Abstract:
Modular lumbar interbody fixation systems and methods with reconstruction endplates are provided. A representative system includes: a pair of engaging plates adapted to fit between and engage the vertebral bodies, at least one engaging plate of the pair of engaging plates being a reconstruction endplate, the reconstruction endplate having a trough and configured to receive a fixing agent; and an alignment device positionable between the pair of engaging plates, the alignment device being operative to maintain a disc space between the vertebral bodies during use.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to copending U.S. provisional application entitled, “Modular Lumbar Interbody Fixation Systems With Reconstruction Endplates,” having Ser. No. 60/895,595, filed on Mar. 19, 2007, which is entirely incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention is generally related to promotion of spinal fusion between neighboring vertebrae. 
       DESCRIPTION OF THE RELATED ART 
       [0003]    The human spine is composed of a column of thirty-three bones, called vertebrae, and their adjoining structures. The twenty-four vertebrae nearest the head are separate bones and are capable of individual movement. These vertebrae are generally connected by anterior and posterior longitudinal ligaments and by discs of fibrocartilage, called intervertebral discs, positioned between opposing faces of adjacent vertebral bodies. The remaining nine vertebrae are fused to form the sacrum and the coccyx and are incapable of individual movement. The vertebral body and the dorsal vertebrae enclose an opening termed the vertebral foramen, through which the spinal cord, a column of nerve tissue which communicates nerve impulses between the brain and the rest of the body, and spinal nerve roots pass and are protected from damage. 
         [0004]    Fusion of vertebral bodies may be required for any number of reasons. Most often, such fusion is necessitated when an intervertebral disc is damaged, degenerates, or otherwise becomes diseased, causing great discomfort by way of impinging on the spinal cord and/or nerve roots. When more conservative treatments and minimally invasive procedures have been exhausted, it may become necessary to surgically remove the damaged disk and fuse the associated vertebral bodies in order to restore the original spatial relationships, as well as desired stability. 
         [0005]    After an intervertebral disc is removed, an implant device is typically inserted between neighboring vertebrae to maintain normal disc spacing and restore spinal stability, thereby facilitating an intervertebral fusion. An implant device typically contains a pair of engaging elements to engage the vertebrae. Prior to inserting the engaging elements, a vertebral drill is typically inserted within the surgical wound to drill into the cortical endplate and remove fibrous and nuclear material. A vertebral tap may then be used to cut threads into the ends of the neighboring vertebrae. The engaging elements are typically packed with bone graft to facilitate a spinal fusion. 
         [0006]    Exemplary devices include those described in U.S. Pat. Nos. 6,045,579 and 6,080,193, which are incorporated herein by reference. These devices incorporate side struts, which are typically formed out of a material such as titanium and are relatively stiff. Because the struts are inflexible, the load distribution may result in accelerated subjacent degeneration of adjacent motion segments. 
         [0007]      FIG. 1  schematically depicts adjacent vertebral bodies  102  and  104  that are normal in size and shape. Intervertebral disc  108  fills the space between vertebral bodies  102  and  104 . In contrast,  FIG. 2  schematically depicts adjacent vertebral bodies  202  and  204  in which upper vertebral body  202  is degraded and intervertebral disc  208  has been removed. In particular, the lower surface of the upper vertebral body is relatively irregularly shaped and, as such, presents a challenge in performing spinal fusion. In this regard, such a vertebral body typically is removed by a corpectomy procedure and an expandable cage or similar device is put in its place. Unfortunately, such procedures are relatively invasive and can place tremendous stress on the patient. 
       SUMMARY 
       [0008]    Modular lumbar interbody fixation systems and methods with reconstruction endplates are provided. An exemplary embodiment of such a system comprises: a pair of engaging plates adapted to fit between and engage the vertebral bodies, at least one engaging plate of the pair of engaging plates being a reconstruction endplate, the reconstruction endplate having a trough and configured to receive a fixing agent; and an alignment device positionable between the pair of engaging plates, the alignment device being operative to maintain a disc space between the vertebral bodies during use. 
         [0009]    Another exemplary embodiment of a system comprises: a first pair of engaging plates adapted to fit between and engage a first and a second vertebral body, the first and the second vertebral bodies being adjacent in the spine; a first alignment device positionable between the first pair of engaging plates, the first alignment device being operative to maintain a disc space between the first and the second vertebral bodies during use; a second pair of engaging plates adapted to fit between and engage a third and a fourth vertebral body, the third and the fourth vertebral bodies being adjacent in the spine, the second and the third vertebral bodies being identical or distinct; and a second alignment device positionable between the second pair of engaging plates, the second alignment device being operative to maintain a disc space between the third and the fourth vertebral bodies during use, wherein at least one engaging plate of the first and second pairs of engaging plates is a reconstruction endplate, the reconstruction endplate being configured to receive a fixing agent. 
         [0010]    An exemplary embodiment of a method comprises: removing an intervertebral disc between a first and a second vertebral bodies; preparing a first spinal implant comprising: a pair of engaging plates, and an alignment device, wherein at least one engaging plate of the pair of engaging plates is a reconstruction endplate having a trough; filling the at least one reconstruction endplate with a fixing agent; and inserting the first spinal implant between the first and the second vertebral bodies. 
         [0011]    Other systems, methods, features and/or advantages will be or may become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features and/or advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0013]      FIG. 1  illustrates a side view of adjacent vertebral bodies that are normal in size and shape. 
           [0014]      FIG. 2  illustrates a side view of adjacent vertebral bodies in which the upper vertebral body is degraded. 
           [0015]      FIG. 3  illustrates a side view of an embodiment of a modular lumbar interbody fixation system with one reconstruction endplate. 
           [0016]      FIG. 4  illustrates a side view of an embodiment of a modular lumbar interbody fixation system with two reconstruction endplates. 
           [0017]      FIG. 5  illustrates a side view of another embodiment of a modular lumbar interbody fixation system with multiple reconstruction endplates. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]      FIG. 3  illustrates an embodiment of a modular lumbar interbody fixation system  300  with one reconstruction endplate. The modular lumbar interbody fixation system  300  comprises a spinal implant  310  configured to be inserted into the intervertebral space between adjacent vertebral bodies  202  and  204 . In this embodiment, the lower surface of vertebral body  202  is degraded and irregularly shaped. Spinal implant  310  comprises engaging plates  312  and  314  and adjustment device  320 . Spinal implant  310  is used to replace an intervertebral disc  208  (shown removed in  FIG. 2 ) that has been removed for various reasons including disease, degeneration, etc. Spinal implant  310  is adapted to maintain normal disc spacing, to restore spinal stability, and to facilitate a fusion between vertebral bodies  202  and  204 . 
         [0019]    Engaging plate  312  is configured to engage with vertebral body  202 , and engaging plate  314  is configured to engage with vertebral body  204 . Engaging plate  312 , in particular, is a reconstruction endplate, which may be shaped like a trough and configured to receive a fixing agent  330 , such as cement. When engaging plate  312  is placed in position and filled with fixing agent  330 , the fixing agent  330  tends to fill the irregularities of vertebral body  202  and secures engaging plate  312  to vertebral body  202 . In other embodiments, engaging plate  314  may also be a reconstruction endplate, to secure engaging plate  314  to a non-degraded vertebral body. Engaging plates  312  and  314  may be constructed of titanium, titanium alloy, ceramics, carbon composites, other metals, etc. Engaging plate  314 , which is not specifically a reconstruction endplate in this embodiment, may be securely attached to vertebral body  202  by way of, for example, cement between the respective surfaces, or pins and/or screws inserted through the engaging plate and into the vertebral body it engages. Engaging plate  312  also may be attached by way of, for example, pins and/or screws, to supplement the attachment provided by fixing agent  330 . In this regard, in some embodiments, the engaging plates accommodate reconstruction of failed interbody fusion devices and/or total disk replacements. It should also be noted that, in some embodiments, various components, such as wedges, can be used in addition to fixing agent to accommodate deficiencies. 
         [0020]    Engaging plates  312  and/or  314  may contain a plurality of openings disposed therein to allow bone development and growth through the engaging plates  312  and  314  and through spinal implant  310 . The engaging surfaces of engaging plates  312  and  314  may be substantially planar to provide a relatively large contact area between the engaging plates and vertebral bodies  202  and  204 . In this way, subsidence of the vertebral bodies  202  and  204  may be prevented because the force imparted to the vertebral bodies  202  and  204  from the spinal implant  310  is not concentrated across a relatively small area of the vertebral bodies. Alternatively, the engaging surfaces of engaging plates  312  and/or  314  may be non-planar. The engaging plates may contain a plurality of spikes or protrusions extending toward the vertebral bodies for enhancing an engagement between the vertebral body and the engaging plate. The protrusions may extend into vertebral bodies  202  and/or  204  to prevent spinal implant  310  from moving out of the intervertebral space. In  FIG. 3 , engaging plate  314  is shown having protrusions  316  and  318  for enhancing an engagement with vertebral body  204 . 
         [0021]    Adjustment device  320  is configured to fit between engaging plates  312  and  314 . Adjustment device  320  comprises two struts,  322  and  324 , but adjustment device  120  may comprise one or more struts in other embodiments. As described herein, a “strut” refers to any support member disposed between engaging plates  312  and  314  to separate engaging plates  312  and  314 . Struts  322  and  324  may be attached to engaging plates  312  and  314  and/or attached directly to vertebral bodies  202  and  204 . Notably, struts may be relatively stiff struts or relatively flexible. In some embodiments, varying degrees of flexibility can be provided which can provide better load distribution for preventing accelerated subjacent degeneration of adjacent motion segments. 
         [0022]    Struts  322  and  324  may have a predetermined height that defines the height of the spinal implant  310 . By way of example, a strut can have a nominal height of between approximately 30 mm and approximately 40 mm. Alternatively, struts  322  and  324  may each have an adjustable height. Engaging plates  312  and  314  may be configured to receive struts of various heights to allow the height of spinal implant  310  to be varied to fit the needs of the patient. In an embodiment, the struts  322  and  324  have differing heights to cause the height of spinal implant  310  to vary. In this manner, spinal implant  310  may be used to correct a lateral deviation in the spinal column as may occur in scoliosis. Struts  322  and  324  may contain a hinge pin to allow an upper member of the strut to pivot with respect to a lower member of the strut. In this manner, the struts may be pivoted such that the ends of the struts are properly aligned when a height difference exists between struts  322  and  324 . 
         [0023]    Spinal implant  310  may contain a retaining plate proximate the posterior end to provide a backing against which bone graft may be packed and to maintain bone graft between the engaging plates. The retaining plate may be substantially planar and may contain openings to allow bone ingrowth therethrough. A removable endcap may be positioned proximate the anterior end to contain bone graft within the fusion device and to prevent the migration of bone graft outside the engaging plates. The endcap may contain one or more openings for allowing bone ingrowth between a vertebral body and bone graft contained between the engaging plates. The endcap may be made of a plastic material, such as polyethylene, that tends to be non-irritating and non-abrasive to the surrounding tissues. 
         [0024]      FIG. 4  illustrates an embodiment of a modular lumbar interbody fixation system  400  with two reconstruction endplates. In this embodiment, vertebral bodies  202  and  404  both are degraded, having irregularly shaped surfaces facing the intervertebral space where an intervertebral disc has been removed. In spinal implant  410 , which is configured to fit in the intervertebral space between vertebral bodies  202  and  404 , engaging plates  312  and  414  are both reconstruction endplates. As a reconstruction endplate, engaging endplate  414  may be shaped like a trough and configured to receive a fixing agent  430 , such as cement. When engaging plate  414  is placed in position and filled with fixing agent  430 , the fixing agent  430  tends to fill the irregularities of vertebral body  404  and secures engaging plate  414  to vertebral body  404 . 
         [0025]      FIG. 5  illustrates an embodiment of a modular lumbar interbody fixation system  500  with multiple reconstruction endplates. In modular lumbar interbody fixation system  500 , three adjacent vertebral bodies are depicted, vertebral bodies  506 ,  202 , and  404 . Here, vertebral body  506  also is degraded, having at least an irregular lower surface. However, in other embodiments, vertebral body  506  may not be degraded. Spinal implant  410 , described above in connection with  FIG. 4 , is inserted in the intervertebral space between vertebral bodies  202  and  404 . Additionally, spinal implant  510  is inserted in the intervertebral space between vertebral bodies  506  and  202 . In other embodiments, spinal implant  510  may be inserted between vertebral bodies above or below vertebral bodies  506  and  202  and need not be adjacent to or inclusive of vertebral bodies  506  and  202 . 
         [0026]    Spinal implant  510  is similar to spinal implant  310 , described above in connection with  FIG. 3 , in that spinal implant  510  comprises engaging plates  512  and  514  and adjustment device  520 . Engaging plates  512  and  514  are similar to engaging plates  312  and  314 . In particular, engaging plate  512  is a reconstruction endplate, configured to receive cement  530 . Additionally, engaging plate  514  may be a reconstruction endplate also in other embodiments. As depicted, engaging plate  514  has protrusions  516  and  518  to better engage with vertebral body  202 , but these protrusions are optional, and there may be one protrusion or more than two protrusions if desired. Adjustment device  520 , similar to adjustment device  320 , comprises two struts,  522  and  524 , but adjustment device  520  may comprise one or more struts in other embodiments. Struts  522  and  524  may be similar to struts  522  and  524 , but may differ in stiffness. In particular, depending on the needs of the patient, struts  522  and  524  may be relatively more stiff than struts  522  and  524 , or struts  522  and  524  may be relatively more flexible than struts  322  and  324 . 
         [0027]    In other embodiments, three or more spinal implant devices may be used, with or without reconstruction endplates as desired, with the struts of each spinal implant device having varying degrees of flexibility. Clearly, in some applications, gradation from stiffer to more flexible devices can occur in both directions along the spine. 
         [0028]    It should be emphasized that the above-described embodiments are merely possible examples of implementations. Many variations and modifications may be made to the above-described embodiments without departing substantially from the spirit and principles of the invention. All such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and protected by the following claims.