Patent Publication Number: US-8540725-B2

Title: Instruments, implants and methods for positioning implants into a spinal disc space

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 12/383,190 filed on Mar. 20, 2009 now allowed, which is a continuation of U.S. patent application Ser. No. 11/107,192, filed Apr. 15, 2005, which is now issued as U.S. Pat. No. 7,575,580. The referenced applications each being hereby incorporated by reference herein in their respective entireties. 
    
    
     BACKGROUND 
     Normal intervertebral discs between endplates of adjacent vertebrae distribute forces between the vertebrae and cushion vertebral bodies. The spinal discs may be displaced or damaged due to trauma, disease or aging. A herniated or ruptured annulus fibrosis may result in nerve damage, pain, numbness, muscle weakness, and even paralysis. Furthermore, as a result of the normal aging processes, discs dehydrate and harden, thereby reducing the disc space height and producing instability of the spine and decreased mobility. Most surgical corrections of a disc space include a discectomy, which can be followed by restoration of normal disc space height and bony fusion of the adjacent vertebrae to maintain the disc space height. 
     Access to a damaged disc space may be accomplished from several approaches to the spine. One approach is to gain access to the anterior portion of the spine through a patient&#39;s abdomen. However, extensive vessel retraction is often required and many vertebral levels are not readily accessible from this approach. A posterior approach may also be utilized. This approach typically requires that both sides of the disc space on either side of the spinal cord be surgically exposed, which may require a substantial incision or multiple access locations, as well as extensive retraction of the spinal cord. To alleviate problems associated with both anterior and posterior approaches to the spine, a postero-lateral approach to the disc space may be utilized. 
     There remains a need for improved instruments, implants and techniques for use in a postero-lateral approach to a spinal disc space that facilitate disc space preparation and implant insertion to provide bilateral stability to the subject disc space. 
     SUMMARY 
     There are provided instruments, implants and methods useful for implant insertion from a postero-lateral approach to the spinal disc space, although application with other approaches are also contemplated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of an inserter instrument and an implant in an initial position in a spinal disc space. 
         FIG. 2  is an enlarged perspective view of the implant of  FIG. 1 . 
         FIG. 3  is an enlarged plan view showing the implant engaged with the distal end of the inserter instrument in the initial position of  FIG. 1 . 
         FIG. 4  is a plan view of the inserter instrument and the implant in a final position in the spinal disc space. 
         FIG. 5  is an enlarged plan view showing the implant engaged with the distal end of the inserter instrument in the final position of  FIG. 4 . 
         FIG. 6  is a plan view of the distal end of the inserter instrument with the implant removed and with the inserter in the initial position. 
         FIG. 7  is a perspective view of the distal end of the inserter instrument in an engaged position with the implant and the implant oriented in the final position. 
         FIG. 8  is a perspective view of the distal end of the inserter instrument in a release position with the implant and the implant oriented in the final position. 
         FIG. 9  is a top plan view of the distal end of the inserter instrument in a release position immediately after placing the implant in the final position. 
         FIG. 10  is a top plan view of the distal end of the inserter instrument in the release position and the inserter withdrawn proximally from the implant oriented in the final position. 
         FIG. 11  is a perspective view of the distal end of the inserter instrument with the posterior arm removed and the anterior arm in the initial position. 
         FIG. 12  is a perspective view of the distal end of the inserter instrument with the posterior gripping arm removed and the anterior arm in the final position. 
         FIG. 13  is a top plan view of a portion of the shaft assembly and an interior portion of a handle assembly of the inserter instrument. 
         FIG. 14  is a perspective view of the interior portion of the handle assembly shown in  FIG. 13  including a frame of the handle assembly. 
         FIG. 15  is the view of  FIG. 13  including the frame of  FIG. 14  and also an articulating driver of the handle assembly. 
         FIG. 16  is a perspective view showing a portion of the shaft assembly with a hub removed and a proximal portion of the interior of the handle assembly. 
         FIG. 17  is the view of  FIG. 16  with a lock driver engaged about a lock screw of the handle assembly. 
         FIG. 18  is a perspective view of the distal portion of the inserter instrument in the release position with the implant removed. 
         FIG. 19  is a perspective view of the distal portion of the inserter instrument in the engaged position with the implant removed. 
         FIG. 20  is a perspective view of another embodiment inserter instrument and implant. 
         FIG. 21  is a perspective view of a distal portion of the inserter instrument and the implant of  FIG. 20  with the implant partially engaged to the inserter instrument. 
         FIG. 22  is the perspective view of  FIG. 21  in horizontal section through the distal portion of the inserter instrument and implant. 
         FIG. 23  is an enlarged perspective view in horizontal section showing engagement of the inserter instrument with the implant. 
         FIG. 24  is a perspective view showing the implant and inserter instrument of  FIG. 20  positioned through a retractor sleeve. 
     
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
     For the purposes of promoting an understanding of the principles of the present invention, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is intended thereby. Any alterations and further modification in the described processes, systems, or devices, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates. 
     Instruments, implants and techniques provide and facilitate implant insertion into a spinal disc space through a single opening and positioning of the implant so that it provides balanced, bi-lateral support of the adjacent vertebrae. The instruments and implants can be employed in postero-lateral approaches to the disc space to obtain proper positioning of the implant in the portion of the disc space most distal from the postero-lateral opening. The instruments and implants facilitate moving the implant across the disc space to the distal portion of the disc space so that the implant extends between distal and proximal portions of the disc space to provide bi-lateral support of the adjacent vertebrae. The inserter instruments provide a low profile engagement with the implant to minimize the footprint of the assembly and minimize exposure and retraction of tissue and neural elements to accommodate implant insertion. 
     In  FIGS. 1 and 3  there is shown one embodiment inserter instrument  60  engaged to a trailing end of implant  30  at the distal end of inserter instrument  60 . A vertebral body V 1  is shown with the implant  30  positioned in a disc space adjacent thereto in an initial position. In the initial position, implant  30  is inserted into the disc space while inserter instrument  60  maintains implant  30  in general alignment along longitudinal axis  61  of inserter instrument  60 . In postero-lateral procedures, implant  30  extends obliquely to sagittal plane C of the patient when in the initial position. 
     In  FIGS. 4 and 5 , inserter instrument  60  has been manipulated to reposition implant  30  to a final position for implantation in the disc space. In the orientation of the final position, implant  30  is substantially obliquely oriented to longitudinal axis  61  of inserter instrument  60 . Furthermore, implant  30  includes an axis of symmetry C 1 . Axis C 1  is oriented so that it is aligned along or generally parallel to sagittal plane C of the patient. In the final position, implant  30  extends across sagittal plane C and contacts the adjacent vertebral endplates to provide balanced bi-lateral support of the adjacent vertebrae. Inserter instrument  60  can then be disengaged from implant  30  and withdrawn from the patient. 
     The disc space can be accessed and prepared from the postero-lateral approach using spreaders, cutters, chisels, reamers, and other instruments to prepare the disc space and adjacent vertebral endplates to receive implant  30 . Examples of such instruments and techniques are discussed in U.S. Patent Application Publication No. 2002/0165550, published Nov. 7, 2002, which is incorporated herein by reference in its entirety. 
     One embodiment of implant  30  is shown in further detail in  FIG. 2 , it being understood that any suitable implant can be engaged to inserter instrument  60 . Implant  30  includes a body formed by a wall  32  extending about a central cavity  42 . Cavity  42  extends between and opens at an upper bearing surface  52  and a lower bearing surface  54 . Upper and lower bearing surfaces  52 ,  54  contact the adjacent vertebral endplates to support the adjacent vertebrae when implant  30  is implanted in the spinal disc space. Surfaces  52 ,  54  may include grooves  50  formed therein to facilitate engagement with the vertebral endplates and resist the implant from migrating in the disc space. Other surface features are also contemplated, including teeth, spikes, knurlings, peeks and valleys, and other projections and/or recesses. 
     Implant  30  includes convexly curved anterior wall portion  34  and an opposite concavely curved posterior wall portion  36 . Wall portions  34 ,  36  are connected by a convexly curved leading end wall portion  38  and a convexly curved trailing end wall portion  40 . The overall shape of wall  32  provides a banana, kidney or boomerang type shape that facilitates placement of implant  30  along a non-linear insertion path in the disc space from the proximal postero-lateral opening to a distal portion of the disc space opposite the postero-lateral opening. In the implanted position, posterior wall portion  36  is oriented toward the spinal foramen. The anterior wall portion  34  extends anteriorly to provide anterior support of the vertebrae. The elongated shape of implant  30  facilitates placement through the postero-lateral opening while minimizing the retraction of tissue and neural elements needed to accommodate placement of the implant through the postero-lateral approach. It should be understood the leading end wall portion  38  can be a trailing end wall portion, and trailing end wall portion  40  can be a leading end wall portion, in situations where wall portion  38  is engaged with an inserter instrument and wall portion  40  is first inserted into the disc space through the postero-lateral opening. 
     A central opening  49  in anterior wall portion  34  and a central opening  51  in posterior wall portion  36  provide avenues for bone growth into cavity  42 . Implant  30  further includes a recessed area  44  that extends around the trailing end wall portion  40  and along at least a portion of the length of anterior wall portion  34 . A receptacle  46  is formed in posterior wall portion  36 . As discussed further below, the recessed area  44  and receptacle  46  are configured for engagement by respective portions of a grasper assembly  110  of inserter instrument  60 . Lateral pin holes  48  in recessed areas  44  of anterior wall portion  34  can provide additional areas for engagement by the inserter instrument. 
     As shown in  FIG. 1 , inserter instrument  60  includes a shaft assembly  90  and a proximal handle assembly  100  extending along longitudinal axis  61 . Implant  30  is engaged to inserter instrument  60  with grasper assembly  110  at the distal end of shaft assembly  90 . Handle assembly  100  is operably coupled with grasper assembly  110  through shaft assembly  90  to remotely manipulate grasper assembly  110  to grasp and release implant  30  from inserter instrument  60 . Grasper assembly  110  is also remotely operable to reposition implant  30  relative to longitudinal axis  61  from an initial position, shown in  FIGS. 1 and 3 , to a final implanted position, shown in  FIGS. 4-5 . 
     Shaft assembly  90  of inserter instrument  60  includes a first shaft  62  and a second shaft  63 . Second shaft  63  extends along and parallel to first shaft  62 , and includes a C-shaped side oriented toward a C-shaped side of first shaft  62 . The C-shaped sides together form a passage that receives a locking shaft  68  ( FIG. 6 .) therein. Shaft assembly  90  further includes a hub  70  at a proximal end thereof adjacent handle assembly  100 . Second shaft  63  is engaged to hub  70 . First shaft  62  and locking shaft  68  extend through hub  70  and into handle assembly  100   
     Handle assembly  100  includes an outer cylindrical handle member  72  have grip-enhancing external surface features. A rotatable articulator driver  74  is between a proximal end of handle member  72  and a proximal end member  86 . Handle assembly  100  further includes a rotatable lock driver  76  at a distal end of handle member  72  between handle member  72  and hub  70 . Drivers  74 ,  76  each include a series of radial protuberances and valleys between protuberances to enhance the ability to grip and apply the necessary force to rotate drivers  74 ,  76 . 
     Further details of handle assembly  100  are shown in  FIGS. 13-17 . In  FIG. 13  handle member  72 , drivers  74 ,  76 , and second shaft  63  are removed. Locking shaft  68  extends through hub  70  to a lock screw  66  at a proximal end of locking shaft  68 . First shaft  62  extends through hub  70  and also through lock screw  66  to an articulator screw  64  at a proximal end of first shaft  62 . Screws  64 ,  66  are linearly movable to linearly move the respective shafts  62 ,  68  in response to rotation of the respective drivers  74 ,  76  thereabout. 
     In  FIG. 14 , a frame  78  is positioned about shafts  62 ,  68  and screws  64 ,  66 . Frame  78  includes a distal slot  80  that receives lock screw  66 , a proximal slot  82  that receives articulator screw  64 , and an intermediate slot  84  therebetween. Slots  80 ,  82  are elongated sufficiently to allow proximal and distal translation of screws  64 ,  66  to remotely manipulate grasper assembly  110 . End member  86  at the proximal end of frame  78  can receive and transmit impaction forces to facilitate insertion of the implant into the disc space. 
     In  FIG. 15  there is shown articulator driver  74  rotatably positioned about and threadingly engaged to articulator screw  64 . Rotation of articulator driver  74  about screw  64  linearly advances first shaft  62  in a proximal or distal direction, depending on the direction of rotation. The linear movement of first shaft  62  in turn articulates grasper assembly  110  between the initial position and the final position, as discussed above and as discussed further below. 
     In  FIG. 16  there is shown lock screw  66  and shafts  62 ,  63  are removed. In  FIG. 17  lock driver  76  is threadingly engaged to and rotatably positioned about lock screw  66 . Rotation of lock driver  76  linearly advances locking shaft  68  in a proximal or distal direction, depending on the direction of rotation. The linear movement of locking shaft  68  in turn manipulates grasper assembly  110  between a release position and an engaged position relative to the implant positioned therein. In the release position, grasper assembly  110  is opened to receive or release the implant, as shown in  FIGS. 8 and 18 , for example. In the engaged position, the implant positioned in grasper assembly  110  is engaged by the grasper assembly  110  and to couple the implant to inserter instrument  60 , as shown in  FIGS. 7 and 19 , for example. 
     As shown in  FIGS. 6-12  and  18 - 19 , grasper assembly  110  includes a first arm  112  and a second arm  114 . First arm  112  includes a concavely curved inner surface  113 , and second arm  114  includes a second concavely curved inner surface  115 . Surfaces  113 ,  115  are oriented toward one another, and are shaped to conform to the outer wall surfaces of implant  30  about trailing end wall portion  40  and in recessed area  44  and receptacle  46 , respectively. First arm  112  may include a pin  102  that is positionable into a pin hole  48  in recessed area  44  to further engage implant  30  to grasper assembly  110  and to maintain the implant in engagement therewith. Other embodiments contemplated that pin  102  is not provided, such as shown in  FIGS. 18 and 19 . 
     First arm  112  includes a proximal lever portion  116  having a first end  118  pivotally coupled to a distal end of first shaft  62  with a pin  108 , and a second end  120  pivotally coupled to a distal end of second shaft  63  with a pin  104 . Lever portion  116  includes a forked arrangement for positioning along the outer surfaces of shafts  62 ,  63  to accommodate placement of a heel portion  122  and toe portion  106  of second arm  114  therebetween. 
     Second arm  114  includes proximal heel portion  122  having a bulbous shape positioned in contact with a distal foot  69  of locking shaft  68  ( FIGS. 6 ,  18 - 19 ). Heel  122  includes a slotted hole  124  extending between a distal end  126  and a proximal end  128 . Pin  104  pivotally engages second end  120  of first grasping arm  112  to the distal end of second shaft  63 . Pin  104  also extends through slotted hole  124  to couple second arm  114  to the distal end of second shaft  63  while also allowing limited radial translation of second arm  114  relative to first arm  112 . Slotted hole  124  is configured between its distal end  126  and proximal end  128  to allow second arm  114  to move toward and away from first arm  112  to selectively grip and release the implant therebetween. Second arm  114  further includes a toe portion  106  opposite heel portion  122 . Toe portion  106  is pivotally coupled with first shaft  62  and first end  118  of first grasping arm  112  with pin  108 . 
     Linear distal movement of first shaft  62  by rotating articulator driver  74  causes distal displacement of first end  118  relative to second end  120 , which in turn pivots first arm  112  and second arm  114  about pin  104  and the fixed second shaft  63 . This movement in turn moves grasper assembly  110  from its initial position, as shown in  FIGS. 1 and 3 , to its final position, as shown in  FIGS. 4-5 . In one embodiment, axis C 1  of implant  30  forms an angle A 1  ( FIG. 3 ) with longitudinal axis  61  in the initial position, and an angle A 2  ( FIG. 5 ) in the final position. In one specific embodiment, angle A 1  is about 80 degrees to generally orient implant  30  along axis  61 . Angle A 2  is about 55 degrees to orient implant  30  in a substantially oblique orientation to axis  61 . Other embodiments contemplate other angular orientations, ranging from 70 degrees to 110 degrees for angle A 1  and ranging from 35 degrees to 75 degrees for angle A 2 . Still other embodiments contemplate other angular ranges for angles A 1  and A 2 . 
     Arms  112 ,  114  are further moveable to grip and release implant  30  from therebetween. In the release position, shown in  FIGS. 8-10  and  18 , pin  104  is adjacent distal end  126  of slotted hole  124  and foot  69  of locking shaft  68  is moved distally to a location spaced a distance  105  from an end wall  65  of a slot in second shaft  63 . This allows second arm  114  to rotate away from first arm  112 . To move arms  112 ,  114  to the engaged position, foot  69  is advanced distally with distal movement of locking shaft  68  by rotation of locking driver  76 . As shown in  FIG. 7 , distal movement of foot  69  displaces it a second greater distance  105 ′ from end wall  65  of second shaft  63 , and locking shaft  68  articulates second arm  114  toward first arm  112 . This movement positions pin  104  adjacent the proximal end  128  of slotted hole  124 . The articulation of second arm  114  in the clockwise direction can be continued to firmly grasp implant  30  between first and second arms  112 ,  114  as shown in  FIGS. 5 and 7 , for example. 
     Heel portion  122  includes a circular outer perimeter  123  that contacts foot  69  in the engaged position. While in the engaged position, grasper assembly  110  can be moved from the initial position to the implanted position. During this movement, the circular perimeter  123  allows foot  69  to maintain contact with heel portion  122  and maintain arms  112 ,  114  in the engaged position with implant  30 . 
     In use, arms  112 ,  114  of inserter instrument  60  are placed in the release position to receive implant  30  therebetween. Lock driver  76  is rotated to move arms  112 ,  114  to the engaging position to firmly grip implant  30  with grasping assembly  110  in the initial position. Implant  300  is delivered to the postero-lateral opening in the disc space and the leading end of the implant is positioned through the opening while being maintained in the initial position. The implant is advanced in the initial position along axis  61  in a direction substantially obliquely oriented to sagittal plane C until the trailing end of implant  30  is positioned in the disc space. Impaction forces can be delivered to the proximal end of the inserter instrument if necessary. 
     When implant  30  is in the appropriate position in the disc space, articulator driver  74  can be rotated to manipulate first shaft  62  and grasper assembly  110  to move implant  30  from the initial position to the final position in the disc space. In the final position, axis C 1  of implant  30  is oriented along or generally parallel to sagittal plane C. Lock driver  76  can then be rotated to move locking shaft  68  proximally to allow arms  112 ,  114  to the release position for withdrawal of inserter instrument from the disc space. 
       FIGS. 20-23  show another embodiment implant and implant inserter. Implant inserter  160  includes an elongated shaft assembly  190 , a grasper assembly  210  at a distal end of shaft assembly  190 , and a handle assembly  200  at a proximal end of shaft assembly  190 . Implant  130  is releasably engageable at the distal end of shaft assembly  190  with grasper assembly  210 . Handle assembly  200  is operable to manipulate grasper assembly  210  to grasp and release the implant  130 , and to deliver implant  130  to the spinal disc space. While specific applications in postero-lateral approaches to the disc space are contemplated as discussed above, other approaches to the disc space are also contemplated. 
     As shown in further detail in  FIGS. 21-22 , implant  130  includes an overall size and shape similar to that discussed above for implant  30 . Implant  130  includes an outer wall  132  extending about a central cavity  142 . Cavity  142  extends between and opens at an upper bearing surface  152  and a lower bearing surface  154 . Upper and lower bearing surfaces  152 ,  154  contact the adjacent vertebral endplates to support the adjacent vertebrae when implanted. Surfaces  152 ,  154  may include pyramidally shaped teeth  150  formed thereon to facilitate engagement with the vertebral endplates and resist the implant from migrating in the disc space. Other surface features are also contemplated, including grooves, spikes, knurlings, peeks and valleys, and other projections and/or recesses. 
     Implant  130  includes convexly curved anterior wall portion  134  and an opposite concavely curved posterior wall portion  136 . Wall portions  134 ,  136  are connected by a convexly curved leading end wall portion  138  and a convexly curved trailing end wall portion  140 . The overall shape of wall  132  provides a banana, kidney or boomerang type shape that facilitates placement along a non-linear insertion path in the disc space. The elongated shape facilitates placement through the postero-lateral opening while minimizing the retraction of tissue and neural elements needed to accommodate insertion of the implant through the postero-lateral approach. It should be understood the leading end wall portion  138  can be a trailing end wall portion, and trailing end wall portion  140  can be a leading end wall portion, in situations where wall portion  138  is engaged with an inserter instrument and wall portion  140  is first inserted into the disc space. 
     A number of openings  149  in posterior wall portion  136  and elongate slots  152  in anterior wall portion  134  provide avenues for bone growth into cavity  142 . Implant  130  further includes a recessed area  146  that extends into trailing end wall portion  140  adjacent posterior wall portion  136 , and a receptacle  148  in trailing end wall portion  140  adjacent anterior wall portion  134 . As discussed further below, the recessed area and receptacle  146 ,  148  are configured to receive grasper assembly  210  of inserter instrument  160 . Leading end wall portion  138  can be similarly provided with recessed area and a receptacle so that implant  130  can be engaged with an inserter  160  for insertion from either direction into the spinal disc space. 
     Inserter instrument  160  includes shaft assembly  190  extending along longitudinal axis  161 . Handle assembly  200  is at a proximal end of shaft assembly  190 , and includes a handle member  172  extending transversely to longitudinal axis  161 . A hub member  170  extends proximally from shaft assembly  190  along longitudinal axis  161 . Hub  170  includes a slotted portion  174  formed in and opening along one side thereof. A lock driver  176  is rotatably positioned therein. Hub  170  further provides a proximally oriented platform for delivery of impaction forces to facilitate insertion of the implant engaged to grasper assembly  210 . 
     As shown in  FIGS. 22-23 , shaft assembly  190  includes a first or outer shaft  162  having a central passage  164  formed therethrough. Locking shaft  168  is received in and linearly movable in passage  164  relative to outer shaft  162 . Lock driver  176  is threading engaged about a lock screw (not shown) at the proximal end of a locking shaft  168 . Rotation of lock driver  176  linearly translates locking shaft  168  distally and proximally in passage  164 . 
     Grasper assembly  210  includes a first arm  166  formed at a distal end of outer shaft  162 . Outer shaft  162  includes an enlarged portion  172  to offset first arm  166  laterally from passage  164 . First arm  166  includes a spherically shaped distal end portion that is rotatably received in recessed area  146 . In the illustrated embodiment, recessed area  146  include a complementary spherical shape to interface with first arm  166  and allow rotation of implant  130  about first arm  166 . Implant  130  is rotatable to position a distal end wall  180  of outer shaft  162  in abutting contact therewith at trailing end wall portion  140 . Locking shaft  168  includes a second arm  163  formed at a distal end thereof. Locking shaft  168  and second arm  163  are distally linearly movable with lock driver  176  to advance second arm  163  into receptacle  148 . The distal end of second arm  163  can be beveled to facilitate insertion into receptacle  148 . 
     In the locking position shown in  FIG. 23 , locking shaft  168  prevents implant  130  from rotating about first arm  166  and holds implant  130  firmly on inserter instrument  160 . The distal end of outer shaft  162  includes a recessed area  182  adjacent first arm  166 , and implant  130  includes a toe  156  between recessed area  146  and receptacle  148 . When second arm  163  is positioned in receptacle  148 , the toe  156  is received in recessed area  182  as shown in  FIG. 23 . This provides a dovetail locking arrangement between implant  130  and grasper assembly  210  that implant  130  from being axially pulled or rotated relative to inserter instrument  160 . 
     When implant  130  is positioned in the disc space, inserter instrument  160  can be disengaged therefrom by rotating lock driver  176  to proximally withdraw locking shaft  168  distally and remove second arm  163  from the receptacle  148 . The inserter instrument  160  can then be withdrawn proximally from the disc space. Intrusion into tissue and neural elements in the approach to the disc space is minimized since inserter instrument  160  has the same footprint transversely to longitudinal axis  161  when engaged to implant  130  and when disengaged to implant  130 . The footprint of the implant and inserter instrument assembly is also minimized during insertion since arms  163 ,  166  extend into implant  130  at or adjacent trailing end wall portion  140 , and do not occupy space anteriorly or posteriorly of implant  130 . 
     The above-described instruments and methods have been disclosed with reference to use in substantially open surgical procedures. However, it is contemplated that the implants, instruments and methods may be utilized through guide sleeves or tubes, such as retractor sleeve  200  shown in  FIG. 24 . Such instruments can provide greater protection to adjacent tissues, to reduce the size of access incisions, to provide direct visualization of the surgical site, and/or to provide greater control of the method. The implants, instruments and methods may further be used in combination with disc space preparation and implant insertion through microscopic or endoscopic instruments that provide direct visualization of the surgical site. 
     The instruments discussed herein are suited for inserting an implant through a postero-lateral opening in a spinal disc space. The inserter instruments provide the surgeon the ability to control insertion of an implant into the spinal disc space from a postero-lateral approach. The inserter instruments facilitate positioning of the implant in the disc space such that the implant extends across the disc space to provide bilateral support of the adjacent vertebrae, and also facilitate positioning of the implant in the disc space along a non-linear insertion path. The inserter instruments can also be used to position multiple implants at various locations in the disc space, and also for insertion of one or more implants from other approaches to the disc space. 
     Implants  30 ,  130  can be interbody fusion devices or cages that can be packed with bone growth material or other known substance and inserted into a spinal disc space to promote bony fusion between vertebrae. Furthermore, the structural features of implant  30 ,  130  can have application for a disc prosthesis or a disc nucleus prosthesis that is to be inserted into the disc space. The illustrated implants  30 ,  130  have a boomerang or banana shape that is suited for insertion to provide bilateral support in the disc space through a unilateral, postero-lateral approach. It is also contemplated that the disc space can be accessed and prepared for implant insertion using any other known techniques and instruments and other approaches to the disc space, such as posterior, lateral, anterior or antero-lateral approaches. 
     Implants  30 ,  130  can include other shapes and also include interior bars, struts and walls. The upper and lower bearing surfaces can include double convexity to provide an intimate fit in the disc space and a profile that matches the concavity of the endplates, providing implant stability and promoting fusion. The sidewall openings and hollow interior cavity can maximize the volume available to receive bone growth material and also the contact surface area between the bone growth material and the adjacent bony structure. Furthermore, differences in heights between the upper and lower bearing surfaces at the anterior and posterior walls can be provided to establish lordosis when implants  30 ,  130  are inserted in the disc space. 
     The implants described herein can be made from any biocompatible material, including synthetic or natural autograft, allograft or xenograft tissues, and can be resorbable or non-resorbable nature. Examples of tissue materials include hard tissues, connective tissues, demineralized bone matrix and combinations thereof. Further examples of resorbable materials are polylactide, polyglycolide, tyrosine-derived polycarbonate, polyanhydride, polyorthoester, polyphosphazene, calcium phosphate, hydroxyapatite, bioactive glass, and combinations thereof. Further examples of non-resorbable materials are non-reinforced polymers, carbon-reinforced polymer composites, PEEK and PEEK composites; shape-memory alloys; titanium and titanium alloys; cobalt chrome alloys; stainless steel; ceramics; and combinations thereof. Instruments described herein can be made from any suitable surgical grade material, including stainless steel, aluminum, plastics, and combinations of materials. 
     Any suitable osteogenetic material or composition is contemplated for placement within the cavities defined by the implants described herein. Such osteogenic material includes, for example, autograft, allograft, xenograft, demineralized bone, synthetic and natural bone graft substitutes, such as bioceramics and polymers, and osteoinductive factors. Where bony material is placed within the cavities of the implant, the material can be pre-packed into the hollow cavities before the device is implanted, or can be pushed through the wall openings after the device is in position in the spinal column. A separate carrier to hold the materials within the device can also be used. These carriers can include collagen-based carriers, bioceramic materials, such as BIOGLASS® hydroxyapatite and calcium phosphate compositions. The carrier material can be provided in the form of a sponge, a block, folded sheet, putty, paste, graft material or other suitable form. Moreover, the osteogenetic compositions contained within the implant can comprise an effective amount of a bone morphogenetic protein, transforming growth factor .beta.1, insulin-like growth factor 1, platelet-derived growth factor, fibroblast growth factor, LIM mineralization protein (LMP), and combinations thereof or other therapeutic or infection resistant agent, held within a suitable carrier material. 
     While the invention has been illustrated and described in detail in the drawings and the foregoing description, the same is considered to be illustrative and not restrictive in character. All changes and modifications that come within the spirit of the invention are desired to be protected.