Post Tibial Blocks

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In talking to a number of colleague podiatrists about technique of posterior tibial anaesthesia administration, it has come to my attention there is extreme variety in technique use:
- some 10cm proximal to the medial malleoli,
- some adjacent to malleoli,
- some inject in to touch tibia and withdraw,
- some go quite superficial.

All report there technique works. I am just interested in techniques peolpe are using. As there seems no "standard" out there?



Sally Belcher

 

Like all areas of clinical practice, there is variability in practice (usually based on who taught them in the first place). Everyone inevtiably says their technique is the "best".

General priniciples are the same for all forms of regional anaesthesia; to ensure an adequate block, the target nerve tissue must be correctly located to decrease the liklihood of a partial or incomplete block.

In the case of the posterior tibial nerve, the most important consideration is to be aware of variability in the bifurcation point of the medial and lateral plantar nerves, and the medial calcaneal branch.

Because of this, most people would agree that coming more proximal up into the leg is generally more sensible to avoid this issue. At this point the neurovascular bundle is relatively deep, so taking the needle to the tibia and withdrawing about 10mm is about the right location, in my experience.

That being said, the most *accurate* way to do any regional nerve block is to use a nerve stimulator. Most anaesthetists and podiatric surgeons who do sciatic nerve blocks (eg at the level of the politeal fossa), are required to do this because of the depth of the sciatic nerve at this level.

I have seen some anaesthetists also use nerve stimulators to do posterior tibial nerve blocks...but that is usually because they arent that use to doing them. They do tend to waste more time than you really need to...

Like anything...getting a good block 100% of the time is a dream, so 'top-ups' are an accepted part of clinical practice.

LL

 

Sally:

My preferred technique for posterior tibial nerve blocks is a technique I learned during my first year podiatric surgery residency from 1983-4 at the Veteran's Administration Hospital in Palo Alto, California. It was popularized by John Ruch, DPM, from the Podiatry Institute (under the guidance of Dalton McGlamry, DPM). This ankle block technique involves actually palpating the nerves of the ankle to give a complete ankle block with no more than 3.0 ccs (yes, three ccs) of local anesthetic.

I have attached a handout that I made (hand drawn and hand printed-before personal computers) during my Biomechanics Fellowship in late 1984 at the request of Joshua Gerbert, DPM, to give as a lecture to the surgery students and residents at the California College of Podiatric Medicine to teach them the technique. Once the technique is learned, it greatly aids the clinician in being able to give very precise ankle blocks in most patients with a minimum of local anesthetic.

 

Because I have Diagnostic ultrasound I use it for TN blocks.

It takes the guess work out of where the nerve is.

As a student I was taught to inject behind the NVB from the medial side of the tendo-achilles. Now this seems crackers to me.

What US shows is that is you go approx 30 mm prox to the medial malleolus the TN lies reliably posterior to the PTA not deep to it.

If you can locate the PTA then inject posterior to it by about 5mm you should be close to TN, no risk for vessels and also depending on adipose thickness not needing to inject much behond 8mm deep.

Just to be an onnoxiously nerdy oneupmanshipper to Kevin I recently demonstrated a TN block for plantar heel pain injection using 0.3 mls of 2% lidocaine . . . how sad is that?

cheers

Martin


The St. James Foot Clinic
1749 Portage Ave.
Winnipeg
Manitoba
R3J 0E6
phone [204] 837 FOOT (3668)
fax [204] 774 9918
www.winnipegfootclinic.com

 

Quite.

Just a question for you and Kevin - what about cankles? How does your injection technique/ dosing regime differ in cases involving surgery under local anaesthetic to patients with cankles?

:boxing:

 

Hi Lee

"cankles" is not a term I know or could translate a typo for so not sure how to answer that.

Since I only do skin lesion surgery I dont need to worry about duration too much. The 0.3 mls "silly" block I did on myself just for fun . to wind up my buddy simonf ( I love opportunities to show off use of US).

Interestingly it only affected plantar calcaneal area and last approximately 1 hr. Normally I'd use 3mls of plain 2% lidocaine to knock out entire plantar for longer so I take you point.

cheers

Martin

 

Martin,

'Cankles' is a portmanteau used in the UK for those individuals in whom it is not always easy to delineate their 'calf' from their 'ankle'

Probably not one for the medical notes though....

 

LOL!

I didn't think you guys over the pond would be using the phrase 'cankles' but thanks to Ian for the illustration. There's a new piece of terminology for you (although, as Ian said, it's not generally a professional term or even a polite descriptive term).

Sounds like your ultrasound guided tibial nerve block was more of a medial calc nerve block?

There's loads of ways of performing tibial nerve blocks. I read an article in JAPMA a few years ago (some technique tip for locating the nerve clinically) but have since forgotten it - something to do with drawing a line from the tip of the medial malleolus to the most posterior and plantar part of the heel and then some other line at a certain distance crossing the first (you can see that I obviously stuck to that technique religiously!). Dopplers are always good for locating the artery and then infiltrating the nerve. Nerve stimulators are used by some practitioners. As long as you're doing a lot of them, you'll get more consistent results. And if your technique is working consistently - great!

:drinks

 

Here's a link to a nice website with lots of regional anaesthesia (they used to have some videos too):

http://nysora.com/peripheral_nerve_blocks/classic_block_tecniques/3035-ankle_block.html

 

I think that it is most likely that the fluid contact was limited to fibres which eventually became the MCN. At level I blocked at it is unlikely that any branching had occured. One of my holy grails currently is to see how reliably technique can be developed to identify TN branching using high res Diagnostic ultrasound exam. Apart from the problem of resolution ( I am using 14 MHz which should be able to "see" TN branches), there is an issue of the plane of the branching. Most of the literature I have read which considers this descibes the MCN as branching posterior to the TN which means that there is really no way to position the probe at the right angle to visualise this adequately. I am hoping to do some cadaver studies using US and this is one question I am keen to explore further. Using US to seek evidence of TN pathology within the TTunnel is an interstesting possibility since electrodiagnostic testing of early compression neuropathy lacks sensitivity.

cheers

Martin

The St. James Foot Clinic
1749 Portage Ave.
Winnipeg
Manitoba
R3J 0E6
phone [204] 837 FOOT (3668)
fax [204] 774 9918
www.winnipegfootclinic.com

 

Nice one.

I guess like most US work, it's user dependant. With experience, I guess it's possible to pick up pathology potentially missed between slices on an MR scan on your dynamic US scan. We are currently changing providers of our US scans as we ended up 'double-scanning' (US then MR) too many people when the US would come back negative for all sorts, even though the clinical signs and symptoms said otherwise! Good luck with it

 

You are right about the reliability and user dependancy for US. It is a steep learning curve and I have spent a lot of time learning to use US and figuring out its limitions both generally and within my own developing skills

It has become a bit of a passion for me. I would strongly recommend anyone doing MSK foot work to get a decent machine (not one of the poor quality ones often touted by podiatrists selling machines) and learn to use it. I keep my machine running constantly and now essentially use it as part of my physical exam when it might help sort out tissue abnormality. It is mostly impossible to get "good" information from a static US image. Used dynamically there is a new level of interpretation possible.

I have met too many surgeons who dismiss US because they get unreliable results from whoever does their exams. I believe US really needs to be done by the clinician who needs the information, it is more akin to PE than pure imaging.

hope that inspires to look more at this

cheers

Martin

 

Ultrasound improves the success rate of a tibial nerve block at the ankle.

Redborg KE, Antonakakis JG, Beach ML, Chinn CD, Sites BD.
Reg Anesth Pain Med. 2009 May-Jun;34(3):256-60