Abstract:
A spinal implant inserter having a) an outer sleeve having a bore, and b) a forked inner shaft having a proximal rod and a pair of distal tynes extending therefrom, each distal tyne comprising an engagement feature having a laterally-extending dovetail feature. An assembly comprising the implant inserter and an implant having a pair of mating dovetail features.

Description:
CONTINUING DATA 
       [0001]    This application claims priority from U.S. Ser. No. 61/385,959, filed on Sep. 23, 2010, and entitled “Stand Alone Intervertebral Fusion Device” (DEP6341USPSP), and is related to non-provisional U.S. Ser. No. ______, filed on even date, entitled “Stand Alone Intervertebral Fusion Device” (DEP6341USNP), the specifications of which are incorporated by reference in their entireties. 
         [0002]    This application claims priority from U.S. Ser. No. 61/466,309, filed on Mar. 22, 2011, and entitled “Novel Implant Inserter Having a Laterally-Extending Dovetail Engagement Feature” (DEP6392USPSP), the specification of which is incorporated by reference in its entirety. 
         [0003]    This application claims priority from U.S. Ser. No. 61/466,321, filed on Mar. 22, 2011, and entitled “Fusion Cage with In-Line Single Piece Fixation” (DEP6394USPSP), and is related to non-provisional U.S. Ser. No. ______, filed on even date, entitled “Fusion Cage with In-Line Single Piece Fixation” (DEP6394USNP), the specifications of which are incorporated by reference in their entireties. 
     
    
     BACKGROUND OF THE INVENTION 
       [0004]    Spine surgeons have expressed a desire to locate an implant with a low vertical profile instrument to minimize retraction and increase visibility of the implant. Ideally, the instrument and its connection point are sized to be fully contained within the profile of the implant, thus being smaller than the implant and allowing easy positioning or placement of the implant. Additionally, the connection to the instrument should be desirably rigid, with no toggle or rotation in any plane. This rigidity prevents implant movement during the passing of instruments or bone screw insertion. 
         [0005]    Conventional inserter instruments possessing chamfer features typically work in one plane, wherein a grabber tip collapses upon the implant in a medial/lateral direction and thereby secures the implant to the instrument. However, even with exacting tolerances, toggle often appears if the user of the conventional instrument were to apply a moment to the posterior edge of the implant (in flexion/extension) in one plane. Conventional inserters with chamfer features also do not take advantage of dissimilar angles at the interface in more than one plane, and so fail to ensure that the anterior surface of the implant bottoms out on the inserter grabber tip. 
         [0006]    U.S. Pat. No. 5,443,514 (Steffee) discloses an inserter that grips the side of a spinal implant. See FIGS. 4-6 of Steffee. 
         [0007]    US Patent Publication No. 2005-0143749 (Zalenski) discloses an inserter having engagement features forming a vertically-extending dovetail shape. See FIGS. 2A-2C of Zalenski. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention relates to an intervertebral implant having a novel “compound angle” recess, such as a dovetail shape, designed and sized to couple to a delivery instrument. The interface between the implant and securing instrument is designed with laterally-extending, angled chamfer features extending in more than one direction to prevent toggle and rotation. Once the split tip instrument is collapsed to its closed position, the implant is drawn into the inserter and allowed to bottom out on a distal wall of the inserter. 
         [0009]    The instrument of the present invention is advantageous over conventional inserter instruments having threads and other known grabber features, which sometimes need to withstand impaction and may move upon insertion of a bone anchor or instruments through the device. 
         [0010]    The dual angle nature of the present invention ensures that the implant is axially square and/or co-linear with the instrument and so further ensures that a larger surface area of the instrument absorbs any required impaction. 
         [0011]    The present invention may also have an added angle, wherein the dimension on the anterior portion of the feature is sized to be smaller than the posterior portion of the feature. See  FIG. 6 . 
         [0012]    In particular embodiments, the instrument of the present invention has a forked inner shaft with distal tynes extending therefrom, wherein each distal tyne forms a medially-extending dovetail feature. This dovetail feature possesses the compound angulation that prevents the undesired movements discussed above. 
         [0013]    In preferred embodiments of the present invention, the proximal wall of the implant has a corresponding pair of recesses opening onto its respective lateral walls. Each of these recesses forms a dovetail silhouette on its respective lateral wall of the implant. 
         [0014]    The invention is generally related to a method and apparatus for assisting in a safe, one-handed insertion of an implant. The implant implantation device generally includes (i) a frame that includes a trigger mechanism, (ii) an outer sleeve mechanically coupled to the frame, (iii) a forked inner shaft having distal tynes for mechanically engaging an implant, the forked inner shaft slidably disposed within the outer sleeve and (iv) a retaining element for directing the distal tynes towards a closed position. The retaining element can be a spring. 
         [0015]    Optional elements on the inserter may include a knob, a drag adjustment screw, at least one protrusion, and a depth control member. The knob can be mechanically coupled to the outer sleeve for causing the outer sleeve and the forked inner shaft to be rotated about the frame. The drag adjustment screw can provide tension between the trigger mechanism and the forked inner shaft. The at least one protrusion can be located on the outer sleeve for slidably engaging a distraction instrument. The depth control member can be slidably coupled to the outer sleeve for providing a predetermined insertion depth of the implant. 
         [0016]    The distal tynes of the inserter hold the implant therebetween during insertion of the implant between the vertebrae. Each distal tyne includes an engagement feature at its tip for mechanically engaging the implant. The engagement feature comprises a dovetail-shaped protrusion extending in the lateral direction. Generally, the engagement feature has a medial face, with each medial face having a proximal end portion having a height and a distal end portion having a height, wherein the height of the distal end portion is greater than the height of the proximal end portion. At the same time, the front wall of the implant comprises a pair of mating laterally-extending dovetail recesses opening onto a respective side wall and forming a dovetail silhouette on each side wall, wherein each engagement feature of the instrument is received in a respective recess of the spinal implant. 
         [0017]    The forked inner shaft can include at least one marking to identify a position of the implant in relation to the patient. The marking can be a pin located on a surface of the forked inner shaft. The marking can be a plurality of machined slots on a surface of the forked inner shaft. 
         [0018]    Mechanically engaging the implantation instrument to the implant may include the steps of (i) opening the forked inner shaft located on an end of the implantation instrument, (ii) aligning the tynes of the forked inner shaft with the recesses of the implant, and (iii) closing the tynes to mechanically engage the tynes to the implant. 
         [0019]    The method may further include the steps of (iv) distracting a prepared disc space with a distraction instrument, (v) inserting the implant into the prepared disc space with the implantation instrument, (vi) releasing the implant from the implantation instrument, and (vii) removing the implantation instrument and distraction instrument. 
         [0020]    In some embodiments, inserting the implant into a prepared disc space may include the step of aligning the implantation instrument with the distraction instrument. 
         [0021]    The invention has many advantages. For example, the invention provides safe one-handed insertion of an implant into a prepared disc space. The invention reduces the amount of time required to complete the surgical procedure. The invention also provides for various manipulations of the implant without physically contacting the implant. For example, the invention can align an endplate of the implant radially and provide a lordotic angle for implantation. The invention can be used for packaging the implant, and the invention can be used to hold the implant during the implant sterilization process. 
         [0022]    Therefore, in accordance with the present invention there is provided an instrument for inserting an implant, comprising;
       a) an outer sleeve having a bore, and   b) a forked member having a proximal rod and a pair of distal tynes extending therefrom, each distal tyne comprising a proximal portion and a distal portion having a distal wall having an engagement member extending distally therefrom, each engagement member having a medial face forming a dovetail shape,
 
wherein the proximal rod and the proximal portion of each tyne are slidably received within the bore of the outer sleeve, and
 
wherein the distal portion of each tyne extends out of the bore of the outer sleeve.
       
 
         [0025]    Also in accordance with the present invention there is provided an assembly comprising:
       a) the above-described inserter, and   b) a spinal implant having a front wall, a pair of opposing side walls and a back wall,   wherein the front wall comprises a pair of recesses opening onto a respective side wall to form a dovetail shape in each respective side wall,       
 
         [0029]    wherein each engagement feature of the instrument is received in a respective recess of the spinal implant. Also in accordance with the present invention there is provided an orthopedic implant having a front wall, a pair of opposing side walls, a back wall, and top and bottom surfaces, wherein the front wall comprises a pair of recesses, each recess opening onto a respective side wall and forming a dovetail shape in the respective side wall. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0030]      FIG. 1A  shows a cross-sectional view of an insertion instrument of the present invention. 
           [0031]      FIG. 1B  shows a plan view of the insertion instrument of  FIG. 1A . 
           [0032]      FIGS. 2A-2C  show a perspective view of three embodiments of a forked inner shaft of the present invention. 
           [0033]      FIG. 3  shows a perspective view of the implant being inserted into a prepared disc space using the insertion instrument of  FIGS. 1A-2C . 
           [0034]      FIG. 4  show two views of an instrument of the present invention having dovetail gripping features approaching an implant having corresponding dovetail recess features. 
           [0035]      FIG. 5  discloses an intervertebral fusion cage of the present invention. 
           [0036]      FIG. 6  discloses a corner of an implant having a sidewall having recess therein, wherein the recess comprises two acute angles α and β. 
           [0037]      FIG. 7  discloses a perspective view of an inserter tip of the present invention. 
           [0038]      FIG. 8  discloses a perspective view of a lighted inserter tip of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0039]    The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The same number appearing in different drawings represents the same item. The drawings are not necessarily to scale, with emphasis instead being placed upon illustrating the principles of the invention. 
         [0040]    In general, the present invention is related to an apparatus and a method for safely inserting an implant into a spine. The implant can be an artificial disc or spinal fusion cage, or a spinal plate. Referring to  FIGS. 1A and 1B , insertion instrument  100  is shown in a side cross-sectional view and a plan view, respectively. Insertion instrument  100  includes a frame or driver body assembly  110 , an actuator assembly  126  and a forked inner shaft  160  ( FIG. 2A-2C ). Insertion instrument  100  is a normally closed device, that is, the proximal rod of the forked inner shaft  160  is normally substantially contained within actuator assembly  126 . 
         [0041]    Actuator assembly  126  includes an outer sleeve  130 , a proximal inner shaft  140 , and a retaining pin  148 . Outer sleeve  130  includes a tapered end  175  which slidably engages tapers  163  on the forked inner shaft  160  ( FIG. 2A-2C ), allowing for compression and expansion of the forked inner shaft  160  when in use. Inner shaft  140  includes a female threaded end  142  and a male threaded end  144 . Female threaded end  142  mates with a spring retaining screw  152  and male threaded end  144  mates with the forked inner shaft  160 . Internal compression spring  150  is fastened to the actuator assembly  126  and is held in place by spring retaining screw  152 . Once actuator assembly  126  is assembled, it is inserted into driver body assembly  110  and retained within assembly  110  with retaining pin  148 . Optional knob  170  can be mechanically attached to outer sleeve  130  to allow outer sleeve  130  and proximal inner shaft  140  to rotate about the driver body assembly  110 . Optional guides  171  can be attached to outer sleeve  130  to slidably mate with spinal disc distraction instrument  950  ( FIG. 3 ). Depth control member  173  can also be fixedly or slidably attached on outer sleeve  130  for providing a predetermined insertion depth of the implant. 
         [0042]    Driver body assembly  110  includes handle  112 , handle transition  114 , strike boss  116 , trigger mechanism  120 , and pivot pin  122 . Trigger mechanism  120  can be any type of trigger mechanism known in the art. Trigger mechanism  120  pivots about pivot pin  122  in the driver body assembly  110 . When trigger mechanism  120  is squeezed toward handle  112 , the forked inner shaft  160  ( FIG. 2A-2C ) extends from actuator assembly  126  and expands to release an implant. When trigger mechanism  120  is released, forked inner shaft  160  recedes into actuator assembly  126  and compresses, thereby engaging the implant or returning to its normally closed position. Optional drag adjustment screw  124  is rotatably coupled to driver body assembly  110  for adjusting the drag force between trigger mechanism  120  and spring retaining screw  152  of actuator assembly  126 . 
         [0043]      FIGS. 2A-2C  show various forked inner shafts  160  of the present invention. Each forked inner shaft  160  includes engagement features  162  for mechanically engaging the implant. engagement features  162  may be various shapes and sizes depending upon implant selection. As shown, engagement features  162  may be dovetail-shaped ( 162   a ,  162   b ,  162   c ,  162   d ). Engagement features  162  can engage implants having multiple heights. It should be understood engagement features  162  can be any shape which can engage any type of implant. In an alternative embodiment, proximal inner shaft  140  and forked inner shaft  160  can be integral. 
         [0044]    Each forked inner shaft  160  includes female threaded hole  161  for mating to male threaded end  144  of proximal inner shaft  140  of actuator assembly  126 . It should be understood that any means known in the art can be used to attach forked inner shaft  160  to proximal inner shaft  140 . 
         [0045]    Each forked inner shaft  160  includes tapers  163  and relatively long expansion/compression slot  164  to allow forked inner shaft  160  to expand and compress during use.  FIGS. 2A-2C  show forked inner shaft  160  in the expanded position. Each forked inner shaft  160  also includes sizing slot  166  to allow for a variation of tab and forked inner shaft slot dimensional differences. Expansion/compression slot  169  ( FIG. 2B ) is an alternative embodiment of sizing slot  166 . In some embodiments, the forked member has a quick connect feature. 
         [0046]    Cephalad markers  168  can be included on a surface of forked inner shaft  160  to allow the user to determine the position of the implant. Markers  168  can be pin  168   a  or machined slots  168   b . In some embodiments, the inserter (squeeze handle) has a quick connect feature. 
         [0047]    In one method of using the present invention, and now referring to  FIGS. 4   a  and  4   b , the user first squeezes the trigger mechanism  120  ( FIG. 1 ) on the implantation instrument  100 , thereby causing the engagement features  162   c ,  162   d  on the instrument to separate. The user then approaches the target implant (in this case, a cervical plate  201 ) with the implantation instrument so that the dovetail features of these two devices align, whereby the engagement features  162  straddle the opposed engagement indents  906  on the implant. Once engagement features  162  straddle the engagement indents  906 , the user then releases the trigger mechanism  120 , causing engagement features  162  to collapse inwards and engage engagement indents  906  on the implant. 
         [0048]    In other embodiments, the reverse is provided, wherein the user squeezes the instrument to engage the implant. 
         [0049]    Now referring to  FIG. 5 , there is provided an intervertebral fusion cage  301  of the present invention. This cage comprises a front wall  303 , a back wall  304 , a pair of opposing side walls  305  connecting the front and back walls, a top surface  306  adapted to engage an upper vertebra, a bottom surface (not shown) adapted to engage a lower vertebra, and a throughhole  307  extending between the top and bottom surfaces for promoting fusion therethrough, wherein the front wall comprises a pair of recesses  311 , each recess opening onto a respective sidewall and forming a dovetail shape in the respective sidewall. The front wall of this particular cage also has screwholes  313  extending therethrough. The screwholes are typically threaded and are adapted to receive bone screws for securing the cage to opposing vertebral bodies without the need for posterior instrumentation, thereby providing “stand alone&#39; capabilities. 
         [0050]    Now referring to  FIG. 6 , also in accordance with the present invention, there is provided a spinal implant having a front wall, a pair of opposing side walls, a back wall, and top and bottom surfaces, wherein the front wall comprises a pair of recesses, each recess opening onto a respective side wall and forming at least two acute angles α and β in the respective side wall. The acute nature of these two angles in the same recess creates the condition necessary to preclude toggle and rotation. 
         [0051]    In some embodiments, the top and bottom surfaces of the implant are spaced at a distance suitable for contacting opposing vertebral endplates. This feature is advantageous for spinal implants inserted into a disc space. 
         [0052]    In some embodiments, the implant of the present invention has a throughhole extending from its top surface to its bottom surface. This throughhole feature promotes bony fusion through the implant and so provides a performance advantage for fusion cage embodiments of the present invention. 
         [0053]    In some embodiments thereof, a bone graft material is contained in the throughhole of the fusion cage. This graft material also promotes fusion through the implant and so provides a performance advantage for fusion cage embodiments of the present invention. 
         [0054]    In some implant embodiments, the fusion cage has a front wall that is manufactured separately from the remainder of the implant. Preferably, the front wall is metallic and the remainder of the implant is polymeric. This preferred embodiment advantageously provides strength in the front wall so that screw holes can pass therethrough without fracturing the wall. 
         [0055]    In some embodiments, first and second bone fasteners extend through the screwholes located in the front wall of the fusion cage. This feature allows the cage to be secured to the opposing vertebrae and so eliminates the need for posterior instrumentation. In some embodiments thereof, the first fastener further extends through the top surface of the implant, while the second fastener further extends through the bottom surface of the implant. 
         [0056]    In some embodiments, the first and second bone fasteners extend only through the front wall, as in a plate embodiment. 
         [0057]    In some embodiments, the implant has an articulation interface, as in an articulating motion disc. 
         [0058]      FIG. 3  discloses an instrument of the present invention inserting an implant of the present invention into a disc space. 
         [0059]    As shown in  FIG. 3 , distraction instrument  950  is inserted over pins (not shown) that are secured into vertebral bodies  962 ,  964 . Cervical fusion cage  330  is passed between the forks of distraction instrument  950  using implantation instrument  100  ( FIGS. 1A-1B ). In an alternate embodiment, guides  170  on insertion instrument  100  slidably engage slots in the forks of distraction instrument  950  to help the user guide cervical fusion cage  330  into prepared disc space  970 . Once the cervical fusion cage  330  is in a desired location within prepared disc space  970 , the user actuates (e.g., squeezes, or releases or rotates a knob) trigger mechanism  120  ( FIG. 1A ), which releases cervical fusion cage  330  into the prepared disc space  970 . The user can determine the desired position by observing cephalad markers  168  ( FIGS. 3A-3B ) located on a surface of forked inner shaft  160 . In an alternative embodiment, implantation instrument  100  can include a depth control member  173  ( FIG. 1A ) (which might be an adjustable and slidable), such that cervical fusion cage  330  can be inserted into prepared disc space  970  at a predetermined depth. 
         [0060]    Lastly, the implantation instrument  100  and distraction instrument  950  are removed, causing superior vertebra  962  and inferior vertebra  964  to engage cervical fusion cage  330 . 
         [0061]    Now referring to  FIG. 7 , there is provided one embodiment of an inserter tip  701  of the present invention. This inserter tip includes barrel stop  703  that prevents the bone screw from stripping. There is a distal quick connect/release feature  705  that allows for ease of connection to the remainder of the inserter instrument. Barrels  707  prevent the implant from being placed too far posteriorly. Relief features  709  on the dovetail allow for the engagement feature to disengage with ease from the implant. Lastly, barrels  711  can be a fixed barrel or adjustable via sliding member such as a ratcheting feature. 
         [0062]    Now referring to  FIG. 8 , there is provided one embodiment of a lighted inserter tip  801  of the present invention. The inserter cannula is fitted with at least one secondary lumen  803  adapted for delivering light or delivering a fiber optic. Light emanating from the secondary lumen is shown by the dashed lines in  FIG. 8 . Alternatively, light can be fed down the major lumen that holds the inserter tip (not shown). In one embodiment, at least the engagement features  805  of the tip are made of hard clear plastic that allows visibility of the other instruments passed through the barrels. 
         [0063]    While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.