Rail-based modular disc 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 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:
 a plurality of 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 plurality of 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,   a first of the plurality of modular segments being integral with a first rail,   a second of the plurality of modular segments being integral with a second rail, the second modular segment being slidably connected to the first rail, and   a third of the plurality of modular segments being slidably connected to the second rail,   wherein each of the first and second rails include an extended portion that extends beyond the generally continuous periphery of the unitary body of the implanted position,   the extended portion of the first rail being selectively removable from the first of the plurality of modular segments once the second of the plurality of modular segments is in the implanted position, and   the extended portion of the second rail being selectively removable from the second of the plurality of modular segments once the third of the plurality of modular segments is in the implanted position,   wherein both the second and third modular segments are separated from each other and slidably connected to the extended portions of the first and second rails respectively when the prosthesis is in the expanded position to guide the second and third modular segments respectively to the implanted position.   
   
   
       2 . The modular disc prosthesis of  claim 1 , wherein a third rail is integral with the third modular segment, the third rail including an extended portion that extends beyond the generally continuous periphery,
 wherein the modular disc prosthesis further comprises a fourth modular segment slidably connected to the extended portions of the third rail when the prosthesis is in the expanded position to guide the fourth modular segment to the implanted position, the extended portion of the third rail being selectively removable from the third of the plurality of modular segments once the fourth of the plurality of modular segments is in the implanted position.   
   
   
       3 . The modular disc prosthesis of  claim 1 , wherein the extended portions of the first and second rails each have a rigidity in a first transverse direction relative to the longitudinal axis of the respective rail that differs substantially from a rigidity in a second transverse direction relative to the longitudinal axis of the respective rail. 
   
   
       4 . The modular disc prosthesis of  claim 1 , wherein each of the second and third modular segments comprise an inner portion and an outer portion, each outer portion being operatively coupled with a portion of the respective inner portion, the inner portions of the second and third modular segments being slidably engaged with the first and second rails, respectively. 
   
   
       5 . The modular disc prosthesis of  claim 4 , wherein the inner portion of the second and third modular segments and the outer portion of the second and third modular segments are made of polymers of different durometers. 
   
   
       6 . The modular disc prosthesis of  claim 1 , wherein the first, second and third modular segments each comprise a moldable polymer material and the extended portion of each rail comprises an extrudable polymer material. 
   
   
       7 . 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:
 a plurality of modular segments that, when in the implanted position, are arranged side by side in generally one of a medial-to-lateral orientation and a posterior-to-anterior orientation, the plurality of modular segments being configured for assembly in sequence from a first end to a second end of the prosthesis along the orientation,   a first of the plurality of modular segments being operatively coupled with first means for slidably guiding a second modular segment along a first longitudinal axis when the second modular segment is manipulated from the expanded position to the implanted position, the second modular segment being slidably connected to the first means for slidably guiding the second modular segment along the first longitudinal axis,   the second modular segment being operatively coupled with second means for slidably guiding a third modular segment along a second longitudinal axis when the third modular segment is manipulated from the expanded position to the implanted position, the third modular segment being slidably connected to the second means for slidably guiding the third modular segment along the second longitudinal axis,   wherein both the second and third modular segments are separated from each other and are slidably connected to the first and second means for slidably guiding, respectively, when in the expanded position,   the modular segments being in contact with each other when in the implanted position and defining a unitary body having a generally continuous periphery that generally corresponds to the evacuated nucleus disc space,   the first means for slidably guiding the second modular segment extending beyond the generally continuous periphery and along the first longitudinal axis when the first modular segment is in the implanted position, the first means for slidably guiding the second modular segment being selectively detachable from the first modular segment once the second modular segment is in the implanted position,   the second means for slidably guiding the third modular segment extending beyond the generally continuous periphery and along the second longitudinal axis when the second modular segment is in the implanted position, the second means for slidably guiding the third modular segment being selectively detachable from the second modular segment once the third modular segment is in the implanted position.   
   
   
       8 . The modular disc prosthesis of  claim 1 , wherein the first and second rails are substantially parallel. 
   
   
       9 . The modular disc prosthesis of  claim 7  wherein the third modular segment is operatively coupled with third means for slidably guiding a fourth modular segment along a third longitudinal axis when the fourth modular segment is manipulated from the expanded position to the implanted position, the fourth modular segment being slidably connected to the third means for slidably guiding the fourth modular segment along the third longitudinal axis, the third means for slidably guiding the fourth modular segment extending beyond the generally continuous periphery and along the third longitudinal axis when the third modular segment is in the implanted position, the third means for slidably guiding the fourth modular segment being selectively removable once the third modular segment is in the implanted position. 
   
   
       10 . 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:
 a plurality of modular segments that cooperate 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,   a first of the plurality of modular segments being integral with a first rail, the first rail including an extended portion that extends beyond the generally continuous periphery of the unitary body of the implanted position, the extended portion of the first rail having a length,   a second of the plurality of modular segments slidably connected to the first rail and being integral with a second rail, the second rail including an extended portion that extends beyond the generally continuous periphery of the unitary body of the implanted position, and   a third of the plurality of modular segments being slidably connected to the second rail,   wherein both the second and third modular segments are separated from each other and slidably connected to the extended portions of the first and second rails respectively when the prosthesis is in the expanded position to guide the second and third modular segments respectively to the implanted position, and   wherein the third segment is capable of being separated from the first segment by a distance that is greater than the length of the first rail when in the expanded position.   
   
   
       11 . The modular disc prosthesis of  claim 10 , wherein a third rail is integral with the third modular segment, the third rail including an extended portion that extends beyond the generally continuous periphery,
 wherein the modular disc prosthesis further comprises a fourth modular segment slidably connected to the extended portions of the third rail when the prosthesis is in the expanded position to guide the fourth modular segment to the implanted position, the extended portion of the third rail being selectively removable from the third of the plurality of modular segments once the fourth of the plurality of modular segments is in the implanted position.   
   
   
       12 . The modular disc prosthesis of  claim 10 , wherein the extended portions of the first and second rails each have a rigidity in a first transverse direction relative to the longitudinal axis of the respective rail that differs substantially from a rigidity in a second transverse direction relative to the longitudinal axis of the respective rail. 
   
   
       13 . The modular disc prosthesis of  claim 10 , wherein each of the second and third modular segments comprise an inner portion and an outer portion, each outer portion being operatively coupled with a portion of the respective inner portion, the inner portions of the second and third modular segments being slidably engaged with the first and second rails, respectively. 
   
   
       14 . The modular disc prosthesis of  claim 13 , wherein the inner portion of the second and third modular segments and the outer portion of the second and third modular segments are made of polymers of different durometers. 
   
   
       15 . The modular disc prosthesis of  claim 10 , wherein the first, second and third modular segments each comprise a moldable polymer material and the extended portion of each rail comprises an extrudable polymer material. 
   
   
       16 . The modular disc prosthesis of  claim 10 , wherein the first and second rails are substantially parallel. 
   
   
       17 . The modular disc prosthesis of  claim 10 , wherein the plurality of modular segments are arranged side by side from a first end of the prosthesis to a second end of the prosthesis and are configured for assembly in sequence from the first end to the second end of the prosthesis. 
   
   
       18 . The modular disc prosthesis of  claim 10 , wherein the extended portion of the first rail is selectively removable from the first of the plurality of modular segments once the second of the plurality of modular segments is in the implanted position.