So, apparently I had been "identified" as a "super prosthesis user" by a group of researchers. And I was invited to talk about embodiment in context of the "rubber hand illusion" at a user interface or robotic control workshop [link].
- So is that what I am: a "user"?
- Executive summary
- Prosthetic arm holding up, working and comfort as well as function
- Prosthetic arm comfort
So is that what I am: a "user"?
- Not that I was identified as a particularly inventive designer or inventor, as somehow, that part had gone past them. I mean, I am not wearing just any type of arm now, or what was it they were reading on this web site. Was there something to consider here, here or here? I spent the first three years of me wearing a prosthetic arm investigating all kinds of issues, ending up improving critically failing parts of my prosthesis so it would hold up, work and be comfortable. And I got official ethics approval for testing my own prosthetic arm stuff on the job as well - after all, there are interesting questions of responsibility, outside pressure and expectation, and informed consent, in any situation when using new inventions and devices, also on one's own. This might be more dangerous conceptually than anything else, so my butt is covered.
- Also, I was not identified by these researchers as a inter-actor and person to work out solutions with others, that also seemed not to have caught their attention. Did they think I invented, built, and made everything all by myself? I had great support, there were and are great cooperations, but I went looking for these, too.
- Definitely, I did not get identified by these researchers as someone with a degree of persistence, which is outright weird, considering this web blog. I would really believe of myself that I am of relatively average intellect with regard to my environment, but extremely persistent - but, what do I know. In this case of my prosthetic arm, curiosity was good to have, but really, persistence killed that cat.
- Certainly, they did not identify me as analyzer also of the arm amputee predicament [link]. Cold analysis of the wider context of technical development is a real asset. I may have to tell you about it some other time.
- And what I also did not understood was why they did not identify me simply as someone that complains a lot. Because, really, that, I did, and that, I do. Somewhere in the five stages of grief, Kubler Ross probably put complaints and disappointment, like, when I as an arm amputee was grieving why society cannot build good prosthetic arms for us, and why social value and selection mechanisms always favor trash over gold, circus over development. For any good reasons maybe, but still, I could have just kept my mouth shut all these years. Like everyone else. So, how could one not see the obvious and identify me as that? Would it be too impolite to write to me, "Dear Sircomplainsalot, we have recognized your efforts, kind regards, the researchers"? Is this a politeness contest?
- And certainly, they did not identify me for my hard real work efforts. Even though the whole point of going after better prosthetic arm technology had almost always been to enable me to perform real work, to perform strenuous tasks, to perform stuff that is intrinsically hard. So I cannot say I feel properly and authentically identified as what I feel I am, and as what I should be recognized as.
Of the real roles I filled, to get me where things are today, "user" is certainly by far the most passive one. A user uses what is placed in front of him. His main occupation is to consume, to apply, to employ, to use an apparatus others devised and built.
- Is "passive" the role researchers see me as because that is were they hoped I would be? Is me having to be passive to conform to their expectations an aspect deeply buried in the stereotype of the driveling, naive, subservient and totally compliant arm amputee others may have us nailed down as? I am not making that up - a number of very differentiated and reflecting people told me that was going on in their heads. So we have to look out for that one: who wants us passive? What does it help society if we - arm amputees - stay passive? Where does that come from, and where does that go?
- And I can tell you, you not pass to this choice of menu chart style identification ("I identify you as (A) seriously active person or (B) ... - "B") without at least a comment from me. I did not "just happen" to use my prosthesis more fluently than others. That path had been paved with really good intentions, all of whose fruition was seen to their very end. It was not just a trail of tears and blood - it was far more than that. At times the process of obtaining a prosthetic arm that actually was minimally worth wearing at all, that felt like manually dragging a dead cow over the Piazza San Marco all by myself, one armed and all - but then, I should have mentioned that I was not afraid of sweating [link].
The questions that I had been asked in that "capacity" as "super prosthesis user" by these researchers were:
- what makes a "super prosthesis user", in terms of the individual differences of the wearer or amputee's brain and mind,
- do these prosthesis users cognitively represent their prosthesis more as a tool or as a body part? We certainly wonder that also for this user of Touch Bionics technology, who put this image on the Facebook page of Touch Bionics, where it represented, officially, what these people probably think of us. Meantime, we wait for an answer to whether Touch Bionics also cognitively represents, generally though, patiently ...
As I had recently participated in other research, where extensive interviews and reflection regarding these issues of embodiment and their relation to prosthesis design had taken place, I feel that these questions can be answered as that: what do I do differently from others, which then ends up with me using my prosthetic arm a lot more fluently? How does being an inventor, cooperating with others to achieve better prosthetic function, being persistent, complaining and trouble shooting, all fit together?
First of all, these question actually border on becoming dangerously relevant, when one asks back: where are you, the researchers, going with this?
- Because currently, researchers will argue that, for example, electric feedback for a prosthetic hand is quite necessary, ultimately so they can get more arm amputees to actually wear their contraptions and believe these to be their own body parts.
- Now, they just may not know what they are talking about. But then, I do: from a study [link], where I had diligently and subserviently participated a few years ago, I know for a fact that nothing (and I have experienced a range of issues in that direction) ever had escalated my phantom pains as much as that experimental sensory feedback ended up doing. It was pure hell on earth for a short bit. I would pay extra to not have that, and so, please do not make us do that. If at all, make the hundred fold amount of that money that I will have to pay to not get electro-feedback-ed tax-deductible. Thank you a million times.
- Furthermore, there is a certain risk of people trying to hack our brains to make prosthetic arms seem part of our bodies and thus indispensable: objectively, clearly, and with ice cold analysis, many commercially sold components and prosthetic arms made from them, they are simply put pure crap. That, in short, is the painful reality. As user, may have to have a very good explanation to not reject that crap. As engineer, one needs a really good legal service that protects the wording, the newspeak, the use of "bionic", the application of the CE-label, all that - as "legal" is not always the same as "just". To say that one makes a prosthetic arm "better" also is one of the most repugnant euphemisms in that context. The real wording will have to be that one attempts to make a prosthetic arm "less objectionable". In that context, I may have to send the developers and researchers back to the bench for a complete re-do - not of the understanding of how our brains can be tricked into accepting crap into our body schemes, but, for a re-do of the build, make, design aspects, of currently made and sold prosthetic arms. If the engineering passes all objective criteria of a prosthetic arm holding up, of a prosthetic arm working, and a prosthetic arm being comfortable, then I will agree: if then, >85% of arm amputees still reject that type of prostheses, we probably would like to check the brains for possible signs of common sense. However, with extremely rare exceptions (ha ha, that is why you came here really, admit it), these prostheses do not exist yet, definitely not on the free market, and most definitely not in relation to some very large manufacturers' component portfolios. So the risk is that these researchers want to smuggle crap past our crap detectors and with arm amputees having no lobby, that really seems a big problem. Ultimately, they probably will try to outsmart our naturally grown intelligence with artificial intelligence, and I will say, that could well play out as statistical game. Enough mysteries around to guess that. Enough said.
So: with relation to embodiment, where *am* I standing?
To become what these people euphemistically termed a super proficient prosthetic arm user, these aspects helped me:
- I am certainly a person of just about average intelligence, which means, average, when comparing myself with people that are just a bit like myself, or, when I look around in my immediate environment. As all things are relative. So within my own perception, I definitely never felt that I was anything extraordinary. Others sometimes cognitively understood things not so fast, that I had understood faster, mysteriously so, or, they at times cognitively understood stuff faster than me. Generally, a lot of people appear to be just a deep mystery to me, unless they explain themselves though, unless we can talk things through, and I always figured, that was life. One does not need to understand the mysteries of everyone else though, and so, if necessary, one really needs to talk. Other things are not a mystery - so, why does the armadillo cross the road. I tried to do good, and I made efforts and such. But then, I am sure, that I also could do better, even significantly better, by investing myself more. But I do get around to stuff eventually. At least as far as I see it, there are no research issues in the subject domain of embodiment along any line that have relevance to the question what makes a prosthetic arm really useful. We all have our views, thoughts, insights, weblogs, inventions, papers, ideas that are unpublished and ultimately, a goal where we want to go. And I am happy, in the context of this website, if we are after building good prosthetic arms first and check what that does to us mentally later. There is a clear priority and sequence for you. So, how are you today.
- The absolutely extraordinary aspect here is that my prosthetic arm holds up, works, and is comfortable. That, dear friends, in this day and age, is entirely outrageous! These terms - hold up, work, comfort - are actually impossible to achieve for mortals and thus entirely impossible to understand for outsiders, and they therefore would require in-depth explanation. You can perform fMRI scans of my brain until the magnet melts and never get a clue as to real realities there. So, isn't it so great that there are all these cheap web posts here that you can read. The fact that my prosthetic arm now actually delivers these attributes is far from clear, expectable or understandable if one at all knows the details of just how prosthetic arms are made, come about, how companies that build these arms work, and how social or financial aspects relate. The reason I may have come closer to an ideal prosthetic arm to wear is that I saw through these factors through focused investigation, and that I identified actual solutions. Anyone that is a bit like me would have done the same, in a flash - so nothing extraordinary on that front.
- Having a really great prosthetic arm - one that holds up, works and is comfortable - does not, per se, guarantee that one also masters it. So, I then wore and used the prostheses for such an extended amount of time that wearing it did, in fact, to a degree, become second nature. I wore it for some 12 to 18 hours a day, for weeks and months and years on end. I defined dedicated "hook zones" where I would force myself to always use the prosthesis, no matter what. Of course that is similar to commanded drill exercise, and that drill exercises work is certainly a statistically established fact - mostly a bit better with contextual interference as it appears (e.g., [bibcite key=gal2011preliminary,hasson2001training,ollis2005influence]. Really, there are just a few training principles that I did use, that are far simpler to understand than one would ever wish for. At least, I was able to understand them. I just figured out that it was best I applied myself. And I did not even invent any idea there myself: one of my physiotherapists had said, get a body powered arm, and wear it a lot, for at least five years. Isn't that simple and bleak. There is also beauty in an empty desert. I can understand that this may be a bit too bleak for you, so you may be more the philosophical type. There, one of my favorite quotes is by Mark Rippetoe: "There is never an absolute answer to everything, except of course that you have to do your squats". Still bleak, but, philosophically bleak. So I probably improved usage without apparent training structure, on the job, wherever it was, with whatever activity there was to do, incessantly, all the time. Of course my hook is as embodied as any tool can be. My brain uses it automatically, it has done so as early as six weeks into having one, why, because the fit was not too bad already then and because body powered control is seamless, snug, integrates itself quite fabulously into a dynamic brain that revels in motion, where muscles to open/close the device are practically disjunct from the ones used to position or move the arm - which has not been studied yet by the masters of disasters.
So, that really was straight forward. Again, even shorter:
- Life is too short to make exceptions. So to go, and to apply oneself.
- First, make the arm so it holds up, works and is comfortable.
- Secondly, wear it all the time and keep wearing it, so you get used to it eventually - which is super easy: why would anyone not want to wear a prosthetic arm that does what anyone could ever wish for: hold up, work, and be comfortable?
Apparently that is not obviously not obvious, so what are the secrets?
The thing that does set my prosthetic arm that I use mostly (a body powered heavily tweaked thing) off against the large rest is that I spent 3 years harassing, bugging and developing. Not a single other amputee that I know or know of tweaked a promising technical setup to its absolute perfection.
The result is a build that is heavily customized, and it does a few things far better than anyone else has it:
- my wrist adapter is relatively sturdy, as it does not wiggle; wiggle makes you crazy and you stop wearing a conventional commercial wrist after a while, if not for other reasons then due to mental irritation;
- and so my prosthesis and its wrist withstand vibration; if you ever type papers for deadlines and so on, you know what I mean, the hook of the prosthesis also hammers on the keyboard, and after a few millions of hammer blows most wrists fall apart - so my wrist connector definitely must be up to that; we built one that withstands that;
- my normal body powered cables fall apart after 4-10 days only, and that it is a massive deterrent to wear a prosthetic body powered arm with subsequent actual use for gripping; I put an own invention on there that is a new and clever mechanical bowden cable setup and so no wonder no one else has it: it makes cables last with minimal friction for > 9 months;
- my prosthetic arm really is comfortable to wear, also the shoulder "harness" does not compress the brachial plexus, and with that shoulder anchor we built comes ...
- ... shorter control motion, so also there the arm is tweaked to maximum comfort.
No one knows that commercial stock part derived body powered arms suck, and, all do not have these features. Everyone believes these to be old and shitty and crappy and such. So no one can wear and use their arms like I can - and it is not my brain that is superior on controlling an otherwise crappy device: the thing I did differently was turning established principles (body powered technology, Bowden cable setup) to manufactured, real, tangible and wearable technical perfection. What it took for that was the realisation that body powered arms as is, as sold by commercial providers, only build on a solid principle but their parts manufacturing at times is real crap. This is different from myoelectric technology, where both control principle and manufacturing usually are crappy and thus represent a control paradigm that is beyond hope.
I had set priorities and standards, and because I worked very hard to implement them. Not sure if researchers looking for super user capabilities are after that type of brain: if anything, there is not a whole lot of gullibility there, and for anyone trying to sell crap, that's a big minus.
Prosthetic arm holding up, working and comfort as well as function
Withstanding pulls and vibration
This usually damages the wrist unit, and its connector or adapter part.
Pulling on a body of 60-90 kg weight certainly is a very hard test for prostheses where the manufacturer claims they are "robust" but not to perform "rock climbing". If you analyze this carefully, in both instances is a partial body weight lifted and in both instances must there be no grip problem or drop. But: they never understood that - which tells us a lot about the "engineering" they put into these wrist connectors.
Lethal (for the wrist) vibrations start with typing, serious typing, over days and weeks.
Or riding a bicycle.
After a few weeks a commercial wrist such as by Otto Bock will start to wiggle, which is extremely irritating.
Then you may eventually apply for a new wrist.
Until you get a replacement from first moment of irritating wiggle, 3 to 8 months go by.
So, most wrist units really suck simply because for the time duration that you own them, they just wiggle most of the time. Not to speak of myoelectric wrist connectors that are not able to sustain any real work (euphemism for what large prosthetic companies call "total abuse" while advertising their own body powered hooks as "robust") anyway.
So the build and make of commercial wrists is typically insufficient. To a degree where one cannot comfortably wear the arm under full work load.
That is why we built our own quick lock / ball lock wrist unit.
Summary: Pulls and vibration summary: because prosthetic connectors and parts are often not built to withstand substantial pull forces or vibration, a very negative experience may result from typical commercial parts.
The problem was solved with:
Gripper build quality
Commercial prosthetic grippers often have very serious issues in terms of sudden or graceful degradation. If they are not built to fail, then, back to the bench. Their mechanical failure is a reason in itself to stop chasing after a prosthetic arm.
- One particular Otto Bock hook would jam or un-jam depending on ambient temperature.
- Another one, the Movohook 2 Grip, would start to wiggle in the base joint because of absent ball joint parts and just metal grinding on plastic so we put in brass inlays.
- The iLimb software would just not start.
- The iLimb cover would die all by itself - with a totally unproductive customer service dialog that I had to invent yet another own solution for that.
- The iLimb precision grip is not a precision grip really.
Why the Swiss Federal Technical University tried and successfully succeeded to visually expose some of the current technical commercial shortcomings of myoelectric "bionic" prostheses in full public television, without immediately afterwards fixing the obviously embarrassing results, still is not totally clear to me. Also, how they got the victims of that great show circus prank to even pay substantial amounts of money for getting exposed, certainly will go down as a masterpiece in negotiation with people with disabilities.
Sloppy construction and low build quality is attributed to construction. At the same time, low strength and construction blends into functional design, where grips may fail because a particular grip, geometrically, technically, is ill devised for a given situation.
Gripper build summary: because of an almost built-to-fail quality for many commercial prosthetic grippers, a very negative experience may result.
So a careful choice of grippers is important.
I made good experiences with:
Control reliability and durability
Cable control if built with conventional stock parts and cable materials may cause cables to tear apart within as little as 4-10 days.
- The cable deflection around the body was at fault
- The cable mount anywhere on the prosthesis was also a problem
The effects of that are somewhat curious to many. They may be perceived as very, very boring, if you spend a year getting repairs as that: every 4-10 days you need another appointment for repair with the prosthetist. That may take 1-2 weeks. So you wear the arm for up to or more than about 1 week and are out of work for 2-3 weeks in total, until you have it back. So overall, you can wear the prosthesis for 4-5 days a month, and then you provide a lot of collateral service to that arm. I thus had around 45 prosthetist appointments in 2 years, each about 3 hours of duration or so. You can fMRI all you want but that? That's a fucking joke.
If you cannot clearly imagine what it really, emotionally and technically, means, for the bodily integration of a prosthetic arm into your body scheme, that the thing dies, "destroyed in seconds", from 100 to 0 within seconds, all the fucking time, and no suitably urgent repair service anywhere near, then read our paper where it is described more cleanly and without the use of vulgar words, with all its consequences. You spend so much time in the repair shop that them not having free broadband internet inside these small customer cell like window free rooms is a first reason one vows to get one's butt out of there, for good.
Many people will then only use their prosthesis on a significantly lower physical level, on a lower level of loading, as also, research currently is unable and unwilling to consider real forces or torque as part of what they consider necessary to inform better design. We thus cannot expect the insufficiently built components to go away anytime soon.
Only correctly mounting the cable will remedy that. I performed this, as first person on this planet for the benefit of body powered prosthetic arms, with a new development. It took me one afternoon with focus and dedication to invent the better solution, an evening to build a prototype on my bench, a week to convince the prosthetist to build my prototype as final version, and a few years to amend the text so I could get the patent office to accept my submission.
Myoelectric control is not built to function under real work conditions to begin with. It stops working once sweat sets in. Also, limb positioning effects and other such effects cause 75% of users to experience involuntary or unintended malfunction of the myoelectric device regularly, routinely.
Lifting the arm at the elbow will cause the tickets to drop even though no intention to open the device was present, and no voluntary "open" signal was given. More here.
Control issues summary: controls fail due to bad build, or bad concept, and this gives a really bad experience also because if performed in public, it is very embarrassing.
Solution here was this:
- Focus on using body powered arm as there, control issues could be solved
- Build and patent own curved flexible cable deflection to extend cable survival
All that said, adequate gripper delivery competes with not wearing a prosthesis, which is not acknowledged by industry or research on any level.
A systematic evaluation has been performed and a few grips of importance for further development were identified.
Technical testing of grip functionality can be done for any specific situation:
Grip functionality summary: grips fail due to bad concept, and this gives a really bad experience also because if performed in public, it is very embarrassing.
- Focus on reliable grip geometries
Prosthetic arm comfort
Myoelectric prostheses may cause burns due to electric issues (below).
They may also cause blisters due to mechanic issues (below) this is a picture after typing for about 10 hours with a myoelectric iLimb. The blisters took about 1-2 weeks to heal.
Comfort summary: prosthetic socket "comfort" is a must-have, simply because down-times with always painful stump skin injury force the user to become more proficient without the prosthetic arm on, which (in context of the other significant problems) can be a real eye opener to the other alternative reality where "the stump *is* the best prosthesis" (R. Baumgartner). Actually it often really is. If you cannot afford down times of electric burns (4-6 weeks to heal) or friction rashes (1-2, sometimes 4 days to heal) you will need a comfortable body powered socket with edge free carefully layered suspension.
- Wear body powered arms more often as they do not have socket fit and internal edge issues, and there is no electrode burn
- Wear fitting soft liner and tubular gauze underneath and proper stump skin care
Shoulder harness of body powered arm
The factory issue conventional figure 9 harness is also an ill devised design that is bound to cause problems in the long run. Do not worry if you go WTF right now - you will find out eventually. If you do not solve that problem, you may restrict grip force and neurological function significantly.
After I had established that the neurological problems of double crush injury with overuse and brachial plexus compression were a consequence of the figure 9 harness strap design, we got the insurance funding for a shoulder anchor that would take my body powered control a lot further. The shoulder anchor provides perfect cable control while avoiding brachial plexus compression.
Shoulder harness summary: To allow for maximal grip force with the body powered arm, you will exert force on the harness. The commercially sold Figure-9 harness is usually mounted with a soft shoulder strap. This causes brachial plexus compression with possibly serious neurological problems in the long run.
What happens on other levels
Humanity and the voightkampff dilemma
If you suggest that for any reason, I am more human when I wear prosthetic technology, which when built in the typical, conventional way, very clearly damages me, then you may succumb to a sort of dilemma. This makes you risk failing this as voightkapmff test, causing interesting complications of the whole scenario of us - non-disabled and arm amputees - respecting each other, see here.
To get out of that dilemma, and to prevent you from falling into that trap risking social cohesion, the only way out is that you either build me a prosthetic arm that avoids all the above named serious and grave problems of whose order of magnitude you probably had no idea. Or you accept that I do no wear a prosthetic arm. Or you very gladly accept that I go after building my own parts and, if ever, try to understand what exactly it was I did there.
Gullibility of an arm amputee - lower levels thereof?
Once I wear no prosthetic arm, once I only use one hand for life and living, the average prosthetic researcher or commercial sales person might well have the impression that I am super gullible. Quite possibly, being one handed neurologically enforces a reduction in gullibility, making it extra hard for prosthetic salesmen to sell crappy hand wear. I did not invent this or dream it up: people told me that an arm amputee is clearly expected to be naive, submissive and driveling, happy with all kind of crap that is given to him. Explicitly. In basically these words. And that they were shocked beyond measure when that was not the case.
Unprecedented effects may have been the cause that I ended up building an actually useful prosthetic arm. Interesting, isn't it? It may well be that arm amputation causes gullibility to become considerably less as a totally ignored side effect [bibcite key=christman2008mixed,kaye2013aping]. The reason normal commercial prosthetic parts fall apart is also not because of some absurdly extreme use I apply. A forensic pathologist I do lift people a bit or turn them to examine them, but our body weights are what they are. Stuff falls apart because the engineering that goes into many commercial parts is just really really really bad. Really below all standards. To point that out, sure, I need inspiring degrees of guts because the companies may not react nicely. But funny thing, I apply normal lazy ass standards to building my arm parts, the prosthetic arm holds up then, I can wear it for a lot longer, work as I should, and all of a sudden I am an "inspiration". All I did was drag the prosthetist for three years to the goal line where we all were promised body powered technology would be: at comfortable robust arms. I may be reasonably fit and don't shy away from applying myself but the physical effort that I perform is slightly below what my (bi manual) colleagues do, for example. It could be inspiring was it anywhere near top, but it is just not. So it is not all that outstanding. The swimmer colleagues that trained with me with two hands, the same trainings over a few years or so, guess what, they were just faster. If you wear a split hook, any grasp is already a perfect precision grasp so you simply cannot fail that. If you wear a perfect precision grasp device for a few years and use it all the time, given my slightly above average propensity to suck up motion coordination invariably lands me in an area where I can comfortably use my prosthesis but to be honest, I am not concentrated or focused enough and dream around and some nonsense, so I still trash 4-5 coffee cups a year just on stupidity. If a device such as the new Equilux has uselessly hard pads, making my own with soft silicone using 3D printed molds may come across as "inspiring" but really, I may just be a bit of a nerd in relation to learning new stuff and one of my best friends heads tool development in a large company. So after a Saturday afternoon crash course in solid modeling I started to make my own 3D stuff which is all there is to it. Just google the one or other trick and tada.
To get a prosthesis so one can at least wear it as a part of what one wears similarly to shoes, a glove or another tool such as a hearing aid or prescription glasses, a lot of work was done by me and completed or fine tuned by others after I had started pushing into that direction. That is why I am not a "super user". I just clearly pointed out what I did not accept as commercial short coming and worked hard to solve that problem.
If you now cannot understand how that all is relevant, then, that is where words end. All the best though.
|Pulls and vibration summary: because prosthetic connectors and parts are often not built to withstand substantial pull forces or vibration, a very negative experience may result from typical commercial parts. The death of these parts and their replacement - funding, waiting for total death of part, suffering it getting there - can be unbearable.||The problem was solved with our own development that we patented:
|Control issues summary: controls fail due to bad build, or bad concept, and this gives a really bad experience also because if performed in public, it is very embarrassing. Sweat and other issues that cannot be solved kill myoelectric controls reliably and repeatedly. Bad build kills body powered control parts very reliably as well.||Solution here was this:
|Gripper build summary: because of an almost built-to-fail quality for many commercial prosthetic grippers, a very negative experience may result. So a careful choice of grippers is important. If you are after solving manual problems in everyday life and for work, you want to give this your utmost attention.||I made good experiences with:
|Grip functionality summary: grips fail due to bad concept, and this gives a really bad experience also because if performed in public, it is very embarrassing. Non-reliable gripper configurations are not useful. Stay away if you want to avoid public embarrassment.||Solution:
|Comfort summary: prosthetic socket "comfort" is a must-have, simply because down-times with always painful stump skin injury force the user to become more proficient without the prosthetic arm on, which (in context of the other significant problems) can be a real eye opener to the other alternative reality where "the stump *is* the best prosthesis" (R. Baumgartner). Actually it often really is. If you cannot afford down times of electric burns (4-6 weeks to heal) or friction rashes (1-2, sometimes 4 days to heal) you will need a comfortable body powered socket with edge free carefully layered suspension.||Solution:
|Shoulder harness summary: To allow for maximal grip force with the body powered arm, you will exert force on the harness. The commercially sold Figure-9 harness is usually mounted with a soft shoulder strap. This causes brachial plexus compression with possibly serious neurological problems in the long run. If you do not take this seriously you may not be able to wear a body powered arm any more, and myoelectric prostheses are really not working once you sweat.||Solution:|