Page 33 - Clinical relevance of current materials for cranial implants

Autologous bone is inferior to alloplastic cranioplasties
INTRODUCTION
In patients who underwent a decompressive craniectomy, a cranioplasty is commonly 2 required to protect the brain, restore aesthetics, relieve neurological symptoms, as well
as for psychosocial reasons1. The number of cranioplasties performed has increased
over the last years, reaching 20-25 per million inhabitants per year in 2010 (in Europe,
Middle East and Africa)2.
Autologous bone is widely used for cranioplasty, relatively inexpensive, easy to obtain, exhibits good fit and contour, presents no risk of disease transmission and is viable3. Bone resorption and infection are the most frequently reported complications, with a large range in degree, timing and occurrence4-6.
In the past, some cranioplasties were manufactured by molding autologous bone grafts in alginate or plaster. Poly (methyl methacrylate) (PMMA) was cast into the mold and polymerized to avoid the exothermic reaction occurring adjacent to the brain during hardening7,8. Currently, PMMA is also used in a customized 3-dimentional (3D) mold to achieve better cosmetic results9. Autologous bone may not be available because of fracture, infection, resorption, depletion, or even discontinuation of an institutional bone-bank due to increasing storage costs and (inter)national regulations. In these cases alloplastic materials may be used, e.g. titanium, PMMA, hydroxyapatite (HA), and poly(ether ether ketone) (PEEK)2,10-12.
Computer-aided design and computer-aided manufacturing (CAD/CAM) and other 3D virtual planning technologies have been applied to overcome the shortcomings of intraoperative molding and allow for the creation of patient-specific implants (PSI). A PSI aims for a perfect fit as the design is based on the patient’s computed tomography (CT) or cone-beam CT data. More sophisticated materials enable manufacturing by 3D printing and rapid prototyping techniques, allowing for more complex shapes when personalized and unique shapes are required13,14. Consensus on the preferred method or material is lacking. The ideal material is similar to cortical bone, biocompatible, radiolucent, nontoxic, has a low complication rate, is easy to use in the operation room, can be used to create an optimal PSI, brings excellent cosmetic results, and is low in cost10.
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