Abstract:
A spinal fusion implant including a body and a jacket is disclosed. The jacket includes at least two radiopaque markers extending therefrom for use in determining the position of the implant after placement between intervertebral bodies. Methods of implanting and evaluating positioning of the implant are also disclosed.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to spinal surgery, namely, the fusion of adjacent intervertebral bodies. 
         [0002]    Back pain can be caused by many different maladies, not the least of which are problems that directly impact the intervertebral disks of the spine. Typical disc issues include, inter alia, degeneration, bulging, herniation, thinning and abnormal movement. One method of treatment of such disc problems that has been widely utilized in the field of spinal surgery is a spinal fusion procedure, whereby an affected disc is removed, and the adjacent vertebral bodies are fused together. Currently, implants, pedicle screws and the like are utilized to facilitate the fusion. 
         [0003]    One type of implant that has recently gained favor are so-called stand-alone cages. These intervertebral implants effectuate spinal fusion without the need for secondary fixation through the use of, for instance, pedicle screws. One example of such a stand-alone cage is disclosed in U.S. Pat. No. 8,349,015 (“the &#39;015 Patent”), the disclosure of which is hereby incorporated by reference herein. In the &#39;015 Patent, a PEEK body is surrounded by a metallic jacket and anchors are inserted through both superior and inferior surfaces the implant and into the upper and lower adjacent vertebral bodies respectively. 
         [0004]    Although stand-alone cages are successful in effectuating spine fusion, intraoperative and postoperative visualization of the implants remains a challenge. This is especially true given the advent of polymeric implants that are constructed of PEEK and therefore do not show up when conducting standard imaging processes. Nonetheless, surgeons typically need to verify proper implant position, location and rotation. 
         [0005]    It has been known for some time to imbed radiopaque markers in polymeric bodies, so that at least the markers show up on X-rays or other images taken of the implant. Surgeon can compare the positions of the markers to each other and/or the anatomical features of the spine to determine whether the implant is properly placed. However, implants with such a design require additional manufacturing efforts (i.e., imbedding the markers in the polymeric) that are costly, time consuming and may adversely affect the structural integrity of the implants. 
         [0006]    Therefore, there exists a need for an improved spinal implant that overcomes the aforementioned drawbacks. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    The present invention provides a unique design that allows for evaluation of the placement of a spinal fusion implant. In its most basic sense, the invention includes at least two extensions extending from a jacket surrounding an implant body that are radiopaque. These extensions can be viewed via an imaging technique and their orientation with respect to each other or other aspects of the implant can aid a surgeon in determining whether the implant is properly placed. Of course, the specific configuration of the extensions may widely vary, as can the specific implants themselves. 
         [0008]    A first aspect of the present invention is an intervertebral implant including a body sized and shaped for placement between first and second adjacent vertebrae, a jacket disposed around the spacer and at least two radiopaque markers extending from the jacket to enable identification of an orientation of the implant. 
         [0009]    In certain embodiments of the first aspect, the implant may further include first and second anchors secured to the implant and the first and second vertebrae. The at least two radiopaque markers may be located on opposite sides of the jacket. In an aligned orientation, only one of the at least two markers is visible from a first aspect, and when the implant is in a misaligned orientation portions of both of the at least two markers are visible from the first aspect. The body may be at least partially radiolucent. The at least two radiopaque markers may include four radiopaque markers, and the four radiopaque markers may be angled with respect to upper and lower surfaces of the implant. The jacket may include two rails and the at least two radiopaque markers may extend between the rails. The at least two radioapque markers may be triangular. 
         [0010]    Another aspect of the present invention is a method of determining the orientation of an implant placed between two intervertebral bodies including the steps of viewing opposed radioactive markers located on front and back sides of a jacket of the implant and determining the orientation of the implant based on the orientation of the markers. In an aligned orientation, only a single marker is visible from a first aspect. In a misaligned orientation, at least portions of each of the markers are visible from the first aspect. The first aspect may be from an anterior side of a patient. 
         [0011]    Another aspect of the present invention is a method of implanting an implant between two intervertebral bodies including the steps of accessing the space between the intervertebral bodies, placing the implant between the intervertebral bodies, viewing opposed radioactive markers located on front and back sides of a jacket of the implant; and determining the orientation of the implant based on the orientation of the markers. In an aligned orientation, only a single marker may be visible from a first aspect. In a misaligned orientation, at least portions of each of the markers may be visible from the first aspect. The first aspect may from an anterior side of a patient. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    A more complete appreciation of the subject matter of the present invention and of the various advantages thereof can be realized by reference to the following detailed description in which reference is made to the accompanying drawings in which: 
           [0013]      FIG. 1  is a perspective view of an implant according to one embodiment of the present invention. 
           [0014]      FIG. 2  is a top view of the implant of  FIG. 1 . 
           [0015]      FIG. 3  is a side view of the implant of  FIG. 1 . 
           [0016]      FIG. 4  is a front view of the implant of  FIG. 1 . 
           [0017]      FIG. 5  is a side view of an implant according to another embodiment of the present invention. 
           [0018]      FIG. 6  is a side view of an implant according to another embodiment of the present invention. 
           [0019]      FIG. 7  is a side view of an implant according to another embodiment of the present invention. 
           [0020]      FIG. 8  is a side view of an implant according to another embodiment of the present invention. 
           [0021]      FIG. 9  is a side view of an implant according to another embodiment of the present invention. 
           [0022]      FIG. 10  is a side view of an implant according to another embodiment of the present invention. 
           [0023]      FIG. 11  is a side view of an implant according to another embodiment of the present invention. 
           [0024]      FIG. 12  is a side view of an implant according to another embodiment of the present invention. 
           [0025]      FIG. 13  is a side view of an implant according to another embodiment of the present invention. 
           [0026]      FIG. 14  is a side view of an implant according to another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    As shown in  FIGS. 1-4 , an implant  10  is disclosed that includes a PEEK body  12  and a metallic jacket  14 . Jacket  14  is sized and shaped so as to fit around an exterior of PEEK body  12 , and both components include portions of an upper channel  16  and a lower channel  18  (the latter of which is best shown in  FIG. 4 ) that are designed to accept an anchor (like anchor  120  shown in  FIG. 5 ). This design allows for implant to be placed between adjacent intervertebral bodies and anchors to thereafter be secured to both the implant and the vertebral bodies, thereby creating a stand-alone fusion cage construct. In the particular embodiment shown in the figures of the present application, the various implants are designed for lateral placement between adjacent vertebral bodies. In other words, the implants are sized and shaped to be placed from the side of a patient and across the disc space. The particular lateral implants shown may exhibit lengths within the range of 40-60 mm, widths within the range of 18-22 mm and heights in the range of 8-18 mm. However, it is contemplated that the present invention has applicability to implants of many different sizes and shapes, including those designed for placement in other orientations, e.g., anteriorly, posteriorly, posterior-laterally or the like. Depending upon the particular insertion orientation, the implants may be sized within different ranges. 
         [0028]    PEEK body  12  includes teeth  22  on and a plurality of apertures  24  through its top and bottom surfaces. The teeth aid in at least initially securing the implant between adjacent vertebral bodies, while the apertures may be packed with bone graft material to allow for bone to grow between the vertebral bodies. Of course, it is contemplated that the implant may be designed such that teeth are not included and/or one or more apertures may be provided. Moreover, although described as being constructed of PEEK, it is noted that body  12  may be constructed of many different materials, including many different polymeric materials in accordance with the present invention. It is also contemplated to construct body  12  of biologic materials, such as allograft bone. 
         [0029]    Jacket  14 , on the other hand, is comprised of a metallic material and designed such that it entirely surrounds PEEK body  12 . Because jacket  14  is comprised of a metallic material, it can be seen when conducting an x-ray or other imaging technique. This is in contrast to the polymeric material of body  12 , which cannot optimally be seen in such imaging procedures (PEEK can be seen depending upon x-ray settings). Jacket  14  is shown as including end portions separated by four rails (two on each side of the jacket), but can be of any shape sufficient to surround body  12 . 
         [0030]    Jacket  14  includes four extensions  26  (two on each side of the implant) which extend toward an upper surface of implant  10 . Extensions  26  are shown as being equally spaced from ends of jacket  14 , as well as about its center. Of course, extensions  26  may be positioned at any position on jacket  14 . These structures provide specific reference points for a surgeon viewing implant  10  under an imaging process. For instance, a typical image will be taken from a front portion of a patient&#39;s body, and if implant  10  is correctly placed, extensions  26  on the front and back side of the implant will align such that only two extensions  26  will be visible in the image. However, when implant  10  is not properly aligned (e.g., rotated in one direction or the other), the image will begin to show extensions  26  on the posterior side of the implant (i.e., at least portions of all four extensions will show). 
         [0031]    It is noted that other portions of jacket  14  may also aide in the determination of the placement of implant  10 . For instance, the end portions of the implant (best shown on the left and right sides of the view of  FIG. 3 ) can be utilized by a surgeon in a similar fashion to extensions  26 . Likewise, the rails on the front and back of jacket  14  can be utilized to determine whether the implant is canted toward one of the upper or lower intervertebral body. This canting may occur because of subsidence, improper bone preparation or an improper placement. Extensions  26  are oriented so that they face the upper surface of implant  10 . This allows for a quick determination as to whether the implant is properly oriented within the disc space. In other embodiments, extensions  26  could be oriented such that they face the bottom of the implant, or even to one side or the other. As is best shown in  FIG. 3 , body  12  may include its own radiopaque marker  28 , which can be utilized in conjunction with extensions  26  to determine proper position of implant  10 . 
         [0032]    Of course, although described as being constructed of a metallic material, it is noted that jacket  14  may be constructed of many different types of materials, including different metals. In fact, the entirety of jacket  14  need not be radiopaque, although it is in the various embodiments of the present invention. Rather, extensions  26  may be the sole portion of jacket  14  constructed of radiopaque material, thereby allowing visualization during an imaging process. 
         [0033]      FIGS. 5-13  disclose several additional embodiment implants in accordance with the present invention. For ease of reference, like reference numerals are utilized for similar elements of the implants, albeit within different 100-series of numbers. For instance,  FIG. 5  depicts an implant  110  that includes a PEEK body  112 , a jacket  114  and extensions  126 . Extensions  126  are wider and include less of a distance therebetween than that of extensions  26  of implant. This design may allow for an easier determination of misalignment of implant  110 , as the space between extensions  126  simply closes when viewed from the anterior side of the patient. Otherwise, extensions  126  are largely similar to those of implant  10 . 
         [0034]    Implant  210  of  FIG. 6  includes a single extension  226  on each side. Therefore, instead of four extensions, implant  210  includes two. In the particular embodiment shown, extensions  226  are oriented at a center of implant  210 , but could be positioned in other locations on jacket  214 .  FIG. 7  depicts an implant  310  in which extensions  326  extend between rails of jacket  314  on each side of the implant. This design not only provides a similar functionality to the foregoing implants, but also potentially adds stability to the construct of jacket  314 .  FIG. 8  depicts a design similar to implant  310 , but with two extensions  426  extending between rails on both sides of the implant. Therefore, instead of the two extensions shown in  FIG. 7 , the embodiment of implant  410  includes four. Implant  510  of  FIG. 9  includes four angled extensions  526  that extend between the rails. Again, the functionality of extensions  526  otherwise remains the same. 
         [0035]      FIG. 10  depicts an embodiment in which instead of extensions, jacket  614  includes holes  626  formed in the rails thereof. Holes  626  provide the surgeon with similar viewing capabilities in an imaging process as the above-discussed embodiments do. For instance, a properly placed implant will show two complete holes extending through the jacket, whereas a tilted or otherwise improperly placed implant will show the hole somewhat obscured.  FIG. 11  depicts an embodiment in which eight holes  726  are included in jacket  714 .  FIG. 12  depicts a design in which instead of holes, jacket  814  includes necked down sections  826  that can be utilized in a similar fashion to the holes. 
         [0036]    Implant  910  of  FIG. 13  includes triangular extensions  926  that can be utilized in a similar fashion as is discussed above in connection with implant  10 . The triangular shape of extensions  926  allow for them to extend to a height on implant  910  that is possible with the above-discussed extensions. Moreover, the center area of extensions  926  allow for better visualization of the remainder of implant  910 . This can be utilized to, among other things, better assess the amount of bone growth that has occurred through body  912  of an implanted implant  910 . Finally, implant  1010  of  FIG. 14  depicts and embodiment similar to that of  FIG. 7 . However, instead of extending towards only one of the upper or lower surface of the implant, extensions  1026  extend towards both. This design may allow for an easier determination of where those upper and lower surfaces are in an implanted implant. 
         [0037]    In one embodiment of the invention, an intervertebral implant comprises:
       a body sized and shaped for placement between first and second adjacent vertebrae;   a jacket disposed around the spacer; and   at least two radiopaque markers extending from the jacket to enable identification of an orientation of the implant.       
 
         [0041]    In another embodiment of the invention, a method of determining the orientation of an implant placed between two intervertebral bodies comprises the steps of:
       viewing opposed radioactive markers located on front and back sides of a jacket of the implant; and   determining the orientation of the implant based on the orientation of the markers,   wherein in an aligned orientation, only a single marker is visible from a first aspect.       
 
         [0045]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.