The use of segmented spinal implants where the segments are implanted sequentially using insertion guides for so-called “minimally invasive” surgical techniques is known.  United States Patent Application No.  2008/0133017 to Beyar, et al. ( hereinafter “Beyar”) discloses a two-level, motion preserving total disc replacement system using dual-level segments, each segment comprising a top “slice” and a bottom “slice” in order to construct both levels of the motion-preserving device. 
U.S. Pat.  No.  7,591,853 to Felt, et al. ( hereinafter “Felt”) discloses a segmented disc nucleus implant that includes a hard inner core surrounded by a compliant outer shell.  While the compliant outer shell facilitates motion preserving aspects, the inner core can be constructed of harder materials such as polyetheretherketone (PEEK) to facilitate structures for reliably interlocking the segments. 
A system that, like the device of Felt but unlike the device of Beyar, replaces only the disc nucleus for enhanced reduced invasiveness, and that further enhances the motion preserving aspects of the device of Felt would be welcomed.