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Imaging Article

ltrasound Imaging for Popliteal Sciatic Nervelock

vinash Sinha, M.B.Ch.B., F.R.C.A. and Vincent W. S. Chan, M.D., F.R.C.P.C.

Background and Objectives: Ultrasound is a novel method of nerve localization but its use for lowerextremity blocks appears limited with only reports for femoral 3-in-1 blocks. We report a case series ofpopliteal sciatic nerve blocks using ultrasound guidance to illustrate the clinical usefulness of this technol-ogy.

Case Report: The sciatic nerve was localized in the popliteal fossa by ultrasound imaging in 10 patients usinga 4- to 7-MHz probe and the Philips ATL HDI 5000 unit. Ultrasound imaging showed the sciatic nerve anatomy,the point at which it divides, and the spatial relationship between the peroneal and tibial nerves distally. Needlecontact with the nerve(s) was further confirmed with nerve stimulation. Circumferential local anesthetic spreadwithin the fascial sheath after injection appears to correlate with rapid onset and completeness of sciatic nerveblock.

Conclusions: Our preliminary experience suggests that ultrasound localization of the sciatic nerve in thepopliteal fossa is a simple and reliable procedure. It helps guide block needle placement and assess localanesthetic spread pattern at the time of injection. Reg Anesth Pain Med 2004;29:130-134.

Key Words: Popliteal, Catheter, Ultrasound, Anatomy, Local anesthesia.

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ltrasound imaging is a new method of periph-eral nerve localization and can possibly im-

rove block success and safety.1,2 To date, mosteports of ultrasound guidance for regional anes-hesia have been limited to brachial plexus blocks inhe interscalene,3,4 supraclavicular,5,6 infraclavicu-ar,7-9 and axillary3,10 regions and paravertebralerve blocks.11,12 Its application for lower extremitylocks appears underutilized with only 2 studies onemoral 3-in-1 blocks.13,14 We herein report a caseeries of 10 patients in whom popliteal sciatic nervelocks were performed under ultrasound guidancend describe the ultrasound characteristics of theciatic nerve in this region and the needle techniquef nerve localization.

From the Department of Anesthesia, University of Toronto,oronto, Ontario, Canada.Accepted for publication January 4, 2004.Correspondence: Vincent Chan, M.D., F.R.C.P.C., Department

f Anesthesia and Pain Management, Toronto Western Hospital,niversity Health Network, 399 Bathurst St., Toronto, Ontario,anada M5T 2S8. E-mail: vincent.chan@uhn.on.caReprints will not be available.© 2004 by the American Society of Regional Anesthesia and

ain Medicine.1098-7339/04/2902-0012$30.00/0

wdoi:10.1016/j.rapm.2004.01.001

30 Regional Anesthesia and Pain Medicine, Vol 29

ase Report

We performed popliteal blocks under ultrasoundmaging guidance in 10 American Society of Anes-hesiologists physical status I patients (23 to 66ears old, 168 to 183 cm, 58 to 89 kg) scheduled toave foot and ankle surgery. The patients wereositioned prone, and the surface landmarks of theopliteal triangle (the tendons of semitendinosusnd semimembranosus muscles medially, the ten-on of the biceps femoris muscle laterally, and theopliteal crease inferiorly) were identified andarked. We used the Philips ATL HDI 5000 ultra-

ound unit (ATL Ultrasound, Bothell, WA) witholor flow Doppler, compound imaging and imageideo recording features. After betadine skin prep-ration, a linear 5-cm, 4- to 7-MHz probe inside aterile cover was applied onto the posterior thighpproximately 8 cm proximal to the popliteal creasef the operative leg.The probe positioned horizontally at this level

aptured a transverse view of the sciatic nerve (ie,he ultrasound beam 90° to the nerve) and showedhe sciatic nerve as a single oval, well-circum-cribed, hyperechoic structure (Fig 1) in all 10 pa-ients. The nerve was consistently superficial and

ithin 1 to 2 cm lateral to the pulsatile hypoechoic

, No 2 (March–April), 2004: pp 130–134

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Ultrasound Imaging for Popliteal Sciatic Nerve Block • Sinha and Chan 131

opliteal artery, which was commonly 3 to 4 cmeep to the skin (Fig 1). In some cases, the vein waseen but easily compressed by the probe. Also seenere the biceps femoris muscle laterally and semi-

endinosus and semimembranosus muscles medi-lly. The femur appeared as a dense hyperechoicine found deep to the neurovascular structures.

After local anesthetic skin infiltration, a 3.5-inch,7-gauge insulated Tuohy block needle (Arrow,eading, PA) was inserted below the midpoint of

he probe perpendicular to the ultrasound beamFig 2). In this orientation, the needle was seen inross section on ultrasound as a hyperechoic “dot”ithout full image of the needle shaft. Only needle

nd thigh tissue movement was observed in realime. Once the needle was deemed in contact withhe nerve on ultrasound, foot dorsi-flexion or plan-ar flexion was sought using a nerve stimulatorStimuplex; Braun Medical, Bethlehem, PA) untilptimal stimulation was obtained at less than 0.5A. A 20-gauge stimulating catheter (Stimucath;rrow) was then advanced 4 to 5 cm beyond theeedle tip. After catheter stimulation with 0.5 to 1A, 15 mL of 1.5% lidocaine with epinephrine

:200,000 and 15 mL of 0.5% bupivacaine werenjected incrementally over 2 to 3 minutes.

In the transverse view, local anesthetic spreadas examined after injection of 5 mL, 10 mL, 20L, and 30 mL to examine local anesthetic spread.ircumferential spread (Fig 3A, video [see videolip in this article at www.rapm.org]) was noted inpatients resulting in rapid onset (within 10 min-

tes) and complete anesthesia in the foot within 20

ig 1. Transverse sonogram in the popliteal region show-ng the sciatic nerve as a hyperechoic nodule (arrow)ateral to the popliteal artery (A). Abbreviations: med,

edial; lat, lateral.

inutes. In contrast, spread seen only to one side of m

he nerve, not encompassing the whole nerve, wasssociated with a partial block (Fig 3B). We couldlso capture a longitudinal view of the sciatic nervend the overlying stimulating needle by rotating therobe vertically from the horizontal position andcanning the nerve along its long axis (Fig 4).

iscussion

The use of popliteal nerve block to relieve painfter foot and ankle surgery is gaining popularitynd can speed hospital discharge in outpatients.15

he provision of a perineural catheter and localnesthetic infusion can further extend the period ofain control well beyond that following the singlenjection technique. Reduced opioid consumption,educed opioid-related side effects, and improvedatient satisfaction are benefits recently reported.16

nfortunately, the failure rate of single-shot popli-eal blocks may be as high as 21% with manyequiring supplementation.17 It is conceivable thatltrasound imaging may improve the accuracy oferve localization and needle placement. Direct vi-ualization of nerve location and local anestheticpread may also reduce block failure rate andhorten onset time.13,14,18 Furthermore, imagingan help prevent accidental puncture to vessels andther neighboring structures.Achieving consistent, interpretable ultrasound

mages of nerves and the block needle requiresome degree of technical skill and correct ultra-ound probe orientation. Using the classical popli-

ig 2. An example of ultrasound-guided needle tech-ique showing one hand holding the probe and one handolding the insulated needle in the popliteal fossa. Theeedle is advanced below the midpoint of the ultrasoundrobe perpendicular to the ultrasound beam. Abbrevia-ions: C, popliteal crease; med, medial border formed byhe semitendinosus and semimembranosus muscle ten-ons; lat, lateral border formed by the biceps femoris

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132 Regional Anesthesia and Pain Medicine Vol. 29 No. 2 March–April 2004

eal block approach,19 we advance the needle in theosterior thigh while the ultrasound probe is posi-ioned horizontally. In this orientation, we can onlynfer needle position through associated move-

ent, as the needle moves perpendicular to theltrasound beam. If visualization of the needle shaft

s desired, the ultrasound probe must have a longi-udinal orientation to the nerve (probe now verti-al) so that the beam is aligned with the long axis ofoth the needle and the sciatic nerve (Fig 4).The point at which the sciatic nerve divides

bove the popliteal crease is highly variable (0-15 mm, mean of 61 mm � 27 mm).20 This can because for difficult localization of both the pero-eal and tibial nerves using the nerve stimulationechnique. To prevent incomplete anesthesia, a

ig 3. (A) Transverse sonogram showing circumferentialnjection. (B) Transverse sonogram showing incomplete

ig 4. Longitudinal view of the sciatic nerve with theverlying stimulating needle (arrows). Abbreviations:

3eph, cephalad; caud, caudad.

ouble injection technique has been advocated tonesthetize individually both components of theciatic nerve.20 With ultrasound scanning, weere able to identify precisely the point at which

he sciatic nerve divides in each of the 10 pa-ients. Distally, we could also examine the spatialelationship between the common peroneal andibial nerves. We found the 2 nerves situated sidey side (Fig 5A) in 9 patients but, unexpectedly,top one another (Fig 5B) in 1 patient. This laterrientation would make it difficult, if not impos-ible, to individually localize both branches of theciatic nerve with the conventional nerve stimu-ation technique. Ultrasound visualization of theciatic nerve and its terminal branches at the timef nerve block shows the optimal site of needlelacement. This is a significant advantage overonventional “blind” approaches.Anatomical studies show the presence of an ad-

entitial sheath enveloping the sciatic nerve and itsivisions and dye spread within this sheath in ca-avers.21 Our observation of local anesthetic spreadround the nerves and extensive spread proximallylong the nerves lends support to the adventitialheath concept (Fig 6). We have observed bothymmetrical circumferential (Fig 3A) and asymmet-ical spread (Fig 3B) around the nerves. Our pre-iminary observation suggests that faster block on-et and greater success happen with circumferentialocal anesthetic spread along the course of theerve. To optimally assess local anesthetic spread, it

s necessary to scan the nerve both distally androximally and not at a single-nerve location. Ex-ensive proximal local anesthetic spread after a

anesthetic spread around the sciatic nerve after a 30-mLnesthetic spread. Abbreviation: LA, local anesthetic.

locallocal a

0-mL injection can also account for successful

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Ultrasound Imaging for Popliteal Sciatic Nerve Block • Sinha and Chan 133

lock of both the peroneal and tibial divisions, de-pite injection at the site of stimulation of only oneivision. Conceivably, if ultrasound visualizationuring local anesthetic injection can identify the

ig 5. (A) Transverse sonogram showing peroneal andibial divisions of the sciatic nerve lying side by side. (B)ransverse sonogram showing peroneal and tibial divi-

ions atop of each other. Abbreviation: F, femur.

xtent of circumferential and proximal spread, it isot necessary to block nerves individually, thusvoiding multiple attempts and, potentially, nervenjury.

Advanced ultrasound technology today yieldsigh-quality anatomical images with distinct clar-

ty. Our preliminary ultrasound experience ofcanning the sciatic nerve and its branches in theopliteal fossa is encouraging. As for other pe-ipheral nerves, we believe ultrasound imaging ofhe sciatic nerve will prove valuable for nerveocalization clinically and can possibly predictlock success and completeness. Whether ultra-ound is useful for localizing the sciatic nerve ineeper locations of the lower extremity is notnown at the present time and warrants futuretudies.

cknowledgement

The ultrasound machine was on loan from Philipsedical Systems Canada.

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