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0t--surgical superalloy

j-holland

Aluminum
Joined
Sep 12, 2013
Location
WA - Washington
surgery of human spine deftly performed involves super-humans using super-alloys. rods of 4-6 mm diameter link
surgical screws--pedicle screws-- together in a ridgid chain intended for lifetime presence--problem--traditional rod composition
of titanium or cobalt chrome have fracture failure of 22%--
so a new alloy put in use 5 years ago claims fracture proof --many thousands now in use with zero fracture failure
composition-- molybdenum rhenium--maker recently announced lifetime hardware replacement if failure occurs

Princess Eugenie is good natured enough to display her xray rod architecture on operating table face down tracheal tube in place
 

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Wow, that is exotic. I normally think of Mo as a minor to modest alloying element. Even in M series high speed steels, it's usually less than 10%. I usually don't think of Re at all!

The "MoRe Unique Implants" article (in this trade mag issue) points out this class of alloys is normally used in very high temperature applications, as actual heating elements or as heat shields, thermocouple capsules, rocket nozzles, etc.

Totally tangential off-topic: The Gnomewrench in the Dwarfworks by Nick O'Donohoe (ISBN 0-441-00633-7, Ace Books, 1999) is set during WW2 and deals with USA conditions during the war. The protagonist is a sales engineer for an industrial furnace manufacturer, and near the start of the book he gets a government order for a cast molybdenum hearth plate. Turns out it's for the Manhattan Project. Searching for a supplier, he hooks up with a colony of metalcrafting dwarves (with attendant nasty gnomes). They were listed in the Thomas Register! So, it's a fantasy, but sort of a magic realism industrial thing. If you like it, there's a 2nd volume and the molybdenum hearth plate (or what's left of it) shows up again.
 
surgery of human spine deftly performed involves super-humans using super-alloys. rods of 4-6 mm diameter link
surgical screws--pedicle screws-- together in a ridgid chain intended for lifetime presence--problem--traditional rod composition
of titanium or cobalt chrome have fracture failure of 22%--
so a new alloy put in use 5 years ago claims fracture proof --many thousands now in use with zero fracture failure
composition-- molybdenum rhenium--maker recently announced lifetime hardware replacement if failure occurs

Princess Eugenie is good natured enough to display her xray rod architecture on operating table face down tracheal tube in place
What is causing the Ti rods to fail? Are they just undersized and are fatiguing? Seems odd that they would be undersized so frequently. Is it a stress corrosion cracking issue? Ti is fairly good at that, but MMPDS does say its 'marginally susceptible". A failure rate of 22% for things that get put in someones body sounds ridiculously bad.

MoRe is only slighty stronger staticly than Ti, (160ksi vs 135ksi) so I wouldn't imagine that matters much.
 
What is causing the Ti rods to fail? Are they just undersized and are fatiguing? Seems odd that they would be undersized so frequently. Is it a stress corrosion cracking issue? Ti is fairly good at that, but MMPDS does say its 'marginally susceptible". A failure rate of 22% for things that get put in someones body sounds ridiculously bad.

MoRe is only slighty stronger staticly than Ti, (160ksi vs 135ksi) so I wouldn't imagine that matters much.

“Another interesting observation,” said Dr. Yadav to OTW, “was that surgeons visiting our headquarters for the past 3-4 years have been bending the same 4.5mm MoRe rod sample and even with bending, rebending of the same rod over 300 times, the rod has not fractured. So the combination of the basic science, clinical experience and anecdotal observation convinced us that the era of 15% - 20% of rods breaking in complex spine surgery could be put behind us. We felt that providing this lifetime warranty against rod breakage made clinical and business sense and would lead to more patients benefiting from MoRe technology and avoiding repeat surgeries.”

claim is MoRe 4.5mm rod has equivalent strength as 6 mm Ti--but real leap forward is fatigue resistance
one would think every possible combination of alloying metals would have been concocted --money is the reliable motivator-$8 to 14,000 for a handful of hardware is a potent fuel for innovation
 
“Another interesting observation,” said Dr. Yadav to OTW, “was that surgeons visiting our headquarters for the past 3-4 years have been bending the same 4.5mm MoRe rod sample and even with bending, rebending of the same rod over 300 times, the rod has not fractured. So the combination of the basic science, clinical experience and anecdotal observation convinced us that the era of 15% - 20% of rods breaking in complex spine surgery could be put behind us. We felt that providing this lifetime warranty against rod breakage made clinical and business sense and would lead to more patients benefiting from MoRe technology and avoiding repeat surgeries.”
300 cycles? That's it? who only bends their spine 300 times?
claim is MoRe 4.5mm rod has equivalent strength as 6 mm Ti--but real leap forward is fatigue resistance
one would think every possible combination of alloying metals would have been concocted --money is the reliable motivator-$8 to 14,000 for a handful of hardware is a potent fuel for innovation
For that to be true the MoRe would need more than double the strength of Ti, so somewhere in the 300ksi range. The data I see shows it only being like 10% higher.

This all sounds like a giant pile of marketing BS. Maybe there is good science and testing behind it, but they (MiRus) aren't sharing any of it. Nor can I find any scientific papers discussing it.
 
300 cycles? That's it? who only bends their spine 300 times?

For that to be true the MoRe would need more than double the strength of Ti, so somewhere in the 300ksi range. The data I see shows it only being like 10% higher.

This all sounds like a giant pile of marketing BS. Maybe there is good science and testing behind it, but they (MiRus) aren't sharing any of it. Nor can I find any scientific papers discussing it.
you are somewhat on target regarding disclosure--manufacturer of MoRe is privately held and likely working under
FDA provisional human trials oversight--I have not yet located reference to specific clinical trial information regarding MoRe
but here is an example of why global entities seek registration --credibility and money--mostly money --imo

federal agency NIH hands out 500 million usd yearly to applicants globally--a deserving medical facility in Pakistan
registered a retrospective review of literature regarding metal density of implants used in spinal surgery of children study was recently concluded with announcement no findings would be shared with anyone--amount of federal funding for this
process is unstated
 

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300 cycles? That's it? who only bends their spine 300 times?
I believe the 300 cycles is for plastic deformation, and that most "normal operation" of a human spine is going to keep the braces in the elastic range. But the article doesn't explicitly support that conclusion.
I'm certainly no expert on biocompatibility, but I suspect the Ti failures are a combination of microfracturing, stress corrosion, and fatigue lifetime. Ti is supposed to have a definite fatigue limit, so you'd expect the reinforcements be designed so that "normal operation" doesn't exceed that stress limit. However, microfractures and stress corrosion cracks are dandy stress raisers. The MoRe alloy apparently suffers less of both of those.
 








 
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