Abstract:
A tool for directing bone replacement material under pressure comprising an elongated hollow tube having a proximal end, a distal end, and a longitudinal axis; the distal end including at least one opening having a deflection structure configured to deflect the bone replacement material out of the tube at an angle relative to the longitudinal axis of the tube in response to pressure applied to the bone replacement material such that the deflected bone replacement material creates a force with at least a portion of the force generally oriented perpendicular to the longitudinal axis of the tube.

Description:
RELATED APPLICATIONS  
       [0001]     This application is a continuation of U.S. patent application Ser. No. 09/608,079, filed Jun. 30, 2000, which is a continuation of U.S. patent application Ser. No. 09/738,726, filed Dec. 15, 2000, now U.S. Pat. No. 7,025,771, issued Apr. 11, 2006. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates to a tool for use injecting bone replacement material into a cavity within a bone, especially when the cavity includes a bag which is to be inflated within the cavity.  
         [0003]     U.S. Pat. No. 5,549,679 issued Aug. 20, 1996 and U.S. Pat. No. 5,571,189 which issued Nov. 5, 1996 disclose an expandable fabric bag and method for stabilizing a spinal motion segment. In those patents, a damaged disc is reamed out and an expandable fabric bag is inserted into the cavity thus formed. Bone graft material is then inserted into the bag to fill and expand the bag such that the filled bag will take the place of the reamed out disc. Over time, the material within the bag will cause stabilization by either fibrous or bony fusion or a combination of these between the adjacent vertebrae. The bag filling is through an opening which is closed off after filling.  
         [0004]     The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R.sctn.1.56(a) exists.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005]     The invention provides a tool which dramatically increases the distraction forces within an expandable fabric bag held within a reamed out disc. Distraction consists of a force that is perpendicular to the long axis of the injection tube, thereby producing distraction or increased separation distance between the bony structures that are perpendicular to the long axis of the injection tube. This allows the spacing between the vertebrae to be adjusted by inflating the bag as desired. The tool may be used in connection with any surgical application in which graft material is to be deployed and is not limited to use in connection with discs or where bags are required. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     A detailed description of the invention is hereafter described with specific reference being made to the drawings in which:  
         [0007]      FIG. 1  is a perspective view of a distal end of a filling tool of the invention;  
         [0008]      FIG. 2  is a side elevational view of the distal end of the tool of  FIG. 1 ;  
         [0009]      FIG. 3  is a cross-sectional view of the distal end of the filling tool of the invention showing bone material therewithin;  
         [0010]      FIG. 4  is a cross-sectional view of a bag to be filled showing the filling tool inserted into the bag opening;  
         [0011]      FIG. 5  is a perspective view of a distal end of an alternate filling tool of the invention;  
         [0012]      FIG. 6  is a side elevational view of the distal end of the tool of  FIG. 5 ;  
         [0013]      FIG. 7  is a top view of the opening at the distal end of the tool of  FIG. 5 ;  
         [0014]      FIG. 8  is a representation of the effects of temperature change on the filled tubes of the invention showing a filled tube in cross-section;  
         [0015]      FIG. 9  is a perspective view of a graft insertion tool suitable for use with inserting a band;  
         [0016]      FIG. 10  is a side view of the tool shown in  FIG. 9 ;  
         [0017]      FIG. 11  is a top down view of the tool of  FIG. 9 ;  
         [0018]      FIG. 12  is a side view of the tool of  FIG. 9  seen dislocating the fibers of a band; and  
         [0019]      FIG. 13  is a top down cut away view of the tool of  FIG. 9  as may be seen during graft insertion. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]     U.S. Pat. Nos. 5,571,189 and 5,549,679 are incorporated herein by reference. They show an expandable fabric bag which is to be inflated within a reamed out disc space by introduction of bone replacement material through the bag opening. As shown in  FIG. 4 , bag  10  of the patents is a fabric bag having an opening  12 . The opening  12  may be closed off by any number of methods. It has been found that insertion of the bone graft material into the bag may result in low distraction forces and may allow the fill tube to be blown back out of the bag opening when fill pressure is increased.  
         [0021]     The bone replacement material might be one or more of the following, or any other biocompatible material judged to have the desired physiologic response: 
    A) Morselized bone graft, cortical, cancellous, or cortico-cancellous, including autograft, allograft, or xenograft.     B) Any bone graft substitute or combination of bone graft substitutes, or combinations of bone graft and bone graft substitutes, or bone inducing substances, including but not limited to:    
 
         [0024]     Hydroxyapatite  
         [0025]     Bone morphogenic protein  
         [0026]     Calcified or decalcified bone derivative 
    C) Bone cements, such as ceramic and polymethylmethacrylate bone cements.    
 
         [0028]     The inventive fill tool  18  of  FIGS. 1-4  involves an elongated hollow tube  20  having a proximal end which is attached to a source of bone replacement material under pressure and a distal end  22  which includes the inventive features. As seen, the distal end  22  includes a deflector  24  which deflects flow of bone replacement material  26  out the side openings  30 ,  32  at an angle. One or more side openings  30 ,  32  may be present. The deflector  24  as shown in  FIG. 3  includes two side openings  30 ,  32  and the deflector is basically a tapered wedge which diverts flow outwardly to both sides. If only a single side opening is present, the deflector would deflect all flow to that side opening.  
         [0029]     As shown in  FIG. 4 , a single side opening  30  allows deflection of the bone replacement material into the expandable fabric bag  10  at an angle relative to the longitudinal axis of the filling tool such that internal forces building up within the bag do not cause the tool  18  to be ejected out along its longitudinal axis. Rather, any forces inside the bag are exerted back on the sides of the tool  18  against the side walls of the bag, preventing ejection of the tool  18  and allowing more pressure to be applied within the bag  10 .  
         [0030]     The forces during filling provided by the device are perpendicular to the axis of the tube to stop tear through, to prevent the tube from being pushed out during filling, to direct the flow to get the distraction desired and to reduce the overall forces required. A straight tube with an open end has no distraction forces perpendicular to the tube and merely lays a long column of replacement material that needs to buckle before more material can be extruded from the tube. The inventive device breaks up the column of replacement material in the tube by cantilever forces. A straight tube with an open end creates a rigid bar of replacement material that can break a containment bag or damage body structures they press against or cause the tube to be ejected from the neck of the bag or body cavity opening.  
         [0031]      FIGS. 5-7  show an alternative fill tube  40  having a single side opening  30 . As shown, the apex  42  is partially closed and the tube is angled toward the apex  42  to help guide and direct the material within the tube out to the side opening  30 .  
         [0032]     Tests show a dramatic increase in distraction forces for filling a bag with a tool of the invention in comparison to a fill tool which has an opening in line with its longitudinal axis. Since bone replacement material tends to become quite rigid under pressure, injection of bone replacement material into the bag at an angle relative to the longitudinal axis of the fill tube allows the bag to inflate and create forces which are not directed to eject the fill tool.  
         [0033]     If the internal diameter of the tube is D, the length of the side opening  30  is preferably between about 1½ to 3D. If the side opening  30  length is only 1D or smaller, harder pushing is required and packing of the material may result in the tube. The distal end of the tube  40  towards the apex  42  is also preferably angled to direct the flow and to break down any material that has packed back into more discrete pieces. The end adjacent the apex  42  of the tool may be completely closed or open up to ½D which still provides good side direction of product.  
         [0034]      FIG. 8  depicts a filled tube  20 ,  40  of the invention which has been filled with bone replacement material  26 . The invention contemplates cooling the tubes prior to use and warming them just prior to use such that expansion of the metal tube causes expansion to help decrease friction to the tube. In addition, if thawing occurs at the metal interface with the bone replacement material, a liquid layer will be formed to lubricate the replacement material within the tube. This allows easier egress of material within the tube.  
         [0035]     As may be seen in  FIG. 9 , the tool may also be used to insert a single walled band into a cavity formed in a spinal disc as disclosed in co-pending U.S. patent application entitled Expandable Tube for Spinal Stabilization, to Kuslich, and is filed concurrently herewith. The entire contents of the aforementioned concurrently filed application is incorporated herein by reference. As shown in  FIG. 12  and  13 , the band  50  is shown with a graft insertion tool  60  being inserted into the interior  52  of the band  50  by passing through one of the spaces or pores  54 . The shape of the tool  60  as may best be seen in  FIGS. 9-11  is essentially an elongate shaft  62  having a tapered or pointed distal end  64 .  
         [0036]     The tapered distal end  64  of the tool  60  is sized to enlarge the opening  54  to allow passage of the tool  60  into the interior  52  by pushing aside the various fibers  56  as may best be seen in  FIG. 12 . The fibers  56  are disposed to open the pore  54  from its nominal diameter of 0.25 to 5 mm to an enlarged opening sufficient to allow passage of a portion of the shaft  62  therethrough  
         [0037]     The extent of tool penetration into the band interior  52  must be sufficient to allow the side opening  66  to be fully contained within the band interior  52 . The tool  60  may include more than one side opening  66 .  
         [0038]     As shown in  FIG. 13 , the side opening  66  allows insertion of the bone graft material into the band interior  52 . The tool  60  includes a means for pushing graft material from within the shaft  62 , through the side opening  66  and into the band interior  52 .  
         [0039]     While this invention may be embodied in many different forms, there are shown in the drawings and described in detail herein specific preferred embodiments of the invention. The present disclosure is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated. For example, the inventive device and methods may be used whenever replacement material needs to be directed into a defined location and not just when a bag is to be filled within a disc cavity.  
         [0040]     This completes the description of the preferred and alternate embodiments of the invention. Those skilled in the art may recognize other equivalents to the specific embodiment described herein which equivalents are intended to be encompassed by the claims attached hereto.