Femoral nerve block
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.
Ultrasound-guided femoral nerve block
The positioning of the patient is identical to that in the conventional technique. The probe is applied roughly in the direction of the inguinal ligament, making it possible to identify characteristic anatomic structures: the femoral vein and artery and the femoral nerve in cross-section. The latter almost always appears as a hyperdense triangle lateral to the artery. The nerve is covered by the iliac fascia, which shows up in the ultrasonic image with a fine, white double contour.