Page 198 - Clinical relevance of current materials for cranial implants

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Chapter 10
The various materials differ substantially as to their suitability. Many different types of PMMA or PMMA-based materials are available in the medical field. PMMA is a reconstructive polymer, which is formed through the polymerization of PMMA particles with a liquid MMA. This conversion is never complete and residual monomers will remain in the implant. These residual monomers may cause toxic reactions5 and it is not possible to 3D print PMMA yet. PMMA does not have the properties for bony ingrowth, and therefore no commensurately growth with the cranium will follow. PMMA is relatively cheap, easy to use and radiolucent.
Not all hospitals have the opportunity to use computer software for designing and manufacturing a cranioplasty. But some surgeons do use molds for example of nylon, plaster, or silicon -(virtually designed or not) to improve the esthetic outcome of PMMA cranioplasties6. In those cases there are a number of options to mechanically improve the cranioplasty. As shown in chapter 4 the manufacturing of PMMA cranioplasties under pressure ensures reduced porosity in the material. The results of chapter 4 lead to the advice to manufacture all PMMA cranioplasties preoperatively, in a safe environment under pressure of at least 2.2 bar to increase the mechanical properties. There are more benefits to manufacturing the cranioplasty preoperatively. One important advantage is that the cranial implant can be virtually designed using 3D planning software. Based on such a 3D planning, the implant can be manufactured using computer-aided manufacturing techniques. Another benefit could be that the polishing of the cranioplasty after manufacturing can be applied, resulting in a reduced biofilm and less bacterial adhesion7. This may result in less re-operations due to a decreased number of infected cranioplasties. In our opinion, preoperative planning and manufacturing of the cranial implant leads to a more predictable surgical intervention and may result in a better fitting implants6.
PEEK is used for Patient-Specific Implants (PSI) in adults. With the use of the patient’s CT-scan and dedicated software it is possible to design a cranioplasty with an accuracy of at least 1 mm6. In chapter 5 no significant prediction factor was found for the failure of PEEK cranioplasties in 40 cranioplasties. PEEK is a relatively new material used in cranial reconstructions and at the moment it is mainly used for secondary reconstructions8. This may be the main reason why it shows a relatively high general complication rate, in particular infections3,8. If PEEK could be used for the initial reconstruction the infection rate may be less because the overall health condition of the patient is better.