Q: Dr. Eppley, I am interested in forehead augmentation/reconstruction for a congenital skull deformity. In terms of using cement on my forehead, by how much can we get an additional thickness there, i.e. what distance can we add to the flatness/deficiency? Why is it cement (on the forehead) instead of a prefabricated implant? I have a very rough terrain of the forehead. In our opinion the implant’s inner side would hide all the problems beneath, but the cement treatment might be not creating a proper elliptical smoothness unlike an implant should do. Correct us please if we are wrong, it is just to dispel our concerns.
A: The amount of expansion of any skull bone surface is based exclusively on how much the overlying scalp will stretch. How much the scalp can stretch is a function of many factors, including scar from prior surgery and an innate ‘looseness’ factor. As a general statement, skull expansion can achieve up to 25mm in thickness if a full coronal incision is used for access.
Forehead augmentation/reconstruction can be done very successfully, using either intraoperatively applied bone cements or prefabricated implants. One is not necessarily better than the other. A bone cement is an intraoperatively made putty froml iquid and powder components. It is applied as a putty to the bone surface and then shaped by hand to whatever external shape is needed. It has an intimate connection to every nook and cranny of the irregular bone surface as its outer surface is shaped into a smooth round/elliptical shape. Bone cements can be either of PMMA (acrylic) or hydroxyapatite (HA) compositions. Most large volume bone cement cranioplasties use PMMA due to its lower cost. A prefabricated skull/forehead implant is made from the patient’s 3D CT scan using computer designing software for its creation. It is then fabricated in a silicone material for implantation. It too will have a good fit to the underlying bone surface and an external shape of whatever is so designed. It is the costliest of all the alternatives due to the design process.
In short, your perception of the differences between a bone cement and prefabricated implant is not accurate. They are just different ways to get to the same place. They differ primarily, however, in the cost to do them.
Dr. Barry Eppley