The purpose of this study is to determine whether intrathecal morphine (ITM) alone or its combination with peripheral nerve blocks (PNB) provides better analgesia for patients undergoing total knee arthroplasty (TKA).

Total knee arthroplasty (TKA) surgery is associated with severe pain. The success of knee rehabilitation following surgery depends largely on adequate pain control that permits early physical therapy. Postoperative modern analgesic recommendations specific to TKA propose either spinal block with intrathecal morphine (ITM) or a combination of general anesthesia with single shot femoral nerve block (SFNB). Femoral nerve block (FNB) too has proven analgesic advantages in TKA surgery. However, we do not know if the combination of the two analgesic techniques, ITM and peripheral nerve blocks (PNB), provides superior analgesia to ITM alone.

Thus, this study aims to determine whether ITM alone or its combination with PNB provides better analgesia for patients undergoing total knee arthroplasty (TKA).

Eligible patients undergoing unilateral TKA under spinal anesthesia consenting to a multimodal analgesic regimen inclusive of ITM, FNB, and SNB will be recruited. All patients will receive spinal with intrathecal morphine. Patients will be randomly assigned using a computer generated table of random numbers to receive either spinal with intrathecal morphine (morphine group), a combination of intrathecal morphine and femoral nerve block (morphine-femoral group), or a combination of intrathecal morphine and femoral nerve block as well as sciatic nerve block (morphine-femoral-sciatic group).

Inclusion Criteria:

• ASA I-III patients undergoing unilateral TKA under spinal anesthesia and nerve blocks
• Ages 18-80
• BMI ≤ 38 kg/m2

Exclusion Criteria:

• BMI > 38 kg/m2
• chronic pain disorders
• Significant pre-existing neurological deficits or peripheral neuropathy affecting the lower extremity
• abuse of drugs or alcohol
• Contraindication to a component of multi-modal analgesia
• Contraindication to spinal anesthesia or failure to institute spinal anesthesia after performing femoral and sciatic blocks
• Bilateral TKA surgeries
• History of significant psychiatric conditions that may affect patient assessment
• Pregnancy
• Moderate to severe obstructive sleep apnea.
• Previous adverse reactions resulting from intrathecal opioids (respiratory depression, urinary retention, severe pruritis, severe nausea or vomiting, severe sedation)
• inability to provide informed consent.