A study of the mechanical and tribological behaviour of articular cartilage affected by osteoarthritis with particular application to hemiarthroplasty
Creators: name: Ajdari, Niloofar
Publisher: name: Imperial College London
Year: 2016

description: Articular cartilage is a layer of low-friction, load-bearing soft tissue that covers the articulating bony ends in diarthrodial joints (Lu &amp; Mow, 2008). This tissue, has the ability to withstand severe loading regimes while providing a low-friction surface (Katta et al., 2007). It usually undergoes minimal wear during the lifetime of the joint. However, trauma and degenerative joint diseases, such as osteoarthritis, can cause damage to the tissue. Osteoarthritis (OA) is a pathology with a complex etiology, aﬀecting the diarthrodial joints. Morphological, biochemical, structural, and biomechanical changes of the extracellular matrix and the cells are associated with OA, which leads to the degeneration of the articular cartilage (Knecht, Vanwanseele &amp; Stüssi, 2006). Since the functionality of diarthrodial joints cannot be sustained without articular cartilage, the accurate and early diagnosis of the pathology is essential to the prevention or reduction of long-term disability. The functional behaviour of articular cartilage in diarthrodial joints is determined by its morphological and biomechanical properties. Whereas morphological alterations are mainly detectable in the advanced stages of osteoarthritis, biomechanical properties seem to be more sensitive to early degenerative variations since they are determined by the biochemical composition and structural arrangement of the extracellular matrix (Knecht, Vanwanseele &amp; Stüssi, 2006). There is no cure available for OA at present and the pathology is being diagnosed only via imaging methods. Therefore, there is a need to apply fundamental engineering principles to the medical world in order to shed light on the pathogenesis and progression of OA. In this research mechanical and tribological assessments were used to thoroughly characterise the mechanical behaviour of the tissue. Selective mechanical and enzymatical degradation of the AC constituents was then induced to simulate OA, and the effects of different types and stages of degradation on the mechanical and tribological response were investigated. The mechanical properties of osteoarthritic AC with various grades of OA, were then evaluated and compared to OA-like AC in order to correlate similarities in the variations to the structure and the mechanical response as a result of degradation. Quantifying the mechanical response of the tissue at different stages of OA and different levels of degradation was done to provide both a thorough understanding of the effect of the pathology’s progression on AC as well as to provide a potential tool for future diagnosis of OA via mechanical parameters rather than morphological ones alone. Having investigated the tribological and mechanical properties of OA and OA-like AC, the second part of the study focused on one of the current solutions for OA, hemiarthroplasty (HA), in an attempt to contribute to the improvement of the outcome of the operation. A key factor in determining the longevity of the implant is the friction properties of the material used as a counter-surface in contact with AC and their effect on the mechanical characteristics of the tissue. Therefore, in this study, the frictional and mechanical response of articular cartilage when loaded against three implant biomaterials-cobalt-chromium alloy, ceramic (Al2O3) and polymer (polycarbonate-urethane)-were investigated and critically assessed.