Screening of knee-joint vibroarthrographic signals using statistical parameters and radial basis functions

Externally detected vibroarthrographic (VAG) signals bear diagnostic information related to the roughness, softening, breakdown, or the state of lubrication of the articular cartilage surfaces of the knee joint. Analysis of VAG signals could provide quantitative indices for noninvasive diagnosis of articular cartilage breakdown and staging of osteoarthritis. We propose the use of statistical parameters of VAG signals, including the form factor involving the variance of the signal and its derivatives, skewness, kurtosis, and entropy, to classify VAG signals as normal or abnormal. With a database of 89 VAG signals, screening efficiency of up to 0.82 was achieved, in terms of the area under the receiver operating characteristics curve, using a neural network classifier based on radial basis functions

Knee Joint Vibration Signal Analysis with Matching Pursuit Decomposition and Dynamic Weighted Classifier Fusion

Analysis of knee joint vibration (VAG) signals can provide quantitative indices for detection of knee joint pathology at an early stage. In addition to the statistical features developed in the related previous studies, we extracted two separable features, that is, the number of atoms derived from the wavelet matching pursuit decomposition and the number of significant signal turns detected with the fixed threshold in the time domain. To perform a better classification over the data set of 89 VAG signals, we applied a novel classifier fusion system based on the dynamic weighted fusion (DWF) method to ameliorate the classification performance. For comparison, a single leastsquares support vector machine (LS-SVM) and the Bagging ensemble were used for the classification task as well. The results in terms of overall accuracy in percentage and area under the receiver operating characteristic curve obtained with the DWF-based classifier fusion method reached 88.76% and 0.9515, respectively, which demonstrated the effectiveness and superiority of the DWF method with two distinct features for the VAG signal analysis

Screening of knee-joint vibroarthrographic signals using probability density functions estimated with Parzen windows

Pathological conditions of knee joints have been observed to cause changes in the characteristics of vibroarthrographic (VAG) signals. Several studies have proposed many parameters for the analysis and classification of VAG signals; however, no statistical modeling methods have been explored to analyze the distinctions in the probability density functions (PDFs) between normal and abnormal VAG signals. In the present work, models of PDFs were derived using the Parzen-window approach to represent the statistical characteristics of normal and abnormal VAG signals. The Kullback-Leibler distance was computed between the PDF of the signal to be classified and the PDF models for normal and abnormal VAG signals. Additional statistical measures, including the mean, standard deviation, coefficient of variation, skewness, kurtosis, and entropy, were also derived from the PDFs obtained. An overall classification accuracy of 77.53%, sensitivity of 71.05%, and specificity of 82.35% were obtained with a database of 89 VAG signals using a neural network with radial basis functions with the leave-one-out procedure for cross validation. The screening efficiency was derived to be 0.8322, in terms of the area under the receiver operating characteristics curve. (C) 2009 Elsevier Ltd. All rights reserved

APPLICATIONS IN VIBROARTHROGRAPHY: ASSESSMENTS OF INSTABILITY IN TOTAL HIP ARTHROPLASTY, CAM-POST ENGAGEMENT IN TOTAL KNEE ARTHROPLASTY, AND VISCOSUPPLEMENTATION IN OSTEOARTHRITIC KNEES

Measurement of joint sounds and vibrations for non-invasive orthopaedic diagnostic purposes has slowly advanced since the 1960s. Most work has been focused in the development of methods for screening of abnormal knees. To date the technique has not gained clinical traction as is it fraught with various obstacles and skepticism. This doctoral thesis is neither an argument in favor of nor against the clinical use of vibroarthrography for musculoskeletal diagnostics in humans, but rather an exploration of its potential in cases of orthopaedic interest. These areas include 1) instability in total hip arthroplasty, 2) cam-post engagement in posterior stabilized total knee arthroplasty, and 3) viscosupplementation in osteoarthritic knees. It was expected that each of these unique cases would be characterized by dynamic phenomena that could be measured in the form of surface vibrations at the skin.Methods previously presented in various vibroarthrography research were adopted, modified, and expounded upon to best suit the needs of each experiment. In a mechanical hip simulator, it was found that vibroarthrography could be effectively used to distinguish the difference between 1 mm and 2 mm of hip separation. In posterior stabilized total knee arthroplasty subjects, it was found that multiple vibroarthrographic features may be used to approximate the occurrence of cam-post engagement, and that vibrations measured at the joint surface may be correlated to cam-post engagement velocity. In osteoarthritic knees, the relationship between clinical evidence, viscosupplementation, and vibroarthrography varied on a case by case basis.To the knowledge of the author, all three of these experiments are the first of their kind. Ultimately, the methods and results presented within provide new foundations for vibroarthrography that may be used to further explore the clinical potential of this noninvasive diagnostic

In Vivo Mechanics of Cam-Post Engagement in Fixed and Mobile Bearing TKA and Vibroarthrography of the Knee Joint

The objective of this dissertation was to determine the mechanics of the cam-post mechanism for subjects implanted with a Rotating Platform (RP) PS TKA, Fixed Bearing (FB) PS TKA or FB Bi-Cruciate Stabilized (BCS) TKA. Additionally, a secondary goal of this dissertation was to investigate the feasibility of vibroarthrography in correlating in-vivo vibrations with features exhibited in native, arthritic and implanted knees. In-vivo, 3D kinematics were determined for subjects implanted with nine knees with a RP-PS TKA, five knees with a FB-PS TKA, and 10 knees with a FB-BCS TKA, while performing a deep knee bend. Distance between the cam-post surfaces was monitored throughout flexion and the predicted contact map was calculated. A forward dynamic model was constructed for 3 test cases to determine the variation in the nature of contact forces at the cam-post interaction. Lastly, a different set of patients was monitored using vibroarthrography to determine differences in vibration between native, arthritic and implanted knees. Posterior cam-post engagement occurred at 34° for FB-BCS, 93o for FB-PS and at 97° for RP-PS TKA. In FB-BCS and FB-PS knees, the contact initially occurred on the medial aspect of the tibial post and then moved centrally and superiorly with increasing flexion. For RP-PS TKA, it was located centrally on the post at all times. Force analysis determined that the forces at the cam-post interaction were 1.6*body-weight, 2.0*body-weight, and 1.3*body-weight for the RP-PS, FB-BCS and FB-PS TKA. Sound analysis revealed that there were distinct differences between native and arthritic knees which could be differentiated using a pattern classifier with 97.5% accuracy. Additionally, vibrations from implanted knees were successfully correlated to occurrences such as lift-off and cam-post engagement. This study suggests that mobility of the polyethylene plays a significant role in ensuring proper cam-post interaction in RP-PS TKA. The polyethylene insert rotates axially in accord with the rotating femur, maintaining central cam-post contact. This phenomenon was not observed in the FB-BCS and FB-PS TKAs

Vibration reponse analysis in orthopaedics and its application at the lumbar spine

Vibration response analysis has been carried out on human lumbar spines in-vitro and in-vivo. Random vibration in the frequency range between 20 Hz and 2 kHz was applied to the L5 spinous process in the antero-posterior direction while motion response was measured at the other spinous processes of the lumbar spine. Transfer mobility which defines the lumbar spine's motion response to vibratory force was evaluated by using the fast Fourier transform and spectral averaging technique. There was high damping during the in-vitro tests and the lumbar spine was found to behave as a segmented beam hinged at the thoracic and sacral ends. Fundamental mode shape was observed at frequencies lower than 150 Hz and this pattern was also observed with simulated fusion of the facet joints and interbody fusion. Mobility summated for the whole range of frequency could be modelled by an exponential expression. Useful parameters have been identified and they were found to relate to the lumbar spine's vibratory characteristics resulting from structural modifications. Vibration testing performed on normal subjects revealed that a relaxed lumbar spine was highly damped and non-resonant. First flexural vibration mode was observed only under the action of the back extensors. Averaged figures have been established for the coefficients of an exponential expression which fits closely to the summated mobility curve. The mobility and its attenuation coefficients in different frequency bands have been evaluated from twelve normal subjects. Localized attenuation of vibration response and the reduction in mobility were observed on a patient with osteoporotic lumbar spine. Mobility in the low frequencies was reduced while the medium and high band mobility were enhanced in patients with postero-lateral fusion and instrumentation for fixation of the lumbar spine. The attenuation pattern of these patients was consistent, and corresponded to the existence of structural enhancement.Vibration response analysis has been carried out on human lumbar spines in-vitro and in-vivo. Random vibration in the frequency range between 20 Hz and 2 kHz was applied to the L5 spinous process in the antero-posterior direction while motion response was measured at the other spinous processes of the lumbar spine. Transfer mobility which defines the lumbar spine's motion response to vibratory force was evaluated by using the fast Fourier transform and spectral averaging technique. There was high damping during the in-vitro tests and the lumbar spine was found to behave as a segmented beam hinged at the thoracic and sacral ends. Fundamental mode shape was observed at frequencies lower than 150 Hz and this pattern was also observed with simulated fusion of the facet joints and interbody fusion. Mobility summated for the whole range of frequency could be modelled by an exponential expression. Useful parameters have been identified and they were found to relate to the lumbar spine's vibratory characteristics resulting from structural modifications. Vibration testing performed on normal subjects revealed that a relaxed lumbar spine was highly damped and non-resonant. First flexural vibration mode was observed only under the action of the back extensors. Averaged figures have been established for the coefficients of an exponential expression which fits closely to the summated mobility curve. The mobility and its attenuation coefficients in different frequency bands have been evaluated from twelve normal subjects. Localized attenuation of vibration response and the reduction in mobility were observed on a patient with osteoporotic lumbar spine. Mobility in the low frequencies was reduced while the medium and high band mobility were enhanced in patients with postero-lateral fusion and instrumentation for fixation of the lumbar spine. The attenuation pattern of these patients was consistent, and corresponded to the existence of structural enhancement

Dynamics, Electromyography and Vibroarthrography as Non-Invasive Diagnostic Tools: Investigation of the Patellofemoral Joint

The knee joint plays an essential role in the human musculoskeletal system. It has evolved to withstand extreme loading conditions, while providing almost frictionless joint movement. However, its performance may be disrupted by disease, anatomical deformities, soft tissue imbalance or injury. Knee disorders are often puzzling, and accurate diagnosis may be challenging. Current evaluation approach is usually limited to a detailed interview with the patient, careful physical examination and radiographic imaging. The X-ray screening may reveal bone degeneration, but does not carry sufficient information of the soft tissue conditions. More advanced imaging tools such as MRI or CT are available, but expensive, time consuming and can be used only under static conditions. Moreover, due to limited resolution the radiographic techniques cannot reveal early stage arthritis. The arthroscopy is often the only reliable option, however due to its semi-invasive nature, it cannot be considered as a practical diagnostic tool. Therefore, the motivation for this work was to combine three scientific methods to provide a comprehensive, non-invasive evaluation tool bringing insight into the in vivo, dynamic conditions of the knee joint and articular cartilage degeneration. Electromyography and inverse dynamics were employed to independently determine the forces present in several muscles spanning the knee joint. Though both methods have certain limitations, the current work demonstrates how the use of these two methods concurrently enhances the biomechanical analysis of the knee joint conditions, especially the performance of the extensor mechanism. The kinetic analysis was performed for 12 TKA, 4 healthy individuals in advanced age and 4 young subjects. Several differences in the knee biomechanics were found between the three groups, identifying age-related and post-operative decrease in the extensor mechanism efficiency, explaining the increased effort of performing everyday activities experienced by the elderly and TKA subjects. The concept of using accelerometers to assess the cartilage degeneration has been proven based on a group of 23 subjects with non-symptomatic knees and 52 patients suffering from knee arthritis. Very high success (96.2%) of pattern classification obtained in this work clearly demonstrates that vibroarthrography is a promising, non-invasive and low-cost technique offering screening capabilities

Desenvolvimento de protótipo para sensorização da interface de implantes ósseos

Over the last few years there has been an increase in the number of arthroplasties performed worldwide. With the growing number of young patients performing this surgery, new technologies are required to evaluate the bone-implant interface in order to avoid revision surgeries. The present work aims to develop a prototype for sensing the bone-implant interface for multifunctional instrumented/bioelectronic implants: the network-based cosurface capacitive system with ability to be extracorporeally controlled by clinicians. This prototype is composed by both hardware and software components. The hardware can also be seen as the data acquisition system and the software is the monitor and the control system. Considering that the societal scenario did not allow the manufacture of this new system prototype, the hardware was only designed for future implementation and validation. The software is a web application that allows the clinician to monitor and control the data acquisition system. For the development of the web application it was used Django, python, HTML5, CSS, and the storage and management of data were performed with MySQL. In order to assess its performance, different simulation tests were performed: (i) monitoring tests using random bone-implant interface states, in which capacitance data was generated from a polynomial function that characterizes the average capacitance change for different bone-implant bonding states; (ii) monitoring tests simulating an increasing bonding scenario. Through the web application it is possible to analyse the data collected from the data acquisition system in two dimensional plots or three dimensional plots. This software solution was also designed to allow downloading the data to an Excel file to give the user the possibility to perform different analyses related boneimplant interface state. The project for the data acquisition system is constituted by a Raspberry Pi, an I2C multiplexer, a capacitor-to-digital converter (EVAL AD-7746), and the sensing technology. The Raspberry Pi is responsible for the TCP-IP communication with the monitoring system and the I2C communication with the capacitor-to-digital converter through the I2C multiplexer. It is also responsible for saving data in the correct database. The capacitor-to-digital converter acquires the data from the sensing technology, which is based on three different printed circuit boards, containing twelve capacitors. Thus, it is intended to prove that with a sensing system comprising a network of cosurface capacitors it is possible to acquire bone-implant interface bonding during the daily life of patients, including region and magnitude debonding dataAo longo dos últimos anos tem-se verificado um aumento do número de artroplastias realizadas mundialmente. Com o crescente número de jovens a serem submetidos a esta cirurgia, torna-se necessário desenvolver novas tecnologias para a avaliação da interface osso-implante de modo a diminuir o número de cirurgias de revisão. O presente trabalho tem como objetivo o desenvolvimento de um protótipo para a sensorização da interface de implantes ósseos para incorporar implantes instrumentados, constituídos por uma rede de sistemas capacitivos e com a possibilidade de ser controlada extracoporealmente por médicos especializados. O protótipo é constituído por componentes de hardware e software. O hardware consiste no sistema de aquisição de dados e o software permite o controlo e monitorização do hardware. Considerando o estado social atual não foi possível produzir o protótipo deste novo sistema de monitorização, por esse motivo o hardware foi apenas projetado de forma a ser implementado e validado futuramente. O software é uma aplicação web que permite que o médico especialista monitorize o sistema de aquisição de dados. Para o desenvolvimento deste software foi utilizado Django, python, HTML5, CSS, e a gestão e armazenamento de dados foi feita através do MySQL. A validação das funcionalidades do software foi realizada através de dois testes diferentes: (i) testes de monitorização com base em estados aleaórios da interface osso-implante, onde os valores de capacidade foram obtidos com base numa polinomial que caracteriza a variação de capacidade para diferentes estados de ligação osso-implante; (ii) simulação de um teste de aproximação do osso à estrutura capacitiva. Através da aplicação web, é possível visualizar os resultados obtidos a partir de gráficos tridimensionais e bidimensionais. O website também permite o download de um ficheiro Excel com os dados adquiridos, para o utilizador realizar análises independentes relacionadas com o estado da interface osso-implante. O projeto do sistema de aquisição de dados é constituído por um Raspberry Pi, um multiplexer I2C, um conversor analógico-digital (EVAL-AD7746) e o sistema de sensorização. O Raspberry Pi estabelece uma comunicação TCP-IP com o sistema de monitorização e uma comunicação I2C com o conversor analógico-digital através de um multiplexer I2C. Este dispositivo guarda os dados recolhidos em bases de dados. O conversor analógico-digital recolhe os dados do sistema capacitivo de sensorização, que é constituído por três placas de circiuito impresso, onde cada uma contém um total de doze condensadores. Assim, pretende-se comprovar que com um sistema constituído por uma rede de condensadores é possível fazer uma aquisição de dados relativamente ao estado da interface osso-implante durante o dia-a-dia do pacienteMestrado em Engenharia Mecânic

Investigations into the ability of Piezoelectric Sensors to Monitor the Integrity of the Cemented Bond between Bone and Implant

This study investigates the utility of piezoelectric transduction to assess the structural health of a system through impedance analysis, with application to the field of ‘smart’ orthopaedic implants. The work is motivated by the high proportion of orthopaedic implant failures that occur due to loosening of the bond between the implant and the corresponding bone surface. The ultimate aim is to prove that piezoelectric sensors embedded within orthopaedic implants have the potential identify implant loosing before it would be shown in imaging techniques. Orthopaedic knee implants were selected as a case study for proof of concept for the proposed health monitoring system. Three distinct experiments were conducted: 1) Small piezoelectric sensors are attached to model tibial trays which are in turn attached with bone cement to sawbone blocks. The measured sensor impedance over a range of input frequencies is measured and analysis of the frequency impedance traces is carried out to determine what changes in the trace are indicative of the bone cement between the sawbone and aluminium curing; 2) Commercially available tibial trays cemented to sawbone tibias are progressively loosened under a fatigue load in a compressive testing rig. Results from three Linear Variable Differential Transducers (LVDTs) measuring the micromotion between the implant and sawbone are compared with frequencyMimpedance traces taken from a piezoelectric sensor attached to the top side of the tibial tray; and 3) Varying amounts of bone cement is used to cover the surface between a sawbone block and model tibial tray. Frequency-impedance readings are taken from a piezoelectric sensor adhered to the top side of the tray. Support vector machines are used to classify between the varying amounts of cement on each test sample. Experimental results and data analysis demonstrate the potential of piezoelectric sensors ability to provide information on the integrity of bone cement bond. Findings include: 1) Piezoelectric sensors can determine at what point bone cement bond between sawbone and an aluminium plate has cured; and 2) It is possible to identify different levels of cement coverage between sawbone and aluminium plate with an accuracy of up to 92 % with piezoelectric sensors. These findings establish the veracity of piezoelectric transduction as a means of identifying orthopaedic implant loosening in vivo. This investigation provides a firm basis for future work bringing the ideal of using piezoelectric sensors as a technique for detecting loose implants in vivo closer to becoming a reality.Open Acces

Desempenho de sistema de monitorização capacitivo em implante ósseo instrumentado

Musculoskeletal disorders are becoming an ever-growing societal burden and, as a result, millions of bone replacements surgeries are performed per year worldwide. Although total joint replacements are recognized among the most successful surgeries of the last century, implant failure rates exceeding 10% are still reported. These numbers highlight the necessity of technologies to provide an accurate monitoring of the bone-implant interface state. This work aims to identify the performance of an instrumented implant to monitor implant stability using a planar capacitive technology. A 5x10x0.8 mm printed circuit with two 5x2 mm electrodes was fabricated to be integrated in an implantable device, with the objective of assessing the effect of a fully implantation into a biological specimen. The implant was fabricated with a conic geometry, to achieve a press-fit fixation, with 55 mm of length and a minimum/maximum diameters of 12 and 15 mm, respectively. After implantation, the system was put under compression and decompression cycles, so the bone-implant interface could be altered. In the compression cycle, the observed capacitance values decreased, indicating the sensor was moving away from the bone; and contrarily, in the decompression cycle, the capacitance increased with the progressive unloading. Values were obtained in intervals of [2.2090; 3.0764] pF for the compression and [1.9806; 3.1841] pF for the decompression. The mean percentage of capacitance change for the compression cycle was 3.67% and 5.06% for the decompression, indicating a greater change rate in the decompression cycle. Additional tests were carried where the implant and the sensor were rotated 90 and 180º, to show the influence of different interfaces in the measured capacitance. The latter tests allowed to support the results obtained without rotation, as different sensor positions provided different behaviors of the capacitance change. Further development is still needed related to the experimental setup, more specifically the in vitro specimens fixation and the environment control of the experiment room. In addition, energy harvesting to create self powering systems to avoid exernal links or finite-life alternatives are also a necessity for future instrumented implants. This work further demonstrated the potential of capacitive technologies to monitor the bone-implant fixation. Therefore, it also contributed towards the design of a new era of high-sophisticated implantable medical devices.Distúrbios musculares estão a tornar-se um fardo cada vez maior para a sociedade atual, e, como resultado, milhões de artroplastias são realizadas anualmente por todo o mundo. Apesar da artroplastia estar reconhecida entre os procedimentos mais bem sucedidos do último século, ainda se observa uma taxa de falha em implantes de cerca de 10%. Estes números realçam a necessidade das tecnologias conseguirem fornecer um diagnóstico preciso da interface osso-implante, podendo reduzir significativamente a necessidade de cirurgias de revisão. Este trabalho tem como objetivo avaliar o desempenho de um implante instrumentado para monitorizar a estabilidade em implantes, utilizando uma tecnologia capacitiva planar. De forma a verificar o efeito de uma inserção completa em espécimes biológicos, um circuito impresso de dimensões 5x10x0.8 mm com dois elétrodos de 5x2 mm foi fabricado com o objetivo de ser integrado dentro de um implante. O implante foi projetado com uma geometria cónica, de forma a obter uma fixação press-fit, com diâmetros mínimo/máximo de 12 e 15 mm, respetivamente, e um comprimento de 55 mm. Depois de implantado, o sistema foi posto sobre ciclos de compressão e de descompressão de forma a alterar a interface osso-implante. Nos ciclos de compressão, os valores observados da capacidade decresceram, indicando que o sensor se estava a afastar do osso; contrariamente, nos ciclos de descompressão, a capacidade tendia a aumentar com o descarregamento. Os valores foram obtidos no intervalo de [2.2090; 3.0764] pF para os ciclos de compressão e de [1.9806; 3.1841] pF para a descompressão. A percentagem média de variação da capacidade para os ciclos de compressão foi de 3.67% e de 5.06% para os de descompressão, indicando uma maior taxa de variação nos ciclos de descompressão. Adicionalmente, foram realizados testes em que o implante e o sensor foram rodados 90 e 180 de forma a verificar o efeito de interfaces diferentes na capacidade medida. Estes últimos testes permitiram também corroborar a validade dos testes de compressão e descompressão, visto que orientações diferentes do sensor deveriam dar tendências diferentes nas curvas de capacidade. No entanto ainda é necessário um desenvolvimento adicional relativamente ao setup experimental, mais concretamente na fixação dos espécimes biológicos durante os ensaios in vitro, assim como no controlo das condições ambiente do laboratório. Adicionalmente, o desenvolvimento de sistemas de energy harvesting são uma necessidade para o futuro dos implantes instrumentados de forma a ter um sistema auto-sustentável, evitando ligações com o exterior ou soluções de vida limitada. Este trabalho permitiu comprovar o potencial de tecnologias capacitivas para a monitorização do estado da interface osso-implante. Assim, também contribuiu para o desenvolvimento de uma nova era de dispositivos médicos implantáveis altamente sofisticados.Mestrado em Engenharia Mecânic