Percentage of patients 18 years of age and older who completed a baseline and, within the reporting period of Jan. 1, 2018 - Dec.31, 2018, a follow-up patient-reported knee functional assessment (eg. IKDC, KOOS, KOOS-PS, KOOS Jr. Oxford Knee, Kujala, or equivalent CAT assessment if available) to measure improvement. The use of Patient Reported Outcomes (PROs) in clinical research is well documented.