Patent Publication Number: US-2012029639-A1

Title: Interbody spinal implants and insertion techniques

Description:
BACKGROUND 
     The present invention relates generally to interbody spinal implants and to methods and systems for inserting one or more interbody spinal implants between adjacent vertebrae. 
     Several techniques and systems have been developed for correcting and stabilizing the spine and for facilitating fusion at various levels of the spine. The spinal anatomy including the bony structure of vertebral bodies, vascular structures, neural structures, musculature, and other vital tissue along the spinal column make it difficult to position an interbody implant in the disc space between adjacent vertebral bodies. In addition, when an implant is placed into a disc space, the channel or path that the implant took to enter the disc space provides a path for retrograde movement of the implant from the disc space. Also, when approaches other than a direct anterior approach are taken, current implants do not provide the desired fit and angulation between endplates of the adjacent vertebrae. 
     Preservation of cortical bone of the endplates is desired in order to maximize the stability of the fusion area. Therefore, the cortical bone of the endplates of the superior and inferior vertebrae is ideally left entirely or substantially intact. Positioning some implants from approaches that parallel or extend substantially parallel to the sagittal plane can be difficult to achieve with an interbody implant. With some implants, surface area contact between the implant and the hard cortical bone of the endplate can be too small so that the implant subsides too much and tends to want to break through the endplates. Unilateral fixation is not always an option because of stability issues of a narrow implant. While a lateral approach to the disc space avoids certain critical anatomical structures that impede access in other approaches, insertion of implants into the disc space from a lateral approach is challenging without performing a partial removal of the endplate and osteophytes. As a result, additional improvements in spinal fusion implants and insertion instruments and techniques are needed that make utilization of a lateral approach more palatable, although utilization of such implants and instrument is not necessarily limited to a lateral approach. 
     SUMMARY 
     According to one aspect, an implant for a spinal column is disclosed that is capable of being inserted into a patient in a first orientation having a reduced or minimum height and then rotated to a second orientation providing a second greater height, wherein in each orientation the height of the implant extends in a direction from one endplate to the other endplate of adjacent vertebrae. In one embodiment, the implant includes first and second side-by-side elongated members that are separately rotated from the first orientation to the second orientation after insertion in the disc space. In another embodiment, the first and second implant members are interconnected by a housing that is located about mid-length of the first and second members. 
     In yet another aspect, an implant for a spinal column is disclosed that is capable of being inserted into a patient in a first orientation having a reduced or minimum height and then rotated to a second orientation providing a second or maximum height, wherein in each orientation the height of the implant extends in a direction from one endplate to the other endplate of adjacent vertebrae. In one embodiment, the implant includes a first member that is connected with a housing, and the first implant member is rotated from the first orientation to the second orientation while connected to the housing in the disc space. After the first member of the implant is rotated, a second member of the implant is inserted in a first orientation into the disc space and connected to the housing. The second implant member of the implant is then rotated from its first orientation to the second orientation while in side-by-side relation to the first member of the implant. 
     In a further aspect, an implant for a spinal column is disclosed that includes first and second elongated members extending in side-by-side relation that are rotatable in a housing that interconnects the first and second members. The implant includes a height that tapers from an outer sidewall of the first member to an outer sidewall of the second member when the first and second members are rotated in the housing to an implantation orientation. In one embodiment, the housing is located about mid-length along the first and second members and extends completely around the first and second members so that each of the first and second members includes first and second portions projecting from the housing in opposite directions from one another. 
     In another aspect, an implant for a spinal column is disclosed that includes at least three components. The components includes an anterior rotating spacer member, a posterior rotating spacer member, and a center housing extending along the sagittal plane that holds the spacer members together. The housing allows both spacer members to rotate around its respective central longitudinal axis so that the spacer members can be inserted into the disc space in a first orientation and then rotated for implantation at a second orientation. In the first orientation the insertion height of the implant is smaller than its implanted height obtained after rotation of the spacer members. In one embodiment, each spacer member is rotated 90 degree around its central longitudinal axis between the first and second orientations. 
     During implantation of the implant into the disc space in a lateral approach, the implant is maintained so that its insertion height is oriented toward the endplates until the implant is properly positioned along the transverse length of intervertebral space. After the implant is in the desired position in its insertion height orientation, the spacer members are rotated to an implantation orientation where superior and inferior bone engaging surfaces of the spacer members contact the adjacent endplates and distract the vertebrae to restore the intervertebral height. The spacer members can either be rotated independently or simultaneously while the housing preserves both insertion and final widths of the spacing between the spacer members. The housing can also be configured to allow the width of the spacing between the spacer members to be varied. In one embodiment, each of the spacer members includes first and second portions extending in opposite directions from the housing, where the first and second portions each include convexly curved superior and inferior bone engaging surfaces extending from a respective end of the spacer member to the housing. In a further embodiment, the bone engaging surfaces include ridges, teeth or other suitable engagement structure to securely engage the implant to the respective adjacent endplate. In yet a further embodiment, the spacer members include one or more cavities or holes to receive bone growth material and/or bone growth between the adjacent vertebrae. 
     In another implantation method, the implant is provided with only one spacer member engaged to the housing initially. The housing and first spacer member are implanted in the disc space with the spacer member rotated in a reduced height orientation. The first spacer member is then rotated about its longitudinal axis to a second orientation where its upper and lower bone engaging surface are positioned in contact with the endplates of the adjacent vertebrae. A second spacer member is then positioned in the disc space in a reduced height orientation alongside the first spacer member. The second spacer member is engaged to the housing while in its insertion orientation and then rotated to an implanted orientation adjacent to the first spacer member to contact its upper and lower bone engaging surfaces with the endplates of the adjacent vertebrae. The housing maintaining the spacing between the sides of the first and second spacer members. 
     Related features, aspects, embodiments, objects and advantages of the present invention will be apparent from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic plan view looking toward the axial plane of an endplate of a vertebral body of a spinal column with an interbody spinal implant positioned thereon. 
         FIG. 2  is a diagrammatic elevation view looking toward the coronal plane at a vertebral level of the spinal column including the vertebral body and interbody spinal implant of  FIG. 1 . 
         FIG. 3  is a diagrammatic elevation view looking toward the sagittal plane at a vertebral level of the spinal column including the vertebral body and interbody spinal implant of  FIG. 1 . 
         FIG. 4  is a diagrammatic elevation view looking toward the sagittal plane at a vertebral level of the spinal column including the vertebral body and interbody spinal implant of  FIG. 1  with the interbody spinal implant positioned in an initial insertion orientation. 
         FIG. 5  is a perspective rear view of a spinal interbody implant with members thereof in an initial insertion orientation. 
         FIG. 6  is a plan view of the spinal interbody implant of  FIG. 5  in its initial insertion orientation, 
         FIG. 7  is an end elevation view of the spinal interbody implant of  FIG. 5  in its initial insertion orientation with the vertebrae of the vertebral level shown diagrammatically. 
         FIG. 8  is a side elevation view of the spinal interbody implant of  FIG. 5  in its initial insertion orientation with the vertebrae of the vertebral level shown diagrammatically. 
         FIG. 9  is a perspective rear view of the spinal interbody implant of  FIG. 5  with members thereof in an implantation orientation. 
         FIG. 10  is a plan view of the spinal interbody implant of  FIG. 9  in its implantation orientation 
         FIG. 11  is an end elevation view of the spinal interbody implant of  FIG. 9  in its implantation orientation with the vertebrae of the vertebral level shown diagrammatically. 
         FIG. 12  is a side elevation view of the spinal interbody implant of  FIG. 9  in its final implantation orientation with the vertebrae of the vertebral level shown diagrammatically. 
         FIGS. 13A-D  illustrate another embodiment spinal interbody implant and an insertion sequence therefore. 
         FIG. 14  is a perspective view of another embodiment spinal interbody implant in an insertion orientation. 
         FIG. 15  is a perspective view of an implant body of the spinal interbody implant of  FIG. 14  removed from the housing. 
         FIG. 16  is a perspective view of another embodiment housing. 
         FIGS. 17A-17B  show another embodiment interbody spinal implant with an implant member in an insertion orientation connected with housings of  FIG. 16  at each end of the implant member. 
         FIGS. 18A-18B  show the interbody spinal implant member of  FIGS. 17A-17B  in an implanted orientation. 
         FIGS. 19A-19J  illustrate an insertion technique of another embodiment interbody spinal implant. 
     
    
    
     DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
     For the purposes of promoting an understanding of the principles of the 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 thereby intended. Any such alterations and further modifications in the illustrated devices, and such further applications of the principles of the invention as illustrated herein are contemplated as would normally occur to one skilled in the art to which the invention relates. 
     Methods, techniques, instrumentation and implants are provided to restore and/or maintain a collapsed, partially collapsed, damaged, diseased, or otherwise impaired spinal disc space at a desired disc space height and adjacent endplate orientation. The instruments and implants may be used in techniques employing minimally invasive instruments and technology to access the disc space, although access in non-minimally invasive procedures is also contemplated. Access to the collapsed disc space can be uni-portal, bi-portal, or multi-portal, but is preferentially uni-portal. The instruments and implants may also be employed in a direct lateral approach to the spinal disc space, although other approaches are also contemplated, including antero-lateral, postero-lateral, oblique, posterior, and anterior approaches. Also, the surgical methods, techniques, instruments and implants may find application at all vertebral segments of the spine, including the lumbar, thoracic and cervical spinal regions. 
       FIG. 1  illustrates a plan view looking caudally toward the axial plane of a vertebral body V 1 . Spinal interbody implant  10  is positioned on the vertebral endplate E 1 . Vertebral body V 1  is further shown in an anterior view and lateral view in  FIGS. 2 and 3 , respectively. Vertebral body V 1  along with vertebral body V 2  and spinal disc space D comprise a level of spinal column segment SC. Implant  10  is positioned in disc space D so its longitudinal axis  12  extends laterally across sagittal plane S and parallel to or generally parallel to coronal plane C. Implant  10  is positioned in disc space D between vertebrae V 1  and V 2  so that when it is in its implanted orientation it contacts endplates E 1  and E 2 . According to one procedure, implant  10  is positioned into disc space D from a direct lateral approach. As used herein, a “direct lateral approach” is an approach that is parallel or substantially parallel to the coronal plane and thus orthogonal to or substantially orthogonal to the sagittal plane. The term “substantially parallel” means that the approach may vary up to 30 degrees from the parallel to the coronal plane. 
       FIG. 4  illustrates a lateral view of the spinal column segment SC with implant  10  in a rotated position  10 ′ to orient its sidewalls toward respective ones of the endplate E 1 , E 2  to provide implant  10 ′ with a reduced profile in the caudal-cephalad direction and facilitate insertion between endplates E 1 , E 2 . In this orientation of implant  10 ′, it defines an insertion height that is small enough to allow insertion without interference of endplates E 1 , E 2  and without requiring distraction or over-distraction of vertebrae V 1 , V 2 , and minimizing or eliminating removal of osteophytes and endplate material. Once implant  10 ′ is located in the proper medial-lateral position in disc space D, implant  10 ′ is rotated 90 degrees around its longitudinal axis  12  to orient its superior and inferior bearing surfaces to contact and support respective ones of the endplates E 1 , E 2 , such as shown in  FIG. 3 , and, if necessary, to distract the vertebrae V 1 , V 2  to provide a desired disc space height. 
       FIGS. 5-8  shows another embodiment of implant  10  designated as implant  50 . Implant  50  comprises an elongate body  52  sized to fit within the intervertebral disc space D between adjacent vertebral members V 1 , V 2 . In  FIGS. 5-8 , body  50  is oriented to provide a reduced height H 1  to form a low profile orientation for insertion into disc space D so that at least one of the side walls is spaced from the respective adjacent endplate E 1 , E 2 .  FIGS. 9-12  show implant  10  with body  52  manipulated to an implanted configuration forming a height H 2 , H 3  between opposite vertebral endplate contacting surfaces that is sized to contact endplates E 1 , E 2 . Body  52  of implant  50  includes a length L between a leading end  54  and a trailing end  56  sized to extend substantially from a location adjacent the lateral edges of endplates E 1 , E 2  from one side of the disc space D to the opposite side of disc space D. Length L provides bi-lateral support for the vertebrae V 1 , V 2  and contacts the hard cortical bone that extends around the perimeter of endplates E 1 , E 2 , such as shown in  FIG. 12 . Furthermore, body  52  defines a width W 1  in the anterior-posterior direction along the sagittal plane when it is in its insertion configuration so that body  52  extends from a location adjacent the anterior edge of endplates E 1 , E 2  to a location spaced posteriorly of coronal plane C, as shown in  FIG. 7 . When body  52  is manipulated to its implanted configuration as shown in  FIG. 11 , body  52  defines a smaller width W 2  in the anterior-posterior direction along the sagittal plane. The superior and inferior bone engaging surfaces of body  52  contact the endplates E 1 , E 2  at least along the anterior edges of vertebral endplates E 1 , E 2 , while the posterior portion of body  52  is located on or adjacent to the coronal plane to provide support along the central axis of the spinal column. As set forth in greater detail below, implant  50  includes one or more inner chambers or cavities through body  52  that may receive bone growth material and/or bone grafts so that bone grows through the body  52  to fuse with the vertebral members V 1 , V 2 . Other embodiments contemplate an implant  50  that is solid or without cavities or chambers in the members of the implant, but allows bone growth between and around the members of the implant. 
     Further details regarding the embodiment of implant  50  will now be discussed. Implant body  52  includes an elongated first member  60  and an elongated second member  80  extending in side-by-side relation through a housing  100 . When implanted in disc space D in a direct lateral approach, first member  60  is located anteriorly of second member  80 , and housing  60  extends along the sagittal plane S. First member  60  includes a first portion  62  extending along a central longitudinal axis from leading end  54  to housing  100 , and a second portion  64  extending along the same central longitudinal axis from housing  100  to trailing end  56 . In one embodiment, first and second portions  62 ,  64  are connected to one another with a neck  63  that extends through housing  100 . In another embodiment, first and second portions  62 ,  64  are separate from one another and separately connected to housing  100 . First portion  62  includes a central cavity  66  extending through and opening at superior and inferior bone engaging surface portions  68 ,  70 , respectively. Second portion  64  includes a central cavity  72  extending through and opening at superior and inferior bone engaging surface portions  74 ,  76 , respectively. Each of the superior and inferior bone engaging surface portions  68 ,  70  of first portion  62  defines an outwardly extending convex curvature extending from leading end  54  to housing  100 . In addition, superior and inferior bone engaging surface portions  68 ,  70  each define an outwardly extending convex curvature between opposite side walls  69 ,  71 , Sidewalls  69 ,  71  are parallel to one another and extend from superior bone engaging surface portion  68  to inferior bone engaging surface portion  70  and from housing  100  to leading end  54 . Each of the superior and inferior bone engaging surface portions  74 ,  76  of second portion  64  defines an outwardly extending convex curvature extending from trailing end  56  to housing  100 . In addition, superior and inferior bone engaging surface portions  74 ,  76  define an outwardly extending convex curvature between opposite side walls  75 ,  77 . Sidewalls  75 ,  77  are parallel to one another and extend from superior bone engaging surface portion  74  to inferior bone engaging surface portion  76  and from housing  100  to trailing end  56 . In the insertion orientation of implant  50 , first member  60  is rotated about its central longitudinal axis in housing  100  so that parallel sidewalls  69 ,  71  and parallel sidewalls  75 ,  77  are oriented toward respective ones of the endplates E 1 , E 1  to form the reduced height H 1  for insertion of implant  50  into disc space D. 
     Second member  80  includes a first portion  82  extending along a central longitudinal axis thereof from leading end  54  to housing  100 , and a second portion  84  extending along the same central longitudinal axis from housing  100  to trailing end  56 . In one embodiment, first and second portions  82 ,  84  are connected to one another with a neck  83  that extends through housing  100 . In another embodiment, first and second portions  82 ,  84  are separate from one another and separately connected to housing  100 . First portion  82  includes a central cavity  86  extending through and opening at superior and inferior bone engaging surface portions  88 ,  90 , respectively. Second portion  84  includes a central cavity  92  extending through and opening at superior and inferior bone engaging surface portions  94 ,  96 , respectively. Each of the superior and inferior bone engaging surface portions  88 ,  90  of first portion  82  defines an outwardly extending convex curvature extending from leading end  54  to housing  100 . In addition, superior and inferior bone engaging surface portions  88 ,  90  of first portion  82  each define an outwardly extending convex curvature between opposite side walls  89 ,  91 . Sidewalls  89 ,  91  are parallel to one another and extend from superior bone engaging surface portion  88  to inferior bone engaging surface portion  90  and from housing  100  to leading end  54 . Each of the superior and inferior bone engaging surface portions  94 ,  96  of second portion  84  defines an outwardly extending convex curvature extending from trailing end  56  to housing  100 . In addition, superior and inferior bone engaging surface portions  94 ,  96  define an outwardly extending convex curvature between opposite side walls  95 ,  97 . Sidewalls  95 ,  97  are parallel to one another and extend from superior bone engaging surface portion  94  to inferior bone engaging surface portion  96  and from housing  100  to trailing end  56 . In the insertion orientation of implant  50 , second member  80  is rotated in housing  100  about its central longitudinal axis so that parallel sidewalls  89 ,  91  and parallel sidewalls  95 ,  97  are oriented toward respective ones of the endplates E 1 , E 1  to form the reduced height H 1  for insertion of implant  50  into disc space D. 
     First and second members  60 ,  80  are coupled to housing  100  and extend from housing  100  in side-by-side and spaced relation. Housing  100  maintains their spaced relation from one another along length L in both the initial insertion configuration and in the implanted configuration. As shown in  FIGS. 6 and 7 , in the initial insertion configuration, inferior bone engaging surface portions  70 ,  76  of first member  60  are oriented toward and face inferior surface portions  90 ,  96  of second member  80 . When implant  50  is located in the desired position in disc space D, first and second members  60 ,  80  are each rotated about its respective central longitudinal axis in either a clockwise or counter-clockwise direction so that inner side walls  71 ,  77  of first member  60  are located adjacent to and face inner side walls  91 ,  97  of second member  80  and position the inferior and superior bone engaging surface portions in contact with the respective vertebral endplates E 1 , E 2 , as shown in  FIGS. 10-11 . 
     Housing  100  includes a body  102  that is elongated in a direction extending between the anterior and posterior sides of implant body  52  to define a length that is substantially the same as width W 2  of implant  50 . Housing  100  also defines a height that is less than height H 2 , H 3  of implant  50  so that housing  100  does not contact the endplates E 1 , E 2  in the implanted orientation of implant  50 . Housing  100  defines a cavity  104  for rotatably receiving necks  63 ,  83  therein. One side of body  102  defines a slot or opening  106  that allows body  102  to be flexed open to receive first and second members  60 ,  80  therein when implant  50  is assembled, and then allow body  102  to be closed to secure first and second members  60 ,  80  in housing  100 . Housing  102  frictionally engages necks  63 ,  83  to maintain first and second members  60 ,  80  in spaced relation from one another while allowing first and second members  60 ,  80  to be rotated from the initial insertion orientation to the implanted orientation in the disc space D. The arrangement of implant  50  with first and second members  60 ,  80  in side-by-side relation allows the overall height of implant  50  to be minimized in its initial insertion than would be possible with a single member, while providing a greater width in the implanted configuration to increase stability of implant  50  and the surface area contact with the adjacent endplates E 1 , E 2 . In addition, in another embodiment, housing  100  allows first and second members  60 ,  80  to be moved toward and away from one another to adjusting the spacing between the adjacent inner side walls so that the positioning of first and second members  60 ,  80  can be adjusted in situ in the disc space to optimize the fit with the adjacent endplates E 1 , E 2 . 
     In the implanted configuration, the aligned superior bone engaging surface portions  68 ,  88  of first portions  62 ,  82  and aligned superior bone engaging surface portions  74 ,  94  of second portions  64 ,  84  form a continuously curved convex outer profile in or along the sagittal plane, and the aligned inferior bone engaging surface portions  70 ,  90  of first portions  62 ,  82  and aligned inferior bone engaging surface portions  76 ,  96  of second portions  64 ,  84  also form a continuously curved convex outer profile. The maximum height H 2  along the posteriorly facing side walls  91 ,  97  is greater than the maximum height H 2  along the anteriorly facing side walls  69 ,  75  to establish lordosis correction between endplates E 1 , E 2  of vertebrae V 1 , V 2 , and also to allow second member  80  to contact the endplates E 1 , E 2  along coronal plane C where the concavity of endplates E 1 , E 2  is greatest. The superior and inferior bone engaging surface portions of first and second members  60 ,  80  may also include grooves or recesses that interrupt the convex outer profile to form vertebral endplate engaging structures across the width of first and second members  60 ,  80 , and also to accommodate the central cavities extending through the implant portions  62 ,  64 ,  82 ,  84 . The bone engagement structures can comprise grooves, recesses, ridges, serrations, knurlings, spikes, roughened surfaces, or smooth surfaces for engaging the endplates E 1 , E 2  of the adjacent vertebral members V 1 , V 2 . As illustrated, the bone engagement structures extend in a direction between the adjacent sidewalls of the respective member  60 ,  80 . Other embodiments contemplate engagement structures that extend in a direction between leading end  54  and trailing end  56 , or obliquely to the length and/or width of first and second members  60 ,  80 . 
     The leading end  54  of implant  50  is rounded or tapered between the respective superior and inferior bone engaging surface portions of first and second members  60 ,  80  so that the body  52  conforms to the anatomy of the endplates E 1 , E 2  in the disc space. A rounded leading  54  can also distract the adjacent vertebral members V 1 , V 2  as the body  52  is inserted in a collapsed disc space D if implant  50  is oriented and inserted in its implanted configuration. Trailing end  56  can be flat and solid as shown. Other embodiments contemplate that the trailing end  56  can include one or more holes, threaded openings, slots or other structure of one or both of first and second members  60 ,  80  to facilitate engagement with an insertion instrument. In addition, first member  60  can define a length between its leading and trailing end portions that is the same as the length of second member  80  between its leading and trailing end portions. In another embodiment, the length of first member  60  is less than the length of second member  80  so that when first member  60  is positioned in the anterior portion of the disc space D, its leading and trailing end portions do not overhang the lateral edges of the vertebral endplates E 1 , E 2 , while second member  80  is positioned medially-laterally in the central portion of the disc space D and thus can have a greater length than first member  60  without projecting from or overhanging the endplates E 1 , E 2 . 
     Referring to  FIGS. 13A-13D , another embodiment of implant is shown and designated as implant  150 . Implant  150  is similar to implant  50  in that it includes a body  152  with a first member  160 , a second member  180 , and a housing  200  that connects first and second members  160 ,  180  in side-by-side relation. However, housing  200  is connected to the leading end  154  of first and second members  160 ,  180  so that each of first and second members  160 ,  180  extend substantially only in one direction from housing  200 . Housing  200  includes a body  202  having a pair of connected nodes  204 ,  206  that define receptacles  208 ,  210 , respectively. The leading end  154  of first and second implant members  160 ,  180  is positioned in respective ones of receptacles  208 ,  210  to maintain first and second members  160 ,  180  in spaced relation to one another. 
     First and second members  160 ,  180  are substantially identical to one another in the illustrated embodiment, although first and second members  160 ,  180  that substantially differ from one another are not precluded. First member  160  includes a superior bone engaging surface  162  and an opposite inferior bone engaging surface  164  that extend between leading and trailing ends  154 ,  156 . First member  160  also includes opposite parallel sidewalls  166 ,  168  that extend between superior and inferior bone engaging surfaces  162 ,  164  and between leading and trailing ends  154 ,  156 . First member  160  includes a cavity or chamber  170  extending between and opening at superior and inferior bone engaging surfaces  162 ,  164 . Superior and inferior bone engaging surfaces  162 ,  164  are convexly curved between leading end  154  and trailing end  156  to conform to the concave curvature of the endplates E 1 , E 2  when first member  160  is positioned in disc space D. In the illustrated embodiment, superior and inferior bone engaging surfaces  162 ,  164  are smooth, although providing bone engagement features along these surfaces is also contemplated. Second member  180  includes a superior bone engaging surface  182  and an opposite inferior bone engaging surface  184  that extend between leading and trailing ends  154 ,  156 . First member  180  also includes opposite parallel sidewalls  186 ,  188  that extend between superior and inferior bone engaging surfaces  182 ,  184  and between leading and trailing ends  154 ,  156 . First member  180  includes a cavity of chamber  190  extending between and opening at superior and inferior bone engaging surfaces  182 ,  184 . Superior and inferior bone engaging surfaces  182 ,  184  are convexly curved between leading end  154  and trailing end  156  to conform to the concave curvature of the endplates E 1 , E 2  when second member  180  is positioned in disc space D. In the illustrated embodiment, superior and inferior bone engaging surfaces  182 ,  184  are smooth, although providing bone engagement features along one or more of these surfaces is also contemplated. 
     In one procedure involving insertion of implant  150  into disc space D, second member  180  is connected at its leading end  154  to housing  200 . Second member  180  is rotated to a reduced profile orientation with side walls  186 ,  188  oriented toward endplates E 1 , E 2  and then inserted along with housing  200  into the disc space, as shown in  FIG. 13A . Second member  180  is then rotated to an implanted orientation so that superior and inferior bone engaging surfaces  182 ,  184  contact the respective endplates E 1 , E 2 . First member  160  is then inserted in a reduced profile orientation where side walls  166 ,  168  are oriented toward respective ones of the endplates E 1 , E 2 , and guided into the disc space D to engage its leading end to housing  200  as shown in  FIG. 13C . First member  160  is then rotated while engaged to housing  200  so that superior and inferior bone engaging surfaces  162 ,  164  contact the respective vertebral endplate E 1 , E 2 . The sequential insertion and rotation of first and second members  160 ,  180  allows placement of first and second members  160 ,  180  in closer relation to one another since first and second members are not simultaneously connected to housing  200 . In their reduced profile orientation, the height between the superior and inferior bone engaging surfaces of first and second members  160 ,  180  requires a greater spacing between first and second members  160 ,  180  than when one of the first and second members  160 ,  180  is rotated to its implanted orientation. In addition, it is also contemplated that first member  160  can be first inserted into the disc space D and then rotated to its implanted orientation, and then second member  180  inserted and connected to housing  200  for rotation to its implanted orientated. 
     Referring now to  FIG. 14 , there is shown an implant  250  that includes a single elongated body  252  attached to a housing  280 . Elongated body  252 , shown in isolation in  FIG. 15 , extends on a central longitudinal axis  253  between a leading end  254  and an opposite trailing end  256 . Body  252  includes opposite parallel sidewalls  258 ,  260  that extend from leading end  254  to trailing end  256 . Implant body  252  also includes a superior bone engaging surface  262  and an opposite inferior bone engaging surface  264 . Bone engaging surfaces  260 ,  262  each extend between side walls  258 ,  260  and also between leading and trailing ends  254 ,  256 . A central cavity  266  extends through and opens at bone engaging surfaces  260 ,  262 . Bone engaging surfaces  260 ,  262  may be smooth or include ridges, spikes, teeth or other bone engaging structure extending therealong. In addition, side walls  258 ,  260  each includes a hole  261  (only one shown) extending therethrough into central cavity  266 . 
     Implant body  252  also includes a neck  268  extending outwardly from leading end  254  that is received in a receptacle  282  of housing  280 . Neck  268  includes a head  270  at its outer end that retains implant body  252  in housing  280 . Housing  280  includes a C-shaped body  284  with receptacle  282  extending through opposite sides thereof, and a slot  286  at one end thereof that allows the receptacle to be widened to receive neck  268  and head  270 . In  FIGS. 14 and 15 , body  252  is shown in an insertion orientation where side walls  258 ,  260  are oriented to face endplates of the adjacent vertebrae. Once implant  250  is positioned in the disc space in this insertion orientation, body  252  is rotated about central longitudinal axis  253  as indicated by arrow  288  so that bone engaging surfaces  260 ,  262  contact the endplates of the adjacent vertebrae. Body  252  can be located in the center of receptacle  282  as shown in  FIG. 14 , or moved laterally (anteriorly or posteriorly if body  252  is positioned along the coronal plane) in receptacle  282  to one of the anterior or posterior receptacle portions  282   a ,  282   b . The center, anterior and posterior receptacle portions of receptacle  282  can be compartmentalized with ribs or projections that extend partially into receptacle  282  to form discrete receptacle portions, but that allow the receptacle portions to be in communication with one another so that neck  268  can be moved from one portion to the other without removing neck  268  and head  270  from housing  280 . In addition, housing  280  defines an internal lipped region  290  around receptacle  282  that receives head  270 . Movement of implant body  252  along longitudinal axis  253  is prevented by contact of leading end  254  with one side of housing  280  and contact of head  270  with housing  280  in lipped region  290 . In still other embodiment, one or more additional implant bodies are engaged to housing  280  in side-by-side relation to implant body  252 . 
     Referring now to  FIG. 16 , there is shown another embodiment housing  300 . Housing  300  is similar to the other embodiment housings discussed herein, but includes a gearing mechanism to assist in moving an implant member across its receptacle. Housing  300  includes an oval or C-shaped body  304  with a receptacle  302  that extends through and opens at opposite sides of body  304 . Body  304  also includes a slot  306  at one end thereof that allows body  304  to be flexed to widen receptacle  302  to accommodate placement of a portion of the implant body therein, and to prevent the implant body from binding in housing  300  as the implant body is rotated. Body  304  include a portion of its length that narrows in width between the sides in which receptacle  302  opens and toward one of its ends to accommodate placement in a disc space, as discussed further below. Receptacle  302  includes a first portion  302   a  located at one end thereof and a second portion  302   b  located at the opposite end of receptacle  302 . Second portion  302   b  is enlarged relative to the remaining portion of receptacle  302  to facilitate insertion of an implant body therein when the implant body is in its initial insertion orientation. In addition, housing body  304  includes an internal lipped region  308  that extends around receptacle  302 . Internal lipped region  308  also includes gear teeth  310  extending therealong that are recessed away from receptacle  302  and extend from receptacle portions  302   b  to receptacle portion  302   a . As discussed further below, gear teeth  310  engage corresponding teeth on a head of the implant member to assist in moving the implant member from receptacle portion  302   b  to receptacle portion  302   a  as the implant body is rotated about its central longitudinal axis. 
       FIGS. 17A-17B  show a spinal interbody implant  320  that includes an elongate implant body  252 ′ connected with first and second housings  300 ,  300 ′ at the opposite ends of implant body  252 ′. Implant body  252 ′ can be, for example, identical to implant body  252  discussed above or any of the other implant bodies discussed herein. However, implant body  252 ′ includes a modified head  270 ′ at one end of body  252 ′ and an identical second neck  268  and modified head  270 ′ at the opposite end of body  252 ′ (not shown) to engage the second housing  300 ′. Housings  300 ,  300 ′ are mirror images of one another, and housing  300 ′ include gear teeth like gear teeth  310  of housing  300 . Modified heads  270 ′ include teeth  271 ′ extending around the circular perimeter thereof that engage and mesh with gear teeth  310  of the respective housing  300 ,  300 ′. 
     In the insertion orientation of implant  320  shown in  FIGS. 17A-17B , implant body  252 ′ is positioned in or adjacent to receptacle portion  302   b  of housings  300 ,  300 ′ and inserted into disc space D with the side walls  258 ,  260  positioned to face the respective vertebral endplates when in disc space D. Housings  300 ,  300 ′ are located adjacent the lateral edges of vertebra V 1  and the other adjacent vertebra when implant  310  is positioned in a lateral approach along the coronal plane, as shown in  FIG. 17B . The tapered anterior portion of body  304  allows positioning of housings  300 ,  300 ′ as far anteriorly as possible while preventing housings  300 ,  300 ′ from projecting laterally outwardly from disc space D. Implant body  252 ′ is then rotated about its central longitudinal axis to an implanted orientation shown in  FIGS. 18A-18B . As implant body  252 ′ is rotated, the teeth of head  270 ′ engage with the gear teeth  310  of the corresponding housing  300 ,  300 ′ to facilitate rotation of implant body  252 ′ to its implanted orientation, and to advance implant  252 ′ in the disc space as far anteriorly as possible relative to the vertebrae and the implanted positions of housings  300 ,  300 ′. Implant member  252 ′ can remain the sole implant member between housings  300 ,  300 ′. Alternatively, in procedures where side-by-side implant members are desired, a second implant member can be located in receptacle portions  302   b  of housing  300 ,  300 ′. 
       FIGS. 19A-19J  show an insertion technique along with portions of instruments associated with inserting a pair of elongate implant implants in side-by-side relation in the disc space. In  FIG. 19A  there is shown housing  300  connected with an elongate implant member  352  having a leading end engaged to housing  300 . Housing  300  is shown without gear teeth  310  in  FIGS. 19A-19B  and  19 D- 19 F for purposes of clarity, but it is understood that housing  300  includes gear teeth  310  in one embodiment. Other embodiments contemplate that any of the housing embodiments discussed herein could be employed in the insertion technique. Implant member  352  can be the same or similar to implant member  252  discussed above, but includes a modified head  370  at only one end thereof, with head  370  including teeth extending around the perimeter thereof to mesh with the gear teeth  310  of housing  300 . Implant member  352  is engaged to housing  300  in its initial insertion orientation prior to implantation. Also shown is an inserter  400  that includes an elongated sleeve  402  and a central shaft  404  housed within sleeve  402 . Shaft  404  is engageable to an opening or receptacle in the trailing end of implant member  352  via a threaded connection, interference fit, or other suitable connection. Sleeve  404  includes a head  406  at its distal end with upper and lower distally extending flanges  408 ,  410  that are received in grooves of implant member  352 . The grooves are recessed into the upper and lower bone engaging surfaces of implant member  352  and open at the trailing end of implant member  352  to receive respective ones of the flanges  408 ,  410 , as shown in  FIG. 19B . Using inserter  400 , housing  300  and implant member  352  are inserted together into the disc space with implant member  352  in its insertion orientation, and then inserter  400  is rotated as indicated by arrow  412  in  FIG. 19C  to rotate implant member  352  around its central longitudinal axis in housing  300  to its implantation orientation. In procedures utilizing a direct lateral approach, rotation of implant member  352  translates implant member  352  anteriorly in housing  300  and moves implant member  352  toward the anterior side of the vertebrae to first restore the anterior height of the disc space. 
     Referring now to  FIG. 19D , a second implant member  352 ′ is inserted that is similar to implant member  352 , but can include a greater height in its implanted orientation than implant member  352  to accommodate its placement more toward the center of the disc space, such as discussed above with respect to interbody implant  50  and its implant members  60 ,  80 . Inserter  400  is engaged to the trailing end of second implant member  352 ′ in a manner like that discussed above with respect to implant member  352 . Second implant member  352 ′ is positioned in the disc space in its insertion orientation to engage its leading end with housing  300 , and then rotated to its implanted orientation in housing  300  as shown in  FIG. 19E . The head  370 ′ of second implant member  352 ′ need not be provided with teeth since second implant member  352 ′ will not be moved along the length of the receptacle of housing  300 , although providing such teeth on the head of implant member  352 ′ is not precluded. 
     In  FIG. 19F , inserter  400  is shown engaged to a cap  420  that is to be engaged to the trailing ends of implant members  352 ,  352 ′. Cap  420  engages and maintains the relative spacing between implant members  352 ,  352 ′ to provide a stable construct. Cap  420  includes a body  422  and four flanges  424   a ,  424   b ,  424   c ,  424   d  that are received in respective ones of the grooves in the superior and inferior bone engaging surfaces of implants members  352 ,  352 ′, as shown in  FIG. 19G . Body  422  also includes a central hole  426 , and a pair of lateral holes  428 ,  430  on opposite sides of central hole  426 , as shown in  FIG. 19H . Central hole  426  receives the shaft  404  of inserter  400  with flanges  408 ,  410  positioned on the upper and lower sides of body  422 . Lateral holes  428 ,  420  align with holes or bores in the trailing ends of respective ones of implant members  352 ,  352 ′ so that fasteners  440 ,  442  ( FIG. 19I ) can be placed through respective ones of the lateral holes  428 ,  430  to secure cap  420  to implant members  352 ,  352 ′, as shown in  FIG. 19J . Lateral holes  428 ,  430  each include a counter bore so that fasteners  440 ,  442  are recessed or flush with the outer surface of cap  420  in the final construct of the interbody spinal implant. 
     Materials for the implants disclosed herein can be chosen from any suitable biocompatible material, such as titanium, titanium alloys, cobalt-chromium, cobalt-chromium alloys, stainless steel, PEEK, bone, polymers, or other suitable metal or non-metal material and combinations and composites thereof. Of course, it is understood that the relative size of the components can be modified for the particular vertebra(e) to be instrumented and for the particular location or structure of the vertebrae to which the anchor assembly will be engaged. 
     Although various embodiments have been described as having particular features and/or combinations of components, other embodiments are possible having a combination of any features and/or components from any of embodiments as discussed above. As used in this specification, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, the term “a member” is intended to mean a single member or a combination of members, “a material” is intended to mean one or more materials, or a combination thereof. Furthermore, the terms “proximal” and “distal” refer to the direction closer to and away from, respectively, an operator (e.g., surgeon, physician, nurse, technician, etc.) who would insert the medical implant and/or instruments into the patient. For example, the portion of a medical instrument first inserted inside the patient&#39;s body would be the distal portion, while the opposite portion of the medical device (e.g., the portion of the medical device closest to the operator) would be the proximal portion. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that all changes and modifications that come within the spirit of the invention are desired to be protected.