"Applied Physics 101"

[snarfler]

I am not a Prosthetist. I am an Engineer. What is an Engineer? We design things. We create what doesn't exist or improve what does. We do not however drive trains. We remain humble and work by a simple rhyme, "I never blow the whistle or get to ring the bell but let that puppy jump the tracks and see who catches hell"
 
Allen,
PTB stands for Patella Tendon Bearing. Meaning your socket is designed to bear weight on your Patella Tendon. To find your PTB, remove your leg and liner. Take your thumbs and place them directly below your Patella (knee cap) now apply your fingers to the area behind your leg. This is the area that takes the majority of your weight in your socket. Its like a 1 inch band around your leg. Aside from medial and lateral support, all other areas are nonessential. You may wish to read more about it here:  www.oandplibrary.org/al/1962_02_001.aspre

The kit I mentioned is available (I imagine) from any Prosthetist or perhaps one could do it themselves. See further advise for Steve.

 Steve,
I have to admit the thought of you cutting up after market "Titties" is admirable and hilarious. Please don't be offended. I admire your zeal to find the right product. If I understand you correctly, the product you need is called Jellied Fiberglas and available at any auto parts store such as Pep Boys. Here's how I used it successfully.
 
Lightly sand the inside of the socket. Place a small piece of craft foam over your Tibia and Fibula. Don your liner perfectly making certain the pin is correctly positioned. Now apply a 3 ply sock. Now apply a Bread bag. Now apply a disposable 1 ply sock. Whip up a small amount of Jellied Fiberglas and apply a thin but fare amount to the socket but avoid the distal* area. Step into the socket and enjoy the warmth of the slightly exothermic effect of the product as it hardens. If you've mixed the product properly, it should harden in less than 20 minutes or so.

Once hard, you may hit the button and remove your leg. What you will find is the 1 ply liner has adhered to the Fiberglas which has adhered to your socket. Leave it there. Remove the bread bag and 3 ply liner. As the product continues to cure it will shrink slightly. Hence the 3 ply. Now don your leg and you will enjoy a perfect first generation socket.

The best distal* cushion is to cut a circle from an old liner.

Note this well my friends that the best advise I can give you is to refer you back to the person who made the leg. Even slight changes to a leg can result in knee or even hip problems which neither I nor this board will be held responsible for.


*Distal, The area furthest away, the end of your stump or residual limb. You never want pressure in this area as your bone can chew through your skin. Any pressure must be placed on the sides of your limb and the PTB. 

[snarfler]

Oh. I forgot. Remove your liner and discard the foam from your Tibia and Fibula. Good luck.

[SteveInMd]

Snarfler - thanks for your pro-quality input. I've been a creative do-it-yourselfer long enough to realize I need to stick to reversible modifications whenever possible. Fiberglass resin to the inside of my socket risks a real problem that would be very tough to reverse. And I fear my insurance would balk at paying for a replacement if I ruined the one I have.

So I'm currently messing around with a low-temp thermoplastic I had on hand. Softens to something similar to modeling clay at about 60 degrees C. It's actually from a splint made by my OT in rehab. Seems to be "friendly plastic" a.k.a polycaprolactone. Soak it in hot water, fish it out, pat it dry, and it can molded to shape over the next 5 minutes or so. I've found that household waxed paper makes an excellent mold release. So I've messed it up a dozen times already, and I'll have fun messing up the modification six more times before I'm done.

But a silicone bra half stuck to the bottom of one's stump strikes me an innovation worth trying for many of my stumpy peers. It solves a problem that previously had me . . . stumped.

Steve

[allenuk]

My problem is that I want a flexible cushion between stump and socket. The nearest I've seen (apart from gels and Steve's 'invention') is the 'pump-up' socket, developed my Michael Love, a New York prosthetist. He runs a website and forum called 'Amputee Treatment Center', but as far as I know the device (based on pumping varying amounts of air into a 'balloon'-type lower liner) is only available from him, in New York. Bit far away for me.

A

[SteveInMd]

Feb 8, 2014 4:51:54 GMT -7 allenuk said:

My problem is that I want a flexible cushion between stump and socket. . . .

Perhaps Allen and/or Stonecutter might benefit from this, fits *inside* the liner, but comes up higher than the silicone bra idea:
www.silipos.com/Products/Prosthetics/Pads-&-Accessories/Mineral-Oil-Gel-Roll-On

Otherwise, I suppose either of you might consider Snarfler's concept, but perhaps using soft silicone resin rather than fiberglass:
www.smooth-on.com/Silicone-Rubber-an/c2_1115/index.html?osCsid=4dsi76v9t2qsfngf4rfumrrh73

If #1 is inadequate, and #2 is daunting, I suppose trying a thicker liner might be an option.  I see they come in 3mm, 6mm, and even 9mm thickness.  A thicker liner might require re-casting to create a more commodious socket, however.

And for Stonecutter, when my own distal tibia was sore and banging against the inside of the socket, I took a couple of maxi-pads (yeah, feminine hygiene products, what is it with this guy and women's stuff?), and stuck them on the inside of the socket just to the left and right of where the tibia was hitting.

The  pads don't hold up well to wear in the socket, but they come with adhesive backing in a range of thicknesses; they're cheap and widely available.

Hope some of this helps,

Steve

[SteveInMd]

I just wanted to share a fascinating image I came across.  CAT scans of two different patients, each with bilateral BKAs, while wearing their prostheses.  It's essentially a cross-section image as if the legs were sliced down the middle ("coronal plane").  Shows hardware, bone, flesh, liner, air pockets, surgical remnants, and more.  The left is a pin lock socket, the right would seem to be a suction type.


It's from:  "Seasonal variations of stump volume in transtibial amputees" by George Papaioannou.  I came across it from looking at another publication by Mr. Papaioannou, A Novel Socket Design with Volume Adaptation Properties   
That last paper discusses a socket design quite similar in concept to Michael Love's "Pump It Up!" but with more exacting development.  Perhaps if western New York is too far for Allen to travel, a trip to Cyprus might be feasible.

Best wishes,

Steve

[allenuk]

I know you don't 'do' geography over there...

But just for the record, London-Cyprus is about the same distance as New York-Los Angeles!

A.

[SteveInMd]

Feb 11, 2014 4:53:23 GMT -7 allenuk said:

I know you don't 'do' geography over there...

But just for the record, London-Cyprus is about the same distance as New York-Los Angeles!

A.

Nonsense.  Rochester, NY is quite a distance from NYC.  And you'd be flying, so distance as-the-crow-flies is not the same as overall traveling experience.  According to Travelocity, London to Cyprus would be:

10:10a          4:50p          4h 40m, Nonstop 
LGW              LCA             $319.40
London           Larnaca       roundtrip per person


Whereas the same dates for London to Rochester would be:
12:00p           7:07p          11h 7m, 1 stop
LHR                ROC           $850.10 
London            Rochester    roundtrip per person


Just as important is that Cyprus could be a lovely holiday for a Brit.  Rochester would be even less tolerable than your current horrid UK winter.

Of course, the Cypriot socket is only under development.  However, that could mean free hardware in exchange for being a research participant.  The Rochester socket would probably be utterly unaffordable and surely not reimbursed by the NHS.

Well, maybe both options are totally out of reach.  But nicer to dream of Cyprus than Rochester.  ;-)

 

 

[ann-]

Hi Allen, I am having a similar problem as you seem to be having with one of my BK stumps. I have quite a long pointed stump and have been several years now getting something I can comfortably walk in for more than a few minutes and am currently in the process of trying a liner which is a new venture on this particular leg for me (check socket fitting tomorrow fingers x'd).

I used PTB's back in the 70's and I think they worked well, least they did for me. Back then, mine were made of metal (painted pink) with leather sockets inside. I used these, on one side, till the mid 90's but by then the manufacture side of things had changed and I had no option to change to what most Bk's seem use in the UK, which is more of a total surface fit socket, up until now I have been just been using socks with a peelite inner socket, but am now switching to a Alps Liner. To be honest I preferred the PTB system, I actually preferred the metal legs and leather sockets too, the legs were a lovely shape (for ladies) with a shaped ankle, and the leather sockets kept you much cooler, there weren't the problems with sweating as there are now and the legs were genuinely more comfortable.

From what I am seeing BK amps seem to be having real problems with the fit of their prostheses at the moment and I am not sure why this is. Generally, I have noticed my stump change shape since I changed to the modern type of sockets in the 1990's, it seems to have lost muscle tone and I bottom out very quickly, which has caused problems with end of the bone.

I have seen a flexible liner similar to what you mention, I am not sure of the material used, it was white and very flexible and went between a carbon fibre socket and the liner/sock worn on the leg .... this wasn't part of the set up for an NHS leg though!

[allenuk]

Hello Ann.

I think the flexible liner you are talking about is possibly a Silipos-type 'comfort sock' or stocking. It's like a proper liner, but much thinner, and goes against the skin before the liner proper goes on.

I've had versions of it on and off over the years, without success, so I suspect there might be something in what you say about modern manufacturing methods NOT contributing to socket comfort.

It might well be that plastics are easier to work, easier for prosthetists to cut and amend, than metal, and that's why 'they' have led the move towards such materials.

(In fact, that tired old video of my stump, link below, shows me putting on (a) a 2nd Skin Gel, then (b) a 'comfort sock', and then (c) my main liner... I must make a new video, as my fan base is getting towards double figures).

www.youtube.com/watch?v=uxj3PjGthQs

I'll do a new one showing me using bits of Steve's recommendations, the A-Cup insert, which seems to work okay for me in combination with a Gel pad.

You'd have thought that something as crucial as this, i.e. tissue loss (which MUST happen more or less to all amputees) would have been pursued by the big companies by now... which is why, obliquely, I had a bit of a pop at that student doing prosthetic 'design' the other week. First things first!

Best wishes,

Allen.

[allenuk]

Thanks for the travel tips Steve...

...and fair enough, some Americans DO 'do' geography. Mea Culpa.

But I doubt if I'd get let in to Rochester or anywhere similar, given my political past, unless they're kinder to reds than they used to be.

We might never know.


Best regards from a submerging UK,

A.

[ann-]

No sorry Allen, the flexible liner definitely 'wasn't' a silipos sock (am very familiar with these). This was more rigid kind of inner liner, though it was fairly soft, but more kind of hardware that went with the socket. If you think of the actual socket main frame set up of the leg as Hardware and your normal roll on liners/socks that you use as software. It was definitely Hardware and you actually either put your stump into it, like you would a socket, or maybe pulled it over on top of your liner and socks, though am not too sure on that. The carbon fibre on the outside, also had 'windows' cut in it to allow less pressure on the bony areas. It was also quite lightweight so quite impressive.

[cherylm]

Okay, I'm jumping in here..... That vacuum assisted pinless suspension socket that they had to work so very, very hard at fitting me into last year seems to address a lot of the problems that you folks are talking about. I will say that I don't have a REALLY boney stump...there's just one little spot where bone and skin come very close to each other, and my leg guys have always been able to make adjustments to cover that spot. But with my old pin-lock sockets, I did have ongoing problems with shrinkage, muscle atrophy, and (occasionally) bottoming out and/or "belling."

The vacuum-assisted suspension seems to have addressed all of those issues for me. The fit is much more "natural feeling" to me...I ALMOST stand directly on the end of my stump, with none of that troublesome empty space at the base of a pin-lock socket. The fit is much more along the lines of "overall" contact with the socket, with the vacuum pump holding it all stable. When this socket was first fitted to me, I went through another very sudden and very noticeable batch of shrinkage, but that settled down within about a week. At that point they recast the socket and it's been very stable ever since.

The thing I've been most impressed with, though, is that I've actually regained muscle activity in my stump! The fit of the socket seems to allow for my remaining bits of calf muscle to participate much more in propelling the prosthesis when I walk. I can now actually SEE that muscle flex when I try to do so...before, I could "feel" that there was muscle frantically attempting to flex at my tries, but there was no visible response (just a tiny little flutter deep down inside when I felt for it with my fingers). The result is that I have no pain at the point where bone and skin used to knock into the socket wall, I don't develop back, buttocks, or thigh pain while walking at all, and I can walk longer distances at a much closer to "normal" speed. All of this surprised me...until this leg, I'd honestly believed that I had a "really good" system.

The downside? Well this semi-high-tech leg still takes MUCH too long to put on (although much less than the 45 minutes it took when I first got it!)...and the pump occasionally comes on at really inconvenient times and startles folks...and that same pump is also oddly visible and liable to knock into things once in a while. But the advantages SOOOO outweigh the drawbacks that I'm completely "sold!" And by the end of all those attempts to fit this leg to me, the leg team got pretty efficient at the casting/fitting process.

I don't know if getting away from pin-lock would be as advantageous for your problems as it's been for me, but it might be something to consider.................

[ann-]

wow ... regaining muscle, Cheryl, sounds very interesting. I tried one of the early vacuum sockets about fifteen years ago and it caused me problems, though I don't think it probably fitted me properly. Though it was the end of the stump that caused problems and eventually developed a pressure sore.
I don't currently use pin-lock myself, not sure if Allen does. Glad things are working so well for you now though.

[cherylm]

Thanks, Ann!

[snarfler]

I think it would be in your best interest if I may try again to explain something. Your biological leg is in a, "Flux" state. Constant motion and change. Within your leg you have bone. Bone is in "Static" state. Fixed. Unchanging. The socket is also Static. The shape of your Flux skin over your Static bone creates "Anatomy".

If we could put on a socket and shoot some screws into your bone you would have a perfect fit. Not very practical I'm afraid. In order for the socket to be effective, it must conform perfectly to the anatomy of your leg. To accomplish this we need an interface that will adapt the static socket to the static bone bypassing the flux state in between. Hence the use of a Liner.

All with me so far? So. If we increase the interface with Duct tape foam or Boobies, What do we lose? (Anybody? Anybody?) Anatomy That's right And when we lose anatomy we decrease socket fit. Not improve it. Now for our Lab work. Now open a new jar of Peanut Butter. The jar represents your socket. Now thrust your index finger into the Peanut Butter. Wiggle your finger about. Will increasing the Peanut Butter improve the fit? No. In fact the closer the Finger and jar conform to one another, the greater the fit. Make sense? Our mathematical reference would be Mass times Velocity Squared Divided by Impact over Pi Times the Radius Squared at the PTB. Any questions?

[allenuk]

All true, but what's missing from (a) your analysis and (b) my leg is TISSUE.

I used to have tissue - skin, muscle, etc., etc., filled with water and other similar bodily fluids, and they were my cushion between bone and the outside world.

And, when I first had a plastic leg, my tissue continued to work fine - providing a nice cushion between plastic leg and bone - and I could walk easily.

Over the years, the tissue disappeared. Withered away, just went. Leaving me with skin and bone, and a bit of calf muscle folded over the stump, which has also largely withered away.

So the bit we're trying to simulate is the peanut butter. Because in our NHS-led system of total-contact prostheses, without the cushion, it can hurt. Hurt quite a lot, to the point where walking is cut from miles to yards.

So prof, how do we get new peanut butter?

A

[ann-]

Well, I got new peanut butter from a revision and reconstruction ... which might bit more radical than you are wanting Allen. It was done for slightly different reasons, but that side is now much less problematic to fit, though of course is somewhat shorter.

I am close to considering having the other side done similarly, although its being suggested that it should all be accommodated prosthetically .... currently though I am in a similar situation to you with it and have spent almost the last two years now trying to get something to fit, but its not happening and soooooo frustrating. Imagine you are pretty frustrated with it all too.

[SteveInMd]

Feb 16, 2014 6:18:11 GMT -7 allenuk said:

 ....<snip>....
So the bit we're trying to simulate is the peanut butter. Because in our NHS-led system of total-contact prostheses, without the cushion, it can hurt. Hurt quite a lot, to the point where walking is cut from miles to yards.

So prof, how do we get new peanut butter?

A

Perhaps if the distal peanut butter is lacking, the proximal stuff could be put into use. A trans-tibial prosthesis with a "thigh cuff" and knee joint can be fabricated:
TT-socket-ThighCuff.bmp (292.3 KB)

(I'm not sure if the attachments will show, or you have to click somewhere)

Thigh cuffs can be fit to distribute some of the weight-bearing away from the tissues below the knee.
These apparently are most commonly used for amputees with knee instability. Having artificial knee joints alongside the natural joint can be cumbersome and present its own complications. The prosthetists at the NHS should certainly be aware of these. You might have some arguing and persuading to do to get them to fabricate one.

Best wishes,

Steve

[ann-]

Hi Steve, I used something not dissimilar to this for over thirty years, though it wasn't for knee instability, actually b/k's using prostheses with thigh corsets were pretty much the norm when I became an amputee. Mine was made out of aluminium and leather, so constructed slightly differently to the one you show, but initially did a pretty good job of keeping me mobile .... the difficulties came in the 1990's when some UK centres were no longer able to make this type and there were problems getting them made to fit properly.
Luckily my revision made it possible for me to wear a conventional b/k leg and seem to have been able to make that transition without too many problems.

I am aware of a few of the larger prosthetic centres still able to make this type of prosthesis, but as you say it might be difficult getting done and there are disadvantages that go with it too, so think anyone would need to get some advice on this.

[snarfler]

At one time corsets were the norm until the advent of Suspension and suction which rely on the PTB. The metamorphosis occurring to your leg is very ordinary. Atrification. I suggest when you get your new socket that you have them make an insert of medium density Pe-Lite with a leather lining. Not the White plastic flexible insert which I personally found useless and no less than a 6 mm liner. Using Pe-Lite allows you to make adjustments along the way, increases liner life and can be completely updated. If someone would be good enough to teach me how to post a picture I will show you one that I had made. Also lining a socket with felt is more effective than using socks. Felt is available at most fabric stores. I spray the socket with adhesive. I prefer 3M. Them apply the fabric and trim. The difference is that the Felt is Static where the socks are Flux. Remember we don't want to increase Flux.

[SteveInMd]

Feb 18, 2014 22:54:27 GMT -7 snarfler said:

...<snip>.. I suggest when you get your new socket that you have them make an insert of medium density Pe-Lite with a leather lining.  
...<snip>.. If someone would be good enough to teach me how to post a picture I will show you one that I had made. Also lining a socket with felt is more effective than using socks. Felt is available at most fabric stores. I spray the socket with adhesive. I prefer 3M. Them apply the fabric and trim. The difference is that the Felt is Static where the socks are Flux. Remember we don't want to increase Flux. 

Leather would be lovely to use in prostheses. Does anyone, anywhere use leather any more?

Snarfler, I'd definitely like to see some images of your handiwork, and I think others would benefit. It's quite easy to post images, just DON'T use "quick reply." Just reply to a post on a thread using the "quote" button. You can actually delete the quoted material from your reply, if you like. Then you get a menu. One option is to use the "add attachment" button, to insert an image into your post. You can also use the button that looks like a picture in a frame to use the URL of an image available on the web. You could upload all images you want to share to photobucket (or other image site) and use the URL of the uploaded image. Or, if Google Images shows an illustrative image, you can use the URL of that. A picture is worth a thousand words....

[ann-]

Feb 18, 2014 22:54:27 GMT -7 snarfler said:

At one time corsets were the norm until the advent of Suspension and suction which rely on the PTB. The metamorphosis occurring to your leg is very ordinary. Atrification. I suggest when you get your new socket that you have them make an insert of medium density Pe-Lite with a leather lining. Not the White plastic flexible insert which I personally found useless and no less than a 6 mm liner. Using Pe-Lite allows you to make adjustments along the way, increases liner life and can be completely updated. If someone would be good enough to teach me how to post a picture I will show you one that I had made. Also lining a socket with felt is more effective than using socks. Felt is available at most fabric stores. I spray the socket with adhesive. I prefer 3M. Them apply the fabric and trim. The difference is that the Felt is Static where the socks are Flux. Remember we don't want to increase Flux.

Am already using Pe-Lite, though leather linings are not usually used here nowadays. And also am just about to experiment with a liner, though not sure of the thickness being used.
I have been told the atrophy is likely to be due to the use of total surface bearing sockets, though it seems that there is very little choice about that.

[snarfler]

Feb 19, 2014 12:58:47 GMT -7 ann- said:

Feb 18, 2014 22:54:27 GMT -7 snarfler said:

Feb 18, 2014 22:54:27 GMT -7 snarfler said:

At one time corsets were the norm until the advent of Suspension and suction which rely on the PTB. The metamorphosis occurring to your leg is very ordinary. Atrification. I suggest when you get your new socket that you have them make an insert of medium density Pe-Lite with a leather lining. Not the White plastic flexible insert which I personally found useless and no less than a 6 mm liner. Using Pe-Lite allows you to make adjustments along the way, increases liner life and can be completely updated. If someone would be good enough to teach me how to post a picture I will show you one that I had made. Also lining a socket with felt is more effective than using socks. Felt is available at most fabric stores. I spray the socket with adhesive. I prefer 3M. Them apply the fabric and trim. The difference is that the Felt is Static where the socks are Flux. Remember we don't want to increase Flux.

Am already using Pe-Lite, though leather linings are not usually used here nowadays. And also am just about to experiment with a liner, though not sure of the thickness being used.
I have been told the atrophy is likely to be due to the use of total surface bearing sockets, though it seems that there is very little choice about that.

Attachments:

[snarfler]

Please do pardon me Ann. You've known me for a long time and such things leave me befuddled. I shall try again.