Aim of the study To investigate whether auricular acupuncture (AA) will reduce postoperative pain and analgesic requirement in comparison with sham AA in patients after elective knee arthroplasty

Design Prospective randomized controlled blinded clinical trial

Participants:

• Patients < 80 und > 50 years old
• scheduled for knee arthroplasty under general anesthesia with < 120 minutes duration
• Without previous opioid medication
• Able to give informed consent

Outcome measures

• Postoperative analgesic requirement
• Incidence of side effects
• Physiological parameters

Inclusion Criteria:

1. Patients with an American Society of Anesthesiologists physical status of I to III scheduled for elective knee arthroplasty under general anesthesia
2. Surgery time does not exceed 120 minutes
3. Patients without previous opioid medication
4. Patients ranged 50-80 years old
5. Patients who have given written informed consent

Exclusion Criteria:

1. Recidivist alcoholics
2. Local auricular skin infection
3. Age < 50 and > 80 years
4. Surgery time more than 120 minutes
5. Intraoperative complications (bleeding, required blood transfusion more than 6 units of packed cells, cardiovascular instability, required catecholamines)
6. Patients who consumed opioid medication at least 6 months before surgery
7. Patients with prosthetic or damaged cardiac valves, intracardiac and intravascular shunts, hypertrophic cardiomyopathy and mitral valve prolaps (risk of bacterial endocarditis according to guidelines of AHA)
8. Patients who are unable to understand the consent form
9. History of psychiatric disease