Abstract:
An endoprosthesis including first and second attachment surfaces for attachment to spinal structure, and a fixation element rotatingly disposed in at least one of the attachment surfaces, the fixation element being rotatable between a stowed position, wherein the fixation element does not substantially protrude from the at least one of the attachment surfaces, and a deployed position, wherein the fixation element does substantially protrude from the at least one of the attachment surfaces for entering and being fixed to the spinal structure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 USC §119 to U.S. Provisional Patent Application Ser. No. 60/789,220, filed on Apr. 5, 2006, and 60/849,447, filed Oct. 5, 2006, which are incorporated herein by reference. 
     
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to spinal prostheses and particularly fixation of prostheses for disc or partial spinal disc replacement. 
       BACKGROUND OF THE INVENTION 
       [0003]    Spinal disc or partial spinal disc replacement is a common procedure with thousands having been performed already and. Examples of such replacement discs are ProDisc (Spine Solutions, Inc.) and SB Charite III (Link Spine Group, Inc.) 
         [0004]    By replacing a disc and not merely fusing vertebrae, which is the common alternative practice to disc replacement, the mobility of the patient&#39;s adjacent discs may be preserved and thus may delay the onset of arthritic changes to adjacent vertebrae. 
         [0005]    Although many prosthetic disc devices are described in the literature, there is still a need for improvement in ease of performance 
         [0006]    Artificial discs usually have spikes, keels, screws or other protrusions attached to or integrated into the outer surfaces of these prostheses in order to assist in the initial fixation to the endplates of the treated vertebrae that help in the prevention of migration of the prostheses away from their correct positioning in the intravertebral space. 
         [0007]    When a disc is to be placed into the intravertebral space, a space needs to be prepared that will take into account the total height of the prosthesis, including the added height of the protrusions. A solution is required that would not necessitate a distraction of the added height of the protrusions. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention is directed to a spinal prosthesis, as is described more in detail herein below. Attachments members or fixation elements, such as spikes, ridges, keels, teeth, pegs, and fins and any other extrusions or protrusions (all these terms being used interchangeably throughout the specification and claims), initially do not significantly protrude above the external end plates of the prosthesis. The fixation elements are deployed to a position that extends or protrudes beyond the exterior surface of the endoprosthesis only after inserting the endoprosthesis (or prosthesis or implant, all these terms being used interchangeably throughout the specification and claims) into the inter-vertebral space. Only when the prosthesis is in its correct final position, the protrusions are manipulated into position for fixation. The initial low-profile of the implant reduces the amount of distraction needed and avoids over-distraction or chiseling of the vertebrae. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    In the drawings: 
           [0010]      FIGS. 1A and 1B  are simplified illustrations of a vertebral disc endoprosthesis, constructed and operative in accordance with an embodiment of the present invention, having fixation elements that are press-fit into channels; 
           [0011]      FIGS. 2A and 2B  are simplified illustrations of a vertebral disc endoprosthesis, constructed and operative in accordance with an embodiment of the present invention, having fixation elements that are screwed into channels; 
           [0012]      FIGS. 3A and 3B  are simplified illustrations of a vertebral disc endoprosthesis, constructed and operative in accordance with another embodiment of the present invention, having fixation elements that are press-fit into channels and have a dove tail; 
           [0013]      FIGS. 4A and 4B  are simplified illustrations of a vertebral disc endoprosthesis, constructed and operative in accordance with another embodiment of the present invention, having fixation elements that are press-fit into channels and are formed with a trapezoidal backing; 
           [0014]      FIGS. 5A and 5B  are simplified illustrations of a vertebral disc endoprosthesis, constructed and operative in accordance with another embodiment of the present invention, having fixation elements that are press-fit into channels, have a trapezoidal backing and a protruding part in the form of a dove tail; 
           [0015]      FIGS. 6A-6C  are simplified illustrations of a vertebral disc endoprosthesis, constructed and operative in accordance with another embodiment of the present invention, having fixation elements that comprise pins inserted in sharp angle holes; 
           [0016]      FIGS. 7A-7C  are simplified illustrations of a vertebral disc endoprosthesis, constructed and operative in accordance with another embodiment of the present invention, having fixation elements that comprise pins that are curved; 
           [0017]      FIGS. 8A-8C  and  FIGS. 9A-9C  are simplified illustrations of a vertebral disc endoprosthesis, constructed and operative in accordance with another embodiment of the present invention, having fixation elements that are rotatingly disposed in channels, in respective stowed and deployed positions, wherein the fixation elements have fixing members that terminate in a dove tail; 
           [0018]      FIGS. 10A-10C  and  FIGS. 11A-11C  are simplified illustrations of a vertebral disc endoprosthesis, constructed and operative in accordance with another embodiment of the present invention, having fixation elements that are rotatingly disposed in channels, in respective stowed and deployed positions, wherein the fixation elements have fixing members that terminate in an elongate sharp or narrow edge; 
           [0019]      FIGS. 12A-12C  and  FIGS. 13A-13D  are simplified illustrations of a vertebral disc endoprosthesis, constructed and operative in accordance with another embodiment of the present invention, having fixation elements that are rotatingly disposed in channels, in respective stowed and deployed positions, wherein the fixation elements pivot about a pivot pin; 
           [0020]      FIGS. 14A-14C  and  FIGS. 15A-15C  are simplified illustrations of a vertebral disc endoprosthesis, constructed and operative in accordance with another embodiment of the present invention, having fixation elements that are rotatingly disposed in channels, in respective stowed and deployed positions, wherein the fixation elements have fixing members that terminate in an elongate sharp or narrow edge; 
           [0021]      FIGS. 16A-16C  are simplified illustrations of a variant of the embodiment of  FIGS. 14A-15C , which geometrically locks the fixing member of the fixation element in place; 
           [0022]      FIGS. 17A-17C  are simplified illustrations of a vertebral disc endoprosthesis, constructed and operative in accordance with another embodiment of the present invention, having fixation elements with a plurality of fixing members formed thereon; 
           [0023]      FIG. 18  is a simplified illustration of a surgical procedure for manipulating the fixation elements, in accordance with an embodiment of the present invention; and 
           [0024]      FIGS. 19A-19D ,  20 A- 20 D,  21 A- 21 C and  22  are simplified illustrations of fixation elements, constructed and operative in accordance with different embodiments of the present invention, wherein  FIGS. 19A and 19B  illustrate a fixation element that has a spike,  FIGS. 19C and 19D  illustrate other variants of the fixation element, respectively with two and three spikes,  FIGS. 20A and 20B  illustrate a fixation element manufactured from more than one part,  FIGS. 20C and 20D  illustrate a fixation element that includes locking members for locking the fixation element in the stowed and deployed positions,  FIGS. 21A and 21B  illustrate another kind of locking member for locking the fixation element in the stowed and deployed positions in the channel,  FIG. 21C  illustrates another kind of locking member for locking the fixation element in the stowed and deployed positions, and  FIG. 22  the fixation element formed with a hole in the spike. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0025]    Reference is now made to  FIGS. 1A and 1B , which illustrate a vertebral disc endoprosthesis  10 , constructed and operative in accordance with an embodiment of the present invention. Endoprosthesis  10  may be a spinal endoprosthesis for disc or partial spinal disc replacement, similar to that described in PCT published patent application WO 2005/084590, the disclosure of which is incorporated herein by reference. 
         [0026]    Endoprosthesis  10  may be fashioned from any combination of materials used for spinal prostheses, such as but not limited to, ceramic, aluminum oxide, zirconium oxide, metal, metal alloy, cobalt-chromium-tungsten-nickel alloy, cobalt-chromium-manganese alloy, cobalt-chromium alloy, cobalt-chromium-molybdenum alloy, chromium-nickel-manganese alloy, powder metal alloy, 316L stainless steel, Ti 6Al-4V ELI (nominally 6 percent aluminum, 4 percent vanadium, balance by weight titanium, extra-low interstitial grade), polymer, polyurethane, polyethylene, wear resistant polyethylene, cross-linked polyethylene, thermoplastic elastomer, biomaterial, polycaprolactone, diffusion hardened material, Ti-13-13, zirconium alloy, niobium alloy, with or without a porous coating system, hydrophilic coating system, hydroxyapatite coating system, and tri-calcium phosphate coating system. 
         [0027]    In accordance with a non-limiting embodiment of the invention, endoprosthesis  10  may include a first articulating member  12  formed with a generally concave articulating surface  14 , and a second articulating member  16  formed with a generally convex articulating surface  18  which articulates with concave articulating surface  14 . The first and second articulating members  12  and  16  may have generally planar attachment surfaces  20  and  22 , respectively, for attachment to structure of the spine. The attachment surface  20  may be generally flat, but can be curved or irregular, depending on the application. 
         [0028]    In accordance with a non-limiting embodiment of the invention, attachment surfaces  20  and  22  include fixation elements (e.g., spikes or other protrusions)  24  to improve the attachment to the spine structure. 
         [0029]    It may be disadvantageous to have fixation elements  24  in place on attachment surfaces  20  and  22  before the endoprosthesis  10  is inserted. For example, if the fixation elements  24  were to initially protrude from attachment surfaces  20  and  22 , it may be difficult to insert endoprosthesis  10  into the intervertebral space and position it in the recommended/preferred/best position. The fixation elements  24  could interfere with insertion because the spikes could catch or snag on spinal structure prior to reaching the final desired position of the endoprosthesis. An additional disadvantage is that if the fixation elements  24  were to initially protrude from attachment surfaces  20  and  22  the endoprosthesis total height would be slightly higher. The added height could make initial placement of the endoprosthesis more difficult. 
         [0030]    In accordance with a non-limiting embodiment of the invention, attachment surfaces  20  and  22  are formed with one or more channels  26  and fixation elements  24  are inserted into channels  26  only after endoprosthesis  10  into the intervertebral space. In the embodiment of  FIGS. 1A and 1B , fixation elements  24  are press-fit into channels  26  by pushing them into channels  26  in either the direction of arrow  23  or  25  (whichever is more convenient). The fixation elements  24  of this embodiment are formed with an arcuate backing  28  (in which case channel  26  may be arcuate as well) with an elongate sharp edge  30 . The elongate sharp edge  30  digs into the spinal structure upon insertion of fixation elements  24  into channel  26  and fixes the endoprosthesis  10  into the intervertebral space. 
         [0031]    In the embodiment of  FIGS. 2A and 2B , fixation elements  34  are provided, which are formed as a thread rod or bar and are screwed into channels  26  by screwing in either the direction of arrow  23  or  25  (whichever is more convenient). The fixation elements  34  may be self-tapping and screw into the spinal structure to fix the endoprosthesis  10  into the intervertebral space. Channels  26  may be tapped or may be previously un-tapped, in which case fixation elements  34  may form threads in channels  26  as they are screwed in place. The fixation element  34  may have a driver interface  35 , such as a regular screwdriver slot, Philips screwdriver slot or hexagonal Allen socket (the latter being in the illustrated embodiment), for screwing by means of a suitable tool. 
         [0032]    In the embodiment of  FIGS. 3A and 3B , fixation elements  36  are press-fit into channels  26  and the protruding part is in the form of a dove tail  38 . 
         [0033]    In the embodiment of  FIGS. 4A and 4B , fixation elements  40  are press-fit into channels  26 . Fixation elements  40  are formed with a trapezoidal backing  41  (in which case channel  26  may be complementary trapezoidal) with an elongate sharp edge  42 . 
         [0034]    In the embodiment of  FIGS. 5A and 5B , fixation elements  44  are press-fit into channels  26 . Fixation elements  44  are formed with a trapezoidal backing  45  (in which case channel  26  may be complementary trapezoidal) and the protruding part is in the form of a dove tail  46 . 
         [0035]    In the embodiment of  FIGS. 6A and 6B , fixation elements  50  comprise pins inserted in sharp angle holes  52  or  54  into the vertebra. The pins may have protrusions  56  when in place, as shown in  FIG. 6C . 
         [0036]    In the embodiment of  FIGS. 7A and 7B , the fixation elements are the same as that of  FIGS. 6A and 6B , except that the pins are curved (bent or plastic deformation and the like) and fit in a curved track  58  ( FIG. 7C ) formed in the prosthesis. 
         [0037]    Reference is now made to  FIGS. 8A-8C . In accordance with a non-limiting embodiment of the invention, attachment surfaces  20  and  22  are formed with one or more channels  26  and fixation elements  60  are rotatingly disposed in channels  26 . In the embodiment of  FIGS. 8A-8C , fixation elements  60  are formed as a rod or bar  62  with a fixing member  64  that protrudes from rod  62 . Fixing member  64  (which in the illustrated embodiment is in the form of a dove tail) may initially sit in a groove  65  (seen best in  FIG. 9A ), which extends from channel  26 . The fixation element  60  can rotate about a longitudinal axis  66  of rod  62 . The fixation element  60  may have a driver interface  68 , such as a regular screwdriver slot, Philips screwdriver slot or hexagonal Allen socket (the latter being in the illustrated embodiment), for turning by means of a suitable tool. 
         [0038]    Initially, fixing member  64  sits in groove  65 . Upon rotation of fixation element  60 , fixing member  64  turns out of groove  65  and is deployed to the position shown in  FIGS. 9A-9C  to press or “bite” into the spinal structure and fix the endoprosthesis into the intervertebral space. 
         [0039]    Reference is now made to  FIGS. 10A-11C . This embodiment is basically the same as that of  FIGS. 8A-9C , except that in the embodiment of  FIGS. 10A-11C , there are fixation elements  70  that have fixing members  72  that terminate in an elongate sharp or narrow edge instead of terminating in a dove tail. 
         [0040]    Reference is now made to  FIGS. 12A-12C . In accordance with a non-limiting embodiment of the invention, attachment surfaces  20  and  22  are formed with one or more channels  26  and fixation elements  75  are rotatingly disposed in channels  26 . Fixation elements  75  are each arranged to pivot about a pivot pin  76  and are each formed with a fixing member  78  (e.g., tab or the like) that protrudes therefrom. 
         [0041]    Initially, fixing member  78  sits in channel  26 . Referring now to  FIGS. 13A-13D , a wedging tool  79  may be inserted into channel  26  which causes fixation element  75  to pivot and forces fixing member  78  out of channel  26 . Fixing member  78  is thus deployed to the position shown in  FIGS. 13A-13D  to press or “bite” into the spinal structure and fix the endoprosthesis into the intervertebral space. 
         [0042]    Reference is now made to  FIGS. 14A-15C . This embodiment is basically the same as that of  FIGS. 10A-11C , with like elements being designated by like reference numerals, except that the channel  26  is shaped differently in the embodiment of  FIGS. 14A-15C .  FIGS. 16A-16C  show a variant of the embodiment of  FIGS. 14A-15C , wherein the channel  26  has a terminal end  77 , which geometrically locks fixing member  72  of fixation element  70  in place. By “geometric locking” it is meant that a portion of the fixing member  72  moves in the channel, and is prevented from moving further in the channel at least partially by a geometric shape or geometric arrangement of the channel with respect to the fixing member. For example, the terminal end  77  may be angled and/or curved so that fixing member  72  is wedged thereagainst and tends to stay in place. 
         [0043]    Reference is now made to  FIGS. 17A-17C . This embodiment is basically the same as that of  FIGS. 10A-11C , except that in the embodiment of  FIGS. 17A-17C , fixation elements  70  have a plurality of fixing members  72  formed thereon, and they may be deployed outwards simultaneously by rotating fixation elements  70  as described hereinabove. 
         [0044]    Reference is now made to  FIG. 18 , which illustrates a top view of a surgical procedure for manipulating the fixation elements, in accordance with an embodiment of the present invention, such as within a typical lumbar vertebra  202 . Vertebra  202  includes an anterior portion  204 , a posterior portion  206 , a spinal cord  198  and a root  200 . A manipulating tool  208  may be used for deploying the fixation elements (moving them to a protruding position). Tool  208  may be constructed similar to that of a screwdriver, Allen wrench and the like, depending on the tool interface of the fixation element. Tool  208  may be used in a variety of manipulation procedures, such as but not limited to, TLIF (transforaminal lumbar interbody fusion) or PLIF (posterior lumbar interbody fusion). Tool  208  preferably enters the intervertebral disc space between the spinal cord  198  and the root  200 . Rotating tool  208  about its axis of rotation  210  turns the fixation elements and deploys them to protrude outwards for fixing to spinal structure. The fixation elements may be returned to the stowed (generally flush) position by simply turning in the opposite direction with tool  208 . Thus tool  208  enables manipulating the protrusion elements with a relatively low risk of injuring spinal tissue, and provides the option for revision surgery, for locating the protrusion elements inside the body of the prosthesis, and for easy removal of the prosthesis. 
         [0045]      FIGS. 19A ,  19 B,  19 C,  19 D,  20 A,  20 B,  20 C,  20 D,  21 A,  21 B,  21 C and  22  illustrate further embodiments of initial fixation elements. 
         [0046]      FIGS. 19A and 19B  illustrate a basic design of a fixation element  212 , which has a spike  214 . The spike may be pyramid shaped with equal or unequal sides  220 . A cylinder shaped body  216  may allow rotation around axis of rotation  210  and has a wrench head  218  for applying torque. Wrench head  218  may be any geometrical head or socket for applying torque, for example hexagonal, square, or slotted. 
         [0047]      FIGS. 19C and 19D  illustrate other variants of fixation element  212 , respectively with two and three spikes  214 . 
         [0048]      FIGS. 20A and 20B  show that fixation element  212  may be manufactured from more than one part. For example, spike  214  may comprise a pointed portion  226  that is inserted in a notch  224  formed in body  216 . Pointed portion  226  may be welded or bonded or otherwise joined to body  216 . 
         [0049]      FIGS. 20C and 20D  illustrate a version of fixation element  212 , which includes locking members  213  for locking the fixation element  212  in the stowed and deployed positions in the channel  26  in any of the embodiments of the invention, wherein the fixation element is rotated between the stowed and deployed positions in the channel  26 . For example, locking members  213  may include detents  215  (e.g., notches or dimples) which “click” into position with lugs  217  (shown in dashed lines in  FIG. 20D ) found in channel  26 . 
         [0050]      FIGS. 21A and 21B  illustrate another kind of locking member for locking the fixation element  212  in the stowed and deployed positions in the channel  26  in any of the embodiments of the invention. In this embodiment, the locking member is a leaf spring  230  and a snap  232  that may snap into place in the channel to keep the fixation element  212  in the desired position. 
         [0051]      FIG. 21C  illustrates another kind of locking member for locking the fixation element  212  in the stowed and deployed positions. In this embodiment, a chamfered surface  234  may help define positioning of the fixation element  212  and keep it in the desired position. 
         [0052]      FIG. 22  illustrates another feature, in which the fixation element  212  is formed with a hole  236  in spike  214 . Hole  236  may be used to pull or maneuver fixation element  212 , for example with a cable or a rigid tool. 
         [0053]    Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations.