Lateral femoral cutaneous nerve block with different volumes of Ropivacaine: a randomized trial in healthy volunteers

Frederik Vilhelmsen,Daniel Hägi-Pedersen,Kasper Højgaard Thybo,Jakob Hessel Andersen,Ole Mathiesen,Leif Broeng,Jakob Klim Danker,Mariam Nersesjan

doi:10.1186/s12871-019-0833-4

Abstract

BackgroundNerve block of the lateral femoral cutaneous nerve (LFCN) is a predominantly sensory block. It reduces pain following total hip arthroplasty (THA), but the non-responder rate is high. We hypothesized, that an increased volume of ropivacaine, would result in greater coverage of incisions used for THA.MethodsWe conducted a randomized, blinded trial in 20 healthy volunteers. Participants were randomized to receive bilateral LFCN-blocks with 8 mL ropivacaine 0.75% on the left side and 16 mL ropivacaine 0.75% on the right side, or vice versa. Allocation was blinded to both participants and outcome assessors. Before nerve block performance, incision lines for posterior and lateral THA approaches were depicted with invisible ultraviolet-paint, thereby securing sufficient blinding during outcome assessment. The blocked area was mapped using temperature and mechanical discrimination tests. Quadriceps muscle strength was monitored. Primary outcome was coverage of the posterior incision line assessed by temperature discrimination test.ResultsWe found no difference in coverage of the posterior or lateral incision lines when comparing LFCN-blocks with 8 mL versus 16 mL of ropivacaine. The blocked area was significantly larger in the 16 mL group, assessed by both temperature discrimination test (p = 0.012) and mechanical discrimination test (p = 0.034). We observed no difference between groups regarding quadriceps muscle strength (p = 1.0).ConclusionsA LFCN-block with increased volume of ropivacaine from 8 mL to 16 mL did not result in a greater coverage of posterior or lateral incision lines used for THA, but in a larger blocked sensory area.Trial registrationClinicaltrials.gov: NCT03138668. Registered 3rd of May 2017.

Highlights

Nerve block of the lateral femoral cutaneous nerve (LFCN) is a predominantly sensory block
We investigate if LFCN-blocks with 16 mL ropivacaine results in a greater coverage of the incision line for the posterior total hip arthroplasty (THA) approach compared with LFCN-blocks with 8 mL ropivacaine, assessed by temperature discrimination test
We aimed to show an increase in coverage of the incision line from 20 to 40% by doubling the volume of ropivacaine injected from 8 mL to 16 mL

Summary

Introduction

Nerve block of the lateral femoral cutaneous nerve (LFCN) is a predominantly sensory block. It reduces pain following total hip arthroplasty (THA), but the non-responder rate is high. Total hip arthroplasty (THA) is often associated with moderate to severe postoperative pain [1] and peripheral nerve blocks have been used as part of a multimodal analgesic strategy [2,3,4,5]. The lateral femoral cutaneous nerve (LFCN) block is a predominantly sensory block and has been suggested to mitigate pain after hip surgery [7,8,9]. A clinical trial from 2016 showed that LFCN-blocks with 8 mL ropivacaine 0.75% reduced moderate to severe movement related pain after THA surgery using the posterior approach, but the non-responder rate was high (42%) [8]. Several other studies have investigated the anatomical sensory distribution of a LFCN-block and consistently revealed a limited coverage of THA incisions using 5 to 10 mL of local anesthetics [10,11,12].

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