# \"In Vivo\" Validation of 3D-Printed Innovative Surgical Template for Lumbar Spinal Arthrodesign.  
[PERSON]  
1 Department of Industrial Engineering, University of Salerno, Via Giovanni Paolo II, 132, 84084 Fisciano, SA, Italy; [EMAIL_ADDRESS] (F.N.); [EMAIL_ADDRESS] (N.C.)  
[PERSON]  
2 Techno DESIGN S.r.l, via Rosa Jemma, 2, 84091 Battipaglia, SA, Italy; [EMAIL_ADDRESS]  
[PERSON]  
3\"San Giovanni di Dio e Ruggi d'Aragona\" University Hospital, Largo Citta di Ippocrate, 84131 Salerno, Italy; [EMAIL_ADDRESS]  
[PERSON]  
1 Department of Industrial Engineering, University of Salerno, Via Giovanni Paolo II, 132, 84084 Fisciano, SA, Italy; [EMAIL_ADDRESS] (F.N.); racppetit@unisa.  
Generally, the standard procedure that uses pedicle screws involves: identifying the entry point for the screw; choosing the trajectory based on X-rays and cannulating the pedicle along it; probing with the appropriate device to detect breaches; and tapping and screw introduction.  
This procedure is usually performed \"hand-based\" with all the related aspects that affect confidence in implantology. Even the experienced surgeons sometimes have to correct the trajectory of the screws during surgery. The correct introduction in the vertebra is normally monitored with many harmful radiographic shots [1].  
New navigation systems are normally utilized to allow viewing on a screen, in real time, the anatomical structures to be treated, avoiding dangerous X-ray shots. These systems present three technical issues: positioning accuracy, calibration, and high costs [1].  
For these reasons, patient-specific surgical templates produced in three-dimensional biocompatible material via rapid prototyping technology represent a valid alternative.  
[PERSON] [2] demonstrated that the surgical template improves screw placement precision by comparing the accuracy with and without templates. [PERSON] [3] proposed a particular surgical template that could accommodate drill having different diameters.  
Normally, during the pre-operative step the identification of the screw direction is performed. The surgical template is designed based on the results of the previous step. A multilevel surgical template was designed, via CAD software, by [PERSON] et al. [4]. Even though several aspects were automated in this way, multilevel templates did not always guarantee excellent positioning. In [5], the authors tried to find the smallest diameter of the pedicles. They calculated the optimal orientation and the maximum size of the screws via least squares method. In this case, problems raised for highly deformed spines. A method that finds the isthmus of the pedicles intended as the smallest section and from its centre projects a perpendicular straight line i.e., the optimum direction for the screws was presented in [6]. In [7], the authors have shown a computer-aided method for calculating the best path for pedicle screw insertion (sufficiently equidistant from the barycentric points of the pre-set coronal sections of the pedicle), with appropriate dimensioning of the screw based on the smallest cross section of the pedicle. Recently, other researchers [8; 9] have worked on writing algorithms to find the best trajectories, diameters, and maximum length for screws. In [10], a new hook-shaped rapid-prototyped template has been tested on a single patient and a comparison with twelve similar techniques presented in previous articles has been performed, demonstrating the accuracy in surgery and the usability of the proposed template. Nevertheless, a real clinical trial has not been conducted on a sufficiently wide sample of cases.