Open-label Milnacipran for Persistent Knee Pain One Year After Total Knee Arthroplasty (TKA)

Inclusion Criteria: 1. Subject is a male or female adult outpatient age 18 or older at the time of consent. 2. Subject has chronic persistent pain 1 year after TKA without history of new injury, infection, or implant failure. 3. Subject has VAS \> or = 40 mm at screen and baseline visits. 4. Subject has an understanding, ability and willingness to fully comply with study procedures and restrictions. 5. Subject has the ability to provide written, personally signed and dated informed consent to participate in the study, in accordance with the International Conference on Harmonisation (ICH) Good Clinical Practice (GCP) Guideline E6 and applicable regulations, before completing any study-related procedures. Exclusion Criteria: 1. Subjects unable to complete assessments due to language or cognitive impairment 2. Subjects with a history of bipolar disorder or psychosis as confirmed by the Mini International Neuropsychiatric Interview (MINI). 3. Subject currently has (or had a history within the last 6 months of) a drug dependence or substance abuse disorder according to Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition Text Revision (DSM-IV-TR) criteria (excluding nicotine). 4. Subjects who are currently considered a suicide risk, any subject who has previously made a suicide attempt or who has a prior history of or are currently demonstrating active suicidal ideation. 5. Subject has any clinically significant ECG or clinically significant laboratory abnormality (including a positive urine drug screen) at Screening. 6. Subject has a concurrent chronic or acute illness, disability, or other condition that might confound the results of safety assessments administered in the study or that might increase risk to the subject. Similarly, the subject will be excluded if he or she has any additional condition(s) that in the Investigator's opinion would prohibit the subject from completing the study or would not be in the best interest of the subject. This would include any significant illness or unstable medical condition that could lead to difficulty complying with the protocol. 7. Subjects who do not agree to use adequate and reliable contraception throughout the study. 8. Subject previously completed, discontinued or was withdrawn from this study. 9. Subject has taken an investigational drug or taken part in a clinical trial within 30 days prior to Screening. 10. Subjects treated with antidepressant medication within 4 weeks of screening visit (6 weeks for fluoxetine). 11. Subjects with known sensitivity to milnacipran. 12. Subjects with liver disease or reduced liver function 13. Subjects with obstructive uropathies 14. Subjects who consume alcohol in amounts viewed by the Investigator to be contraindicated 15. Subjects taking monoamine oxidase inhibitors 16. Subjects with uncontrolled narrow angle glaucoma 17. Subjects who are pregnant, may become pregnant, or who are nursing 18. Subjects with seizure disorders 19. Subjects with bleeding disorders or use of other medications that may cause bleeding.