Should acetabular cups move as part of bedding in process?

[chimera191]

Following some very sage advice from Pat & co I've been trying to find out a lot more about the underlying cause of my ASR resurfacing situation that results in need for THR.  So apologies if I'm about to ask some very stupid questions.

I'd reported on another post that both cup and head had moved, they have, and that I thought they were cemented.  Common opinion was the cup wouldn't have been and the surgeon has confirmed this, but that the head was. 

However he also said something that struck me as odd and that I've been reflecting upon.  He confirmed that my cup had moved from a placement of 45 degrees to 52-3 degrees, but that this happened initially and then stabilised.  I quote him as saying " Hips often "bed-in" in this manner but most cups don't move as much as seen in Metal on Metal hips."

I guess I would have thought, particularly given the precise nature of DePuy's ASR placement instructions and the reliance and development of computer aided placement, that such products wouldn't be subject to such vagaries subsequently, but I would welcome any guidance and experience in this area please?

[obxpelican]

Cups are press fit, actually pounded in and then with the acetabular component firmly in place the cup should not move. 

It's almost always surgical error, at least everything I've ever read.


Chuck

[Dannywayoflife]

I've read that cups do migrate in the first few weeks but your talking tenths of a mm not the degree that yours seems to of moved. I aggree with chuck sounds like poor surgery to me.

[obxpelican]

Danny,

If you see Treacy ask him what he thinks about the quote Hips often "bed-in" in this manner but most cups don't move as much as seen in Metal on Metal hips  I think Treacy would have a good chuckle.

I read that and scratch my head, I'm like, HUH????  What is this doc smoking?  They move the whole range where the inclination should be?  Heck, 52 degrees you could actually have a chance at keeping your HR if it were not an ASR of course.  But a cup that is loose and shifts that far?

Chimera, your doctor made a mistake on the cup, any doctor can do that, it has happened to the best of doctors.  On top of it all you got a recalled device which of course is not his or your fault, but the cup, he did that and if he believes that a cup could/should migrate that far you should run don't walk and find another surgeon to do your revision.  And for the record there is no difference in how a cup is seated be it MOM or any other material it's all the same general method. 

All this is IMHO. 

I hope the revision goes well and you are walking straight, painless lines again.


Chuck

[Pat Walter]

Hi

I wanted to also comment that if you watched surgeons pound the acetabular cups into place, you would realize that they don't move.  That is part of placing the cup, the surgeons will take the tool and wiggle and try to move it.  Each surgeon has his own test to make sure the cup is properly placed.  I never heard of cups migrating during a break-in period.  Of course, I am not a doctor and don't know everything.  I have watched live surgeries and know the cups are placed very securly.  You can watch videos which give you the same view of how cups are pounded and placed in the acetabulum.

I wish you good luck with your upcoming revision.

Pat

[John C]

I got the impression from my surgeon that the rough surface on the cup caused what he called a "scratch fit", meaning that the rough surface dug into the bone, and created a solid fit. He also said that any micro motion during the initial healing period could cause the bone to not ingrow, and cause later loosening of the cup. I got the impression that if he saw any movement in the cup from where he initially hammered it in place, it would be cause for concern.

[Dannywayoflife]

Ha I'll ask Treacy that when I see him chuck  ;D I know what his answer will be though! He seems to have a low tolerance for surgeon incompetence and bull s##ting! ;D