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Richard Erlacher
09/21/12 21:46
Read: 573 times
Denver, Co

#188422 - The price target comes from a few prosthetists
Responding to: Oliver Sedlacek's previous message
Oliver Sedlacek said:
In general I think that any new product must be developed in three phases:

A - make it work

B - make it good

C - make it cheap

I don't know where you got the target sales cost figure of $5K from,

I agree with your assertions. I got the price target from talking to a couple of prosthetists. They work independently as contractors to hospitals/healthcare provider groups, rather than being part of a hospital/or healthcare organization. I'd guess a real prototype will cost on the order of $75k U.S. but I don't see a way to push the price down to where I was told a fellow might actually afford such a device. After all, it's only applicable to subset of the cases that the prosthetist has to handle, and, in fact, only to a subset of those. As a result, the apparatus must not only be reasonably priced, but also reasonable in size.

but that seems ridiculously cheap for any form of medical equipment. After all, I suspect the advanced prothesis cost more than that. I would press on with the concept you like best because designing it down to a hard cost target may mean that you just give up or you make something substandard that doesn't do the job. If you are first to market you will be setting the price expectation.

Well, this is just another proof-of-concept challenge, though it's mostly mechanical rather than being mostly electronic. The problem that I'm addressing at the moment is the definition of the problem, as nobody seems to know what the relative importance of such things as tissue density and distance to the bony structures is. They do agree that they are important, though. In the past, the problem was addressed as a whole, simply by taking a cast of the amputation stump and noting the location of the bony protuberances and major structures. In this approach, some importance has to be assigned to the relative locations of hard vs. soft tissue.

Over time, the technology associated with fitting prosthetic devices of the type that specifically interests me has been focused on fir, suspension, and alignment of the prosthetic limb. Much effort and technology has been devoted to the development of energy-storing types of feet. Collaboration between surgeons and prosthetists has reduced the business of fitting below-knee prostheses to a process of assembling off-the-shelf components, together with casting and applying an individualized socket, in which most of the weight is borne on the amputee's patellar tendon, much as it is on a normal leg. Most often, a somewhat flexible liner, somewhat reminiscent of a condom, is rolled onto the stump. This liner has a step-pilot on it, one that fits into a socket built into the portion just below the socket for the stump, and that aids in holding the stump in position, therefore suspending the prosthesis from that liner. Additionally, an external sleeve is applied to the entire assembly, restricting the airflow between the socket and the liner, which then forms a pneumatic suspension. Unfortunately, the most popular form of liner allows the suspension to yield in the vertical plane, thereby allowing a bit of "pistoning" which, in those cases, such as my own, where there may be one or more bony protuberances, tjat cam caise problems as the upper and lower surfaces corresponding with those protuberances alternative take pressure.

The fit is VERY critical, and, with current technology, is possible to accommodate thanks to cooperation between surgeon and prosthetist. However, in cases, such as my own, a traumatic amputation, the surgery was done with an emphasis on restoring the knee to full operation at the expense of neat and clean arrangement of the bones. The fit of my prostheses has been complicated by the resulting protuberance, and by the rather odd swelling that I still experience.

Prosthetists keep quite an array of components in stock, which means they have to invest a considerable amount in those components, hence, as individual businessmen, they are unable to invest many thousands of dollars in equipment that is applicable to only one type of prosthetic application. Oddly enough, the problem of fit is much better addressed today than it was ~30 years ago when I had my second amputation. The problem I'm trying to address is the fit, which is probably the most straightforward portion of the problem. This is the most costly portion, too, because it requires considerable labor and all the involved components are lost if the fit is unsuccessful. The suspension is the aspect of the task that is most critical to my own comfort, but there's a simple solution to that, and it's also bsed on fit, as the off-the-shelf liners popular today don't work on many traumatic amputation patients, such as I am.

I've spent lots of money on prostheses, as has the Veterans' Administration, yet I've had few really successfully fitted limbs, due to the way in which the job is done. I'm thinking that automating the fit of stump and socket will reduce the labor cost and material waste that often occurs in this process. Unfortunately, it has to be done inexpensively, because the individual prosthetist won't be able to invest a large amount in an apparatus that deals with something in which he's already invested a considerable amount.

The technology now exists by which, under computer control, a positive model of the stump with computer-edited modifications to accommodate differences in tissue texture, both the socket and the liner can be made with great precision and without ad-hoc application of experienc/black-magic. This has never been done, so far. With 3-D printers capable of producing a positive model without the error inherent in making a negative model (cast) and transferring/altering it in order to make a positive model on which the socket and liner can be based, I'm convinced that the process can be vastly refined.


List of 49 messages in thread
How would you do this?      Richard Erlacher      09/10/12 10:30      
   I have no idea if this would work, but ....      Erik Malund      09/10/12 10:32      
      How would one actuate them?      Richard Erlacher      09/10/12 12:29      
   strain guage      Mahmood Elnasser      09/10/12 11:03      
      Yes, you might be onto something.      Richard Erlacher      09/10/12 12:49      
         Computer-controlled?      Per Westermark      09/10/12 16:37      
            computer controlled      Richard Erlacher      09/10/12 19:52      
               Calibration + redundant force-limitation      Per Westermark      09/11/12 00:03      
               Interesting problem      Jim Granville      09/13/12 15:06      
                  Yes, it seemed coarse, at first.      Richard Erlacher      09/13/12 17:08      
                     Precision is cheap ?      Jim Granville      09/14/12 15:15      
                        I don't follow ...       Richard Erlacher      09/15/12 09:59      
                           Precision      Jim Granville      09/15/12 19:09      
                              other considerations      Richard Erlacher      09/15/12 20:15      
         Tomographic imaging?      Christoph Franck      09/11/12 04:47      
            There's one major problem ... maybe two ...      Richard Erlacher      09/11/12 09:20      
               $100 MRI unit      Erik Malund      09/11/12 09:31      
                  I'm not sure ...       Richard Erlacher      09/12/12 09:57      
         Voice coil and LVDT?      Oliver Sedlacek      09/12/12 02:37      
            Not having a lot of experience with this sort of stuff ...      Richard Erlacher      09/12/12 10:07      
               Danger/problems with hydraulic since no spring effect      Per Westermark      09/12/12 13:55      
                  A few things puzzle me with this approach      Richard Erlacher      09/13/12 02:07      
   Ultra Sound Probing      Michael Karas      09/10/12 16:36      
      Ultra-sound is better for measuring surface or sub-surface      Per Westermark      09/10/12 16:39      
   I would not use volumetric imaging      Justin Fontes      09/13/12 11:05      
      I'm not sure what you mean      Richard Erlacher      09/13/12 16:59      
         another thought      Rick Gebhardt      09/17/12 13:43      
            I consider that one of the more "pregnant" approaches      Richard Erlacher      09/17/12 15:25      
               Lots of options available      Per Westermark      09/17/12 16:14      
                  You've got to consider cost      Richard Erlacher      09/18/12 16:50      
                     Cost/safety      Per Westermark      09/18/12 18:29      
                     Cost target?      Oliver Sedlacek      09/21/12 08:37      
                        The price target comes from a few prosthetists      Richard Erlacher      09/21/12 21:46      
   comercial CMM      Mahmood Elnasser      09/17/12 13:58      
      This only received cursory examination       Richard Erlacher      09/17/12 15:28      
         pneumatic actuator      Rick Gebhardt      09/17/12 20:14      
            Yes ... but what would this cost?      Richard Erlacher      09/17/12 23:30      
               100 rods?      Per Westermark      09/18/12 02:04      
                  Patient size ...      Christoph Franck      09/18/12 06:12      
                     That's what I'm considering      Richard Erlacher      09/18/12 07:50      
                     AAACK! ... another double post ...       Richard Erlacher      09/18/12 07:50      
                  it's not as big as you think!      Richard Erlacher      09/18/12 07:40      
                     90% coverage      Maarten Brock      09/19/12 03:47      
                        So maybe vacuum pump for the too fat people      Per Westermark      09/19/12 06:38      
   I do not know if this is relevant, but      Erik Malund      09/19/12 07:52      
      I'll have to look into this.      Richard Erlacher      09/19/12 09:13      
         Single air pressure sensor sensor for tip force guestimate      Per Westermark      09/19/12 11:27      
   What about infrared?      Marshall Brown      09/21/12 03:03      
      How would you do this so it would retail for under $5k      Richard Erlacher      09/21/12 08:21      

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