Janet and John

Janet and John, discussing my 8-question approach.

Executive summary

The 8 question method to evaluate any prosthetic arm allows anyone to quickly assess the capacity of any proposed or given technology or setup to medically sustain and support an arm amputee.

In other words, we can now answer the question whether we are looking at a viable type of prosthesis from a pure use focused and application focused view, such as my own focused view.

At this moment I will remind you of the title of this website: I write about technical right below elbow amputee issues.

Of the 8 questions that we will discuss and ask in each and every prosthetic arm case, failing the first 7 results in a total hard fail – that means that a prosthetic arm failing any of the first 7 questions is not recommendable from a pure rehab/medical view, as far as my experience goes. So in other words, the following questions 1-7 must be answered with yes, otherwise the test is failed and the device cannot be considered to be worn daily for real work. In my view, any device that fails this is probably not worthwhile pursuing.

Question 8 is a reminder to you that the appearance test so far has not been passed by anyone.

The 8 Questions:

1. Is your device easy to put/slap on and easy to take/pull off, no hassles? [Design]
2. Is the device so it’s skin /tissue interface has no electric parts that could cause burns, and is it so it has no edges/shapes/surfaces that cause any friction, and that the skin stays intact while wearing it? [Testing]
3. Is the device well balanced, weight good, and the grip angles good? [Testing]
4. Does the device by and large perform the required tasks? [Testing]
5. Does the device by and large exceed robustness and stability versus typical maximal use case load, and for how long? [Testing]
6. Is the device so it has a realistic field use error rate under heavy use/sweat of below 0.03%? [Testing]
7. Upkeep easy and cheap and only infrequently necessary? [Long term use]
8. Does it exceed appearance test? Is it at least acceptable? [Ask user]

Doing this saves everyone a lot of time. They are all easy and fast to answer.

Background

A prosthetic arm is to be regarded as a balancing tool first, and a grasp/lift/push tool second, from a medical / orthopedic viewpoint.

Diagnosis¹ constructs the deviant body [in: A Manifesto for the Cyborg Body, Bryn Shaffer]

A medical device is not anything.

To constitute such, it must come with a rather narrow intent, and a rather narrow success towards that intent. Not only does a product that is declared to be a prosthetic arm in form of a legally relevant medical device have to be built with the intent to remedy negative consequences of arm amputation, but it also has to be proven to be successful at it. A product that is merely declared to be intended to serve an arm amputee as add-on to their prosthetic arm, such as, say, an over-boiled spaghetti, that is sold by, say, Fillauer, still is not a medical product unless it actually solves a truly medical problem. As amputee I am at liberty to wear an over-boiled spaghetti, but medical device manufacturer wanna bes are not at any such liberties like at all. Currently, Fillauer thinks by not selling their correlate for an over-boiled spaghetti directly to me they somehow dodge a bullet [link], but they make matters a lot worse. If a prosthetic arm does not actually fulfill a medical necessity as defined via actual use requirements and as medically prescribed with specification, it may formally not constitute a medical device in any proper sense and thus, cause formal compliance issues [link]. It remains the rather urgent interest of manufacturers to keep their products well within real needs and compliant with real requirements of users and their medical diagnoses related to their upper extremity differences, because otherwise, they lose influence over the resulting fall out. And the fall out currently is rather comprehensive. Not loud or shrill, not screaming and screeching, but disturbingly quiet and civil, however, superbly disturbing if one understands what this is or could be about. But let us not get ahead of ourselves just yet. Medical diagnoses are, spaghetti aren’t.

Insurances may have to check for actual and detailed correctly worded specific medical prescription aspects.

Users have to make sure their specific needs are included in their medical device prescription.

Having 1 hand less is not as such a true medical condition

In the context of arm amputation, it is important to initially consider that the number of hands is not medically prescribed or required, and that the mere absence of a hand or part of the arm, in and of itself, does not constitute a proper medical diagnosis in any specific sense at that stage.

Coping with acute loss (as such) may be different, in that it may cause mental strain and issues, but that is not saying two hands constitute a medical necessity per se. All that is usually required to write with the other hand is practice. All that is usually required to sit out the acute phase of hand loss is stubbornness, patience and time where all one does is applying oneself. It sure gets the emotions up and down trying out prosthetic hand devices, as they look great in one moment and as they break a few minutes later. But these diversions are not to be confused with stubborn, patient slow and sustainable learning how to go on in life with one hand. And how to go about getting a truly useful prosthetic arm.

Having a hand less is not as such a medical condition as its treatment is not medical, at least as such. So, there is no specific medical (including surgical) treatment that, according to the principle of practicality, efficiency, functionality and sustainability, allows for effective² treatment.

More precisely, there appears to be no medical need for two hands as such or per se.

There may be actual practical requirements for all sorts of things in life, ranging from shelter to income, over shoes and umbrellas, to refrigerators, toilets and so on and so forth.  It may feel inconvenient often, and it may actually be inconvenient sometimes. The more one practices the luckier one may get. And of course, “if one only puts one’s mind to it one can do anything” is ableist bullshit as there are things one simply cannot do – unequipped 10 finger musical instrument play is one example. Having sex with all 10 fingers really doing something, that does not work either, because half the fun has been cut of or wasn’t there to begin with. Some of us know what we are missing. So do not go explain how one can overcome this and do anything one puts one’s mind to that: those that did live a full life with 10 fingers know that one won’t ever play a true rasgueado with an arm stump. There are distinct inconveniences and impossibilities, admitted.

But to have two hands? The question here is that of a specifically medical need? Playing a rasgueado is not a medical need, ever. We may ask someone else to play one for us.

From both a functional and overall perspective, having only one hand is – per se – not a decisively or practically significant problem for whatever is part of the average ADL (activities of daily living) [1] [2]³.

Therefore, any actual problems of true medical nature should be examined in light of their actual tangible and secondary medical characteristics as their relevance plays out in order to find adequate solutions.

This is not saying that arm amputation is harmless. Not a bit.

One major constituent of the problem list that arm amputees may carry around is what arm amputation does inside the perception of all these other people, and how that echoes back to the amputee [link]. These however are all hints at overt or latent psychiatric issues (as normal people have no problem with encountering an arm amputee and treating them as equals [link]).

One visual problem that is significant for arm amputees is that “it looks like that”, but with that, “it only looks like that”. From the way we look as arm amputees, the average person may believe that they can visually see and thus profoundly understand what we miss: some bit that looks like a hand, and if we are lucky, that moves a bit like a hand. And if one looks at the programs that e.g. technical or design students do in order to take advantage of some dedicated disability funding, they usually run after that carrot that is being hung in front of their eyes.

However, you cannot just put any bit of hand shaped design there. Because you need to see with all of your brain and all of your heart as well, before you try to act. There are things to learn far beyond what meets the eye.

Neck, back and shoulder pain are real, and overuse of other [intact] arm is real

Nack/ back shoulder pain and risk of falling

Asymmetry in unilateral arm amputation causes an out of balance gait and running pattern. The spine is loaded asymmetrically.

The risk of falling is increased [3, 4, 5, 6], and a remedy that has shown to help reduce these effects of unilateral arm amputation or limb difference, is, to wear a counterweight to balance out the lighter weight of the amputated arm.

The unilateral reduced load of the spine on the amputated side due to lighter weight of amputated arm and underuse of that arm, and the unilateral overload of the spine on the other side due to unilateral use and overuse of the arm does not just (immediately, now) cause asymmetric spine loading and an increased risk of falling – it also leads to an increased risk of orthopedic problems over time.

These include significant neck pain, which affects about 39% of the population with arm amputations and increases with age, with a prevalence of approximately p ∼3.5+0.884×Age  [7].

The evidence for arm prostheses theoretically offering relief regarding both the issue of overloading the other arm and the misloading of the spine must be considered established. However in order to achieve that, particular properties play a crucial role, and if you want to know these, keep reading.

For starters, only the (almost) daily wearing of a functional and weight-balancing arm prosthesis provides actual relief, and thus, only such a prosthesis can be considered a medical device with a medical purpose. In order for the device to be worn every day, it must not chafe the skin of the stump, it must not cause irritation, it must not break, fall apart or start to irritate the user by wiggling, and while it usually does not have to look perfect, its look has to be good enough for rock’n’roll.

Overuse

Unilaterally upper limb amputees are more prone to developing musculoskeletal manifestations and overload syndromes due to repetitive movements and overuse of the unaffected side during daily activities.

This overuse furthermore may lead to more adaptive and compensatory movements, resulting in changes in the shoulder girdle complex and spinal kinematics.

These alterations in body mechanics may cause chronic back and neck pain, which in turn significantly affect functional performance, overall health, and quality of life.

Additionally, they can interfere with prosthesis adaptation and impair both physical function and psychosocial well-being, negatively impacting long-term patient outcomes [8].

The theoretically protective function of an arm prosthesis can only become manifest if it is strictly functional with regard to the specific application such that it effectively relieves the other arm [9]. There, and for all real work, body-powered prostheses also and simply are just better at accomplishing such work [10] [link].

Daily wearing of weight-balancing prosthetic arm

Daily wearing of a weight-balancing prosthesis is reported to be a technical prerequisite: “an abnormal body posture is particularly noticeable during clinical examinations of the arm when the amputee does not wear their prosthesis” [11].

“The asymmetries that occurred, which were significant in the depicted muscle groups, were completely reversible with full weight-loss compensation” [11].

“The type and use of the prosthesis impacted clinical changes insofar as patients who wore heavier prostheses exhibited higher weight-loss compensation and consequently lower manifestations of clinical parameters. This must be considered before deliberations on orthopedic technical care” [11].

In this context, it should be added that myoelectric arm prostheses have demonstrably no effect on improving postural damage in arm amputees [12].

Also, arm amputees themselves do not seem to believe that wearing a prosthetic arm every day helps them too much [13], most likely until they hit overuse and neck/pain a few years later, so an early medical prescription, clear and understandable explanations to the patient, and accompanying users through difficult times, to improve compliance and adherence, may be relevant adjuncts to starting off with a prosthetic arm, whereas it must be so it that can be worn every day for months and years, not just hours or days.

In other words, to be classified as medical device, at all, a prosthetic arm must be fashioned, made, designed and built s0 that the amputee actually can and will wear it every day, without causing skin issues and without technical failures.

Any of these beta-version types of prosthetic arms that chafe up my skin, that fail all the time, that are more in the way than real help, are not to be considered medical devices on purely medical grounds and logic.

Conceptual Biomechanical Parallels in Competitive Sports

In freestyle (as well as butterfly), Richard Quick considered the arms of the swimmer as balancing tools first and propulsion tools second [14].

Based on this, me and my trainer at the time were able to analyze and revise my freestyle swimming technique, leading to my qualification and participation in the FINA World Master Championships 2012 in Riccione, Italy, where I competed successfully as an S9-classified swimmer without aids in a non-disabled master championship [15].

This has nothing to do with cyborgs or ‘super-abled’ individuals [link]; it is pure and rigorous swim sport.

Using arms in swimming as balancing tools first and as propelling tools second – do not worry, the propelling was well provided for.

As a side note: there are very few swimmers in the IPC disability swimming category S9 worldwide who qualify for comparable non-disabled world championships. So that concept that we used for my participation there appears to stand on rather solid applied principles.

Another example of understanding arm use is from golf.

When a colleague and I wanted to have the Zuoz golf course designed by Les Furber in August 1998, and I designed the submission with illustrations that then won the bid, we learned from an Irish golf pro the methodology of a particularly reliable golf swing developed and taught by Ben Hogan [16], using the body such that the swing moved from the knees to the pelvis, from the pelvis to the entire trunk, and only then over the shoulders to the arms and into the club.

Those who use their arms in a particular way for (controlled) power exertion do so thoughtfully from the entire trunk movement, incorporating balance and equilibrium, especially of the shoulder girdle and spine, into the overall structure.

So to think of an arm, also a prosthesis, as some device that allows the extension of muscle activity from the trunk.

The complications are long term and the remedy has clear specifications

To fill the role of counteracting asymmetry effect on spine, a prosthetic arm has to have the right weight/weight distribution and correct length. Not even  that is a given [link].

And in order to enact that, for such a prosthesis to have the desired medically required effect, as a first imperative, it then has to be worn usually every day.

From a technical perspective, the prosthesis must be both wearable and worn daily and functionally efficient for demanding bimanual tasks under the criterion of cost-benefit optimization.

It is neither acceptable for the prosthesis to cause such skin irritations after 1-2 hours or days of use that recovery takes several days, nor is it acceptable for it to cause neurological issues due to pressure on the brachial plexus, nor can it break down every few days or weeks, requiring days to weeks of interruption in use. Equally, poor control reliability with errors in excess of 0,03% is intolerable. Any of these will block or impede the possibility for the device to be worn every day.

A prosthesis can only serve as a medically useful, robust, comfortably functioning placeholder for weight balancing and as support for heavy and repetitive tasks, if it meets the relevant technical criteria.

This also means that if some crooked prosthetic arm device that isn’t like that is approved as medical device for arm amputees, then, by sheer logic, overseeing body is either corrupt, or does not to their job, or they are incompetent, or, cynical, or any combination of that – but no matter what, the line marking the end of polite explanations has been crossed by then.

Since prosthesis technology, technical orthopedics, and prosthetic manufacturers demonstrably do not consider these principles systematically, their comprehensive implementation is demonstrably the responsibility of the user (for this topic, check this top-rated case report of 27 closely printed A4 pages and 207 literature references).

To be able to wear it every day

For its medical purpose to be delivered to the user, it has to be possible to wear it every day.

Skin/tissue problems

Problems that occur and that make wearing a prosthetic arm impossible are dermatological / skin issues: a prosthesis that incurs skin rashes [link], skin burns [link], friction blisters and bruises [link] on the arm stump will have to be put aside for at least a few days if not a week, until these injuries heal, whereas some may takes weeks to heal.

That then would be reasons to point the designer of the prosthesis to the fact that a re-design is in order until that aspect is remedied.

A device that repeatedly if not always causes skin issues within a few hours or weeks, that require the prosthesis to stay off until the skin problems are healed, is not a medical device, as far as I see it. It defies the purpose of a medical device that acts as prosthetic arm.

Robustness problems

For the arm to be worn every day, it also has to be so robust and solid as to sustain any activity the user performs [e.g., link, and, many more, e.g. Otto Bock cable, Otto Bock wiggle hook, Otto Bock bolt/wrist, Touch Bionics / Ossur gloves, Fillauer steel cable add-on]. Metric values about some tasks are available [link].

That can either be done by in-house pre-sales testing (to see if the prosthesis stays intact or breaks), or, by overengineering (i.e., by building it so it doesn’t break no matter what).

If the device breaks all the time, the effort to repair it may be excessive and the device will be abandoned because the upkeep is insane, crazy, gaga, idiotic. Such a device is not to be regarded as a medical device, because it evades the designated purpose of being able to be worn and thus used every day.

To make sense to wear it every day

It also has to be sensible to wear it every day.

I will wear a prosthesis once it makes sense to wear it, and a reliable, comfortable support function that provides sense through proper asymmetry balance and overuse prevention by providing hard work, heavy work, and highly repetitive work support, that makes sense, medically speaking.

The medical intent of alleviating the cost of overuse (of other arm) and asymmetry is only achieved by using parts that actually do that.

For the effect of counterbalancing the asymmetry, the weight and parts center of gravities have to be optimal. That effect is better when the prosthesis is actively used, and when it not passively hanging on the body.

For the support of hard work with heavy or repetitive bimanual activities, the gripper design and function have to support not just any activity but that what the user does with it, or, should do.

For heavy and repetitive actions, the gripper angles have to be right [link]. Also, center of gravity is an aspect [link].

These aspects, if not apparent right away, will manifest themselves over days, weeks and months. One may feel drained, worn out, if these things are ill designed [link].

Questions 1-6 can be figured out by the designer, also through own testing. They’re not really hard to answer either. A prosthetic arm that passes all questions seems relevant for testing.

Questions

1. Is your device easy to put/slap on and easy to take/pull off, no hassles? [Design]

If no, fail. Find better design.

A vast majority of arm amputees reject surgery for prosthetic fitment such as osseointegration [17], as it tends to be extremely expensive, and as it comes with a range of complications such as infections and fractures [18]. Nerve connector implants, bone implants, all do not lessen the burden of dependency but shift it and tend to rather increase it, incurring risk, associated cost and pain to the user.

It is with good reason that the roadmap of the Eurohand 2008 (a hand surgery congress) thus projected any risk and implant free type of prosthetic technology as the technology to further develop [link].

In other words, any advanced prosthetic hand technology has to be easy to put on and easy to take off, as a simple to understand and simple to use requirement.

So if this first question is a no, because a particular type of prosthesis bases on surgery, invasively placed materials, high risk, high costs, shift of dependencies to the “extreme”, and without general (not considering here any exceptional rare individual) justifications, then it will have to be rejected from a pure use-only for medical orthopedic purposes.

Of course there are always the risk affine users, the test pilots, the exceptional candidates for all sorts of experimental try-outs.

But here, we talk about sensible builds of prosthetic arms by sensible engineers and for users that manage a sensible balance of realistic risk estimates and true damages.

If easy to slap on/take off is a clear yes, next question.

2. Is the device so it’s skin /tissue interface has no electric parts that could cause burns, and is it so it has no edges/shapes/surfaces that cause any friction, and that the skin stays intact while wearing it? [Testing]

If no: failed.

A device that causes skin problems, particularly one that does so all the time, can’t be worn every day.

Skin problems will take time to heal while the prosthesis may not be worn or only with increased discomfort or / and health risk.

Also if there are open wounds, open blisters, oozing abrasions, or a stump stoma with a bolt there, etc. that may infect and cause problems, then this constitutes a fail for question 2.

No disability law will require me wearing a prosthesis that causes skin injuries, so even if insurance pays the device, I do the right thing by not wearing such a prosthesis.

Wearing a prosthesis every day means to always and under any typical circumstance keep the skin intact. If a medical device manufacturer aims at building prosthetic arm suspension parts, those will be their absolute priorities.

So, and, no, I wasn’t making that up.

Electric burn rash, recovery several weeks [link]:

Friction from myoelectric socket after wearing it for 1 day for light office work such as typing or filing stuff, significant recovery time (consider that I am not the only person getting looked at – you are, too, and if you for any reason think it is particularly cool or even necessary (for you? or for whom?) that I wear such a device, that may imply you’re not strictly human – and if you are an academic researcher, then either you do not (yet) know that is what a myoelectric socket does routinely (when I made these very uncomfortable experiences and posted that on a support forum, they wrote back saying that was a normal experience) which indicates that maybe you should not do what you are doing, or, you do know that this is a typical skin appearance after a day at the office when wearing a myoelectric socket, but then, for other reasons you may not be fit for that role as truth seeker in the domain of prosthetic arms):

Mechanical friction and sweat rash after wearing Ossur Iceross silicone liner directly on skin, recovery with no wearing of prosthesis usually a few days, may start to itch and burn and pop up as early as 2 hours into wearing the prosthesis [link]:

Any of these mean the question has to answered with no, meaning, no, the suspension causes skin problems.

As already stated above, insisting that I wear a prosthesis despite such actual suffering (the itch of that rash can be quite insane, and the pain of the bruising /blisters can be quite considerable) may be a step towards dehumanizing yourself, in an overt and extroverted way [link].

To allow me to wear my prosthetic arm every day, I wear Alpha gel liners and underneath, cotton tube gauze. That works: it keeps the rash / friction injuries away [link]. See this for detailed explanations how that works [link].

If your suspension is not entirely care free with regard to skin issues, then you must revise control/suspension interface. Until you get it right. There is no wiggle room.

Only if the answer to “does not cause any skin issues over any amount of time” is yes, next question.

3. Is the device well balanced, weight good, and the grip angles good? [Testing]

If no, wearing it every day will start to hurt. Test failed, not acceptable. Revise design.

Read details of angular constraints here [link] and consider the post-grip wiggle as quantifier if performing own testing.

Useful grip angles of terminal device mean that I can approach the object and “just” grip it. Usually a forward and inward bent straight precision grip seems to be what interacts well with the environment. Various additional Trautman hook like design variations, with opening of the gripper behind the tips that touch each other, may help holding a bar, rod, stick, broom, vacuum cleaner, handle of a device, and so on, as found in various gripper or hook shapes.

Not useful grip angle of terminal device is the gripper touch line that runs from left to right horizontally, as enacted by some “bionic” hands.

If the answer to good grip angles having been a relevant design factor, and device aspect is yes, passed, next question.

4. Does the device by and large perform the required tasks? [Testing]

If no, it will be of little use. Failed at this stage. Revise design until that’s fixed.

If yes, next question.

5. Does the device by and large exceed robustness and stability versus typical maximal use case load, and for how long? [Testing]

If no, it’ll break and then be of little use. Fail. Revise design until that’s fixed.

I mean, engineers and designers or researchers have to consider that I wear a prosthesis so it takes a load off my shoulder. It has to provide, not consume. The device has to be there for me, and not require me to be there for the device always. Once you have a watch that requires daily charging on a cable or charger, then you have such a cumbersome device that requires too much attention, too much fiddling. Once you drive a car that requires maintenance every few weeks, then your car may need too much attention, cost too much effort. There are all sorts of things that don’t work that well. Let the prosthesis not be one more cumbersome thing that always falls apart, or stops working. Let it be flawless and robust, way past daily requirements.

If yes, next question.

6. Is the device so it has a realistic field use error rate under heavy use/sweat of below 0.03%? [Testing]

If no, using it will cost too much in dropped items [link], or, more likely, the user will be afraid to use it and then risk overuse. Fail. Revise design until that’s fixed.

You want to take this seriously. Read the background information regarding 40 years of failure, and about grip error related cost.

If the answer to this question is that a real world testing yielded grip error rates reliably and always way under 0,03% and therefore “yes”, next question.

7. Upkeep easy and cheap and only infrequently necessary? [Long term use]

If no, user will quickly run out of options. Fail, not usable.

I am not babysitter of poor design. I am user of perfect (or close to perfect) design.

Revise design until that’s fixed.

8. Does it exceed appearance test? Is it at least acceptable? [Ask user]

This is a soft factor. This is the only aspect that does not mean the device can’t be worn. No device passes this, and yet, of all factors listed above, it is probably the only one that only really affects the user. Any designer of such a device cannot claim that the design will be “recognizable” as that exactly would be a problem.

If no, user will not like it if it’s ugly.

Table and device comparisons

With one easy to oversee and read table, we can list what devices are actual medical products that can have a medical purpose. Devices that do not even pass this very simple easy to understand and easy to pass requirements list should be considered as non-medical devices only.

A client that is equipped with any test failing  device should be explicitly informed that:

• they willfully forgo bodily asymmetry prevention
• they willfully forgo bodily overuse prevention
• they willfully forgo a minimal grip performance / reliability requirement
• they risk possibly massive extra cost
• they risk preventable and potentially uncomfortable or painful health issues
• that the device is not in a final state of development, but still in early prototype stages
• that special ethics and formal medical use permission may have to be sought for use of any experimental technology in medical care

Legend: 1 Yes 0 No b body powered m myoelectric

Commercial devices

Cybathlon 2024 Prosthetic Arm Race devices

Despite limited information and pre-event [link], we can rate the announced devices as to their usefulness based on the available information and under the 8 question approach.

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