In terms of anatomy (enarthrodial differentiation), evolution (detorsion) and malformation (ovest and intermediate dysplasias) the talo-calcaneo-navicular joint is related to the hip. Hence the concept and definition of "coxa pedis". The proximal and distal enarthrodial differentiation on the lower limb with the interposed knee joint is the biochemical basis for the rotatory mechanisms. The opposite detorsions of the talar and femoral neck on the same plane maintaint a constant angle of functional declination of the talus. The angle of detorsion of the talus neck starts higher (50° at birth) and ends earlier (5-7 years) than the corresponding detorsion of the femoral neck (40° and 12-14 years). This should be borne in mind in deciding whether the detorsion of the lower extremity in primary or secondary: if on the one hand an anteversion of the femoral neck when rotating the limb inward may produce an outward rotation and anteversion of the talar neck, it is also true that a primary anteversion of  the talar neck (pes cavus-valgus) also during the inward rotation of the lower limb may lead to the absence of femoral retroversion, due partly to the absence of action by the ileopsoas, producing secondary femoral anteversion. Naturally this diagnostic problem arises again in considering treatment.