Abstract:
A cage assembly adapted to be implanted in a spinal column for treating degenerative or ruptured discs and replacing damaged vertebral bodies. The assembly includes one or more rigid cages formed in an annular configuration and having opposed upper and lower perimeter surfaces, an annular side wall extending between said surfaces, a transverse inner wall extending across said cage, a plurality of raised ridges projecting outwardly from each of said perimeter surfaces for engaging the spinal column and securing the assembly therein. Apertures are provided in the side wall for use in positioning said cage in the spinal column and a pair of aligned openings extend axially through the cage for packing the cage with bone graft material. At least one spacing element having the same annular configuration as the cages can be provided to effect the stacked attachment of one cage with another in rigid axial alignment.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to prosthetic devices adapted to be implanted between the vertebrae for treating degenerative or ruptured discs and for replacing damaged vertebral bodies. More particularly, the invention comprises a rigid vertebral body replacement cage which is annular in configuration and shaped for its particular application. The cages can be formed in a half-moon shape to be used in the center of the vertebral body, a modified kidney-shape to be used in the anterior portion of the vertebral body or of a smaller oval configuration for lateral applications on the sides of the vertebral body. The cages are configured to be used singularly or in stacked combination to replace a damaged disc and/or vertebrae and can also be secured inside the fibrous disc column connecting adjoining vertebrae to provide the necessary support in the spinal column.  
         [0002]     While vertebral body replacement devices have been in use for several years, efforts have been ongoing to improve them. As a result of their configuration, the vertebral body replacement cages of the present invention are not only particularly well suited for their intended purpose, they are very versatile in their applications, easily placed into proper position during the operative procedure, whether used individually or in a stacked configuration and, when used in a stacked configuration, are far more easily joined together in a secure stack of desired length than those cages heretofore available. The result is a substantial improvement in vertebral body replacement devices.  
         [0003]     Briefly, the present invention is directed to a vertebral body replacement cage assembly adapted to be implanted between the vertebrae for treating degenerative or ruptured discs and for replacing damaged vertebral bodies. The assembly comprises one or more rigid cages that are configured to be used singularly or in a stacked combination to fill differently sized evacuated spaces. Each cage is formed of a biologically accepted inert material, is of an annular configuration and is particularly shaped and sized for its particular application. The assembly also includes one or more spacing elements for joining together two or more cages in a stacked configuration to provide the assembly with its desired axial length.  
         [0004]     Each cage in the assembly of the present invention defines opposed upper and lower perimeter surfaces, an annular side wall extending between said surfaces and, for several applications, a transverse inner wall. The upper and lower perimeter surfaces each define a plurality of outwardly projecting spaced ridges thereon for biting and gripping into the vertebral end plates. The annular side wall of the cage has a plurality of tool engaging openings therein to facilitate insertion of the cage in any desired angular orientation and cooperates with the transverse wall to define a pair of openings extending axially through the cage which are adapted to be packed with bone graft material to expedite the fusion of the cage in the spinal column. A plurality of indexing apertures are provided in the perimeter surfaces of the cage for receiving a corresponding plurality of indexing pins on a spacing element for stacked applications.  
         [0005]     The spacing elements in the cage assembly preferably have the same general annular shape as the cages with which they are used but are shorter in axial dimension. The spacing elements each define the above-identified indexing pins and two pair of opposed outwardly projecting locking tabs that are adapted to engage wall portions of a pair of adjacent cages when the indexing pins on the spacing element are inserted into the indexing apertures on a pair of adjacent cages, thereby effecting an operative assembly of a desired axial length corresponding to the length of the evacuated area. Thus, the present invention provides a very versatile assembly for replacing damaged discs and/or vertebrae which can also be secured inside the fibrous disc column connecting adjoining vertebrae to provide the spinal column with the necessary support. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS IN THE DRAWINGS  
       [0006]      FIG. 1  is a perspective view of a first embodiment of the vertebral body replacement cage of the present invention.  
         [0007]      FIG. 2  is a perspective view of a first embodiment of the vertebral body replacement cage of the present invention which has been modified for stacked applications.  
         [0008]      FIG. 3  is a perspective view of the cage shown in  FIG. 1  with a spacing element attached thereto.  
         [0009]      FIG. 4  is a perspective view of a pair of the first embodiment of the replacement cages of the present invention secured together by a spacing element in a stacked configuration in accordance with the present invention.  
         [0010]      FIG. 5  is a perspective view of a second embodiment of a vertebral body replacement cage of the present invention wherein the cage is of a modified kidney-shape.  
         [0011]      FIG. 6  is a perspective view of a second embodiment of a vertebral body replacement cage of the present invention wherein the cage is of a modified oval shape.  
         [0012]      FIG. 7  is a perspective view of the oval-shaped cage of  FIG. 6  with a spacing element attached thereto.  
         [0013]      FIG. 9  is a partial sectional view as seen from above of the oval-shaped cage shown in  FIG. 6  proximate the extended end of an insertion tool used therewith.  
         [0014]      FIG. 10  is a perspective view of a kidney-shaped vertebral body replacement cage of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]     Referring now in detail to the drawings, the vertebral replacement cage of the present invention is of a rigid construction and preferably provided in three basic shapes with each shape being provided in several different sizes (horizontally and vertically) to fill differently sized evacuated spaces in differently sized individuals. The cage is annular in configuration and in the embodiment shown in  FIGS. 1 and 2 - 4 , is “half-moon”-shaped for use in the center of the vertebral body. Three other shapes of the replacement cage are illustrated in  FIGS. 5, 6  and  10  and will be discussed later herein.  
         [0016]     Cage  10 , illustrated in  FIGS. 1-4 , is preferably constructed of commercially pure titanium, a titanium alloy or of a radiolucent material such as polyetherketoneketone (PEKK), although it could be formed of other biologically acceptable inert materials that would provide the cage  10  with a rigid structure. Cage  10  defines an upper surface  12 , an opposed lower surface  14 , an annular side wall  16  and a transverse inner wall  18 . While only the upper surface  12  of the cage is visible in the drawings, lower surface  14  is preferably identical in configuration. Accordingly, the following description generally will be with references only to the upper surface  12 . It is to be understood, however, that the description is equally applicable to the lower surface  14  of the cage. transverse portion  12   b . A plurality of outwardly projecting sharp raised ridges  20  are formed in the perimeter portion  12   a  of surface  12  for biting into and gripping the vertebral end plates (not shown). The ridges  20  preferably are disposed at slightly offset angles with respect to each other or, alternatively with respect to the ridges on different portions of the cage, to reduce the possibility of the ridges sliding in any direction along the end plates and to prevent rotation of the cage on the end plate. For example, as shown in  FIG. 1 , the ridges on one side of the transverse wall  18  are all in parallel alignment, but misaligned with the ridges  20  on the other side of wall  18 . All of the ridges  20  taper outwardly from its relatively sharp edge along inclined walls  24  into enlarged open areas  26  between the individual ridges.  
         [0017]     For stacked applications (see  FIGS. 2-4 ), a plurality of indexing apertures  28  are also provided in the outer surfaces  12  and  14  of cage  10 . Preferably, three such apertures  28  are provided in each of the opposed surfaces, one aperture being disposed in each surface proximate each end of the cage and the third aperture at the juncture of the perimeter and transverse surfaces as seen in  FIG. 2 .  
         [0018]     A plurality of tool engaging openings  30  are disposed in the side wall  16  of the cage. Openings  30  can be threaded or otherwise configured to receive a conventional insertion tool (not shown) and are preferably spaced about the cage  10  so as to provide one such opening  30  at each of the opposed ends of the cage and a plurality of openings  30  along the anterior and posterior sides of the cage. In the preferred configuration illustrated in  FIGS. 1-4 , the openings  30  are arranged in groups of three to accommodate the insertion tool illustrated in  FIG. 9 . In each opening or aperture grouping, a threaded circular aperture  30   a  is disposed between a pair of unthreaded generally rectangular openings  30   b  to accommodate the insertion tool  75  which includes a rotatable threaded shank  77  disposed between a pair of prongs  79  so that the tool can grip the cage for insertion  1  and  2 , the groupings of openings  30  are provided at each end of the cage  10  at the interior side of the cage so as to be centered thereon and at a 45 degree inclination with respect to the central axis of transverse inner wall  18 . So positioned, the tool can grip the cage at either end thereof and at 90 and 45 degree angles with respect to the cage ends. Only one aperture grouping at a 45 degree inclination is needed in view of the symmetry of the cage. As a result of such a configuration convenient access is always provided to at least one of the groupings to facilitate insertion of the cage in any desired angular orientation. So configured, the cage  10  also defines a pair of axially aligned openings  32  and  34  extending therethrough which can easily be packed with bone graft material to expedite the fusion of the cage in the spinal column.  
         [0019]     For those applications that require a prosthesis of greater length than can be effectively provided by a single vertebral body replacement cage and to provide greater flexibility in cage length (vertical elevation) without having to provide a corresponding inventory of cages, cage  10  is adapted for use with one or more spacing elements  38  to provide a rigid stack of cages. To provide such versatility, cage  10  includes two pair of opposed tab receiving slots  37  in opposite sides of the transverse inner wall  18  proximate the upper and lower surfaces of wall  18 . Slots  37  are used in the securement of one or more spacing elements  38  to provide such a stack of cages as will be described.  
         [0020]      FIG. 3  illustrates the securement of a cage  10  to a spacing element  38  to form a secure stack of two such cages as seen in  FIG. 4 . Spacing element  38  is preferably constructed of titanium and is of a substantially identical annular configuration as the cages  10  with which it is being used. Spacing element  38  defines opposed identical upper and lower perimeter surfaces  40  and transverse surfaces  42  extending therebetween. Again, only the upper surfaces are seen in the drawings. Unlike the perimeter surfaces of cage  10 , the perimeter surfaces of element  38  are preferably flat. A plurality of indexing pins  44  project from both the upper locations of the indexing apertures  28  in cages  10 . In addition, spacing element  38  is provided with two pair of identical spaced locking tabs  46  and  48  extending in opposed axial directions as seen in  FIG. 3 . Each pair of tabs defines a pair of tapered transversely extending projections  50  adjacent the extended tab ends which are adapted to be received in the transversely extending tab slots  37  formed in the opposed sides of the interior transverse wall  18  of cage  10 .  
         [0021]     As a result of the resilient nature of the locking tabs  46  and  48 , the spacing element  38  is easily secured to one of cages  10  by merely aligning the indexing pins  44  on element  38  with the indexing apertures  28  in the cage and pressing the pins into the apertures. The resilient locking tabs  46  or  48  will extend about the opposite sides of the inner transverse wall  18  of the cage and the projections  50  adjacent the ends of the tabs will snap into the slots  36  in the cage wall  18 , rigidly securing the spacing element  38  to the cage  10 . A second cage of the same or different vertical elevation can then easily be inserted over and locked to the opposite side of the spacing element  38  as shown in  FIG. 4  to provide the desired overall length of the cage assembly. If needed, a second spacing element and an additional cage could be added to the stack to increase further the overall length of the cage assembly.  
         [0022]     As noted earlier, different shapes of cage  10  are provided for different applications. For example, the cage would preferably be formed in an annular somewhat kidney-shaped configuration such as that shown in  FIG. 5  for use in the anterior portion of the vertebral body. Such a configuration is referred to herein as a modified kidney-shaped configuration and is formed by three circular segments  100   a ,  100   b  and  100   c  joined together such that segments  100   a  and  100   c  lie on a common horizontal plane and segment  100   b  is disposed forwardly of and equidistantly between segments  100   a  and  100   c . While such a modified kidney-shaped cage  100  configuration is preferred for use in the anterior portion of the vertebral body, a  FIG. 5 , the modified kidney-shaped cage  100  is substantially identical in all respects to cage  10  except for its shape and, in its preferred configuration, the absence of a transverse wall and a slightly different tool opening configuration. The openings formed at 45 degrees with respect to the transverse wall also may be omitted in cage  100 . It is to be understood, however, the different tool opening configurations and positionings could be employed in each of the cages embodying the present invention.  
         [0023]     When used in certain applications such as on the sides of the vertebral body, the cage of the present invention can be of a smaller oval-shaped configuration as seen in  FIG. 6 . As seen therein, the oval-shaped cage  200  is of the same configuration as cages  10  and  100  except for its shape, slightly smaller size and the fact that the oval-shaped cage  200 , like cage  100 , does not employ a transverse interior wall and has fewer tool engaging openings  230 . For stacked applications, cage  200  is shown as having only two indexing apertures  228  disposed at its extended ends. Because the embodiment of cage  200  shown in the drawings does not include a transverse wall like wall  18  of the first embodiment, the slots  237  for receiving the projections  250  on the resilient tabs  246  and  248  on the spacing element  238  used with cage  200  may be positioned on the opposed interior side walls of cage  200 . Only one such slot is visible in  FIG. 6 .  
         [0024]     The spacing elements  238  used with cages  200  are modified accordingly such that the cage engaging projections  250  extend outwardly from tabs  246  (only one being seen in  FIG. 7 ), not inwardly as in the spacing elements  38 . Spacing elements  238  are used with two or more cages  200  of different elevations to form a stack of a desired elevation just as cages  10  and spacing elements  38  are employed in the first embodiment. As seen in  FIG. 7 , the oval shape of the spacing elements again conforms to the cage configuration. Similarly, when used with a cage  100  having the modified kidney-shaped configuration of  FIG. 5 , the spacing element also would have a modified kidney-shape. While not shown, the spacing element indexing and attachment means as shown with respect to spacing elements  238 .  
         [0025]     It is to be understood that other changes and modifications also could be employed in the present invention without departing from the spirit and scope thereof. For example, a conventional kidney-shaped cage  400  (see  FIG. 10 ) could be employed in lieu of the modified kidney-shape of cage  100 . Cage  400 , like cage  10 , could include a transverse wall portion  418 . Accordingly, a spacer element employed with cage  400  would be kidney-shaped and preferably index and attach using generally the same indexing pin and locking tab configuration employed in the spacing elements  38  used with cages  10 .