Abstract:
The present invention teaches an improved spinal fusion implant and method of implanting same. The implant includes a shell and an insert, the insert capable of situating first and second plates of the shell with respect to each other and of preventing unwanted loosening of fasteners placed through the shell and into the adjacent vertebral bodies. The method includes implanting a shell, selecting an insert from a plurality of inserts, and placing an insert between first and second plates of the shell.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. application Ser. No. 12/387,963 filed May 8, 2009, the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention is directed to spinal implants, and more particularly, spinal fusion implants. 
         [0003]    The deterioration of vertebral bodies and/or vertebral discs is a major cause of back and neck pain in many patients. Through the years, many different techniques for restoring the natural anatomical spacing in the spine and thereby alleviating this pain have been developed and practiced by surgeons. For instance, implants and techniques for implanting such implants have been designed to preserve motion between adjacent vertebral bodies. These motion preserving implants are adapted to emulate a removed spinal disc. Examples of such implants (and the methods of implanting same) are disclosed in U.S. Pat. No. 6,989,032 (“the &#39;032 patent”) and U.S. Pat. No. 7,169,182 (“the &#39;182 patent”), the disclosures of which are hereby incorporated by reference herein. Nonetheless, even given the success of such motion preserving devices, it is still sometimes necessary to fuse adjacent vertebral bodies so that no movement is permitted therebetween. 
         [0004]    Spinal fusion surgery typically involves removing the disc material from between adjacent vertebral bodies, which thereby creates an empty intervertebral space. In this space is implanted an implant or cage that is then fixably mounted to the end plates of the adjacent vertebral bodies. Bone growth is often permitted through the implant, and is in fact sometimes provoked by the placement of bone growth inducing substances within the cage. However, even given this bone growth through the cage, it is sometimes necessary to at least initially mount the cage to the vertebral bodies through the use of fixation elements such as screws. Furthermore, it has also determined that providing an angled implant or cage can aid in returning the adjacent vertebral bodies to their natural “lordotic” angle. 
         [0005]    Even if a surgeon initially determines that he or she wishes to perform a motion preserving surgery on a patient, sometimes it becomes apparent during the procedure that a fusion procedure would benefit the patient. Likewise, surgeons often recognize the need to fuse vertebral bodies at levels adjacent to the initial one in question. Thus, it is desirable to have a fusion implant that can easily be implemented and implanted utilizing the tools and procedure used in a motion preserving surgery. Moreover, it is also desired to have such a fusion implant be easily implanted using those tools, easily affixed to the intervertebral bodies, and prevented from becoming dislodged even after just initially being implanted. 
         [0006]    Therefore, there exists a need for an improved spinal fusion device. 
       SUMMARY OF THE INVENTION 
       [0007]    A first aspect of the present invention is a spinal implant for fusing together first and second vertebral bodies. In accordance with one embodiment of this first aspect, the implant includes a first member having a first surface for engaging the first vertebral body, a second surface, and a first opening extending between the first and second surfaces. The implant also includes a second member having a third surface for engaging the second vertebral body, a fourth surface, and a second opening extending between the third and fourth surfaces. A living hinge connecting the first and second members is also included and preferably allows for movement of the first and second members with respect to one another. Finally, an insert is disposed between the first and second members, the insert covering the first and second openings about the second and fourth surfaces. 
         [0008]    In accordance with other embodiments of the first aspect, the second and fourth surfaces may include a projection for retaining the insert between the first and second members, and in other embodiments each of the second and fourth surfaces include these projections. The insert may be constructed of bone, polymer, metal, or the like. Furthermore, the implant may include a first screw disposed in a first opening and a second screw disposed in a second opening, and the insert may include a portion for preventing backout of the first and second screws. In still further embodiments, the first member may include a third opening extending between the first and second surfaces, and the second member may include a fourth opening extending between the third and fourth surfaces. In this embodiment, the insert may include a main body, a first portion for covering the first and second openings, and a second portion for covering the third and fourth openings. The insert may also include an aperture for engagement with a tool. In accordance with this further embodiment, a first screw may be disposed in the first opening, a second screw may be disposed in a second opening, a third screw may be disposed in the third opening, and a fourth screw may be disposed in the fourth opening. The insert includes a first portion for preventing backout of the first and second screws and a second portion for preventing backout of the third and fourth screws. Finally, in accordance with certain embodiments, the implant may include a bone growth aperture extending through the first member, the insert, and the second member, and the implant may be designed to provide a nonparallel relationship between the first and second surfaces, such that the vertebral bodies exhibit a similar relationship. 
         [0009]    The second aspect of the present invention is also directed to a spinal implant for implantation between first and second vertebral bodies. In accordance with one embodiment of this second aspect, the implant includes a shell and an insert. The shell preferably includes a first plate for engaging the first vertebral body, the first plate including a first hole formed therethrough, a second plate for engaging the second vertebral body, the second plate including a second hole formed therethrough, and a resilient member connecting the first and second plates. The insert on the other hand may include a main body and a portion capable of covering at least one of the first or second holes when the insert is disposed between the first and second plates. 
         [0010]    In accordance with other embodiments of the second aspect, the implant may include a first screw disposed in the first hole, and a second screw disposed in the second hole. A portion of the insert is preferably capable of preventing backout of both of the first and second screws when the insert is disposed between the first and second plates. The insert may be constructed at least partially from materials selected from the group consisting of bone, polymer, and metal. At least one of the first and second plates may include a projection for retaining the insert between the first and second plates, but in certain embodiments both the first and second plates may include such projections. The implant may also include a third hole formed through the first plate and a fourth formed through the second plate, and a first screw disposed in the first hole, a second screw disposed in the second hole, a third screw disposed in the third hole, and a fourth screw disposed in the fourth hole. The insert may include a first portion for preventing backout of the first and second screws and a second portion for preventing backout of the third and fourth screws. A bone growth aperture may extend through the first member, the insert, and the second member. The insert may include an aperture for engagement with the tool. Preferably, the first and second plates are located in nonparallel planes, and such may be caused by the insert being placed therebetween. 
         [0011]    The third aspect of the present invention is a method of fusing together first and second vertebral bodies. In accordance with one embodiment of the present invention, the method includes the steps of preparing a space between the first and second vertebral bodies to a spinal implant, implanting a shell, the shell including a first plate, a second plate, and a living hinge connecting the first and second plates, placing a first screw through the first plate and into the first vertebral body, placing a second screw through the second plate and into the second vertebral body, and inserting an insert between the first and second plates, wherein the insert prevents backout of the first and second screws. 
         [0012]    In accordance with other embodiments of this third aspect, the inserting step may cause the first and second plates to move with respect to each other and such movement between the first and second plates is preferably translated to the first and second vertebral bodies. The method may also include the step of choosing an insert from a plurality of inserts. Moreover, the method may include the step of placing a third screw through the first plate and into the first vertebral body, and the step of placing a fourth screw through the second plate in the intervertebral body. Preferably, the insert prevents backout of the first, second, third, and fourth screws. The method may also include the step of retaining the insert between the first and second plates, where this retaining step may include engaging the insert with projections formed on the first and second plates. Finally, the method may also include the step of allowing bone growth through an aperture formed through the first plate, the insert, and the second plate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    A more complete appreciation of the subject matter of the present invention and the various advantages thereof can be realized by reference to the following detailed description with reference to the accompanying drawings in which: 
           [0014]      FIG. 1  is a perspective view of an intervertebral fusion implant according to one embodiment of the present invention. 
           [0015]      FIG. 2  is a front view of the implant shown in  FIG. 1 . 
           [0016]      FIG. 3  is a rear view of the implant shown in  FIG. 1 . 
           [0017]      FIG. 4  is a right side view of the implant shown in  FIG. 1 . 
           [0018]      FIG. 5  is a top view of the implant shown in  FIG. 1 . 
           [0019]      FIG. 6  is a cross-sectional view of the implant shown in  FIG. 1  taken along line A-A of  FIG. 5 . 
           [0020]      FIG. 7  is a perspective view of a shell from the implant of  FIG. 1 . 
           [0021]      FIG. 8  is a front view of the shell shown in  FIG. 7 . 
           [0022]      FIG. 9  is a right side view of the shell shown in  FIG. 7 . 
           [0023]      FIG. 10  is a perspective view of an insert from the implant shown in  FIG. 1 . 
           [0024]      FIG. 11  is a front view of the insert shown in  FIG. 10 . 
           [0025]      FIG. 12  is a rear view of the insert shown in  FIG. 10 . 
           [0026]      FIG. 13  is a right side view of the insert shown in  FIG. 10 . 
           [0027]      FIG. 14  is a top view of the insert shown in  FIG. 10 . 
           [0028]      FIG. 15  is a prospective view of adjacent vertebral bodies having been prepared to receive a fusion implant. 
           [0029]      FIG. 16  is a prospective view of the vertebral bodies of  FIG. 15  having the shell shown in  FIG. 7  implanted therebetween. 
           [0030]      FIG. 17  is a prospective view similar to the one shown in  FIG. 16  with screws implanted through the shell and into the adjacent vertebral bodies. 
           [0031]      FIG. 18  is a view similar to that of  FIG. 17  with the insert of  FIG. 10  partially implanted. 
           [0032]      FIG. 19  is a view similar to  FIG. 18  with the insert completely implanted. 
       
    
    
     DETAILED DESCRIPTION 
       [0033]    Referring to the drawings, wherein like reference numerals refer to like elements,  FIGS. 1-6  depict a first embodiment intervertebral fusion device or spinal implant for fusing together first and second vertebral bodies, designated generally by reference numeral  10 . As is shown in the drawings, implant  10  includes a shell  12  and an insert  14 . Moreover, implant  10  is also provided with a plurality of fasteners (shown in the drawings as screws  16   a - d ) for placement through portions of the shell and into adjacent vertebral bodies. However, one of ordinary skill in the art would readily recognize that other types of fasteners could be utilized, e.g., pins or the like. The specifics of each of the components of implant  10 , as well as their operation and use will be discussed more fully below. 
         [0034]    As is shown in  FIGS. 1-6  and even more specifically shown in  FIGS. 7-9 , shell  12  includes a first plate or member  18 , a second plate or member  20 , and a pair of resilient or living hinge members  22   a  and  22   b.  First member  18  includes a first surface  24  for engaging an upper vertebral body, a second surface  26  for engagement with insert  14 , a plurality of bone growth apertures collectively referred to by reference numeral  28 , and two fastener holes  30  and  32 . First surface  18  is formed with a plurality of vertebral body engaging members, including teeth  34  and surfaces  36 . Second surface  26  is formed with countersunk surfaces  38  and  40  in the vicinity of fastener holes  30  and  32 , respectively, and a projection  42  extending toward second member  20 . Similarly, second member  20  includes a third surface  44  for engagement with the lower vertebral body, a fourth surface  46  for engagement with insert  14 , a plurality of bone growth apertures collectively referred to with reference numeral  48 , and two fastener holes  50  and  52 . Also in a similar fashion to first member  18 , third surface  44  is formed with vertebral engaging elements including teeth  54  and surfaces  56 , while second surface  46  includes countersinks  58  and  60  in the vicinity of fastener holes  50  and  52 , respectively, and projection  62  extending toward first  18 . Moreover, as is best shown in  FIG. 8 , extending from second surface  26  of first member  18  are extensions  64  and  66 , and extending from fourth surface  46  of second member  20  are extensions  68  and  70 . These extensions create a substantially rectangular space  72  for reception of insert  14 , as will be discussed more fully below. First plate  18  may also include apertures  74  and second plate  20  may include apertures  76 , which are utilized in engaging an insertion tool. 
         [0035]    Resilient members  22   a  and  22   b  are shown as living hinges. Essentially, these elements are curved elements being made of a material capable of bending upon an application of force to one of or both of first and second members  18  and  20 . For example, upon placement of differently sized inserts  14  between the first and second members, hinges  22   a  and  22   b  are capable of allowing for the expansion or the contraction of the device. While shown in the drawings as being composed of the same material as first and second members  18  and  20 , it is noted that members  22   a  and  22   b  can be constructed of different materials. Likewise, the overall shape of members  22   a  and  22   b  can vary from the rounded structures shown in the drawings. 
         [0036]    In the embodiment shown in the drawings, shell  12  is formed of titanium, but it is noted that other materials such as stainless steel, polymer, or the like can be utilized. It is also noted that the specific configuration of shell  12  may widely vary in different embodiments of the present invention. For example, the overall shape of the shell which is shown as being similar in nature to the implants shown and described in the &#39;032 and &#39;182 patents, but may vary depending upon the different portion of the spine in which it is to be implanted or the design of an implant of which it is to emulate. The vertebral engaging surfaces may also vary, including the specific vertebral engaging members disposed thereon. Furthermore, the apertures extending through the first and second members may vary, including the overall amount of bone growth apertures and screw holes. While fastener holes  30 ,  32 ,  50 , and  52  are shown as being angled, other angles and/or perpendicular configurations are contemplated. Likewise, the configuration of projections  42  and  62  may also vary as can the space  72  for accepting insert  14 . 
         [0037]    Turning now to the configuration of insert  14 , it is noted that such is preferably of a unitary construction. However, in other embodiments, different configurations are contemplated. With specific reference to  FIGS. 10-14 , insert  14  includes a main body  80  having a front face  82 , a rear face  84 , a top surface  86 , a bottom surface  88 , a left side surface  90 , and a right side surface  92 . Extending from the left and right are flanges  94  and  96 , such that they form a continuous surface with front face  82 , flange  94  includes a rear face  95 , and flange  96  includes a rear face  97 . In addition, as is shown in the drawings, formed through top surface and bottom surface is an aperture  98 , which generally cooperates with apertures  28  and  48  of first and second members  18  and  20 , respectively, in order to provide for a bone growth channel between adjacent vertebral bodies. Finally, front face includes an aperture  100 , which is shown as being threaded for engagement with an insertion tool (not shown). 
         [0038]    It is to be understood that insert  14  may widely vary from that which is shown in the drawings. For one, insert  14  may vary to properly cooperate with variations of shell  12 . Certain portions of insert  14  may also vary and still be capable of cooperating with shell  12  as shown. For instance, flanges  94  and  96  may simply be extensions of front face  82  (i.e., rectangular) rather than the rounded structures that are illustrated in the drawings. Moreover, aperture  100  may be configured differently to engage an insertion tool (not shown). For instance, insert  14  may include an aperture  100  which is meant to cooperate with a spring detent or the like. Additionally, insert  14  may include a differently configured aperture  98  (or multiple apertures) for cooperation with like apertures formed in first and second members  18  and  20  of shell  12 . Finally, insert  14  may be constructed of many different types of materials. For example, it is contemplated to form insert  14  of PEEK™ or of a biological material such as bone. In the case of the latter, the patient&#39;s own bone may be utilized to form insert  14  by any one of many known processes. 
         [0039]    During a surgical procedure in which the above-discussed implant  10  is implanted, the surgeon first sees to the preparation of the intervertebral space between the adjacent vertebral bodies in order to be capable of receiving shell  12 . This is shown in  FIG. 15  and may include the removal of disc material and/or the preparation of the end plates of the vertebral bodies. Shell  12  is then inserted in the prepared space (see  FIG. 16 ). In this regard, an insertion tool (not shown) may be engaged with apertures  74  and/or  76  of the first or second plates, or shell  12  may simply be placed by hand into the space. The above-discussed features of surfaces  24  and  44  (i.e., spikes  34  and surfaces  36 ) may aid in the retainment of shell  12  between the adjacent vertebral bodies. Once in place, fasteners (such as screws  16   a - 16   d  shown in  FIGS. 1-6 ) may be placed through fastener holes  30 ,  32 ,  50 , and  52  and into the adjacent vertebral bodies (see  FIG. 17 ). Once again, it is noted that fastener holes  30 ,  32 ,  50 , and  52  may be angled in any fashion to allow for specific placement of the fasteners through shell  12  and into the intervertebral bodies. It is noted that although the fasteners are shown in  FIGS. 1-6  as screws having specific configurations, many different fastener configurations may be employed in fixing shell  12  to adjacent vertebral bodies, including differently configured screws. 
         [0040]    With shell  12  in place, insert  14  may then be placed between first and second plates  18  and  20 , preferably into above-discussed space  72 . Insert  14  partially inserted into shell  12  is shown in  FIG. 18 . In placing insert  14 , a tool (not shown) may be engaged with the threading of aperture  100 , or, in the case of a differently configured aperture, another type of connection. Prior to engaging the insert with the tool, a surgeon may select one insert  14  from a plurality of differently sized and/or shaped inserts. These different inserts ultimately affects the disposition of plates  18  and  20  of shell  12 . For example, a larger sized insert would increase the distance between plates  18  and  20 , while differently shaped inserts may affect the amount of angle between the plates. Thus, depending upon the spacing or lordotic angle desired between adjacent vertebral bodies, different inserts having different sizes and/or differently angled upper and lower surfaces may be selected. 
         [0041]    Once the surgeon makes the proper determination of the insert to utilize, it is coupled with a tool (not shown) or placed by hand between plates  18  and  20  (see  FIG. 18 ). This placement of the insert preferably moves plates  18  and  20 , and thusly the adjacent vertebral bodies to the position desired. Living hinges  22   a  and  22   b  allow for this movement while at the same time forcing plates  18  and  20  toward insert  14 . At a certain point, front face of insert  14  is pushed past projections  42  and  62  so that the insert is forcibly maintained within space  72  of shell  12  (see  FIG. 19 ). In this regard, it is noted that projections  42  and  62  are designed as ramps, which preferably allow for the easy insertion of insert  14  within space  72 . However, once front face of insert  14  passes projections  42  and  62 , the insert is thereby retained within the space. It is noted that other configurations for projections  42  and  62  may be employed. Once in this position, flanges  94  and  96  of insert  14  are disposed at least partially over a portion of the fasteners placed within fastener holes  30 ,  32 ,  50 , and  52 . In the preferred embodiment shown in the drawings, flanges  94  and  96  are placed over the heads of screws  16   a - 16   d  (best shown in  FIG. 2 ). This final position for insert  14  and its projections preferably prevents the loosening or backout of the screws that may occur. In other words, flanges  94  and  96  prevent the screws from coming out of the vertebral bodies. 
         [0042]    As is mentioned above, insert  14  may be made of various materials. For example, the insert may be constructed at least partially of metal, polymer, and/or bone material. In the latter case, insert  14  may encourage growth of bone through aperture  28 , aperture  98 , and aperture  48  to thereby fuse the adjacent vertebral bodies. Furthermore, it is contemplated that bone growth including substances may be placed within these apertures (or one of the apertures) in order to even further facilitate or, in the case of inserts constructed of nonbone material, promote such growth. It is contemplated that other embodiments of shell  12  and insert  14  may include additional apertures which promote further grown from adjacent vertebral bodies therethrough. 
         [0043]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.