Abstract: The invention relates to a retention pin for fixing a support plate or other prosthesis on bone tissue. The pin is made of a material which is bio-compatible with human tissue and comprises two half-pins each having a half-head for bearing against the prosthesis and a retention shank projecting therefrom, with the outline of each shank being semi-cylindrical and with the two half-pins being generally symmetrical to each other about a radial separation plane passing at least partially along the axis of the pin and extending at least as far as the inside faces of the half-heads from which the respective retention shanks project.