Popliteal Block – Lateral Approach
The lateral approach to the popliteal nerve block is an intermediate level procedure that will allow you to further increase your skills as a sonographer. You will be “flying inverted” when you perform this block: Since the probe is placed below your needle entry point (popliteal fossa), you will initially feel lost as to how to move your needle to approach the nerve(s). When you move the needle down, it will appear on the screen as moving up (since in fact you are moving towards the probe itself – thus flying inverted). With some practice you will be able to perform this block while keeping your patient in a supine position and obtain optimal results.
Indications: Lower Extremity procedures
External Landmarks: Popliteal fossa, Vastus Lateralis, Biceps Femoris Approach: In-Plane, “Inverted flying”
Local Anesthetic Volume: 20 - 30 mls.
Level of Expertise: Intermediate
Anatomy: The sciatic nerve separates into two separate trunks some 5-10 cms before it arrives at the popliteal fossa. The common peroneal nerve is the more lateral of the two branches, and they can be easily seen with an ultrasound device not far from the popliteal artery. Positioning: Supine, with the patient's leg slightly elevated and flexed so that the ultrasound probe can be easily placed in the popliteal fossa.
View of the popliteal nerves with a non-linear array ultrasound
- I-Streme Echo
- Nerve stimulator (optional)
- 20-30 mls local anesthetic syringe
- 25 gauge needle for local infiltration
- Echogenic needle (optional)
- 4 inch needle for block
- 7.5 or 5 MHz setting
- Place the probe with its button facing you within the popliteal fossa and locate the popliteal artery and identify the tibial and common peroneal nerves.
- Slide the probe cephalad while having these structures in view until you find the area where the tibial and common peroneal nerves coalesce.
- Prep the area where you are to introduce your needle – lateral part of knee and up to 10 cm above it.
- Locate the vastus lateralis and biceps femoris muscles and the crease between them.
- Your needle entry point should be some 7 cm above the lateral femoral epicondyle - Direct your needle towards the sciatic nerve at the point where it divides. Remember that “up is down” and “down is up” when moving your needle.
- Look for a foot twitch if you are using a nerve stimulator to confirm that your needle is in proximity to the nerve(s). Remember that common peroneal stimulation causes a dorsiflexion or eversion of the foot. Tibial nerve stimulation provokes plantar flexion and inversion. Since the common peroneal is most lateral, flexion and eversion are what you will see most often. - Watch out for the artery since you could inadvertently inject anesthetic into it.
- Intravascular injection into the axillary artery or vein.
- Nerve injury.