A modular disc prosthesis that is adapted to be implanted in an evacuated disc nucleus space, the prosthesis having an expanded position before implantation and an implanted position after implantation, the prosthesis comprising at least three modular segments that, when in the implanted position, are arranged side by side from a first end of the prosthesis to a second end of the prosthesis, the at least three modular segments being configured for assembly in sequence from the first end to the second end of the prosthesis and cooperating with each other when in the implanted position to define a unitary body having a generally continuous periphery that generally corresponds to the evacuated nucleus disc space, the modular disc prosthesis further comprising: a first segment of the at least three modular segments having a width and being rigidly attached to a first rail extending at least partially along one side of the width of the first modular segment, a second segment of the at least three modular segments being rigidly attached with a second rail and having a width, the second segment being slidably connected to the first rail on one side of the width of the second segment, the second rail extending at least partially along another side of the width of the second segment, and a third segment of the at least three modular segments having a width and being slidably connected to the second rail on one side of the width of the third segment, wherein each of the first and second rails include a stem portion that extends beyond the generally continuous periphery of the unitary body of the implanted position, the stem portion of the first rail being selectively removable from the first segment once the second segment is in the implanted position, and the stem portion of the second rail being selectively removable from the second segment once the third segment is in the implanted position, wherein the second and third segments are able to slide along the first and second rails respectively to the implanted position, wherein the first, second and third segments each comprise a moldable polymer material and the extended portion of each rail comprises an extrudable polymer material. a first segment of the at least three modular segments having a width and being rigidly attached to a first rail extending at least partially along one side of the width of the first modular segment, a second segment of the at least three modular segments being rigidly attached with a second rail and having a width, the second segment being slidably connected to the first rail on one side of the width of the second segment, the second rail extending at least partially along another side of the width of the second segment, and a third segment of the at least three modular segments having a width and being slidably connected to the second rail on one side of the width of the third segment, wherein each of the first and second rails include a stem portion that extends beyond the generally continuous periphery of the unitary body of the implanted position, the stem portion of the first rail being selectively removable from the first segment once the second segment is in the implanted position, and the stem portion of the second rail being selectively removable from the second segment once the third segment is in the implanted position, wherein the second and third segments are able to slide along the first and second rails respectively to the implanted position, wherein the first, second and third segments each comprise a moldable polymer material and the extended portion of each rail comprises an extrudable polymer material. <EOS>