Total knee arthroplasty is a commonly performed orthopaedic surgery for the treatment of end-stage osteoarthritis when conservative management becomes ineffective. TKA is associated with significant acute postoperative pain and many patients experience severe postoperative pain despite the use of multimodal analgesia. Poor acute postoperative pain control impacts rehabilitation, prolongs recovery and increases opioid consumption and chronic post-surgical pain.

Liposomal bupivacaine (Exparel, Pacira Pharmaceuticals Inc, Parsippany, New Jersey, USA) is a multivesicular formulation of bupivacaine that prolongs drug release and can extend the duration of analgesia. The adductor canal block (ACB) has been shown to reduce pain intensity and opioid consumption after total knee arthroplasty. The use of liposomal bupivacaine in the adductor canal block has recently been FDA-approved. However, the results of its efficacy from existing clinical trials have been mixed. In addition, the doses in the clinical trials have been different, and the optimal dose for perineural application of liposomal bupivacaine is unclear, including for the adductor canal block.

In this project, the investigators propose to conduct a randomized controlled trial to investigate the effect of different doses of liposomal bupivacaine in the adductor canal block on acute postoperative pain intensity and opioid consumption after robotic assisted total knee arthroplasty. The investigators will also assess secondary outcomes including knee functional scores, chronic pain and quality of recovery.

Inclusion Criteria:

• ASA I-III
• Age 18-80 years old
• Scheduled for elective primary unilateral total knee arthroplasty (TKA) with robotic surgery
• Able to speak and understand Cantonese or Mandarin or English
• Able to provide informed oral and written consent

Exclusion Criteria:

• Revision TKA
• Single-stage bilateral TKA
• Complex primary TKA requiring use of stem/augment/constrained liner
• Surgeries with significant intraoperative complications which may alter rehabilitation protocol eg collateral ligament injury, fracture requiring fixation
• Known allergy to opioids, local anaesthetic drugs, paracetamol, non-steroidal anti-inflammatory drugs (NSAIDS) including COX-2 inhibitors
• History of chronic pain other than chronic knee pain
• History of immunosuppression
• Chronic use of glucocorticoids
• Chronic opioid use (morphine, fentanyl, hydromorphone, ketobemidone, methadone, nicomorphine, oxycodone, or meperidine)
• History of congestive heart failure (NYHA 2)
• Alcohol or drug abuse
• Impaired renal function (defined as effective glomerular filtration rate < 30ml/min/1.73m2
• Impaired liver function (defined as plasma bilirubin over 34mol/L; international normalized ratio [INR] >= 1.7, alanine aminotransferase [ALT] over 100U/L, aspartate aminotransferase [AST] over 100U/L)
• Coagulopathy (platelet count <100,000/ml and/or INR >= 1.5) or the use of anticoagulants (not including aspirin) that precludes the use of adductor canal blocks
• Pre-existing neurological or muscular disorders
• Psychiatric illness
• Impaired mental state
• Pregnancy
• Local infection
• On immunosuppressants
• High body mass index (BMI) (>=40)
• Patient refusal for regional nerve blocks or to conduct clinical trial