Pain after amputation is a significant problem among amputees. Phantom limb pain may appear in up to 85% of patients and is usually resistant to a wide variety of treatments.It is believed that regional anesthesia, by preventing the establishment of central sensitization, may play a role in reducing the incidence of acute and chronic pain. Therefore the investigators will compare two methods of postoperative analgesic after after amputation by their efficiency and complication.

Peripheral nerve transection results in an afferent nociceptive barrage that initiates spinal cord hyperexcitability with expansion of the receptive fields of dorsal horn neurons that respond to the nearest intact afferents. These neuroplastic changes are believed to be responsible for the development of postsurgical chronic pain syndromes, including phantom limb and stump pain.At present, there are no randomized studies with sample sizes that ensure power, or blinded for end-point assessment,to support the evidence on pharmacological and non-pharmacological treatments of Pain after amputation. Consequently, our study was designed to arrive at clear conclusions about treatment efficacy and to give stronger recommendations for clinical practice.

Inclusion Criteria:

1. Patients of American Association of anesthetists（ASA）Grade 1 or 2
2. Aged between 18 and 65 years
3. Undergoing elective total knee replacement

Exclusion Criteria:

1. Mental illness can not match
2. Nerve block, epidural anesthesia contraindicated
3. People who have Slow-type arrhythmias
4. History of chronic headaches and long-term use of analgesic drugs
5. People who were postoperative consciousness, language or hearing impaired