Purpose: To compare the efficacy of a continuous posterior lumbar plexus (PSOAS) block to a continuous three-in-one femoral nerve (FEM) block in patients undergoing primary total knee replacement (TKR).
Methods: Sixty patients were randomly allocated to receive iv patient-controlled morphine analgesia (PCA), PCA plus a continuous FEM block with 30 mL ropivacaine 0.5% and epinephrine 1:200,000 bolus followed by an infusion of ropivacaine 0.2% at 12 mL.hr(-1) for 48 hr, or PCA plus a continuous PSOAS block with the same bolus and infusion regimen as the FEM group. Postoperative morphine consumption, verbal analogue scale pain scores at rest and during physiotherapy, and evidence of sensory and motor blockades were noted.
Results: Both regional techniques significantly reduced 48 hr morphine consumption (FEM 37.3 +/- 34.7 mg, P = 0.0002; PSOAS 36.1 +/- 25.8 mg, P < 0.0001) compared to PCA (72.2 +/- 26.6 mg). Pain scores at rest, six and 24 hr after TKR were lower in the FEM and PSOAS groups compared to the PCA group (P < 0.0001). Although sensory and motor blockades of the obturator nerve were achieved more often in the PSOAS group than in the FEM group (P < 0.0001), morphine consumption and pain scores did not differ between the two groups.
Conclusion: Both continuous PSOAS block and continuous three-in-one FEM block provided better analgesia than PCA but no differences were seen between the two regional techniques.