The common
peroneal nerve arises from the upper part of the popliteal fossa in the back of
the thigh, as one of the two terminal branches of the sciatic nerve.
After descending obliquely and laterally across the lateral angle of the
popliteal fossa, it runs toward the lateral aspect of the neck of the fibula to
divide into the superficial and deep peroneal nerves. The superficial
peroneal nerve goes toward the lateral compartment of the leg to innervate the
peroneal muscles and becomes subcutaneously at the lower third of the leg.
The deep
peroneal nerve traverses the anterior compartment of the leg, terminating at
the dorsum of the foot. The tibial nerve is the second of the two
terminal branches given off by the popliteal fossa in the back of the
thigh. It descends vertically through the middle of the popliteal fossa
from its apex and disappears between the two heads of the gastrocnemius
muscle. The popliteal artery is medial to the tibial nerve in the upper
part of the popliteal fossa, lateral to it in the lower part, and deep to the
nerve in the lower part, and deep to the nerve in the middle of the
fossa. Thus, the pulsations of the popliteal artery perceptible at the
joint line of the knee is a good landmark for the nerve.
The tibial
nerve descends the back of the leg to innervate the muscles of the posterior
compartment. On the medial side of the ankle, it divides into the medial
and lateral plantar nerves, which proceed toward the respective side of the
foot. Before dividing into the plantar nerves, the tibial nerve gives off
the medial calcaneal branch.
In
combination with a saphenous nerve block at the knee, the common peroneal and
tibial nerve blocks are indicated for surgery below the knee not involving the
use of a tourniquet.
Position.
For the common
peroneal nerve block, the patient is supine, with the thigh flexed at the hip
joint, the leg flexed at the knee, and the foot flat on the bed. As an
alternative position, the patient lies laterally with the bottom leg extended
and the upper leg flexed at the knee.
For a block
of the tibial nerve, the patient is in a prone position with the knee extended.
If it is not possible to put the patient in a prone position, the block can be
attempted by placing the leg on a pillow and reaching for the nerve from
underneath the knee. As an alternative approach, the patient can be
placed in the lateral position with the leg extended.
Landmarks. The injection site for the
common peroneal nerve block can be identified by locating the head of the
fibula below the lateral posterior condyle of the tibia. At the neck of
the fibula (below the head), the common peroneal nerve can be felt when firm
pressure is applied.
The
injection site for the tibial nerve block is marked by the pulsation of the
popliteal artery at the bend of the knee and the vertical middle of the
popliteal fossa.
Procedure. For the common peroneal nerve
block, a skin wheal is raised at a point in the region of the anterior neck of
the fibula (below the head), and a 23-G needle is directed posteriorly and
medially to touch the bone. Paresthesia or twitching of the leg muscles
causing dorsiflexion of the ankle is elicited with the nerve stimulator to
locate the nerve. After the injection site has been identified, 5-6 ml
local anesthetic is injected.
For the
tibial block, a skin wheal is made in the middle of the popliteal fossa over
the vertical midline. A 22-G, 3.75-cm needle is then inserted at 90E to
the skin toward the pulsation of the artery, if palpable. The tibial
nerve lies superficial to the artery at this site. Localization of the
nerve may be ascertained either by using a nerve stimulator (plantar flexion of
the ankles and toes) or by eliciting paresthesia. When the needle is
close to the nerve, 10 ml local anesthetic solution is injected.
Multiple
insertions that may puncture the popliteal artery or produce post-block
dysesthesia should be avoided.
Block of the
common peroneal nerve can result in neuritis of the common peroneal nerve if
injected directly into the nerve. Intraneural injection should thus be avoided.
If the patient reports severe paresthesia or pain immediately after injection
of 0.5 ml local anesthetic solution, the injection should be stopped. The
needle should be withdrawn slightly, and another 0.5 ml solution
injected. If the pain disappears, the remaining solution (5 ml) should
then be injected. Other complications associated with these blocks are
dysesthesia, hematoma, and injection.