11 Proximal Sciatic Nerve Block


11 Proximal Sciatic Nerve Block

11.1 Anatomical Overview

The sacral plexus can be divided into three parts:

  • Pudendal plexus

  • Coccygeal plexus

  • Sciatic plexus

The sacral plexus is not subdivided in all anatomy textbooks. However, as the division is useful from the clinical aspect, it is used as a basis here.

11.1.1 Sciatic Plexus

The sciatic plexus derives its roots from part of the anterior ramus of the fourth lumbar nerve and from the entire anterior ramus of the fifth lumbar nerve, which together form the lumbosacral trunk, along with the anterior rami of the first and second and part of the third sacral nerves. The anterior ramus of the first sacral nerve is not only the biggest branch of the lumbosacral plexus but the biggest anterior ramus overall.

All of the roots of the plexus converge from their exit sites toward the greater sciatic foramen so that the plexus forms a triangular sheet, the apex of which points toward the infrapiriform foramen where the sciatic nerve emerges (Fig. 11.1). The nerve plexus lies for the most part on the piriformis muscle and is covered toward the pelvis by the parietal peritoneum and the tissues lying below it that form the parietal pelvic fascia and branches of the internal iliac artery. The articular branches that supply parts of the hip joint capsule and the periosteal branches that innervate the periosteum of the sciatic tuber, greater trochanter, and lesser trochanter also come from the sciatic plexus.

Fig. 11.1 Course of the sciatic nerve, main nerve of the sacral plexus. 1 Sciatic nerve

11.1.2 Sciatic Nerve (L4–S3)

The sciatic nerve derives its fibers from all the roots of the sacral plexus. It is the biggest and longest nerve in the body, it supplies the widest area, and at the same time it has the greatest resistance among all the nerve cords, with a tear strength of 91.5 kg (!). Excessive stretching can even tear the nerve trunk from its roots in the spinal cord. The roots of the sciatic nerve unite into the trunk immediately before the greater sciatic foramen at the lower border of the piriformis (Fig. 11.2).

Fig. 11.2 After emerging from the lesser pelvis through the infrapiriform foramen, the sciatic nerve, covered by the gluteal muscles, runs peripherally midway between the greater trochanter and the ischial tuberosity, behind and medial to the lesser trochanter. The three palpable bony points (posterior superior iliac spine, greater trochanter, and ischial tuberosity) are used for orientation in all dorsal techniques of proximal sciatic nerve block. 1 Posterior superior iliac spine 2 Piriformis muscle 3 Lesser trochanter 4 Sciatic nerve 5 Ischial tuberosity 6 Greater trochanter

The sciatic nerve consists of two components, the common fibular nerve (synonym: common peroneal nerve) and the tibial nerve, which are surrounded in the lesser pelvis and thigh by a shared connective-tissue sheath and therefore have the appearance of a single nerve trunk. The division into the two branches can occur at varying levels (Fig. 11.3 and Fig. 11.4).

Fig. 11.3 Exit of the sciatic nerve from the infrapiriform foramen in a fenestrated gluteus maximus muscle. 1 Needle is in the posterior superior iliac spine 2 Piriformis muscle 3 Needle is in the furthest lateral part of the greater trochanter 4a Fibular part of the sciatic nerve 4b Tibial part of the sciatic nerve 5 Needle is in the ischial tuberosity
Fig. 11.4 The red circle marks the penetrating needle in an anterior sciatic nerve block. 1 Piriformis muscle 2 Sciatic nerve 3 Posterior cutaneous nerve of the thigh 4 Quadratus femoris muscle

At dissection, the nerve can almost always be separated into its two divisions as far as the hip region, even if they run in a common sheath (Ericksen et al 2002).

The sciatic nerve usually leaves the true pelvis (lesser pelvis) through the infrapiriform foramen as a 1.4 cm (up to 3 cm) wide and 0.4 to 0.5 cm (up to 0.9 cm) thick nerve cord (Fig. 11.3 and Fig. 11.4) and enters the gluteal region. It divides into the tibial nerve and the common fibular nerve at the latest where it enters the popliteal fossa.

The sciatic nerve provides motor innervation through its tibial division to all of the flexor muscles of the thigh (with the exception of the short head of the biceps femoris) and the lower leg and with its fibular division it innervates the short head of the biceps femoris and the fibular muscles and all the extensors in the lower leg and foot. It provides sensory innervation through both divisions to the skin of the lower leg and foot.

Practical Note

If the trunk of the sciatic nerve is paralyzed, external rotation of the thigh and knee flexion are greatly impaired. Complete anesthesia leads to the corresponding impairment. Because of the unopposed extensor action of the quadriceps muscle, the leg behaves like a stilt. The foot is unstable at the ankle and can no longer be dorsiflexed (foot drop).

11.1.3 Posterior Cutaneous Nerve of the Thigh (S1–S3)

The posterior cutaneous nerve of the thigh, which is the sensory supply to the posterior aspect of the thigh, leaves the pelvis together with the sciatic nerve and the inferior gluteal nerve through the infrapiriform foramen. The nerve lies medial to the sciatic nerve and reaches the posterior surface of the thigh under the gluteus maximus muscle. There it lies subfascially, but close to the fascia lata, through which it passes at varying levels. The distribution of the posterior cutaneous nerve of the thigh is variable and extends from the distal third of the buttocks as far as the distal boundary of the popliteal fossa.

Overview of the Nerves of the Sciatic Plexus

The superior gluteal nerve and the inferior gluteal nerve along with the posterior cutaneous nerve of the thigh and the sciatic nerve belong to the sciatic plexus.

Only the sciatic nerve (tibial nerve, common fibular nerve) and the posterior cutaneous nerve of the thigh are important for anesthesia and analgesia of the leg.

11.1.4 Periosteal Innervation

Relevant Facts for Anesthesia and Pain Therapy

The periosteum of the femur is supplied posteriorly by the sciatic nerve in the upper third, by the obturator nerve in the middle third, and in the distal third by the sciatic nerve laterally and by the femoral and obturator nerves medially.

Innervation of the knee is provided anteriorly by branches of the femoral nerve and sciatic nerve and posteriorly by parts of the sciatic nerve, the obturator nerve, and the saphenous nerve.

The periosteum of the tibia and fibula apart from the lateral head of the tibia and the head of the fibula (common fibular nerve) is supplied by the tibial nerve (important for lower leg amputations, fractures).

The ankle receives its sensory supply from the tibial nerve and sural nerve.

The periosteum of the tarsal bones is innervated by the sural nerve and parts of the tibial nerve, the metatarsals, and the phalanges by the deep fibular nerve and the terminal branches of the tibial nerve (Wagner 1994).

11.2 Anterior Proximal Sciatic Nerve Block (with Patient in Supine Position)

11.2.1 Technique of Anterior Sciatic Nerve Block

The classical technique of anterior sciatic nerve block was described in 1963 by G.P. Beck (Beck 1963). The technique was modified by Meier (Meier 1998) to simplify the procedure and allow placement of a catheter.

Anterior Block of the Sciatic Nerve (according to Beck, Classical Technique)


Inguinal crease, gap between the rectus femoris and sartorius muscles. (Note: We have dispensed with the extensive description of orientation with various landmarks and lines, as the method described below has been proven for years.)


The patient lies supine with the leg to be anesthetized extended.


The puncture site is approximately 10 cm (hand breadth) below the inguinal crease (Fig. 11.5).

Fig. 11.5 In practice, it has proved effective not to measure distances to find the insertion site for the anterior sciatic nerve block. Orientation is a good hand′s breadth below the inguinal crease or below the insertion site for a femoral nerve block. Right thigh, caudal view.

The puncture site is the muscle gap between the rectus femoris and the sartorius. In this muscle gap, vertical pressure is exerted on the femur with two fingers, and the bone is used as an abutment (“two-finger grasp”; Fig. 11.6, Fig. 11.7, Fig. 11.8). The blood vessels are pushed medially by this maneuver and the likelihood of accidental vascular puncture is reduced (Fig. 11.7, Fig. 11.8, Fig. 11.9, Fig. 11.10). A 15-cm needle is then advanced at an angle of 75 to 85° to the skin in cranial, posterior and slightly lateral direction (Fig. 11.8 and Fig. 11.10). When a cranial direction is maintained, the sciatic nerve is reached further proximal by a few centimeters, depending on the angle of insertion; if the nerve is reached more tangentially, it is easier to advance an indwelling catheter (Fig. 11.11). For ultrasound visualization, a curved array transducer is recommended owing to the depth (Fig. 11.12, Chapter 11.2.5). The sciatic nerve can be reached well using this technique.

Fig. 11.6 Two-finger grasp for identifying the muscle gap between rectus femoris and sartorius muscles (right thigh, seen from above). This grasp will also push the blood vessels medially.
Fig. 11.7 Anterior sciatic nerve block using the muscle gap between rectus femoris and sartorius muscles for orientation. The puncture site is a good hand′s breadth below the puncture site for femoral nerve block. Note the cranial and slightly lateral needle direction (“below the femur”) and the two-finger grasp in the muscle gap, which pushes the blood vessels medially. Right thigh. 1 Femoral nerve catheter
Fig. 11.8 Anterior sciatic nerve block using the muscle gap between rectus femoris and sartorius muscles for orientation. The insertion site is a good hand′s breadth below the insertion site for femoral nerve block. Note the “two-finger grasp” in the muscle gap that pushes the vessels medially. When the needle is inserted under nerve stimulation, there is occasionally a response in the anterior part of the thigh in the quadriceps muscle after about 2 to 4 cm through stimulation of branches of the femoral nerve. 1 Rectus femoris muscle 2 Sartorius muscle 3 Femoral artery 4 Femoral nerve 5 Fibers of the femoral nerve
Fig. 11.9 Anterior sciatic nerve block using the muscle gap between rectus femoris and sartorius for orientation: anatomical cross-section and MRI at the level of the puncture. 1 Rectus femoris muscle 2 Sartorius muscle 3 Femur 4 Sciatic nerve 5 Blood vessels a Right leg, seen from below. b MR image, right thigh.
Fig. 11.10 Anterior sciatic nerve block: visualization of the nerve using ultrasound. The curved array transducer is usually used due to the penetration depth.
Fig. 11.11 Two-finger grasp to identify the muscle gap between the rectus femoris and sartorius muscles. The vessels are pushed medially. Right thigh, cranial view.
Fig. 11.12 Anterior proximal sciatic nerve block (lateral view). When the needle is directed cranially, the sciatic nerve is reached a few centimeters further proximal, depending on the needle angle. A more tangential approach to the nerve makes advancement of a catheter easier. Right thigh, lateral view. 1 Cranial needle direction 2 Purely sagittal needle direction

Branches of the femoral nerve are often stimulated after the needle is advanced a few centimeters. The position of the needle tip is corrected (usually laterally) until no further response can be detected from the quadriceps femoris muscle and it is then advanced further. Stimulation is initially with a current of 0.8 to 1.0 mA. After 6 to 10 cm, the adductor fascia is reached, which is often signaled by an obvious loss of resistance. The needle is advanced further until a motor response is produced in one of the two divisions of the sciatic nerve (fibular nerve, dorsiflexion: tibial nerve, plantar flexion; Fig. 11.13).

Fig. 11.13 The correct muscle response for all proximal sciatic nerve blocks should be seen in the foot. Either the (medially located) tibial part (plantar flexors) or the (laterally located) fibular part (dorsiflexors) is stimulated. In the Labat and Mansour techniques, a response by the ischiocrural muscles (thigh flexors or “hamstring muscles”) can also be regarded as a correct response. 1 Response of tibial part of the sciatic nerve: plantar flexion 2 Response of fibular part of the sciatic nerve: dorsiflexion

Practical Note

The correct position of the needle is indicated by a response in the foot. If there is a response in the ischiocrural muscles, the needle must be withdrawn significantly and corrected laterally (“below the femur”) (Fig. 11.14, Fig. 11.15, Fig. 11.16). Then 30 mL of a medium-acting or long-acting local anesthetic is injected.

Fig. 11.14 If the ischiocrural muscles (thigh flexors) are stimulated during anterior sciatic nerve block, the needle tip is too far medial; it must be corrected lateral to the sciatic nerve. To do this, the needle should be withdrawn a few centimeters and then the tip of the needle advanced more laterally (“below the femur”) by turning the needle hub medially. The correct response in anterior sciatic nerve blocks should always be sought in the foot (fibular or tibial division of the sciatic nerve). 1 Sciatic nerve 2 Motor branches to the ischiocrural muscles
Fig. 11.15 Visualization of the motor branches of the sciatic nerve, which supply the ischiocrural muscles and run medial to the sciatic nerve, here with anteriorly advanced needle. Right thigh, posterior view. 1 Greater trochanter 2 Sciatic nerve 3 Needle tip 4 Motor branches to the ischiocrural muscles
Fig. 11.16 Two-finger grasp for identifying the muscle gap between rectus femoris and sartorius muscles. This grasp will also push the blood vessels medially. When the ischiocrural muscles (hamstring muscles) are stimulated, the needle must be withdrawn and the tip of the needle advanced laterally by also moving the needle hub medially. Right thigh, seen from above.

  • In the continuous technique, following injection of the local anesthetic, a 20G catheter is advanced 4 cm proximally by the needle (Fig. 11.17 and Fig. 11.18). Short, mild resistance can occur when the catheter tip reaches the end of the needle (Fig. 11.17), but this is normally easily overcome, and the catheter can then be advanced smoothly.

  • The technique should be performed with peripheral nerve stimulation.

  • If sciatic nerve block is combined with a femoral nerve block, anesthetizing the femoral nerve first is useful as this leads to anesthesia of the anterior thigh and helps to improve patient comfort (Fig. 11.17).

  • The technique can also be performed in obese patients (Fig. 11.19 and Fig. 11.20).

Fig. 11.17 Advancing an indwelling sciatic catheter. Using a cranial needle direction, the catheter can usually be advanced easily after overcoming the slight resistance when the catheter tip has reached the end of the needle. 1 Femoral nerve catheter in situ
Fig. 11.18 Anterior sciatic nerve block with needle introduced and catheter advanced cranially. 1 Piriformis muscle 2 Sciatic nerve 3 Needle with catheter 4 Posterior cutaneous nerve of the thigh 5 Branches of the ischiocrural muscle group
Fig. 11.19 Anterior sciatic nerve block is possible even in obese patients, in whom the sciatic nerve can be expected at a depth of 13 to 15 cm. Note the hand grasp!
Fig. 11.20 Obese patients in particular benefit from the combination of a femoral nerve catheter and a sciatic nerve catheter: nerve block prior to total knee replacement.

11.2.2 Indications and Contraindications (in Combination with Femoral Nerve Block)


  • Operations on the knee, lower leg, or foot (e.g., knee replacement, tibial head osteotomy, arthrodesis, lateral ligament suture, forefoot operation).

  • Reposition of fractures in the lower leg and foot area.

  • Amputations in the thigh (Fig. 11.21), lower leg, and foot.

  • Regional sympathetic block (e.g., perfusion disorders, wound healing disorders, CRPS 1).

  • Pain therapy (e.g., postoperative, achillodynia, oligoarthritis).

  • Postoperative pain therapy after total knee replacement, particularly when there is incomplete extension in the knee joint (Fig. 11.22).

  • Traumatology (e.g., pain-free positioning for diagnostic investigation).

Fig. 11.21 Planned thigh amputation, operation on the thigh stump, phantom and/or stump pain are proper indications for continuous proximal sciatic nerve block. The patient can control the needle passage by giving phantom information about the response to the nerve stimulator (“the foot is now moving downward”). Ultrasound-guided puncture can be helpful here.
Fig. 11.22 Particularly when extension of the knee is prevented, continuous block of the sciatic nerve in conjunction with a femoral nerve block is of great importance to achieve good postoperative mobility after insertion of a total knee replacement. KAI: continuous anterior sciatic nerve block; “3-in-1” femoral nerve block.


  • General contraindications (see Chapter 20.2)

  • Special contraindications: none

11.2.3 Side Effects and Complications

There are no known special complications of sciatic nerve block. There have been few reports of side effects. Major complications including late sequelae are very rare. Dysesthesia for 1 to 3 days, which resolved spontaneously, has been described.

11.2.4 Remarks on the Technique

In Beck′s classical anterior technique (Beck 1963) the sciatic nerve is reached relatively distally. For this reason, anesthesia of the posterior cutaneous nerve of the thigh is often inadequate, which may cause problems in patients requiring a tourniquet at the thigh. In addition, with the Beck technique the sciatic nerve may be difficult to locate. With the modified technique, directing the needle at an angle of 75° to the skin causes needle contact with the sciatic nerve 3 to 4 cm more proximally; therefore both the sciatic nerve and the posterior cutaneous nerve of the thigh are reached (Meier 1999a).

The diameter of the sciatic nerve, the largest nerve in the body, is impressive. In anatomical studies only part of the nerve was stained after injection of 10 mL of methylene blue through the catheter (Meier 1999a; Fig. 11.23).

Fig. 11.23 Anterior sciatic nerve block with the approaching needle and the catheter advanced too far. 1 Piriformis muscle 2 Sciatic nerve 3 Needle with catheter 4 Posterior cutaneous nerve of the thigh and inferior clunial nerves

Tips and Tricks

  • The leg should be in neutral position.

  • Digital support (“two-finger grasp”) markedly reduces the risk of vascular puncture and the skin–nerve distance is shortened considerably (Meier 1999b).

  • In contrast to the Beck classical anterior technique, the Meier approach is about 1 to 1.5 cm further medial and distal so that contact with the periosteum of the femur is avoided (Meier 1999a).

  • The course of the deep blood vessels can also be established with a Doppler probe (Büttner and Meier 1999).

  • Using the Meier approach, the tip of the needle reaches the nerve 3 to 4 cm more proximal than with the technique described by Beck. The posterior cutaneous nerve of the thigh can therefore also be anesthetized (Meier 1999b).

  • If no stimulation response is produced, the needle should be withdrawn and corrected laterally (Meier 2001).

  • The catheter can be advanced more smoothly if the local anesthetic has been injected beforehand.

  • Advancing the catheter more than 4 cm beyond the tip of the needle has no advantages (Fig. 11.24).

  • No change in patient position is required when the technique is combined with a femoral nerve block.

  • The onset of the block (as indicated by corresponding sympathetic block) can be checked through the rise in plantar temperature using a skin thermometer (Büttner and Meier 1999).

Fig. 11.24 Our studies with dye (methylene blue) in non-preserved cadavers have shown that a minimum volume of 20 mL is required to block the entire sciatic nerve. Right gluteal region, posterior view after a volume of 10 ml of dye. 1 Sciatic nerve: fibular division, surrounded by dye 2 Sciatic nerve: tibial division, not surrounded by dye

Practical Note

To achieve complete anesthesia of the sciatic nerve, at least 20 mL of a local anesthetic should be injected. When positioning the patient, it should be ensured that the leg to be anesthetized is in neutral position. Bone contact is not necessary and the stimulating needle can be advanced past the femur (lesser trochanter) much more easily when the leg is in neutral position.

The distance from the skin of the anterior thigh to the sciatic nerve is around 6 to 10 cm in adults when the needle is directed vertically. With the needle directed cranially, the nerve is reached after 8 to 12 cm, and sometimes only after 13 to 15 cm in muscular or obese patients (Brown 1996, Chelly et al 1997, Bridenbaugh and Wedel 1998, Ericksen et al 2002). Paresthesia should be avoided.

During stimulation, note that contractions of gluteus maximus or tensor fasciae latae do not represent an adequate response. The vicinity of the sciatic nerve is indicated by a response in the area supplied by the nerve (hamstring muscles, triceps surae, tibialis anterior, fibular group; Wagner and Missler 1987, Kaiser et al 1990, Wagner 1994).

The motor response should be optimized so that plantar flexion (tibial nerve) or dorsiflexion (common fibular nerve) is produced in the foot.

In a study by Neuburger et al (2001), the stimulated muscle group (whether innervated by the tibial nerve or fibular nerve) had no effect on the block result. With correct stimulation (below 0.5 mA), a success rate over 95% can be achieved (Niesel 1994, Chelly et al 1999).

Practical Note

Performing the block with an immobile needle technique is beneficial as it enables aspiration to exclude vascular puncture and accidental intravascular injection of local anesthetic (Winnie 1975, Büttner and Meier 1999).

For anesthesia, 30 mL of a medium-acting or long-acting local anesthetic of adequate concentration should be injected (Wagner and Taeger 1988, Bridenbaugh and Wedel 1998, Chelly and Delaunay 1999; Fig. 11.25). In combination with a lumbar plexus block (psoas or so-called “3-in-1 block”), a further 30 to 40 mL of local anesthetic is required. When complete anesthesia of the leg is required, the combination of an anterior sciatic nerve block with femoral nerve block is a good alternative, as both blocks can be performed in the same sterile field without a change in position or repeated disinfection (Fig. 11.7 and Fig. 11.10).

Fig. 11.25 Spread of the local anesthetic after anterior sciatic nerve block (contrast was added to the local anesthetic). → Catheter

The femoral nerve block should be performed before the sciatic nerve block. This allows a largely pain-free anterior proximal sciatic nerve block to be performed.


A catheter for continuous anesthesia or analgesia can be placed (Meier 1999a) because the sciatic nerve is surrounded by a fascial sheath from its emergence from the infrapiriform foramen until it enters the popliteal fossa (Clara 1959, Benninghoff and Goerttler 1975). Advancing the catheter more than 4 to 5 cm can lead to deviation of the catheter into the true pelvis (lesser pelvis) and should be avoided (see Fig. 11.24).

In a study by Meier (1999b) of 85 patients, the catheter was kept in situ for an average of 4 days (up to a maximum of 8 days). No infections were observed at the puncture site. No side effects, complications, or neurological deficits were found.

Continuous anterior sciatic nerve block.

Pain therapy through a continuous anterior sciatic nerve block can be provided with 6 mL/h of ropivacaine 0.33% (3.3 mg/mL) or bolus injections of 20 mL of ropivacaine 0.2 to 0.375% (2–3.75 mg/mL) every 6 to 8 hours (Meier 2001). The maximum dose of ropivacaine should not exceed 37.5 mg/h. Büttner and Meier (1999) reviewed continuous pain therapy with ropivacaine in clinical practice, which was performed without complications in over 6,000 peripheral catheters.


The anterior technique allows block of the sciatic nerve with the patient in supine position. No change of position is required. The anesthesia can therefore also be performed, for example, in the presence of vertebral fractures, fractures of the pelvis or long bones, and also in the case of obesity, chronic polyarthritis, and other positioning problems. If a femoral nerve block is performed before the anterior sciatic nerve block and periosteal contact is avoided, the technique can be performed with little pain. The modified technique according to Meier enables anesthesia that includes the posterior cutaneous nerve of the thigh. A catheter can be placed readily without the potential risks seen with transgluteal or parasacral sciatic nerve block (Chapter 11.5 and Chapter 11.6). As a continuous technique, the procedure can be used for postoperative pain therapy after major surgery on the knee, lower leg, and foot, and for the treatment of pain syndromes distal to the knee and for regional sympathetic block.

11.2.5 Anterior Proximal Sciatic Nerve Block Using Ultrasound

Curved array: 5 to 2 MHz, linear multifrequency broadband transducer with phased-array technique Penetration depth: 10 to 20 cm

Needle: 8 to 15 cm

Ultrasound Orientation

The sciatic nerve is visualized on the anterior proximal technique in supine position at the inside of the thigh 8 to 10 cm distal to the inguinal fold at the level of the lesser trochanter or slightly distal to it. The leg is abducted and rotated externally.

The following structures are sought:

  • The femur as a convex hyperechoic line with an acoustic shadow behind it

  • The femoral vessels (femoral artery and deep femoral artery)

Medial to and below the femoral arteries is the adductor muscle group, the largest muscle of which is the adductor magnus. The adductors originate at the femur. The sciatic nerve is in the layer between the adductor magnus and the gluteus maximus (Fig. 11.26). The sciatic nerve is hyperechoic here and has a round to oval shape (1.66 ± 0.68 cm maximum diameter) and can be visualized at a depth of 6.21 ± 0.68 cm below the surface of the skin (Chan et al 2006).

Fig. 11.26 Anatomical cross-section of the proximal third of the thigh in the region of the anterior puncture of the sciatic nerve under ultrasound guidance. Enlargement, see Fig. 11.27. a Clinical setting. b Anatomical cross-section. c Anatomical cross-section (labeled). 1 Vastus medialis muscle 2 Sartorius muscle 3 Femoral and deep femoral arteries 4 Gracilis muscle 5 Adductor longus muscle 6 Adductor magnus muscle 7 Semimembranosus muscle 8 Semitendinosus muscle 9 Biceps femoris muscle 10 Gluteus maximus muscle 11 Sciatic nerve 12 Femur

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Jun 8, 2020 | Posted by in ANESTHESIA | Comments Off on 11 Proximal Sciatic Nerve Block

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