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Sciatic nerve block
Sciatic Nerve Block Jacques E. Chelly, MD, PhD, MBA
In combination with a lumbar plexus, femoral, or saphenous nerve block, sciatic nerve blocks provide complete anesthesia and postoperative analgesia for lower-extremity surgery. Contrary to common belief, sciatic nerve blocks are relatively simple to perform and master. However, the deep location of the sciatic nerve mandates proper training and thorough knowledge of anatomy. Recently, there has been a resurgence of interest in sciatic nerve block techniques and several new and more reliable techniques have been described. This article provides an overview of the relevant anatomy, development in the field, and describes several common approaches to the sciatic nerve. Copyright 2003, Elsevier Science (USA). All rights reserved.
ciatic nerve blocks, in combination with a lumbar plexus, femoral, or saphenous nerve block, provide complete anesthesia and postoperative analgesia for lower-extremity surgery. Contrary to common belief, sciatic nerve blocks are relatively easy to master and accomplish and it is surprising that sciatic nerve blocks are among the least frequently practiced nerve block procedures.1-3 Recently, there has been a renewed interest in the use of sciatic nerve block techniques and a number of novel approaches to block the sciatic nerve with simplified anatomy and improved success rate.
S
Anatomy The sciatic nerve is a motor and sensory nerve originating from the sacral plexus, which is formed from the ventral rami of the fourth lumbar to the fourth sacral nerves. From its origins, it is constituted by the tibial nerve medially and posteriorly and by the common peroneal nerve laterally and anteriorly. These two nerves are enclosed in a common sheath. The sciatic nerve, the superior and inferior gluteal nerves, and the pudendal nerve, which comprise the sacral plexus, converge to form a triangle. The superior gluteal nerve innervates the gluteus minus and medialis, while the sciatic nerve enters the buttocks region below the pirifomis muscle through the greater sciatic foramen. At this level originates the nerve innervating the hamstring muscles that run down to the semimembranous and semitendinous muscles and the posterior cutaneous nerve of the thigh, which provides superficial innervation to the posterior aspect of the thigh. In the buttocks, the sciatic nerve runs over the obturator internus, superior and inferior gemelli, and quadra-
From the Department of Anaesthesiology, University of Pittsburgh, Pittsburgh, PA. Address reprint requests to Jacques Chelly, MD, PhD, MBA, Professor and Vice Chairman of Clinic Research, Department of Anesthesiology, University of Pittsburgh, A1305 Scaife Hall, 3550 Terrace St., Pittsburgh, PA 15261. Copyright 2003, Elsevier Science (USA). All rights reserved. 1084-208X/03/0701-0005$35.00/0 doi:10.1053/trap.2003.123521
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tus femoris muscles. In the gluteal region, the sciatic nerve lies medial and posterior to the femur. In the thigh, the sciatic nerve runs toward the popliteal fossa, within the posteromedial compartment of the thigh in a groove between the biceps femoris laterally and the semimembranous semitendinous muscles medially. Before entering the popliteal fossa, the sciatic nerve separates into the tibial nerve that runs medially toward the posterior aspect of the leg and the common peroneal nerve that runs laterally toward the head of the fibula. Accordingly, the sciatic nerve can then be reached at different levels from the greater sciatic foramen to the lower part of the thigh. In addition, at the level of the thigh, it is possible to define a (sciatic line) running from the inferior border of the gluteus maximus to the popliteal fossa, allowing performance of a sciatic block at any level of this line.
The Choice of the Technique Although posterior and lateral popliteal approaches to the sciatic nerve are performed most commonly for ankle and foot surgery,4-8 and higher approaches to the sciatic nerve are performed more commonly for surgery below, above, and at the knee,9-12 it is important to recognize that there is no clinical evidence in support of one particular sciatic approach over another. An exemption to this rule are surgical indications requiring sensory and motor blocks of the posterior aspect of the thigh (which benefit most from a parasacral10-12 or posterior approach13-18). For any nerve, the indications of a given approach is based on the specific surgical requirement, the need for a single versus continuous nerve block, timing of block procedure in relationship to the surgery, and the need for special patient positioning. We typically place nerve blocks preoperatively and before the patient’s transfer to the operating room. The need for the patient’s positioning plays a key role in technique selection in our practice. For instance, with the patient in the supine position, it is possible to approach the sciatic nerve through an anterior approach19-23 or a lateral approach (at the greater trochanter24-26 or lower in the thigh above the popliteal fossa27,28). With the patient in the lateral position (Sim’s position), it is possible to reach the sciatic nerve as it exits the greater sciatic foramen (parasacral approach13-17) at the level of the buttock (posterior approach18), and at the level of the ischial tuberosity (gluteal29, or subgluteal crease).30,31 With the patient in lithotomy position, the sciatic nerve can be blocked at the level of the ischeal tuberosity (Raj et al’s32 approach). Finally, with the patient in the prone position, the sciatic nerve block can be performed through a low gluteal or high popliteal approach. Except for the lithotomy approach, all other approaches to the sciatic nerve have been used for both single and continuous nerve blocks. As previously indicated, there are clinical advantages of one approach over the others according to the type of surgery or the
Techniques in Regional Anesthesia and Pain Management, Vol 7, No 1 (January), 2003: pp 18-25
use of a tourniquet. The choice of the approach often depends on the patient’s mobility (morbidly obese, trauma, intensive care unit) and the extent of the patient’s injury. Because a combination of sciatic and lumbar plexus blocks often is indicated, the choice of the approach also should take into consideration the approach used to block the lumbar plexus/femoral/ saphenous nerve. For instance, when the sciatic block is combined with a lumbar plexus block, we favor a parasacral, posterior, and gluteal and subgluteal approach. In contrast, when the sciatic block is combined with either a femoral block or a saphenous nerve block, we favor an anterior or lateral approach. Finally, in the case of placement of a perineural catheter, the choice of the technique also may be dictated by the requirement to keep the perineural catheter outside of the surgical field.
injecting 2 to 3 mL of local anesthetic through a 25-gauge, 39-mm needle.
Patient in the Supine Position In the supine position, the sciatic nerve can be approached either anteriorly or laterally. Around the lesser trochanter, the sciatic nerve runs medial and posterior to the femur. A few centimeters distally until the popliteal fossa, the sciatic nerve runs posterior to the femur until its division into the tibial and common peroneal nerves. The relationship between the sciatic nerve and the femur dictates that anteriorly this nerve only can be approached at the proximity of the lesser trochanter.33 In contrast, the sciatic nerve can be approached laterally at any level between the greater trochanter to the popliteal fossa.
Anterior Approach
Techniques General Considerations Single-shot sciatic nerve blocks irrespective of the approach require a lesser volume than for blocks performed at the level of the popliteal fossa (15-25 mL vs 30-40 mL). This lower volume requirement is important especially when considering the total volume required to perform a combined sciatic and a lumbar plexus block with a single stimulation technique. The use of a nerve stimulator is essential to optimize the success rate of any sciatic nerve block. A 100- or 150-mm, 21to 22-gauge insulated needle (depending on the size of the patient and the approach chosen), is connected to a nerve stimulator, usually set up to deliver 1.5 mA, 2 Hz, and 0.1 ms. Irrespective of the approach, the stimulation of the sciatic nerve produces either a dorsiflexion of the foot with an extension of the toes or an eversion (stimulation of the common peroneal nerve), or a plantar flexion of the foot and toes or an inversion (stimulation of the tibial nerve). A contraction of the hamstring muscle usually indicates that the needle is too medial. When the appropriate muscle response is obtained, the position of the needle is adjusted to maintain the same motor response with a current of 0.4 mA. After negative aspiration for blood, 2 mL of the local anesthetic solution is injected slowly and the current of the nerve stimulator is increased to 2 mA to reproduce the muscular contraction and verify that the needle still is close to the nerve. The total volume of local anesthetic is injected slowly 5 mL at a time with negative aspiration for blood in between. In the case of a placement of a perineural catheter for a continuous nerve block, an 18-gauge insulated introducer Tuohy needle is used to locate the sciatic nerve. After injection of the initial bolus (15-20 mL), a 20-gauge catheter is introduced 3 to 4 cm beyond the tip of the needle. If a stimulating catheter is used, the initial bolus is injected via the perineural catheter. The catheter usually is secured with tape and covered with a transparent bandage allowing for direct visualization of the insertion site and catheter. With continuous nerve blocks, 5 to 8 mL/hr of a local anesthetic solution (0.2% ropivacaine) is infused over 24 to 72 hours, depending on the indication. Alternatively, patient-controlled analgesia with no basal infusion rate and 2.5 to 4 mL per bolus with a 30- to 45-minute lock-out period can be used. Because the sciatic nerve runs deep, local anesthesia of the skin and surrounding tissues is necessary to avoid pain during the introduction of the needle. This is achieved best by SCIATIC NERVE BLOCK
Anatomic landmarks for the anterior approach. Beck19 in 1963 first described an anterior approach to the sciatic nerve based on the use of landmarks defining the inguinal ligament (the anterior iliac spine and the pubis tubercle) and the greater and lesser trochanters. The complexity of the landmarks necessary to determine the site of introduction of the needle greatly limited the use of this approach. More recently, we described an approach based on only 2 anatomic landmarks: the lower border of the anterior iliac spine and the superior border of the pubis tubercule, landmarks independent of the physical characteristics of the patient. It is of special interest to recognize that both the Beck19 and the Chelly and Delaunay20 approaches defined the same site for the introduction of the needle, but through different landmarks. In 2001, Barbero et al,21 using the same basic Chelly and Delaunay20 landmarks proposed the formula S (site of introduction of the needle ⫽ [size cm ⫺ 100]/10.2), which takes into consideration the size of the patient. More recently, VanElstraete et al22 and Souron et al23 in 2002 proposed anatomical landmarks based on the inguinal crease and the femoral artery.
Anterior Approach Technique A line is drawn between the lower border of the anterior superior iliac spine and the superior angle of the pubic tubercle. A perpendicular line is drawn in the middle and extended distally by 8 cm to define the site of introduction of the needle. A 150-mm insulated needle connected to a nerve stimulator is introduced through the skin and the quadriceps muscle. Because of the proximity of the femoral nerve, in most cases movement of the patella is elicited. To confirm that the needle on its way to the sciatic nerve is some distance from the femoral nerve, the intensity of the current is decreased to 0.5 mA to ensure that the femoral nerve stimulation ceases (patella movement stops). Then the intensity of the current is increased to 2 to 5 mA and the needle is introduced at a depth of 8 to 13 cm before stimulation of the sciatic nerve is elicited. With this approach, in most cases the first attempts produce bone contact. The depth at which the femur is contacted allows for an estimation of the depth at which the sciatic nerve will be located (distance of bone contact plus 3-4 cm). Next, the needle is withdrawn to the skin after the skin is moved medially 1.5 to 2 cm and the needle is introduced by repeating the same approach. If the needle path continues to be obstructed by the femur, it is most likely that the needle is being introduced at the
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level of the lesser trochanter. In this case, an internal rotation of the foot helps swing the lesser trochanter laterally and allows for needle passage toward the sciatic nerve. Alternatively, the site of the needle insertion is moved 1 cm cephalad to avoid the lesser trochanter altogether. The anterior approach to the sciatic nerve is performed typically in combination with a femoral nerve block. It is recommended to first perform the femoral block because it allows the sciatic block to be performed with minimum discomfort to the patient and the introduction of the needle into the hamstring muscle (sciatic innervation) is associated with some discomfort and is a signal that the needle has been introduced too far. In obese patients (⬎100-120 kg), the 150-mm length may not be long enough to assess the sciatic nerve with an anterior or high lateral approach. In these cases, a lithotomy or low lateral approach is indicated.
Technique The posterior iliac spine and the ischeal tuberosity are identified and a line joining these 2 points is drawn. The site of introduction of the needle is 7 cm distal from the posterior iliac spine. A 22-gauge, 100-mm, insulated needle connected to a nerve stimulator is introduced perpendicular to the skin. Within 6 to 8 cm, a stimulation of the sciatic nerve is elicited. In the case of a continuous nerve block, a catheter is placed using a 100-mm, 18-gauge, insulated Tuohy needle with the bevel oriented laterally. To facilitate the introduction of the catheter, Gaertner et al34 recommend introducing the introducer needle or cannula at a 10° posterior and cephalad angle. Because the parasacral approach often is combined with a lumbar plexus block, the depth at which the lumbar plexus is stimulated is a good indicator of the depth at which the sciatic nerve will be stimulated.
Lateral Approaches Anatomic landmarks for the lateral approaches. For a high lateral approach, the greater trochanter is used; for a low lateral approach, the tip of the patella and the groove between the biceps femoris and the vastus lateralis are used. Lateral approach techniques. For a high lateral technique, the greater trochanter is identified and the 150-mm insulated needle connected to a nerve stimulator is introduced perpendicular to the skin, 3 cm distal from the greater trochanter and below the posterior border of the femur. Within 10 to 13 cm, the sciatic nerve is stimulated. If the needle is introduced too anteriorly, the needle usually contacts the femur within 3 to 6 cm. If the placement of a perineural catheter is indicated, a 150-mm, 18-gauge insulated introducer Tuohy needle is used with the bevel oriented cephalad. For a low lateral technique, the groove between the biceps femoris and the lateral border of the vastus lateralis muscle is identified and marked. The site of introduction of the needle is the intersection between the groove line and a vertical line drawn 10 cm cephalad from the tip of the patella. A 100-mm insulated needle connected to a nerve stimulator is introduced posteriorly at a 30° angle. Initially, a local contraction of either the biceps femoris or vastus lateralis is observed while the insulated needle is being introduced. Within 4 to 6 cm, the local contractions disappear, and within an additional 1 to 3 cm, a sciatic motor response is elicited. If the placement of a perineural catheter is indicated, a 100-mm, 18-gauge, insulated Tuohy needle is used with the bevel oriented cephalad.
Patient in the Lateral Position Parasacral Approach The parasacral approach results in a block of the sacral plexus after its emergence from the greater sciatic foramen. Thus, this technique produces a block of the sciatic nerve as well as the other nerves that comprise the sacral plexus (superior and inferior gluteal nerves, posterior cutaneous nerve of the thigh, and pudendal nerve). Furthermore, this approach also frequently blocks the corresponding sympathetic trunks (increased risk for urinary retention), and the obturator nerve, because of their proximity. The anatomic landmarks are the posterior iliac spine and the ischeal tuberosity.
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Posterior Approach The posterior approach is the oldest and most commonly performed approach to block the sciatic nerve, especially for a single block.
Anatomic Landmarks Labat’s original description in 1922 was based on the use of only 2 anatomic landmarks, the greater trochanter and the posterior iliac spine. Winnie18 introduced another landmark, the sacral hiatus.
Technique (Classic Approach) The greater trochanter, the posterior iliac spine, and the sacral hiatus are identified and marked. A line is drawn between the greater trochanter and the posterior iliac spine. A second line is drawn between the greater trochanter and the sacral hiatus. A third line is drawn perpendicular to the greater trochanter and the posterior iliac spine line at its middle. The site of introduction of the needle is the intersection of these perpendicular lines with the greater trochanter-sacral hiatus line. Depending on the size of the patient, a 100- to 150-mm, insulated needle connected to a nerve stimulator is introduced perpendicular to the skin. First, a direct contraction of the gluteus maximus muscle is elicited, which is then followed by stimulation of the sciatic nerve. Isolated stimulation of the pyriformis muscle indicates that the needle is too cephalad. In some cases, the patient indicates that he/she is feeling an electrical impulse in the perineum, which indicates that the needle missed the sciatic nerve and went too far through the sciatic foramen. In this case, the needle needs to be withdrawn and reoriented either more medially or laterally. For continuous nerve blocks, an 18-gauge, 100- to 150-mm, insulated Tuohy needle is used with the bevel oriented cephalad and medially.35,36 In 1989, Rucci et al37 proposed a construct to define the site of introduction of the needle based on the use of the posterior iliac spine, the greater trochanter, and the ischial tuberosity. More recently, Casals Merchan et al38 proposed the use of the posterior superior iliac spine and the sacral hiatus.
3 Fig 1.
Anatomy of the sciatic nerve. JACQUES E. CHELLY
SCIATIC NERVE BLOCK
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Fig 2. High sciatic nerve approaches: ASIS, anterior superior iliac spine; SBPS, superior border of the pubic symphisis; GT, greater trochanter; IT, ischeal tuberosity; PS, pubic symphisis; PSIS, posterior superior iliac spine; SH, sacral hiatus. X represents the site if introduction of the needle.
Gluteal and Subgluteal Approach Anatomic Landmarks This approach is based on the use of 2 anatomic landmarks: the greater trochanter and the ischeal tuberosity. At this level, the sciatic nerve runs posterior and medial to the femur on the posterior aspect of the adductor magnus.
Gluteal Block This approach was described by Sutherland in 1998 and represents a variant of an approach described earlier by Raj et al.32 A 22-gauge, 100-mm needle is introduced perpendicular to the skin in the middle of the line drawn between the ischeal tuberosity and the greater trochanter. Within 5 to 7 cm, the sciatic nerve is stimulated. 29
Subgluteal Block The subgluteal block has been introduced recently by di Benedetto et al30 and is gaining popularity because of its simplicity and reliability. A line is drawn joining the greater trochanter and the ischeal tuberosity. From the midpoint of this line, a perpendicular line is extended caudally for 4 cm. (At this level, a skin depression can be palpated, representing the groove between the biceps femoris and semitendinous muscles.) This point represents the site of the introduction of the needle. A 100-mm insulated needle connected to a nerve stim-
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ulator is introduced through the skin at an 80° angle. The sciatic nerve usually is located at a depth of 5 to 7 cm. In the case of continuous nerve blocks, an 18-gauge, 100-mm, insulated Tuohy needle with the bevel oriented cephalad is used. This approach is very interesting for the placement of a perineural catheter before surgery because in most cases the position of the catheter is outside the surgical site.
Sciatic Nerve Block With the Patient in the Prone Position Although the sciatic nerve can be approached anywhere from the gluteal region to the popliteal fossa, the most common approach used clinically is just above the popliteal fossa (popliteal block).
Anatomic Landmarks This approach is based on the use of the 3 anatomic landmarks that define the posterior popliteal fossa: the popliteal crease, and the medial border of the femoris biceps muscle laterally, and the tendon of the semitendinous muscle medially.
Technique A line is drawn joining the medial border of the femoris biceps muscle laterally and the lateral border of the semitendinous muscle medially at the level of the popliteal crease. From the JACQUES E. CHELLY
Fig 3. High posterior popliteal approach.
SCIATIC NERVE BLOCK
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middle of this line, a perpendicular line is extended 15 cm cephalad. The site of insertion of the needle is 1 cm laterally. A 100-mm, insulated needle connected to a nerve stimulator is introduced through the skin at a 60° angle. The sciatic nerve usually is located at a depth of 8 to 10 cm. In the case of continuous nerve blocks, a 100-mm, 18-gauge, insulated Tuohy needle with the bevel oriented cephalad is used.
6. 7.
8.
Patient in the Lithotomy Position
9.
Although it is conceivable that in the lithotomy position the sciatic nerve can be approached at different levels of the thigh on the sciatic line, only one approach has been described, by Raj et al.32 This gluteal approach is indicated particularly in patients who cannot be moved from the supine position (trauma and especially morbidly obese patients, in whom a 150-mm needle is too short to perform an anterior approach). However, this position is not appropriate for the placement of a perineural sciatic catheter.
10.
11.
12.
13.
Anatomic Landmarks This approach is also based on the use of 2 anatomic landmarks: the greater trochanter and the ischeal tuberosity.
Technique The leg is flexed at the hip and the knee and supported by an assistant. A line is drawn between the ischeal tuberosity and the greater trochanter of the femur. The site of introduction of the needle is the middle of the line. A 22-gauge, 100-mm, insulated needle connected to a nerve stimulator is introduced perpendicular to the skin. Within 4 to 6 cm, the sciatic nerve is stimulated.
14. 15. 16. 17.
18. 19. 20. 21.
Conclusions Sciatic nerve blocks provide effective anesthesia and postoperative analgesia in patients undergoing lower-extremity surgery. A considerable resurgence of interest in this technique is exemplified by a multitude of approaches and their modifications aimed at making this block more reliable and user friendly. This review focuses primarily on the technical aspects of choosing the optimal approach and outlining the historic perspective and technique subtleties that vary among the different techniques. The effectiveness of single or continuous sciatic or any other peripheral nerve block is maximized when these techniques are used as part of a multimodal, multidisciplinary approach to pain management.
References 1. Hadzic A, Vloka JD, Kuroda MM, et al: The practice of peripheral nerve blocks in the United States: A national survey. Reg Anesth Pain Med 23:241-246, 1998 2. Hadzic A, Vloka JD, Kuroda MM, et al: A survey of exposure to regional anesthesia techniques in American anesthesia residency training programs. Reg Anesth Pain Med 24:11-16, 1999 3. Chelly JE, Greger J, Hagberg CA, et al: Training of residents in peripheral nerve blocks during anesthesiology residency training. J Clin Anesth 14:584-588, 2002 4. Hansen E, Eshelman MR, Cracchiolo A 3rd: Popliteal fossa neural blockade as the sole anesthetic technique for outpatient foot and ankle surgery. Foot Ankle Int 21:38-44, 2000 5. McLeod DH, Wong DHW, Vaghadia H, et al: Lateral popliteal sciatic
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nerve block compared with ankle block for analgesia following foot surgery. Can J Anaesth 42:765-769, 1995 Rongstad K, Mann RA, Prieskorn D, et al: Popliteal sciatic nerve block for postoperative analgesia. Foot Ankle Int 17:378-382, 1996 Hadz˘ ic A, Vloka JD: A comparison of the posterior versus lateral approaches to the block of the sciatic nerve in the popliteal fossa. Anesthesiology 88:1480-1486, 1998 Singelyn FJ, Aye F, Gouverneur JM: Continuous popliteal nerve block: An original technique to provide postoperative analgesia after foot surgery. Anesth Analg 84:383-386, 1997 Kilpatrick AW, Coventry DM, Todd JG: A comparison of two approaches to sciatic nerve block. Anaesthesia 47:155-157, 1992 Davies MJ, McGlade DP: One hundred sciatic nerve blocks: A comparison of localization techniques. Anaesth Intensive Care 21: 76-78, 1993 Bailey SL, Parkinson SK, Little WL, et al: Sciatic nerve block: A comparison of single versus double injection technique. Reg Anesth 19:9-13, 1994 di Benedetto P, Casati A, Bertini L, et al: Postoperative analgesia with continuous sciatic nerve block after foot surgery: A prospective, randomized comparison between the popliteal and subgluteal approaches. Anesth Analg 94:996-1000, 2002 Mansour NY: Reevaluating the sciatic nerve block: Another landmark for consideration. Reg Anesth 18:322-323, 1993 Morris GF, Lang SA: Continuous parasacral sciatic nerve block: Two case reports. Reg Anesth 22:469-472, 1997 Morris GF, Lang SA, Dust WN, et al: The parasacral sciatic nerve block. Reg Anesth 22:223-228, 1997 Bruelle P, Cuvillon P, Ripart J, et al: Sciatic nerve block: Parasacral approach. Reg Anesth 23:S78, 1998 Souron V, Eyrolle L, Rosencher N: The Mansour’s sacral plexus block: An effective technique for continuous block. Reg Anesth Pain Med 25:208-209, 2000 Winnie AP: Regional Anesthesia. Surg Clin North Am 55:861-892, 1975 Beck GP: Anterior sciatic nerve block. Anesthesiology 24:222-224, 1963 Chelly JE, Delaunay L: A new anterior approach to the sciatic nerve block. Anesthesiology 91:1655-1660, 1999 Barbero C, Fuzier R, Samii K, et al: Anterior approach to the sciatic nerve block: The puncture site is dependent on the patient’s size. Anesthesiology 95:A925, 2001 Van Elstraete AC, Poey C, Lebrun T, et al: New landmarks for the anterior approach to the sciatic nerve block: Imaging and clinical study. Anesth Analg 95:214-218, 2002 Souron V, Delaunay L: Sciatic nerve block via the anterior approach: Description of new landmarks. Anesth Analg 2003 (in press) Ichiyanagi K: Sciatic nerve block: Lateral approach with patient supine. Anesthesiology 20:601-604, 1959 Dalens B, Tanguy A, Vanneuville G: Sciatic nerve blocks in children: Comparison of the posterior, anterior, and lateral approaches in 180 pediatric patients. Anesth Analg 70:131-137, 1990 Guardini R, Waldron BA, Wallace WA: Sciatic nerve block: A new lateral approach. Acta Anaesthesiol Scand 29:515-519, 1985 Chelly JE, Greger J, Al-Samsam T, et al: Continuous lateral sciatic blocks for acute postoperative pain management after major foot and ankle surgery. Foot Ankle Int 23:749-752, 2002 Naux E, Pham-Dang C, Petitfaux F, et al: Sciatic nerve block: A new lateral mediofemoral approach. The value of its combination with a “3-in-1” block for invasive surgery of the knee. Ann Fr Anaesth Reanim 19:9-15, 2000 Sutherland IDB: Continuous sciatic nerve block infusion: Expanded case report describing a new approach. Reg Anesth Pain Med 23:496-501, 1998 di Benedetto P, Bertini L, Casati A, et al: A new posterior approach to the sciatic nerve block: A prospective, randomized comparison with the classic posterior approach. Anesth Analg 93:1040-1044, 2001 di Benedetto P, Casati A, Bertini L: Continuous subgluteus sciatic nerve block after orthopedic foot and ankle surgery: Comparison of two infusion techniques. Reg Anesth Pain Med 27:168-172, 2002 Raj PP, Parks RI, Watson TD, et al: A new single-position supine JACQUES E. CHELLY
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34. 35. 36.
approach to sciatic-femoral nerve block. Anesth Analg 54:489-493, 1975 Ericksen ML, Swenson JD, Pace NL: The anatomic relationship of the sciatic nerve to the lesser trochanter: Implications for anterior sciatic nerve block. Anesth Analg 95:1071-1074, 2002 Gaertner E, Petit S, Cuby C, et al: Parasacral catheter placement for lower limb surgery. Reg Anesth Pain Med 26:71, 2001 (suppl) Smith BE, Fischer HB, Scott PV: Continuous sciatic nerve block. Anaesthesia 39:155-157, 1984 Grant SA, Nielsen KC, Greengrass RA, et al: Continuous peripheral
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nerve block for ambulatory surgery. Reg Anesth Pain Med 26:209214, 2001 37. Rucci FS, Trafficante FG, Moresi M: A new approach to sciatic nerve block in the gluteal region. Eur J Anaesthesiol 6:363-372, 1989 38. Casals Merchan M, Eshan F, Martinez Manas F, et al: Sciatic nerve block. Description of a new posterior approach in the gluteal area. Rev Esp Anestesiol Reanim 47:245-251, 2000 39. Whitelaw G, DeMuth K, Demos H, et al: The use of the Cryo/Cuff versus ice and elastic wrap in the postoperative care of knee arthroscopy patients. Am J Knee Surg 8:28-30, 1995
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In combination with a lumbar plexus, femoral, or saphenous nerve block, sciatic nerve blocks provide complete anesthesia and postoperative analgesia for lower-extremity surgery. Contrary to common belief, sciatic nerve blocks are relatively simple to perform and master. However, the deep location of the sciatic nerve mandates proper training and thorough knowledge of anatomy. Recently, there has been a resurgence of interest in sciatic nerve block techniques and several new and more reliable techniques have been described. This article provides an overview of the relevant anatomy, development in the field, and describes several common approaches to the sciatic nerve. Copyright 2003, Elsevier Science (USA). All rights reserved.
ciatic nerve blocks, in combination with a lumbar plexus, femoral, or saphenous nerve block, provide complete anesthesia and postoperative analgesia for lower-extremity surgery. Contrary to common belief, sciatic nerve blocks are relatively easy to master and accomplish and it is surprising that sciatic nerve blocks are among the least frequently practiced nerve block procedures.1-3 Recently, there has been a renewed interest in the use of sciatic nerve block techniques and a number of novel approaches to block the sciatic nerve with simplified anatomy and improved success rate.
S
Anatomy The sciatic nerve is a motor and sensory nerve originating from the sacral plexus, which is formed from the ventral rami of the fourth lumbar to the fourth sacral nerves. From its origins, it is constituted by the tibial nerve medially and posteriorly and by the common peroneal nerve laterally and anteriorly. These two nerves are enclosed in a common sheath. The sciatic nerve, the superior and inferior gluteal nerves, and the pudendal nerve, which comprise the sacral plexus, converge to form a triangle. The superior gluteal nerve innervates the gluteus minus and medialis, while the sciatic nerve enters the buttocks region below the pirifomis muscle through the greater sciatic foramen. At this level originates the nerve innervating the hamstring muscles that run down to the semimembranous and semitendinous muscles and the posterior cutaneous nerve of the thigh, which provides superficial innervation to the posterior aspect of the thigh. In the buttocks, the sciatic nerve runs over the obturator internus, superior and inferior gemelli, and quadra-
From the Department of Anaesthesiology, University of Pittsburgh, Pittsburgh, PA. Address reprint requests to Jacques Chelly, MD, PhD, MBA, Professor and Vice Chairman of Clinic Research, Department of Anesthesiology, University of Pittsburgh, A1305 Scaife Hall, 3550 Terrace St., Pittsburgh, PA 15261. Copyright 2003, Elsevier Science (USA). All rights reserved. 1084-208X/03/0701-0005$35.00/0 doi:10.1053/trap.2003.123521
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tus femoris muscles. In the gluteal region, the sciatic nerve lies medial and posterior to the femur. In the thigh, the sciatic nerve runs toward the popliteal fossa, within the posteromedial compartment of the thigh in a groove between the biceps femoris laterally and the semimembranous semitendinous muscles medially. Before entering the popliteal fossa, the sciatic nerve separates into the tibial nerve that runs medially toward the posterior aspect of the leg and the common peroneal nerve that runs laterally toward the head of the fibula. Accordingly, the sciatic nerve can then be reached at different levels from the greater sciatic foramen to the lower part of the thigh. In addition, at the level of the thigh, it is possible to define a (sciatic line) running from the inferior border of the gluteus maximus to the popliteal fossa, allowing performance of a sciatic block at any level of this line.
The Choice of the Technique Although posterior and lateral popliteal approaches to the sciatic nerve are performed most commonly for ankle and foot surgery,4-8 and higher approaches to the sciatic nerve are performed more commonly for surgery below, above, and at the knee,9-12 it is important to recognize that there is no clinical evidence in support of one particular sciatic approach over another. An exemption to this rule are surgical indications requiring sensory and motor blocks of the posterior aspect of the thigh (which benefit most from a parasacral10-12 or posterior approach13-18). For any nerve, the indications of a given approach is based on the specific surgical requirement, the need for a single versus continuous nerve block, timing of block procedure in relationship to the surgery, and the need for special patient positioning. We typically place nerve blocks preoperatively and before the patient’s transfer to the operating room. The need for the patient’s positioning plays a key role in technique selection in our practice. For instance, with the patient in the supine position, it is possible to approach the sciatic nerve through an anterior approach19-23 or a lateral approach (at the greater trochanter24-26 or lower in the thigh above the popliteal fossa27,28). With the patient in the lateral position (Sim’s position), it is possible to reach the sciatic nerve as it exits the greater sciatic foramen (parasacral approach13-17) at the level of the buttock (posterior approach18), and at the level of the ischial tuberosity (gluteal29, or subgluteal crease).30,31 With the patient in lithotomy position, the sciatic nerve can be blocked at the level of the ischeal tuberosity (Raj et al’s32 approach). Finally, with the patient in the prone position, the sciatic nerve block can be performed through a low gluteal or high popliteal approach. Except for the lithotomy approach, all other approaches to the sciatic nerve have been used for both single and continuous nerve blocks. As previously indicated, there are clinical advantages of one approach over the others according to the type of surgery or the
Techniques in Regional Anesthesia and Pain Management, Vol 7, No 1 (January), 2003: pp 18-25
use of a tourniquet. The choice of the approach often depends on the patient’s mobility (morbidly obese, trauma, intensive care unit) and the extent of the patient’s injury. Because a combination of sciatic and lumbar plexus blocks often is indicated, the choice of the approach also should take into consideration the approach used to block the lumbar plexus/femoral/ saphenous nerve. For instance, when the sciatic block is combined with a lumbar plexus block, we favor a parasacral, posterior, and gluteal and subgluteal approach. In contrast, when the sciatic block is combined with either a femoral block or a saphenous nerve block, we favor an anterior or lateral approach. Finally, in the case of placement of a perineural catheter, the choice of the technique also may be dictated by the requirement to keep the perineural catheter outside of the surgical field.
injecting 2 to 3 mL of local anesthetic through a 25-gauge, 39-mm needle.
Patient in the Supine Position In the supine position, the sciatic nerve can be approached either anteriorly or laterally. Around the lesser trochanter, the sciatic nerve runs medial and posterior to the femur. A few centimeters distally until the popliteal fossa, the sciatic nerve runs posterior to the femur until its division into the tibial and common peroneal nerves. The relationship between the sciatic nerve and the femur dictates that anteriorly this nerve only can be approached at the proximity of the lesser trochanter.33 In contrast, the sciatic nerve can be approached laterally at any level between the greater trochanter to the popliteal fossa.
Anterior Approach
Techniques General Considerations Single-shot sciatic nerve blocks irrespective of the approach require a lesser volume than for blocks performed at the level of the popliteal fossa (15-25 mL vs 30-40 mL). This lower volume requirement is important especially when considering the total volume required to perform a combined sciatic and a lumbar plexus block with a single stimulation technique. The use of a nerve stimulator is essential to optimize the success rate of any sciatic nerve block. A 100- or 150-mm, 21to 22-gauge insulated needle (depending on the size of the patient and the approach chosen), is connected to a nerve stimulator, usually set up to deliver 1.5 mA, 2 Hz, and 0.1 ms. Irrespective of the approach, the stimulation of the sciatic nerve produces either a dorsiflexion of the foot with an extension of the toes or an eversion (stimulation of the common peroneal nerve), or a plantar flexion of the foot and toes or an inversion (stimulation of the tibial nerve). A contraction of the hamstring muscle usually indicates that the needle is too medial. When the appropriate muscle response is obtained, the position of the needle is adjusted to maintain the same motor response with a current of 0.4 mA. After negative aspiration for blood, 2 mL of the local anesthetic solution is injected slowly and the current of the nerve stimulator is increased to 2 mA to reproduce the muscular contraction and verify that the needle still is close to the nerve. The total volume of local anesthetic is injected slowly 5 mL at a time with negative aspiration for blood in between. In the case of a placement of a perineural catheter for a continuous nerve block, an 18-gauge insulated introducer Tuohy needle is used to locate the sciatic nerve. After injection of the initial bolus (15-20 mL), a 20-gauge catheter is introduced 3 to 4 cm beyond the tip of the needle. If a stimulating catheter is used, the initial bolus is injected via the perineural catheter. The catheter usually is secured with tape and covered with a transparent bandage allowing for direct visualization of the insertion site and catheter. With continuous nerve blocks, 5 to 8 mL/hr of a local anesthetic solution (0.2% ropivacaine) is infused over 24 to 72 hours, depending on the indication. Alternatively, patient-controlled analgesia with no basal infusion rate and 2.5 to 4 mL per bolus with a 30- to 45-minute lock-out period can be used. Because the sciatic nerve runs deep, local anesthesia of the skin and surrounding tissues is necessary to avoid pain during the introduction of the needle. This is achieved best by SCIATIC NERVE BLOCK
Anatomic landmarks for the anterior approach. Beck19 in 1963 first described an anterior approach to the sciatic nerve based on the use of landmarks defining the inguinal ligament (the anterior iliac spine and the pubis tubercle) and the greater and lesser trochanters. The complexity of the landmarks necessary to determine the site of introduction of the needle greatly limited the use of this approach. More recently, we described an approach based on only 2 anatomic landmarks: the lower border of the anterior iliac spine and the superior border of the pubis tubercule, landmarks independent of the physical characteristics of the patient. It is of special interest to recognize that both the Beck19 and the Chelly and Delaunay20 approaches defined the same site for the introduction of the needle, but through different landmarks. In 2001, Barbero et al,21 using the same basic Chelly and Delaunay20 landmarks proposed the formula S (site of introduction of the needle ⫽ [size cm ⫺ 100]/10.2), which takes into consideration the size of the patient. More recently, VanElstraete et al22 and Souron et al23 in 2002 proposed anatomical landmarks based on the inguinal crease and the femoral artery.
Anterior Approach Technique A line is drawn between the lower border of the anterior superior iliac spine and the superior angle of the pubic tubercle. A perpendicular line is drawn in the middle and extended distally by 8 cm to define the site of introduction of the needle. A 150-mm insulated needle connected to a nerve stimulator is introduced through the skin and the quadriceps muscle. Because of the proximity of the femoral nerve, in most cases movement of the patella is elicited. To confirm that the needle on its way to the sciatic nerve is some distance from the femoral nerve, the intensity of the current is decreased to 0.5 mA to ensure that the femoral nerve stimulation ceases (patella movement stops). Then the intensity of the current is increased to 2 to 5 mA and the needle is introduced at a depth of 8 to 13 cm before stimulation of the sciatic nerve is elicited. With this approach, in most cases the first attempts produce bone contact. The depth at which the femur is contacted allows for an estimation of the depth at which the sciatic nerve will be located (distance of bone contact plus 3-4 cm). Next, the needle is withdrawn to the skin after the skin is moved medially 1.5 to 2 cm and the needle is introduced by repeating the same approach. If the needle path continues to be obstructed by the femur, it is most likely that the needle is being introduced at the
19
level of the lesser trochanter. In this case, an internal rotation of the foot helps swing the lesser trochanter laterally and allows for needle passage toward the sciatic nerve. Alternatively, the site of the needle insertion is moved 1 cm cephalad to avoid the lesser trochanter altogether. The anterior approach to the sciatic nerve is performed typically in combination with a femoral nerve block. It is recommended to first perform the femoral block because it allows the sciatic block to be performed with minimum discomfort to the patient and the introduction of the needle into the hamstring muscle (sciatic innervation) is associated with some discomfort and is a signal that the needle has been introduced too far. In obese patients (⬎100-120 kg), the 150-mm length may not be long enough to assess the sciatic nerve with an anterior or high lateral approach. In these cases, a lithotomy or low lateral approach is indicated.
Technique The posterior iliac spine and the ischeal tuberosity are identified and a line joining these 2 points is drawn. The site of introduction of the needle is 7 cm distal from the posterior iliac spine. A 22-gauge, 100-mm, insulated needle connected to a nerve stimulator is introduced perpendicular to the skin. Within 6 to 8 cm, a stimulation of the sciatic nerve is elicited. In the case of a continuous nerve block, a catheter is placed using a 100-mm, 18-gauge, insulated Tuohy needle with the bevel oriented laterally. To facilitate the introduction of the catheter, Gaertner et al34 recommend introducing the introducer needle or cannula at a 10° posterior and cephalad angle. Because the parasacral approach often is combined with a lumbar plexus block, the depth at which the lumbar plexus is stimulated is a good indicator of the depth at which the sciatic nerve will be stimulated.
Lateral Approaches Anatomic landmarks for the lateral approaches. For a high lateral approach, the greater trochanter is used; for a low lateral approach, the tip of the patella and the groove between the biceps femoris and the vastus lateralis are used. Lateral approach techniques. For a high lateral technique, the greater trochanter is identified and the 150-mm insulated needle connected to a nerve stimulator is introduced perpendicular to the skin, 3 cm distal from the greater trochanter and below the posterior border of the femur. Within 10 to 13 cm, the sciatic nerve is stimulated. If the needle is introduced too anteriorly, the needle usually contacts the femur within 3 to 6 cm. If the placement of a perineural catheter is indicated, a 150-mm, 18-gauge insulated introducer Tuohy needle is used with the bevel oriented cephalad. For a low lateral technique, the groove between the biceps femoris and the lateral border of the vastus lateralis muscle is identified and marked. The site of introduction of the needle is the intersection between the groove line and a vertical line drawn 10 cm cephalad from the tip of the patella. A 100-mm insulated needle connected to a nerve stimulator is introduced posteriorly at a 30° angle. Initially, a local contraction of either the biceps femoris or vastus lateralis is observed while the insulated needle is being introduced. Within 4 to 6 cm, the local contractions disappear, and within an additional 1 to 3 cm, a sciatic motor response is elicited. If the placement of a perineural catheter is indicated, a 100-mm, 18-gauge, insulated Tuohy needle is used with the bevel oriented cephalad.
Patient in the Lateral Position Parasacral Approach The parasacral approach results in a block of the sacral plexus after its emergence from the greater sciatic foramen. Thus, this technique produces a block of the sciatic nerve as well as the other nerves that comprise the sacral plexus (superior and inferior gluteal nerves, posterior cutaneous nerve of the thigh, and pudendal nerve). Furthermore, this approach also frequently blocks the corresponding sympathetic trunks (increased risk for urinary retention), and the obturator nerve, because of their proximity. The anatomic landmarks are the posterior iliac spine and the ischeal tuberosity.
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Posterior Approach The posterior approach is the oldest and most commonly performed approach to block the sciatic nerve, especially for a single block.
Anatomic Landmarks Labat’s original description in 1922 was based on the use of only 2 anatomic landmarks, the greater trochanter and the posterior iliac spine. Winnie18 introduced another landmark, the sacral hiatus.
Technique (Classic Approach) The greater trochanter, the posterior iliac spine, and the sacral hiatus are identified and marked. A line is drawn between the greater trochanter and the posterior iliac spine. A second line is drawn between the greater trochanter and the sacral hiatus. A third line is drawn perpendicular to the greater trochanter and the posterior iliac spine line at its middle. The site of introduction of the needle is the intersection of these perpendicular lines with the greater trochanter-sacral hiatus line. Depending on the size of the patient, a 100- to 150-mm, insulated needle connected to a nerve stimulator is introduced perpendicular to the skin. First, a direct contraction of the gluteus maximus muscle is elicited, which is then followed by stimulation of the sciatic nerve. Isolated stimulation of the pyriformis muscle indicates that the needle is too cephalad. In some cases, the patient indicates that he/she is feeling an electrical impulse in the perineum, which indicates that the needle missed the sciatic nerve and went too far through the sciatic foramen. In this case, the needle needs to be withdrawn and reoriented either more medially or laterally. For continuous nerve blocks, an 18-gauge, 100- to 150-mm, insulated Tuohy needle is used with the bevel oriented cephalad and medially.35,36 In 1989, Rucci et al37 proposed a construct to define the site of introduction of the needle based on the use of the posterior iliac spine, the greater trochanter, and the ischial tuberosity. More recently, Casals Merchan et al38 proposed the use of the posterior superior iliac spine and the sacral hiatus.
3 Fig 1.
Anatomy of the sciatic nerve. JACQUES E. CHELLY
SCIATIC NERVE BLOCK
21
Fig 2. High sciatic nerve approaches: ASIS, anterior superior iliac spine; SBPS, superior border of the pubic symphisis; GT, greater trochanter; IT, ischeal tuberosity; PS, pubic symphisis; PSIS, posterior superior iliac spine; SH, sacral hiatus. X represents the site if introduction of the needle.
Gluteal and Subgluteal Approach Anatomic Landmarks This approach is based on the use of 2 anatomic landmarks: the greater trochanter and the ischeal tuberosity. At this level, the sciatic nerve runs posterior and medial to the femur on the posterior aspect of the adductor magnus.
Gluteal Block This approach was described by Sutherland in 1998 and represents a variant of an approach described earlier by Raj et al.32 A 22-gauge, 100-mm needle is introduced perpendicular to the skin in the middle of the line drawn between the ischeal tuberosity and the greater trochanter. Within 5 to 7 cm, the sciatic nerve is stimulated. 29
Subgluteal Block The subgluteal block has been introduced recently by di Benedetto et al30 and is gaining popularity because of its simplicity and reliability. A line is drawn joining the greater trochanter and the ischeal tuberosity. From the midpoint of this line, a perpendicular line is extended caudally for 4 cm. (At this level, a skin depression can be palpated, representing the groove between the biceps femoris and semitendinous muscles.) This point represents the site of the introduction of the needle. A 100-mm insulated needle connected to a nerve stim-
22
ulator is introduced through the skin at an 80° angle. The sciatic nerve usually is located at a depth of 5 to 7 cm. In the case of continuous nerve blocks, an 18-gauge, 100-mm, insulated Tuohy needle with the bevel oriented cephalad is used. This approach is very interesting for the placement of a perineural catheter before surgery because in most cases the position of the catheter is outside the surgical site.
Sciatic Nerve Block With the Patient in the Prone Position Although the sciatic nerve can be approached anywhere from the gluteal region to the popliteal fossa, the most common approach used clinically is just above the popliteal fossa (popliteal block).
Anatomic Landmarks This approach is based on the use of the 3 anatomic landmarks that define the posterior popliteal fossa: the popliteal crease, and the medial border of the femoris biceps muscle laterally, and the tendon of the semitendinous muscle medially.
Technique A line is drawn joining the medial border of the femoris biceps muscle laterally and the lateral border of the semitendinous muscle medially at the level of the popliteal crease. From the JACQUES E. CHELLY
Fig 3. High posterior popliteal approach.
SCIATIC NERVE BLOCK
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middle of this line, a perpendicular line is extended 15 cm cephalad. The site of insertion of the needle is 1 cm laterally. A 100-mm, insulated needle connected to a nerve stimulator is introduced through the skin at a 60° angle. The sciatic nerve usually is located at a depth of 8 to 10 cm. In the case of continuous nerve blocks, a 100-mm, 18-gauge, insulated Tuohy needle with the bevel oriented cephalad is used.
6. 7.
8.
Patient in the Lithotomy Position
9.
Although it is conceivable that in the lithotomy position the sciatic nerve can be approached at different levels of the thigh on the sciatic line, only one approach has been described, by Raj et al.32 This gluteal approach is indicated particularly in patients who cannot be moved from the supine position (trauma and especially morbidly obese patients, in whom a 150-mm needle is too short to perform an anterior approach). However, this position is not appropriate for the placement of a perineural sciatic catheter.
10.
11.
12.
13.
Anatomic Landmarks This approach is also based on the use of 2 anatomic landmarks: the greater trochanter and the ischeal tuberosity.
Technique The leg is flexed at the hip and the knee and supported by an assistant. A line is drawn between the ischeal tuberosity and the greater trochanter of the femur. The site of introduction of the needle is the middle of the line. A 22-gauge, 100-mm, insulated needle connected to a nerve stimulator is introduced perpendicular to the skin. Within 4 to 6 cm, the sciatic nerve is stimulated.
14. 15. 16. 17.
18. 19. 20. 21.
Conclusions Sciatic nerve blocks provide effective anesthesia and postoperative analgesia in patients undergoing lower-extremity surgery. A considerable resurgence of interest in this technique is exemplified by a multitude of approaches and their modifications aimed at making this block more reliable and user friendly. This review focuses primarily on the technical aspects of choosing the optimal approach and outlining the historic perspective and technique subtleties that vary among the different techniques. The effectiveness of single or continuous sciatic or any other peripheral nerve block is maximized when these techniques are used as part of a multimodal, multidisciplinary approach to pain management.
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nerve block for ambulatory surgery. Reg Anesth Pain Med 26:209214, 2001 37. Rucci FS, Trafficante FG, Moresi M: A new approach to sciatic nerve block in the gluteal region. Eur J Anaesthesiol 6:363-372, 1989 38. Casals Merchan M, Eshan F, Martinez Manas F, et al: Sciatic nerve block. Description of a new posterior approach in the gluteal area. Rev Esp Anestesiol Reanim 47:245-251, 2000 39. Whitelaw G, DeMuth K, Demos H, et al: The use of the Cryo/Cuff versus ice and elastic wrap in the postoperative care of knee arthroscopy patients. Am J Knee Surg 8:28-30, 1995
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