Abstract:
A prosthetic device and method, according to which a member of a relatively flexible, soft material is connected with a member of a relatively stiff material and the connected members are implanted in a spinal column using a non-rigid and a rigid connection.

Description:
BACKGROUND  
       [0001]     The present invention relates to an intervertebral prosthetic device for stabilizing the human spine, and a method of implanting same. Spinal 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.  
         [0002]     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 and are supported by the respective spinous processes of the vertebrae to prevent the collapse of the intervertebral space between the adjacent vertebrae and provide motion stabilization of the spine. Many of these devices are supported between the spinous processes of the adjacent vertebrae.  
         [0004]     In some situations it is often necessary to remove the laminae and the spinous process from at least one of the adjacent vertebrae to get proper decompression. In other situations, the defective disc is removed and two vertebral segments are fused together to stop any motion between the segments and thus relieve the pain. When two adjacent vertebrae are fused, the laminae and the spinous process of at least one vertebrae are no longer needed and are therefore often removed.  
         [0005]     However, in both of the above situations involving removal of a spinous process, it would be impossible to implant an intervertebral prosthetic device of the above type since the device requires support from both processes.  
       SUMMARY  
       [0006]     According to an embodiment of the invention, an intervertebral prosthetic device is provided that is implantable between two adjacent vertebrae, at least one of which is void of a spinous process, to provide motion stabilization.  
         [0007]     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  
       [0008]      FIG. 1  is a side elevational view of an adult human vertebral column.  
         [0009]      FIG. 2  is a posterior elevational view of the column of  FIG. 1 .  
         [0010]      FIG. 3  is an enlarged, front elevational view of one of the vertebrae of the column of  FIGS. 1 and 2 .  
         [0011]      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 intervertebral prosthetic device according to an embodiment of the invention implanted between two adjacent vertebrae.  
         [0012]      FIG. 5  is an enlarged, isometric, exploded view of the prosthetic device of  FIG. 4 .  
         [0013]      FIG. 6  is a cross-sectional view of the implanted device of  FIGS. 4 and 5 .  
         [0014]      FIG. 7  is an enlarged, isometric, exploded view of an alternate embodiment of the prosthetic device of  FIG. 5 . 
     
    
     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 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.  
         [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  which 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 inferiorly 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 below.  
         [0019]     Referring to  FIG. 4 , 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  and that it is therefore necessary to provide supplemental support and stabilization of these vertebrae. As stated above, it will also be assumed that the spinous process  22  of V 4  has been removed.  
         [0020]     An intervertebral disc prosthetic device  40  according to an embodiment of the invention is provided which is adapted to be implanted between the spinous processes  22  of the vertebrae V 3  and V 5 . The prosthetic device  40  is shown in detail in  FIGS. 5 and 6  and includes a spacer  42  which is substantially rectangular in shape with the exception that two curved notches  42   a  and  42   b  are formed its respective end portions. A laterally extending channel  42   c , having a substantially rectangular cross section, extends through the entire width of the spacer  42  approximately midway between the notches  42   a  and  42   b .  
         [0021]     An insert  44  is provided that is dimensioned so as to extend in the channel  42   c  with minimum clearance. Tabs  46   a  and  46   b  extend out from the respective ends of the insert  44  and elongated openings  46   c  and  46   d  extend through the respective tabs. The length of the insert  44  substantially corresponds to the length of the channel  42   c  so that when the insert is inserted in the channel, the tabs  46   a  and  46   b  project outwardly from the channel.  
         [0022]     Two protrusions  48   a  and  48   b  extend from the sides of the tab  46   a  and two protrusions  48   c  and  48   d  extend from the sides of the tab  46   b . The protrusions are for the purpose of receiving tethers, or the like, to tether the device  40  to the vertebrae V 4  and/or V 5 .  
         [0023]     Since the spinous process of the vertebrae V 4  has been removed, the device  40  is implanted between the spinous process  22  of the vertebrae V 3  and the spinous process  22  of the vertebrae V 5 . In the implanted position shown in  FIGS. 4 and 6 , the spinous process  22  of the vertebrae V 3  extends in the notch  42   a  of the spacer  42 , and the spinous process  22  of the vertebrae V 5  extends in the notch  42   b . The dimensions of the device  40  are such that, when it is implanted in this manner, the elongated openings  46   c  and  46   d  extend over the pedicles  26   a  and  26   b  ( FIG. 3 ) of the vertebrae V 4 .  
         [0024]     Then, two screws, one of which is referred to by the reference numeral  49  in  FIGS. 4 and 6 , are inserted through the elongated openings  42   c  and  42   d , respectively, of the spacer  42 . Torque is applied to the screws  49  so that they are driven into the pedicles  26   a  and  26   b  of the vertebrae V 4 . The elongated openings  46   c  and  46   d  in the tabs  46   a  and  46   b , respectively, enable the screws  49  to be adjusted laterally and to be angled towards the pedicles  26   a  and  26   b  as necessary so that they can be driven into the pedicles.  
         [0025]     Although not shown in the drawing, tethers can be tied between the protrusions  46   a - 46   d  and the vertebrae V 3 , V 4 , and/or V 5  to provide additional support and resistance.  
         [0026]     As examples of the materials making up the spacer  42  and the insert  44 , the spacer can be of a relatively soft material, such as soft plastic, including silicone, while the insert can be of a relatively stiff material, such as hard plastic or rubber. In the latter context, the surgeon could be provided with several inserts  44  that vary in stiffness, and once the condition of the vertebrae V 4  and V 5  ( FIG. 4 ), and therefore the desired stiffness, is determined, the proper insert  44  can be selected.  
         [0027]     When the device  40  is implanted in the manner discussed above, the relatively flexible, soft spacer  42  provides non-rigid connections to the vertebrae V 3  and V 5  that readily conforms to the processes  22  of the vertebrae V 3  and V 5  and provides excellent shock absorption, while the insert  44  adds stiffness, compressive strength and durability, and the screws  49  provide a rigid connection to the vertebrae V 4 .  
         [0028]     A prosthetic device  50  according to another embodiment is shown in detail in  FIG. 7  and includes a spacer  52  which is substantially rectangular in shape with the exception that a curved notch  52   a , is formed in one end portion. A tab  52   b  projects from the other end of the spacer  52  for reasons to be described.  
         [0029]     A spacer  54  is also provided which is substantially rectangular in shape with the exception that a curved notch  54   a  is formed in one end portion and a tab  54  projects from the other end of the spacer  52 .  
         [0030]     A connector  56  is designed to fit over the tabs  52   b  and  54   b  of the spacers  52  and  54 , respectively, to connect them. To this end, the connector  56  has a through opening  56   a  with a cross section slightly greater than the cross sections of the tabs  52   b  and  54   b .  
         [0031]     Two tabs  56   b  and  56   b  extend out from the respective ends of the connector  56 , and elongated openings  56   c  and  56   d  extend through the respective tabs for receiving screws, for reasons to be described.  
         [0032]     Two protrusions  58   a  and  58   b  extend from the sides of the tab  56   b  and two protrusions  58   c  and  58   d  extend from the sides of the tab  56   c . The protrusions are for the purpose of receiving tethers, or the like, to tether the device  40  to the vertebrae V 4  and/or V 5 .  
         [0033]     To connect the spacers  52  and  54 , their respective tabs  52   b  and  54   b  are inserted into the opening  56   a  of the connector  56  from opposite ends of the opening until the corresponding shoulders of the spacers  52  and  54  engage the corresponding ends of the connector  56 . The spacers  52  and  54  and the connector are sized so that the tabs  52   a  and  54   a  engage the inner wall of the connector  56  in a friction fit so as to retain the spacers  52  and  54  in the connector.  
         [0034]     Since the spinous process of the vertebrae V 4  has been removed, the device  50  is implanted between the spinous process  22  of the vertebrae V 3  and the spinous process  22  of the vertebrae V 5 . In the implanted position, the spinous process  22  of the vertebrae V 3  extends in the notch  52   a  of the spacer  42 , and the spinous process  22  of the vertebrae V 5  extends in the notch  52   b . The dimensions of the device  50  are such that, when it is implanted in this manner, the elongated openings  56   c  and  56   d  extend over the pedicles  26   a  and  26   b  ( FIG. 3 ) of the vertebrae V 4 .  
         [0035]     Although not shown in the drawing, tethers can be tied between the protrusions  58   a - 58   d  and the vertebrae V 3 , V 4 , and/or V 5  to provide additional support and resistance.  
         [0036]     The spacers  52  and  54  could be fabricated from a relatively soft material, such as soft plastic, including silicone, while the connector  56  could be fabricated from a relatively stiff material, such as hard plastic or rubber. In the latter context, the surgeon could be provided with several connectors  56  that vary in stiffness. Thus, once the surgeon ascertains the condition of the vertebrae V 3 , V 4 , and V 5  ( FIG. 3 ) and determines the particular stiffness that is needed, the proper connector  56  can be selected.  
         [0037]     Thus, when the device  50  is implanted between the processes  22  of the vertebrae V 3  and V 5  in the manner discussed above, the relatively flexible, soft spacers  52  and  54  provide a non-rigid connection to the vertebrae V 3  and V 5  that readily conforms to the processes  22  of the vertebrae V 3  and V 5 , and provides excellent shock absorption. Also, the connector  56  adds stiffness, compressive strength and durability, and the screws  49  provide a rigid connection to the vertebrae V 4 .  
         [0038]     It is understood that other 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 prosthetic device of the above embodiments.     One or more of the components of the above devices may have through holes formed therein to improve integration of the bone growth.     The surfaces of the body member defining the notch can be treated, such as by providing teeth, ridges, knurling, etc., to better grip the spinous processes and the adapters.     The body member can be fabricated of a permanently deformable material thus providing a clamping action against the spinous process.     The spacers and associated 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 prosthetic devices to receive tethers for attaching the devices to a vertebrae or to a spinous process.     The prosthetic device of each of the above embodiments can be placed between two vertebrae in the vertebral column  10  other than the ones described above.     The prosthetic device of each of the above embodiments can be fabricated from materials other than those described above.     The relative stiff components described above could be made of a resorbable material so that their stiffness would change over time.     The prosthesis of the above embodiments can be implanted between body portions other than vertebrae.     In the embodiment of  FIG. 7 , the spacers  52  and  54  can be fabricated from a relatively stiff material and the connector  56  from a relatively soft, flexible material.     The prostheses of the above embodiments can be inserted between two vertebrae following a discectemy in which a disc between the adjacent vertebrae is removed, or a 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.    
 
         [0052]     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.