TKA Melatonin and Sleep Quality

This study will compare postoperative sleep quality in two groups of patients undergoing primary total knee arthroplasty (TKA): * Group 1 will take one melatonin (5 mg) tablet nightly, \~30 minutes before bedtime during the 6 week postoperative period * Group 2 will take one placebo (5 mg Vitamin C) tablet nightly, \~30 minutes before bedtime during the 6 week postoperative period The primary outcome will be sleep quality at 6 weeks. Sleep quality will be measured using the Pittsburgh Sleep Quality Index (PSQI). The survey will be administered preoperatively, 6-weeks, 90-days and 1 year postoperatively. Preoperative surveys will be completed in-person, on-site by study participants. All postoperative surveys will be distributed via email. Secondary outcomes include: * (KOOS Jr, LEAS, VR-12, VAS) administered preoperatively, at 6-weeks, 90-days and 1-year post-operatively. * Total opioids prescribed in first 3 months postoperative will be collected using iStop * Frequency of CMS defined surgicalcomplications in the first 90-days after primary TKA. * Adverse events of Melatonin during the first 6 weeks (collected via email survey sent to participants once per week, for the first 6 weeks) * Study medication compliance at 6 weeks (collected via email survey sent to participants once per week, for the first 6 weeks)