Total knee arthroplasty surgery is associated with severe postoperative pain and adequate pain management is necessary for early postoperative mobilization and rehabilitation. Although good postoperative pain control may be achieved by continuous epidural anesthesia or femoral nerve block, both methods have adverse effects such as muscle weakness, which may delay postoperative mobilization.

The adductor canal block (ACB) is a relatively new block providing analgesia for knee surgery, which not only blocks the largest sensory branch of the femoral nerve but also results in less reduction of quadriceps muscle strength, compared with the femoral nerve block (FNB) in adult patients.

Randomized controlled trials have revealed that ACB provides at least equal analgesia as FNB, preserves quadriceps muscle strength better than FNB, and thus allowing for functional recovery within the first 24-hour post-TKA. However, one important limitation of single-shot peripheral nerve block is the short duration of analgesia. Because the average duration of severe pain after TKA takes 2-3 days, a continuous ACB via catheter would seem to be a good choice. Unfortunately, perineural catheters may be technically difficult to insert, are prone to premature dislodgement, and may increase infection risk. There also were some case reports of local anesthetic-induced myotoxicity after continuous ACB.

Inclusion Criteria:

• ASA physical status I or II
• undergoing elective primary total knee arthroplasty surgery under spinal anesthesia.

Exclusion Criteria:

• Patients with a known history of significant hepatic,
• renal, heart disease, autoimmune disease,
• any known convulsive disorder, any psychiatric disorders, chronic pain,
• pregnant females, regular use analgesics, anti-depressants, or opioids in the previous 2 months, revision surgery, morbid obesity, allergy to local anesthetics or morphine