Patent Publication Number: US-10314722-B2

Title: Inserter for expanding an expandable device

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 14/736,689, filed Jun. 11, 2015, now U.S. Pat. No. 9,445,921, which is a continuation-in-part application of U.S. application Ser. No. 14/474,555, filed Sep. 2, 2014, now U.S. Pat. No. 9,078,767, which claims the benefit of U.S. Provisional Patent Application No. 61/948,645, filed Mar. 6, 2014, each of which is herein incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The subject invention relates generally to the field of surgery, and particularly to surgical devices, instruments and methods of using the same. 
     BACKGROUND OF THE INVENTION 
     A variety of physical conditions involves two bodily tissue surfaces that, for treatment of the condition, need to be separated from one another and supported away from one another. Such tissue expansion may be to gain exposure to select tissue structures, to apply a therapeutic pressure to select tissues, to return tissue structures to their anatomic position and form, or in some cases to deliver a drug or growth factor to alter, influence or deter further growth of select tissues. Depending on the condition being treated, the tissue surfaces may be opposed or contiguous and may be bone, skin, soft tissue, or a combination thereof. 
     One particular device for treating these conditions by distracting and supporting tissue surfaces simultaneously is described in U.S. Pat. No. 6,595,998, entitled “Tissue Distraction Device”, which issued on Jul. 22, 2003 (the &#39;998 Patent). Other examples of such tissue distracting and supporting devices that are used for achieving spinal interbody fusion are described in U.S. Pat. No. 7,931,688 entitled “Expandable Interbody Fusion Device”, which issued on Apr. 26, 2011 (the &#39;688 Patent), and U.S. Pat. No. 7,967,867 entitled “Expandable Interbody Fusion Device”, which issued on Jun. 28, 2011 (the &#39;867 Patent). The &#39;998 Patent, the &#39;688 Patent and the &#39;867 Patent each discloses sequentially introducing in situ a series of elongate inserts referred to as wafers in a percutaneous approach to incrementally distract opposing vertebral bodies to stabilize the spine and correct spinal height, the wafers including features that allow adjacent wafers to interlock in multiple degrees of freedom. The &#39;998 Patent, the &#39;688 Patent and the &#39;867 Patent are assigned to the same assignee as the present invention, the disclosures of these patents being incorporated herein by reference in their entirety. 
     An issue that has arisen regarding such interbody fusion devices that use inserts or wafers to incrementally expand such devices is the determination of when full expansion has been achieved as a result of ligamentotaxis and no further inserts may be inserted. It is therefore desirable for a surgeon to know when a sufficient number of inserts has been introduced to stabilize the spine and correct spinal height and whether any additional inserts may be introduced. One approach addressing this issue is described in commonly assigned U.S. Pat. No. 8,828,019, entitled “Inserter for Expanding an Expandable Interbody Fusion Device”, issued on Sep. 9, 2014 (“the &#39;019 Patent”) and incorporated herein by reference in its entirety. 
     Accordingly, in addition to interbody fusion applications, there is a similar need for other applications that use an expandable device and inserter to insert such a device into body tissue and expand the device in situ, including the capability to determine when proper expansion of the device has been achieved and no further inserts may be introduced. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an improved device to expand body tissue and to introduce inserts after the device has been expanded. A further object is to provide an inserter that has the capability of allowing a surgeon to determine that suitable expansion has been reached and no additional inserts may be inserted. 
    
    
     
       DESCRIPTION OF THE FIGURES 
         FIG. 1 a    is a top perspective of an apparatus including an inserter releasably attached to an expandable spinal interbody fusion device in accordance with an embodiment of the present invention, the expandable interbody fusion device being unexpanded. 
         FIG. 1 b    is a side elevation view of the apparatus of  FIG. 1   a.    
         FIG. 1 c    is a top plan view of the apparatus of  FIG. 1   a.    
         FIG. 2  is an enlarged view of the distal portion of the apparatus as circled in  FIG. 1   c.    
         FIG. 3 a    is top perspective view of the unexpanded fusion device of  FIG. 1   a.    
         FIG. 3 b    is top perspective view of the fusion device of  FIG. 3  after being expanded. 
         FIG. 4  is an exploded top perspective view of the expanded device of  FIG. 3   b.    
         FIG. 5 a    is a side elevation view of the expanded device of  FIG. 3   b.    
         FIG. 5 b    is a sectional view of the device of  FIG. 5 a    as seen along viewing lines B-B of  FIG. 5   a.    
         FIG. 5 c    is a sectional view of the device of  FIG. 5 a    as seen along viewing lines C-C of  FIG. 5   a.    
         FIG. 6 a    is a top perspective view of an insert used in the expandable spinal interbody fusion device of  FIG. 3   a.    
         FIG. 6 b    is a top plan view of the insert of  FIG. 6   a.    
         FIG. 6 c    is a longitudinal cross-sectional view of the insert as seen along viewing lines VI-VI of  FIG. 6   b.    
         FIG. 6 d    is a bottom plan view of the insert of  FIG. 6   a.    
         FIG. 6 e    is a distal end elevation view of the insert of  FIG. 6   a.    
         FIG. 7 a    is a top perspective view of an elevator used in the expandable spinal interbody fusion device of  FIG. 3   a.    
         FIG. 7 b    is a top plan view of the elevator of  FIG. 7   a.    
         FIG. 7 c    is a longitudinal cross-sectional view of the elevator as seen along viewing lines VII-VII of  FIG. 7   b.    
         FIG. 7 d    is a bottom plan view of the elevator of  FIG. 7   a.    
         FIG. 7 e    is a distal end elevation view of the elevator of  FIG. 7   a.    
         FIG. 8  is an exploded top perspective view of the track and components of the inserter of  FIG. 1 a   , including the translatable lifting platform and translatable driver. 
         FIG. 8 a    is an enlarged view of the distal portion of the inserter track and components as circled in  FIG. 8 . 
         FIG. 9  is a cross-sectional view of the inserter and device of  FIG. 1 a    as seen along viewing lines IX-IX of FIG.  c.    
         FIG. 9 a    is an enlarged view of the encircled portion A of  FIG. 9 . 
         FIG. 9 b    is an enlarged view of the encircled portion B of  FIG. 9 . 
         FIG. 10 a    is a cross-sectional view of the distal end of the inserter and device as seen along viewing lines A-A of  FIG. 2  with the expandable device unexpanded. 
         FIG. 10 b    is a cross-sectional view of the distal end of the inserter and device as seen along viewing lines B-B of  FIG. 2  with the expandable device unexpanded. 
         FIG. 11  is a top partial perspective view of the distal end of the lifting platform and the elevator of the expandable device in the position depicted in  FIGS. 10 a    and  10   b.    
         FIG. 12  is a cross-sectional view of the lifting platform and elevator as seen along viewing lines XII-XII of  FIG. 11 . 
         FIGS. 13 a  and 13 b    are views similar to  FIGS. 10 a  and 10 b    with the lifting platform having been distally moved to a position lifting the elevator and expanding the expandable device and a first insert partially entering the expanded device. 
         FIG. 14  is a view similar to  FIG. 10 a    showing the first insert inserted into the expanded expandable device. 
         FIGS. 15 a  and 15 b    are views similar to  FIGS. 13 a  and 13 b    with the lifting platform having been moved distally to a position lifting the elevator and the first insert to further expand the expandable device with a second insert partially entering the expanded device. 
         FIGS. 16 a  and 16 b    are views of the expandable device expanded as shown in the views of  FIGS. 15 a  and 15 b    with the second insert having been further distally moved to a position moving the elevator away from the first insert and creating a space for the insertion of the second insert. 
         FIG. 17  is a view similar to the view of  FIG. 14  showing the first and second inserts inserted into the expanded expandable device. 
         FIG. 18  is a cross-sectional view as seen along the viewing lines XVIII-XVIII of  FIG. 17 . 
         FIG. 19  is a proximal perspective view of the expanded spinal interbody fusion device with a guide pin releasably connected thereto subsequent to the inserter having been detached from the guide pin with inserts not being shown for clarity. 
         FIG. 20  is a top perspective of an apparatus including an inserter releasably attached to an expandable spinal interbody fusion device in accordance with a further embodiment of the present invention with the inserter being modular. 
         FIG. 21  shows a vertebral body having a compression fracture displacing its superior and anterior edge. 
         FIG. 22  shows a vertebral body, following treatment of a compression fracture. 
         FIG. 23  illustrates a plan view of an insertion apparatus according to another embodiment of the invention, placed within a vertebral body of  FIG. 21 , shown in cross-section. 
         FIG. 24  shows a side view of the insertion apparatus of  FIG. 23  being deployed within a vertebral body, shown in sectional view. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     For the purposes of promoting and understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the invention is thereby intended. It is further understood that the present invention includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the invention as would normally occur to one skilled in the art to which this invention pertains. 
     The invention provides a combination of an implantable expansion and support device and instrumentation to place the device into body tissue. The application of the invention as a spinal implant in spinal interbody fusion is detailed initially. Turning now to  FIGS. 1 a - c   ,  2 ,  3   a - b  and  4 , an apparatus  1  for use in spinal interbody fusion is shown. Apparatus  1  comprises an expandable spinal interbody fusion device  10  and an inserter  100 . The inserter  100  is an instrument used for inserting the device  10  into an intradiscal space between opposing vertebral bodies of a spine, expanding the device in situ and for inserting inserts into the expanded device  100 . The expandable interbody fusion device  10  includes a first element, such as superior endplate  12 , a second element, such as inferior endplate  14 , at least one insert  16  and expansion structure including an elevator  18 , as will be detailed hereinbelow. The height, H, across the superior and inferior endplates  12 ,  14  in the unexpanded condition as illustrated in  FIG. 1 b    is less than the normal anatomic height of a typical intradiscal space. The invention contemplates expanding the interbody fusion device  10  by the inserter  100  from an unexpanded condition as shown in  FIG. 3 a    to the expanded height as shown in  FIG. 3 b    to ultimately restore the normal anatomic height of the disc space and thereafter inserting one or more inserts, such as inserts  16 , as will be described, to form a stack of inserts  16  between the expanded superior endplate  12  and inferior endplate  14 . In the particular arrangement being described, fusion device  10  is configured and sized for implantation into the spine from the posterior approach. In the unexpanded state as shown in  FIG. 3 a   , device  10  has a length of approximately 25 mm, a width of approximately 10 mm, and an unexpanded height H of approximately 7 mm. Fusion device  10  may also be configured and sized for implantation into the spine using posteriolateral, anterior or lateral approaches, as will be described. 
     The superior endplate  12  as shown in  FIGS. 3 a - b    and  18  is elongate and comprises a hub  20  having pair of side surfaces  22  and  24  extending longitudinally on each side of the hub  20  and a pair of end surfaces  26  and  28  extending respectively at the proximal rear end and the distal front end of the superior endplate  12 . The hub  20  is sized and configured to fit within a cavity  48  of the inferior endplate  14  for telescoping movement therewithin, as will be described. The lower surface  30  of the hub  20  ( FIG. 18 ) is generally flat and planar. Suitable friction or crush ribs may be provided between the hub  20  and cavity  48  of inferior endplate  14  at inner surface  44   a  to temporarily hold the superior and inferior endplates  12 ,  14  together in the direction of expansion as the device  10  is introduced into the intradiscal space to be distracted. 
     With continued reference to  FIGS. 3 a - b    and  18 , the superior endplate  12  includes a graft chamber defined by an opening  38  extending through the upper outer surface  12   a  and the lower surface  30 . In accordance with one arrangement, the superior endplate  12  is formed of a biocompatible polymer such as polyethylethylketone (PEEK). PEEK is used in fusion applications for its combination of strength, biocompatibility, and elasticity which is similar to human bone. Other composites may include derivatives of PEEK such as carbon fiber reinforced PEEK and PEKK, respectively. In a particular aspect, the superior endplate  12  may further include an upper endcap that defines the outer surface  12   a . The endcap may be a separate plate formed of material for the promotion of bone growth, such as titanium, and may be attached to the endplate  12  with suitable conventional techniques. As an alternative, the upper surface  12   a  may be defined by a coating of a suitable layer of bone growth promotion material, such as titanium, which may be deposited by conventional techniques. 
     The inferior endplate  14  of the interbody fusion device  10  as shown in  FIGS. 3 a - b    and  18  is elongate and comprises a pair of opposing spaced apart sidewalls  40  and  42  extending along the longitudinal direction and projecting upwardly from the lower outer surface  14   a . A pair of spaced apart end walls  44  and  46  extend laterally across the device  10  and project upwardly from outer surface  14   a . Rear end wall  44  is disposed at the rear or proximal end of the device  10  and front end wall  46  is disposed at the front or distal end of the device  10 . The side walls  40 ,  42  together with rear end wall  44  and front end wall  46  form an open, upwardly facing fully bounded interior cavity  48  as shown in  FIGS. 3 a    and  4 . The interior cavity  48  is sized and configured to receive the superior endplate  12  including the hub  20  in relatively close fit between the side walls  40  and  42  and the end walls  44  and  46  of the inferior endplate  14  in a non-expanded condition as shown in  FIGS. 1 a - b   . The hub  20  of superior endplate  12 , as well as the entire stack of inserts  16 , remains fully contained within the inferior endplate  14  during telescoping expansion of the device  10  as shown in  FIGS. 18 and 19 , contributing to the torsional strength of the expanded device  10 . 
     The inferior plate  14  as shown in  FIGS. 4 and 19  includes a lower inner support surface  54  on which elevator  18  is supported. Inner surface  54  defines the bottom surface of the cavity  48 . Inferior endplate  14  further defines a fully bounded insert channel  50  extending through the rear end wall  44  in communication with interior cavity  48  and through which one or more inserts  16  are introduced. The height of channel  50  as measured vertically from inner surface  54  is slightly greater than the combined thicknesses of insert  16  and elevator  18 . With insert  16  being slidably received through channel  50  on top of elevator  18 , as will be described, only one insert  16  may be introduced at a time. As device  10  is expanded and further inserts  16  are sequentially introduced, all inserts  16  lying above the lowermost insert  16 , which would be situated on top of elevator  18 , will be prevented from backing out of the device  10  by the interior surface  44   a  of rear end wall  44  ( FIG. 4 ). The rear end wall  44  further defines a threaded connection opening  56  ( FIG. 10 a   ) for threaded releasable receipt of a guide pin  108  for use in the introduction of inserts  16  and in the delivery of bone graft material into the device  10 , as will also be described. Rear end wall  44  may also additionally include a pair of bilateral openings, such as holes  58 , adjacent the sidewalls  40  and  42  for use in releasably attaching the inserter  100  to the device  10  for the establishment of a rigid connection to the device  10  for insertion into the intradiscal space. 
     Elevator  18  is supported on inner surface  54  of inferior endplate  14  with the lateral width of elevator  18  being dimensioned for relatively close sliding fit between opposite interior surfaces  40   a  and  42   a  of side walls  40  and  42 , as shown in  FIGS. 5 c    and  18 . As such, lateral movement of elevator  18  in directions transverse to the direction of expansion is substantially constrained. In addition, inferior endplate  14  includes a rail  14   b  projecting inwardly from each interior surface  40   a  and  42   a  and upwardly from lower inner surface  54  toward superior endplate  12 . The upward projection of each rail  14   b  from inner surface  54  is slightly greater than twice the thickness of elevator  18 . Rails  14   b  slidably project into recesses  310  extending into the base  305  of elevator  18  at each lateral side. Rails  14   b  substantially constrain movement of elevator  18  in the axial direction while the clearance in recesses  310  allows free movement of elevator  18  in the direction of expansion along rails  14   b  as shown by the arrow  130  in  FIG. 10 a   . As such, elevator  18  is captively supported within inferior endplate  14  and is independently movable along the direction of expansion toward and away from each of the superior endplate  12  and the inferior endplate  14 . 
     As shown particularly in  FIGS. 4, 5   a - b  and  18 , the inferior endplate  14  includes a graft chamber defined by an opening  60  extending through the lower outer surface  14   a  and the lower inner surface  54  in communication with cavity  48 . In accordance with one arrangement, the inferior endplate  14  is formed of a material different from the material of the superior endplate  12 . In this aspect, the inferior endplate  14  may be formed of a biocompatible metal, such as titanium, for its strength properties. Titanium is chosen for strength, biocompatibility, processing capability, and fluoroscopic imaging properties (radiolucency). Other alternative materials include cobalt chrome, stainless steel (both stronger than titanium but much less radiolucent), or biocompatible ceramics such as silicon nitride or zirconia, which are radiolucent. Titanium and silicon nitride have demonstrated good apposition to bone and superiority to PEEK. In this regard where inferior endplate  14  is formed of titanium, the lower outer surface  14   a  would provide for the promotion of bone growth. Lower outer surface  14   a  may also, however, be coated with a suitable layer of bone growth promotion material, such as titanium, and deposited in a conventional manner so as to match the roughness/porosity of the superior endplate outer surface  12   a.    
     Where inferior endplate  14  is formed of titanium or other suitable metal that is radiopaque, windows  62  may be formed through sidewalls  40  and  42  as shown in  FIGS. 3 a - b    and  19  so as to allow visual observation of bony through growth by suitable imaging techniques, such as fluoroscopy. Further details of interbody fusion device  10  are described in commonly assigned U.S. Pat. No. 8,900,312, patent application Ser. No. 13/795,054 entitled “Expandable Interbody Fusion Device with Graft Chambers”, filed on Mar. 12, 2013 (“the &#39;312 Patent”) and incorporated herein by reference in its entirety. 
     Details of insert  16  are shown in  FIGS. 6 a - e   . The insert  16  comprises an elongate and generally flat body  200  having an upper surface  202  and a lower surface  204 , both of which are generally planar and substantially parallel so that the inserts  16  can form a stable stack within the interbody fusion device  10  upon expansion. Insert  16  includes a trailing rear proximal end  206  and a leading front distal end  208 . The body  200  is formed to have a generally U-shaped, horseshoe configuration, with a pair of spaced opposing arms  212  and  214  projecting rearwardly from a base  205  and defining a rearwardly facing generally U-shaped opening  216  extending through the rear end  206  and through upper surface  202  and lower surface  204 . The lateral width of body  200  between side surfaces  212   a  and  214   a  is dimensioned for a relatively close sliding fit between interior surfaces  40   a  and  42   a  of side walls  40  and  42  of inferior endplate  14 , as shown in  FIG. 5 b   . Such close dimensioning reduces the potential of lateral movement of insert  16  during insert introduction and within cavity  48  of inferior endplate  14 . A surface  218  between the upper surface  202  and the lower surface  204  at the base  205  of opening  216  defines a pushing surface for receipt of a driver of inserter  10 , as will be described. The opening  216  at the rear end of each insert  200  is provided to allow bone graft material to flow into the device  10  through the insert openings  216  and into the openings  38  and  60  extending through the superior endplate  12  and the inferior endplate  14 , respectively. A pair of inclined surfaces  208   a  extends upwardly from and communicating with lower surface  204  on each lateral side the insert  16  adjacent the front distal end  208 . 
     The insert  16  includes a feature for interlocking engagement with elevator  18  in a complementary cooperative connection. Distal front end  208  of insert body  200  includes therein a latching receptacle  220  defined by a pair of spaced opposing arms  222   a  and  222   b  for receipt therein of a flexible latch  318  ( FIG. 7 a - e   ) on elevator  18 , as will be described. Arms  222   a  and  222   b  include inwardly projecting locking surfaces  224   a  and  224   b  respectively for cooperative locking engagement with elevator latch  318 . Unlike the inserts described in the &#39;312 Patent, the inserts  16  described herein do not function to assist in the separation of superior endplate  12  and inferior endplate  14  or any subsequent inserts  16  inserted into interbody fusion device  16 , as that lifting function is provided herein by inserter  100  in conjunction with elevator  18 . It is contemplated that the inserts  16  described herein be formed of a biocompatible material that is sufficiently rigid to form a solid stack as the successive inserts are inserted into the device. Thus, in one specific embodiment, the inserts  16  are formed of PEEK or a carbon-fiber reinforced PEEK, or similar polymeric material. 
     Turning now to  FIGS. 7 a - e   , details of the elevator  18  are shown. The elevator  18  comprises an elongate and generally flat body  300  having an upper surface  302  and a lower surface  304 , both of which are generally planar and substantially parallel. The elevator  18  has a thickness between upper surface  302  and lower surface  304  that is slightly greater than the thickness of insert  16 . As such, when as noted below the thickness of an insert  16  is, for example, 1.0 mm, the thickness of elevator  18  may be 1.03 mm. Elevator  18  includes a trailing rear proximal end  306  and a leading front distal end  308 . The elevator body  300  is formed to have a generally U-shaped, horseshoe configuration similar to the configuration of insert  16 . Elevator body  300  includes a pair of spaced opposing arms  312  and  314  projecting rearwardly from a base  305  and defining a rearwardly facing generally U-shaped opening  316  extending through the rear end  306  and through upper surface  302  and lower surface  304 . Base  305  has a rearwardly facing surface  305   a  that communicates with opening  316 . The opening  316  at the rear end of elevator  18  is provided to allow bone graft material introduced into the device  10  to flow through the insert openings  216  of inserts  16  and into the openings  38  and  60  extending through the superior endplate  12  and the inferior endplate  14 , respectively. The rear proximal end  306  includes an inclined surface  312   a  and  314   a , respectively at the free end of each arm  312  and  314  extending downwardly from and communicating with the upper surface  302 . The rear proximal end  306  further includes an inclined lifting surface  312   b  and  314   b , respectively at the free end of each arm  312  and  314  extending upwardly from and communicating with the lower surface  304 . The front distal end  308  includes adjacent base surface  305   a  an inclined lifting surface  308   a  extending upwardly from and communicating with lower surface  304 . The inclined lifting surfaces  312   b ,  314   b  and  308   a  are angled in the same direction with approximately equal angles. The lifting surfaces  312   b ,  314   b  and  308   a  define inclined ramps with multiple points of contact for cooperative contact with complementary surfaces of an expansion component on the inserter  100  for lifting elevator  18 , as will be described. Inclined surface  308   a  is generally centrally located along the elongate axis of elevator, while surfaces  312   b  and  314   b  are spaced bilaterally. Thus, lifting surfaces  308   a ,  312   b  and  314   b  define three triangulated points of contact. Elevator has a recess  310  extending into the elevator base  305  at each lateral side thereof. Recesses  310  are sized to receive rails  14   b  on the interior surfaces of inferior endplate  14 , as described. In one specific embodiment, the elevator  18  is formed of titanium alloy, type 2, which may be anodized for lubricity. Other materials, such as PEEK, may also be used as the material for elevator  18 . 
     Distal front end of elevator body  300  includes a flexible latch  318  projecting upwardly from upper surface  302 . Latch  318  comprises a pair of spaced opposing flexible arms  320   a  and  320   b  that are configured to flex toward each other. Flexible arms  320   a  and  320   b  include outwardly directed locking surfaces  322   a  and  322   b  respectively, for cooperative receipt within receptacle  220  of each insert  16 , as shown in  FIG. 5 b   . Upon receipt of latch  318  into receptacle  220 , locking surfaces  224   a  and  224   b  resiliently engage locking surfaces  322   a  and  322   b , respectively. Latch  318  projects above the upper surface  302  and a height slightly greater than the thickness of an insert  16 . The lateral width of elevator body  300  between the side surfaces  312   c  and  314   c , respectively of arms  312  and  314  is dimensioned for a relatively close sliding fit as noted hereinabove between interior surfaces  40   a  and  42   a  of inferior endplate  14 , as shown in  FIG. 5   c.    
     Turning again now to  FIGS. 1 a - c    and  FIGS. 8 and 8   a , details of the inserter  100  are described. Inserter  100  is elongate having a distal end  100   a  and at a proximal end  100   b  a frame  101 . A trigger actuator  102  to effect expansion of device  10  and insertion of inserts  16  into device  10  after expansion includes a frame  101  at the proximal end  100   b  of inserter. A plurality of inserts  16  are movably supported in a linear array on an elongate track  104  for individual successive insertion into device  10 . Track  104  supports at least one insert  16  and may, for example, support an array of five inserts  16 , although fewer or more inserts  16  may be supported as desired. 
     The distal end  100   a  is shown in exploded detail in  FIGS. 8 and 8   a . The inserter  100  includes elongate track  104  and an outer elongate track cover  106 , the cover  106  being substantially rigidly joined to track  104 . Track  104  is configured as a closed channel and is supported within outer track cover  106 . Cover  106  is fixedly secured to frame  101 , although in a particular arrangement as will be described, cover  106  may be removably attached to frame  101 . An elongate guide pin  108  is supported within an opening  110  extending lengthwise through the cover  106 . The distal end  108   a  of the guide pin  108  is threaded for releasable threaded engagement into opening  56  in the proximal rear end wall  44  of the inferior endplate  14 . The proximal end of guide pin  108  is provided with a threaded knob  112  for compressing and releasably attaching the cover  106 , and thereby the track  104  to the device  10 . The track cover  106 , in one arrangement, includes a pair of opposing pins  114  that engage corresponding holes  58  in rear wall  44  of inferior endplate  14  ( FIG. 19 ) to assist in rigidly securing the inserter  100  to the device  10 . It should be appreciated that other securement structure may be used to releasably attach the inserter  100  to the device  10 . Track  104 , in one embodiment, is formed of stamped stainless steel and cover  106  is an extruded aluminum alloy. Stainless steel or strong reinforced plastic could also be used for cover  106 . 
     The track  104  at the distal end  100   a  of the inserter  100  supports an expansion component defined by an axially translatable lifting platform  116  movably supported on track  104  for relative axial movement thereto to cooperatively slidably contact elevator  18  for expanding the device  10 . The lifting platform  116  is elongate and generally flat having an upper surface  118  and a lower surface  120 , both of which are generally planar and substantially parallel ( FIG. 18 ). The lifting platform  116  has a thickness between upper surface  118  and lower surface  120  that is dimensioned to be the same as the thickness of elevator  18 , i.e., slightly greater than the thickness of an insert  16 . Lifting platform  116  is supported by the inserter  100  for reciprocating axial movement in projecting and retracting directions. The proximal end of the lifting platform  116   d  is coupled to the trigger actuator  102  to effect such projecting and retracting directions, as will be described. 
     Lifting platform  116  projects slidably axially outwardly from track  104  and includes at its free distal end an inclined lifting surface  116   a  extending downwardly from and communicating with upper surface  118 . At a location spaced proximally of lifting surface  116   a , lifting platform further includes a pair of laterally spaced inclined surfaces  116   b  and  116   c . The inclined lifting surfaces  116   a ,  116   b  and  116   c  are angled in the same direction with angles approximately equal to the angles respectively of inclined lifting surfaces  312   b ,  314   b  and  308   a  of elevator body  300 . Inclined surfaces  116   a ,  116   b  and  116   c  define inclined ramps with multiple complementary points of contact for cooperative contact with elevator  18 . Inclined surface  116   a  is generally centrally located along the elongate axis of lifting platform  116 , while surfaces  116   b  and  116   c  are spaced bilaterally. Thus, lifting surfaces  116   a ,  116   b  and  116   c  define three triangulated points of contact that are located and spaced to cooperatively contact lifting surfaces  308   a ,  312   b , and  314   b , respectively during movement of lifting platform  116  in the projecting direction. Lifting platform  116 , particularly inclined surfaces  116   a ,  116   b  and  116   c , may be coated or otherwise include a suitable lubricant to facilitate sliding contact with elevator  18  for expansion of device  10 . Where lifting platform  116  is made of stainless steel, for example, such lubricant may include a molybdenum disulfide (MoS 2 ) material. 
     Still referring to  FIGS. 8 and 8   a , inserter  100  further supports at its distal end  100   a  a driver  124  for axial translational movement within track  104 . The proximal end  124   a  ( FIG. 8 ) of driver  124  is coupled to trigger actuator  102  to effect translational movement of the driver  124 , as will be described. The distal end of driver  124  comprises a pushing surface  124   b  sized and configured to enter into the opening  216  of an insert body  200  to engage pushing surface  218  and push the insert  16  from track  104  into the device  10  upon axial distal movement of driver  124 . Furthermore, driver  124  includes an upper surface  124   c  on which inserts  16  are movably supported in a linear array. Also included as shown in  FIG. 8  is an indexing member  125  that cooperates with driver  124  to distally incrementally move inserts  16  in the projecting direction to be positioned for individual contact with driver pushing surface  124   b  while preventing retrograde movement of inserts  16  as they are positioned. 
     With further reference still to  FIG. 8 a   , inserter  100  comprises a flexible graft shield  128  projecting distally from inner track  104 . Graft shield  128  is supported at one end  128   a  in a cantilevered manner with an opposite end  128   b  being unsupported and free to flex. Graft shield  128  is elongate and generally flat and is sized and configured to substantially block communication between the opening  38  through the superior endplate  12  and inserts  16  slidably inserted into device  10 . As will be described, graft shield  128  is configured to extend into device  10  through channel  50  between the superior endplate  12  and the expansion structure adjacent the lower surface  30  of the superior endplate  12 . 
     Turning now to  FIGS. 9 and 9   a - b , the details of the trigger actuator  102  of the inserter  100  and its operating mechanism and function are described. Trigger actuator  102  comprises a pair of hand grips  132  and  134  biased apart by an extension spring  136 . Hand grip  132  is fixedly secured to frame  101  of inserter  100 . Hand grip  134  is pivotally connected to frame  101  at pivot point  138  and is movable toward hand grip  132  against the bias of extension spring  136  by manual pressure. Hand grip  134  has gear teeth  140  that interface with a gear rack  146  slidably coupled to the frame  101 . The gear mechanism is sized to provide the appropriate translation of the gear rack  146  in the projecting direction as trigger actuator  102  is actuated. Also slidably coupled to the frame  101  are a driving slide  150  that is configured for relative and joint movement with driver  124 , and a lifting slide  154  that is configured for joint movement with lifting platform  116 . Gear rack  146  includes a lower surface  146   a  defining a tooth pattern, an upper surface  146   b  defining a pushing surface  146   d , a ramp surface  146   e , and a distal end  146   c . Distal end  146   c  includes a pawl  148  configured for limited rotation about pivot point  148   a , the distal end of pawl  148  being biased toward the driving slide  150  by a compression spring  152 . Prior to actuation of trigger  102  the pawl  148  is constrained from rotation about pivot point  148   a  by the lower surface  150   a  of driving slide  150 . Upon a first actuation of trigger  102 , and therefore translation of the gear rack  146  in the projecting direction, the pawl  148 , under bias of compression spring  152 , slides along lower surface  150   a . When sufficient translation of gear rack  146  has occurred such that the pawl  148  has passed the distal end of driving slide  150 , pawl  148  rotates counterclockwise as viewed in  FIG. 9 a    about pivot point  148   a  to a position limited by contact with upper surface  146   f  of gear rack  146 . 
     Pawl  148  includes a pushing surface  148   b  sized to engage pushing surface  154   a  at proximal end of lifting slide  154 . Further actuation of the trigger  102  promotes contact of pushing surfaces  148   b  and  154   a  and therefore movement of the lifting slide  154  and lifting platform  116  in the projecting direction causing expansion of the device  10 . 
     Lifting slide  154  further includes a proximal elongate tethering portion  154   b  with pushing surface  154   c  sized to engage pushing surface  150   b  at proximal end of driving slide  150 . Upon translation of lifting slide  154  in the projecting direction, pushing surface  154   c  engages pushing surface  150   b  for joint translation therebetween. 
     Driving slide  150  further includes an upper boss feature  156  defining pushing surfaces  156   a  and  156   b  sized to fit within slot a  124   d  ( FIG. 8 ) of driver  124 . Slot  124   d  comprises complementary axially spaced apart pushing surfaces  124   e  and  124   f , respectively. The length of slot  124   d  is sized such that translation of driving slide  150  during first actuation of trigger  102  does not induce contact between pushing surfaces  156   b  and  124   f  and therefore does not impart translation of driver  124 . 
     Driving slide  150  further includes a pawl  158  configured for limited rotation about pivot point  158   a , the proximal end of pawl being biased toward the gear rack  146  by bilateral torsion springs (not shown). Prior to actuation of trigger  102  the pawl  148  is constrained from rotation about pivot point  158   a  by a ledge surface  160  rigidly coupled to frame  101 . Upon translation of the driving slide  150  in the projecting direction, the pawl  158 , under bias of the torsion springs, slides along upper ledge surface  160 . When sufficient translation of driving slide  150  has occurred such that the pawl  158  has passed the distal end of ledge surface  160 , pawl  158  rotates counterclockwise as viewed in  FIG. 9 a    about pivot point  158   a  to a position limited by contact with lower surface  150   c  of driving slide  150 . Such translation is configured to be slightly longer than the translation required by the lifting platform  116  to achieve full expansion of device  10  such that rotation of pawl  158  will not occur in the absence of full expansion of device  10 . Further, rigidly coupled to pawl  158  for rotation therewith are bilateral flags  162  positioned in slots  163  in frame  101  ( FIG. 1 a   ), the flags  162  projecting laterally outwardly of both sides of frame  101 . Upon joint rotation of pawl  158  and flags  162  the user is visually alerted to the position of the driving slide  150  and lifting slide  154  thereby indicating to the user that full expansion of device  10  has been achieved and that no further inserts can be introduced. 
     Pawl  158  further comprises a pushing surface  158   b  sized to engage pushing surface  146   d  of gear rack  146  and a ramp surface  158   c  sized to engage ramp surface  146   e  of gear rack  146 . After full actuation and a complete stroke of trigger  102  and release of grip pressure, the gear rack  146  and hand grips  132 / 134  are returned under the bias of the extension spring  136 . During retraction of the gear rack  146 , cooperative ramp surfaces  146   e  and  158   c  collide inducing pawl  158  to rotate clockwise thereby allowing passage of the gear rack  146 . Upon sufficient translation of the gear rack  146  in the retracting direction such that the ramp surface  146   e  has passed the proximal edge of ramp  158   c , pawl  158  rotates counterclockwise about pivot point  158   a  back to a position limited by contact with lower surface  150   c  of driving slide  150 . 
     It should be appreciated that upon completion of first actuation of trigger  102  and completion of the first stroke, lifting platform  116  remains projected maintaining the expanded state of device  10  and that driving slide  150  remains in a partially projected state due to tether  154   b  of lifting slide  154 . It should also be noted that pawl  158  remains in a rotated state limited by contact with driving slide  150  while pawl  148  is returned to its original collapsed state limited by lower surface  150   a  of driving slide  150 . 
     Upon a second actuation of trigger  102  gear rack  146  translates again in the projecting direction such that pushing surface  146   d  contacts pushing surface  158   b  of pawl  158  causing joint translation of gear rack  146  and driving slide  150 . Upon further actuation, pushing surface  156   b  of driving slide  150  contacts pushing surface  124   f  of driver  124  causing joint translation therebetween, thereby engaging pushing surface  218  of insert  16  and pushing the insert  16  from track  104  into the device  10  during completion of the second stroke of trigger actuator  102 . 
     For the purpose of returning the track lifting platform  116  to its original position in the retracting direction a cam  164  and gear  166  are provided. The gear  166  interfaces with a second gear rack  154   d  rigidly connected to the lower surface of lifting slide  154 . The cam  164  is coupled to gear  166  for opposite rotation therebetween and is positioned to contact a notch  170  ( FIG. 8 a   ) in the driver  124  after an insert  16  has been partially inserted into the device  10 . Further trigger actuation returns the lifting platform  116  to its original position while the driver further inserts the insert  16 . When full trigger actuation is achieved, the gear rack  146  and hand grips  132 / 134  are returned under the bias of the extension spring  136 . To reset the position of driving slide  150  manually, the user pulls up on bilateral tabs  162   b  rigidly coupled to flags  162  thereby imparting rotation of pawl  158  and translation of driving slide  150  in the retracting direction. Due to the rotated state of flags  162  and pawl  158 , driver slide  150  can be returned to its original retracted position with pawl  158  rotation limited by ledge  160  surface. A two way ratchet mechanism  168  prevents unwanted motion of driving slide  150  in the wrong direction. In the event full expansion of device  10  is achieved and the surgeon prefers to abort the procedure without further introduction of an insert  16 , hex fitting  174  ( FIG. 1 a   ) coupled to gear  166  may be actuated by a hex wrench or other suitable tool. Rotation of fitting  174  rotates gear  166  which directly translates lifting slide  154  and hence lifting platform  116  proximally to release the expansion of device  10  with no insert  16  introduced. 
     It should now be understood how the trigger actuator  102  operates to expand device  10  and introduce one or more inserts  16 . During the first stroke, only lifting platform  116  is translated in the projecting direction to cause expansion of device  10 . Driver  124  remains stationary during the entire first stroke. After the hand grips  132 / 134  are returned to the starting position under the bias of extension spring  136  upon completion of the first stroke, lifting platform  116  remains stationary in the projecting position maintaining the expanded state of device  10  as hand grips  132 / 134  return. During the second stroke of trigger actuator  102 , driver  124  is translated in the projecting direction while the lifting platform  116  is initially stationary in the projecting direction. When driver  124  has inserted an insert  16  partially into the expanded device  10  continued operation of trigger actuator  102  retracts lifting platform  116  in the retracting direction. As lifting platform  116  retracts, driver  124  continues to advance in the projecting direction to push insert  16  fully into position upon completion of the second stroke. 
     Thus, for the particular device being described for insertion into the intradiscal space in the posterior approach, expansion of device  10  is achieved during the first stroke of trigger actuator  102  and full insertion of an insert  16  during completion the second stroke. For longer devices, such as those insertable from the lateral approach, the mechanism of inserter  100  may be adjusted such that the longer device is expanded in a first stroke, the inserts  16  inserted partially into the expanded device during a second stroke, and fully inserted in the third stroke. It should thus be appreciated by those skilled in the art that the number of strokes employed for expansion of device  10  and insertion of an insert  16  into the expanded device  10  may be varied by suitable adjustment of the operating mechanism of trigger actuator  102 . Such adjustment may include, for example, varying the number of pushing surfaces  146   d  that are provided on gear rack  146  for engagement with pawl  158 . 
     Turning now to  FIGS. 10 a - b    and  11 - 12  the assembly of the device  10  and the inserter  100  is described. The superior endplate  12  and the inferior endplate  14  are assembled in an unexpanded condition to the inserter  100  with the superior endplate  12  residing fully within cavity  48  of inferior endplate  14 . In such condition elevator  18  is captively retained between superior endplate  12  and inferior endplate  14  as described above and shown in  FIG. 5 c    for independent movement along the direction of expansion  130 . The inserter  100  is releasably attached to the device  10  upon threaded engagement of the guide pin  108  into threaded opening  56  in the proximal rear end wall  44  of the inferior endplate  14 . Graft shield  128  extends into device  10  through channel  50  between the superior endplate  12  and the elevator  18  adjacent the lower surface  30  of the superior endplate  12 . With the inserter  100  fixed to the device  10 , lifting platform  116  and driver  124  are axially translatable relative to the device  10  in the projecting and retracting directions. In this unexpanded condition, there are no inserts  16  in the device  10 . In the arrangement being described, there are five inserts  16  supported in a linear array on track  104 . 
     In the position illustrated in  FIGS. 10 a - b    and  11 - 12  lifting platform  116  is in a retracted position relative to device  10  and elevator  18 . Insert  16 , as seen in  FIG. 10 a   , is disposed on track  104  exteriorly of and ready for insertion into device  10 . In this position the lower surface  120  of lifting platform  116  is situated on lower inner surface  54  of inferior endplate  14 . Likewise lower surface  304  of elevator  18  is supported by lower inner surface  54  of inferior endplate  14 . As such, lifting platform  116  and elevator  18  are on substantially the same plane, with the upper surface  118  of lifting platform  116  being substantially coplanar with the upper surface  302  of elevator  18 . With the inserter  100  attached to the device  10 , elevator  18  is fixed in the axial direction relative to axial movement of lifting platform  116 . 
     In the condition shown in  FIGS. 10 a - b   , apparatus  1  comprising unexpanded device  10  releasably attached to inserter  100  is ready for use in inserting device  10  into an intradiscal space between two opposing vertebral bodies. Prior to insertion, opening  38  through superior endplate  12  may be pre-packed with a suitable bone graft material for the promotion of fusion through device  10  to the opposing vertebral bodies. Graft shield  128  extends into device  10  through channel  50  between the superior endplate  12  and the elevator  18  adjacent the lower surface  30  of the superior endplate  12  defining a pocket for receipt of the graft material. The free end  128   b  of graft shield  128  rests unattached on an interior ledge  12   b  of superior endplate  12  adjacent the distal end thereof. Opening  38  is therefore open adjacent outer surface  12   a  of superior endplate  12  and closed by graft shield  128  adjacent lower surface  30 . As such, graft shield  128  provides a barrier between the graft material and the elevator  18  and inserts  16  inserted into device  10  during expansion. Pre-packing of bone graft material in opening  38  on graft shield  128  advantageously allows for less introduction of graft material in situ and provides more assurance that sufficient graft material will be contained throughout device  10  and into openings  38  and  60  through superior endplate  12  and inferior endplates  14  and in a stress-loaded condition against opposing vertebral bodies. In addition, graft shield  128  provides a barrier substantially preventing graft material within opening  38  from being disturbed during expansion and by substantially blocking graft material from interfering with the expansion of device  10  or with the slidable insertion of inserts  16  which may be impeded by graft material on the sliding interfacing surfaces. 
     At this point in the surgical procedure, inserter  100  is used to insert unexpanded device  10  into the intradiscal space. Device  10  may be implanted as explained hereinabove into the spine posteriorly or posteriolaterally, either bilaterally or unilaterally, or in an anterior or lateral approach depending upon the surgical indication and the surgeons preference. Once device  10  is inserted in the intradiscal space in a suitable location, actuator  102  as described hereinabove is then operated in a first actuation. Initially during the first stroke lifting platform  116  is translated axially while driver  124  remains stationary. Lifting platform  116  is moved from the retracted position of  FIGS. 10 a - b    to a projecting direction whereby lifting platform  116  is moved further into device  10 . During movement in the projecting direction, lifting surfaces  116   a ,  116   b  and  116   c  of lifting platform  116  contact cooperative lifting surfaces  308   a ,  312   b , and  314   b , respectively of elevator  18 . The cooperative engagement causes elevator  18  to move in the direction of expansion away from lower inner surface  54  of inferior endplate  14  and toward superior endplate  12 . The upper surface  302  of elevator  18  contacts lower surface  30  of superior endplate  12  and elevator  18  slidably moves in the direction of expansion along rails  14   b  toward superior endplate  12  and away from inferior endplate  14  as shown in  FIGS. 13 a - b   , thereby expanding device  10 . 
     When complete expansion of device  10  is achieved the first stroke of trigger actuator  102  is completed and hand grips  132 / 134  are returned to the original starting position, as described above. Trigger actuator  102  is then operated in a second actuation to start a second stroke. As the second stroke commences, lifting platform  116  remains stationary holding device  10  in the expanded condition while axial translation of driver  124  begins. Continued operation of actuator  102  pushes insert  16  distally so that the distal front end  208  moves freely into expanded device  10  through channel  50  until the distal front end  208  of insert  16  is partially inserted into expanded device  10  between superior endplate  12  and inferior endplate  14  adjacent the proximal end of device  10 , as illustrated in  FIGS. 13 a   - b.    
     With insert  16  partially inserted in device  10 , continued operation of the actuator  102  during the second stroke causes lifting platform  116  to move proximally thereby moving lifting platform  116  in a retracting direction. With distal front end  208  of insert  16  supporting superior endplate  12 , continued proximal movement of lifting platform  116  causes lifting surfaces  116   a ,  116   b  and  116   c  of lifting platform  116  to sufficiently disengage cooperative lifting surfaces  308   a ,  312   b , and  314   b , respectively of elevator  18  to allow elevator  18  to move away in the direction of expansion from superior endplate  12  and toward inferior endplate  14  along rails  14   b  and return to the position of elevator  18  shown in  FIGS. 10 a - b   . As elevator  18  returns to the position whereby the lower surface  120  of lifting platform  116  is situated on lower inner surface  54  of inferior endplate  14 , a space like the space  64  as described hereinbelow with reference to  FIG. 16 b   , is created between lower surface  30  of superior endplate  12  and upper surface  302  of elevator  18 . Such space between the superior endplate  12  and the elevator  18  is slightly greater than the thickness of an insert  16  and is in direct communication with lower surface  30  of superior endplate  12  and upper surface  302  of elevator  18 . During completion of the second stroke of actuator  102  driver  124  continues to move axially distally slidably pushing insert  16  fully into such space of expanded device  10 , as shown in  FIG. 14 , with lower surface  204  of insert  16  facing and being in slidable contact with upper surface  302  of elevator  18 . Driver  124  is retracted proximally to the original position shown in  FIGS. 10 a - b    when the hand grip  134  of actuator  102  is released. 
     During insertion of insert  16  into device  10 , receptacle  220  described hereinabove at the distal end  208  of insert  16  cooperatively receives complementary flexible latch  318  on the upper surface  302  of elevator  18  such that locking surfaces  224   a ,  224   b  and  322   a ,  322   b  resiliently interlock, as shown in  FIG. 5 b   . Such interlocking substantially resists any back out of the insert  16  through channel  50  as driver  124  is withdrawn away from insert  16  in the retracted position. In the event device  10  is further expanded, as described hereinbelow, the initial insert  16  is moved upwardly with superior endplate  12  by elevator  18 . As elevator  18  then returns downwardly toward inferior endplate  14  as will be explained, latch  318  is separated from receptacle  220  as space  64  is created. With the initial insert  16  moved upwardly, it is situated above channel  50  and held captive by the interior surfaces of inferior endplate  14 , including interior surface  44   a  of rear end wall  44 . It should be appreciated that while insert  16  is held in position within device  10  by interlocking of receptacle  220  and latch  318 , other structure to resist back out movement of insert  16  may be provided, such as interlocking structure between insert  16  and one or more interior surfaces of the inferior endplate  14 , or interlocking structure between adjacent inserts  16 . Upon completion of insertion of insert  16 , opening  216  of insert  16  is at least partially aligned with opening  316  of elevator  18 , opening  38  of superior endplate  12  and opening  60  of inferior endplate  14 . Once inserter  100  is removed from the expanded device upon completion of the surgical procedure, insert opening  216 , elevator opening  316  and graft chambers  38  and  60 , respectively, will all be in at least partial alignment and communication with each other. 
     In the event the surgeon determines that additional inserts  16  are required in order to provide proper correction of the height of the intradiscal space, actuator  102  may be operated to insert one or more additional inserts  16  in the same manner as described with respect to the insertion of first insert  16 .  FIGS. 15 a - b    show device  10  with one insert  16  having been inserted and a second insert  16  partially introduced after device  10  has been further expanded during a first stroke of actuator  102  by elevator  18  upon lifting by the lifting platform  116  in the same process as described with respect to  FIGS. 13 a - b   . As the second insert  16  enters the further expanded device  10  during the second stroke, lifting platform  116  is pulled proximally in a retracting direction, sufficiently disengaging lifting surfaces  116   a ,  116   b  and  116   c  of lifting platform  116  from cooperative lifting surfaces  308   a ,  312   b , and  314   b , respectively of elevator  18  to allow elevator  18  to freely return to inner surface  54  of inferior endplate  14 . However, in the event elevator  18  fails to fully or partially return to such position, during pushing of second insert  16  into device  10  by driver  124 , the inclined surfaces  208   a  adjacent the front distal end  208  of second insert  16  contacts inclined surfaces  312   a  and  314   a , respectively at the upper free end of each arm  312  and  314  of elevator  18 , as shown in  FIGS. 16 a - b   , to urge elevator  18  toward and against lower surface  54  of the inferior endplate  14  creating a space  64  between lower surface  204  of the first insert  16  and upper surface  302  of elevator  18 . Alternatively, or in addition, a suitable biasing element may be included to normally urge elevator  18  toward inner surface  54  of inferior endplate  14 . Inferior endplate  14  may be formed to include a lip  46   a  on the front end wall  46  adjacent the distal end of cavity  48  to contain a spring  107  which would serve as the biasing element, as shown, for example, in  FIG. 15 a   . It should be understood that the features urging elevator  18  toward lower inner surface  54  of inferior endplate  14  function during the insertion of first insert  16  as well as with all subsequently inserted inserts  16 . 
     Continued operation of actuator  102  during the second stroke will continue to move second insert  16  until fully inserted shown in  FIG. 17 . During insertion of second insert  16  into device  10 , the resilient interlocking features of receptacle  220  described hereinabove of the second insert  16  cooperatively interlock with the complementary interlocking features of flexible latch  318  on the distal end of elevator  18 . Upon completion of insertion of second insert  16 , opening  216  of insert  16  is at least partially aligned with opening  216  of the first insert, opening  38  of superior endplate  12  and opening  60  of inferior endplate  14 , all of which will be in communication upon removal of inserter  100 . The second insert  16  is the lowermost insert and resides on upper surface  302  of elevator  18  directly below and in contact with first insert  16 , as shown in  FIGS. 17 and 18 . Driver  124  is then again retracted proximally to the original position shown n  FIGS. 10 a - b    when the hand grip  134  of actuator  102  is released. 
     When the intradiscal space has been expanded to its maximum anatomic extent as the spine reaches ligamentotaxis and the device  10  cannot be further expanded, the surgeon will be able to determine such condition by tactile feedback. Insertion of an insert  16  into device  10  can only be achieved after elevator  18  reaches its ultimate movement in the direction of expansion toward superior endplate  12 . As such, failure to compress hand grips  132 / 134  in a manner to complete the first stroke of actuator  102  will allow the surgeon to recognize that ligamentotaxis has been reached and the proper intradiscal height has been restored. Inasmuch as the insertion of an insert  16  follows the expansion of device  10  upon full movement of elevator  18  in the direction of expansion toward inferior endplate  14 , incomplete insertion of an insert  16  may be avoided. An indication that full expansion of device  10  has been reached may also be determined visually as described hereinabove by observation that flags  162  on actuator  102  have rotated relative to frame  101 . The surgeon would then terminate the procedure by actuating hex fitting  174 , as described hereinabove. Inserter  100  would then be removed from the expanded device  10  by rotatably removing knob  112  from the proximal end of guide pin  108 . As shown in  FIG. 19 , the guide pin  108  may remain releasably connected to expanded device  10  to serve as a locator for subsequent attachment to an apparatus containing suitable bone graft to assist in the delivery of such material into channel  50  of inferior endplate  14  through which inserts  16  were inserted. As such, upon removal of inserter  100  from expanded device  10 , a substantially unobstructed path exists from channel  50  though opening  316  of elevator  18  and openings  216  of inserts  16  and into openings  38  and  60  extending through the superior endplate  12  and the inferior endplate  14 , respectively, to allow bone graft material introduced into expanded device  10  through channel  50  to flow fully through device  10 . 
     In accordance with certain specific applications of device  10  for posterior implantation as described hereinabove, the overall length of the device  10  as defined by the length of the inferior endplate  14  is about 25 mm. The width of the device  10  is approximately 10 mm. The height of the unexpanded device  10  of  FIGS. 1 a - c    with the superior endplate  12  fully nested within the inferior endplate  14  is approximately 7 mm. With the introduction of five inserts  16 , each of which has a thickness of approximately 1.0 mm, the height of device  10  may be expanded from an unexpanded height of approximately 7 mm to an expanded height of approximately 12 mm. It should be appreciated that these dimensions are only illustrative and the number of inserts  16  as well as the dimensions of device  10  may vary depending upon the particular surgery and application. For example, device  10  for posterior implantation may have an initial unexpanded height in the range of approximately 7-10 mm, a width in the range of approximately 10-14 mm, and a length in the range of approximately 20-35 mm, with up to eight inserts  16  for the taller sizes. For implementing such posterior-size devices  10 , trigger actuator  102  may have an operating mechanism as described herein for expanding device  10  in a first stroke and fully inserting an insert  16  in a second stroke. 
     For certain applications of device  10  that may be implanted from a lateral approach, device  10  may have an unexpanded height in the range of approximately 8-10 mm, a width in the range of approximately 14-26 mm, and a length in the range of approximately 35-60 mm. To implant such devices  10  from the lateral approach, trigger actuator  102  may have an operating mechanism adjusted to expand device  10  in a first stroke, partially insert an insert  16  in a second stroke, and fully insert an insert  16  in a third stroke. 
     Channel  50 , extending through the rear end wall  44 , is sized and configured to facilitate the introduction of a suitable bone graft material by a graft delivery apparatus that may use guide pin  108  as a locator, as shown in  FIG. 19 . Such a graft delivery apparatus may have an entry tip sized and configured for entry into channel  50 . In a particular arrangement, it may be desirable to increase the entry opening to further ease the delivery of graft material. In such instance, a portion of rear end wall  44  may be notched out to form a channel portion  50   a  of increased height directly below threaded opening  56 . Channel portion  50   a  situated below threading opening  56  would direct the entry flow of bone graft material into the center of expanded device  10 . Channel portion  50   a  may be suitably configured to cooperatively receive the entry tip of the graft delivery apparatus, with such channel portion  50   a  being rectangular, square or arcuate. In the example of device  10  for posterior applications, channel portion  50   a  may be particularly configured to be square. Where such device  10  has an initial unexpanded height of 7 mm and a width of 10 mm, channel portion  50   a  may have a width of 3 mm and a height of 3 mm as measured vertically from inner surface  54 . In the example of device  10  for lateral applications, channel portion  50   a  may be particularly configured to be generally rectangular. Where such device  10  has an initial unexpanded height of 8 mm and a width of 16 mm, channel portion  50   a  may have a height of 3 mm as measured vertically from inner surface  54 , and a width of 6 mm. For purposes of delivering bone graft material in the form of autograft, it is desirable that the minimum dimension of channel portion  50   a , or any portion of channel  50  used as an entry port for such autograft material be no less than about 2 mm. It should be appreciated, however, that depending upon the viscosity of bone graft material to be delivered, such minimum dimension may vary. 
     Turning now to  FIG. 20 , an alternative inserter  400  embodying a modular construction is described. Inserter  400  comprises an actuator  402  and a releasable cartridge  404 . Actuator  402  includes a pair of hand grips  407  and  408  that are biased apart by an extension spring in the same manner as in trigger actuator  102  described hereinabove. Actuator  402  includes a frame  410  housing an operating mechanism  411  substantially the same as the operating mechanism of trigger actuator  102 . Grip  407  is fixedly secured to frame  410  while grip  408  is pivotally connected to frame  410  by a pivot pin  412 . Frame  410  supports a rotatable flag  414  that is coupled to the operating mechanism  411  as in trigger actuator  102 . Frame  410  includes a pair of spring-loaded flexible latches  416  projecting upwardly from an interface surface  410   a  adjacent the proximal end  410   b  of frame  410 . Adjacent the distal end  410   c  of frame  410  a support surface  410   d  is provided. Actuator  402  in a particular embodiment is reusable. Frame  410 , as well as frame  101 , and hand grips  407 ,  408 , as well as hand grips  132 ,  134  are all formed of stainless steel in a particular arrangement, although other materials, such as aluminum alloys and plastics may also be used. 
     Cartridge  404  comprises a track  406  contained within an outer cover  418  similar to track  104  and cover  106  of trigger actuator  102 . Cartridge  404  likewise houses a translatable lifting platform, a translatable driver and an indexing member (all not shown) that are constructed the same as lifting platform  116 , driver  124  and indexing member  125  of trigger actuator  102 , and that function in the same manner. A support  420  comparable to support  172  is secured to the bottom of cover  418 . Cartridge  404  supports a plurality of inserts  16  in a linear array for insertion into the expandable device  10 . Cooperative latching structure is provided at the bottom surface of cover  418  for releasable engagement with latches  416  of actuator  402 . In a particular embodiment, cartridge  404  is disposable. 
     Cartridge  404  is releasably attached to frame  410  by initially engaging support  420  with support surface  410   d  on frame  410  and then rotating cartridge down toward proximal end  410   b  until latches  416  releasably attach to the cooperative latching structure at the bottom of cartridge  404 . Upon attachment of cartridge  404  with actuator  402 , components of operating mechanism  411  interface with the driver and the lifting mechanism within track  406  in a manner comparable to actuator  102 , including the receipt of boss feature  422  (the same as boss feature  156 ) into a slot that is the same as slot  124   d  of driver  124 . Cartridge  404  may be released from actuator  402  by actuation of release levers  424  supported by frame  410  on both sides thereof and movably coupled to latches  416 . In all other respects, modular inserter  400  operates the same as trigger actuator  102  described hereinabove. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the invention are desired to be protected. For instance, an inserter with a graft shield, such as shield  128 , may be used with expandable spinal interbody fusion devices having an expansion structure without an elevator  18  as described hereinabove. For example, an inserter with a graft shield  128  may be used with the expandable interbody fusion device shown and described in the &#39;312 Patent referenced hereinabove wherein the device is expanded upon introduction of a series of wafers. Shield  128  may be used similarly as described herein to provide a barrier between a graft opening through one of the endplates, such as the superior endplate, and the wafers. Such a barrier would substantially prevent bone graft material pre-packed into such opening from interfering with sliding receipt of such wafers during insertion and expansion of the device. In addition, it should also be appreciated that actuators other than trigger actuators, such as with threaded rotary mechanisms, may be used with the inserter  100  described herein. 
     While one use of the invention as described herein is as an expandable spinal interbody fusion device, the invention may also be used in any situation where it is desirable to expand two tissue surfaces and to support such tissue surfaces after they have been separated. The tissue may be bone, skin, soft tissue, or combinations thereof. Further, the surfaces may be opposed surfaces of contiguous elements or surfaces of opposed elements. Thus, in addition to being used as a spinal interbody fusion device as set forth herein, the invention may also be used to treat vertebral compression fractures, for replacement of vertebral bodies (VBR), as a wedge opening high tibial osteotomy, tibial tuberosity elevation, as well as for treating other compression fractures including, but not limited to tibia plateau fractures, calcaneous, distal tibial fractures, or distal radius (wrist) fractures. One method for treating these conditions includes distracting and supporting the tissue surfaces simultaneously, as described in the &#39;998 Patent. The approach described herein, which includes expanding the tissue and then supporting the expanded tissue, may be used to treat these same conditions. Such procedures may be performed percutaneously through a cannula or other minimally invasive instrument or in an open procedure. 
     The expansion device is now described in this section by its application as a spinal implant to vertebral compression fractures.  FIG. 21  shows a vertebral body  500  having a compression fracture displacing its superior and anterior edge  502 .  FIG. 22  shows vertebral body  500  wherein the height has been restored.  FIG. 23  illustrates an extrapedicular approach to vertebral body  500  wherein an access cannula  504  is placed through the posterolateral wall  506  of vertebral body  500 . Other approaches may optionally be used for placing a cannula into a vertebral body such as a transpedicular approach to the vertebral body wherein an access cannula may be placed through the pedicle. In the extrapedicular approach, two cannulae  504  may be placed bilaterally, one on each side. 
     The procedure for the placement of access cannula  504  into verterbral body  500  is more fully described in the &#39;998 Patent, incorporated herein by reference. Cannula  504  in this particular arrangement is preferably rectangular in cross-section, although cannulae of other cross-sections, such as circular may be used. Further, cannula  504  may be of fixed configuration or expandable. Once access cannula  504  is in place, an expandable device  10  supported by inserter  100  may be introduced into vertebral body  500  through cannula  504 . This application of the invention contemplates expanding expandable device  10  by the inserter  100  from an unexpanded condition as shown, for example in  FIG. 3 a    to the expanded height as shown in  FIG. 24  to ultimately reduce the vertebral compression fracture and substantially restore the normal anatomic height of vertebral body  500 , inserting one or more inserts, such as inserts  16 , as described herein, to form a stack of inserts  16  between the expanded superior endplate  12  and inferior endplate  14  of expandable device  10 . In the particular arrangement being described for vertebral compression fracture reduction, expandable device  10  may have a length of approximately 25 mm, a width of approximately 10 mm, and an unexpanded height H of approximately 7 mm. The height H may be expanded by 5 mm and supported by the introduction of five inserts  16 , as shown in  FIG. 24 , each insert  16  as described herein having a thickness of 1 mm. It should be appreciated that the height H may be increased by other amounts and more or less than five inserts used, and that device  10  may be configured in other dimensions as set forth in the &#39;998 Patent. 
     When the fracture is reduced as depicted in  FIG. 22 , or when the physician determines that an adequate number of inserts  16  has been inserted, the inserter  100  may be ‘separated from device  10  and removed from cannula  504  while expanded device  10  remains within vertebral body  500 . Access cannula  504  is left in place. Suitable bone filler may be injected into vertebral body  500  through cannula  504  to encapsulate device  10 , provide weight bearing structure and increase stability of vertebral body  500 . Bone filler may flow through device  10  and the insert column and out to the surrounding bone to interdigitate with cancellous bone. 
     It should therefore be understood that while various embodiments of the invention have been presented herein, various changes, modifications and further applications may be made without departing from the spirit of the invention and the scope of the appended claims.