Case-study of a user-driven prosthetic arm design: bionic hand versus customized body-powered technology in a highly demanding work environment [article out]


This is a blog post of one of the rare focused and well based scientific journal articles that really explains how real work, body powered and myoelectric arms relate and go together for a unilateral right below elbow amputee in a physically demanding work environment.

The prior presentation of this paper [poster at Cybathlon symposium 2016], which had been more pragmatically worded (with me thinking people would know anyway), this was now written up as article and published. During that process, the reviewers clearly made great points of all kinds of aspects I never knew were not sky clear to everyone.

So maybe, writing a ~ 30 page case study with > 210 references does clarify stuff, at least potentially and for those that actually read it. But possibly, it still requires attention to even just read it.

Knowledge does not come easy, Highlander! (Nakano, in: Highlander III The Final Dimension)

If you are more interested in visionary posts, read about the gadget features of the prosthetic arm in Kingsmen: The Golden Circle [link]. And technically, myoelectric control did have it coming. That technology remained uncool for four decades [link].

Publication [link]

R&D relevance

After this one, R&D representatives now possibly have it harder to say that I have not tried to explain as clearly as possible what seems to be the Big Elephant in the room possibly since the Fifties - why, that is, body powered arms are better than myoelectric arms, which are junk, at least as far as real work is considered. Which obviously everyone that actually wears these knows. The control error rates for myoelectric arms, as published academically over four decades, have not moved a bit towards improvement [link].

Just, how do you tell an engineer what the problems are?


You don't. Normally. The nice thing is, that in true engineering, things are not difficult. Either things run. Or they do not. Instead of Otto Bock's slogan "Quality for life" (which in my experience was more of a "junk for a few days", in some instances "junk for a few seconds / minutes", in others "junk for a few weeks / months"), I found my own approach and mission vision of "Buy Once Wear Forever" far more satisfying from my user perspective.

My meta-point in argument however never was that good engineering could not build good prosthetic arms. But that research, development and the whole academia by and large combined with wrong industry incentives (with only a few exceptions) are mostly resistant to facts, water proof to arguments, and perfectly protected from hard exposure.  And that they build stuff for planet "fantasy" whereas the heavy lifting and sweaty life occurs elsewhere, on planet "reality". Of which these people may not know much. Researchers love it there, on "planet fantasy". They may have a very hard time to accept reality. They mostly keep that a closely guarded secret, so only rarely are we given an honest insight into how their brains work.

Case example 1: In a recent paper (Jaquier, Noémie, Claudio Castellini, and Sylvain Calinon (20187) "Improving hand and wrist activity detection using tactile sensors and tensor regression methods on Riemannian manifolds"), we read the incredibly poetic sentence, "Despite recent advances in externally-powered prosthetics, intuitive and robust control of polyarticulated prosthetic hands and wrists by amputees remains an unsolved problem, mainly due to unadapted user interfaces and inadequate sensorization. Despite remarkable advanced in this direction, a full, clinically accepted application still has to appear. The recent results of the ARM competition of the Cybathlon, won by Robert Radocy of TRS Prosthetics wearing a body-powered prosthesis, stand as a powerful warning for the scientific community" [pdf]. The Cybathlon being won by a body powered arm was a given, they had that coming. Tell me, how can the victory of pure engineering beauty be a "warning" to an engineer?  Can anyone explain how this is a "warning" if at all you are the one that hunts for exactly these solutions, and how is that victory not just a clear answer as to what device works and which one is junk, excuse the bluntness? As this website verbalizes increasingly, the  material facts are clear - it is the anatomy of the powers and the people that populate this that are behind why we have no better prostheses than the ones we have. With 70 years of successfully avoiding to build a prosthetic arm that successfully hides the handicap, we will assume intent and plan. The amputee must remain visible, an unspoken research plan successfully acted out by what types of people? So, trying to be loud is not always advisable. Because too much of it then raises the question of who is behind this apparent nonsense. Who are we dealing with here, may really not be engineers, like, the real type and sort, with engineer's blood in their blood vessels, the ones that make stuff work, the ones that look at what works and what does not and goes Oh, That's How A Prosthetic Arm Is Successful and moves on into a logical direction. Conversely, I must say that it is a bit cheeky when I state this - because anyone who adheres to the myoelectric paradigm for too long needed a really good excuse to begin with, because that stuff cannot be coerced to work under real life conditions. We knew that since a very long while. We tried hard. We tweaked our butts off. We threw considerable money after it. We have the right spirit and we failed. And who knows, that could be a warning too ; ) "Do we have to repeat every mistake others made? - Yes, one can learn from mistakes". But this is not a website for intellectuals, otherwise we'd experimentally place adherence to failing engineering attemps past Riding the Dead Horse into the realm of modern interpretations of postbaptismal concupiscence to see where that gets us, and while that path now definitely seems extremely intriguing, I am afraid it won't fix them prosthetic grippers into submission right away. On second thought, exactly that just may ; )

Case example 2: Once a sophisticated hand model with sophisticated gesture control was finished, a pre-alpha-version of sorts, and the engineer that had built it told me, while I wore it as a test in his office, that it would totally hold up. When I grabbed a cup of water and steered to hold it over his laptop or keyboard, he went "whoa". At that moment, we all understood what had happened. The moment of truth in engineering had come. The product will work fine as long as the amputee ruins his own laptop computer, but if the engineer's laptop computer is endangered by the very same situation, different tolerated error rates. If you read the referenced paper here, that we wrote, the error rate part was deeply inspired by that moment of truth. Because there are moments of truth, and these moments will tell the pure engineer whether it works or not. Of course, it is not always easy to try out, experiment, test, accept failure, so reading about such can speed up the process of understanding if at all one is into reading. But to anyone that doesn't get it, I will suggest to simply cut their hedges, with a heavy motor saw, in the full sunny summer heat at 37 deg C, for two or three hours, wear a myoelectric arm, see what happens, and then consider whether reading would have been cool. Sometimes, even rocket science is not rocket science. Instead, simple primary school level methods prevail. "Do your homework". "Read".

Prosthetic technician relevance

It is a fact that prosthetic technicians usually make substantial financial revenue over the percentage they charge on hardware.

From that, the average prosthetic technician that looks after their income will have a vital interest in prosthetic devices costing a lot, in insurances paying all these devices, in being able to sell more costly devices over anyone's lifetime and in having amputees that manage to play along with a subservient smile. That combination can be a real bitch, though, so a real life estimate of at least 85% of potential prosthetic arm users do not wear one. For superbly obvious reasons. And that is also what constitutes our reality.

Case example 1: I went into one prosthetic arm shop here in Zurich to get my cable adjusted.I warned them and said, if you want me to come along to explain the parts to you I will come along. You must not shorten the cable, and if you screw up and have no replacement cable, you have to shorten it, so you cannot screw up. They felt they were so above me that they told me to sit down and not worry. Ultimately, they "fixed" the arm and as they obviously screwed up, they had to shorten the cable. That experience is emblematic for the trade. Amputees are laughed at, frowned upon and not taken seriously.

Case example 2: I had asked Ossur customer service, of which Luis da Silva Oliveira responded, regarding silicone glue, as my Ossur liner fabric always separated from the silicone early into the use. He replied with an arrogant mail writing that "he thanked me for my valuable help" and  he "wanted to avoid to not present my solution back to me". Also he could not name me a price "for legal reasons". He was not a bit helpful. I had asked a question, not helped or provided a solution.

Case example 3: I have so far returned four user questionnaires for Touch Bionics where they promised to send a free glove cover after each of these. I have not received a single glove. The clear promise to send a free glove in return for a filled in questionnaire without sending one is a clearly disdaining treatment of customers; one may not go as far to call it fraudulent, because, since when is the promise of Touch Bionics a contract.

I could go on. The list is a lot longer. These experiences clearly shape our reality. Which does not mean you - as researcher, developer or prosthetic technician - necessarily think that it is good we have these insights and experiences just the same way.

You may think that we should just suck it up. And with that, you may live on an entirely different planet. And while that may be nice there, it just means, that among other aspects, clear communication is not a given. Not that that in itself, depending the angle, would be bad either. Not all reporting of bad devices across planets makes for immediate betterment of society. Sometimes it may be best to shut up and suck it up. But not always.

And so as one relevant example for this interesting tension field, I also have correspondence of two large global prosthetic component manufacturers that both told me to get occupational therapy after I had alerted them of some of their device malfunction or crappy design features. What appears to be an utterly absurd reaction of what could have been engineers from my view, may be seen as a totally sensible answer from view of a commercial manufacturer that has zero interest in fixing the device. Their customer representatives appear to lack both respect and training. Then, if all you have is that type of hammer all we need is a nail - and no wonder they believe that all that needs fixing is the attitude and the mouth of the user. They quite simply lack all that is needed to solve this differently.

If however you directly depend on selling me expensive crap very often, you will be only successful if you manage to successfully manage my clearly voiced expectations. To better sell bad cars you need to be a really good salesman. And don't we all know that on average (with exceptions), prosthetic technicians, or researchers and developers, are usually not good sales people. They promise, but do not deliver. Instead of being persuasive, they will try forceful methods. They will be respectless, confrontative, aggressive, and talk from top down. Overall their situation is difficult because the parts they get are not always great.

They are stuck in a skewed incentive situation with crappy products, all of which are too expensive. As prosthetic technician, one could try to lobby towards a better cost or reimbursement structure. However, it is also cool that the leading OANDP Edge decided to better not include reference to our new article (below) in their January 2018, after they had been friendly enough to publish it on their website. We can safely conclude that at this moment, the industry regards this paper as a clear threat.

And an industry that regards a very cost effective, robust and functional customer user driven prosthetic component solution as a "threat" rather than a great example of how it is done, is not an industry we can generally and safely accept as supportive from a user view. That is a parasitic and hostile industry (and yes, there might be singular exceptions). From a user view, not everything that is cheaply copied, that wiggles at first serious touch and that, when considering its low function, still costs too much, is cool and great. And so the question of exactly who does exactly what there and exactly why becomes more relevant.

And when they see a clean, insurance approved, and insurance funded, robust engineering solution as a threat, we are not dealing with prosthetic technicians that have a pure interest in seeing arm amputees thrive under heavy work conditions. That behavior then also very clearly is outside any normal boundaries and warrants more problematic investigations into loss of authenticity, loss of self coherence and ultimately, also a search into possible conceptual errors of the magnitude of postbaptismal concupiscence.

User relevance

Yes : )

But not all arm amputees want to perform physically demanding work, such as heavy lifting, farming, or such. Only those that do will be delighted with developments to make prosthetic arms more reliable that way. On second thought, others may find myoelectric arms cumbersome too - they break almost all by themselves nowadays.

Everyone else should hate this, after all, wearing an arm that can NOT perform is the perfect excuse to not vacuum too much, cut hedges too much, or to overdo whatever there is to be overdone. To these I can only say, sorry everyone. But: I came into a world where no one before me had paved the way for hard work. Otherwise I would have ordered the parts, we would have built a functional heavy duty arm and all would have been totally sweet without all this here. So all this here also is the functional consequence of users not making their complaints heard before my time. Blame these people if you must. Ripples of past outbursts of likely postbaptismal concupiscence there as well.

But we digress.



Final draft [PDF].

 author="Schweitzer, Wolf
 and Thali, Michael J.
 and Egger, David",
 title="Case-study of a user-driven prosthetic arm design: bionic hand
 versus customized body-powered technology in a highly demanding 
work environment",
 journal="Journal of NeuroEngineering and Rehabilitation",

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Cite this article:
Wolf Schweitzer: - Case-study of a user-driven prosthetic arm design: bionic hand versus customized body-powered technology in a highly demanding work environment [article out]; published 04/01/2018, 14:29; URL:

BibTeX: @MISC{schweitzer_wolf_1656617814, author = {Wolf Schweitzer}, title = {{ - Case-study of a user-driven prosthetic arm design: bionic hand versus customized body-powered technology in a highly demanding work environment [article out]}}, month = {January}, year = {2018}, url = {} }