Saphenous/vastus medialis nerve block

Several techniques of saphenous nerve block have been described in the literature: their common feature is a rather high failure rate (well over 20%) due to the difficulties in localiza-tion of the nerve (most techniques are "blind" infiltrations). The saphenous nerve is a purely sensory nerve; thus it cannot be located by electrical stimulation. However, since it runs within the same fascial gutter as that containing the motor nerve supplying the vastus media-lis muscle, nerve stimulation can be used to identify the motor nerve [47]. For the nerve stimulation technique, the child is placed supine. The landmarks are the inguinal ligament, the femoral artery and the upper border of the sartorius muscle (Figure 3). A short, short-beveled insulated needle is inserted perpendicularly to the skin, 0.5 cm lateral to the femoral artery just above the upper border of the sartorius until twitches are elicited in the vastus medialis muscle. At this point, 0.1 to 0.2 mL/Kg of local anesthetic is injected, which results in block-ade of both the vastus medialis nerve and the saphenous nerve.


     Figure 3. Saphenous/vastus medialis nerve block
     1. Sartorius muscle (lateral border)
     2. Saphenous nerve
     3. Femoral artery
     4. Pubic spine (or tubercle)
     5. Anterior superior iliac spine
     6. Site of puncture