Development and Characterization of Velocity Workspaces for the Human Knee.

The knee joint is the most complex joint in the human body. A complete understanding of the physical behavior of the joint is essential for the prevention of injury and efficient treatment of infirmities of the knee. A kinematic model of the human knee including bone surfaces and four major ligaments was studied using techniques pioneered in robotic workspace analysis. The objective of this work was to develop and test methods for determining displacement and velocity workspaces for the model and investigate these workspaces. Data were collected from several sources using magnetic resonance imaging (MRI) and computed tomography (CT). Geometric data, including surface representations and ligament lengths and insertions, were extracted from the images to construct the kinematic model. Fixed orientation displacement workspaces for the tibia relative to the femur were computed using ANSI C programs and visualized using commercial personal computer graphics packages. Interpreting the constraints at a point on the fixed orientation displacement workspace, a corresponding velocity workspace was computed based on extended screw theory, implemented using MATLAB(TM), and visually interpreted by depicting basis elements. With the available data and immediate application of the displacement workspace analysis to clinical settings, fixed orientation displacement workspaces were found to hold the most promise. Significant findings of the velocity workspace analysis include the characterization of the velocity workspaces depending on the interaction of the underlying two-systems of the constraint set, an indication of the contributions from passive constraints to force closure of the joint, computational means to find potentially harmful motions within the model, and realistic motions predicted from solely geometric constraints. Geometric algebra was also investigated as an alternative method of representing the underlying mathematics of the computations with promising results. Recommendations for improving and continuing the research may be divided into three areas: the evolution of the knee model to allow a representation for cartilage and the menisci to be used in the workspace analysis, the integration of kinematic data with the workspace analysis, and the development of in vivo data collection methods to foster validation of the techniques outlined in this dissertation

Advancement of a Forward Solution Mathematical Model of the Human Knee Joint

Sometimes called degenerative joint disease, osteoarthritis most often affects the knee, which is a leading cause of pain and reduced mobility. While early treatment is ideal, it is not always successful in combating osteoarthritis and improving joint function, therefore creating the need for total knee arthroplasty (TKA), which is a late-stage treatment where damaged bone and cartilage are replaced by artificial cartilage. Joint arthroplasty is a common and successful procedure for end-stage osteoarthritis. Unfortunately, TKA patient satisfaction rates lag behind those of total hip arthroplasty [1,2], which remains an impetus to create new designs. Due to ethical issues, time requirements, and prohibitive expenses of testing new designs in vivo, mathematical modeling may be an alternative tool to efficiently assess the kinetics and kinematics of new TKA designs. In general, the knee is one of the most complicated joints in the human body, including multiple articulating surfaces and the complexity of soft tissues encompassing the knee joint. Therefore, mathematically modeling the knee is a challenging and complex process. With increasing computational power and advanced knowledge and techniques, advanced mathematical models of the knee joint can be created utilizing various modeling techniques [3]. Furthermore, mathematical modeling can advance our knowledge related to knee biomechanics, especially those parameters that are otherwise challenging to obtain, such as soft tissue properties and effects pertaining to knee mechanics. Mathematical modeling allows the user to evaluate multiple designs and surgical approaches quickly and cost-efficiently without having to conduct lengthy clinical studies. Mathematical models can also provide insight into topics of clinical significance and can efficiently analyze outcome contributions that cannot be controlled in fluoroscopic studies, such as anatomical, mechanical, and kinematic alignment comparisons for the same subject. Furthermore, mathematical models can evaluate the effect of TKA design concerns such as changing conformity of the polyethylene or using femoral components with single or multi radius designs [3]. The objectives of this dissertation are to advance a forward solution model to create a more sophisticated and physiological representation of the knee joint.This is achieved by developing a muscle wrapping algorithm, integrating a validated inverse dynamics model, adding more muscles, incorporating several different TKA types including revision TKA designs, and expanding the model to include other daily activities. All these modifications are incorporated in a graphical user interface. These advancements increase both functionality and accuracy of the model. Several validation methods have been implemented to investigate the accuracy of the predicted kinetics and kinematics of this mathematical model

Two-dimensional dynamics model of the lower limb to include viscoelastic knee ligaments

A dynamic, 2D, anatomical knee joint model has been developed to simulate knee reactions to external input forces. A deformable contact area approach is used to find contact forces and moments, and a method of applying nonlinear viscoelastic ligament strain rate response was also developed and implemented on the model to account for the effects of viscoelasticity on the ligament fibers. The ligaments were then tested for various deficiencies to identify their effects on the natural frequency of the knee. Internal knee forces from ligaments, muscles, and contacting surfaces are modeled and then numerically found for different exercises. Static and dynamic equations for knee motion are developed. These equations are then transformed into differential algebraic equation (DAE) systems for modeling various exercises. The DAE systems and the model simulations are performed using Matlab solver ODE15S, and predicted data from the model is compared to data published in literature for validation

Mechanical vs Kinematic alignment in Total Knee Arthroplasty: an in-silico biomechanical analysis

openL'allineamento meccanico è un metodo utilizzato per ottenere un asse anca-ginocchio-caviglia neutro. L'allineamento cinematico, invece, è una tecnica alternativa nell'artroplastica totale del ginocchio (TKA) che mira a preservare l'asse cinematico naturale e l'equilibrio legamentoso del ginocchio del paziente. Lo scopo di questo studio è quello di confrontare biomeccanicamente l'effetto dell'allineamento meccanico e cinematico su un ginocchio dopo la TKA. I modelli in-silico sono spesso utilizzati per studiare la cinematica del ginocchio in condizioni sane o patologiche. È stato creato un modello anatomico del ginocchio nativo segmentando le immagini TC di femore, rotula e tibia. Inoltre, sono stati inclusi nel modello il legamento collaterale mediale (MCL), il legamento collaterale laterale (LCL), il legamento patellofemorale mediale (MPFL), il retinacolo laterale e il tendine rotuleo per ottenere una rappresentazione completa dell'articolazione. I legamenti dell'articolazione del ginocchio sono stati modellati utilizzando elementi shell bidimensionali. Sono stati implementati due modelli di ginocchio tridimensionali basati sul ginocchio nativo derivato dalla segmentazione per simulare le due diverse tecniche chirurgiche, l'allineamento meccanico e l'allineamento cinematico. Per valutare le prestazioni dei modelli, è stato simulato un movimento di squat da 0 a 120 gradi. Lo studio si è concentrato sulle articolazioni patellofemorale e tibiofemorale, analizzando la cinematica delle due articolazioni oltre alle aree di contatto e le forze di contatto nei due approcci di allineamento. In conclusione, questo studio evidenzia i potenziali vantaggi di ripristinare la joint line, allineandola alla sua posizione naturale, che può portare a risultati clinici superiori nella TKA ad allineamento cinematico. Tuttavia, la persistenza di complicazioni patellofemorali rimane un’incertezza, soprattutto quando si utilizzano impianti convenzionali progettati per l'allineamento meccanico applicati per mezzo dell'approccio di allineamento cinematico.Mechanical alignment is a method used to achieve a neutral hip-knee-ankle axis. Kinematic alignment, on the other hand, is an alternative technique in Total Knee Arthroplasty (TKA) that aims to preserve the natural kinematic axis and ligament balance of the patient's knee. The purpose of this study is to biomechanically compare the effect of mechanical and kinematic alignment on a knee after TKA. In-silico models are often used to study knee kinematics in healthy or pathological conditions. An anatomical model of the native knee was created by segmenting CT images of the femur, patella and tibia. Additionally, the model incorporated the medial collateral ligament (MCL), lateral collateral ligament (LCL), medial patellofemoral ligament (MPFL), lateral retinaculum, and patellar tendon to achieve a comprehensive joint representation. Ligaments of knee joint were modelled using two-dimensional shell elements. Two three-dimensional knee models based on the native knee derived from segmentation were implemented to simulate the two different surgical techniques, mechanical alignment and kinematic alignment. To evaluate the performance of the models, a squat movement from 0 to 120 degrees was simulated. The study focused on the patellofemoral and tibiofemoral joints, analysing the kinematics of the two joints as well as the contact areas and contact forces in the two alignment approaches. In conclusion, this study highlighted the potential benefits of achieving a joint line restoration closely aligned with its natural position, which may lead to superior clinical outcomes in kinematically aligned TKA. However, the persistence of patellofemoral complications remains a concern, especially when using conventional implants designed for mechanical alignment in the kinematic alignment approach

Parameterization of a Next Generation In-Vivo Forward Solution Physiological Model of the Human Lower Limb to Simulate and Predict Demographic and Pathology Specific Knee Mechanics

The human knee from a mechanical perspective is arguably one of the more complex of the joints of the human body and for this very reason there are a number of pathological factors that can adversely affect knee function, leading to pain, stiffness and an overall reduced quality of life. To rectify these disease conditions, a variety of intervention techniques exist, all of which are predicated on a thorough understanding of the forces and motions that occur at the knee.Various techniques have been developed to further the understanding of how the knee functions; however, many of these strategies involve time and cost consuming processes in order to assess functionality of the knee. Mathematical modeling is a methodology that uses mathematical equations of motion to solve for forces, or in the case of forward modeling, motions given a known set of forces. Such a model is capable of replicating the functionality of the knee in vivo.One application of such a model is in the context of total knee arthroplasty design. Intended for the restoration of functionality after late stage osteoarthritis, total knee arthroplasty devices are highly dependent on their associated design features and the use of a theoretical model affords the opportunity to test the performance of a device without ever needing to manufacture or implant it.In addition, there are also surgical applications where a mathematical model can test joints that otherwise cannot be evaluated under conventional means. This includes modeling of the healthy knee, as well as various functionality-limiting pathological conditions. Perhaps more importantly is the ability to evaluate different intervention techniques to determine the effectiveness in doing so identify which technique most effectively resolves the pathological issues.Advances to the model have focused on parameterization while contributing to a validated normal knee model, an enhancement on the efficiency of the muscles that drive flexion, facilitated methods to evaluate articular geometries and enhancements providing more realistic physiological motions. The model has also been enhanced to account for demographics, as well as abnormal pathology with additional parameters added to better understand gait mechanics at the knee

Subject Specific Computational Models of the Knee to Predict Anterior Cruciate Ligament Injury

Knee joint is a complex joint involving multiple interactions between cartilage, bone, muscles, ligaments, tendons and neural control. Anterior Cruciate Ligament (ACL) is one ligament in the knee joint that frequently gets injured during various sports or recreational activities. ACL injuries are common in college level and professional athletes especially in females and the injury rate is growing in epidemic proportions despite significant increase in the research focusing on neuromuscular and proprioceptive training programs. Most ACL injuries lead to surgical reconstruction followed by a lengthy rehabilitation program impacting the health and performance of the athlete. Furthermore, the athlete is still at the risk of early onset of osteoarthritis. Regardless of the gender disparity in the ACL injury rates, a clear understanding of the underlying injury mechanisms is required in order to reduce the incidence of these injuries. Computational modeling is a resourceful and cost effective tool to investigate the biomechanics of the knee. The aim of this study was twofold. The first aim was to develop subject specific computational models of the knee joint and the second aim to gain an improved understanding of the ACL injury mechanisms using the subject specific models. We used a quasi-static, multi-body modeling approach and developed MRI based tibio-femoral computational knee joint models. Experimental joint laxity and combined loading data was obtained using five cadaveric knee specimens and a state-of-the-art robotic system. Ligament zero strain lengths and insertion points were optimized using joint laxity data. Combined loading and ACL strain data were used for model validations. ACL injury simulations were performed using factorial design approach comprising of multiple factors and levels to replicate a large and rich set of loading states. This thesis is an extensive work covering all the details of the ACL injury project explained above and highlighting the importance of 1) computational modeling in inj

Subject Specific Computational Models of the Knee to Predict Anterior Cruciate Ligament Injury

Knee joint is a complex joint involving multiple interactions between cartilage, bone, muscles, ligaments, tendons and neural control. Anterior Cruciate Ligament (ACL) is one ligament in the knee joint that frequently gets injured during various sports or recreational activities. ACL injuries are common in college level and professional athletes especially in females and the injury rate is growing in epidemic proportions despite significant increase in the research focusing on neuromuscular and proprioceptive training programs. Most ACL injuries lead to surgical reconstruction followed by a lengthy rehabilitation program impacting the health and performance of the athlete. Furthermore, the athlete is still at the risk of early onset of osteoarthritis. Regardless of the gender disparity in the ACL injury rates, a clear understanding of the underlying injury mechanisms is required in order to reduce the incidence of these injuries. Computational modeling is a resourceful and cost effective tool to investigate the biomechanics of the knee. The aim of this study was twofold. The first aim was to develop subject specific computational models of the knee joint and the second aim to gain an improved understanding of the ACL injury mechanisms using the subject specific models. We used a quasi-static, multi-body modeling approach and developed MRI based tibio-femoral computational knee joint models. Experimental joint laxity and combined loading data was obtained using five cadaveric knee specimens and a state-of-the-art robotic system. Ligament zero strain lengths and insertion points were optimized using joint laxity data. Combined loading and ACL strain data were used for model validations. ACL injury simulations were performed using factorial design approach comprising of multiple factors and levels to replicate a large and rich set of loading states. This thesis is an extensive work covering all the details of the ACL injury project explained above and highlighting the importance of 1) computational modeling in inj

Posterior stabilized knee design biomechanical considerations

Numerous posterior stabilized knee systems are available for primary and revision total knee arthroplasty. Design of these systems requires an understanding of the articulating geometries and kinematic/kinetic biomechanical considerations of the normal knee. The findings for the normal knee are integrated into the design of a prosthetic system. The natural femoral, tibial and patella articulating geometries are defined to enable subsequent kinematic and kinetic analyses. The articulating geometries are characterized from review of anthropometric studies of the tibiofemoral and patellofemoral joint. The kinematic analysis of the natural knee defines knee motion in terms of rotation, adduction/abduction, range of motion and femoral rollback. Typical activities for total knee recipients are characterized under these headings. Instant center theory is also applied to the natural knee as it facilitates linking natural knee motion and prosthetic motion analysis. Natural knee kinetics for the gait cycle is characterized. The maximum gait cycle compressive and shear loads and knee motions attained from clinical studies using force plate, cinematography and computer optimization techniques are reviewed. The resultant loads and motions obtained from the studies form a benchmark used to establish laboratory testing parameters. The kinematic and kinetic analysis for generic posterior stabilized design is studied. Interaction of the femoral cam, tibial spine, femoral condyles and tibia plateau geometry are reviewed for a proposed and existing posterior stabilized geometry. Additional posterior stabilized design issues including: subluxation resistance, range of motion, bone conservation for the femoral housing resection, internal/external femoral rotation, tibial polyethylene insert modularity with the tibial tray and tibial polyethylene insert conformity with the femoral condyles are reviewed. A survey of designs on the market indicates a wide range of results for bone conservation for the femoral housing resection, internal/external rotation, and degree of conformity