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Thread: Delicate engineering problem
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12th Nov 2020, 03:46 PM #1Diamond Member
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Delicate engineering problem
Hi Guys,
I have another one for you....lol But very hard to explain....
I have a metal implant in my right femur that my prosthetic leg attached directly to.( Osseointegration)
The outside 'bushing' (30mm dia x 10mmm high ) is located via two small shear pins and secured in place ( to a 'abutment' )by a LH thread S/S 6mm CS cap screw about 15mm long.( don't ask my why its LH thread...grrrr)
This adapter attachs to a 20mm dia shaft with a male morse taper at each end.( about 100mm long)
A Surgeon tried to remove the screw to remove the adapter and remove the shaft. He managed to mangle the hex in the capscrew and not get it out. It was originally fitted properly and torqued to only 15Nm when it went in....
It should not have been a problem.
Anyway it was and now we/I have to work out a way to get it out.
The implant CANNOT be exposed to any jarring as it acts directly on my skeleton and hurts like hell. ( ie cannot 'tap' an oversized allen key in to get purchase.)
My idea is to use a Nut Splitter ( either manual OR hydraulic ) Once the Adapter is broken off, it should ne easy to grip the cap screw with vice grips and remove it.
I've never used a nut splitter so I was wondering if anyone who has used one, what they're thoughts were?
In my mind it seems perfect. No jarring at all and relatively quick.
The Surgeon has been using a Dremel to cut the bushing off, but that takes many discs to do, takes several hours and HEAT generated is a problem. Overheated the bone is bad.
The bushing is stainless steel...no idea of grade. Medical grade? I assume its better than 304? 316 maybe? SOmetime Titantium is used. Would that be more difficult?
(Still can't attach pics only ones I have uploaded previously....sorry.....No idea why....no errors. )
This is the bushing I want to split.
Steve
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12th Nov 2020, 04:04 PM #2Most Valued Member
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Could you cut a short length off a larger allen key, grind it to a press in fit, use a clamp that reaches to the other side to press it in and then use a 1/4" drive socket on the allen key to undo it?
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12th Nov 2020, 06:13 PM #3
so am I right that the surgeon tried to "undo" a right handed thread and ended up overtightening the left handed thread?
"I have to work out a way to get it out"
Isn't this a surgical problem for which there's, at a minimum, an implied warranty?
so, how sterile do the "surgery tools" need to be?
Any old rusty nut splitter or one that is medically certified?
ditto for the vice grips.
I've seen the "screw driver" used to insert syndesmosis screws -- used to hold broken bones together -- and had to look really hard to even see the driver bit. Nothing like a Makita battery screw driver or a pneumatic rattle gun.
so a question we need to know the answer to is how sterile do the tools need to be?regards from Canmore
ian
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12th Nov 2020, 06:13 PM #4Golden Member
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Hydraulic nut splitter, no jarring but it would need to be held well to avoid it turning on its axis.
https://www.ebay.com.au/i/3530758712...25af523f5df268CHRIS
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12th Nov 2020, 06:25 PM #5Philomath in training
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There looks to be a brand on the bush. It may be worth contacting them to see what their thoughts were. I would have thought that this has happened before.
Michael
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12th Nov 2020, 06:28 PM #6Gear expert in training
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If it's titanium, grinding will produce white sparks, not the usual yellow from steel. The colour of the metal itself can also give it away, but it's a bit more subtle. In the photo, the 2 bright lines in the watch bracelet are stainless, the "warmer", duller grey in the middle and the outside edges is titanium
PXL_20201112_071900448.jpg
Perhaps an oscillating multitool (like a Fein Multimaster) would cut it; no impact, but the vibrations may still feel unpleasant
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12th Nov 2020, 07:17 PM #7Most Valued Member
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Figure 2 here shows https://www.rehab.research.va.gov/jo...4-11-0280.html the parts.
If it is the same or at least similar you can see that the bolt screws in axially.
Figure 4 gives a better look
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12th Nov 2020, 07:34 PM #8Most Valued Member
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These guys supply Hermle connectors in Oz. Maybe they can tell you the material it’s made from. Although the material shouldn’t be a factor in how you remove it.
https://gvmd.com.au/Chris
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12th Nov 2020, 07:39 PM #9Diamond Member
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We thought about that .
The cap screw is very badly damaged and I'm not sure there is anything to grip. It might be an option. Will have to fabricate a puller to apply pressure to the allen key bit.( not a big deal.)
Another concern is pressure increasing friction on the cap screw and making it even harder to turn....
Will keep it in mind, thanks.
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12th Nov 2020, 07:50 PM #10Diamond Member
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I don't know if that is what he did. I was under anesthesia. All I got was " I tried both ways", thats when my heart sank......Its like getting a Violinist to build a stud wall for you......
I don't have much faith in that sort of thing. I think I would be wasting my breath. He has already done enough damage. Know what I mean.
Its complicated.
All the parts are outside of the body so I do not think sterility is a huge concern. Nothing is going to touch the stoma.
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12th Nov 2020, 07:54 PM #11Diamond Member
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Yes, that is what I was thinking of.
Should not be hard to stop it rotating. 3 hands should do it...lol
I know nut splitters are not complicated but I don't know how it will fair in this situation. I 've never needed to use one. ( I'm an Instrument Fitter)
They crush the nut,and I don't care about the screw, I just need to make it doesn't damge the abutment under it.
I can ask some Mech Fitters at work, maybe.
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12th Nov 2020, 07:59 PM #12Diamond Member
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Trouble is he is not a prothestic specialist. Hes' an orthopaedic surgeon. He's my only choice in WA unless I fly to Sydney and that is not going to happen soon.(Covid)
Actually, the Sydney surgeon was the first to have a go, and 'ran out of time'......( no worries, I'll just fly home then.....)
Everytime somone has a go, I have to have a Genral Anesthesia....
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12th Nov 2020, 08:03 PM #13Diamond Member
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12th Nov 2020, 08:05 PM #14Diamond Member
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12th Nov 2020, 08:09 PM #15Diamond Member
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They appear to be the exact parts I have. I'm prety sure the Bush is stainless. I am familar with the colour of titanium.
https://gvmd.com.au/prosthetics-parts-1/
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