Which Is A Better Material For An Onlay Cranioplasty?
Q: Dr. Eppley, I am interested in an onlay cranioplasty for back of my head. It is true that hydroxyapatite would be very light and much more like my bone than PMMA materials. Is PMMA heavier than hydroxyapatite? Would I feel the heaviness in my back of my head if I choose PMMA for the surgery? I know that PMMA would work to make my head round, What are the pros and cons of using PMMA? Are there any side effects of PMMA to my body? Thanks.
A: There is no real weight differences between PMMA and hydroxyapatite (HA), so that is not a concern. The differences between them is three fold. First, PMMA is a plastic material and it just as hard as bone if not actually harder. Secondly, it is a well tolerated and commonly used cranioplasty material. But it is not bone so, like a breast implant, it is well tolerated and accepted by the body but it never truly becomes part of the breast. It is simply walled off (encapsulated or surrounded by scar) HA is a lot more like bone biologically since it is the inorganic mineral content of bone. Because it it more like bone, the body actually grows into it and integrates into it. It is not as strong as PMMA or bone and is more ‘brittle’ much like a ceramic. The risk of fracture is greater on hard impact although I have yet to see fracture of the material as ever having occurred or being a problem that I have heard of. Lastly, there are cost differences betwene the two in terms of volume used. PMMA has a flat rate cost that is substantially less than that of HA as it comes in 40 gram packets. HA is charged by volume in grams per 10 grams used. So the equivalent material cost for, let’s say 40 grams of material, is about 4X the cost over PMMA. That is a several thousand dollar cost difference between the use of the two materials.
As you can see, the choice between PMMA and HA offers certain advantages and disadvantages for each material.