for the purposes of promoting an understanding of the principles of the invention , reference will now be made to the embodiments illustrated in the drawings and 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 present invention contemplates a procedure and device that is implemented following removal of a portion or substantially all of the natural nucleus pulposus of an intervertebral disc . one important purpose of the invention is to maintain the proper disc height during the introduction of a biomaterial that is intended to replace the removed nuclear material . removal of disc material can be accomplished chemically , such as by the use of chymopapain . however , the more common approach is by discectomy , which can be conducted as an open surgical procedure , via microscope - assisted visualization , or through percutaneous access . a typical percutaneous discectomy procedure is illustrated in fig2 - 4 . in the first step , a guide wire g is directed into an affected disc d between two vertebrae , such as the l 2 and l 3 lumbar vertebrae . as shown in fig3 , the guide wire g penetrates the annulus fibrosus a and the nucleus pulposus n , and it preferably anchored at opposite sides of the annulus a . the guide wire g can be positioned and placed under indirect vision , such as fluoroscopy , or stereotactically , or using other known procedures for properly orienting the guide wire within the spinal disc d . the procedure shown in the figures utilizes a posterior approach , which is preferable for implementation of the present invention . of course , other approaches may be utilized for the discectomy in accordance with known surgical procedures . in addition , the access location may be dictated by the location of a fissure or herniation of the disc . a trephine t is advanced over the guide wire and driven through the annulus a , thereby forming a portal into the disc nucleus . as shown in fig4 , a tissue removal device r can be advanced through the trephine t or through a working channel cannula aligned with the disc portal . the device r can then be used to remove all or part of the nucleus n of the disc d . as depicted in dashed lines in fig4 , a second trephine t ′ can be used to create a second annular portal to facilitate complete removal of the nucleus pulposus of the disc . the tissue removal device r can be of a variety of types , such as a rongeur , tissue morcellator , rotary and / or reciprocating vacuum - assisted cutter , and even a chemical introducer to direct a chemical such as chymopapain into the nuclear space . removal of the nucleus leaves a cavity c ( see fig5 ) surrounded by the substantially intact annulus a the present invention contemplates the introduction of a biomaterial into the disc cavity c that is capable or restoring disc height and preferably substantially normal disc function . for instance , any of the biomaterials discussed above can fill the newly formed cavity . in accordance with the preferred embodiment , the biomaterial is a fluid with an appropriate flowability and / or viscosity . in particular , the biomaterial must have sufficient flowability to permit relatively easy introduction into the disc cavity c , but with sufficient viscosity to hold its shape within the disc . since the material being used to fill the disc cavity c is a fluid , the present invention provides means for holding a proper disc height as the material flows into the cavity , to thereby ensure that the cavity is filled — i . e ., that the volume of implant biomaterial is the same as the volume of nucleus pulposus removed in the discectomy . moreover , the methods and devices of the invention provide a means for maintaining the cavity volume as the biomaterial transforms to its solid state . thus , in accordance with one embodiment of the invention , a cannulated distractor 10 is provided as shown in fig5 - 8 . the distractor 10 includes a distal end 12 that extends into the disc cavity c and a proximal end 14 that is configured to engage a device for injecting the biomaterial into the disc space . the distractor 10 includes a cannula 11 that terminates in a distraction tip 18 at the distal end of the device . a lumen 16 is defined along the entire length of the device from the proximal end 14 to the and through the distraction tip 18 . the distraction tip 18 is sized to extend through the portal formed in the disc annulus a ( see fig3 ). the distractor 10 can include a shoulder 20 proximal to the distraction tip 18 , in which the shoulder is sized to prevent passage through the annular portal . the shoulder 20 can operate to limit the distance that the distraction tip 18 extends into the disc cavity c . the distractor 10 can be provided with means for temporarily fixing the distractor in position or supporting the distractor on the adjacent vertebrae . as shown in fig7 , the distraction tip 18 is intended to be inserted through the annular portal and is configured to restore the appropriate intradiscal height in the cavity c . thus , in one embodiment , the distraction tip 18 can include a tapered leading portion 24 . this leading portion 24 can be introduced into the cavity c and as the tip is advanced further into the cavity the leading portion will gradually distract the adjacent vertebrae as the leading portion 24 bears against the disc endplates e . in a specific embodiment , the tapered portion 24 can be substantially bullet - shaped , as shown in fig8 . with this configuration , the distraction tip 18 can have any rotational orientation when the tip is inserted through the annular portal . alternatively , the distraction tip can be configured like the tip 40 shown in fig9 . with this embodiment , the tip includes opposing generally flat sides 50 and intermediate edges 52 of the wedge portion 42 . the tip 40 can be introduced into the disc space with the flat sides 50 of the wedge facing the disc endplates e . once the tip is fully within the disc cavity c , the tip can be rotated so that the edges 52 contact and distract the endplates . the edges 52 themselves can be wedge - shaped , having a greater width at their proximal end than at their distal end . returning to fig6 - 8 , in accordance with one feature of the invention , the distraction tip 18 includes a number of side orifices 30 and an end orifice 32 that all communicate with the central lumen 16 . as depicted in fig7 , the orifices 30 , 32 provide an exit path for fluid injected through the lumen 16 . preferably , the orifices are oriented to be unobstructed by the vertebral endplates e . the distraction tip 40 shown in fig9 is also provided with side orifices 46 in the flat sides 50 and an end orifice 48 . with this embodiment , the edges 52 need not include orifice ( s ) because the edges will be occluded by contact the endplates . since fluid is intended for introduction through the distraction tip 30 , it is preferable that some feature be provided to ensure a substantially fluid - tight seal at the entrance to the disc cavity c through the annular portal . thus , in one embodiment of the invention , the distraction tip 30 can include annular rings 26 that are intended to bear against the disc endplates e and / or the disc annulus a in a sealing relationship . the rings 26 can be integral with the distraction tip 30 , or can be separate components mounted on the distraction tip , such as in the form of elastomeric seal rings . the seal rings can be mounted within annular grooves formed in the distraction tip . the distractor 10 includes a fitting 36 defined at the proximal end 14 of the cannula 11 . the fitting 36 provides means for making a fluid - tight connection with a device adapted to inject the biomaterial into the disc . one exemplary device 70 is shown in fig1 . the injector 70 includes a chamber 72 for storage of the biomaterial . in some cases , the chamber 72 may constitute multiple chambers where the injectable biomaterial is obtained by mixing various constituent materials . for instance , certain materials may be curable in situ and may require combining a curing agent with a base material . to facilitate mixing of the biomaterial constituents , the injector 70 can include a mixing chamber 74 . a manual control 76 can be provided that forces the contents of the chamber 72 into the mixing chamber 74 . alternatively , the injector 70 can incorporate a mechanism that drives the fluid from the injector under pressure , such as a syringe or a pump . the injector 70 includes a fitting 80 that is configured for fluid - tight engagement with the fitting 36 of the cannulated distractor 10 . in a preferred embodiment , the two fittings 36 , 80 represent mating components of a luer ® fitting . the injector can include a nozzle 78 that extends into the cannula 11 , or more specifically into the lumen 16 , when the injector 70 is engaged to the cannulated distractor . a grip 82 can be provided to allow manual stabilization of the injector . as explained above , the cannulated distractor 10 of the present invention may be utilized after a discectomy procedure . for purposes of illustration , it has been assumed that a total discectomy has been performed in which substantially all of the nucleus pulposus has been removed , leaving a disc cavity c as shown in fig5 . of course , the principles of the invention can apply equally well where only a portion of the disc nucleus has been removed through a partial discectomy . if a bilateral approach has been used ( as represented by the first and second trephines t and t ′), one of the annular portals can be sealed with a material compatible to the disc annulus fibrosus . when the nucleus has been cleared , the guide wire g can be repositioned within the disc d , again preferably using known guidance and positioning instruments and techniques . the cannulated distractor 10 can then be advanced over the guide wire until the distraction tip 18 is properly situated within the nuclear cavity c . preferably , the proper depth for the distraction tip 18 can be determined by contact of the shoulder 20 with the outer annulus a , or by contact of an associated depth feature with the adjacent vertebral bodies . with the distraction tip 18 , the tapered portion 24 gradually separates the adjacent vertebral endplates e as the distraction tip is driven further into the disc space . a mallet , impactor or other suitable driver can be used to push the tapered portion 24 into position against the natural tension of the disc annulus . it is understood that the goal of this step is to fully distract the intervertebral space to a proper disc height for the particular spinal level . for instance , for the l 2 - l 3 disc space , the appropriate disc height may be 13 - 15 mm , so that the distraction tip is positioned within the cavity c to achieve this amount of distraction . as shown in fig5 , preferably only one cannulated distractor 10 is utilized , since the distraction tip 18 necessarily occupies a certain portion of the volume of the cavity c . however , a second cannulated distractor and associated distraction tip may be necessary ( such as through a second annular portal as shown in fig4 ) to achieve the proper disc height . it should be understood that the process thus far would be similar for the distraction tip 40 . however , unlike the tapered distraction tip 18 , the distraction tip 40 requires an additional step to distract the disc space . specifically , the distraction tip 40 is initially inserted with its flat sides 50 facing the endplates e . the tip must then be rotated until the edges 52 bear against and support the endplates . the flat sides 50 can include an angled transition to the edges , or the edges 52 can be rounded to facilitate the distraction as the distraction tip is rotated in situ . when the distraction tip , such as tip 10 , is inserted to its proper depth within the disc cavity c , the annular portal is sealed , whether by contact with the shoulder 20 , or by engagement of the rings 26 with the endplates e or the interior of the annular portal . at this point , the biomaterial fluid can be injected into the cannulated distractor , and specifically into the lumen 16 . to accomplish this step , the injector , such as injector 70 , can be mated with the fitting 36 at the proximal end 14 of the cannulated distractor . optimally , the guide wire g is removed and the fitting 80 of the injector engages the fitting 36 . the nozzle 78 extends into the lumen 16 . the nozzle can be sized so that the exit end of the nozzle is near or within the distraction tip 18 . at this point , the injector 70 can be actuated in accordance with its construction so that the biomaterial fluid is displaced from the injector and into the lumen 16 . the biomaterial exits through the orifices 30 , 32 in the distraction tip 18 to fill the cavity c . the orifices 30 , 32 are preferably positioned and sized to achieve complete and rapid dispersion of the biomaterial throughout the cavity . again , the goal of this step of the process is to completely fill the entire volume of the cavity , or to replace the entire volume of nucleus pulposus removed during the discectomy . where the fluid biomaterial is an in situ curable or settable material , time may also be of the essence to ensure a homogeneous mass once the material is completely cured . it should be apparent that the distraction tip 18 , 40 maintains the proper disc height while the biomaterial is injected . the tip can be retained in position until the injected material cures or sets . once the material has sufficiently cured , the distraction tip 18 , 40 can be removed . since the distraction tip occupies a certain volume , additional biomaterial can be injected through the tip as it is being withdrawn , if required , thereby filling the gap left by the tip . in certain embodiments , the distraction tip 18 can be a modular and removable from the cannula 11 , as shown in fig8 . thus , the tip 18 and cannula 11 can be provided with a removable mating element 19 , such as a press - fit ( as shown in fig9 ) or a threaded or luer ® type fitting ( not shown ) as would occur to a person of skill in this art . a removable distraction tip can serve several purposes . in one purpose , the injected biomaterial may require a lengthy curing time . while the material is curing , it is of course necessary to keep the distraction tip in position to maintain the proper disc height . however , it may not be necessary to retain the other components of the system in position , such as the injector 70 and cannula 11 . a modular distraction tip allows the cannula 11 to be removed while the tip remains in position , acting as a disc spacer while the biomaterial cures . in another purpose , a number of differently sized tips can be mounted to a commonly sized cannula . each patient has a different spinal anatomy , which means the appropriate disc height at a given spinal level may vary between patients . moreover , the disc height can vary with spinal level . thus , a plurality of differently sized distraction tips 18 can be provided to ensure proper spacing across the spinal disc d . another purpose behind a removable distraction tip 18 is achieved by embodiments in which the tip is formed of a biocompatible material that allows the tip to remain resident within the disc space . in this embodiment , the distraction tip material must be compatible with the biomaterial used to replace the natural nucleus . for instance , if the biomaterial is only intended to restore disc height , but not the natural biomechanical properties of the natural nucleus , then the material of the distraction tip 18 may provide a generally rigid scaffolding . on the other hand , and most preferably , the injected biomaterial is intended to emulate the biomechanical characteristics of the disc to allow the spinal segment to operate as close to a normal spinal segment as possible . in this instance , a rigid scaffold would of course frustrate the normal flexion , compression and torsional responses of the disc . thus , the distraction tip 18 in embodiments where the tip is left in situ can be formed of a biodegradable or bioresorbable material that absorbs into the matrix of the cured biomaterial forming the disc nucleus prosthesis . whether the distraction tip is removed or remains within the disc space , it is preferable that the tip occupy as little volume as possible . on the other hand , the distraction tip must be sufficiently strong to sustain the compression loads that it will face while distracting adjacent vertebrae and holding the disc space height while the injected biomaterial cures . in the specific embodiments shown in fig5 and 7 , the distraction tip 18 is shown traversing across a substantial portion of the nuclear cavity c . alternatively , the distraction tip can have a reduced length from the shoulder 20 so that the tip extends only partially into the cavity . distraction of the disc space can be abetted by certain positions of the patient on the operating table where , for instance , the anterior aspect of the disc space is naturally distracted by the position of the spine . proper distraction of the disc space may be better accommodated by an anterior approach , rather than the posterior approach shown in fig5 and 7 . in alternative embodiments , the distraction tip can assume a wide range of geometries , some dictated by the annular portal formed during the discectomy procedure . in the embodiment of fig5 - 8 , a circular annular portal has bee created and a circular distraction tip 18 utilized to seal the portal . in some cases , a planar or wedge - shaped distraction tip , similar to the tip 40 shown in fig9 , can be utilized where the opening through the annulus has an area greater than the tip itself . in these cases , the extra space between the tip and the interior surface of the portal can provide an opening for a direct visualization instrument , or some other appropriate instrument . preferably , this approach is better suited where the biomaterial is not injected under pressure , such as cases where a gravity feed is employed ( see fig1 and associated discussion below ). in other cases , surgeons perform the discectomy through rectangular or cruciate portals in the disc annulus . a complementary shaped distraction tip can be utilized to conform to and fill the annular portal . for instance , the distraction tip can assume the configuration shown in fig1 - 14 . a cruciate - shaped tip 55 is shown in fig1 with a central lumen 56 communicating with a number of openings 56 . it is understood that the arms of the cruciate - shaped tip can have a thinner cross - section than shown in the figure , provided they are sufficiently strong to support the adjacent vertebrae in their proper distracted position . likewise , the openings 56 can be distributed in a variety of patterns through the hub and legs of the cruciate shape . an i - beam distraction tip 60 is shown in fig1 having a central lumen 61 communicating with a number of openings 62 . the distraction tip 63 in fig1 has a c shape and includes a lumen 64 and openings 65 . these two beam configurations provide sufficient support for the necessary distraction . again , the thickness of the arms of the beams can be reduced as necessary to minimize the cross - section of the distraction tip 60 , 63 . regardless of the overall configuration of the distraction tip , it is most preferable that volume of the tip within the nuclear cavity c be minimized . the bullet - shaped tip , such as tip 18 , may be less desirable from that standpoint , while the wedge type , such as tip 40 , may be preferable . in addition , regardless of the overall configuration , the distraction tip must communicate with the lumen 16 and must provide some means for discharge of the biomaterial fluid through the tip . in the illustrated embodiments , the distraction tips 18 , 40 include orifices 30 , 31 and 46 , 48 , respectively , that communicate with the corresponding lumens 16 , 44 . alternatively , the distraction tips can be in the form of an open scaffold or skeletal framework . again , the scaffold or framework must be sufficiently strong , especially in compression , to properly distract the disc space and hold the disc height for an appropriate length of time . in some embodiments , the distraction tip can be formed of a material having interconnected interstices , such as a porous material . the porous distraction tip can present a solid scaffold with a multitude of fluid flow paths through the material . the porous material can be a metal , such as a porous tantalum ; however , a porous polymer , such as polylactic acid , is preferred so that the scaffold does not obscure visualization of the disc space after the procedure is completed . in the procedures discussed above , the distraction tip has been described as providing an avenue for the injection of a biomaterial into the nuclear cavity c following a discectomy procedure . the distraction tips of the present invention serve equally well as a conduit for the introduction of other fluids to the disc space . for instance , the distraction tips can be used to inject a biomaterial such as the material disclosed in provisional application ser . no . 60 / 336 , 332 , entitled “ pretreatment of cartilaginous endplates prior to treatment of the intervertebral disc with an injectable biomaterial ”, mentioned above , the disclosure of which is incorporated herein by reference . this provisional application discloses materials for the pretreatment of the disc endplates , for instance , to improve the biological functioning of a degenerative disc . the cannulated distractors of the present invention , such as distractor 10 , can be initially used for the disc pretreatments disclosed in the above - mentioned provisional application . once the pretreatment has been completed , the cannulated distractor can then be used for the injection of the curable biomaterial . likewise , the present inventive cannulated distractor can be used for multiple fluid injections , including multiple injections to effect curing of a biomaterial within the nuclear cavity c . for instance , certain biomaterials may include a first constituent that is introduced into the disc space , followed by a second constituent or curing agent . the second constituent can initiate curing of the resulting composition . an alternative embodiment of the invention is depicted in fig1 . in this embodiment , a cannulated distractor 85 is provided that includes a generally frusto - conical distraction tip 86 and a shoulder 87 . the tip 86 is configured to act as a wedge to distract the disc space as the cannulated distractor 86 is impacted into the disc space . the shoulder 87 acts as a stop against the adjacent vertebral bodies to limit the distance that the tip is driven into the disc space . preferably , the distraction tip 86 has a length from the shoulder 87 to its distal end that is sufficient to span the length of the portal in the disc annulus a , but is limited in its extent into the nuclear cavity c . with this embodiment , the distraction tip 86 does not displace any significant volume within the cavity c . the cannulated distractor 85 defines a lumen 88 extending the entire length of the distractor . the lumen 88 is sized to receive an injection tube 94 therethrough . the injection tube 94 can include a fitting 96 for engaging an injection apparatus 98 . the fitting 96 can be of any suitable type , such as the luer ® fitting mentioned above . the injection apparatus can be similar to the injector 70 shown in fig1 , or can assume a variety of configurations for the introduction of a fluid into the disc cavity . in one embodiment of the invention , the biomaterial fluid is introduced into the cavity by way of gravity feed . in this instance , the injection apparatus 98 can be simply in the form of a reservoir with an atmospheric vent to allow the biomaterial to flow downward into the disc space by gravity alone . of course , the patient must be properly presented to accommodate gravity filling of the disc cavity c . in this embodiment , the cannulated distractor 85 operates as a support or guide for the injection tube 94 . the tube 94 can be in the form of a smooth tipped , relatively large gauge needle that is sized to accommodate optimum flow of the biomaterial into the disc space . the tube 94 can be introduced through and gradually withdrawn from the cannulated distractor 85 ( as indicated by the arrow in fig1 ) as the biomaterial flows into the cavity c . in addition , the diameter of the tube 94 can be sized relative to the diameter of the lumen 88 so that the discharge opening 95 of the tube 94 can be pivoted with a sweeping motion through the cavity c . this aspect of this embodiment facilitates complete direct filling of the disc cavity c with the biomaterial . where the cannulated distractor is used to introduce pre - treatment materials , such as those discussed above , this feature allows positioning of the discharge opening 95 to direct the pre - treatment materials where they are needed . in certain embodiments , the lumen 88 can be provided with a seal 89 , which can be in the form of an elastomeric seal ring . the seal 89 can form a fluid - tight seal around the injection tube 94 , which can be especially important where the biomaterial is injected under pressure . in addition , the seal 89 can operate as a form of joint to support the injection tube 94 as the discharge opening 95 is manipulated within the disc cavity . in another feature of the invention , the cannulated distractor can provide a vent for the discharge of excess biomaterial when the disc cavity c is full . the vent is particularly useful where the biomaterial is introduced under gravity feed . in one specific embodiment , a vent hole 92 is provided in the distractor 85 . when the disc cavity is full , the biomaterial will seep through the vent opening 92 , providing a direct visual indication that the cavity is full . preferably , the vent opening 92 includes a tube that projects away from the cannulated distractor 85 to improve the visibility of the vent in situ . alternatively , the vent can be formed by a difference in diameter between the injection tube 94 and the lumen 88 , and in the absence of the seal 89 . the vent 92 is well - suited to procedures involving gravity feed of the biomaterial into the disc space . however , the vent can also be useful where the material is fed under pressure . for example , the vent 92 can be maintained initially open as the biomaterial is injected into the cavity c through the injection tube 94 . when the cavity is completely full , biomaterial will seep from the vent 92 . as this point , the vent can be closed and additional biomaterial injected into the disc space to increase the pressure within the cavity c . the seeping through the vent provides an immediate indication that the cavity is full , and can provide a starting point for the introduction of a calibrated amount of additional biomaterial to achieve a proper cavity pressure . with each of the embodiments , once the biomaterial has cured and the cannulated distractor removed , the portal or portals in the disc annulus can be filled to prevent herniation of the newly formed prosthetic disc material . the annular portal can be sealed with any suitable material , such as fibrin glue , or a polymerizable material , or the like . the material used to seal the annulus should be sufficiently strong to remain intact as the intradiscal pressure is increased due to hydration or biomechanical movement of the spine . in accordance with certain embodiments , the cannulated distractors , and particularly the distraction tips , described above can be formed a variety of bio - compatible materials . as explained above the distraction tips must be sufficient strong to maintain proper distraction of the disc space until the biomaterial has been fully injected and cured , if necessary . in certain embodiments , the distraction tips are formed of a bio - compatible metal , such as stainless steel or titanium . in other embodiments , the distraction tips are formed of a polymer or plastic that is preferably radiolucent to permit visualization of the distraction tip in situ to verify the position of the component . 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 .
a system and method is provided for maintaining a proper intervertebral disc height during the replacement or augmentation of the spinal disc . in one embodiment , a cannulated distractor is used to distract the adjacent vertebrae and maintain a proper disc space height . the cannulated distractor is fluidly connected to a source of fluent material for injection into the disc space . the distraction includes a distraction tip resident within the disc space that includes a central lumen and a number of openings communicating with the lumen to dispense the fluent material within the disc space .