A Validated Necrosis Assay to Determine the Need for Revision Surgery in Metal-on-metal Total Hip Arthroplasty

Inclusion Criteria: * Patients presenting for a metal on metal hip revision who have cobalt and chromium metal ion levels tested within 6 months of the date of the planned revision surgery. * Patients presenting for a metal on poly hip revision * Revision hip patients must be greater than one year postoperative * The diagnosis at the time of the index, or primary, hip replacement was osteoarthritis. * Patients who have hip osteoarthritis but have not had a total hip surgery (control) Exclusion Criteria: * Patients presenting for a metal on metal hip revision who have cobalt and chromium metal ion levels tested \>6 months of the date of the planned revision * Patients with a total hip on the contralateral side. * Patients with a prior history of periprosthetic infection * Revision cases where the diagnosis at the time of the index, or primary, hip replacement was not osteoarthritis. * Prisoners * Patients not willing to consent for the proposed treatment * Patients with an altered mental status * Active, concurrent metastatic infection * Active, superficial infection * Patients presenting for a metal on poly hip revision to treat trunionosis