The technique for performing both a femoral and three-in-one nerve block is identical except that the three-in-one block requires a larger volume of local anesthetic (25 to 30 mL versus 20 mL). Three-in-one nerve block provides better analgesia of the femoral neck and hip joint.
The femoral nerve is formed from the posterior branches of L2-L4 and is the largest branch of the lumbar plexus. The nerve emerges from the psoas muscle and descends between the psoas and iliacus muscles. It passes under the inguinal ligament in the groove formed by these muscles lateral to the femoral artery and divides into anterior and posterior branches.
The anterior branches innervate the anterior aspect of the thigh, and the posterior branches innervate the quadriceps muscle and continue below the knee as the saphenous nerve to provide sensory innervation from the medial side of the calf to the medial malleolus.
The lateral femoral cutaneous nerve arises from the second and third lumbar nerve roots. The nerve emerges from the lateral border of the psoas muscle and travels under the iliac fascia, across the iliac muscle, and under the inguinal ligament 1 to 2 cm medial to the anterior superior iliac spine. It branches into anterior and posterior branches 7 to 10 cm below the anterior superior iliac spine. The anterior branch innervates the skin over the anterolateral aspect of the thigh to the knee, whereas the posterior branch of the nerve innervates the lateral part of the thigh from the greater trochanter to the middle of the thigh.
The obturator nerve arises from the anterior divisions of L2-L4. It descends through the fibers of the psoas muscle and emerges from its medial border near the brim of the pelvis. It then passes behind the common iliac arteries and runs along the lateral wall of the lesser pelvis, above and in front of the obturator vessels to the upper part of the obturator foramen. Here, it enters the thigh through the obturator canal and divides into an anterior and a posterior branch. The obturator nerve is responsible for sensory innervation of the skin of the medial aspect of the thigh and motor innervation of the abductor muscles of the lower extremity.
- Arrange the equipment and take verbal/written consent
- Place the patient in a supine position
- Do a quick neuromuscular exam
- Prepare the skin overlying the femoral triangle following usual aseptic precautions
- Palpate the femoral artery 1 to 2 cm distal to the inguinal ligament and inject a subcutaneous wheal of local anaesthetic (1% Lignocaine) 1 to 2 cm lateral to this point. Keep the nondominant hand on the femoral artery throughout the remainder of the procedure.
- Insert a 22-gauge needle just lateral to the artery at a 30-60 degree angle to the skin. Slowly advance the needle cephalad until one of the following occurs:
- a “pop” with sudden loss of resistance (signifying penetration into the femoral nerve sheath) is felt
- a paresthesia is elicited,
- the needle pulsates laterally, which signifies a position adjacent to the femoral artery. Inject 25 to 30 mL of aesthetic (0.25% Bupivacaine).
- The block usually takes 15 minutes to take effect. If proximity to the nerve is uncertain (e.g., a pop is not appreciated, a pares- thesia is not elicited, or the needle does not move with pulsa- tion of the femoral artery), inject the anesthetic in a fanlike distribution lateral to the femoral artery in an attempt to anesthetize the nerve.
- It is also recommended to apply finger pressure 2 to 4 cm below the injection site to help spread the local anesthetic proximally to the obturator and lateral femoral cutaneous nerves.
How is three-in-one block/femoral N block different from FICB?
The injection site for FICB is more lateral as compared to Femoral/Three-in-one block and thus FICB is less likely to injure the vessels. Additionally, FICB is a compartment block and thus requires more volume of local anaesthetic.