A method and apparatus for repairing a damaged intervertebral disc nucleus in a minimally invasive manner utilizes a modular disc prosthesis preferably comprised of at least three modular segments and at least two rails that operably connect adjacent modular segments. In one embodiment, each modular segment includes a harder inner portion and a softer outer portion. Preferably, the rails operate to slidably connect and interlock adjacent modular segments. A stem portion of the rails that extends outside the periphery of the body of the prosthesis is removable after implantation such that the modular segments form an implanted unitary device that closely mimics the geometry of the disc nucleus cavity.