Onlay frontal cranioplasty using wire reinforced methyl methacrylate*
Introduction
Full-thickness calvarial vault defects may be repaired with autologous bone or alloplastic materials, such as methyl methacrylate, hydroxyapatite, titanium, or porous polyethylene (Beumer et al., 1979, Remsen et al., 1986; Sanan and Haines, 1997; Verheggen and Merten, 2001; Chen and Wang, 2002; Cho and Gosain, 2004; Hoffmann and Sepehrnia, 2005; Movassaghi et al., 2006). Partial thickness defects or skull surface contour irregularities are particularly well suited to methyl methacrylate reconstruction because the inner table is present and the dura mater is not exposed to the exothermic polymerization reaction. Second, monomeric methyl methacrylate is liquid so that it easily fills shallow defects. Third, once polymerized, methyl methacrylate (PMMA) can be contoured and tapered to match the surrounding native bone. Finally, PMMA avoids donor site morbidity associated with autologous bone grafting.
Despite its many advantages, PMMA has smooth surface characteristics that prevent tissue ingrowth and adhesion (Jackson and Hoffmann, 1956; Blum et al., 1997; Sanan and Haines, 1997; Cho and Gosain, 2004). Therefore, it has low composite tensile strength and it can be sheared and dislodged. Furthermore, PMMA has a classic cleavage step river fractographic pattern (i.e. crack initiation and propagation of brittle PMMA flows through the material and coalesces like tributaries through a headwater to form a river.) that causes accelerating crack velocity propagation (Berry, 1960; James et al., 1992). This explains the multiple fracture fragments found when operating on a dislodged/fractured PMMA cranioplasty. In order to reduce dislodgement and/or fracture propagation, we have adapted wire reinforced masonry techniques to increase the tensile strength of partial thickness and surface contour PMMA cranioplasty reconstructions.
Section snippets
Clinical report
After exposing the partial thickness calvarial defect or skull surface contour deformity, a wire-passing drill bit is used to create 2-mm oblique tunnels through the outer table of the skull around the perimeter of the defect (Fig. 1). The tunnels are designed at 2–3 cm intervals, like flanges on the hub of a bicycle wheel, around the perimeter of the defect or contour irregularity. Stainless steel wire (26 gauge) is passed through a tunnel on one side, across the defect, and through a
Discussion
Methyl methacrylate is a popular alloplastic material commonly used to reconstruct calvarial defects because it is easy to contour, does not undergo resorption, and will not interfere with computed tomography (CT) or magnetic resonance imaging (MRI) (Kricun et al., 1991; Blum et al., 1997; Cho and Gosain, 2004). Despite its favorable characteristics, methyl methacrylate has a higher infection rate than autologous bone (Cho and Gosain, 2004). Methyl methacrylate cannot be used when a paranasal
Conclusion
Reinforced methyl methacrylate is our alloplastic material of choice to repair partial thickness calvarial defects and surface contour deformities in adults. The technique is simple, rapid, safe, effective, and cost-efficient.
Statement of financial interest
We hereby certify, that to the best of our knowledge, no financial support or benefits have been received by any co-author, by any member of our immediate family or any individual or entity with whom or with which we have a significant relationship from any commercial source which is related directly or indirectly to the scientific work which is reported on in the article.
Acknowledgements
We would like to thank Clarence D. Lin, BS, for his excellent artistic assistance.
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List of Products Used: Methyl methacrylate (Advanced Biomaterial Systems, Chatham, NY) was disclosed in this manuscript. No other products, devices, or drugs were used or identified.