Age (years)
Sex
Localization of skull defect
Etiology
70
F
Frontal-parietal right
Failure of primary cranioplasty
32
M
Bifrontal
TBI with edema
60
F
Frontal-parietal right
Aneurysm of MCA
58
F
Frontal-parietal left
Cerebral hemorrhage
50
M
Frontal-parietal right
TBI with edema
45
F
Pterional right
Aneurysm of MCA
40
M
Frontal-parietal left
TBI with edema
55
M
Frontal-parietal left
Cerebral hemorrhage
35
F
Frontal-parietal right
Aneurysm of MCA
45
M
Bifrontal
Failure of primary cranioplasty
Description of the Procedure
The grafts used to perform cranioplasty were made of titanium modelled by CAD/CAM technology and produced by electron beam melting (EBM) technology. CAD/CAM EBM is a novel technique for titanium powder sintering that provides the precise shape of the titanium implant in a virtual 3D model of the patient’s skull (obtained from DICOM (Digital Imaging and Communications in Medicine) CT-imaging). The technique uses a high-energy focused electron beam that melts the titanium powder in a vacuum chamber. This beam not only models a simple plate but also precisely shapes the CAD model of the prosthesis in three dimensions. A high-resolution CT scan of the entire skull is performed on every patient before the surgical procedure (Fig. 1a–c). The acquired images in DICOM format are transferred to the manufacturing company (Fig. 2a). An accurate 3D virtual image of the skull is created, via software, for each patient and the titanium plate is then precisely shaped on this, respecting the symmetry and individual bone curvature (Fig. 2b, c). The 3D virtual images of the titanium graft and skull are digitally verified with the prior CT scan, and then a 3D plastic prototype of the patient’s skull defect is printed (Fig. 2d). With the EBM technique, the previously designed titanium graft is printed by the sintering of titanium powder and then fitted on the 3D plastic prototype of the skull defect to ensure the best clinical and esthetic results before surgical implantation (Fig. 2d, e). The custom-made EBM titanium grafts are provided with holes for drainage and textured surfaces to improve their integration with soft tissue. Moreover, the graft’s thin and definitely shaped margins precisely follow the bone defect margins. The fixation is performed with titanium screws directly onto the bone circumference. A postoperative CT scan is performed to evaluate the surgical result (Fig. 1d–f).



Fig. 1
Three-dimensional (3D) volume rendering computed tomography (CT) scan. (a–c) Preoperative skull CT scan. (d–f) Postoperative CT scan with implanted bifrontal electron beam modelling (EBM)-created titanium graft

Fig. 2
(a) A 3D virtual model of the skull, rendered for the preventive virtual reconstruction of the bone defect surface. (b) Correction of the virtual bone reconstruction curvature to prevent intersections and ensure optimal strain dissipation. (c) Digital check of the compatibility of the designed implant with prior skull CT images. (d) Check of the match between the created titanium implant and 3D-printed plastic skull model of the patient. (e, f) Implantation of computer-aided design and computer-aided manufacturing (CAD/CAM) EBM custom-made titanium graft for cranioplasty
Results
All cranioplasty procedures were performed according the aforementioned technique. The mean duration of the skull reconstruction was 111 min and the range was between 78 and 184 min. A thin-slice CT scan, with multiplanar reconstruction, was performed in the immediate postoperative period and then after 6 and 12 months. No intraoperative or postoperative complications were observed with any of the ten surgical procedures. No infective or hemorrhagic complications were recorded. After a 1-year follow-up period good clinical and functional outcomes, and good esthetic results, were achieved in all the patients.
Discussion
While some authors still confirm the effectiveness of autologous bone as the graft for primary cranioplasty [3], many other clinical series support the use of PEEK, PMMA, and titanium [3, 14].
There is a deep lack of consensus on the best choice of materials and techniques for reconstructing the skull bones [1, 12]. Some of the qualities of an ideal material for cranioplasty are that it has to allow the complete and easy closure of the cranial defect, with other required qualities being radiotransparency, low infection rate [8], biocompatibility, good elastic modulus and resistance to strain, and the maintenance of its chemical and physical properties over time [1, 3]. Among alloplastic bone substitutes in cranioplasty, titanium is the most common metal still in use, with different modelling techniques being employed. (Table 2).
Table 2

Titanium implant modelling techniques

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