Spinal implants and methods of providing dynamic stability to the spine

Abstract

The present application discloses a plurality of spinal implants and methods for repairing annular defects in intervertebral discs and for providing dynamic stability to the motion segment of the spine in the vicinity of the repaired disc. Each of the implants comprises a head portion and a tail portion. In the illustrated embodiments, the head portion of each implant is enlarged relative to the tail portion. Each of the head portions and tail portions is adapted to support adjacent vertebrae and resist collapse of the intervertebral disc. A tapered portion of each implant engages end plates of the adjacent vertebrae to resist forces tending to push the implant out of the intervertebral space. The tail portion of each implant includes a tail flange (which in some embodiments is of similar diameter to the head portion) that abuts extradiscal lips of the adjacent vertebrae and resists forces tending to push the implant deeper into the intervertebral space.

1 . A spinal implant adapted to be implanted in an intervertebral disc located between a first vertebral disc and a second vertebral disc to repair an annular defect in the intervertebral disc, and to provide dynamic stability to a motion segment of a spine in the vicinity of the intervertebral disc, comprising: 
 a head portion including at least a first head segment and a second head segment, each of the first and second head segments having a length greater than zero as measured along a longitudinal axis of the implant, the first head segment having a constant height along its length, the second head segment tapering along at least a portion of its length from a greater height to a lesser height away from the first head segment; and    a tail portion extending from the head portion and including at least a first tail segment and a second tail segment, the first tail segment adjoining the second head segment, each of the first and second tail segments having a length greater than zero as measured along a longitudinal axis of the implant, the second tail segment tapering along at least a portion of its length from a lesser height to a greater height away from the first tail segment.    
   
   
       2 . The spinal implant of  claim 1 , wherein the first tail segment has a constant height along its length.  
   
   
       3 . The spinal implant of  claim 1 , wherein upon permanent implantation within the intervertebral disc the head portion abuts and supports facing endplates of the first and second vertebral discs to aid in preventing collapse of the intervertebral disc while providing dynamic stability to the motion segment, and the tail portion abuts and supports the facing endplates to further aid in preventing collapse of the intervertebral disc while providing dynamic stability to the motion segment, and also abuts extradiscal lips of the first and second vertebral discs to thereby prevent the implant from penetrating the intervertebral disc beyond a desired amount.  
   
   
       4 . The spinal implant of  claim 1 , wherein the head portion further includes at least a third head segment that extends from the first head segment opposite the second head segment.  
   
   
       5 . The spinal implant of  claim 4 , wherein the third head segment tapers along at least a portion of its length from a greater height to a lesser height away from the first head segment.  
   
   
       6 . The spinal implant of  claim 1 , wherein cross-sections of the implant taken along the longitudinal axis thereof are circular, oval, elliptical or rectilinear.  
   
   
       7 . The spinal implant of  claim 1 , wherein the implant is constructed of one or more of bone, polymers or metals.  
   
   
       8 . A spinal implant adapted to be implanted in an intervertebral disc located between a first vertebral disc and a second vertebral disc to repair an annular defect in the intervertebral disc, and to provide dynamic stability to a motion segment of a spine in the vicinity of the intervertebral disc, comprising: 
 a head portion including at least a first head segment and a second head segment, each of the first and second head segments having a length greater than zero as measured along a longitudinal axis of the implant, the first head segment tapering along at least a portion of its length from a greater height to a lesser height away from the second head segment, the second head segment tapering along at least a portion of its length from a greater height to a lesser height away from the first head segment; and    a tail portion extending from the head portion and including at least a first tail segment and a second tail segment, the first tail segment adjoining the second head segment, each of the first and second tail segments having a length greater than zero as measured along a longitudinal axis of the implant, the first tail segment having a constant height along its length, the second tail segment tapering along at least a portion of its length from a lesser height to a greater height away from the first tail segment.    
   
   
       9 . The spinal implant of  claim 8 , wherein the tapered portion of the first head segment tapers at a constant rate.  
   
   
       10 . The spinal implant of  claim 8 , wherein the tapered portion of the second head segment tapers at a rate that increases away from the first head segment.  
   
   
       11 . The spinal implant of  claim 8 , wherein the head portion further includes at least a third head segment having a length greater than zero that is interposed between the first head segment and the second head segment.  
   
   
       12 . The spinal implant of  claim 11 , wherein the third head segment has a constant height along its length.  
   
   
       13 . A method of repairing an annular defect in an intervertebral disc located between a first vertebral disc and a second vertebral disc, and providing dynamic stability to a motion segment of a spine in the vicinity of the intervertebral disc, the method comprising the steps of: 
 removing at least a portion of the intervertebral disc;    preparing an implantation site in the vicinity of the intervertebral disc; and    implanting a spinal implant device at the implantation site;    wherein the step of preparing the implantation site includes the steps of: 
 reaming the implantation site to remove bone material from endplates of each of the first and second vertebral discs and thereby shape a portion of each of the endplates to receive the implant device in a substantially complementary fit; and  
 countersinking the implantation site to remove bone material from extradiscal lips of each of the first and second vertebral discs and thereby shape a portion of each of the extradiscal lips to receive the implant device in a substantially complementary fit.  
   
   
   
       14 . The method of  claim 13 , further comprising the step of measuring a distance between the endplates to determine an appropriate size for the implant device.  
   
   
       15 . A method of repairing an annular defect in an intervertebral disc located between a first vertebral disc and a second vertebral disc, and providing dynamic stability to a motion segment of a spine in the vicinity of the intervertebral disc, the method comprising the steps of: 
 removing at least a portion of the intervertebral disc;    preparing an implantation site in the vicinity of the intervertebral disc; and    implanting a spinal implant device at the implantation site;    wherein the implant comprises a head portion including at least a first head segment and a second head segment, each of the first and second head segments having a length greater than zero as measured along a longitudinal axis of the implant, the first head segment having a constant height along its length, the second head segment tapering along at least a portion of its length from a greater height to a lesser height away from the first head segment, and a tail portion extending from the head portion and including at least a first tail segment and a second tail segment, the first tail segment adjoining the second head segment, each of the first and second tail segments having a length greater than zero as measured along a longitudinal axis of the implant, the first tail segment having a constant height along its length, the second tail segment tapering along at least a portion of its length from a lesser height to a greater height away from the first tail segment.