Patients with skull defects after craniotomy for example tumor resection, head trauma, stroke, need a reimplantation of the bone afterwards. For some circumstances, their own bone cannot be reimplanted due to infection, tumor infiltration, damage to the bone, or aseptic bone necrosis. In these cases a Patient Specific Implant (PSI) needs to be designed to fit into the patient's skull defect. Several materials are currently used such as titanium, poly-ether-ether-ketone (PEEK) or poly-methylmethyl-acrylate (PMMA) for PSI fabrication. At the moment, PSI are commercially available from different companies (DePuy Synthes®, EOS®, Xilloc®). Apart from the high costs of commercially available PSI, it takes usually several weeks until the designed and manufactured PSI is delivered to the hospital ready for reimplantation.

On the other hand, a method for software-based PSI design and intraoperative fabrication of the PSI under sterile conditions was described by Stieglitz et al. This method is currently used in everyday clinics in the department of neurosurgery in Bern. In short summary, the design of the PSI is based on the preoperative CT-scan of the patient's head with the skull defect, the imaging data set is uploaded and processed with IPlanNet software by BrainLab®. With the help of the software, a 3D model of a negative mould of the PSI is designed and printed. In the operation room, the PSI is fabricated under sterile conditions using the PSI mould. The design of the PSI mould with the help of IPlanNet is demanding and takes some few hours depending on the complexity of the case to be designed. In certain cases the accuracy of the fabricated PSI mould is not optimal, so that the surgeon intraoperatively has to adapt for the inaccuracy to achieve the best cosmetic and functional results at the expense of the operation duration, a known risk factor for postoperative wound infection and other perioperative complications.

Therefore, the investigators have developed an automated computer-based algorithm for PSI design (CAPSID). With the help of this tool, an accurate PSI and its corresponding mould can be calculated and designed based on the preoperative CT scan of the patient within 5-15 minutes and the corresponding mould can be printed. This step is automated and thus, independent of the neurosurgeons experience and skills in 3D processing software. The mould can be used for intraoperative fabrication of the implant under sterile conditions in the common way as described above. The possible advantages of the clinical establishment of this procedure would be a higher accuracy of the PSI compared to the conventional PSI fabrication method with better cosmetic results, lower costs and faster availability and production leading to shorter waiting time for the patient, and as a consequence of the higher accuracy leading to shorter operation time, with a reduction of risk of operative adverse events for the patient. Furthermore, the proof of practicability of this new method, could lead to new concepts in the field of Computer-based Patient Specific Implants in modern medicine in general. A clinical trial is necessary to proof the advantages and practicability of the investigators' concept of computer-based algorithm for PSI design (CAPSID) for patients with skull defects.