In-vitro characterisation of articular cartilage with application to hemiarthroplasty

Abstract

Osteoarthritis (OA) is a common form of arthritis that causes joint degradation and affects one in five adults over 45 years of age in the UK. It is characterised by chronic and irreversible degeneration of articular cartilage (AC). Hemiarthroplasty (HA) is a surgical procedure, where the diseased cartilage on one side of the joint is replaced with an implant, while the other side remains intact. The main aim of this study is to analyse the mechanical and frictional response of different shoulder humeral component materials against the natural glenoid. This has been developed as a two-stage process. In a simple geometry HA model, the cartilage coefficient of friction, mechanics and wear have been examined in a pin-on-plate cartilage testing device. In the first stage of this study, friction and wear properties of four different grades of human osteoarthritic AC were measured using pin-on-disc technique against three major types of implant materials used in hemiarthroplasty including Cobalt-Chromium (Co-Cr), Ceramic (Al2O3) and Polycarbonate-urethane (PCU) polymer. Mechanical and frictional properties of the samples were characterised by compression, shear tests and surface roughness measurements using white light interferometry (WLI). Results indicated that at the same stage of OA, the cartilage tribological and mechanical properties deteriorated when using Co-Cr. The second stage of this study focuses on creating a more anatomically realistic model of the hemi-replaced shoulder joint and assesses the cartilage frictional behaviour for both healthy and enzymatically digested AC. A custom-made joint simulator has been built and has been used to investigate the response of shoulder joints under representative loads. The glenoid has been tested against different humeral component materials to understand the friction/wear response of the cartilage. The correlation between enzymatically damaged and healthy cartilage has been investigated. Histological analysis will be performed on the tissue to observe any structural changes due to wear. The results from this study can aid the surgeons to choose the best possible material for hemiarthroplasty according to the disease state of the patient. In the joint simulation of HA, the cartilage coefficient of friction, surface roughness has been studied for both metal and ceramic humeral heads articulating against glenoid cartilage in a pendulum friction simulator. It was demonstrated that: 1) The coefficient of friction increased when metal implants were used compared to ceramic. 2) The COF was higher for enzymatically digested AC compared to healthy samples. 3) Ceramic heads produced lower surface roughness parameters compared to metal implant. The methodologies and findings obtained in this thesis have opened a new line of research and can be adopted for related future studies; additionally, the anatomic pendulum friction natural joint simulation could be used for pre-clinical studies in less invasive procedures.