subparaneural versus circumferential extraneural injection ... · free movement of the foot during...

ORIGINAL ARTICLE

Subparaneural Versus Circumferential Extraneural Injectionat the Bifurcation Level in Ultrasound-Guided Popliteal

Sciatic Nerve BlocksA Prospective, Randomized, Double-Blind Study

Olivier Choquet, MD,* Guillaume Brault Noble, MD, MSc,* Bertrand Abbal, MD,*Didier Morau, MD, MSc,* Sophie Bringuier, PharmD, PhD,†‡ and Xavier Capdevila, MD, PhD*§

Background: The ideal spread of local anesthetic for effective, rapid,and safe sciatic nerve block is debated. We hypothesized that sub-paraneural ultrasound-guided injection results in faster onset and has abetter success rate than extraneural circumferential spread.Methods: Patients undergoing elective tibial, foot, and ankle surgerywith popliteal sciatic nerve blocks were prospectively enrolled. Afterrandomization, the needle tip position was adjusted to ensure circum-ferential extraneural or subparaneural spread; 0.3 mL/kg of mepivacaine10 mg/mL was injected. Post hoc video analysis was used to groupthe patients according to extraneural, subparaneural, and unintentionalintraepineural spread.Results: There were 26 (43.3%) patients in the subparaneural groupand 22 (36.7%) in the extraneural group. Block onset time was shorterin the subparaneural group than in the extraneural group (11 [3–21]minutes; mean [95% confidence interval], 11 [8.97–13.02] minutesand 17 [6–30] minutes; mean [95% confidence interval] 18.37 [14.17–22.57] minutes, respectively; P = 0.002). The duration of sensory blockadeincreased (397 [178–505] minutes vs 265 [113–525] minutes; P = 0.04).The success rate of the block also increased. Unintentional intra-epineural injection occurred in 8% of patients (3 patients in the sub-paraneural group and 1 patient in the extraneural group; NS). Blockonset time was shorter than for the subparaneural and extraneural groups(6 [3–12] minutes, 12 [3–21] minutes, and 18 [6–30] minutes; P = 0.01).Conclusions: A subparaneural injection accelerated the onset timeand increased the duration of tibial nerve sensory blockade comparedwith circumferential extraneural injection. With unintentional intra-epineural spread, the onset time was significantly shorter than for theother groups.

(Reg Anesth Pain Med 2014;39: 306–311)

Sciatic nerve block in the popliteal fossa is a commonly usedperipheral nerve block for surgery below the knee. The over-

all success rate of the block at 30 minutes, using ultrasoundguidance, ranges from 60% to 100%.1–3 The question of theideal location and spread of local anesthetic (LA) resulting ineffective, rapid, and safe sciatic nerve block remains.4 The sciatic

From the *Department of Anesthesiology and Critical Care, MontpellierUniversity Hospital; † Department of Anesthesiology and Critical Care Med-icine, Lapeyronie University Hospital; ‡Epidemiology and Clinical ResearchDepartment, Arnaud de Villeneuve University Hospital; and §Institut Nationalde la Sante et de la Recherche Médicale U1046, UM1, Montpellier, France.Accepted for publication March 11, 2014.Address correspondence to: Xavier Capdevila, MD, PhD, Department of

Anesthesiology, Lapeyronie University Hospital, Route de Ganges, 34295Montpellier Cedex 5, France (e‐mail: [email protected]).

The authors declare no conflict of interest.Support was provided only from institutional sources.Copyright © 2014 by American Society of Regional Anesthesia and Pain

MedicineISSN: 1098-7339DOI: 10.1097/AAP.0000000000000095

306 Regional Anesthes

Copyright © 2014 American Society of Regional Anesthesia and Pain

nerve divides into tibial and common peroneal componentsat the popliteal fossa and is surrounded by a closely adherentconnective tissue layer, the paraneural sheath.5–7 Dependingon where the needle tip is inserted and the spread of LA solu-tion, significant differences in onset time and duration of sen-sory and motor blockades have been reported.8–13 The recentliterature highlights the importance of obtaining an extraneuralconcentric distribution of LA around the sciatic nerve1,14,15 oran extraneural injection surrounding both tibial and peronealnerves distal to the bifurcation.12,13,16 In 2 studies, a proximalinjection below the paraneural sheath seemed superior to anextraneural distal injection around both separate tibial and pe-roneal nerves.8,10 Only 1 study focused on LAvolume,11 com-pared extraneural circumferential spread with subparaneural(subfascial) spread of LA solution around the sciatic nervebifurcation. On one hand, the pharmacodynamic importanceof the common paraneural sheath is questionable.17,18 On theother hand, although unintentional intraepineural injection hasnow been reported in 6% to 17% of ultrasound-guided peripheralnerve blocks,8,19,20 no study has reported the block pharmacody-namic profile related to unintentional intraepineural injections. Inthis randomized double-blind study, we hypothesized that asubparaneural ultrasound-guided injection of LA results in fasteronset and has a better success rate than extraneural circumferentialspread of LA around the entire sciatic nerve at the bifurcationlevel. We also evaluated the block pharmacodynamic profile ofthe unintentional intraepineural injections.

METHODSAfter institutional ethical committee approval (CPP Sud

Mediterranée III, Nimes, France), registration in the French Da-tabase for Clinical Trials (EUDRACT no. 2010-A00289-30),and written informed consent, patients scheduled for electivetibial, foot, and ankle surgery with popliteal sciatic nerve blockswere prospectively enrolled in this study. The design and de-scription of the study adhered to the guidelines of the Conso-lidated Standards of Reporting Clinical Trials (CONSORT)statement. Exclusion criteria were the presence of a bleedingdisorder, peripheral neuropathy or chronic pain syndrome, in-fection or injury at the needle entry point, allergy to LA, patientsless than 18 years of age, pregnancy, cognitive impairment, pa-tient refusal, and participation in another clinical trial. Patientswere randomly assigned to receive circumferential extraneuralor subparaneural ultrasound-guided injections of LA at thelevel of the popliteal sciatic nerve bifurcation. Randomizationwas generated by our institutional biostatistics department usinga computer-generated random sequence. The anesthesiologistin charge of the patient performed the ultrasound-guided blockaccording to the randomization group. The patient, surgeon, andanesthesiologist collecting the data were blinded to the type ofblock performed.

ia and Pain Medicine • Volume 39, Number 4, July-August 2014

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Regional Anesthesia and Pain Medicine • Volume 39, Number 4, July-August 2014 Sciatic Nerve Block Comparison

On the day of surgery, patients were given oral pre-medication (hydroxyzine 1 mg/kg) 90 minutes before the pro-cedure and 500 mL of saline were infused with an intravenous20-gauge catheter. Patients underwent systematic administra-tion of oxygen at a rate of 6 L/min. Standard monitoring wasused, including noninvasive arterial blood pressure, heart rate,and pulse oximetry. Each patient was placed in the prone posi-tion, with a pillow under the anterior part of the ankle to permitfree movement of the foot during nerve stimulation. During theprocedure, all patients received sedation via target-controlledinfusion (propofol, Marsh model, concentration at the site of ac-tion 1.2 ng/mL). Ultrasound-guided lateral, short-axis, in-planesciatic popliteal nerve blocks (linear array probe LA 435K,8–18 MHz; Agile, Kontron Medical, France) were performed byanesthetists with more than 3 years' experience with ultrasound-guided blocks. The skin was prepared with an alcoholic povidone-iodine solution. An insulated, 22-gauge, 50-mm needle (StimuplexA; BBraun, Germany) was advanced at an angle of 90 degreesto the skin until the tip was positioned according to the randomi-zation group. The needle tip position was adjusted as necessarywithin the selected target to ensure circumferential extraneuralor subparaneural spread of LA around the sciatic nerve (Fig. 1A,B). A nerve stimulator (Stimuplex HNS 12; BBraun) was set toa pulse duration of 0.1 millisecond, current intensity of 0.2 mA,and frequency of 1 Hz. Once the needle was in place, the physi-cian verified that there was no motor response to nerve stimula-tion, no paresthesia, and no blood aspiration occurred. Mepivacaine10 mg/mL was injected in 5-mL increments to a total volumeof 0.3 mL/kg, with a maximum of 30 mL. A video of theultrasound-guided block sequence was recorded and stored forpost hoc analysis. A second anesthesiologist blinded to the pa-tient randomization group collected the data: duration of theprocedure, needle passes, onset time of sensory and motorblockades in sciatic nerve components, duration of the block,and paresthesia or pain during the procedure. The blinded anes-thesiologist did not have the opportunity to see the screen of

FIGURE 1. Spread distribution in the patient groups. A, Subparaneuracomponents (white arrows). B, Extraneural spread (dotted line) aroun

© 2014 American Society of Regional Anesthesia and Pain Medicine


the ultrasound machine during the procedure and to know thepatient group allocation. Sensory blockade was assessed every3 minutes after injection as a loss of cold, pinprick, and lighttouch sensations in the areas of the tibial (plantar surface ofthe foot) and common peroneal (dorsal surface of the foot)nerves. Sensory blockade was classified as follows: 0, anesthe-sia; 1, hypoesthesia; 2, normal sensation. At the same time, mo-tor blockade was tested for the tibial nerve (plantar flexion ofthe foot) and the common peroneal nerve (dorsal flexion ofthe foot). Motor blockade was classified as follows: 0, com-plete motor blockade; 1, weak response against resistance; 2, nomotor blockade. A block was considered successful (block per-mitting surgery) when a score of 0 was obtained for sensoryblockade, whatever the score for motor blockade in the sciaticnerve components is. A block was considered a failure if a scoreof 0 was not obtained for sensory blockade within 30 minutesafter LA injection in the areas tested. The duration of sensoryand motor block was evaluated by the anesthesiologist blindedto the type of block (light touch and foot movements) within thefirst 6 hours in the postanesthetic care unit.

After every 10 patients, an expert anesthesiologist not in-volved in the study randomly reviewed ultrasound video clipsof the injections and scored the ultrasound criterion. Cross-sectional short-axis sciatic nerve measurements were recorded forthe common sciatic nerve and both nerve components. Changesin nerve dimension and appearance (swelling) were measuredand noted. Using post hoc video analysis, including measure-ments of the diameter of sciatic nerve components before andafter LA injection, the patients were separated into 3 groupsdepending on the characteristics of LA spread: extraneural, sub-paraneural, or unintentional intraepineural spread. Extraneuraland subparaneural spread of LA solution was defined as pre-viously reported.8,10,11,14 Unintentional intraepineural injectionassociated with extraneural or subparaneural spread of LAwas de-fined as an increase in the diameter of one or both sciatic nervecomponents of more than 10%, with swelling and fascicular

l spread (dotted line) between the tibial and common peroneald both components of the sciatic nerve (white arrows).

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Choquet et al Regional Anesthesia and Pain Medicine • Volume 39, Number 4, July-August 2014

separation (Fig. 2A, B).21–23 Patients were contacted by phone24 hours and 1 week postoperatively to document any remainingmotor or sensory deficits. Patients were followed up by the sur-geon on the day of surgery to assess full recovery from the nerveblock and again 1 week later. Complete recovery from the blockand the lack of residual postoperative neurologic symptoms suchas paresthesia, dysesthesia, or motor deficits were carefully notedby the patients and the surgical team in a specific file.

Sample Size Calculation and Statistical AnalysisThe primary end point in both patient groups was the onset

time of sensory blockade. The mean onset time of sensory blockfor ultrasound-guided circumferential extraneural injection justbefore sciatic nerve bifurcation is between 26 and 31minutes.12,13

We hypothesized a 30% reduction in the onset time with sub-paraneural injection at the site of bifurcation. We assumed a stan-dard deviation of 10 minutes. For a 2-tailed α = 0.05 and a powerof 80%, a sample size of 24 patients per group was required. Toallow for a dropout of 10% of patients, 60 patients were random-ized. Statistics are presented as median (minimum-maximum) forquantitative data and numbers (percentage) for qualitative para-meters. Continuous variables were compared using the Mann-Whitney U test or the Kruskal-Wallis test. Discrete variables werecompared using the χ2 test or the Fisher exact test when indicated.For multiple comparisons, a Bonferroni correction was applied.Avalue of P < 0.05 was considered statistically significant. Statis-tical analyses were performed using SAS software (version 8.2;SAS Institute Inc, Cary, North Carolina).

RESULTSSixty consecutive patients consented to participate in the

study and were randomly assigned to one of the 2 groups(Fig. 3). Forty-eight patients completed the study assessmentsand were included in the final analysis: 26 (43.3%) in the

FIGURE 2. Unintentional intraepineural injection. A, Surrounding bothincrease in the diameter of the tibial nerve but not in the common pe

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subparaneural group and 22 (36.7%) in the extraneural group.Twelve patients (20%) were excluded after randomization be-cause of protocol violations, incomplete data, or a sciatic nervethat was poorly visualized. In the extraneural group, 6 patients(10%) presented block failure (incomplete sensory blockade af-ter 30 minutes). The demographic data for the 48 patients stud-ied are presented in Table 1. There was no significant differencebetween patients for anthropometric characteristics, proceduretime, volume of LA, number of needle passes, and type of sur-gery. No motor response to nerve stimulation was observed.The onset time for surgical block in the subparaneural groupwas shorter than in the extraneural group (respectively, median[range] values at 11 [3–21] minutes and 17 [6–30] minutes, forsurgical block excluding the 6 failure patients), and sensoryblockade of the tibial nerve lasted longer. With regard to thefailure rate, the 6 patients presenting block failure (incompletesensory blockade after 30 minutes) belonged to the extraneuralgroup. After post hoc echographic analysis, 21 (43.8%) of48 extraneural injections, 23 (47.9%) of 48 subparaneuralspreads, and 4 (8.3%) of 48 unintentional intraepineural injec-tions were observed (Table 2). The patients in the unintentionalintraepineural spread group had shorter onset time for surgicalblock than those in the subparaneural and extraneural groups.The duration of sensory blockade was significantly shorter inthe extraneural group compared with the subparaneural and un-intentional intraepineural groups. The onset time of sensoryand motor blockade according to the location of the LA spreadare presented in Figure 4. No patients reported neurologiccomplications or paresthesia.

DISCUSSIONIn this prospective randomized study, we found that, com-

pared with a circumferential extraneural injection at the bifurca-tion level of the sciatic nerve, a subparaneural injection at the

sciatic nerve components (white arrows). B, Note the swelling androneal nerve.



FIGURE 3. CONSORT flowchart for the study.


same level resulted in earlier onset of surgical block, a bettersuccess rate, and increased duration of tibial nerve sensoryblockade. However, the onset time was significantly shorter inpatients with unintentional intraepineural spread compared withsubparaneural or extraneural injections.

TABLE 1. Demographics and Procedure Parameters From Intentio

Subparan

DemographicsAge (range), yAged ≥55 y, n (%)Male, n (%)American Society of Anesthesiologists score (range)Body mass index (range), kg/m2

Procedure dataTypes of surgery, n (tibia/ankle/foot)Procedure time (range), minVolume of LA (range), mLBlock failure, n (%)Time to anesthetic surgical block (range), min*Time to obtain an anesthetic block (range), minDuration of tibial nerve sensory block (range), min* 3Duration of peroneal nerve sensory block (range), min* 3Single skin puncture, n (%)Block–related pain, n (range)

Data are expressed as median (range, minimum–maximum) or as numbe

*Not including failure patients.

NS indicates not significant.



Our study compared circumferential extraneural and sub-paraneural injections performed strictly at the same level. Bothparameters have been considered as factors to improve the suc-cess rate and decrease block onset time in patients.8–11,14,15 Pre-vious studies evaluated the benefit of injections targeting both

n-to-Treat Analysis of Randomized Patients (N = 48)

eural Group (n = 26) Extraneural Group (n = 22) P

49 (20–69) 53.5 (18–65) NS11 (42.3) 7 (31.8) NS7 (26.9) 10 (45.4) NS2 (1–2) 2 (1–2) NS

22 (18–33.7) 22.3 (17–37.7) NS

26 (2/8/16) 22 (2/7/13) NS4 (1–10) 5 (1–15) NS

20 (14–30) 20 (14–30) NS0 (0) 6 (27.3) 0.006

11 (3–21) 17 (6–30) 0.00211 (3–21) 19 (6–48) 0.00197 (178–505) 265 (113–525) 0.0497 (180–515) 310 (167–512) NS26 (100) 19 (86) NS20 (10–50) 20 (0–60) NS

r of patients (percentage) as appropriate.

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TABLE 2. Demographics and Procedure Parameters From Post Hoc Analysis of Injection Spread (N = 48)

Extraneural Group(n = 21)

Subparaneural Group(n = 23)

Intraepineural Group(n = 4) P

DemographicsAge (range), y 38 (18–65) 55 (20–69) 40.5 (25–54) NSAged ≥55 y, n (%) 6 (28.6) 12 (50) 0 (0) NSMale, n (%) 10 (47.6) 5 (20.8) 2 (50) NSAmerican Society of Anesthesiologists score (range) 1.5 (1–2) 2 (1–2) 1 (1–1) NSBody mass index (range), kg/m2 22.3 (17.1–30.1) 22.8 (18–37.7) 22 (20.3–24.4) NSSpread group dataProcedure time (range), min 5 (1–15) 5 (1–10) 3 (3–3) NSVolume of LA (range), mL 20 (14–30) 20 (14–30) 20 (18–20) NSTime to anesthetic block (range), min* 18 (6–30) 12 (3–21) 6 (3–12) 0.01†Duration of tibial nerve sensory block (range), min* 263 (113–525) 423 (182–515) 377 (230–410) 0.05‡Duration of peroneal nerve sensory block (range), min* 297 (167–512) 423 (182–515) 377 (230–378) NS

Data are expressed as median (range, minimum-maximum) or as number of patients (percentage) as appropriate.

*Not including failure patients.

†Intraepineural versus both extraneural and subparaneural.

‡Subparaneural and intraepineural versus extraneural.

Choquet et al Regional Anesthesia and Pain Medicine • Volume 39, Number 4, July-August 2014

the distal tibial and common peroneal nerves compared withproximal extraneural injections,12,13,16 subparaneural proximalto distal extraneural injections,9,10 or at 2 different levels ofthe paraneural compartment.8 We noted quite the same resultsconcerning the onset time in subparaneural and extraneuralgroups than in the study by Perlas et al.10 However, the in-jections of LA solution were differently located along the sciaticnerve course. Perlas et al10 compared a proximal subparaneuralinjection with a double more distal (probably 4–5 cm distallyfrom the injection point of the subparaneural group) extraneuralinjection on the 2 separated nerve components. This is a differ-ence between our 2 studies despite the overlap in the spread ofLA solution between both Perlas et al10 study groups. In ana-tomic5 and 3-dimensional ultrasound11 studies focused on LAspread, it has been demonstrated that the mean paraneural dis-tance covered by LA spread can reach 9 cm, erasing the ex-pected difference between injections at the prebifurcation andbifurcation levels. Our results highlight the fact that paraneuralinjection is more important than circumferential spread in the

FIGURE 4. Onset times for sensory and motor blockade forboth sciatic nerve components. 0, full sensory blockade;1, hypoesthesia; CPN, common peroneal nerve; M, motor blockadeonset time; S, sensory blockade onset time; TIB, tibial nerve.*P < 0.05, intraepineural versus subparaneural and extraneural.

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pharmacodynamic profile of a popliteal sciatic nerve block.17,18

In an in vitro study on rat sciatic nerves, Leeson and Strichartz18

reported that the paraneural sheath halved the uptake rate of li-docaine, penetration into the nerve, and the washout rate. Thisexperimental report confirms our results, which demonstratea significant decrease in surgical block onset time and a pro-longed duration of sensory blockade in patients receiving asubparaneural injection. Missair et al11 reported identical resultswith a shorter onset time and a longer duration of sciatic nerveblocks in patients receiving 30 mL of 0.5% ropivacaine sub-fascially compared with patients receiving the same volumeextrafascially. However, the authors did not separate the dura-tion of sensory blockade in the common peroneal and tibialnerves. We report that the difference in block duration is effec-tive for the tibial nerve but not for the common peroneal nerve.

An injection inside the common sheath can be differenti-ated from an intraneural injection. In 4 patients (8.5%) in ourpost hoc analysis, an intraepineural injection was noted. Threeof the patients noted with an intraepineural location of LAbelonged to the subparaneural group and one to the group ex-traneural (NS). Published data suggest that a subparaneuralspread of LA may be recommended.7,9,10,24 However, there isa need for comparative studies to establish a safe and objectivemethod of performing such an injection. Despite the absenceof nerve injuries in our 4 patients of the intraepineural group,it has been reported that patients who received a subparaneuralinjection noted a higher incidence of transient paresthesia.12 AsKarmakar and colleagues24 recently reported, using low-resolutionultrasound systems do not ensure that the tip of the needle isstrictly outside the epineural space. Furthermore, the lack of sen-sitivity of nerve stimulation does not allow to detect the needle'stip position within the epineurium ( absence of motor responseat 0.2 mA).Unintentional intraneural injections have been re-ported in 6%8 to 17%19,20 of ultrasound-guided peripheral nerveblocks. As previously demonstrated in subgluteal sciatic nerveblocks,19 we report that an intraepineural injection associated witha subparaneural or an extraneural spread significantly shortenedthe onset time of sciatic nerve block compared with a nonintra-epineural spread in the other 2 groups. Hara et al19 did not re-port any difference in the duration of the block between the




intraneural and nonintraneural injection groups. However, theauthors did not distinguish between extraneural extrafascialand paraneural (subfascial) injections. We report a significantdifference in the duration of tibial sensory block between theunintentional intraepineural injection group and the extraneuralinjection group but not the subparaneural group, highlightingthe importance of the paraneural sheath in the pharmacodynamicprofile of the block. That difference can be related to the struc-tural aspects of both nerves,25 the relationship the componentshave with the paraneural sheath as a barrier to LA spread, andthe vascularization of the common peroneal nerve that limits thewashout of the LA, and so increases the duration of the block.26

There are some limitations in the present study. Like mostprocedure-related studies, it is not possible to blind the anesthe-siologist doing the block to group allocation. To minimize thepossibility of bias, the procedure was assessed and the blockpharmacodynamic parameters were documented by an inde-pendent physician blinded to the group allocation. We reportedno neurologic deficit even in the unintentional intraepineuralgroup. The study was not powered to detect clinically meaningfuldifferences with regard to safety.

In conclusion, the results of this study suggest that asubparaneural injection at the sciatic nerve bifurcation levelresults in faster onset and longer duration of sensory blockadethan a circumferential extraneural injection. This highlightsthe importance of the paraneural sheath in the pharmacody-namic profile of the block. Furthermore, associated uninten-tional intraepineural injection decreased the onset time ofsensory and motor blockade further.

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