Page 87 - Clinical relevance of current materials for cranial implants

INTRODUCTION
After decompressive craniectomy a cranioplasty is recommended to protect the brain, improve esthetics, and increase psychosocial well-being.1–5 Most documented materials for cranioplasty are autologous bone, titanium, poly(methyl methacrylate) (PMMA), hydroxyapatite (HA), and poly(ether ether ketone) (PEEK), each with their own benefits. However, there is still no consensus on the optimal material for cranial reconstructions.6,7
One of the most frequently used alloplastic materials is PMMA, which was developed 4 in 1901 by Dr. Otto Röhm and was adopted early in aeronautical engineering8. After
several years PMMA was introduced in the clinic and was gradually applied for dental
applications, hip- and knee arthroplasties, and cranial reconstructions8–12.
Especially in cranial reconstruction, material handling has undergone a transformation in the last decade. Traditionally, PMMA powder and MMA liquid are hand-mixed and cured directly in the cranial defect9,12. An important disadvantage of this procedure is the high temperatures reached during curing, which could inadvertently be transferred to the bone, dura, and brain. Nowadays, a 3-dimensional (3D) mold of the cranial defect can be manufactured to produce patient-specific implants (PSIs). Subsequently, PMMA is pressed into a mold and cured. After cooling down, minor adjustments can be made to the implant after which it is placed into the cranial defect13–16. There is extensive literature available on the behavior of PMMA; however, controversy exists especially toward toxicity17. An important remaining question is whether the material behavior of PMMA changes over time in nonload-bearing locations in the human body, such as the calvarium.
Advances in medical technology, such as patient-specific allogenic reconstruction, have led to an improvement of patient outcomes18. Therefore, it is important to understand in vivo material behavior over time. It is also important to understand why implants fail, so the design and material may be further improved on.
In this study a 15-year-old ex vivo cranioplasty was retrieved. The chemical, structural, and mechanical properties of this fractured cranioplasty were evaluated to investigate changes of these properties in the human cranium and to find the origin of the failure.
In vivo fractured PMMA cranioplasty
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