure.

On intrinsic equivalences of the finite helical axis, the instantaneous helical axis, and the SARA approach. A mathematical perspective

Relevance There are data in the literature describing the trajectory of displaced center of rotation of the knee joint. However, data on the exact location of instantaneous centers of rotation at various angles of the knee flexion are not available. Objective To identify the localization of instantaneous centers of rotation at various angles of the knee flexion and present the results in the form of a template. Material and methods The bench testing was performed using a specially developed device that provides fixation of the anatomic cadaver preparation of the lower extremity. The device made it possible to identify the zero instantaneous center of rotation using a radiographic positive marker. Control radiographs were performed to determine the "movement" of instantaneous centers of rotation at every 10° of flexion to reach an angle of 120°. The exact location of instantaneous centers of rotation at different knee flexion angles were obtained with a graphical editor and tibia internal rotation identified during the knee flexion. Results The identified instantaneous centers of rotation were applied to the contour of the distal femur to form the template and allow scaling. Conclusions The template developed could be useful for computer hexapod assisted orthopaedic surgery in the treatment of knee stiffness, for mechanotherapy and joint replacement.

The location of the instantaneous centre of rotation (ICR) of a lumbar unit has a considerable clinical importance as a spinal health estimator. Consequently, many studies have been conducted to measure or estimate the ICR during rotations in the three anatomical planes; however the results reported are widely scattered. Even if some inter-subjects variability is to be expected, such inconsistencies are likely explained by the differences in methods and experiments. Therefore, in this paper we seek to model three behaviours of the ICR during lateral bending and axial rotation based on results published in the literature. In order to assess the metabolic and mechanical sensibility to the assumption made on the ICR kinematics, we used a previously validated three dimensional non-linear poroelastic model of a porcine intervertebral disc to simulate physiological lateral and axial rotations. The impact of the geometry was also briefly investigated by considering a 11^circ wedge angle. From our simulations, it appears that the hypothesis made on the ICR location does not significantly affect the critical nutrients concentrations but gives disparate predictions of the intradiscal pressure at the centre of the disc (variation up to 0.7 MPa) and of the displacement fields (variation up to 0.4 mm). On the contrary, the wedge angle does not influence the estimated intradiscal pressure but leads to minimal oxygen concentration decreased up to 33% and increased maximal lactate concentration up to 13%. While we can not settle on which definition of the ICR is more accurate, this work suggests that patient-specific modeling of the ICR is required and brings new insights that can be useful for the development of new tools or the design of surgical material such as total lumbar disc prostheses.

Cranial cruciate ligament rupture is a common cause of femorotibial instability in dogs. Despite numerous techniques being described for achieving joint stabilization, no consensus exists on the optimal management strategy. This ex vivo study utilized the path of the instantaneous center of rotation (ICR) to compare normal, pathological and treated joints. Fluoroscopic recordings of seven limbs from a previous study of canine stifle joint stability following center of rotation of angulation-based levelling osteotomy (CBLO) with and without hamstring loading were analyzed using least-squares approximation of the ICR and estimation of percentage gliding (vs. rolling) to determine if alterations in ICR path and gliding caused by CCL transection and following meniscal release could be normalized by CBLO. In intact joints, the ICR path was located mid-condyle, but this shifted significantly proximally and caudally following CCL transection and medial meniscal release (p < 0.007, p < 0.04). Hamstring loading resulted in qualitative and some quantitative improvements in joint movement based on percentage gliding movement analysis. The ICR path after CBLO remained significantly different to the intact location with or without a hamstring load (p < 0.02, p < 0.04), potentially consistent with CBLO aims of mild residual instability. CBLO resulted in percentage gliding characteristics not significantly different to intact joints (p > 0.08). Qualitative improvements in ICR path and percentage gliding quantities and variability suggest that hamstring loading positively influences joint biomechanics and that further investigation of this role ex vivo and clinically is warranted.

Pseudo-omnidirectional robots with independently steerable wheels require a method to synchronize the steering motion of the wheels in order to keep a unique instantaneous center of rotation (ICR). For standard wheels, the instantaneous center of rotation is defined as the intersection point of all wheel axes. We present a novel approach to deal with the problem of continuously shifting the center of rotation of a pseudo-omnidirectional rover from an initial to a demanded position in the Cartesian plane. The main contribution is the consideration of substantial velocity and acceleration limits on the steering units, as well as mechanical constraints and noise affected sensor measurements. We solve this problem by deriving a relationship between the steering accelerations of the single wheels and the acceleration of the center of rotation. We furthermore provide a contribution to the tracking of the ICR in the presence of significant sensor noise. Our results are evaluated by tests on the rover breadboard developed during the activities for the ExoMars mission.