Design and evaluation of a prosthetic anterior cruciate ligament replacement medical device

Rupture of the anterior cruciate ligament (ACL) is a relatively common sports-related injury for which the current treatment is reconstruction with an autograft or allograft. Drawbacks associated with each of the current options would make a prosthetic alternative advantageous, however, artificial ligaments are not widely used, having failed due to lack of biocompatibility and mechanical insufficiencies. To develop the next-generation prosthetic ACL, design control principles were applied including specification of comprehensive design inputs, risk analysis, and verification testing. A design was proposed utilizing polyvinyl alcohol and ultrahigh molecular weight polyethylene, selected for good biocompatibility and mechanical strength and stiffness suitable for ACL replacement. A biomimetic fibrous rope pattern was designed for the intra-articular ligament section of the prosthetic that produced a close match the static tensile behavior of the native ACL and which also demonstrated good resistance to fatigue and creep. A calcium phosphate coating was recommended for the sections of the device lying within the bone tunnel to increase the rate of osseointegration. The proposed design was then evaluated in a computational simulation to assess functional restoration and the effects of installation parameters such as tension and tunnel orientation on knee kinematics. The encouraging results of preclinical verification testing support further in vivo evaluation of the proposed design.PhDCommittee Chair: Ku, David; Committee Co-Chair: Cherkaoui, Mohammed; Committee Member: Cort, Laurent; Committee Member: Gleason, Rudolph; Committee Member: Guldberg, Rober

Towards Functional Preoperative Planning in Orthopaedic Surgery

Las cirugíıas del aparato locomotor suponen más de 20 millones de intervencionesanuales para la corrección de lesiones que afectan a músculos, articulaciones,ligamentos, tendones, huesos o nervios; elementos que conforman el sistema musculoesquelético. Este tipo de afecciones de la biomecánica pueden tener diversos orígenes; siendo los principales los traumatismos, las lesiones degenerativas en huesos y tejidos blandos, los malos hábitos posturales o motores, y los de origen congénito.El uso de las tecnologías actuales en los procesos de corrección de estas afecciones forma parte del día a día en los quirófanos y en la monitorización de los pacientes.Sin embargo, el uso de técnicas computacionales que permitan la preparación de las intervenciones quirúrgicas antes de proceder con la cirugía están todavía lejos de formar parte del proceso de evaluación preoperatoria en este tipo de lesiones. Por este motivo, el objetivo principal de esta tesis consiste en demostrar la viabilidad del uso de herramientas computacionales en la planificación preoperatoria de diferentes cirugías ortopédicas.Entre los tipos de cirugías más comunes, la mayor parte de ellas se centran en las articulaciones del tren inferior de la anatomía humana. Por este motivo, este trabajo se centraría en el análisis de diferentes cirugías cuya finalidad es solucionar lesiones en las principales articulaciones del tren inferior: región sacrolumbar, cadera, rodilla y tobillo.Para poder realizar el análisis de estas cirugías se hizo uso de algunas de lasherramientas computacionales más usadas habitualmente y cuya capacidad en diversos ámbitos ha sido comprobada. Se ha utilizado la reconstrucción 3D para la obtención de modelos anatómicos sobre los que comprobar la viabilidad de las cirugías. Estas reconstrucciones se basan en las imágenes médicas obtenidas mediante Tomografia Axial Computerizada (TAC) o Resonancia Magnética (RM). Las imágenes procedentes de RM permiten diferenciar todos los tejidos de la anatomía, incluyendo los blandos tales como tendones o cartílagos; mientras que los TAC facilitan la diferenciación de los huesos. Esta última es la prueba más habitual en los diagnósticos.Para su análisis y reconstrucción se hizo uso de los software Mimics v 20.0 y3-matic 11.0 (Materialise NV, Leuven, Belgium). Como alternativa para la generación de los modelos cuando no se dispone de las imágenes necesarias para realizar la reconstrucción o cuando se requiere dotar de flexibilidad a estos modelos, se recurrió al modelado en el software de análisis por elementos finitos Abaqus/CAE v.6.14 (Dassault Syst`emes, Suresnes, France). Dicho software fue además utilizado para la simulación del efecto de las diferentes cirugías sobre la región de interés. Para resalizar las simulaciones, se incluyeron en los modelos aquellos parámetros, elementos y condiciones necesarios para poder representar las caraterísticas propias de cada cirugía. Finalmente, para aquellas situaciones que requerían del análisis de datos se hizo uso de tecnologías de machine learning. La solución seleccionada para estos casos fueron las redes neuronales artificiales (ANN). Dichas redes se desarrollaronhaciendo uso del software MATLAB R2018b (MathWorks, Massachusetts, USA).El estudio de la rodilla se centra en uno de los ligamentos clave en la estabilidad de la rótula y que, sin embargo, es uno de los menos analizados hasta ahora, el ligamento medial patelofemoral. La reconstrucción de este ligamento es la principal solución clínica para solventar esta inestabilidad y diferentes cirugías utilizadas para dicho fin han sido analizadas mediante el desarrollo de un modelo paramétrico en elementos finitos que permita su simulación. En este modelo es posible adaptar la geometría de la rodilla de forma que se puedan simular diferentes condiciones que pueden afectar a la estabilidad de la rótula, tales como la displasia troclear y la patella alta.El estudio de la región sacrolumbar se centra en el análisis de diferentes posibles configuraciones para las cirugías de fusión vertebral. El análisis se centró en la fijación con tornillos y la influencia del Polimetimetacrilato (PMMA) como elemento de fijación en las vértebras. Para ello, se reconstruyó el modelo óseo de diferentes pacientes que necesitaron este tipo de intervención. Sobre estos modelos se simularon mediante elementos finitos las diferentes configuraciones consideradas de forma que se pudiera comparar su comportamiento en diferentes casos.En el caso de la cadera, el estudio se centra en el análisis de la artroplastia total de cadera, que implica el reemplazo de la articulación anatómica por una prótesis habitualmente de titanio. Cuando este tipo de cirugías es realizado, es común que surjan posteriormente problemas derivados de la disposición de la prótesis y que pueden llevar al pinzamiento entre sus componentes y, en algunas ocasiones, su dislocación.Esto ocurre cuando el rango de movimiento de la articulación es reducido. Este tipo de sucesos son más comunes cuando se realizan los movimientos de extensión externa (EE) o de rotación interna (RI) de la extremidad. El estudio se desarrolló con el objetivo de elaborar una herramienta computacional capaz de predecir este choque y dislocación basándose en el diámetro de la cabeza del femur y de los ángulos de abducción y anteversión. Para ello, se recurrió al uso de redes neuronales artificales(ANN). Se configuró una red independiente para cada movimiento (EE y RI) y cada posible evento (pinzamiento y dislocación), de forma que se obtuvieron cuatro redes completamente independientes. Para el entrenamiento y primer testeo de las redes se recurrió a un modelo paramétrico en elementos finitos de la prótesis con el que se realizaron diferentes simulaciones determinando el rango de movimiento para cada caso. Finalmente, las redes fueron de nuevo validadas con el uso de datos procedentes de pacientes que sufrieron dislocación tras ser sometidos a este tipo de cirugías.Finalmente, el estudio de la región del tobillo se centró en la lesión de la sindesmosis del tobillo. Este tipo de lesiones implica la rotura de algunos de los ligamentos que unen los principales huesos de esta articulación (tibia, peroné y astrágalo) junto con parte de la membrana intraósea, que se extiende a lo largo de la tibia y el peroné ligando ambos huesos. Cuando se produce este tipo de lesiones, es necesario recurrir a la inclusión de elementos que fijen la articulación y prevengan la separación de los huesos. Los métodos más comunes y que centran este análisis comprenden la fijación con tornillos y la fijación mediante botón de sutura. Para poder realizar un análisis que permita comparar la efectividad y incidencia de este tipo de cirugías se recurrióa la reconstruccción 3D de la articulación de un paciente que sufrió este tipo de lesión. Con este modelo geométrico, se procedió al desarrollo de diferentes modelos en elementos finitos que incluyeran cada una de las alternativas consideradas. Las simulaciones de estos modelos junto a las situaciones anatómicas y lesionadas, permitió hacer una aproximación sobre la solución quirúrgica que mejor restablece el estado incial sano de la región afectada.Locomotor system surgeries represents more the 20 million interventions per year for the correction of injuries that affect muscles, joints, ligaments, tendons, bones or nerves; elements that form themusculoskeletal system. This kind of biomechanical affections may have several sources, being the main ones traumas, bones and soft tissues degenerative injuries, poor postural or motor habits and those of congenital source. The use of current technologies in the correction process for these injuries is part of the day-to-day in the operating rooms and the monitoring of patients. However, the use of computational tools that allow preoperative planning is still far from being part of the preoperative evaluation process in this kind of injuries. For this reason, the main goal of this thesis consists in demonstrating the viability of the use of computational tools in the preoperative planning of different orthopaedic surgeries. Among the most common surgeries, most of them focus in the lower body joints of the human anatomy. For this reason, this work will focus in the analysis of different surgeries whose purpose is to solve injuries in the main joints of the lower body: lumbosacral region, hip, knee and ankle. Some of the most commonly used computational tools, and whose capability in different fields has been widely proven, were used in order to be able of performing the analysis of these surgeries. 3D reconstruction has been used for obtaining anatomical models in which the viability of the surgeries could be verified. These reconstructions are based on the medical images obtained through Computerized Tomography (CT) or Magnetic Resonance Imaging (RMI). Images from RMI allow differentiating all the tissues of the anatomy, including soft ones such as tendons and cartilages; while CT scans make easier the bones differentiation. This last procedure is the most commonly used in diagnoses. For their analysis and reconstruction software Mimics v 20.0 and 3-Matic 11.0 (Materialise NV, Leuven, Belgium) were used. As alternative for the models generation when the necessary images for the reconstruction are not available or when flexibility is required for these models, modelling in the Finite Element Analysis software Abaqus/CAE v.6.14 (Dassault Syst‘emes, Suresnes, France) was used. This software was also used for the simulation of the effects of the different surgeries in the interest region. In order to perform the simulations, those parameters, elements and conditions necessary to represent the characteristics of each surgery were included. Finally, for those situations requiring data analysis, machine learning technologies were used. The selected solution for these cases were Artificial Neural Networks (ANN). These networks were developed using the software MATLAB R2018b (MathWorks, Massachusetts, USA). The study of the knee joint focuses in one of the key ligaments for the patellar stability and which, however, is one of the least analysed so far, the medial patellofemoral ligament. The reconstruction of this ligament is the main clinical solution for solving this instability and different surgeries used for that purpose have been analysed through the development of a finite element parametric model that allows their simulation. In this model adapting knee geometry is possible so that those conditions that can affect the stability of the patella, such as trochlear dysplasia or patella alta, can be simulated. The study of the lumbosacral region focuses in the analysis of different possible configurations for spine fusion surgeries. The analyses focused in the pedicle screws fixation and the influence of polymethyl methacrylate (PMMA) as fixation element in the vertebrae. To do this, osseous models for different patients that required this kind of intervention were reconstructed. The different configurations considered were simulated on these models through finite element analysis comparing their behaviour. In the case of the hip, the study focuses in the analysis of the total hip arthroplasty, which implies replacing the anatomical joint by a prosthesis, usually made of titanium. When this kind of surgery is performed, it is common for later issues arising from the arrangement of the prosthesis and which can lead to impingement between its components and, on some occasions, their dislocation. This happens when the range of movement of the joint is limited. This kind of events are more common when the external extension (EE) or internal rotation (IR) movements of the leg are performed. The study was developed with the goal of elaborating a computational tool able to predict the impingement and dislocation based on the diameter of the head of the femur and the anteversion and abduction angles. To do this, artificial neural networks (ANN) were used. An independent network was configured for each movement (EE and IR) and for each possible event (impingement and dislocation), so that four completely independent networks. For the training and the first testing of the networks, a parametric finite element model of the hip was used; with which different simulations were performed determining the range of movement for each case. Finally, the networks were validated again with the use of data proceeding from patients that suffered dislocation after going through this kind of surgery. Finally, the study of the ankle region focused in the ankle syndesmosis injury. This kind of injuries implies the tear of some ligaments that connect the main bones of the joint (tibia, fibula and talus) together with part of the intraosseous membrane, which extends along the tibia and fibula linking both bones. When this kind of injuries happens, it is necessary to resort to the inclusion of elements that fix the joint and prevent the bones distance. The most common methods, which focus this analysis, include the screws fixation and the suture button fixation. In order to carry out an analysis that allows comparing the effectiveness and incidence of this kind of surgeries, a 3D reconstruction of the joint from a patient that suffered this kind of injury was used. With this geometrical model, different finite element models including each of the considered alternatives were developed. The simulations of these models, together with the injured and anatomical situations, allowed an approximation of the surgical solution that better restores the initial healthy state of the affected region.<br /

Experimental and Computational Characterization of the Anterior Cruciate Ligament: Challenges and Considerations for Soft Tissue Biomechanics

The anterior cruciate ligament (ACL) is one of several major stabilizing soft tissue structures in the articular knee joint. However, the ACL is often torn, and has a low ability to self-heal, with upwards of 300,000 ACL replacement surgeries performed in the United States alone each year. There have been detrimental long-term effects of these replacements, especially the occurrence of early-onset osteoarthritis. Much research has been performed in the area of knee biomechanics to understand the role of the ACL in knee function, tissue biomechanics, and graft replacements. The ACL is known to be hyperelastic, anisotropic, and heterogeneous, with complex insertion sites. This dissertation focuses on characterization and computational modeling of the intrinsic full-field mechanical properties of the ACL. Understanding these properties leads to insight on tissue failure mechanisms and could one day aid in the prevention of ACL failures. In this thesis I have developed a novel method for individually aligning the distinct anteromedial (AM) and posterolateral (PL) bundles of the ACL, in order to perform mechanical testing of both bundles in a well-understood loading state. I have also performed entire ACL experiments with clinical applications. To obtain full-field data, I have incorporated the use of digital image correlation (DIC), a non-contact deformation measurement technique. A patterning method to adapt DIC to soft materials is developed and discussed. Using DIC, full-field surface displacements and strains of the ACL have been acquired. These contours provide new information on the spatial deformation of the ACL’s bundles, providing new information on its hyperelastic and anisotropic response. The experimental results have been further utilized to develop a finite element (FE) model of the AM bundle of the ACL. Within this computational model, a complex geometry and microstructurally-based constitutive model are used to simulate observed experimental behavior. The numerical model demonstrates strain responses in agreement with the full-field experimental results, as well as stress/strain behavior in line with that of experiments. Few studies have discussed the full-field experimental response and computational modeling of the AM and PL bundles; this thesis provides insight into the complexity of the ACL and considerations for its accurate characterization.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/138606/1/kmallett_1.pd

Soft Tissue Constitutive Forms and Their Implications for Whole Knee Computational Models

This work sought to determine the extent to which approximations in the constitutive theories and geometric representations of individual soft tissues affected the predictive power of computational knee models. Two tissue systems were evaluated: articular cartilage and structural ligaments, particularly focusing on the anterior cruciate ligament (ACL). These tissues were selected due to the rates and debilitating effects of their associated injuries and diseases, as well as their ubiquitous inclusion in computational knee models. The mechanical consequences of various levels of articular cartilage constitutive complexity were investigated during physiologically representative loading. Additional complexity, compared to the common assumption of linear elasticity, was introduced through the systematic incorporation of nonlinear, directional, and spatially heterogeneous mechanical properties. Failure to include experimentally motivated cartilage material models resulted in overpredictions of joint motion and local tissue deformation. There were some diminishing returns with increasing complexity. In particular, there was a relatively small effect corresponding to the specific interpolation method used in the construction of each spatially heterogeneous mechanical property field. After determining the sensitivity of the representative computational knee model to cartilage constitutive behavior, the impacts of articular cartilage focal defect size and location were analyzed. Cartilage focal defects were shown to have a large effect on deformation in the neighborhood around their perimeters, though no consistent trends of altered deformation were observed in adjacent and opposing tissues. A defect of increased size was also shown to alter joint kinematics, while small defects, independent from their location, were found to have a minimal effect. There has been a tremendous body of work directed at describing the deformation of ligaments. This work is largely built on the assumption that ligaments behave as transversely isotropic solids; however, there are limited and conflicting mechanical characterization data available for ligaments. Various constitutive theories were assessed on their ability to represent the stress-strain responses of structural ligaments in multiple loading configurations. Traditionally and commonly accepted transversely isotropic, hyperelastic constitutive theories proved incapable of describing the mechanical response of ligaments, predominantly failing in the transverse direction. Therefore, a new constitutive theory was developed and shown to have superior accuracy in describing the breadth of experimental stress-strain responses from multiple loading directions. With this new understanding related to the deformation of ligaments, the internal loading and detailed anatomy of the ACL were evaluated. Specifically, the double bundled, prestrained structure of the ACL was quantified computationally for the first time, and its effect on joint motion and local tissue deformation during normal clinical assessments was examined. The incorporation of prestrain was shown to be an important mechanical feature of knee stability, bringing predicted joint motions within the acceptable ranges of healthy knees.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/144170/1/bmarchi_1.pd

An Investigation Of The Design And Function Of Knee Joint-sparing Massive Endoprostheses

Distal femoral and proximal tibial joint-sparing bone tumour implants allow to preserve the knee, in limb salvage surgery. The aim of this thesis was to compare implant survival, functional outcomes, acceptance, proprioception and gait in patients with knee sparing implants and conventional knee sacrificing implants. Using FEA, a distal femoral implant and cadaver bone were modelled and parametrised to find the design that improves implant fixation. A survivorship study of 104 consecutive patients following knee sparing surgery (mean follow-up 36.1 ± 11.0 months) found an implant survival rate of 78% and this is comparable to the reported survival for joint sacrificing prostheses. Younger patients showed improved implant survival compared to older individuals. Plate fracture was not observed and aseptic loosening was the main reason for revision. Radiographic analysis indicated that implantation accuracy increased implant survival. Patient questionnaires showed that patients with knee sparing implants had more normal functional outcome and acceptance compared with patients with knee sacrificing implants. However, proprioception (joint position sense) was reduced in these patients. Using optoelectronic gait analysis system, hip, knee and ankle joint angle in 19 patients and 3 healthy subjects were measured. Ground reaction force and time in stance were also investigated. Joint symmetry in the joint sacrificing group was improved compared to the joint-sparing group, however overall, the joint-sparing tibial group demonstrated a more normal gait pattern. FEA results indicated that lower resection levels, reduced plate thickness and implant materials with lower modulus, decreased the stresses in the bone adjacent to the implant while loaded the bone more to reduce risk of stress shielding. To conclude, knee sparing endoprostheses provide a reliable alternative to knee sacrificing implants in limb reconstruction in selected patients. However, the current design of joint-sparing implants can be optimised to potentially improve bone remodelling and implant fixation

Mechanical Behaviour of Tendinopathic Tendon: An Engineering Perspective

Tendinopathy is a debilitating disease affecting millions of people worldwide. The aetiology of this disease is not well understood, and treatment remains difficult due to a lack of evidence-based management. This dissertation sought to quantify the mechanical behaviour of tendon in order to understand the difference between healthy and tendinopathic tendons. The findings in this dissertation offer insights that may contribute toward the development of better clinical management of tendinopathy

Development and Validation of a Kinematically-Driven Computational Model of the Patellofemoral Joint

The patellofemoral joint represents one of the most challenging musculoskeletal systems to understand and manage. Disruption in the normal tracking of the patellofemoral joint can lead to elevated stress and microtrauma to the articular cartilage, cascading to the development of osteoarthritis. To develop effective treatment therapies, relationships between altered patellar motion and subsequent changes in articular cartilage loading must be measured. Computational modeling provides joint-specific changes in contact mechanics, but current techniques are limited by force-based assumptions and lack validation. The objective of this work was to develop a subject-specific modeling framework driven by highly accurate knee joint kinematics as a tool to estimate knee joint contact stress in vivo. First, a repeatable knee joint testing system for simultaneous measurement of patellofemoral joint kinematics and joint contact pressures was established. Measurements of patellofemoral and tibiofemoral translations and rotations were highly repeatable with intraclass correlation coefficients greater than 0.98/0.90 and 0.80/0.97, respectively. Measurements of joint contact pressure were repeatable within 5.3% - 6.8%. Second, a unique patellofemoral modeling framework employing the discrete element method combined with accurate knee joint kinematics was developed using two cadaveric knee joint specimens. Model-generated stresses were validated using experimentally measured pressures. The model predicted the experimental data well, with percent error (%) differences in contact stress distribution being less than 13%, validating the model’s ability to predict the experimental changes in joint contact. Lastly, this validated model was implemented in a group of individuals with patellofemoral osteoarthritis (n=5) and a control group (n=6) during a downhill walking task. The model predicted unique patellofemoral joint stress patterns between the two groups such that individuals with patellofemoral osteoarthritis experienced greater (58%) lateral facet joint contact stress early within the loading phase of the gait cycle compared to the control group (38%). This dissertation has validated and implemented a novel modeling technique driven by highly accurate, subject-specific kinematics to estimate patellofemoral joint contact stress during a downhill walking task. Future use of these models can provide quantitative evidence of the effectiveness of current patellofemoral treatment solutions and allow for the development of improved rehabilitation strategies