Responses: Knee for sub-zero temperatures

Responses: Knee for sub-zero temperatures

zach harvey

2/18/2011

Thanks to all who replied. There was some good information that I copied and
pasted below.

Zach Harvey, CPO

__________________________________________________________________________________________________________________________________


Original question:

Has anyone found a good solution for a prosthetic knee choice for k3/ k4
living in a region with extremely cold weather? It seems that hydraulic and
rheologic fluids stiffen up in extremely cold weather.

Thanks, Zach Harvey, CPO

__________________________________________________________________________________________________________________________________


Responses:

This is actually the only remaining indication for the use of pneumatics over
hydraulics. The classic solution for sub-zero applications of fluid controlled
prosthetic knees is to use a pneumatic version because they aren’t affected much
by cold air. They might be stiff for a few steps, but quickly operate normally
due to the heat of the friction generated. I’m not thrilled with any of the
available pneumatics but perhaps you’ve had good luck with one or another.

You need to check the fine print, but many of the MPC knees are NOT warranted
for operation below certain temperatures because the computer control might be
affected and patient safety is at risk. Since the Rheo operates primarily based
on the viscosity of the fluid, that would seem to be the least desirable
approach for super-cold applications.

In theory, the silicone fluid in today’s hydraulics is much less affected by
temperature that was originally the case, but even the best automotive oils
thicken in super-cold weather. Whatever knee you select, it would be prudent to
contact the manufacturer and get their opinion on how it would operate at the
anticipated temperatures.

You might also ask the folks in Alaska what their real-world experience has
been.

Best regards.


__________________________________________________________________________________________


... from DAW. We have had success in this temperature zone using our pneumatic
knees with special low temp grease in the cylinders. We even had a patient ride
his motor cycle across Siberia. The motorcycle had problems, but the knee worked
fine.

_________________________________________________________________________________________________________________________________


Cold tempertures require simple solutions, pneumatics work better than fluid but
simple mechanicals work best because they require less force and stand up better
to temperture changes. Four and Five bar knees work great in severe climates
without hydraulic fluid.

_______________________________________________________________________________
_________________________________________________________________________________________________________________________________


Greetings from Northern Ontario Canada. We spend at least four months in sub
zero temperatures ( 0 degrees Celcius down to minus 40 degrees Celcius ) over
the course of the year, so as you can imagine this issue rears its ugly head
here routinely. What we have found first off is that pnuematic cylinders just
don't function well in the cold so we don't typically use them. As
for hydraulic cylinders, the smaller the cylinder the better. Smaller cylinders
mean less fluid in the cylinders overall and as the cylinders cycle, the fluids
are moving faster and through smaller ports which we believe creates a higher
fluid temperature due to friction which inturn affects the cylinder fluids
viscosity. Hope this helps

_________________________________________________________________________________________________________________________________


Silicone oil is supposed to be less affected to changes of temperature.

_________________________________________________________________________________________________________________________________


I think ossur has a special Cold weather fliud for its mauch and total knees.

_________________________________________________________________________________________________________________________________


English company, Orthomobility, provided me with information on a knee that they
are working on which will be insensitive to temperature changes due to adaptive
flow technology.