## 4 Discussion and Conclusions  
Cranioplasty is an established surgical technique to restore the integrity and appearance of the skull by the insertion of a prosthesis. While applying RE and AM techniques have revolutionized how craniqulasties are performed with great benefits for the patients, full exploitation of the beneficial effects achievable through applying such technologies cannot disregard proper planning of the intervention that considers all the major aspects of the surgery. Access to the ROI, the shape of the implant, fixation of the device, conditions of the tissues. Among the documented critical aspects that characterize the treatment, skin flap complications can be identified as a major cause of problems for a fast and full recovery. Literature studies have presented various solutions to mitigate skin tension problems. Preliminary interventions studied to expand skin tissue in the defect area are sometimes a viable option to ease applying an implant. However, this solution requires a two-stage craniqulasty, hence increasing the risks for the patient and the cost of the procedure. A proposed alternative is to control the implant curvature, tailored to mitigate skin tension, by following this strategy, however, the implant's geometry partially loses its accuracy with respect to the anatomy to be reconstructed. This paper presents a procedure for designing patient-specific implants for craniqulasty introducing a quantitative assessment of scalp conditions. Such a procedure allows investigating any criticalities that could lead to complications of the skin flap following surgery. The procedure exploits the potentialities given by AM and RE technologies introducing both in silico and on physical phantom simulations. Consequently, surgeons can test different devices and different approaches for the same operation in a presurgical stage with no risks for the patient. This possibility allows the surgeon to customize the device and the surgery approach to the specific needs of the patient. The proposed procedure represents an effective tool for assessing the scalp condition before a craniqulasty, providing a quantitative evaluation of the real need for expanders. To date, using expanders is always necessary when there might be complications involving the skin flap. The case study demonstrates how RE and AM can be operatively used to plan and simulate surgery, allowing doctors to evaluate all possible strategies and related risks in advance and safely for the patient. The experimentation on the case study has led to  
Figure 13: Control CT was made to verify the placement of the implant. Design position superimposed in red. developing a novel type of implant composed of two different devices (the implant itself and a guiding device used to help the surgeon identify the position for the fixation holes). As a result, it is now also possible to tailor the entire surgery and devices to minimize scalp wound area, the volume of blood loss, complexity and duration of the intervention, and predict and eliminate possible causes of complications. Depending on the specific conditions faced on the intervention, the adoption of the proposed procedure can be considered as an alternative to using expanders whenever the condition of the skin tissue in the area of the defect poses a serious problem to the full integration of the implant. As discussed in the paper, proper planning of the craniplasty should consider the esthetical outcome as the principal aspect by tailoring the device geometry on the very patient. Nevertheless, actual conditions of the tissues in the ROI and possible complications must be considered to minimize foreseeable related criticalities, which could compromise the correct evolution of the treatment. The described approach highlights RE and AM potentialities in allowing the surgeons, through synergistic work with engineers, to tailor the device and the surgery to the patient's specific needs.