Employing high-frequency alternating magnetic fields for the non-invasive treatment of prosthetic joint infections

Cute. And decidedly on-topic. Exploiting the skin effect so that the heating is localised exactly where it is needed is satisfyingly clever.

Not what you'd expect from Dallas.

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Bill Sloman, Sydney

Yes, but...I didn't understand the advantage about using a high power at a low duty cycle to control the temperature instead of just using a lower power at 100% duty cycle?

They claimed it heated the joint more evenly but I don't see why that would be the case.

m

if hot is 60'C, 82'C would be painful without meds

The idea seems to be to blast the surface to cooking temperatures in a fraction of a second and then let it cool by thermal conduction into the bulk of the implant before the patient themself gets cooked too deeply.

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This email has not been checked by half-arsed antivirus software

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onal treatment.

ating is localised exactly where it is needed is satisfyingly clever.

a low duty cycle to control the temperature instead of just using a lower p ower at 100% duty cycle?

ld be the case.

They're not trying to raise the temperature of the entire plate, only the s urface where the biofilm is. So relying on the skin effect to concentrate t he power dissipation at the surface, the idea is to input a high enough pow er flux to overwhelm the conductive transfer of heat into the mass and ther eby achieve the desired temperature at the surface. That temperature is onl y required for a few milliseconds. I'm no chemist but I can understand they don't want to pyrolyze the biofilm into something worse than it is already , they only want to alter its structure insofar as it impedes the action of antibiotics.

You are right, you are no chemist. The "biofilm" is not a chemical layer as much as it is a biological layer of cells bound to the implant and to each other. Of course this attachment is achieved by the cellular secretion of polymeric substances that serve as a glue.

The biofilm makes the infection hard to treat because antibiotics circulate in the bloodstream and only reach the implant by diffusion. Further they don't penetrate the biofilm well. The biofilm helps the infecting bacteria in other ways as well. So the goal is to do whatever damage to the biofilm as can be done.

It's not an issue of transforming the biolayer into something "worse". The issue is trying to not cook the human tissues as little as possible. The biolayer is very thin, so the RF skin effect makes it possible to heat a very small layer of the metallic implant and therefore the low total heat dose will heat a fairly thin layer of tissue, biolayer or human.

Just like the sonic impulses used to break a kidney stone, this treatment seems to use a number of pulses to try to kill as many bacterial cells as possible. Interesting that it makes the antibiotic more effective. I suppose breaking down the biofilm exposing more cells to the diffused antibiotic makes this work. In turn the body has to complete the process of attacking the bacteria and eliminating them.

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Rick C

te:

ional treatment.

heating is localised exactly where it is needed is satisfyingly clever.

at a low duty cycle to control the temperature instead of just using a lowe r power at 100% duty cycle?

would be the case.

he surface where the biofilm is. So relying on the skin effect to concentra te the power dissipation at the surface, the idea is to input a high enough power flux to overwhelm the conductive transfer of heat into the mass and thereby achieve the desired temperature at the surface. That temperature is only required for a few milliseconds. I'm no chemist but I can understand they don't want to pyrolyze the biofilm into something worse than it is alr eady, they only want to alter its structure insofar as it impedes the actio n of antibiotics.

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And you're no cell biologist. The biofilm is not "a biological layer of cel ls", it is :" biofilm, a thin film (

On Thursday, 17 August 2017 19:59:06 UTC-4, snipped-for-privacy@gmail.com wrote :

:

rote:

tional treatment.

heating is localised exactly where it is needed is satisfyingly clever.

t a low duty cycle to control the temperature instead of just using a lower power at 100% duty cycle?

ould be the case.

surface where the biofilm is. So relying on the skin effect to concentrate the power dissipation at the surface, the idea is to input a high enough p ower flux to overwhelm the conductive transfer of heat into the mass and th ereby achieve the desired temperature at the surface. That temperature is o nly required for a few milliseconds. I'm no chemist but I can understand th ey don't want to pyrolyze the biofilm into something worse than it is alrea dy, they only want to alter its structure insofar as it impedes the action of antibiotics.

There's a big class action lawsuit against the maker (3M?) of one of the jo int warming devices. It's claimed it causes deep infections by depositing germs that are lurking near the hospital floor in a film on the implant, and the resulting infections can require removal replacement (taking a long time a nd a lot of pain/inconvenience) or even amputation.

--sp

te:

te:

entional treatment.

e heating is localised exactly where it is needed is satisfyingly clever.

at a low duty cycle to control the temperature instead of just using a low er power at 100% duty cycle?

would be the case.

he surface where the biofilm is. So relying on the skin effect to concentra te the power dissipation at the surface, the idea is to input a high enough power flux to overwhelm the conductive transfer of heat into the mass and thereby achieve the desired temperature at the surface. That temperature is only required for a few milliseconds. I'm no chemist but I can understand they don't want to pyrolyze the biofilm into something worse than it is alr eady, they only want to alter its structure insofar as it impedes the actio n of antibiotics.

joint

ms that are lurking near the hospital floor in a film on the implant, and t he resulting infections can require removal replacement (taking a long time and a lot of pain/inconvenience) or even amputation.

Will look into it.

snipped-for-privacy@gmail.com wrote on 8/17/2017 10 :04 PM:

.com wrote on 8/17/2017 7:58 PM:

ust 17, 2017 at 9:50:35 AM UTC-4, snipped-for-privacy@yahoo.com wr ote:

, and a major breakthrough from conventional treatment .

98-017-07321-6

pic. Exploiting the skin effect so that the heating is localised exactly where it is needed is satisfyingly clever.

s.

t using a high power at a low duty cycle to control th e temperature instead of just using a lower power at 1

00% duty cycle?

joint more evenly but I don't see why that would be t he case.

raise the temperature of the entire plate, only the s urface where the biofilm is. So relying on the skin ef fect to concentrate the power dissipation at the surfa ce, the idea is to input a high enough power flux to o verwhelm the conductive transfer of heat into the mass and thereby achieve the desired temperature at the su rface. That temperature is only required for a few mil liseconds. I'm no chemist but I can understand they do n't want to pyrolyze the biofilm into something worse than it is already, they only want to alter its struct ure insofar as it impedes the action of antibiotics.

m" is not a chemical layer as

ogical layer of cells bound to the implant and to each

the cellular secretion of

t serve as a glue.

tion hard to treat because antibiotics circulate

n the bloodstream and only reach the implant by diffus ion. Further they

l. The biofilm helps the infecting bacteria

her ways as well. So the goal is to do whatever damag e to the biofilm

an issue of transforming the biolayer into something " worse". The

tissues as little as possible. The

ery thin, so the RF skin effect makes it possible to h eat a

therefore the low total heat

rly thin layer of tissue, biolayer or human.

ust like the sonic impulses used to break a kidney sto ne, this treatment

to try to kill as many bacterial cells as

e. Interesting that it makes the antibiotic more effe ctive. I

ng more cells to the diffused

s work. In turn the body has to complete the process of

gist. The biofilm is not "a biological layer of cells" , it is :" biofilm, a thin film (

How does an external joint warming device "deposit" germs on the implant? What type of joint warming device is being discussed?

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Rick C

Google 3M Bair Hugger.

It should go without saying that I have no idea if there is any merit to the claims.

speff wrote on 8/18/2017 1:03 AM:

Ok, I read a bit on this and I think the detail that Fred goes into may be unjustified. There seems to be virtually no real evidence the Bair Hugger is causing a problem in the first place. Since there is no real data about the issue, I don't see how anyone could make a detailed claim about the nature of the infections or mechanism.

The claim is that the devices disrupts the flow of air in the OR which appears to be controlled to minimize stirring up the "crud" from the floor, which results in more crud in the air and so more landing in the surgery site. The way the device is used appears to exclude the surgery site, so there is no reason to believe it has any other impact. So mentioning that the germs being deposited "a film on the implant" is a bit ambitious. I think the most that can be claimed is that the crud blowing in the air can transport bacteria to the surgical site and the rest is the same as any OR infection from the crud that is stirred up by any other means such as walking.

I can't think why this infection would be any different than others. The issue is just that they could be happening which still has not been indicated by any data, just claims by the competitor who happens to be the original inventor.

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Rick C

A lot of replies to your question, but no answers. It's understood what the advantage between short high power and pulsed longer duration is. The question is: why pulsed long duration & not continuous low power long duration? Same energy, same duration, but continuous. Would be easier. Not likely to produce high temperature spikes.

Bob

If you think no one gave an answer you didn't understand anything read. The short pulses bring the temperature at the surface of the implant up for a moment, which then quickly dissipates heating *only* a thin layer at the surface of the implant. A prolonged lower power heating would heat *much* more tissue. The duty cycle is used *not* to heat the tissue, but to prevent heating of tissues away from the implant.

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Rick C