In-Hospital Design and Manufacturing of Polyetheretherketone Peek Cranial Implants

Introduction: The artificial replacement of the cranial vault, known as cranioplasty, is a necessary surgical procedure following the prior partial removal of the skull to alleviate intracranial pressure resulting from conditions such as brain swelling after stroke, intracranial hemorrhage, neoplasms, or severe traumatic brain injury. The most common technique for cranioplasty has been the autologous bone flap reimplantation.

However, complications frequently arise with autologous bone reimplantation. After 2 years, 50% of the patients exhibit resorption and require implant placement. Polyetheretherketone PEEK is particularly suited for the production of patient-specific cranial implants. PEEK implants are milled from solid PEEK blocks, which limit the implant design. Larger reconstructions can typically only be covered with the use of two implants, which are then connected with titanium plates. Such reconstructions do not offer complete protection and are prone to complications. Implant-grade PEEK is costly, and the subtractive technique, involving milling from material blocks, causes significant material wastage, leading to high manufacturing costs. When ordering an implant, the surgeon is only partially involved in the design process and the implants are not available the same day. Here, we show the implementation of independent in-hospital PEEK implant manufacturing through 3D printing which enables rapid, cost-effective, and design-optimized production of PEEK implants for the benefit of our patients.

Methods: Firstly, a new software was developed, which utilizes CT imaging data before and after craniectomy. An automated 3D segmentation was conducted on both CT scans. Subsequently, the 3D reconstructions were automatically superimposed, and a subtraction of the postoperative CT from the preoperative CT was performed. This resulted in a 3D model of a bone flap precisely corresponding to the skull defect. The entirely hologram-based software was operated by the treating surgeon using holographic glasses. In the three-dimensional space, the surgeon could make changes to the shape of the bone flap and create holes for the attachment of sutures. Furthermore, the surgeon contoured the implant to compensate for muscle atrophy of the temporalis muscle. The created cranial implant was directly verified for its fit in the cranial defect using the 3D hologram of the skull. Finally, the implant was printed by a specialized PEEK 3D printer (Kumovis R1, Germany) using implant-grade PEEK filament (Evonik, Germany).

Results: We have established a workflow for in-hospital production of cranial PEEK implants using a hologram-based application. Through automatic segmentation, matching and subtraction of the patient’s CT scans, an exact model of the patient-specific bone flap was generated. The creation of the 3D implant file took less than 20 minutes, and the implant printing process, depending on the implant's size, ranged between 2 and 6 hours.

Conclusion: The in-hospital design and manufacturing of cranial implants, employing a hologram-based application, actively involves the treating surgeon in the implant design process, reduces production time, and proves cost-effective ([Figs. 1]–[4]).

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Artikel online veröffentlicht:
05. Februar 2024