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Levitated Prosthetic Limb

Eliminate the Pressure Points of a prosthetic limb
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Probably I should make a better research before I talk about this idea. However, where there are so many resourceful people around, who needs that.

I learned that despite the advancements in prosthetics technology, the fitting process of artificial limbs is still accomplished by tailoring the prosthetic limbs for their users. For example, if your leg is amputated, after the healing process, someone will have to design a specific prosthetic leg for you. Then continue refitting since the shape of your limb changes during the healing process. Sometimes, - similar to new-shoe blisters, (of course a lot more serious) the prosthesis may cause the surgery points to open up, causing complications. Especially, the diabetic patients can suffer greately. In my opinion the fundamental problem is the fact that weight of a person cannot be transmitted through an artificial limb to the cut leg without compressing (stretching, pinching etc) the skin between the artificial limb and the leg.

Therefore my idea and question is:

Couldn’t we fit the end of a cut bone with a special magnetic device that can heal into the leg and then build a reversed powerful magnet into the artificial limb that would repel that device? This way we could eliminate or decrease the pressure on the skin. What would it take to build one? Powerful magnet, superconductors?


cekirge, Mar 15 2002

Osseointegrated Prostheses http://osseointegra...ns.com.au/index.htm
Diret to bone mounted prostheses [oneoffdave, Jul 06 2005]


       Interesting idea. I don't think that current battery tech. would be up to the job of powering this. Plus you'd need some sort of super conducting magnet to generate that much lift quickly. Perhaps an internal generator could help by boosting the power but it'd have to be v.efficient to work properly. Don't think current technology could do this but I like the idea.
dare99, Mar 15 2002

       Except for when the regulating electronics go wrong and fire the leg off in the manner of a gauss gun!
dare99, Mar 15 2002

       the magnet would have to be a rare earth magnet like neodymium in order to be of any use, in which case you would be likely to get lead and metal posioning... the particles in your blood would get caught in the field around the magnet... and you would get cancer... bad idea...   

       -To Dog Ed, the magnetic field itself will hold and trap the fine metals in your blood against the wall of the veins and cells near the tissue close to the magnet... you can however shield or better redirect the fields away from the limb... now that I think of it this might actually work... I have some extra HD neodymium magnets that have a near monopole... this could work becuase they are nearly flat and the magnetic side is primarily on one side and almost non-existent on the other...
oxygon, Mar 15 2002

       oxygon--could one coat a neodynium magnet with teflon to permanently seal it off from body fluids? And even if the magnets take only a fraction--say, a third--of the weight off the limb/prosthetic socket then that would probably benefit the amputee greatly...hmmm. Think it over...
Dog Ed, Mar 15 2002

       I'm stumped.
Perhaps there should be a silicone or somesuch 'buffer zone' material between the organic leg and the artificial leg. Not silicone like in breast implants, but like in hearing aid molds. Example: There are some hearing aid molds which have a combination of hard (external) and relatively speaking - soft (internal). The hard surface can be solidly attached to artificial leg and the softer material adjacent to to leg itself. Eventually the softer material shrinks a bit as well as hardens, though the comfort factor is superior to those units which are hard from the beginning and also don't 'break up' (when putting aid on or removing) as easily as those which are made entirely of softer material. Replace the mold as needed - once a year may be as often as necessary. Croissant for thought of making many peoples lives easier - even in your imagination.
thumbwax, Mar 15 2002

       You might want to try this with real magnets first, and see what happens as you put a lot of pressure on them when in a repulsive orientation.   

       I've found that it takes quite a bit of force to keep them aligned. If you find a solution to that, you might have something. Maybe you could have a standard plug-shaped rare-earth magnet in the bone, and a doughnut-shaped rare-earth magnet in the prosthetic in order to force alignment. I dunno.   

       Also, consider that if you have a limb gap, you'll have impact forces due to flesh/prosthetic collisions with each step. I'm not saying it's a huge or unsurmountable problem, but something to keep in mind for joints like knees.
lumpy, Mar 15 2002

       Would it be silly to have those plates and screws that they put on badly broken bones attached to the bone and then protruding from the leg and supporting the prostetic limb far enough away to prevent rubbing? This would not neccesarily be permanent though I do not know how it would be changed over to normal prostetics without further surgery. Are there alredy prostetics like this?
chud, Mar 15 2002

       Permanent magets in repulsion are always unstable. You need active control which is expensive and complex, to make magnetic repulsion bearings usable. In this case you need attraction too to prevent the limb flying off under load reversal (the knee sometimes works in tension). You could have the active element in the prosthetic, sensing inductance and pulsing an electromagnet to regulate distance, but I think you would need at least 3 independent coils to make it stable. You might just get enough power to run it from damping the motion of the ankle joint with a dc generator but I doubt it. I suspect power requirements of 100W or so and £10000 per prosthetic. This is cutting edge robotics tech, but I don't think it can be done otherwise. Anyone?
shameless_self_reference, Sep 09 2002

       *seemingly* oh how gently put... I have a big mouth and a 1979 Boys Own Book of Knowledge. If I said "Lucasian Professor of Theoretical Physics at Cambridge University" you probably wouldn't believe me, so we'll just keep it a mystery shall we?
shameless_self_reference, Sep 09 2002

       An interesting idea. One problem I see is that the rare earth magnets can be POWERFUL, enough so to possibly try and rip loose of the bone to rotate into attraction position, which would probably be a Bad Thing Indeed.   

       Another problem is that all the weight would be borne by the bone, then, rather then using the tension of the <now unattached> muscles. Not a bad idea, though, especially for a newbie.   

       Very good first run.<I know, by now you're not really a newbie anymore, but I've been gone for a while...>   

       Shameless, would active control be necessary, in the relatively constrained area of a prosthetic? Design it right, and the two can only telescope, not rotate with respect to each other, aside from catastrophically...   

       Attraction could probably easily be met by just some straps and a belt.   

       Oxygon, have any websites referencing the problem with the metal in your blood? I googled, but got quack pages about magnetic bracelets.
StarChaser, Sep 11 2002

       StarChaser: I dont know... As far as my memory serves me I was reading a website a few years back that noted the ill effects of magnet laiden matresses and clothing, etc. Neodymium Rare Earth Magnets would have to be used for "cekirges" device becuase they offer the strongest magnetic field short of strong electromagnetic fields (which would be a bigger problem for the same *if not even more* reasons). I cant state any facts or research studies but I thought the website did make some very good points about possible *ill effects*... I would only say that common sense may jump the gun hear but it sounds logical to me.
oxygon, Sep 11 2002

       [sc] I suppose you're saying you could have a whole artificial knee joint and put the stump into a sort of cup that constrained it to translation along the bone axis. I was thinking along completely non-contact lines but you are of course correct! You need a keyway of sorts on the leg to stop rotation(?) Say we have a 70kg adult. I don't think we'll get the 350N we need from this given the area of the bone end and the airgap. You might get a 30mm diameter magnet on the bone but then you need a gap between it and its repulsive pair for the flesh flap over the end of the stump you are trying to offload (5mm thick?). Allowing 5mm of clear air you are talking about a 10mm effective airgap. With rare earth magnets at 0.9 tesla remenant magnetisation you might get 10 bar repulsive pressure with zero air gap (you don't get your whole B^2*A/2*mu because of mutual demagnetisation). But you have the 5mm of flesh flap as an airgap, so you might just get 5 bar, giving 33N. Not worth the hassle of the implant I think! Yum, there were some juicy numbers in that idea, more please.
shameless_self_reference, Sep 11 2002

       I'm inclined to suggest embedding a titanium pin in the end of the severed bone, and using nailbed cells grown in culture, create a cuticle to seal the hole. Then, attach the prosthetic to the pin; alternately use a titanium 'bone' and build the prosthetic around it. Bonus points for modeling the skeleton of the prosthetic on CAT scans of the other leg.
Chrontius, Jul 05 2005

       Pin-protruding-from-bone prosthetics are baked. Users screw the prosthetic onto the pin. Initially they have to spend some time progressively putting more and more weight onto the pin before it is usable. The prosthetic limb extends where the bone would normally be.   

       The pin is threaded on both ends and does not remove itself from the bone; the bone heals around the concealed part of the pin, the pin is permanent. The skin heals right next to the pin without any cuticle grafting.   

       People with these prosthetics feel the prosthetic is part of them and some even claim thay can feel things the prosthetic touches.
joeforker, Jul 05 2005

       I suspect this (ie what follows) is a silly idea, but....following on from the previous anno, why is it not possible to build a "prosthetic bone" ( similar to the replacement hip or knee joints, but including the complete bone shaft and a 'foot bone'), and have skin grow over it?
Suppose you have a below-the- knee amputation. You start by surgically fitting a 'socket' to the stump of the bone, short enough that the skin can be stretched over it and allowed to heal and grow. Then, you fit a short segment of 'bone' (titanium or whatever), and again stretch the skin over that. As the skin grows, you increase the size of the implant until you have bujilt a complete skin-covered leg.
Yes, I know it will lack muscles and will function no better than a regular external prosthesis, but at least this 'internal prosthesis' is solidly attached to the bone of the stump.
Basepair, Jul 05 2005

       As an 'expert' in this area I felt I had to comment. Silicone socks are already used to cushion the limb/prothesis interface. You need really good contact between the prostheiss and the limb to keep dexterity and I think this would reduce that. My current limb attaches via a pin mounted on a silicone sock. Comfy and easy to don and doff. Though a new limb is a bit like a new shoe and does take a little breaking in.
oneoffdave, Jul 06 2005

       One-off, if you don't mind my asking, is there a reason it's not possible to reconstruct a limb at least as functional as a passive prosthesis by implanting progressively larger 'bone extensions' (effectively as they sometimes do when replacing damaged joints)?

Actually, now that I think about it, maybe it would be a lot of hassle for solving a small problem. I guess the only advantage would be in the 'direct' connection of bone-to- prosthesis (and the associated freedom from chafing), and maybe this isn't such a big problem in the long term?
Basepair, Jul 06 2005

       [basepair] Theoretically it would be possible, though 'turning the corner' for a foot and making the ankle of a suitable flexibility would be tricky. I wouldn't go for it myself as it would take a lot of work/surgery and you'd have long perionds of not being able to use it.
oneoffdave, Jul 08 2005

       Yeah, I sort of figured it might not be worth the hassle. And I would imagine that 'growing' the sole of the foot would be tricky - I think the original one has all kinds of weird subcutaneous structures to make it tough enough.
Basepair, Jul 08 2005


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