Tibial torsion is a condition in which the tibia has a rotation along its axis. To calculate the worth of the rotation it is necessary to make a series of studies and evaluations to determine the right angle, The problem is when these exams are performed all of measures depend on the judgment and expertise of the doctor who will perform this. Such key points as the axes of rotation can be assessed and determined by different methods that may give different results. Because of this, we propose to design a device to obtain in an easy, transparent and understandable way the difference on the transverse plane of the angles between the axes of the knee and ankle, which indicates the worth of rotation. We analyzed different proposals of prototypes, choosing the one that better suits the needs that we want to cover. The prototype is compound by a ultrasonic sensors located at the ends of the axes of rotation of the ankle and they provide a distance using an algorithm developed which allows determination of the angle of twist. To validate the prototype we worked with adult patients, in whom clinical outcomes compared with existing current prototype results, showing that the device yielded the expected results and works according to specifications.