Abstract:
A spinal implant helps stabilize vertebrae for fusion. The implant is particularly adapted for percutaneous implantation, but may also be used with other access techniques. The implant includes first and second plates that extend through a slot in a frame. When installed, the frame extends laterally through the interspinous space, and the plates extend superiorly-inferiorly along respective lateral sides of the spinous processes. The plates are moved toward one another and relative to the slot to clamp the implant to the spinous processes. The slot may be variably sized along its length, and the plates may move into differently sized portions of the slot during the clamping process.

Description:
BACKGROUND 
     The present invention relates generally to spinal stabilization, and more particularly to spinal fusion implants and procedures for implanting the same, particularly percutaneously. 
     A wide variety of spinal fusion devices are used following partial or total discectomies for stabilization of the spine at that site. Many such devices are secured extradiscally, such as to the pedicles or spinous processes. For example, the SPIRE brand fusion products available from Medtronic, Inc. of Minneapolis, Minn. are typically secured to the spinous processes. See also the devices and methods disclosed in U.S. Pat. Nos. 7,048,736 and 7,727,233. The implantation of such devices may involve significant muscle dissection and associated surgical time, as they are typically ill suited for minimally invasive surgical techniques. As a result, use of these devices may require significant recovery time. Thus, while numerous spinal fusion stabilization devices have been proposed, there remains a need for alternative approaches, particularly those suited for percutaneous implantation. 
     SUMMARY 
     The present invention provides a spinal implant that helps stabilize vertebrae for fusion. The implant is particularly adapted for percutaneous implantation, but may also be used with other access techniques. The implant, in one or more embodiments, includes first and second plates that extend through a slot in a frame. When installed, the frame extends laterally through the interspinous space, and the plates extend superiorly-inferiorly along respective lateral sides of the spinous processes. The plates are moved toward one another and relative to the slot to clamp the implant to the spinous processes. 
     In some embodiments, the present invention provides a spinal implant device comprising a first plate, a second plate, a frame, and a locking element. The first plate curvingly extends along a first curved longitudinal axis and has a first medial face configured to abut adjacent spinous processes with biting projections thereon. The second plate curvingly extends along a second curved longitudinal axis and has a second medial face configured to abut the adjacent spinous processes with biting projections thereon. The frame extends along a third curved longitudinal axis and has a longitudinal slot therethrough. The first and second plates are disposed through the slot such that the first and second axes are transverse to the third axis and the first and second medial faces face toward each other in spaced relation. The locking element engages a proximal end of the frame and is longitudinally moveable relative to the frame such that longitudinal displacement of the locking element toward a distal end of the frame narrows a distance between the first plate and the second plate. In some embodiments, longitudinal displacement of the locking element toward a distal end of the frame causes the first and second plates to enter relatively narrower sections of the slot. The first plate may comprise first and second end sections, with an intermediate portion disposed therebetween, with the intermediate portion having a reduced cross section relative to the first and second end sections, and with the intermediate section disposed in the slot. The first end section of the first plate may advantageously have a tapered tip portion disposed opposite the intermediate section. The tapered tip portion may have the largest cross section of the first plate. The first plate may comprise an elongate base and the associated biting projections; wherein the base has a substantially D-shaped cross-section normal to the first axis, with the medial face being substantially flat. The second plate may be similar to the first plate, with the first and second plates being substantially mirror images of each other in some embodiments. The slot may have a variable height. For example, the slot may comprise two portions of enlarged height, disposed in longitudinally spaced relation. 
     In other embodiments, the first plate curvingly extends along a first curved longitudinal axis, and the first plate has a first medial face configured to abut adjacent spinous processes with biting projections thereon. The second plate curvingly extends along a second curved longitudinal axis, and the second plate has a second medial face configured to abut the adjacent spinous processes with biting projections thereon. The curvilinear frame extends along a third curved longitudinal axis and having a longitudinal slot therethrough. The first and second plates are disposed through the slot such that the first and second axes are transverse to the third axis and the first and second medial faces face toward each other in spaced relation. The locking element engages a proximal end of the frame and is longitudinally moveable relative to the frame. The implant is changeable from a first configuration to a second configuration. In the first configuration, the first and second plates are disposed a first distance apart. In the second configuration: the first and second plates are disposed a second distance apart, the second distance less than the first distance; the first and second plates are disposed more distally relative to frame than in the first configuration; the locking element is disposed more distally relative to the frame than in the first configuration. The slot may comprise a distal end, with the first plate abutting the distal end of the slot in the second configuration and the locking element abuts the second plate in the second configuration. The first plate may comprise first and second end sections, with an intermediate portion disposed therebetween, with the intermediate portion having a reduced cross section relative to the first and second end sections, and the intermediate section disposed in the slot. The slot may have variable height, with two spaced apart first sections of enlarged height and two spaced apart second sections of reduced height; one of the second sections of reduced height is disposed between the first sections of enlarged height and one of the first sections is disposed between the second sections. The first and second plates may be disposed in the first sections of the slot in the first configuration and disposed in the second sections of the slot in the second configuration. 
     In various embodiments, the present invention has one or more of the above attributes, alone or in any combination. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a spinal motion segment with an implant according to one embodiment of the present invention prior to being clamped to the spinous processes. 
         FIG. 2  shows the implant of  FIG. 1  in a lateral perspective view. 
         FIG. 3  shows the first and second plates of the implant of  FIG. 1  in perspective view. 
         FIG. 4  shows the medial face of the first plate of the implant of  FIG. 1 . 
         FIG. 5  shows a cross section of the first plate of the implant of  FIG. 1  along line V-V of  FIG. 4 . 
         FIG. 6  shows the frame of the implant of  FIG. 1   
         FIG. 7  shows the implant of  FIG. 1  prior to clamping. 
         FIG. 8  shows a platform mounted to a guide pin. 
         FIG. 9  shows a guide dilator positioned to the interspinous space. 
         FIG. 10  shows the frame insertion swing arm disposed over the guide dilator. 
         FIG. 11  shows the frame being positioned via the channel of the frame insertion swing arm. 
         FIG. 12  shows insertion of the first and second plates disposed in the slot, with the plate insertion swing arm for the first plate partially removed to expose the first plate medial face. 
         FIG. 13  shows insertion of the implant positioned after insertion of the first and second plates, prior to clamping. 
         FIG. 14  shows the implant clamped to the spinous processes. 
     
    
    
     DETAILED DESCRIPTION 
     In one embodiment, the present invention is directed to an implant  20  for spinal fusion that attaches to adjacent spinous processes  14 , 16  to fixate the corresponding vertebrae  10 , 12  relative to the other. In at least one embodiment, the implant  20  includes two fixation plates  30 , 40  and an interconnecting frame  50 . The fixation plates  30 , 40  are disposed on respective lateral sides of adjacent spinous processes  14 , 16 , and the frame  50  extends laterally through the corresponding interspinous space  18 . The fixation plates  30 , 40  and frame  50  are advantageously inserted, and locked together, using a percutaneous approach. 
     One embodiment of the implant  20  is shown in  FIGS. 1-7 . The implant  20  of  FIG. 1  includes first and second plates  30 , 40 , a frame  50 , and a locking element  70 . The first plate  30  is an elongate member that extends along a curving longitudinal axis  31 . As such, the first plate  30  is longitudinally curving, as shown in  FIG. 4 . The first plate  30  may be divided into a superior section  36 , an intervening intermediate section  37 , and an inferior section  38 , which are arranged sequentially in abutting relationship along the axis  31 . As can be seen, the superior end may be relatively flat, while the inferior end advantageously is in the form of a tapering tip  39 . The intermediate section  37  has a reduced cross section compared to the superior and inferior sections  36 , 38 , advantageously with suitable smooth transitions therebetween. The main or base portion  32  of the first plate  30  has a generally flat medial face  33 , and advantageously has a generally D-shaped cross section normal to the longitudinal axis  31 . The medial face  33  has plurality projections or teeth thereon, which extend medially away from the longitudinal axis  31 . These projections  34  are for biting into the spinous processes  14 , 16  when the implant  20  is clamped thereto, as discussed further below. The “diameter” of the base portion  32 , excluding the tip  39  but including the teeth  34 , is advantageously slightly smaller than the “diameter” of large part of tip  39 , such that the base portion  32  fits within the profile of the tip  39  projected along the longitudinal axis  31 . This arrangement allows the majority of the first plate  30  to be slid into a hollow delivery tube  142  (see further discussion below) leaving just the tip  39  exposed, with the tube  142  being not larger in diameter than the tip  39 . 
     The second plate  40  is likewise an elongate member that extends along a curving longitudinal axis  41 . As such, the second plate  40  is longitudinally curving. The second plate  40  may be divided into a superior section  46 , an intervening intermediate section  47 , and an inferior section  48 , which are arranged sequentially in abutting relationship along the axis  41 . As can be seen, the superior end may be relatively flat, while the inferior end advantageously is in the form of a tapering tip  49 . The intermediate section  47  has a reduced cross section compared to the superior and inferior sections  46 , 48 , advantageously with suitable smooth transitions therebetween. The main or base portion  42  of the second plate  40  has a generally flat medial face  43 , and advantageously has a generally D-shaped cross section normal to the longitudinal axis  41 . The medial face  43  has a plurality of projections or teeth  44  thereon, which extend medially away from the longitudinal axis  41 . Like the teeth  34  of the first plate  30 , the teeth  44  on the second plate  40  are for biting into the spinous processes  14 , 16  when the implant  20  is clamped thereto, as discussed further below. The “diameter” of the base portion  42 , excluding the tip  49  but including the teeth  44 , is advantageously slightly smaller than the “diameter” of large part of tip  49 , such that the base portion fits within the profile of the tip  49  projected along the longitudinal axis  41 . This arrangement allows the majority of the second plate  40  to be slid into a hollow delivery tube  142  leaving just the tip  49  exposed, with the tube  142  being not larger in diameter than the tip  49 . 
     The first and second plates  30 ,  40  may be substantially mirror images of each other, although this is not required in all embodiments. 
     The frame  50  is an elongate member that advantageously extends along an associated longitudinal axis  51  from a proximal section  52  to a distal section  54 , as shown in  FIG. 6 . The frame  50  includes a longitudinal slot  60  that is sized and configured to accept the first and second plates  30 , 40  therethrough, with the slot  60  being in both the proximal section  52  and the distal section  54 . The slot  60  may be relatively uniform in height  61 , but is advantageously variable in height. For example,  FIG. 6  shows the slot  60  with two spaced apart enlarged height sections  62  interleaved with two spaced apart reduced height sections  64 , with suitable smooth transitions therebetween. The proximal section  52  includes a longitudinal bore  52  extending into the slot  60 . The bore  53  is sized and configured to engagingly receive the locking member  70 , as described further below. Other than the bore  60 , the distal and proximal ends of the slot  60  are advantageously fully enclosed. The distal section  54  advantageously tapers distally to form a tapered tip  56 . The frame  50  is advantageously rigid, although flexible frames  50  may alternatively be used in some embodiments. 
     The locking element  70  helps clamp the first and second plates  30 , 40  to the spinous processes  14 , 16  by moving at least the second plate  40  longitudinally toward the first plate  30 . The locking element  70  is illustrated as a setscrew, although other types of locking elements, such as barbed one-way pins, quarter-turn fasteners, and the like may alternatively be employed. 
     The implant  20  is formed of suitable biocompatible materials, such as stainless steel, titanium and its alloys, polymers such as PEEK, and the like. 
     The implant  20  may be implanted by positioning the frame  50  in the interspinous space  18  so that the longitudinal axis  51  passes through the sagittal plane defined by the adjacent spinous processes  14 , 16 . The frame  50  should be oriented so that the slot height  61  is parallel to the anatomical axial plane. The locking element  70  is advantageously partially inserted into the bore  53  prior to the placement of the frame  50 . The first and second plates  30 , 40  are then positioned transverse, e.g., perpendicular, to the frame  50 , advantageously through the enlarged height sections  62  of the slot  60 , so that each plate  30 , 40  extends proximate the superior and inferior spinous processes  14 , 16  on respective lateral sides thereof. Advantageously, the first and second plates  30 , 40  are disposed through the slot  60  so that the intermediate sections  38 , 48  rest in the corresponding enlarged height sections  62  of the slot  60 . After insertion, prior to clamping, the first and second plates  30 , 40  are separated by a distance D insert  (measured along axis  51 ). The locking element  70  is then advanced proximally relative to the frame  50  so as to apply a force to the second plate  40  along axis  51 . This force is typically a result of the locking element  70  abutting the second plate  40  directly, but may be indirect, such as through an intervening shim, if desired. This force causes second plate  40  to displace distally out of enlarged section  62  and into the distally adjoining reduced section  64 . As the second plate  40  presses against the spinous processes  14 , 16 , the displacement force of the locking element  70  causes the frame  50  to in effect “pull back” so that the distal tip  56  of the frame  50  is moved closer to the sagittal plane through the interspinous space  18 . This causes the first plate  30  to move out of its corresponding enlarged section  62  of the slot  60  and into the distally adjoining reduced section  64 . Further displacement of the frame  50  causes the plates  30 , 40  to be clamped to the spinous processes  14 , 16 , with the teeth  34 , 44  of the plates  30 , 40  biting into the spinous processes  14 , 16 . When clamped, the first and second plates  30 , 40  are separated by a distance D clamp , which is smaller than distance D insert . This clamping of the implant  20  to the spinous processes  14 , 16  immobilizes the spinous processes  14 , 16  relative to each other, thereby stabilizing the vertebrae  10 , 12  and the corresponding disc space suitably for fusion to occur. 
     The above process may be carried out using a relatively large access with a posterior approach, similar to that described in U.S. Pat. Nos. 7,048,736 and 7,727,233. However, the implantation process is advantageously carried out percutaneously, as described further below. 
     The implant  20  may be percutaneously implanted using an installation assembly  100  as shown in  FIGS. 8-14 . A reference guide, such as a Steinman pin  102 , is directed to the desired interspinous space  18 . A platform  104  is then secured to the pin  102 , such as by routing the pin  102  trough a pin boss  110  on the platform  104  and securing the platform  104  thereto. The platform  104  is advantageously mounted to the pin  102  at a predetermined height along the pin  102  that allows the swing arm installation described below to position the components of the implant  20  as desired. It should be understood that the platform  104  is also supported by ways not shown, such as legs and the like, to the surgical table. The position of the platform  104  is locked relative to the patient and the surgical table once positioned properly on the pin  102 . As such, the pin  102  may be removed at this point of the surgical procedure if desired. A guide dilator  120  is then attached to the platform  104  so that it rotates about an axis  106  parallel to the spinal column. The guide dilator  120  has a tapered tip  122 , and includes a pivot arm section  124  and a curvate section  126 . The pivot arm section  124  extends outward from the platform  104 , and advantageously includes a short jog section as illustrated. The curvate section  126  is curved at a uniform radius of curvature that enables the tip  122  to stop in the desired interspinous space  18  when the platform  104  is positioned correctly. If not previously removed, the pin  102  should be removed at this point in the procedure. A frame insertion swing arm  130  is then attached to the platform  104 . The frame insertion swing arm  130  includes a curvate guide tube  132  with a channel  134 . The guide dilator  120  slides within the channel  134  to guide the distal end of the frame insertion swing arm  130  to the desired location. The guide dilator  120  is then removed and the frame  50  inserted into the channel  134 . The frame  50  is then advanced down the channel  134  using any suitable means until the frame  50  is properly disposed through the interspinous space  18 . A plate insertion swing arm  140  is then attached to the platform  104  for rotation about a laterally running axis. The plate insertion swing arm  140  includes a curved hollow tube  142  that curves at a suitable rate to extend through the frame slot  60  when swung into position. The first plate  30  is advantageously preloaded into the distal portion of the hollow tube  142  before rotating the plate insertion swing arm  130  down into position. The tip  39  of the first plate  30  is tapered, as discussed above, in order to dilate the affected tissue during this swinging action. The tissue is protected from the teeth  34  of the first plate  30  because the teeth  34  are disposed inside the hollow tube  142 . Similarly, another plate insertion swing arm  140  is used to insert the second plate  40  through the slot  60  of the frame  50 . Once the plates  34 , 40  are positioned properly through the slot  60 , the plate insertion swing arms  140  are rotated back out of position while using a suitable push rod or the like to expel the plates  30 , 40  from the corresponding hollow tubes  142 . The plate insertion swing arms  140  are then removed from the platform  104 . A suitable tool (not shown) is then advanced through the channel  134  to actuate the locking mechanism  70  to clamp the implant  20  to the spinous processes  14 , 16 . The frame insertion swing arm  130  is then removed, followed by the pin  102 . Such a procedure may be accomplished with three small incisions, one each for the frame  50  and the two plates  30 , 40 . Each of the components of the implant  20  is implanted using a percutaneous, swing arm-based approach to properly position the components, and subsequently clamp the implant  20  in position. The use of such a percutaneous method allows for less surgical damage and quicker recovery. 
     The swing arms  130 , 140  and guide dilator  120  discussed above may be pivotally mounted to the platform  104  in any suitable fashion, such as via C-shaped snap on sections, clamshell connectors, or the like. The swing arms  130 , 140  and guide dilator  120  discussed above may also have corresponding positive stops (not shown) on the platform  104  to prevent over-rotating them beyond their respective desired positions. 
     The angle β between the frame axis  51  and the axis  31  of first plate  30  (or axis  41  of second plate  40 ) may be 90°, i.e. perpendicular. However, the reduced cross sectional shape of the intermediate sections  37 , 47  not only allows the plates  30 , 40  to be moved into the reduced height sections  64  of slot  60 , but also allows for small angular variations, such as ±15° or less from perpendicular, for angle β so as to accommodate spinal morphological variations between the vertebrae  10 , 12 . 
     The discussions above have been in the context of the plates  30 , 40  having teeth  34 , 44  generally arranged in an array on their medial faces  33 , 43 . However, other arrangements may be used, and any suitable form of biting projections may alternatively be employed. 
     All U.S. patents and patent application publications mentioned above are hereby incorporated herein by reference in their entirety. 
     The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the scope of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.