parallel to the longitudinal axis x 2 of the bore 2 with the result that the shank is efficiently drawn towards the inside of the bore 2 in particular taking into account the direction and intensity of the effort of traction t the diameters d 2 and d 6 can be provided to be substantailly equal with the result that the shank 5 is firmly maintained in place after having been positioned the shank 5 is provided with two bores 7 distributed along its axis x 5 the bore 7 nearest the end 5 a of the shank 5 being used the fact that the shank 5 comprises a plurality of orifices 7 makes it possible to use an orifice 7 relatively close to the end 5 a of the shank 5 and to avail of such an orifice including when the shank 5 is cut in order to adapt its length to the thickness e of the malleolus 3 the number of bores 7 may of course be increased if necessary the bore 2 is made via the outer face 3 a of the malleolus 3 with the aid of the ancillary tool shown in fig3 and 4 this tool 10 comprises a spacer block 11 provided to be disposed between the tibia t and the astragalus a.