What happens...

[triathlete98]

Debating with the physician asst. on what happens the device fails or the bones fail the joint!  Freindly discussion, but it sounds like revisions are due to implantation failure or bone failure?  Anyone???

[Dannywayoflife]

Don't quote me on this but I have the impression that devices generally fail because they loosen. I may well be wrong tho.
Danny

[triathlete98]

hmmm...which part?

[hipnhop]

I dont think the device fails. It the things around the device that fails. The BHR device is solid. They must be referring to loosening, bone wear, but as for a crack in the device.  I dont think so.

[triathlete98]

  good i'll go back with that!!!

[Tin Soldier]

I think it's something like this, in this order:

1.  Acetabular cup loosening
2.  Metallosis from edge-loading/steep cup angle
3.  Femoral neck fracture

Which make up the vast majority of revisions in that order, but I may be wrong.  I think Hern or John C quoted a recent study at the AAOS that presents the numbers on these.  It was a good study, in that the metallosis that everyone is freaked out about is actually a small number of the revisions.  The revisions are still quite low (2% to 4%), depending on the surgeon.

As Danny pointed out in McMinn's early studies, the big yellow 500 lb pendelum was used to test the BHR.  The components can take a lot of abuse. 

[Dannywayoflife]

I do find it hard to believe that a well placed BHR cup can loosen though. I mean having seen the way the bone grows into it and really grows around the beads is just amazing.
Does anyone else think that the skill of the surgeon at the implantation stage could have an effect on that years down the road?
As I said in another thread recently having seen the photos of the bhr cup and a sintered cup under a electron light microscope the difference was stark. The bhr was far far rougher. Therefore will that mean it's harder for it to loosen?

[Tin Soldier]

I like to think of the sci fi terms, "assimilation" and "cyborg".  I'm happy to be one with CoCr.  We need someone to dedicate a years worth of recovery where we can implant a microscopic camera and do time-lapse photographry of the bone growing into the backside of the cup.  It would be like watching ivy grow up a tree on a nature show.  Cool huh?

[Dannywayoflife]

Yeah. You could see on my last x rays at around 10 weeks the bone had grown into the cup. I know the bone keeps remodelling for a long time after tho.

[curt]

     The devices and coatings on the various devices have evolved as well.  The ability to go completely without cement and rely on press fit and bone growth is amazing.  I would think that the only risk would be with the bone failing to recover well enough and quickly enough to promote the in-growth and prevent cup movement.  I have no idea what the risk of a failure/loosening is once the in-growth has occurred.  It must be small if even the very conservative surgeons are letting everyone go crazy at a year.

Curt

[Dannywayoflife]

That's what I'm wondering how can these things loosen when the bone is so aggressively grown into them. I'm mean with the bhr beads the bone actually grows around the beads! I've seen photos of bone removed from a recovered device and the bead has been removed leaving a piece of bone shaped like a horse shoe where the bead used to be. And that's not taking into account the rougher surface of the beads that the bone can bond onto.
I wonder if the cups that have slipped or loosened if proper bone ongrowth and ingrowth took place early on?

[John C]

I have been reading so much on this stuff over the past five years or so, that my poor memory is pretty taxed, but I will try to add to the discussion with what I think I remember, as long as you guys remember that I may not be remembering correctly.
There have been very rare cases where the actual devices have failed in the past, but it is incredibly rare. The two failures modes that I have seen pictures of are stems that have broken off of the inside of the cap, and beads that have pulled off of the back of the cups. Both of these are so incredibly rare that no one should worry about them.
Once you get past the risk of femoral neck fracture, usually in the first six months, failure (other than due to infection) is usually due to the component loosening from the bone. I have read of four things causing this:1. Sometimes instead of solid bone growing into the prosthesis, a fibrous material grows in that is not as strong as bone, and may eventually fail. 2. Wear particles cause the body to react with cells whose effects can eat away at bone, called osteolysis, causing loosening. 3. Bone necrosis (dying bone), possibly due to vascular issues. This would likely show up fairly soon. 4. Breakdown of the cement. This appears to be less of a problem with resurfacing, since the cement is under compression stresses, rather than shear stresses as with a THR.
Either component can come loose with time, but I think I read that Dr Gross felt that the femoral component was most likely to loosen over the long term, which is why he was motivated to develop the cementless cap. As many have pointed out, Mr McMinn's long term success rates would not show this to be much of a problem.

[Dannywayoflife]

Just to add to that Jon I think you summed that up pretty well. The wear particles causing the macrophage to try and consume the particles I would argue is down to poor surgical technique as the most common cause of that is a misplaced cup.
And also the necrosis with the circulation that can also be due to poor surgical technique.
I believe the failures you talk about with the stem snapping have been associated with the devices that have the thinner stems such as the asr and C+. I remember Derrick Mcminn talking about that in the northan lights debate.
Also something else I remember from that debate(something I never realised) is that devices like the C+ cemented use a totally different cementing technique, which is some cases has lead to femoral loosening.
I've been thinking for a while now that the real factor in the longevity of these devices will be how long they can stay welded to the bone. And for that reason I am doing everything In my power to keep my bones healthy and rock hard!