Sciatic nerve block "out-of-plane" distal to the bifurcation: effective and safe

Abstract

Ultrasound guided distal sciatic nerve block (DSB) at bifurcation level shows fast onset and provides excellent success rates. However, its safe performance might be difficult for the unexperienced physician. Just slightly distal to the bifurcation, the tibial nerve (TN) and common fibular nerve (CFN) can be shown clearly separated from each other. Therefore, we investigated if ablock done here would provide similar quality results compared to the DSB proximally to the division, with apotentially lower risk of nerve damage. In this randomized, prospective trial, 56patients per group received either aDSB distal to the bifurcation "out-of-plane" (dist.) or proximally "in-plane" (prox.) with 30 ml of Mepivacaine 1% each. Success was tested by ablinded examiner after 15and 30 min respectively (sensory and motor block of TN and CFN: 0= none, 2= complete, change of skin temperature). Videos of the blocks were inspected by an independent expert retrospectively with regard to the spread of the local anesthetic (LA) and accidental intraneural injection. Cumulative single nerve measurements and temperature changes revealed significant shorter onset and better efficacy (dist/prox: 15 min: 3.13± 1.86/1.82± 1.62; 30 min: 5.73± 1.92/3.21± 1.88; T15 min: 30.3± 3.48/28.0± 3.67, T30 min. 33.0± 2.46/30.6± 3.86; MV/SD; ANOVA; p< 0.01) combined with ahigher rate of subparaneural spread in the dist. group (41/51 vs.12/53; χ2; p< 0,01). Procedure times were similar. There were no complications in either group. The subparaneural spread of the LA turned out to be crucial for better results in the distal group. The steep angle using the out-of-plane approach favors needle penetration through the paraneural sheath. The distance between the branches allows the safe application of the LA, so an effective block can be done with just one injection. DSB slightly distal to the bifurcation, in an out-of-plane technique between the TN and CFN, can be done fast, effectively and safe.