Femoral nerve block is commonly performed by insertion of the block needle 1-2 cm lateral to the femoral artery just below the inguinal ligament as seen in the picture which requires multiple attempts at localization of the femoral nerve Performing the block at the level of the inguinal skin crease however, has given us more consistent results in the practice as it gives more superficial position of the femoral artery and nerve, Greater width of the femoral nerve, More consistent femoral nerve-artery relationship.
Steps of of the Technique:
A 22G, 50 mm short bevel insulated needle attached to nerve stimulator (0.6 mA) is inserted adjacent to the lateral border of the femoral artery at the level of inguinal crease, a skin fold 3 to 6 cm below and parallel to the inguinal ligament. The needle is slowly advanced at an angle of 60° cephalad to the horizontal plane while seeking a quadriceps muscle twitch (rhythmic movements of the patella).
If a quadericeps muscle twitch is not obtained, the needle is withdrawn and redirected 10° laterally (The Figure below). If this maneuver does not elicit a quadericeps muscle twitch, the subsequent needle insertions should be placed at increments of 5 mm lateral to the previous insertion sites. Once a quadericeps muscle twitch is obtained at <0.4 mA, the local anesthetic of choice is injected. However, when the initial response is a sartorius muscle twitch, the quadriceps muscle twitch is sought by incrementally re-directing the needle laterally 10° at a time, and advancing the needle several mm beyond the point at which the sartorius muscle twitch was induced. After injecting 30 ml of local anesthetic the onset of blockade is expected within 3-5 minutes when the current is < 0.4 mA. The block is documented by loss of sensation in the anterio-medial thigh and saphenous nerve distribution, as well as the presence of quadriceps muscle relaxation.
