Patients being treated for metal on metal acetabular revision surgery by a physician at OrthoCarolina, PA will be screened for eligibility. These patients will be approached by their surgeon and asked to volunteer their participation in the study. Potential subjects will meet with a research coordinator to discuss details of the study and those you volunteer participation will be asked to sign an informed consent prior to the collection of study data. . Basic demographic information (initials, age, gender, height, weight, BMI), dates of original index surgery, reason for revision, type of implant being removed, and standard of care cobalt and chromium metal ion levels will be collected via chart review.