Competitive prosthetic action - compare movement and function

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Competitive prosthetic action - compare movement and function; published September 21, 2008, 13:01; URL: https://www.swisswuff.ch/tech/?p=46.

BibTeX: @MISC{schweitzer_wolf_1571524805, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Competitive prosthetic action - compare movement and function}}, month = {September},year = {2008}, url = {https://www.swisswuff.ch/tech/?p=46}}


Current new developments in hand prosthetics are the iLimb (TouchBionics) and the Michelangelo hand (Otto Bock). Both are termed bionic hands. As these could be seen as very attractive, emotionally appealing and extremely expensive, they are a fascinating subject to examine.

This post also precedes some of my more refined attempts at defining, describing, specifying, evaluating and actually comparing prosthetic performance, such as a variation on the Carroll test.

One thing that amazes me is the obvious discrepancy between the feelings of the wearer (inside) and the feelings of the person watching the wearer (outside): when watching someone else wearing it from the outside, the iLimb - as I felt - looked artificial, stiff, slow, performed extremely loudly and to me appeared to be rather annoying, just as a car with a defective exhaust when seeing someone else wear it. Yet, operating it myself sucked me into a dream world of simulated hand function that I viewed entirely differently and it put a wide smile on my face. Seeing someone else smile at their own iLimb and witnessing the obvious discrepancy between its artificial appearance, slow and very restricted functionality and noisiness on one hand, and the smile it put on the wearer on the other hand, then completed a rather distressing experience to me.

It is ultimately the question why am I wearing a prosthesis? Is it merely a highly priced conversation piece, an item to wrap oral history around, a think to talk about such as the iLimb that is a the centerpiece of a large series of mostly social parading of the prosthetic object? Would I spend a staggering 78'000 CHF of my own money just to get someone tap my shoulder in a grocery store saying, "congratulations to your fine prosthesis, one can hardly see at all that it is an artificial limb"? See how much is that in dollars! I wear a prosthesis to show to others that I am willing to fake having a hand, I wear a prosthesis for sheer functionality. I'd wear one as fashion statement but for that, a self-funded 78'000 CHF hand necessarily must combine computing and programming options of a top-of-the-line workstation (huge one available for 15'000 CHF), the mechanical properties of a luxury class car (50'000 CHF), the stability and ease of handling of a Bosch drill hammer (1'000 CHF) *and* the battery or energy functionality as well as versatile electronics of a top-of-the-line laptop (available for 8'000 CHF). And we start off with a head start for good old mechanics here - the hook relaxes people as they see within a mile against the wind that I am missing a part, that there's a standard item to replace some of it, and it is also one reliable piece of hardware (even though we had to work on that both for the wrist and the hook).

The fluency and immediacy of available motion is an extremely important feature for my hook or mechanical hand. An experienced physiotherapist told me to go for a body powered prosthesis if only for that reasons - and stick with it for a couple of years. He said that only then will I grow into using it so much that I will really be able to rely on its advantages. The argument of fluency and immediacy becomes apparent when comparing the iLimb in its respective appearances on YouTube, and my hook in the following videos. And recently I realized that one cannot thoroughly get accustomed to such a prosthetic setup without letting it grow on oneself, without allowing oneself to naturally incorporate its function into one's life.

In response to TouchBionics "get a grip on functionality" demo videos http://www.touchbionics.com/professionals.php?pageid=44&section=5 I recorded similar activities using the Otto Bock MovoHook 2Grip for 1:1 comparison. My evaluation  bases on my current personal requirements as a right below elbow amputee.

Recently, detailed accounts of iLimb usage by Darin Sargent (see: theadventuresoftheilimb.wordpress.com) highlight activities such as reading a newspaper or working having it on in the kitchen. As I see it, Darin Sargent really and ultimately tells us throughout his extensive online video collection that basically he was real lucky to get insurance to pay for the iLimb (he did not pay 78'000 CHF) but it appears as if the product was never formally evaluated by his insurance for function or performance.

As his website articles imply, he uses it more as a social prop than as a functional replacement. And we learn that his insurance paid for it. That is like learning that they just finished a gold toilet for the king. Maybe that is nice for the king - but I really see no further conclusion to be made. His website implies that Darin has no idea how to conduct a technical evaluation and he even uses words that indicate that he looks down on people that go down into the pits and actually have to rely on their prostheses for work. If he despises manual labor and the big problems that come with evaluating prostheses for that purpose he has every right to say so. If he looks down on people that wear hooks for performance and hands for appearance I don't care - maybe that's what he has to do.

So the overall impression I get is that yet another high ranking army officer / priest / motivational speaker / retired person walking around with a hugely expensive dummy hand prop is not a very good ambassador for prosthetic manual dexterity. Just to bring that question to the point.

Price definitely plays a role in prosthetics. So it is relevant to note that my current setup (Otto Bock parts, two MovoHook 2Grip 10A80 hooks, one System hand voluntary opening, cable controlled socket with rapid swap mechanism, all parts pimped for optimal performance) costs a mere fraction of a prosthesis featuring the iLimb by TouchBionics.

Comparison of the prices for terminal devices (iLimb hand wiothout prosthetics: around 50'000 CHF (not covered by insurance); Otto Bock system hand: about 800 CHF; Otto Bock hook: about 1'200 CHF - prosthetic arm with iLimb hand: around 78'000 CHF, prosthetic arm using body powered technology: around 6'000 CHF) shows that we are dealing with extreme differences in prosthetic cost.

Now, I like to be able to smoothly and without much technological overhead work through technical situations by wearing a contextually intelligent solution on my arm stump.That does not mean that I only and exclusively wear a hook? No!

  • I like the constant and reliable availability of function (without recharging or additional weight) of the hook. Using it for cutting, grinding, working with aggressive solvents, the hook as many times proven technical advantage over any other replacement as all it takes is a scrub, disinfectant, ultrasound cleaning and we are back on track. At intervals, I get the silicon covers replaced but these are really cheap parts.
  • I like to wear the Otto Bock system hand for certain situations and have that reliable too. And very good looking.
  • Currently I am working on an art project as well.

As TouchBionics advertise the possibility to actually conduct a number of manipulations using their iLimb I found it relevant to offer a 1:1 comparison to this type of functionality. It may help to identify areas of improvement, it may help to adjust unrealistic expectations, and it may help to illustrate functionality. Images or pictures, videos or short films just provide a better illustration than mere words saying 'been there, done that'. - And then, most of these are situations that are just a bit harder to do with the amputation stump alone, they may take more time without prosthesis, or risk getting the stump injured.

Taking off wrist watch

I can remove my wrist watch using the stump or the hook but also using the Otto Bock Voluntary Opening System Hand. I am now wearing a Regal Prosthetics silicon glove that features great appearance and sturdy finger tips. Key to getting a wrist watch off fast is finding out how to best twiddle the lock. Here, I slide the plastic band through the lock and then pull a bit to get the lock pin out of the hole. Then I use an oblique pull trick for the wrist band to flip the pin over to the other side so it does not lock again (video: 0:10 to 0:15 seconds). All in all I get the wrist watch off in just under 20 seconds and that is in slow demo mode and with a mechanical prosthetic hand. Always remember: if you are after realistic looks, go for a good silicone glove (regardless of what you wear underneath); if you are after smooth, silent and immediate action, get cable control (regardless of the terminal device); if you need precise and full force grip or push/pull action, get a hook and if you want to look anthropomorphic get a mechanical hand.

Manipulating objects

Here is a demo that shows moderately fast and moderately precise manipulation of objects. Note that no battery, no temperature dependency and no electricity interference cause any particular problems with this type of prosthesis.

Ironing a shirt

Doing laundry and ironing and folding clothes is something I routinely do. Grasp/pinch operations are small in extent but often fast to allow for an overall smooth course of the job. I don't have to recharge any battery, the hook (or hand, if I use that) is ultra responsive particularly compared to some of the bionic myoelectric demos we see.

Accessing USB stick

The iLimb can be used to hold objects. Alright! The hook does that too. I can grab a USB stick real fast and get it ready to plug it into a computer. Real fast. Or I can do it slow as in this demo video.

The Bionic Chef - using prosthetics in  the kitchen

I love the iLimb's look but I fear it cannot be used in the kitchen other than keeping it out of harm's way:

Here is an attempt at opening a popcorn bag after over three months (!) of wearing the iLimb hand:

These are very valuable demonstrations.

Some people are not sold a product but a dream, not performance but a promise, not a hand but another replica of one. Magritte's "ce n'est pas une pipe" definitely applies, here more than anywhere else. And I am not saying it is bad to chase a dream. Even more as in some instances, insurances seem to pay for the iLimb even though I cannot understand why. What I believe is that if you are trying to nail down performance you may have to take other routes. And when I go down the real hand looking hand for my Otto Bock System Hand, or when I choose the artistic prosthesis path, I may go down alternate routes as well.

I am very curious to learn about new technology but I am very curious to test real limits. Now, I don't have anyone that cooks or prepares my meals - I do the cooking myself.

And I don't have to guess or hem and haw about the steps to do in cooking - I learned it from professional cooks, among them my grandmother, who was a trained chef. I go right for the jugular and so kitchen spells out as sharp blades, humidity or wetness, heat or ice, as irregular objects, fast maneuvers and at times sweating.

The Otto Bock hook is up for the job; I use it to turn meat on the grill or in the pan, manipulate the oven tray, or - as shown here - to sample spaghetti. Obviously I crank open cans or slice up food packs - that is a given. What I mean by hand(s) on product testing is to get the prosthesis real dirty and show close range action:

Reading newspaper

The way the iLimb is portrayed often implies that what people do there now had not been possible at all beforehand. So someone may be saying "I can now hold a bottle to fill it up with water" (great, but has he been deprived of any water during the last five years?), another may be enjoying finally being able to hold on to a newspaper (great, but did you think I had to bend down to the floor to do that?).

Watch the following video and keep in mind that fast, efficient, functional, cheap and light does not always spell out as 'unevolved'.

Carrying boxes

This is such an elegant test for a prosthetic arm. Don't negotiate. Just transport these. That'll be all. Thank you. No myoelectric demo so far showed better performance for such simple tasks. Is this a rare thing to do? You do go shopping as well, I take it?

Pouring Corn Huskers lotion on my hand

Going one handed all day, the skin can get rough. So quite clearly we ask "can we use Corn Huskers lotion using a hook?" and the answer is, "Yes, we can!". No need to search any further.

Opening and closing a door

I liked the idea of using doors to evaluate prostheses. Here we see my hook as I run through a door. It'd a one swift move bang open close bang non stop motion. As I close it I get force feedback that the door is closed all the way.

Typing on a keyboard using the hook

Someone told me they'd stop using computers altogether were they to lose a hand. I wouldn't suggest that. Typing can be done fast and easy. One particularly important point here is to use a stable wrist (if it rattles or squeaks and the hook tip isn't exactly where it is supposed to be I get irritated).

Light a match

I would not see how this should be a problem with just about any grip mechanism. This would be more difficult with a passive hand but even then you could just fix the match box against a fixed surface.

Pick up bag

I very often use the prosthetic device to carry items. It takes the load off the other arm and it is easy to do. The hook is better than the system hand because of the stronger spring pull and the shape (obviously). The motion patterns become integrated after a while and the cable control actually started to feel natural.

The iLimb videos, on the other hand, feature far wider smiles of their owners but my grip motion itself with the hook is fast, fluid, relatively strong and precise. A colleague once noted that he found it impressive how natural my integration of the cable controlled hook's open/close action had become.

Pick up CD

Why anyone with unilateral arm amputation would use their prosthesis to pick up a CD is beyond me but as it seems to be a favorite benchmark activity, here we go.

Pick up peach using hook

That was not hard to do. Again, I do not understand why someone with one sound hand would use the prosthesis to pick up a peach.

Pick up peach using system hand

This was not hard to do either.

Pick up glass using system hand

The system hand seems to be a tad bit better for handling drinking glasses or soca / beer cans. But the speed and fine tuned action is hard to match with myoelectric systems. Besides, my prosthesis won't have a lot of problems with spilled fluid.

Pick up glass using hook


Pick up roll of tape using hook

Picking up a roll of tape is a no brainer. Getting the tape off the roll is where trouble starts and I have to say that my tool using skills have seen some rather unusual additions as of lately.

Fill up water bottle using hook

Why filling up water bottles is such a reason to buy an expensive motorized hand is beyond me. But I don't hide how it's done with a cable controlled mechanism - I just do it. Whether I place a bottle or mug in the sink and aim the tap water into its opening or whether I lift it using the sound hand or prosthesis is hard to say. I do not even think about it most of the time. However if someone likes to see a demo of actually use the prosthesis to hold a water bottle while it is being filled up, here we go.

Open/close heavy file cabinet drawers

Handling file cabinet drawers is a real mundane every-day light-weight task yet I cannot imagine how I'd do that with a myoelectric or mechanical hand. Here's how it's done with the hook - painfully simple.

Operating buttons

Hitting switches is the most often performed point-aim-hit action that I do and using the hook, these never fail. I walk out a door, hit the switches fast and without problem - but not so with the prosthetic hand. The hand can be used to press buttons - elevator buttons, light buttons - but the hook is really good at it.


I feel as if integration of prosthetic action into body motion and self controlled direction is rather intuitive to achieve with cable control. For that, however, the cable control parts need to be as functional as can be. In my instance, this was a bit of work - but we got there (see other articles on this website).

When people say that "countless activities" are what they achieve with their prosthesis, it pays to make them list and evaluate each single one. So many activities are painfully simple and unspectacular that real issues with prosthetic performance boil down to a very select few benchmark applications:

Going to toilet, wiping butt. It would never occur to me to use a prosthetic hand for that. If this is achieved particularly well with a prosthesis, I assume that a rather supple wrist mechanism would be far more important than individual finger movement.

Getting dressed. That one's a no brainer. With or without any type of prosthesis.

Brushing teeth. I hold the toothbrush with the stump or the prosthesis. Then I squeeze toothpaste on it.

Putting on tie. The tie can be kept in place with the prosthesis or the stump. No extra effort required.

Preparing and eating meals. The hook wins. With the hook, preparing and eating meals is easily accomplished.


The issue of comparative technical build and design of both myoelectric and body-powered prosthetic arms is discussed in this article in depth:

Publication [link]

11 Replies to “Competitive prosthetic action - compare movement and function”

Comments are closed.

Do NOT follow this link or you will be banned from the site!
HTML Snippets Powered By : XYZScripts.com
I footnotes