This study is being conducted to determine the rate of symptomatic and asymptomatic nonmalignant, noninfective soft tissue mass presence (referred to in the literature as pseudotumour, ALVAL, ARMD, cysts or lesions) in primary metal on metal hip replacement patients. The primary objective of the study is to determine the prevalence of masses in unbiased Metal on Metal (MoM) samples drawn from one study centre. The subjects receiving the Metal on Metal devices will be observed at two specific time points. Secondary objectives are to evaluate whether the occurrence of masses is related to any of several potential factors including patient and implant characteristics and time since the implant procedure took place.

Inclusion Criteria:

• Patients implanted with the M2a Magnum who were evaluated via MRI and metal ion analysis between 2012 and 2013.

Exclusion Criteria:

• If the primary device was implanted for less than 36 months (in the case of patients already revised) or has been in place for less than 36 months (in the case of patients with the device still in place).
• If the patient is contraindicated for any of the diagnostic tests.
• If the patient fails to consent to participating in the study.

Patients receiving either the M2a Magnum or M2a 38mm Metal on Metal primary hip replacement devices from a single study centre.