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Popliteal fossa block: Lateral approach to the sciatic nerve
Popliteal Fossa Block: Lateral Approach to the Sciatic Nerve Caroline ter Rahe, MD, and Santhanam Suresh, MD
Regional anesthesia for foot and ankle surgery in children is usually provided using a caudal blockade. However, there are certain conditions that preclude the use of a caudal block. The use of a sciatic nerve block in addition to a femoral nerve block can provide good analgesia for these procedures. In a sedated or anesthetized child, it may be easier to perform this nerve block with the patient in a supine position. The use of a nerve stimulator and a sheathed needle can assist in locating the nerve. This nerve block may offer the additional advantage of a longer duration of pain relief. Copyright 2002, Elsevier Science (USA). All rights reserved.
he sciatic nerve block is becoming popular in adults for the management of pain in surgery involving the foot, ankle, and knee.1,2 A caudal block is often used to provide postoperative pain relief for most foot and ankle surgeries in children. However, there are certain relative contraindications to a caudal block, including spinal dysraphism, parental disagreement, and technical difficulties in performing the block. In these instances, we have resorted to the use of a combined sciatic nerve and femoral nerve block for surgeries involving the foot and ankle. Advantages with the use of a peripheral nerve block include the avoidance of postoperative opioids that may decrease postoperative morbidity, including nausea and vomiting.3
T
Anatomy and Technique for Performing the Block The sciatic nerve arises from the L4 through S5 roots of the sacral plexus, passes through the pelvis, and becomes superficial at the lower margin of the gluteus maximus muscle. The nerve then descends into the lower extremity in the posterior compartment of the thigh. It supplies sensory innervation to the posterior thigh and to the entire leg and foot below the level of the knee, except for the medial aspect, which is supplied by the saphenous nerve, a branch of the femoral nerve. The popliteal fossa is a diamond-shaped area located behind the knee. This fossa is bordered laterally by the biceps femoris muscle and tendon, medially by the tendons of the semitendinosus and semimembranosus muscles, and inferiorly by the
From the Northwestern University Medical School, Children’s Memorial Hospital, Department of Anesthesiology, Chicago, IL. Address reprint requests to Santhanam Suresh, MD, Attending Anesthesiologist, Department of Anesthesiology, #19, Children’s Memorial Hospital, 2300 Children’s Plaza, Chicago, IL 60614. E-mail: [email protected]. Copyright 2002, Elsevier Science (USA). All rights reserved. 1084-208X/02/0603-0000$35.00/0 doi:10.1053/trap.2002.123509
heads of the gastrocnemius muscle. The sciatic nerve divides into two branches, the larger tibial nerve located medially and the smaller common peroneal nerve located laterally. The nerves are at the apex of the popliteal fossa where they are in close proximity to each other and are enclosed in a connective tissue sheath for a short distance before dividing into the component nerves.4,5 This division occurs at about 5 to 8 cm above the crease at the knee. The tibial nerve, the larger of the two branches, courses through the fossa under the popliteal fascia lateral to the midline. Superiorly, it lies under the biceps femoris muscle in close proximity to the posterior border of the biceps femoris tendon. Inferiorly, it passes between the heads of the gastrocnemius muscles. The common peroneal nerve follows the tendon of the biceps femoris muscle laterally and travels around the fibular head as it leaves the popliteal fossa. The two nerves innervate the entire leg below the knee, except the anteromedial cutaneous area of the leg and foot, which is innervated by the saphenous nerve, a branch of the femoral nerve. There are three approaches to providing a nerve block of the sciatic nerve:6 1. Posterior approach of Labat 2. Anterior approach 3. Lateral popliteal approach The disadvantage of the classic posterior approach to blocking the sciatic nerve at the level of the knee (popliteal nerve block) is the need to position the patient prone to perform the block. Infrequently, this maneuvering is inconvenient or is contraindicated, particularly in patients with unstable cervical spine injuries, hemodynamic instability, or severe limb pain. The lateral popliteal approach to the sciatic nerve can be performed with the patient in the supine position.7-10 When combined with a femoral nerve block, the anesthesia is effective for all surgeries on the foot and ankle. This block has the advantage of preserving hamstring function and allows early ambulation with crutches. This block can be performed with the patient in the supine position (Fig 1). The lower leg is elevated on a pillow. The biceps femoris tendon is palpated; the tendon is then traced upward for about 3 to 5 cm. A 22-gauge insulated needle is inserted anterior to the tendon in a horizontal plane with a cephalad angulation. A nerve stimulator is attached to the sheathed needle, and with low-voltage stimulation (0.2 to 0.5 mV), the foot is observed for plantar or dorsiflexion. This confirms the correct placement of the needle. On injection of 1 mL of local anesthetic solution, the stimulation is ablated thereby indicating correct positioning of the needle. A dorsiflexion or eversion of the foot identifies the common peroneal nerve, and a plantar flexion of the foot is required to identify the tibial nerve. An elicited inversion of the foot, as
Techniques in Regional Anesthesia and Pain Management, Vol 6, No 3 (July), 2002: pp 141-143
141
Fig 1. Lateral approach to the sciatic nerve. Reproduced with permission from: Polaner DM, Suresh S, Cote CJ: A Practice of Anesthesia for Infants and Children (ed 3). Philadelphia, PA, WB Saunders, 2000.
recently demonstrated by Benzon et al,11 is the best predictor of a complete sensory blockade of the foot after a sciatic nerve block at the popliteal level. Inversion is caused by the action of both the tibialis anterior muscle, which is innervated by the tibial nerve, and the tibialis anterior muscle, which is innervated by the deep peroneal nerve, a branch of the common peroneal nerve. Therefore, in the case of an elicited inversion of the foot, the needle tip is located very close to both branches of the sciatic nerve or to the sciatic nerve itself before it divides into the tibial nerve and common peroneal nerve. Multiple stimulations of both sciatic nerve components below the knee provide a better success rate when a sciatic block is performed at the popliteal level using the lateral approach. Insertion of the block needle 7 cm above the lateral femoral epicondyle between the biceps femoris and vastus lateralis muscles, at a 30-degree angle relative to the horizontal plane and at a depth of 45 mm in an average-sized patient, should place the tip of the needle close to the popliteal nerve. The lateral approach to the popliteal sciatic nerve is an effective, quick, and easy method to perform the block. Using 20 mL 0.5% plain bupivacaine, analgesia lasts a median of 18 hours compared with subcutaneous local anesthetic infiltration that lasts on average 6.2 hours.2 In adult studies it
142
has been shown that the sciatic nerve block is longer lasting than an ankle block or subcutaneous infiltration and provides excellent postoperative analgesia.2
Complications Intraneural injection must be avoided. Use of a low-voltage nerve stimulator ensures the proper placement of the needle. It is rare to see intravascular placement of the needle with this approach. Intravascular injection can be avoided with incremental injection of local anesthetic solution with frequent aspiration. The popliteal vessels are surrounded by a vascular sheath, which is clearly separated from the nerves by popliteal fossa fat. In a cadaver study all the dye injectates were located laterally and posteriorly to the popliteal vessels. The lateral approach is unlikely to result in an intravascular injection, which makes this a safer approach for popliteal nerve block.
Conclusion The lateral popliteal approach to the sciatic nerve is an easy but satisfying nerve block. In combination with the femoral nerve TER RAHE AND SURESH
block, we can provide excellent analgesia for foot, ankle, and knee surgery. Because of the ease of performance and the duration of the analgesia, we have now resorted to using this block for unilateral foot surgery that may involve bony procedures. This may also be used as a supplement to a caudal block for longer surgical procedures.
References 1. Cappellino A, Jokl P, Ruwe PA: Regional anesthesia in knee arthroscopy: A new technique involving femoral and sciatic nerve blocks in knee arthroscopy. Arthroscopy 12:120-123, 1996 2. McLeod DH, Wong DV, Vaghadia, et al: Lateral popliteal sciatic nerve block compared with ankle block for analgesia following foot surgery. Can J Anaesth 42:765-769, 1995 3. Suresh S, Barcelona S, Young N: Postoperative pain management in children undergoing tympanomastoid surgery: Is a local block better than intravenous opioids? Anesthesiology 91:A1281, 1999 (abstract) 4. Vloka JD, Hadzˇic´ A, Kitain E, et al: Anatomic considerations for
LATERAL APPROACH TO THE SCIATIC NERVE
5.
6.
7. 8.
9. 10. 11.
sciatic nerve block in the popliteal fossa through the lateral approach. Reg Anesth. 21:414-418, 1996 Vloka JD, Hadzˇic´ A, Lesser JB, et al: A common epineural sheath for the nerves in the popliteal fossa and its possible implications for sciatic nerve block. Anesth Analg 84:387-390, 1997 Dalens B, Tanguy A, Vanneuville G: Sciatic nerve blocks in children: Comparison of the posterior, anterior, and lateral approaches in 180 pediatric patients. Anesth Analg 70:131-137, 1990 Vloka JD, Hadzic A, Koorn R, et al: Supine approach to the sciatic nerve in the popliteal fossa. Can J Anaesth 43:964-967, 1996 Paqueron X, Bouaziz H, Macalou D, et al: The lateral approach to the sciatic nerve at the popliteal fossa: One or two injections? Anesth Analg 89:1221-1225, 1999 Guardini R, Waldron BA, Wallace WA: Sciatic nerve block: A new lateral approach. Acta Anaesthesiol Scand 29:515-519, 1985 Zetlaoui PJ, Bouaziz H: Lateral approach to the sciatic nerve in the popliteal fossa. Anesth Analg 87:79-82, 1998 Benzon HT, Kim C, Benzon HP, et al: Correlation between evoked motor response of the sciatic nerve and sensory blockade. Anesthesiology 87:547-552, 1997.
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Regional anesthesia for foot and ankle surgery in children is usually provided using a caudal blockade. However, there are certain conditions that preclude the use of a caudal block. The use of a sciatic nerve block in addition to a femoral nerve block can provide good analgesia for these procedures. In a sedated or anesthetized child, it may be easier to perform this nerve block with the patient in a supine position. The use of a nerve stimulator and a sheathed needle can assist in locating the nerve. This nerve block may offer the additional advantage of a longer duration of pain relief. Copyright 2002, Elsevier Science (USA). All rights reserved.
he sciatic nerve block is becoming popular in adults for the management of pain in surgery involving the foot, ankle, and knee.1,2 A caudal block is often used to provide postoperative pain relief for most foot and ankle surgeries in children. However, there are certain relative contraindications to a caudal block, including spinal dysraphism, parental disagreement, and technical difficulties in performing the block. In these instances, we have resorted to the use of a combined sciatic nerve and femoral nerve block for surgeries involving the foot and ankle. Advantages with the use of a peripheral nerve block include the avoidance of postoperative opioids that may decrease postoperative morbidity, including nausea and vomiting.3
T
Anatomy and Technique for Performing the Block The sciatic nerve arises from the L4 through S5 roots of the sacral plexus, passes through the pelvis, and becomes superficial at the lower margin of the gluteus maximus muscle. The nerve then descends into the lower extremity in the posterior compartment of the thigh. It supplies sensory innervation to the posterior thigh and to the entire leg and foot below the level of the knee, except for the medial aspect, which is supplied by the saphenous nerve, a branch of the femoral nerve. The popliteal fossa is a diamond-shaped area located behind the knee. This fossa is bordered laterally by the biceps femoris muscle and tendon, medially by the tendons of the semitendinosus and semimembranosus muscles, and inferiorly by the
From the Northwestern University Medical School, Children’s Memorial Hospital, Department of Anesthesiology, Chicago, IL. Address reprint requests to Santhanam Suresh, MD, Attending Anesthesiologist, Department of Anesthesiology, #19, Children’s Memorial Hospital, 2300 Children’s Plaza, Chicago, IL 60614. E-mail: [email protected]. Copyright 2002, Elsevier Science (USA). All rights reserved. 1084-208X/02/0603-0000$35.00/0 doi:10.1053/trap.2002.123509
heads of the gastrocnemius muscle. The sciatic nerve divides into two branches, the larger tibial nerve located medially and the smaller common peroneal nerve located laterally. The nerves are at the apex of the popliteal fossa where they are in close proximity to each other and are enclosed in a connective tissue sheath for a short distance before dividing into the component nerves.4,5 This division occurs at about 5 to 8 cm above the crease at the knee. The tibial nerve, the larger of the two branches, courses through the fossa under the popliteal fascia lateral to the midline. Superiorly, it lies under the biceps femoris muscle in close proximity to the posterior border of the biceps femoris tendon. Inferiorly, it passes between the heads of the gastrocnemius muscles. The common peroneal nerve follows the tendon of the biceps femoris muscle laterally and travels around the fibular head as it leaves the popliteal fossa. The two nerves innervate the entire leg below the knee, except the anteromedial cutaneous area of the leg and foot, which is innervated by the saphenous nerve, a branch of the femoral nerve. There are three approaches to providing a nerve block of the sciatic nerve:6 1. Posterior approach of Labat 2. Anterior approach 3. Lateral popliteal approach The disadvantage of the classic posterior approach to blocking the sciatic nerve at the level of the knee (popliteal nerve block) is the need to position the patient prone to perform the block. Infrequently, this maneuvering is inconvenient or is contraindicated, particularly in patients with unstable cervical spine injuries, hemodynamic instability, or severe limb pain. The lateral popliteal approach to the sciatic nerve can be performed with the patient in the supine position.7-10 When combined with a femoral nerve block, the anesthesia is effective for all surgeries on the foot and ankle. This block has the advantage of preserving hamstring function and allows early ambulation with crutches. This block can be performed with the patient in the supine position (Fig 1). The lower leg is elevated on a pillow. The biceps femoris tendon is palpated; the tendon is then traced upward for about 3 to 5 cm. A 22-gauge insulated needle is inserted anterior to the tendon in a horizontal plane with a cephalad angulation. A nerve stimulator is attached to the sheathed needle, and with low-voltage stimulation (0.2 to 0.5 mV), the foot is observed for plantar or dorsiflexion. This confirms the correct placement of the needle. On injection of 1 mL of local anesthetic solution, the stimulation is ablated thereby indicating correct positioning of the needle. A dorsiflexion or eversion of the foot identifies the common peroneal nerve, and a plantar flexion of the foot is required to identify the tibial nerve. An elicited inversion of the foot, as
Techniques in Regional Anesthesia and Pain Management, Vol 6, No 3 (July), 2002: pp 141-143
141
Fig 1. Lateral approach to the sciatic nerve. Reproduced with permission from: Polaner DM, Suresh S, Cote CJ: A Practice of Anesthesia for Infants and Children (ed 3). Philadelphia, PA, WB Saunders, 2000.
recently demonstrated by Benzon et al,11 is the best predictor of a complete sensory blockade of the foot after a sciatic nerve block at the popliteal level. Inversion is caused by the action of both the tibialis anterior muscle, which is innervated by the tibial nerve, and the tibialis anterior muscle, which is innervated by the deep peroneal nerve, a branch of the common peroneal nerve. Therefore, in the case of an elicited inversion of the foot, the needle tip is located very close to both branches of the sciatic nerve or to the sciatic nerve itself before it divides into the tibial nerve and common peroneal nerve. Multiple stimulations of both sciatic nerve components below the knee provide a better success rate when a sciatic block is performed at the popliteal level using the lateral approach. Insertion of the block needle 7 cm above the lateral femoral epicondyle between the biceps femoris and vastus lateralis muscles, at a 30-degree angle relative to the horizontal plane and at a depth of 45 mm in an average-sized patient, should place the tip of the needle close to the popliteal nerve. The lateral approach to the popliteal sciatic nerve is an effective, quick, and easy method to perform the block. Using 20 mL 0.5% plain bupivacaine, analgesia lasts a median of 18 hours compared with subcutaneous local anesthetic infiltration that lasts on average 6.2 hours.2 In adult studies it
142
has been shown that the sciatic nerve block is longer lasting than an ankle block or subcutaneous infiltration and provides excellent postoperative analgesia.2
Complications Intraneural injection must be avoided. Use of a low-voltage nerve stimulator ensures the proper placement of the needle. It is rare to see intravascular placement of the needle with this approach. Intravascular injection can be avoided with incremental injection of local anesthetic solution with frequent aspiration. The popliteal vessels are surrounded by a vascular sheath, which is clearly separated from the nerves by popliteal fossa fat. In a cadaver study all the dye injectates were located laterally and posteriorly to the popliteal vessels. The lateral approach is unlikely to result in an intravascular injection, which makes this a safer approach for popliteal nerve block.
Conclusion The lateral popliteal approach to the sciatic nerve is an easy but satisfying nerve block. In combination with the femoral nerve TER RAHE AND SURESH
block, we can provide excellent analgesia for foot, ankle, and knee surgery. Because of the ease of performance and the duration of the analgesia, we have now resorted to using this block for unilateral foot surgery that may involve bony procedures. This may also be used as a supplement to a caudal block for longer surgical procedures.
References 1. Cappellino A, Jokl P, Ruwe PA: Regional anesthesia in knee arthroscopy: A new technique involving femoral and sciatic nerve blocks in knee arthroscopy. Arthroscopy 12:120-123, 1996 2. McLeod DH, Wong DV, Vaghadia, et al: Lateral popliteal sciatic nerve block compared with ankle block for analgesia following foot surgery. Can J Anaesth 42:765-769, 1995 3. Suresh S, Barcelona S, Young N: Postoperative pain management in children undergoing tympanomastoid surgery: Is a local block better than intravenous opioids? Anesthesiology 91:A1281, 1999 (abstract) 4. Vloka JD, Hadzˇic´ A, Kitain E, et al: Anatomic considerations for
LATERAL APPROACH TO THE SCIATIC NERVE
5.
6.
7. 8.
9. 10. 11.
sciatic nerve block in the popliteal fossa through the lateral approach. Reg Anesth. 21:414-418, 1996 Vloka JD, Hadzˇic´ A, Lesser JB, et al: A common epineural sheath for the nerves in the popliteal fossa and its possible implications for sciatic nerve block. Anesth Analg 84:387-390, 1997 Dalens B, Tanguy A, Vanneuville G: Sciatic nerve blocks in children: Comparison of the posterior, anterior, and lateral approaches in 180 pediatric patients. Anesth Analg 70:131-137, 1990 Vloka JD, Hadzic A, Koorn R, et al: Supine approach to the sciatic nerve in the popliteal fossa. Can J Anaesth 43:964-967, 1996 Paqueron X, Bouaziz H, Macalou D, et al: The lateral approach to the sciatic nerve at the popliteal fossa: One or two injections? Anesth Analg 89:1221-1225, 1999 Guardini R, Waldron BA, Wallace WA: Sciatic nerve block: A new lateral approach. Acta Anaesthesiol Scand 29:515-519, 1985 Zetlaoui PJ, Bouaziz H: Lateral approach to the sciatic nerve in the popliteal fossa. Anesth Analg 87:79-82, 1998 Benzon HT, Kim C, Benzon HP, et al: Correlation between evoked motor response of the sciatic nerve and sensory blockade. Anesthesiology 87:547-552, 1997.
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