 Sound will be recorded by means of a wearable sensor set capable of recording the articular noise produced during level walking. This instrumentation will be coupled to motion analysis technology, so as to provide a temporal correlation between the recorded noise and the gait cycle. It will be developed in the first phase of the project. In parallel surface analyses will be conducted on retrievals that are stored in the Lab since 2000, in one of the biggest retrieval study ever conducted in our country. Type of damage, surface roughness of both ceramic components will be analysed and compared to clinical data. 