Nuances to Ultrasound-Guided Subgluteal Sciatic Nerve Block Part 1

April 25, 2014
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Full Commentary on “Ultrasound-Guided Sciatic Nerve Block in Overweight and Obese Patients”             

by Abdallah et al, Regional Anesthesia & Pain Medicine Vol 38, Number 6, Nov-Dec 2013, p547-552


There are a number of points made in this article that I find very interesting and that I believe are worth discussing further. Some of my comments are in praise of the intent of the article, some comments are extensions of important points that were brought out by this article and some are differences in opinion (or at least clarifications of concepts) that I would like to make. The first point that catches my attention is the fact that the article emphasizes that with the utilization of ultrasound to perform a nerve block, it can be performed more quickly with equal effectiveness and with an added bonus of potentially decreasing the incidence of multiple complications. I also like that both arms of the study were performed only with ultrasound though this should only be attempted once a considerable degree of skill and experience is attained. I would recommend for most folks the use of nerve stimulation in addition to ultrasound. Nerve stimulation should be used as an alarm and to help confirm the position of the needle within the correct tissue plane (as described below) or to positively identify the contacted structure as the sciatic nerve.

Unknowingly, I incorporated several years ago the “Subgluteal Space Technique” that was described by Karmakar et al. My rationale was one of practical importance: speed & patient comfort. I recognized after the fact that I may be decreasing the incidence of complications by avoiding direct nerve contact. At the time that I started using an infragluteal/subgluteal approach to the sciatic nerve, I was routinely performing this block for Total Knee Arthroplasty (TKA). I believed at that time that it was important to perform the sciatic block high above the popliteal space because a lower block might risk missing some of the fibers supplying the posterior knee. I have found since that time that it is not necessary to block the sciatic nerve this high, and a popliteal approach is sufficient (see The ‘Right’ Way for more on this).

Identifying the sonoanatomy in the infragluteal region is relatively simple (Click HERE to read further Tips on identifying sonoanatomy for Subgluteal Sciatic Nerve Blocks), however it always bothered me (not as much as it bothered the patient I imagine!) to pull back some distance to readjust the needle more than once when my out-of-plane needle angle did not intercept the sciatic nerve several centimeters deep to the skin as I had intended. The relatively thin single injection needles will bend, and sometimes I would just pick a poor trajectory. Beyond this, sometimes it is difficult to get the sciatic nerve to twitch, multiple passes take extra time, and it is not always possible to recognize the needle tip with an out-of-plane technique (and I am using a relatively sharp 30 degree beveled needle). I used an in-plane technique for a while to address some of these concerns, but trajectory is an even bigger issue with that approach, and it entails traversing a great deal of real estate that is difficult to easily make numb.

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Not sure you want to tackle the anterior sciatic or subgluteal sciatic nerve block for your TKA’s? Click HERE to learn how to do a popliteal sciatic nerve block that will be just as effective and much easier to accomplish!

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