The device (5), designed to be fixed to the distal end of a fastener-positioning instrument, comprises a plane transverse distal end (9), a split first longitudinal channel (10) and a second longitudinal channel (20), in which channels the anchoring bar and the stop bar of a fastener can slide, respectively. The device has a longitudinal bearing face that defines a half -space. The device further includes : a cam (19) forming a stop/sliding surface for the distal end of the stop bar, in order to produce a pivoting movement of the stop bar cams (15, 25) for the lateral splaying of the proximal part of the stop bar and an escapement cam (17), allowing the lateral displacement of the distal part of the stop bar and its disengagement from the first cam.
