Concentric interior insert ball and dual socket joint

Abstract

A constrained spinal implant is inserted between adjacent vertebrae to function as an disk prosthesis. The prosthesis has two plates fastened to adjacent vertebrae facing each other. The facing sides of the plates each have a depending skirt formed as concentric arcs of about 90 degrees. The skirts are either bowed or tapered in the axial direction. Depressions are centrally located between the arcs of the plates and a ball is universally movable in the depressions.

1 . A constrained spinal implant for placement between adjacent vertebrae to replace disk material comprising a first plate and a second plate adapted to interlock about a central axis, said first plate having a substantially planar vertebrae engaging side and a disk side, a first skirt on said disk side extending approximately normal to said plate, said first skirt formed to include opposing spherical bearing surfaces on an inner surface thereof, a first depression along said central axis of said disk side of said plate centrally located between said opposing spherical bearing surfaces, said second plate having a second planar vertebrae engaging side and a second disk side, a second skirt on said second disk side extending approximately normal to said second plate, said second skirt formed to include opposing spherical bearing surfaces on an outer surface thereof, a second depression along said central axis of said second disk side of said second plate centrally located between said opposing spherical bearing surfaces and a universally rotatable ball captured in said depressions; 
 whereby said substantially planar vertebrae engaging side of said first plate is adapted to contact a vertebrae and said substantially planar vertebrae engaging side of said second plate is adapted to contact an adjacent vertebrae with said depressions each adapted to form a bearing surface for said ball along said central axis and whereby said first and second skirts are interlocked forming a universal joint and shaped to limit lateral, flexion and extension motion.    
   
   
       2 . The constrained spinal implant for placement between adjacent vertebrae of  claim 1  wherein said first skirt and said second skirt are concentric in a plane substantially parallel with said first and second plates.  
   
   
       3 . The constrained spinal implant for placement between adjacent vertebrae of  claim 2  wherein said spherical bearing surfaces on said first and said second plates are constructed and arranged to couple said first plate to said second plate for universal movement therebetween.  
   
   
       4 . The constrained spinal implant for placement between adjacent vertebrae of  claim 1  wherein said opposed spherical bearing surfaces of said first skirt are adapted to contact said opposed spherical bearing surfaces of said second skirt.  
   
   
       5 . The constrained spinal implant for placement between adjacent vertebrae of  claim 1  wherein said opposed spherical bearing surfaces of said first skirt and said second skirt each extend approximately 90 degrees along the perimeter of said first and said second skirts respectively.  
   
   
       6 . The constrained spinal implant for placement between adjacent vertebrae of  claim 2  wherein said first skirt and said second skirt are concentric in a plane parallel with said first and second plates, said opposed spherical bearing surfaces of said first interrupted skirt adapted to contact said opposed spherical bearing surfaces of said second interrupted skirt to form an interlocked universally movable outer ball and socket.  
   
   
       7 . The constrained spinal implant for placement between adjacent vertebrae of  claim 1  wherein said first plate includes a central bore, a sleeve slidably secured in said bore, said first depression formed in said sleeve.  
   
   
       8 . The constrained spinal implant for placement between adjacent vertebrae of  claim 1  wherein said opposed spherical bearing surfaces of said first interrupted skirt and said opposed spherical bearing surfaces of said second interrupted skirt are concentric segments of a sphere whereby said concentric bearing segments of said first skirt are adapted to contact said concentric segments of said second skirt to form an interlocked universal joint.  
   
   
       9 . The constrained spinal implant for placement between adjacent vertebrae of  claim 1  wherein said first plate includes a cavity between said depression and said vertebrae side, an O-ring spring secured in said cavity, said ball adapted to flex said O-ring spring resulting in resilient compression.  
   
   
       10 . The constrained spinal implant for placement between adjacent vertebrae of  claim 1  wherein said second plate includes a cavity between said second depression and said vertebrae side, an O-ring spring secured in said cavity, said ball adapted to flex said O-ring spring resulting in resilient compression.  
   
   
       11 . The constrained spinal implant for placement between adjacent vertebrae of  claim 1  wherein a plurality of first plates of different sizes, a plurality of balls of different sizes and a plurality of second plates of different sizes comprise a kit whereby a proper sized constrained spinal implant can be selected from said kit.  
   
   
       12 . The constrained spinal implant for placement between adjacent vertebrae of  claim 1  wherein an elastic membrane extends between said first plate and said second plate about the periphery of said first plate and said second plate.  
   
   
       13 . The constrained spinal implant for placement between adjacent vertebrae of  claim 12  wherein said elastic membrane is continuous and a viscous polymeric composition is located within said membrane.  
   
   
       14 . The constrained spinal implant for placement between adjacent vertebrae of  claim 1  wherein at least one of said vertebrae engaging side or said second vertebrae engaging side includes a plurality of spikes for engaging vertebrae.  
   
   
       15 . A drive tool for positioning a constrained spinal implant between adjacent vertebrae comprising an elongated shaft having a first end conforming to a superior endplate of a constrained spinal implant and a second end forming a handle with an impact tip, whereby said spinal implant is positioned within said first end with said handle available to align said implant with said impact tip available for receipt of mallet impact to allow a forced placement of the implant between the vertebrae.  
   
   
       16 . The drive tool for positioning a constrained spinal implant according to  claim 15  wherein said first end is C-shaped having an upper surface and a lower surface sized to fit between an upper plate and a lower plate of said spinal implant with said C-shape engaging said endplate.  
   
   
       17 . A method of assembling a constrained spinal implant comprising the steps of: 
 a) providing a first plate, said first plate having a planar vertebrae engaging side and a disk side, a first shaped skirt on said disk side extending approximately normal to said plate, said skirt formed to include opposing spherical bearing surfaces, a depression in said disk side of said plate centrally located between said opposing spherical bearing surfaces,    b) providing a second plate having a second planar vertebrae engaging side and a second disk side, a second shaped skirt on said second disk side extending approximately normal to said second plate, said second skirt formed to include opposing separated spherical bearing surfaces, a second depression in said second disk side of said second plate centrally located between said opposing arcs,    c) providing a ball and placing said ball in said depression,    d) orienting said first plate and said second plate parallel with each other and rotated about ninety degrees with respect to said second plate,    e) moving said first plate closer to said second plate to engage said ball into said depression and said second depression in axial alignment, and    f) rotating said first plate with respect to said second plate about a central axis until said spherical bearing surfaces of said first plate interlock with said opposing spherical bearing surfaces of said second plate to form a universally moveable connection therebetween.    
   
   
       18 . The method of assembling a constrained spinal implant according to  claim 17  wherein said shaped skirt is contoured to provide a predetermined lateral bending of said first plate with respect to said second plate.  
   
   
       19 . The method of assembling a constrained spinal implant according to  claim 17  wherein said shaped skirt is contoured to provide a predetermined flexion bending of said first plate with respect to said second plate.  
   
   
       20 . The method of assembling a constrained spinal implant according to  claim 17  wherein said shaped skirt is contoured to provide a predetermined extension bending of said first plate with respect to said second plate.  
   
   
       21 . A constrained spinal implant for placement between adjacent vertebrae to replace disk material comprising; 
 a first plate having a first substantially planar vertebrae engaging side and a disk side, a first continuous skirt on said disk side extending approximately normal to said plate, said first skirt formed to include substantially opposing spherical bearing surfaces on an inner surface thereof, a spherical depression formed along said central axis of said disk side of said plate centrally located between said opposing spherical bearing surfaces;    a second plate having a second substantially planar vertebrae engaging side and a second disk side, a second skirt on said second disk side extending approximately normal to said second plate, said second skirt formed to include opposing spherical bearing surfaces on an outer surface thereof, a second spherical depression along said central axis of said second disk side of said second plate centrally located between said opposing spherical bearing surfaces, and    a universally rotatable ball captured in said depressions, said ball and said spherical depressions defining an inner universally moveable ball and socket, said spherical bearing surfaces of said first and said second skirt interlocking to define a universally movable outer ball and socket.    
   
   
       22 . The constrained spinal implant for placement between adjacent vertebrae of  claim 21  wherein at least one of said first or second skirts is shaped to limit lateral, flexion and extension motion.  
   
   
       23 . The constrained spinal implant for placement between adjacent vertebrae of  claim 21  wherein said inner ball and socket and said outer ball and socket both pivot about the same central point.  
   
   
       24 . The constrained spinal implant for placement between adjacent vertebrae of  claim 21  wherein said inner ball and socket is constructed and arranged to be compressible.  
   
   
       25 . The constrained spinal implant for placement between adjacent vertebrae of  claim 21  wherein said outer ball and socket is constructed and arranged to prevent axial separation of said first and said second plates.