Abstract:
A vertebral implant for use in establishing desired spinal curvatures includes separate implant bodies. Each body may include an associated angle between inferior and superior surfaces of the body. Further, the implant bodies may be stacked so that the associated angles are oriented in different anatomical planes. The implant bodies may be secured to one another with a connector. The implant bodies may be used either independently or in conjunction with one another to achieve a desired spinal curvature. Each implant body may include bone engagement features that extend outward from the superior and inferior surfaces of the implant body. The implant bodies may include recesses that are positioned to correspond to the bone engagement protrusions in other implant bodies to allow contact between the inferior and superior surfaces of the respective implant bodies.

Description:
BACKGROUND 
     The human spine serves many functions. The vertebral members of the spinal column protect the spinal cord. Furthermore, moveable facet joints and resilient discs disposed between the vertebral members permit motion between individual vertebral members. The spinal column also supports other portions of the human body. When viewed from a posterior or anterior direction, the vertebral members are generally aligned, although the width of the vertebral members generally increases from the cervical region to the lumbar region. However, when viewed from a lateral direction, the spine is curved to absorb loads and maintain the balance of the upper body. Abnormal curvatures may occur in some patients. For example, kyphosis may describe an exaggerated posterior curvature in the thoracic region. Lordosis may describe an exaggerated anterior curvature of the lumbar region. Scoliosis may describe an abnormal lateral curvature. 
     The composite sum of the angular relation between adjacent vertebral members makes up the overall curvature of the spine. Thus, one technique to correct abnormal spinal curvatures is to insert interbody implants that include a desired correction angle between vertebral bodies in the spine. The correction angle may be in the coronal plane or the sagittal plane. It is certainly possible to include implants that provide both coronal and sagittal correction of multiplanar defects. For example, a single interbody implant may provide a desired angular correction in the coronal plane and a separate desired angular correction in the sagittal plane. An implant with this configuration provides a compound correction that is the vector combination of the two corrections. A full set of implants may be provided that account for all possible corrections in both coronal and sagittal planes. However, when one considers the number of correction angles that are possible in both directions, it becomes impractical to manufacture, stock, and have available all of the possible combinations for implantation into a patient. Furthermore, implants that provide correction in both coronal and sagittal planes provide a unique combination of correction angles that are likely unusable in most cases. 
     SUMMARY 
     Illustrative embodiments disclosed herein are directed to a vertebral implant for use in establishing desired spinal curvatures. The vertebral implant may include separate implant bodies. Each body may include an associated angle between inferior and superior surfaces of the implant body. Further, the implant bodies may be stacked so that the associated angles are oriented in different anatomical planes. For example, the associated angle in one body may correspond to a coronal plane in a patient while the associated angle in another body may correspond to a sagittal plane in a patient. 
     The implant bodies may be secured to one another with a connector. The implant bodies may be used either independently or in conjunction with one another to achieve a desired spinal curvature. Each implant body may include bone engagement features that extend outward from the superior and inferior surfaces of the implant body. The implant bodies may include recesses that are positioned to correspond to the bone engagement protrusions in the other implant bodies to allow contact between the inferior and superior surfaces of the respective implant bodies. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a vertebral implant according to one embodiment; 
         FIG. 2  is a top view of a vertebral implant according to one embodiment shown relative to a vertebral body; 
         FIG. 3  is an anterior view of a vertebral implant illustrating a set of different coronal angle implants according to one embodiment; 
         FIG. 4  is a lateral view of a vertebral implant illustrating a set of different sagittal angle implants according to one embodiment; 
         FIG. 5  is a perspective view of a vertebral implant according to one embodiment; 
         FIG. 6  is a perspective view depicting an exploded assembly of a vertebral implant according to one embodiment; 
         FIG. 7  is an anterior view of a coronal angle implant according to one embodiment; 
         FIG. 8  is a perspective view of a coronal angle implant according to one embodiment; 
         FIG. 9  is a perspective view of a coronal angle implant according to one embodiment; 
         FIG. 10  is a lateral view of a sagittal angle implant according to one embodiment; 
         FIG. 11  is a perspective view of a sagittal angle implant according to one embodiment; 
         FIG. 12  is a perspective view of a sagittal angle implant according to one embodiment; 
         FIG. 13  is a top view of a vertebral implant according to one embodiment shown relative to a vertebral body; 
         FIG. 14  is a top view of a vertebral implant according to one embodiment shown relative to a vertebral body; 
         FIG. 15  is a perspective view of a vertebral implant according to one embodiment; 
         FIG. 16  is an anterior view of a vertebral implant according to one embodiment; and 
         FIG. 17  is a lateral view of a vertebral implant according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The various embodiments disclosed herein relate to a vertebral implant in which interchangeable sets of coronal angle implants and sagittal angle implants may be used either independently or in conjunction with one another to achieve a desired angle of spinal correction. Reference number  10  in  FIG. 1  generally identifies one example of an implant with a coronal angle implant  20  in a stacked configuration with a sagittal angle implant  30 . The representative vertebral implant  10  is illustrated as a disc replacement implant that is inserted between vertebral bodies of a patient as part of a disc replacement surgery. In addition, the vertebral implant  10  may include a height sufficient to replace one or more vertebral levels as part of a vertebrectomy or corpectomy surgery. The vertebral implant  10  is illustrated with the coronal angle implant  20  disposed superior to the sagittal angle implant  30 , though it should be understood that the opposite relationship may be used as desired. 
     The vertebral implant  10 , including the coronal angle implant  20  and sagittal angle implant  30  may be constructed from biocompatible metal alloys such as titanium, cobalt-chrome, and stainless steel. The vertebral implant  10  may be constructed from non-metallic materials, including for example, ceramics, resins, or polymers, such as UHMWPE and implantable grade polyetheretherketone (PEEK) or other similar materials (e.g., PAEK, PEKK, and PEK). The vertebral implant  10  may be constructed of synthetic or natural bone or bone composites. The coronal angle implant  20  and sagittal angle implant  30  may be constructed of the same or different materials. For example, the coronal angle implant  20  may include a different modulus of elasticity than the sagittal angle implant  30  to provide more or less resistance to motion in a given plane. Furthermore, coronal angle implant  20  and the sagittal angle implant  30  may include the same or different heights. Those skilled in the art will comprehend a variety of material choices that are suitable for the illustrated vertebral implant  10 . 
     As suggested above, the exemplary vertebral implant  10  may be inserted between vertebral bodies in the region normally occupied by an interbody disc.  FIG. 2  illustrates the vertebral implant  10  in position relative to a dashed line representation of a vertebral body V.  FIG. 2  also illustrates a sagittal reference plane SP and a coronal reference plane CP. As shown, the sagittal plane SP is the imaginary anatomical plane that bilaterally separates the body into left and right halves. The coronal plane CP is the imaginary anatomical plane that separates the body into anterior and posterior regions.  FIGS. 3 and 4  illustrate anterior and lateral views of the exemplary vertebral implant  10  according to the view lines shown in  FIG. 2 . Specifically,  FIG. 3  is shown from a direction substantially normal to the coronal plane while  FIG. 4  is shown from a direction substantially normal to the sagittal plane. 
       FIGS. 3 and 4  show that the coronal angle implant  20  and the sagittal angle implant  30  are substantially tapered or wedge-shaped in a particular direction.  FIG. 3  depicts a coronal angle a associated with the coronal angle implant  20 . By comparison, the sagittal angle implant  30  does not include any significant angle or tilt in the coronal plane. In other words, selecting an appropriate coronal angle implant  20 , independent of the selected sagittal angle implant  30 , may provide a desired coronal angle correction α. To that end,  FIG. 3  also shows various alternative coronal angle implants  20   a - c  that may be used in lieu of coronal angle implant  20  if different coronal angles, α 1 , α 2 , or α 3  are desired. Together, the coronal angle implants  20 ,  20   a - c  may form part of a set  22  of coronal angle implants that comprises individual implants that include different coronal angles. The set  22  may include individual implants that include different heights as well. As a non-limiting example, the set  22  may include a plurality of different implants, each including a different coronal angle α varying from about −20 degrees to about +20 degrees. Furthermore, each coronal angle implant  20 ,  20   a - c  may include a designator  24  to distinguish the individual implant  20 ,  20   a - c  from others in the set  22 . In one embodiment, the designator  24  may include a graphical marking indicating the coronal angle in degrees. In one embodiment, the designator  24  may include an alphanumeric identifier representing one of a sequence of characters. In one embodiment, the designator  24  may include a color code. In each case, the designator  24  may be engraved, etched, printed, marked, adhered, or otherwise displayed on the coronal angle implant  20 ,  20   a - c  or on packaging associated with the implant. Other possible designators  24  may be used as well. 
       FIG. 4  depicts a sagittal angle β associated with the sagittal angle implant  30 . By comparison, the coronal angle implant  20  does not include any significant angle or tilt in the sagittal plane. In other words, selecting an appropriate sagittal angle implant  30 , independent of the selected coronal angle implant  20 , may provide a desired sagittal angle β. Similar to  FIG. 3 ,  FIG. 4  shows various alternative sagittal angle implants  30   a - c  that may be used in lieu of sagittal angle implant  30  if different sagittal angles, β 1 , β 2 , or β 3  are desired. Together, the sagittal angle implants  30 ,  30   a - c  may form part of a set  32  of sagittal angle implants that includes individual implants with different sagittal angles β. The set  32  may include individual implants that include different heights as well. As a non-limiting example, the set  32  may include a plurality of different implants, each including a different sagittal angle β varying from about −40 degrees to about +40 degrees. Furthermore, each sagittal angle implant  30 ,  30   a - c  may include a designator  34  to distinguish the individual implant  30 ,  30   a - c  from others in the set  32  as described above. 
       FIG. 5  depicts one embodiment of a vertebral implant  110  incorporating a coronal angle implant  120  and a sagittal angle implant  130  as described above. The embodiment shown in  FIG. 5  also includes a connector  140  that holds the coronal angle implant  120  and the sagittal angle implant  130  together.  FIG. 6  illustrates an exploded view of the vertebral implant  110  and more clearly shows various features of the coronal angle implant  120  and the sagittal angle implant  130 . 
     The illustrated connector  140  includes an I-beam cross section and is sized to fit within a similarly shaped recess  142  that is formed in the coronal angle implant  120  and the sagittal angle implant  130 . One portion  142   a  of the recess  142  is formed in the coronal angle implant  120  while the other portion  142   b  of the recess  142  is formed in the sagittal angle implant  130 . In one embodiment, the recess  142  is symmetrically distributed within the coronal angle implant  120  and the sagittal angle implant  130 . In one embodiment, a majority of the recess is disposed in one or the other of the coronal angle implant  120  and the sagittal angle implant  130 . The connector  140  includes enlarged portions  144 , 148  disposed on opposite ends of a narrow intermediate portion  146 . When the enlarged end portions  144 ,  148  are inserted into the corresponding portions  142   a ,  142   b  of the recess  142 , contact between undercut surfaces  150 , 152  and the enlarged end portions  144 ,  148  prevents the coronal angle implant  120  and the sagittal angle implant  130  from separating. It should be understood that while an I-beam shape is portrayed for the connector  140 , other shapes that include enlarged ends might be used to achieve the same effect. For example, the connector  140  may include shapes such as an hourglass or a dumbbell. The connector  140  may include other cross section shapes, including a C-shape, and S-shape, an X-shape, or other shape that sufficiently prevents separation of the coronal angle implant  120  and the sagittal angle implant  130 . In other embodiments, retainer clips such as a C-clip, U-clip, or retainer ring may be used to hold the coronal angle implant  120  and sagittal angle implant  130  together. 
     The coronal angle implant  120  and the sagittal angle implant  130  also include retainers  154  that secure the connector  140  within the recess  142  in the coronal angle implant  120  and the sagittal angle implant  130 . In the embodiment shown, the retainers  154  are implemented as pairs inwardly biased fingers that are spaced apart a distance that is less than the width of the intermediate portion  146  of the connector. The retainers  154  may be deflected away from each other to allow the connector  140  to fit into the recess  142 . Once the connector  140  is inserted completely within the recess  142 , the retainers  154  deflect to their normal position within a recess  156  in the connector  140 . In the embodiment shown, the vertebral implant  110  includes a total of four retainers  154 , with two each in the coronal angle implant  120  and the sagittal angle implant  130 . In another embodiment, the coronal angle implant  120  and the sagittal angle implant  130  each include a single retainer  154 . In another embodiment, a flexible retainer  154  may be disposed on the connector  140  and configured to engage a corresponding recess in the coronal angle implant  120  and the sagittal angle implant  130 . Those skilled in the art will comprehend that other ways of securing the connector  140  in the coronal angle implant  120  and the sagittal angle implant  130  may be used. 
     The coronal angle implant  120  and the sagittal angle implant  130  also include a plurality of bone engagement features  160  disposed about the superior and inferior surfaces of each implant  120 ,  130 . In the embodiment shown, these bone engagement features  160  are depicted as ramped teeth, though it should be understood that other types of features might be used. For example, the bone engagement features  160  may be implemented as pyramid shaped, diamond shaped, cone shaped, or other protruding feature adapted to engage, embed, scour, scrape, or decorticate the end plates of a vertebral body. 
     In conjunction with the bone engagement features  160 , the coronal angle implant  120  and the sagittal angle implant  130  each include a plurality of recesses  162  disposed at the surface that contacts the other implant. Specifically, the coronal angle implant  120  includes these recesses  162  at the inferior surface  164 . Similarly, the sagittal angle implant  130  includes recesses  162  at the superior surface  166 . In embodiments where the relative position of the coronal angle implant  120  and the sagittal angle implant  130  are reversed, the recesses  162  may be disposed at the opposite surface (i.e., the surface that is positioned in contact with the other implant  120 ,  130 ). In other embodiments, the recesses  162  are disposed on both superior and inferior surfaces of the implant  120 ,  130 . 
     The recesses  162  on the coronal angle implant  120  are substantially aligned with the bone engagement features  160  of the sagittal angle implant  130 . Conversely, the recesses  162  on the sagittal angle implant  130  are substantially aligned with the bone engagement features  160  of the coronal angle implant  120 . With this configuration, the coronal angle implant  120  and the sagittal angle implant  130  are able to be positioned with the inferior surface  164  of the coronal angle implant  120  in contact with the superior surface  166  of the sagittal angle implant  130 . 
     Furthermore, since the bone engagement features  160  are disposed about the superior and inferior surfaces of each implant  120 , 130 , each implant  120 , 130  may be surgically installed without the other. Thus, for example, if a particular patient requires coronal angle correction, a coronal angle implant  120  that includes the appropriate coronal angle α may be inserted between vertebral bodies in the appropriate region of the spine. Similarly, if a particular patient requires sagittal angle correction, a sagittal angle implant  130  with the appropriate sagittal angle β may be inserted between vertebral bodies in the appropriate region of the spine. If a particular patient requires a multiplanar correction, a coronal angle implant  120  with an appropriate coronal angle α and a sagittal angle implant  130  with an appropriate sagittal angle β may be used together and inserted between vertebral bodies in the appropriate region of the spine. Accordingly, each of the coronal angle implant  120  and the sagittal angle implant  130  may be used either in conjunction with the other implant, or by itself. 
       FIGS. 7 ,  8 , and  9  depict various views of the exemplary coronal angle implant  120 .  FIG. 7  shows a posterior view of the coronal angle implant  120  and illustrates the coronal angle α.  FIG. 8  shows a perspective view of the coronal angle implant  120  depicted from inferior and posterior directions. The inferior surface  164  of the coronal angle implant  120  is more clearly visible in  FIG. 8 . Further,  FIG. 8  shows that the coronal angle implant  120  includes an inner wall  170  that defines an inner cavity  172 . Further, the recess  142   a  for connector  140  extends across the cavity  172  but ends at a stop surface  168 . That is, the recess  142   a  does not extend all the way through the coronal angle implant  120 . Thus, an inserted connector  140  is constrained within the recess  142   a  by the stop surface  168  and the retainers  154 . 
       FIG. 9  shows a perspective view of the coronal angle implant  120  depicted from superior and anterior directions. The inner wall  170  and inner cavity  172  are clearly visible in this particular view.  FIG. 12  shows that a similar cavity  182  exists in the sagittal angle implant  130 . Notably, the connector  140  is exposed within these cavities  172 ,  182 . As a result, the connector  140  may be constructed with a bone growth promoting material such as BMP, DBM, hydroxyapatite, allograft, autograft or other osteoinductive growth factors to facilitate fusion between vertebral bodies and the implant  10 . These and other types of bone growth promoting materials may be packed into the cavities  172 ,  182  around the connector  140  to further promote fusion between the implant  110  and vertebral bodies. 
       FIGS. 10 ,  11 , and  12  depict various views of the exemplary sagittal angle implant  130 .  FIG. 10  shows a lateral view of the sagittal angle implant  130  and illustrates the sagittal angle β.  FIG. 11  shows a perspective view of the sagittal angle implant  130  depicted from superior and posterior directions.  FIG. 11  shows that the sagittal angle implant  130  includes an inner wall  180  that defines an inner cavity  182  similar to the cavity  172  in the coronal angle implant  120 . Furthermore,  FIG. 11  shows that the recess  142   b  for connector  140  extends across the cavity  182  but ends at a stop surface  174 . That is, the recess  142   a  does not extend all the way through the sagittal angle implant  130 . Similar to the coronal angle implant  120  configuration, an inserted connector  140  is constrained within the recess  142   b  by the stop surface  174  and the retainers  154 .  FIG. 12  shows a perspective view of the sagittal angle implant  130  depicted from inferior and anterior directions. The inner wall  180  and inner cavity  182  are clearly visible in this particular view. 
     The vertebral implants  10 ,  110 ,  120 ,  130  disclosed above generally include a kidney shape, though other shapes and contours may be used. In further embodiments, the vertebral implant may take on other types of configurations, such as, for example, a circular shape, semi-oval shape, bean-shape, D-shape, elliptical-shape, egg-shape, or any other shape that would occur to one of skill in the art. The vertebral implant could also be described as being annular, U-shaped, C-shaped, V-shaped, horseshoe-shaped, semi-circular shaped, semi-oval shaped, or other similar terms defining an implant including at least a partially open or hollow construction. For example,  FIG. 13  shows one embodiment of a vertebral implant  210  that includes a horseshoe configuration. The implant  210  may be implanted from an anterior, lateral, or posterior approach. In other embodiments, the vertebral implant may take on substantially solid configurations, such as, for example, block-like or plate-like configurations that do not define an open inner region. The embodiments shown in  FIGS. 1-4  provide one example of a substantially solid configuration. Other embodiments may include an annular configuration similar to the embodiments illustrated in  FIGS. 5-12 . Other embodiments may include multiple, unattached portions, such as TLIF or PLIF cages or the exemplary implant  310  shown in  FIG. 14 . 
     As discussed above, the vertebral implants disclosed herein may be used in disc replacement or vertebral replacement surgeries.  FIGS. 15 ,  16 , and  17  show an embodiment  510  of a vertebral implant that includes a spacer  540  that serves at least two purposes. First, the spacer  540  includes enlarged portions  542  to retain the coronal angle implant  520  and the sagittal angle implant  530 . Thus, the spacer  540  is similar to the connector  140  in this regard. Second, the spacer  540  adds additional height H to the vertebral implant  510  that may be necessary for vertebrectomy and corpectomy procedures. Consistent with previous embodiments, the coronal angle implant  520  includes an associated coronal angle α for spinal correction in the coronal plane. Similarly, the sagittal angle implant  530  includes an associated sagittal angle β for spinal correction in the sagittal plane. The coronal angle implant  520  is shown in a superior position relative to the spacer  540  and sagittal angle implant  530 . In other embodiments, the sagittal angle implant  530  may be disposed superior to the spacer  540  and coronal angle implant  520 . 
     Embodiments disclosed above have not included any particular surface geometry, coating, or porosity as are found in conventionally known vertebral implants. Surface features such as these are used to promote bone growth and adhesion at the interface between an implant and a vertebral body. Examples of features used for this purpose include, for example, teeth, scales, keels, knurls, and roughened surfaces. Some of these features may be applied through post-processing techniques such as blasting, chemical etching, and coating, such as with hydroxyapatite. The superior and inferior bone interface surfaces of the vertebral implant may also include growth-promoting additives such as bone morphogenetic proteins. Alternatively, pores, cavities, or other recesses into which bone may grow may be incorporated via a molding process. Other types of coatings or surface preparation may be used to improve bone growth into or through the bone-contact surfaces. 
     Spatially relative terms such as “under”, “below”, “lower”, “over”, “upper”, and the like, are used for ease of description to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the device in addition to different orientations than those depicted in the figures. Further, terms such as “first”, “second”, and the like, are also used to describe various elements, regions, sections, etc and are also not intended to be limiting. Like terms refer to like elements throughout the description. 
     As used herein, the terms “having”, “containing”, “including”, “comprising” and the like are open ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. The articles “a”, “an” and “the” are intended to include the plural as well as the singular, unless the context clearly indicates otherwise. 
     The present invention may be carried out in other specific ways than those herein set forth without departing from the scope and essential characteristics of the invention. For instance, the geometries described herein may be implemented in ALIF, PLIF, or TLIF cages with an interior cavity for inserting bone growth promoting materials. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.