Body powered vs. myoelectric vs. cosmetic vs. none

I now got a customized socket to try out a myoelectric prosthesis (used Otto Bock parts, initially functioning, no warranty). As my stump features some extra twitch packs (how do you call the muscle packs they put on your stump so you have a chance of creating extra myoelectric signals for modern prostheses?) I figured let us see how myoelectric stuff works as one day that may become interesting.

This adds to my collection in that I currently have a body powered setup (fully fledged), a cosmetic prosthesis (light weight, elegant) and the option of wearing none. Before opting for any bionic arm I was interested to see what issues might arise.

Due to my long stump that could cause problems with a pin lock (and thus cause the prosthetic arm to be too long) the myoelectric arm was fitted with a hard inside socket that is fixed to the elbow through encasing the elbow with its hard shell.

I compared different aspects of prosthetic fit and usage. This does not at all claim any conclusion for other people. I am just detailing my own experience but if you are interested, I have a series of videos to show performance of my body powered arm 1:1 rather than talking about it. Myoelectric prostheses may not be able to perform even nearly as well as body powered yet the commercial promise is immense.

Conversely, the website Adventures of an iLimb shows that a top of the line myoelectric arm may be good as an extremely expensive social prop but I have yet to see a performance beyond “I can use it to hold a bottle” that does warrant the expense of 60’000 CHF uncovered by insurance due to lack of proven superior function.

Body powered prosthesis Myoelectric prosthesis Cosmetic prosthesis None Comparison result
Fit of socket Silicon liner is very comfortable Hard socket that encases elbow is very uncomfortable Cotton sock is comfortable but tends to itch after a while Perfectly comfortable Cosmetic or body powered arms win, as well as not wearing any.
Ability to pull socket off arm Liner and pin lock provide a very sturdy and comfortable resistance to pull forces Hard socket hurts a lot when pulled even a bit This prosthesis does not take a lot of pulling force but the fit is so comfortable that even pulling it off (instead of properly unmounting it) does not cause pain Not an issue at all Body powered wins. Cosmetic prothesis remains comfortable but for that, pulling is a non issue. Myoelectric socket very painful.
Extending elbow No problem Not possible – very painful No problem No problem Myoelectric prosthesis problem
Lean on elbow such as when reading a book on a lawn or sofa No problem Not possible – very painful No problem No problem Myoelectric prosthesis problem
Grasp item Light to moderate weights can be grasped with voluntary opening terminal devices Very strong grip, max. 12 kg No grasp possible Very limited grasp (elbow) Myoelectric better than body powered, both better than cosmetic or not wearing any
Control grasping power Excellent control Not possible to fine tune and control power for the most part, or at least quite risky No grasp possible Excellent control over very limited amount of grasping power Body powered and no prosthesis at all win
Carrying or lifting an item No problem Very difficult – cannot extend elbow, pulling on socket is extremely painful Not possible Use stump as “hook” to carry a bag or to press items against chest but only for limited weight and limited choice of object shapes Body powered wins over wearing no prosthesis
Kitchen work Kitchen work can be done (except with round items – onions, tomatoes, potatoes, etc.); heat, dirt and water are no problem Humidity and getting it dirty are problems Not possible Not possible Body powered wins
Restriction of motion in shoulders A bit but not too much No No No Harness of body powered prosthesis limits range of motion in a minor way
Typing Excellent (hook) Possible Excellent Slow Body powered or cosmetic prosthesis win
Reliability Excellent (if built right) The open / close function was sometimes a bit erratic. The function suddenly ceased permanently on day two of using it, I have no idea why; after reading many complaints on-line I am not willing to spend more money to get such a painfully uncomfortable item fixed Excellent Excellent Myoelectric is a bit difficult
Speed Excellent (if built right) Not bad at all! Even though I was using an old Otto Bock system hand, speed did not constitute any issue at all. I was rather pleasantly surprised! Excellent Excellent That old myoelectric hand was not so bad after all
Directness Excellent The myoelectric hand feels more remote, indirect and detached My cosmetic arm feels like the ultimate detachment from reality to me Excellent I vote for body powered or none as far as the aspect ‘directness’ is concerned
Looks Excellent – both MovoHook 2Grip and Otto Bock system hand with very nice looking cosmetic glove provide a good appearance Bulky due to battery but otherwise this can look good Excellent Excellent So looks are not a big problem
Weight and stability Excellent – weight and stability are perfect Heavy weight; delicate electronics are in the way of stability Excellent weight, average stability Excellent weight-wise (no weight at all) – but I have to protect my stump to be able to handle heavy or scratchy objects So weight is not a big problem
Summing up points (blue +4, cyan +3, pink + 2, red +1) 58 32 46 51
Cost 6’800 CHF around 45’000 to 60’000 CHF around 5’000 CHF free
Summary Minor inconvenience (harness) – otherwise perfect Painful to wear, very painful and useless when lifting objects, only perfect for strong grip forces when sitting down and having elbow at bent angle Not very functional – otherwise offering a shape placeholder and perfectly comfortable Not very functional and not a shape placeholder – otherwise perfect

Very early on I figured it would be important to establish how the overall feel of my myoelectric arm compares against the rest.

At first it struck me that myoelectric prostheses do not seem to look fast. If I was wearing one I generally felt that others would believe that I would look quite disabled because of that delay. And that might actually be the case – but the delay of the myoelectric arm does not feel weird when I put one on myself (instead of watching how it looks on video).

I then seem to get warped into a delusional field of a ‘wow, power performance’ assumption and then feel that the speed of the myoelectric hand is perfectly good! In fact, it felt great – even though the hand was as slow as can be seen on videos documenting myoelectric hands. Instead of feeling it would look and feel weird I throughly enjoyed the experience of the time warped illusion of wearing the fastest hand in the world. Besides, whether the myoelectric is faster or not is probably of no particular extra importance inasmuch as “apearing to be visibly disabled” is concerned.

So suddenly, I could not care less about speed. But as it turns out, reliability (unreliable open/close action; irreparable break down on day 2 for whatever reason) and a consistent painful experience with a hard socket despite a perfect build technically seem to constitute major road blocks to getting happy with a myoelectric arm for me. I rated the pain 11 out of 10, the level was hell, fire and damnation and not anywhere near tolerable. The feeling of having to rely on an unreliable painful prosthesis is in fact horrible. No full elbow extension, no full elbow bending, no lifting of weights with prosthetic hand, no leaning on elbow, no stability in that the socket would still slide off at the earliest sight of a single sweat drop. Am I spoiled? My epoxy socket and silicon liner of the cable controlled prosthesis are no issue at all – they are comfortable and I really like them on. Both the initial and the updated socket (I have two in case one breaks down) are a comfortable fit and the Ossur silicon liner and pin lock work great for me.

Neither reliability nor comfortable fitting seem to be a major specific topic of current upper extremity prosthetics research – gadgetry and mimicking aspects of what they believe is a naturally looking hand motion seem to be what engineers are interested in constructing. So I do not even perceive myself addressed by these people’s research. They must be building these arms or hands for other people such as shoulder or transhumeral amputees. They are probably not targeting for people like me – that is: people that have a somewhat tender arm and elbow, that require full elbow motion, that have to actually carry stuff and require full open/close command obedience.

They could also offer a cable controlled motorized prosthesis. Why worry about stupid electrodes with delays, errors, mistakes, interference if all I need is a little switch that I can yank on and off using my cable control? My socket and the cable are all perfect – all that an electric hand could do better was improve grip power and improve grip patterns by, say, a selector switch.

Back to the hard socket. I now truly understand why people “find prostheses horrible” – and mind you, my myoelectric socket is a perfect fit! This is an arm I first liked to use – there is a certain strange pride in getting a squeaking motor to compress a cardboard box if it is sitting inside your prosthetic hand – but after pain started to really torture me and after getting nervous about the socket not sitting too stable and the open/close function not being triggered whenever I wanted it to go off, I am now almost relieved to not be able to wear it any more (the myoelectric function suddenly stopped on one of the cables; a quick troubleshooting established that it was not the electrodes or the battery). While Touchbionics seems to advertise with the slogan “BIONICS – GET A GRIP ON FUNCTIONALITY”, I would rather support the slogan “FUNCTIONAL PROSTHETICS – GET A GRIP ON REALITY”.

You know at first I thought I was crazy. Why would anyone want to wear a hugely (and I am a tough person, trust me on that) painful and mechanically restricting prosthesis that comes off the arm when lifting more than a minimal weight. So I asked around. You know what the weirdest thing was? Everyone said, right on, you got it, that is exactly how these prostheses feel. My observations that I laid out in detail here (see above) were all confirmed. They told me that these hard socket type arm prostheses felt like that twenty years ago and they still feel that way. That is why they were not wearing their arms any more either. So, on one hand (ha, ha) I was relieved to see that my observations all matched other peoples’ experiences. But then I wondered what type of industry that was that constructively and positively failed to learn in the last decades.

Again, Fred seemed to be proven right:“Your body has only so much tolerance for gadgetry” (Fred Downs, head of prosthetics for the Veterans Health Administration, CBS 60 Minutes, April 12th 2009)

A really remarkable feature of the myoelectric arm to me appears to be the option of opening and closing at a force that is relatively strong. But I cannot use that force for carrying anything – extending the elbow is really very painful, bending it all the way does not work. And if a force pulls too hard the arm slides off. My arm is slender and long, it has straight contours and no way a hard socket will stay in place. Now, I had bruises after the first day, bruises after the second day, and the arm started to really really hurt. And as I do not process arm stump pain normally, but with a low level of tolerance, these sensations give very clear answers as to what prosthesis will or will not work for me. And I am very relieved to know that a number of others see things the exact same way.

As myoelectric is no option in the near and far foreseeable future now, I will have to keep using cable controlled, cosmetic or none. Maybe one day there will be a hybrid arm – one that switches motorized functions using cable control. Or a really good looking functionally appealing mechanical high tech hand (a product missing in the current landscape of arm prosthetics).

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Body powered vs. myoelectric vs. cosmetic vs. none; published May 10, 2009, 21:17; URL: http://www.swisswuff.ch/tech/?p=173.

BibTeX: @MISC{schweitzer_wolf_1406711002, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Body powered vs. myoelectric vs. cosmetic vs. none}}, month = {May}, year = {2009}, url = {http://www.swisswuff.ch/tech/?p=173} }