Rail-based modular disc nucleus prosthesis

Abstract

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.

1 . A minimally invasive method of implanting a modular disc prosthesis into an evacuated disc nucleus space, the method comprising:
 inserting a first modular segment into the disc nucleus space through an opening, the first modular segment having a width with a first rail that extends out of the disc nucleus space when the first modular segment is located within the disc nucleus space;   sliding a second modular segment along the first rail into the disc nucleus space through the opening until the second modular segment interlocks with the first modular segment, the second modular segment having a width with a second rail that extends out of the disc nucleus space when the second modular segment is located within the disc nucleus space;   removing a portion of the first rail that extends from the interlocked first and second modular segments;   sliding a third modular segment along the second rail into the disc nucleus space through the opening until the third modular segment interlocks with the second modular segment, the third modular having a width; and   removing a portion of the second rail that extends from the interlocked second and third modular segments to form an implanted modular disc prosthesis having a generally continuous periphery that corresponds generally to the evacuated nucleus disc space and having a total width at least equal to the widths of the first, second and third modular segment and greater than a width of the opening that is substantially only the width of a largest of the widths of any one of the modular segments.   
   
   
       2 . The minimally invasive method of implanting a modular disc prosthesis of  claim 1 , the third modular segment having a third rail that extends out of the disc nucleus space when the third modular segment is located within the disc nucleus space, the method further comprising:
 sliding a fourth modular segment along the third rail into the disc nucleus space through the opening until the fourth modular segment interlocks with the third modular segment, the fourth modular segment having a width; and   removing the portion of the third rail that extends from the interlocked third and fourth modular segments.   
   
   
       3 . The minimally invasive method of implanting a modular disc prosthesis of  claim 2 , the fourth modular segment having a fourth rail that extends out of the disc nucleus space when the fourth modular segment is located within the disc nucleus space, the method further comprising:
 sliding a fifth modular segment along the fourth rail into the disc nucleus space through the opening until the fifth modular segment interlocks with the fourth modular segment, the fifth modular segment having a width; and   removing the portion of the fourth rail that extends from the interlocked fourth and fifth modular segments.   
   
   
       4 . The minimally invasive method of implanting a modular disc prosthesis of  claim 1 , wherein the steps of sliding the second and third modular segments are performed using an insertion tool and the steps of removing the first and second rails is accomplished by using a cutting mechanism provided at the distal end of the insertion tool.