This is a pilot open-label, non-randomized, single institution study of BMAC administration in patient's with moderate to severe osteoarthritis of the knee who will undergo total knee replacement. Several weeks prior to total knee replacement, patients will have a sample of bone marrow taken from their pelvic region and concentrated using an investigational device called the Arthrex Angel Concentrated Platelet Rich Plasma (cPRP) System also known as the Angel System. The concentrated bone marrow will be immediately delivered back to the patient arthroscopically to the knee of interest. Blood and tissues samples will be collected at scheduled visits for molecular and histological analysis. Adverse events will be monitored throughout the trial. Assessment of healing will be performed by physical exam and standardized questionnaires related to the health of the patient.