Page 98 - Clinical relevance of current materials for cranial implants

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Chapter 4
DISCUSSION
This ex vivo study reports the material properties of a fractured PMMA cranioplasty made of CMW-3, after being part of the human cranium for 15 years, and fresh specimens of CMW-3. The following trends were observed: (I) the chemical and mechanical properties of CMW-3 did not significantly change during the 15 years in vivo (II) failure of the cranioplasty can be attributed to the heterogeneity in thickness and porosity (III) improvements in the mechanical properties of PMMA cranioplasties can be achieved by ensuring a consistent thickness of the cranioplasty, and by curing the implant under increased pressure.
Failed cranioplasties are generally not subjected to further investigations beyond basic microbiological evaluation in cases of infection. In our study, a single failed PMMA cranioplasty was analyzed and compared to fresh specimens of CMW-3. It is crucial to determine how the human body influences material properties of such implants over time, to ensure optimal clinical outcomes and possibly prevent further operations for the patient.
PMMA-based polymers have been used for many years in medical devices with their specific formulations and applications. It is used intra-operatively for fixation of artificial joints to bone, for dentures, and for cranial reconstructions8–12. The information on chemical and mechanical behavior of PMMA following long-term implantation in the cranium is scant. In the literature,1 patient was victim in a bicycle accident after cranioplasty which resulted in a fractured PMMA cranioplasty22. Marchac et al. included 32 patients who underwent a cranioplasty with PMMA, one cranioplasty was removed because of fracture due to trauma23. In another study a patient underwent a computer-based titanium mesh cranioplasty which fractured spontaneously. The authors hypothesized that the fracture of the implant occurred because of continuous pressure on the implant during the night, when the patient slept on the affected side24. Fracture is more frequently described in cranioplasties manufactured from hydroxyapatite25,26. Staffa et al.25 reported 25 patients who all underwent a cranioplasty of hydroxyapatite, of which one cranioplasty fractured due to trauma. Stefini et al.26 included 1549 patients with an hydroxyapatite cranioplasty, four were reported as fractured. The low incidence rate of fracture of cranioplasties could be due to underreporting of this complication in the literature. It is also possible that patients have no complaints and therefore do not notice the fracture.