Abstract: Patient-specific finite element models of human knee joint have been extensively developed to understand the contact mechanics of the joint. For simplicity, the tissues are widely considered as elastic solids, even fluid pressurization in cartilage and meniscus is essential for the load sharing and redistribution in the joint and for the homeostasis of the tissues. Recent development in constitutive modeling yet needs to be implemented in joint modeling. Fibril reinforcement and fluid pressure were introduced in 3D knee joint models in the last decade. The time-dependent response of the joint, including creep and relaxation of the joint produced by the soft tissues, can be now determined within a reasonable time using high-performance computing. The in-vivo creep response of human knee joint can be even measured with advanced medical imaging to validate the finite element model. Concerns remain pertaining the reliability of constructed joint geometry and finite element solutions, which may be resolved with advances in imaging, imaging processing and new algorithms in the finite element solvers. Future patient-specific knee models may combine stress/strain analysis and simulation of mechanobiology, which can then be used to understand and possibly predict, e.g., the onset of knee osteoarthritis, or the outcome of physiotherapy.

Key Words: Articular cartilage, Contact mechanics, Fibril reinforced model, Fluid pressure, Poromechanics

in Cartilage Tissue and Knee Joint Biomechanics, Elsevier / Academic Press, 2023 September 18, ISBN: 978-0-323-90597-8

Chapter 16: 16.1. Introduction  /  16.2. Methods: 16.2.1 General modeling process; 16.2.2 Modeling fluid pressurization in cartilaginous tissues within joint contact; 16.2.3 Model verification and validation; 16.2.4 Model development workflow  /  16.3. Applications of knee joint models  /  16.4. Expectations and challenges  /  16.5. Concluding remarks  /  111 references

The mechanics of articular cartilage has been intensively studied with increasing modelling work since the initial biphasic model was born in 1980. Researchers tried over two decades to understand why the early versions of the biphasic models could not capture the great transient load response that had been observed in experiments. Another long-standing argument was the mechanism that dominates the transient response of articular cartilage: the fluid-pressure or the inherent viscoelasticity of the solid matrix? A recent focus seems to be modelling the cell mechanics in articular cartilage in the realm of continuum mechanics. The purpose of this chapter is to introduce fundamental theories and address some common issues in the mechanical modelling of articular cartilage.

Key words: articular cartilage mechanics, biphasic model, fibril-reinforced model, poromechanical behaviour, strain-rate dependence, viscoelasticity

In Computational modelling of biomechanics and biotribology in the Musculoskeletal System - Biomaterials and tissues

Elsevier Science, 2020 April 08, 2nd edition (ISBN: 978-0-85709-661-6)

Baaba S Otoo, LePing Li, David A Hart, Walter Herzog

Journal of Biomechanical Engineering, http://doi.org/10.1115/1.4051922

Cartilage tissue covers the ends of the bones which make up knee joints. This cartilage is not connected to any blood supply and depends on genes in its cells to produce the needed proteins for maintenance. These genes are expressed in response to loading of our knee joints during everyday activities. Cartilage has an uneven surface with some parts more prone to defects suggesting these genes may be expressed differently at different sites. We developed a method to assess how the genes of some core proteins implicated in osteoarthritis are expressed at different locations when the cartilage is loaded naturally.

Sabri Uzuner, LePing Li, Serdar Kucuk, Kaya Memisoglu

Journal of Biomechanical Engineering, https://doi.org/10.1115/1.4047343

The menisci play a vital role in knee mechanical function. Unfortunately, meniscal tears often occur, which require meniscectomy and cause mechanical changes in the knee leading to osteoarthritis. We used computer models to predict the altered knee mechanics after medial meniscectomies, focusing on fluid pressure changes in cartilage and meniscus. We found medial meniscectomies caused an imbalance of load support between the medial and lateral compartments of knee. Furthermore, the load is continuously transferred between cartilage and meniscus during static standing due to fluid pressure changes. Our results may be used to understand meniscal tear and surgical consequence.