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Performance rating of prosthetic options [rational approach / numbers]

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Performance rating of prosthetic options [rational approach / numbers]; published November 23, 2013, 04:08; URL: https://www.swisswuff.ch/tech/?p=2360.

BibTeX: @MISC{schweitzer_wolf_1568633344, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Performance rating of prosthetic options [rational approach / numbers]}}, month = {November},year = {2013}, url = {https://www.swisswuff.ch/tech/?p=2360}}


We all know that a wrongly built or wrongly chosen prosthetic arm can be more of a handicap than none at all.

Also, we know that pretty stuff may be pretty but at the end of the day, the pain of overuse is what remains.

So how does it all add up?

Looking back on my various experiences, I went ahead to rate all kinds of applications or activities across various prosthetic types and terminal devices.

I then went ahead and weighted these performance scores to see how a functional and overuse weighted scoring would come out. At the end of the day, no arm amputee escapes physical reality and so give or take five to ten years, they may either give up manual activity for the most part or start to fall apart if the quality of prosthetic support is not up to par.

Table (below): Rating 0-10 for point scores, with 0 = worst and 10=best result, various types of prostheses compared: np = no prosthesis, v2p = V2P Prehensor (body powered), bh = Becker hand (body powered), hh = Hosmer hook (body powered), hwh = Hosmer work hook (body powered), pa = passive arm (also termed cosmetic arm), my = myeoelectric prosthesis. Subjectively awarded functional point scores PA,T both depend on activity (A) and type of prosthesis (T). Each point score value has distinct reasons rooted in the combination of activity and particular property of the particular type of prosthesis. The detailed explanations are the key to understanding why a particular activity works better or worse with a particular prosthetic solution.

Activity np v2p bh hh hwh pa my
Dressing - pull up trousers 6 10 6 10 10 6 2SOCKET
Brush teeth 10 10 10 10 7 10 7
Shave 10 10 10 10 4 7 10
Milk carton 10 10 10 10 10 10 10
Cut breadIMPROVE 3 4 3 3 2 8 2WEIGHT, CONTROL, SHAPE
Butter breadIMPROVE 5 5 5 5 3 8 5
Pack bag 10 10 10 10 4 7 10
Pack laptop 5 10 7 9 4 3 1SOCKET,CONTROL
Wallet, keysIMPROVE 4 10 7 5 3 4 4
Load carIMPROVE 8 8 8 8 8 5 1SOCKET,CONTROL
Steer car 10 8 6 8 4 3 0SOCKET,CONTROL
Carry bags 10 8 8 8 8 10 1SOCKET
Handle filesIMPROVE 4 9 6 8 4 4 2CONTROL
Type keyboard 8 9 9 10 9 9 5
Pull body 3 10 5 10 10 2 2SOCKET
Handle bodyIMPROVE 2 7 4 7 10 2 2SOCKET, CONTROL
AutopsyIMPROVE 0 0 5 2 3 0 0
PresentationIMPROVE 4 3 6 3 3 7 2
Take notesIMPROVE 4 8 6 8 4 4 2CONTROL
Food tray 10 10 10 10 7 10 6
Cut meat 8 8 10 10 8 10 8
Salad 2 10 7 10 10 2 7
Hang laundry 7 9 9 10 10 6 2SOCKET,CONTROL
Carry laundry 10 10 10 10 10 4 2SOCKET,CONTROL
Fold laundry 7 6 6 10 7 4 2SOCKET,CONTROL
Iron laundry 6 9 8 10 4 2 2SOCKET,CONTROL
Solder wires 8 9 9 10 9 9 5
Drill handling 6 8 8 10 6 4 1SOCKET,CONTROL
Mount stuff 2 7 9 9 9 1 2SOCKET,CONTROL
Cut hedges 0 10 7 7 7 0 1SOCKET,CONTROL
Clean up 5 10 10 10 10 3 2SOCKET,CONTROL
Swipe, brush 5 10 10 10 10 4 2SOCKET,CONTROL
Floors wet clean 3 8 6 8 6 1 7
Floors vacuum 4 10 9 10 6 3 3
Ride bikeIMPROVE 3 4 4 4 3 5 1
Run 10 0 0 0 0 0 0
Swim 10 0 0 0 0 0 0
Average 5.6 7.7 7.0 7.8 6.2 4.3 3.2
Price [CHF] 700 6850 6650 6550 6700 3000 45000

General comments:

  • There are activities I simply cannot be bothered with. I do not button my shirt - I always leave the buttons closed also for laundry and ironing, so I wear them as I wear a pullover or t-shirt. I usually do not bind shoe strings, as that is an outdated concept that forces a minimal closing pressure on the shoe. Much rather, I use lock laces or similar setups, and since decades I prefer slip-on shoes and boots.
  • Some activities are ANPPN (activities of no particular prosthetic need). These ANPPN do not receive much attention here. Pouring a glass of water, using the bathroom, and the likes. Particularly for a right below elbow amputee like me (you realize the name of this blog site, don't you) (and remember, it was you that clicked to come here).

Low scores across all prosthetic devices indicate areas for future improvement that are actually sensible. As academic research keeps driving thousands of dollars into the mental brick walls of our societies, this will end up being on our own to-do lists:

  • Cutting and buttering bread really requires a flat soft and curved way to fix the bread. Maybe an arched flat metal strip would do the trick? It is not so important really, but if the little things really are so important as the builders of "bionic" hands say, then this would be unsolved.
  • Handling wallet, keys and cell phone. This is a get-into-the-car activity. Or an get-out-of-the-car activity. Of course one can solve it using a hand bag. But where are we. The cell phone goes into the pro clip to act as navigation system, and the wallet goes into the glove box. A wide strong and all comprehensive grip to handle a multitude of complex shape objects is not available; the best approximation is a surface tweaked V2P Prehensor.
  • Handle files, handle paperwork, handle envelopes. With so and so many arm amputees working in offices rather than being truck drivers or manual workers, you would think that the perfect paper handling tool was ready to order and ship by now. But no. This application domain is a catastrophe. Sit down and open 50 envelopes using the gadget of your choice. Report back here if you still have something to say. So I use brute force and hook devices for that.
  • Autopsies. Obviously there are other prosthetic options needed. The current options are not too useful, to be honest.
  • Handling bodies. Here, a different grip type might have to be invented. This will require some serious head scratching for sure. Until then, the Hosmer work hook will have to do.
  • Presentations. Surely, no currently available prosthetic arm is worth its money here. If you stand there and give a talk, you will understand. Video a presentation of someone with a prosthetic arm, if you still don't get it. Not even the new "bionic" arms are other than clumsy and stiff. You might as well not wear any prosthetic hand or arm, and still get the same rub.
  • Taking notes, holding on to an iPad, is problematic. There are workarounds (such as Jon Kuniholm's iPad sleeve) but a prosthetic arm type solution is still at large here.
  • Riding a bicycle - based on these scores - clearly marks an area for necessary improvement. Luckily, there is Mert's hand. So, this one can be check-marked off the list.

To make the listing of all PA,T more applicable, different numeric weights {w,o,h} and {u} were assigned to arrive at weight scores W(D){w,o,h}  for various activity domains D.

  • The work domain (w) for me contains work as forensic pathologist during an active week with on-call service.
  • The office domain (o) activity weightings cover a work day with predominantly (but not only) file and computer based work.
  • Home and sports activities (h) are things I do when not at work.
  • Overuse (u) is a very important factor list to score high on activities that tend to cause overuse problems in the other arm; proficiency in these domains is an important contribution of a prosthetic device to stay healthy.

Domain w (Work) o (Office) u (Overuse) h (Home)
Dressing - pull up trousers 1 1 0 1
Brush teeth 1 1 0 1
Shave 1 0 0 1
Milk carton 3 0 0 1
Cut bread 3 0 0 1
Butter 3 0 0 1
Pack bag 1 1 3 0.5
Pack laptop 1 1 3 0.2
Wallet, keys 6 1 1 1
Load car 6 1 5 1
Steer car 7 1 4 1
Carry bags 5 1 6 1
Handle files 3 8 1 0.3
Type keyboard 3 3 20 3
Pull body 10 4 10 0
Handle body 10 0 10 0
Autopsy 3 0 0 0
Presentation 0 7 0 0
Take notes 10 3 0 0
Food tray 4 1 0 0
Cut meat 4 1 0 1
Salad 4 1 0 1
Hang laundry 0 0 6 2
Carry laundry 0 0 8 2
Fold laundry 0 0 7 2
Iron laundry 0 0 7 2
Solder wires 0 0 0 2
Drilling machine 0 0 0 2
Mount stuff 0 0 4 2
Cut hedges 0 0 7 2
Clean up 0 0 8 2
Swipe, brush 0 0 8 2
Floors wet clean 0 0 9 2
Floors vacuum 0 0 10 2
Ride bike 0 0 0 2
Run 0 0 0 2
Swim 0 0 0 2

With that, all point scores PA,T can be multiplied with respective weights W(D){w,o,h}to yield domain  specific ratings P(D){w,o,h}.

It is not enough to create a numerical preference for better function. It is furthermore important to model the relative impact of overuse in order to quantify functional aspects for long term sustainability. As amputee: what good is a good function when in five years time, I suffer from overuse? As manufacturer: what good is a good function when in five years time, amputees suffer overuse, lose their jobs, cannot work any longer, lose insurance support for work related prosthetic equipment and then do not buy and use prosthetic equipment any more? If this was a rational world that rated function and long term sustainability, this would be the considerations.

So to complicate matters further, the domain dependent functional point scores P(D){w,o,h} were added to the P(D)u overuse prevention score to award prosthetic types with good scores on both axes, but divided by a penalty score PS = P{w,o,h} / P{u} to arrive at overuse penalized scores pps= [ P{w,o,h} + P{u}] / [ P{w,o,h} / P{u}]. These figures yield high results where both function and overuse prevention are high.

Last but not the least, the price for each penalized point score was obtained and thus, one can easily see both performance and price per performance when focusing on overuse prevention and performance at the same time. That is the type of evaluation necessary for everyone, however one has to adapt the activities and also, one's own performance scores have to be evaluated as not everyone will rate performance exactly the way I do.

Results for normalized penalized point scores [pps] weighted for application domains and relative financial cost per penalized point score point [CHF] (distributed between 0 and 100 CHF) are:

Domain np v2p bh hh hwh pa my
Unweighted [pps] -0.53 +0.99 +0.34 +0.96 +0.73 -1.14 -1.35
Work [pps] -0.48 +0.93 +0.49 +0.99 +0.61 -1.14 -1.37
Office[pps] -0.49 +0.98 +0.39 +0.96 +0.70 -1.23 -1.30
Home, sports[pps] -0.56 +1.04 +0.32 +0.96 +0.68 -1.09 -1.38
Unweighted [CHF] 0.00 2.40 3.20 2.30 2.65 4.30 100.00
Work [CHF] 0.00 2.80 3.30 2.60 3.15 4.65 100.00
Office[CHF] 0.00 2.50 3.20 2.40 2.80 5.35 100.00
Home, sports[CHF] 0.00 2.50 3.30 2.40 2.80 3.95 100.00

We see the following:

  • Body powered arms in general and hooks in particular are an extremely rational choice for best function, for overuse prevention and also, financially. Their preference is not the slightest bit irrational, outdated, backwards or confused.
  • It should become readily understandable why it can be an extremely rational choice for an amputee to prefer living without a prosthetic if all the options given are (a) cosmetic and (b) myoelectric. Why? Because both functionally and in terms of overuse prevention, the stump rates still better.
  • Tweaking scores for overuse penalization produces a penalized point score that is different from what is being advertised as cool these days. So, advertising and societal stereotyping clashes with real values here. So for work purposes, Hosmer hooks and the V2P Prehensor should be the very first product that prosthetists recommend. For the purpose of having a hand appearance, the Becker hand wins this comparison hands down, and prosthetists might have to realize that rationally and based on functional and health considerations, they should recommend that hand rather than less functional systems.
  • Body powered arms can be hard to understand, if one looks at the intricacies of the technology. Interestingly, we have the situation that body powered arms built to modern standards might require specialized knowledge that is lacking in many places and yet, body powered arms are portrayed as outdated. Conversely, gluing together a myo arm is not half as difficult and yet, its conceptual deficiencies have not been addressed in over 70 years now.
  • What should one wear if one prefers a hand shape? The Becker hand yields about 300% of the passive arm's penalized point scores and roughly 370-390% of a myo arm's penalized point scores. For a hand shaped prosthetic device, that is a great result.
  • Spending time with the bare stump rather than wearing a prosthetic arm is not extremely cheap (due to possible complications of using it as a hand), but it certainly is not very functional. However bad functionally and in terms of overuse, a stump may still be better than a cosmetic arm or a myoelectric arm.
  • For the application domains given, both the myoelectric arm and the passive arm seem to be a real waste of money, and despite that, they are functionally bad: they are worse than not wearing a prosthetic at all generally, for work, for office duty and even for staying at home to clean, do laundry etc. and some sports. These prostheses represent luxury purchases or devices for particular or special tasks. They constitute a health risk, a dead weight and a liability. Conceptually, these are 'dead horses' unless socket issues, control issues (including energy sources and electrode issues) are resolved. These issues had remained unsolved for over 70 years now, so it may be time to either address them in a more thorough manner or re-focus on body powered technology.
  • Always and alternatively, other means than current stump-sided solutions may be considered.
  • Body powered arms must be built right in order for the amputee to enjoy the benefits of that concept. Not every prosthetist is good at building a good body powered arm. It is crucial to understand the details there.
  • Myoelectric arms are expensive. And they are neither particularly healthy or useful. The combination of expensive and not healthy is not good. Their application might have to be restricted to particular situations where body powered arms (if well built) fail.
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