Instruments for implanting bone inserts between two bone stumps (4, 5) of long bones, comprising a metal plate (3) extending longitudinally according to a predetermined direction (D) and suitable for connecting the above-mentioned two bone stumps (4, 5), a first guiding unit (6) for cutting an end portion of a first bone stump (4), a second guiding unit (7) for cutting an end portion of a second bone stump (5).