How to mount a knee implant stem into a test apparatus 1

[Naveen93]

I'm working on designing a simple test apparatus that I can mount a knee implant or animal knee to replicate the flexion motion of the knee. Basically there's a cylindrical holder for the tibial component on the bottom and then another cylinder perpendicular to this on a sliding platform to hold the femoral component. Basically, just imagine your knee as you're sitting down and imagine handles to the sides of your femur (upper leg) that can control which way it flexes.

This is a simplistic apparatus that I'm still working on and I need to troubleshoot it to see how it works for my specific project's application ... the problem is that I can't start with troubleshooting because I can't find an easy way to even mount my specimens onto the apparatus into the cylindrical holder.

I have a porcine knee in the freezer that was potted into aluminum cylinders that would perfectly fit the holder on the apparatus. The problem was that I have no experience with the dental cement I used and very few tools at my disposal, so it ended up being a little off axis so when I put it in the cylindrical holders of my apparatus, (again, it has handles that go up and down in one direction), the fact that it was misaligned caused the flexion to be very rigid and unable to go through the entire angle of the motion.

Right now my focus is on trying to mount a knee implant. Since these are relatively expensive and I already messed up trying to do a permanent dental cement potting on the porcine knee, I was wondering if anyone has any ideas of a simpler way to do this.

I was almost thinking of just putting the stem of the knee implant into the cylindrical holder of the apparatus and then stuffing the holder with play-dough or something like that so that the stem of the implant is relatively secure. It doesn't have to be perfect since again, this is more of just a simple troubleshooting than some important part of my project. Anyone have any thoughts on this?

 

[ornerynorsk]

Since you mentioned potting cement already, check out "dopping wax". Very strong, easy to use, inexpensive, readily available.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[Naveen93]

Thanks, I will check that out. My brilliant idea of using play-dough didn't work out too well since it's not strong enough, the two components jostle around during flexion motion to the point where they eventually lose contact.

 

[gruntguru]

Sounds like your setup is over constrained - the rotation axis is defined by the test rig and also by the specimen. What you really need to do is introduce a couple of additional degrees of freedom to the apparatus. If the femur is fully supported, the tibia will only have one degree of freedom - rotation about the hinge axis of the knee.

je suis charlie

 

[tbuelna]

Your joint implants should have some digital models used to manufacture them, right? So you could CNC machine some tooling holes in each implant part, and then make a fixture that uses the tooling holes to accurately position the implant parts during the bonding/potting process.