Knee replacement surgery for osteoarthritis is a commonly performed procedure in Canada with 75,000 of these surgeries performed each year. Success rate for knee replacement surgery is high but more than 20% of patients are still dissatisfied mainly due to reports of ongoing pain. Pain control following knee surgery is important in order to allow patients to engage in recovery and rehabilitation. The current standard of pain management after surgery centers around the use of opioids which is a concerning practice as highlighted by the opioid epidemic. Duloxetine is an antidepressant that has pain relieving properties and it has been studied in patients undergoing knee replacement surgery. Studies to date have not been designed optimally to demonstrate the full effects of opioid dose reduction and the use of duloxetine as a medication following knee replacement surgery. This research study seeks to start duloxetine before surgery, at the recommended therapeutic dose, and for the duration of the early rehabilitation period. If the study is successful, this low-cost medication can improve satisfaction rates and change the standard way the pain management is typically carried out for patients undergoing the knee replacement surgery.