The present invention relates to a surgical instrument for a technique for attaching bone fragments using a cannulated screw, the implantation of which is guided by a pin. The instrument (1) comprises: (i) a central channel (5) defining a longitudinal axis (6), enabling the slable and rotatable insertion of said instrument (1) onto said guide pin (ii) a nesting structure (15) suitable for being inserted into a recess made in the head of said cannulated screw and for blocking the rotation thereof (iii) cutting edges (20, 21) suitable for boring at least one of said bone fragments by rotating said surgical instrument (1) about said longitudinal axis (6) and (iv) a means (11) for gauging the insertion depth of said guide pin in said bone fragments. Said instrument (1), which is conveniently inserted onto said guide pin and rotatably moved, enables either the boring of at least one of the bone fragments by means of said cutting edges (20, 21), or the screwing of said cannulated screw, inserted onto said guide pin, by engaging with said nesting structure (15).La présente invention concerne un instrument chirurgical pour une technique de fixation de fragments dos au moyen dune vis canulée dont limplantation est guidée par une broche. Linstrument (1 ) comporte : (i) un canal central (5) définissant un axe longitudinal (6), permettant lengagement en coulissement et en rotation dudit instrument (1 ) sur ladite broche de guidage, (ii) une structure demboîtement (15), adaptée pour venir sinsérer dans un logement ménagé dans la tête de ladite vis canulée et pour assurer leur verrouillage en rotation, (iii) des arêtes de coupe (20, 21 ), aptes à forer lun au moins desdits fragments dos par rotation dudit instrument chirurgical (1 ) autour dudit axe longitudinal (6), et (iv) des moyens (1 1 ) pour jauger la profondeur denfoncement de ladite broche de guidage dans lesdits fragments dos. Cet instrument (1 ), convenablement engagé sur ladite broche de guidage et manœuvré en rotation
