The mechanical behavior of the human musculoskeletal system has become an important area of medical research. In orthopedics, for example, developments in replacement and reconstructive surgery of artificial joints required extensive knowledge of the mechanical functioning of human joints. Following the implantation of a total knee replacement (TKR), in fact, the anatomical structures can be considerably altered for various reasons. In some cases, ligaments may not be able to perform their function because of the pathology or trauma that led to surgical intervention. Other times the ligaments must be sacrificed or modified to allow the insertion and functionality of the prosthesis. These structural changes are usually decided by the surgeon during the operative planning phase based on anamnestic, clinical-functional analysis and diagnostic images; often, however, decisions are changed or changed directly in the operating room. Only at the end of the operative intervention and of the post-operative rehabilitative path of the patient it is possible to verify the functional result obtained and the choices made in the operating room are not always effective. The possibility of predicting the outcome of the intervention in terms of joint mobility, functionality and stress of the various structures involved thanks to quantitative data, deriving from the simulation of the operating conditions and of the knee load, would allow the surgeon to orientate towards a better choice among the various options and hopefully to improve the results of the arthroplasty operations. An important parameter of the patient subjected to TKA (Total Knee Arthroplasty) is the posterior inclination of the tibial plateau (PTS, Posterior Tibial Slope19) because it modifies the kinematics of the knee20. Usually the PTS angle is chosen based on the companies’ recommendations (3° or 7° are the most common choices). However, studies on human cadavers subjected to TKR have shown how the variation of the posterior tibial slope influences the stability in knee flexion-extension. From this assumption, the present thesis makes exploits a 3D anatomical model of the knee joint to study the effects of PTS in order to provide the surgeon with information necessary in the pre-operative planning phase in arthroplasty operations. The model used had previously been created starting from the CAD files of the femur, fibula, tibia and left leg patella and was dynamically simulated using the SimWise 4D software that allows for analysis of forces, displacements, moments, angles and more again, related to the implemented model. Furthermore, this software allows to import CAD files of the prosthetic device whose behavior wanted to be studied. In this thesis work, a knee joint Vanguard® Posterior Stabilized (PS) Complete Knee System was used in which the posterior cruciate ligament is eliminated in addition to the anterior cruciate ligament (almost always sacrificed in arthroplasty operations). In the model the ligaments are represented as linear springs (Linear Spring / Damper) endowed with a non-linear viscoelastic characteristic, as proposed and commonly accepted in literature35. They are not attached directly to the bone, but through blocks connected to the bone components. The following tests were simulated to qualitatively and quantitatively evaluate the characteristic parameters of the joint kinematics: anterior-posterior drawer test, internal-external rotation test and the varus-valgus test. These three types of tests were performed at different knee flexion angles (0 °, 20 ° and 90 ° degrees) and at different tibial plateau inclination (-3 °, 0 °, + 3 °, + 6 °, +9 °). From the comparison of the results obtained with the data present in the literature it was observed how the increase in PTS seems to lower the tension of the collateral ligaments during the tests of the anterior-posterior drawer and internal-external rotation, while it does not modify the tension during the test of varus-valgus. Furthermore, an incorrect balancing of the collateral ligaments tension emerged in the three tests performed. The modification of PTS also seems to influence laxity (movement with low resistance of the femur in contrast to the tibia) although its variation can be mainly attributed to the absence of the cruciate ligaments. Furthermore, the strains of the collateral ligaments have a critical condition during the internal rotation test on a flexed knee at 20 ° and a tibial inclination at + 6 ° where there is complete cancellation of the tension on the collateral ligaments. This condition is of clinical interest since it seems to derive from the interference between the central peg of the tibial component and the slot of the femoral component within which it should flow. This interaction would involve the transmission of the torque to the taproot inserted in the tibia and therefore could entail a risk of failure of the medium-term prosthesis. Since this is a model of dimensions referred to a specific subject, it is not possible to extend the validity of the results obtained to other cases that could present diversified morphologies and structural features, and in particular the indication for choosing a position rather than another will have to take into account multiple factors, not only biomechanical but also certainly, of the clinical history. However, the qualitative and quantitative information obtained may be the basis of future studies related to the influence of the posterior tibial inclination as the effects on walking kinematics and on other types of tests (such as the squat test). Furthermore, the data validation could provide the surgeon with a clinical indication on the value of the PTS to be imposed during the implantation of the knee prosthesis.
Il comportamento meccanico del sistema muscoloscheletrico umano è un importante argomento della ricerca medica. In ortopedia gli sviluppi nella chirurgia sostitutiva e ricostruttiva delle articolazioni artificiali ha richiesto una vasta conoscenza del funzionamento meccanico delle articolazioni umane. In seguito all’intervento di impianto di una protesi totale di ginocchio , le strutture anatomiche possono essere alterate considerevolmente per vari motivi. In alcuni casi i legamenti possono non essere in grado di svolgere la propria funzione a causa della patologia o del trauma che ha portato alla necessità di intervento oppure altre volte i legamenti devono essere sacrificati o modificati per permettere l’inserimento e la funzionalità della protesi. Queste modifiche strutturali vengono decise, dal chirurgo in fase di planning operatorio sulla base dell’analisi anamnestica, clinico-funzionale e delle immagini diagnostiche; spesso, però, le decisioni vengono cambiate o modificate direttamente in sala operatoria. Solo al termine dell’intervento operatorio e del percorso riabilitativo post-intervento del paziente si ha la possibilità di verificare il risultato funzionale ottenuto e non sempre le scelte prese in sala operatoria si rivelano veramente efficaci. La possibilità di effettuare una predizione dell’esito dell’intervento in termini di mobilità articolare, di funzionalità e di sollecitazione delle varie strutture interessate grazie a dati quantitativi, derivanti dalla simulazione delle condizioni di funzionamento e di carico del ginocchio, permetterebbe di orientare il chirurgo verso una scelta migliore fra le varie opzioni e, auspicabilmente, di migliorare i risultati degli interventi di artroplastica. Un importante parametro del paziente sottoposto a TKA (Total Knee Arthroplasty) è l’inclinazione posteriore del piatto tibiale (PTS, Posterior Tibial Slope19) perché modifica la cinematica del ginocchio. Solitamente l’angolo di PTS viene scelto in base alle raccomandazioni delle aziende (3° o 7° sono le scelte più comuni), tuttavia studi su cadaveri umani sottoposti a TKR hanno dimostrato come la variazione del posterior tibial slope vada ad influenzare la stabilità in flessione ed estensione del ginocchio. Da questo presupposto, il presente lavoro di tesi si avvale dell’utilizzo di un modello anatomico tridimensionale dell’articolazione di ginocchio per studiare gli effetti del PTS in modo da fornire indicazioni necessarie al chirurgo in fase di pianificazione pre-operatoria negli interventi di artroprotesi. Il modello utilizzato era già stato realizzato in precedenza a partire dai file CAD di femore, fibula, tibia e patella di gamba sinistra ed è stato simulato dinamicamente mediante il software SimWise 4D che consente di effettuare analisi su forze, spostamenti, momenti, angoli e altro ancora, relativi al modello implementato. Inoltre, questo software consente di importare i file CAD del dispositivo protesico di cui si vuole studiare il comportamento. In questo lavoro di tesi è stata utilizzata una protesi di ginocchio totale Vanguard® Posterior Stabilized (PS) Complete Knee System in cui viene eliminato oltre al legamento crociato anteriore (quasi sempre sacrificato nelle operazioni di artroprotesi) anche il legamento crociato posteriore. Nel modello i legamenti vengono rappresentati come delle molle lineari (Linear Spring/ Damper) dotati di particolare caratteristica viscoelastica non lineare, secondo quanto proposto e comunemente accettato in letteratura35. Esse non sono attaccate direttamente all’osso, ma tramite blocchetti collegati alle componenti ossee. Per valutare qualitativamente e quantitativamente i parametri caratteristici della cinematica articolare sono state simulate le seguenti prove: test del cassetto anteriore-posteriore, test di rotazione interna-esterna e il test di varo valgo. Queste tre tipologie di prove sono state effettuate a diverso angolo di flessione del ginocchio (0°, 20° e 90° gradi) e a diversa inclinazione del piatto tibiale (-3°, 0°, +3°, +6°, +9°).Dal confronto dei risultati ottenuti con i dati presenti in letteratura si è osservato come l’aumento del PTS sembri abbassare la tensione dei legamenti collaterali durante le prove del cassetto anteriore-posteriore e rotazione interna-esterna, mentre non ne modifichi la tensione durante la prova di varo-valgo. Inoltre è emerso un non corretto bilanciamento della tensione dei legamenti collaterali nelle tre prove effettuate. La modifica del PTS sembra influenzare anche la lassità (movimento con bassa resistenza di contrasto del femore rispetto alla tibia) sebbene la sua variazione si possa attribuire principalmente all’assenza dei legamenti crociati. Inoltre gli andamenti della tensione dei legamenti collaterali hanno evidenziano una condizione critica durante la prova di rotazione interna su ginocchio flesso a 20° e inclinazione tibiale a +6° in cui si ha il completo annullamento della tensione sui legamenti collaterali. Questa condizione è di particolare interesse clinico in quanto sembra derivare dall’interferenza tra il piolo centrale della componente tibiale e l’asola del componente femorale entro cui dovrebbe scorrere. Questa interazione comporterebbe la trasmissione del momento torcente al fittone inserito nella tibia e quindi potrebbe comportare un rischio di fallimento della protesi a medio-termine.Trattandosi di un modello di dimensioni riferite ad un soggetto specifico, non è possibile estendere la validità dei risultati ottenuti ad altri casi che potrebbero presentare morfologie e caratteristiche strutturali diversificate, e in particolare l’indicazione per la scelta di una posizione piuttosto che un’altra dovrà tener conto di molteplici fattori, non solo biomeccanici ma anche certamente, di tipo clinico anamnestico. Tuttavia le informazioni qualitative e quantitative ottenute possono essere la base di futuri studi legati all’influenza dell’inclinazione posteriore tibiale come gli effetti sulla cinematica del cammino e su altri tipi di prove (come il test dello squat). Inoltre la validazione dei dati ottenuti potrebbe fornire un’indicazione clinica al chirurgo sul valore del PTS da imporre durante l’impianto della protesi di ginocchio.
Studio degli effetti dell'inclinazione posteriore del piatto tibiale nella cinematica del ginocchio protesizzato mediante l'utilizzo di un modello computazionale
ZELAYA LOPEZ, JHAN JAIRO OSWALDO
2018/2019
Abstract
The mechanical behavior of the human musculoskeletal system has become an important area of medical research. In orthopedics, for example, developments in replacement and reconstructive surgery of artificial joints required extensive knowledge of the mechanical functioning of human joints. Following the implantation of a total knee replacement (TKR), in fact, the anatomical structures can be considerably altered for various reasons. In some cases, ligaments may not be able to perform their function because of the pathology or trauma that led to surgical intervention. Other times the ligaments must be sacrificed or modified to allow the insertion and functionality of the prosthesis. These structural changes are usually decided by the surgeon during the operative planning phase based on anamnestic, clinical-functional analysis and diagnostic images; often, however, decisions are changed or changed directly in the operating room. Only at the end of the operative intervention and of the post-operative rehabilitative path of the patient it is possible to verify the functional result obtained and the choices made in the operating room are not always effective. The possibility of predicting the outcome of the intervention in terms of joint mobility, functionality and stress of the various structures involved thanks to quantitative data, deriving from the simulation of the operating conditions and of the knee load, would allow the surgeon to orientate towards a better choice among the various options and hopefully to improve the results of the arthroplasty operations. An important parameter of the patient subjected to TKA (Total Knee Arthroplasty) is the posterior inclination of the tibial plateau (PTS, Posterior Tibial Slope19) because it modifies the kinematics of the knee20. Usually the PTS angle is chosen based on the companies’ recommendations (3° or 7° are the most common choices). However, studies on human cadavers subjected to TKR have shown how the variation of the posterior tibial slope influences the stability in knee flexion-extension. From this assumption, the present thesis makes exploits a 3D anatomical model of the knee joint to study the effects of PTS in order to provide the surgeon with information necessary in the pre-operative planning phase in arthroplasty operations. The model used had previously been created starting from the CAD files of the femur, fibula, tibia and left leg patella and was dynamically simulated using the SimWise 4D software that allows for analysis of forces, displacements, moments, angles and more again, related to the implemented model. Furthermore, this software allows to import CAD files of the prosthetic device whose behavior wanted to be studied. In this thesis work, a knee joint Vanguard® Posterior Stabilized (PS) Complete Knee System was used in which the posterior cruciate ligament is eliminated in addition to the anterior cruciate ligament (almost always sacrificed in arthroplasty operations). In the model the ligaments are represented as linear springs (Linear Spring / Damper) endowed with a non-linear viscoelastic characteristic, as proposed and commonly accepted in literature35. They are not attached directly to the bone, but through blocks connected to the bone components. The following tests were simulated to qualitatively and quantitatively evaluate the characteristic parameters of the joint kinematics: anterior-posterior drawer test, internal-external rotation test and the varus-valgus test. These three types of tests were performed at different knee flexion angles (0 °, 20 ° and 90 ° degrees) and at different tibial plateau inclination (-3 °, 0 °, + 3 °, + 6 °, +9 °). From the comparison of the results obtained with the data present in the literature it was observed how the increase in PTS seems to lower the tension of the collateral ligaments during the tests of the anterior-posterior drawer and internal-external rotation, while it does not modify the tension during the test of varus-valgus. Furthermore, an incorrect balancing of the collateral ligaments tension emerged in the three tests performed. The modification of PTS also seems to influence laxity (movement with low resistance of the femur in contrast to the tibia) although its variation can be mainly attributed to the absence of the cruciate ligaments. Furthermore, the strains of the collateral ligaments have a critical condition during the internal rotation test on a flexed knee at 20 ° and a tibial inclination at + 6 ° where there is complete cancellation of the tension on the collateral ligaments. This condition is of clinical interest since it seems to derive from the interference between the central peg of the tibial component and the slot of the femoral component within which it should flow. This interaction would involve the transmission of the torque to the taproot inserted in the tibia and therefore could entail a risk of failure of the medium-term prosthesis. Since this is a model of dimensions referred to a specific subject, it is not possible to extend the validity of the results obtained to other cases that could present diversified morphologies and structural features, and in particular the indication for choosing a position rather than another will have to take into account multiple factors, not only biomechanical but also certainly, of the clinical history. However, the qualitative and quantitative information obtained may be the basis of future studies related to the influence of the posterior tibial inclination as the effects on walking kinematics and on other types of tests (such as the squat test). Furthermore, the data validation could provide the surgeon with a clinical indication on the value of the PTS to be imposed during the implantation of the knee prosthesis.File | Dimensione | Formato | |
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Descrizione: Effetti del PTS sulla lassità e sulla tensione dei legamenti collaterali
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https://hdl.handle.net/10589/150126