Observational Study Investigating the Effectiveness of Fentanyl Matrix in Relieving Pain and Improving Function in Patients With Osteoarthritis of the Knee or Hip

Inclusion Criteria: * Patients who complain of chronic pain caused by osteoarthritis of the knee or hip persisting for 3 months or longer * Patients who can fully observe the overall clinical study requirements including K-WOMAC completion at the investigator's discretion * Patients who complain of severe pain (NRS score = 7) because pain was not treated enough with the previous analgesic * Patients who have never been administered strong opioid analgesics over the last one month Exclusion Criteria: * Patients with a history of the drug or alcohol abuse in the past or now * Childbearing women who are pregnant or likely to be pregnant during the study period and male subjects who are neither infertile nor willing to refrain from sexual relations but whose partner does not conduct an effective contraception (implant, injections, oral contraceptives, intrauterine device, etc.) * Patients who are unable to use a transdermal system due to skin disease * Patients with serious mental disorder * Patients with history of hypersensitivity to opioid analgesics * Patients with history of CO2 retention * Patients who are not eligible for the study participation based on warnings, precautions and contra medications in the package insert of the study drug at the investigator's discretion