Abstract:
A vertebral stabilization plate assembly is provided. The plate assembly includes a flexible core located in a mid-portion section of the plate assembly; at least a first and a second attachment portion positioned above and below (or above and below—depending on orientation of flexible core) the flexible core, wherein the first and the second attachment portions comprise a plurality of fastener holes through which a plurality of fasteners are inserted to attach the plate assembly to at least two vertebral bone structures; and at least one flexible cable that extends through at least a first portion of the flexible core to maintain a position of the flexible core within the plate assembly, wherein the plate assembly is weight-bearing and attaches to the at least two vertebral bone structures and extends across a disc space located between the at least two vertebral bone structures.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 60/826,979, entitled CERVICAL DYNAMIC STABILIZATION SYSTEM and filed on Sep. 26, 2006, the entirety of which is incorporated herein by reference. 
     
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates in general to a vertebral stabilization implant. In particular, the present invention relates to a vertebral column dynamic stabilization device that supplements vertebral stabilization via the anterior column and/or the middle column lip and that can also facilitate disc regeneration. 
         [0004]    2. Description of Related Art 
         [0005]    Each vertebra has a cylindrical-shaped vertebral body in the anterior portion of the spine with an arch of bone to the posterior that covers the neural structures. Between each vertebral body is an intervertebral disk, a cartilaginous cushion to help absorb impact and dampen compressive forces on the spine. To the posterior, the laminar arch covers the neural structures of the spinal cord and nerves for protection. At the junction of the arch and anterior vertebral body are articulations to allow movement of the spine. 
         [0006]    When a surgeon is faced with a ruptured disc but not necessarily a severely degenerative segment, traditionally a microdiscectomy is performed where a simple removal of the disc fragment is performed and the fragment is removed from the cord. One problem with this solution is although the endplates of the disc and the lateral portions of the disc may be left intact; there can be a collapse of the spine, with excessive collapse of the interspace in height. This can lead to secondary neural foraminal stenosis. 
         [0007]    Other solutions involve flexible rod attachments. For example, a posterior system for the lumbar spine with a pedicle screw base system and a flexible rod attachment is known as the Zimmer Spine Dynesis System. The Zimmer system though is a posterior system and has no application in the cervical spine or for anterior applications. 
         [0008]    Recent solutions have looked at the possibility of replacing the disc in an interdiscal position with a motion device, which involves total disc replacement, and there are multiple devices on the market and patented available for this use. Other solutions involve cervical plates that provide rigid stabilization of an anterior column. These concepts aid fusion with a supplementation of stability after a bone graft is placed into the disc space. The stabilization of the vertebra to allow fusion is often assisted by a surgically implanted device to hold the vertebral bodies in proper alignment and allow the bone to heal. However, there are disadvantages to these current stabilization devices. 
       SUMMARY OF THE INVENTION 
       [0009]    In accordance with one aspect of the present invention, a device as described in further detail below provides a flexible plate that allows partial sharing of the weight of the vertebral bodies to promote bone healing or support at partial discectomy. A bone will not heal if it is stress-shielded from all weight bearing. If a partial discectomy is not supported, then it will collapse. Therefore, one aspect of the subject application provides a device that is strong enough to resist collapsing forces or abnormal angulation during the healing of the bone and/or disc. 
         [0010]    In accordance with another aspect, the present invention provides a dynamic stabilization device which includes a weight bearing plate and a flexible core. According to yet another aspect of the present invention, an anterior column dynamic stabilization device is provided which allows supplementation of stabilization via the anterior column. The flexible core is located in the midportion of the plate and is mobile in all planes of motion, allowing six planes of motion to mimic a natural motion of the neck. The plate may include attachment features such as caps, screws, and a lip to provide additional stability. 
         [0011]    According to another aspect of the present invention, anterior column stabilization and/or stabilization of the middle lip of the vertebral body column is provided. Due to the placement and structure of a stabilization plate, disc regeneration is also facilitated. In one embodiment, the plate or device stabilizes the vertebrae, such as in a patient&#39;s neck, in an “open” position, preventing a subsequent collapse after partial removal of disc material. With the vertebrae stabilized in the open or height-maintained position, the disc material is allowed to fibrose in naturally over a healing period (e.g., six-to-eight-week period) to yield regeneration and fibrosis of the disc in the open space between the vertebrae. Due to the structure of the stabilization plate, the motion segment is preserved. After the disc has fibrosed in or regenerated, the plate can also provide some additional stability to the segment in the absence of fusion. 
         [0012]    It is to be appreciated that the present invention is distinctly different from an artificial disc, which involves replacement of a disc with a mechanical device when a total discectomy is performed. Rather, the subject invention can supplement the patient&#39;s natural disc and adds stability to the anterior and/or middle column lip to facilitate disc regeneration. Furthermore, the subject invention may be used to supplement fusion of a disc with partial weight sharing of the bone. The subject invention is also different from any type of nuclear replacement, which is a biologic or gel replacement of the disc nucleus. That is, the present invention can allow the disc to heal naturally as opposed to requiring a nuclear replacement. 
         [0013]    According to still another aspect of the invention, a vertebral stabilization plate assembly that facilitates anterior columnar stabilization is provided. The plate assembly comprises a flexible core located in a mid-portion section of the plate assembly; at least a first and a second attachment portion positioned above and below the flexible core, wherein the first and the second attachment portions comprise a plurality of fastener holes through which a plurality of fasteners are inserted to attach the plate assembly to at least two vertebral bone structures; and at least one flexible cable that extends through at least a first portion of the flexible core to maintain a position of the flexible core within the plate assembly, wherein the plate assembly is weight-bearing and when attached to the at least two vertebral bone structures, extends across a disc space located between the at least two vertebral bone structures. 
         [0014]    According to another aspect of the invention, a vertebral stabilization plate assembly that facilitates anterior columnar stabilization is provided. The plate assembly includes a flexible core located in a mid-portion section of the plate assembly; at least a first and a second attachment portions positioned above and below and at least partially overlapping the flexible core, wherein the first and the second attachment portions comprise a plurality of screw holes through which a plurality of screws are inserted to attach the plate assembly to at least two vertebral bone structures; and a plurality of caps having a general U-shaped configuration that each fit around top and bottom end portions of the flexible core, wherein the plate assembly is weight-bearing and when attached to the at least two vertebral bone structures, the plate assembly has a compression capability that holds a disc space located between the at least two vertebral bone structures open while still allowing compression, rotation, flexion, and extension that mimics natural movement of the at least two vertebral bone structures, thereby preventing collapse of the disc space. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The foregoing and other aspects of the present invention will become apparent to those skilled in the art to which the present invention relates upon reading the following description with reference to the accompanying drawings, in which: 
           [0016]      FIG. 1  is a front or top view of a first embodiment of the present invention; 
           [0017]      FIG. 2  is a side view of the first embodiment of the present invention; 
           [0018]      FIG. 3  is a side view of a second embodiment of the present invention; 
           [0019]      FIG. 4  is an expanded front or top view of the second embodiment of the present invention; 
           [0020]      FIG. 5  is an expanded side view of an embodiment of the present invention that contains a lip portion on the flexible core of the plate assembly as it may appear in relation to two vertebrae; 
           [0021]      FIG. 6  is an expanded side view of another embodiment of the present invention that contains a lip portion on the flexible core of the plate assembly and 
           [0022]      FIG. 7  is a front or top view of an embodiment of the present invention as it may appear in relation to two vertebrae. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    A plate of the present invention can be used to facilitate disc regeneration and vertebral stabilization as well as to provide supplementation to a bone graft. The subject plate can also supplement stabilization for fusion and/or can allow partial weight bearing or weight loading in a dynamic way to a bone graft. Furthermore, the plate can provide partial protection from extrusion or over-collapse, thus allowing the bone to regenerate or heal at a faster rate via Wolff&#39;s law. Conventional cervical plates employ mechanical weight bearing and require the use of a titanium plate but lack a plate having a flexible core that permits the full range of motion in six planes. 
         [0024]    As mentioned above, the present invention can have non-fusion applications, such as when a standard discectomy is performed in a conventional manner, but where anterior column secondary stability is desired to prevent any over-collapse of the space. Additionally, the present invention can be applied to tissue regeneration technology to allow stabilization of a disc space in an open, non-collapsed position, thereby allowing regeneration of the disc. 
         [0025]    More specifically, the present invention can involve a stabilization plate that includes a flexible core portion which permits not only a full range of motion but also permits the plate to bear weight. Having a plate assembly helps to promote natural healing of a disc after partial surgical excision of a disc or injury to a disc. Unlike conventional spinal implants or devices, no other implant is needed to assist in the weight-bearing forces such as during the healing period. 
         [0026]    For example, the stabilization plate as described herein has a compression capability to hold a surgical space open at approximately 6-7 mm in height while still allowing compression, rotation, flexion, and extension in approximately the 5-7 degree range and allowing approximately 2-3 mm of motion in any plane. The stiffness of the stabilization plate can be determined by the density selection of the flexible core material of the plate. 
         [0027]    It is possible that the present invention may allow for potential applications in stem cell technology, cartilage regenerative injection technology, or subsequent stabilization for biomaterials for nuclear implants. Each of these devices and/or injections requires stabilization of an injured segment in a neutral position and can apply the flexible core of the present invention. It is to be appreciated that in these other applications, the flexible core will not necessarily create fusion or regeneration, unless bone or bone generation materials are also provided. The subject application will now be described in further detail with reference to  FIGS. 1-7 . 
         [0028]    Referring now to  FIG. 1 , a plate assembly  10  includes a flexible core  12  with attachment portions  4 ,  6  above and below (or adjacent to either side of) the flexible core  12 . In an embodiment, the attachment portions  4 ,  6  are comprised of a metal. The attachment portions  4 ,  6  can be made of titanium or other suitable metals. Alternatively, the attachment portions  4 ,  6  may be comprised of a hard material that is non-metallic. A plurality of screws can be placed in the vertebral body in a plurality of screw-holes  18  (or other fastener-holes  18 ) that correspond to each attachment portion  4 ,  6  located above and below the flexible core  12 . It should be appreciated that the attachment portions  4 ,  6  can also be described as being positioned at each opposite end of the flexible core and/or in end portions of the plate assembly. The attachment portions  4 ,  6  have a width that can be larger than the flexible core  12 . The attachment portions  4 ,  6  contain the screw-holes  18  to allow attachment of a plurality of screws to the plate assembly  10  and to a bone structure without the occurrence of any pull-through. A cover lock  22  can be provided to ensure that the screws do not back-out of the screw-holes  18 . 
         [0029]    In addition, a plurality of cover locks can be added in any embodiment described herein and also are used to prevent the displacement of the flexible core  12 . In an example embodiment, the flexible core  12  comprises a dense but mobile plastic. It is to be appreciated that other flexible and/or elastic materials may be used. For example, the flexible core may include a soft gel material. Also, the flexible core  12  may be multi-component and/or multi-material. In general, the flexible core  12  with the flexible/elastic properties allows the six planes of motion to mimic a natural motion of the vertebrae. The flexible core  12  may be maintained in position with at least one flexible cable  20 , which extends through the flexible core  12 . In the shown example, there are two flexible cables. However, a different number of cables (e.g., none, one or more than two) may be used. The flexible cables  20  can be made of titanium or other strong but flexible materials. The flexible cables  20  assist in providing resistance to forces that rotate, flex, and extend the flexible core  12 . The flexible core  12  may also be made of a biologically compatible material and may act as a flexible central bumper. 
         [0030]    Turning now to  FIG. 2 , a side view of the first embodiment is shown. One flexible cable  20  can be seen in relatively the middle portion of the flexible core  12 . In other embodiments, the flexible cable  20  may be in locations other than the middle portion of the flexible core  12 . In this embodiment, the flexible core  12  extends between each attachment portion  4 ,  6  and extends across multiple vertebrae. 
         [0031]    A side view of another embodiment is illustrated in  FIG. 3 . In this embodiment, caps  14 ,  16  fit around the two end portions (or top and bottom portions depending on the orientation of the flexible core  12 ) of the flexible core  12  and have a generally U-shaped configuration. The caps  14 ,  16  in this embodiment can have a width that is larger than the width of the flexible core  12 . The flexible core  12  extends across multiple vertebrae. Furthermore, the flexible core  12  can extend almost the entire length of the plate assembly  10  due to the shape and orientation of the caps  14 ,  16 . 
         [0032]      FIG. 4  shows an embodiment that demonstrates one way to assemble the plate assembly  10 . In this embodiment, the caps  14 ,  16  are shown oriented in the manner in which they will be assembled onto the flexible core  12 . The screw-holes  18  on each cap  14 ,  16  correspond to screw-holes  18  located on the flexible core. An initial step in assembling this embodiment is to ensure that each cap ( 14 ,  16 ) is oriented onto the flexible core  12  to permit the entry of screws. This orientation will only be performed once the plate assembly  10  is in the proper location for purposes of supplementation of a bone graft. Once screws are inserted into each screw-hole  18 , the plate assembly  10  is thus assembled. 
         [0033]    In yet another embodiment, according to  FIG. 5 , the flexible core  12  contains a lip  30  as illustrated when implanted into two vertebral bone structures  40 ,  42 . The lip  30  extends from the flexible core  12  into an area located between two rigid vertebral bone structures  40 ,  42 . The lip  30  contains edges  32  that mate with the corresponding edges  32  of the vertebral bone structures  40 ,  42 . The lip  30  can extend slightly from the anterior column into the middle column of a vertebral body, under the lips of the vertebral body. However, the lip  30  does not extend well into the disc space or replace any disc in any way. The lip  30  extends slightly to engage the anterior column lips for further stability of the flexible core  12 . This embodiment also shows that screws  50  can be used to connect the plate assembly  10  to the vertebral bone structures  40 ,  42 . It is to be appreciated that in other embodiments, other fastener devices may be used in place of the screws  50 . 
         [0034]    Referring now to  FIG. 6 , an assembly is shown that contains a flexible core  12  with a lip  30 . The lip contains edges  32  that mate with the corresponding edges of vertebrae structures. The edges  32  can be comprised of an angular edge as in  FIG. 6  or an edge that is formed from a substantially right angle, as in  FIG. 5 . The embodiment in  FIG. 6  also contains caps  14 ,  16  that fit around the two end portions of the flexible core  12 ; and the caps  14 ,  16  have a generally U-shaped configuration. The flexible core  12  extends across multiple vertebrae (e.g., at least two vertebrae). In addition, the flexible core  12  extends almost the entire length of the plate assembly  10  due to the shape and orientation of the caps  14 ,  16 . Though screws  50  can be used to connect the plate assembly  10  to the vertebrae structure as shown, it should be understood that other fastener devices may be used in place of the screws  50 . 
         [0035]    Furthermore, it should be appreciated that in any of the embodiments described herein, the shape of the flexible core  12  is generally rectangular to fit across multiple vertebrae. Other shapes for the flexible core  12  may be provided so long as the present invention fits across multiple vertebrae.  FIG. 7  depicts a top view of an example stabilization plate assembly  10  attached to at least two vertebral bone structures  40 ,  42  via screws  50 . 
         [0036]    The present invention may be used in a cervical region or in application to the lower levels in the lumbar spine. For example, the present invention can be used in the L4-5 or L5-S1 vertebrae levels for supplementation of a disc injury, however, the profile, or height, of the flexible core and the plate should be kept to a minimum amount. Moreover, the plate assembly can be employed with respect to other parts of the spine as well. As mentioned above, cover locks can be added to any embodiment of the design to prevent the backout of any screw or fastener device and to prevent the displacement of the flexible core. 
         [0037]    It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure.