Chapter 37. Sciatic Nerve Block

Victor Pauchet first described the sciatic nerve block in L'Anesthésie Régionale in 1920: “the site of needle insertion for blocking the sciatic nerve at the level of hip: 3 cm along the perpendicular that bisects a line drawn between the greater trochanter and the posterior superior iliac spine.”1 Although this technique is referred to as “The classic approach of Labat,” it was in fact first described by Labat's teacher, Pauchet. Perhaps the reason for the name designation comes from the fact that the sciatic nerve block was first described in anesthesia literature in 1923 by Gaston Labat in his book, Regional Anesthesia: Its Technic and Clinical Application.2 Of note, Labat in the same year founded the American Society of Regional Anesthesia (ASRA). Anecdotally, Labat intended to name the new group “the Labat Society” in his honor, but the name ASRA remains today as we know it. Labat's book went through several reprintings of the first edition and was one of the first English language anesthesia textbooks of regional anesthesia in the United States. Curiously, this book was similar to L'Anesthésie Régionale, written by Labat's tutor, Pauchet, from 1918 to 1920 in the University of Paris.

Alon Winnie eventually modified the Labat approach in 1975.3 In 1963, Beck4 described an anterior approach, and, in 1975, Raj proposed a lithotomy approach.4,5 These alternative approaches were devised to allow the sciatic nerve to be blocked in the supine patient. Since its original description, a number of new approaches to sciatic nerve blocks were proposed, most of which include minor modifications of questionable clinical significance. Based on the clinical studies of various approaches, the most useful of these newer techniques appear to be the subgluteal and parasacral approaches introduced by di Benedetto and Mansour, respectively.6–8 Discussion of all described techniques and approaches is beyond the scope of this chapter. Instead, this chapter focuses on the classic approach to sciatic nerve block, parasacral and subgluteal modifications, and the anterior approach.

Indications & Contraindications

Indications for sciatic nerve block include lower-limb surgery, often combined with a femoral or psoas compartment block.8 For distal surgery of the lower extremity, however, more distal approaches such as ankle block or popliteal sciatic nerve block are preferable when feasible. Note that the sciatic nerve block almost always needs to be combined with supplemental block, which involves components of the lumbar plexus (femoral nerve).

Contraindications to sciatic nerve block are few, and may include local infection and bed sores at the site of insertion, coagulopathy, preexisting central or peripheral nervous systems disorders, and allergy to local anesthetics.

Functional Anatomy

The union of the lumbosacral trunk with the first three sacral nerves forms the sacral plexus (Figure 37–1). The lumbosacral trunk originates from the anastomosis of the last two lumbar nerves with the anterior branch of the first sacral nerve. This structure receives the anterior branches of the second and third sacral nerves, forming the sacral plexus. The sacral plexus is shaped like a triangle pointing toward the sciatic notch, with its base spanning across the anterior sacral foramina. It rests on the anterior aspect of the piriformis muscle and is covered by the pelvic fascia, which separates it from the hypogastric vessels and pelvic organs. Seven nerves stem from the sacral plexus: six collateral branches and one terminal branch—the sciatic nerve, the largest nerve of the plexus.

Strictly speaking, L4 through S3 nerve roots form the sacral plexus. These roots of the sacral plexus form on the anterior surface of the lateral sacrum and are assembled into the sciatic nerve on the ventral surface of the piriformis muscle9 (Figure 37–2). The sciatic nerve is the largest peripheral nerve in the body and measures more than 1 cm in breadth at its origin. It exits the pelvis through the greater sciatic notch below the piriformis muscle, then descends between the greater trochanter of the femur and the ischial tuberosity. The nerve then runs along the posterior thigh to the lower third of the femur, where it diverges into two large branches, the tibial and common peroneal nerves. This division may occur at any level proximal to the lower third of the femur.10,11 Fifteen percent of the time, the common peroneal and tibial nerves are separated from their onset at the sacral plexus; in this case, the common peroneal nerve typically pierces piriformis muscle. The course of the sciatic nerve can be estimated by drawing a line on the back of the thigh beginning from the apex of the popliteal fossa to the midpoint of the line joining the ischial tuberosity to the apex of the greater trochanter. From its onset, the sciatic nerve also gives off numerous articular (hip, knee) and muscular branches.

In the upper part of its course, the sciatic nerve lies deep in the gluteus maximus muscle and rests on the posterior surface of the ischium (Figures 37–3 and 37–4). The sciatic nerve crosses the external rotators, obturator internus, and gemelli muscles, then passes on to the quadratus femoris. The quadratus femoris separates the sciatic nerve from the obturator externus and the hip joint. Medially, the posterior cutaneous nerve of the thigh and the inferior gluteal plexus accompany the sciatic nerve, whereas more distally the sciatic nerve lies on the adductor magnus. The long head of the biceps femoris crosses the sciatic nerve obliquely. The articular branches of the sciatic nerve arise from the upper part of the nerve and supply the hip joint by perforating the posterior part of its capsule. However, the articular branches are sometimes derived directly from the sacral plexus. The muscular branches of the sciatic nerve innervate the gluteus, the biceps femoris, the ischial head of the adductor magnus, the semitendinosus, and the semimembranosus muscles (Figure 37–5; Table 37–1). The branches of the ischial head of the adductor magnus and semimembranosus muscles arise from a common trunk. The nerve to the short head of the biceps femoris comes from the common peroneal division, whereas the other muscular branches arise from the tibial division of the sciatic nerve.

The parasacral area is delineated by the ventral aponeurosis of the piriformis muscle dorsally, by the pelvic aponeurosis medially, and by the aponeurosis of the obturator internis muscle laterally.9 The common peroneal component passes through the piriformis muscle or above it, and only the tibial component passes below the muscle.

Choice of Local Anesthetic

Despite its large size, sciatic block requires a relatively low volume of local anesthetic to achieve anesthesia of the entire trunk of the nerve.12 Generally, 20–25 mL of local anesthetic are sufficient. The choice of the type and concentration of local anesthetic should be based on whether the block is planned for surgical anesthesia or analgesia13 (Table 37–2). When prolonged pain relief is desired long-acting local anesthetic may be more appropriate.14,15 Epinephrine is not routinely used for sciatic nerve block because of the possibility of injury due to stretching or sitting on the anesthetized nerve with the long duration of block with epinephrine-containing local anesthetics. However, its use may be justified in patients undergoing above-knee amputation, in whom these issues are not pertinent and prolonged analgesia is always beneficial.

Equipment

All approaches to the sciatic nerve block necessitate assembly of a nerve block tray before placing the block. As with all regional anesthesia techniques, the heart rate, blood pressure, and pulse oximeter are routinely monitored before performing the block. Resuscitation equipment and emergency medications must be immediately available and ready to use. Supplemental oxygen via face mask is routinely used before giving sedation. A standard regional anesthesia tray is prepared with the following equipment:

• Sterile towels and 4-in. × 4-in. gauze packs
• 20-mL syringe with local anesthetic
• Sterile gloves, marking pen, and surface electrode
• One 1½-in., 25-gauge needle for skin infiltration
• A 10-cm long, short-bevel, insulated stimulating needle (15 cm for anterior approach)
• Peripheral nerve stimulator

Interpreting Responses to Nerve Stimulation

Twitches of the hamstrings, calf, foot, or toes at 0.2–0.5 mA current all can be used as signs of successful localization of the sciatic plexus (nerve). Table 37–3 presents common responses to nerve stimulation and the course of action to take to obtain the proper response.16

Sciatic nerve blockade technique may result in significant patient discomfort because the needle passes through the gluteus muscles. Adequate sedation and analgesia are important to ensure patient comfort. Midazolam 2–6 mg can be given for patient positioning, and alfentanil 500–750 mcg is given just before needle insertion. A typical onset time for this block is 10–25 minutes, depending on the type, concentration, and volume of local anesthetic used. The first signs of blockade onset are usually reported by the patient in the form of a feeling that the foot is “different” and/or that he or she cannot wiggle the toes.

General Considerations

The posterior approach to sciatic blockade has wide clinical applicability for surgery and pain management of the lower extremity. In contrast to common belief, this block is relatively easy to perform and is associated with a high success rate when properly performed.17,18 It is particularly well suited for surgery on the knee, calf, Achilles tendon, ankle, and foot. It provides complete anesthesia of the leg below the knee with the exception of the medial strip of skin, which is innervated by the saphenous nerve (Figure 37–6). When combined with a femoral nerve or lumbar plexus block, anesthesia of almost the entire leg can be achieved.

Distribution of Anesthesia

Sciatic nerve blockade results in anesthesia of the skin of the posterior aspect of the thigh, hamstrings, and biceps muscles, part of the hip and knee joints, and the entire leg below the knee, with the exception of the skin of the medial aspect of the lower leg (see Figure 37–6). Depending on the level of surgery, the addition of a saphenous or femoral nerve block may be required.

Classic Posterior Approach

Anatomic Landmarks

Landmarks for the posterior approach to sciatic blockade are easily identified in most patients (Figure 37–7). Proper palpation technique is of utmost importance because the adipose tissue over the gluteal area may obscure these bony prominences. The landmarks are outlined by a marking pen:

1. 1. Greater trochanter

2. 2. Posterior superior iliac spine

3. 3. Needle insertion site 4 cm distal to the midpoint between the two landmarks

Technique

The patient is in the lateral decubitus position with a slight forward tilt. The foot on the side to be blocked should be positioned over the dependent leg so that twitches of the foot or toes can be easily noted. After cleaning with an antiseptic solution, local anesthetic is infiltrated subcutaneously at the determined needle insertion site. The anesthesiologist performing the block should assume an ergonomic position to allow precise needle maneuvering and monitoring of the responses to nerve stimulation.

The fingers of the palpating hand should be firmly pressed on the gluteus muscle to decrease the skin–nerve distance (Figure 37–8). The skin below the index and middle finger is stretched for greater precision during block placement. The palpating hand should not be moved during block placement; even small movements of the palpating hand can substantially change the position of the needle insertion site because the skin and soft tissues in the gluteal region are highly movable. The needle is introduced at an angle perpendicular to the spherical skin plane (Figure 37–8). The nerve stimulator should be initially set to deliver 1.5 mA current (2 Hz, 100 μsec) to allow detection of twitches of the gluteal muscles and stimulation of the sciatic nerve.

As the needle is advanced, the first twitches observed are from the gluteal muscles. These twitches merely indicate that the needle position is still too shallow. The goal is to achieve visible or palpable twitches of the hamstrings, calf muscles, foot, or toes at 0.2–0.5 mA current. Twitches of the hamstrings are equally acceptable because this approach blocks the nerve proximal to the separation of the nerve branches to the hamstrings muscle. Once the gluteal twitches disappear, brisk response of the sciatic nerve to stimulation is observed (hamstrings, calf, foot, or toe twitches). After the initial stimulation of the sciatic nerve is obtained, the stimulating current is gradually decreased until twitches are still seen or felt at 0.2–0.5 mA current. This typically occurs at a depth of 5–8 cm.

After negative aspiration for blood, 15–25 mL of local anesthetic is injected (Figure 37–9). Any resistance to the injection of local anesthetic should prompt needle withdrawal by 1 mm. The injection is then reattempted. Persistent resistance to injections should prompt complete needle withdrawal and flushing to ensure needle patency before reintroduction.

Continuous Block

The continuous sciatic nerve block is an advanced regional anesthesia technique, and experience with the single-shot technique is recommended to ensure its efficacy and safety. Continuous sciatic nerve block was described by Gross in 1956.19 The current technique used is similar to the single-shot injection; however, slight angulation of the needle in the caudal direction is necessary to facilitate threading of the catheter. Securing and maintenance of the catheter are easy and convenient. This technique can be used for surgery and postoperative pain management in patients undergoing a wide variety of lower leg, foot, and ankle surgeries. Perhaps the single most important indication for use of this block is for amputation of the lower extremity.

Technique

The continuous sciatic block technique is similar to the single-shot technique. A standard regional anesthesia tray is prepared and an 8–10 cm long, insulated stimulating needle (preferably Tuohy-style tip) is used. Proper positioning at the outset and maintenance of the position during the continuous sciatic nerve block are crucially important to allow for precise catheter placement. A slight forward pelvic tilt prevents the “sag” of the soft tissues in the gluteal area and significantly facilitates block placement.

With the patient in the lateral decubitus position and a slight forward pelvic tilt, the landmarks are identified and marked with the pen. After a thorough skin cleaning with antiseptic solution, the skin at the needle insertion site is infiltrated with local anesthetic. A 10-cm long continuous-block needle is connected to the nerve stimulator (1.5 mA) and inserted at an angle perpendicular to the skin sphere. The opening of the needle should face distally (pointing toward the patient's foot) to facilitate catheter insertion. The initial intensity of the stimulating current should be 1.0–1.5 mA.

As the needle is advanced, the first twitches obtained are from the gluteus muscle. Deeper needle advancement results in stimulation of the sciatic nerve. The principles of nerve stimulation and needle redirection are identical with those in the single-shot technique. After obtaining the appropriate twitches, manipulate the needle until the desired response is seen or felt using a current of 0.2–0.5 mA. At this point, a bolus of local anesthetic is injected (20 mL) after negative aspiration for blood. This is followed by insertion of the catheter 5–10 cm beyond the needle tip (Figure 37–10). Before administering local anesthesia, the catheter is checked for inadvertent intravascular placement by a negative test for blood.

A number of techniques to secure the catheter to the skin have been proposed. A benzoin skin preparation, followed by application of a clear dressing and a cloth tape is a simple and often sufices. The infusion port should be clearly marked as “continuous sciatic block.”

Continuous Infusion

Continuous infusion is initiated after an initial bolus of dilute local anesthetic through the catheter. Ropivacaine 0.2% is commonly used for this purpose (15–20 mL). Diluted solutions of bupivacaine or l-bupivacaine are also suitable, but can result in undesirably greater motor blockade. The infusion is initiated at 10 mL/h or 5 mL/h when a patient-controlled analgesia (PCA) dose is planned (5 mL).20,21

Parasacral Approach

Described by Mansour in 1993, the parasacral sciatic nerve block features relatively simple landmarks, and it is well suited for continuous infusion of local anesthetic.8,22–27 In addition, the extension of the sciatic nerve block has characteristics of a plexus block. As such, there is a high success rate, anesthesia of the entire sacral plexus, and motor blockade of the obturator nerve.23,24,28 Ripart25 reports a 94% success rate in his series of 400 parasacral sciatic nerve block cases.

The parasacral approach to sciatic blockade has a wide clinical applicability for surgery and analgesia of the lower extremity, particularly when combined with a femoral or psoas compartment block.23,28 The technique is associated with a high success rate and is particularly well suited for surgery on the popliteal fossa and the knee.23

Distribution of Anesthesia

Parasacral sciatic nerve blockade results in anesthesia of the skin of the posterior thigh, hamstrings, and biceps muscles; part of the hip and knee joint; and the entire leg below the knee except the medial cutaneous skin of the lower leg (see Figure 37–6). Morris23 demonstrated extension of anesthesia to the obturator nerve after sciatic nerve block, as tested by the presence of adductor muscle weakness on a numeric scale. However, Jochum29 suggested that the obturator nerve is only occasionally blocked by the parasacral sciatic nerve block. These conflicting data may be due to the fact that the parasacral plexus could be responsible for one third of adductor muscle strength. Depending on the level of surgery, the addition of a psoas compartment or femoral nerve block may be required.

Anatomic Landmarks

Landmarks for the parasacral approach to sciatic blockade are easily identified in most patients (Figure 37–11). Proper palpation technique is of the utmost importance because the adipose tissue over the gluteal area may obscure these bony prominences (Figures 37–12 and 37–13). The following landmarks are outlined by a marking pen:

• Posterior–superior iliac spine (PSIS)
• Ischial tuberosity (IT)
• A line between the PSIS and the IT is drawn. The needle insertion point lies 6 cm caudad to the PSIS on this line. The insulated needle is inserted at this point and advanced in a sagittal plane.

Technique

The patient is positioned in a lateral decubitus position, similar to the position required for the classic posterior approach to sciatic block (Figure 37–13). The dependent limb at the knee and hip is kept straight, and the limb to be blocked is flexed at both the hip and knee. Appropriate sedation and analgesia are mandatory to ensure the patient's comfort throughout the procedure. After cleaning with an antiseptic solution, local anesthetic is infiltrated subcutaneously at the determined needle insertion site. The practitioner performing the block should assume an ergonomic position to allow precise needle maneuvering and monitoring of the responses to nerve stimulation.

The needle is inserted perpendicular to the skin and advanced slowly (Figure 37–14). The motor response of the sciatic plexus is usually obtained at a depth between 6 and 8 cm. The goal is to achieve visible or palpable twitches of the hamstrings, calf muscles, foot, or toes at the current intensity of 0.2–0.5 mA. Twitches of the hamstrings are equally acceptable because this approach blocks the sciatic nerve proximal to the separation of the nerve branches to the hamstring muscles. The distal motor response may be either a tibial or a peroneal response with equal success of sciatic nerve blockade (Figure 37–15). Extension or flexion of the toes (responses of the common peroneal nerve and tibial nerve, respectively) rarely occur deeper than 8 cm. It is not necessary to stimulate both the common peroneal nerve and the tibial nerve; either response is adequate.30,31

Once the aforementioned distal motor response is obtained with low-intensity stimulation (<0.5 mA), the local anesthetic solution is injected slowly while performing frequent aspiration tests. Twenty to 25 mL of local anesthesia is sufficient to produce sciatic nerve blockade (Figure 37–16).

Cuvillon et al.7 compared the parasacral sciatic nerve block with Winnie's approach, eliciting one or two stimulations. Winnie's approach with double-injection technique required more time to perform the block compared to Winnie's single-injection technique and the parasacral method. Although the onset of sensory and motor blocks were significantly faster with the double-injection method, the additional time needed to perform the double-injection block eliminated the advantage of the faster onset.

Continuous Parasacral Sciatic Nerve Block

The continuous parasacral sciatic nerve block is similar to the single-shot injection; however, slight caudad angulation of the needle is necessary to facilitate threading of the catheter. Securing and maintenance of the catheter are easy and convenient.32 This technique can be used for surgery and postoperative pain management in patients undergoing a wide variety of knee, lower leg, foot, and ankle surgeries. Perhaps the single most important indication for use of this block is for cancer surgery of the lower extremity and for knee surgery.

Several kits for catheter insertion are currently commercially available. An ideal kit should include an insulated needle with a short bevel, a stimulating needle for catheter insertion, a catheter, an electrical wire connection, and an antibacterial filter (Figure 37–17). With the patient in the lateral decubitus position, the landmarks are identified and marked with a pen. After a thorough skin cleaning with an antiseptic solution, the skin is infiltrated with local anesthetic at the needle insertion site. A continuous-block needle is connected to the nerve stimulator and inserted at an angle perpendicular to the skin sphere. The opening of the needle should face distally (pointing toward the patient's foot) to facilitate catheter insertion.33 The initial intensity of the stimulating current should be 1.0–1.5 mA.

As the needle is advanced, twitches of the gluteus muscle are obtained first. Deeper needle advancement results in stimulation of the piriformis muscle first, then the sciatic nerve. The principles of nerve stimulation and needle redirection are identical with those of the single-shot technique. After obtaining the appropriate twitches, manipulate the needle until the desired response is seen or felt using a current of 0.2–0.5 mA. At this point, a bolus of local anesthetic is injected (20 mL) after negative aspiration for blood (Figure 37–18). This is followed by insertion of the catheter tip. Before administering the local anesthetic, the catheter is checked for inadvertent intravascular placement. If confirmation of catheter placement is desired, contrast media can be injected through the catheter and radiographic images can be studied.31 The presence of a spindle 2–3 cm in length with an oblique orientation crossing the sciatic notch on the anteroposterior radiograph and/or shadowing of the sacral roots are considered to indicate injection into the correct plane and adequate placement of the catheter (Figure 37–16). For continuous infusion, ropivacaine 0.2% is maintained at 5 mL/h and a PCA dose is often planned (5 mL, lock-out time 30–45 minutes).

Di Benedetto34 recently described a subgluteal approach to the sciatic nerve block. The study by di Benedetto suggested that the sciatic nerve is easily approachable through the posterior subgluteal approach. This technique is also a good alternative to the more proximal approaches to the sciatic nerve, with the potential for reducing the discomfort experienced by the patient during block placement. The landmarks with the subgluteal approach are the greater trochanter of the femur, the ischial tuberosity, and a line between the two with the midpoint marked. From the midpoint, another line is drawn perpendicularly and extended 4 cm in the caudad direction to identify the needle insertion point. A 20-gauge, 10-cm needle and nerve stimulator, are used and 20 mL of local anesthetic is injected when twitches of the sciatic nerve are obtained at ≤0.5 mA current.

Traditional approaches to the sciatic nerve at the pelvic level require identification of pelvic bone structures. Although the size of the buttocks is variable among different individuals and in the same individual at different stages of adult life, the relation of the sciatic nerve to the pelvis is constant throughout life. Using this premise, Franco35 has suggested a more simplified approach to the sciatic nerve block that does not require palpation of deep bony structures. The landmarks in this approach are the intergluteal sulcus, the midline of the intergluteal sulcus, and a point 10 cm lateral to the midline of the intergluteal sulcus where the block needle will be inserted. The curvature of the buttocks is disregarded when locating the needle insertion point. However, it is important not to stretch the skin when measuring the needle insertion point; this can distort the anatomy and lead to difficulties with localizing the sciatic nerve. The equipment, nerve stimulation and required volume of local anesthetic are comparable to those of the traditional approaches.

Complications & Strategies in Posterior Approaches & How to Avoid Them

Table 37–4 lists some general and specific instructions on possible complications of sciatic nerve blockage and methods to avoid them.

General Considerations

The anterior approach to sciatic block is an advanced nerve block technique. The block is suited for surgery on the leg below the knee, particularly on the ankle and foot. It provides complete anesthesia of the leg below the knee with the exception of the medial strip of skin innervated by the saphenous nerve (Figure 37–19). When combined with the femoral nerve block, anesthesia of the entire knee and leg below the knee level is achieved.36 The anterior approach is much less clinically desirable compared with the posterior approach. This is because the distribution of anesthesia is more limited and a much higher level of skill is required to achieve reliable anesthesia and avoid multiple needle insertions. In addition, this technique is not suitable for catheter insertion because of the deep location and perpendicular angle of insertion required to reach the sciatic nerve. Consequently, this block is best reserved for patients who cannot be repositioned into the lateral position needed for the posterior approach. The block has been suggested to be useful to manage postoperative pain in children in whom the anterior approach allows block placement in the supine position.37,38 This obviously presents an advantage over other approaches to the sciatic block because these children are typically anesthetized for surgery using general anesthesia and the anterior approach does not require patient repositioning.

Since the original description by Beck,4 several investigators have suggested modifications with more reliable landmarks for this block. However, all described approaches derive the needle insertion site at nearly identical points regardless of whether they use bony prominences, soft tissue, or femoral artery as landmarks.36,39–43 In addition, even if these different approaches varied slightly in the site of needle insertion, the long path by the needle required to reach the sciatic nerve (8–12 cm) and the tendency of long, blunt-tipped needles to bend on insertion through the tissues make any proposed advantages questionable at best.

Equipment

A standard regional anesthesia tray is prepared with the following equipment:

• Sterile towels and 4-in. × 4-in. gauze packs
• 20-mL syringes with local anesthetic
• Sterile gloves, marking pen, and surface electrode
• One 1½-in., 25-gauge needle for skin infiltration
• A 15-cm long, short-bevel, insulated stimulating needle
• Peripheral nerve stimulator

Anatomic Landmarks

The following landmarks should routinely be outlined using a marking pen (Figure 37–20):

1. 1. Femoral crease

2. 2. Femoral artery pulse

3. 3. Needle insertion point is marked 4–5 cm distally on the line passing through the pulse of the femoral artery and perpendicular to the femoral crease

Technique

The leg to be blocked is fully extended on the table with the patient in the supine position. After cleaning the area with an antiseptic solution, local anesthetic is infiltrated subcutaneously at the determined needle insertion site. The fingers of the palpating hand should be firmly pressed against the quadriceps muscle to decrease the skin–nerve distance, and a needle connected to a nerve stimulator (1.5 mA) is introduced at a perpendicular angle to the skin plane (Figure 37–21). Motor response of the sciatic nerve (foot twitch) is typically obtained at a depth of 8–12 cm (visible or palpable twitches of the calf muscles, foot, or toes at a current of 0.2–0.5 mA). After negative aspiration for blood, 20 mL of local anesthetic is slowly injected. Any resistance to injection of local anesthetic should prompt cessation of the attempts to inject and needle withdrawal by 1 mm. The injection is then reattempted. Persistent resistance to injection should prompt complete needle withdrawal and flushing before reintroduction of the needle.

Bone contact is frequently encountered during needle advancement. This indicates that the needle has contacted the femur (usually lesser trochanter). In this case, the foot is first rotated laterally, which should swing the minor trochanter out of the path of the needle and allow deeper advancement of the needle and nerve localization. If this maneuver fails, the needle is redirected or reinserted more medially. Table 37–5 lists some common responses to nerve stimulation and the course of action to take to obtain the proper response during the anterior sciatic blockade.

Although the sciatic nerve block was described long ago, many practitioners avoided this block because of the perceived technical complexity. However, practice and knowledge of anatomy, high success rates can be achieved. Many approaches have been proposed to blocking the sciatic nerve posteriorly, and some of the most relevant have been presented in this chapter. Sciatic nerve block is an important technique for the regional anesthesiologist to master, because the combination of this block and a femoral nerve block or lumbar plexus block can anesthetize almost the entire leg.