Bilateral Total Knee Arthroplasty vs Unicompartment Arthroplasty Retrospective and Clinical Outcome Study

Inclusion Criteria: 1. Must be able to read, understand and provide written informed consent on the Institutional Review Board (IRB) approved Informed Consent Form (ICF) 2. Ability to understand and provide written authorization for use and disclosure of personal health information 3. Subject who are able and willing to comply with the study protocol and follow-up visit 4. Must be 18 years or older to participate 5. Subjects must have a clinically documented osteoarthritis in both knees, single or multiple compartments 6. Subjects must have undergone a primary TKA and primary UKA in the contralateral knee 7. Must be a minimum 2 year (24 months) post-surgery on each knee 8. One or both TKA/UKA surgeries must have been performed by the Principal Investigator. 9. Subjects must be able to return for the follow-up appointment, and have the mental capacity to cooperate with PRO's, questionnaires, physical exam and radiographs Exclusion Criteria: 1. Subjects who underwent UKA with Patella Femoral Joint (PFJ) replacement on the same side. 2. Women who are pregnant