Abstract:
An intervertebral prosthetic device for spinal stabilization and a method of using same according to which a body member is implanted between two adjacent vertebrae so that a spinous processes of a vertebrae extends into a notch formed in the body member. A groove is also formed in the body member that engages one of the vertebrae.

Description:
BACKGROUND  
       [0001]     The present invention relates to an intervertebral prosthetic device for stabilizing the human spine, and a method of implanting same.  
         [0002]     Spinal discs that extend between adjacent vertebrae in vertebral columns of the human body provide critical support between the adjacent vertebrae. These discs can rupture, degenerate, and/or protrude by injury, degradation, disease, or the like, to such a degree that the intervertebral space between adjacent vertebrae collapses as the disc loses at least a part of its support function, which can cause impingement of the nerve roots and severe pain.  
         [0003]     In these cases, intervertebral prosthetic devices have been designed that can be implanted between the adjacent vertebrae, both anterior and posterior of the column, to prevent the collapse of the intervertebral space between the adjacent vertebrae and thus stabilize the spine.  
         [0004]     However, many of these devices have less than optimum biomechanics, are relatively difficult to insert, have insufficient strength, and often do not provide an optimum fit with the anatomy.  
       SUMMARY  
       [0005]     Therefore, the intervertebral prosthetic device according to an embodiment of the invention overcomes the above deficiencies by providing improved biomechanics and increased strength, in addition to being relatively easy to insert, yet provides an improved fit with the anatomy.  
         [0006]     Various embodiments of the invention may possess one or more of the above features and advantages, or provide one or more solutions to the above problems existing in the prior art. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is a side elevational view of an adult human vertebral column.  
         [0008]      FIG. 2  is a posterior elevational view of the column of  FIG. 1 .  
         [0009]      FIG. 3  is an enlarged, front elevational view of one of the vertebrae of the column of  FIGS. 1 and 2 .  
         [0010]      FIG. 4  is an enlarged, partial, isometric view of a portion of the column of  FIGS. 1 and 2 , including the lower three vertebrae of the column, and depicting an intervertebral prosthetic device according to an embodiment of the invention inserted between two adjacent vertebrae.  
         [0011]      FIG. 5  is an enlarged, isometric, view of the prosthetic device of  FIG. 3 .  
         [0012]      FIG. 6  is an enlarged, top plan view of the prosthetic device of  FIG. 5 .  
         [0013]     FIGS.  7  is a cross-sectional view taken along the line  7 - 7  of  FIG. 6 . 
     
    
     DETAILED DESCRIPTION  
       [0014]     With reference to  FIGS. 1 and 2 , the reference numeral  10  refers, in general, to a human vertebral column  10 . The lower portion of the vertebral column  10  is shown and includes the lumbar region  12 , the vertebrae V 6 , and the coccyx  16 . The flexible, soft portion of the vertebral column  10 , which includes the thoracic region and the cervical region, is not shown.  
         [0015]     The lumbar region  12  of the vertebral column  10  includes five vertebrae V 1 , V 2 , V 3 , V 4  and V 5  separated by intervertebral discs D 1 , D 2 , D 3 , and D 4 , with the disc D 1  extending between the vertebrae V 1  and V 2 , the disc D 2  extending between the vertebrae V 2  and V 3 , the disc D 3  extending between the vertebrae V 3  and V 4 , and the disc D 4  extending between the vertebrae V 4  and VS.  
         [0016]     The vertebrae V 6  includes five fused vertebrae, one of which is a superior vertebrae V 6  separated from the vertebrae VS by a disc D 5 . The other four fused vertebrae of the sacrum  14  are referred to collectively as V 7 . A disc D 6  separates the vertebrae V 6  from the coccyx  16  which includes four fused vertebrae (not referenced).  
         [0017]     With reference to  FIG. 3 , the vertebrae V 5  includes two laminae  20   a  and  20   b  extending to either side (as viewed in  FIG. 2 ) of a spinous process  22  that extends posteriorly from the juncture of the two laminae. Two transverse processes  24   a  and  24   b  extend laterally from the laminae  20   a  and  20   b,  respectively. Two articular processes  26   a  and  26   b  extend superiorly from the laminae  20   a  and  20   b,  respectively, and two articular processes  28   a  and  28   b  extend inferiorly from the laminae  20   a  and  20   b,  respectively. The inferior articular processes  28   a  and  28   b  rest in the superior articular process of the vertebra V 2  to form a facet joint. Since the other vertebrae V 1 -V 4  are similar to the vertebrae V 5 , they will not be described in detail.  
         [0018]     Referring again to  FIG. 2 , the vertebrae V 6  of the sacrum  14  includes two laminae  30   a  and  30   b  extending to either side (as viewed in  FIG. 2 ) of a median sacral crest, or spinous process,  32 a that extends inferiorly from a ridge  34  and posteriorly from the juncture of the two laminae. The vertebrae V 6  also includes a pair of sacral wings  36   a  and  36   b  that extend laterally from the laminae  30   a  and  30   b,  respectively. Four additional axially-spaced sacral crests, or spinous processes,  32   b - 32   d  are associated with the fused vertebrae V 7  of the sacrum  14  and extend inferiorly from the spinous process  32   a.    
         [0019]     Referring to  FIG. 4 , it will be assumed that, for one or more of the reasons set forth above, the vertebrae V 5  and V 6  are not being adequately supported by the disc D 4  and that it is therefore necessary to provide supplemental support and stabilization of these vertebrae. To this end, an intervertebral disc prosthetic device  40  according to an embodiment of the invention is implanted between the spinous processes  22  of the vertebrae V 5  and the crest, or spinous process  32   a,  of the vertebrae V 6 .  
         [0020]     The device is shown in detail in  FIGS. 5-7  and includes a solid body member  42  having a generally rectangular cross section in each plane with the exception of several notches and cuts to be described.  
         [0021]     In particular, two curved grooves, or notches,  42   a  and  42   b  are formed in the upper portions of the respective end portions of the body member, as viewed in the drawings. A laterally extending angled cut, or groove  42   c,  having a curved cross section, is formed in the underside of the body member  42  below the notch  42   a,  as viewed in  FIG. 5  and  7 . Similarly, a laterally extending cut, or groove  42   d,  also having a curved cross section, is formed in the underside of the body member  42  below the notch  42   b.  The shape of the cut  42   d  is such that a tab, or hook,  42   e  ( FIG. 7 ) is defined on the underside of the body member.  
         [0022]     Two laterally extending, through openings  42 f are formed through the body member  42  for receiving cables, or the like, to tether the device to the vertebrae V 5  and V 6  when the device  40  is implanted between the vertebrae VS and V 6  in the position shown in  FIG. 4 .  
         [0023]     Referring to  FIG. 4 , the device  40  is inserted between the vertebrae V 5  and the vertebrae V 6  with the spinous process  22  of the vertebrae V 5  extending in the notch  42   a  of the body member  42 , and the crest, or spinous process,  32   a  of the vertebrae V 6  extending in the notch  42   b  of the body member. The groove  42 c ( FIGS. 5 and 7 ) thus extends superiorly and extends around the corresponding edges of the laminae  30   a  and  30   b  ( FIG. 2 ) of the vertebrae V 5 , and the groove  42   d  extends inferiorly and fits around the ridge  34  ( FIG. 2 ) of the vertebrae V 6 , with the tab  42   e  extending under the latter ridge.  
         [0024]     It is understood that the body member  42  can be fabricated from any conventional material or combination of materials. For example, it could have an inner core of a relatively hard material, such as hard rubber or plastic, which is surrounded by a relatively soft material such as silicone, which can be molded around the core.  
         [0025]     The device  40  is relatively easy to insert between the vertebrae V 5  and V 6  in the manner described above, and readily fits the vertebrae. The grooves  42 c and  42 d, as well as the tab  42 e, aid in retaining the device  40  in the implanted position, and the core  42 f adds strength to the device  40 , while the soft material surrounding the core minimizes damage to the processes  22  and  30   a  of the vertebrae V 5  and V 6 , respectively.  
       Variations  
       [0026]     It is understood that variations may be made in the foregoing without departing from the invention and examples of some variations are as follows: 
        Any conventional substance that promotes bone growth, such as HA coating, BMP, or the like, can be incorporated in the body member  42 ;     The body member  42  may have through holes formed therein to improve integration of the bone growth;     The body member  42  may vary in shape, size, composition, and physical properties;     The number and location of the notches and grooves formed in the body member  42  can vary;     The prosthetic device  40  can be placed between two vertebrae in the vertebral column  10  other than the ones described above;     The body member  42  can be fabricated from materials other than those described above;     Bilateral extrusions, or the like, can be provided on the body member  42  to enable a tethering device to be attached to the component;     The prosthetic device  40  can be implanted between body portions other than vertebrae;     The prosthetic device  40  can be inserted between two vertebrae following a discectemy in which a disc between the adjacent vertebrae is removed, or corpectomy in which at least one vertebrae is removed;     The spatial references made above, such as “under”, “over”, “between”, “flexible, soft”, “lower”, “top”, “bottom”, etc. are for the purpose of illustration only and do not limit the specific orientation or location of the structure described above.        
 
         [0037]     The preceding specific embodiments are illustrative of the practice of the invention. It is to be understood, therefore, that other expedients known to those skilled in the art, or disclosed herein, may be employed without departing from the invention or the scope of the appended claims, as detailed above. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts a nail and a screw are equivalent structures.