What is the role of spinal anesthesia in total knee arthroplasty?

Spinal Anesthesia for Total Knee Arthroplasty

Neuraxial anesthesia, specifically spinal anesthesia, is the preferred anesthetic technique for total knee arthroplasty due to its association with significantly lower complication rates and improved outcomes compared to general anesthesia. 1

Benefits of Spinal Anesthesia for TKA

• Spinal anesthesia is associated with significantly reduced odds of multiple complications compared to general anesthesia for knee arthroplasty, including:

  • Lower pulmonary complications (OR: 0.69,95% CI: 0.58-0.81) 1
  • Reduced acute renal failure (OR: 0.73,95% CI: 0.65-0.82) 1
  • Decreased deep venous thrombosis (OR: 0.77,95% CI: 0.64-0.93) 1
  • Lower infection rates (OR: 0.80,95% CI: 0.76-0.85) 1
  • Reduced blood transfusion requirements (OR: 0.84,95% CI: 0.82-0.87) 1

• Spinal anesthesia leads to significantly lower postoperative opioid requirements compared to general anesthesia, with clinically relevant reductions in opioid dosages 2

• Patients receiving spinal anesthesia experience less pain in the early postoperative period compared to those receiving general anesthesia 2, 3

Optimal Spinal Anesthetic Technique

• For standard TKA procedures, low-dose spinal bupivacaine (5-10 mg) is effective and facilitates faster recovery room discharge compared to higher doses 4

• Mepivacaine 2% provides greater hemodynamic stability during the first 30 minutes after administration compared to bupivacaine 0.5%, requiring less vasopressor support 5

• Patients receiving mepivacaine 2% require less postoperative opioid medication and can ambulate sooner after the procedure (mean 452.2 minutes vs 681.0 minutes with bupivacaine) 5

• Adding spinal morphine to local anesthetic can enhance postoperative analgesia as part of a multimodal approach 1, 6

Multimodal Analgesia Protocol with Spinal Anesthesia

• Combine spinal anesthesia with peripheral nerve blocks (particularly adductor canal or femoral nerve blocks) for optimal pain control 7, 6

• Include scheduled administration of paracetamol (acetaminophen) as baseline analgesia 7, 6

• Add conventional NSAIDs or COX-2 selective inhibitors unless contraindicated 7, 6

• For breakthrough pain, use:

  • Strong intravenous opioids for high-intensity pain 7, 6
  • Weak opioids for moderate to low-intensity pain 7, 6

• Implement cooling and compression techniques to the surgical site to reduce local inflammation and pain 7, 6

Peripheral Nerve Block Options

• Femoral nerve block (FNB) is the primary recommended peripheral technique for post-TKA analgesia based on level 1 evidence 8

• Adductor canal block is an effective alternative that better preserves quadriceps strength compared to femoral nerve block 7, 6

• For extended analgesia, continuous catheter techniques may be preferred over single-shot injections 7, 6

• Avoid combination of femoral and sciatic nerve blocks due to limited and inconsistent evidence of benefit 7, 8, 6

Potential Drawbacks and Considerations

• Spinal anesthesia may be associated with urinary retention, which is one of the few complications more common than with general anesthesia 1

• When performing bilateral blocks for bilateral TKA, reduce the total dose of local anesthetic to minimize risk of systemic toxicity, particularly in elderly patients 7, 6

• Some studies suggest that general anesthesia may facilitate faster discharge from ambulatory surgery centers compared to bupivacaine spinal anesthesia, though mepivacaine spinal anesthesia may be comparable 3

• In fast-track TKA protocols, general anesthesia has shown shorter length of stay in some studies (46 vs 52 hours), though with higher immediate postoperative pain scores 9

Implementation Algorithm

1. Assess for contraindications to spinal anesthesia (patient refusal, coagulopathy, infection at injection site, severe hypovolemia) 1
2. If no contraindications, proceed with spinal anesthesia using:
   • Mepivacaine 2% for shorter procedures or when faster recovery is desired 5
   • Low-dose bupivacaine (5-10 mg) with spinal morphine for longer procedures 4
3. Supplement with peripheral nerve block (preferably adductor canal or femoral nerve block) 7, 6
4. Implement multimodal analgesia protocol with scheduled acetaminophen, NSAIDs/COX-2 inhibitors, and opioids as needed 7, 6
5. If spinal anesthesia is contraindicated or unsuccessful, use general anesthesia combined with peripheral nerve blocks 7, 6