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The Anterior Approach to the Sciatic Nerve

The Neuraxiom Method

October 5, 2008

The anterior approach to the sciatic has been a project that has been going on for a while here at Neuraxiom Labs.  While we’ve been using the posterior approaches to the sciatic posted here on April 8,2007 with great success, we have been working to create a set of reliable techniques to safely block the sciatic from the front of the thigh primarily for procedures of the knee.   Over that time we would perform ultrasound surveys of the upper thigh AFTER performing the sciatic block from the posterior approach.  In this way the sciatic was already surrounded by local anesthetic solution, creating enhanced ultrasound borders and making it easier to identify on survey. 

With this information we could compare relationships with surrounding anatomical features and thereby create dependable guidance for finding the nerve in the pre-operative thigh.

Because of the variability in patient anatomy, it was necessary to have more than one method of locating the sciatic nerve to provide backup techniques in case one method was inconclusive or the practitioner wants confirmation of target location.  Because of this we present 3 separate methods of target identification or needle placement.

The last method presented is called “Flashing the Adductor” and it is novel for this target because it identifies the space surrounding the target rather than the target itself.  Because of its nature some people may be initially dubious as to its effectiveness.  Following the procedure through to its end will provide the necessary proof of the concept.

For full details on the anterior approach visit the page devoted to it by clicking on the menu choice on the left side of any page or by clicking this link.

Below you will see an animation showing the various structures of the thigh which can be identified on ultrasound survey.

In the next panel below you will find a short flash tutorial about finding the sciatic on the anterior approach.  The full details of the anterior approach to the sciatic  can be found by clicking on this link Anterior Approach to the Sciatic or by choosing the “Anterior Approach” menu choice under “Sciatic” on the menu bar at the top left of any page on the site.

Once again, thanks for visiting the Neuraxiom website.

Jack

Spot the Sciatic in the survey picture below.

Disclaimer and Warning

Let’s get this out of the way!
Neuraxiom.com is intended for use by medical professionals, specifically those who perform invasive regional anesthetic procedures.  If you’re reading this and don’t know what I mean, you’ve stumbled into the wrong place and you should click here now.

 By now you should be aware that not everything you hear and read is true, real or appropriate to real life.  So the following disclaimer is there for the obvious reasons.  The short form is: IF IT DOESN'T MAKE SENSE OR SEEM RIGHT TO YOU, DON'T DO IT.  Having said all of this we hope that information found in this site is helpful to you in making decisions regarding you practice.  Most of the techniques described here are either new and non-invasive (like ultrasound surveys) or invasive things you already do (like sticking needles into people). 
So then:
Neuraxiom.com and those people associated with it make no warranties as to the correctness, safety or appropriateness of any therapies, medications, dosages, techniques or any other aspects of medical practice or patient care and safety.  Nothing in this site should be interpreted to imply that anything but YOUR BEST MEDICAL JUDGMENT is appropriate for making safe medical decisions and implementing therapies for your patients.

November 1, 2008 - Case Report

Acute Respiratory Failure following Interscalene Block

A report of an uncommon complication from an interscalene block occurring under very common circumstances is presented to raise awareness of its possibility.  Click here to read the whole article.

Patient falls following femoral or sciatic nerve block.

It has become clear over the past few months that even though the leg blocks that we are doing are becoming more perfect in terms of their ease and success rate, the overall technique needs improvement and quickly because of the inherent risk and danger of patient falls in the aftermath of a successful block. 

There are many reasons that a patient will try to stand and walk following lower extremity surgery with a femoral and/or sciatic block in place.  Many are motivated to begin their rehabilitation and recover from their surgery as quickly as possible.  Some are done as outpatients and are told to weight bear as tolerated by their surgeons.  Some equate a pain-free leg with the good strong leg they had before they aged or were injured.  But the fact is that no matter why they try to stand and walk after surgery a major contributor to falling is the femoral and/or sciatic block that left their leg muscle weak or paralyzed is the major contributor to the collapse of the leg and the fall that ensues.

... a slap up the backside of the head

I was recently in communication with a patient who experienced such a fall and the injuries that occurred far out-weighed the problem that brought her to surgery in the first place.  This email conversation, the endemic fall rate following block where I work, and articles and blurbs I’ve read in the journals, was like a slap up the backside of the head to me leading me to the thought;  this isn’t a little local problem and I should do more to help others avoid this avoidable problem.

Approach to the Problem

The standard approach is through pre and peri-operative teaching, maybe you tell them about not ambulating with a block before surgery in a class of some kind, at the same time they may be hearing about rehab after the procedure.  You tell them again just before and/or after the actual block just about the time you’re loading them up with the midazolam (the memory enhancer).  It’s mentioned again when they reach the floor, in amongst the other “welcome to the unit – this is the call bell, this is the bathroom, I’ll be right back as soon as I pass meds to my other patients” information.

All of the info that the patient gets during this time is while they are under a lot of stress.  This is like studying for a test during your very first solo skydiving jump.  Retention is less than ideal.

This is why I propose a different approach.  In addition to these other ineffective measures I propose a largish colorful sticker (such as that shown at the top of this page) placed directly on top of the leg dressing, oriented toward the patient which says, “Nerve Block Working – Do Not Stand or Walk”.  You can add other things to it but this or something like this should be the largest words on the sticker.  It would also be a good idea to have a picture which conveys some of the information.  If you have the international symbol for “Falling Patient” you could use that or you could make one of your own. 

Please help keep your patients from falling.  If you have any ideas for how to solve this problem please pass them on to me and I will put them up on the site.  Thanks.

If you are interested in downloading the picture above for use as a sticker click here. then right click on the picture and choose to “Save Picture as” on your system.  The picture is sized so that 2 of them will fit on a 8.5’X11” page.

Phrenic Sparing Interscalene Block -PSIB Study Database Summary

Neuraxiom/USinRA PSIB Database Summary
as of March 11, 2010, 15:05:10 h EST

PSIB - the Phrenic Sparing Interscalene Block Study Project Underway

We’ve been collecting Interscalene Block Case Data from you since October 2006.  Thanks to all of those that have contributed.  Follow this link --> PSIB to go to the data entry page.  Read the article below to find out what the PSIB study is about.  Go to the PSIB Project Page to learn more. View the data that’s been collected so far by either going to the PSIB Project Page or by going directly to the PSIB Database Listing and Summary Page.

 Read the Full Introduction to the Project Here.

Revision: October 8, 2006                         Interscalene Brachial Plexus Nerve Block

An Open Study by UsinRA and Neuraxiom

“Phrenic Sparing Interscalene Brachial Plexus Block” -PSIB    An Open Study to Make a Good Block Better

Searching for the Interscalene Brachial Plexus Block that has the Least Incidence of Ipsilateral Hemidiaphragm Paralysis

The Phrenic Sparing Interscalene Block (PSIB) Study is an innovative approach to solving problems and moving the area of ultrasound guided brachial plexus blocks ahead. You are invited to enter data on cases into the project database anonymously and are able to view the data as it is collected. You may interpret the data and draw your own conclusions then submit your interpretations and conclusions (if you like) to the forum for open discussion. We're hoping to apply this method to other areas of concern is the future. A lot depends on your participation. We'll keep it short and sweet.  Let's start from the beginning and tell how this came to be.The PSIB Project page can be found on a page by following this link or by choosing it from the menu bar branching from the Interscalene Block page titled the PSIB Project Page.

Find the Entire Introduction Article Here

December 2, 2006

A Low Volume Interscalene Brachial Plexus Block

Anyone who has performed blocks under ultrasound guidance has  noted that some nerve targets can be completely surrounded with local anesthetic solution with volumes far below those previously thought necessary to complete a solid block.  Some of the people who have used ultrasound guidance to perform blocks have actually stopped the injection when the nerve was seemingly adequately surrounded with the local anesthetic solution and then noted that the resulting the nerve block is completely effective and appears identical in every way to the block as performed with a much larger volume.

So, is it a good idea to do the same block was less volume?  Is there any real benefit in modifying the block technique to base it on a smaller volume of local anesthetic?

In most cases the goal of of modifying a block technique by lowering the volume of local anesthetic injected may seem equivocal, change for change sake.  But it could be argued that any time you can create the same therapeutic effect with lower doses of a drug, the proposed change would be applaudable.  Less drug would theoretically lead to less side effects, the actual results would have to wait for a large study.

But in some nerve blocks the goal of lowering the volume of the anesthetic used would have a more immediate and therapeutically beneficial consequence.  The interscalene block of the brachial plexus represents just such a block. According to the current results of the PSIB project study carried out by Neuraxiom.com and USINRA.EU and published here on Neuraxiom.com, approximately 70% of the unintended blocks of the phrenic nerve which occur as a side effect of the interscalene block are volume related.  Specifically too much volume.

So if you think the paralyzed hemidiaphragm is a bad thing, or at least undesirable in some cases, then modifying the block procedure to lower the volume used for the block would be a good thing.

As it happens, in the case of the interscalene block, nature has provided us with some anatomical assistance; a sheath fitted around the proximal portion of the brachial plexus.  This tubular containment is not new.  It has been available to us for most of mankind's existence it is not even newly recognized.  I'm sure it was identified from nearly the earliest anatomical dissections of the human body.  I'm also sure that we share this feature with many other mammalian species.  What is new, is that this sheath is finally accessible, on a routine and accurate basis, by any practitioner with an ultrasound machine.

This is the basis of the Low Volume Interscalene Brachial Plexus Nerve Block.  Please follow this link to the Low Volume Interscalene Block page on the Neuraxiom site to find out more about what we’re doing about it.
 

Variant Anatomy of Brachial Plexus

vs.

 Anterior and Middle Scalene Muscles

While viewing a great number of necks by ultrasound I ,time and again, noted "holes" in the anterior scalene muscles of some patients.  By "holes" I mean dark (hypoechoic) circles about 3-5 mms in diameter.  The spots were usually near the centers of the anterior scalenes when viewed in their short axis.  When I  first saw them I assumed they were blood vessels, having no visible pulse, veins then.  But when I turned on the color doppler there was no flow in them.  Looking through the anatomy books I could find no reference to structures passing through the anterior scalene.  Asking some local ENT surgeons about these observations brought me no new information or possibilities.

Then during my work on the illustration of the scans of the supraclavicular space for the supraclavicular brachial plexus block page of this site, I noted holes in the middle scalene muscle on the scan.  This was too much.  I began a search in earnest.  Finally a google search of "scalene variations" brought me the lead I was looking for.  A neurosurgery journal article on findings of the long thoracic nerve passing through the middle scalene, and the related article on the dorsal scapular nerve passing through the middle scalene as well.  This answered my second question.   Then onto the first question.  What are the "holes" in the anterior scalene?

The answer is obvious, they're nerves. The nerves of the brachial plexus, taking a detour to their ultimate destinations.  Turns out the standard picture of the brachial plexus tells only part of the story.    It's possible that only a slight majority of people have the standard anatomical structure described in most anatomy books.

Consider. 

A study from the University of Texas, Medical Branch at Galveston published in Clinical Anatomy, (1997; 10(4):250-2) examined dissections of 51 cadavers showed that the standard description of the brachial plexus routed between the anterior and middle scalenes in the interscalene approach occurred in only 60% of instances, and ;

• Scalenus minimus occurred in 46% (bilateral in 14/51)
• C5 + C6 (fused together) passed through the anterior scalene in 15% (bilateral in 4/51)
• C5 root passed through the anterior scalene in 13% (bilateral in 3/51)
• C5 & C6 (separately) passed through the anterior scalene in 6% (bilateral in 1/51)
• C5 root traveling anterior of the anterior scalene in 3%

A Brazilian study published in Acta Cirurgica Brasileira (Vol 18, Suppl. 5, Sao Paulo, 2003) regarding 27 cadaver dissections reported that ;

• the phrenic had it's complete origin from the brachial plexus in 20% of sides dissected (73% = Right, 27% = Left)
• there was an accessory phrenic nerve in 12 of the cadavers
• the long thoracic nerve pierced the middle scalene in 63 %
• the dorsal scapular nerve traveled through the middle scalene in 73% of sides

"The American Surgeon", (Vol. 72, Number 2, Feb 2006, pp 188-192 (5)) article concerning dissection of 93 cadavers, 186 sides found variant anatomy in the relationship between the brachial plexus and the anterior scalene.

• C5 root anterior to the anterior scalene in 12 sides
• the anterior scalene was doubled in 1 cadaver and the upper trunk of the brachial plexus passed between them
• the upper trunk of the brachial plexus passed anterior to the anterior scalene in 4 cases and passed through the anterior scalene in 12 cases
• C5 passed anterior and C6 passed through the anterior scalene 1 cadaver

OK, enough considering,  what does this mean to us (or to just me).  Well 2 things,

1. It explains the "holes" we (I) see in the scalenes sometimes. 
2. It may account for the occasional, inexplicable block failure.  A nerve lying inside the muscle belly and sequestered from the local anesthetic will remain unblocked and subsequently main account for 100% of the pain experienced by the patient.

How does it change the approach?  The intramuscular passage of a root or trunk of the brachial plexus is relatively easy to spot with ultrasound and if you are aware of what it signifies, it seems prudent to place some local around it.

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