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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 orthopedic surgeon Chennai, India
 

The acatabular component needs to have an outside diameter to fill the acatabulum. Typically in a THR you ream about 3-6 millimeters larger then the actual acatabular size to get to good bone then fill the inside of the shell with polyethylene to an inside diameter to match the femoral component being used. In a resurf or a big head metal-metal THR the inside of the acatabulum is 6-8 mm smaller then the outside diameter and that is how much bone is reamed. The size in a resurf is dictated by the femoral neck size which determines the femoral head size (in M-M THR the acatabulum is selected on anatomy and the head size selected to match).

All that said you see that reaming and acatabular size are esentially the same for all types of implants. Hope that makes it clear.

Scott Rubinstein
www.hiportho.com
 

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