Because the principle investigator will participate a visiting scholar program for one year in other country, this study has been terminated.

With ongoing advancements in healthcare leading to prolonged life expectancy, orthopedic surgeries are increasingly performed in elderly patients. Total knee arthroplasty, in particular, has been increasing with the growing demand for improved mobility and quality of life. Total knee arthroplasty is performed on patients with advanced and painful osteoarthritis of the knees, but it can result in moderate to severe postoperative pain during the recovery period.

To relieve anxiety or stress during surgery under regional anesthesia, sedation can be provided. Dexmedetomidine is a sedative-analgesic agent acting as α2-adrenergic receptor agonist, and its analgesic effect has been well established in various procedures or surgeries.

Magnesium has been reported to produce important analgesic effects including the suppression of neuropathic pain, potentiation of morphine analgesia, and attenuation of morphine tolerance. Although the exact mechanism is not yet fully understood, the analgesic properties of magnesium are believed to stem from regulation of calcium influx into the cell and antagonism of N-methyl-D-aspartate (NMDA) receptors in the central nervous system. In this study, investigators will evaluate the reducing effect of magnesium on the post-total knee arthroplasty pain in patients sedated with dexmedetomidine under spinal anesthesia.

Inclusion Criteria:

• Patients who undergo total knee arthroplasty under spinal anesthesia
• Patients who want to sedation during the surgery
• American Society of Anesthesiologists physical status classification 1 and 2

Exclusion Criteria:

• General anesthesia
• Patients who do not want to sedation during the surgery
• Patients who do not receive patient controlled analgesia postoperatively
• Muscular disease
• Hypermagnesemia
• Atrioventricular block