The invention relates to an insertion instrument for joint sockets of prostheses,comprising an elongate shaft (1), a suction head (2) being provided at the frontend thereof for connection to a joint socket, a suction device with a piston guidedin the shaft (1), a suction duct merging into the suction head and an actuatingelement which is guided along a guiding track (14) on the shaft (1). Accordingto the invention, the guiding track (14) is helically formed and comprises a lockingdevice, preferably in the form of a recess (15), for the actuating element in asuction position. Due to the helical form of the guiding track, the actuatingelement executes a rotational and longitudinal movement during its displacement.The longitudinal movement produces a negative pressure in the suction duct,thereby ensuring the maintenance of said pressure, while the rotating movementcauses the rotation of the actuating element to an extent that it reaches its lockingposition at the end of the guiding track. The handling of the instrument is thussimplified.
