Abstract:
A vertebral replacement implant assembly for inserting in a space left by one or more removed vertebrae between adjacent intact vertebrae, according to which at least two elongated members are disposed in the space and a connector member is connected between adjacent elongated members in a manner so that a dimension of the assembly thus formed can be varied. Further, a graft containment device for use with a vertebral implant.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to an implant for replacement of one or more vertebral bodies and their adjacent disks, and more particularly, to implant components that permit optimal anatomy accommodation and facilitate grafting. 
     BACKGROUND 
     A variety of spinal injuries and deformities can occur due to trauma, disease, or congenital effects. These injuries and deformities can, ultimately, result in the destruction of one or more vertebral bodies. One type of spinal deformity, a kyphosis, involves a prolapse of the vertebral column towards the front of the body, often caused by the destruction of the vertebral body itself. This destruction can be in the form of a trauma type injury, such as a fracture or burst injury to the vertebral body, or a non-traumatic deformity caused by a tumor or a degeneration of the bone in the vertebral body. 
     In most treatments of a kyphosis, a high degree of anterior reconstruction of the spine is required, most frequently involving total removal of the damaged vertebral body. In a typical anterior approach, partial or total surgical excision of the vertebral body and the two adjacent vertebral disks is carried out. The remaining space is then distracted to manipulate the spine to its correct orientation. Various forms of reconstruction using an osteosynthesis device, such as a vertebral replacement body, can then be performed in the space created by the removal of the vertebral body and disks. However, existing vertebral body replacement devices permit only limited bone ingrowth, are relatively hard to place, and offer limited adjustability to accommodate a patient&#39;s specific vertebral anatomy. 
     Therefore, a vertebral body replacement is needed that permits greater bone ingrowth, facilitates placement of bone graft between adjacent healthy vertebrae, and allows greater adjustability to accommodate a patient&#39;s specific vertebral anatomy. 
     SUMMARY 
     The present disclosure relates to a vertebral replacement implant for interposition in a space left by one or more at least partially removed vertebrae between adjacent intact vertebrae. In one embodiment, a first tubular body is sized to span a first portion of the space between the intact vertebrae, and a second tubular body is sized to span a second portion of the space between the intact vertebrae. A connector is connected to corresponding ends of the first and second bodies, and an endplate assembly is attached to the other end of the first body. In another embodiment, a graft containment device is used with the vertebral replacement implant. The graft containment device has an internal cavity, a sidewall, an open upper end, a closed lower end with apertures extending therethrough, and an engagement device for maintaining the containment device within the cavity of the vertebral replacement implant. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an perspective view of a destroyed vertebral body within a vertebral column. 
         FIG. 2  is an exploded perspective view of a vertebral body replacement assembly according to one embodiment of the present invention. 
         FIG. 3  is a perspective view of a vertebral body replacement disposed within the vertebral column of  FIG. 1 . 
         FIG. 4  is perspective view of the assembled vertebral body replacement assembly of  FIG. 2 . 
         FIG. 5  is an exploded perspective view of a vertebral body replacement assembly according to a second embodiment of the present invention. 
         FIG. 6   a  is an exploded perspective view of an endplate and graft basket assembly in accordance with a first embodiment of the present invention. 
         FIG. 6   b  is a perspective view of the assembled assembly shown in  FIG. 5   a.    
         FIG. 7   a  is an exploded perspective view of an endplate and graft basket assembly in accordance with another embodiment of the present invention. 
         FIG. 7   b  is a perspective view of the assembly shown in  FIG. 6   a.    
     
    
    
     DETAILED DESCRIPTION 
     Referring first to  FIG. 1 , the reference numeral  10  refers to a vertebral column with a damaged vertebra  12   a  extending between two intact vertebrae  12   b  and  12   c . A disk  14   a  extends between vertebrae  12   a  and  12   b , and a disk  14   b  extends between vertebrae  12   a  and  12   c . In a typical surgical excision, a major portion of the vertebra  12   a  is removed together with disks  14   a  and  14   b  creating a void between the two intact vertebra  12   b  and  12   c . A vertebral body replacement according to an embodiment of the present invention is provided to fill the void between the two intact vertebrae  12   b  and  12   c.    
     Referring now to  FIG. 2 , a vertebral body replacement assembly according to an embodiment of the present invention is referred to, in general, by the reference numeral  20  and includes tubular body  22  connected between two endplate assemblies  24  and  26  in a manner to be described. The body  22  defines a hollow bore  32  therethrough which is configured to receive an implantable material, typically bone osteosynthesis material (not shown), which may be in the form of autogenous, allograft or synthetic bone void filler material. 
     The tubular body  22  is provided with a plurality of angularly and axially spaced apertures  34  in communication with the bore  32 . The apertures  34  provide a path for bone or tissue ingrowth and vascularization to further enhance the stability of the implant. As specifically shown in  FIG. 2 , the apertures  34  are large enough and are positioned such that graft material can be packed, with maximum surgical accessibility, into the body  22  after the assembly  20  is installed and adjusted in a manner to be described. In one embodiment, the apertures  34  may extend between 28% and 46% of the length of the body  22 , allowing as much opening as possible for the placement of graft material. After surgical installation, at least one aperture  34  is accessible to allow graft material to be packed into the body  22 . To permit monitoring of the healing process and to determine whether bone formation has advanced through the body  22 , the apertures  34  may be aligned angularly to permit x-ray visualization through the apertures  34 . 
     A plurality of angularly spread threaded apertures  36  are formed through the body  22  generally in the middle of the body  22 , for reasons to be described. 
     External threads  38  are formed on the outer surface of the tubular body  22  and may extend for substantially the entire length of the body. In some embodiments, the external threads  38  may extend from the ends of the tubular body  22  to the apertures  34 . Since the primary load on the body  22  will be in axial compression, rather than bending, the wall forming the body  22  can be relatively thin, such as approximately one (1) mm thick. 
     The endplate assembly  24  includes a flange  40 , which can cover a substantial load-bearing area of the corresponding end face of the adjacent intact vertebral body ( FIG. 1 ). A hollow cylinder  42  is integrally formed with the flange  40  and includes a number of angularly spaced threaded openings  44  with each being adapted to receive a set screw  46  therein. The cylinder  42  and the flange  40  of the endplate assembly  24  define a through bore  48 , the inside surface of which is provided with internal threads  50  which extend along the entire length of the cylinder  42  and into the flange  40  as necessary. The threads  50  are configured to mate with the external threads  38  of the corresponding end portion of the body  22  to connect the body to the endplate assembly  24 . 
     A plurality of angularly spread vascularization apertures  40   a  extend through the flange  40  to promote tissue growth in the space between the adjacent vertebrae. One or more spikes  54  project outwardly from the end face of the flange  40  and are configured to penetrate the adjacent vertebra to help maintain the position of the implant in situ. The outer surface of the plate assembly  24  may also include a series of flats  45  adjacent the threaded openings  44 . In one embodiment, the flats  45  form a hexagonal driving pattern that may be engaged by a surgical tool. The endplate assembly  24  may be angled to create a desired vertebral column alignment. 
     The endplate assembly  26  is identical to the assembly  24  and therefore will not be described in detail. Further details and embodiments of the endplate assemblies  24  and  26  are disclosed in U.S. Pat. Nos. 5,702,453; 5,776,197; 5,776,198; and 6,344,057 B1 to Rabbe et al. (“the Rabbe patents”) which are incorporated herein by reference. 
     It is understood that the dimensions of the tubular body  22  and/or the end plate assemblies  24  and  26  can vary in accordance with size of the vertebral column  10 . Once these dimensions have been selected for a particular patient, each of the endplate assemblies  24  and  26  is threaded onto the body  22  until a desired height is attained so as to fit in the vertebral column  10  assuming that the disks  14   a  and  14   b  are removed, as shown in  FIG. 3 . To this end, and referring to  FIG. 2 , the external threads  38  on the body  22  are cut in opposite directions so that the endplate assemblies  24  and  26  can be drawn together or apart by rotating only the body. The advantage of this arrangement is that it is easier to adjust the height of the total assembly  20  to fit in the vertebral column  10  while maintaining the proper orientation of the endplate assemblies  24  and  26 . Alternatively, the cut of the threads  38  can be the same at each end of the body  22  so that the endplate assemblies  24  and  26  are rotated in opposite directions onto the body  22 . An advantage of the latter arrangement is that in situ the assembly is unable to unthread itself. 
     After the end portions of the body  22  are threaded into endplate assemblies  24  and  26 , one or more set screws  46  are threaded into an opening or openings  44  of the assemblies  24  and  26  to fix each of the assemblies to a corresponding end of the tubular body  22 . The set screw(s)  46  exert a clamping pressure against the body  22  to hold it in place and prevent its rotation with respect to the endplate assemblies  24  and  26 . Each set screw  46  can be a breakable locking screw in which the head of the screw shears off when the tightening torque limit is reached. Such a locking screw is disclosed in U.S. Pat. No. 6,478,795, the disclosure of which is incorporated by reference. 
     A support assembly  56  is provided to engage the body  22  and the endplate assemblies  24  and  26  to ensure that the assembly  20  will not migrate after installation. The support assembly  56  includes a stabilization plate  58  having two circular ends  58   a  and  58   b  the bottom faces of which can be serrated, or roughened, to mate with installation devices (not shown) as described in detail in the above-cited Rabbe patents. A clamp assembly  60  is provided and includes a pair of clamp halves  64  which extend to the respective sides of the plate  58  and which are preferably C-shaped to firmly grip and support the plate. Each of the clamp halves  64  includes an aperture  64   a  which receives a threaded rod  66  extending from one end of a base  68 . A nut  70  is threaded on the rod  66  and can be rotated to draw the clamp halves  64  together about the stabilization plate  58 . An aperture  68   a  extends through the base  68  and receives a locking screw  72  which includes a threaded shank  72   a  which is adapted to engage one of the threaded apertures  36  in the body  22  to secure the support assembly  56  to the body. 
       FIG. 4  depicts the components of  FIG. 2  in an assembled condition. In particular, the endplate assemblies  24  and  26  are threaded over the respective threaded end portions of the body  22  until the desired height of the assembled components is achieved, as discussed above. The clamp halves  60  are attached but not clamped to the stabilization plate  58  which is spaced laterally from the assembly  20 , and the assembly thus formed is disposed between the intact vertebra  12   b  and  12   c  ( FIG. 3 ). The circular ends  58   a  and  58   b  of the plate  58  are then attached to the intact vertebrae  12   b  and  12   c  in a manner described in detail in the above-cited Rabbe patents. The clamp halves  60  are then moved along the length of the plate  58  until the aperture  68   a  of the base  68  is aligned with an appropriate one of the threaded apertures  36  in the threaded body  22 . As so aligned, the locking screw  72  can then be easily threaded through the aperture  68   a  and into one of the apertures  36  to secure the base  68  to the body  22 . The clamp halves  60  are then fully clamped onto the plate  58  by tightening the nut  70  on the threaded rod  66  to secure the assembly  20  in the vertebral column  10 . It is noted that  FIG. 3  depicts the vertebral body replacement assembly  20  of  FIG. 2  inserted in the vertebral column  10  of  FIG. 1  with the support assembly  56  not being shown in the interest of clarity. 
       FIG. 5  depicts a vertebral body replacement assembly  20 ′ according to a second embodiment of the present invention. The assembly  20 ′ includes two tubular bodies  22  similar to the embodiment of  FIG. 2  connected to a tubular connector  80  to achieve an extended vertebral height. The connector  80  is formed from a generally cylindrical enclosure  82  which defines a bore  84  therethrough. The bore  84  may receive bone implant material (not shown), which may be in any form as previously described. 
     The cylindrical enclosure  82  includes a number of threaded openings  86  adapted to receive set screws  88  therein which can be in the form of a breakable locking screw as described above. The inside surface of the bore  84  is provided with internal threads  90  which are configured to mate with the external threads  38  of the tubular bodies  22 , so that each opposite end portion of the connector  80  can be threadedly engaged with a body  22 . Rotation of the connector  80  thus causes axial movement of both bodies  22  relative to the connector, to vary the height of the assembly  20 ′. 
     Once the proper height of the assembly  20 ′ is obtained for the particular patient, the set screws  88  are threaded into an appropriate one of the threaded openings  86  in the connector  80  in order that the set screws  88  extend into contact with the bodies  22  to secure the connector to the bodies. Although only two set screws  88  are depicted, it is understood that additional set screws can be used, as needed. 
     After the connector  80  has been connected between the bodies  22  as described above, each of the endplate assemblies  24  and  26  is threaded onto its corresponding body  22  until the desired height is attained. The set screws  46  are then threaded into corresponding openings  44  in each of the endplate assemblies  24  and  26  to attach the latter assemblies to the bodies  22  in the manner described above. It is understood that the connector  80 , the bodies  22  and the endplate assemblies  24  and  26  can all be threadedly engaged to achieve the desired height before the set screws  88  and  46  are used to secure the bodies  22 . Further, the sequence of tightening set screws to immobilize a threaded interface may be conducted in any order to achieve the desired result. 
     According to the embodiment of  FIGS. 6   a  and  6   b , an endplate assembly  24 ′ is provided that includes components that are substantially identical to the components forming the endplate assembly  24 , which components are given the same reference numerals. According to the embodiment of  FIGS. 6   a  and  6   b , a plurality of angularly spaced recesses  94  are formed in the upper surface of the flange  40 , as viewed in  FIG. 6   a , and the cylinder  42  of the endplate assembly  24 ′ is configured to accept a graft basket  96 . 
     The graft basket  96  is formed by a cylindrical wall  98  and a base  100  having a bottom surface which define a cavity  102  suitable for receiving graft material (not shown). The cylindrical wall  98  need not be perfectly cylindrical but rather may be tapered or angled. The wall  98  and the base  100  are provided with a plurality of apertures  104  suitable to promote tissue ingrowth and vascularization. The apertures  104  may permit a line of sight to form through the apertures  34  of body  22 , through the bore  32 , and through the basket  96 . 
     The basket  96  is designed to fit entirely within the bore  48  of the cylinder  42 , and one or more positioning tabs  112  project outwardly from the cylindrical wall  98  of the basket and into the recesses  94 . The recesses  94  are aligned and sized to receive the positioning tabs  112  in a press fit or a snap fit to locate the basket  96  within the cylinder  42  as shown in  FIG. 6   b.    
     It is understood that another endplate assembly can also be provided which is similar to the endplate assembly  24 ′ and can be connected as part of the assembly  20  as shown in  FIGS. 1-5 . 
     According to the embodiment of  FIGS. 7   a  and  7   b , an endplate assembly  24 ″ is provided that includes components that are substantially identical to the components forming the endplate assembly  24 , which components are given the same reference numerals. According to the embodiment of  FIGS. 7   a  and  7   b , the inner wall of the cylinder  42  is provided with threads  116  and is configured to receive a graft basket  118  which is similar to the basket  96  of the previous embodiment and includes identical components of the latter basket which are given the same reference numerals. 
     The basket  118  does not have tabs but, rather, has a outwardly extending lip  120  integrally formed with the cylindrical wall  98 . The outer circumference of the lip  120  is provided with external threads  122  which threadedly engage the threads  116  of the cylinder  42  to secure the basket  118  in the cylinder, as shown in  FIG. 7   b . It is understood that another endplate assembly can also be provided which is similar or identical to the endplate assembly  24 ″ and can be connected as part of the assembly  20  as shown in  FIGS. 1-5 . 
     Endplate assembly  24 ′ or  24 ″ and its corresponding and opposite endplate assembly may both be threaded sufficiently far onto opposite end portions of the body  22  to permit the assembled components to be inserted into the vertebral column  10 . Graft material may be packed into the body  22 . The graft baskets  96  or  118  can be fit into the endplate assemblies  24 ′ or  24 ″, respectively, with similar baskets inserted into the corresponding and opposite endplate assembly. The baskets can be filled with implantable graft material which may be osteogenic material or other bone growth promoting material. It is understood the packing of the graft material may occur before or after the endplate assemblies are attached to the body  22 . In some embodiments, the baskets  96  and  118  may be sized to extend beyond their respective cylinders  42  and into the body  22 , and may even fill the bore  32 . 
     The assembled components may then be inserted into the vertebral column  10  and the endplate assemblies may be advanced toward the intact vertebral endplates thereby engaging the contents of the baskets with the vertebral endplates. As described above, set screws such as  46  may be used to lock the endplate assemblies to the body  22 . Additional graft material may be inserted through the apertures  34  of body  22  to further fill the bore  32 , including any voids created by advancing the endplate assemblies. 
     Alternatives 
     In the embodiment of  FIG. 2 , the threads  38  on the body  22  can be internal while the threads  50  of the endplate assemblies can be external. In this case, the inner diameter of the body  22  would naturally be slightly greater than the outer diameter of the cylinder of the endplate assemblies. In one alternative embodiment, the hollow cylinder  42  of the endplate assembly  24  may only extend along a portion of the longitudinal axis and only a portion may include threads. In another alternative embodiment, the threads  38  on the body  22  extend over only the end portions of the tubular body  22 . Moreover, while threads have been illustrated as a preferred interface, other rotational and non-rotational interfaces may be utilized, for example but without limitation, ratchets, rack and pinion, frictional engagement, and gears. It will be appreciated that with alternative designs, the body  22  and the endplate assemblies may no longer include cylindrical interfaces such that other configurations may be utilized. 
     To determine, in post surgical examination, whether bone formation has occurred, the apertures  34  may be positioned to permit x-ray visualization through one aperture  34 , across the bore  32 , and through another aperture  34 . For example, there may be an even number of angularly spaced apertures  34 , evenly spaced such that a straight line of sight may be formed through two aligned apertures  34 . 
     In the embodiment of  FIG. 5 , the threads  90  on the connector  80  can be external while the threads  38  on the bodies  22  can be internal. 
     In  FIG. 5 , to further increase the overall length of the assembly  20 ′, three or more bodies  22  can be threadedly engaged with connectors  80  between the adjacent bodies  22 . 
     The connector, or connectors  80  can be angled or curved to modify the overall lordosis or kyphosis of the assembly  20 ′. Still further, at least one end or portion of the body  22  may be angled or curved. 
     The apertures  104  or other openings in the baskets  96  and  118  may be modified to suit the specific material implanted. 
     In the embodiment of  FIGS. 7   a  and  7   b , the lip  120  may be omitted and external threads may be formed on the outer surface of the cylindrical wall  42 . 
     The graft baskets, such as  96  and  118 , maybe formed from a resorbable polymer material. Furthermore, any or all of the components disclosed can be made from any material suitable for implantation. 
     The above graft basket embodiments are not limited to use with a specific endplate assembly, but are easily applicable to other endplate assemblies such as those described in the above Rabbe patents. 
     Although only a few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims. 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.