There are several important considerations for regional anesthesia involving the lower extremity. First, it is important to clarify the goals of the block: a surgical block versus supplementation to a general anesthetic primarily for postoperative pain control. It is also important to consider the surgical use of tourniquets. This is especially important if the regional anesthetic goal is to provide a surgical block, as a tourniquet placed outside the field of the regional anesthetic will limit the time that a patient can tolerate the surgical procedure. Similar to upper-extremity nerve blocks, aseptic practice should be used during regional anesthesia involving the lower extremity. This includes use of sterile gloves, thorough cleansing of the skin, and barrier precautions when appropriate. In addition, one should always deposit local anesthetic at the site of needle entry. For the remainder of the discussion, we will assume that these considerations have been addressed.
A lumbar plexus block may be used as an analgesic option for surgeries of the hip, anterior thigh, and/or knee. It can provide anesthesia to the entire lower extremity when combined with a sciatic nerve block.
The lumbar plexus is primarily derived from the anterior or ventral rami of the L1 to L4 nerve roots, but there are also contributions from T12 in 50% of patients. This neural plexus is formed within the psoas major muscle63 and includes the iliohypogastric, ilioinguinal, genitofemoral, lateral femoral cutaneous, femoral, and obturator nerves. Local anesthetic blockade of the femoral, lateral femoral cutaneous, and the obturator nerves is most important for lower-extremity regional anesthesia. The sciatic nerve, discussed later in the chapter, receives contributions from the lower lumbar and sacral plexuses (Fig. 49-36).
Anatomy of the lumbar plexus and the cutaneous innervation of the lumbar plexus. [Reprinted with permission from Hadzic A, Vloka J. Peripheral Nerve Blocks: Principles and Practice. New York, NY: MCGraw-Hill; 2004.]
Two basic approaches have been described for blockade of the lumbar plexus: (1) a posterior approach and (2) a perivascular approach. Although the posterior approach is most often used for procedures involving hip or femoral neck repair, the perivascular approach is most commonly utilized for surgical procedures involving the knee.
Psoas Compartment Block (Posterior)
With the patient in a lateral decubitus position (operative site up), the hips are flexed. A line connecting the iliac crests (Tuffier line) is drawn. The spinous process at midline is most often the L4. On the operative side, a line is drawn 5 cm parasagittal to the midline (Fig. 49-37). A point 3 cm caudal to the Tuffier line on this parasagittal demarcation is then made. This will be the entry point of a 10-cm, 21-gauge insulated needle for the purpose of nerve stimulation. The needle is inserted perpendicular to the skin until the L5 transverse process is encountered. The needle is then directed cephalad in a manner that allows the regionalist to walk off the transverse process. A quadriceps motor response confirms correct needle position, and approximately 30 mL of local anesthetic is then injected after careful, sequential aspiration attempts confirming that the needle is not intravascular.
Posterior approach to the lumbar plexus (psoas compartment block). IC, iliac crest; SP, spinous process.
A modification of the above technique involves use of a Touhy needle to identify the psoas compartment via stimulation and loss of resistance techniques. As above, this modified technique uses quadriceps contraction to signify proper location of the needle.64
Inguinal Perivascular Approach (Three‐in-One Block)
This block is based on the premise that injection of local anesthetic in sufficiently large amounts will track up fascial planes between the iliacus muscle and the psoas muscle, ultimately anesthetizing the nerves of the lumbar plexus that exit at the level of the inguinal ligament (the femoral, lateral femoral cutaneous, and the obturator). The approach is identical to the femoral nerve block described later, with the caveat that firm pressure is applied distal to the needle insertion to allow fascial tracking of the local anesthetic. Some authors have advocated high volumes of local anesthetic as a means of greater spread. Imaging studies have demonstrated that medial and lateral spread of the local anesthetic provide blockade of the obturator and lateral femoral cutaneous nerves, respectively.65
As with any regional anesthetic technique, local toxicity can occur secondary to vascular absorption and/or direct intravascular injection. The lumbar plexus block is associated with increased risk of local anesthetic toxicity due to proximity of vascular structures and use of large volumes of local anesthetics to obtain the desired spread.
It is important to note that the depth of the lumbar plexus for men and women can differ. Median depth for men is 8.5 cm and for women is 7.0 cm.66
The femoral nerve block is used to provide analgesia to the lower extremity, often in combination with other nerve blocks. Occasionally, it may be used as the sole anesthetic for isolated procedures involving the thigh. More often, it is used for postoperative analgesia in cases of midshaft femoral fracture repair and/or after surgical procedures involving the knee.
The femoral nerve arises from the posterior branches of L2, L3, and L4 of the lumbar plexus. From the plexus, it travels between the psoas and iliacus muscles until it passes under the inguinal ligament. At this point, it assumes a position lateral and somewhat posterior to the femoral artery, where the division to anterior and posterior branches occurs. The anterior branches are largely cutaneous, whereas the posterior branches supply motor input to the quadriceps muscle and provide articular branches to the knee.
The terminal branch of the posterior division of femoral nerve is the saphenous nerve, which supplies sensory input to the medial aspect of the leg from the knee to the medial malleolus.
With the patient supine, the anterior superior iliac spine (ASIS) is identified on the ipsilateral side to be blocked. A line is then identified from the ASIS to the public tubercle. This is commonly known as the approach of Labat.67 After the skin is anesthetized, a 3- to 4-cm 22-gauge needle is inserted perpendicular to the skin at a point below the inguinal ligament and lateral to the pulse of the femoral artery. A path through the fascia iliaca will be denoted by a pop (Fig. 49-38). A contraction of the sartorius muscle in the medial aspect of the thigh will be appreciated if a nerve stimulator is being used. The path should continue deeper with redirection laterally. A patellar "snap" from contraction of the quadriceps muscle is confirmation that the posterior branch of the femoral nerve has been encountered.
Femoral nerve block: landmark technique. FA, femoral artery.
An alternative approach to blockade of the femoral nerve is to elicit a paresthesia, which might be encountered using the nerve stimulation technique as well. Once a paresthesia is obtained, 20 mL of local anesthetic can be injected in a fan-like distribution.
Yet another approach to femoral nerve blockade is an ultrasound-guided approach.68,69
A linear transducer is placed at the level of the inguinal ligament in order to identify the femoral vessels and to achieve medial and lateral orientation. Using an in-plane technique, a 22-gauge bevel needle (2-4 cm) is used to approach the femoral nerve from the lateral aspect. The ultrasound is then used to guide the needle under the fascia lata, a linear, hyperechoic structure, toward the fascia iliaca (Fig. 49-39). Once the fascia iliaca is identified, the needle is advanced until a "pop" is felt and confirmed visually, indicating penetration of the fascia iliaca. The local anesthetic is then injected. Another finding consistent with correct needle placement is circumferential spread of the local anesthetic around the nerve after injection.
Femoral nerve block: ultrasound surface anatomy and ultrasound pictures. A. Surface anatomy. B. Ultrasound anatomy.
The saphenous nerve can act as a supplement to a sciatic nerve block for a lower-extremity surgery involving the medial portion of the leg or foot.
The saphenous nerve is the largest sensory component of the femoral nerve, and it is the only component to innervate below the level of the knee. The saphenous nerve courses through the femoral triangle and becomes more superficial as it travels between the sartorius and gracilis muscles in the thigh. The saphenous nerve also has a close relationship with the saphenous vein as it progresses caudally. Thus the trans-sartorial and perivenous are 2 common approaches to saphenous nerve blockade (Fig. 49-40).
Levels of saphenous nerve blockade.
Trans-Sartorial Approach to Saphenous
In the supine position with leg extension, the sartorius muscle is identified on the medial aspect of the upper leg. An 18-gauge loss-of-resistance needle is inserted 1 to 2 cm above the level of the patella, and with a posterior and caudad direction, it is passed through the body of the sartorius muscle. A sub-sartorial loss of resistance, usually achieved at 1.5 to 3.0 cm, indicates the usual plane where the nerve is located. Ten milliliters of local anesthesia is then deposited. This approach has been demonstrated to have an 80% success rate.70
Perivenous Approach to Saphenous
The patient is placed in the supine position and the tibial tuberosity identified. At this level, there is a close relationship between the saphenus nerve and tibial vein; the saphenous nerve lies medial and posterior to the vein. A tourniquet may aid in identification of the perivenous anatomy. Once identified, a small amount of local anesthetic is deposited on either side of the vein. Five to 10 mL of local anesthesia should be sufficient. This can also be done with ultrasound visualization (Fig. 49-41).
Ultrasound paravenous examination and corresponding surface anatomy. SN, saphenous nerve; SV, saphenous vein.
An alternative approach is a field block. With the tibial tuberosity identified, a subcutaneous wheal of local anesthetic is injected from the medial aspect of the tibial tuberosity to the medial portion of the gastronomies muscle.
The proximity of the femoral nerve to the vascular bundle generates some risk for vascular puncture and subsequent hematoma development. Thus special care should be taken to ensure proper understanding of the new anatomy in patients who have had femoral revascularization procedures. In fact, the presence of a new graft can be considered a relative contraindication if the anatomy cannot be identified using ultrasonography.
Femoral and lower-extremity nerve blocks have also been implicated as coexisting risk factors for falls.71 As such, patients, family, and health care providers should be informed of this potential risk in order to minimize the chance of a fall in the postoperative period.
In addition, because blockade of the femoral nerve is commonly used in conjunction with a sciatic nerve block to achieve complete lower-extremity analgesia, the total amount of local anesthetic used should be carefully considered in order to avoid local anesthetic toxicity.
It is important to also note that prolonged tourniquet time may increase the risk for nerve palsy,72 a complication that may be confounded by the addition of a local anesthetic.
Finally, continuous femoral nerve techniques, as compared with intravenous narcotics, have been shown to reduce hospital duration in patients undergoing total knee arthroplasty.73
Lateral Femoral Cutaneous
This block is used primarily in conjunction with other blocks of the lower extremity to offer complete lower-extremity analgesia. It may act as a supplement to skin graft harvesting, although it has been reported as the sole anesthesia for these procedures.74
The lateral femoral cutaneous nerve (LFCN) arises as a direct branch from the lumbar plexus (L2 to L3) and courses via the lateral edge of psoas muscle to enter the thigh deep to the inguinal ligament. It emerges from the fascia inferior and medial to the anterior superior iliac spine (ASIS). As it travels beneath the fascia lata, it divides into an anterior and posterior branch. The anterior branch provides sensory innervation to the anterolateral thigh, whereas the posterior branch provides sensory innervation to the true lateral portion and a small posterior portion of the thigh from the hip to the knee (Fig. 49-42).
Distribution of anesthesia for the anterior lower extremity. Lateral cutaneous nerve of the thigh. [Reprinted with permission from Hadzic A, Vloka J. Peripheral Nerve Blocks: Principles and Practice. New York, NY: McGraw-Hill; 2004.]
With the patient supine, the ASIS is identified on the ipsilateral side to be blocked. A mark approximately 2 cm medial and 2 cm caudad to the ASIS is made. A 22-gauge, 4-cm needle is advanced perpendicular to the surface of the skin until the fascia lata is encountered, as noted by a pop. Local anesthetic is then injected in a fan-like maneuver in a lateral to medial direction. Ten to 15 mL of local anesthetic should be sufficient.
There have been descriptions of using nerve stimulator techniques with improved success with localization.75
Ultrasound localization of the LFCN is possible with knowledge of its intrafascial location.
If the block is to be used as a sole anesthetic for a skin graft collection procedure, it is clearly important to determine the field of sensory blockade before starting the collection.
The obturator nerve provides sensory innervation to the articular surfaces of the knee. Therefore, blockade of this nerve is an important consideration for total knee arthroplasties and anterior cruciate ligament repairs. However, obturator nerve blockade should not be thought of as a complete anesthetic for these procedures due to contributions from the femoral nerve.
The obturator nerve is formed from the anterior divisions of L2, L3, and L4 of the lumbar plexus. These anterior divisions organize within the body of the psoas muscle and emerge on the medial border as the obturator nerve. As such, the obturator nerve can be found situated within the obturator canal, where it divides into anterior and posterior divisions. The anterior division provides sensory innervation to the hip via an articular branch and motor supply to the adductor muscles of the thigh. The anterior branch also provides a highly variable sensory component to the medial thigh.76 The posterior division supplies the motor component to deep adductors and sensory innervation via an articular branch to the posterior knee joint.
The classic description involves nerve stimulator techniques, but paresthesias are not an uncommon associated finding. With a supine patient, the pubic tubercle is identified. A mark is placed 2 cm lateral and 2 cm caudad to the pubic tubercle.
A 22-gauge needle (8-10 cm) is then inserted perpendicular to the skin with a medial slant. When the inferior pubic ramus is encountered, the needle is withdrawn slightly and walked off caudad and lateral. The needle will walk off the rami into the obturator canal (after approximately 3 cm), identified by adductor contraction. Approximately 10 mL of local anesthetic should be injected.
Wassef77 described an interadductor approach. A skin mark delineating the obturator canal is made below the inguinal ligament and 1 to 2 cm lateral to the palpated femoral artery. The adductor longus tendon is identified near the pubic insertion and an 8-cm, 22-gauge needle is inserted behind the tendon, directed laterally and superiorly using the skin mark as a guide. Adductor contraction is the end point.
Ultrasound-guided obturator block has recently been used as an adjunct to femoral blocks for knee surgery (Fig. 49-43).
Ultrasound view of obturator block. In-plane, obturator nerve at the confluence of the adductor longus muscle, adductor brevis muscle, and pectineus muscle. Ant O n., anterior branch of obturator; Pos O n., posterior branch of obturator.
Neurovascular bundles place patients at risk for intravascular injections and/or hematoma formation. In the case of spasticity, obturator nerve blockade and/or neurolytics may be used. It may also prove useful as an aide in ascertaining patients who may benefit from additional modalities for relief of spasticity, such as Botox injections.
The sciatic nerve is the largest of the lower-extremity nerves and has several well-described levels that can be approached for blockade. Sciatic nerve blockade can be used as a complete anesthetic for surgeries of the foot or ankle where a lower-leg tourniquet will be needed and an ankle block would not be sufficient. However, a sciatic nerve block should be used in conjunction with a saphenous nerve block if the medial portion of the leg or ankle is in the surgical field.
The sciatic nerve is composed of the ventral rami from L4 to S3, which join on the anterior surface of the piriformis muscle. The sciatic nerve is the largest nerve in the body, with a width of 2.0 cm. As it passes through the greater sciatic foramen, it passes lateral to all of the other structures that emerge inferior to the piriformis (inferior pudendal vessels, pudendal nerve, inferior gluteal nerve and vessels) (Fig. 49-44).
Sciatic nerve motor innervation. [Reprinted with permission from Hadzic A, Vloka J. Peripheral Nerve Blocks: Principles and Practice. New York, NY: McGraw-Hill; 2004.]
The posterior femoral cutaneous nerve courses with the sciatic and the inferior gluteal nerves and vessels and is important because this nerve supplies the posterior portion of the thigh. It is important to note that the posterior cutaneous nerve will only be anesthetized via a high sciatic block.
The sciatic nerve courses inferolaterally deep to the gluteus maximus at a midpoint between the ischial tuberosity and the greater trochanter of the femur. The sciatic nerve itself is a combination of the common peroneal (lateral) and the tibial (medial) nerves joined by an epineurial sheath. These 2 nerves separate approximately 8 cm superior to the popliteal fossa.
There are many different approaches to the sciatic nerve. Several considerations are given to which technique is chosen: patient ability to roll over or aid in positioning, level of the surgery, and body habitus are important factors
With the patient supine and neutral position of the leg, a line connecting the pubic tubercle and the anterior superior iliac spine is drawn at the level of the inguinal ligament. A second parallel line is drawn inferomedially from the greater trichinae toward the lesser trochanter. A perpendicular line one-third the initial distance is then drawn perpendicular. This is the point of insertion for a 22-gauge, 10- to 15-cm needle. The lesser trochanter is contacted and the needle directed slightly medial. Five centimeters past the point of the lesser trochanter, a paresthesia or a contraction consistent with a sciatic nerve stimulation is encountered. Injection of 20 to 25 mL of local anesthetic is done incrementally (Fig. 49-45).
Surface anatomy for anterior approach to the sciatic. X, needle insertion site.
Posterior Approach (Classic Approach of Labat)
The positioning for the classic approach to the sciatic may make it impractical in patients who are suffering with a lower-extremity trauma. With the patient positioned in the lateral decubitus position (operative side up), the hip is flexed with the heel of the operative side resting on the nonoperative knee. Marking is done to identify the posterior superior iliac spine (PSIS) and the greater trochanter. A line connecting these 2 is bisected perpendicularly, and a point 5 cm caudad is identified (Fig. 49-46). This is the point of insertion with a 22-gauge, 10-cm needle. Paresthesia, sciatic motor response, and/or bone is contacted as the needle is advanced. If a paresthesia or motor response is elicited, then slow injection of 20 to 30 mL of local anesthetic is performed. If bone is contacted, methodical redirection of the needle is performed, with a medial and then lateral redirection until paresthesia or motor response is encountered.
Posterior approach to the sciatic nerve. GT, greater trochanter; PSIS, posterior superior iliac spine; X, point of needle insertion.
A description of a subgluteal approach to the sciatic was given by Di Benedetto et al78 and has been used with success. With the patient in the lateral decubitus position, operative side up and hips flexed, and the operative knee at 90 degrees, a line is drawn connecting greater trochanter and the ischial tuberosity. At the bisection of this line, a perpendicular line is then drawn 4 cm caudal. This is the entry point of the 22-gauge, 10-cm needle. Surface anatomy indicates that this is below the bulk of the gluteal muscles in a depression that represents the biceps femoris and the lateral border of the vastus lateralis. In the original description, a nerve stimulator technique was used. However, several descriptions have recently been published discussing ultrasound-guided techniques.79-81 A curvilinear probe (2-5 MHz) with the patient in the above semilateral position has been used with an in-plane and out-of-plane approach to the nerve (Fig. 49-47). Single-injection and catheter-based techniques have been described.
Subgluteal approach. Surface anatomy and ultrasound imaging. GT, greater trochanter; IT, ischial tuberosity.
Popliteal Fossa Approach to the Sciatic
For the posterior approach, the patient is positioned prone. With the knee in a flexed position, the base of a triangle is delineated by the skin crease of the posterior knee. The medial border of the triangle is the semimembranosus muscle and the lateral border is the biceps femoris muscle. In order to block the sciatic nerve before it separates into its 2 smaller components, it is recommended that the point of needle insertion be 7 to 10 cm above the skin crease.82 A paresthesia or muscle twitch confirming either sciatic component is accepted.
Ichiyanagi83 originally described a lateral approach to the popliteal fossa. The patient is supine with the leg in a neutral position. The leg may be supported so it is flexed at the knee to ease identification of structures (Fig. 49-48). The groove between the vastus lateralis and biceps femoris muscles is identified. A 22-gauge, 10-cm needle is inserted until contact with the femur is made. Once the femur is contacted, the needle is redirected posterior and the sciatic nerve should be encountered 1 to 2 cm beyond the femur contact distance. Acceptable nerve stimulation is either tibial nerve (plantar flexion at ankle, inversion of foot) or common peroneal nerve (ankle dorsiflexion or eversion of the foot).
Lateral approach to the sciatic nerve. BF, biceps femoris; VL, vastus lateralis.
Some authors84 have advocated for separate stimulation of each component of the sciatic, citing a greater success rate (88% for double stimulation vs 54% for only tibial). The volume of local anesthetic for the lateral and posterior approaches has widely varied in the literature from 20 to 40 mL.
Ultrasound in-plane techniques have also been used with great success for both the posterior and lateral approaches. The positioning for the lateral approach necessitates having the patient in 90-degree flexion in order to place the ultrasound probe on the posterior portion of the popliteal fossa. The entry point of the needle is exactly the same as in the lateral approach, but direct visualization of the local anesthetic ensures circumferential spread (Fig. 49-49).
Ultrasound images of sciatic nerve. A. Common peroneal and tibial prior to divide in popliteal fossa. B. After divide into common peroneal and tibial nerves. CPN, common peroneal nerve; PA, popliteal artery; TN, tibial nerve.
Unlike other lower extremity blocks, the time required for the sciatic nerve analgesia to become apparent may be considerable. It is not unusual to have analgesia after 30 to 40 minutes. In contrast, femoral nerve sensory deficits can be appreciated relatively quickly.
As stated above, patient ability to position certainly guides the level at which the sciatic nerve is blocked. Patients with a body mass index greater than 35 may prove difficult for subgluteal approaches using ultrasound technology.
The femoral and sciatic nerves terminate in the lower extremity into 5 terminal branches. The saphenous is the only contribution from the femoral nerve; the other 4 terminal branches—the deep peroneal, superficial peroneal, posterior tibial, and the sural—originate from the sciatic nerve.
The sensory innervation of the foot is provided by these 5 nerves (Fig. 49-50). Local anesthetic blockade of any one of these nerves or a combination will provide anesthesia and/or analgesia for surgery of the foot. Consideration must be paid to the possible use of a tourniquet. An ankle block is ideal for surgery on the toes or metatarsals.
Ankle block distribution of anesthesia. [Reprinted with permission from Hadzic A, Vloka J. Peripheral Nerve Blocks: Principles and Practice. New York, NY: McGraw-Hill; 2004.]
The sciatic nerve branches into the common peroneal and the tibial nerves at the level of the popliteal fossa. The common peroneal further divides into the superficial and deep peroneal nerves. The tibial nerve is the larger of the 2 branches of the sciatic, and it terminates as the posterior tibial nerve and the sural nerve. It courses through the lower extremity in a neurovascular bundle accompanied by the posterior tibial artery and vein. At the ankle level, the posterior tibial nerve can be found posterior to the medial malleolus.
Classic description is with a patient in the prone position, although this procedure can be accomplished in the supine position with the lower leg resting on a table or elevated. The posterior tibial artery is palpated, and a 22-gauge, 4-cm needle is inserted medial to the Achilles tendon, directed anteriorly toward the medial malleolus. If a paresthesia is elicited, a small volume of local anesthetic is injected (5 mL). In no paresthesia, then the needle is advanced until it contacts the medial malleolus and then the local anesthetic is deposited. This is essentially a field block.
Deep Peroneal and Superficial Peroneal Nerves
The patient is positioned as discussed earlier with the foot elevated, resting on a bump. Extension of the great toe identifies the extensor hallicis longus (EHL) tendon. A 22-gauge, 4-cm needle is inserted perpendicular to the skin lateral to the EHL tendon in the groove between the EHL and the extensor digitorum longus tendon (Fig. 49-51). The needle is advanced until bone is contacted, and then 5 mL of local anesthetic is injected as the needle is slowly pulled back. This raised skin wheal serves as an initiation point for the superficial peroneal nerve. A superficial wheal is made to the lateral malleolus, and then the needle is redirected toward the medial malleolus. Approximately 5 mL of local anesthetic should be appropriate.
Surface anatomy with deep peroneal nerve block. The initial needle puncture is also the site for the superficial peroneal nerves.
An approach similar to the posterior tibial nerve is used for the sural nerve. A 22-gauge, 4-cm needle is inserted lateral to the Achilles tendon, directed anteriorly toward the malleolus, and approximately 5 mL of local anesthetic is injected.
Descriptions of the use of ultrasound guidance have been noted. A proposed use of ultrasound is in limiting the amount of local anesthesia necessary with deposition near nerves as opposed to the "field" block, where large volumes may be used to provide complete foot anesthesia. Specifically, ultrasound has been used to identify the sural nerve in association with the lesser saphenous vein. Injection of small amounts of local anesthetic (5 mL) according to these anatomical landmarks using ultrasound guidance has been shown to generate a denser and longer-lasting block as compared with traditional landmark techniques alone.85
As with all other blocks, knowing the anatomy is essential. Ankle blocks can be quite uncomfortable for patients, and they require multiple injection sites. Local anesthetic volumes need to be monitored.
The saphenous nerve is the only contribution from the femoral that has a terminal branch at the level of the ankle. For procedures on the medial aspect of the foot or ankle, this nerve is important to block.