Abstract:
A laterally expandable spinal implant includes a central body and two wings that are adapted to be received within an inner chamber formed within the central body. The wings have guide rails that fit into grooves defined in the central body. To ensure that the implant is properly secured, each guide rail has an outer end with a cutting surface that cuts into vertebral end plates when the wings are extended. The two wings are connected together through a central turnbuckle shaft that has geared teeth and threading on both ends that engage threaded cavities in the wings. Through the gear teeth, the turnbuckle shaft is able to be rotated so as to laterally extend the wings from the central member. A locking mechanism locks the turnbuckle shaft to prevent the wings from retracting.

Description:
BACKGROUND  
         [0001]    The present invention generally concerns spinal implants, and more specifically, but not exclusively, concerns a laterally expandable vertebral implant.  
           [0002]    A major cause of persistent, often disabling, back pain can arise by disruption of the disc annulus, chronic inflammation of the disc, or relative instability of vertebral bodies surrounding a given disc, such as might occur due to a degenerative disease. In the more severe cases, some form of mechanical limitation to the movement of the vertebrae on either side of the subject disc is necessary. In such cases, the disc tissue is irreparably damaged, thereby necessitating removal of the entire disc. However, when the disc nucleus is removed without subsequent stabilization the same disabling back pain often reoccurs due to persistent inflammation and/or instability.  
           [0003]    Various approaches have been developed to stabilize the adjacent vertebral bodies following excision of this material. In one approach, two adjacent vertebrae are fused together through a fusion device that is implanted between the vertebrae. Many of these existing implant designs have drawbacks that lower the spinal fusion rates. Among these design drawbacks, one such flaw is that the implants subside into the vertebral end plates, thereby reducing the spacing between the vertebral bodies. With prior fusion devices, and even some prosthetic devices, a large portion of the load is placed against the weakest part of the vertebral body, which can lead to cavitation of the device into the surrounding vertebral endplates with subsequent collapse of the inner discal space and even damage of the vertebrae itself. Another frequent cause for subsistence is created by having a small area of contact between the implant and the endplates. As one should appreciate, the less surface area of contact between the implant and the end plates, the greater the risk of subsistence.  
           [0004]    Another flaw of many implants is the lack of stability created after implantation. Stability is crucial to the success of a fusion. The implant must be securely fixated to the vertebral bodies in order to ensure that no movement occurs between the two. If movement does occur between the vertebral bodies and the implant, the bone may not properly fuse, thereby creating stability problems. Moreover, some designs limit the amount of graft material, which may be able to be used with the implant. The larger area of graft material that is able to contact the endplates, the better chances of a good, solid bone growth between the two vertebrae.  
           [0005]    Some designs have created implants in which the majority of the implant is positioned over the harder cortical bone of the apophyseal ring of the vertebrae in order to reduce the chances of subsistence. However, with these designs, the implant is made from multiple separate components that are individually assembled together within the disc space. Each component is implanted separately and then attached to one another within the disc space. As should be appreciated, assembling such an implant in the disc space can be rather difficult. Such implants also tend to lack a stiff central body, which is essential to the stability of the implant as well as entire fusion construct. Moreover, such implants have no mechanism to fix the implant to the vertebral body. Typically, one has to use bone screws to secure the implant to the vertebral bodies, which makes the implantation process more complicated and difficult. In addition, such implants generally have a single lateral width, and therefore, it is generally very difficult, if not impossible, to adjust for differently sized vertebrae. Another flaw is that these designs typically do not provide a mechanism for ensuring that the spacers are properly positioned. Since the lateral spacers of these types of implants are independently assembled within the disc space, the lateral members can be positioned at unequal positions along the apophyseal ring, thereby increasing the risk that the implant will subside into the vertebral end plates.  
         SUMMARY  
         [0006]    In one aspect, a spinal implant includes a cage defining an interior cavity and an expansion mechanism received in the cavity of the cage. A pair of wings are operatively coupled to the expansion mechanism, and the wings each have opposing vertebrae engaging surfaces that are configured to engage opposing vertebrae. The expansion mechanism is operable to laterally move the wings between the vertebrae from a compact configuration in which at least a majority of the wings are received in the cavity of the cage to an expanded configuration in which the wings extend from the cage with the vertebrae engaging surfaces on each of the wings engaging the vertebrae.  
           [0007]    Another aspect concerns a fusion device for implanting between opposing vertebrae that define a disc space. The device includes a central member and at least one pair of lateral members slidably coupled to the central member. The device further includes means for extending the lateral members from the central member into the disc space between the vertebrae with each of the lateral members engaging both of the vertebrae.  
           [0008]    In a further aspect, an apparatus includes a spinal implant. The spinal implant includes a central member defining an interior cavity and a pair of openings defined on opposite sides of the central member that open into the interior cavity. A pair of wings are slidably received in the openings in the central member. A shaft is coupled to the wings, and the shaft has at least one threaded portion threadedly engaging at least one of the wings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a top perspective view of a spinal implant according to one embodiment in an expanded configuration.  
         [0010]    [0010]FIG. 2 is an exploded view of the FIG. 1 implant.  
         [0011]    [0011]FIG. 3 is a top perspective view of the FIG. 1 implant in a compact configuration.  
         [0012]    [0012]FIG. 4 is an end view of the FIG. 1 implant in a compact configuration.  
         [0013]    [0013]FIG. 5 is a top perspective view of the FIG. 1 implant in an expanded configuration.  
         [0014]    [0014]FIG. 6 is an end view of the FIG. 1 implant in an expanded configuration.  
         [0015]    [0015]FIG. 7 is a perspective view of the FIG. 1 implant attached to an inserter tool.  
         [0016]    [0016]FIG. 8 is an enlarged, perspective view of the FIG. 1 implant coupled to the FIG. 7 tool.  
         [0017]    [0017]FIG. 9 is a partial cross-sectional view of the FIG. 1 implant positioned in an interdiscal space in an expanded configuration.  
         [0018]    [0018]FIG. 10 is a side view of the FIG. 1 implant in the interdiscal space.  
         [0019]    [0019]FIG. 11 is a top view of the FIG. 1 implant in the interdiscal space.  
         [0020]    [0020]FIG. 12 is a perspective view of a spinal implant according to another embodiment.  
     
    
     DETAILED DESCRIPTION  
       [0021]    For the purposes of promoting an understanding of the principles of the present invention, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is intended thereby. Any alterations and further modification in the described processes, systems, or devices, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates. Some embodiments of the invention are shown in great detail, although it will be apparent to those skilled in the relevant art that some of the features may not be shown for the sake of clarity.  
         [0022]    A laterally expandable spinal implant  100  according to one embodiment of the present invention will now be described with reference to FIGS.  1 - 6 . As shown in FIGS. 1 and 2, the implant  100  includes a central member or cage  102 , a pair of lateral members or wings  104  that are adapted to laterally extend from the cage  102 , and an expansion mechanism  106  (or means) that is operable to extend the wings  104 . In the illustrated embodiment, the expansion mechanism  106  includes a turnbuckle or threaded shaft  108  that connects the wings  104  together. In other embodiments, the expansion mechanism can include hydraulic pistons, mechanical linkages, and the like. The shaft  108  includes a gear  110  that is centrally located on the shaft  108  between opposing threaded portions  112  and  114 . In one embodiment, threads  116  on the threaded portions  1   12  and  114  are oppositely threaded (i.e., one is a left handed thread and the other is a right handed thread.) In one form of the present invention, the threads  116  of the threaded portions  112  and  114  have an equal pitch such that the wings  104  are able to extend from the central member  102  at the same rate. This ensures that the implant  100  has a symmetrical configuration, which in turn aids in centering the implant  100  over the vertebrae. The threaded portions  112  and  114  threadedly engage threaded openings  118  that are defined in each of the wings  104 . In another embodiment, only one end of the shaft  108  is threaded, while the other end of the shaft  108  is unthreaded. With this embodiment, the wings  104  are still extended by rotating the shaft  108 .  
         [0023]    Implant  100  further includes a lock mechanism  120  that is used to lock the wings  104  in an expanded configuration in which the wings  104  laterally extend from the cage  102 . In the embodiment illustrated in FIG. 1, the lock mechanism  120  includes lock cavities  122  that are defined in each of the wings  104  next to the threaded openings  118 . As illustrated in FIG. 2, the lock cavities  122  open into the threaded opening  118  in the wings  104 . In one embodiment, each lock cavity  122  is only partially threaded such that once the wings  104  are in the expanded configuration, the shaft  108  can be slid from the threaded opening  118  into the lock cavity  122 . By being only partially threaded near the entrance of the cavity  122 , the shaft  108  is unable to rotate such that the wings  104  are unable to be retracted. In another embodiment, the lock cavity  122  is unthreaded, but has a depth shallower than the threaded openings  118  so as to keep the wings  104  in the expanded configuration, when the shaft is moved into the lock cavities  122 .  
         [0024]    Referring to FIG. 2, each wing  104  includes opposing vertebrae engaging surfaces  202  that are configured to engage opposing vertebrae, as well as medial  204  and lateral  206  side surfaces. As shown, the wings  104 , according to the illustrated embodiment, have a generally tapered shape so as to coincide with the vertebral endplate geometry. The vertebrae engaging surfaces  202  generally taper from the medial sides  204  to the lateral sides  206 . To further reduce trauma upon insertion of the implant  100 , the wings  104  have beveled edges  208  between the vertebrae engaging surfaces  202  and the lateral surfaces  206 . In the illustrated embodiment, the medial sides of the wings  104  are generally flat so as to allow the wings  104  to contact one another in a compact state when the wings  104  are retracted within the cage  102 . The medial sides  204  of the wings  104  define access channels  210  around the threaded opening  114  and the lock cavity  122 . In one form, access channel  210  is sized to receive the gear  110  on the shaft  108 . The access channel  210  has an opening  212  that allows the physician to gain access and rotate the gear  110  so as to expand the implant  100 . In the illustrated embodiment, the lateral sides  206  have a generally curved shape in order to coincide with the shape of the apophyseal ring of the vertebrae.  
         [0025]    With continued reference to FIG. 2, the cage  102  has a proximal or tool engaging end wall portion  214 , an opposite distal end wall portion  216 , and a pair of opposing lateral wall portions  218  that together define an interior cavity  220 . The cage  202  further has a pair of opposing vertebrae engaging surfaces  222  that are configured to engage opposing vertebrae. To coincide with vertebrae geometry, surfaces  222  in the illustrated embodiment are tapered such that surfaces  222  angle towards one another from the proximal end wall portion  214  to the distal end wall portion  216 . As shown, the interior cavity  220  extends through both vertebrae engaging surfaces  222 . In the illustrated embodiment, the cage  102  has a generally rectangular shape. The vertebrae engaging surfaces  222  can include texturing so as to prevent expulsion of the implant  100  from the vertebrae. For instance, the vertebrae engaging surfaces  222  in the illustrated embodiment have ridges  224  that aid in preventing expulsion of the implant  100 . As should be appreciated, in other forms of the present invention, the vertebrae engaging surfaces  222  can include other types of texturing for preventing expulsion of the implant  100 . The proximal end wall portion  214  defines a tool opening  226  through which an insertion tool can be inserted into the interior cavity  220 , and lateral walls  218  define wing openings  228  through which the wings  104  are slidably received into the interior cavity  220 .  
         [0026]    [0026]FIGS. 3 and 4 illustrate the implant  100  when in a compact state in which the wings  104  are retracted inside the interior cavity  220 . As shown in FIG. 3, the wings  104  have one or more guide rails  302  that engage corresponding guide channels  304  formed around the wing openings  228 . In the illustrated embodiment, each wing  104  has four guide rails, with a pair positioned along each opposing vertebrae engaging surface  202  of the wing  104 . In order to provide further stability, the guide rails  302  and the corresponding channels  304  in the illustrated embodiment have a general dovetail shape. Moreover, as discussed in further detail below, the dovetail shape of the guide rails  302  ensure that the wings  104  remain secure in the vertebrae once implanted. When the implant  100  is in a compact state, the majority of the wings  104  are received in the interior cavity  220  of the cage  102 . In the compact state, the medial sides  204  contact each other and the entrances  212  of the access channels  210  define an access opening  306  through which an insertion tool can gain access to gear  110  on shaft  108  in order to rotate the shaft  108 .  
         [0027]    As previously mentioned, the gear  110  is used to rotate the shaft  108 , thereby causing the wings  104  to extend from the cage  102 . FIGS. 5 and 6 show the implant  100  with the wings  104  in a laterally expanded state in which the wings  104  extend from the cage  102 . As should be appreciated, the expansion mechanism  106  allows the wings  104  to extend at varying distances from the cage  102  such that the size of the implant  100  can be adjusted to correspond to the size of the selected vertebrae. As shown in FIG. 6, outer lateral ends  402  of the guide rails  302  define an inward notch  404  such that the outer lateral ends  402  form cutting edges  406 . As the wings  104  are extended, the cutting edges  406  cut channels into the vertebrae. The cutting edges  406  act like spikes to embed the wings  104  into the vertebral endplates. Once the wings  104  are extended, the dovetail shape of the guide rails  302  help to ensure that the wings  104  are firmly secured to the vertebrae. Once the wings  104  are in the desired extended position, the shaft  108  is then slid into the lock cavity  122  (FIG. 2) in order to lock the wings  104  in the desired extended position. After implantation, bone graft material can be packed into the interior cavity  220  via tool opening  226  to promote fusion of the vertebrae. With the wings  104  slightly extended, bone graft material can even be packed before implantation. Following implantation, the interior cavity  220  provides a large area in which a fusion mass can be formed between the vertebrae.  
         [0028]    An implant inserter assembly  700  that includes the implant  100  coupled to an inserter  702  according to one embodiment of the present invention is illustrated in FIGS. 7 and 8. The inserter  702  includes a driving handle  704 , an actuation knob  706 , a shaft portion  708 , a gripping knob  710  and a head portion  712 . In the illustrated embodiment, the handle portion  704  is solid and includes an impaction surface  714  against which a hammer or the like can strike to drive implant  100  between the vertebrae. The actuation knob  706  is connected to a drive shaft  802 , which extends from the actuation knob  706 , through the shaft  708 , and through the head  712 . When the implant  100  engages the inserter  702 , the actuation knob  706  is able to extend the wings  104 . As shown in FIG. 8, the drive shaft  804  has at one end a drive gear  804  with teeth  806  that engage an intermediate gear  808  that is coupled to the head  712  through a carrier member  810 . During implantation, the intermediate gear  808  engages gear  110  on the shaft  108  of the implant  100 . As the actuation knob  706  is rotated, the drive shaft  802  rotates drive gear  804 . In turn, the drive gear  804  rotates the intermediate gear  808 , which then is used to rotate the shaft  108  in order to extend the wings  104 . The gripping knob  710  is rotated in order to extend gripping fingers  812  inside the interior cavity  220  such that the inserter  702  engages the tool opening  226  of the implant  100 . The gripping knob  710  and the gripping fingers  812  can be optional, such that in one embodiment knob  710  and fingers  812  are not included. To provide a large surface area for impaction, the head  712  has a generally rectangular shape to generally coincide with the shape of the proximal end wall portion  214  of the implant  100 .  
         [0029]    [0029]FIGS. 9, 10 and  11  show various views of the implant  100  when implanted between adjacent vertebrae  902  and  904 . Before implantation, a portion of the annulus is removed to create a larger disc space for the implantation of the implant  100 . The vertebral end plates are prepared by removing cartilaginous material connected to them. A window  906 , which generally corresponds in shape and size to the cage  102 , is formed in both vertebrae  902  and  904 . Before implantation, the wings  104  are positioned in their retracted position inside the interior cavity  220  of the implant  100 , and the implant  100  is attached to the inserter  702  in the manner as illustrated in FIG. 7. The implant  100  is then impacted into the window  906  formed between vertebrae  902  and  904 . Rotation of the actuation knob  706  on the inserter  702  causes the shaft  108  on the implant  100  to rotate, thereby expanding the implant  100 . As previously mentioned, this causes the wings  104  to laterally expand from the cage  102  between the vertebrae. In one embodiment, the wings  104  are extended from the cage  102  at the same rate to ensure that the implant  100  remains centered between the vertebrae  902  and  904 . As the wings  104  extend, the cutting edges  406  of the guide rails  302  cut into the vertebrae  902  and  904 , thereby ensuring that the implant is securely fastened to the vertebrae  902  and  904 . The wings  104  are expanded until they are positioned over the apophyseal ring, which contains the harder cortical bone. As shown in FIG. 9, the shape of the wings  104  generally correspond to the geometry of the end plates of vertebrae  902  and  904 . Due to the large surface area provided by the implant  100  and by being supported on the harder cortical bone of the apophyseal ring, the risk of subsidence of the implant  100  into the vertebrae  902  and  904  is reduced. Moreover, the construction of implant  100  allows for the implant to have variable dimensions such that the implant  100  can accommodate vertebrae of varying sizes. Once the implant  100  has been expanded to the desired expansion configuration, the turnbuckle  108  can be moved into the block cavity  122  such that the wings  104  are locked into position.  
         [0030]    Referring to FIG. 12, an implant  1200  according to another embodiment of the present invention incorporates a number of the same features described above, with the exceptions noted below. As should be appreciated, the locking mechanism  120  in this embodiment differs from the one described above. In the embodiment illustrated in FIG. 12, the locking mechanism  120  includes a leaf spring  1202  that is attached to the distal end wall portion  216  of the cage  102 . As shown, the leaf spring  1202  engages the gear  110  on the shaft  108 . The leaf spring  1202  is positioned such that the shaft  108  can only be rotated in one direction so that the wings  104  can only move in a laterally expanding direction. The spring  1202  resists rotation of the shaft in the opposite direction, so that once the wings  104  are extended to the desired location the spring  1202  locks the wings  104  into position.  
         [0031]    While specific embodiments of the invention have been shown and described in detail, the breadth and scope of the present invention should not be limited by the above described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents. It is understood that only selected embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.