having discussed the problems associated with post - operative partial discectomy with respect to fig1 a - 1c , reference will now be made to fig2 , which illustrates a preferred embodiment of the invention , wherein a device in the form of a stent 202 is used to occlude a defect 204 in a human disc , as shown . in this preferred embodiment , the device is composed of a flexible material , which may be cloth , polymeric or metallic . for reasons discussed below , a titanium mesh screen is preferred with respect to this embodiment of the invention . a flexible device is also preferred because the surgeon is presented with a very small working area . the incision through the skin is typically on the order of 1 to 1 . 5 inches in length , and the space at the disc level is approximately 1 centimeter on the side . as a consequence , the inventive device and the tools associated with insertion and fixation described below must be sufficiently narrow to fit within these confines . as shown in fig3 a - 3c , a flexible screen enables the device to be collapsed into an elongated form 302 , which , in - turn , facilitates introduction into a sheath 304 associated with insertion . a push rod 306 may then be introduced into the other end of the sheath 304 , and either the sheath pulled backwardly or the push rod pushed forwardly , or both , resulting in the shape shown in fig3 c , now suitable for implantation . to further assist in fixation with respect to the surrounding physiology , anchors 402 may be provided around a peripheral edge of the device , as shown in fig4 a . fig4 b shows an end view of the device of fig4 a , and fig5 illustrates the device with anchors generally at 500 , being fixed relative to a defective disc 504 bounded by upper and lower vertebrae at 502 . it will be apparent to those of skill that each of the devices disclosed herein may be made in different sizes , having varying peripheral dimensions , for example , to match differently sized defects . fig6 a and 6b illustrate how a distracting tool 602 may be used to force the anchors into the vertebrae . that is , having introduced the device into the approximate area , the tool 602 , having a forward shape corresponding to that of the expanded mesh shape , may be introduced therein , as shown in fig6 b . with force being applied to the tool 602 , the anchors may be permanently set into the surrounding bone / tissue . fig7 a illustrates an alternative approach to fixation , wherein one or more notches 700 may be made into the upper and lower vertebra , preferably through the use of an air - operated drill 704 shown in fig7 b , having a cutting wheel 702 adapted for such a purpose . fig7 c illustrates the way in which a flexible body 708 may be retained by the notches 700 described with respect to fig7 a and 7b . fig8 illustrates an alternative orientation of a flexible body having a convex surface facing outwardly with respect to the wall of the disc being repaired . fig9 a illustrates a further alternative associated with fixation wherein anchors 902 which penetrate the outer wall of the disc 905 are used to hold a flexible repair device 900 in place as shown . fig9 b shows yet a further alternative fixation modality , wherein disc anchors 906 , which do not penetrate the outer wall of the disc , but , rather remain there within , are used to hold the device 904 in place . fig9 c illustrates yet a further alternative mode of fixation , wherein anchors 908 are used to hold the device to upper and lower vertebra , as opposed to the anchors of fig9 a and 9b , which are used with respect to the disc . regardless of whether fixation takes place within the vertebra or within the disc , it will be noted that according to the preferred embodiment of the invention , both the device used to occlude the defect and the fixation means are sufficiently flexible that the defect remains occluded with movement of the spine , that is , with the patient leaning forwardly and backwardly which will tend to change the spacing between the upper and lower vertebra . fig1 illustrates yet a different embodiment of the invention wherein , as opposed to a piece of flexible material or mesh , a resilient plug 1002 is instead utilized to occlude the disc defect . as in the case of the flexible sheath - like embodiments described above , such plugs are preferably offered in different sizes to correlate with differently sized defects . in terms of a preferred material , a device according to the invention will therefore remain sufficiently flexible during movement while being capable of exerting continuous outward forces and withstanding repetitive compression and distraction of millions of cycles . the device would , therefore , preferably be made of a material that has these characteristics , while , additionally being radio - opaque for x - ray imaging , without producing too many unwanted artifacts in magnetic resonance imaging . a wire mesh of titanium is therefore preferable , since this has the proper x - ray / mri characteristics while exhibiting the requisite flexibility for the cyclic flexion and extension . with respect to the embodiment of fig1 , a resilient , rubber - like material may be used to occlude the defect as shown in the drawing from a side - view perspective . the invention is not limited in the sense that any conformable device may be used with a first shape permitting the device to be introduced into the defective area and a second shape wherein the device includes a defect . as shown in fig1 a - 11c , for example , a wire 1102 having a “ memory effect ” may be used , preferably having a final diameter which is larger than void 1104 . fig1 b shows the coil 1102 in cross - section between upper and lower vertebra . preferably , this embodiment would use a metal wire that may be straightened , but retain the memory of its coiled shape . as such , the apparatus of fig1 c may be used to introduce the wire in straightened form 1108 with a plunger 1110 , such that as the wire exits at 1106 , it returns to its memorized state of a coil ( or alternative second shape operative to include the defect ). as yet a different alternative mode of introduction , a material may be injected into the disc in liquid form , then allowed to hardened into a size sufficient to occlude the annular hole . as shown in fig1 , material 1202 may be injected into the void of the disc space using a plunger 1204 inserted into a tube 1206 . upon introduction in this manner , the liquid would then solidify , forming a resilient plug . various materials may be utilized for this purpose , including various polymers which are caused to solidify by various means , including thermal or optical activation , or chemical reaction as part of multi - part compounds . a preferred material with respect to this embodiment would be a hydrogel . hydrogels may be placed into the disc in a dehydrated state , and , once inside the disc , they imbibe water . after hydration , hydrogels have the same biomechanical properties as a natural nucleus and , in addition , as the hydrogels swell , they become too large to extrude back through the annular window . u . s . pat . nos . 5 , 047 , 055 and 5 , 192 , 326 provide a listing of hydrogels , certain of which are applicable to this invention . an elastomer may be used as an alternative to a hydrogel or other material . a number of elastomers may be suited to the invention , including a silicon elastomer , which comprises a cured dimethylsiloxane polymer and hexsyn , having a composition of one - hexane with three to five percent methylhexaiene . a preformed elastomer may be inserted into the inclusion upon curing or , alternatively , as discussed with reference to fig1 , may be injected into the disc space and liquid form . chemicals may be added to accelerate curing , as discussed above , or , a hot or cold probe , or uv light may be introduced to facilitate or accelerate the curing process . preferably , such materials would include a radio - opaque additive which would enable the physician to verify the position of the implant with an x - ray . ideally , the radio - opaque additive would not change the mechanical properties of the gel or elastomer , and would ideally incorporate contrast throughout to enhance detail . now making to fig1 and 14 , fig1 a and 13b illustrate an alternative type of stent having leaves or other appendages that may be folded into a compact state for insertion , fig1 a , and which expand , through memory affect , for example , to a state such as that shown in fig1 b . a stent such as this , as well as other devices disclosed herein such as the coil form of fig1 , may be used in conjunction with a gel or other void - filling material as described above . as shown in fig1 a , a stent 1402 of the type shown with respect to fig1 b , may be introduced into the void , after which the remaining volume of the void may be filled with a material 1404 which solidifies into a resilient material . fig1 b is a side - view drawing of the embodiment of fig1 a . an expandable stent of this kind may be incorporated into the elastomer or other resilient material to help prevent migration of the prosthesis through the annular hole . in contrast to embodiments of the invention wherein a stent is used independently , in this particular embodiment , the stent would preferably not touch vertebra , since it would be surrounded entirely by the elastomer or other gel material . fig1 a - 15e illustrate various alternative embodiments according to the invention wherein a patch material is used inside , outside , or partially inside and outside of a defect to be blocked . fig1 a illustrates a flat patch attached onto the outside of the disc . fig1 b illustrates a patch attached on the outside but wherein a central portion extends inwardly into the void . fig1 c illustrates a patch disposed within the disc to block the defect . fig1 d illustrates how a patch may be anchored to the bone above and below the disc , and fig1 e illustrates how the patch may be anchored to the disc itself . the patch material be a fiber , including natural materials , whether human , non - human or synthetic ; an elastomer ; plastic ; or metal . if a fiber material is used , it may be selected so as to promote tissue in - growth . growth of a patient &# 39 ; s tissue into the material would assure a more permanent closure of the annular window . the patch may be attached within appropriate means , including stitches , staples , glue , screws or other special anchors . in addition to the use of patches attached with sutures , staples or other materials , the annular defect may be closed with staples or other devices which attach to the annulus without the need for patch material . for example , as shown in fig1 a , darts 1602 may be inserted through the wall of the annulus 1604 , then linked with sutures 1606 , preferably in woven or criss - crossed fashion , as shown in fig1 b . as an alternative , appropriately shaped darts 1702 may be criss - crossed or otherwise interlocked to the close the annular hole , as shown in the top - view cross - section drawing of fig1 a or a side - view of fig1 b . the use of flexible stents as described elsewhere herein may take on other forms , as shown in fig1 a - 18d . the device of fig1 a , for example , preferably includes a body 1802 , preferably including a blunt anterior end to prevent penetration of the anterior annulus , and outer spikes 1806 , preferably having different lengths , as best seen in the on - axis view of fig1 b . such a stent configuration may provide more areas of contact with the vertebral end plates , thereby decreasing the chances of stent extrusion . as shown in fig1 c , the longer spikes 1806 are configured to bend during insertion , thereby preventing posterior extrusion . the shorter spikes , 1806 ′, are sized so as not to engage the vertebrae , and therefore may be made thicker to prevent deflection by disc material . as an option , the shorter spikes 1806 ′ may also be angled in the opposite direction as compared to the longer spikes 1806 to resist migration of the disc material . as yet a further option , the longer spikes may vary in length on the same stent so as to be conformal to the vertebral end plate concavity . as shown in fig1 d , multiple spike stents of this kind may be inserted so as to interlock with one another , thereby preventing migration of the group . as shown in fig1 a - 19c , shapes other than spiked stents may be used in interlocking fashion . in fig1 a , a first piece 1902 is inserted having a removable handle 1904 , after which pieces 1902 ′ and 1902 ″ are inserted , each having their own removable handles , as shown . in fig1 b , the handles are pulled , so as to bring the pieces together , and in fig1 c , the handles are removed , and the pieces are either snapped together or , through the use of suitable material , sutured into place . fig2 a - 20e illustrate a different configuration of this kind , wherein a body 2002 having anchor or wire - receiving apertures 2004 is inserted into the annular hole , as shown in fig2 b , at which time a wire 2006 is inserted through the body 2002 as shown in fig2 c . as shown in fig2 d , the wire is installed sufficient to lock one portion of the body into place , and this is followed with a wire on the opposite side , thereby holding the body 2002 in a stabilized manner . it will be appreciated that although multiple wires or anchors are used in this configuration , bodies configured to receive more or fewer wires or anchors are also anticipated by this basic idea . fig2 a - 21c illustrate a different alternative , wherein wires 2102 each having a stop 2104 are first inserted through the annular window , after which blocking beads having snap - in side configurations are journaled onto the wire across the annular hole , as shown in fig2 b . fig2 c illustrates how , having locked multiple beads onto the wire , the defect is affectively occluded . fig2 a and 22b illustrate the use of a removable dam component . as shown in fig2 a , bodies 2202 , each having removable handles 2204 , are first inserted on the side portions of the defect , each member 2202 including slots , grooves or apertures 2206 , configured to receive a dam 2210 , which may be made of a rigid or pliable material , depending upon vertebral position , the size of the defect , and other factors . fig2 b illustrates the dam 2210 locked in position . certain of the following embodiments illustrate how the invention permits the use of a flexible device which allows movement between the vertebrae yet blocks extrusion of nucleus through an annular hole or defect . in fig2 a , for example , a flexible element 2302 is tacked into position on the upper vertebrae , as perhaps best seen in fig2 d , though it should be apparent that a fixation to the lower vertebrae may also be used . fig2 b illustrates how , once the member 2302 is fastened in place , it may flex under compression , but return to a more elongated shape in distraction , as shown in fig2 c . the blocking element 2302 may be made from various materials , including shape - memory materials , so long as it performs the function as described herein . fig2 a illustrates a different configuration , which is tacked to both the upper and lower vertebrae , and fig2 b and 24c show how the device performs in compression and distraction , respectively . since devices attached to both the upper and lower vertebrae need not automatically assume a memorized shape , alternative materials may preferably be used , including biocompatible rubbers and other pliable membranes . it is important that the flexible member not be too redundant or stretched so as to compress the nerve , as shown in fig2 . fig2 illustrates an alternative z - shaped installation configuration . as an alternative to inherently flexible materials which occlude a defect while accommodating compression and distraction , interleaving members may alternatively be used , as shown in fig2 - 28 . fig2 a is a view from an oblique perspective , showing how upper and lower plate 2702 and 2704 of any suitable shape , may be held together with springs 2706 , or other resilient material , between which there is supported interleaving tines 2708 . as better seen in fig2 b , the springs 2706 allow the upper and lower plates 2702 and 2704 to move toward and away from one another , but at all times , tines 2708 remain interleaving , thereby serving to block a defect . fig2 a and 28b illustrate the way in which interleaving members or tines are preferably inserted directly to vertebrae . since each member overlaps with the next , such tines are preferably installed from front to back ( or back to front , as the case may be ), utilizing a tool such as 2810 , as shown in fig2 b . the instrument 2810 forces each tack into one vertebrae at a time by distracting against the other vertebrae , thereby applying pressure as the jaws are forced apart , driving the tack into the appropriate vertebrae . the tack may be held into place on the instrument by a friction fit , and may include a barbed end so as not to pull out following insertion . as a further alternative configuration , a collapsed bag may be placed into the disc space , then filled with a gas , liquid or gel once in position . the bag may be empty , or may contain a stent or expanding shape to assist with formation . in the case of a gel , silicon may be introduced so as to polymerized or solidify . as shown in fig2 a and 29b , the use of a non - contained silicon vessel may be used , but , under distraction , may remain in contact with the vertebrae , thereby increasing the likelihood of a reaction to silicone . the invention therefore preferably utilizes a contain structure in the case of a silicon filler , as shown in fig3 a , such that , upon distraction , the vessel remains essentially the same shape , thereby minimizing vertebral contact . it is noted that , depending upon the configuration , that the invention may make use of a bioabsorbable materials , that is , materials which dissolve in the body after a predetermined period of time . for example , if darts such as those shown in fig1 and 17 are used , they may bioabsorb following sufficient time for the in - growth of recipient tissue sufficient to occlude the defect independently . any of the other configurations described herein which might not require certain components in time may also take advantage of bioabsorbable materials . furthermore , although the invention has been described in relation to preventing the release of natural disc materials , the invention may also be used to retain bone graft for fusion ; therapeutic materials including cultured disc cells , glycosaminoglycans , and so forth ; and artificial disc replacement materials . disc fusions are generally performed for degenerative disc disease , spondylolysis ( a stress fracture through the vertebra ), spondylolisthesis ( slippage of one vertebra on another ), arthritis of the facet joints , spinal fractures , spinal tumors , recurrent disc herniations , and spinal instability . the procedure attempts to eliminate motion between vertebra to decrease a patient &# 39 ; s pain and / or prevent future problems at the intervertebral level . devices such as spinal cages are generally used in conjunction with such procedures to maintain the separation between the vertebrae until fusion occurs . some surgeons believe that cages are not necessary to maintain the separation , and instead use pedicle screws or hooks and rods to perform this function . whether or not a cage is used , bone graft is generally introduced through a hole formed in the disc space to achieve an interbody fusion . unfortunately , bone material placed into the disc space can extrude through the hole used for insertion . bone graft extruded through a hole in the posterior portion of the disc may cause nerve root impingement . the procedure to fuse vertebra across the disc space from a posterior approach is known as a plif ( posterior lumbar interbody fusion ). bone can also be placed into the disc space from an anterior approach alif ( anterior lumbar interbody fusion ). extruded bone from an anterior approach would not lead to nerve impingement but could decrease the likelihood of a successful fusion by decreasing the volume of bone graft . the present invention may be used to prevent the loss of the bone graft material associated with fusion techniques , whether or not a cage is used . in this particular regard , however , some of the devices disclosed herein may be more suitable than others . generally speaking , since the goal is not to preserve disc function and motion , the stent , plug , and patch embodiments may be more appropriate . although the plug embodiment would be a good choice when there is ample room in the spinal canal to allow insertion , the expandable stent design would be beneficial when plug insertion risks nerve injury . conversely , since the goal is to maximize the amount of bone inserted into the disc space , the embodiments using hydrogels and elastomers might not be optimum , since such materials may occupy too much space in some circumstances . the preferred choice of materials may also be changed since motion is not being maintained . materials and designs with shape memory may be beneficial . as another example , the polymer plug embodiment may changed to a metal such as titanium . a metal plug may be fabricated with threads and screwed into place , as shown in fig3 a , or the device may feature ridges and be impacted into place ( fig3 b ). as shown in fig3 c , the ridges may also be asymmetric to resist posterior migration . in all cases , the teeth , screw threads or ridges would extent at least partially into the adjacent vertebra for secure purchase , as depicted in fig3 d . such plugs may also be positioned bilaterally , that is , with two per level , as shown in fig3 .
methods and apparatus for treating disc herniation provide a conformable device which assumes a first shape associated with insertion and a second shape or expanded shape to occlude the defect which typically follows partial discectomy . the device may take different forms according to the invention , including patches size to cover the defect or plugs adapted to fill the defect . in a preferred embodiment , however , the device is a gel or other liquid or semi - liquid which solidifies to occlude the defect from within the body of the disc itself . in another preferred embodiment , a mesh screen is collapsed into an elongated form for the purposes of insertion , thereby minimizing the size of the requisite incision while avoiding delicate surrounding nerves . such a configuration also permits the use of instrumentation to install the device , including , for example , a hollow tube or sheath adapted to hold the collapsed screen , and a push rod to expel the collapsed device out of the sheath for use in occluding the disc defect . a device according to the invention may further include one or more anchors to assist in permanently affixing the device with respect to the defect .