An osteosynthesis device comprising at least one fixation pin suitable for being implanted in a bone material so as to ensure an at least partial reduction of a bone fracture, said osteosynthesis device comprising locking means designed to lock in position said at least one fixation pin implanted into said bone material, said locking means comprise: (a) a support structure provided with means for its fixation to the bone material, said support structure comprising a locking aperture through its thickness, said locking aperture being centred on an aperture axis and being delimited by an aperture contour, at least part of which is provided with an aperture thread,said locking aperture being adapted to be passed through by said at least one fixation pin, and (b) a tightening means designed to be fitted into said locking aperture and to come into abutment against a part of said at least one fixation pin in order to ensure its locking in position, said tightening means consists of a locking nut centred on a nut axis, said locking nut being delimited by - an upper nut part provided with a recess adapted for its driving into rotation by means of a suitable tool, - a lower nut part located at the opposite of said upper nut part, - an outer peripheral envelope comprising a nut thread adapted to cooperate with said aperture thread of said locking aperture, and - an inner contour delimiting an axial hole adapted for the passage of said at least one fixation pin, characterized in that said locking nut still comprising a deformable tightening structure adapted to be deformed when said locking nut is screwed into said aperture thread and to come into abutment against a part of said at least one fixation pin housed within said axial hole. said osteosynthesis device comprising locking means designed to lock in position said at least one fixation pin implanted into said bone material, said locking means comprise: (a) a support structure provided with means for its fixation to the bone material, said support structure comprising a locking aperture through its thickness, said locking aperture being centred on an aperture axis and being delimited by an aperture contour, at least part of which is provided with an aperture thread,said locking aperture being adapted to be passed through by said at least one fixation pin, and (b) a tightening means designed to be fitted into said locking aperture and to come into abutment against a part of said at least one fixation pin in order to ensure its locking in position, (a) a support structure provided with means for its fixation to the bone material, said support structure comprising a locking aperture through its thickness, said locking aperture being centred on an aperture axis and being delimited by an aperture contour, at least part of which is provided with an aperture thread,said locking aperture being adapted to be passed through by said at least one fixation pin, and (b) a tightening means designed to be fitted into said locking aperture and to come into abutment against a part of said at least one fixation pin in order to ensure its locking in position, said tightening means consists of a locking nut centred on a nut axis, said locking nut being delimited by - an upper nut part provided with a recess adapted for its driving into rotation by means of a suitable tool, - a lower nut part located at the opposite of said upper nut part, - an outer peripheral envelope comprising a nut thread adapted to cooperate with said aperture thread of said locking aperture, and - an inner contour delimiting an axial hole adapted for the passage of said at least one fixation pin, characterized in that said locking nut still comprising a deformable tightening structure adapted to be deformed when said locking nut is screwed into said aperture thread and to come into abutment against a part of said at least one fixation pin housed within said axial hole.