The system (S) has a T-shaped rod (13) with length (L') greater than length (L) of a triangular/trapezoidal recess of an expanded base of a rectangular shaped elongated diaphyseal part of a plate. Ends (15) of the rod are in contact with peripheral edges (16) of the recess when a pin is inserted into an oblong hole. The rod is formed with a rectangular shaped elongated opening (17) opposite to the recess. The opening is set with a positioning screw (18) such that the plate is longitudinally and transversally displaced by displacing the screw along the opening and the pin along the hole. The length of the oblong hole is 6 to 12 mm, and length of the opening is 12 to 14 mm.
