An osteosynthesis device comprising at least one fixation pin suitable for being implanted in a bone material (R) 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 (R), said locking means comprise: (a) a support structure provided with means for its fixation to the bone material (R), 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 (R), said locking means comprise: (a) a support structure provided with means for its fixation to the bone material (R), 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 (R), 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 . <EOS>