We hypothesize continuous adductor canal block with steroid adjuvant would offer no inferior analgesics and rehabilitation ability than continuous femoral nerve block for postoperative patients receiving total knee arthroplasty.

A total of 80 patients who will undergo total knee arthroplasty will be randomized into two groups:

Treatment groups Treatment details Femoral Group (40 patients) Continuous femoral nerve block (bolus: 0.5% Ropivacaine 10-15 ml ; infusion of 0.15 % Ropivacaine 4-6ml/h) Adductor Group (40 patients) Adductor canal block with steroid adjuvant (bolus: 0.5% Ropivacaine 10-15ml; Dexamethasone 4mg) (Total 80 patients will be recruited)

• All patients will receive single shot tibial nerve block with local anaesthetics (0.5% Ropivacaine 5-8ml) before surgery for analgesia of posterior knee.
• All patients will receive the same preemptive and postoperative multimodal medications for perioperative analgesia.
• All groups will receive standardized method of spinal anaesthesia and standardized method of intraoperative sedation for the surgery.
• Intravenous patient controlled analgesia (PCA) with morphine will be given for 48h to patient as rescue analgesia.

Inclusion Criteria:

• Diagnosis of primary osteoarthritis
• Scheduled for elective total knee arthroplasty
• Signed written informed consent
• Planned use of spinal anaesthesia
• Cognitive sound to use assessment tools

Exclusion Criteria:

• Patients refusing to give consents
• Scheduled for revision total knee replacement
• Patient outside range of 30 to 80 yrs old
• Non-chinese population
• Cognitive impairment/ inability to use the outcome assessment tools
• Contraindications to regional anesthesia
• severe cardiovascular disease (unstable angina, second or third degree heart block)
• pre-existing neurologic disease including psychiatric disorder
• drug abuser
• Pre-operative history of neurological abnormality in the ipsilateral leg e.g. history of stroke, neurogenic pain or previous nerve injury.
• Allergy or contraindication to drugs used in this study: morphine, Non-steroidal anti-inflammatory drugs (NSAID) such as ketorolac , diclofenac, dihydrocodeine, local anaesthetics (lignocaine, ropivacaine, bupivacaine), epinephrine
• Moderate or severe renal impairment (serum creatinine > 160 micromol/l)