Q: Dr. Eppley, I want to have the flat spot on the back of my head built up. I understand that various materials can be used to do it but don’t know which one would be better. What are my options?
A: Bone cements in cranioplasty can be either polymethylmethacrylate (PMMA) or various calcium-containing materials. All of these materials are joint powders and liquids that are mixed in surgery to create a self-curing putty that offers enough set times to create the desired shape on the bone. The most ‘natural’ bone cement is that of the synthetic calcium compositions, of which the most common ones used are calcium phosphate-based also known as hydroxyapatites. (HA) They are natural to the bone because the inorganic mineral content of human bone is hydroxyapatite. Another calcium-containing bone cement is that of calcium carbonate, known commercially as Kryptonite. It offers superior biomechanical properties (less prone to fracture) than the calcium phosphate-based masterials but is no longer commercially available. Whether PMMA or HA is better for any cranioplasty is based on a variety of factors (cost, inlay vs onlay, size of incision) and not necessarily because one is more natural or more synthetic. There are different material properties for each type of bone cement and these must be considered also.
Dr. Barry Eppley
Q: Dr. Eppley, I am interested in getting a forehead augmentation. I know that there are different materials to use, one of which is PMMA. I have a few questions about PMMA. Does PMMA bone cement have a risk of granulomas like PMMA injections? Are the outlines of it visible? Does it have a risk of extrusion? Thank you!
A: In answer to your questions:
1) PMMA cranioplasty material does not cause granulomatous reactions. That is a unique phenomenon of small PMMA particles in soft tissue
2) Besides getting getting the right contour and amount of augmentation, one of the major objectives of any form of cranioplasty is to get a smooth transition form the material to the surrounding bone. This usually requires intraoperative burring of the edges after the material is set to have feather edges so there are not visible outlines after surgery.
3) There is no risk of extrusion of a PMMA cranioplasty. Extrusion of any implant material occurs because it is either placing excessive pressure on the overlying soft tissues or is infected and it is being pushed out by the pressure of the purulent fluid build-up. A PMMA cranioplasty is rigidly fixed to the underlying bone by microscrews prior to it being placed as a rebar method. This prevents any micromotion or displacement after surgery. The material is also impregnated with antibiotics which provides several weeks of antibiotic release after surgery for infection prevention.
Dr. Barry Eppley