Myoelectric prosthesis - presales evaluation

Before going out there and considering any of these, it is good to find out the range of "manu"facturers there is.

General issues

I have a long history of tinkering and come from a high tech oriented engineering family; an aunt grew semiconductor single layer crystals, my dad headed a robotics department, an uncle was a high-frequency electricity circuit specialist and worked for a patent office, another uncle developed polymer coatings for artifical blood vessels, my grandfather built construction lines, some relatives are in construction, one is a surveyor and so from computers to cars, mechanical parts to design issues, hardware to software, we would be a very interested group of people, interested in all sorts of issues.

From that, I don't just sit there and go 'Oh'. Other than just inspecting a manufacturer's product range, I want to know whether technical problems are dealt with productively, whether a "list of known issues" (similar to good public domain software) or a problem history is published (open and closed tickets), whether product specifications are detailed (how long has each part worked, where on a particular model did how many complaints get back to the company) and so on.

I want to know what other people that are both independent and critical have to say. Are there constructively critical analyses available at all? Why not? Is it a technical product at all (and then if yes, can we know tolerances, weight, material, ...) or is it sold basically as a "Playmobil" item ("what you buy is what you see on the picture of the cardboard box and no tech specs published")?

Is there a precise price and if no why not? How was the water resistance tested and what was the result? How was performance in dirty environments tested and what was the result? What spontaneous failures had what exact usage history? In other words, I want the full and extensive Stiftung Warentest rundown on these products, and I want this information upfront.

And there is a good reason. Most if not all of these prosthetics are paid for by public money or semi-public money from insurances. If I am going to ask for any of this for a myoelectric prosthesis I would like to know precisely why. If I am financing it myself, I want to know even more.

Motion patterns. Naturally and most often, our hands use motion patterns rather than individual finger movements. A scientific article (ingram2008statistics) (Ingram, 2008 - Copyright Springer-Verlag 2008) showed that individual thumb and index finger movement along with some often used grip patterns could do the trick. Multi-electrode software is being developed in various places; both in Sweden as well as the USA.

The statistics of natural hand movements - Journal Experimental Brain Research - Publisher Springer Berlin / Heidelberg - ISSN 0014-4819 (Print) 1432-1106 (Online) - Issue Volume 188, Number 2 / June, 2008 - DOI10.1007/s00221-008-1355-3 - Pages 223-236 - Subject Collection Biomedical and Life Sciences - Springer Link Date Friday, March 28, 2008

James N. Ingram 1 , Konrad P. Körding 2, Ian S. Howard 1 and Daniel M. Wolpert 1

(1)  Department of Engineering, University of Cambridge, Trumpington Street, Cambridge, CB2 1PZ, UK
(2)  Rehabilitation Institute of Chicago, Departments of Physiology, Physical Medicine and Rehabilitation and Applied Mathematics, Northwestern University, Chicago, IL 60611, USA

Humans constantly use their hands to interact with the environment and they engage spontaneously in a wide variety of manual activities during everyday life. In contrast, laboratory-based studies of hand function have used a limited range of predefined tasks. The natural movements made by the hand during everyday life have thus received little attention. Here, we developed a portable recording device that can be worn by subjects to track movements of their right hand as they go about their daily routine outside of a laboratory setting. We analyse the kinematic data using various statistical methods. Principal component analysis of the joint angular velocities showed that the first two components were highly conserved across subjects, explained 60% of the variance and were qualitatively similar to those reported in previous studies of reach-to-grasp movements. To examine the independence of the digits, we developed a measure based on the degree to which the movements of each digit could be linearly predicted from the movements of the other four digits. Our independence measure was highly correlated with results from previous studies of the hand, including the estimated size of the digit representations in primary motor cortex and other laboratory measures of digit individuation. Specifically, the thumb was found to be the most independent of the digits and the index finger was the most independent of the fingers. These results support and extend laboratory-based studies of the human hand.

Reliability. This is a huge issue. A nurse reported myoelectric failure in the middle of an emergency injection procedure, other people report about very awkward myoelectric failures in the middle of a critical applications in public - and as disabled person, that is a real nightmare. I will rather wear a robust and predictably functioning mechanical hand with a failure rate of 1/10'000 or less than any sophisticated device that will fail the grip in 1/5 to 1/10 situations.

Cost and insurance coverage. This is also a relevant issue. If insurance covers it, we need the prosthesis to be as functional as possible for as cheap as possible. - If I pay for it myself, I am going to look for the 'toy' aspects of the arm as expensive toys require lots of twiddle appeal and a wide spectrum of user accessible applications. Can I program it myself? Can I teach the software motion patterns? Can I work with 10-20 electrodes? Can I use the socket with the many electrodes to control a computer directly via USB and an interface control panel? Is the battery an industry standard the I can easily replace? Is it modular? - As when buying a scanner, intelligent driver software and industry standard compliance are the key issues here.

1. Otto Bock - Myoelectric Arm Prosthesis

Otto Bock sells the Sensorhand Speed.

To me, the hand does not appear to be very fast. The grip is thought to crush light objects while the hand seems to be relatively powerful (compared to the iLimb which is specifically designed for light weights rather than medium to heavy ones).

As a sturdy myoelectric prosthesis, however, Otto Bock may be a good option particularly as they also sell a strong grip mechanism.

On the more interesting high tech end, Otto Bock develops the Michelangelo hand.

2. Touchbionics - iLimb

The iLimb is a great product. It is designed for the 'myoelectric / light usage' application domain.

As I wear a prosthesis to please two basic groups of people (A: myself, B: my immediate surrounding such as friends, co workers) I ask myself what - in context of 'light usage' - would I use the iLimb for. I (A) want the prosthesis to be reliable and as that, optimally sophisticated. Others (B) would want my disabled arm (with or without prosthesis) to not disturb them as the main feature. Comparatively, cable controlled means to get ultrafast, silent, lightweight and elegant control.

Meetings, parties, dinners. Social functions cause me - as the visibly disabled person - to be responsible for the tension management. While I (A) require some function, the rather noisy wee-wee-wee of the motor is a bit distracting for others (B) and may conflict with a moderate functionality (holding glass or bottle works well; keeping knife or fork still rather risky). Now, I play things safe and ask the waiter to have the meat cut up in the kitchen for me anyway - and at that moment I can do without prosthesis or with anything else. Tension may be managed efficiently in a variety of ways.

People attack my notion of calling a prosthesis 'toy' and the troubleshooting and improvement of it 'playing' - but in reality, engineering always takes a good amount of extended tinkering and good results of systematic 'playing' (testing boundary conditions, trying to extend limitations, trying to highlight systematic design issues) are always welcome in any engineering community. In this instance and given the noisy product, I'd tinker with hardware or software solutions to firstly limit the motor speed - either by allowing for a "social" program or by adding a knob potentiometer to reduce voltage to all motors, as the high pitched wee-wee sounds surely stem from a full speed action of a little motor - whereas a lower speed likely would be less noisy. Maybe the noise does not come from all motors equally. This is one of the reasons why, given any such system, I'd want to be given the option to extensively 'play' with it. The device needs to have accessible wires and full documentation.

Playing the guitar. No way - I tried with other attachments to the prosthetic socket and there is simply no way that I play using a prosthesis. As I am on my own playing with the left hand 'only', no need for an iLimb or other prosthetic options here.

High reliability applications, full force tool working. With a cable controlled prosthesis, I am spoiled - I get full action 24/7 and I can push or pull full force. The iLimb has a beautifuly fitting lock around complex objects but it may require great caution to not use too much force.

High reliability applications, low force fine control work. For dissecting tissue and fine medical / tissue handling operations, I see a huge potential for the iLimb. That is where the product will excel if the fingers can be built cut proof and if the myoelectric control can be geared towards a very high reliability. This includes both control and battery that will have to operate under operating theatre type garment conditions (full sweat).

3. Dr. Stefan Schulz / Handprothese.DE - FluidHand

Repeated requests to that company regarding their product remained unanswered (status of November 2008).

4. Motion Control Utah Arm -Motion Control ETD Electric Terminal Device

5. TRS

Cite this article:
Wolf Schweitzer: - Myoelectric prosthesis - presales evaluation; published 19/07/2008, 20:45; URL:

BibTeX: @MISC{schweitzer_wolf_1638800160, author = {Wolf Schweitzer}, title = {{ - Myoelectric prosthesis - presales evaluation}}, month = {July}, year = {2008}, url = {} }