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.
Topic: Dr de Smet article - BHR versus Conserve Plus (Read 2654 times)
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