Intramedullary apparatus (IM) (100) for treating a fractured bone of an animal, comprising: an extended IM nail (110) along a longitudinal axis and having at least three locking holes (112) defined on it at the same distance along the longitudinal axis, in which the IM nail (110) is configured to be inserted into a medullary cavity of a fractured bone bone fragment, so that the IM nail (110) can be attached to the fragment bone by means of a blocking element (134) correspondingly inserted into one of the blocking holes (112) through the bone fragment； and a positional reference element (120) having a longitudinal vernier scale (122) thereon, in which the positional reference element (120) is configured to be removably mounted on the IM nail (110) by two positioning elements (132) inserted in two of the locking holes (112) so that the longitudinal vernier scale (122) is parallel to the longitudinal axis of the IM nail (110), and each of the locking holes (112) it can be located by the longitudinal vernier scale (122), in which the locking holes (112) are through holes substantially perpendicular to the longitudinal axis, characterized in that the locking holes comprise at least one vertical locking hole (112 ) perpendicular to the longitudinal axis in a vertical direction, and at least one horizontal locking hole (114) perpendicular to the longitudinal axis in a horizontal direction, at least one locking hole v ertical (112) and said at least one horizontal locking hole (114) intersect in the longitudinal axis.Aparato intramedular (IM) (100) para tratar un hueso fracturado de un animal, que comprende: un clavo IM extendido (110) a lo largo de un eje longitudinal y que presenta por lo menos tres orificios de bloqueo (112) definidos sobre este a igual distancia a lo largo del eje longitudinal, en el que el clavo IM (110) está configurado para ser insertado en una cavidad medular de un fragmento óseo del hueso fracturado, de manera que el clavo IM (110) pueda ser fijado
