Relationship between Microstructure and Mechanical Properties of Proximal Tibia in Rats during Aging

Abstract

The proximal tibia, an integral part of the knee joint, undergoes complex structural and mechanical changes as individuals get older. This multifaceted region encompasses layers like cartilage, the epiphysis, the growth plate, and the metaphysis. These changes are often attributed to osteoarthritis (OA), a common joint disorder affecting the elderly. However, the mechanisms behind OA remain poorly understood. Consequently, a complete examination of each layer of the joint and their interactions is essential for a global understanding of the ageing process and the impact of osteoarthritis. This thesis explores microarchitectural and mechanical changes in the trabecular metaphysis due to ageing, using extensive 3D morphometric analyses and finite element modelling. The study also investigates age-related structural changes in the growth plate region. Micro-computed tomography images of rat proximal tibias were used. The trabecular metaphyseal architecture was meticulously characterized. The global morphometric parameter analysis and spatially resolved assessments uncover structural variations within the bone itself and between young and aged samples. The finite element model reveals the elastic behaviour of the region along different directions. Age-related structural changes within the growth plate are also identified through global 3D analysis, including thickness distribution. The variations observed in the architectural features between the lateral and medial metaphyseal regions, as well as the variations along the longitudinal axis, highlight the significant heterogeneity of trabecular bone in this area. This variability underscores the complex bone response to mechanical loads. With age, structural changes increase bone heterogeneity, impacting mechanical behaviour and load-bearing capacity. The coherence between results from structural and finite element analyses emphasis the robust relationship between microarchitecture and mechanical properties. The growth plate also undergoes distinct changes with age, notably densification, involving a loss of structural integrity. This study provides valuable insights into the intricate connection between microstructural variations and mechanical properties within the metaphyseal trabecular bone and growth plate. It highlights the complex adaptation of bone to mechanical demands and emphasises the role of microstructural changes in shaping mechanical behaviour. These findings contribute to our understanding of age-related changes of bone microstructure.