How is a sciatic nerve block at the popliteal fossa administered for pain management?

Updated: Jun 19, 2018
  • Author: Anthony H Wheeler, MD; Chief Editor: Meda Raghavendra (Raghu), MD  more...
  • Print
Answer

Answer

In some cases, physicians choose to block the tibial and peroneal branches of the sciatic nerve at the popliteal fossa. By definition, the popliteal fossa is defined cephalically by the semi-membranosis and semi-tendinosis muscles medially and the biceps femoris muscle laterally. Its caudal extent defined by the gastrocnemius muscle both medially and laterally. If this quadrilateral is bisected, as shown in the image below, the clinically pertinent area would be the cephalolateral quadrant.

Here, both tibial and common peroneal nerve blockade is possible. The tibial nerve is the larger of the 2 and separates from the common peroneal nerve at the upper limit of the popliteal fossa. The tibial nerve continues the straight course of the sciatic nerve, running lengthwise through the popliteal fossa directly under the popliteal fascia between the heads of the gastrocnemius muscles. With the patient prone, the patient is asked to flex the leg at the knee, which allows more accurate identification of the popliteal fossa.

When identified, it is divided into equal medial and lateral triangles as shown in the image below.

A mark, such as “X,” is placed 5 cm superior to the skin crease of the popliteal fossa and 1 cm lateral to the midline of the triangles. A 22-gauge, 4-cm to 6- cm needle is directed at a 45-60 degree angle to the skin, and then the needle is advanced in an anterior and superior direction. Paresthesia is sought and if obtained 38-48 mL of local anesthetic is injected. Potential problems include vascular obstructions that also occupy the popliteal fossa. Intravascular injections should occur infrequently when proper precautions and technique are used. In these cases ultrasound guidance and nerve stimulation may be helpful.


Did this answer your question?
Additional feedback? (Optional)
Thank you for your feedback!