1,721,036 research outputs found
Closed-chain rotational mechanism having decoupled and homokinetic actuation
No full textThe invention concerns a mechanism having the necessary conditions in order that the rotational motion of a body can be actuated in a decoupled and homokinetic way by motors (M1, M2, M3) installed on the same frame (A), by means of transmission based on homokinetic joints (CV). In particular, decoupled and constant relations are generated between the motors speeds (q1, q2, q3) and the time derivatives of the variables describing the body orientation (f1, f2, f3), thus maintaining the homokinetic condition of the transmission during the simultaneous movements of more motors. The invention therefore concerns new architectures of decoupled and homokinetic joints, with two or three degrees of freedom. They are characterised by uniform input-output kinetostatic relations and suitably wide working spaces
The Geometrical Arrangement of Knee Constraints That Makes Natural Motion Possible: Theoretical and Experimental Analysis
No full textThe study of the knee natural motion, namely the unresisted motion that the knee exhibits in the absence of external loads, provides insights into the physiology of this articulation. The natural motion represents the baseline condition upon which deformations of its passive structures (i.e., ligaments and cartilage) take place when loads are applied. Moreover, during natural motion, the strain energy density stored within ligaments and cartilage is minimized. This reduces the chance of microdamage occurrences and the corresponding metabolic cost for tissue repairing. The study of the knee natural motion is thus fundamental in understanding the joint physiology. This paper shows that the line of action of resultant forces of all the knee constraints provided by the passive structures must intersect the instantaneous helical axis (IHA) to make the knee natural motion possible. In other words, the lines of action of all these constraints must cross the same line at each flexion angle to guarantee the natural motion of the joint. This geometrical property is first proven theoretically and then verified in four in vitro and one in vivo experiments. The geometrical characterization of the knee natural motion presented in this study provides a fundamental property that must be satisfied to allow the correct joint mobility. The knowledge of this property may thus allow the definition of better models, treatments, and devices
Prediction of Individual Knee Kinematics From an MRI Representation of the Articular Surfaces
Full text linkOBJECTIVE: The knowledge of individual joint motion may help to understand the articular physiology and to design better treatments and medical devices. Measurements of in-vivo individual motion are nowadays invasive/ionizing (fluoroscopy) or imprecise (skin markers). We propose a new approach to derive the individual knee natural motion from a three-dimensional representation of articular surfaces.METHODS: We hypothesize that tissue adaptation shapes articular surfaces to optimize load distribution. Thus, the knee natural motion is obtained as the envelope of tibiofemoral positions and orientations that minimize peak contact pressure, i.e. that maximize joint congruence. We investigated four in-vitro and one in-vivo knees. Articular surfaces were reconstructed from a reference MRI. Natural motion was computed by congruence maximization and results were validated versus experimental data, acquired through bone implanted markers, in-vitro, and single-plane fluoroscopy, in-vivo.RESULTS: In two cases, one of which in-vivo, maximum mean absolute error stays below 2.2° and 2.7mm for rotations and translations, respectively. The remaining knees showed differences in joint internal rotation between the reference MRI and experimental motion at 0° flexion, possibly due to some laxity. The same difference is found in the model predictions, which, however, still replicate the individual knee motion.CONCLUSION: The proposed approach allows the prediction of individual joint motion based on non-ionizing MRI data.SIGNIFICANCE: This method may help to characterize healthy and, by comparison, pathological knee behavior. Moreover, it may provide an individual reference motion for the personalization of musculoskeletal models, opening the way to their clinical application
Joint kinematics from functional adaptation: A validation on the tibio-talar articulation
Full text linkBiologic tissues respond to the biomechanical conditions to which they are exposed by modifying their architecture. Experimental evidence from the literature suggests that the aim of this process is the mechanical optimization of the tissues (functional adaptation). In particular, this process must produce articular surfaces that, in physiological working conditions, optimize the contact load distribution or, equivalently, maximize the joint congruence. It is thus possible to identify the space of adapted joint configurations (or adapted space of motion) starting solely from knowledge of the shape of the articular surfaces, by determining the envelope of the maximum congruence configurations. The aim of this work was to validate this hypothesis by testing its application on 10 human ankle joints. Digitalizations of articular surfaces were acquired in 10 in-vitro experimental sessions, together with the natural passive tibio-talar motion, which may be considered as representative of the adapted space of motion. This latter was predicted numerically by optimizing the joint congruence. The highest mean absolute errors between each component of predicted and experimental motion were 2.07° and 2.29 mm respectively for the three rotations and translations. The present kinematic model replicated the experimentally observed motion well, providing a reliable subject-specific representation of the joint motion starting solely from articulating surface shapes
Analysis of the three-dimensional motion of the knee under the effect of single-axis loads
No full textIn this study, the knee stiffness was characterized in vitro on the whole flexion range by a loading rig. Results show considerable tibio-femoral displacements also in directions different from the loading one
Prediction of the subject-specific knee passive motion from non-invasive measurements
No full textThe passive motion of the knee is the natural motion of the joint in unloaded conditions. It is the joint starting condition when loads are applied, thus affecting the joint behaviour also in loaded conditions. For this reason, the knowledge of this motion is useful in all applications which aim at replicating or restoring the natural behaviour of the knee, such as lower-limb modelling, surgical planning, prosthetic design. Several studies measured the passive motion of the joint and the mean results can be used as a reference [1-3]. However, there is an increasing request of subject-specific results that would allow personalization of model parameters or of prosthesis geometry on a patient. In these cases, the subject motion would be required. An accurate estimation of the joint motion is difficult to obtain in vivo: non-invasive techniques can be inaccurate (skin-markers) or too complicated (fluoroscopy) for standard practice, while more invasive techniques (bone-pins) are not acceptable in several applications. Thus, new techniques are needed to predict the natural joint motion with a good accuracy, starting from non-invasive measurements. Two techniques were proposed for the knee passive motion modelling. Both methods start from the consideration, supported by relevant experimental analyses [2,3], that in passive conditions the knee behaves as a single degree-of-freedom (1DOF) system guided by the passive structures of the joint. The first technique (T1) predicts the passive motion by maximizing the joint congruence at all flexion angles [4]: it only requires the 3D model of articular surfaces with menisci, that can be obtained by MRI. T1 was developed for the ankle joint. At this stage, its application to the knee revealed a good accuracy, but the errors increased at high flexion angles, particularly for some motion components. The second technique (T2) models the knee as a 1DOF spatial mechanism, featuring the two articular contacts and the three isometric fibres of the anterior cruciate, posterior cruciate and medial collateral ligaments [3,5]. T2 was very accurate to replicate the passive motion of specimens over the full flexion arc, but a reference motion is needed to adjust the model parameters and the specimen motion was previously used [3]. The limitations of T1 and T2 are overcome in this paper by combining the two methods. An estimate of the joint motion is obtained by T1. This estimate is used as an input for T2 by which a new motion prediction is defined. The idea is that ligament constraints of T2, starting from the estimate provided by T1, can improve the overall motion prediction over the full flexion arc. The technique is here presented and applied on a specimen
A New Test Rig for Human Joint and Prosthesis Characterization
No full textIn vitro experimental studies are of great importance in human joint biomechanics. Data from in vitro tests allow the study of kinematics, kinetostatics, and dynamics of human joints. Understanding the joint behavior is required for prosthesis and orthosis design as well as for model validation. Several in vitro test rigs are reported in the literature. Most devices currently in use are either specifically designed for a prescribed set of tests, thus limiting possible applications, or obtained by adapting industrial machines to biomechanics, which results in a poor fit to the intended application, e.g., limiting the flexion range achievable during tests. In general, the main issue for these rigs is to apply specific external loads variable in time with flexion, without introducing additional unwanted constraints to the relative motion of the main bones. In this study, a new test machine is presented as an evolution of a previous one. In particular, the new systems for load application, joint motion, and femur-to-rig fixation are shown, which make the use of the machine more quick and efficient and extend its possible applications to a wider range of loading conditions and joint motion
La ricerca sulle protesi del ginocchio: verso modelli patient-specific
No full textI nuovi dispositivi ortopedici mirano ad una personalizzazione in grado di rispondere alle specifiche necessità del singolo paziente. Recentemente è stato sviluppato un approccio che consente la sintesi di protesi ed ortesi in grado di replicare accuratamente il moto naturale del paziente, anche a partire da una rappresentazione 3D delle superfici articolari ottenibile ad esempio da risonanza magnetica
A new test rig for static and dynamic evaluation of knee motion based on a cable-driven parallel manipulator loading system
No full textThe evaluation of the knee joint behavior is fundamental in many applications, such as joint modeling, prosthesis and orthosis design. A new test rig for in vitro analysis of the knee joint behavior is presented in this paper. Based on a cable-driven parallel manipulator loading system, the rig can simulate general knee loading conditions, such as clinical tests and common daily activities like walking and sit to stand, in a wide range of flexion angles. The joint natural response in terms of movement is measured by an optoelectronic system. Furthermore, the new rig allows the estimation of the contribution of the principal leg muscles in guaranteeing the equilibrium of the joint. Despite its simplicity and low cost, the rig presents good accuracy, repeatability and versatility that allows its application on a wide range of specimen sizes. It represents an advanced application of cable-driven parallel robots for in vitro motion analysis of the knee subjected to general loads
In-vitro experimental determination of knee stiffness
No full textThe quantification of knee stiffness, i.e. the relation between applied loads and bone displacements, is fun-damental both for the clinical discrimination between healthy and pathological states and for the definition and validation of numerical models of the joint. Considering the knee as a 1 unresisted degree-of-freedom (dof) system, its stiffness analysis requires the application of constant loads for each value of the flexion an-gle, taken as free parameter of the unresisted motion, while recording the variation of the remaining 5 dofs describing the relative position and orientation of the femur with respect to the tibia. In spite of the relevance of these data, no many studies are available in the liter-ature on this topic [1-4]. In particular, the displacements/rotations not corresponding to the loading direc-tion were not deeply investigated. In this study, knee stiffness was characterized by a loading rig [5]. The results for the drawer test are shown as representative
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