The invention relates to a joint prosthesis intended to be mounted between two bones to be joined together. The joint prosthesis comprises a spacer part, intended to be placed between the joint surfaces of the bones to be joined. The spacer part is manufactured of biodegradable polymer, co-polymer, polymer mixture and/or composite. The spacer part is, at least under tissue conditions, porous and elastic. The joint prosthesis further comprises fixation parts which are arranged to fix the spacer part to the bones to be joined, and which are manufactured of biodegradable material.