ultrasound-guided popliteal block through a common ... · background and objectives: the...

Ultrasound-Guided Popliteal Block Through a CommonParaneural Sheath Versus Conventional Injection

A Prospective, Randomized, Double-blind Study

Anahi Perlas, MD, FRCPC,*Þ Patrick Wong, MD, FRCPC,* Faraj Abdallah, MD,*Lili-Naz Hazrati, MD, PhD, FRCPC,þ Cyrus Tse, BSc,* and Vincent Chan, MD, FRCPC*Þ

Background and Objectives: The macroscopic anatomy of a com-mon paraneural sheath that surrounds the sciatic nerve in the poplitealfossa has been studied recently in a human cadaveric study. It has beensuggested that an injection through this sheath could be an ideal locationfor local anesthetic administration for popliteal block. The aim of thepresent study was to evaluate the hypothesis that popliteal sciatic nerveblockade through a common paraneural sheath results in shorter onset timewhen compared with conventional postbifurcation injection external to theparaneural tissue. To illustrate the microscopic anatomy of the paraneuraltissues, we performed histological examinations of a human leg specimen.Methods: Following institutional review board approval and writteninformed consent, 89 patients undergoing an ultrasound-guided poplitealblock for foot or ankle surgery were included in the study. They wereprospectively randomized to receive a single injection of local anestheticat the site of bifurcation through a common paraneural sheath (group 1) or2 separate circumferential injections of the tibial and common peronealnerves distally to sciatic nerve bifurcation (group 2).Results: Patients in group 1 had a 30% shorter onset time of both sen-sory and motor block. This was associated with a more extensive proximaland distal longitudinal spread of local anesthetic in this group. Nerve di-ameter and cross-sectional area remained unchanged in both groups afterinjection, which is consistent with extraneural injection. A greater pro-portion of patients in group 1 required a single needle pass for blockperformance.Discussion: An ultrasound-guided popliteal sciatic nerve block througha common paraneural sheath at the site of sciatic nerve bifurcation is asimple, safe, and highly effective block technique. It results in consistentlyshort onset time, while respecting the integrity of the epineurium andintraneural structures.

(Reg Anesth Pain Med 2013;38: 218Y225)

The introduction of real-time ultrasound guidance for periph-eral nerve blockade has enhanced the understanding of pe-

ripheral nerve anatomy and its implications for clinical practice.However, significant controversy still exists as to the optimalplane or space for local anesthetic deposition for specific blocks.Arguably, the optimal location for local anesthetic deposition isclose enough to the nerve to ensure consistent success and fastonset, while at the same time preserving the integrity of theepineurium and internal neural structures, therefore combiningsafety with efficacy and efficiency.

The anatomical correlation of ultrasound findings of thesciatic nerve at the popliteal fossa has been studied recently inhuman cadavers, both by gross dissection and histology.1 Thesciatic nerve is formed by 2 independent nerves. The tibial nerve(TN) and common peroneal nerve (CPN) run alongside each otheron their course down the thigh. They each have their own epi-neurium and are in turn surrounded by an additional layer ofconnective tissue that has been called a ‘‘paraneural sheath.’’1,2 Ithas been suggested that injection through this common paraneuralsheath results in extensive spread of the local anesthetic whilepreserving the integrity of the 2 individual nerves, potentiallymaking it an ideal location for local anesthetic deposition.1

In this prospective randomized controlled trial, we aim tostudy the clinical effect of popliteal sciatic nerve blockade throughthe common paraneural sheath and compare it to conventionalpostbifurcation injection external to the paraneural tissue. Ourhypothesis was that sciatic nerve blockade through a commonparaneural sheath at the site of nerve bifurcation results in shortersensory block onset time than blockade outside the paraneuralsheath distal to sciatic nerve bifurcation. A secondary hypothesisis that penetrating the paraneural sheath does not result in a higherincidence of unintended intraneural injection. Other outcomesstudied included the longitudinal spread of the local anestheticsolution along the course of the sciatic nerve, nerve diameter be-fore and after the injection as a sign of intraneural injection, blockperformance time, and the incidence of new postoperative neu-rological symptoms.

METHODS

Clinical StudyThe study protocol was registered at clinicaltrials.gov (ID

no. NCT 01568476). There were no changes to the clinical studyprotocol after registration. After institutional review board ap-proval, patients scheduled to undergo elective foot or ankle sur-gery and eligible for a popliteal block were invited to participatein this prospective study. Inclusion criteria were American Soci-ety of Anesthesiologists physical status I, II, or III; 18 to 85 yearsof age; weight of 50 to 120 kg; and height of 150 cm or greater.Exclusion criteria were allergy to local anesthetics, coagulopathy,malignancy or infection in the popliteal area, significant periph-eral neuropathy or neurological disorder, pregnancy, and a history

ORIGINAL ARTICLE

218 Regional Anesthesia and Pain Medicine & Volume 38, Number 3, May-June 2013

From the *Department of Anesthesia and Pain Management, TorontoWestern Hospital, University Health Network; and †Department of Anes-thesia and ‡Center for Research in Neurodegenerative Diseases, Universityof Toronto, Toronto, Ontario, Canada.Accepted for publication February 13, 2013.Address correspondence to: Anahi Perlas, MD, FRCPC, Department of

Anesthesia & Pain Management, Toronto Western Hospital, Universityof Toronto, McLaughlin Pavilion 2-405, 399 Bathurst St, Toronto,Ontario, Canada M5T 2S8 (e-mail: [email protected]).

Supported in part by a Research Merit Award 2011Y2013 from theDepartment of Anesthesia, University of Toronto. Ultrasoundequipment support was received from Philips and SonoSite.

Presented in part at the University of Toronto Shield’s Research DayMay 2012 and at the 37th Annual Regional Anesthesia Meeting andWorkshops, May 2012.

The authors declare no conflict of interest.Copyright * 2013 by American Society of Regional Anesthesia and Pain

MedicineISSN: 1098-7339DOI: 10.1097/AAP.0b013e31828db12f

Copyright © 2013 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.

mailto:[email protected]

of alcohol or drug dependency. After providing written informedconsent, patients were randomized into 2 study groups accordingto a computer generated list of random numbers. Randomizationcodes were held by an independent investigator not involvedin block procedures. Group allocation was concealed in sealedopaque envelopes until the surgical date. Patients and investigatorsperforming outcome assessments were blinded to group allocation.

One hour before the expected surgical time, peripheral in-travenous access was established, and an infusion of normal salinestarted at a maintenance rate. Routine electrocardiogram, nonin-vasive blood pressure, and pulse oximeter monitors were applied,and baseline readings obtained. Midazolam 1 mg to 3 mg was in-travenously administered for anxiolysis as necessary. Patients wereplaced in the prone position. All regional blocks were performed bystaff, fellow anesthesiologists, or senior residents under staff su-pervision. The skin over the popliteal fossa was sterilized withdisposable swabs of 2% chlorhexidine in 70% isopropyl alcohol.A Philips CD50 ultrasound unit (Philips, Andover, Massachusetts)or SonoSite M-Turbo ultrasound unit (SonoSite Inc, Bothell,Washington) with a high-frequency (5Y12 or 6Y13 MHz) lineararray transducer was used. A 50-mm, 22-gauge stimulating needle(B. Braun, Bethlehem, Pennsylvania) was used for every patient.Skin was infiltrated with 2 to 3 mL of 2% lidocaine. A standardlocal anesthetic solution of equal parts of lidocaine 2% plain andbupivacaine 0.5% with 1:200,000 epinephrine was used for a totalvolume of 30 mL. The sciatic nerve was identified in a transverseplane, between the semitendinous and semimembranous musclesmedially, and the biceps femoris laterally. The nerve was followed

distally along its course, until the tibial and common peronealnerves start to diverge.

Group 1The block was performed at the site of sciatic nerve bifur-

cation. Given the large size of the sciatic nerve, the paraneuralsheath is substantial at this level and recognizable with ultrasoundas an outer layer of mixed echogenicity surrounding the nerve(Figs. 1A and B). As the 2 terminal nerves start to diverge fromeach other, there is a natural point of cleavage that allows easypenetration of the paraneural sheath with a short bevel needle inan out-of-plane approach. The needle end point was to lie be-tween the TN and CPN within the common paraneural sheathand external to the epineurium of each individual nerve. Afternegative aspiration, the standard anesthetic solution was injectedas a single injection within the sheath compartment in 5-mL in-crements for a total volume of 30 mL, ensuring local anestheticspread between and around the 2 nerves.

Group 2The TN and CPN were followed distally along their course

until they clearly become 2 separate entities no longer sharinga common paraneural sheath (Figs. 2A and B). At this point, theblock needle was advanced in either an out-of-plane or in-planeapproach as considered necessary by the attending anesthesiolo-gist. Following negative aspiration, 15 mL of standardized local an-esthetic solution was injected around each TN and CPN separately,

FIGURE 1. A and B, Sonogram of a patient in group 1. The sciatic nerve can be seen at the site of bifurcation in the popliteal fossa.The TN and CPN are distinguishable from one another and invested in a common paraneural sheath. PA indicates popliteal artery;PV, popliteal vein; interrupted line denotes the outer border of the common paraneural sheath.

FIGURE 2. A and B, Sonogram of a patient in group 2. The TN and CPN appear distally to sciatic nerve bifurcation. At this level, eachnerve is invested by a separate paraneural sheath. PA indicates popliteal artery; interrupted lines denote paraneural sheaths.

Regional Anesthesia and Pain Medicine & Volume 38, Number 3, May-June 2013 Ultrasound-Guided Popliteal Block

* 2013 American Society of Regional Anesthesia and Pain Medicine 219


ensuring circumferential local anesthetic spread around eachnerve, for a total volume of 30 mL. At this level, even though aparaneural sheath accompanies each nerve separately, it is inti-mately related to each nerve’s epineurium and difficult to distin-guish consistently on ultrasound image. Therefore, the operatorsdid not specifically attempt to puncture the paraneural tissues, butrather they sought circumferential spread of local anesthetic asis standard practice for many peripheral nerve blocks.

The following data were recorded during the block proce-dure by an unblinded observer: procedure time, number of skinpunctures, nerve diameter before and after injection, proximaland distal longitudinal spread of local anesthetic, and occurrenceof any immediate block-related complications. Longitudinal localanesthetic spread was assessed by scanning proximally alongthe course of the sciatic nerve and distally along the 2 terminalbranches. An upper and lower limit of spread as assessed by thisdynamic scan were marked on the patient’s skin with a surgicalmarker, and both proximal and distal distances were measuredfrom the skin puncture site using a surgical measuring tape. Inaddition, once the block procedure was complete, an independentobserver blinded to group allocation assessed sensory and motorblock progression every 5 minutes for 45 minutes or until com-plete block. Sensory function was assessed as sensation to pin-prick in both the TN (plantar surface of the foot) and CPN(dorsum of the foot) territories. Sensation to pinprick was gradedas 0 = no sensation to pinprick, 1 = decreased sensation to pin-prick, or 2 = normal pinprick sensation. Motor function (plantarflexion for TN and dorsiflexion for CPN) was graded as 0 = nomovement (complete block), 1 = movement present but weak(partial block), and 2 = normal movement. A composite sensory-

motor score was obtained for each patient at each assessmenttime point by adding both sensory and motor scores in each nerveterritory. A score of 8 represents full sensory and motor baselinefunction. A score of 0 represents complete loss of sensory andmotor functions in the distribution of both target nerves. A thightourniquet was used for every patient during surgery, so aftercompletion of the study assessments, patients received eithera spinal or general anesthetic at the discretion of the attendinganesthesiologist. Patients were contacted on the phone 24 hoursand 1 week postoperatively to document any new motor or sen-sory deficits.

Histological ExaminationTo illustrate the anatomy of the sciatic nerve and its para-

neural sheath, we performed a histological analysis of the area ofinterest in a human leg surgical specimen obtained from an above-knee amputation at the level of the midthigh. A separate researchethics board approval and approval by the local Department ofPathology were obtained. A detailed description of the technicalaspects is included in Appendix 1.

Sample Size Calculation and Statistical AnalysisThe mean onset time of sensory block for ultrasound-guided

injections using similar local anesthetic doses distally to sciaticnerve bifurcation is approximately 21 T 10 minutes.3,4 Basedon our empirical clinical observations, we hypothesize a 30%reduction of the onset time when the block is performed throughthe common paraneural sheath at the site of bifurcation. Basedon prior studies, we assume an SD of 10 minutes. For a 2-tailed> = 0.05 and a power of 80%, we estimate a required sample

FIGURE 3. Consort chart.

Perlas et al Regional Anesthesia and Pain Medicine & Volume 38, Number 3, May-June 2013

220 * 2013 American Society of Regional Anesthesia and Pain Medicine


size of 40 patients per group. To allow for a 10% patient dropout,89 patients were randomized. Continuous data, including age,height, weight, body mass index, block onset time, proceduretime, local anesthetic spread, and nerve size, were summarized asmean T SD and were compared using nonpaired Student t test.Categorical data, such as sex, postoperative disposition, the in-cidence of complete block at 30 minutes, and the incidence ofpostoperative neurological symptoms, were expressed as eitherratio or percentage, and distribution was compared using Mann-Whitney U test. SPSS for Windows, version 15.0 (SPSS Inc,Chicago, Illinois), was used for analysis.

RESULTSNinety-six patients were screened for participation in the

study. Seven patients were excluded before randomization be-cause of at least 1 exclusion criteria (n = 4) or because of logis-tical reasons (n = 3). The remaining 89 patients were randomizedto either group 1 (n = 43) or group 2 (n = 46). Four patients ingroup 1 and 1 patient in group 2 were excluded after randomi-zation (Fig. 3). Eighty-four patients completed study assessmentsand were included in the analysis. Both an intention-to-treat and aper-protocol analysis were performed with no change in the re-sults with either approach.

Patient demographics were similar in both groups (Table 1).One patient in each group received a partial unintentional intraneuralinjection as determined by subepineural administration of localanesthetic with increase in nerve size. This was observed duringthe early phase of the injection, and the needle was repositionedto be extraneurally after less than 5 mL had been injected ineither case. Neither of the 2 patients reported paresthesia at thetime of injection, and neither patient sustained neurologicaldeficits postoperatively. Even though intraneural injection wasunintended, this may occur in clinical practice. Therefore, bothpatients completed all study assessments, and their data wereincluded in the final analysis. Sensory and motor block onset

times were approximately 30% shorter in group 1 versus group2 (Table 2), and the combined sensory-motor score was lower ingroup 1 at every time point until 35 minutes after injection,denoting a faster block progression (Fig. 4). Procedure time(from the start of scanning to end of injection) was similar (about8 minutes), and nerve size remained essentially unchanged in bothgroups throughout and at the end of injection (Table 3). Agreater proportion of blocks were achieved with a single skinpuncture in group 1 (87% vs 68%, P = 0.05). Four patientsin group 1 and 1 patient in group 2 had residual sensory blockby 24 hours. Neurological function had returned to baseline inall patients 7 days postoperatively at the time of the telephoneinterview.

The histological preparations show that the paraneural tissueis a large circumferential pad of well-vascularized adipose andconnective tissue surrounding the sciatic nerve. At the site wherethe TN and CPN start to diverge, this paraneural tissue is sharedby both TN and CPN (Figs. 5A and B). An injection of dyewithinthis common paraneural sheath resulted in spread withinthe sheath, around both nerves, and external to the epineuri-um of the individual nerves, therefore preserving the integrityof the intraneural structures (Figs. 5 and 6). The dye spreaddiffusely and preferentially in the adipose tissue component ofthe paraneural sheath (Fig. 6). Beyond and distal to the pointof nerve bifurcation, the paraneural sheath divides so thatthe TN and CPN are invested by their own individual sheath(Figs. 7A and B).

DISCUSSIONSciatic nerve block at the popliteal fossa reduces postop-

erative pain and opioid requirements and improves patient sat-isfaction following outpatient foot and ankle surgery.5Y7

Popliteal sciatic nerve block has been associated with variablesuccess rates, often requiring high doses of local anesthetic, anda prolonged onset time, even with ultrasound guidance.8Y10

TABLE 1. Demographics

Group 1 (n = 39) Group 2 (n = 45) P

Sex, male-female ratio, n 20:19 25:20 0.86Age, mean T SD, y 42 T 16 39 T 14 0.42Height, mean T SD, cm 169 T 12 171 T 13 0.84Weight, mean T SD, kg 82 T 21 82 T 20 0.64Body mass index, mean T SD, kg/m2 29 T 8 29 T 7 0.65Outpatient-inpatient ratio 1:5.5 1:4.6 0.78

TABLE 2. Results

Group 1 (n = 39) Group 2 (n = 45) P

Time to complete sensory block, mean T SD, min 14 T 9 21 T 10 0.006Time to complete motor block, mean T SD, min 15 T 11 23 T 10 0.007Complete block by 30 min, % 76 49 0.026Procedure time, mean T SD, min 8 T 4 9 T 3 0.77Proximal local anesthetic spread, mean T SD, cm 9.6 T 3 8.2 T 3 0.036Distal local anesthetic spread, mean T SD, cm 4.8 T 2 3.7 T 2 0.036Total local anesthetic spread, mean T SD, cm 14.1 T 4 11.7 T 4 0.008Single skin puncture, % 87 68 0.05Residual sensory block at 24 h, n (%) 4 (11) 1 (2) 0.122Incidence of neurological symptoms at 7 d, n (%) 0 0 Not applicable




Possible reasons postulated for such long onset time include alarge nerve size (up to 2 cm in diameter) and a larger proportionof nonneuronal tissue as the sciatic nerve travels distally.11Y13 Ithas been shown that blocking both terminal branches separately,distal to sciatic nerve bifurcation, shortens onset time for bothposterior and lateral approaches.3,4 Circumferential local anes-thetic spread has also been shown to affect onset time favorably.14

Another possible reason for this slow onset is the existenceof a substantial external paraneural layer of connective and ad-ipose tissue that surrounds the sciatic nerve along its course,which may constitute a relative barrier to local anestheticspread. This external layer of paraneural tissue has been rec-ognized for many years, although inconsistent terminology hasbeen used.1,2,5 Vloka et al11 named it ‘‘common epineurialsheath,’’ suggesting somehow that this layer may be part of orrelated to the epineurium.2 The term ‘‘paraneural sheath’’ hasbeen recently proposed by Andersen et al1 to describe this layerof extraneural tissue based on anatomic-sonographic correlationin human cadavers. In the study of Andersen et al, injectionthrough this common paraneural sheath resulted in extensivelongitudinal spread of the local anesthetic around the nerveswhile remaining external to the epineurium of both terminalnerves, suggesting this may be an ideal location for local an-esthetic deposition.1

A recent study by Tran et al15 reported the effectivenessof what they called a ‘‘subepineurial’’ injection at the site ofsciatic nerve bifurcation, suggesting these were intraneural in-jections. However, in contrast with this nomenclature, there was nochange in nerve diameter upon injection, and the accompanyingfigures also suggest that these injections were in fact external to the

epineurium (ie, into the paraneural sheath). Consistent terminologywith regard to nerve boundaries and surrounding tissues is im-portant beyond semantics to ensure a common language whencomparing different approaches or techniques.2,16

This prospective clinical study aimed to establish the blockcharacteristics of popliteal nerve block performed through thiscommon paraneural sheath (as described by Andersen) at the siteof sciatic nerve bifurcation and to better characterize this sheathhistologically in a human leg specimen. The paraneural sheatharound the sciatic nerve exists all along the thigh. Although localanesthetic could conceivably be injected through this sheath atany level, the site where the 2 terminal nerves start to divergeoffers a natural point of cleavage between the nerves, wherethe sheath becomes sonographically more apparent. It appearson high-frequency ultrasound as a common layer of mixedechogenicity external to both the TN and CPN. This sheath canbe easily punctured at the point of divergence between the2 terminal nerves, and the local anesthetic injected as a singlebolus to ‘‘bathe’’ both nerves fully, within this sheath com-partment (Figs. 1 and 5). In our experience, an out-of-planeapproach is ideally suited to penetrate this common paraneuralsheath at the site of bifurcation where the TN and CPN usuallylie side by side.

Patients in the control group (group 2) received a con-ventional separate injection of both TN and CPN distal to sci-atic nerve bifurcation with circumferential local anestheticspread, as this has been associated with the shortest blockonset times previously described.3,4 Although in group 1 an out-of-plane approach seems ideally suited to puncture the sheathat the bifurcation site, we feel the needle trajectory (in-plane

FIGURE 4. Combined motor and sensory block progression. A combined score from 0 to 8 points is used, where 8 = full sensoryandmotor function and 0 = full sensory and motor block. Red bars correspond to group 1; blue bars correspond to group 2. *Statisticallysignificant difference.

TABLE 3. Nerve Size Before and After Injection

Group 1 (n = 39) Group 2 (n = 45)

Preinjection Postinjection P Preinjection Postinjection P

TN diameter, mean T SD, mm 6.7 T 1.8 6.7 T 1.8 0.981 7.1 T 2.5 7.1 T 2.4 0.982TN area, mean T SD, mm2 40 T 17 40 T 18 1 45 T 26 45 T 27 0.95CPN diameter, mean T SD, mm 6.1 T 1.6 5.9 T 2.0 0.657 6.6 T 2.4 6.2 T 2.3 0.529CPN area, mean T SD, mm2 33 T 16 32 T 23 0.963 39 T 25 34 T 23 0.487




or out-of-plane) is not as crucial when blocking 2 individualnerves separately (group 2). Depending on the specific patientanatomy, an in-plane or an out-of-plane approach may be pref-erable. Thus, we left the needle orientation for group 2 at thediscretion of the attending anesthesiologist.

The results confirm our hypothesis that blockade through acommon paraneural sheath at the site of sciatic nerve bifurca-tion is associated with faster onset of sensory (and motor) blockthan distal blockade (Table 2). One possible reason for thisfaster onset and predictable success is that this space of looseconnective tissue provides a sort of conduit around the nerves.The longitudinal spread of the local anesthetic solution was30% more extensive in group 1 versus group 2, resulting in alarger surface area of contact with the local anesthetic solution(Table 2). Even though on first appearance the results from ourstudy seem to contradict previous findings comparing proximalto distal injections,3,4 the key difference from previous studies isthat here the paraneural sheath is specifically identified andpenetrated to deposit the local anesthetic in a more intimatecontact with the external surface of the nerves’ epineurium.

Nerve size (diameter and cross-sectional area) remainedunchanged in both groups after local anesthetic injection, whichis consistent with extraepineurial (extraneural) needle place-ment (Table 3). This is desirable to minimize the possibility ofmechanical nerve injury and contribute to safety.

In addition, this technique is simple to perform. As the2 nerves typically lie side by side in a medial to lateral sense, withthe patient in the prone position, a blocking needle advanced inan out-of-plane approach punctures the paraneural sheath in theplane of separation between the 2 nerves. Eighty-seven percentof blocks in group 1 were achieved with a single needle puncture(vs 65% in group 2), and minimal or no needle manipulationwas required.

Our results are very similar to the findings of Tran andcolleagues,15 which further suggests to us that we are indeeddescribing a similar technique with different nomenclature ratherthan 2 conceptually different blocks.

Limitations of the present study include the fact that, likemost procedure-related studies, it is not possible to blind theoperator to group allocation. To minimize the possibility of bias,

FIGURE 5. A and B, Histology of the sciatic nerve and the paraneural tissues at the site of sciatic nerve bifurcation (as would be seen ingroup 1). The TN and CPN are surrounded by a common paraneural sheath of connective and fatty tissue, external to the epineurium ofeach nerve. An injection of black dye through the surface of the paraneural sheath resulted in spread around both nerves.

FIGURE 6. The CPN and a section of the paraneural sheath examined with greater magnification. The paraneural sheath is formedby loose connective and adipose tissue. Note that the black dye is found in the paraneural tissue. It is located outside the epineuriumof the nerve, and most related to the adipose tissue component.




16 different operators (most of whom were unrelated to thestudy) performed the block procedures. In addition, assessmentof neurological function and documentation of study outcomeswere carried out by an independent investigator blinded to groupallocation whenever feasible as described. Despite these mea-sures, performance bias may not be completely ruled out.

Another limitation is that we studied analgesic blocks. Theadministration of concomitant general or spinal anesthesia doesnot allow us to comment on the suitability of these blocks toprovide surgical anesthesia, or to study the rate of ‘‘conversionto general anesthesia.’’

In addition, even though no neurological deficits werereported in any patient, nerve injury is a rare complication ofperipheral nerve blockade, and this study is not powered to detectclinically meaningful differences with regard to safety.

In conclusion, the results of this study suggest that an injectionthrough a common paraneural sheath at the site of sciatic nervebifurcation is simple and highly effective. It results in a faster onsetof sensory andmotor blockade than previously reported approacheswithout an increase in the incidence of intraneural injection. Al-though there is likelymore than 1 safe and effective approach to anynerve block, a single injection through the common paraneuralsheath of the sciatic nerve complies with most of the metrics as-sociated with the ‘‘best’’ local anesthetic deposition site for poplitealblock.17 Our data suggest that this is possibly due to an optimallocal anesthetic spread within this common sheath, intimately sur-rounding the epineurium of both nerves and resulting in enhancedlongitudinal spread.

REFERENCES

1. Andersen HL, Andersen S, Tranum-Jensen J. Injection inside theparaneural sheath of the sciatic nerve: direct comparison amongultrasound imaging, macroscopic anatomy, and histologic analysis. RegAnesth Pain Med. 2012;37:410Y414.

2. Franco C. Connective tissues associated with peripheral nerves. RegAnesth Pain Med. 2012;37;363Y365.

3. Prasad A, Perlas A, Ramlogan R, Brull R, Chan V. Ultrasound-guidedpopliteal block distal to sciatic nerve bifurcation shortens onset time: aprospective randomized double-blind study. Reg Anesth Pain Med.2010;35:267Y271.

4. Buys MJ, Arndt CD, Vagh F, Hoard A, Gerstein N. Ultrasound-guidedsciatic nerve block in the popliteal fossa using a lateral approach: onset

time comparing separate tibial and common peroneal nerve injectionsversus injecting proximal to the bifurcation. Anesth Analg.2010;110:635Y637.

5. White P, Issioui T, Skrivanek G, Early JS, Wakefield C. The use of acontinuous popliteal sciatic nerve block after surgery involving the footand ankle: does it improve the quality of recovery? Anesth Analg.2003;97:1303Y1309.

6. Ilfeld BM, Morey TE, Wang RD, Enneking FK. Continuous poplitealsciatic nerve block for postoperative pain control at home: arandomized, double-blinded, placebo-controlled study. Anesthesiology.2002;9:959Y965.

7. Singelyn FJ, Gouverneur JM, Gribomont BF. Popliteal sciatic nerveblock aided by a nerve stimulator: a reliable technique for foot andankle surgery. Reg Anesth. 1991;16:278Y281.

8. Brown DL. Popliteal block. In: Brown DL, ed. Atlas of RegionalAnesthesia. Philadelphia, PA: WB Saunders Co; 1992:109Y113.

9. Hadzic A, Vloka JD. A comparison of the posterior versus lateralapproaches to the block of the sciatic nerve in the popliteal fossa.Anesthesiology. 1998;88:1480Y1486.

10. Perlas A, Brull R, Chan VW, McCartney CJ, Nuica A, Abbas S.Ultrasound guidance improves the success of sciatic nerve block at thepopliteal fossa. Reg Anesth Pain Med. 2008;33:259Y265.

11. Vloka JD, Hadzic A, Lesser JB, et al. A common epineural sheath forthe nerves in the popliteal fossa and its possible implications for sciaticnerve block. Anesth Analg. 1997;84:387Y390.

12. Chelly JE, Delauney L. A new anterior approach to the sciatic nerveblock. Anesthesiology. 1999;91:1655Y1660.

13. Moayeri N, Groen GJ. Differences in quantitative architecture of sciaticnerve may explain differences in potential vulnerability to nerve injury,onset time, and minimum effective anesthetic volume. Anesthesiology.2009;111:1128Y1134.

14. Morau D, Levy F, Bringuier S, et al. Ultrasound-guided evaluation of thelocal anesthetic spread parameters required for a rapid surgical poplitealsciatic nerve block. Reg Anesth Pain Med. 2010;35:559Y564.

15. Tran DQH, Dugani S, Pham K, Al-Shaafi A, Finlayson RJ. Arandomized comparison between subepineural and conventionalultrasound-guided popliteal sciatic nerve block. Reg Anesth Pain Med.2011;36:548Y552.

16. Endersby R, Albrecht E, Perlas A, Chan V. Semantics, misnomer, oruncertainty: where is the epineurium on ultrasound? Reg Anesth Pain

Med. 2012;37:360Y361.

17. Sites BD, Neal J. Keep it simple. Reg Anesth Pain Med.2012;37:465Y469.

FIGURE 7. A and B, TN and CPN in the popliteal fossa distally to sciatic nerve bifurcation (as would be seen in group 2). The 2 nerves havemacroscopically diverged from each other. Each nerve is now surrounded by its own separate paraneural connective and fatty tissue.




APPENDIX 1Technical Aspects of Histological Study

Using a similar technique and equipment as described forthe clinical study, the sciatic nerve was identified under ultra-sound and followed distally from the midthigh to the poplitealfossa, where the site of bifurcation, the TN, CPN, and commonparaneural sheath were identified. An insulated 50-mm, 22-gaugeregional anesthesia needle (Stimuplex; B. Braun) was advancedunder ultrasound guidance through the paraneural sheath andplaced between the 2 nerves (as in group 1). Ten milliliters ofblack Surgipath Tissue Marking & Margin Dye solution (Leica,

Buffalo Grove, Illinois) were injected at this site. Following in-jection, the superficial tissues of the popliteal fossawere dissectedfrom the skin down to the vicinity of the sciatic nerve. The sciaticnerve was excised from the macroscopically apparent bifurca-tion point down to 3 cm distally. The excision was performed‘‘en block’’ to include the immediate paraneural tissues. Thesample was fixed and embedded in paraffin, and 6-Km sectionswere stained with hematoxylin/eosin and prepared for histologyas per standard institutional practice. The sections were thenscanned with Aperio digital slide scanner at 20� magnificationfor further histological analysis.




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