Abstract:
A prosthetic device and method, according to which first end plate engages a first vertebral body, and a second end plate engages a second vertebral body. An insert lockingly engages one of the end plates and engages the other end plate in a manner to permit relative movement therebetween.

Description:
BACKGROUND  
       [0001]     This invention relates to an intervertebral endoprosthetic device and a method of assembling same and, more particularly, to such a device and method in which a locking mechanism is provided to lock two components of the device.  
         [0002]     Spinal discs in the human body may rupture or degenerate to such a degree that the disc has to be surgically removed. In these cases, intervertebral prosthetic devices are available that are designed to be implanted between the adjacent vertebrae to prevent the collapse of the intervertebral space between adjacent vertebrae while maintaining a certain degree of stability and range of pivotal and rotational motion therebetween. Such devices typically include two or more articular elements that are attached to the respective adjacent vertebrae and are adapted to move relative to each other.  
         [0003]     Many of these devices, especially those that are inserted in the cervical spine, are either made out of a single component, or are made from multiple components which are permanently fixed together. Therefore, these devices do not offer modularity or revisability without removing the entire assembly.  
         [0004]     Although modular systems do exist for use in the lumbar spine, these systems use hinges on the components, or modules, to connect the components. However this type of connection is not robust and/or tends to malfunction, causing disassociation that often results in significant complications.  
         [0005]     All patents listed in Table 1 are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Preferred Embodiments and Claims set forth below, many of the devices and methods disclosed in the patents of Table 1 may be modified advantageously by using the teachings of the present invention.  
                       TABLE 1                       Patent/Publication No.   Patented/Published Date   Inventor                   5,425,773   Jun. 20, 1995   Boyd et al.       5,562,738   Oct. 8, 1996   Boyd et al.       6,146,421   Nov. 14, 2000   Gordon et al.       2002/0099444   Jul. 25, 2002   Boyd et al.       2003/0040799   Feb. 27, 2003   Boyd et al.       2004/0002758   Jan. 1, 2004   Landry et al.       6,682,561   Jan. 27, 2004   Songer et al.       2004/0068318   Apr. 8, 2004   Coates et al.       6,726,720   Apr. 27, 2004   Ross et al.       2004/0083000   Apr. 29, 2004   Keller et al.                  
 
       SUMMARY  
       [0006]     According to an embodiment of the invention, an intervertebral prosthesis is provided that includes an insert that is encapsulated in a base member of the prosthesis in a manner to provide minimal opportunity for disassociation.  
         [0007]     Various embodiments of the invention discussed below 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 sectional view of a vertebral column of a human body having a damaged disc.  
         [0009]      FIG. 2  is an enlarged partial view of the vertebral column of  FIG. 1  and depicting an implanted intervertebral prosthesis according an embodiment of the invention.  
         [0010]      FIG. 3  is an exploded isometric view of the prosthesis of  FIG. 2   
         [0011]      FIG. 4 a  partial sectional/partial elevational view showing a step in assembling the prosthesis of  FIGS. 2 and 3 .  
         [0012]      FIG. 5  is an enlarged sectional view of the assembled prosthesis of  FIGS. 2 and 3 .  
         [0013]      FIGS. 6 and 7  are partial exploded isometric view of two alternate embodiments.  
         [0014]      FIGS. 8 and 9  are isometric views of two additional alternate embodiments. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]     Referring first to  FIG. 1 , the numeral  10  refers to a vertebral column with a damaged intervertebral disc  12  extending between two adjacent vertebrae  14  and  16  in the cervical, thoracic, or lumbar spine, or in other regions of the vertebral column.  
         [0016]     Referring to  FIG. 2 , it will be assumed that a typical surgical discectomy was performed to remove the disc  12  and create a void between the two intact vertebrae  14  and  16 , and that an intervertebral disc prosthesis  20  according to an embodiment of the invention is implanted in the above void.  
         [0017]     The prosthesis  20  is shown in detail in  FIGS. 3 and 4  and includes an insert  22  interposed between an upper end plate  24  and a lower end plate  26 , as viewed in the drawings. The upper end plate  24  is generally rectangular in shape with a curved anterior, or front surface, as viewed in  FIGS. 3 and 4 , and an upper surface that is either flat or contoured to match the corresponding surface of the vertebrae  14  ( FIG. 2 ). A semi-spherical recess  24   a  is formed in the lower surface of the end plate  24 , and a tab  24   b  extends upwardly from its anterior end.  
         [0018]     The lower end plate  26  is also generally rectangular in shape with a curved anterior end surface, and its upper surface includes a generally rectangular recessed area  26   a  bounded on its two sides and its end by a groove  26   b.  An access notch  26   c  is formed in the anterior end portion of the end plate  26  that extends from the outer surface of the end plate to the recessed area  26   a,  and a ramp  26   d  is formed at the base of the notch. A tab  26   e  extends downwardly from the anterior end of the end plate  26 . The lower surface of the end plate  26  is flat as shown, but could be contoured to match the corresponding surface of the vertebrae  16  ( FIG. 2 ).  
         [0019]     It is understood that the end plates  24  and  26  are fastened to the vertebrae  14  and  16 , respectively, in any conventional manner which would include locating the tabs  24   b  and  26   e  over the corresponding outer anterior surface of the vertebrae  14  and  16 , respectively, as shown in  FIG. 2 , to prevent posterior movement of the prosthesis. For example, fasteners, such as screws, or the like, could be driven through any part of the end plates  24  and  26 , including the tabs  24   b  and  26   e,  and into the vertebrae  14  and  16  to fasten the prosthesis  10  to the vertebrae. According to another example, bone-engaging surfaces, or fins, can be provided on the upper surface of the end plate  24  and the lower surface of the end plate  26 , to engage the vertebrae  14  and  16 , respectively, to enhance secure implantation of the prosthesis  10 .  
         [0020]     The insert  22  has a domed upper portion  30  formed integrally with, and extending upwardly from, a substantially rectangular lower portion  32 . The domed upper portion  30  fits within the recess  24   a  of the end plate  24  with minimal clearance to form an articulating joint, permitting rotational movement between the insert  22  and the end plate  24 .  
         [0021]     Two parallel, longitudinally extending, notches  32   a  and  32   b  are provided in the rectangular portion  32  and are spaced slightly inwardly from the respective side walls of the rectangular portion. Thus, each portion of the rectangular portion  32  extending between a notch and its corresponding side wall is relatively flexible. A peripheral dovetail projection  32   c  extends from the side walls and the posterior wall of the rectangular portion  32 , and is sized to extend in the corresponding portions of the groove  26   b  of the end plate  26 .  
         [0022]     A tab  32   d  extends outwardly from the anterior end of the insert  22 , and has a flat upper surface that is designed to be engaged by a suitable tool. This enables the surgeon to apply a force to the tab  32   d  in a direction towards the end plate  26  to aid in locking the insert  22  to the lower end plate  26  in a manner to be described.  
         [0023]     The insert  22  is attachable to the lower end plate  26  by initially positioning it over the plate at a slight angle to the plane of the latter end plate as shown in  FIG. 4 . That portion of the projection  32   c  that extends from the posterior wall of the rectangular portion  32  of the insert  22  is inserted in the corresponding portion of the groove  26   b  of the end plate  26 . Then the anterior portion of the insert  22  is forced downwardly towards the end plate  26  by engaging a tool with the upper surface of the tab  32   d  and pressing downwardly. The above-mentioned, relatively flexible, side portions of the rectangular portion  32 , including the portions of the projection  32   c  extending from the side walls of the rectangular portion, snap into the corresponding portions of the groove  26   b.    
         [0024]     As a result, the insert  22  is locked to the end plate  26  and is substantially encapsulated between the end plates  24  and  26  to considerably reduce the chances for disassociation. Thus, the prosthesis  10  is completed implanted between the vertebrae  14  and  16  as shown in  FIG. 5 , and the assembly formed by the connected insert  22  and end plate  26  can rotate relative to the end plate  24 .  
         [0025]     The insert  22  is modular, and as such, can be revised, or replaced, by another insert of a different size, design, or the like. To this end, the insert  22  can be unlocked from the lower end plate  26  by inserting a proper tool (not shown) through the notch  26   c  and, using the ramp  26   d  as a guide, wedging the tool between the lower surface of the rectangular portion  32  of the insert  22  and the upper surface of the end plate  26 . The tool can then be pivoted about the ramp  26   d  to force the insert in a direction away from the end plate  26  to effect the separation. The insert  22  can then be completely disconnected from the end plate  26  by sliding the insert anteriorly relative to the end place  26 . This permits the insert  22  to be replaced while maintaining the end plates  24  and  26  in their original positions, secured to the vertebrae  14  and  16 .  
         [0026]      FIG. 6  depicts an alternate embodiment of the invention and includes structure and components of the previous embodiment that are given the same reference numerals. According to the embodiment of  FIG. 6 , the tab  32   d  is eliminated and an opening  32   e  is formed in a flat end portion of the rectangular portion  32  for receiving a tool, for forcing the insert  22  towards the end plate  26  in the assembly step discussed above. Otherwise, the embodiment of  FIG. 6  is identical to that of  FIGS. 2-5 .  
         [0027]     The embodiment of  FIG. 7  is similar to that of  FIGS. 2-5  and identical structure and components are given the same reference numerals. According to the embodiment of  FIG. 7 , two spaced parallel rails  26   f  and  26   g  project upwardly from the recessed area  26   a  of the lower end plate  26 , and are adapted to extend in the notches  32   a  and  32   b  respectively. In this context, the depths of the notches  32   a  and  32   b  can be increased, when compared to their depths in the embodiment of  FIGS. 2-5 . Thus, when the insert  22  is locked to the end plate  26  as described above in connection with the embodiment of  FIGS. 3-5 , the rails  26   f  and  26   g  extend in the notches  32   a  and  32   b,  respectively, to further secure the insert to the end plate. Otherwise, the embodiment of  FIG. 7  is identical to that of  FIGS. 3-5  with the understanding that the opening  32   b  of the embodiment of  FIG. 7  could be replaced by the tab  32   d  of the embodiment of  FIG. 3 .  
         [0028]     The embodiments of  FIGS. 8 and 9  are similar to the embodiment of  FIGS. 2-5  an identical structure and components are given the same reference numerals. According to the embodiment of  FIG. 8 , the tabs  24   b  and  26   e  on the end plates  24  and  26 , respectively, of the embodiment of  FIGS. 2-5  are eliminated, and two lugs  24   c  and  26   h  are provided on the anterior ends of the respective plates. The lugs  24   c  and  26   h  are dove-tailed to form a trapezoidal cross section to enable a corresponding tool to grip them to assist the surgeon in manipulating the prosthesis  10  relative to the vertebrae  14  and  16 . Although the tab  32   d  is shown on the insert  22  in the embodiment of  FIG. 8 , it is understood that the opening  32   d  of  FIG. 6  could be provided. Also, the rails  26   f  and  26   g  of the embodiment of  FIG. 7  could be provided, or left off, of the embodiment of  FIG. 8 . Otherwise the embodiment of  FIG. 8  is identical to those of the previous embodiments.  
         [0029]     The embodiment of  FIG. 9  is identical to that of  FIG. 8  with the exception that the lug  24   c  is extended upwardly as viewed in the drawing, and the lug  26   h  is extended downwardly. Thus, in addition to providing gripping surfaces as discussed above in connection with the embodiment of  FIG. 7 , the lugs  24   c  and  26   h  also perform the function of the tabs  24   b  and  26   e  of the embodiment of  FIGS. 2-5 . It is understood that, although the tab  32   d  is shown on the insert  22  in the embodiment of  FIG. 9 , the opening  32   e  of  FIG. 6  could be provided. Also, the rails  26   f  and  26   g  of the embodiment of  FIG. 7  could be provided, or left off, of the embodiment of  FIG. 9 . Otherwise the embodiment of  FIG. 9  is identical to those of the previous embodiments.  
         [0030]     In all of the above embodiments, the end plates  24  and  26  and may be formed of any suitable biocompatible material including, titanium alloys, cobalt-chrome alloys, stainless steel, alumina, zirconia, polycrystalline diamond, pyrolytic carbon, and the insert  22  can be formed of ultra-high molecular weight polyethylene (UHMWPE), polyetheretherketone (PEEK cross-linked UHMWPE), or other suitable materials. The surfaces of the end plates  24  and  26  and/or the insert  22  may include features or coatings which enhance the purchase or ingrowth qualities of the prosthesis  10 . For example, a plazma or biocompatible and osteoconductive material, such as hydroxyapatite (HA), may coat all or a portion of one or more of the above surfaces. Other suitable coatings or treatments may include a porous bead coating, a porous mesh coating, osteogenic peptide coating, growth factor coating, rh-BMP coating, and/or grit blasting. The respective surfaces of the domed portion  30  of the insert  22  and the recessed portion  24   a  of the upper end plate  24  may be selected or treated to be sufficiently durable to provide acceptable wear characteristics as a result of their articulating movement.  
         [0000]     Variations  
         [0031]     It is understood that variations may be made in the foregoing without departing from the invention and examples of some variations are as follows:  
         [0032]     (1) The prosthesis  10  can be implanted between body portions other than vertebrae.  
         [0033]     (2) The prosthesis  10  can be inserted between two vertebrae following a corpectomy in which at least one vertebrae has been removed.  
         [0034]     (3) The insert  22  may vary somewhat in shape, size, composition, and physical properties, depending upon the particular area in which the prosthesis is implanted, and more particularly, the space between the end plates  24  and  26  after they have been connected to the vertebrae  14 , and  16 , respectively.  
         [0035]     (4) The upper domed portion of the insert  22  can be replaced by a protrusion of a different shape.  
         [0036]     (5) The dome could be formed on the lower surface of the end plate  24  and the corresponding recess formed in the upper surface of the insert  22 .  
         [0037]     (6) The prosthesis  10  can be implanted between the vertebrae  14  and  16  in a position that is inverted from the position shown in  FIG. 2 . In this case the end plate  26  would be connected to upper vertebrae  14  and the end plate  24  connected to the vertebrae  16 , in which case one or both of the end plates  24  and  26  could vary in shape.  
         [0038]     (7) In the embodiment of  FIG. 7 , rather than provide the rails  26   f  and  26   g  in the end plate  26  and the corresponding notches  32   c  and  32   d  in the insert  22 , the rails could be provided in the insert and the notches in the end plate.  
         [0039]     (8) A lug ( 24   c  or  26   h ) can be provided on one of the end plates  24  and  26  and not on the other.  
         [0040]     (9) The opening  32   d  in the embodiment of  FIGS. 2-5  may be eliminated.  
         [0041]     (10) The spatial references made above, such as “under”, “over”, “between”, “upper”, “lower”, etc. are for the purpose of illustration only and do not limit the specific orientation or location of the structure described above.  
         [0042]     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.