Ovid: Peripheral Nerve Blocks: A Color Atlas

Lower Extremity Multiple-Stimulation Techniques

Andrea Casati

The lower limb is innervated by two plexus: the lumbar and the sacral. Among the nerves that emerge from these plexus, the sciatic nerve, which divides into the tibial and common peroneal nerves; the femoral nerve, which divides into seven terminal branches including the saphenous nerve (Fig. 14-1; [1]); and the nerve to the vastus intermedius muscle (Fig. 14-1; [2]) and the nerve to the vastus lateralis (Fig. 14-1; [3]) may be blocked using a multiple-stimulation technique. As discussed in Chapter 8, the use of a multiple-stimulation technique allows one to minimize the volume of local anesthetic required to produce surgical anesthesia. This is especially important for lower limb blocks because both a block of the femoral and sciatic nerve are required, which results in an increased risk of local anesthetic toxicity due to overdosing when the single-stimulation technique is used. Another important advantage of the multiple-injection technique is the reduced toxicity associated with intravascular injections of local anesthetics. Thus, it is well known that a negative blood aspiration before the injection of local anesthetics—although necessary—does not prevent the risk for unintentional intravascular injection.

It has been reported that withdrawing and redirecting the stimulating needle to elicit multiple motor responses might result in slightly more discomfort to the patient. For this reason an appropriate sedation with small doses of benzodiazepine combined with appropriate analgesia with opioids is indicated with the use of multiple-stimulation techniques. To minimize the risk of intraneural injection, it is important that patients remain able to report any pain during the local anesthetic injection. For this same reason, lower extremity blocks should also be performed only after the complete resolution of neuroaxial blocks.

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A. Multiple-Stimulation Technique to Block the Femoral Nerve

To perform a femoral nerve block using a multiple-stimulation technique, three different muscular stimulations should be elicited: (a) the contractions of the vastus medialis, induced by stimulation of the vastus medialis/saphenous nerve; (b) the contractions of the vastus intermedius muscle with movements of the patella, induced by the stimulation of the vastus intermedius nerve; and (c) the contractions of the vastus lateralis muscle, induced by stimulation of the vastus lateralis nerve.

Patient Position: Supine with the leg in neutral position.

Needle Size: A 22-gauge, 50-mm insulated needle.

Volume: 5 to 6 mL per nerve.

Anatomic Landmarks: The pulse of the femoral artery and the inguinal crease.

Approach and Technique: The insulated needle connected to a nerve stimulator (1.5 mA, 2 Hz, 0.1 ms) is inserted immediately lateral to the femoral artery above the inguinal crease and advanced perpendicularly to the skin. The contraction of the vastus lateralis is usually the first to be elicited. After the appropriate motor response is obtained, the needle position is then adjusted to maintain the same motor response with a stimulating current intensity ≤0.5 mA. After negative aspiration, 5 to 6 mL of local anesthetic is injected slowly. The stimulating needle is then withdrawn from the skin, and the current intensity is increased to 1.5 mA. The needle is reoriented 2° to 5° laterally and introduced slightly deeper in search of a contraction of the vastus intermedius nerve and movement of the patella. After the appropriate motor response is obtained, the needle position is then adjusted to maintain the motor response with a stimulating current intensity ≤0.5 mA. After negative aspiration, another 5 to 6 mL of the same anesthetic solution is injected. Finally, the insulated needle is withdrawn to the level of the skin, and the current intensity is increased to 1.5 mA. The needle is redirected more laterally by increasing the angle by another 5° and reintroduced in search of the contraction of the vastus lateralis muscle. After the appropriate motor response is obtained, the needle position is then adjusted to maintain the motor response with an intensity ≤0.5 mA. After negative aspiration, a final 5 to 6 mL of local anesthetic solution is injected.

Tips

To minimize the risk for arterial puncture, the initial insertion of the needle should be the closest to the femoral artery. Thereafter the needle is redirected laterally.
The contraction of the vastus lateralis muscle is often associated with residual movements of the patella and sometimes can be only seen distally at the level of the knee.
Very often, the contraction of the vastus lateralis is preceded by a contraction of the sartorius muscle. To obtain the desired motor response, the needle needs to be introduced slightly deeper.

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Figure 14-1. Saphenous nerve. (1) Vastus lateralis nerve; (2) Vastus medialis nerver; (3) Saphenous nerve.
In contrast to a three-in-one perivascular block, the multiple-stimulation technique to block the femoral nerve does not allow the possibility of also blocking the lateral femoral cutaneous nerve and the obturator nerve. If these blocks are required, they need to be performed individually.
With this technique, a complete sensory and motor femoral block occurs within 20 minutes.

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B. Multiple-Stimulation Technique to Block the Sciatic Nerve

The sciatic nerve block produces motor responses that vary according to the level at which the nerve is being stimulated. At a high level (parasacral, posterior, and sub-gluteal), three types of responses are elicited: (a) the dorsiflexion or eversion of the foot, induced by the stimulation of the common peroneal branch of the sciatic nerve; (b) the plantar flexion of the foot and toes produced by the stimulation of the tibial branch of the sciatic nerve; and (c) the contraction of the biceps femoris induced by the stimulation of the branches innervating the hamstring muscles. Above the knee (lateral and posterior popliteal nerve block), only contraction of the foot and toe muscles are observed. Although the sciatic nerve divides into the common peroneal and tibial nerves above or at the popliteal fossa, the two branches can be clearly identified from its origin; and in about 10% of cases they are two separate nerves already at the ischiatic foramen. Nevertheless, and except in amputated limb cases, the distal motor responses (dorsiflexion or eversion) and flexion of the foot and toes are searched to block the common peroneal and tibial nerves, respectively.

High Sciatic Approaches

Patient Position: Sims position (lateral with the knee flexed and the operative side up).

Volume: 10 mL per nerve.

Classic Posterior (Labat) Approach

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

Anatomic Landmarks: The greater trochanter, the sacral hiatus, and the posterosuperior iliac spine. The sciatic nerve is often divided into a common peroneal (Fig. 14-2; [1]) and tibial branch (Fig. 14-2; [2]), close to the origin of the sciatic nerve. At this level it is also possible to identify the superior gluteal nerve (Fig. 14-2; [3]), the nerve to the hamstring muscle (Fig. 14-2; [4]), the posterior cutaneous nerve of the thigh (Fig. 14-2; [5]), the piriformis muscle (Fig. 14-2; [6]), and the medius muscles (Fig. 14-2; [7]).

Subgluteal Approach

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

Anatomic Landmarks: The greater trochanter and the ischial tuberosity.

Approach and Technique: The needle is introduced perpendicularly to the skin and advanced slowly until a stimulation of either the common peroneal or the tibial nerve is elicited. After the appropriate motor response is obtained, the needle position is then adjusted to maintain the same motor response with a stimulating current intensity ≤0.5 mA. After negative aspiration, 8 to 10 mL of the local anesthetic solution is injected. The stimulating needle is withdrawn to the level of the skin, the current intensity is set back to 1.5 mA, and the needle is then redirected 2° to 5° (if the tibial nerve was stimulated first) or medially (if the common peroneal nerve was stimulated first) and

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advanced until the appropriate motor response is elicited. The position of the needle is then adjusted to maintain the same motor response with a stimulating current ≤0.5 mA. After negative blood aspiration, 8 to 10 mL of local anesthetic solution is injected.

Figure 14-2. Vastus intermedius muscle. (1) Tibial nerve; (2) Common Peroneal nerve; (3) Inferior gluteal nerve; (4) Posterior cutaneous nerve of thigh; (5) Nerve to quadrus femoris; (6) Inferior gluteal nerve; (7) Gluteus minimus.

Tips

Considering the length of the stimulating needle and the depth at which the sciatic nerve is located, changes in the angle of the stimulating needle should be minimal (no more than 2° to 5°). Consideration should also be given not to flex the stimulating needle.
The depth at which the first motor response is obtained allows the clinician to control the limit at which the needle should be introduced next (the tibial nerve is slightly more posterior and medial to the common peroneal nerve).

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The subgluteal approach is as successful as the Labat classic posterior approach and has the advantage of being less painful.
If bone contact occurs, the needle is withdrawn from the skin. For either the Labat or the subgluteal approach, bone contact usually indicates the sciatic nerve should be found more superficially.

Low Sciatic Approaches

Popliteal Approaches

At the level of the popliteal fossa, the two branches of the sciatic nerve clearly divide. The more caudal the sciatic approach, the more separated are the two branches of the sciatic nerve (common peroneal and tibial nerves) (Fig. 14-3). There is also a spatial distribution of common peroneal and tibial nerves that needs to be considered. The tibial nerve lies closer to the bone and more medial. Thus it is slightly more anterior and deeper than the common peroneal nerve when approached from the lateral side of the thigh. In contrast, the common peroneal nerve is located more laterally and superficially, and it exits the popliteal fossa just above the head of the fibula.

To perform a multiple-stimulation sciatic block at the popliteal fossa, a proximal approach is usually recommended.

Posterior Popliteal Sciatic Nerve Block

Patient Position: Prone.

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

Volume: 10 mL per nerve.

Anatomic Landmarks: The popliteal crease, the medial border of the femoris biceps laterally, and the lateral border of the semi-tendinous tendon medially.

Approach and Technique: The needle is introduced perpendicular to the skin in search of a motor response related to either the stimulation of the common peroneal or tibial nerve (usually the common peroneal nerve). The needle position is adjusted to maintain the same motor response with a stimulating current ≤0.5 mA. After negative aspiration for blood, 10 mL of local anesthetic solution is injected. As with all approaches to the sciatic nerve, the first motor response determines how the needle is oriented when searching for the next motor response. If the first motor response elicited is the dorsiflexion of the foot (common peroneal nerve), the needle will be directed more medially and slightly deeper in search of a stimulation of the tibial nerve (plantar flexion with flexion of the toes). If the first motor response is the plantar flexion of the foot (tibial nerve), the stimulating needle is redirected more laterally.

Lateral Popliteal Sciatic Nerve Block

Patient Position: Supine, with a pillow under the leg.

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

Volume: 10 mL per nerve.

Anatomic Landmarks: The patella and the groove between the femoris biceps muscle and the vastus lateralis.

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Figure 14-3. Sciatic nerve at the level of the popliteal fossa.

Approach and Technique: A vertical line is drawn at the level of the superior border of the patella. The site of needle introduction is demarcated by the intersection of this line and the line drawn at the level of the groove between the femoralis biceps and the vastus lateralis muscles. The needle is inserted at an angle 20° to 30° posterior to the horizontal plane with a slight caudal direction. It is advanced slowly, usually in search of the common peroneal nerve, which produces either a dorsiflexion and toes extension or an eversion of the foot. The needle position is then adjusted to maintain the same motor response with a stimulating current intensity ≤0.5 mA. After negative aspiration, 8 to 10 mL of local anesthetic solution is injected. The needle is then withdrawn from the skin and oriented at 45° in search of the tibial nerve, which is located more medially and

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slightly deeper than the common peroneal nerve. Its stimulation produces a plantar and toes flexion. The needle position is then adjusted to maintain the same motor response with a stimulating current intensity ≤0.5 mA. After negative aspiration, 8 to 10 mL of local anesthetic solution is injected.