Types Of Motion Research Articles

A self-powered spring-based triboelectric vibration sensor

Abstract Self-powered vibration sensors have gained attention due to their versatility. However, a limitation of many existing self-powered sensors is their single-direction functionality, which hinders their effectiveness in capturing multidirectional human movement’s swinging motions. To address this, this study introduces an innovative self-powered vibration sensor based on the triboelectrification effect of an inverted pendulum metal ball. This novel sensor excels at detecting micro-vibrations through the freestanding sliding electrification of a metal ball using Kapton tape. The generated charge is transferred through interdigital electrodes arranged in a spiral pattern. To ensure adaptability to various motion types, the metal ball is affixed to a spring and configured as an inverted pendulum. This setup allows the sensor to detect both linear and rotary motions across a range of acceleration levels. The fabricated sensor exhibits remarkable sensitivity, measuring 0.203 V/mm. It was affixed to the human body to detect low-frequency vibrations, particularly those below 20 Hz. Impressively, it can detect millimeter-scale vibrations, even up to 3 mm, at different rotational angles (0°, 30°, 60°, and 90°). This outcome highlights the promising performance of our vibration sensor in the field of human motion monitoring, making it a significant advancement in the realm of self-powered vibration sensors.

The effect of fresh and used ankle taping on lower limb biomechanics in sports specific movements

ObjectivesWe aimed to investigate the effects of ankle taping on lower extremity biomechanics related to injury development and how these effects change after sports-specific use. DesignRandomized, repeated measures design with three conditions: Barefoot, tape applied fresh, and tape after sports-specific use (between-subject factor: sex). MethodsTwenty-five healthy participants (ten female) performed sports-specific movements, including running, drop jumping, and 180° change of direction, under the three conditions. Kinetic and kinematic data were collected using 3D motion capturing and force platforms. ResultsTape applied fresh and tape after sports-specific use significantly reduced peak ankle inversion. Biomechanical risk factors for anterior cruciate ligament or running overuse injuries were either unchanged or decreased with tape applied fresh, except for the peak loading rate of the resultant ground reaction force, which increased between 4% and 18% between movement types. After 15 minutes of sports-specific use of the tape, the alterations induced by tape applied fresh remained for some biomechanical risk factors while they became closer to barefoot again for others, indicating a differential response to prolonged use of taping for different biomechanical variables. ConclusionsAnkle taping protects the ankle joint by reducing biomechanical risk factors associated with ankle sprains, and most biomechanical risk factors for anterior cruciate ligament or running overuse injuries are not increased. Further research is needed to explore the duration of protective effects, variations across sports, and its impact on patients with chronic ankle instability, contributing to a more comprehensive understanding of ankle taping's influence on lower extremity biomechanics.

Clear Aligner Therapy Concerns: Addressing Discrepancies Between Digitally Anticipated Outcomes and Clinical Ground Realities.

Expeditious strides in the fields of biomaterials, computer-aided design, and manufacturing have catapulted clear aligner therapy (CAT) to become a comprehensive orthodontic treatment modality. The efficiency of achieving planned tooth movement with clear aligners is a significant consideration while setting up the final treatment goals, as well as calculating treatment times and costs based on the available evidence. Contemporary research outcomes confirm that one of the most commonly reported clinical concerns with CAT is the discrepancy between the prescribed outcome in the digital treatment plan and the clinically achieved outcome from a given series of aligners. Inaccurate prediction of tooth movements may not only lead to a prolonged duration of aligner treatment with an additional need for refinement strategies; but it may also cause other concerns, such as patient burnout and increased potential for relapse. The authors of this paper have elucidated some of the critical elements that may help address this discrepancy between digitally prescribed and clinical outcomes based on an evidence-based approach with regard to the predictability and accuracy of CAT. A strong diagnostic acumen, judicious case selection, solid biomechanical understanding of various types of orthodontic tooth movements, a research framework that keeps pace with technological and material developments and provides evidence-based knowledge of the limitations of CAT; and above all, the ability of the clinician to continually innovate as per different clinical scenarios, all contribute to attaining treatment predictability, efficacy, and efficiency with CAT.

EAPTON: Event-based Antinoise Powerlines Tracking with ON/OFF Enhancement

Abstract Event-based powerlines detection and tracking is a thriving research topic with significance in autonomous powerlines inspection, especially for payload-limited UAVs. Currently, event-based line detection methods are developed to address line detection in dynamic scenes, including UAV-based powerlines tracking. However, due to the motion sensitivity of event cameras, it is challenging to eliminate false line detection caused by clustered events from a complex background. Taking inspiration from animals’ motion vision, we propose the EAPTON algorithm to address the vulnerable robustness against complex backgrounds. In our method, the brightness increments (ON events) and decrements (OFF events) are separately processed in parallel pathways, which is prevalent in animals’ motion vision. To increase selective sensibility to powerlines, we utilize the feature that twin-born ON and OFF events will simultaneously arise on the bilateral side of the powerlines. We verified our algorithm in a simulated powerlines inspection scenario with background noise, it outperforms the SOTA algorithm in robustness. Surprisingly, we found that the relative motion type between UAV and the target (e.g., powerlines) is strongly correlated with the statistical asymmetry of the ON/OFF events, which provides a modal of visual cues for motion estimation in other robotic tasks and may shed a light on the explanation of why ON/OFF neural mechanism exists in numerous animals motion vision systems.

Peculiarities of identification and customs commodity examination of children’s goods

Special attention is paid to the issue of identification and safety of children's products, which is aimed at ensuring the safety and quality of this category of goods. In the scientific article, the issue of classification of goods of group 95 in accordance with the Ukrainian Commodity Nomenclature of Foreign Economic Activity was considered, and a study of the practice of appointing customs examinations was conducted. The main identifying features of the classification of scooters in the category of goods for children are: purpose; design features, their modification; type of movement; number and diameter of wheels; type of ride Attention should also be paid to the following identification features of children’s goods, which are necessary both during customs control and during the examination of toys: the size of the toy, the material of manufacture, design features, application and main functional purpose. The development and improvement of current methods of identification of toys will simplify the procedure of their inspection and increase the objectivity of the results. The work summarizes the ways to classify children’s scooters in the procedure of commodity examination. The diagnostic tasks of the forensic commodity examination to determine safety, compliance with standards, which the expert must solve during the study of a children’s scooter, are defined. State-of-the-art research methods, in particular, visual inspection, functional tests, measurement of geometric parameters, mechanical tests, chemical analysis of materials, technical expertise, safety tests, computer modeling and analysis, electrical and electronic tests, expert evaluation are used to establish indicators. quality and safety of goods and obtaining objective information. The main identification tasks of the commodity examination of children’s scooters, the most typical defects of these products and defects that indicate their low quality are indicated. The mechanism of forensic commodity examination of children's scooters is described.

A(n) (Anarche)typical Journey Through New York: Don Delillo’s Cosmopolis as an American Postmodern Odyssey

A(n) (Anarche)Typical Journey through New York: Don Delillo’s Cosmopolis as an American Postmodern Odyssey. Journeys made across the North American territories were often made in search of something: a better life, a further frontier space or the lifestyle and the bigger opportunities from the other coast. Other times, mostly towards the second half of the 20th century, these journeys were made out of the sheer pleasure of travelling, having no pre-established routes and allowing themselves to drift endlessly and leave rhizomatic traces on America’s map. In the case of Don DeLillo’s Cosmopolis, these two types of geographical narratives overlap in Eric Packer’s chaotic limousine ride across New York, through which he tries to reach his hairdresser but is forever delayed by various things happening on the streets. Through an in-depth geocritical analysis of why the quintessence of the 21st century’s American space proves to be unnavigable in straightforward and ordered ways anymore, this paper will use Corin Braga’s “anarchetype” to define this type of movement and also to link it to the multiple and decentred identity of the postmodern subject. In addition, the protagonist’s journey through Manhattan will be seen as a postmodern odyssey where the destination eludes the traveller to the point in which the journey’s meaning does not even depend on it anymore. Keywords: Don DeLillo, Cosmopolis, anarchetype, geocriticism, postmodern odyssey, rhizomatic journey, American literature

Computer Simulation of Charge Transfer In a DNA Molecule within a Simple Model of an Open Quantum System

The quantum-statistical model proposed earlier by Skourtis and Nitzan to describe a charge (hole) propagation in a fragment of artificial DNA molecule has been generalized and further investigated. A numerical simulation of a charge transport was carried out taking into account two different dissipative processes, including the capture of the charged carrier by the environment and the decoherence of its quantum wave properties due to the influence of stochastic fields of the environment. The interaction of the carrier with the environment is regulated by a small set of phenomenological parameters whose values vary in the process of simulation. Within this model, the propagation of a hole carrier in DNA is described by solving the quantum Franke-Kossakovski–Lindblad–Glauber–Sudarshan equation (hereinafter referred to as the Lindblad equation) for the carrier density matrix using the Lindblad MPO Solver program. Results of numerical analysis of the model are in a good agreement with experimental observations and demonstrate two different types of the charged carrier motion, presumably tunneling and incoherent hopping. The model is put in more general context and non-unitary dynamics of the hole carrier is treated within the framework of a theory of continuous quantum measurements by the environment in an open quantum system. The main concepts of the theory of decoherence and superselection for open quantum systems and the prospects for their application for further study of various mechanisms of motion of a charged carrier in DNA are briefly discussed.

The meaning of autistic movements.

What is already known?Moving the body in 'stereotyped', 'repetitive', 'ritualised' or 'unusual' ways is part of the criteria for receiving a diagnosis of autism. However, the reasons for these movements and their personal value are not well understood. Certain ways of moving have become part of a disorder, and have received negative judgements, whereas other movements have not.What this paper adds?We searched online blogs for descriptions of movement written by autistic adults, using their preferred language and definitions. The blog authors said that many types of movement attracted negative judgement, including mis-coordination shown during sports, dancing in unusual places or moving repetitively, such as when stimming. However, movement provided personal benefits, and could enhance thinking and focus, provide meaningful routine, contribute to sensory regulation, release energy, increase body awareness, emotion regulation and strengthen self-identity.Implications for practice and policyMovement could be a well-being resource, used to reduce distraction, overwhelm, confusion and distress for autistic people. This should be considered within personal coping strategies and psychological therapies. The examples provided in this study could inform autism assessments, to ensure that the meanings of movements are considered alongside the appearances of movement. Some movements such as stimming have the same functions as many other ways of moving, including dancing and exercising, which could help to reduce stigma around being autistic if reflected in policy and practice. Improving understanding is important for informing how autism is assessed, and how personal experiences of being autistic are heard.

Dynamic response and seismic vulnerability assessment of the near-fault steep slope

Existing field data demonstrates that structures situated near faults, such as slopes, dams, and bridges, are particularly vulnerable to damage. Near-fault ground motions exhibit marked disparities from their far-field counterparts, necessitating thorough investigation. This study conducts a comprehensive analysis of ground motion characteristics utilizing response spectra, Hilbert-Huang Transform (HHT), and marginal spectra to discern near-fault pulse-like ground motions (PLGMs), near-fault non-pulse-like ground motions (NPGMs), and far-fault ground motions (FFGMs). PLGMs distinguished by their heightened energy content, typically induce more pronounced amplification effects compared to NPGMs and FFGMs. Employing an efficacy criterion, optimal intensity measures (IMs) are identified and linked to dynamic response, referred to as engineering demand parameters (EDPs). Velocity-based IMs demonstrate substantial correlations across diverse ground motion types for both plastic volume ratio (PVR) and crest displacement (Dc). Lastly, probabilistic seismic demand models are leveraged to establish seismic vulnerability curves for steep slopes exposed to PLGMs and NPGMs. Notably, with Dc as the EDP, the exceedance probabilities associated with the three IMs under PLGMs generally surpass those under NPGMs. This underscores the propensity of PLGMs to trigger larger displacements in slopes, rendering them more prone to failure.

MMG 3DOF model identification with uncertainty of observation and hydrodynamic maneuvering coefficients using MCMC method

The trajectory prediction using ship maneuverability mathematical models is one of the essential technologies implemented in autonomous surface ship. Several ship maneuverability mathematical models and each one with a particular hydrodynamic coefficient approximation using towing tank tests are existed. However, it is presented difficult to directly inverse estimate the hydrodynamic maneuvering coefficients of a ship maneuverability mathematical model from operational data consisting of ship trajectory and maneuvering operation records. This paper proposed a method for estimating the hydrodynamic maneuvering coefficients of the MMG 3DOF model using three types of time-series ship motions (surge, sway, and yaw velocity) as observed data. In the assumption of this paper, there is uncertainty in observations and the hydrodynamic maneuvering coefficients of the MMG 3DOF model. The proposed method outputs samples of the simultaneous posterior probability distribution of the hydrodynamic maneuvering coefficients by the MCMC method using the observed data and stochastic model. A robust trajectory with a wide range can be presented by conducting ship maneuvering simulations using these samples. To verify the feasibility of the proposed method, this paper conducted observation system simulation experiments (OSSE) using the KVLCC2 L7 model and applied the proposed method to several free-running model ship tests. Results showed that on the assumption that MMG 3DOF model can explain the ship's state and trajectory in real world, the proposed method can estimate the ship hydrodynamic maneuvering coefficients of the MMG 3DOF model corresponding to the observed ship trajectory and control data including the error of observed data.

Passive earth pressure due to surcharge loading under three modes of wall movement

ABSTRACT Passive earth pressure behind retaining walls under rotational movements has been widely investigated recently. However, the behavior of surcharge loading under rotational movement has not been fully explored in the literature. This paper numerically investigates the impact of different types of wall movement; translation, rotation about the top and rotation about the bottom, on the two and three-dimensional passive earth pressure due to uniform surcharge loading. Results prove that the limit pressures under rotational mode are significantly lower than those in translational mode, ranging from 63% to 98% of those used in the literature. Overestimating coefficients in the design of retaining structures can lead to insecurity and instability. Furthermore, the distribution of passive earth pressure with depth is no longer rectangular. Shape factors are then evaluated to facilitate the practical application of passive earth pressure coefficients under rotational wall movements.

Anatomical factors of the maxillary tuberosity that influence molar distalization.

To examine the areas of the maxillary tuberosity (MT) (coronal, apical, width, and height) with respect to the presence or absence of the third molar to establish possible anatomical limitations for molar distalization. A total of 277 tuberosities were evaluated through sagittal computed tomography (CT) images, divided for measurement into coronal (free of bone), apical (area of influence of the maxillary sinus), and tuberosity (bony area) zones, and stratified by the presence or absence of the third molar, sex, and two age subgroups. Mann-Whitney U test was used to compare the groups considering the third molar. The medians of the width and height of the tuberosity decreased significantly in the absence of the third molar (P < 0.001). The apical area also showed differences, with negative values in the absence of the third molar and positive values in the presence of the third molar (P < 0.001). However, no differences were observed for the coronal area (P > 0.05). In the absence of the third molar, the size of the MT, represented by its width and height, was smaller and negative values (decrease) were observed for the maxillary sinus. The sagittal CT provides useful information regarding the amount of bone tissue available for distalization and relationship of the second molar with respect to the maxillary sinus, which allows individualizing each case in relation to the amount and type of movement expected.

Characterizing pedestrian contact interaction trajectories to understand spreading risk in human crowds

A spreading process can be observed when particular information, substances, or diseases spread through a population over time in social and biological systems. It is widely believed that contact interactions among individual entities play an essential role in the spreading process. Although contact interactions are often influenced by geometrical conditions, little attention has been paid to understand their effects, especially on contact duration among pedestrians. To examine how the pedestrian flow setups affect contact duration distribution, we have analyzed trajectories of pedestrians in contact interactions collected from pedestrian flow experiments of uni-, bi- and multi-directional setups. Based on turning angle entropy and efficiency, we have classified the type of motion observed in the contact interactions. We have found that the majority of contact interactions in the unidirectional flow setup can be categorized as confined motion, hinting at the possibility of long-lived contact duration. However, ballistic motion is more frequently observed in the other flow conditions, yielding frequent, brief contact interactions. Our results demonstrate that observing more confined motions is likely associated with the increase of parallel contact interactions regardless of pedestrian flow setups. This study highlights that the confined motions tend to yield longer contact duration, suggesting that the infectious disease transmission risk would be considerable even for low transmissibility. These results have important implications for crowd management in the context of minimizing spreading risk.This work is an extended version of Kwak et al. (2023) presented at the 2023 International Conference on Computational Science (ICCS).

Knowledge differences between general practitioners and orthodontists about Invisalign clear aligner treatment – a cross-sectional survey-based study

ABSTRACT Purpose This study investigated the knowledge differences between general practitioners and orthodontists about the Invisalign system. Materials and methods A web-based survey regarding 10 Invisalign treatment domains was distributed to 161 orthodontists and 213 general practitioners. The responses were ranked using a Likert-type scale and analysed with the Chi-square test and Bonferroni adjustment. Results The response rate was 52.1% for general practitioners and 63.4% for orthodontists. Comparing Invisalign to conventional fixed appliances, orthodontists agreed/strongly agreed that Invisalign aligners are suitable for all types of cases (p = 0.001). Orthodontists also agreed that it causes less tooth discomfort (p = 0.01) and an increased number of attachments can affect its esthetic perception (p = 0.014) but general practitioners opted for the ‘Do Not Know’ option (p ≤ 0.01). General practitioners also responded ‘Do Not Know’ to whether Invisalign treatment finishes in a shorter duration (p = 0.001), achieves all types of tooth movement (p < 0.001) and results in better periodontal health (p = 0.001). Orthodontists were more likely to disagree/strongly disagree that Invisalign treatment results in less tooth root resorption (p = 0.008), better American Board of Orthodontics Objective Grading System and Peer Assessment Rating scores (p < 0.001) and low risk of relapse (p < 0.001), while general practitioners opted for the ‘Do Not Know’ option (p < 0.0001, p < 0.0001 and p < 0.0001, respectively). Conclusion Regarding Invisalign treatment, this study found that orthodontists were generally evidenced-based but general practitioners lacked such knowledge, suggesting that general practitioners must be provided with relevant evidenced-based information.

Diagnostics of velocity-flow characteristics in laminar flows

Understanding and evaluating various types of fluid movement is important for the analysis and design of systems and devices related to hydraulics and hydrodynamics, including hydrocarbon production and transport systems. Knowledge of stationary and non-stationary types of motion makes it possible to predict and control the behavior of a fluid under various conditions. The article discussed the issues of diagnosing stationary and non-stationary and gravitational flows. It has been established that the time of transition to a stationary mode in pipelines mainly depends on the geometric parameters of the pipeline and the rheological properties of the pumped systems. It is known that many issues related to the management of technological processes and the improvement of efficiency in oil and gas production are closely associated with the movement of homogeneous and heterogeneous fluids with various rheological and physico-chemical properties in pipelines during extraction, collection, and transportation, which have different forms and hydraulic characteristics. In the laminar flow regime, a methodology has been developed to determine the transition time to a steady-state operation mode, based on the flow characteristics of viscous and visco-plastic fluids, taking into account inertia forces. It has been determined that, unlike viscous fluids, the time to reach a steady-state operation mode for visco-plastic flows also varies depending on the formation of the flow core, which is determined by the initial yield stress. In the article, a mathematical expression is provided for determining the flow rate for visco-plastic fluids in laminar flow, taking into account the pressure losses due to inertia forces for viscous fluids. The results obtained are explained to eliminate the difference and increase accuracy when determining the flow rate using the Poiseuille formula for visco-plastic laminar flows.

Beat Pilot Tone (BPT): Simultaneous MRI and RF motion sensing at arbitrary frequencies.

To introduce a simple system exploitation with the potential to turn MRI scanners into general-purpose radiofrequency (RF) motion monitoring systems. Inspired by Pilot Tone (PT), this work proposes Beat Pilot Tone (BPT), in which two or more RF tones at arbitrary frequencies are transmitted continuously during the scan. These tones create motion-modulated standing wave patterns that are sensed by the receiver coil array, incidentally mixed by intermodulation in the receiver chain, and digitized simultaneously with the MRI data. BPT can operate at almost any frequency as long as the intermodulation products lie within the bandwidth of the receivers. BPT's mechanism is explained in electromagnetic simulations and validated experimentally. Phantom and volunteer experiments over a range of transmit frequencies suggest that BPT may offer frequency-dependent sensitivity to motion. Using a semi-flexible anterior receiver array, BPT appears to sense cardiac-induced body vibrations at microwave frequencies ( 1.2 GHz). At lower frequencies, it exhibits a similar cardiac signal shape to PT, likely due to blood volume changes. Other volunteer experiments with respiratory, bulk, and head motion show that BPT can achieve greater sensitivity to motion than PT and greater separability between motion types. Basic multiple-input multiple-output ( MIMO) operation with simultaneous PT and BPT in head motion is demonstrated using two transmit antennas and a 22-channel head-neck coil. BPT may offer a rich source of motion information that is frequency-dependent, simultaneous, and complementary to PT and the MRI exam.

Remote Effect of Fascial Manipulation on Knee Pain: A Case Report

The study on the remote effect of fascial manipulation on knee pain presents a case report of a patient with knee pain who underwent a single session of fascial manipulation to reduce pain and improve daily activities. The report explains the anatomy of the knee joint and the potential causes of knee pain, including bony and soft tissue involvement. Fascial manipulation is a technique that involves applying mechanical force to areas of fascial dysfunction to stimulate the body’s natural inflammatory response. The therapy is based on applying physical friction to the densified connective tissue with an elbow or knuckle to raise the temperature and change the consistency of loose connective tissue rich in hyaluronic acid. The locations picked were proximal and distal to the problematic area, and no point was treated over the painful region, which is consistent with the notion of pain being caused by aberrant fascial tensions. Manipulation of the connective tissue is thought to cause mechanical stress and heat, resulting in less macromolecular crowding and defragmentation of the Hyaluronic Acid (HA) polymers and normalised fascial gliding across the connective tissue. Reduced discomfort and enhanced range of motion are two more regularly reported effects of Fascial Manipulation. The patient was urged to resume his everyday activities after each treatment session to favour typical physiological motions that would align collagen fibres along normal lines of force. The report concludes that fascial manipulation can be a beneficial technique for managing knee pain, and it can be complemented with exercises and stretches to improve outcomes.

Exploration of deep learning-driven multimodal information fusion frameworks and their application in lower limb motion recognition

Research on Lower Limb Motion Recognition (LLMR) based on various wearable sensors has been widely applied in exoskeleton robots, exercise rehabilitation, etc. Typically, employing multimodal information tends to yield higher accuracy and stronger robustness compared to using unimodal information. Due to the inevitable reliance on feature engineering in shallow machine learning-based LLMR methods, this study leverages the powerful non-linear feature mapping capability of deep learning (DL) to construct several end-to-end LLMR frameworks, including: Convolutional Neural Networks (CNNs), CNN-Recurrent Neural Networks (RNNs) and CNN-Graph Neural Networks (GNNs). The effectiveness of the proposed frameworks is verified in distinct tasks, including the recognition of seven types of lower limb motions in healthy subjects and three types of motions in patients with stroke, as well as the phase recognition task during the sit-to-stand (SitTS) process in patients with stroke, achieving the highest mean accuracy of 95.198 %, 99.784 %, and 99.845 %, respectively. Further research and integration of two transfer learning techniques, adaptive Batch Normalization (BN) and model fine-tuning, significantly enhance the applicability of the proposed frameworks in inter-subject prediction. Additionally, systematic analyses are conducted to assess the strengths and weaknesses of different models in terms of recognition performance, complexity, and adaptability to variations in the number of modalities and sensor channels. Experimental results indicate that the proposed frameworks hold promise in providing potential support for the development of human-robot collaborative lower limb exoskeletons or rehabilitation robots.

Accuracy and uncertainty of predicted maximum and residual displacements of RC bridge columns under earthquake excitations

Fundamental to the performance-based seismic design is the accuracy of predicted responses under earthquake excitations. This study evaluates the accuracy and uncertainty of predicted maximum and residual displacements of concrete bridge columns subjected to different types of ground motions. A series of nonlinear time-history analyses considering a wide range of element formulations and model parameter combinations was performed to reproduce measured responses from previous shake table tests. Variations in element formulation had little influence on the accuracy and uncertainty of predicted maximum displacements. The gradient inelastic force-based element, however, predicted bar tensile strain profiles across the plastic hinge with higher resolution, but at a higher computational cost than displacement-based and beam with hinges elements. Models with tangent stiffness-based Rayleigh damping produced the most accurate predictions of the maximum drift ratios with an RMSE of 0.011, indicating that the maximum displacement (or drift ratio) can be predicted with reasonable accuracy. Residual displacements, on the other hand, were predicted with unreasonable levels of error and uncertainty. A data-driven model was thus proposed to correct predicted residual displacement. Following correction, the RMSE of the predicted residual drift ratios was reduced by 43 % to 0.006.

Dynamic Magnetic Resonance Imaging Protocol: An Effective and Useful Tool to Assess Discoid Lateral Meniscus Instability in Children.

One of the most common symptoms in cases of discoid lateral meniscus (DLM) in children is a "snapping" knee. The clock in extension, followed by a pop in flexion, perceived by the clinician, reflects the meniscal displacement caused by the peripheral meniscocapsular detachment. Standard magnetic resonance imaging (MRI) results in a 40% false-negative rate for detecting this instability. The hypothesis was that a dynamic MRI protocol could reduce the false negative rate and improve the efficiency of the MRI in detecting the direction of instability. Eight DLM knees (8 patients) with snapping knees (grade 2 of Lyon's classification) were included in this monocentric prospective preliminary study in a referral center of pediatric orthopaedic surgery. Every patient underwent a dynamic MRI protocol with both T2-Fat-Sat sagittal and coronal slices, performed "after the clock" and again "after the pop" in a knee with standard 20 degrees of flexion during acquisition. All the MRI data were correlated with an arthroscopic description of the peripheral tear of the DLM according to Ahn's classification to assess for diagnostic accuracy. The standard MRI protocol resulted in a false-negative rate of 50% for detecting the direction of instability. The dynamic MRI protocol allowed the identification of, and classification of the meniscal instability, meniscal shift, and meniscocapsular tear in 8 of 8 patients (0% false-negative rate), perfectly correlated with arthroscopic findings. This preliminary series, although short, allowed us to understand all the types of movements and lesions associated with the child's discoid meniscus. The detailed case analysis showed a strong benefit of such a protocol for planning the surgical suture procedure. The functionality and reliability of the dynamic MRI protocol is a good and method relatively simple method which does not require specific equipment, minimizing any additional cost compared with standard MRI. Level IV.