Don't worry about any detailed analysis or technical feature, about concise specifications or spring angles. Whatever it is you are wearing or not wearing in terms of prosthetic arms, what ultimately counts is your EODF (End Of Day Feeling).
I remember the first provisional prosthesis. Gawd was that piece butt ugly. The first Otto Bock wrist jammed on location right there in the technician's office. The Otto Bock system hand immediately jammed permanently minutes after I started to use it in my office. Seconds later the plastic string ripped out. As the orthopedic technician did not feel it necessary to look at that as an emergency I started to go to the do it yourself store and fix the sucker. I bought steel cable and cable clamps, plastic covers and I hooked the system up from scratch. Days later, the cable had been ripped by the hook's cable hinge mechanism. The aluminium hook jammed when it got warm. The shoulder strap stank as not only did I sweat like a horse from all that stress, the Otto Bock original plastic cover appeared to be designed to make people hate body powered technology.
At the end of these days I was wretched. EODF: wretched, worn out.
Since then, a lot happened.
Now I can not only document the detailed tweaking of such a prosthetic arm to make it comfortable and sturdy to wear, also I have a good overview of what I require in terms of terminal device and wrist, in terms of appearance and in terms of overall feel to feel good about this. And I cannot say that I would have foreseen the outcome of this.
V2P Prehensor with manually tweaked 'winter tyres' (nitrile glove fingers): Perfect. I feel absolutely immersed and relaxed, the grip power almost never walks out on me. The angle and position of the V2P Prehensor pincer is perfect for my requirements. Not having to constantly worry takes away a great deal of stress. It looks wild, I know. But not having to explain to people as the the V2P Prehensor makes it obvious (yes it's a prosthetic part) is also relaxing. It's perfect for house work, dish washing, around the car, and in fact anywhere in the office. If a "hand look" is not required this is the most favorite of parts. It is exactly like flooring a Mini Cooper from a stop: it puts the widest smile on my face. The performance is just ever so fat. I don't even think about it - my body puts it on first thing in the morning and I found that since I use the V2P that I wear the arm all day, until bed time. People may stare - but the usefulness of this part somehow tricks me into using my prosthesis more and more often. The EODF is as best as it currently can be.
Becker Lock Grip hand: Perfect. It looks like a prosthetic hand and it performs gracefully. Going for lunch, eating a banana, carrying mobile phone and wallet - this hand does a lot. Many objects of daily life are shaped so a hand is better than a hook to operate them. So naturally, the Becker hand is a perfect choice. There are critical and stressful moments, one of them is carrying my food tray in the mensa or cafeteria - everyone is looking. The Becker hand is just as great as the V2P Prehensor, so far they have never failed me. Still, wearing the Becker hand can be a wee bit more stressful compared to the V2P Prehensor and that is purely on mechanical grounds: the Becker hand spring is less easy on the cable or harness as the V2P Prehensor is - or in other words, if I pull the same weight on the cable with the V2P Prehensor, I get a better grip power. Trying to eat a pizza and then cleaning the hand afterwards? Yes it can be done :) Also, the V2P Prehensor is ideal for typing, whereas the Becker hand obviously needs to be tricked to optimally type. The EODF is not bad, I have been wearing the Becker hand day in and day out. But I found myself taking the arm off just to chill. In terms of prosthetic hands, the Becker hand is by far the best item around.
Otto Bock parts (hand, hook): These are compromise parts. We ordered them out of pity. We just felt like supporting a struggling German company as they are still European - of sorts. Of course Otto Bock cannot explain all of their product surprises to me (not that they were not invited to) - but one thing is for sure: if I wanted to sell crappy bolts myself I'd get them made in China and then not quality checked here, so whether Otto Bock still should count as a European brand probably remains obscure. So: the Otto Bock hook is great unless you want to precisely grab very small objects, wash dishes or carry a food plate in the mensa or cafeteria. The Otto Bock hand also. Other than that they are sure nice. I like the hook in that it is sleek, slender and helps me sewing, working with tissue specimen and do some hard work it probably wasn't built to do. But that's not my fault: they advertised it as robust. As the Otto Bock parts don't deliver as much performance over a full day, these days can be more stressful depending on what is going on. Wearing the Otto Bock hook to lunch is just hard work. It can be done but, wee. Use the Becker hand and peel a banana and you know what I mean. When I had the Otto Bock hook / hand option as only option I remember that I often removed the prosthetic arm whenever I could. The EODF for these is better described as worn out, sometimes as wretched.
Myoelectric Otto Bock hand on a hard socket: At best, the resting feeling is bearable, most of the time it is plain awful as I have a highly restricted range of motion (cannot stretch or extend elbow), and when I go shopping or otherwise use the arm for grasping, pain levels can be hell. From the slightest weight up, the arm decided to slide off the elbow so that added to feeling not just in pain but nervous. Later, my experiences were confirmed to match those of two other amputees of over 15 years experience. So it wasn't that my myoelectric Otto Bock arm 'just had a bad day'. I just so entirely fail to see how other customers can do this to themselves. The EODF of this setup was that I was consistently more than overly happy to throw that arm into the corner. And mind you, I am an interested and open person and I bought the parts and paid for that socket myself. It was the experience of wearing that arm that turned me from victim to aggressive. If someone tells me that people are ever so happy to pull their prosthetic arm off for relaxation, I fully understand. I just wouldn't continue like that. So the EODF for the myoelectric arm would be described by me as 'completely out of it'.
Cosmetic arm: Well these are almost in the way sometimes. I cannot say my cosmetic arm makes me feel relaxed. It is nice to wear to cover up missing a hand when going for a walk. But other than that I would not try it. Driving is stressful. Shopping is stressful. People still stare. EODF tense and worn out.
Wearing no prosthesis: It feels slick, free, natural and the skin is happy. But I am missing something. And when I do stuff I still use the stump, and after a while, my neck and shoulders strain. Also I overuse my left arm. Due to lack of compression on the stump I also get quite a bit more stump pain. So the EODF is not too good, after all.
Systematic analysis: Obviously, there are different aspects to every action or manipulation that one does. Depending on the concise details, what stresses me, and what happens with the grip or action, those are different also for each prosthetic terminal device.
The three key questions are:
- A: What must not happen, what does the stressful part consist in? When does the situation start to collapse?
- B: How good is the prosthesis or a particular terminal device in preventing that?
- C: What can I do to improve that? How can I contribute to a good result?
The system is complex in that the more failures I get, the more stressful occurrences I have, the more likely I am to avoid these in the future. As not wearing prostheses is considered a hallmark of upper extremity prosthetics at least some of the research and some of the industry probably failed on a large scale, so I feel that we will have some questions to ask.
If you come here as academic researcher to 'help disabled people' (frequently named as motivation for playing with robot hands) and if you are surprised that bionic myoelectric gadgets are not what really ends up helping technically interested geeks through their days maybe it could be time to adjust your research hypotheses to reality.
Some facts that are easily missed when ignoring the EODF:
- I build up stress bit by bit over a day. Every little bit counts.
- Appearance has to be spiffy but not necessarily conceal the absence of the arm. People stare no matter what. They stare also if the attempt is made to conceal the prosthesis. So, don't waste energy concealing it. Often the degree of concealment is bought by sacrificing function. But people stare anyway.
- Reliable function matters a lot. The more reliable function the arm has, the less functionally stressful moments add up to a bad EODF. Read again: 'the more reliable function'. There was not written 'the more features'. I rather have a sturdy wiggle free arm that works 24/7, than a 128 function setup that is out of order every 2 days.
- Comfort of wearing the arm matters a lot. If it is not comfortable, pain and discomfort adds to stressful social and functional situations. I only wear the arm all day if it fits perfectly well. Substandard comfort equates to me not wearing the arm.
Ultimately, everyone will probably optimize their EODF (End of Day Feeling).
As long as prostheses are crappy, every crap adds up to stress levels and that is what I get, what I feel, what I live, at the end of the day. On top of all the other shit. And that's also at least to a part what my dreams are made of. And that's why I am after this subject like the devil after the lost soul.