Cases
Custom cranioplasty with PMMA using rapid prototyping and 3D CAD
Case presented by Dr. Villiam Dallolio, Massimo Orsi, Enrico De Micheli, Luigi Monolo from Neurosurgical Unit, Lecco Hospital, Lecco, Italy and Ing. Samuele Puricelli , Ing. Francesco Davolio from Bioengineering Laboratory, Lecco Hospital, Lecco, Italy.
a. A 45-year old patient presented with a right, frontal-temporal defect, with dimensions of approximately 10x12 cm. Infection developed following an implant of a poly methylmethacrylate prosthesis using a previous technique. Initial pathology resulted from an automobile accident.
b. The custom prosthesis technique includes a planning and modeling phase.
The planning phase consists in
- Acquisition of CT imaging. Using Computed Tomography, Picker PQS and adaptor, an imaging acquisition protocol is followed. Imaging is saved in digital DICOM format.
- Elaboration of CT imaging. CT imaging is imported into MIMICS software and then elaborated, segmented, reconstructed.
- Virtual 3D model of the prosthesis. Based on imaging data, in order to achieve an exact fit of the prosthesis to the natural contour of the skull, a virtual 3D model of the prosthesis is elaborated. This model is then graphically assembled with a virtual 3D model of the patient skull in order to verify contour and fit.
c. The modeling phase uses rapid prototyping technique to realize the tools needed for PMMA prosthesis creation.
Following polymerization, any excess material is removed from the prosthesis which is sterilized in etylene oxide and packaged.
d. Surgical procedure is simplified with this technique. Following the existing incision, the scalp is opened and the soft underlying tissue is carefully detached from the dura. When using PMMA, the surgeon must avoid exposure of the bone margin to limit any bleeding, conversely to what occurs with autogenous bone and biomaterial.
The prosthesis is positioned and the fit is verified. If necessary, modifications to the prosthesis may be easily done with a surgical drill. Paired holes in the prosthesis and skull are determined and fixing is performed with 0-silk sutures or titanium plates and screws (or recently with Nitinol memory staples). Holes (4mm) are made in the center of the prosthesis for dural tenting suture to prevent epidural fluid accumulation. Drainage tubing is positioned. The scalp is closed and a compressive bandage is wrapped to prevent subgaleal collection.
e. Outcome was excellent. The prosthesis fit was exact, without any further modification, resulting in a normal cranial contour.
CONCLUSION: The authors propose an innovative cranioplasty technique with PMMA. Using computed tomography, Materialise MIMICS and professional CAD equipment, a virtual 3D model of the prosthesis is designed and then manufactured using a rapid prototyping process which allows automatic modeling of a custom prosthesis, prior to surgery. Follow-up studies in 6 custom cranioplasties suggest the following: preformed custom prostheses, using CT images of the patient, result in superior cosmesis compared to intraoperatively-constructed prostheses; completion of the PMMA polymerization process prior to surgery significantly reduces inflammatory risk; and, a cost savings may be attributed to shortened operating times, reduced incidence of infection and improved mechanical precision and process.