An Extension Study of Duloxetine in Osteoarthritis and Knee Pain (Extension of F1J-JE-HMGX, NCT02248480)

Inclusion Criteria: (Consecutive Participants) * Participants who have completed the 15-week treatment in the preceding study HMGX. (New Participants) * Participants with present osteoarthritis (OA) based on American College of Rheumatology (ACR) classification of idiopathic OA of the knee. * Have pain for ≥14 days of each month for 3 months prior to study entry. * Have a score of ≥4 on the BPI average pain score at the start of the study. (Consecutive and New Participants) * Females of child-bearing potential must test negative (-) on a pregnancy test. Exclusion Criteria: (New Participants) * Participants who have any previous diagnosis of psychosis, bipolar disorder, or schizoaffective disorder. * Participants who have major depressive disorder as determined using depression module of the Mini-International Neuropsychiatric Interview (M.I.N.I.). * Participants who have received intrarticular hyaluronate or steroids, joint lavage, or other invasive therapies to the knee in the past 1 week. * Participants who have had knee arthroscopy of the index knee within the past year or joint replacement of the index knee or osteotomy at any time. * Participants have a prior synovial fluid analysis showing a white blood cell (WBC) ≥2000 cubic millimeters (mm3) that is indicative of a diagnosis other than OA. * Participants who have a history of having more than one medical allergy. * Are non-ambulatory or require the use of crutches or a walker. * Have frequent falls that could result in hospitalization or could compromise response to treatment. * Have a history of drug abuse or dependence within the past year, including alcohol and excluding nicotine and caffeine. * Have a positive urine drug screen for any substances of abuse or excluded medication. * Have received administration of another investigational drug within the 30 days prior to enrollment. * Have had previous exposure to duloxetine or completed/withdrawn from any study investigating duloxetine. (Consecutive and New Participants) * Participants who have serious cardiovascular, hepatic, renal, endocrine, respiratory, or hematologic illness, peripheral vascular disease, or other medical condition or neuropsychiatric conditions or clinically significant laboratory abnormalities or electrocardiographic abnormalities. * Participants who have alanine aminotransferase (ALT) or aspartate aminotransferase (AST) higher than 100 international units per liter (IU/L) or total bilirubin higher than 1.6 milligrams/deciliter (mg/dL). * Participants having serum creatinine level higher than 2.0 mg/dL, or had renal transplantation or receiving renal dialysis. * Participants who have a diagnosis of inflammatory arthritis (that is, rheumatoid arthritis) or an autoimmune disorder (excluding inactive Hashimoto's thyroiditis and Type 1 diabetes). * Participants who have uncorrected thyroid disease, uncontrolled narrow-angle glaucoma, history of uncontrolled seizures, or uncontrolled or poorly controlled hypertension. * Participants who have end stage bone disease or surgery planned during the trial for the index joint. * Participants treated with a monoamine oxidase inhibitor (MAO) within 14 days prior to baseline, or those with the potential need to use MAO inhibitor during the study or within 5 days of discontinuation of investigational drug. * Participants who answer 'yes' to any of the questions about active suicidal ideation/intent/behaviors occurring within the past month (Columbia-Suicide Severity Rating Scale, suicide ideation section-questions 4 and 5; suicidal behaviors section). * Have a primary painful condition that may interfere with assessment of the index joint, i.e., knee. * Pregnant participants, female participants who wish to be pregnant during the clinical study period, or participants who are breast-feeding; or male participants who wish pregnancy of the partner. * Participants who cannot use appropriate contraceptive method or do not want to use that from the start of the study until one month after the end of administration of the investigational drug. * Considered as inappropriate participation to the study for any medical or other reason by the investigator.