High Popliteal Block

 Peacock of Australia - photo by Tom Yanagi, M.D.

by Andrew Wall, M.D.

Patient positioning may be an obstacle when performing lower extremity peripheral nerve blocks, especially of the sciatic nerve.  Traditionally, the sciatic nerve is blocked in the lateral decubitus position for a subgluteal approach or prone for a popliteal approach.  This requires repositioning a heavily sedated patient on a narrow gurney or operating room table, which is often cumbersome and time consuming.

One solution for below the knee surgery is a popliteal block in the supine position with a saphenous supplemental block via the subsartorial approach.  This combination may be done quickly in the supine position with minimal position change.

The lower extremity is positioned with the hip flexed approximately 30 degrees.  The lower leg is supported with a Ferkle device which allows for adequate access to the popliteal area.   While seated, place the probe on or slightly superior to the popliteal crease and locate the popliteal artery, tibial and common peroneal nerves.  The nerves will be superficial and lateral to the vessels.  If the nerves are hard to visualize, have the patient dorsiflex and plantarflex.  The tibial and peronial nerves move with this maneuver.  Trace the structures cephalad until the nerves merge, usually 7-10cm above the crease.  Needle entry will be in the crease between the vastus lateralis and bicpes femoris.  This is different than other PNB approaches where entry is next to the probe.

Sciatic Nerve Block

Rest your “probe arm” elbow on the bed, this adds stability and prevents the probe from sliding as your muscles fatigue.  When injecting local in the skin and soft tissues, be sure to glance up at the screen to make sure you are on the right trajectory.  It can be tricky at first because directions are reversed.  For example, steepening the angle moves toward the top of the screen – not away from it.  The structures are deep using this approach so a 4 inch needle is mandatory.  If the patient is especially large a curvilinear probe may be preferable.  Inject 30cc of the local of choice; circumferential spread is desirable.

Saphenous Nerve Block

Next, externally rotate the leg onto the bed exposing the inner thigh.  Prep the skin from mid-thigh to knee and use the linear (curvilinear for large patients) probe to identify the SFA under the sartorius muslce just medial to the vastus medialis.  This artery dives deep to become the popliteal. Before doing so, it gives off the genicular artery.  The saphenous nerve runs with the SFA and continues superficially with the genicular.  The nerve is not always visible, but the artery should be, and they share a fascial sheath.  Inject 10-15cc of local in this plane to supplement the saphenous distribution of the lower extremity.  Less local is required because of the size of the nerve. 

This regional block combination allows one to use less local than the traditional femoral/popliteal combination.  Since the saphenous nerve is strictly sensory there is no quad weakness.  On the downside, this approach to the saphenous nerve is less reliable (60-80%) than a traditional femoral nerve block.  Therefore, if using a “regional only” technique a femoral/sciatic is probably necessary.

The following hyperlink provides an excellent illustration of the anatomy for the saphenous nerve block:

Sub-Sartorial Nerve Block Illustration

Madera, California - photo by Tom Yanagi, M.D.