# \"In Vivo\" Validation of 3D-Printed Innovative Surgical Template for Lumbar Spinal Arthrodesign.
## 5 Discussion and Perspectives  
The standard freehand procedure for pedicle screw insertion is normally characterized by a long learning curve, and the success of the surgery depends on the surgeon's experience. The surgical device presented is an aid that optimizes the standard procedure. Under this point of view, it becomes an alternative to the very expensive navigation systems that involve additional personnel and equipment. A patented algorithm finds optimal insertion directions and defines length and diameter of the screws based on a custom-made CAD model, obtained via RE. In order to avoid incorrect relative positioning between the template and the verteb surface, the proposed template features a novel shape that makes its placement univocal and comfortable for the surgeon. An innovative contact surface between template and verteb has been designed improving the coupling between the template itself and the vertebas, avoiding possible mismatching. Moreover, the device is designed to disengage the template from the bone surface, making it completely innovative. The production of a 3D-printed template takes, on average, 1.5 man-hours using the RP machine. Since the template design is based on the use of a patented algorithm [11; 12; 15], the authors are already working on a modelling system that will allow the semi-automatization of the template design based on the 3D model of the spine. Nevertheless, the surgeon will continue to interact with template designers in order to explain to them his/her preferences about the entry point (for which the surgeon remains responsible) and the template's size and anchorage. This device, which gives the surgeon the optimal screw trajectories and provides information regarding the length and diameter of the screws, significantly reduces the risk that the screws get out of the verteb surface, damaging the vascular and/or the nervous system, and at the same time risking to fracture the bone. Moreover, the duration of the arthrodesis surgery is significantly shortened. Accordingly, the patient's bleeding, the quantity of drugs, as well as the staff members' stress levels, are significantly reduced. There is also an important reduction of the harmful X-rays. Figure 9: Post-operative coronal X-ray check—patient code: 5 BML4L501. For this type of research, it is important to highlight the percentage reduction of both the average insertion time for a single screw and the corresponding number of X-ray shots, measured with and without the surgical guide. The averaging of the results of interest taken from the surgeries are shown below:  
* Standard procedure (no template): 27 min for the insertion of one screw and a total of 25 X-rays shots per screw;
* Novel procedure (with template): 10 min for the insertion of one screw with the aid of the template and 2 X-rays shots per screw. The proposed novel device is experimental, and so the duration of the surgeries has been stretched, since the surgeons involved have payed closer attention to a procedure that was somewhat unfamiliar. Anyway, surgery execution times fell within the range stipulated by the Lazio region local health trust [18]. The use of the proposed novel device achieved improvements in terms of precision, duration and safety, even though the surgical procedure remained the same. The procedure itself and the use of templates showed some limitations that can be highlighted as the limitation of the study. First of all, the use of templates needs for excellent bone skeletonization of the interface area of the surgical template; in positioning and use of the template, the support of a second staff unit is preferable to ensure that the template is kept in position; nevertheless, surgeons are used to having secondary staff to help the surgery. In order to avoid any kind of mismatch or error in surgery, the surgical template cannot be used if the surgeon wrongly removes part of the bone or if the ligaments to be removed are calcified (not detectable by X-ray). In those cases, the standard procedure has to be performed.