Abstract:
A prosthetic assembly and method of implanting same, according to which a least one cross-bar is secured to the spinal column. A spacer engages the spinous process of a vertebra of the spinal column. The cross-bar is connected to the spacer via an adapter.

Description:
BACKGROUND 
       [0001]    The present invention relates to an intervertebral prosthetic assembly for stabilizing the human spine, and a method of implanting same. 
         [0002]    Intervertebral discs that extend between adjacent vertebrae in vertebral columns of the human body provide critical support between the adjacent vertebrae while permitting multiple degrees of motion. 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]    Intervertebral prosthetic devices have been designed that can be implanted between the adjacent vertebrae, both anterior and posterior of the column. Many of these devices are supported between the spinous processes of the adjacent vertebrae to prevent the collapse of the intervertebral space between the adjacent vertebrae and provide motion stabilization of the spine. 
         [0004]    However, in some cases it is often necessary to perform a laminectomy to remove the laminae and the spinous process from at least one vertebra to remove an intervertebral disc and/or to decompress a nerve root. Typically, in these procedures, two vertebral segments are fused together to stop any motion between the segments and thus relieve the pain. In this situation, it would be impossible to implant an intervertebral prosthetic device of the above type since the device requires support from the respective spinous processes of both adjacent vertebrae. 
         [0005]    The present invention is thus directed to an intervertebral prosthetic assembly that is implantable between two adjacent vertebrae to provide motion stabilization, despite the fact that at least one vertebra is void of a spinous process. 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 
         [0006]      FIG. 1  is a side elevational view of an adult human vertebral column. 
           [0007]      FIG. 2  is a posterior elevational view of the column of  FIG. 1 . 
           [0008]      FIG. 3  is an enlarged, front elevational view of one of the vertebrae of the column of  FIGS. 1 and 2 . 
           [0009]      FIG. 4  is an 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 assembly according to an embodiment of the invention implanted between two adjacent vertebrae. 
           [0010]      FIG. 5  is an enlarged view of a portion of the column and the assembly shown in  FIG. 4 . 
           [0011]      FIGS. 6 and 7  are views similar to that of  FIG. 5 , but depicting alternate embodiments of the assembly of  FIG. 5 . 
           [0012]      FIGS. 8 and 9  are partial elevational/partial sectional views of two additional alternate embodiments of the assembly of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    With reference to  FIGS. 1 and 2 , the reference numeral  10  refers, in general, to the lower portion of a human vertebral column. The column  10  includes a lumbar region  12 , a sacrum  14 , and a coccyx  16 . The flexible, soft portion of the column  10 , which includes the thoracic region and the cervical region, is not shown. 
         [0014]    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 V 5 . 
         [0015]    The sacrum  14  includes five fused vertebrae, one of which is a superior vertebra V 6  separated from the vertebra V 5  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 sacrum  14  from the coccyx  16 , which includes four fused vertebrae (not referenced). 
         [0016]    With reference to  FIG. 3 , the vertebra 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 vertebrae V 1 -V 4  are similar to the vertebra V 5 , and since the vertebrae V 6  and V 7  are not involved in the present invention, they will not be described in detail. 
         [0017]    Referring to  FIGS. 4 and 5  it will be assumed that, for one or more of the reasons set forth above, the spinous process  22  of V 4  has been removed, the vertebrae V 3 , V 4 , and/or V 5  are not being adequately supported by the discs D 3  and/or D 4 , and that it is desired to provide supplemental support and motion stabilization for these vertebrae. 
         [0018]    To this end, a spacer  40  is provided that is fabricated from a relatively flexible, soft material, and is substantially rectangular in shape with the exception that a curved notch, or saddle,  40   a  is formed at one end for receiving the spinous process  22  of the vertebra V 3 . 
         [0019]    A through opening  40   b  extends through the spacer in a spaced relation to the saddle  40   a , and a flexible cross-bar  42  extends through the opening  40   b  in the spacer  40  and generally transverse to the axis of the spine. The cross-bar  42  spans a substantial portion of the width of the vertebra V 4 . 
         [0020]    Two transversely-spaced retainers  44   a  and  44   b  ( FIG. 4 ) are fastened to the vertebra V 4  by two screws  46   a  and  46   b , respectively. Each screw  46   a  and  46   b  has a head (not shown) extending in a corresponding retainer, and an externally threaded shank extending from the head that is screwed in the vertebra V 4 . The respective end portions of the cross-bar  42  extend through openings in the retainers  44   a  and  44   b.    
         [0021]    A strap  48  extends through another opening  40   c  in the spacer  40  and around the process  22  of the vertebra V 3  to secure the spacer to the process. 
         [0022]    The spacer  40  is thus firmly secured in its implanted position shown in  FIG. 4 , and stabilizes the vertebrae V 3 -V 5 . Also, the relatively flexible, soft spacer  40  readily conforms to the process  22  of the vertebra V 3  and provides excellent shock absorption and deformability, resulting in an improved fit. 
         [0023]    The embodiment of  FIGS. 6 and 7  is similar to that of  FIGS. 4 and 5  and identical components are given the same reference numerals. According to the embodiment of  FIGS. 6 and 7 , a spacer  50  is provided that is fabricated from a relatively flexible, soft material, and is substantially rectangular in shape with the exception that a saddle  50   a  is formed at one end of the spacer for receiving the spinous process  22  of the vertebra V 3 . Also, a transversely extending notch, or groove  50   b  is formed in the other end of the spacer  50 , and two through openings  50   c  and  50   d  extend through the spacer, for reasons to be described. 
         [0024]    A central portion of the cross-bar  42  of the previous embodiment extends into the notch  50   b  and generally transverse to the axis of the spine, and spans a substantial portion of the width of the vertebra V 4 . As in the previous embodiment, the respective end portions of the cross-bar  42  extend through openings in the retainers  44   a  and  44   b  ( FIG. 4 ) which are mounted to the vertebra V 4  by the screws  46   a  and  46   b , respectively. The strap  48  extends through the opening  50   c  in the spacer  50  and around the process  22  of the vertebra V 3  to secure the spacer to the vertebra. According to the embodiment of  FIGS. 6 and 7 , a second strap  52  ( FIG. 7 ) extends through the opening  50   d  in the spacer  50  and around the notch  50   b  and the cross-bar  42 , to secure the cross-bar to the spacer. 
         [0025]    The spacer  50  is thus firmly secured in the same implanted position as shown in connection with the spacer  40  of the embodiment of  FIGS. 4 and 5 , and stabilizes the vertebrae V 3 -V 5 . Also, the relatively flexible, soft, spacer  50  readily conforms to the process  22  of the vertebra V 3  and provides excellent shock absorption and deformability resulting in an improved fit. 
         [0026]    The embodiment of  FIG. 8  is similar to that of the embodiments and  FIGS. 4 and 5  and identical components are given the same reference numerals. According to the embodiment of  FIG. 8 , a spacer  60  is provided that is fabricated from a relatively flexible, soft material, and is substantially rectangular in shape with the exception that a saddle  60   a  is formed at one end for receiving the spinous process  22  of the vertebra V 3 . 
         [0027]    A flexible cross-bar  62  is provided that has two slightly-spaced, circular flanges  62   a  and  62   b  formed on its central portion. The central portion of the cross-bar  62 , along with the flanges  62   a  and  62   b  are embedded in the spacer  60  in any conventional manner, such as by forming the spacer of a rubber material and molding it over the cross-bar. 
         [0028]    As in the previous embodiments, the respective end portions of the cross-bar  62  extend through openings in the retainers  44   a  and  44   b  ( FIG. 4 ), which are mounted to the vertebra V 4  by the screws  46   a  and  46   b , respectively, as described above. Also, although not shown in  FIG. 8 , it is understood that the strap  48  of the embodiment of  FIGS. 4 and 5  can extend through the spacer  60  and around the process  22  of the vertebra V 3  to secure the spacer to the vertebra. 
         [0029]    The spacer  60  is thus firmly secured in the same implanted position as shown in connection with the spacer  40  of the embodiment of  FIGS. 4 and 5 , and stabilizes the vertebrae V 3 -V 5 . Also, the relatively flexible, soft spacer  60  readily conforms to the process  22  of the vertebra V 3  and provides excellent shock absorption and deformability resulting in an improved fit. 
         [0030]    The embodiment of  FIG. 9  is similar to that of  FIGS. 4-8  and identical components are given the same reference numerals. According to the embodiment of  FIG. 9  a spacer  70  is provided that is fabricated from a relatively flexible, soft material, and has a generally U-shaped cross section. A saddle  70   a  is defined at one end of the spacer  70  for receiving the spinous process  22  of the vertebra V 3 . 
         [0031]    A flexible cross-bar  72  is provided that has two slightly-spaced protrusions  72   a  and  72   b  that extend transverse to the axis of the cross-bar and form, with the corresponding portion of the cross-bar, a U-shaped portion that receives the spacer  70 . In this context, the spacer  70  could be formed of a rubber material that is molded over the cross-bar  72 . 
         [0032]    As in the previous embodiments, the respective end portions of the cross-bar  72  extend through openings in the retainers  44   a  and  44   b  ( FIG. 4 ), which are mounted on the vertebra V 4  by the screws  46   a  and  46   b  in the manner described above. Also, although not shown in  FIG. 9 , it is understood that the strap  48  of the embodiment of  FIGS. 4 and 5  can extend through the spacer  70  and around the process  22  of the vertebra V 3  to secure the spacer to the vertebra. 
         [0033]    The spacer  70  is thus firmly secured in the same implanted position as shown in connection with the spacer  40  of the embodiment of  FIGS. 4 and 5 , and therefore stabilizes the vertebrae V 3 -V 5 . Also, the relatively flexible, soft spacer  70  readily conforms to the process  22  of the vertebra V 3  and provides excellent shock absorption deformability resulting in an improved fit. 
       Variations 
       [0034]    It is understood that variations may be made in the foregoing without departing from the invention and examples of some variations are as follows: 
         [0035]    (1) The assemblies of the above embodiments 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. 
         [0036]    (2) The cross-bars in each of the previous embodiments can be rigidly connected to the pedicles of the vertebra by means other than the screws and retainers described in the above examples. 
         [0037]    (3) The components disclosed above can be fabricated from materials other than those described above and may include a combination of soft and rigid materials. 
         [0038]    (4) Any conventional substance that promotes bone growth, such as HA coating, BMP, or the like, can be incorporated in the spacers in the above embodiments. 
         [0039]    (5) The surfaces of the spacers disclosed above that define the saddles that receive the spinous process can be treated, such as by providing teeth, ridges, knurling, etc., to better grip the spinous process. 
         [0040]    (6) The spacers disclosed above can be fabricated of a permanently deformable material thus providing a clamping action against the spinous processes. 
         [0041]    (7) One or more of the components disclosed above may have through-holes formed therein to improve integration of the bone growth. 
         [0042]    (8) The components of one or more of the above embodiments may vary in shape, size, composition, and physical properties. 
         [0043]    (9) Through-openings can be provided through one or more components of each of the above embodiments to receive tethers for attaching the devices to a vertebra or to a spinous process. 
         [0044]    (10) The assemblies of each of the above embodiments can be placed between two vertebrae in the vertebral column other than the ones described above. 
         [0045]    (11) The number and lengths of the cross-bars in one or more of the embodiments can be varied. 
         [0046]    (12) The cross-bars can be flexible or rigid. 
         [0047]    (13) The assemblies of the above embodiments can be implanted between body portions, or anatomical structures other than vertebrae. 
         [0048]    (14) The spatial references made above, such as “under”, “over”, “between”, “flexible, soft”, “lower”, “top”, “bottom”, “axial”, “transverse”, etc. are for the purpose of illustration only and do not limit the specific orientation or location of the structure described above. 
         [0049]    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.