Toxicity of (bio) Materials used for Cranioplasty Implants in Humans

Objectives: Cranioplasty implants are important to prevent the ‘syndrome of the trephined’ and to recontour cranial abnormalities. When autologous bone graft resorbs, the remaining defect needs to be replaced by alloplastic materials. Being the most popular one, Polymethyl-Methacrylate has proven to be cytotoxic. To ensure patient’s safety, we conducted a systematic review on the toxicity of all types of materials used for cranioplasty implants in human subjects.

Methods: A systematic PRISMA-conform search was performed with multiple search-engines: Pubmed, Embase, Web of Science and Cochrane. We included all articles citing cases presenting toxic effects caused by cranioplasty implant material. The exclusion criteria were infections, operation related complications and toxicity objectified by imagery. At first all abstracts were reviewed. Full texts which met the inclusion were assessed for quality.

Results: Our search identified 460 articles. After abstract selection 216 were kept. A total of 26 articles respected the inclusion criteria with a reported 39 cases (40 implants) in total. PMMA accounted for 16 cases (41,0%) and demonstrated following toxic effects: foreign body granuloma (FBG), aseptic implant exposure (AIE), intra-operative nerve palsy, hypersensitivity type III leading to death. Calcium-phosphate derivatives accounted for 14 cases (35,9%) which showed AIE, FBG and folliculitis. Titanium allergy was seen in 2 cases (5,1%) of which one was fatal, and AIE in two others. One PEEK implant caused an intracerebral FBG. Of the 26 included articles 17 were appraised with high and only one with low risk of bias.

Conclusion: Due to the high risk of bias conclusions need to be assessed carefully. PMMA proved to have the most toxicity cases presented in the literature. This could be due to residual monomers. Brittle CaP parts can induce a chronic inflammatory infection. We could say that titanium and PEEK are materials which are safe.