Abstract:
A technique for harvesting bone graft material for spinal and other fusion surgeries. In the disclosed embodiment, a bone cutting blade is placed in a disc space between two vertebrae to be fused. The blade cuts into the vertebrae and forms solid segments of autologous bone inside each vertebra. Each bone segment is urged out of its associated vertebra until a first portion of the segment enters the opposite vertebra, an intermediate portion spans the disc space, and a second portion remains in the associated vertebra. Each segment thus forms a strut graft to promote a healthy and permanent fusion. In another embodiment, a wire is placed in the disc space and rotated to cut grooves in the vertebrae, causing a slurry of morselized cortical and cancellous bone to ooze into a cage that is placed in the disc space. The slurry heals to fuse the vertebrae solidly and permanently.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a procedure and system for harvesting bone graft material for use in skeletal bone fusion surgery, particularly in fusions of the spinal vertebrae. 
         [0003]    2. Discussion of the Known Art 
         [0004]    An object of spinal fusion surgery is to join adjacent vertebrae at an affected level of a patient&#39;s spine by inducing growth of solid bone tissue in the intervertebral disc space. The grown bone tissue acts to fuse the vertebrae together solidly and permanently. This procedure has long been known to reduce or eliminate severe back pain suffered by a patient when he or she assumes postures that cause the vertebrae at the affected level to move relative to one another in a certain manner. 
         [0000]    See, e.g., my pending U.S. patent application Ser. No. 14/180,495 filed Feb. 14, 2014, titled Determining and Placing Spinal Implants or Prostheses, published as US 2014/0163573 (Jun. 12, 2014), and incorporated fully by reference. 
         [0005]    In a typical fusion procedure, the disc space is cleaned and bone, or a bone-like graft material, is deposited in the space to promote the growth of bone tissue between the vertebrae and produce a healthy fusion. Among the available graft materials, bone graft harvested directly from the patient&#39;s own bone tissue (“autograft”) or from a donor, ceramics, bone morphogenic proteins, and/or stem cell based grafts are commonly used as bone growth stimulants. Of these, autograft obtained from the patient&#39;s iliac crest or pelvic area is known to work best to promote a successful fusion. 
         [0006]    Using the patient&#39;s own bone tissue for graft material works well to form a confluence of the material with the vertebral bones to be fused. It is also known that (a) the more autograft material used, the greater the likelihood of achieving a successful fusion, and (b) a solid piece of autograft material works better than smaller chips to promote fusion. Basic principles of orthopaedic surgery suggest an optimum fusion will occur when a solid bone piece is inserted to span the entire intervertebral disc space, and when opposite ends of the piece enter or penetrate the end plates of the two vertebrae that face the disc space. 
         [0007]    U.S. Pat. No. 7,201,775 (Apr. 10, 2007) discloses a procedure that calls for implanting a hollow cylindrical stabilizing device (see FIGS. 7 &amp; 8 of the patent) between the end plates of two vertebrae to be fused, and rotating the device so that it gouges and shears off portions of the end plates, which portions are then forced inside of the device. The device has openings so that when oriented as in FIG. 11C of the patent, the bone portions inside the device are exposed to the vertebrae through the openings to promote a fusion, according to the patent. The procedure runs a risk of crushing the end plates and destroying the integrity of the remaining vertebral bone, however. That is, one or both vertebrae can become prone to fracture and compress into the spinal canal. Further, the device does not translocate or displace an intact piece of bone directly from one vertebra so as to enter the body of the other vertebra. 
         [0008]    U.S. Pat. 8,328,870 (Dec. 11, 2012) describes an interbody fixation system including a cage having blades mounted inside the cage. When the blades are turned not more than about 45 degrees as shown in FIGS. 2 and 6C of the patent, the blades bite into the end plates of the opposed vertebrae and fix the position of the cage on and between the end plates, according to the patent. See also, U.S. Pat. No. 7,618,423 (Nov. 17, 2009) which relates to a system for performing spinal fusion including a graft holder assembly, a locking assembly, and a pair of bone graft implants that are introduced into a disc space to effect fusion; U.S. Pat. No. 8,353,912 (Jan. 15, 2013) disclosing an ultrasonic cleaning device for leveling the surfaces of the vertebral end plates after the disc space is cleaned and before graft material is deposited in the space, and U.S. Pat. No. 8,343,178 (Jan. 1, 2013) describing an ultrasonic saw blade for cutting hard bone without damaging adjacent soft tissue. All of the foregoing U.S. patents are fully incorporated by reference. 
         [0009]    Notwithstanding known meticulous procedures to obtain and use autograft material from a patient during a surgical procedure, there is no guarantee that a reliable and strong fusion will ultimately result, and that a so-called “non-union” will be avoided. A need therefore exists for a system and procedure for obtaining and depositing autograft material between two vertebrae to be fused so that the material spans the intervertebral disc space, enters the vertebral bodies, and grows rapidly to produce a healthy, strong, and permanent fusion. 
       SUMMARY OF THE INVENTION 
       [0010]    According to one aspect of the invention, a procedure for harvesting bone graft material for use in a skeletal bone fusion surgery, includes inserting a cutting blade to a certain position inside a space between first and second bones to be fused, and rotating the blade so that it cuts into both of the bones and forms solid bone segments within each of the first and the second bones. Each bone segment is displaced to a position at which a first end portion of the segment is located in the first bone, an intermediate portion of the segment spans the space between the two bones, and a second end portion of the segment is located in the second bone. The bone segment thus forms a strut graft that acts as a pathway for bone growth to fuse the first and the second bones with one another. 
         [0011]    According to another aspect of the invention, a procedure for harvesting bone graft material for use in a skeletal bone fusion surgery, includes inserting a cutting blade to a certain position inside a space between first and second bones to be fused, and rotating the blade so that it cuts multiple grooves into the bones, and produces a slurry of morselized cortical and cancellous bone that oozes from the two bones. The slurry is confined in the region of the bones so that upon healing, the slurry becomes solid bone that fuses the first and the second bones with one another. 
         [0012]    For a better understanding of the invention, reference is made to the following description taken in conjunction with the accompanying drawing and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0013]    In the drawing: 
           [0014]      FIG. 1  is a diagram of two adjacent spinal vertebrae to be fused with one another according to a first embodiment of the invention; 
           [0015]      FIG. 2  shows a tool shaft with an associated cutting blade at a distal end of the shaft, according to the invention; 
           [0016]      FIG. 3  is a diagram of the tool shaft in  FIG. 2  inserted inside a disc space between the vertebrae in  FIG. 1 , and a cage to which the shaft is pivoted for rotation with the cutting blade; 
           [0017]      FIG. 4  is an enlarged, isometric view of the tool shaft and cutting blade inserted in the disc space as in  FIG. 3 ; 
           [0018]      FIG. 5  is a view similar to  FIG. 4 , showing the cutting blade turned 90 degrees from the position in  FIG. 4  by the tool shaft; 
           [0019]      FIG. 6  illustrates two semicircular bone segments formed inside the vertebrae after the cutting blade is rotated over 360 degrees by the tool shaft; 
           [0020]      FIG. 7  is an isometric view of a pusher or paddle fixed at a distal end of a cannulated shaft that slides over the tool shaft; 
           [0021]      FIG. 8  is a view similar to  FIG. 7 , showing paddle inserted in the disc space and turned 90 degrees from the angular position of the paddle in  FIG. 7  by the cannulated shaft; 
           [0022]      FIG. 9  illustrates the bone segments in  FIG. 6  forming two strut grafts between the vertebrae when the paddle is in the position shown in  FIG. 8 , according to the invention: 
           [0023]      FIG. 10  shows the vertebrae in  FIG. 1  to be fused with one another according to a second embodiment of the invention, including a cage placed in the disk space; 
           [0024]      FIG. 11  shows a distal end of a cannula inserted in the disc space through an opening in a side wall of the cage in  FIG. 10 ; 
           [0025]      FIG. 12  shows a cutting tip of a flexible wire inserted through the cannula and into the disk space, with the tip angled toward one of the vertebrae; 
           [0026]      FIG. 13  shows the tip of the wire cutting multiple grooves in the vertebrae when the tip is rotated and displaced laterally in the disc space by the cannula; and 
           [0027]      FIG. 14  shows a bony slurry produced by the cut vertebrae and confined by the cage so as to fuse the vertebrae with one another, according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    The present invention resides in harvesting bone graft material directly from bones to be fused in a surgical procedure on a patient, in situ. In the illustrated embodiment, the procedure is a spinal fusion wherein the bones to be fused are spinal vertebrae, and the harvested material spans the disc space between the vertebrae and enters the vertebral bodies. As a result, the graft material grows quickly to obtain a healthy, solid, and permanent fusion. While the invention is illustrated and described below as applied to a spinal fusion, persons skilled in the art will recognize that the invention can be applied in other bone fusion surgeries, for example, fusions of the ankle. 
         [0029]      FIG. 1  is a diagram showing two adjacent vertebrae  10 ,  12  in a patient&#39;s spine. The spine has an axis S, and the two vertebrae  10 ,  12  are separated by a disc space  14 . The vertebrae have end plates  10   a,    12   a  that face one another across the disc space  14 . 
         [0030]    In one embodiment of the invention, shown in  FIGS. 2 to 9 , a bone cutter  20  has a base  22  and a generally U-shaped, two-dimensional ultrasonic cutting blade  24 . The blade  24  has a cutting edge  24   a  formed along legs  24   b,    24   c,  and a closed end  24   d  of the “U” shaped blade  24 . As shown in  FIG. 2 , the blade legs  24   b,    24   c  are spaced apart by width WC, and the closed end  24   d  of the blade is at a length L from the bone cutter base  22 . The base  22  is fixed at  26  to a distal end  28  of a tool shaft  30  having an axis A, and the tool shaft  30  has an axial pivot  31  extending from the distal end  28 . As seen in  FIG. 3 , the pivot  31  at the distal end  28  of the shaft  30  is received in a corresponding pivot opening  32  formed in a spacer or cage  33  after the cage is placed in the disc space  14  between the vertebrae  10 ,  12 . 
         [0031]    The cage  33  can be formed of a surgical metal, polymer, ceramic, or composites thereof. In addition to providing a common axial pivot or anchor point for the tool shaft  30  and other instrumentation to be aligned between the end plates  10   a,    12   a  of the vertebrae, the cage  33  supports the vertebral bones  10 ,  12  above and below the disc space  14  to prevent subsidence of graft bone segments obtained as described below. The cage  33  also enhances the stability of the entire construct to ensure a successful fusion. 
         [0032]    If surgery is performed using a posterior approach, the cage  33  enters the disc space  14  from the posterior side, and should be urged anteriorly as far as possible to lodge against the disc annulus while the vertebral bones  10 ,  12  compress against the cage. To provide an effective anchor point for the pivot  31  on the tool shaft, the cage  33  should be relatively large and have a curvilinear shape to conform with the anterior disc space occupied by the cage  33 . Cages usually have an aperture to allow bone graft material to be deposited inside them, and for the material to contact vertebrae above and below the cage so that a solid bond between the vertebrae will grow through the cage itself. 
         [0033]    Because, as explained below, the inventive procedure obtains bone graft material directly from the vertebrae to be fused rather than an outside source, it is therefore not critical for the cage  33  to act primarily as a fusion device. The cage  33  can work mainly as a fixation device that connects to the vertebral bones  10 ,  12  above and below the cage. An example of a suitable cage that also acts as a fixation device is available from Biomet, Inc., as the C-THRU™ Anterior Spinal System. The Biomet cage has with a large chamber that opens at the superior and inferior (top and bottom) ends of the cage for in which graft material can be packed. Although the cage  33  as shown in  FIG. 3  is not centered directly beneath the portions of the vertebrae  10 ,  12  to be cut, it may be desirable to use a cage such as the Biomet with a chamber that opens at both ends, and to form an opening in a side of the cage to allow the cutting blade  24  at the distal end of the tool shaft  30  to pass into the chamber. The cage  33  can then be centered directly beneath the facing surfaces on the bones  10 ,  12  to be cut. (See  FIG. 11 , cage  100 ). 
         [0034]    As seen in  FIG. 2 , the “U” shape cutting blade  24  extends radially outward from its base  22  at the distal end  28  of the tool shaft  30 . The legs  24   b,    24   c  and the closed end  24   d  of the blade  24  extend in a plane that coincides with the shaft axis A. The bone cutter  20  including the cutting blade  24  is dimensioned and configured to be inserted with the tool shaft  30  to a desired position in the disc space  14 , with the plane of the cutting blade  24  held generally parallel to the end plates  10   a,    12   a  of the vertebrae to be fused, as shown in  FIG. 4 . The cutting edge  24   a  of the blade  24  is activated, for example, by a conventional ultrasonic driver coupled to the tool shaft  30  in a known manner. Ultrasonically energized bone cutting blades are known generally, and persons skilled in the art can construct and use the blade  24  as described herein. See, e.g., the website at www.misonix.com. 
         [0035]    In the inventive procedure, the tool shaft  30  is rotated about the shaft axis A by, e.g., a removable or cannulated handle (not shown in the drawing) having an axial thru passage that is keyed to a cross sectional profile of the shaft, or by a flexible motor drive, so that the cutting edge  24   a  of the blade  24  is urged over a circular path that cuts into the vertebral end plates and adjacent regions inside the vertebrae  10 ,  12 . See  FIG. 5 . As a result, as depicted in  FIG. 6 , the cutting blade  24  forms two solid, semicircular bone segments  40 ,  42  in the vertebral bodies  10 ,  12  wherein the radius of each segment  40 ,  42  corresponds to the length L of the blade  24  from the shaft axis A, and the thickness of each segment corresponds to the spacing WC between the blade legs  24   b,    24   c.    
         [0036]    The bone segments  40 ,  42  are comprised of autologous graft material that is then used to form strut grafts between the same vertebrae  10 ,  12  from which the grafts are formed. Note that in  FIG. 6  that flat surfaces  40   a,    42   a  of the segments are exposed to face one another across the intervertebral disc space  14 . While the tool shaft  30  may be withdrawn with the cutting blade  24  from the disc space  14  at this time, it is preferred that the shaft and the blade remain in place as noted below. 
         [0037]    After removing a handle or other drive from the tool shaft  30 , and as shown in  FIGS. 7 to 9 , an elongated pusher or paddle  50  is inserted into the disc space  14  until the paddle overlies the cutting blade  24  and extends substantially entirely over the exposed flat surfaces of the vertebral bone segments  40 ,  42 . In the disclosed embodiment, the paddle  50  is formed at a distal end of a cannulated shaft  51  whose axial passage is keyed to the cross section of the tool shaft  30 . The cannulated shaft  51  is slid over the tool shaft  30 , a handle  52  is provided at the proximal end of the shaft  51 , and the paddle  50  is inserted inside the disc space  14 . Using the handle  52 , the paddle  50  is rotated (together with the blade  24  if left in place) through the same circular path initially cut by the blade  24  through the vertebrae  10 ,  12 . 
         [0038]    If the cage  33  is of such size that it encompasses areas of the vertebral end plates  10   a,    12   a  that will be cut by the blade  24 , the blade  24  and the paddle  50  must then be able to be inserted and operate within the perimeter of the cage. In such a case, the cage may be formed with a through passage between its anterior and posterior facing side walls. The dimensions of the passage must be such as to allow of the tool shaft  30  with the bone cutting blade  24 , the cannulated shaft  51  with the paddle  50 , and any other needed instrumentation to pass and operate inside the cage  70  when performing the inventive fusion procedure. 
         [0039]    In the illustrated embodiment, the paddle  50  has two “U” shaped arms  54   a ,  54   b  that extend outward and 180 degrees apart from one another as shown in  FIGS. 7 to 9 . Each paddle arm  54   a,    54   b  has a width WP that does not exceed the width WC of the bone cutter blade  24 . Likewise, the length of each paddle arm  50   a,    50   b  does not exceed about one-half the length of either of the exposed surfaces  40   a  or  42   a  of the bone segments  40 ,  42  facing the disc space  14 . The entire paddle  50  may also be formed from one or more balloons which, when inflated, take the form of a rigid pusher or paddle device. 
         [0040]    When the paddle  50  is inserted in the disk space  14 , the paddle arms  54   a ,  54   b  are generally parallel to and overlie the exposed surfaces  40   a,    40   b  of the bone segments  40 ,  42  formed by the blade  24 . The cannulated shaft  51  is turned about its axis A until each paddle arm  54   a,    54   b  abuts the exposed surface of one of the bone segments, and the shaft  51  is turned about  90  degrees farther so that the paddle arms  54   a,    54   b  urge the bone segments  40 ,  42  to rotate in unison within their associated vertebra until, as shown in  FIG. 9 , (i) a leading portion of each segment  40 ,  42  enters the vertebra opposite the vertebra in which the segment was formed, (ii) a central portion of each segment spans the disc space  14  entirely, and (iii) a trailing portion of each segment remains inside the vertebra in which it was formed. 
         [0041]    When displaced as described above and shown in  FIG. 9 , each one of the bone segments  40 ,  42  forms a vertical bridge strut graft that completely spans the disc space  14  and also enters the vertebrae  10 ,  12  above and below the space. Each strut graft acts as a pathway for bone growth and promotes a healthy fusion of the vertebrae. The tool shaft  30  is then withdrawn from the cage  33  inside the disc space  14 , and the paddle  50  and the blade  24  can remain in a vertical orientation between the displaced bone segments  40 ,  42  without affecting the quality of the ensuing fusion. 
         [0042]    After the cutting blade  24  cuts through the vertebrae  10 ,  12 , and especially after the bone segments  40 ,  42  are rotated, there will likely be a massive release of blood since the bone is very vascular. Accordingly, in addition to inserting and using a cage such as the mentioned Biomet device for the cage  33  in the disk space  14 , a system should be in place to extinguish such hemorraging. One approach is to use a coagulating agent such as, for example, the Surgiflo® Hemostatic Matrix available from Ethicon US, LLC, and injecting the agent through an applicator tube into a port formed on the cage  33 . Also, with much bleeding, there may be a need to seal the disc space  14  so that the coagulating agent stays within the disc space. That is, the disc space  14  may need to be capped or sealed closed to confine the blood, the coagulating agent, and the graft bone segments within the disc space. With the coagulating agent injected into the closed disc space which provides a pressurized environment, bleeding will stop. 
         [0043]    Further, the cage may also have ports so situated that the coagulating agent makes a seal between the upper and the lower surfaces of the cage, and the adjacent vertebral bone. This would prevent bloody fluid from escaping above and below the cage through small gaps. 
         [0044]    When the paddle  50  is rotated, it is urged against the exposed surfaces  40   a,    42   a  of the bone graft segments  40 ,  42  after the segments were cut and formed by the blade  24 . The paddle  50  does not occupy any space in which new bone graft is being deposited. That is, the paddle  50  is not embedded in any new bone growth, but remains in a final vertical position with the bone segments  40 ,  42  at each side, and with the vertebral bones  10 ,  12  above and below the paddle. 
         [0045]    As the bones  10 ,  12  heal and the graft bone segments  40 ,  42  grow, the paddle  50  becomes firmly anchored inside the vertebrae  10 ,  12  and thereby adds stability to the overall construct by pinning the vertebrae together. To that end, the paddle  50  may be constructed, for example, with extensible pins to engage the exposed surfaces  40   a,    42   a  of the bone segments and/or the vertebrae  10 ,  12  above and below the paddle  50 . Such engagement would stabilize the entire construct and ensure that the paddle  50  and the graft bone segments  40 ,  42  do not migrate. Together with the cage  33 , the paddle  50  also prevents subsidence with collapse of the disc height. 
         [0046]    It is also possible for the paddle  50  to be constructed of balloons so that, if desired after inflation and use, the paddle can be deflated and easily removed after it is rotated to a vertical position with the bone segments  40 ,  42  at either side. In such an embodiment, however, any additional fixation that would otherwise result from using a more solid form of the paddle  50  will not be realized unless the balloons are later filled with a material such as, e.g., methyl methacrylate that hardens in place. 
         [0047]    The paddle  50  may also be constructed in a known manner so that the two arms  54   a,    54   b  of the paddle overlie one another at one side of the cannulated shaft as the paddle is being inserted inside the disc space  14 . When between the vertebrae  10 ,  12 , one of the arms may then be displaced to the opposite side of the shaft so that the paddle extends fully across the exposed surfaces  40   a,    42   a  of the bone segments above and below the paddle. 
         [0048]    It is preferable that the solid bone cutting blade  24  remain in situ, and no attempt made to withdraw the blade from between the bone segments  40 ,  42  after the blade forms the segments and the paddle  50  is inserted into the disk space  14 . This ensures the paddle  50  will displace the bone segments  40 ,  42  over the identical path cut by the blade  24  through the vertebrae  10 ,  12 , since a variance of even one millimeter to either side of the path can cause the paddle  50  to lock against solid uncut vertebral bone and prevent the paddle from displacing the segments  40 ,  42  fully to the positions in  FIG. 9 . If the cage  33  provides enough precision with respect to the position of the blade  24  and the paddle  50  during use, however, it may be possible to remove the cutting blade  24  prior to inserting and using the paddle  50 . 
         [0049]    The above procedure has the following features: 
         [0050]    1. The bone cutting blade  24  can be activated ultrasonically to make the vertebral cuts safely and precisely; 
         [0051]    2. The cutting blade  24  and the paddle  50  can be made small enough to be inserted into the intervertebral disc space  14  during a minimally invasive surgical procedure; and 
         [0052]    3. In addition to adding stability to the construct, the cage  70  provides a common pivot point for the rotation of the bone cutting blade  24  and the paddle  50 , to ensure the bone segments  40 ,  42  are displaced smoothly and accurately by the paddle after being formed by the blade. 
         [0053]    Another embodiment of the inventive system and procedure is illustrated in  FIGS. 10 to 14 . Instead of cutting and forming the solid autograft segments  40 ,  42  and displacing them as described above, a bone cutting instrument having a straight rather than a two-dimensional or “U” shaped cutting edge like the blade  24  is inserted into the disc space  14  instead. The instrument is operated to strike the vertebral bones  10 ,  12  and groove them in such a way that a slurry of morselized cortical and cancellous bone rich in osteogenic cells and blood oozes from the vertebrae. By confining the slurry within the disc space  14 , the slurry also remains present in the vertebrae  10 ,  12 , and thus forms a solid bony fusion of the two vertebrae. 
         [0054]    A cage  100  is set in the disc space between the vertebrae  10 ,  12 . See  FIG. 10 . The cage  100  may be similar to the earlier mentioned Biomet C-THRU Anterior Spinal System device, or equivalent. In addition, the cage  100  should have sufficient size and volume to contain and confine the slurry to be produced from the vertebrae as detailed below, and be constructed so its edges seal any gaps between the cage and either bone  10 ,  12 . As described above with respect to the embodiment of  FIGS. 1 to 9 , such sealing prevents liquid graft material from migrating outside the internal chamber of the cage  100  and the intervertebral disc space. For example, a seal can be formed by constructing the cage  100  with internal and/or external channels that guide a sealing agent around the circumference of the superior and inferior edges of the cage  100 , and the agent can be injected into the cage during the procedure. The mentioned Surgiflo® Hemostatic Matrix is an example of such a sealing agent. 
         [0055]    As seen in  FIGS. 11 to 13 , a cannula  102  is inserted through an opening  104  in the wall of the cage  100 , and the cannula  102  has a distal tip  106  that is angled toward the vertebrae above and below the perimeter of the cage. A flexible, sharp tipped wire  108  is inserted through the cannula  102 , past the distal tip  106  of the cannula, and against the end plate  10   a  or  12   a  of a confronting vertebra. A motor or other drive mechanism coupled to a proximal end of the cannula  102  spins the cannula so that the sharp tip of the wire  108  cuts into the end plates  10   a,    12   a  of both vertebrae  10 ,  12 . 
         [0056]    The wire  108  is pushed farther into the cannula  102  so that the wire tip cuts a groove completely through the end plates and adjacent regions of the vertebrae  10 ,  12 , as seen in  FIG. 12 . The position of the wire  108  at the tip  106  of the cannula is adjusted and the cannula  102  is moved axially in anterior and posterior directions so that the combined width WC of all the vertebral cuts is increased as desired. See  FIG. 13 . The cannula  102  and wire  108  are then withdrawn from inside the cage  100  and the disc space. 
         [0057]    As a result and as shown in  FIG. 14 , all of the bony slurry  110  obtained from the cut vertebrae will either be contained inside the cage  100  in the disc space, or within the vertebrae  10 ,  12  in the region of the grooved cuts. Upon healing, the slurry forms a solid bony fusion of the vertebrae. If needed, a second cage or other device can be provided to cap or otherwise seal the cage  100  and the disc space to ensure the slurry stays so confined before healing. 
         [0058]    While the foregoing represents preferred embodiments of the invention, it will be understood by those skilled in the art that various modifications, adaptations, and additions may be made without departing from the spirit and scope of the invention. For example, while the invention is described herein as applied to a spinal fusion, the invention may be adapted for other bone fusion procedures as well, for example, ankle bone fusions. Accordingly, invention includes all such modifications, adaptations, and additions that are within the scope of the following claims.