Abstract:
Apparatus and method if using a modular spinal implant system for use between adjacent vertebrae near vascular anatomy. The system includes an implant configured the fit between adjacent vertebrae, the implant having annular side walls with upper and lower surfaces configured to enclose a hollow interior, and an attachment plate rotatably coupled to the implant and configured to rotate to variable orientations relative to the implant to avoid the vascular anatomy, the attachment plate having a superior portion that is narrower than an inferior portion, the attachment plate having at least one vertebra attachment hole configured for attaching to at least one adjacent vertebrae using one or more bone screws.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to U.S. Provisional Patent Application No. 61/059,181 to Ahn, filed Jun. 5, 2008, and entitled “MODULAR ANTERIOR LOCKING INTERBODY CAGE”, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention is directed to systems, methods, and devices applicable to spinal surgery. More specifically, the present invention is directed to a modular spinal spacer designed to accommodate the vascular anatomy for use by medical personnel (i.e., doctor) in spinal and other surgical procedures. In some embodiments of the present invention relates to a modular spinal spacer for insertion into a disk space defined between two adjacent vertebrae near vascular anatomy, in order to restore an appropriate height between the vertebrae and to allow bone fusion to take place between adjacent vertebrae. 
         [0004]    2. Background of the Invention 
         [0005]    Vertebrae are the individual irregular bones that make up the spinal column (aka ischis)—a flexuous and flexible column. There are normally thirty-three vertebrae in humans, including the five that are fused to form the sacrum (the others are separated by intervertebral discs) and the four coccygeal bones which form the tailbone. The upper three regions comprise the remaining 24, and are grouped under the names cervical (7 vertebrae), thoracic (12 vertebrae) and lumbar (5 vertebrae), according to the regions they occupy. This number is sometimes increased by an additional vertebra in one region, or it may be diminished in one region, the deficiency often being supplied by an additional vertebra in another. The number of cervical vertebrae is, however, very rarely increased or diminished. 
         [0006]    A typical vertebra consists of two essential parts: an anterior (front) segment, which is the vertebral body; and a posterior part—the vertebral (neural) arch—which encloses the vertebral foramen. The vertebral arch is formed by a pair of pedicles and a pair of laminae, and supports seven processes, four articular, two transverse, and one spinous, the latter also being known as the neural spine. 
         [0007]    When the vertebrae are articulated with each other, the bodies form a strong pillar for the support of the head and trunk, and the vertebral foramina constitute a canal for the protection of the medulla spinalis (spinal cord), while between every pair of vertebrae are two apertures, the intervertebral foramina, one on either side, for the transmission of the spinal nerves and vessels. 
         [0008]    Conventional interbody spacer assemblies are used in spinal fusion procedures to repair damaged or incorrectly articulating vertebrae. Conventional interbody spacer assemblies come in different cross sections. Some spacer assemblies may be hollow and may include openings in the side(s) thereof to provide access for bone matter growth. The use of interbody spacers are primarily to support the anterior load of the spinal column and provide a method for insertion and containment of bone graft material to facilitate spinal fusion. Often these spacers are used in conjunction with supplemental fixation in the form of pedicle screws or anterior plate systems. 
         [0009]    Historically one of the failure modes of interbody spacers used in combination with anterior plate systems particularly in the lumbar spine in one of placing the anterior plate due to the vascular system lying directly over the area of interest. This has been previously addressed by surgically mobilizing the vascular structures or particularly in the upper lumbar levels avoiding the use of anterior lumbar plate&#39;s altogether and utilizing posterior supplemental instrumentation. Some implant designs have integrated features that provide for integrated supplemental fixation such as spikes, protrusions, screws, once installed but generally do not provide the same level of rigidity as a plate creating a paradoxical relationship where implant manufacturers must choose between either making the implant system easier to insert or making the implant system more effective in stabilize the spine to facilitate fusion. 
         [0010]    There exists a need for further improvements in the field of spinal spacer assemblies of the present type that are designed to avoid the vascular structures. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    In a first aspect, embodiments of the present invention provide a modular spinal implant system for use between adjacent vertebrae near vascular anatomy. The system includes an implant configured to fit between adjacent vertebrae, the implant having annular side walls with upper and lower surfaces configured to enclose a hollow interior, and an attachment plate rotatably coupled to the implant and configured to rotate to variable orientations relative to the implant to avoid the vascular anatomy, the attachment plate having a superior portion that is narrower than an inferior portion, the attachment plate having at least one vertebra attachment hole configured for attaching to at least one adjacent vertebrae using one or more bone screws. 
         [0012]    In many embodiments, the attachment plate is selected from a variety of attachment plates configured to avoid the vascular anatomy proximate the vertebrae. 
         [0013]    In many embodiments, the inferior portion includes one or more vertebra attachment holes. 
         [0014]    In many embodiments, the superior portion includes one vertebra attachment hole and the inferior portion includes two vertebra attachment holes. 
         [0015]    In many embodiments, the implant material is selected from the group consisting of titanium, stainless steel, cobalt-chromium, carbon, PEEK (polyethylketone), graphite, woven carbon, Kevlar, and other suitable synthetic material. 
         [0016]    In many embodiments, the implant is made of a non metal synthetic material. In further embodiments, the implant further includes one or more metal plates integrally formed within an anterior portion of the annular side wall 
         [0017]    In many embodiments, the attachment plate is made from titanium, stainless steel, or cobalt-chromium. 
         [0018]    In many embodiments, mating surfaces between the attachment plate and implant include an interlock configuration. 
         [0019]    In many embodiments, the system further includes a bone autograft, allograft or a bone graft substitute positioned within the hollow interior of the implant. 
         [0020]    In another aspect, embodiments of the present invention provide a method of installing a modular spinal implant system between adjacent vertebrae. The method includes inserting the modular spinal implant system between adjacent vertebrae, the system includes an implant configured to fit between adjacent vertebrae, the implant having annular side walls with upper and lower surfaces configured to enclose a hollow interior and an attachment plate rotatably coupled to the implant before, during, or after implantation and configured to rotate to variable orientations relative to the implant to avoid the vascular anatomy, the attachment plate having a superior portion that is narrower than an inferior portion, the attachment plate having at least one vertebra attachment hole configured for attaching to at least one adjacent vertebrae using one or more bone screws, rotating the attachment plate to avoid the vascular anatomy, and attaching the attachment plate to at least one adjacent vertebra using one or more bone screws. 
         [0021]    In many embodiments, the attachment plate is selected from a variety of attachment plates configured to avoid the vascular anatomy proximate the vertebrae. 
         [0022]    In many embodiments, prior to inserting the system, the method further includes retracting a portion of the vascular anatomy. 
         [0023]    In many embodiments, the implant material is selected from the group consisting of titanium, stainless steel, cobalt-chromium, carbon, PEEK (polyethylketone), graphite, woven carbon, Kevlar, and other suitable synthetic material. 
         [0024]    In many embodiments, the method further includes filling the hollow interior with bone autograft, allograft or a bone graft substitute. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  shows a top view of one embodiment of an oval shaped body or cage. 
           [0026]      FIG. 2  shows a top view of a “D” shaped body. 
           [0027]      FIG. 3A  shows a L5/S1 anterior view of a modular anterior locking interbody cage (MALIC) system in place between vertebrae proximate vascular structures. 
           [0028]      FIG. 3B  shows one embodiment of attaching a plate to the implant. 
           [0029]      FIG. 4A  shows one example of an anterior view of the spine in which a vascular portion may require retraction for implantation and attachment of an attachment plate. 
           [0030]      FIG. 4B  shows retraction of the vascular portion. 
           [0031]      FIG. 4C-4E  show different sizes and shapes of attachment plates to attach to an implant that may be used to avoid the vascular. 
           [0032]      FIG. 5  shows examples of surface treatment of the plate and implant where they join. 
           [0033]      FIG. 6A  shows a top view of one embodiment an implant that is a non metal synthetic material (NMSM)/metal amalgam. 
           [0034]      FIGS. 6B-6E  show other embodiments of a NMSM/metal amalgam implant. 
           [0035]      FIG. 7  shows a view of a lateral x-ray showing an implant of  FIG. 6A  positioned within between adjacent vertebrae. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]    One or more detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. 
         [0037]      FIG. 1  shows one embodiment of an anterior locking interbody cage for use as an anterior interbody fusion device  100  in the lumbar spine  105 . The disc interspace is shaped like a “D”  110 . The device  100  has a generally oval or circular shaped body or cage, when viewed from above, having an annular wall enclosing a hollow interior or area  115  that would permit bony growth into spinal bones above and below the device when implanted. The hollow area  115  would be filled with bone autograft, allograft or a bone graft substitute. 
         [0038]      FIG. 2  shows a “D” shaped body  200  body or cage, when viewed from above, having an annular wall enclosing a hollow interior or area  215  that would permit bony growth into spinal bones above and below the device when implanted. The hollow area  215  would be filled with bone autograft, allograft or a bone graft substitute. 
         [0039]    There are some advantages using the oval or circular shape shown in  FIG. 1  over “D” shape  200  shown in  FIG. 2 . For example, the “D” shaped device can only be placed in the disc space in one orientation. The “D” shape has posterior corners that can impinge on the aortic/venous iliac vessels. The “D” design is not suitable for a lateral approach  120 . In contrast, an oval shaped device permits more implant options, so that the device could be placed in different rotational orientations within the spine, and would have the advantage of sliding safely past aortic/venous iliac vessels. The oval shaped device  100  also allows variability to approach the disc space from multiple angles  120 , again permitting variability to better accommodate the vascular anatomy, such as. For example, oval shaped device may also be placed into patients through a lateral approach  120 , which a “D” design does not afford, the lateral approach being favored by many surgeons in an anterior approach to L4/5. 
         [0040]      FIG. 3A  shows a L5/S1 anterior view of one embodiment of a modular anterior locking interbody cage (MALIC) system  300  configured to be placed between vertebra. The system  300  includes an interbody fusion device or implant  305  and an attachment plate  310 . The implant  305  may be made of a metal, a non metal synthetic material, or a NMSM/metal amalgam, discussed below. The attachment plates  310  are coupled to the implant with a screw, and would allow a variation of attachment plates  310  to be attached onto the implant  305 , making the system  300  modular. The attachment plates are designed to accommodate the vascular  325  anatomy. Using a screw or other fixation means such as a rivet or snap locking mechanism for attachment with the implant allows the attachment plate to rotate to various orientations to avoid the vascular anatomy. The attachment plate may be coupled to the implant either before, during, or after implantation. The screw attachment also allows the attachment plate to be removable from the body in case it needs to be replaced or repositioned. 
         [0041]    The attachment plate  310  has a superior portion (anatomically cranial) and an inferior portion (anatomically caudal). The superior portion is narrower than the inferior portion. The attachment plate  310  in turn would have holes that would allow the placement of bone screws  320  into the vertebra above and/or below, locking the implant  305  in place. The attachment plate  310  may be made from metal, such as titanium, stainless steel or cobalt-chromium. The attachment plate  310  may also be made from high strength composites or plastics such as PEEK. 
         [0042]    In addition, the attachment plate  310  adjacent to the device  305  may have a contouring that would allow a male/female counterpart contouring on a front surface of the device. This would allow a surface interlock that would resist rotational forces between the attachment plate  310  and the device  305 . The primary reason for the attachment plate  310  shape is the complexity of the vascular anatomy, especially at the spinal levels superior to L5-S1, that can make access in one area of the spine easier than another. This would allow the surgeon a variety of attachment plates  310  to choose from, selecting the best shape to accommodate the complex vascular anatomy. By creating this modularity in attachable plates this device would have a variety of attachable plates that would accommodate different vascular anatomic challenges, allowing surgery to be performed in a safer manner. This would be done without sacrificing biomechanical strength and the plate would in turn lock onto the MALIC. 
         [0043]      FIG. 3B  is a side view showing one embodiment of attaching the attachment plate  310  to the implant  305 . Screw  335  attaches the attachment plate  310  to the implant  305 , in particular, attaching to the embedded metal plate  340  within the implant  305 . Bone screws  325  are then used to attach the attachment plate to the vertebra above and/or below implant  305 . 
         [0044]      FIG. 4A  shows one example of an anterior view of the spine in which a vascular portion requires retraction for implantation and attachment of an attachment plate  310  to a body  305  and adjacent vertebrae. In this example of the vertebral levels above L5-S1 area, the vascular portion  325  is draped over the left side of the vertebrae. The vascular  325   a  and/or  325   b  is retracted  330 , such as shown in  FIG. 4B , to make room for the attachment plate  310  to attach to the implant  305  and vertebrae.  FIG. 4C-4E  show different sizes and shapes of attachment plates  310  that may be used to avoid the vascular, having superior portions narrower than inferior portions. In  FIG. 4C , attachment plate  310   a  may include provisions for one screw attaching to a vertebra above the implant  305  and two screws attaching to a vertebra below the implant  305 . In  FIG. 4D , attachment plate  310   b  attaches to a vertebra below the implant  305 . In  FIG. 4E , attachment plate  310   c  may include provisions for one screw attaching a vertebra above the implant  305  and two screws attaching to a vertebra below the implant  305 . 
         [0045]    In some cases, it may be desirable to have surface treatment of the attachment plate  310  and implant  305  where they join. For example,  FIG. 5  shows two examples A and B. The mating surfaces in A have adjacent irregular contouring and B have regular pyramidal male/female interlocking features to provide additional stability of the assemble components that may include rotational stability. 
       Non Metal Synthetic Material/Metal Amalgam 
       [0046]      FIG. 6A  shows one embodiment an implant  400 , having a generally oval or circular shape similar to device  100 , with an amalgam body of non metal synthetic material (NMSM) and metal material. In some embodiments, implant  400  may be used in place of implant  300  in the systems describe above. The device  400  includes an oval body  405  or cage with an annular wall  415  having upper and lower surfaces enclosing a central opening  410  or hollow interior. The upper and lower surfaces are configured to contact adjacent spine member and may have raised ridges projecting outwardly from each of the surfaces for engaging the spinal column. The annular wall  415  of the implant  405  includes an anterior portion  415   a , a posterior portion  415   b  and lateral portions  415   c . The implant  405  is made from a non-metal synthetic material with a metal plate  420  integrally formed within the anterior side of the non metal synthetic material implant  405 . The metal plate  420  does not fully extend around the implant  405 . The non-metal synthetic material may be made from carbon, PEEK (polyethylketone), graphite, woven carbon, Kevlar, or other suitable synthetic material that has strength capable of withstanding compression and rotational forces. The metal material may be titanium, stainless steel or cobaltlchromium. The amalgam feature could also be applied to NMSM threaded cages placed in the anterior lumbar spine, as well as cages placed in the interbody space from a lateral approach. This amalgam feature may also apply to cages, cylindrical or rectangular placed in the cervical or thoracic spine. While the preferred shape of the implant is oval, other shapes may also be used, such as circular, kidney or “D” shaped. 
         [0047]    There are numerous advantages of a NMSM/metal amalgam for an implant. For example, one advantage is the metal within the device allows a surgeon to identify the position of the device in space to assist in implantation at the proper location and orientation with in the spine. Another advantage is that the NMSM material allows a surgeon to assess fusion postoperatively after the implantation of the device. This is due to the fact that x-rays penetrate the NMSM to allow bony visualization through the device. The surgeon would be able to evaluate the fusion of the device to the spine by using the lateral x-rays taken only through lateral portions of the NMSM device alone. 
         [0048]    One weakness of using a NMSM device alone (i.e., without metal) is the difficulty in holding the device with instruments or less durable antirotation feature. Often the holding instruments (typically made of PEEK) overwhelm the NMSM device during implantation, resulting in deformation and damage. Another advantage of the disclosed NMSM/metal amalgam is that the metal can allow a firmer “grabbing” of the device with implantation tools. Holding or grabbing the proposed NMSM/metal amalgam device with an implantation tool, which would hold the metal plate(s), would avoid such damage to the implant and allow better control during implantation. Advantage of more durable feature to prevent rotation between the implant and plate. The combination of metal in the form of a fixation element within the NMSM device is a novel concept. In some embodiments, a plurality of tool engaging openings (not shown) may be disposed in the annular wall  415  having the metal plate(s)  420 . The openings can be threaded or otherwise configured to receive a conventional insertion tool (not shown). 
         [0049]      FIGS. 6B-6E  show other embodiments of a NMSM/metal amalgam implant. In  FIG. 6B , the metal within the device may include one or more metal plates, for example, plates  420   a ,  420   b . In  FIG. 6C , the metal within the NMSM/metal amalgam device could take the form of multiple washers or threaded inserts  425 . In  FIG. 6D , the metal within the NMSM/metal amalgam device could take the form of a plate  430  with threaded screw holes  435 . In  FIG. 6E , the metal within the NMSM/metal amalgam device could include both anterior plate(s)  420  on the anterior side and posterior plate(s)  440  on the posterior side of the device. 
         [0050]      FIG. 7  shows a view of a lateral x-ray showing the implant  400  positioned within between adjacent vertebrae  450 . By positioning the metal within the anterior portion  415   a , and optionally the posterior portion  415   b , the surgeon would be able to evaluate the fusion of the device to the spine by using the lateral x-rays taken only through lateral portions  415   c  of the NMSM device alone. An anterior  415   a /posterior  415   b  x-ray would not be as desirable as the metal components of the device would obscure the fusion. There are numerous advantages of a NMSM/metal amalgam for an implant. For example, one advantage is the metal within the device allows a surgeon to identify the position of the device in space to assist in implantation at the proper location and orientation with in the spine. Another advantage is that the NMSM material allows a surgeon to assess fusion postoperatively after the implantation of the device. This is due to the fact that x-rays penetrate the NMSM to allow bony visualization through the device. Surgeons typically do not assess fusion through an anterior/posterior x-ray, and this is the view of the fusion that the metal components of the device would obscure. 
         [0051]    Example embodiments of the methods and components of the present invention have been described herein. As noted elsewhere, these example embodiments have been described for illustrative purposes only, and are not limiting. Other embodiments are possible and are covered by the invention. Such embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.