Replacement or supplementation of a nucleus pulposus using a hydrogel

Abstract

A nucleus pulposus of an intervertebral disc is supplemented or replaced by an elongated, physiologically fully hydrated hydrogel prosthesis inserted into the central region of an intervertebral disc, where it can fold upon itself to form a prosthesis body within the central region of the annulus fibrosus. The hydrogel prosthesis may have expanded portions that assist in preventing expulsion of the prosthesis through the insertion aperture. An instrument for inserting the prosthesis has a cutter for severing the elongated prosthesis within the central region of the intervertebral disc after a sufficient amount has been implanted.

1 . A method for supplementing or replacing a nucleus pulposus located in a central region of an annulus fibrosus of an intervertebral disc, comprising 
 introducing into said central region of said annulus fibrosus a quantity of a biocompatible, physiologically fully hydrated hydrogel in the form of an elongated solid hydrogel body.    
     
     
         2 . The method of  claim 1 , wherein said elongated hydrogel body has a generally cylindrical shape.  
     
     
         3 . The method of  claim 1 , wherein said elongated hydrogel body is capable of folding upon itself to substantially fill said central region of said annulus fibrosus.  
     
     
         4 . The method of  claim 1 , wherein said elongated hydrogel body has a ratio of length to principal transverse dimension not less than about 5:1.  
     
     
         5 . The method of  claim 1 , wherein said elongated hydrogel body has a ratio of length to principal transverse dimension of about 350:1.  
     
     
         6 . The method of  claim 1 , wherein said elongated hydrogel body has a principal transverse dimension not greater than about 10 millimeters.  
     
     
         7 . The method of  claim 1 , wherein said elongated hydrogel body has a principal transverse dimension of about 2.5 millimeters.  
     
     
         8 . The method of  claim 1 , wherein said hydrogel has an elastic modulus not greater than about 4 megapascals.  
     
     
         9 . The method of  claim 1 , wherein said hydrogel has an elastic modulus between about 0.05 megapascals and about 4.0 megapascals.  
     
     
         10 . The method of  claim 1 , wherein said elongated hydrogel body is inserted into said central region of said annulus fibrosus through said annulus fibrosus.  
     
     
         11 . The method of  claim 1 , wherein said elongated hydrogel body is inserted into said central region of said annulus fibrosus through a cannula inserted through said annulus fibrosus.  
     
     
         12 . The method of  claim 1 , wherein said elongated hydrogel body is inserted into said central region of said annulus fibrosus through an adjacent vertebra.  
     
     
         13 . The method of  claim 1 , wherein a containment vessel is provided within said central region of said annulus fibrosus, and said elongated hydrogel body is inserted into said containment vessel.  
     
     
         14 . The method of  claim 1 , wherein at least one portion of said elongated solid hydrogel body has a cross-sectional area greater than a principal cross-sectional area of said elongated hydrogel body.  
     
     
         15 . The method of  claim 1 , wherein at least one end of said elongated hydrogel body is provided with a terminal portion having a transverse cross-sectional area greater than a principal cross-sectional area of said elongated hydrogel body.  
     
     
         16 . The method of  claim 1 , wherein at least one end of said elongated hydrogel body is provided with a flared terminal portion having a transverse cross-sectional area greater than a principal cross-sectional area of said elongated hydrogel body.  
     
     
         17 . The method of  claim 1 , wherein at least one end of said elongated hydrogel body is provided with a generally spherical end portion having a transverse cross-sectional area greater than a principal cross-sectional area of said elongated hydrogel body.  
     
     
         18 . The method of  claim 1 , wherein said elongated hydrogel body has at least one portion between its ends having a transverse cross-sectional area greater than a principal cross-sectional area of said elongated hydrogel body.  
     
     
         19 . The method of  claim 18 , wherein said portion having a transverse cross-sectional area greater than a principal cross-sectional area of said hydrogel body has a generally spherical shape or a barb shape.  
     
     
         20 . The method of  claim 1 , wherein at least a portion of said elongated hydrogel body is compressed during insertion into said central region of said annulus fibrosus.  
     
     
         21 . The method of  claim 1 , wherein said hydrogel contains a polyvinyl alcohol copolymer.  
     
     
         22 . The method of  claim 1 , wherein said hydrogel contains a copolymer of polyvinyl alcohol and poly(vinylpyrrolidone).  
     
     
         23 . The method of  claim 1 , wherein said hydrogel contains a mixture of poly(vinyl alcohol) and poly(vinyl pyrrolidone).  
     
     
         24 . The method of  claim 1 , wherein said hydrogel body additionally comprises a radiopaque material.  
     
     
         25 . The method of  claim 24 , wherein said radiopaque material is barium sulfate.  
     
     
         26 . An elongated, physiologically fully hydrated solid hydrogel body having a ratio of length to principal transverse dimension not less than about 5:1.  
     
     
         27 . The body of  claim 26 , having a ratio of length to principal transverse dimension of about 350:1.  
     
     
         28 . The body of  claim 26 , wherein said hydrogel has an elastic modulus not greater than about 4 megapascals.  
     
     
         29 . The body of  claim 26 , wherein said hydrogel has an elastic modulus between about 0.05 megapascals and about 4.0 megapascals.  
     
     
         30 . The body of  claim 26 , having a generally cylindrical shape.  
     
     
         31 . The body of  claim 26 , having at least one portion with a cross-sectional area greater than a principal cross-sectional area of said body.  
     
     
         32 . The body of  claim 26 , having at least one end provided with a terminal portion of transverse cross-sectional area greater than a principal cross-sectional area of said body.  
     
     
         33 . The body of  claim 26 , having at least one end provided with a flared terminal portion of transverse cross-sectional area greater than a principal cross-sectional area of said body.  
     
     
         34 . The body of  claim 26 , having at least one end provided with a generally spherical terminal portion of transverse cross-sectional area greater than a principal cross-sectional area of said body.  
     
     
         35 . The body of  claim 26 , having at least one portion between its ends with a transverse cross-sectional area greater than a principal cross-sectional area of said body.  
     
     
         36 . The body of  claim 35 , wherein said at least one portion has a generally spherical shape or a barb shape.  
     
     
         37 . The body of  claim 26 , being capable of folding upon itself to physiologically fill a central region of an annulus fibrosus.  
     
     
         38 . The body of  claim 26 , manufactured by molding or extrusion.  
     
     
         39 . The body of  claim 26 , wherein said hydrogel contains a polyvinyl alcohol copolymer.  
     
     
         40 . The body of  claim 26 , wherein said hydrogel contains a copolymer of polyvinyl alcohol and poly(vinylpyrrolidone).  
     
     
         41 . The body of  claim 26 , wherein said hydrogel contains of a mixture of poly(vinyl alcohol) and poly(vinyl pyrrolidone).  
     
     
         42 . The body of  claim 26 , further comprising a radiopaque material.  
     
     
         43 . The body of  claim 42 , wherein said radiopaque material is barium sulfate.  
     
     
         44 . The method of  claim 1 , wherein a predetermined length of said elongated hydrogel body is severed from a continuous length of said elongated hydrogel body within said central region of said annulus fibrosus.  
     
     
         45 . An instrument for inserting an elongated hydrogel body into a central region of an annulus fibrosus, comprising a generally tubular body, having a distal end adapted to be inserted through an annulus fibrosus into a central region of an intervertebral disc and a proximal end, a coupling at said proximal end, a guide structure supported on said tubular body and extending along said tubular body and having a distal end positioned near said distal end of said tubular body and a proximal end, and a cutting portion extending through said guide structure from said distal end of said guide structure to said proximal end of said guide structure and having a looped wire portion disposed near said distal end of said guide structure for cutting the hydrogel body.  
     
     
         46 . The instrument of  claim 45 , wherein said guide structure is a guide tube.  
     
     
         47 . The instrument of  claim 45 , wherein said wire loop is provided with a handle.  
     
     
         48 . A method of hydrating a hydrogel, comprising contacting said hydrogel with a substantially isotonic solution for a period of time sufficient to achieve a desired level of hydration.  
     
     
         49 . The method of  claim 48 , wherein said period of time is sufficient to achieve an equilibrium level of hydration.  
     
     
         50 . The method of  claim 48 , wherein said solution is a substantially isotonic aqueous solution of dextran.  
     
     
         51 . A method of making a prosthesis, comprising providing a biocompatible hydrogel in a form suitable for use as a prosthesis, and hydrating the hydrogel in accordance with the method of  claim 48 .  
     
     
         52 . A prosthesis produced by a method in accordance with  claim 51.