Persistent motor stim during cervical RFA

[GorillaPanic]

---

Members do not see this ad.

Hey all,

I had a weird experience yesterday doing cervical RF that has left me puzzled. Placed needles at lateral pillar of C4, C5, and C6 with pt in prone. Landed on os and walked the needles laterally hugging the waist. Felt very good about my placement, but had very brisk motor response with testing of C5 and C6. Thought perhaps I was too anterior (the alignment on fluoro wasn't perfect), so I backed out until my tips were at the midpoint of the trapezoid which got rid of the motor response at C5, but continued to have motor response at C6 needle despite multiple attempts to reposition. This was real motor stimulation with movement of the wrist and thumb.

As an experiment, I pulled back so far that I was now resting entirely posterior to the pillar, and still got positive motor response. Anatomically this doesn't make sense at all, and I'm super confused. I thought perhapas I was too generous with the local before placing the needles, so as an experiment I used minimal local to anesthetize the left side and placed a single needle at C6 in the posterior half of the trapezoid... and then got motor response on left side as well! Obviously did not proceed.

Is there something super obvious I'm overlooking? Fluoro images of the saga are attached.

 

[willabeast]

Two things. Could the voltage for stim have been too high? Where was the grounding pad?

 

[GorillaPanic]

Two things. Could the voltage for stim have been too high? Where was the grounding pad?

Consistently got stimulation at 1.5V (initially got stim at 0.5V, so 3x this). Grounding pad usually placed by staff while I"m doing other things and I hadn't taken specific notice of location, so maybe this had something to do with it? I think I recall it being peeled off the lower back/flank area when we took down the drapes.

 

[callmeanesthesia]

Do you have an MRI axial image through the area?

 

[GorillaPanic]

I'll see if I can pull some images, though I did look at them with one of my neurology trained colleagues and nothing out of the ordinary..

 

[willabeast]

Consistently got stimulation at 1.5V (initially got stim at 0.5V, so 3x this). Grounding pad usually placed by staff while I"m doing other things and I hadn't taken specific notice of location, so maybe this had something to do with it? I think I recall it being peeled off the lower back/flank area when we took down the drapes.

location pad should be in nurses notes. reason I ask is I got a + stim. that was related to grounding pad placement once.

 

[Agast]

I had a lumbar patient with persistent motor response and it turned out he had a large fluid pocket in his glute from an old fall causing seroma. My hypothesis is that the electrical current traveled through the fluid and caused muscle contraction around the sciatic nerve

 

[hyperalgesia]

Maybe anatomical variant...

 

[RoloTomassi]

I get this every once in a while in neck and back, clear extremity myotomal contraction despite backing out quite a bit. I just burn way back there to be on the safe side.

 

[BobBarker]

I have never had that happen. Did you do a RFA after that went normal?

 

[clubdeac]

Pics look great

 

[BobBarker]

I have a hypothesis. Grounding pad over the ecg leads or very close.

 

[MD87]

I have had similarly odd experiences once before in the c-spine - didn't get motor stim but every time I started the ablation the patient felt pain in a pattern that was very consistent with a nerve root. Ended up barely touching the articular pillar because any deeper and they would feel it in the arm. My guess is that some people may have tiny interconnections between the nerve root and the MB. Just a guess, though.

 

[oneforfighting]

Have had this happen in the lumbar spine before a couple of times. Confusing and a bit spooky.

 

[Taus]

Have had this happen in the lumbar spine before a couple of times. Confusing and a bit spooky.

Yep. Same. 2-3 times in a decade. Vigorous leg motor stim til needle tip barely on bone at most posterior aspect of joint before it stopped.

 

[bubaghanush]

I had something similar once with multiple adjustments, then realized I was reading the numbers wrong on the probes. Something like 323 and 332 and what I thought was l4 and l5.

 

[hyperalgesia]

One time I had this happen and, after repositioning several times, very close inspection of the image revealed the probe extended a few mm past the canula. It was the wrong probe for the canula and was extending into the foramen.

Was very glad for motor testing.

 

[Orin]

This was real motor stimulation with movement of the wrist and thumb.

As an experiment, I pulled back so far that I was now resting entirely posterior to the pillar, and still got positive motor response. Anatomically this doesn't make sense at all, and I'm super confused.

What local do you use? Fluid causes electrical flow so if you dropped a low concentration local on the pedicle while trying to keep the patient comfortable, it may have created a field that stimulated the nerve root or DRG despite your RF tip being in a great location.

 

[Laryngospasm]

Likely some sort of communication within the nerve root itself from what should be separate nerve pathways.

 

[epidural man]

I have had similarly odd experiences once before in the c-spine - didn't get motor stim but every time I started the ablation the patient felt pain in a pattern that was very consistent with a nerve root. Ended up barely touching the articular pillar because any deeper and they would feel it in the arm. My guess is that some people may have tiny interconnections between the nerve root and the MB. Just a guess, though.

This

There is a recent anatomical study of the medial branches. These things branch and connect much more than ever previously appreciated.