Pain, confusion, and breaks in normal sleep cycles have been challenges commonly faced by patients after undergoing joint surgeries. To address these issues, melatonin, an inexpensive over-the-counter supplement, has shown in previous to help manage sleep disorders, prevent and treat post-operative confusion in patients over 70 years of age, and reduce pain. The purpose of this study is to establish whether melatonin can aid in reducing pain and post-operative confusion and improve sleep quality after total knee replacement

Sleep disruption is a challenge commonly faced by patients and care providers in the perioperative period [1,2] and has been shown to affect postoperative performance after total knee arthroplasty [3] . Postoperative sleep disruption is likely influenced by environmental factors [4] and anesthetic exposure [5,6] and is known to be exacerbated by postoperative pain [7] . In a reciprocal manner, sleep disruption has been shown to exacerbate pain perception [8,9] .

Melatonin is an inexpensive over-the-counter dietary supplement with an established safety profile [10] that has shown promise in managing sleep disorders and amelioration of chronic and acute pain. Evidence suggests that exogenous melatonin can be efficacious in improving sleep disruption in tracheostomized patients in the ICU [11] as well as those experiencing jet lag [12,13] .

Previous studies have found conflicting results regarding the potential for melatonin to improve sleep and pain in the perioperative period [14] . These discrepancies may result from differences in surgical and anesthetic conditions, differences in melatonin dose and administration regimens, variations in study quality, different methods of assessing pain and sleep quality, and different patient populations. There is no consensus as to what dose, duration, and timing of melatonin administration in the perioperative period are most likely to improve sleep quality or quantity. This study was designed to explore the effect of a stable regimen of exogenous perioperative melatonin, administered over 6 consecutive nights, on postoperative pain, sleep quality, and sleep efficiency in patients undergoing total knee arthroplasty under regional anesthesia with sedation. To our knowledge, this study is the first to examine perioperative subjected sleep quality as well as sleep time and efficiency as measured by the validated objective tool of wrist actigraphy in this population.

This study examined the hypotheses that sleep disruption occurs in the context of total knee arthroplasty performed under regional anesthesia with sedation and that perioperative melatonin can modulate pain and sleep disruption after total knee arthroplasty.

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Inclusion Criteria:

• Patients 18-90 years old undergoing elective, primary total knee replacement
• American Society of Anesthesiologists (ASA) Physical Status I-III
• Epidural anesthesia/Patient Controlled Analgesia candidate

Exclusion Criteria:

• Mental impairment
• Pre-operative use of benzodiazepines, narcotics, or prescription/over-the counter (OTC) sleep aids
• Pre-operative use of calcium channel blockers
• Insomnia
• Recent drug or alcohol abuse
• Psychiatric disorders other than anxiety, including depression
• Diabetes