Dr de Smet article - BHR versus Conserve Plus

[happyhopper]

Hi everyone.
I have been reading Dr de Smet's article BHR versus Conserve Plus.  (www.hip-clinic.com/Main menu/Hip Info/publications).
I understand most of it until I get to the sections on head coverage angles.  Can anyone simply this for me??
Many thanks.

[Tin Soldier]

That was one of the first articles I read when looking into HR.  The cup coverage angle is a very important part of HR and succes of a HR device.  All it is, is the amount of cup covering the femoral ball.  The angle is made by how many degrees less than 180 do the 2 edges directly across from each other make?  If a little less than 180, you'd have just a little less cup all the way around the edge of the cup than a full hemisphere.  Hope that makes sense. 

With the BHR there is a little less coverage than the C+.  The ASR, which we know has had a troubled past, has even less coverage of the ball than the BHR.  This may not make that much of a difference if you have an experienced surgeon who installs the 2 components in a proper position with each other (40 degrees or so of abduction, can't remember the front back angle). 

The thought is that you will get more wear from edge-loading or having the main force (weight) pushing at the edge of the cup.  In a perfect world, the weight or force from the femoral side would be equally distributed to the cup.  I don't think its physically possible to do that in a human joint like the hip.  So there will always be some excessive loading on vairous areas of the cup.  A lot of it will be at the edge of the cup, so you want to reduce that as much as possible to reduce wear,...high metals,...metallosis,...revision.  I think the ASR may have had a little more to the story, in that the cup was not a perfect spherical shape, it flared just slightly at the edge.  I think that was the main reason it had a higher failure rate.  So the surgeon does their best to find that happy spot for the cup.  They want that cup to be in a position that distributes the weight as evenly as possible all the way through standard ROM.  I think there are then a lot of factors that play into that decision for the surgeon, thus the need to have an experienced surgeon. 

[Dannywayoflife]

Great reply by Tin as usual :) the asr failed for a lot of reasons one of the big ones as eluded to by tin was the coverage of the cup. This was vastly reduced because they used some of the bearing surface as mode to attach the cup introducer. Also the clearances were very very very tight which caused excessive wear.

[happyhopper]

Thanks, things are now much clearer.