Total Disc Implant

Abstract

A total disc implant (TDI) is provided for total replacement of a spinal disc or discs in a human patient or other mammal, wherein the TDI is designed to maintain a substantially full range of natural motion (ROM) following implantation. The TDI generally comprises, in one preferred form, upper and lower end plates for affixation to adjacent vertebral bodies, with an intervening insert disposed therebetween. The end plates each include elongated part-cylindrical surfaces oriented generally perpendicular to each other, with one of said surfaces extending in an anterior-posterior direction and the other extending in a medial-lateral direction. The intervening insert defines concave upper and lower part-cylindrical seats oriented for respectively engaging these part-cylindrical surfaces, wherein these part-cylindrical seats are defined by offset radii to include a somewhat flattened central base region merging smoothly with upwardly curving radiused sides.

What is claimed is: 
     
         1 . A disc implant, comprising:
 a pair of end plates for affixation to adjacent vertebral bodies; and   a pair of bearing components formed respectively on said end plates and respectively defining a pair of elongated, generally part-cylindrical bearing surfaces extending generally on orthogonal axes relative to each other.   
     
     
         2 . The disc implant of  claim 1  wherein one of said part-cylindrical bearing surfaces extends generally in an anterior-posterior direction, and the other of said part-cylindrical bearing surfaces extends generally in a medial-lateral direction. 
     
     
         3 . The disc implant of  claim 1  wherein at least one of said part-cylindrical bearing surfaces has a cross sectional shape defined by laterally spaced-apart, offset radii to include a generally flattened base segment interposed between a pair of curved sides. 
     
     
         4 . The disc implant of  claim 1  wherein one of said part-cylindrical bearing surfaces has a convex shape for articulation with the other of said part-cylindrical bearing surfaces having a concave shape. 
     
     
         5 . The disc implant of  claim 1  wherein said part-cylindrical bearing surfaces each have a convex shape, and further including an insert having opposed and generally concave recessed bearing seats defined thereon and disposed generally on orthogonal axes relative to each other for respective articulation with said part-cylindrical bearing surfaces. 
     
     
         6 . The disc implant of  claim 5  wherein at least one of said generally concave recessed bearing seats has a cross sectional shape defined by offset radii to include a generally flattened base segment interposed between a pair of curved sides. 
     
     
         7 . The disc implant of  claim 1  wherein said part-cylindrical bearing surfaces each include have an elongated shape defining opposite end segments of generally convex shape separated by a central segment defining a generally concave bearing seat. 
     
     
         8 . The disc implant of  claim 7  wherein said generally concave bearing seat of each of said part-cylindrical bearing surfaces has a cross sectional shape defined by offset radii to include a generally flattened base segment interposed between a pair of curved sides. 
     
     
         9 . The disc implant of  claim 7  wherein said opposite end segments of each of said one of said part-cylindrical bearing surfaces has a convex shape formed with increasing diametric size in a direction toward the associated concave central segment. 
     
     
         10 . The disc implant of  claim 1  wherein each of said end plates includes a lordotic taper. 
     
     
         11 . The disc implant of  claim 1  wherein at least one of said end plates has a tapered thickness increasing in a posterior to anterior direction. 
     
     
         12 . The disc implant of  claim 1  wherein each of said end plates includes means for affixation to adjacent vertebral bodies. 
     
     
         13 . The disc implant of  claim 1  wherein each of said end plates includes a porous bone ingrowth surface for affixation to adjacent vertebral 
     
     
         14 . The disc implant of  claim 13  wherein said porous bone ingrowth surface of each of said end plates has a generally convex shape for engagement with and affixation to adjacent vertebral bodies. 
     
     
         15 . The disc implant of  claim 1  wherein each of said end plates includes at least one generally axially protruding fixation element for affixation to adjacent vertebral bodies. 
     
     
         16 . The disc implant of  claim 1  wherein said pair of part-cylindrical surfaces respectively comprise a ceramic material and a biocompatible metal. 
     
     
         17 . The disc implant of  claim 5  wherein said part-cylindrical bearing surfaces and said insert comprise a ceramic material. 
     
     
         18 . The disc implant of  claim 5  wherein said pair of part-cylindrical bearing surfaces comprise a ceramic material, and wherein said insert comprises a biocompatible metal. 
     
     
         19 . A disc implant, comprising:
 a pair of end plates for affixation to adjacent vertebral bodies, said pair of end plates respectively including a pair of bearing components respectively defining a pair of elongated, generally part-cylindrical convex bearing surfaces extending generally on orthogonal axes relative to each other; and   an insert having opposed and generally concave recessed bearing seats defined thereon and disposed generally on orthogonal axes relative to each other for respective articulation with said part-cylindrical bearing surfaces.   
     
     
         20 . The disc implant of  claim 19  wherein one of said part-cylindrical other of said part-cylindrical bearing surfaces extends generally in a medial-lateral direction. 
     
     
         21 . The disc implant of  claim 19  wherein at least one of said generally concave recessed bearing seats has a cross sectional shape defined by laterally spaced-apart, offset radii to include a generally flattened base segment interposed between a pair of curved sides. 
     
     
         22 . The disc implant of  claim 19  wherein each of said end plates includes a lordotic taper. 
     
     
         23 . The disc implant of  claim 19  wherein at least one of said end plates has a tapered thickness increasing in a posterior to anterior direction. 
     
     
         24 . The disc implant of  claim 19  wherein each of said end plates includes means for affixation to adjacent vertebral bodies. 
     
     
         25 . The disc implant of  claim 19  wherein each of said end plates includes a porous bone ingrowth surface for affixation to adjacent vertebral bodies. 
     
     
         26 . The disc implant of  claim 25  wherein said porous bone ingrowth surface of each of said end plates has a generally convex shape for engagement with and affixation to adjacent vertebral bodies. 
     
     
         27 . The disc implant of  claim 19  wherein each of said end plates includes at least one generally axially protruding fixation element for affixation to adjacent vertebral bodies. 
     
     
         28 . The disc implant of  claim 19  wherein said bearing surfaces comprise a ceramic material. 
     
     
         29 . The disc implant of  claim 28  wherein said insert comprises a ceramic material. 
     
     
         30 . The disc implant of  claim 28  wherein said insert comprises a biocompatible metal. 
     
     
         31 . A disc implant, comprising:
 a pair of end plates for affixation to adjacent vertebral bodies; and   a pair of bearing components formed respectively on said end plates and respectively defining a pair of elongated, generally part-cylindrical bearing surfaces extending generally on orthogonal axes relative to each other;   one of said part-cylindrical bearing surfaces having a convex shape for articulation with the other of said part-cylindrical bearing surfaces having a concave shape.   
     
     
         32 . The disc implant of  claim 31  wherein one of said part-cylindrical bearing surfaces extends generally in an anterior-posterior direction, and the other of said part-cylindrical bearing surfaces extends generally in a medial-lateral direction. 
     
     
         33 . The disc implant of  claim 31  wherein at least one of said part-cylindrical bearing surfaces has a cross sectional shape defined by laterally spaced-apart, offset radii to include a generally flattened base segment interposed between a pair of curved sides. 
     
     
         34 . The disc implant of  claim 31  wherein each of said end plates includes a lordotic taper. 
     
     
         35 . The disc implant of  claim 31  wherein at least one of said end plates has a tapered thickness increasing in a posterior to anterior direction. 
     
     
         36 . The disc implant of  claim 31  wherein each of said end plates includes means for affixation to adjacent vertebral bodies. 
     
     
         37 . The disc implant of  claim 31  wherein each of said end plates includes a porous bone ingrowth surface for affixation to adjacent vertebral bodies. 
     
     
         38 . The disc implant of  claim 37  wherein said porous bone ingrowth surface of each of said end plates has a generally convex shape for engagement with and affixation to adjacent vertebral bodies. 
     
     
         39 . The disc implant of  claim 31  wherein each of said end plates includes at least one generally axially protruding fixation element for affixation to adjacent vertebral bodies. 
     
     
         40 . The disc implant of  claim 31  wherein said part-cylindrical bearing surfaces comprise a ceramic material. 
     
     
         41 . The disc implant of  claim 31  wherein said pair of part-cylindrical surfaces respectively comprise a ceramic material and a biocompatible metal. 
     
     
         42 . A disc implant, comprising:
 a pair of end plates for affixation to adjacent vertebral bodies; and   a pair of bearing components formed respectively on said end plates and respectively defining a pair of elongated bearing strip extending generally on orthogonal axes relative to each other;   each of said part-cylindrical bearing surfaces defining opposite end segments of generally convex shape separated by a central segment defining a generally concave bearing seat.   
     
     
         43 . The disc implant of  claim 42  wherein said generally concave bearing seat of each of said part-cylindrical bearing surfaces has a cross sectional shape defined by offset radii to include a generally flattened base segment interposed between a pair of curved sides. 
     
     
         44 . The disc implant of  claim 42  wherein said opposite end segments of each of said one of said part-cylindrical bearing surfaces has a convex shape formed with increasing diametric size in a direction toward the associated concave central segment. 
     
     
         45 . The disc implant of  claim 42  wherein one of said bearing surfaces extends generally in an anterior-posterior direction, and the other of said bearing surfaces extends generally in a medial-lateral direction. 
     
     
         46 . The disc implant of  claim 42  wherein each of said end plates includes a lordotic taper. 
     
     
         47 . The disc implant of  claim 42  wherein at least one of said end plates has a tapered thickness increasing in a posterior to anterior direction. 
     
     
         48 . The disc implant of  claim 42  wherein each of said end plates includes means for affixation to adjacent vertebral bodies. 
     
     
         49 . The disc implant of  claim 42  wherein each of said end plates includes a porous bone ingrowth surface for affixation to adjacent vertebral bodies. 
     
     
         50 . The disc implant of  claim 49  wherein said porous bone ingrowth surface of each of said end plates has a generally convex shape for engagement with and affixation to adjacent vertebral bodies. 
     
     
         51 . The disc implant of  claim 42  wherein each of said end plates includes at least one generally axially protruding fixation element for affixation to adjacent vertebral bodies. 
     
     
         52 . The disc implant of  claim 42  wherein said part-cylindrical bearing surfaces comprise a ceramic material. 
     
     
         53 . The disc implant of  claim 42  wherein said pair of part-cylindrical surfaces respectively comprise a ceramic material and a biocompatible metal.