A medical instrument provisionally fastens a polyaxial pedicle screw having a threaded shank. The shank has a shank head, on which a holding sleeve is arranged. A clamping plunger is mounted in the holding sleeve such that the clamping plunger acts on the shank head, such that the holding sleeve can be positionally fixed on the shank head by relative loading of the holding sleeve and the clamping plunger. The instrument has a coupling unit for engaging the holding sleeve and a pressure tappet for applying force to the clamping plunger. The coupling unit and the pressure tappet can be moved relative to each other. The instrument has a sleeve, in which the coupling unit is arranged such that the coupling unit can be moved in the axial direction, decoupled from the holding sleeve in a first position, and fastened to the holding sleeve in a second position.