Abstract:
An expandable housing for an interbody fusion system has movable tapered external helical threaded members that travel along tracking to operably engage against the top and bottom shell members, urging them apart to cause expansion in the height of the housing. In an embodiment, the tapered members are disposed in a dual arrangement such that independent engagement of the tapered members along lateral portions of the top and bottom shells cause an angular tilt to the exterior surface of the housing when the tapered members are moved to different degrees. This function permits adjustment in the angular relationship between adjacent vertebrae and assists the lordotic adjustment of the patient&#39;s spine. When the functions of the device are used in combination by the surgeon, the device provides an effective tool for in situ adjustment when performing lateral lumbar interbody fusion.

Description:
RELATED APPLICATIONS 
       [0001]    The present U.S. non-provisional patent application is related to and claims priority benefit to an earlier-filed provisional patent application titled EXPANDABLE LATERAL INTERBODY FUSION SYSTEM, Ser. No. 61/871,780, filed Aug. 29, 2013. The identified earlier-filed application is hereby incorporated by reference into the present application as though fully set forth herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to surgical procedures and apparatus for treating lumbar back pain. 
       BACKGROUND OF THE INVENTION 
       [0003]    Lumbar spinal fusion is a surgical procedure to correct problems relating to the human spine. It generally involves removing damaged disc and bone from between two vertebrae and inserting bone graft material that promotes bone growth. As the bone grows, the two vertebrae join, or fuse, together. Fusing the bones together can help make that particular area of the back more stable and help reduce problems related to nerve irritation at the site of the fusion. Fusions can be done at one or more segments of the spine. 
         [0004]    Interbody fusion is a common procedure to remove the nucleus pulposus and or the annulus fibrosus that compose the intervertebral disc at the point of the back problem and replace it with a cage configured in shape and dimension to restore the distance between adjacent vertebrae to that of a proper condition. Surgical approaches to implement interbody fusion vary, and access to the patient&#39;s vertebral column can be made through the abdomen or back. One other surgical method for accomplishing lumbar spinal fusion in a less invasive way involves accessing the vertebral column through a small incision on the side of the body. This procedure is known as lateral lumbar interbody fusion. 
         [0005]    Once the intervertebral disc is removed from the body during the lateral lumbar interbody fusion, the surgeon typically forces different trial implants between the vertebral endplates of the specific region to determine the appropriate size of the implant for maintaining a distance between the adjacent vertebrae. Another consideration is to maintain the natural angle between lumbar vertebral bodies to accommodate the lordosis, or natural curvature, of the spine. Therefore, during selection of a cage for implantation, both intervertebral disc height and lordosis must be considered. Prior art fusion cages are often pre-configured to have top and bottom surfaces angles to one another to accommodate the natural curvature of the spine. It is unlikely that these values can be determined precisely prior to the operation, which is a drawback in present procedures. Prepared bone graft is generally packed into the cage implant once it is properly sized and before it is inserted in between the vertebral bodies. 
         [0006]    Present lateral interbody fusion cage devices are generally limited to providing height expansion functions, but not a lordotic adjustment capability. In implementing a trial-and-error approach to sizing and fitting the interbody fusion cage into the target region for the particular geometric configuration for that patient, the patient is subjected to significant invasive activity. The bone graft material is generally added and packed in to the fusion device after the desired height expansion has been reached and final adjustments made. 
       SUMMARY OF THE INVENTION 
       [0007]    An embodiment of the device comprises an expandable housing comprised of opposing shell members. Movable tapered screw-like elements having an external helical thread are disposed in the housing and operably engage against the top and bottom shell members, urging them apart to cause expansion in the height of the housing. This function permits adjustment of the distance (height) between adjacent vertebrae when in place. The tapered members are disposed in a dual arrangement such that independent engagement of the tapered members along lateral portions of the top and bottom shells cause an angular tilt to the exterior surface of the housing when the wedge members are moved to different degrees. This function permits adjustment in the angular relationship between adjacent vertebrae and assists the lordotic adjustment of the patient&#39;s spine. When the functions of the device are used in combination by the surgeon, the device provides an effective tool for in situ adjustment when performing lateral lumbar interbody fusion. 
         [0008]    An embodiment of the device further comprises a track configuration within the housing for guiding the tapered external helical threaded members in their engagement with the top and bottom shell members. The track comprises raised elements on each of the interior surfaces of the top and bottom shell members that permit an interlocking engagement for lateral stability of the housing when in a contracted position. As the housing expands, the track area provides space for storage of bone graft material. One embodiment may provide for an elastic membrane to be positioned around the housing to prevent bone graft material from seeping out of the cage and to provide a compressive force around the cage to provide structural stability to the housing. 
         [0009]    An embodiment of the device further comprises drive shafts for operating the tapered external helical threaded members. The drive shafts permit the surgeon, through the use of a supplemental tool, to manipulate the shafts which operatively move the tapered external helical threaded members in controlling the expansion of the housing and angular adjustment of the top and bottom shell members for in situ fitting of the interbody fusion device. A locking mechanism is provided for preventing rotation of the shafts when the tool is not engaged and after manipulation by the tool is completed. The tool also facilitates insertion of bone graft material into the fusion body during in situ adjustment. 
         [0010]    An embodiment of the present invention provides a surgeon with the ability to both expand the fusion cage and adjust the lordotic angle of the fusion cage in situ during operation on a patient and to introduce bone graft material at the operation site while the device is in place. This embodiment of the present invention therefore provides a fusion cage having geometric variability to accommodate the spinal condition unique to each patient. 
         [0011]    Embodiments of the present invention therefore provide an interbody cage device for use in lateral lumbar interbody fusion procedures that combines the functions of height expansion for adjusting the distance between adjacent vertebrae with lordotic adjustment to control the angular relationship between the vertebrae. Embodiments of the inventive interbody cage device further provide a storage capacity for containing bone graft material in the interbody cage device as disc height and lordotic adjustment takes place in situ. 
         [0012]    The present invention also provides a device that may be used in environments other than in interbody fusion applications. It may generally be used to impart a separating effect between adjacent elements and to impart a variable angular relationship between the elements to which it is applied. 
         [0013]    These and other features of the present invention are described in greater detail below in the section titled DETAILED DESCRIPTION OF THE INVENTION. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0014]    An embodiment of the present invention is described herein with reference to the following drawing figures, with greater emphasis being placed on clarity rather than scale: 
           [0015]      FIG. 1  is a view in side elevation from the side of the expandable shell device. 
           [0016]      FIG. 2  is a perspective view of a bottom section of the expandable shell. 
           [0017]      FIG. 3  is a top plan view of the bottom section of the expandable shell. 
           [0018]      FIG. 4  is a top plan view of the expandable shell device. 
           [0019]      FIG. 5  is a perspective view of a tapered external helical threaded member. 
           [0020]      FIG. 5A  is a view in side elevation from the side of the tapered external helical threaded member. 
           [0021]      FIG. 5B  is a view in side elevation from the front of the tapered external helical threaded member. 
           [0022]      FIG. 6  is a cross-sectional view of the device taken along lines  6 - 6  in  FIG. 1 . 
           [0023]      FIGS. 7A-7C  are a series of views in side elevation of the device as it undergoes expansion. 
           [0024]      FIG. 8  is a view in side elevation of the device showing an expansion of the device to accommodate a lordotic effect. 
           [0025]      FIG. 9A  is a perspective expanded view of thrust bearing for the drive shaft. 
           [0026]      FIG. 9B  is a perspective view of the drive shafts and thrust bearings. 
           [0027]      FIG. 9C  is a top plan view in cross section of the area of engagement of the drive shafts with the thrust bearings. 
           [0028]      FIG. 10  is a side elevation view of the housing as expanded. 
           [0029]      FIG. 11A  is a top plan view of another embodiment of the device. 
           [0030]      FIG. 11B  is a top plan view of yet another embodiment of the device. 
           [0031]      FIG. 12A  is a top plan view of the drive shafts disengaged by the locking mechanism. 
           [0032]      FIG. 12B  is a top plan view of the drive shafts engaged by the locking mechanism. 
           [0033]      FIG. 13A  is a perspective view of the locking mechanism. 
           [0034]      FIG. 13B  is a top plan cross sectional view of the drive shafts disengaged by the locking mechanism. 
           [0035]      FIG. 13C  is a top plan cross sectional view of the drive shafts engaged by the locking mechanism. 
           [0036]      FIG. 14  is a view taken along lines  14 - 14  in  FIG. 11A . 
           [0037]      FIGS. 15A-C  are a series of views in side elevation taken from the end of the device as it undergoes expansion showing the lordotic effect. 
           [0038]      FIG. 16  is a perspective view of the operating tool. 
           [0039]      FIG. 17  is a view showing a manner of attachment of the operating tool to the drive shafts of the device. 
           [0040]      FIG. 18  is a breakaway perspective view of the handle of the operating tool. 
           [0041]      FIG. 19  is a perspective view of gears in the handle engaged for operation of both drive shafts. 
           [0042]      FIG. 20  is a perspective view of gears in the handle disengaged for operation of a single drive shaft. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0043]    With reference to the drawings figures, an interbody fusion body device is herein described, shown, and otherwise disclosed in accordance with various embodiments, including preferred embodiments, of the present invention. The interbody fusion device  10  is shown generally in  FIG. 1 . It is comprised of a housing  12  having a top shell  14  and a bottom shell  16 . The overall housing may have a length of 50 mm and a width of 20 mm, as an example. The shell material may be comprised of a suitable materials, such as titanium alloy (Ti-6AL-4V), cobalt chromium, or polyether ether ketone (PEEK). Other materials may be suitable that can provide sufficient compositional integrity and that have suitable biocompatible qualities. The interior of the shells are configured with a cascading step tracking  18  and  20  placed along their lateral edges. As shown in  FIG. 2 , step tracking  18  begins towards the midpoint of an inner surface of bottom shell  16  with successive track steps increasing in height as the tracking extends to a first end of bottom shell  16 . Correspondingly, step-tracking  20  begins towards the midpoint of the inner surface of bottom shell  16  with successive track steps increasing in height as that portion of the tracking extends to a second opposite end of bottom shell  16 . Step tracking  18  comprises dual track runs  22  and  24  while step tracking  20  comprises dual track runs  26  and  28  as shown in  FIG. 3 . Corresponding step tracking  30  and  32  is provided on top shell  14  as shown in  FIG. 4 . When the device is in its fully compressed state where top shell  14  lies adjacent to bottom shell  16 , as shown in  FIG. 1 , step tracking  18  intermeshes with step tracking  30  and step tracking  20  intermeshes with step tracking  32 . 
         [0044]    The respective track runs comprise a series of risers, or track steps, which are spaced apart to receive the threads of tapered external helical threaded members. The tapered external helical threaded members provide a wedging action for separating the top and bottom shell thereby increasing the height of the housing to effect expansion between the vertebral bodies in which the device is placed. As shown in  FIG. 4 , track run  22  receives tapered external helical threaded member  34 , track run  24  receives tapered external helical threaded member  36 , track run  26  receives tapered external helical threaded member  38 , and track run  28  receives tapered external helical threaded member  40 . Track run  22  aligns collinearly with track run  26  such that the travel of tapered external helical threaded members  34  and  38  within the respective track runs occurs within that collinear alignment. The thread orientation of tapered external helical threaded members  34  and  38  are opposite of each other such that their rotation will result in opposite directional movement with respect to each other. As shown in  FIG. 4 , a drive shaft  42  runs along the collinear span of track runs  22  and  26  and passes through tapered external helical threaded members  34  and  38 . Shaft  42  has a square cross sectional configuration for engaging and turning the tapered external helical threaded members. As shown in  FIG. 5 , the central axial opening  44  of the tapered external helical threaded members are configured to receive and engage the shaft  42 . Shaft  42  may alternatively comprise any shape for effectively creating a spline, such as a hexagonal shape, and central axial openings  44  may comprise a corresponding configuration for receiving that shape. As shaft  42  is rotated by its end  48  in a clockwise direction, tapered external helical threaded members  34  and  38  are rotated and their respective thread orientations cause the screws to travel apart from each other along track run  22  and track run  26 , respectively. Correspondingly, as shaft  42  is rotated by its end  48  in a counter-clockwise direction, tapered external helical threaded members  34  and  38  are caused to travel towards each other along track run  22  and track run  26 , respectively. 
         [0045]    Similarly, track run  24  aligns collinearly with track run  28  such that the travel of tapered external helical threaded members  36  and  40  within the respective track runs occurs within that collinear alignment. The thread orientation of tapered external helical threaded members  36  and  40  are opposite of each other such that their rotation will result in opposite directional movement with respect to each other. Also, shaft  46  passes through and engages tapered external helical threaded members  36  and  40 . However, the orientation of tapered external helical threaded members  36  and  40  is reversed from the orientation of tapered external helical threaded members  34  and  38 . Under this orientation, as shaft  46  is rotated by its end  50  in a counter-clockwise direction, tapered external helical threaded members  36  and  40  are rotated and their respective thread orientations cause the screws to travel apart from each other along track run  24  and track run  28 , respectively. Correspondingly, as shaft  46  is rotated by its end  50  in a clockwise direction, tapered external helical threaded members  36  and  40  are caused to travel towards each other along track run  24  and track run  28 , respectively. 
         [0046]    As shown in  FIG. 2 , the step tracking is configured with a cascading series of risers of increasing height. For example, each track run has risers  52 - 60  as shown for step tracking  18  in  FIG. 2 . As the thread of a tapered external helical threaded member travels into the gap between riser  52  and  54 , the positional height of the tapered external helical threaded member body, as supported on risers  52  and  54 , increases within the housing  12 . As the tapered external helical threaded member continues to travel along the track run, its thread passes from the gap between risers  52  and  54  and enters the gap between risers  54  and  56  which raises the tapered external helical threaded member body further within housing  12  as it is supported on risers  54  and  56 . As the tapered external helical threaded member continues its travel along the remainder of the step risers  58  and  60  its positional height increases further. As the positional height of the tapered external helical threaded member body increases, it urges top shell  14  apart from bottom shell  16  as shown in the series of 
         [0047]      FIGS. 7A-7C . The combined effect of rotating the tapered external helical threaded members to cause their movement towards the outer ends of the respective track runs causes an expansion of the housing  12  as shown in  FIG. 7 . The fully expanded shell is shown in  FIG. 10 . The housing  12  may be contracted by reversing the movement of the tapered external helical threaded members such that they travel back along their respective track runs towards the midpoint of the housing. The housing will optimally provide expansion and contraction to give the implant device a height over a range of around approximately 7.8 mm to 16.15 mm in the present embodiment. The device of this embodiment of the invention can be adapted to provide different expansion dimensions. 
         [0048]    The pairs of tapered external helical threaded members in each collinear dual track run may be rotated independently of the pair of tapered external helical threaded members in the parallel track run. In this arrangement, the degree of expansion of that portion of the housing over each collinear track run may be varied to adjust the lordotic effect of the device. As an example shown in  FIG. 8 , tapered external helical threaded members  36  and  40  have been extended to a particular distance along track run  24  and track run  28 , respectively, causing the top shell  14  to separate from bottom shell  16  thereby expanding housing  12 . Tapered external helical threaded members  34  and  38  have been extended to a lesser distance along parallel track run  22  and  26 , respectively, causing that portion of the top shell over track runs  22  and  26  to separate from bottom shell to a lesser degree. The series of  FIGS. 15A-15C  show this effect where tapered external helical threaded members  36  and  40  are extended apart from each other in further increasing increments where the tapered external helical threaded members  34  and  38  maintain the same relative distance to each other. 
         [0049]    In  FIG. 15A , the respective positioning of the set of tapered external helical threaded members  36 - 40  is approximately the same as the set of tapered external helical threaded members  34 - 38  in their respective tracking. In this position, the top shell  14  is essentially parallel with bottom shell  16 . In  FIG. 15B , the set of tapered external helical threaded members  36 - 40  move further distally apart along their tracking as the set of tapered external helical threaded members  34 - 38  remains at their same position in  FIG. 15A . In this setting, the lateral edge of top shell  14  along which tapered external helical threaded members  36  and  40  travel is moved higher with respect to the lateral edge of top shell  14  along which tapered external helical threaded members  34  and  38  travel, giving a tilt to top shell  14  with respect to bottom shell  16 . In  FIG. 15C , the set of tapered external helical threaded members  36 - 40  move even further distally apart along their tracking with respect to that of the set of tapered external helical threaded members  34 - 38 , giving an even greater tilt to top shell  14  with respect to bottom shell  16 . Through the independent movement of the respective tapered external helical threaded member sets, the device can achieve a lordotic effect of between 0° and 35° in the present embodiment. The device of this embodiment of the invention can be adapted to provide different lordotic tilt dimensions. 
         [0050]    The tapered external helical threaded members have a configuration comprising a body profile that has an increasing minor diameter from D r1  to D r2  as shown in  FIG. 5 . The threads  33  have a pitch to match the spacing between the riser elements  52 - 60  in the tracking runs as shown in  FIG. 4 . Threads  33  can have a square profile to match the configuration between the risers, but other thread shapes can be used as appropriate. The increasing diameter and tapering aspect of the helical threaded members cause top shell  14  and bottom shell  16  to move apart as described above. The contact at the tops of the risers  52 - 60  is made at the minor diameter of the helical threaded member. 
         [0051]    Thrust bearings are provided to limit the axial direction motion of the drive shafts within shell  12 . As shown in  FIG. 9A , thrust bearing  62  comprises a two-piece yoke configuration that mate together and press-fit around ends of the shafts. The top part  64  of the thrust bearing yoke defines openings for receiving a round portion  66  of the shaft ends. In  FIG. 9C , square shaft  42  has a rounded portion  66  of lesser diameter than the square portion of the shaft. A mating piece  65  of the thrust bearing engages with top part  64  to encircle the rounded portion  66  of drive shaft  42 . 
         [0052]    Pin elements  68  in the top portion  64  and bottom portion  65  engages a corresponding holes  69  in the mating piece to provide a press fit of the thrust bearing around the shaft. Journal grooves  67  can also be provided in thrust bearing  62 . Shaft  42  can have an annular ridge  63  around its rounded portion  66  which is received in journal groove  67  as shown in  FIG. 9C . A thrust bearing is provided at each end of the drive shafts as shown in  FIG. 9B . As shown in  FIG. 6 , the thrust bearings restrict the axial movement of the drive shafts in the housing. 
         [0053]    A safety lock is provided at the proximal end of the device for preventing unintended rotation of the shafts. As shown in  FIGS. 12A and 12B , safety lock member  70  is provided for engagement with the proximal ends of drive shafts  42  and  46 . The openings  73  in safety lock member  70  are configured with the shape of the cross-sectional configuration of the drive shafts (see  FIG. 13A ). A portion of the drive shafts has a narrowed, rounded configuration  71  such that the drive shaft can rotate freely while the rounded portion of the shaft is in alignment with the safety lock member openings  73  (see  FIG. 13C ).  FIG. 12B  shows this relationship among the safety lock member  70 , thrust bearing  62  and drive shafts  42  and  46 . When the non-narrowed portions  75  of the shafts are placed in alignment with the safety lock member openings  73 , then rotation of the shafts is prevented (see  FIG. 13B ).  FIG. 12A  shows this relationship among the safety lock member  70 , thrust bearing  62  and drive shafts  42  and  46 . A compression spring  77  can be placed between thrust bearing  62  and safety lock member  70  to urge safety lock member back over the square portion  75  of the drive shafts.  FIG. 12B  shows a lock disengagement when the safety lock member  70  is pushed forward out of alignment with the square portions  75  and placed in alignment with the rounded portions  71  of shafts  42  and  46 . Post  79  can be disposed between safety lock member  70  and thrust bearing  62  on which compression spring  77  can be positioned. Post  79  can be fixedly connected to safety lock member  70  and an opening can be provided in thrust bearing  62  through which post  79  can slide. Post  79  is provided with head  81  to limit the backward movement of safety lock member  70  from the compressive force of spring  77 . 
         [0054]    The interaction of the tapered external helical threaded members with the step tracking contributes to self-locking under a power screw theory. In considering the variables for promoting a self-locking aspect of the tapered threaded members, certain factors are relevant. In particular, those factors include the coefficient of friction of the materials used, such as Ti-6Al-4V grade 5, the length of pitch of the helical threads and the mean diameter of the tapered member. The following equation explains the relationship among these factors in determining whether the tapered external helical threaded members can self-lock as it travels along the step tracking: 
         [0000]    
       
         
           
             
               T 
               R 
             
             = 
             
               
                 
                   Fd 
                   m 
                 
                 2 
               
                
               
                 ( 
                 
                   
                     l 
                     + 
                     
                       π 
                        
                       
                           
                       
                        
                       
                         fd 
                         m 
                       
                        
                       seca 
                     
                   
                   
                     
                       π 
                        
                       
                           
                       
                        
                       
                         d 
                         m 
                       
                     
                     - 
                     
                       fl 
                        
                       
                           
                       
                        
                       seca 
                     
                   
                 
                 ) 
               
             
           
         
       
     
         [0055]    The above equation determines the torque necessary to apply to the drive shafts engaging the tapered external helical threaded members for expanding the shell members. This torque is dependent upon the mean diameter of the tapered external helical threaded members, the load (F) applied by the adjacent vertebral bodies, the coefficient of friction (f) of the working material, and the lead (l) or, in this embodiment, the pitch of the helical threading. All of these factors determine the required operating torque to transform rotational motion into a linear lift to separate the shell members in accomplishing expansion and lordosis. 
         [0056]    The following equation describes the relationship among the factors relating to the torque required to reverse the tapered external helical threaded members back down the tracking: 
         [0000]    
       
         
           
             
               T 
               R 
             
             = 
             
               
                 
                   Fd 
                   m 
                 
                 2 
               
                
               
                 ( 
                 
                   
                     
                       π 
                        
                       
                           
                       
                        
                       
                         fd 
                         m 
                       
                     
                     - 
                     l 
                   
                   
                     
                       π 
                        
                       
                           
                       
                        
                       
                         d 
                         m 
                       
                     
                     + 
                     fl 
                   
                 
                 ) 
               
             
           
         
       
     
         [0057]    Under this equation, the torque required to lower the tapered external helical threaded members (T L ) must be a positive value. When the value of (T L ) is zero or positive, self-locking of the tapered external helical threaded members within the step tracking is achieved. If the value of (T L ) falls to a negative value, the tapered external helical threaded members are no longer self-locking within the step tracking. The factors that can contribute to a failure to self-lock include the compressive load from the vertebral bodies, the pitch and mean diameter of the helical thread not being adequately great, and an insufficient coefficient of friction of the material. The condition for self-locking is shown below: 
         [0058]    πfd m  &gt;l 
         [0059]    Under this condition, it is necessary to select an appropriate combination of sufficient mean diameter size of the tapered member, along with the product material being a greater multiple than the lead or pitch in this particular application so that the tapered members can be self-locking within the step tracking. Based upon average values with a patient lying on their side, the lumbar vertebral body cross sectional area is around 2239 mm 2  and the axial compressive force at that area is 86.35 N. With the working material selected to be Ti-6Al-4V, the operating torque to expand shell housing  12  between L4-L5 of the vertebral column is around 1.312 lb-in (0.148 N-m), and the operating torque to contract shell housing  12  between L4-L5 of the vertebral column is around 0.264 lb-in (0.029 N-m). 
         [0060]    Alternate embodiments of the expandable shell housing provide for different surgical approaches.  FIG. 11A  shows housing  100  for use where a surgeon approaches the lumbar area from an anterior aspect of the patient. The general configuration of the tracking runs for this embodiment is similar to that for device  10 , but the drive shafts for moving the tapered external helical threaded members are applied with a torque delivered from a perpendicular approach. For this, a dual set of worm gears  102  and  104  respectively transfer torque to drive shafts  106  and  108  as shown in  FIG. 14 . 
         [0061]      FIG. 11B  shows housing  200  for use where a surgeon approaches the lumbar area from a transforaminal aspect of the patient. The general configuration of the tracking runs for this embodiment is also similar to that for device  10 , but the torque is applied to the drive shafts from an offset approach. For this, a dual set of bevel gears (not shown) may be used to transfer torque to drive shafts  206  and  208 . 
         [0062]    Housing  12  is provided with numerous niches and open areas in its surface and interior regions to accommodate the storage of bone grafting material. The interstitial spaces between the risers of the cascading step tracking also offers areas for receiving bone-grafting material. A membrane can be provided as a supplement around housing  12  to help maintain compression on the top and bottom shells and to hold in bone grafting material. Tension spring elements  78  can be provided to hold together top member  14  and bottom member  16  as shown in  FIG. 10 . These elements may also serve to provide an initial tension force in the direction opposite of the expansion against the interbody fusion device. This allows the tapered external helical threaded members to climb the risers in the event that contact between the outer shells and the vertebral bodies is not yet made. 
         [0063]    Accordingly, this embodiment of the interbody fusion device of the instant invention is capable of expansion to provide support between vertebral bodies and accommodate the load placed on that region. Furthermore, the inventive interbody fusion device is capable of achieving a configuration that can provide an appropriate lordotic tilt to the affected region. The device, therefore, provides a significant improvement with regards to patient-specific disc height adjustment. 
         [0064]    The device is provided with a tool for operating the interbody fusion device as it is adjusted in situ in a patient&#39;s spine. The operating tool  300  is shown generally in  FIG. 16  and comprises a handle member  302 , a gear housing  304  and torque rod members  306  and  308 . The torque rod members connect to the drive shafts of expandable shell  12 . One embodiment for connecting the torque rod members to the drive shafts of expandable shell  12  is shown in  FIG. 17 . In this arrangement, ends  48  and  50  of drive shafts  42  and  46  can be provided with a hex-shaped head. The ends of torque rod members  306  and  308  can be provided with correspondingly shaped receivers for clamping around ends  48  and  50 . 
         [0065]    Within the gear housing  304 , handle member  302  directly drives torque rod member  308 . Torque rod member  308  is provided with spur gear member  310  and torque rod member  306  is provided with spur gear member  312 . Spur gear  312  is slidably received on torque rod member  306  and can move in and out of engagement with spur gear  310 . Spur gear lever  314  engages with spur gear  312  for moving spur gear  312  into and out of engagement with spur gear  310 . When torque rod member  308  is rotated by handle  302 , and spur gear  312  is engaged with spur gear  310 , rotation is translated to torque rod member  306 . In this condition, torque rod member  308  rotates drive shaft  46  simultaneously with torque rod member  306  rotates drive shaft  42  to effect expansion of shell  12  as shown in  FIGS. 7A-7C . Spur gear  312  can be moved out of engagement with spur gear  310  by retracting spur gear lever  314  as shown in  FIG. 20 . With spur gear  312  out of engagement with spur gear  310 , rotation of handle  302  only turns torque rod member  310 . In this condition, torque rod member  308  rotates drive shaft  46  solely and drive shaft  42  remains inactive to effect the tilt to the top member of shell  12  as shown in  FIG. 8  and  FIGS. 15A-15C  to achieve lordosis. 
         [0066]    To achieve expansion of the device in the described embodiment, the operator will turn handle member  302  clockwise to engage torqueing. This applied torque will then engage the compound reverted spur gear train composed of spur gear members  310  and  312 . This series of gears will then spin torque rod members  306  and  308  in opposite directions of each other. Torque rod member  310  (in alignment with handle member  302 ) will spin clockwise (to the right) and torque rod member  306  will spin counterclockwise (to the left). The torque rod members will then rotate the drive shafts of interbody fusion device  12  expanding it to the desired height. 
         [0067]    To achieve lordosis the operator will move the spur gear lever  314  back towards handle member  302 . By doing so spur gear  312  connected to torque rod member  306  is disengaged from the overall gear train, which in turn will disengage torque rod member  306 . As a result, torque rod member  308  will be the only one engaged with the interbody fusion device  12 . This will allow the operator to contract the posterior side of the implant device to create the desired degree of lordosis. 
         [0068]    Although the invention has been disclosed with reference to various particular embodiments, it is understood that equivalents may be employed and substitutions made herein without departing from the scope of the invention. 
         [0069]    Having thus described the preferred embodiment of the invention, what is claimed as new and desired to be protected by Letters Patent includes the following: