POPLITEAL FOSSA BLOCK
INDICATIONS:
 Surgical procedures below the knee
 Foot/ankle surgery
 Achilles tendon surgery
 Sural nerve biopsy
 Short saphenous vein stripping
DRUGS:
 CHLOROPROCAINE (NESACAINE) 2% for peripheral nerve block,
maximum dose 800mg or 1000mg with epinephrine. Duration is < or equal to
1 hour plain or up to 1.5 hours with epinephrine.
 MEPIVICAINE (CARBOCAINE, POLOCAINE) 1-1.5% for peripheral
nerve block, maximum dosage 400mg plain, 500mg with epinephrine.
Duration is 1-4 hours plain, with epinephrine 2-5 hours.
 ROPIVACAINE (NAROPIN) 0.5-1% for peripheral nerve block, maximum
dosage 250mg. Duration 2-8 hours
 LIDOCAINE (XYLOCAINE) 1-1.5% for peripheral nerve block, maximum
dosage 300mg plain, 500mg with epinephrine. Duration is 1-1.5 hours plain,
and 2-3 hours with epinephrine
All agents expected to onset within 15-20 minutes.
ADJUNCTIVE AGENTS:
SODIUM BICARBONATE Increases the pH, creating a more lipid soluble
solution. Less ionization results in increased speed across the cell membrane, producing
a faster onset of action.
VASOCONSRICTORS INCLUDING EPINEPHRINE, PHENYLEPHRINE OR
NOREPINEPHRINE. Vasoconstriction at the site, decreases absorption, thereby
increasing neuronal uptake and prolonging the duration of action and limiting toxic side
effects.
ANATOMY:
NERVES: Sciatic nerve divides into the tibial and common peroneal nerves 7-10cm
above the crease of the knee in the popliteal fossa. The tibial nerve is larger and runs
parallel and slightly lateral to midline of the leg. The tibial nerve continues deep behind
the gastrocnemius muscle and exits the popliteal fossa. The common peroneal nerve
follows the tendons of the biceps femoris laterally and travels around the fibular head as
it leaves the fossa. Common peroneal and tibial nerves innervate the entire leg below the
knee, EXCEPT the antero-medial leg and foot which are innervated by the saphenous
nerve (L2-L4). Depending on the location of the surgery being performed, a saphenous
nerve block may be needed for adequate analgesia of the affected limb.
MUSCLES: Posterior anatomy: the upper popliteal fossa is bound laterally by the
biceps femoris tendon and medially by the semitendinosus and semimembranous
tendons. Lateral anatomy: Biceps femoris and vastus lateralis muscles are identified by
finding the lateral femoral epicondyle, which is easily palpated as a bony prominence on
the lateral aspect of the knee joint.
ARTERIES AND VEINS: The popliteal artery is lateral to the semitendinosus tendon
and just above the crease of the knee. The popliteal vein is lateral to the artery. The
tibial and common peroneal nerves are within a sheath and are just lateral to the vein and
medial to the biceps tendon 4-6cm deep in the skin.
TECHNIQUE:
The popliteal block is achieved by injecting local into the popliteal fossa where the
common peroneal and tibial nerves lie. There are two approaches, intertendinous and
lateral.
INTERTENDINOUS APPROACH: Have pt. assume prone position with feet off the
edge of the bed to ease twitch identification. Pt. may flex knee joint to ease landmark
identification. Three landmarks are identified and marked with pen: (1)popliteal crease,
(2)tendons of biceps femoris (lateral) and (3)semitendinosus (medial).
Insertion point is located and marked 7cm proximal to popliteal crease at the midpoint
between each identified tendon.
Prepare area using sterile technique. Using a 22 guage stimplex needle with nerve
stimulator, the needle is inserted perpendicular to the skin with initial current of 1.5 mA.
Advance anteriorly until desired nerve is stimulated. Stimulation of tibial nerve results in
plantar flexion and inversion. Stimulation of common peroneal nerve results in
dorsiflexion and eversion. If the nerve is not localized on the first needle pass, the needle
is withdrawn back to the skin and re-directed laterally. When this maneuver fails, the
needle is taken out and repositioned 1cm lateral to the original puncture site and the
entire process is repeated. When stimulation response is localized, the output current of
the nerve stimulator is then gradually adjusted to the lowest current at which these
responses are still obtained (goal is less than 0.4mA). When the stimulation is obtained
at current intensities of less than 0.2mA, the needle should be slightly withdrawn.
Stimulation at such a small current intensity may indicate an intraneural placement of the
needle. After appropriate stimulation at desired current level and aspiration of needle to
ensure non-intravascular placement, injection of 30-40cc’s of local anesthetic may be
injected for block.
LATERAL APPROACH: This technique is utilized if patient’s are unable to turn
prone, i.e. advanced pregnancy, morbid obesity, spine and hemodynamic instability, or
mechanical ventilation. Start with pt. in supine position, and approach from lateral knee.
Identify landmarks: Biceps femoris and vastus lateralis muscles are identified by finding
the lateral femoral epicondyle. Locate groove between biceps femoris and vastus
lateralis. Insertion point is located 7cm proximal from lateral femoral condyle within the
groove of the biceps femoris and vastus lateralis muscles. Mark structures with pen.
Insert needle perpendicular to skin in horizontal plane, with initial current of 0.8mA at
7cm mark.
Advance until desired contact with femur. If no bony contact made with femur, re-insert
needle 5-10mm anterior to mark. Upon bony contact with femur, redirect needle at 30
degrees posterior angle until nerve stimulation. Stimulation of tibial nerve results in
plantar flexion and inversion. Stimulation of common peroneal results in dorsiflexion
and eversion. When the nerve is not localized on the first angled needle pass, the needle
is withdrawn back to the skin and re-directed anteriorly or posteriorly at a 5-10 degree
change in angle. If no further response, withdraw needle and re-insert 5mm more
posteriorly. When appropriate stimulation is identified, aspirate to ensure nonintravascular placement, then inject 30-40cc’s of local anesthetic.
ASSESSMENT OF BLOCK EFFICACY:
Ask pt. to move toes and ankle: motor.
Lightly pinch foot and leg to assess analgesia: sensory to pain.
If pt. responds, may have missed saphenous nerve. Convert to general.
SPECIFIC COMPLICATIONS:
Nerve damage from direct injection of LA into nerve. S/S include severe pain on
attempted injection or marked resistance to injection. Intraneural injection less likely if
using short beveled needle.
Paresthesia is the “electric shock-like” feeling felt as the nerve is touched by the needle.
Do not advance needle further as nerve damage is likely to occur.
Intravascular injection. Monitor for systemic toxicities including confusion, metallic
taste, tinnitus or seizures.
Remember saphenous nerve usually also needs blocked.
STUDY QUESTIONS:
1. What kind of surgical procedures is this block used for?
2. Why would a current intensity of less than 0.2mA be a concern?
3. Stimulation of the tibial nerve elicits what response?
4. Stimulation of the common peroneal nerve elicts what response?
5. What nerve might require a separate block if the antero-medial leg and foot are not
sufficiently blocked?
ANSWERS:
1. foot and ankle surgery, achilles tendon surgery, sural nerve biopsy, or short
saphenous vein stripping
2. intraneuronal placement of needle
3. plantar flexion and inversion
4. dorsiflexion and eversion
5. saphenous nerve block
Barash, P., Cullen, B., Stoelting, R. (2001).Clinical Anesthesia. Lippincott Williams &
Wilkins.
Morgan, E., Mikhail, M., Murray, M. (2002). Clinical Anesthesiology. (3rd ed.) Lange
Medical Books.
www.nysora.com
Hadzic A, Vloka JD. A comparison of the posterior versus lateral approaches to the block
of the sciatic nerve in the popliteal fossa. Anesthesiology 1998;88:1480-6
Vloka JD, Hadzic A, April E, Thys DM. The division of the sciatic nerve in the popliteal
fossa: anatomical implications for popliteal nerve blockade. Anesthesia & Analgesia
2001;92:215-7