Post-operative analgesia following total knee replacement: an evaluation of the addition of an obturator nerve block to combined femoral and sciatic nerve block

Background: Femoral and sciatic nerve block may not provide complete post-operative analgesia following total knee replacement. This study was designed to evaluate whether the addition of an obturator nerve block to combined femoral and sciatic nerve block improves the quality of post-operative analgesia following primary total knee replacement. Methods: Sixty patients were randomised into one of two groups: combined femoral and sciatic nerve block with 15 ml 0.75% ropivacaine to each nerve or combined femoral and sciatic nerve block with 15 ml 0.75% ropivacaine to each nerve and an obturator nerve block with 5 ml 0.75% ropivacaine. Results: Peripheral nerve blocks were successful in 85% of patients. The group which received the obturator nerve block showed a significant increase in the time until their first request for analgesia (mean 257.0 vs. 433.6 min) and a significant reduction in the total requirements for morphine throughout the study period (mean 83.8 vs. 63.0 mg) (P<0.05). There were no systemic or neurological sequelae in any of the groups. Conclusions: The addition of an obturator nerve block to femoral and sciatic blockade improved post-operative analgesia following total knee replacement.