Tribological characterization and in-silico wear assessment of lower limb joint prosthesis

Hip and knee articulations are the main joints in human body and they have the duty of sustaining heavy loads. This task is normally well performed by a healthy joint but, in some cases, the occurrence of diseases can affect the functionality of the joint: when ambulation is limited, surgery is required. Even if the orthoprosthesis is one of the most effective and successful surgical procedure in the modern medicine, around the 10% of the implanted devices will fail and so require a second surgery. The revision operation is a difficult procedure which needs a long scheduling prior to surgery. Currently, hip and knee joint prostheses are analysed and subjected to simulation tests before receiving the required approval for clinical use. These tests are performed with the aim of establish the behaviour of the prosthesis, assess the wear rate of the components and the surface finishing. However, wear tests on a simulator are long and expensive due to the large number of cycles at low frequency that must be executed. The idea was to move toward an in-silico wear assessment. In order to define which are the most influencing parameters on the tribology of the implants it was investigated the Metal Transfer. It is a migration phenomenon of metal particles found on femoral heads and on acetabular cups of retrieved ceramic hip prostheses, which implies an important alteration of the bearing surface. The presence of transferred metal on ceramic heads changes the surface properties and thus affects lubrication, friction and wear. They were studied 35 ceramics femoral heads of different materials, including zirconia, Biolox® Delta, Biolox® and Biolox® Forte. Differences in surface characteristic appear, as an evidence of the phenomenon, between the affected and unaffected areas... [edited by Author]