Femoral nerve blockade is useful in conjunction with other lower extremity blocks in treating complex regional pain syndrome and as an aid to decrease knee and ankle pain during physical therapy.
After informed consent is obtained, the patient is placed in the supine position, and the femoral artery is located. The patient is prepared in a standard aseptic fashion over an area large enough to allow palpation of landmarks, and sterile technique is used throughout the procedure. The femoral artery is palpated below the inguinal ligament. A 1½-in. (4-cm), 22-gauge needle is inserted 1 to 2 cm below the inguinal ligament and lateral to the femoral artery. The needle is advanced in a lateral and posterior direction just distal to the inguinal ligament. A characteristic pop, when using a short, beveled needle, can be used to identify penetration of the fascia lata and the fascia iliaca, remembering that the femoral nerve lies deeper than both. When a nerve stimulator is used, contraction of the quadriceps muscle confirms correct placement of the needle. After negative aspiration, 10 mL of local anesthetic is injected to block the femoral nerve (Fig. 67-13).
FIGURE 67-13. Femoral nerve block. Approach for femoral nerve injection and neural blockade.
At the level of the inguinal ligament, the femoral nerve lies anterior to the iliopsoas muscle and slightly lateral to the femoral artery. It does not lie within the femoral sheath. The nerve lies underneath the fascia lata and fascia iliaca within its own sheath. At the level of the inguinal ligament, the femoral nerve divides into anterior (superficial) and posterior (deep) bundles. The anterior bundle provides cutaneous innervation of the skin overlying the anterior surface of the thigh as well as providing motor innervation to the sartorius muscle. The posterior bundle provides innervation to the quadriceps muscles and the knee joint. It also gives off the saphenous nerve, which supplies cutaneous innervation to the medial aspect of the calf to the level of the medial malleolus. A catheter also can be placed within the femoral nerve sheath for continuous infusion of local anesthetics.
It is important to remember that the upper portion of the anterior thigh is innervated by the ilioinguinal and genitofemoral nerves and is not blocked when performing a femoral nerve block.
Significant complications associated with femoral nerve blockade are uncommon. Dysesthesia may result if the nerve is injured during the injection. Hematoma at the site is a possibility but is usually not clinically significant. If an arterial puncture occurs, prolonged direct pressure is usually adequate to prevent the development of a hematoma. The presence of a femoral artery vascular graft is a relative contraindication to femoral nerve blockade.