Tissue material properties and computational modelling of the human tibiofemoral joint: a critical review

Understanding how structural and functional alterations of individual tissues impact on whole-joint function is challenging, particularly in humans where direct invasive experimentation is difficult. Finite element (FE) computational models produce quantitative predictions of the mechanical and physiological behaviour of multiple tissues simultaneously, thereby providing a means to study changes that occur through healthy ageing and disease such as osteoarthritis (OA). As a result, significant research investment has been placed in developing such models of the human knee. Previous work has highlighted that model predictions are highly sensitive to the various inputs used to build them, particularly the mathematical definition of material properties of biological tissues. The goal of this systematic review is two-fold. First, we provide a comprehensive summation and evaluation of existing linear elastic material property data for human tibiofemoral joint tissues, tabulating numerical values as a reference resource for future studies. Second, we review efforts to model tibiofemoral joint mechanical behaviour through FE modelling with particular focus on how studies have sourced tissue material properties. The last decade has seen a renaissance in material testing fuelled by development of a variety of new engineering techniques that allow the mechanical behaviour of both soft and hard tissues to be characterised at a spectrum of scales from nano- to bulk tissue level. As a result, there now exists an extremely broad range of published values for human tibiofemoral joint tissues. However, our systematic review highlights gaps and ambiguities that mean quantitative understanding of how tissue material properties alter with age and OA is limited. It is therefore currently challenging to construct FE models of the knee that are truly representative of a specific age or disease-state. Consequently, recent tibiofemoral joint FE models have been highly generic in terms of material properties even relying on non-human data from multiple species. We highlight this by critically evaluating current ability to quantitatively compare and model (1) young and old and (2) healthy and OA human tibiofemoral joints. We suggest that future research into both healthy and diseased knee function will benefit greatly from a subject- or cohort-specific approach in which FE models are constructed using material properties, medical imagery and loading data from cohorts with consistent demographics and/or disease states

Subject-specific three-dimensional finite element model of the human knee complex

Knee Osteoarthritis (OA) is a common medical condition that necessitates primary care for 1 in 5 adults over the age of 45 only in the UK. This causes functional limitations and decreases the quality of life. The OA is a metabolically active process which involves all joint tissues, i.e. bone, synovium and muscle which causes some symptoms such as persistent knee pain, morning stiffness and reduced functional capabilities. Most of the disability observed in knee OA is mainly because of pain. This mechanism is usually intensified by daily activities and the pain can relax by rest. Therefore, clinicians are interested to analyse this vital component, while accessing the internal structures such as cartilage or the menisci which is impossible in-vivo. Therefore, computational image-based models are effective tools in order to analyse the biomechanical causes of the OA. In this study, a three-dimensional finite element (FE) model of a healthy knee was constructed, using scanned MRI data. Bones, articular cartilages, menisci, patella, patella tendon and all the relevant ligaments were included in the model in their bio-realistic structures. 3D gait measurements were analysed to define loading and boundary conditions. After validation, the 3D finite element model was used to analyse the possibility of osteoarthritis condition and degeneration within the menisci and knee cartilage tissues. It was shown that the medial region of cartilage layers and menisci in the knee joint sustain higher values of stress for the OA conditions, while for the healthy knee, the stresses are more evenly distributed across the cartilage. This suggests that any treatment for knee osteoarthritis should focus more on the medial region of the tibiofemoral cartilage. Furthermore, the analysis of varus condition was added to the developed OA model and the results showed that the varus condition can exacerbate the OA

Osteochondral Grafting: Effect of Graft Alignment, Material Properties, and Articular Geometry

Osteochondral grafting for cartilage lesions is an attractive surgical procedure; however, the clinical results have not always been successful. Surgical recommendations differ with respect to donor site and graft placement technique. No clear biomechanical analysis of these surgical options has been reported. We hypothesized that differences in graft placement, graft biomechanical properties, and graft topography affect cartilage stresses and strains. A finite element model of articular cartilage and meniscus in a normal knee was constructed. The model was used to analyze the magnitude and the distribution of contact stresses, von Mises stresses, and compressive strains in the intact knee, after creation of an 8-mm diameter osteochondral defect, and after osteochondral grafting of the defect. The effects of graft placement, articular surface topography, and biomechanical properties were evaluated. The osteochondral defect generated minimal changes in peak contact stress (3.6 MPa) relative to the intact condition (3.4 MPa) but significantly increased peak von Mises stress (by 110%) and peak compressive strain (by 63%). A perfectly matched graft restored stresses and strains to near intact conditions. Leaving the graft proud by 0.5 mm generated the greatest increase in local stresses (peak contact stresses = 6.7 MPa). Reducing graft stiffness and curvature of articular surface had lesser effects on local stresses. Graft alignment, graft biomechanical properties, and graft topography all affected cartilage stresses and strains. Contact stresses, von Mises stresses, and compressive strains are biomechanical markers for potential tissue damage and cell death. Leaving the graft proud tends to jeopardize the graft by increasing the stresses and strains on the graft. From a biomechanical perspective, the ideal surgical procedure is a perfectly aligned graft with reasonably matched articular cartilage surface from a lower load-bearing region of the knee

Stress distribution of the tibiofemoral joint in a healthy versus osteoarthritis knee model using image-based three-dimensional finite element analysis

This is the final version. Available on open access from Springer via the DOI in this recordPurpose: Osteoarthritis (OA) is one of the most common pathological conditions to affect the human knee joint. In order to analyse the biomechanical causes and effects of OA, accessing the internal structures such as cartilage or the menisci directly is not possible. Therefore, computational models can be used to study the effects of OA on the stresses and strains in the joint and the susceptibility to deformations within the knee joint. Methods: In this study, a three-dimensional finite element (FE) model of a knee complex was constructed using MRI scans. Medical image processing software was used to create accurate geometries of bones, articular cartilages, menisci, patella, patella tendon and all the relevant ligaments. Finally, a 3D model of OA knee joint was created with a few changes to the cartilage. The cartilage was thinned, and the material properties were altered in order to simulate OA in the joint. 3D gait measurements were analysed to define loading and boundary conditions. Results: The developed model analysed the possibility of osteoarthritis. It was shown that the medial regions of cartilage layers and menisci in the knee joint sustain higher values of stress for OA conditions, while for the healthy knee, the stresses are more evenly distributed across the cartilage in the medial and lateral regions. Conclusion: The results suggest that any treatment for knee osteoarthritis should focus more on the medial region of the tibiofemoral cartilage in order not to cause degradation

Regional comparisons of nano-mechanical properties of the human meniscus; structure and function

Osteoarthritis (OA) is a debilitating disease that is becoming more prevalent in today’s society. OA affects approximately 28 million adults in the United States alone and when present in the knee joint, usually leads to a total knee replacement. Numerous studies have been conducted to determine possible methods to halt the initiation of OA, but the structural integrity of the menisci has been shown have a direct effect on the progression of OA. Menisci are two C-shaped structures that are attached to the tibial plateau and aid in facilitating proper load transmission within the knee. The meniscal cross-section is wedge-like to fit the contour of the femoral condyles and help attenuate stresses on the tibial plateau. While meniscal tears are common, only the outer 1/3 of the meniscus is vascularized and has the capacity to heal, hence tears of the inner 2/3rds are generally treated via meniscectomy, leading to OA. To help combat this OA epidemic, an effective biomimetric meniscal replacement is needed. Numerous mechanical and biochemical studies have been conducted on the human meniscus, but very little is known about the mechanical properties on the nano-scale and how meniscal constituents are distributed in the meniscal cross-section. The regional (anterior, central and posterior) nano-mechanical properties of the meniscal superficial layers (both tibial and femoral contacting) and meniscal deep zone were investigated via nanoindentation to examine the regional inhomogeneity of both the lateral and medial menisci. Additionally, these results were compared to quantitative histological values to better formulate a structure-function relationship on the nano-scale. These data will prove imperative for further advancements of a tissue engineered meniscal replacement

Finite element analysis of the meniscectomised tibio-femoral joint: implementation of advanced articular cartilage models

The article presents advanced computer simulations aimed at the accurate modelling of human tibio-femoral joints (TFJs) in terms of anatomy, physiological loading and constitutive behaviour of the tissues. The main objective of this research is to demonstrate the implications that the implementation of different articular cartilage models have on the prediction of the joint response. Several biphasic material constitutive laws are tested using a finite element package and compared to the monophasic linear elastic description, often still used to predict the instantaneous response of the cartilage in 3D knee models. Thus, the importance of adequately capturing the contribution of the interstitial fluid support is proved using a simplified 3D model; subsequently, a biphasic poroviscoelastic non-linear constitutive law is implemented to study the response of a patient-specific TFJ subjected to simplified walking cycles. The time evolution of stresses, pore pressure, contact areas and joint displacements is captured and compared with existing meniscectomised knee models. Contact pressures and areas obtained using the developed numerical simulations are in agreement with the existing experimental evidence for meniscectomised human knee joints. The results are then used to predict the most likely site for the origin of mechanical damage, i.e. the medial cartilage surface for the specific case analysed in the present contribution. Finally, future research directions are suggested

Finite element analysis of the meniscectomised tibio-femoral joint: implementation of advanced articular cartilage models

The article presents advanced computer simulations aimed at the accurate modelling of human tibio-femoral joints (TFJs) in terms of anatomy, physiological loading and constitutive behaviour of the tissues. The main objective of this research is to demonstrate the implications that the implementation of different articular cartilage models have on the prediction of the joint response. Several biphasic material constitutive laws are tested using a finite element package and compared to the monophasic linear elastic description, often still used to predict the instantaneous response of the cartilage in 3D knee models. Thus, the importance of adequately capturing the contribution of the interstitial fluid support is proved using a simplified 3D model; subsequently, a biphasic poroviscoelastic non-linear constitutive law is implemented to study the response of a patient-specific TFJ subjected to simplified walking cycles. The time evolution of stresses, pore pressure, contact areas and joint displacements is captured and compared with existing meniscectomised knee models. Contact pressures and areas obtained using the developed numerical simulations are in agreement with the existing experimental evidence for meniscectomised human knee joints. The results are then used to predict the most likely site for the origin of mechanical damage, i.e. the medial cartilage surface for the specific case analysed in the present contribution. Finally, future research directions are suggested. © 2013 © 2013 Taylor & Francis

Subject-Specific Finite Element Modeling of the Tibiofemoral Joint in Vivo: Development, Verification and Application

A new methodology for subject-specific finite element (FE) modeling of the tibiofemoral (TF) joint based on in vivo computed tomography (CT), magnetic resonance imaging (MRI), and dynamic stereo-radiography (DSX) data is presented. Two techniques to incorporate in vivo skeletal kinematics as FE boundary conditions were implemented and compared: one used MRI-measured tibiofemoral kinematics in a non-weight-bearing supine position and allowed five degrees of freedom at the joint in response to an axially applied force; the other used DSX-measured tibiofemoral kinematics in a weight-bearing standing position and permitted only axial translation in response to the same force. The model-predicted cartilage-cartilage contact areas were examined against ‘benchmarks’ from a novel in situ contact area analysis (ISCAA) in which the intersection volume between non-deformed femoral and tibial cartilage was characterized to determine the contact. The results showed that the DSX-based model predicted contact areas in close alignment with the benchmarks, and outperformed the MRI-based model. The importance of accurate, task-specific skeletal kinematics in subject-specific FE modeling and the necessity of subject-specific verification are discussed. A study of the effects of partial meniscectomy on the intra-articular contact mechanics was then conducted as an illustration of application of the verified models. A musculoskeletal dynamic model was used to generate the knee joint forces as boundary conditions for the above developed FE models. Thus, a sequence of quasi-static position-dependent FE models was developed for a series of time points throughout a decline walking task. These time points include heel-strike and in increments of 0.05 seconds up to 0.30 seconds, and additionally, the time points of the two peak compressive joint force values for each knee. Several factors were observed to measure the effects on intra-articular contact mechanics. The greatest maximum compressive stress was recorded in the partially meniscectomized compartment or in the opposite compartment of the contralateral knee throughout all time points. The significance of the application of the FE models for evaluation of the biomechanical effects of meniscectomy is demonstrated, and the importance of simultaneously observing joint kinematics and intra-articular contact mechanics at more than one time point during a dynamic task is discussed

Human Knee FEA Model for Transtibial Amputee Tibial Cartilage Pressure in Gait and Cycling

Osteoarthritis (OA) is a debilitating disease affecting roughly 31 million Americans. The incidence of OA is significantly higher for persons who have suffered a transtibial amputation. Abnormal cartilage stress can cause higher OA risk, however it is unknown if there is a connection between exercise type and cartilage stress. To help answer this, a tibiofemoral FEA model was created. Utilizing linear elastic isotropic materials and non-linear springs, the model was validated to experimental cadaveric data. In a previous study, 6 control and 6 amputee subjects underwent gait and cycling experiments. The resultant knee loads were analyzed to find the maximum compressive load and the respective shear forces and rotation moments for each trial, which were then applied to the model. Maximum tibial contact stress values were extracted for both the medial and lateral compartments. Only exercise choice in the lateral compartment was found to be a significant interaction (p\u3c0.0001). No other interactions in either compartment were significant. This suggests that cycling reduces the risk for lateral OA regardless of amputation status and medial OA risk is unaffected. This study also developed a process for creating subject-specific FEA models