Abstract:
A prosthesis for implantation in a de-nucleated intervertebral disc includes a fiber ring-like layer which encloses a polymeric layer to create an annular space. The annular space is inflatable with an in-situ curable liquid polymer and forms an interior cavity. The annular space may be expanded uniformly or differentially to be tailored to the needs of a particular vertebral segment and to achieve optimal disc space width and angle, thereby stabilizing the segment while preserving normal motion of the vertebral segment. The interior cavity provides a void that allows inward deformation of the implant during weight bearing activities and bending. The prosthesis can be elastically deformed through axial elongation to a reduced profile to load into a delivery cannula using pulling techniques.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority of U.S. Provisional Patent Application No. 62/074,873, filed Nov. 4, 2014, which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    This application relates generally to methods and devices for repairing an intervertebral disc. More specifically, the application relates to percutaneously deployed implantable spinal discs and methods for manufacturing and deploying such discs. 
         [0004]    2. Description of Related Art 
         [0005]    A common medical issue is back pain due to spinal disc injuries caused by trauma, the aging process or other disorders. One method of treatment that has been proposed is to remove the existing nucleus pulposus and replace it with a nuclear prosthesis (i.e., an artificial spinal disk) which is formed in situ using open surgery or minimally invasive surgical techniques. 
         [0006]    Prior artificial disc technology has generally employed two types of implants. One type is a total disc designed as a substitute for the entire disc including the nucleus pulposus, the annulus fibrosus, and the vertebral end plates. The second type is a nuclear implant in which the annulus fibrosus and the end-plates are preserved. The shell formed by the annulus fibrosus itself has been used as an envelope to contain a curable biomaterial which is delivered to the cavity formed after a nucleotomy. Alternatively, an additional membrane may be provided inside the annulus fibrosus to form a shell to contain the biomaterial. Some prior art devices use two separate compartments or two nested balloons (a balloon placed within a balloon), which are filled in-situ with materials that have different hardnesses when cured, to simulate a natural disc. 
         [0007]    In addition to artificial discs, a variety of systems have been disclosed that immobilize the spinal segment, namely prostheses designed and intended for intervertebral disc fusion. The various systems include the placement of cages, distendable sacks, fusion grafts, interbody fusion rings, fiber bags and cushions and constraining jackets. These fusion devices employ different techniques than disc replacement systems. Typically, these grafts are porous and they may be rigid or non-rigid. Hardenable and load-bearing materials are introduced and constrained by these structures to stabilize and fuse adjacent vertebrae. 
         [0008]    Various techniques have been proposed for disc space distraction, including mechanical and hydrostatic techniques. For example, some techniques utilize pressurized injection of a biomaterial inside inflatable balloons to separate adjacent vertebra. 
         [0009]    The existing techniques for forming a nuclear prosthesis in situ have not achieved convincing clinical acceptance or commercial success for a variety of reasons, including intricate designs that present problems pertaining to manufacture, implantation, and performance after implantation. Some of the problems associated with previous devices, specifically those related to percutaneous or minimally invasive designs intended for nuclear replacement, include:
   1. Existing devices do not provide an integrated system that provides access to the nucleus pulposus, a nuclear evacuation apparatus that can achieve total or subtotal nucleotomy, and a delivery apparatus for the nuclear implant.   2. Existing devices inadequately seal the inflation device to the balloon, which results in leakage of the injected material around the inflation device during pressurized inflation.   3. Existing devices use inadequate or unreliable valve systems for preventing the curable biomaterial from leaking out of the implant after inflation and prior to curing.   4. Existing devices use hard materials that are insufficiently deformable, elastic and/or compressible. For example, existing devices often use a non-compressible center bearing portion to resist migration or to provide a more flexible region that more closely approximates the physical characteristics of the original nucleus. However, the vertebral end-plates are weakest in the center and strongest at the periphery. The use of a non-compressible center bearing portion increases risk of subsidence in the center. Furthermore, the lack of a central gas chamber or central void that provides a space for inward deformation of the annular portion may increase the risk of implant migration because of sudden or abnormal increase in pressure during loading or twisting.   5. Some existing devices attempt to construct an implant having a rigid outer portion with a more liquid but non-compressible interior. This design may work if the annulus is intact and can provide adequate elasticity. In reality, most patients who are candidates for disc replacement already have a damaged annulus, and this type of device functions poorly with a damaged annulus.   6. Existing devices provide inadequate nuclear evacuation, which causes problems such as eccentric placement, less than optimal peripheral placement with apposition of implant to inner annulus, less than optimal weight distribution to the peripheral end-plates, shifting of the implant and migration.   7. Inadequate closure of the annulotomy defect due to required surgical techniques. Existing techniques often involve cutting a flap through the annulus.   8. The materials used by existing devices are not durable and suffer from failure after usage.   9. Existing devices and techniques fail to restore and maintain sufficient disc space height to keep the spinal support ligaments taut.   
 
         [0019]    Another issue with existing in situ formed prostheses is that it is very difficult to precisely control the force required to withdraw the inflation and pressurization cannula from the implant. If this force is too great, the implant may be dislodged through the annulotomy during detachment of the cannula. If the force required to withdraw the cannula from the implant is too small, the cannula may become prematurely detached from the implant during pressurization. Furthermore, fluid may leak around the connection. 
         [0020]    The disclosed implant system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art. 
       SUMMARY 
       [0021]    It is an object of the present application to provide a novel intervertebral disc for replacing a nucleus pulposus. 
         [0022]    It is another object of the present application to provide a method of forming a nuclear prosthesis out of conformable materials which are adaptable to miniaturization. 
         [0023]    It is yet another object of the present application to provide a method of deforming a prosthesis to load it into a delivery cannula. 
         [0024]    It is a further object of the present application to provide a method of inserting and deploying a prosthesis into an intervertebral disc utilizing minimally invasive surgery or percutaneously. 
         [0025]    It is a still further object of the present application to provide a valve mechanism for preventing leakage of a curable material from an implanted prosthesis. 
         [0026]    It is a yet further object of the present application to provide a device which prevents subsidence and migration. 
         [0027]    It is yet another object of the present application to provide a fluid connector assembly which may provide a secure fluid seal during pressurization of the implant within the disc, while still allowing efficient disengagement from the implant and not becoming prematurely detached from the implant. 
         [0028]    It is a yet further object of the present application to provide a simple, efficient, and repeatable manufacturing method. 
         [0029]    Aspects of the present disclosure relate to an interbody spinal non-fusion implant adapted for percutaneous deployment, and methods and instruments for inserting and deploying such implants. In some exemplary embodiments, a nuclear prosthesis is formed of a hollow ring-like synthetic fiber graft which may be filled with a curable elastomer. A one-way valve may be incorporated into the graft to allow elastomer to be injected into the graft while preventing backflow. The valve may be left in place to cure with the curable elastomer. 
         [0030]    In some embodiment, the implant has a hollow ring-like configuration that allows a generally circumferential increase in size. The expandable implant may be designed to expand symmetrically or asymmetrically to restore disc height and angulation. Asymmetric expansion allow for change in the degree of lordosis, lateral angulation, or degree of compliance, compressibility or elasticity of the implant according to patient needs. The implant parameters may be adjusted to tailor intervertebral axial spacing and angulation for a patient. For example, the expandability of the implant/graft walls may be altered, or the durometer of the curable elastomer may be altered. 
         [0031]    The ring-like implant forms an empty space in its interior. The interior space serves as a buffer zone for inward deformation of the cured elastomer within the lumen of the ring-like fiber graft. 
         [0032]    The nuclear implant offers degrees of motion similar to those afforded by the anatomical spinal disc. Further, the durable biocompatible materials and design features provide a long working life. The nuclear implant has similar weight bearing and hydraulic capabilities as the nucleus pulposus. 
         [0033]    The cured elastomer within the fiber graft provides torsional and compression stability. Thus, regardless of how loads are applied, the vectors of forces are substantially redirected centrally toward the interior cavity. Further, the fabric graft limits outward movement in the radial direction to lower stress on the annulus fibrosus. 
         [0034]    Inflation of the implant separates the vertebral bodies along the cranial-caudal axis. This stretches and tightens the fibers of the annulus fibrosus to stabilization the spinal motion segment. By stabilizing the vertebral segment, while avoiding fusion, the repetitive traumatic forces on the ligaments and facet joints are reduced, thus slowing down the degenerative process and the development of spinal stenosis. Furthermore, by avoiding spinal fusion, the graft curtails the possibility of development of adjacent segment disease. 
         [0035]    An aspect of the present disclosure is to preserve normal motion and reverse or arrest the degenerative cascade leading to segmental instability. This will alleviate pain and preserve the structural stability of the annulus fibrosus, facet joints and other osseous structures and ligaments. 
         [0036]    Embodiments of the present disclosure include an artificial nuclear implant comprising an annular fiber graft which is inflated with an in-situ curable elastomer to form an interior cavity that allows inward deformation of the elastomer. 
         [0037]    In one exemplary embodiment, the annular implant occupies the peripheral aspect of an evacuated disc space and is opposed to the inner margin of the annulus fibrosus and to the end-plates of the adjacent upper and lower vertebral bodies. A fluid is delivered into a lumen of the annular implant to create pressure to expand the implant and distract the adjacent vertebrae. After the access, delivery and inflation devices are removed, the elastomeric material cures in-situ within the annular graft to maintain vertebral distraction. The implant shares weight bearing and stabilization functions with the intrinsic annulus, which has been weakened by degeneration, fissures, or tears. A goal of the implant is to restore normal anatomical intervertebral spacing and angle and stabilization of the vertebral segment, while preserving its normal range of biomechanical movement. 
         [0038]    In one aspect of the present disclosure, an implantable prosthetic device comprises an annular tubular inflatable membrane having an inflation port; a tubular fiber graft enclosing the inflatable membrane; an inflation stem coupled to the inflation port for removably receiving an inflation stylet in a substantially leakproof manner; and a one way valve assembly in the inflation stem to allow fluid to be injected into the interior of the inflatable membrane, the one way valve assembly comprising a flutter-type or duckbill valve. 
         [0039]    In another aspect of the present disclosure, an implantable prosthetic device comprises an annular tubular inflatable membrane having an inflation port and first and second open ends; a tubular fiber graft enclosing the inflatable membrane and having first and second open ends; a coupling member coupling the first and second open ends of the inflatable membrane and fiber graft; and a one way valve assembly coupled to the inflation port to allow fluid to be injected into the interior of the inflatable membrane, the one way valve assembly comprising a flutter-type or duckbill valve. 
         [0040]    In a further aspect of the present disclosure, a kit for implanting an implantable prosthetic device comprises a delivery cannula having an internal lumen with an inner diameter; a graft comprising an annular inflatable ring with an inflation stem for communicating with an interior of the annular inflatable ring, wherein the inflation stem has a proximal end and an opposed distal end and has an outer diameter and an inner diameter, and wherein the inflation stem is disposed in the internal lumen of the delivery cannula; a release cannula slidably disposed in the delivery cannula, the release cannula having a distal portion configured to engage the proximal portion of the inflation port, and an inflation stylet with at least one internal lumen, the inflation stylet having a distal portion with an outer diameter configured to be releasably press fit into the inflation stem. 
         [0041]    In yet another aspect of the present disclosure, a method of manufacturing an implant comprises forming a tubular elastomeric membrane with first and second open ends and an inflation port; enclosing the elastomeric membrane in a tubular fiber graft; and coupling the first and second open ends together. 
         [0042]    In an additional aspect of the present disclosure, a method of forming a graft comprises providing an implant as described herein; deploying the implant into a disc cavity; inflating the implant with a curable material; and allowing the curable material to cure. 
         [0043]    The term “coupled” is defined as connected, although not necessarily directly. The terms “a” and “an” are defined as one or more unless this disclosure explicitly requires otherwise. The terms “substantially,” “approximately,” and “about” are defined as largely but not necessarily wholly what is specified (and includes what is specified; e.g., substantially 90 degrees includes 90 degrees and substantially parallel includes parallel), as understood by a person of ordinary skill in the art. In any disclosed embodiment, the terms “substantially,” “approximately,” and “about” may be substituted with “within [a percentage] of” what is specified, where the percentage includes 0.1, 1, 5, and 10 percent. 
         [0044]    The terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include” (and any form of include, such as “includes” and “including”) and “contain” (and any form of contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, a system, or a component of a system, that “comprises,” “has,” “includes” or “contains” one or more elements or features possesses those one or more elements or features, but is not limited to possessing only those elements or features. Likewise, a method that “comprises,” “has,” “includes” or “contains” one or more steps possesses those one or more steps, but is not limited to possessing only those one or more steps. Additionally, terms such as “first” and “second” are used only to differentiate structures or features, and not to limit the different structures or features to a particular order. 
         [0045]    A device, system, or component of either that is configured in a certain way is configured in at least that way, but it can also be configured in other ways than those specifically described. 
         [0046]    Any embodiment of any of the systems and methods can consist of or consist essentially of—rather than comprise/include/contain/have—any of the described elements, features, and/or steps. Thus, in any of the claims, the term “consisting of” or “consisting essentially of” can be substituted for any of the open-ended linking verbs recited above, in order to change the scope of a given claim from what it would otherwise be using the open-ended linking verb. 
         [0047]    The feature or features of one embodiment may be applied to other embodiments, even though not described or illustrated, unless expressly prohibited by this disclosure or the nature of the embodiments. 
         [0048]    Details associated with the embodiments described above and others are presented below. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0049]      FIG. 1  is a sectional view of an implant according to an embodiment of the present disclosure after implantation into an intervertebral space; 
           [0050]      FIG. 2  is a sectional view of the inflation port and valve assembly of the implant of  FIG. 1 ; 
           [0051]      FIG. 3  is a sectional view taken along line  3 - 3  in  FIG. 2 ; 
           [0052]      FIG. 4  is a plan view of an inflatable membrane of the implant of  FIG. 1 ; 
           [0053]      FIG. 5  is a plan view of a mandrel for making the inflatable membrane of the implant of  FIG. 1 ; 
           [0054]      FIG. 6  is a plan view of a tubular fiber graft of the implant of  FIG. 1 ; 
           [0055]      FIG. 7  is a plan view of an access opening in the tubular fiber graft of  FIG. 6 ; 
           [0056]      FIG. 8  is a partial sectional view of a portion of the implant of  FIG. 1 , prior to installation of a retaining member; 
           [0057]      FIG. 9  is a partial sectional view of a portion of the implant of  FIG. 1 , after installation of a retaining member; 
           [0058]      FIG. 10  is a sectional view of a delivery cannula with the implant of  FIG. 1 , prior to deployment; 
           [0059]      FIG. 11  is a sectional view of an alternative embodiment of an inflation stylet; 
           [0060]      FIG. 12  is a sectional view of the implant of  FIG. 1  which is partially implanted into the intervertebral space; 
           [0061]      FIG. 13  is a sectional view of the implant of  FIG. 1  which is partially implanted into the intervertebral space with a push member; 
           [0062]      FIG. 14  is a diagrammatic view of an implanted implant of  FIG. 1  with the adjacent vertebrae substantially aligned; 
           [0063]      FIG. 15  is a diagrammatic view of an implanted implant of  FIG. 1  with the adjacent vertebrae bent towards one another; and 
           [0064]      FIG. 16  is a diagrammatic view of an implanted implant of  FIG. 1  with the adjacent vertebrae bent towards one another. 
       
    
    
     DETAILED DESCRIPTION 
       [0065]    In the following detailed description, reference is made to the accompanying drawings, in which are shown exemplary but non-limiting and non-exhaustive embodiments of the invention. These embodiments are described in sufficient detail to enable those having skill in the art to practice the invention, and it is understood that other embodiments may be used, and other changes may be made, without departing from the spirit or scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the invention is defined only by the appended claims. In the accompanying drawings, like reference numerals refer to like parts throughout the various figures unless otherwise specified. 
         [0066]      FIG. 1  illustrates an implant  100  in accordance with an exemplary embodiment of the present disclosure after deployment into a disc cavity  102 . The disc cavity  102  is formed by performing a discectomy to remove the natural spinal disc. In some embodiments, the discectomy is performed using minimally invasive techniques, such as percutaneous techniques, so that the annulus fibrosus  104  is left substantially intact, with only a small access opening. 
         [0067]    The implant  100  comprises an annular ring  106  which is filled with a curable elastomeric material  108 , such as a curable silicone elastomer. The properties of material  108  may be selected to provide desired properties for the implant  100 . For example, curing time, cured durometer, and other physical properties, such as elongation, tear, and tensile strength may be selected to provide implant  100  with desired characteristics. 
         [0068]    Implant  100  forms a interior cavity  110  in the interior of annular ring  106 . Interior cavity  110  allows annular ring  106  to deform inwardly to relieve stress and avoid placing excessive pressure on the central region of the vertebral end plates, as will be described in further detail below. 
         [0069]    Annular ring  106  has an inflation port  114  with a one-way valve assembly  116  which allows curable material  108  to be introduced into annular ring  106  while it is still in a flowable state (i.e., prior to curing) while preventing curable material  108  from leaking out. In certain embodiments, annular ring  106  is formed by a tubular inflatable membrane  134  and a tubular fiber graft  136  which encloses the inflatable membrane  134 . 
         [0070]    Referring to  FIG. 2 , inflatable membrane  134  forms an annular balloon  138  with inflation port  114 . A one-way valve assembly  140  is coupled to the inflation port  114 . One-way valve assembly  140  allows curable material to be injected into annular balloon  138  while preventing substantially any material from escaping. In some embodiments, inflation port  114  comprises an inflation neck  208  which is formed integrally with inflatable membrane  134 . In certain embodiments, an inflation stem  142  with a lumen  148  extending from a proximal end  144  to a distal end  146  is inserted into inflation neck  208  and coupled to inflation neck  208  by adhesive, welding, or the like. One way valve assembly  140  may comprise a duckbill valve (i.e., a flutter-type or Heimlich valve)  150  comprising a thin elastomeric material extending from inflation stem  142 . The thin elastomeric material of duckbill valve  150  stretches to allow curable material  108  to flow through it when pressure is applied to curable material  108 . When pressure is removed, the thin elastomeric material constricts to prevent back-flow. Duckbill valve  150  may be coupled to inflation stem  142  prior to assembly with inflatable membrane  134 , or may be coupled to inflation stem  142  after inflation stem  142  is coupled to inflatable membrane  134 . One-way valve assembly  140  and inflation stem  142  may be placed substantially in the inflation neck  208 . That is, they may be placed so that they are outside of the annular portion of inflation membrane  134 . Placing the inflation and valve componentry outside of the annular portion of inflation membrane  134  eases manufacturing, improves the function of implant  100  during deployment, and improves the functionality and durability of implant  100  after deployment. 
         [0071]    In some embodiments, inflatable membrane  134  is formed of an elastic material, such as silicone, so that it is compliant (i.e., it expands as the internal pressure increases). A compliant balloon reduces the need for precise sizing of the membrane. In other embodiments, inflatable membrane  134  is semi-compliant. That is, inflatable membrane  134  expands to a given diameter under a certain amount of pressure, and only expands moderately from this diameter as the internal pressure increases beyond that pressure. Semi-compliant inflatable membranes  134  may be advantageous in some circumstances. 
         [0072]    Inflatable membrane  134  may be formed by conventional techniques, such as extrusion, injection molding or dip casting. In some embodiments, inflatable membrane  134  is formed by injection molding. Referring to  FIGS. 4 and 5 , a core mandrel  152  is used in conjunction with corresponding injection molding dies (not shown). In some embodiments, mandrel  152  comprises three pieces  154 ,  156 ,  158  which may be removably attached to one another by interlocking joints, such as threads or keys. Mandrel  152  is placed into the molding dies, and uncured silicone is injected into the die and allowed to cure to form inflatable membrane  134 . After inflatable membrane  134  is cured, the molding dies are opened, and the mandrel with the inflatable membrane  134  is removed. The mandrel may then be removed through inflation port  114  and inflation neck  208 . In some embodiments, mandrel pieces  154 ,  156  and  158  are disassembled and removed through inflation port  114  and inflation neck  208 . In other embodiments, inflatable membrane  134  may be cut to form first and second legs  160 ,  162  with open ends  120 ,  122  through which mandrel pieces  156  and  158  are removed. In certain embodiments, first and second legs  160 , 162  of inflatable membrane  134  are approximately the same length, although they may be unequal lengths. 
         [0073]    Cutting inflatable membrane  134  to form legs  160 ,  162  allows tubular fiber graft  136  to be formed separately and then installed on inflatable membrane  134 . Referring to  FIGS. 6 and 7 , in some embodiments, tubular fiber graft  136  comprises a textile formed of a biocompatible material. The textile material may be a woven, braided or knitted durable biocompatible material. In some embodiments, tubular graft  136  comprises a first layer comprising a plurality of semi-elastic or substantially inelastic fibers extending longitudinally and circumferentially along graft  136 . In certain embodiments, a second layer of semi-compliant fibers are layered over the first layer. In other embodiments, circumferential fibers are formed from substantially inelastic materials, and hoop fibers are formed from semi-elastic materials. This allows the graft  100  to expand moderately in the cross-sectional plane while constraining radial or equatorial expansion. In this manner, graft  100  mostly deforms inward toward interior cavity  110  and in the axial or craniocaudal plane. In some embodiments, tubular fiber graft  136  incorporates radiopaque markers at one or more locations to enable clinicians to visualize graft  100  during implantation. In certain embodiments, the radiopaque markers comprise radiopaque fibers. 
         [0074]    The cross-sectional diameter of tubular fiber graft  136  is selected to allow inflatable membrane  134  to be inflated to full size while preventing over-expansion of inflatable membrane  134 . The materials are selected so that inflatable membrane  134  does not bond to fiber graft  136  and is free to move within fiber graft  136  to a limited extent. 
         [0075]    In some embodiments, tubular fiber graft  136  is a split annular ring with first and second open ends  164 ,  166 . An opening  168  is provided in tubular fiber graft  136  to provide access to inflation port  114 . Opening  168  may be reinforced by stitching (e.g., a buttonhole stitch). Further, a reinforcing member  170  may be provided to reinforce the opening. Fiber graft  136  is installed over inflatable member  134  by placing inflatable member  134  through either first and second open end  164 ,  166  and threading it through fiber graft  136 . Inflation neck  208  is placed through opening  168 . 
         [0076]    Open ends  164 ,  166  of fiber graft  136  and open ends  120 ,  122  of inflatable membrane  134  are coupled to one another to form implant annular ring  106 . In one embodiment, a coupling member  124  is provided to couple open ends  164 ,  166  and open ends  120 ,  122 . Referring to  FIGS. 8 and 9 , coupling member  124  comprises a cylindrical member with a groove  172 . In  FIGS. 8 and 9 , inflatable member  134  and fiber graft  136  form first and second tubular legs  174 ,  176  with open distal ends  178 ,  180 , respectively. For clarity, inflatable membrane  134  and fiber graft  136  are shown as a single line in  FIGS. 8 and 9 . Coupling member  124  is placed into the interior of open distal end  180  of second tubular leg  176 , and open distal end  178  of first tubular leg  174  is placed over coupling member  124  and distal end  180  of second tubular leg  176 . A retaining member  182  is placed over coupling member  124  to couple distal ends  178 ,  180  to coupling member  124 . In some embodiments, retaining member  182  is a permanently crimpable member which is crimped into groove  172 . Retaining member  182  may comprise a radiopaque material to serve as a radiopaque marker. 
         [0077]    In some embodiments, coupling member  124  may be a solid member which forms a partition to prevent fluid communication between first and second tubular legs  174 ,  176 . In other embodiments, coupling member may have a lumen which connects first and second tubular legs  174 ,  176 . 
         [0078]      FIG. 10  illustrates implant  100  loaded into percutaneous deployment device  112 . Percutaneous deployment device  112  comprises a delivery cannula  128 , a release cannula  130  and an inflation stylet  132 . Deployment device  112  may be placed in an introducer or access cannula  126 . Access cannula  126  extends through annulus fibrosus  104  to provide access to disc cavity  102 . Access cannula  126  is deployed using conventional percutaneous access techniques. Access cannula  126  may be a conventional cannula. In some embodiments, access cannula  126  comprises an access cannula used to remove the nucleus pulposus, such as the access cannula described in US Patent Publication No. 2014/0276832, entitled “Surgical Device,” which is hereby incorporated by reference in its entirety. Implant  100  is stretched out in a deflated state and placed into delivery cannula  128 . The inner diameter of delivery cannula  128  is substantially the same as the outer diameter of inflation stem  142  so that inflation stem  142  fits snugly into delivery cannula  128 . The outer diameter of release cannula  130  is selected to fit snugly into delivery cannula  128 . The distal end  184  of release cannula  130  engages the proximal end  144  of inflation stem  142  so that release cannula  130  can be used to push inflation stem  142  and thus implant  100  out of the end of delivery cannula  128  to deploy implant  100  into disc cavity  106 . Release cannula  130  can also be used to hold inflation stem  142  into place while withdrawing inflation stylet  132  after deployment (as will be described in further detail below). 
         [0079]    Inflation stylet  132  is placed into inflation stem  142 . Inflation stem  142  is elastic and stretched to fit over the outer diameter of inflation style  132  so that the two pieces fit together snugly. The snug fit of inflation stylet  132  into inflation stem  142  together with the snug fit of inflation stem  142  into delivery cannula  128  form a tight seal to substantially prevent leakage during deployment and inflation of implant  100 . Furthermore, the snug fit prevents inadvertent dislodgment of the inflation stylet prior before completion of the inflation, despite the relatively high pressures which may be used to inflate inflatable membrane  134 . 
         [0080]    Referring to  FIG. 11 , in certain embodiments, inflation stem  186  is tapered from a proximal end  194  to a distal end  196 . A distal end  198  of the inflation stylet  198  forms a complementary shape. A lock  200  releasably holds inflation stylet  198  in inflation stem  186 . In certain embodiments, lock  200  comprises a protuberance  192  which engages a groove  190 . In certain embodiments, protuberance  192  comprises a ridge molded around inflation stylet  198 . The size, shape and number of ridges and grooves can be selected to provide a desired force required to detach the inflation stylet from the inflation stem. 
         [0081]    Referring to  FIG. 12 , to deploy implant  100 , the existing nucleus pulposus at the target site is removed by inserting access cannula  126  through a small access opening through the annulus fibrosus  104 . The existing nucleus pulposus is removed through access cannula  126  by performing a discectomy. The annulus fibrosus  104  is left substantially intact to form disc cavity  102 . 
         [0082]    Implant  100 , which has been loaded into percutaneous deployment device  112 , is inserted into the disc space. Release cannula  130  and inflation stylet  132  are pressed toward disc cavity  102  to engage proximal end  144  of inflation stem  142  and begin to deploy implant  100 . In certain embodiments, a push member  210  extends from inflation stylet  132  and engages coupling member  124 . During deployment, push member  210  pushes coupling member  124  toward the far end of the disc cavity  102  to help ensure proper placement of implant  100 . 
         [0083]    Alternatively, release cannula  130  may be advanced so that implant  100  is partially deployed, and curable material  108  may be delivered through inflation stylet  132  to partially inflate inflatable membrane  134 . Release cannula  130  may then be advanced again, and additional curable material  108  may be delivered. This process is repeated until inflation stem  142  has been advanced to the distal end of delivery cannula  128 , thereby fully deploying implant  100 . 
         [0084]    After implant  100  is fully deployed into disc cavity  102 , curable  108  is deployed into the inflatable membrane  134  to press implant  100  firmly against annulus fibrosus  104  and distract adjacent vertebral segments. A pressurized syringe may be used to deploy curable material  108  and supply sufficient pressure achieve the desired intervertebral distraction. After sufficient curable material  108  is deployed, inflation stylet  132  may be removed. Release cannula  130  holds inflation stem  142  into place, thereby preventing inadvertent withdrawal of implant  100  when inflation style  132  is removed. One-way valve  116  prevents curable material  108  from leaking out of implant  100 . Thus, inflation stylet  132  may be removed prior to curing of curable material  108 . When inflation stylet  132  is removed, inflation stem  142 , which is formed of an elastomeric material, collapses so that it only leaves a small amount of material in the opening of the annulus fibrosus (i.e., the annulotomy). The collapsed inflation stem  142  reinforces the function of duckbill valve  150  by preventing duckbill valve  150  from inverting due to the pressure of the curable material (prior to curing). 
         [0085]    Curable material  108  may be a silicone elastomer. The properties of the material, such as the curing time, uncured viscosity, cured durometer, etc. may be selected as desired to provide the desired properties for graft  100 , which are dependent upon the patient under treatment. The curable material  108  may be compatible with the material of inflatable membrane  134  so that they fuse together and form a single component. 
         [0086]    Referring to  FIGS. 13-15 , once implant  100  has cured, it forms a substantially non-compressible ring  106  which is contained within annulus fibrosus  104 . Implant  100  distracts adjacent vertebral segments  202  by pressing against vertebral end plates  204 . Interior cavity  110  is formed in the center of annular ring  106 . When vertebral segments  202  are moved with respect to one another, annular ring  106  deforms into interior cavity  110 . This prevents implant  100  from being subjected to too high of pressures, and prevents implant  100  from applying too high of pressures to vertebral end plates  204 . Furthermore, the peripheral location of implant  100  distributes weight to the peripheral portions of the vertebral end plates, and interior cavity  110  prevents excessive force from being applied to the central region  206  of vertebral end plates  204 . The peripheral portions of the end plate are typically stronger than the central regions. Further, interior cavity  110  provides space for shock absorption and for inward deformation during loading and sudden increases in intradiscal pressure. 
         [0087]    The above specification and examples provide a complete description of the structure and use of exemplary embodiments. Although certain embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the scope of this invention. As such, the various illustrative embodiments of the present devices are not intended to be limited to the particular forms disclosed. Rather, they include all modifications and alternatives falling within the scope of the claims, and embodiments other than the one shown may include some or all of the features of the depicted embodiment. For example, components may be combined as a unitary structure, and/or connections may be substituted (e.g., threads may be substituted with press-fittings or welds). Further, where appropriate, aspects of any of the examples described above may be combined with aspects of any of the other examples described to form further examples having comparable or different properties and addressing the same or different problems. Similarly, it will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. 
         [0088]    The claims are not intended to include, and should not be interpreted to include, means-plus- or step-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase(s) “means for” or “step for,” respectively.