A positioning device (1) for placing a prosthesis device (2) in a spinal column of a living mammal, including at least one holding device (6) for cooperation with the prosthesis device and for guiding thereof during positioning, wherein it includes fixing means (7) for fixation with respect to at least one vertebra (3,3′), and said fixing means includes locking means (9), which in a first, free state, allows adjustment movement of said holding means (6) and thereby of the prosthesis device (2), and in a second, locked state, fixes said holding device (6) and thereby the prosthesis device (2) in a selected position. The invention also concerns a system.