Constraints in prosthetic arm research (literature review)

A recent literature review  [1] lists apparent priorities and requirements for prosthetic arms. It mentions the fact that a prior literature review, dated 20 years earlier, already contained some of these requirements.

The necessary conclusions however are not presented; they really boil down to two reasons why that could be:

  • it should be evaluated whether the reasons given 20 years ago and again now just present excuses and not actual requirements;
  • it should be evaluated exactly who focused on practically resolving these issues through research or components, and why, possibly, they failed.
  • it should be evaluated inasmuch academic research now follows its own self-made "requirements" that, really, have absolutely no relevance in everyday life

Let us look at the research assumptions and these apparent requirements, point by point.

Analyzing prior prosthetic requirement studies

If one actually reads these studies, it becomes clear that

  • researchers often do not really read prior studies;
  • subsequently, they systematically overlook and ignore the results of prior studies;
  • subsequently, they render their own research ill-targeted and ill-designed,
  • and subsequently, their results fail both users and that part of the research community that wants to seriously address actual concerns or issues.

Twenty years ago

A very widely cast survey resulted in 2477 answer sheets in a 1996 study [2].

From that study's "results" section: "The Friedman rank order of the 10 items indicated the top priorities for transradial prosthetic users were as follows: "wrist rotated the terminal device" ranked first (mean 4.72, >5 other factors); "could do coordinated motions of two joints at the same time" ranked second (mean 4.75, >1 other factor); "wrist moved the terminal device from side to side" ranked third (mean = 5.07, >4 other factors); and "wrist moved the terminal device up and down" ranked fourth (mean 5.17, >3 other factors) (see Table 1 ). " Further wishes contained lesser weight, better ability to hold small objects, better ability to hold large objects, better usability for vigorous activities and only as last priority, more similarity in appearance to a human hand.

This spells out as:

  • less weight
  • more robust construction and make
  • better grip ability (most people lack proper understanding of grip quality which is not the same as grip force) (link)
  • better controls for the wrist (not additional degrees of freedom - just controls)

From the study: "Question 44 of the electric survey asked individuals to identify the top five activities (from a list of 34) they would like to be able to perform with their electric prostheses. The top five choices for transradial users were: 1) Type/use a word processor; 2) Open a door with a knob; 3) Tie shoelaces; 4) Use a spoon or fork; and 5) Drink from a glass. The top five choices for transhumeral users were: 1) Type/use a word processor; 2) Cut meat; 3) Tie shoelaces; 4) Open a door with a knob; and 5) Use a spoon or fork."

To address these concerns:

  • Typing requires an aluminum hook and a vibration proof socket / wrist combination.
  • Opening door knobs can be approximated with a prosthetic but is far easier to solve differently - getting a door handle instead, for example, or using the other hand.
  • Tying shoe laces can be done equally well without prosthesis, with a passive arm or with a hook or prosthetic hand; what is required here is a lot of practice.
  • Cutting meat is done well with the stump, with a passive / cosmetic arm, with a hook, or a prosthetic arm. What is required here are the proper techniques and enough practice.
  • Using knife and spoon goes along the same direction.

More speed and more torque was not asked, mentioned or required.

Body powered arm issues

The following main complaints were also identified by me. They also caused me trouble.

Cables needing frequent repairs

Cables as needing frequent repairs are mentioned as the main issue [2]. This was also my main problem and complaint at first.

I thus adapted a Bowden cable sheath mount for use on flexible deformable bodies that avoids unilateral friction and high friction altogether and patented it. Just so that none of these arrogant companies that still owe me apologies can sell it back to me.

But there is no research done to improve exactly that aspect, nor is there any development of a prosthetic component manufacturer. Goes to show that 20 year old requests of customers are systematically ignored, really.

Rotating wrist

Body powered arm users want a wrist that rotates the device. I built one, with friends; it is extremely light, sturdy and robust. It acts as a quick release wrist.

Other requests - move two joints at once - are unreasonable; with a significant disability such as an amputated arm, coordinated synchronized motion of two joints requiring at least six degrees of freedom is quite simply impossible and poses a hard disability imposed restriction.


Comfort of harness is not mentioned in any of these studies ([3][2]) just as claimed by  [1] in their Table 5; and yet, comfort is not so much an issue as actual neurological complications are: I suffered from plexus compression and so we re-designed my shoulder anchor to totally avoid these issues. With that, cable control has become a very precise experience allowing for short extensions with high grip forces.

However, research and prosthetic manufacturers avoided this subject during the last two decades.

Rejecters versus adopters

A recurrent theme of prosthetic arm research is the high degree of rejection.

Curiously, prosthetic arm non-users are the ones that are able to answer that question the best. However, the studies that address that specifically are rare.

From table 2 of a 2007 study  [3], we see that reasons not to wear the prosthetic arm differ between people that reject prosthetic arms as opposed to those that adopt them:

Reject Adopt Ratio
More functional without it 98 60 1.6
More comfortable without it 95 66 1.4
Too difficult / tiring to use 88 39 2.3
Too heavy 88 65 1.4
More sensory feedback without it 85 44 1.9
Inconvenience 93 53 1.8
Appearance 70 33 2.1
Medical factors 55 64 0.8

So top down on the ratio listing, if you want to make prosthetic hands / arms more frequently worn, particularly when addressing concerns of rejecters as opposed to adopters, your priority list in addressing concerns are:

Too difficult / tiring to use

By far the most relevant critique of non-users!!

As I use high grip forces, I reduced friction and weight as well as optimized center of balance for my body powered arm. As far as I know, no one else - also of people I meet in workshops - specifically tweak their prosthetic arm to improve ergonomically.

Even the para-athlete Danny Letain apparently was cited as " (..) Letain, a former locomotive engineer, began using a body-powered prosthesis (a system where a series of straps link the natural movement of the body to manoeuvring the device), shaped as a split hook for grasping objects. But it’s an exhausting process, as the athlete describes in an article from SFU News (..) ". Cordella et al. (2016)  [1] claim that within the active prostheses,the body-powered ones are controlled by cables fastened to the sound limb of the amputee by means of harnesses whereas "the high expenditure of energy required to the user" is one of the drawbacks of this kind of prostheses.

I use body powered arms, and they are most definitely not tiring to use. It appears that they may be doing something fundamentally wrong there.

Wearing an aluminum hook, weight balance is near ideal (link). If you want to improve myoelectric arms, center of gravity and weight both need to be better; if grip quality and reliability is not a main research agenda, then myoelectric arms can only be sold against the market - and that is very, very hard.

But in terms of specifically making prosthetic arms significantly easier to use (i.e., removing the weird and cumbersome "trigger contractions" and instead offering simple Casio watch type buttons and an LCD display to control grip patterns, no research is being done anywhere. Also, less tiring use means to reduce cable friction and optimize device weights against increased performance; that is not done anywhere.

Recently, body posture becomes a focus for "researchers"; in one new study [4] they try to find out differences in body posture when conducting a "clothespin relocation test". This is actually funny. There are absolutely no (available, current) options for prosthetic arms to make them "better" for posture: the myoelectric socket options are totally limited and no one wears a myo arm for sweat generating levels of work anyway (can you guess why?) and body powered arms are usually designed by default in a specific way so the user wants to stop using them, so prosthetists usually make an effort to design them using sweat adopting plastics (ew), uncomfortable harnesses and ugly appearances in order to "motivate" the user to ask insurances to pay for an insanely priced myo arm (which is massively better business for the prosthetist). No one gives a damn about a clothespin there. Seeing as if that is the case, and seeing as if the few arm amputees that DO work hard manual jobs have virtually no design or build options anyway, your guess is as good as mine as to why on earth these "researchers" sit down to relocate clothespins of all things. No arm amputee that I know of, that has one normal (human) hand, relocates clothespins with the prosthetic arm. Now if they went to cut hedges or trim lawns or something else that is "back breaking" work, cool, see if the trunk moves, see what else goes bad, see what we can fix. But that'd be strenuous, and we cannot have that. So as it is, we have "researchers" tinkering away at some minimal activity level clothespin stuff (I guess that is one level up from stamp collecting), we have a ridigly fixed set of options for socket design so posture as such won't be impacted shit, and we have absolutely no heavy to extreme load accepting components anywhere near (and it really requires these components for the type of work that warrants posture improvement to begin with). But no one realizes that.

So, yeah. No wonder nothing changes along that axis.


I invented the "appearance test" (so far rejected by a massively failing industry and fully failing researchers) in the aftermath of appearance-hacking public stares by coming up with the "red hand" in 2009.

If researchers do not start to address well justified appearance concerns we will not be going anywhere with this. Not now, not in 10 or 20 years.

Just as we are still regarding hooks as the ultimate in performance.

More sensory feedback without it

With ultra hard mechanical coupling, my prosthetic hook / wrist / socket / pinlock combination that I wear delivers sufficient coarse tactile feedback for, say, typing on keyboards. However, people like using their hosed arms, and the sentence "I have more sensory feedback without prosthetic arm on" is often given as excuse.

Obviously, body powered arms are just far faster, cheaper, more comfortable and so on compared to myoelectric arms. And harder mechanical couplings also means more vibration that the hardware has to survive.


This is a very overall statement but in essence can only be addressed by making the device totally simple to use, easy to fix and so robust its application is self explanatory.

Even 53% of prosthetic arm adopters list it as reason not to wear the prosthesis.

I have not seen research that obsesses over detailing this important aspect.

More functional without it

Only performance testing under real professional work conditions with true bimanual activities will highlight actual needs for prosthetic arms to excel in.

"Making coffee" or "drinking beer", "holding a bottle" and other Activities of No Particular Prosthetic Need are of no analytical use in addressing this valid concern.

It is particularly pressing, as this aspect concern tops the list of reasons for both prosthetic arm rejecters and adopters. Even worse: "the stump is the best prosthesis" is a truism of upper limb amputation care. Tell me who said this and where to show me you did your research.

Too heavy

This certainly should be seen as a major reason not to add more stuff to prosthetic arms - a requirement is so consequentially ignored by most researchers world wide. Why not come up with motor designs that are very flat and elongated and that then sit towards the elbow?

More comfortable without it

Comfort is just something we all want. Ever thought of that.

No research so far addressed this in an attempt to make a prosthetic arm that ends up being more comfortable to wear for the user than not wearing it.

Medical reasons

A very relevant aspect - medical reasons - are mentioned both by prosthetic arm adopters - obviously wearing a prosthetic arm causes medical problems. Research geared towards reducing negative medical impact of prosthetic use on stumps or overall condition such as posture and joints or nerve compression is mostly absent.

Actual research priorities and how to go about them based on literature review

Center of balance and weight of the prosthetic arm seem to interact with the individual's constitution. How?

Tiredness is named as key reason for non-users relative to users of prosthetic arms as a cause of rejection. This is largely ignored in current research - obviously, as researchers tend to cite sloppily or even wrongly when typing out their research premises or "previous works" (I shall blog post about specific examples later). What does tiredness entail? In my experience, it is an all encompasing EODF (end of day feeling) that results in a less precisely worded "tiredness" (link). Can this be analyzed in sufficient depth?

Functional with it, functional without it. When I am more functional without the prosthetic arm, I obviously sort grip / activity patterns differently, both in left/right and time domain. I obviously understand a lot about grips when I go about stuff without prosthetic arm on. In other words, I get the stuff done "differently" but, in terms of the outcome or result, same same. What is really behind that? What can be learned from that for prosthetic design? When a prosthetic arm alleviates the side-by-side difference for work and play with and without the prosthetic arm on, does that tire out the user less? Why does Otto Bock's demonstration artist use his mouth to sort his PC cables while wearing a Michelangelo hand? Is holding / rolling of cables, handling of rechargers, handling of laptops without dropping them, a relevant activity in our society? Does the research faction know? If they do not read blog entry observations, how will they find out? Not trying to be funny here - these are eye opening moments where a lot can be seen and taken for prosthetic design (if, that is, one plays one's cards right)?

Build profession-specific prosthetic solutions to actual bimanual problems. If you go about it practically, you will find a way.

Crack the appearance test by building a truly life like prosthetic hand. Don't try do dodge this. Really. Just. Do. It.






[1] [doi] F. Cordella, A. L. Ciancio, R. Sacchetti, A. Davalli, A. Cutti, E. Guglielmelli, and L. Zollo, "Literature review on needs of upper limb prosthesis users," Frontiers in Neuroscience, vol. 10, iss. 209, 2016.
 AUTHOR={Cordella, Francesca  and  Ciancio, Anna Lisa  and  Sacchetti, Rinaldo  and  Davalli, Angelo  and  Cutti, Andrea  and  Guglielmelli, Eugenio  and  Zollo, Loredana},   
TITLE={Literature review on needs of upper limb prosthesis users},      
JOURNAL={Frontiers in Neuroscience},      
[2] D. J. Atkins, D. C. Heard, and W. H. Donovan, "Epidemiologic overview of individuals with upper-limb loss and their reported research priorities.," JPO: Journal of Prosthetics and Orthotics, vol. 8, iss. 1, pp. 2-11, 1996.
  title={Epidemiologic overview of individuals with upper-limb loss and their reported research priorities.},
  author={Atkins, Diane J and Heard, Denise CY and Donovan, William H},
  journal={JPO: Journal of Prosthetics and Orthotics},
[3] E. Biddiss and T. Chau, "Upper-limb prosthetics: critical factors in device abandonment," American journal of physical medicine & rehabilitation, vol. 86, iss. 12, pp. 977-987, 2007.
  title={Upper-limb prosthetics: critical factors in device abandonment},
  author={Biddiss, Elaine and Chau, Tom},
  journal={American journal of physical medicine \& rehabilitation},
[4] A. Hussaini, P. Kyberd, and others, "Refined clothespin relocation test and assessment of motion," Prosthetics and Orthotics International, 2016.
  title={Refined clothespin relocation test and assessment of motion},
  author={Hussaini, Ali and Kyberd, Peter and others},
  journal={Prosthetics and Orthotics International},

Cite this article:
Wolf Schweitzer: - Constraints in prosthetic arm research (literature review); published 01/06/2016, 12:11; URL:

BibTeX: @MISC{schweitzer_wolf_1653029267, author = {Wolf Schweitzer}, title = {{ - Constraints in prosthetic arm research (literature review)}}, month = {June}, year = {2016}, url = {} }