An exceptional situation may occur in which the system incorrectly guides the trajectory of the implants, and this may result in incorrect positioning that could affect the health of the patients. In such a case, there is a risk of causing a neurological condition in the patient if the screw should invade the cortical bone up to the spinal cord or nerve roots. However, the risk of this occurring is considered to be less than or equal to the conventional technique on the basis that insertion and final testing depends on the judgment of the neurosurgeon. The placement of the screws is verified before the completion of the surgery by means of a CT scan, which will make it possible to assess the need for possible reinsertion.