Abstract:
An implant configured for placement through an anterior surgical approach made of at least two different materials. The implant may include materials with varying radiolucency and mechanical properties. Such a hybrid implant may offer controlled radiographic visibility and optimized structural properties for implant placement, including placement for use in spinal arthrodesis.

Description:
CROSS REFERENCE  
       [0001]     This application claims priority from U.S. Provisional Patent Application Ser. No. 60/720,555, filed on Sep. 26, 2005, entitled “Hybrid Intervertebral Spinal Fusion Implant.” The following applications also claim priority to the above referenced provisional application and are related to the present application. They are incorporated by reference herein:  
         [0002]     U.S. Utility patent application Ser. No. ______ (Attorney Docket No. P24845) filed on Sep. 26, 2006 and entitled “Transforaminal Hybrid Implant;” and  
         [0003]     U.S. Utility patent application Ser. No. ______ (Attorney Docket No. P27164) filed on Sep. 26, 2006 and entitled “Hybrid Intervertebral Spinal Fusion Implant.” 
     
    
     TECHNICAL FIELD  
       [0004]     The present invention relates generally to the field of medical implants and methods, and more specifically to interbody spinal implants which may be adapted for placement into an implantation space created across the height of a disc space between two adjacent vertebral bodies for the purpose of correcting disease, dysfunction, or degeneration at that interspace, and any related methods. The spinal implants may be made of a plurality of implant materials, which bear differing degrees of radiographic lucency. These materials may include bone and may or may not be resorbable. The implants of some embodiments are adapted such that radiographic visualization of operative placement and eventual bone healing can be observed.  
       BACKGROUND  
       [0005]     Implants for placement in the intervertebral space between adjacent vertebral bodies in the spine come in a wide range of shapes and sizes. These implants are usually made entirely of one material, although the type of material can vary significantly between specific implants. Such implants for use in human spinal surgery include implants made entirely of metals, such as titanium or stainless steel, or synthetic radiolucent materials such as carbon-carbon composites or poly-ether-ether-ketone (PEEK). Implants may have a structure designed to promote fusion across adjacent vertebral bodies by allowing bone to grow through and around the implant. The operative placement of intervertebral implants is optimized by radiographic opacity. However, a relatively radiolucent implant material optimizes postoperative evaluation of bone growth and fusion across an intervertebral space. While these implants may contain marking beads or radio opaque markers they do not structurally benefit from radio opaque materials. In some configurations, metals, some of which are opaque on radiographs, provide greater strength and resistance to impaction during implantation. Metallic implants may offer reduced wall thickness of structural components and offer increased volume for bone graft and other agents within an implant.  
         [0006]     As it is desirable to take advantage of benefits of radiolucent and radio-opaque materials in an implant, there exists a need for an improved implant made of different structural materials with different properties of radiographic appearance. For some implants, it is desirable to provide optimization of mechanical properties, while permitting generous bone filling and bone through-growth. These characteristics may be applied in some embodiments in combination with an ability to radiographically determine bone-implant interaction and bone growth into and around the implant.  
       SUMMARY  
       [0007]     Embodiments of the invention may include an artificial interbody spinal fusion implant made of structural materials with varying radiolucency and mechanical characteristics. Implants may be provided for insertion at least in part into an implantation space formed across the height of a disc space between adjacent vertebral bodies of a human spine. The implant of some embodiments consists of at least two radiographically distinct imaging materials: a radiolucent portion, and a radio-opaque portion. The radio-opaque materials of some embodiments are arranged toward the vertebral endplates with minimal obstruction to radiographic visualization through the implant from anterior to posterior and/or from lateral directions. Embodiments of the implant may include upper and lower portions adapted to be placed within the intervertebral space to contact and support the adjacent vertebral bodies. Upper and lower portions of the implant may include at least one opening in communication with one another and adapted to hold bone growth promoting material and/or bone graft for permitting the growth of bone from vertebral body to vertebral body through the implant. Embodiments of the invention include an artificial interbody spinal implant containing at least two different materials for insertion at least in part into an implantation space formed across the height of a disc space between adjacent vertebral bodies of a spine. Implant embodiments may employ materials that bear a structural role in the design of the implant, and at least a portion of a leading end of the implant may have a reduced height to facilitate insertion of said implant between the two adjacent vertebral bodies. Implants may have a maximum length less than and approximating the posterior to anterior or right to left length of the vertebral bodies. Some embodiments also include a bone engaging surface formed on the exterior of at least the upper and lower portions for engaging the adjacent vertebral bodies, such as one or more protrusions, ratchets, spikes, roughened surfaces or knurling. Embodiments of the implant may be combined with a bone growth or bone healing promoting material such as, but not limited to, bone, bone derived products, demineralized bone matrix, mineralizing proteins, ossifying proteins, bone forming cell differentiating substance, bone morphogenetic protein, hydroxyapatite, and gene therapy material leading to the production of bone. Embodiments of the implant may also be combined with a therapeutic substance for the treatment of infection, tumor or other pathologic process. In some embodiments of the invention, one component material is relatively, or absolutely radiolucent. In some embodiments of the invention, one component material is radio-opaque. One component material of the implant may be at least in part resorbable. In some embodiments, at least a portion of an implant is treated to promote bone in-growth between the implant and adjacent vertebral bodies. Embodiments of the implant may be used in combination with at least one spinal fixation implant. Embodiments of the implant may include a hollow interior and at least one area for attachment or interaction with an insertion device for surgical placement or removal from the intervertebral space. Upper and lower surfaces of some embodiments of the implant may include a plurality of openings. Embodiments of the implant may be designed to be inserted adjacent to a second implant into a disc space between adjacent vertebral bodies, the second implant being of identical or differing shape. At least one opening may be between the leading and trailing ends of embodiments of the implant. Upper and lower portions or surfaces of embodiments of the implant may be at least in part generally parallel to one another or may be configured with an angular relationship to each other for allowing angulation of adjacent vertebral bodies relative to each other.  
         [0008]     Another embodiment of the invention is an intervertebral implant having a generally rounded exterior shape for promoting fusion between an inferior vertebral body and a superior vertebral body. The embodiment includes a first rim around a periphery of the implant, the first rim having a detectable radiographic signature, and a member coupled to the first rim. The member has less of a radiographic signature than the first rim, and the member adds vertebral spacing height to the first rim.  
         [0009]     Yet another embodiment of the invention is a method of implanting an intervertebral implant from an anterior surgical approach. The method includes providing an implant comprising: a first rim around a periphery of the implant, the first rim having a detectable radiographic signature, and a member coupled to the first rim. The member having less of a radiographic signature than the first rim, and the member adds vertebral spacing height to the first rim. The method further includes radiographically observing placement of the implant between superior and inferior vertebral bodies by way of one or more of an anterior to posterior radiographic view and a lateral radiographic view. The method also may include radiographically observing bone growth between the superior and inferior vertebral bodies by way of one or more of an anterior to posterior radiographic view and a lateral radiographic view.  
         [0010]     Still another embodiment of the invention is a method of assembling an intervertebral implant. A implant is provided for the method comprising: a first rim around a periphery of the implant, the first rim having a detectable radiographic signature, a support coupled to the first rim, the support having a detectable radiographic signature, and a second rim coupled to the support, the second rim having a detectable radiographic signature. The method further includes applying a member between the first rim and the second rim, the member having less of a radiographic signature than the first rim.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a side view of two adjacent vertebral bodies in a lumbar spine with an implantation space formed across the height of the spinal disc space.  
         [0012]      FIG. 2  is a top plan view of a vertebral body in a lumbar spine with an implantation space formed through a posterior approach.  
         [0013]      FIG. 3  is a side perspective view of the implantation space of  FIG. 2 .  
         [0014]      FIG. 4  is a perspective view of an implantation space formed through an anterior approach.  
         [0015]      FIG. 5  is a top plan view of a vertebral body in the lumbar spine with an embodiment of an implant positioned in the implantation space of  FIG. 2 .  
         [0016]      FIG. 6  is a side view of two adjacent vertebral bodies with the implant of  FIG. 5  positioned in the implantation space of  FIG. 2  through a posterior approach.  
         [0017]      FIG. 7  is a side view of two adjacent vertebral bodies with an implant positioned in the implantation space of  FIG. 2  through an anterior approach.  
         [0018]      FIG. 8  is a top plan view of the implant of  FIG. 5   
         [0019]      FIG. 9  is a rear perspective view of the implant of  FIG. 5 .  
         [0020]      FIG. 10  is a side view of the implant of  FIG. 5 .  
         [0021]      FIG. 11  is a rear view of the implant of  FIG. 5 ,  
         [0022]      FIG. 12  is a rear perspective view of another embodiment of an implant for use in the implantation space of  FIG. 2 .  
         [0023]      FIG. 13  is a rear view of the implant of  FIG. 12 .  
         [0024]      FIG. 14  is a side view of the implant of  FIG. 12 .  
         [0025]      FIG. 15  is a rear perspective view of an embodiment of an implant suited for anterior placement into a cervical or lumbar intervertebral disc space.  
         [0026]      FIG. 16  is a top plan view of the implant of  FIG. 15 .  
         [0027]      FIG. 17  is a side view of the implant of  FIG. 15 .  
         [0028]      FIG. 18  is perspective view of an embodiment of the implant.  
         [0029]      FIG. 19  is a view of selected components of the implant of  FIG. 18 .  
         [0030]      FIG. 20  is an exploded perspective view of an embodiment of the implant  
         [0031]      FIGS. 21A, 21B , and  21 C are plan (axial), side (lateral), and posterior views respectively of components of an embodiment of the invention.  
         [0032]      FIGS. 22A, 22B , and  22 C are plan (axial), side (lateral), and posterior views respectively of components of an embodiment of the invention.  
         [0033]      FIGS. 23A, 23B , and  23 C are plan (axial), side (lateral), and posterior views respectively of components of an embodiment of the invention.  
         [0034]      FIGS. 24A, 24B , and  24 C are plan (axial), side (lateral), and posterior views respectively of components of an embodiment of the invention.  
         [0035]      FIGS. 25A, 25B , and  25 C are plan (axial), side (lateral), and posterior views respectively of components of an embodiment of the invention.  
     
    
     DETAILED DESCRIPTION  
       [0036]     The following description is intended to be representative only and not limiting and many variations can be anticipated according to these teachings, which are included within the scope of this inventive teaching. Reference will now be made in detail to embodiments of this invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.  
         [0037]      FIGS. 1-3  show an implantation space  100  formed across the height of a spinal disc D between vertebral bodies V in the lumbar spine. In other embodiments, the vertebral bodies may be bodies of the cervical or thoracic spine as well. It is understood that numerous methods exist and that any method and instrumentation designed for the purpose may be applied to prepare the desired implantation space and perform disc and soft tissue removal in such a manner as to be adapted to receive the implants of the present invention. It is also understood that implantation space preparation commonly leaves residual disc material D prior to implant placement.  
         [0038]      FIG. 3  shows the implantation space  100 , which has been prepared by partial disc and soft tissue removal adjacent to the vertebral body V. The preparation in  FIG. 3  is shown as a posterior lumbar surgical approach, and the opening O into the disc space from the posterior is shown. The opening O may also be an opening prepared for transforaminal or oblique surgical approaches. Residual portions P of the vertebral pedicles are also shown.  
         [0039]      FIG. 4  shows the implantation space  100 , which has been prepared by partial disc and soft tissue removal adjacent to the vertebral body V. The preparation in  FIG. 4  is shown as an anterior surgical approach and the entrance E into the disc space from the anterior is shown. This representation can reflect a cervical, thoracic, or lumbar spinal intervertebral space preparation.  
         [0040]      FIG. 5  shows a unilateral implant  200  seated in the implantation space  100  in accordance with an embodiment of the present invention. Bone graft material BG is shown anterior to the unilateral implant  200 , as well as within a central void  210  of the unilateral implant  200 .  
         [0041]      FIG. 6  shows a unilateral implant  200  seated in the implantation space  100 . Bone graft material BG is shown anterior to the unilateral implant  200  but posterior to remaining disc D, as well as within the central void  210  of the unilateral implant  200 .  
         [0042]      FIG. 7  shows an anterior implant  400  seated in the implantation space  100 . Bone graft material BG is shown within a cavity  480  of the anterior implant  400 .  
         [0043]      FIG. 8  shows the unilateral implant  200  with an anterior aspect  202  and a posterior aspect  204 . The central void  210  is shown. Traversing support structures  220 ,  220 ′ extend from anterior  202  to posterior  204  aspects of the implant. In the lateral aspects of the unilateral implant  200  radiolucent blocks  240 ,  240 ′ are shown, each with a central cavity  242 ,  242 ′.  
         [0044]      FIG. 9  shows the unilateral implant  200  as described in  FIG. 8 . The view from a posterior perspective shows the central void  210 , the radiolucent blocks  240 ,  240 ′ and posterior support columns  222 ,  222 ′ which extend from an inferior aspect  260  to a superior aspect  264  of the implant.  
         [0045]      FIG. 10  shows the unilateral implant  200  as described in  FIG. 8  from a lateral view. The radiolucent block  240  is shown positioned between the superior aspect  264  and the inferior aspect  260  of the implant. A posterior support column  222  and an anterior support column  223  between the superior aspect  264  and inferior aspect  260  are shown. In a lateral projection, anterior  202  and posterior  204  aspects to the implant are noted.  
         [0046]      FIG. 11  shows a posterior view of the implant as described in  FIGS. 8 and 9  without appearance of the radiolucent blocks  240 ,  240 ′, in order to show radiographic appearance. Only the posterior support columns  222 ,  222 ′ extending between the inferior aspect  260  and the superior aspect  264  of the implant are visualized radiographically due to the selected radio-opaque nature of the material implemented in this embodiment. Anterior support columns  223 ,  223 ′ are hidden behind posterior support columns  222 ,  222 ′ when the unilateral implant  200  is visualized radiographically directly from the posterior.  
         [0047]      FIG. 12  shows another embodiment of the invention with a center-support implant  300  in rear perspective view. A central volume  310 , and radiolucent lateral blocks  340 ,  340 ′, as well as anterior support structure  324 , and posterior support structure  322  are noted.  
         [0048]      FIG. 13  shows a posterior view of the implant as described in  FIG. 12  without appearance of the radiolucent lateral blocks  340 ,  340 ′ in order to show radiographic appearance. Only the posterior support structure  322 , which overlaps in this view the anterior support structure  324 , seen in  FIG. 12 , is visualized radiographically between the inferior portion  360  and the superior portion  364  of the implant due to the selected radio-opaque nature of the material implemented in this embodiment.  
         [0049]      FIG. 14  shows the center-support implant  300  as described in  FIG. 12  from a lateral view. The radiolucent lateral block  340  is shown positioned between the superior portion  364  and the inferior portion  360  of the implant. In this lateral projection the anterior support structure  324  and posterior support structure  322  of the implant are noted.  
         [0050]      FIG. 15  illustrates an anterior implant  400 . In some embodiments, the anterior implant  400  may be placed through an anterior surgical approach. However, the anterior implant  400  may also be placed by other surgical approaches such as, but not limited to, an anterior-oblique approach or a lateral approach. A large central strut  410  made of radiolucent material is shown traversing the implant. Upper rim  420  and lower rim  422  are attached to the central strut  410  and further supported and connected to one another through supportive structures  440 ,  442 ,  444 ,  446 . Openings through the sides of the implant are noted  450 ,  452 ,  454 ,  456 . These openings may permit for the growth of bone through and into anterior implant  400 , though the invention is not so limited.  
         [0051]      FIG. 16  shows a top plan view of the anterior implant  400  as described in  FIG. 15 . The large central strut  410  is noted. Two cavities  480 , 480 ′ within the anterior implant  400  are shown on either side of the strut  410 . These cavities may permit for the growth of bone through and into anterior implant  400 , though the invention is not so limited.  
         [0052]      FIG. 17  shows a lateral view of the anterior implant  400  as described in  FIGS. 15 and 16 . Upper rim  420  and lower rim  422  are shown, as is the lateral view of the central strut  410 . Given the radiolucent nature of the central strut  410 , on radiographic visualization only the upper rim  420  and lower rim  422  as well as radio-opaque supportive structures  440 , 442  would be noted. The remaining two supportive structures  444 , 446  noted in  FIG. 15  are obscured in a lateral view by the supportive structures  440 , 442 . Further, angulation between the upper rim  420  and lower rim  422  may facilitate insertion of anterior implant  400  between the two adjacent vertebral bodies and permit control of sagittal plane intervertebral alignment.  
         [0053]      FIG. 18  illustrates another embodiment of an implant designed primarily for implantation from an anterior surgical approach. The open anterior implant  600  illustrates an implant having a generally rounded exterior shape for promoting fusion between an inferior vertebral body and a superior vertebral body. Many generally rounded shapes are contemplated under the invention. By way of example and without limitation, the exterior shape may be round, oval, the shape of the cortical rim of a vertebral body, the general shape of the cross-section of a kidney, or the general shape of a racetrack having straight sides connecting substantially rounded ends.  
         [0054]     A first rim  620  is shown around a periphery of the open anterior implant  600 , the first rim  620  has a detectable radiographic signature. The term radiographic signature as used herein refers to a resulting visualization on radiographic devices. A radiolucent block, for example, is faintly to indistinguishably visible on a radiograph, and would therefore be considered to have less of a radiographic signature than a radio-opaque metal such as titanium.  
         [0055]     The illustrated first rim  620  has a substantially uniform width. In other embodiments, the width of the first rim  620  may vary to improve engagement with other portions of the implant or cooperating implants, or may vary to accomplish better anatomical fit. The first rim  620  shown is continuous about the periphery. Some embodiments include a rim that only extends between select portions of the periphery of the implant.  
         [0056]     The first rim  620  illustrated in  FIG. 18  includes protrusions  665  configured to face an adjacent vertebral body and engage the vertebral body. In embodiments where the first rim  620  is made from a metallic material, an advantage may be established in forming protrusions  665 . Metal teeth, protrusions, and other surface characteristics may be both stronger and capable of being more effectively sharpened to better engage bone surfaces. In some embodiments, the first rim  620  is made from titanium, a biocompatible, radio-opaque metal.  
         [0057]      FIG. 18  also illustrates a member embodied in a first segment  610  and coupled to the first rim  620 . The first segment  610  has less of a radiographic signature than the first rim  620  in some embodiments. The first segment  610  may be made from a radiolucent material such as PEEK or any other biocompatible material that is less radiographically visible than the material of the first rim  620 . As shown, the first segment  610  added to the first rim  620  increases the height of the spacing provided by the open anterior implant  600 .  
         [0058]     Another member embodiment of the invention is illustrated in  FIG. 20  and includes tubular member  612 . The tubular member  612  is continuous about the periphery of the implant. The tubular member  612  may also be mated with the first rim  620 .  
         [0059]     The first segment  610  illustrated in  FIGS. 18 and 19  has a chord length C 1 . The cord length C 1  of embodiments of the invention is less than ninety percent of the length of an outer average diameter of the first rim  620 . In some more specific embodiments, the cord length C 1  is less than two-thirds of the length of an outer average diameter of the first rim  620 .  FIGS. 18 and 19  also illustrate an second segment  611  which is generally on the opposite side of the open anterior implant  600  from the first segment  610 .  
         [0060]     In some embodiments, the first segment  610  is configured for positioning on an anterior side of an implant. In other embodiments, the first segment  610  is configured for positioning on a posterior side of an implant. In still other embodiments, the first segment  610  is configured for positioning on a lateral side of an implant. The second segment  611  may be configured for placement adjacent to or opposite from the first segment  610  in conjunction with any placement of the first segment  610 .  
         [0061]      FIGS. 18 and 20  illustrate a second rim configured to couple to the first and second segments  610 ,  611  and the tubular member  612  respectively. The second rim  622  may be coupled around a periphery of the open anterior implant  600 , the second rim  622  has a detectable radiographic signature. The illustrated second rim  622  has a substantially uniform width. In other embodiments, the width of the second rim  622  may vary to improve engagement with other portions of the implant or cooperating implants, or may vary to accomplish better anatomical fit. The second rim  622  shown is continuous about the periphery.  
         [0062]     The second rim  622  illustrated in  FIG. 18  includes protrusions  665  configured to face an adjacent vertebral body and engage the vertebral body. In embodiments where the second rim  622  is made from a metallic material, an advantage may be established in forming protrusions  665 . Metal teeth, protrusions, and other surface characteristics may be both stronger and capable of being more effectively sharpened to better engage bone surfaces. In some embodiments, the second rim  622  is made from titanium, a biocompatible, radio-opaque metal.  
         [0063]     As shown in  FIGS. 18 and 20 , the first and second segments  610 ,  611  and the tubular member  612  respectively are illustrated as approximately the same anterior, posterior, and lateral size as the first and second rims  620 ,  622 . However, in some embodiments, the first and second segments  610 ,  611  and the tubular member  612  extend beyond the extents of the first and second rims  620 ,  622  and may encapsulate at least portions of the first and second rims  620 ,  622 .  
         [0064]     In some embodiments, implants of multiple sizes and configurations may be formed by assembling two or more of various, cooperating rims, supports, and members. An embodiment of the invention may include a kit of variously sized rims, supports, and members that are intended to be assembled by surgeons, product resellers, other users, and distributors.  
         [0065]     Members such as, but not limited to, the first and second segments  610 ,  611  and the tubular member  612  may also be made at least in part of material with a lower modulus of elasticity than the rims or supports. In some circumstances, it may be desirable to provide a modulus of elasticity that more nearly approximates the modulus of elasticity of bone, or that at least reduces the rigidity of the implant somewhat.  
         [0066]      FIGS. 21A-25C  are simplified graphical representations of various configurations of implant embodiments of the invention.  FIG. 21A  is a plan view consistent with an axial radiographic image.  FIG. 21B  is a side view consistent with a lateral radiographic image.  FIG. 21C  is a posterior view consistent with a posterior to anterior radiographic image.  
         [0067]     Each implant depicted in  FIGS. 21A-25C  will be represented by a superior rim  20 , an inferior rim  22 , posterior supports  40 ,  46 , anterior supports  44 ,  42 , and lateral supports  25 ,  26  where appropriate. Each of the supports is represented here as a cylindrical component. However, each may be of any desired configuration, such as but not limited to, rectangular, square, circular, oval, polygonal, or variable in cross-section along its length. Less radiographic or radiolucent members such as the central strut  410 , first segment  610 , second segment  611  and the tubular member  612 , as have been disclosed above, are not shown in  FIGS. 21A-25C , but any size or configuration of such members is contemplated for each of the implants represented. Although angulation for lordotic and kyphotic correction is not illustrated in  FIGS. 21A-25C , such angulation is contemplated for each embodiment.  
         [0068]      FIGS. 21A-23C  and  25 A- 25 C will further illustrate relationships between relative alignments among two or more of the supports, as viewed radiographically from at least one of the anterior, posterior, and lateral sides, and rotational position of the implant about a vertical axis. A vertical axis for the purpose of this orientation is considered vertical as viewed in the posterior views illustrated.  
         [0069]      FIGS. 21A-21C  illustrate supports  40 ,  46  in the posterior half of the implant that are configured to block radiographic visualization of supports  42 ,  44  in the anterior half of the implant when the implant is radiographically viewed from a posterior side of the implant.  FIGS. 21A-21C  also illustrate a support  40  in the posterior half of the implant configured to block radiographic visualization of a support  46  on the contralateral side of the implant when the implant is radiographically viewed from a lateral side of the implant; and a support  42  in the anterior half of the implant are configured to block radiographic visualization of a support  44  on the contralateral side of the implant when the implant is radiographically viewed from a lateral side of the implant.  
         [0070]      FIGS. 22A-22C  show a support  25  in the posterior half of the implant configured to block radiographic visualization of a support  26  on the contralateral side of the implant when the implant is radiographically viewed from a lateral side of the implant. As used herein, the posterior half will include a centerline between the anterior and posterior halves. As shown in  FIG. 22C , when the implant is viewed radiographically from a posterior side, the lateral space between supports  25 ,  26  indicates the rotational position of the implant. Additionally, the alignment of the supports  25 ,  26  with ends of the superior rim  20  when viewed from a posterior side indicates rotational position of the implant.  
         [0071]      FIGS. 23A-23C  illustrate a support  40  in the posterior half of the implant configured to block radiographic visualization of a support  42  in the anterior half of the implant when the implant is radiographically viewed from a posterior side of the implant. When the implant is viewed radiographically from a lateral side, the anterior to posterior spaces between the support  40  in the posterior half of the implant and the support  42  in the anterior half of the implant indicates the rotational position of the implant. Additionally, the alignment of the supports  40 ,  42  with ends of the superior rim  20  when viewed from a lateral side indicates rotational position of the implant.  
         [0072]      FIGS. 24A-24C  illustrate an implant with a superior rim  20  and an inferior rim  22  that are coupled to one another by one or more less radiographically detectable or radiolucent members.  
         [0073]      FIGS. 25A-25C  illustrate and implant where, when the implant is viewed radiographically from a posterior side, lateral spaces S 1 , S 2  between the support  40  in the posterior half of the implant and the supports  42 ,  44  in the anterior half of the implant are substantially equidistant.  FIGS. 25A-25C  also illustrate a support  42  in the anterior half of the implant configured to block radiographic visualization of a support  44  on the contralateral side of the implant when the implant is radiographically viewed from a lateral side of the implant.  
         [0074]     While the implants are intended primarily for use in spinal fusion, it is appreciated that they may be modified or adapted to receive fusion promoting substances and/or materials within them such as, but not limited to cancellous bone, bone derived products, chemotherapeutic agents, antimicrobial agents, or others. In some embodiments, the implants consists of materials such as, but not limited to, titanium and its alloys, ASTM material, cobalt chrome, tantalum, ceramic, poly-ether-ether-ketone (PEEK), various plastics, plastic composites, carbon fiber composites, coral, and can include artificial materials which are at least in part bioresorbable. The radiographic appearance of the structural materials employed in the implants are intended to be of varying nature such that optimal visualization of implant placement, implant-bone interfaces and/or bone ingrowth and through-growth can be achieved.  
         [0075]     While the descriptions reveal various relationships, parallel or not, of upper to lower surfaces of the implants, it should be noted that deliberate angulation between surfaces relative to each other is possible. Subsequently, when implanted into the spine, such implants permit position of the adjacent vertebral bodies in angular relationship to each other to restore the natural curvature of the spine, such as lordosis for example. It should also be noted that significant variations in shape of the implants are possible including but not limited to: kidney shaped, rounded, wedge shaped, cylindrical, trapezoidal, rectangular, oblong, and oval.  
         [0076]     Outer surfaces may contain threading or particular unevenness for improved insertion or anchorage into surrounding tissues or bone. In any of the embodiments of the present invention, the implants may include, be made of, treated, coated, filled, used in combination with, or have a hollow space or opening for containing artificial or naturally occurring materials and/or substances suitable for implantation in the human spine. These materials, and/or substances, may include any source of osteogenesis, bone growth promoting materials, bone, bone derived substances or products, demineralized bone matrix, mineralizing proteins, ossifying proteins, bone morphogenetic proteins, hydroxyapatite, genes coding for the production of bone, and bone including, but not limited to, cortical bone, antibiotics, cancer treating substances, infection treating substances or other disease treating substances. The implant can include, at least in part materials that are bioabsorbable and/or resorbable in the body. The implants of the present invention can be formed of a porous material or can be formed of a material that intrinsically participates in the growth of bone between adjacent vertebral. At least a portion of the implant may be treated to promote bone ingrowth between the implant and the adjacent vertebral bodies.  
         [0077]     The implant of the present invention may be used in combination with a spinal fixation device such as any device, regardless of material, that can be inserted into any portion of the spine, such as but not limited to interbody spinal implants, structural bone grafts, mesh, cages, spacers, staples, bone screws, plates, rods, tethers of synthetic material or wires, or other spinal fixation instrumentation. While the invention has been described with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that various modifications can be made to the invention itself without departing from the spirit and scope thereof. All changes and modifications that are within the spirit of the invention are hereby anticipated and claimed.  
         [0078]     A method under the invention includes implanting an intervertebral implant from an anterior surgical approach. An implant comprising the following is provided: a first rim around a periphery of the implant, the first rim having a detectable radiographic signature, and a member coupled to the first rim, the member having less of a radiographic signature than the first rim. The member adds vertebral spacing height to the first rim. Other implants with compatible radiographic characteristics are also contemplated for use under embodiments of the method.  
         [0079]     The method further includes radiographically observing placement of the implant between superior and inferior vertebral bodies. This observation may be accomplished by capturing radiographic images along one or more of an anterior to posterior radiographic view and a lateral radiographic view. Such radiographic viewing in some embodiments includes viewing from any lateral direction and is not limited to direct posterior, anterior, and lateral directly, but includes oblique departures from these directions. Effective radiographic viewing is enabled by embodiments of the invention that provide medial-lateral and anterior-posterior viewing paths. However, selective placement of radio-opaque materials that both structurally support and notify a surgeon of implant orientation are present in some embodiments of the invention in combination with these viewing paths.  
         [0080]     Radiographically observing placement of the implant may include observing relative alignment of two or more supports extending between the superior and inferior portions of the implant. By observing relative alignment of two or more supports coupled to the first rim, orientation of the implant may be determined.  
         [0081]     The method may also include radiographically observing bone growth between the superior and inferior vertebral bodies by capturing radiographic images along one or more of an anterior to posterior radiographic view and a lateral radiographic view. Such radiographic viewing in some embodiments includes viewing from any lateral direction and is not limited to direct posterior, anterior, and lateral, but includes oblique departures from these directions. Observation of bone growth is enhanced by the provision of viewing paths provided through an implant that only include bone growth volumes and radiolucent materials.  
         [0082]     A method of assembling an intervertebral implant includes providing an implant with a first rim around a periphery of the implant, the first rim having a detectable radiographic signature, a support coupled to the first rim, the support having a detectable radiographic signature, and a second rim coupled to the support, the second rim having a detectable radiographic signature.  
         [0083]     Embodiments of the method include applying a member between the first rim and the second rim. The member of the embodiment having less of a radiographic signature than the first rim. By way of example, the member may be a radiolucent material, such as PEEK. As illustrated herein, the member may include one or more of a central strut  410 , a first segment  610 , a second segment  611 , or a tubular member  612 .  
         [0084]     Applying the member may be accomplished in various ways. The distal end may be formed around at least a portion of one of the first rim, the second rim, and the support. To accomplish this, the material of the member may be cast, injected, or molded directly around at least a portion of one of the first rim, the second rim, and the support. The body may be included as a part of a mold or cast, or encapsulated within a mold or cast for application to a portion of one of the first rim, the second rim, and the support.  
         [0085]     Applying the member may also include interconnecting a material with at least a portion of at least one of the first rim, the second rim, and the support. Interconnecting may also include casting, injecting, or molding material, but without encapsulating a portion of at least one of the first rim, the second rim, and the support. Interconnecting material may also involve forming a member completely separately from the first rim, the second rim, and the support by milling, casting, forming, injecting, or molding. After the member is formed, it may then be applied to the body by any method of adhesion, interdigitation, or interconnection. In some embodiments, interconnecting may be accomplished by snapping the material of the member to, between, or among the first rim, the second rim, and the support.  
         [0086]     While embodiments of the invention have been illustrated and described in detail in the disclosure, the disclosure is to be considered as illustrative and not restrictive in character. All changes and modifications that come within the spirit of the invention are to be considered within the scope of the disclosure.