The intervention with the expanding prothesis is one of the interventions of arthrorisis endo-sinus-tarsic “in support of the neck”, which are, those interventions that aim to correct the reciprocal position of the talus on the calcaneus without affecting the astragalus-calcaneal joint. The method involves the placement of an expandable cylinder inside the tarsus sinus. The expansion stabilizes the connections between astragalus and calcaneus, helping the correction of the listhesis of the head of the astragalus, with consequent correction of the excessive pronation of the backfoot in patients during the growing years, so that the calcaneus and astragalus are remodeled to reach a stable conformation. It also performs a neuro-propioceptive function of correction of the backfoot axis, as demonstrated by the fact
that correction is maintained even after removal of the device.