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Femoral nerve block

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In contrast to the psoas compartment block, the femoral nerve block is a caudad, ventral approach to parts of the lumbar plexus. The technique described here is often called the 3-in-1 block. This name derives from the fact that one injection blocks three nerves (femoral, obturator and lateral femoral cutaneous). However, our own clinical studies suggest that the sensory supply to the thigh is primarily provided by the femoral nerve or its cutaneous branches. It has additionally become widely accepted that, even though an inguinal femoral nerve block can block the lateral femoral cutaneous nerve when an adequate volume of local anaesthetic is injected, but, due to the subfascial dissemination to the lateral, the obturator nerve cannot be blocked. Insurmountable anatomical barriers (including the iliopsoas muscle among others) counteract the simultaneous spread of the local anaesthetic to the mediodorsal. The areas of the lateral femoral cutaneous nerve and the obturator nerve show much variation. Moreover, they are usually not clinically demonstrable as independent supply areas. Neither is there is verified evidence on the supply areas of the obturator nerve in the region of the medial condyle of the femur and the tibial region of the knee joint.

  

Anatomical landmarks

Anterior superior iliac spine, pubic tubercle, inguinal ligament, femoral artery, inguinal fold

 

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Block technique

The patient lies on his back with legs spread slightly apart. The foot of the leg to be anaesthetised should be turned loosely to the outside. The puncture site is located approximately in the region of the inguinal fold, 1.5 cm lateral of the femoral artery, approx. 2-3 cm below the inguinal ligament (IVAN = Inner Vein Artery Nerve). Local anaesthesia is only injected superficially with 0.5 of 1% mepivacaine so as not to block the femoral nerve and to impede stimulation. The stimulation needle (Stimuplex® D 50 mm) is inserted at an angle of approx. 30º to the skin and advanced in a cranial direction. After reaching a depth of around 2-4 cm, the femoral nerve is encountered. Contractions of the quadriceps femoris muscle signal the direct proximity to the nerve. Stimulation of the rectus muscle of the thigh is crucial for the block to be effective. The kneecap must „dance“. Contractions of the sartorius muscle are usually not sufficient. In the femoral nerve block, it is particularly important to conduct the aspiration test carefully when injecting the local anaesthetic. Place a finger beneath the puncture site for compression to prevent the local anaesthetic from flowing in the distal direction and to promote its dissemination in the cranial direction. The latter can also be supported by lifting up the leg.