The use of skull reshaping with cranioplasty techniques that use synthetic materials dates back for over five decades. While the use of bone grafts is never an option in aesthetic skull procedures, it often is not an option in skull reconstruction either due to the size of the skull defect. This makes the use of alloplastic materials, often called bone substitutes or bone cements, as inevitable for many skull restoration procedures.
One of the historic and still most commonly used alloplastic bone substitutes in the skull is poly methylmethacrylate. (PMMA) Even though it is a polymer-based material and will never permit bone ingrowth or bone replacement, its low cost for its large volumes have always made it popular. Its widespread spread in joint replacements in orthopedic surgery as a true bone cement also speaks to its excellent biocompatibility.
Skull reshaping using PMMA has long shown it to be a well tolerated implanted material. A recent published paper in the June 2013 issue of Aesthetic Plastic Surgery entitled ‘Aesthetic Refinement of Secondary Cranioplasty Using Methyl Methacrylate Bone Cements’ is interesting as it provides a more recent patient experience. Over a three year period the authors report on 20 patients who had PMMA implanted in their skull. Their use was reconstructive in nature for trauma and craniotomy patients and was used as a total inlay in the majority of the patients. (85%) The size of the cranioplasties was from 30 to 144 cm2 in size and involved implanted material volumes of 20 to 70 grams.
After an average two year followup period, no patients showed any evidence of implant infection, exposure, or extrusion. In addition, the PMMA reconstructions were structurally stable over this time period all the patients. The key to such successful outcomes in their observation were adequate and healthy overlying scalp tissues.
What does this mean to the aesthetic skull reshaping patients who has or is considering having PMMA implanted? This study is a small patient series that does not have significant long-term follow-up and used the material in an inlay rather than an onlay fashion. On the surface it would seem that this patient series has little correlation to aesthetic skull augmentations. But it does in one important way other than using PMMA…the scalp. All patients had overlying scalps that were healthy, not irradiated or missing tissue. Thus when re-expanded outward at the time of the reconstruction they developed no wound breakdowns or exposure.
PMMA is an effective and safe cranioplasty material. I have implanted far more PMMA in aesthetic patients than is in this paper for reconstructive purposes. I have been impressed with how well PMMA performs even though it is not remotely similar to its distant cousin, the hydroxyapatite bone cements. It does particularly well in the aesthetic skull augmentation patient undoubtably because the scalps are healthy and have never had surgery. Successful skull augmentation outcomes are predicated on normal scalp tissues because they will be stretched as the skull is built up underneath it.
Dr. Barry Eppley