Abstract:
A prosthetic assembly and method of implanting same, according to which a least one rod is secured to the spinal column. A spacer engages the spinous process of a vertebrae of the spinal column. The rod 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]     In some situations it is often necessary to perform a laminectomy to remove the laminae and the spinous process from at least one vertebrae to remove a 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.  
         [0004]     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. However, in the above situation involving removal of a spinous process from one of the vertebrae, 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.  
       SUMMARY  
       [0005]     According to an embodiment of the invention, an intervertebral prosthetic assembly is provided that is implantable between two adjacent vertebrae to provide motion stabilization, despite the fact that at least one of vertebrae is void of a spinous process.  
         [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 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.  
         [0011]      FIG. 5  is an enlarged view of a portion of the column and the assembly shown in  FIG. 4 .  
         [0012]      FIG. 6  is an enlarged isometric view of a component of the assembly of  FIGS. 4 and 5 .  
         [0013]      FIGS. 7-9  are enlarged, isometric views of three alternate embodiments of the component of  FIG. 6 .  
         [0014]      FIG. 10  is a view similar to that of  FIG. 5 , but depicting an alternate embodiment of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0015]     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 sacrum  14 , 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.  
         [0016]     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 .  
         [0017]     The vertebrae V 6  includes five fused vertebrae, one of which is a superior vertebrae V 6  separated from the vertebrae 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 vertebrae V 6  from the coccyx  16  that includes four fused vertebrae (not referenced).  
         [0018]     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 projects 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, and two pedicles  26   a  and  26   b  extend anteriorly from the processes  24   a  and  24   b  to a vertebral body  28 . Since the other vertebrae V 1 -V 3  are similar to the vertebrae V 5 , they will not be described in detail. Also, V 4  is similar to V 5  with the exception that the spinous process  22  of V 4  has been removed for one or both of the reasons set forth above.  
         [0019]     Referring to  FIGS. 4 and 5 , it will be assumed that, for one or more of the reasons set forth above, the vertebrae V 4  and V 5  are not being adequately supported by the disc D 4 , the spinous process  22  of V 4  has been removed, and that it is desired to provide supplemental support and motion stabilization of these vertebrae.  
         [0020]     To this end, two spaced, parallel, flexible rods  30  and  32  are provided that generally span the axial length between the processes  22  of the vertebrae V 4  and V 5 . Two axially-spaced screw retainers  34   a  and  34   b  are connected to the rod  30  and two axially-spaced screw retainers  34   c  and  34   d  are connected to the rod  32 . The screw retainers  34   a ,  34   b ,  34   c , and  34   d  retain pedicle screws  38   a ,  38   b ,  38   c , and  38   d  respectively, each of which extends through, and is supported by, its corresponding retainer.  
         [0021]     The screws  38   a  and  38   c  extend into the pedicles of the vertebrae V 4 , and the screws  38   b  and  38   d  extend into the pedicles of the vertebrae V 5 . It is understood that the rods  30  and  32 , the retainers  34   a - 34   d  and the screws  38   a - 38   d  are installed in connection with the procedure to be described, or that they could have been previously installed in connection with another procedure.  
         [0022]     As shown in  FIGS. 5 and 6 , a spacer  40  is provided that is fabricated from a relatively flexible, soft material, and is substantially rectangular in shape with the exception that two curved notches, or saddles,  40   a  and  40   b  are formed at its respective end portions. The notch  40   a  extends around the spinous process  22  of the vertebrae V 3 , and, since the spinous process of the vertebrae V 4  has been removed, an adapter  44 , shown in detail in  FIG. 7 , is provided for supporting the spacer  40 .  
         [0023]     The adapter  44  comprises a rectangularly-shaped body member  44   a  that is sized so as to extend in the notch  40   a  of the spacer  40 . Two arms  44   b  and  44   c  extend from the body member and can be formed integrally with, or attached to, the body member  44   a . The respective distal end portions of the arms  44   b  and  44   c  curve downwardly from the body member as viewed in  FIG. 7 , and their respective distal end portions are curved inwardly so as to fit over the rods  30  and  32  ( FIG. 5 ). Preferably, the adapter  44  is fabricated from a relatively stiff material, such as hard rubber or plastic.  
         [0024]     The adapter  44  can be moved axially up or down the vertebral column  10  as necessary by moving the arms  44   b  and  44   c  along the rods  30  and  32 , to insure that the spacer  40  fits between the spinous process  22  of the vertebrae V 3  and the body member  44   a  of the adapter.  
         [0025]     In its implanted position shown in  FIG. 5 , the assembly consisting of the rods  30  and  32 , the spacer  40  and the adapter  44  stabilizes the vertebrae V 3  and V 4 . Also, the relatively flexible, soft spacer  40  readily conforms to the processes  22  of the vertebrae V 3  and provides excellent deformability resulting in an improved fit. The adapter  44  adds stiffness, compressive strength and durability, and the arms  44   b  and  44   c  restrain the adapter  44  from lateral movement.  
         [0026]     An alternate embodiment of an adapter is shown, in general, by the reference numeral  50  in  FIG. 8 . The adapter  50  comprises a rectangularly-shaped body member  52  having a tab  52   a  extending from one end thereof. Two through-openings are provided in the tab  52   a  that receive two arms  56   a  and  56   b , respectively. The arms  56   a  and  56   b  thus extend laterally from the body member  52 , with their respective distal end portions being curved inwardly. The arms  56   a  and  56   b  extend in the openings in the tab  52   a  in a friction fit, and therefore can be adjusted laterally by moving them axially in the openings. Also, the angular position of the arms  56   a  and  56   b  relative to the body member  52  can be adjusted by rotating the arms in the openings in the tab  52   a . If necessary, set screws (not shown), or the like, could be provided through additional openings in the tab  52   a  to lock the arms  56   a  and  56   b  in a desired axial and angular position. Preferably, the adapter  50  is fabricated from a relatively stiff material, such as hard rubber or plastic.  
         [0027]     When the adapter  50  is used in place of the adapter  44  in the implanted position shown in  FIG. 5 , the spinous process  22  of the vertebrae V 3  extends in the notch  40   b  of the spacer  40 , and the body member  52  extends in the notch  40   a . The effective lengths of the arms  56   a  and  56   b  can be adjusted so that their respective curved distal end portions extend over the rods  30  and  32 , respectively.  
         [0028]     The arms  56   a  and  56   b  prevent lateral movement of the adapter  50  yet permit the adapter  44  to be moved axially up or down the vertebral column  10  by moving the arms along the rods  30  and  32 . Thus, the axial position of the adapter  50  can be adjusted as necessary to insure that the spacer  40  fits between the spinous process  22  of the vertebrae V 3  and the body member  52  of the adapter.  
         [0029]     The assembly consisting of the rods  30  and  32 , the spacer  40 , and the adapter  50  thus stabilizes the vertebrae V 3  and V 4 . Also, the relatively flexible, soft spacer  40  readily conforms to the process  22  of the vertebrae V 3  and provides excellent deformability resulting in an improved fit, while the adapter  50  adds stiffness, compressive strength and durability, and the arms  56   a  and  56   b  also restrain the adapter  44  from lateral movement.  
         [0030]     Another alternate embodiment of an adapter is shown, in general, by the reference numeral  60  in  FIG. 9 . The adapter  60  comprises a rectangularly-shaped body member  62  having a stem  62   a  projecting therefrom and extending in an axial opening in a bracket  64 . The lengths of the stem  60   a  and the latter opening are such that the amount of stem  60   a  that extends in the opening can be varied to vary the relative axial positions between the body member  62  and the bracket  64 . A set screw  66  extends through a lateral opening in the bracket  64  and engages the stem  60   a  to lock the stem, and therefore the body member  62  to the bracket  64 .  
         [0031]     Two arms  66   a  and  66   b  extend laterally from the bracket  64  and preferably are formed integrally with the bracket. The arms  66   a  and  66   b  curve downwardly as viewed in  FIG. 9 , with their respective distal end portions being curved inwardly so as to fit over the rods  30  and  32  ( FIG. 5 ). The arms  66   a  and  66   b  can be formed integrally with, or attached to, the bracket  64 . Preferably, the adapter  60  is fabricated from a relatively stiff material, such as hard rubber or plastic.  
         [0032]     When the adapter  60  is used in place of the adapter  44  in the implanted position shown in  FIG. 5 , the spinous process  22  of the vertebrae V 3  extends in the notch  40   b  of the spacer  40 , the body member  62  extends in the notch  40   a , and the curved distal end portions of the arms  66   a  and  66   b  extend around the rods  30  and  32 , respectively.  
         [0033]     The arms  66   a  and  66   b  prevent lateral movement of the adapter  60  yet permit the adapter to be moved axially up or down the vertebral column  10  by moving the arms along the rods  30  and  32 . Thus, the axial position of the adapter  60  can be adjusted as necessary to insure that the spacer  40  fits between the spinous process  22  of the vertebrae V 3  and the body member  62  of the adapter.  
         [0034]     The assembly consisting of the rods  30  and  32 , the spacer  40  and the adapter  60  stabilizes the vertebrae V 3  and V 4 . Also, the relatively flexible, soft spacer  40  readily conforms to the processes  22  of the vertebrae V 3  and provides excellent deformability resulting in an improved fit, while the adapter  60  adds stiffness, compressive strength and durability, and the arms  66   a  and  66   b  restrain the adapter  44  from lateral movement.  
         [0035]     The embodiment of  FIG. 10  is similar to that of  FIG. 5  and includes identical components that are given the same reference numerals. According to the embodiment of  FIG. 10 , an adapter  70  is provided that consists of a rectangularly-shaped body member  72  that receives two arms  74   a  and  74   b , respectively. The proximal ends of the arms  74   a  and  74   b  are connected to, or are formed integrally with, the body member  72 , and the arms extend from the body member to the retainers  34   a  and  34   c , respectively and thus extend at an acute angle with respect to the longitudinal axis of the column  12  ( FIG. 2 ). The respective distal end portions of the arms  74   a  and  74   b  are connected to the screws  38   a  and  38   c , respectively, and/or the retainers  34   a  and  34   c , respectively in any conventional manner.  
         [0036]     Assuming the spinous process  22  has been removed from the vertebrae V 4  for one or more reasons set forth above, the adapter  70  is by positioning the spinous process  22  of the vertebrae V 3  in the notch  40   a  of the spacer  40 , and the body member  72  in the notch  42   b . The distal end portions of the arms  76   a  and  76   b  are fastened to the retainers  34   a  and  34   c , respectively to restrain the adapter  70  from lateral movement.  
         [0037]     The assembly consisting of the rods  30  and  32 , the spacer  40 , and the adapter  70  thus stabilizes the vertebrae V 3  and V 4 . Also, the relatively flexible, soft spacer  40  readily conforms to the process  22  of the vertebrae V 3  and provides excellent deformability resulting in an improved fit, the adapter  70  adds stiffness, compressive strength and durability, and the arms  76   a  and  76   b  restrain the adapter  44  from lateral movement.  
       Variations  
       [0038]     It is understood that variations may be made in the foregoing without departing from the invention and examples of some variations are as follows: 
        The arms in each of the previous embodiments can be rigidly connected to their corresponding rods by set screws, or other connection devices.     The components disclosed above can be fabricated from materials other than those described above and may include a combination of soft and rigid materials.     The spacer in each of the above embodiments may be formed integrally with its corresponding adapter.     Any conventional substance that promotes bone growth, such as HA coating, BMP, or the like, can be incorporated in the above embodiments.     The surfaces of the spacer  40  defining the notches  40   a  and  42   b  can be treated, such as by providing teeth, ridges, knurling, etc., to better grip the spinous processes and the adapters.     The spacer  40  can be fabricated of a permanently deformable material thus providing a clamping action against the spinous processes  22 .     One or more of the components disclosed above may have through-holes formed therein to improve integration of the bone growth.     The components of one or more of the above embodiments may vary in shape, size, composition, and physical properties.     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 vertebrae or to a spinous process.     The assemblies of each of the above embodiments can be placed between two vertebrae in the vertebral column  10  other than the ones described above.     The number and lengths of rods and arms in one or more of the embodiments can be varied.     The relatively stiff components described above could be made of a resorbable material so that their stiffness would change over time.     The rods  30  and  32  could be flexible or rigid.     In the embodiment of  FIG. 9 , the adjustment mechanism for moving the assembly consisting of the bracket  64  and the arms  66   a  and  66   b  axially may be on the latter assembly rather than the body member  62 .     In the embodiment of  FIG. 10 , the arms  74   a  and  74   b  could be pivotally mounted to the body member  52 .     The assemblies of the above embodiments can be implanted between body portions other than vertebrae.     The assemblies of the above embodiments can be inserted between two vertebrae following a discectomy 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.        
 
         [0057]     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.