The present invention relates to an osteosynthesis device (1) with a plate (2) and screw (4) for fixing said plate (2) to a bone, in which the head (41) of the screw (4) has a thread ( 412) for its locking on the tapping (33) formed in its receiving hole (3). According to the invention the internal surface of the plate orifice (3) comprises a first frustoconical section (35) which extends at an angle of between 30 and 60 ° with respect to the central axis of the orifice (32) , and a second frustoconical section (36) which extends between said first frustoconical section (35) and the lower face (21) of the plate, at an angle of between 8 and 12 ° with respect to said central axis of orifice ( 32). The inner surface of the orifice (3) further comprises at least three upper clearances (38), and at least three lower clearances (39), which upper (38) and lower (39) clearances are arranged to allow a degree of freedom angulation of the screw (4), and are also arranged so as to preserve a portion of the orifice tapping (33) on all the generatrices of the internal surface of the orifice which are situated in planes parallel to said central axis (32 ). Figure for the abstract: Figure 1 La présente invention concerne un dispositif d’ostéosynthèse (1) à plaque (2) et vis (4) pour fixer ladite plaque (2) sur un os, dans lequel la tête (41) de la vis (4) comporte un filetage (412) pour son verrouillage sur le taraudage (33) ménagé dans son orifice (3) de réception. Selon l’invention la surface interne de l’orifice de plaque (3) comprend un premier tronçon tronconique (35) qui s’étend selon un angle compris entre 30 et 60° par rapport à l’axe central d’orifice (32), et un deuxième tronçon tronconique (36) qui s’étend entre ledit premier tronçon tronconique (35) et la face inférieure (21) de la plaque, selon un angle compris entre 8 et 12° par rapport audit axe central d’orifice (32). La surface interne de l’orifice (3) comprend encore au moins trois dégagements sup
