Femoral Nerve Block

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Femoral nerve is the largest branch of the lumbar plexus and derived from the posterior divisions of L2-L4 lumbar nerves. Femoral nerve supplies innervation to the lower extremity as indicated in Table 20.8 (supplies anterior portion of the thigh and the medial portion of the calf). Subsequent to fusion of nerve roots, the femoral nerve descends laterally between the psoas and iliacus muscles to enter the iliac fossa. It enters the thigh by going underneath the inguinal ligament just lateral to the femoral artery and gives motor branches to the iliacus, sartorius, quadriceps femoris, and pectineus muscles. It also provides sensory innervation to the skin of the anterior thigh and to the skin over the knee joint.

The saphenous nerve is a continuation of the femoral nerve as it passes distal to the foot on the medial portion of the leg. This nerve is the largest branch of the femoral nerve and is derived predominately from L3 and L4 nerve roots. The nerve travels with the femoral artery in the Hunters canal as it moves toward the knee and then to the foot.

Table 20.8 Femoral nerve innervation of the lower extremity.

Motor

Sensory

Sartorius muscle

Anteromedial thigh (from inguinal ligament to the knee)

Quadriceps muscle (knee extension)

Medial aspect of leg (saphenous branch)

Articular branches to hip and knee

As primary anesthetic and/or postoperative pain management with or without a continuous catheter.

Clinical Uses Surgical

Postoperative analgesia for all the following surgeries:

• Anterior thigh surgery

• Arthroscopic knee surgery

• Surgical repair of midfemoral shaft fractures

• Long saphenous vein stripping

Supplemental (in Combination with an Obturator and Sciatic Nerve Block)

• Total knee replacement

• Tibia plateau fracture repair

• Total ankle replacement (saphenous nerve distribution)

• Above and below knee amputation

• Ankle surgery (saphenous nerve distribution)

Technique Preparation

Arrange sterile towels, sterile gloves, gauze pads, marking pen, antiseptic solution, peripheral nerve stimulator, syringes, and needles for local infiltration and nerve block placement.

Dose

20-40 ml syringes of local anesthetic. Needles

25 g 1.5 in. needle for skin infiltration and 5 or 10 cm short bevel insulated stimulation needle. Agents

3% chloroprocaine, 2% lidocaine, 0.5% ropivacaine, 0.5% bupivacaine.

Figure 20.7 Anatomical landmarks for the classical approach to the femoral nerve block. The anterior superior iliac spine that is the attachment of the inguinal ligament is identified as line #1. The inguinal crease is identified as line #2 and the femoral artery (FA) is identified as line #3. The needle insertion site (X) is located just below the inguinal crease and 1-2 cm lateral to the FA.

Figure 20.7 Anatomical landmarks for the classical approach to the femoral nerve block. The anterior superior iliac spine that is the attachment of the inguinal ligament is identified as line #1. The inguinal crease is identified as line #2 and the femoral artery (FA) is identified as line #3. The needle insertion site (X) is located just below the inguinal crease and 1-2 cm lateral to the FA.

Surface Anatomy and Landmarks

Femoral crease, femoral artery, inguinal ligament, pubic tubercle, and anterior superior iliac spine (Fig. 20.7). Patient is placed in supine position and a line is drawn from the anterosu-perior iliac spine to the pubic tubercle. The femoral artery is identified as it passes below this line by feeling for the pulsation. A point is marked on the skin 1-2 cm lateral to the femoral artery pulsation and approximately 1-2 cm below the previously drawn anterosuperior iliac spine to the pubic tubercle line. Subsequent to aseptic precautions, a skin wheal is raised with the infiltrating needle at the point marked. The stimulating needle is connected to the nerve stimulator set at 1.0 mA and inserted through the skin wheal at 45-60° angle to the skin and directed cephalad. Quadriceps muscle is watched for appropriate twitching and the current decreased to a range between 0.2 and 0.5 mA while maintaining a consistent muscle twitch. Maximizing the quadriceps muscle twitch can be obtained by small, gentle, organized, and deliberate movement of the needle in medial and lateral directions until consistent quadriceps muscle stimulation is obtained between 0.2 and 0.5 mA. Confirm a negative aspiration for blood and then inject the chosen local anesthetic through the needle.

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