The vertebral motor unit is, as any part of the body, exposed to the possibility of degenerative pathological conditions that may cause structural disorder. In the cases of pathological conditions in which the correction through appropriate devices or physiotherapy is not sufficient for cure, it is indispensable to carry out an operation known as "pedicle arthrodesis". Pedicle arthrodesis is a surgical technique that consists in fixation of one or more joints of the vertebral column. Usually, the operation is performed by means of implants to be fixed to the vertebral column by hooking them to pedicle screws anchored to the vertebrae. The screws are inserted by previously making in the vertebra two lateral holes, using a surgical perforating implement. The present invention has the purpose of identifying, with the aid of a computer and on an x-ray, or on a three-dimensional reconstruction by means of CT or NMR, generated by a computer, hence without ever coming into contact in vivo with the patient, the optimal direction and the maximum diameter of a pedicle screw so that the screw will not come out of the pedicle.
