The aim of the study is to assess the ideal bearing surfaces in hip replacement by comparing 4 different combinations. In a hip replacement this means what the head and the socket liner are made of.

In hip replacements, arguably the most important thing for survivorship is what rubs against what.

Traditionally surgeons used metal (Cobalt-Chrome) against a conventional polyethylene (plastic). More recently (around 15 years ago) a newer more dense type of polyethylene (called XLPE) had been developed and a new type of head called Oxidized Zirconium was also developed.

In this trial, adults who were undergoing hip replacements were randomized assigned into one of the four groups:

Group 1: old plastic vs metal head Group 2: Old plastic against Oxidized Zirconium Group 3: New plastic versus metal head Group 4 New plastic vs Oxidized Zirconium

All patients were followed up for a minimum of 10 years to assess which group wore the most amount of polyethylene and which group had the best survival rate.

Inclusion Criteria:

• All adults with no history of cancer, infection of the hip and with the capacity to make informed consent for the trial

Exclusion Criteria:

• those under the age of 18 and over 65. Those with a history of cancer and infection. Those without the capacity to make an informed consent.

The assessment of the implants was done by a secondary center that was unaware of which the bearing type was in which patient.