Range from 24% to 44%, with a prevalence of neuropathic-type pain from 6% to 20%-cause impairment in quality of life and functional capacity after total knee arthroplasty(TKA). Duloxetine (cymbalta) is a selective serotonin and nor-epinephrine reuptake inhibitor shown to be effective in treating chronic pain. Serotonin and norepinephrine in the brain and spinal cord are believed to both mediate core mood symptoms and help regulate the perception of pain. Its effects on depression and anxiety symptoms, as well as its effect on pain perception, may be due to increasing the activity of serotonin and norepinephrine in the central nervous system. Approved for the acute and maintenance treatment of major depressive disorder, the acute treatment of generalized anxiety disorder, the management of diabetic peripheral neuropathic pain and the management of fibromyalgia, all in adults (18+).

Investigators will compare the neuropathic pain following TKA in duloxetine group (n=84) with those in non-duloxetine group (n=84). Investigators will classify the participants in to 2 groups (duloxetine and non-duloxetine group) randomly, and primarily evaluate the degree of neuropathic pain using the S-LANSS pain scale (preoperatively and postoperatively 3 and 6 months). All participants will receive postoperative pain control after TKA using the same pain control regimen except duloxetine.

Both groups of participants will receive pain control regimens as follows:

Preemptive analgesia : celebrex celecoxib, Patient controlled analgesia (postoperation 28 hours), During admission : celebrex BP or vimovo BP +ultracet ER BP, targin HS, Discharge medication: celebrex BP or vimovo BP, ultracet ER BP(PRN)

Drug generic names: celecoxib (celebrex), naproxen/esomeprazole (vimovo), acetaminophen/tramadol (ultracet ER), oxycodone/naloxone (targin)

Inclusion Criteria:

• Osteoarthritis of knee requiring TKA

Exclusion Criteria:

• Rheumatoid arthritis
• Other inflammatory arthritis
• Neuropsychiatric patients
• Hepatic insufficiency
• Renal insufficiency
• Patients older than 75
• Allergy or intolerance to study medications
• Patients with an ASA of IV (angina, congestive heart failure, dementia, cerebrovascular accident)
• Chronic gabapentin or pregabalin use (regular use for longer than 3 months)
• Chronic opioid use (taking opioids for longer than 3 months)