437 research outputs found
In vivo kinematics of knee replacement during daily living activities: Condylar and post-cam contact assessment by three-dimensional fluoroscopy and finite element analyses
In total knee replacement, the investigation on the exact contact patterns at the post-cam in implanted patients from real in vivo data during daily living activities is fundamental for validating implant design concepts and assessing relevant performances. This study is aimed at verifying the restoration of natural tibio-femoral condylar kinematics by investigating the post-cam engagement at different motor tasks. An innovative validated technique, combining three-dimensional fluoroscopic and finite element analyses, was applied to measure joint kinematics during daily living activities in 15 patients implanted with guided motion posterior-stabilized total knee replacement. Motion results showed physiological antero-posterior translations of the tibio-femoral condyles for every motor task. However, high variability was observed in the position of the calculated pivot point among different patients and different motor tasks, as well as in the range of post-cam engagement. Physiological tibio-femoral joint rotations and contacts at the condyles were found restored in the present knee replacement. Articular contact patterns experienced at the post-cam were found compatible with this original prosthesis design. The present study reports replaced knee kinematics also in terms of articular surface contacts, both at the condyles and, for the first time, at the post-cam
Kinematic models of lower limb joints for musculo-skeletal modelling and optimization in gait analysis
Kinematic models of lower limb joints have several potential applications in musculoskeletal modelling of the locomotion apparatus, including the reproduction of the natural joint motion. These models have recently revealed their value also for in vivo motion analysis experiments, where the soft-tissue artefact is a critical known problem. This arises at the interface between the skin markers and the underlying bone, and can be reduced by defining multibody kinematic models of the lower limb and by running optimization processes aimed at obtaining estimates of position and orientation of relevant bones. With respect to standard methods based on the separate optimization of each single body segment, this technique makes it also possible to respect joint kinematic constraints. Whereas the hip joint is traditionally assumed as a 3 degrees of freedom ball and socket articulation, many previous studies have proposed a number of different kinematic models for the knee and ankle joints. Some of these are rigid, while others have compliant elements. Some models have clear anatomical correspondences and include real joint constraints; other models are more kinematically oriented, these being mainly aimed at reproducing joint kinematics. This paper provides a critical review of the kinematic models reported in literature for the major lower limb joints and used for the reduction of soft-tissue artefact. Advantages and disadvantages of these models are discussed, considering their anatomical significance, accuracy of predictions, computational costs, feasibility of personalization, and other features. Their use in the optimization process is also addressed, both in normal and pathological subjects
Fluoroscopic and gait analyses for the assessment of the functional performance of an original total ankle replacement
Location-Dependent Human Osteoarthritis Cartilage Response to Realistic Cyclic Loading: Ex-Vivo Analysis on Different Knee Compartments
Objective: Osteoarthritis (OA) is a multifactorial musculoskeletal disorder affecting mostly weight-bearing joints. Chondrocyte response to load is modulated by inflammatory mediators and factors involved in extracellular cartilage matrix (ECM) maintenance, but regulatory mechanisms are not fully clarified yet. By using a recently proposed experimental model combining biomechanical data with cartilage molecular information, basally and following ex-vivo load application, we aimed at improving the understanding of human cartilage response to cyclic mechanical compressive stimuli by including cartilage original anatomical position and OA degree as independent factors. Methods: 19 mono-compartmental Knee OA patients undergoing total knee replacement were recruited. Cartilage explants from four different femoral condyles zones and with different degeneration levels were collected. The response of cartilage samples, pooled according to OA score and anatomical position was tested ex-vivo in a bioreactor. Mechanical stimulation was obtained via a 3-MPa 1-Hz sinusoidal compressive load for 45-min to replicate average knee loading during normal walking. Samples were analysed for chondrocyte gene expression and ECM factor release. Results: Non parametric univariate and multivariate (generalized linear mixed model) analysis was performed to evaluate the effect of compression and IL-1β stimulation in relationship to the anatomical position, local disease severity and clinical parameters with a level of significance set at 0.05. We observed an anti-inflammatory effect of compression inducing a significant downmodulation of IL-6 and IL-8 levels correlated to the anatomical regions, but not to OA score. Moreover, ADAMTS5, PIICP, COMP and CS were upregulated by compression, whereas COL-2CAV was downmodulated, all in relationship to the anatomical position and to the OA degree. Conclusion: While unconfined compression testing may not be fully representative of the in-vivo biomechanical situation, this study demonstrates the importance to consider the original cartilage anatomical position for a reliable biomolecular analysis of knee OA metabolism following mechanical stimulation
Author Correction: 3D measurement techniques for the hindfoot alignment angle from weight-bearing CT in a clinical population
Cone-beam CT (CBCT) scans now enable accurate measurements on foot skeletal structures with
the advantage of observing these in 3D and in weight-bearing. Among the most common skeletal
deformities, the varus/valgus of the hindfoot is the most complex to be represented, and a number
of measure proposals have been published. This study aims to analyze and to compare these
measurements from CBCT scans in a real clinical population with large such deformity. Ten patients
with severe acquired adult fatfoot and indication for surgery underwent CBCT scans (Carestream,
USA) while standing on that leg, before and after surgical correction. Corresponding 3D shape of each
bone of the distal shank and hindfoot were defned (Materialise, Belgium). Six diferent techniques
from the literature were used to calculate the varus/valgus deformity, i.e. the inclination of the
hindfoot in the frontal plane of the shank. Standard clinical measurements by goniometers were taken
for comparison. According to these techniques, and starting from a careful 3D reconstruction of the
relevant foot skeletal structures, a large spectrum of measurements was found to represent the same
hindfoot alignment angle. Most of them were very diferent from the traditional clinical measures. The
assessment of the pre-operative valgus deformity and of the corresponding post-operative correction
varied considerably. CBCT fnally allows 3D assessment of foot deformities in weight-bearing.
Measurements from the diferent available techniques do not compare well, as they are based on
very diferent approaches. It is recommended to be aware of the anatomical and functional concepts
behind these techniques before clinical and surgical conclusions
Validation of a one degree-of-freedom spherical model for kinematics analysis of the human ankle joint
During passive motion, the human tibiotalar (ankle) joint behaves as a single degree-of-freedom (1DOF) system [1,2]. In these conditions, fibres within the ligaments remain nearly isometric throughout the flexion arc and articular surfaces nearly rigid. Relevant theoretical models are showing that the ligaments and the articular surfaces act together as mechanisms to control the passive joint kinematics [3-5]. Kinematic measurements and corresponding model predictions also revealed that the instantaneous screw axes of passive motion pass near to a single point, hereinafter called pivot point [5]. The present study investigates the extent to which this motion is spherical-like
Design, Implementation and Testing of an Automatic Power Management System for Residential Stand-alone Microgrids with Hybrid Power Supply
The paper presents an automatic power management system (PMS) designed for the on-line operation of an experimental low voltage microgrid equipped with two power supplies, a kW-class fuel cell (FC) and a photovoltaic (PV) module emulator, along with a 100-Ah battery storage system, all connected to a 230 VAC node. The connections of the various components to the common AC bus make use of power inverters with specific functionalities: the FC inverter controls the power production taking into account the FC limitations and requirements, the inverter of the PV emulator tracks its maximum power operating point, whilst, in islanded operating conditions, the bidirectional converter of the battery controls the voltage and frequency of the AC node. The AC node feeds electric active and reactive loads able to reproduce arbitrary and programmable profiles. The automatic PMS is implemented in a real time microcontroller and it is able to provide both the microgrid monitoring and supervisory control during grid-connected and islanded conditions and the FC power scheduling throughout various operating modes. The paper describes also the experimental investigation aimed at assessing the dynamic characteristics of the stand-alone microgrid equipped with the developed PMS
Custom-Made Devices Represent a Promising Tool to Increase Correction Accuracy of High Tibial Osteotomy: A Systematic Review of the Literature and Presentation of Pilot Cases with a New 3D-Printed System
Background: The accuracy of the coronal alignment corrections using conventional high tibial osteotomy (HTO) falls short, and multiplanar deformities of the tibia require consideration of both the coronal and sagittal planes. Patient-specific instrumentations have been introduced to improve the control of the correction. Clear evidence about customized devices for HTO and their correction accuracy lacks. Methods: The databases PUBMED and EMBASE were systematically screened for human and cadaveric studies about the use of customized devices for high tibial osteotomy and their outcomes concerning correction accuracy. Furthermore, a 3D-printed customized system for valgus HTO with three pilot cases at one-year follow-up was presented. Results: 28 studies were included. The most commonly used custom-made devices for HTO were found to be cutting guides. Reported differences between the achieved and targeted correction of hip-knee-ankle angle and the posterior tibial slope were 3 degrees or under. The three pilot cases that underwent personalized HTO with a new 3D-printed device presented satisfactory alignment and clinical outcomes at one-year follow-up. Conclusion: The available patient-specific devices described in the literature, including the one used in the preliminary cases of the current study, showed promising results in increasing the accuracy of correction in HTO procedure
A Microcontroller-Based Power Management System for Standalone Microgrids with Hybrid Power Supply
The paper presents a microcontroller-based power management system (PMS) designed for the online operation of an experimental low voltage microgrid equipped with a battery storage system and two power supplies: a kilowatt (kW)-class proton exchange membrane (PEM) fuel cell (FC) and a photovoltaic (PV) module emulator, both connected to a low voltage ac node. The connections of the energy sources to the common ac bus make use of power inverters with specific functionalities. The ac node feeds electric active and reactive load emulators able to reproduce programmable profiles. The automatic PMS provides the microgrid monitoring and the FC power scheduling in both grid-connected and islanded operating conditions. The paper describes the structure and functionalities of the PMS as well as a specific experimental investigation aimed at assessing the dynamic performance of the microgrid in islanded conditions
Superimposition of ground reaction force on tibial-plateau supporting diagnostics and post-operative evaluations in high-tibial osteotomy. A novel methodology.
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