Peripheral Nerve Blocks: A Color Atlas, 3rd Edition

12.Sciatic Nerve Blocks

A. Parasacral Approach

Carl Rest

Patient Position: Lateral with surgical side up.

Indications: Surgical anesthesia and postoperative analgesia of the posterior thigh and leg, as well as the knee, ankle, and foot.

Needle Size: 21-gauge, 100-mm insulated stimulating needle.

Volume: 15 to 20 mL of ropivacaine 0.5% or 0.2% depending on the indication

Anatomic Landmarks: The ischial tuberosity and the posterior superior iliac spine (PSIS) are major surface landmarks for this block. The sciatic nerve is comprised of L4 through S3 ventral rami and exits the pelvis through the inferior portion of the greater sciatic foramen, deep (anterior) to the piriformis muscle. It lies deep to the gluteus maximus muscle and medial to both the gluteus medius and gluteus minimus. It is the most lateral of all structures passing inferior to the piriformis muscle. Medial to it lies the internal pudendal and inferior gluteal vessels and nerves. Occasionally the sciatic nerve divides prior to entering the gluteal region, with the common fibular nerve passing superior to, or through the piriformis muscle.

Approach and Technique: The PSIS and the inferior aspect of the ischial tuberosity are palpated and marked, and a line drawn between the two points (Fig. 12-1). The needle insertion lies along this line, slightly caudal to the superior aspect of the gluteal cleft, or approximately 6–8 cm caudal to the PSIS. The needle is connected to a nerve stimulator (2 Hz, 1.5 mA, 0.1 ms) and advanced in a parasagittal plane. If the sacrum is contacted, the needle is withdrawn and redirected slightly laterally, walking off the border of the sacrum into the greater sciatic foramen. The endpoint of needle advancement is a sustained sciatic stimulation eliciting foot plantar flexion/inversion (tibial nerve) or dorsiflexion/eversion (common fibular nerve) motor response with a current less than 0.5 mA (Fig. 12-2). Following negative aspiration for blood, local anesthetic is slowly injected in 5-mL increments, with intermittent aspiration.

Figure 12-1. The PSIS and the inferior aspect of the ischial tuberosity are palpated and marked, and a line drawn between the two points.

Tips

1.   The posterior femoral cutaneous nerve accompanies the sciatic nerve medially along with the inferior gluteal artery, and is reliably blocked using this approach.

2.   This block is commonly performed in combination with a lumbar plexus block for hip procedures. The depth at which the sciatic nerve is often located is often the same as the one of the femoral nerve. Consequently, we first perform the lumbar plexus block.

3.   The sciatic nerve usually innervates no muscles in the gluteal region. Direct gluteal stimulation on advancement of the needle indicates that the sciatic nerve is still deep to the needle tip.

4.   Pelvic splanchnic and distal sympathetic block are possible given their close proximity to the block site leading to possible urinary retention.

5.   In morbidly obese patients it is sometime necessary to use a 15-cm needle. However, we recommend to first start with a 10-cm needle, unless there is clear evidence that a 15-cm is required.

6.   Close pudendal nerve proximity may lead to genital tingling during needle positioning, and anesthesia following the block. If genital tingling is elicited during needle placement, the needle should be repositioned more laterally and superficially.

7.   This approach is useful for hip procedures as it allows for the concurrent block of additional sacral branches involved in hip joint innervation. Two of these nerves that exit through the greater sciatic foramen are the superior gluteal nerve (L4-S1, coursing superior to the piriformis muscle) and the nerve to the quadratus femoris muscle (L4-S1, coursing anterior to the sciatic nerve).

8.   Weakness in leg adduction with this block is due to block of the sciatic branch to the hamstring portion of the adductor magnus rather than obturator block.

9.   Limit advance of the needle to 2 cm beyond the border of the sacrum to minimize the chance of pelvic organ damage.

 

Figure 12-2. The endpoint of needle advancement is a sustained sciatic stimulation eliciting foot plantar flexion/inversion (tibial nerve) or dorsiflexion/eversion (common fibular nerve) motor response with a current less than 0.5 mA.

Suggested Readings

Birnbaum K, Prescher A, Hessler S, et al. The sensory innervation of the hip joint—an anatomical study. Surg Radiol Anat 1997;19:371–375.

Bruell P. Sciatic nerve block: parasacral approach. Reg Anesth Pain Med 1998;23:78.

Jochum D, Iohom G, Choquet O, et al. Adding a selective obturator nerve block to the parasacral sciatic block: an evaluation. Anesth Analg 2004;99:1544–1549.

Mansour NY, Bennetts FE. An observational study of combined continuous lumbar plexus and single shot sciatic nerve blocks for post–knee surgery analgesia. Reg Anesth 1996;21:287–291.

Morris GF, Lang SA, Dust WN, et al. The parasacral sciatic nerve block. Reg Anesth 1997;22:223–228.

Ripart J, Cuvillon P, Nouvellon E, et al. Parasacral approach to block the sciatic nerve: a 400-case survey. J Reg Anesth Pain Med 2005;30:193–197.

B. Posterior Approach

Daneshvari R. Solariki

Patient Position: Lateral, with the operative site up and the knee flexed (Sims position).

Indications: Anesthesia and immediate postoperative analgesia for surgery at and below the knee or requiring the use of a thigh tourniquet for more than 30 minutes.

Needle Size: 21-gauge, 150-mm insulated needle.

Volume: 15 to 20 mL.

Anatomic Landmarks: The greater trochanter, the posterosuperior iliac spine, and the sacral hiatus.

Approach and Technique: The center of the greater trochanter and the posterior iliac spine are identified and marked, and a line is drawn between these two points. Next, the sacral hiatus is identified and marked. Another line is drawn from the greater trochanter to the sacral hiatus. A perpendicular line is drawn to the midpoint of the greater trochanter–posterior iliac spine line. The intersection between this line and the greater trochanter–sacral hiatus line represents the point of insertion of the needle. The insulated needle connected to a nerve stimulator (1.5 mA, 2 Hz, 0.1 ms) is introduced perpendicular to the skin (Fig. 12-3). The stimulation of the sciatic nerve produces a flexion of the foot and toes or an inversion of the foot (tibial nerve) or a dorsiflexion of the foot and extension of the toes or an eversion of the foot (common peroneal nerve). The needle is positioned to maintain the same motor response with a current of less than 0.5 mA. After negative aspiration for blood, the local anesthetic is injected slowly, with repeated aspiration for blood every 5 mL.

Figure 12-3. The insulated needle connected to a nerve stimulator is introduced perpendicular to the skin.

Tips

1.   A pillow may be placed between the legs at the level of the knee.

2.   Appropriate positioning is critical to establish the proper site for the introduction of the needle.

3.   Already at this level, the sciatic nerve is separated into the common peroneal and the tibial nerves, and the posterior femoral cutaneous nerve of the thigh has branched.

4.   The stimulation of the sciatic nerve is almost always preceded by the stimulation of the gluteus maximus.

5.   A bone contact usually indicates that the needle is too lateral.

6.   Stimulation of the piriformis muscle indicates that the needle is too cephalad.

7.   A motor response at the level of the toes increases the likelihood of success.

8.   When patients complain of pelvic discomfort, it suggests that the needle is too anterior and is going through the greater sciatic notch.

9.   Because the sciatic nerve is found at a depth of 8 to 13 cm, no redirection of the needle should be attempted after it passes the skin to avoid bending the needle.

10.       This approach can be uncomfortable for the patient and therefore requires appropriate local anesthesia with a 38-mm needle and an appropriate sedation.

11.       This approach is not recommended in anticoagulated patients.

12.       A new posterior approach has been described in adults: The patient is positioned either prone or in the lateral position. The site of introduction of the needle is 10 cm lateral from the midpoint of the intergluteal sulcus.

Suggested Readings

Carlo D, Franco MD. Posterior approach to the sciatic nerve in adults: is Euclidean geometry still necessary? Anesthesiology 2003;98:723–728.

Hahn M, McQuillan PM, Sheplock GJ. Regional anesthesia. St. Louis, Mosby-Year Book, 1996:131.

Labat G. Regional anesthesia: its technique and clinical applications. Philadelphia: WB Saunders, 2nd ed., 1930:330.

Winnie AP. Regional anesthesia. Surg Clin North Am 1975;54:861–892.

C. 10-cm Midgluteal Approach

Carlo D. Franco

Patient Position: The patient is placed in the lateral decubitus position with the side to be blocked up. Both lower extremities are flexed slightly at the hips and knees with the buttocks forming a 90° angle with the bed.

Indications: Anesthesia and postoperative analgesia for any surgical procedure in the lower extremity involving the posterior thigh and any area distal to the knee excluding the medial side of the leg, which is innervated by the saphenous nerve, a branch of the femoral nerve.

Needle Size: Usually a 21-gauge, 100-mm insulated needle suffices. In some cases a 20-gauge, 150-mm insulated needle is necessary.

Anesthetic Volume: 25 to 35 mL.

Anatomic Landmarks: The intergluteal sulcus between the buttocks is the only landmark for this approach.

Approach and Technique: This simple approach is based on the fact that the sciatic nerve runs parallel to and about 10 cm from the midline (intergluteal sulcus) in all adults regardless of gender and body habitus. Thus, the block can be performed at 10 cm from the midline at about any point in the gluteal area including the subgluteal fold. In the gluteal area it is usually performed lateral to the midpoint of the intergluteal sulcus only because this point is easy to visualize and teach. The 10-cm measurement must be linear as shown in Figure 12-4,disregarding any individual contour on the patient's buttocks.

This linear distance reflects the distance between the midline and the area immediately lateral to the ischial tuberosity where the nerve runs.

Figure 12-4. With the patient in true lateral position the needle insertion point is easily found by measuring 10 linear cm from the midline (intergluteal sulcus). No other landmarks are identified.

Figure 12-5. The needle is advanced parallel to the patient's midline at 10 cm from it without the need to find any additional landmarks.

A local anesthetic wheal is raised at this point and an insulated needle connected to a nerve stimulator (around 1.5 mA, 1 Hz, 0.1 ms) is then slowly advanced parallel to the midline (parallel to the bed) as shown in Figure 12-5. Usually a motor twitch of the gluteus maximus can be easily seen as the needle passes through this muscle and continues to be visible until the needle reaches the deep surface of the gluteus maximus. The needle then needs to traverse the small amount of connective tissue deep to this muscle before reaching the sciatic nerve. The tip of the needle is then carefully manipulated until a response is still visible at 0.5 mA. The injection of local anesthetic is given slowly with frequent aspirations.

If the needle fails to elicit a sciatic nerve response, the reposition is easy since the nerve could only be either lateral or medial to the needle. The needle is withdrawn completely and a very small (10°) correction is made to the angle of insertion, first lateral and then if necessary medial.

Tips

1.   Positioning of the patient is important, as with any regional anesthesia technique. The patient is placed in true lateral position (not Sim's). Both hips and knees remain slightly flexed and the buttocks are at a right angle with the bed. This position aligns the midline of the patient with the horizontal plane of the bed making it easier to judge the angle of insertion of the needle.

2.   The prone position can be used but it is usually unnecessary and more time consuming.

3.   The sciatic nerve enters the upper gluteal area describing a downward curve from medial to lateral before running down parallel to the midline. Thus, it is recommended to attempt the block in the lower three-fourths of the buttocks because in the upper fourth the nerve is located less than 10 cm from the midline.

4.   The differences between male and female pelvises lie in the shape and diameters of the inner pelvis and not in the total width (bicrestal diameter), which is virtually the same in both sexes. The female inner pelvis is wider while the male bones are thicker. In fact, different hormone-dependent patterns of fat deposition in both sexes explain the perceived differences in pelvis width.

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5.   Deposition of fat in the buttocks does not affect the position of the sciatic nerve with respect to the midline but it does affect its depth and its relative position with respect to the lateral side of the body. In other words, the nerve's relative position in the buttocks changes, but not its absolute position with respect to the midline, which remains fixed at 10 cm.

6.   The gluteus maximus muscle is the only muscle that covers the sciatic nerve superficially in most of the gluteal region. In the uppermost area of the buttocks the small piriformis muscle is also superficial to the nerve.

7.   In our experience any response that can be elicited from stimulation of the sciatic nerve (e.g., dorsal or plantar flexion, eversion and inversion) provides a similar success rate provided the response is obtained at low output.

8.   When reposition of the needle is necessary it is important to realize that small changes in the angle of insertion of the needle have a profound impact in the position of the tip of the needle when dealing with deep structures like the sciatic nerve. A modest 10° correction angle for example has been calculated to move the tip of the needle approximately 1.6 cm at a depth of 9 cm.

Suggested Readings

Franco CD. Posterior approach to the sciatic nerve in adults: Is Euclidean geometry still necessary? Anesthesiology 2003;98:723–728.

Hall J, Froster-Iskenius U, Allanton J. Handbook of normal physical measurements. Oxford: Oxford University Press, 1989:254–308.

Snell RS. Clinical anatomy for medical students, 3rd ed. Boston: Little, Brown and Company, 1986:553–598.

D. Gluteal Approach

Anna Uskova

Patient Position: Lateral decubitus with operative side up and leg to be blocked rolled forward onto the flexed knee (Sim's position).

Indications: Anesthesia and immediate postoperative analgesia for major surgery at and below the knee, including the foot and ankle, especially when tourniquet use is anticipated.

Needle Size: 22-gauge, 10-cm insulated needle. In morbidly obese patients, 15-cm needle may be necessary.

Volume: 15 to 20 mL of ropivacaine 0.5% (anesthesia) or 0.2% (postoperative analgesia).

Anatomic Landmarks: The greater trochanter (GT) and the ischial tuberosity (IT) (Figs. 12-6, 12-7). At this level the sciatic nerve is covered by the gluteus maximus muscle only. A groove may be palpated between the lateral border of quadriceps femoris (vastus lateralis) and biceps femoris (Fig. 12-7). At the level of the thigh, the sciatic nerve runs toward the popliteal fossa (sciatic line), lying on the posterior surface of the adductor magnus, within the posterior medial compartment of the thigh. The septum intermusculare femoralis mediale and a reinforcement of the posterior fascia of the adductor magnus muscle limit this compartment.

Figure 12-6. Anatomic landmarks. GT, greater trochanter; IT, ischial tuberosity.

 

Figure 12-7. Anatomic landmarks. GT, greater trochanter; IT, ischial tuberosity; G, gluteal approach; SG, subgluteal approach.

Approach and Technique: The greater trochanter (GT) and the ischial tuberosity (IT) are identified and marked, and a line is drawn between these two points. Midpoint of this line is the site of the introduction of the needle (G). At this level, a skin depression can be palpated, representing the groove between the biceps femoris and vastus lateralis (Fig. 12-7). After proper local skin infiltration, the insulated needle connected to a nerve stimulator (1.5 mA, 2 Hz, 0.1 ms) is introduced perpendicular to the skin. The needle is advanced until the sciatic nerve is stimulated—inversion/plantar flexion of the foot and toes (tibial nerve) or eversion/dorsiflexion of the foot and extension of the toes (common peroneal nerve). The needle is adjusted to maintain the same motor response with a current at or below 0.5 mA. After a negative aspiration for blood, planned volume of local anesthetic solution is slowly injected, with repeat aspiration every 5 ml (Fig. 12-8).

Figure 12-8. After a negative aspiration for blood, planned volume of local anesthetic solution is slowly injected, with repeat aspiration every 5 ml.

 

Tips

1.   The gluteal approach as compared with other sciatic approaches (classic, high lateral) reduces the risk of misplacements or dislocation of the catheter after surgery and reduces the risk of vascular puncture.

2.   This block is usually performed in combination with a single or continuous lumbar plexus or femoral block.

3.   A variant of the gluteal approach is the subgluteal approach (SG). A line is drawn perpendicularly and extending caudally for 4 cm in the middle of the ischial tuberosity–greater trochanter line. The end of this line represents the site of introduction of the needle (SG) (Fig. 12-7).

4.   Gluteal or subgluteal approach is preferred in obese patients, because at this level the sciatic nerve is the most superficial.

5.   Compared with the classic posterior approach of Labat, this approach, as well as subgluteal, is less painful because the needle is introduced in the groove between the biceps femoris and lateral border of quadriceps femoris muscles.

6.   If the femur is contacted, the needle needs to be withdrawn and redirected medially (toward sacrum).

7.   If direct stimulation of gluteus maximus muscle is noticed (too shallow), needle should be advanced a few millimeters until distal response with foot movement is recorded.

8.   Hamstring contraction represents either a direct muscle contraction or the stimulation of tibial nerve, except the short head of biceps femoris, which is innervated by common peroneal nerve (and not considered part of the hamstring muscles). This response is not reliable for the block below the knee. The needle should be readjusted to elicit a distal (toes) response.

9.   If patient reports painful paresthesia along the leg, the needle should be withdrawn and redirected to achieve painless stimulation with movement of the toes with a current of or below 0.5 mA.

Suggested Readings

di Benedetto P, Bertini L, Casati A, et al. A new posterior approach to the sciatic nerve block: a prospective, randomized comparison with the classical posterior approach. Anesth Analg 2001;93:1040–1044.

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 2002;27:168–172.

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 2002;94:996–1000.

McMinn RMH, Hutching RT, eds. Color atlas of human anatomy. Chicago: Year Book Medical Publishers, 1977:296–297.

Raj PP, Parks RI, Watson TD, et al. A new single-position supine approach to sciatic–femoral nerve block. Anesth Analg 1975;54:489–493.

E. Anterior Approach

Jacques E. Chelly

Patient Position: Supine, with the leg in the neutral position.

Indications: Anesthesia and immediate postoperative analgesia for surgery of the knee and below. Analgesia prior to surgery following a leg trauma.

Needle Size: 20-gauge, 150-mm b-beveled insulated needle.

Volume: 20 to 25 mL.

Anatomic Landmarks: Anterior iliac spine and superior border of the pubic tubercle.

Approach and Technique: A line is drawn between the anterior iliac spine and the superior angle of the pubic tubercle. At its midpoint, a perpendicular line is drawn. The site of introduction of the needle is 8 cm distally (Fig. 12-9). The 150-mm insulated needle connected to a nerve stimulator (1.5 mA, 2 Hz, 0.1 ms) is introduced vertically (Fig. 12-10). Within 3 to 5 cm, movements of the patella are elicited, indicating the proximity of the femoral nerve. The current is then reduced to 0.5 mA and the motor response disappears. The current is increased 2 cm deeper to 5 mA. If the femur is contacted, the needle is removed and introduced 1.5 to 2.0 cm medially, and all steps are repeated. Stimulation of the sciatic nerve is usually obtained at a depth of 10 to 12 cm and produces a dorsiflexion of the foot and extension of toes, or an eversion of the foot (common peroneal nerve stimulation) or a flexion of the foot and toes, or an inversion of the foot (tibial nerve stimulation) (see Fig. 12-2). The needle is positioned to maintain the same motor response with a current of less than 0.6 mA. After negative aspiration for blood, the local anesthetic solution is slowly injected with repeated aspiration every 5 mL.

Figure 12-9. At its midpoint, a perpendicular line is drawn. The site of introduction of the needle is 8 cm distally. Anterior superior iliac spine (ASIS). Superior border of pubis tubercle (SBPS).

Figure 12-10. The insulated needle connected to a nerve stimulator is introduced vertically.

Tips

1.   In this approach, the nerve stimulator has a dual function. First, it helps prevent damage to the femoral nerve during the first 3 to 5 cm of needle introduction, and second, it helps to localize the sciatic nerve. If, during the introduction of the needle, it is found that the needle is directly on the femoral nerve (presence of movement of the patella with a current of 0.5 mA), the needle is directed slightly medially before continuing with any further advancement (Fig. 12-11).

2.   Except for morbidly obese patients (>100 kg), it is rarely necessary to introduce the 150-mm needle. In most cases, the nerve is found at an approximate depth of 10 to 12 cm.

3.   Introduction of an insulated needle through the quadriceps is easy. However, if at a depth of 10 to 12 cm, the introduction of the needle becomes more difficult, this is a sign that the needle is very close to the femur. In such cases, it should be withdrawn to the skin and redirected slightly more medially.

4.   The onset time for a sciatic nerve block is usually longer than other blocks. It usually requires 20 to 30 minutes or even longer.

5.   Using the anterior sciatic approach also allows one to block the femoral nerve through the same skin introduction point. However, to avoid any risk of injury of the femoral nerve by the insulated needle on its way to the sciatic nerve, it is recommended to first block the sciatic nerve and then proceed to block the femoral nerve while retrieving the needle. This technique offers the advantage of only one stick. However, with such a distal approach to the femoral nerve, it is not possible to also block the femoral cutaneous nerve or the obturator (three-in-one block).

6.   Beck first described an anterior approach. The Chelly and Delaunay approach and the Beck approach use different anatomic landmarks, but both lead to the same site (Fig. 12-12) and both approach the sciatic nerve above the lesser trochanter.

 

Figure 12-11. Femoral nerve.

7.   Van Elstraete et al. described new landmarks (2.5 cm medial from the femoral artery and 2.5 cm distal from the inguinal crease). In this case the 150-mm insulated needle connected to a nerve stimulator is introduced at a 10° to 15° angle relative to the vertical plane. This latter approach offers the advantage of being based only on a landmark found below the femoral crease. Van Elstraete appears to approach the sciatic nerve below the lesser trochanter.

Figure 12-12. Anatomic landmarks.

Figure 12-13. The needle is introduced perpendicular to the skin, and stimulation of the sciatic nerve is produced between 4 to 12 cm.

8.   Anterior approach to the sciatic nerve is especially interesting in morbidly obese and trauma patients who cannot be moved. However, in patients weighing over 100 kg, the 150-mm needle may be too short. In these cases, it is possible to approach the sciatic nerve using the lithotomy approach described by Raj, with the patient supine and the hip and the knee flexed. This gluteal approach is based on the identification of the ischial tuberosity and greater trochanter. The middle of the ischial tuberosity–greater trochanter line represents the site of introduction of the needle. The needle is introduced perpendicular to the skin, and stimulation of the sciatic nerve is produced within 4 to 12 cm (depending on the size of the thigh) (Fig. 12-13).

Suggested Readings

Beck GP. Anterior approach to sciatic nerve block. Anesthesiology 1963;24:222–224.

Chelly JE, Delauney L. A new anterior approach to the sciatic nerve block. Anesthesiology 1999;91:1655–1660.

Raj PP, Parks RI, Watson TD, Jenkins MT. A new single-position supine approach to sciatic-femoral nerve block. Anesth Analg 1975;54:489–493.

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 2002;95:214–218.

F. Posterior Popliteal Approach

Jennnifer R. Greger

Patient Position: The patient is placed in the prone position with the leg slightly flexed and the foot elevated.

Indications: Anesthesia and immediate postoperative analgesia for surgery at and below the knee. This block is usually combined with the femoral or saphenous nerve block to obtain complete anesthesia.

Needle Size: 22-gauge, 25-mm b-beveled insulated needle.

Volume: 30 to 40 mL.

Anatomic Landmarks: The popliteal crease, the lateral border of the biceps femoris, and the medial border of the semi-membranous/semi-tendinous tendons (Fig. 12-14). The innervation of the sciatic nerve below the knee is presented in Figure 12-15.

Approach and Technique: The lateral border of the biceps femoris and the medial border of the semi-membranous/semi-tendinous tendons are identified and marked at the level of the popliteal crease. At the level of the popliteal crease, a perpendicular line is drawn in the middle and extended cephalad. The site of introduction of the needle is 1 cm lateral to the 5 cm mark (Fig. 12-16). The 25-mm, b-beveled insulated needle connected to a nerve stimulator (1.5 mA, 2 Hz, 0.1 ms) is introduced perpendicular to the skin and slowly advanced until a branch of the sciatic nerve (either the common peroneal nerve [dorsiflexion of the foot and extension of toes or eversion] or the tibial nerve [flexion of the foot and toes or inversion] [see Fig. 12-2]) is stimulated (at a depth of 1.5 to 2.5 cm). The position of the needle is adjusted to maintain the same motor response with a current less than 0.5 mA. After negative aspiration for blood, the local anesthetic solution is injected 5 mL at a time with multiple aspirations for blood in between.

Figure 12-14. Anatomic landmarks.

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Figure 12-15. The innervation of the sciatic nerve below the knee.

Tips

1.   This is one of the easier blocks to perform.

2.   This block can also be performed with a 50-mm needle with the patient placed in the lateral position.

3.   The anatomic landmarks can be easily identified by asking the patient to perform an active flexion of the leg.

 

Figure 12-16. The site of the introduction of the needle is 1 cm lateral to the 5 cm mark. The insulated needle connected to a nerve stimulator is introduced perpendicular to the skin and slowly advanced until a branch of the sciatic nerve or the tibial nerve is stimulated.

4.   The best positioning of the leg and foot can be achieved by either positioning the patient with the foot outside of the stretcher or placing a pillow under the leg.

5.   Minimal discomfort should be experienced by the patient because only interstitial fat lies between the skin and the nerve. If the patient complains of pain, this suggests that the needle is going through the semi-tendinous/semi-membranous tendons rather than being medial to them.

6.   It is possible to perform the same block using the lithotomy approach.

7.   For surgery performed at the level of the knee, especially with the use of a tourniquet placed at the thigh, a femoral or a lumbar plexus block is required to complete the anesthesia. For surgery below the knee, especially when a tourniquet is placed at the level of the calf or below, a saphenous nerve block is sufficient.

8.   There are at least three techniques that can be used to perform a saphenous nerve block at the level of the knee and with the patient in the supine position. First, a 22-gauge, 38-mm blunt needle mounted on a 10-mL syringe (containing 10 mL of local anesthetic solution) is introduced perpendicular to the skin and through the sartorius muscle, 3 to 4 cm cephalad from the medial femoral condyle. Within 3 cm, a loss of resistance is felt. After negative aspiration for blood, 10 mL of local anesthetic is injected slowly, with aspiration for blood after 5 mL. Second, a 50-mm insulated needle connected to a nerve stimulator (2 mA, 2 Hz, 0.1 ms) is introduced perpendicular to the skin, 3 cm distally to the medial femoral epicondyle. Within 2 to 3 cm, the patient should report an electrical paresthesia in the medial aspect of the leg. The needle position is adjusted to maintain the paresthesia with a current of less than 0.4 mA. After negative aspiration for blood, 6 to 8 mL of local anesthetic is injected slowly. Third, a 25-gauge, 38-mm needle is introduced 3 cm below the tibial plateau and directed from the middle to the medial border of the leg. Ten milliliters of local anesthetic solution is then injected subcutaneously.

9.   This block can be performed at any level of the popliteal fossa. However, the more cephalad from the popliteal crease, the closer are the common peroneal and tibial nerves. Conversely, the more distal, the more separated the nerves become. Indeed, the tibial nerve runs in the middle of the popliteal fossa while the common peroneal nerve runs in a lateral direction toward the head of the fibula.

10.       Variants of the proposed technique include using the perpendicular line in the middle of the popliteal crease as a starting point. If no motor response is elicited, the needle is directed more laterally.

11.       The deep femoral vessels become the popliteal vessels after passing through the adductor hiatus. The popliteal vessels, which are initially medial and anterior and separated from the sciatic nerve, run medial and anterior to the tibial nerve at the lower part of the popliteal fossa. Consequently, the risk of vessel puncture is minimal if the needle is kept in the lateral upper quadrant of the popliteal fossa or if the needle is introduced above the adductor hiatus (above the popliteal fossa). However, this latter approach requires a 100-mm needle to be introduced deeper and through the hamstring muscles, which is more painful to patients.

Suggested Readings

Comfort VK, Lang SA, Yip RW. Saphenous nerve anaesthesia: a nerve stimulator technique. Can J Anaesth 1996;43:852–857.

Rongstad K, Mann RA, Prieskom D, et al. Popliteal sciatic nerve block for postoperative analgesia. Foot Ankle Int 1996:17:378–382.

Rorie DK, Byer DE, Nelson DO, et al. Assessment of block of the sciatic nerve in the popliteal fossa. Anesth Analg 1980;59:371–376.

Vloka JD, Hadzic A, Kitain E. Anatomic considerations for sciatic nerve block in the popliteal fossa through the lateral approach. Reg Anesth 1996;21:414–418.

Vloka JD, Hadzic A, Koorn R, et al. Supine approach to the sciatic nerve in the popliteal fossa. Can J Anaesth 1996;43:964–967.

G. Lateral Popliteal Approach

Ralf Gebhard

Patient Position: Supine with the leg in neutral position.

Indications: Anesthesia and postoperative analgesia for surgery of the lower extremity below the knee (e.g., foot and ankle surgery).

Needle Size and Catheter: 18-gauge, 100-mm insulated needle.

Volume: 40 mL of a mixture of 0.5% ropivacaine and 1.5% mepivacaine v/v.

Anatomic Landmarks: Patella, biceps femoris muscle and the vastus lateralis muscle.

Approach and Technique: The groove between the biceps femoris muscle and the vastus lateralis muscle is palpated and marked. A circumferential line is drawn on the thigh 8 to 10 cm proximal from the top of the patella. The point of needle entry is marked by the intersection of this line with the groove between the biceps femoris muscle and vastus lateralis muscle (Fig. 12-17). After disinfection and local infiltration with 1% lidocaine, a 100-mm insulated needle connected to a nerve stimulator (1.5 mA, 2 Hz, 0.1 ms) is inserted perpendicular to the skin (Fig. 12-18) in search of either the common peroneal or tibial nerve. After adjusting the needle position to maintain a motor response at a current below 0.5 mA and negative aspiration for blood, the volume is injected slowly (10 mL/min) and in 5 mL increments. If a sciatic nerve response cannot be obtained with the described change in needle angle the needle is withdrawn until the local biceps femoris muscle reappears. The needle is then reinserted in 10° increments first more posterior than the initial angle, or in 10° increments more anterior.

Figure 12-17. The point of needle entry is marked by the intersection of this line with the groove between the biceps femoris muscle and vastus lateralis muscle.

Figure 12-18. An insulated needle connected to a nerve stimulator is inserted perpendicular to the skin.

Tips

1.   If the medial aspects of the lower leg and ankle are involved in the surgery, the addition of a saphenous nerve block will be necessary to provide complete anesthesia. This can be achieved by blocking the saphenous nerve selectively above or below the knee or by performing a femoral nerve block. The latter is especially recommended if thigh coverage will be used during surgery.

2.   In most individuals the division of the sciatic nerve into the common peroneal nerve and the tibial nerve occurs below the suggested level of needle insertion. However, if this block is performed closer to the knee, a double stimulation and injection technique accounting separately for both branches may be necessary to achieve a complete block in the sciatic nerve territory of the lower leg.

3.   If the local biceps femoris muscle twitch cannot be elicited, the needle can be inserted in a perpendicular direction until the femur is contacted. Then the needle is withdrawn and reinserted in 10° to 15° increments posterior to the horizontal plane until a sciatic nerve response is obtained.

4.   Plantar flexion (tibial nerve response) as the elicited motor response may yield a more complete block and a faster onset time than dorsiflexion (peroneal nerve response).

5.   This approach is a great alternative to the posterior popliteal and the classic approaches to the sciatic nerve if the patient cannot be positioned in prone or lateral decubitus position.

6.   Slightly supporting the knee by placing a small towel under the popliteal fossa allows for easier needle operation.

Suggested Readings

Hadzic A, Vloka JD. A comparison of the posterior versus the lateral approaches to the block of the sciatic nerve in the popliteal fossa. Anesthesiology 1998;88:1480–1486.

McLeod DH, Wong DH, Vaghadia H, et al. Lateral popliteal sciatic nerve block compared with ankle block for analgesia following foot surgery. Can J Anaesth 1995;42:765–769.

Taboada Muniz M, Alvarez J, Cortes J, et al. Lateral approach to the sciatic nerve block in the popliteal fossa: correlation between evoked motor response and sensory block. Reg Anesth Pain Med 2003;28:450–455.

Vloka JD, Hadzic A, Kitain E, et al. Anatomic considerations for sciatic nerve block in the popliteal fossa through the lateral approach. Reg Anesth 1996;21:14–41.