Acetabular Bone Loss any different THR vs Resurface?

Dr. Vijay Bose

"One of my patients from India who has had a resurfacing, briefed me on the current discussion in the surfachippy forum regarding Dr. Klappers opinion of losing acetabular bone in an attempt to preserve femoral head bone in resurfacing. He wanted to know my opinion and i thought it would be appropriate for me to post my answer in this forum. Dr. Klapper's opinion is way off the mark. The acetabular size is the most important factor which determines the choice of femoral head size in resurfacing and one never removes more acetabular bone in hip resurfacings. In other words if i would be performing a conventional hip replacement on a given patient instead of resurfacing, i would be using precisely the same size acetabular component in both the surgeries. 

I would go as far as saying that if we are taking out more acetabular bone in resurfacing than in conventional hip replacement, then in my opinion there is no role for resurfacing and it must be discontinued immediately. Acetabular conservation is as important if not more than femoral bone conservation and all resurfacing surgeons recognize and acknowledge this fact. The ability to put large heads in resurfacing stems from the fact that thin shelled acetabular components are possible with the modern metal on metal bearings. However when one uses polyethylene it has to have a large thickness, which in turn reduces the femoral head diameter, (assuming the acetabular outer shell diameter remains the same). The same argument holds true for ceramic on ceramic bearing to a lesser extent and therefore slightly large femoral head sizes than metal on poly is possible. However an anatomical size is currently possible only with metal on metal bearings. I strongly object to the terminology of "large or jumbo head metal on metal hip replacement" that some surgeons use to describe the current versions of the total hip replacements which employ the same metal on metal bearing used in resurfacings. I point out in all my lectures that this variety of total hip replacement is the anatomical head replacement giving the same natural size (of the femoral head and the acetabulum) that the patient has in other normal hip and the conventional THR are indeed small head hip replacements. One must never lose this perspective.

I hope this helps to clear the sudden doubt that was cast on the hip resurfacing principle recently.

Dr. Vijay C. Bose
Consultant orthopaedic surgeon
Chennai, India


Dr. Michael Mont May 23, 2009

Concerning acetabular bone loss and resurfacing:

Originally, there were concerns about needing to take more acetabular bone with resurfacing because some of the earlier designs had slightlier thicker acetabular shells that necessitated sacrificing more bone for a given femoral head size.  In addition, there were sometimes gaps in sizes of components available for some designs.  For example, for certain designs the acetabular components varied by 4 mm and for other designs or sized individuals they varied by only 2 mm.  

Fortunately, almost all manufacturers presently make resurfacing
components that have acetabular components that vary by only 2 mm for most sizes and are thin-shelled.  As a result, the acetabular sizes should be equivalent to the sizes one uses for a standard total hip replacement.

Four studies directly address this issue. The Loughead et al. study was the first one that showed more bone resection on the acetabular side.
The Venditolli et al. study,  a prospective randomized design showed no differences in bone resection.  In the Moonot study, bone was conserved in women with resurfacing (2mm average), with men no difference. In the Naal study, there was more acetabular bone resection in the resurfacings.  So the scorecard in these studies is 2:2.

In summary, I don't think there is typically very much difference with modern designs and techniques and if there are small differences they are probably clinically irrelevant.


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