Abstract:
A prosthetic device and method of inserting same between adjacent vertebrae, according to which a first member of a relatively flexible material is adapted to extend between the vertebrae; and at least one second member of a relatively stiff material is supported by the first member.

Description:
BACKGROUND  
       [0001]     The present invention relates to an intervertebral prosthetic device for stabilizing the human spine.  
         [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 are relatively stiff, and, as such, cannot flex to better accommodate the vertebrae and do not provide a sufficient amount of shock absorption. Also, many of these devices, when implanted, suffer from a relatively high fatigue.  
       SUMMARY  
       [0005]     The intervertebral prosthetic device according to the embodiments of the invention overcomes the above deficiencies by providing relatively high shock absorption, as well as a good fit with the anatomy and relatively low fatigue characteristics.  
         [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 the intervertebral prosthetic device according to an embodiment of the invention inserted between two adjacent vertebrae.  
         [0011]      FIG. 5  is an enlarged, isometric, exploded view of the prosthetic device of  FIG. 4 .  
         [0012]      FIGS. 6 and 7  are enlarged, isometric, exploded views of alternate embodiments of the prosthetic device of  FIG. 5 . 
     
    
     DETAILED DESCRIPTION  
       [0013]     With reference to  FIGS. 1 and 2 , the reference numeral  10  refers, in general, to an 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.  
         [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 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 sacrum  14  from the coccyx  16  which includes four fused vertebrae (not referenced).  
         [0016]     With reference to  FIG. 3 , the vertebrae V 4  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  and V 5  are similar to the vertebrae V 4  they will not be described in detail.  
         [0017]     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. 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 4  and V 5 .  
         [0018]     The prosthetic device  40  is shown in detail in  FIG. 5  and includes a relatively flexible, soft, body member  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 body member  42  approximately midway between the notches  42   a  and  42   b.    
         [0019]     An insert  44 , of a relatively stiff material, is provided that is dimensioned so as to extend in the channel  42   c  with minimum clearance. Thus, the insert  44  has a substantially rectangular cross-section that substantially corresponds to that of the channel  42   c , with the exception that it is slightly smaller so as to fit in the channel. The length of the insert  44  substantially corresponds to the length of the channel  42   c.    
         [0020]     When the device  40  is implanted between the two adjacent vertebrae V 4  and V 5  ( FIG. 4 ), the spinous process  22  of one of the vertebrae V 4  or V 5  extends in the notch  42   a  and the spinous process of the other vertebrae extends in the notch  42   b . The relatively flexible, soft body member  42  provides excellent shock absorption, and the insert  44  adds stiffness, compressive strength and durability to the device  40 .  
         [0021]     It is understood that the surgeon could be provided with several inserts  44  that vary in stiffness. Thus, once the surgeon ascertains the condition of the vertebrae V 4  and V 5  ( FIG. 4 ) and determines the particular stiffness that is needed, the proper insert  44  can be selected.  
         [0022]     A prosthetic device  50  according to another embodiment is shown in detail in  FIG. 6  and includes a relatively flexible, soft body member  52  which is substantially rectangular in shape with the exception that two curved notches  52   a and  52   b  are formed in its respective end portions, as viewed in the drawing. A laterally extending channel  52   c , having a substantially rectangular cross section, extends through the body member  52 .  
         [0023]     Two inserts  54  and  56 , of a relatively stiff material, are provided and each is dimensioned so as to extend in the channel  52   c  with minimum clearance. Each insert  54  and  56  has a substantially rectangular cross section that substantially corresponds to that of the channel  52   c , with the exception that the inserts are slightly smaller than the channel so as to fit in the channel. The outer ends of the inserts  54  and  56  are provided with outwardly extending flanges  54   a  and  56   a , respectively.  
         [0024]     The inserts  54  and  56  are inserted into the channel  52   c  from opposite sides in the directions shown by the arrows in  FIG. 6 , until the flanges  54   a  and  56   a  engage the corresponding outer surfaces of the body member  52  to limit the extension of the inserts into the channel. In the inserted positions of the inserts  54  and  56 , their combined length substantially correspond to the length of the channel  52   c.    
         [0025]     When the device  50  is implanted between the two adjacent vertebrae V 4  and V 5  ( FIG. 4 ), the spinous process  22  of one of the vertebrae V 4  or V 5  extends in the notch  52   a  and the spinous process of the other vertebrae extends in the notch  52   b . The relatively flexible, soft body member  52  provides excellent shock absorption, and the inserts  54  and  56  add stiffness, compressive strength and durability to the device  50 .  
         [0026]     It is understood that the surgeon could be provided with several pairs of inserts  54  and  56  that vary in stiffness from pair to pair. Thus, once the surgeon ascertains the condition of the vertebrae V 4  and V 5  ( FIG. 4 ) and determines the particular stiffness that is needed, the proper inserts  54  and  56  can be selected.  
         [0027]     A prosthetic device  60  according to another embodiment is shown in detail in  FIG. 7  and includes a relatively flexible, soft body member  62  which is substantially rectangular in shape with the exception that two curved notches  62   a  and  62   b  are formed in its respective end portions, as viewed in the drawing.  
         [0028]     A groove  62   c  is formed in the front face of the body member  62 , as viewed in the drawing, and extends across its width approximately mid-way between the notches  62   a  and  62   b.  A groove  62   d  is formed in the rear face of the body member  62  and also extends across its width approximately mid-way between the notches  62   a  and  62   b.  The grooves  62   c  and  62   d  thus define a center portion  62   e  of the body member  62  that has a reduced thickness.  
         [0029]     Two substantially U-shaped inserts  64  and  66 , of a relatively stiff material, are provided. The insert  64  is formed by a base  64   a  from which two spaced legs  64   b  and  64   c  extend at right angles, and the insert  66  is formed by a base  66   a  from which two spaced legs  66   b  and  66   c  extend at right angles. The thicknesses of the legs  64   b  and  64   c  of the insert  64  substantially correspond to the depth of the notches  62   c  and  62   d , respectively, the lengths of the legs substantially correspond to one-half the length of the notches, and the space between the legs substantially correspond to the thickness of the center portion  62   e . Similarly, the thicknesses of the legs  66   b  and  66   c  of the insert  66  substantially correspond to the depth of the notches  62   c  and  62   d , respectively. The lengths of the legs substantially correspond to one-half the length of the notches, and the space between the legs substantially correspond to the thickness of the center portion  62   e . Thus, when the inserts  64  and  66  are inserted in the grooves  62   c  and  62   d , each extends over approximately one-half of the center portion  62   e  of the body member  62 .  
         [0030]     An extrusion  68   a  and  68   b  extend from the outer surfaces of the each base  64   a  and  66   b , respectively, for tethering the bases to the vertebrae V 4  and V 5  ( FIG. 4 ).  
         [0031]     The inserts  64  and  66  are inserted into the groove  62   c  from opposite sides in the directions shown by the arrows in  FIG. 7  until their respective bases  64   a  and  66   b  engage the corresponding side walls of the center portion  62   d . In this inserted position, the combined lengths of the inserts  64  and  66  substantially correspond to the length of the groove  62   c.    
         [0032]     When the device  60  is implanted between the two adjacent vertebrae V 4  and V 5  ( FIG. 4 ), the spinous process  22  of one of the vertebrae V 4  or V 5  extends in the notch  62   a  and the spinous process of the other vertebrae extends in the notch  62   b.  The extrusions  68   a  and  68   b  are used to tether the device  60  to the spinous processes  22 .  
         [0033]     The relatively flexible, soft body member  62  provides excellent shock absorption, and the inserts  64  and  66  add stiffness, compressive strength and durability to the device  60 .  
         [0034]     It is understood that the surgeon could be provided with several pair of inserts  64  and  66  that vary in stiffness from pair to pair. Thus, once the surgeon ascertains the condition of the vertebrae V 4  and V 5  ( FIG. 4 ) and determines the particular stiffness that is needed, the proper inserts  64  and  66  can be selected.  
         [0035]     It is understood that, in each of the above embodiments, the material making up the body members  42 ,  52 ,  62 ,  72   74 ,  82 ,  92 , and  94  can be of a flexible, soft plastic, such as silicon, which can be molded into the shapes shown and described. The inserts  44 ,  54 ,  56 ,  64 ,  66 , as well as the connectors  76  and  96  and the body member  84  can be of a relatively stiff rubber, plastic, metal, or other similar material.  
       Variations  
       [0036]     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 each of the above embodiments     The relatively stiff components of the above devices may have through holes formed therein to improve integration of the bone growth.     The body members, inserts, and connectors of one or more of the above embodiments may vary in shape, size, composition, and physical properties. For example the insert  44  of the embodiment of  FIG. 5  can be circular in cross section.     Through openings can be provide through one or more components of each of the above embodiments to receive tethers for attaching the devices to the a vertebrae or to a spinous processes.     The insert  44  of the embodiment of  FIG. 5  can be secured in the channel  42   c  of the body member  40  in any conventional manner.     The inserts  54  and  56  of the embodiment of  FIG. 6  can be secured in the channel  52   c  of the body member  50  in any conventional manner.     The bilateral extrusions, shown in the embodiment of  FIG. 7 , may be provided on the relative stiff component of each embodiment for tethering the device to a vertebrae or a spinous process.     The relative stiff components described above could be made of a resorbable material so that their stiffness would change over time.     The inserts  64  and  66  of the embodiment of  FIG. 7  can be secured in the channel  62   c  of the body member  60  in any conventional manner.     The relatively stiff components described above could be replaced by components having a different stiffness pre-operatively or intra-operatively.     In each of the above embodiments, the components that are made of a relatively flexible, soft material could be made of a relatively stiff material and the components that are made of a relatively stiff material could be made of a relatively flexible, soft material.     The prosthetic devices of the above embodiments can be inserted between the facets of adjacent vertebrae, rather than the spinous processes;     The prosthetic devices of the above embodiments can be implanted between body portions other than vertebrae.     The prosthetic devices 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.     The spatial references made above, such as “under”, “over”, “between”, “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.