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Required specifications for next generation myoelectric prosthesis

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Required specifications for next generation myoelectric prosthesis; published June 23, 2009, 20:45; URL: https://www.swisswuff.ch/tech/?p=187.

BibTeX: @MISC{schweitzer_wolf_1574274959, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Required specifications for next generation myoelectric prosthesis}}, month = {June},year = {2009}, url = {https://www.swisswuff.ch/tech/?p=187}}


The issues that a next generation myoelectric prosthesis must solve can be listed and they can be listed easily. They are important and relevant nevertheless.

  • Compatibility with myoelectric wrists. A next generation myoelectric hand is compatible with the most available motorized wrist. That may be a recent Otto Bock wrist. The iLimb can be fitted on that type of connector as well - and so that may make sense. But the wrist unit must meet certain criteria - see the folllowing point.
  • Compatibility with sockets and pin systems. I have an Ossur Upper X standard (not customized) liner and these are under rather heavy usage. I use an Ossur Icelock 700. That system is extremely comfortable and stable. Other systems are neither extremely comfortable nor extremely stable. And I do l classify as very heavy duty user. Once I carried a bunch of moving boxes as part of my everyday activities. The pin lock started to wiggle - but all that happened was a screw that had come lose, and it was fixed rather quickly. Furthermore, these parts are rather affordable to repair or exchange. I go through about two to three of liners a year. In order to allow me to keep using both the liners and pin lock and as my residual limb is relatively long, it is a very wise idea to build a wrist that allows a pin to protrude through it and to allow a standard liner to be worn while allowing the prosthesis to be fitted at a correct length. One option is to cut out holes for electrodes. Another option is to switch the prosthetic motor using cable control. A third option is to develop a myoelectric liner that picks up signals from the whole stump and that allows the software to partition, employ or ignore different small regions of signal input; that would obviously be the best solution. All are sensible and practical solutions. A prosthesis that can be mounted perfectly comfortable and perfectly stable is nothing I will ever trade in for less. If you are a constructor and miss out on this issue, I guess you won't sell more than a few units worldwide ever. In short, without a wrist unit and hand that allows Ossur / Icelock pins or similar systems to protrude into the wrist, it may be hard to sell too many of these. Conversely, I know for sure that substantial failure rates of prosthetic setups - i.e., prostheses that are made and sold to the customer but that are not worn - are caused by very uncomfortable hard sockets. Also I know that the problem of these hard sockets exists since over two decades now and if an industry wants to sell high tech, I really wonder how much old shit we actually have to put up with.
  • Clearly declared specifications. I miss clear and physical specifications, measured boundaries, in most current prosthetic parts. These are often omitted to camouflage the fact that really we are dealing with technically cheap constructions if we are honest. A next generation prosthesis will have to be well defined, and the term 'well defined' includes technical specifications.
  • Alternative power supply. My cell phone may be a chunk, and the Symbian that runs on it may not be the latest operating system. But Nokia did two things right when they built it: they included a standard 3,5mm headphone jack and a mini-USB 2.0 jack. My cell phone can mount its file system anywhere, transfer images, videos, text files, PDF files or music from and to any computer, be it Mac OS X, Windows or Linux. And I can plug any headphones that have this standard plug. - For a prosthetic arm, I want to be able to use a power supply that I can buy anywhere. If eight standard AA 2700mAh rechargable batteries can do the job, I want to be able to use these. The system cannot cost an arm and a leg and then m,iss out on clever and available solutions for power supply. Also when I forget or run out of batteries and I am abroad, or when I want to have four sets in different locations, I am not interested in yet another proprietary solution. Not using standard power supply options is simply stupid and because proprietary money making is silly, I regard it as bad business. Currently, an Otto Bock recharger costs about 700 bucks, and a battery costs about 500 bucks. Together with Otto Bock's lying about the precision of their bolt diameters, I am not sure such business attitudes deserve so much financial attention.
  • Accessible software. I will buy a next generation arm if - and only if - the software is stable and accessible. If you want anything in surplus of 8'000 CHF for a programmable prosthesis that I pay out of my own pocket, that thing has to be more fun to program and to optimize in terms of grip patterns and functionality than Neverball, more fun to play with than a Celsius V830 Linux workstation, and more fun to play with than a comparatively priced car.I am very well able to compare cost/efficiency relationships in information technology. If that thing is company locked, company protected and if the functionality requires me to travel each time I want it tweaked, no fun.
  • Accessible or exchangeable hardware. The hand will ship with a repair kit. It just will. I want to be able to do initial troubleshooting myself. If not, there will be a replacement hand contained in the package that I can use instead of the damaged original one. If I see stingy behavior when it comes to my own redundancy requirement - and as amputee one has certain redundancy requirements - then I am definitely less likely to be interested.
  • Hand contains a standard shape and size, and it allows for affordable protectors. I accept that I have to pay some 450 CHF for a Regal Prosthetics glove to get my hand to look realistic as a hand. But I also need the option to protect the hand during heavy usage for much less money. I need the option to really go through material here. If the hand has a standard shape and size, I can use industrial work gloves and be alright. The current prosthetic hands often are weirdly shaped so finding fitting gloves can be a problem.
  • The price of the hand will reflect its value. I am disabled and quite visibly so. While I am getting used to that, I find that non conventional solutions may work well - my goal is not so much to have a hand back - seeing how unrealistic such an expectation would be - than it is to be happy. And happiness can be achieved differently.And you as prosthetic manufacturer have to realize that insurances will become more reluctant to pay, insurances will have increasingly less money, and disabled people also will work on getting society to accept visible disability better. You will have to realize that money can make people happy in a variety of ways, and you will see that as upper extremity amputee, reliability and practical functionality cannot be overrated. No wonder there are academic papers that show that on the long run, body powered hook users are happier than people using a myoelectric arm and people using a myoelectric arm with a conventional hand are happier than people wearing a hand that employs an adaptive grip. Why is that? Because reliability is far more important to feeling happy than gadget manufacturers understand. No wonder that amputees themselves appear to build relatively stable (and not primarily complex, unreliable) prosthetic parts.I am currently in my second year of getting used to wearing one of the most stable hook/hand cable controlled prostheses this planet has ever seen - and other people also work on getting their setups optimized. And, boy will I be spoiled. That is what you face in terms of challenge.So for 3'000 bucks per piece, I'll probably buy two or three of your hands. For 20'000 bucks, I will be very serious and critical with your product and maybe buy it, or maybe use that money to travel or buy something entirely differently. For 50'000 bucks, you will either sell me an Artificial Intelligence Dream product that is better than everything Bosch has in store in combination with everything neural network learning has produced as programmable setups - or that money will definitely be invested elsewhere. And for 100'000 CHF, the hand will be absolutely perfect in every regard, including sturdy service free action for some 10 to 15 years. And depending on how I feel about it, I may come up with my own pilot project as even just fiddling with a part creates a sense of healing, feels therapeutic (Otto Bock indeed recommended ergotherapy for me).
  • Grip patterns. It is nice and sweet to emulate human hand grip patterns using a prosthetic hand. But if academic papers and asking amputees both will tell you that a hook is better for a lot of work, then there may be a reason. Without a good answer, one should not discard such clear information. The main reason I see is that operating wrist and hand with all degrees of freedom can be cumbersome, strenuous and really unnecessary; instead, a sturdy wrist unit that allows for rotation and a terminal device that places the grip shape and pattern in the position that is used most often allows for a far more relaxed usage. The hook does all grips I need including pinpoint push action such as typing or light switch operations - I can type without overly stretching elbow or shoulder. So the answer is how to make life easier for amputees - not how to make something non-disabled people believe makes life easier for amputees. Grip patterns for prosthetic hands need to solve everyday problems of amputees - and that takes into account a stiff or restricted wrist unit and a possibly restricted elbow motion. That is why the hook claws are so useful - their shape at least partly fixes a problem that arises from restrictions higher up.
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