Low-cost customized cranioplasty using a 3D digital printing model: a case report
Cranial defects usually occur after trauma, neurosurgical procedures like decompressive craniotomy, tumour resections, infection and congenital defects. The purpose of cranial vault repair is to protect the underlying brain tissue, to reduce any localized pain and patient anxiety, and improve cranial aesthetics. Cranioplasty is a frequent neurosurgical procedure achieved with the aid of cranial prosthesis made from materials such as: titanium, autologous bone, ceramics and polymers. Prosthesis production is often costly and requires complex intraoperative processes. Implant customized manufacturing for craniopathies allows for a precise and anatomical reconstruction in a shorter operating time compared to other conventional techniques. We present a simple, low-cost method for prosthesis manufacturing that ensures surgical success.
Two patients with cranial defects are presented to describe the three-dimensional (3D) printing technique for cranial reconstruction. A digital prosthesis model is designed and manufactured with the aid of a 3D computed tomography. Both the data of large sized cranial defects and the prosthesis are transferred to a 3D printer to obtain a physical model in poly-lactic acid which is then used in a laboratory to cast the final customised prosthesis in polymethyl methacrylate (PMMA).
A precise compliance of the prosthesis to the osseous defect was achieved. At the 6 month postoperative follow-up no complications were observed i.e. rejection, toxicity, local or systemic infection, and the aesthetic change was very significant and satisfactory. Customized 3D PMMA prosthesis offers cost advantages, a great aesthetic result, reduced operating time and good biocompatibility.
KeywordsCranioplasty Cranial implant Skull defects Polymethylmethacrylate resin PMMA prosthesis Cranial vault reconstruction Low cost prosthesis 3D printing
Computer-aided design/computer-aided manufacturing
Digital images and communications in medicine
Loss of a body part has significant repercussions for any individual. The absence of a body part has a great influence in a person’s physical state and state of mind, and causes social interaction difficulty; which frequently limits their hope of recovery . Lack of continuity of the cranial vault bones is usually secondary to severe head injury, but can also be secondary to neurosurgical procedures e.g. decompressive craniotomy or tumor resection. Infections, especially osteomyelitis and congenital anomalies or iatrogenic disorders can cause these type of defects .
In certain cases, cranial defects can become quite extensive or involve adjacent tissue damage. On the one hand, atmospheric pressure on the defect has a direct effect on intracranial structures causing symptoms like headache, confusion, irritability, psychiatric symptoms, contralateral weight sensation and, epilepsy . On the other hand, osseous cranial defects cause aesthetic abnormalities such as herniation or depressions that may severely affect the patient’s quality of life .
Repair of the cranial defects has as a main goal to protect the underlying brain tissue, to decrease pain at the site of the defect, improve the appearance and decrease the patient’s anxiety . The human body cannot regenerate a lost body part, but reconstruction can be obtained through a multi-disciplinary approach and the placement of a prosthesis. Cranioplasty is one of the oldest neurosurgical procedures, practiced since 3000 BC .
For centuries, several materials have been tested to cover osseous defects including coconut shells, allogenic and xenogenic bone grafts, metals and more recently, biosynthetic materials such as resins and ceramics . Methyl methacrylate was used for the first time in 1941; since then, many other derivatives have been used in the operating room . The tendency with any alloplastic material is to increase its biocompatibility. Cranioplasties done with alloplastic materials are already a well-accepted treatment method. The ideal characteristics of prosthetic materials are their inability to cause inflammatory reactions, non-allergenicity or inability to cause hypersensitivity, chemical inertness, non-carcinogenicity, ability to withstand strain and tension, capacity to be sterilized and to be molded into the desired shape when fabricated . Titanium prefabricated prosthesis have some disadvantages, for example, thermal conduction, little chance of intraoperative modifications and a high cost . Intraoperatively produced polymethyl methacrylate (PMMA) prostheses require complex procedures such as: preparation of the mixture with direct contact with the dura mater that can produce exothermal reactions or produce toxic monomers during surgery, implant adjustments for osseous adaptation that causes an increase in operating time. Intraoperative implant adjustments may cause poor aesthetic results in large and complex defects . The advantages of PMMA are the following: it is low cost, no donor is required, it is lightweight, strong, inert, radiolucent, non-ferromagnetic and stable. The disadvantages are that it has a low adherence to the surrounding tissue, it may cause tissue reactions (subcutaneous seroma), and may be bulky in some areas like the orbital rim .
Computer assisted design and prosthetic material modeling result in an excellent cosmetic outcome, and reduce operating time necessary for implant placement .
Case report No. 1
Case report No. 2
In Mexico these procedures have to be payed in full by the patient, limiting their reach and practice in the general population since they are costly. A customized titanium implant costs around US$5000, and those made from PEEK around US$7000 or more depending on their size. The customized prostheses proposed by the authors have a cost of about US$600, including the digital design, printing of a 3D prototype and the PMMA prosthesis itself. Both titanium and PMMA are the most commonly used alloplastic materials [14, 15].
Prosthesis digital design
The CT scan data is stored in the standard format DICOM (Digital Images and Communications in Medicine) which allows generating an interface between the medical equipment and any other device to visualize the images. Through the DICOM viewer, Osirix® generated a three-dimensional reconstruction of all the CT cross-sectional images. A bone filter is applied in order to only observe the bone structure, achieved by taking as reference its attenuation degree.
The implant is generated using the software of the computer-aided design (CAD) ZBrush 4R5® since Osirix® is only a viewer.
The implant design must have a precise shape and volume according to each patient’s cranial anatomy. Finally, the data is exported in a stereolithography extension file (STL) and fed to the printer.
Description of cranial prostheses characteristics
Intraoperative adjustment time
Precision to cranial defect
Intraoperative exothermic reaction
There were no adverse events such as prosthesis exposure, seroma, infections, nor any toxicity or encephalic inflammation since the cerebral tissue was not exposed to an exothermic reaction in the OR. After a 6 month post-operative follow-up, cranioplasty patients had an appropriate neurological progression defined by measuring their cognitive and motor skills.
Hand-manufacturing of a prosthetic implant can only be carried out if the original cranial bone fragment is available. Since the cases treated at our Hospital presented with fragmented cranial fractures, bone preservation was implausible.
PMMA prosthesis manufacturing by hand has been used since 1970 using various processes [1, 16, 17, 18], but these methods have been overtaken by computer assisted design and manufacturing techniques (CAD/CAM) which consist on using images of the cranial defect and manufacturing the PMMA prostheses with a 3D printer [19, 20, 21, 22, 23, 24, 25]. The CAD/CAM technique described by Caro-Osorio & Cols.  in 2013 is no longer an expensive method. The ideal implant material should have the following characteristics: it should be able to adjust to the cranial defect, it must achieve a full defect coverage, full biocompatibility, inertness, non-thermal conductor, radiolucent, non-magnetic, light, rigid, easily placed and low-cost [19, 27].
A titanium prosthesis  is more difficult to manufacture than one made from PMMA . Even though, as Park and cols.  have commented, postoperative patients treated with a titanium implant have a satisfactory postoperative course evaluated with CTs, documenting an adequate implant fixation and cranial symmetry, the main obstacle with this technique is cost.
Preoperative prosthesis manufacturing is simpler, technically speaking, and has the added advantage of lowering surgical time, blood loss and infection rate, and improving the aesthetic result satisfaction when compared to intraoperative moulding .
PMMA preoperative implant manufacturing can be done either by hand or with CAD/CAM techniques. Manufacturing done by hand is cheaper and less time consuming than using a patient’s 3D-CT data to then print a 3D implant [21, 24]. Nevertheless, this last method has recently gained popularity because it does not require to be tried on the bone defect to produce excellent cosmetic results .
Pre-operative production (ie. prefabrication) of a cranioplasty prosthesis involves a computer-aided design system and direct computer-aided manufacturing to obtain the desired shape. This system uses standard 3D CT data.
It is done by locating the cranial defect margin on a skull surface image generated from a 3D head CT-scan. A right-to-left mirrored image or an average 3D skull surface template image is then fitted to the patient’s skull surface image. The area around the defect is cut out and stitched to the previously isolated defect margin. This defect-filling surface is then tapered and printed out in 3D. The 3D print implant model is then recasted in a biocompatible material .
The process differs from ours in that the delineation and the stabilization of the skull defect margin are not required to identify the thickness and the shape of the implant piece. We use the Boolean operation of extraction exclusively between the mirrored side and the side with the defect to obtain the implant piece with the shape and the thickness required.
No complications were observed in either of the cases reviewed in this article, but the population cannot be presumed to be of any statistical significance. Thien A. and cols.  reported in 2015 a 25% tendency in incidence towards titanium prosthesis exposition in contrast to a 12.5% incidence with PEEK. These authors also mentioned that infection rate in patients undergoing decompressive craniotomy was associated with previous cranioplasties . It is evident after reviewing the literature that there is no perfect prosthetic material for cranioplasties free from complications.
The results observed in our cases match the reports from Akam M. and cols.  who concluded that polymethyl methacrylate is a low-cost, long-lasting material which can be used to reconstruct full thickness cranial defects.
For years, prefabricated customized cranial prostheses using 3D printers have demonstrated their use and advantage when compared to other techniques. In the Hospital Civil de Guadalajara Fray Antonio Alcalde, a group comprised of researchers and surgeons work together to obtain low-cost customized implants since titanium and PEEK (polyetheretherketone) prosthesis are too expensive for the type of population we treat.
This study proves the efficacy of customized PMMA prefabricated 3D prosthesis. Cranial symmetry is achieved to perfection, little intraoperative time is needed for adjustments, coaptation is precise. Lastly, compared to PMMA prostheses produced intraoperatively, no exothermal reaction is generated in the operating room, nor are any monomers liberated through gas formation, polymerization heat is avoided and adjustment time is reduced to a minimum.
The main limiting factor in this method is the generation of the DICOM file from the 3D CT since we do not own a bone scanner and we rely entirely on the hospital’s CT scanner availability.
This method allows an encouraging functional, aesthetic, biologically safe and low-cost patient treatment, especially to a low-income patient population like the one that is treated in our facilities, who would not otherwise have the means to pay for their health needs.
Availability of data and materials
Data sharing not applicable to this article as no datasets were generated or analysed during the current study.
Every author listed above has been actively involved in conceptual design, data collection, data analysis and interpretation, as well as manuscript drafting and editing. All authors read and approved the final manuscript.
Ethics approval and consent to participate
Name of Ethics Committee (translated): Research Ethics Committee of the Antiguo Hospital Civil de Guadalajara “Fray Antonio Alcalde”, A translated letter of the Committee’s approval has been submitted together with this manuscript. “All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards”.
Consent for publication
Written informed consent was obtained from the patient for publications of this case report and accompanying images which have been submitted together with this manuscript.
The authors declare that none of them have any competing interests.
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