Posterior psoas vs 3-in-1 approach for lateral femoral cutaneous and obturator nerve block for anterior cruciate ligament repair.

Aim. The aim of this article was to test the hypothesis that the posterior psoas compartment approach to the lumbar plexus help to achieve better blockade of the lateral femoral cutaneous and obturator nerves than the classic anterior 3-in-1 femoral nerve block. Methods. Thirty-six patients who were undergoing anterior cruciate ligament repair were randomly allocated to receive a femoral nerve block using either an anterior 3-in-1 femoral block (group Femoral, N=18) or a posterior psoas compartment approach (group Psoas, N=18) using 30 mL of 1.5% mepivacaine. Successful nerve block was defined as a complete loss of pinprick sensation in the region that is supplied by the lateral femoral cutaneous nerve along with adequate motor block of the obturator nerve 30 minutes after injection. The degree of motor block of the obturator nerve was measured using adduction strength with a mercury sphygmomanometer as previously described by Lang. Results. Thirty minutes after the completion of the block, sensory block of the lateral femoral cutaneous nerve was observed in 14 patients (78%) from the Psoas group and in 3 patients (17%) from the Femoral group (P=0.001). Thirty minutes after the completion of the block, a 119±40 mmHg decrease was found in Psoas group, in contrast to the 25±22 mmHg decrease found in the Femoral group (P<0.0005). Conclusion. The posterior psoas compartment approach provides a more reliable block of the lateral femoral cutaneous and obturator nerves than the anterior 3-in-1 approach.