A method and an insertion unit for inserting an elongate prosthesis into a prosthesis fixing device. This device comprises a bed of grains and biocompatible material, and a vibrating tool is used for insertion, the vibration head of which performs an oscillating motion back and forth about a swivelling axis (3'). According to the invention, said axis (3r) of the vibrating tool essentially coincides with the longitudinal axis (I1) of the elongate prosthesis (1). The method and the insertion unit provide a prosthesis fixing device consisting of said bed, in which the grains are evenly packed along the length of the prosthesis.