Saphenous Nerve Block
The block of the saphenous nerve is a complementary block. It
is mainly used to extend the anesthetized area provided by a sciatic nerve block
to obtain complete anesthesia of the leg and foot, the medial aspect of which is
supplied by the saphenous nerve.
The classic approach is performed
at knee level, with the patient placed in the semiprone or in the supine position
and the knees flexed by 90 degrees. The landmarks are the anterior edge of the medial
head of the gastrocnemius muscle and the tibial tuberosity. A line is drawn at a
45-degree angle with the intercondylar line, from the tibial tuberosity to the anterior
edge of the gastrocnemius muscle. The technique consists of injecting subcutaneously
a ring of local anesthetic along this line. This very simple technique is virtually
free of complications, but its failure rate is rather high.
The saphenous and vastus medialis nerve block
represents an alternate approach to the saphenous nerve.[246]
The saphenous nerve is a purely sensory nerve that runs just medial to the motor
branch of the femoral nerve, which supplies the vastus medialis, within the same
fascial tunnel; this motor nerve can be easily located by nerve stimulation. The
technique is performed with the child lying in the supine position. The landmarks
are the femoral artery, the inguinal ligament, and the upper border of the sartorius
muscle ( Fig. 45-13
). A
short, short-beveled, insulated needle is inserted perpendicular 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. Then, 0.1 to 0.2 mL/kg of local
anesthetic is
Figure 45-13
Saphenous or vastus medialis nerve block, showing the
femoral nerve (1), femoral artery (2), sartorius muscle (3), saphenous nerve (4),
motor nerve supplying the sartorius muscle (5), and vastus medialis muscle (6).
injected, which results in blockade of the vastus medialis muscle and the medial
aspect of the leg and foot, which are supplied by the saphenous nerve in virtually
100% of cases.
Even though these two techniques have not been extensively evaluated,
they appear promising and are particularly interesting in that they provide effective
saphenous nerve block without requiring the high doses necessary to perform a complete
femoral nerve block. They are therefore safe and, in regard to local anesthetic
toxicity, suitable to complement a sciatic nerve block and provide complete anesthesia
of the leg, ankle, and foot.
