Testing myoelectric arm components in general: uncharted territories

Prosthetic arms in general do not usually appear to be tested a lot before getting thrown at the user, which is a statement that I find many examples for (glove may disintegrate all by itself; glove dies after just a few minutes of car washing; bolts never checked for size; etc.).

This is not to say that this is intrinsically bad - no. This is to say that the burden of testing and suffering the associated negative consequences of that also then reside with the user. If - at all - a company finds it unacceptable that users perform the testing and resulting discussions bad in any way, then (and only then) may they wish to consider a different type of product marketing and testing approach.

The question of whether manufacturers of prosthetic components test anything at all, also for skin safety, that question: it now also officially extends to skin electrodes.

As suggested by their ample advertising, a range of "bionic" myoelectric arms are demonstrated and shown around, as being able to sustain bicycle riding. So we have to assume that everyone seems to be of the opinion that it is cool to ride bikes, with, say, wearing an iLimb.

Testing myoelectric arm components in particular: we are invigorated and motivated to bike

As part of campaining the extended use of their "bionic" iLimb and Michelangelo hand product, Otto Bock and Touch Bionics publish ongoing visuals and texts that suggest use - also - of bicycles, as can also easily be checked on their various Facebook or Youtube pages.

And the faces of these people, if they are shown, suggests that using a "bionic" arm for biking does them a world of good.

This all is implicit.

Nowhere does it say, that biking is discouraged, or that complications may lurk.

(C) Copyright Touch Bionics / Otto Bock / RSL Steeper / Bebionic / Youtube / Facebook advertisings

Everyone seems to be a really happy biker here.

Certainly, I do not want to miss out.

So what is easier than doing that.

In November, I took my mountain bike for a quick spin wearing the iLimb.

Testing myoelectric arm components in particular: we suffer the consequences from riding a bike with a "bionic" arm

I did sweat quite a bit, and riding was not so much fun with it; most notably, it was uncomfortable due to hard vibration and shoulder / neck tension.

My hosed arm got really sweaty and the electrodes left clear imprints on the skin.

Other than that, first day was OK.

Then, a rash appeared at the electrodes' sites.

And over four weeks or so later, I still had that nasty and very persistent rash that then had developed at the location of the electrodes.

What type of rash was this?

I had not worm the electric arm so many times since that, and actually not worn any prosthesis for much of the time then.

So really the cause of the rash were the electrodes. Here is a photo from December 22nd or thereabouts.  Liner put on and rolled back to show location matching electrode location.

So, what on earth is this?

The causes of this are not totally understood but the fact is, that electrodes on skin may cause serious rashes [1, 2, 3] (see that literature also for further references):

• With skin electrodes, the density of the electric current may be increased to a degree where tiny gas bubbles may occur.
• Subsequent chemical changes in acidity under the electrode surface may yield free alkali or acidic radicals to destroy the insulating epidermis, locally reducing skin impedance.
• Thermal aspects are not proven to play a role but cannot be excluded.

Myoelectric technology thus can be said to damage its own (sole) mode of functioning.

In other words, it is self limited by technology.

The existence and causation of skin damage and rash by electrodes as such is not even disputed. What remains unclear is the detailed mechanism. The result seems to be reduced skin impedance which also may explain the difficulty in controlling the myoelectric arm in the weeks after.

What struck me was just how long that rash persisted!

• Alkaline and acid induced skin damages also known as chemical burns will take a lot longer to heal than simple friction rashes.
• So from still having that rash 4 weeks after riding a bicycle, it makes sense to assume a different mechanism behind this type of rash compared to conventional overuse induced liner based friction rashes as we know them so well.
• This is a difficult bitch to beat.

It remains unclear to me, just how extensive the sweating has to be in order to induce this type of skin problem.

But my prosthetist confirmed that I was definitely not the only one with this, and, that they had no idea what caused it.

As I already stated: anyone that insists that me wearing a "bionic" arm (which is typically done in an explicit or implicit assumption that one way or another that makes me (appear?) more "human") fails the Voight-Kampff test.

But, to just go and wear prosthetic arms, particularly myoelectric (and particularly there "bionic") arms, may really be a bad idea, if exertion, heavy use, frequent opening and closing activity or sports was what one had in mind. Quite possibly, electrode design plays a role as well.

Testing myoelectric arm components in particular: the wider picture - towards discriminating myoelectric arm demonstrations with actual usage approval (AUA) versus well intentioned but failure under continuous deployment (WIFUCD)

Here, we have the interesting and very relevant dichotomy of demo/test/show effect versus real use.The people in the ads usually pose for the company, and they then put this out as "advertising". They probably never meant the prosthetic arms to really be worn for actual biking. They just wanted to hint at, intend, pose, wave, gesture, or symbolize. Of course this is great! It elevates the mood.

However, the demo/test/show hint, intention, pose, photograph can not be distinguished by the occasional web viewer from actual usage and actual usage approval (AUA). With this I will want to introduce the AUA label for actual usage approval: only stuff that provides sustainable support as confirmed by an independent power user will be able to bear the AUA label.

Contrasting to that, we can label activities or usages that pass the demo but do not hold up under real use as "well intentioned & failed under continuous deployment" (WIFUCD).

Some of the currently published and even hyped up myoelectric hand advertisement activities clearly fall under the WIFUCD label, as they use extensive show casing whereas later you may face realities in your real life that are not just as glorious as these happy glamorous paradings arounds.

@article{besio2010effects,
  title={The effects of concentric ring electrode electrical stimulation on rat skin},
  author={Besio, W and Sharma, V and Spaulding, J},
  journal={Annals of biomedical engineering},
  volume={38},
  number={3},
  pages={1111--1118},
  year={2010},
  publisher={Springer}
}

@article{ma2011electronic,
  title={An electronic second skin},
  author={Ma, Zhenqiang},
  journal={Science},
  volume={333},
  number={6044},
  pages={830--831},
  year={2011},
  publisher={American Association for the Advancement of Science}
}

@article{patriciu2005current,
  title={Current density imaging and electrically induced skin burns under surface electrodes},
  author={Patriciu, Andrei and Yoshida, Ken and Struijk, Johannes J and DeMonte, Tim P and Joy, Michael LG and Stodkilde-Jorgensen, H},
  journal={IEEE transactions on biomedical engineering},
  volume={52},
  number={12},
  pages={2024--2031},
  year={2005},
  publisher={IEEE}
}

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