Motion holding system and apparatus

Abstract

Systems, devices, and methods for maintaining motion in an intervertebral disc. A modular disc implant segment may be constructed from a relatively solid material configured to exhibit certain characteristics of a compressible solid, such as an elastomer. The material may be configured to include one or more structural voids, such as a leaf spring design, to facilitate the compression capability of the modular disc implant segments such that an entire disc composed of multiple modular disc implant segments can compress as the implant recipient moves.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of Provisional Patent Application No. 63 / 521,495, filed on June 16, 2023, and claims priority to that Provisional Patent Application under 35 U.S.SC §119(e), the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure generally relates to medical motion retention systems, devices, and methods, including intervertebral disc nucleus pulposus replacement systems and devices, such as implantable prostheses for repairing intervertebral discs. Background Technology

[0004] The spinal motion segment is composed of anatomical units of the spine, including two vertebral bodies, intervertebral discs, and attached ligaments, muscles, and facet joints. The intervertebral disc consists of endplates at the top and bottom of the vertebrae, a soft inner core (called the nucleus pulposus), and a circumferential annulus fibrosus surrounding the nucleus pulposus. In a normal intervertebral disc, the nucleus pulposus cushions the applied load, thus protecting the other components of the spinal motion segment. The normal nucleus pulposus responds to compressive forces by transmitting these forces to the endplates and annulus fibrosus against the vertebrae. The annulus is composed of collagen fibers and a smaller number of elastic fibers, both of which are effective in resisting tension. However, the annulus itself is not very effective at withstanding compressive shear forces, and in the absence of a functional nucleus pulposus, it loses its ability to maintain the physiological separation of the vertebral bodies. This results in compression and irritation of degenerative nerve roots, and the development of back pain.

[0005] As people age, intervertebral discs typically degenerate naturally. Degenerative disc disease of the spine is one of the most common conditions causing pain and disability in humans. Disc degeneration occurs when the nucleus pulposus dehydrates. When the nucleus pulposus dehydrates, its ability to act as a buffer decreases. Because the dehydrated nucleus pulposus can no longer bear loads, the loads are transferred to the atlas and facet joints. The atlas and facet joints cannot withstand their increased share of the applied compressive and torsional loads, and therefore they gradually degenerate. As the atlas and facet joints deteriorate, many other effects occur, including narrowing of the intervertebral space, osteophyte formation, fragmentation of the atlas, fracture and deterioration of the cartilaginous endplates, and deterioration of the cartilage in the facet joints. The atlas and facet joints lose their structural stability, resulting in subtle but pathological movements between the vertebrae.

[0006] Fracture products of the disc (including macro fragments, microscopic particles, and deleterious biochemical substances) accumulate. Particles and fragments can cause nerve compression and sciatica, and the deleterious biochemical substances can irritate sensitive nerve endings in and around the disc and cause lower back pain. The affected individual experiences muscle spasms, decreased flexibility of the lower back, and pain when attempting general movement of the torso.

[0007] Degeneration of the disc is irreversible. In some cases, the subject will eventually stiffen the joints of the motion segment, effectively restabilizing the disc. Even in cases where restabilization occurs, the process can take many years, and the patient often continues to experience disabling pain. Long episodes of pain, over three months, often lead the patient to seek surgical solutions for the pain.

[0008] Several methods have been designed to attempt to stabilize the spinal motion segment. Some of these methods include: 1) Heating the annular region to destroy nerve endings and strengthen the annulus.

[0010] 2) Applying rigid or semi-rigid support members on the sides of the motion segment or within the disc space.

[0011] 3) Using a generally rigid plastic hinged artificial device to remove and replace the entire disc; permanently removing and fusing the vertebrae adjacent to the affected disc.

[0012] Until recently, spinal fusion was generally considered the most effective surgical treatment to relieve back pain due to disc degeneration. While this treatment is generally effective in relieving back pain, all disc motion is lost in the fused spinal motion segment.

[0013] The loss of motion in the affected spinal segment necessarily limits the overall spinal mobility of the patient. Ultimately, spinal fusion places greater stress on the discs adjacent to the fused segment, as these segments attempt to compensate for the loss of motion in the fused segment, often leading to early degeneration of these adjacent spinal segments.

[0014] Current development has focused on treatments that can preserve some or all of the motion of the affected spinal segment. One of the approaches to stabilize the spinal motion segment without the drawbacks of spinal fusion is total disc replacement. Total disc replacement is a highly invasive and technically demanding procedure that enters the intervertebral disc from an anterior approach or frontal approach and involves separating the anterior longitudinal ligament, removing the cartilaginous endplates between the vertebral bodies and the intervertebral disc, and removing most of the outer annulus and the entire inner nucleus. Then, an artificial total disc prosthesis is placed in the evacuated intervertebral disc space. Many of the artificial total disc replacements currently available are composed of a generally rigid plastic, such as ultra-high molecular weight polyethylene (UHMWPE), because the nucleus is interposed between two metal plates that are anchored or attached to the vertebral endplates.

[0015] An overview of the early development and design history of artificial discs is presented in "Ray, The Artificial Disc: Introduction, history and Socioeconomics", Chpt. 21, Clinical Efficacy and Outcome in the Diagnosis of Low Back Pain, pgs. 205-225, Raven Press (1992).

[0016] These types of artificial total disc replacements have several drawbacks. First, because the artificial disc replacements are relatively large, they require a relatively large surgical exposure to accommodate their insertion. The larger the surgical exposure, the higher the potential for infection, bleeding, or even morbidity. Also, to implant the prosthesis, removal of most of the annulus reduces the stability of the motion segment at least until healing occurs around the artificial disc. Furthermore, because the devices are composed of rigid materials, they can cause severe damage if they migrate from the intervertebral disc space and contact local neural or cardiovascular tissue. Another drawback is that rigid artificial disc replacements do not reproduce normal intervertebral disc biomechanics.

[0017] An alternative to total disc replacement is nucleus replacement, which like artificial disc prostheses is inert, non-rigid, non-biological replacement. Some prior art nucleus replacements use hydrogels because of their water absorption properties, which enable these replacements to swell in situ to allow more complete filling of the evacuated nucleus cavity. However, there is often a trade-off because the more swelling that is achieved by the hydrogel, the less structural support that the implant can provide. Thus, many hydrogel nucleus intervertebral disc replacements typically employ some form of sheath or fabric to constrain the hydrogel material. Without a sheath or other form of constraint, the hydrogel is prone to migration due to its slippery nature. Unfortunately, the sheath or fabric shell will be subject to long-term abrasive damage, which can cause the ability of the sheath or shell to constrain the hydrogel to fail, and thus the hydrogel can be subject to migration.

[0018] Another less desirable method of nucleus replacement involves implanting a balloon or other container into the nucleus and then filling the nucleus with a biocompatible material that hardens in situ. One of the problems with this approach is that the chemical hardening process is exothermic and can generate a large amount of heat that can cause tissue damage. Additionally, if the material leaks into the intervertebral disc cavity and surrounding tissue, this can cause undesirable complications. Also, the in situ solidifying polymers typically require very toxic monomers that can leak into the patient's tissue and even into their bloodstream, causing serious harm. Many of these monomers are known carcinogens.

[0019] Another technique for nucleus replacement involves implanting a plurality of individual support members, such as beads, one at a time into an evacuated intervertebral disc nucleus cavity until the cavity is filled, such as described in U.S. Patent Nos. 5,702,454 and 5,755,797. Because they are small, there is a possibility that one or more of the beads can be extruded from the evacuated intervertebral disc nucleus cavity. From a mechanical perspective, this technique is limited in its ability to produce consistent and reproducible results because the position and interaction of the plurality of beads or support members can shift during and after implantation.

[0020] More recent attempts at a nucleus prosthesis involve the use of multiple elastomeric pieces, which results in an all-elastomeric composition, such as described in U.S. Patent No. 8,100,977. However, the use of implants presents significant difficulties at the polymer-polymer interface, as the frictional forces at the polymer-polymer interlock make it very difficult for the surgeon to implant, and often a secure locking of the modules cannot be achieved. Additionally, elastomeric materials undergo shrinkage over time, and lose some of their pull-out capability. This undesirable behavior of many elastomers is called compression set. Such prior art further describes other solutions, one involving an elastomeric outer shell and an inner hard material to allow the module to slide and lock, where the modulus mismatch issue makes this approach biomechanically unstable. A second approach with a soft interior (hydrogel) and rigid outer shell will separate and displace.

[0021] Accordingly, there is a particular need for a nucleus prosthesis that can be inserted using minimally invasive surgery and that mimics the properties of a natural intervertebral disc. The present disclosure describes systems, devices, and methods for addressing these and other shortcomings of the prior art. SUMMARY

[0022] The present disclosure relates to medical motion preservation systems, devices, and methods. Embodiments include implantable spinal prostheses for repairing intervertebral discs. In some embodiments, such implantable prostheses include interconnected modular intervertebral disc nucleus implants.

[0023] In one embodiment, the one or more modular intervertebral disc implant segments include a relatively solid material(s) configured such that it acts similar to or otherwise exhibits certain properties of a solid substance that at least exhibits compressibility and elasticity, such as an elastomer. For example, the material can be configured to include one or more structural voids, where the structural voids can be occupied by air, liquid, gel, foam, a material with higher compressibility, etc.

[0024] In one particular embodiment, any one or more of the modular intervertebral disc implant segments includes a solid material (such as a biocompatible polymer, metal, etc.) that includes one or more structural voids such that the solid material is capable of being compressed into the respective structural voids when pressure is applied thereto. The solid material can be configured to exhibit elastic recovery properties such that the respective modular intervertebral disc implant segment is capable of recovering from the compressed state so as to partially or fully recover to the original shape of the structural void(s) and thus recover the compressed modular intervertebral disc implant segment(s) to the original geometric profile of the implant segment. In this manner, such a modular intervertebral disc implant segment can mimic or otherwise simulate the natural elastic properties of healthy nucleus pulposus and thereby serve as an implantable prosthesis for repairing a damaged intervertebral disc.

[0025] While a single or multiple modular intervertebral disc implant segments can serve as an implantable prosthesis for repairing a damaged intervertebral disc, one embodiment involves assembling multiple modular intervertebral disc implant segments into an overall compressible and elastic replacement for the extracted nucleus pulposus within the annulus fibrosus. The modular implant segments can be inserted through an access orifice formed in the intervertebral disc (such as through the annulus fibrosus). Each of the modular implant segments can be inserted in sequence into the intervertebral disc space created by the extracted nucleus pulposus through the access orifice(s) opening into the intervertebral disc space, with the second to last inserted modular implant segment respectively connected (or substantially locked) to its immediately preceding inserted adjacent modular implant segment.

[0026] In this example, the end result is a replacement for the extracted nucleus pulposus and an overall prosthesis having compressibility and elastic properties similar to a healthy nucleus pulposus due at least to the use of one or more suitably configured modular intervertebral disc implant segments that utilize one or more structural voids.

[0027] Accordingly, the embodiments described herein include representative examples of connectable (and in some cases interlockable) modular intervertebral disc implant segments that are capable of forming in situ a simulated nucleus pulposus device that exhibits certain elastomeric properties substantially commensurate with a healthy nucleus pulposus in order to restore the intervertebral disc to a simulated pre-damaged state.

[0028] One embodiment relates to a modular connectable segment that can be assembled in situ with one or more other such modular connectable segments to ultimately provide an implanted intervertebral disc prosthesis, yet the modular connectable segment is composed of a generally inelastic material that is capable of being compressed into one or more integrated spaces or voids. In one particular embodiment, a modular intervertebral disc implant segment is provided that includes one or more structural gaps, openings, slits, or other structural voids to facilitate compression of the implant segment in response to an external force, wherein the implant segment is configured to return to its original geometry in response to a reduction in the external force.

[0029] According to one embodiment, an intervertebral disc nucleus replacement apparatus is provided that includes a plurality of modular intervertebral disc implant segments, wherein at least one of the implant segments includes one or more structural voids to facilitate compression of the implant segment(s) in response to an external force, and wherein the implant segment(s) are configured to return to their original geometry in response to a reduction in the external force. Attachment mechanisms are provided on each of the implant segments to facilitate connection of each of the implant segments to at least one other implant segment. The intervertebral disc nucleus replacement apparatus includes the overall structure of the connected implant segments.

[0030] In another embodiment of such an intervertebral disc nucleus replacement apparatus, at least one of the structural voids is configured as a leaf spring having one or more open end gaps.

[0031] In another embodiment, at least one of the structural voids is configured as a leaf spring having one or more closed interior spaces.

[0032] Embodiments of such an intervertebral disc nucleus replacement apparatus can involve each of the modular intervertebral disc implant segments being composed of polyether ether ketone (PEEK). Also in other embodiments, the modular intervertebral disc implant segments are composed of titanium alloy.

[0033] The intervertebral disc nucleus replacement apparatus can further include an implant segment connection mechanism configured to couple to an implant segment connection mechanism in at least one adjacent modular intervertebral disc implant segment. In a more particular example of such an intervertebral disc nucleus replacement apparatus, the implant segment connection mechanism includes both a tongue element and a groove, wherein the groove is configured to facilitate a snap-fit connection by receiving the tongue element from an adjacent modular intervertebral disc implant segment. In yet another particular example of such an intervertebral disc nucleus replacement apparatus, the implant segment connection mechanism includes either a tongue element or a groove, wherein the tongue element or groove on one modular intervertebral disc implant segment is configured to facilitate a snap-fit connection by coupling to a mating tongue element or groove in an adjacent modular intervertebral disc implant segment.

[0034] The nucleus replacement apparatus can include modular intervertebral disc implant segments each including a tool connection mechanism that is releasably connectable to a mounting instrument.

[0035] In another embodiment of such an intervertebral disc nucleus replacement apparatus, the structural voids are arranged in a symmetric manner within at least one of the modular intervertebral disc implant segments, while in other embodiments the structural voids are arranged in a non-symmetric manner within at least one of the modular intervertebral disc implant segments. In one embodiment, the structural voids include a set of top structural voids and a set of bottom structural voids separated by a central portion of lesser compressibility.

[0036] Yet another embodiment of such an intervertebral disc nucleus replacement apparatus further includes a terminal modular intervertebral disc implant segment having a different arrangement of structural voids than the other implant segments.

[0037] Another embodiment relates to a method for implanting an intervertebral disc prosthesis in a patient. The method includes implanting a plurality of modular intervertebral disc implant segments, each having a plurality of structural voids to facilitate compression of the modular intervertebral disc implant segments in response to an external force, and each being composed of a material configured to return to its original geometry in response to a reduction in the external force. The method includes implanting a first modular intervertebral disc implant segment. In conjunction with implanting a second modular intervertebral disc implant segment, the second modular intervertebral disc implant segment is connected to the first modular intervertebral disc implant segment using a connection mechanism disposed on each of the first and second modular intervertebral disc implant segments. The method further includes implanting a last modular intervertebral disc implant segment to form a polymeric intervertebral disc prosthesis in situ in the patient.

[0038] Another embodiment of such a method further comprises attaching one or more additional modular intervertebral disc implant segments to the first modular intervertebral disc implant segment and the last modular intervertebral disc implant segment in the series of modular intervertebral disc implant segments by way of their respective attachment mechanisms.

[0039] In another embodiment, each of the modular intervertebral disc implant segments is composed of polyether ether ketone (PEEK).

[0040] Another embodiment of such a method further comprises attaching an insertion tool to the attachment receptacle on the second modular intervertebral disc implant segment to facilitate its insertion into the intervertebral disc space within the annulus fibrosus, and disconnecting the insertion tool from the attachment receptacle on the second modular intervertebral disc implant segment when the second modular intervertebral disc implant segment has been attached to the first modular intervertebral disc implant segment via its respective attachment mechanism.

[0041] In another embodiment, an intervertebral disc nucleus replacement implant is provided that includes a leaf spring arrangement to provide the necessary compressibility to mimic a natural nucleus to allow for motion between adjacent vertebral bodies.

[0042] In another embodiment of an intervertebral disc nucleus replacement implant, the compressibility of the vertebral motion segment in flexion, extension, and lateral bending is provided by a series of arcuate spring configurations, while the spring leaf element in the leaf spring arrangement of the implant remains attached to the body of the implant to form an open channel.

[0043] In one embodiment, the leaf spring arrangement includes a combination of open leaf spring elements and closed leaf spring elements that are configured to optimize the flexibility of the implant in all vertebral motions.

[0044] An embodiment of such an intervertebral disc nucleus replacement implant involves the use of a material for the intervertebral disc nucleus replacement implant that has a stiffness or compressive modulus similar to that of bone.

[0045] Also, in another embodiment of such an intervertebral disc nucleus replacement implant, the intervertebral disc nucleus replacement implant includes two or more modules to allow for separate insertion of each of the two or more modules through a path in the annulus fibrosus.

[0046] In a more specific embodiment of such an intervertebral disc nucleus replacement implant, the non-elastic material is configured with one or more movable leaf springs that are connected to, but separate from, the body of the implant through open channels, such that the implant as a whole is compressible. In yet another specific embodiment of such an intervertebral disc nucleus replacement implant, the open anterior channel terminates posteriorly in an enlarged, generally circular space to increase the compressibility of the leaf spring arrangement. In an alternative specific embodiment, the open posterior channel terminates anteriorly in an enlarged, generally circular space to increase the compressibility of the leaf spring arrangement.

[0047] In another embodiment of such an intervertebral disc nucleus replacement implant using movable leaf springs, each of the modules has a Z-configuration of channels, with the first open end of the upper channel facing posteriorly, and the second open end of the lower channel facing anteriorly. In an alternative embodiment, each of the modules has a Z-configuration of channels, with the first open end of the lower channel facing posteriorly, and the second open end of the upper channel facing anteriorly.

[0048] In another embodiment of such an intervertebral disc nucleus replacement implant using movable leaf springs, two or more leaf springs are configured in each of the plurality of modules to form the intervertebral disc nucleus replacement implant.

[0049] In other embodiments of such an intervertebral disc nucleus replacement implant using movable leaf springs, the material of the intervertebral disc nucleus replacement implant is PEEK (polyether ether ketone). In another embodiment, the material of the intervertebral disc nucleus replacement implant comprises a thermoplastic material, while in other embodiments the material comprises a composite of an elastomer and a thermoplastic material. In another embodiment, the material of the intervertebral disc nucleus replacement implant comprises an elastomer, while in another embodiment the material of the intervertebral disc nucleus replacement implant comprises a metal. In yet another embodiment, the material of the intervertebral disc nucleus replacement implant comprises a composite of a metal and a polymer (elastomer or thermoplastic material). The implant can be configured for insertion through a posterior lumbar interbody fusion (PLIF), a transforaminal lumbar interbody fusion (TLIF), and for lateral approaches. Also in another embodiment, a dilator and a distraction instrument are used in sequence to cause the modules forming the intervertebral disc nucleus replacement implant to be inserted.

[0050] In yet another embodiment, an apparatus for creating space between two adjacent vertebral bodies is provided, the apparatus comprising a number of coaxially placed, progressively larger members to expand the annulus fibrosis and apply force on the vertebral endplates to effect an increased separation, wherein the final member in the sequence is sized to provide a desired endplate separation and has an internal dimension through which an instrument and interbody implant module pass.

[0051] In still another embodiment, an intervertebral disc nucleus replacement apparatus is provided, the intervertebral disc nucleus replacement apparatus comprising one or more structural voids within a substantially inelastic body member, wherein the structural voids facilitate compressibility of the substantially inelastic body member in the vicinity of the one or more structural voids when the structural voids are disposed within an intervertebral disc as a replacement for an original nucleus pulposus.

[0052] This "SUMMARY" is included to provide a brief introduction to various concepts and embodiments of a sub-group of the concepts and embodiments that will be further described and taught herein, and that are combined in various combinations to form the claimed subject matter. The "SUMMARY" is not intended to identify key or essential inventive concepts, nor does it BRIEF DESCRIPTION OF DRAWINGS

[0053] Figure 1 A first representative embodiment of a modular intervertebral disc implant system is depicted that uses a plurality of modular intervertebral disc implant segments configured to be interconnected to form an intervertebral disc prosthesis.

[0054] Figure 2A A representative embodiment of a modular intervertebral disc implant segment is depicted that can form a portion of an intervertebral disc prosthesis that includes a plurality of modular intervertebral disc implant segments.

[0055] Figure 2B A face of a representative equidistant modular intervertebral disc implant segment is depicted.

[0056] Figure 2C A plurality of cross-sectional views of opposite sides of an equidistant modular intervertebral disc implant segment 200 are depicted.

[0057] Figure 2D A plurality of cross-sectional views of opposite sides of an equidistant modular intervertebral disc implant segment 200 are depicted.

[0058] Figure 2E A representative manner of connecting two (or more) of the modular intervertebral disc implant segments together is depicted.

[0059] Figure 2Fis depicted. An example of an intervertebral disc nucleus prosthesis constructed from a plurality of connected modular intervertebral disc implant segments.

[0060] Figure 2G Some of the faces of a representative intervertebral disc nucleus prosthesis 210 are depicted.

[0061] Figure 2H An exploded view of a representative five-component intervertebral disc nucleus prosthesis is depicted, with end and internal modular intervertebral disc implant segments.

[0062] Figure 2I Another embodiment of an intervertebral disc nucleus prosthesis constructed from a plurality of connected modular intervertebral disc implant segments is depicted.

[0063] Figure 2J A representative end modular intervertebral disc implant segment is depicted, which can be used as an "endcap" for an intervertebral disc nucleus prosthesis.

[0064] Figures 3A to 3E Another embodiment of an intervertebral disc nucleus prosthesis is depicted, which uses a leaf spring design according to the principles of the present disclosure.

[0065] Figure 4 A representative manner in which modular intervertebral disc implant segments can be implanted into the annulus fibrosis 401 is depicted.

[0066] Figure 5 A representative procedure in which a surgeon can implement the teachings herein to implant a monolithic intervertebral disc nucleus prosthesis is depicted. DETAILED DESCRIPTION

[0067] In the following description of various example embodiments, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration various example embodiments described herein. It is to be understood that other embodiments can be used, and structural and operational changes can be made, without departing from the scope of the present disclosure.

[0068] Generally, systems, devices, and methods are disclosed for providing implantable prosthetics for repairing damaged intervertebral discs, including but not limited to interlocking modular intervertebral disc nucleus implant devices. Embodiments include modular intervertebral disc implant segments configured to include one or more interior portions having greater compressibility than an encompassing structure, thereby facilitating compression / deflection of the encompassing structure into the one or more interior portions having greater compressibility. In one embodiment, at least one of the portions having greater compressibility is a structural void that, when positioned in the human body at the time of surgery, is filled with any substance surrounding the encompassing structure, such as air or fluid. Such modular intervertebral disc implant segments can then be inserted in succession into an intervertebral disc space and connected to one another to form an overall structure that can serve as a replacement nucleus pulposus in a damaged intervertebral disc.

[0069] Embodiments of the medical device include an intervertebral disc nucleus replacement device including one or more structural voids within a substantially inelastic body component, wherein the structural voids facilitate compressibility of the substantially inelastic body component near the one or more structural voids when the one or more structural voids are disposed within an intervertebral disc as a replacement for original nucleus pulposus material. For example, some embodiments involve a leaf spring type structure, however the structure is compressible due to the gap(s) created by the leaf spring(s) relative to another portion(s) of the intervertebral disc implant segment.

[0070] In one embodiment, a connectable or interlockable modular intervertebral disc nucleus implant system and device is provided, however the connectable / interlockable modular implant is made of a material that has compressibility but can withstand rigorous manipulation in the body. One such material is polyether ether ketone or "PEEK." The PEEK material used in embodiments herein can exhibit high temperature and chemical resistance, mechanical strength, wear resistance, and biocompatibility. Such materials can also exhibit a compression modulus similar to human bone.

[0071] As mentioned above, one embodiment involves providing one or more structural voids for at least some (or all) of the plurality of modular intervertebral disc implant segments to facilitate compression of the respective modular intervertebral disc implant segments into the structural voids. For example, Figure 1 A first representative modular intervertebral disc implant segment 100A is depicted that is configured to be able to interlock or otherwise connect with at least one adjacently positioned modular intervertebral disc implant segment 100n, however any number of connectable implant segments 100A through 100n can be implemented.

[0072] Figure 1Examples include at least one structural void 104A to facilitate compression of the modular intervertebral disc implant segment (such as a PEEK-constructed modular intervertebral disc implant segment). Any number or configuration of structural voids can be implemented to provide appropriate compressibility and elastic recovery, as depicted by representative structural voids 104A, 104B, 104C, 104D through 104n and / or any other such configurations. It should be appreciated that the representative structural voids 104A, 104B, 104C, 104D, 104n are merely illustrative, as other arrangements and implementations will be readily appreciated by those of skill in the art in light of the teachings herein.

[0073] When multiple such adjacently positioned modular intervertebral disc implant segments 100A through 100n are connected to form an overall compressible structure 102, the overall compressible structure 102 functions as a motion preserving device to replace the extracted, damaged nucleus pulposus. In some embodiments, one or more end modular intervertebral disc implant segments 106A, 106B can have the same or different internal configuration as the intermediate modular intervertebral disc implant segments. As Figure 1 As shown, any total number of modular intervertebral disc implant segments (with or without end segments) can be used. In some embodiments, while size preferences can involve more practical implementations from a total of about three to five implant segments, multiple modular intervertebral disc implant segments can be as low as two and as high as a number that can reasonably be inserted and connected within a given intervertebral disc space.

[0074] Embodiments include implementing any number of structural voids 104A through 104n (collectively, structural voids 104) to provide desired compressibility and required durability / safety profile. In one embodiment, there can be only one such structural void 104, which can be positioned symmetrically or asymmetrically (e.g., skewed to one side) within the modular intervertebral disc implant segment, or alternatively can be configured as a symmetric or asymmetric geometry. Other embodiments involve multiple such structural voids 104, which likewise can be incorporated into the modular intervertebral disc implant segment in a symmetric or asymmetric manner, where multiple voids 104 within the same (or even adjacent) modular intervertebral disc implant segments can use the same or different void 104 shapes.

[0075] Alternative embodiments of the structural void(s) (e.g., open space(s)) include the use of a first material (e.g., PEEK) in one or more adjacent portions having greater compressibility, such that the first material can be compressed into, bent into, or otherwise deflected into the receiving region(s) having a higher coefficient of compressibility. For example, in some embodiments, the structural voids 104A, 104B, 104C, 104D, 104n can not simply represent portions carved out of a first material, but can include substance(s) having greater compressibility than the material otherwise configured into the implant segment 100A through 100n.

[0076] Thus, the overall compressibility is at least influenced by the material used in the portions having greater compressibility, which can be pure void (e.g., air), fluid, gel, foam, and / or other material more compressible than the first material (e.g., PEEK). The first material can be substantially incompressible (or at least insignificantly compressible), or can itself have some degree of compressibility. In some embodiments, the first material and / or the second greater compressibility material can each be made of a homogenous material, or alternatively, one or both of the first material and / or the second greater compressibility material can each be made of a non-homogenous material.

[0077] In Figure 1 In particular examples of embodiments, PEEK modular intervertebral disc implant segment structures are implemented, however one or more structural voids 104A, 104B, 104C, 104D, 104n are incorporated into each of the modular intervertebral disc implant segments 100A through 100n, and include structural means to facilitate their interconnection during surgical implantation procedures. The modular intervertebral disc implant segments can be configured in known manners, including but not limited to extrusion, molding (e.g., injection molding, compression molding, blow molding, etc.), three-dimensional (3D) printing, casting, etc.

[0078] Thus, the structures of the example modular intervertebral disc implant segments provide support columns, support arms, support layers, trusses, "leaf spring" designs, and / or other designs that incorporate structural support as necessary, while facilitating compression of the modular intervertebral disc implant segments into a target region.

[0079] Figure 2A Particular embodiments of such modular intervertebral disc implant segments are shown. While Figure 2A Embodiments in the Figure 2AEmbodiments in the PEEK are described in terms of using PEEK. PEEK has a compressive modulus similar to human bone, thus providing a degree of natural structure for building a nucleus pulposus prosthesis. PEEK also exhibits promoting smooth or otherwise relatively unimpeded motion or sliding between adjacent modular intervertebral implant segments when they are implanted consecutively into a target intervertebral disc space. PEEK also exhibits a very robust life, thus enabling long-term benefit from the intervertebral disc prosthesis. The principles described herein are equally applicable to other materials and compounds that exhibit some or all of these properties, such as metals, other polymers, etc. For example, one embodiment uses titanium alloy for the body of the modular intervertebral implant segment.

[0080] Figure 2A A representative embodiment of a modular intervertebral implant segment 200 is depicted, which can form a portion of an intervertebral disc prosthesis comprising a plurality of such modular intervertebral implant segments 200. Figure 2A A representative embodiment in the PEEK includes a plurality of structural voids including compression absorbing spaces 202A, 202B, 202C, 202D, 202E, and 202F, in which some symmetry. These spaces or voids are strategically positioned, shaped, contoured, and otherwise arranged to properly balance absorption and resistance to the amount of compression provided by the spinal motion that will ultimately be experienced by the human recipient.

[0081] A representative modular intervertebral implant segment 200 also includes an insertion facilitating mechanism 204 to assist in the insertion of the implant segment 200 into a target intervertebral disc space. In the illustrated embodiment, the insertion facilitating mechanism 204 includes an internally threaded hole to receive a threaded instrument that can be used to guide and, in some embodiments, lock the modular intervertebral implant segment into the target intervertebral disc space. It should be appreciated that the modular intervertebral implant segment can be equipped with any attachment mechanism to facilitate its surgical positioning in the intervertebral disc within the annulus fibrosus.

[0082] Figure 2AThe representative modular intervertebral disc implant segment 200 also includes a connection mechanism 206, which in the present example includes a sliding fit component that includes a male connector 206A and a female connector 206B. In this manner, a tool coupled to the modular intervertebral disc implant segment 200 via the internally threaded hole 204 can facilitate coupling of the male connector 206A to the female connector 206B of an adjacently positioned modular intervertebral disc implant segment to connect two adjacent implant segments 200. The male connector 206A and the female connector 206B also facilitate proper alignment of the abutting implant segments upon connection. In some embodiments, the "connection" is an interface or fit of physical elements, however in other embodiments, the connection becomes stronger as it functions as an interlocking coupling. In some embodiments, the interface, fit, or interlocking mechanism can be provided by crossing physical components (e.g., "tongue" and groove), interlocking physical components (e.g., sliding fit), etc. In one interlocking embodiment, the mating physical components are configured to create an interference fit to provide a retention force, and thereby prevent accidental separation of the abutting components.

[0083] Also in other embodiments, magnets can be used to fit adjacent modular intervertebral disc implant segments. For example, some or all of the upper half of the modular intervertebral disc implant segment 200 can include magnetic material magnetized with a first polarity (e.g., north pole), and some or all of the lower half of the implant segment 200 can include magnetic material magnetized with a second polarity (e.g., south pole) to facilitate a magnetic snap fit (with or without additional physical fit or connection elements) between two adjacent modular intervertebral disc implant segments. In such embodiments, the magnetic material in the modular intervertebral disc implant segments can also serve as a radiopaque marker for visualization during surgery.

[0084] Figure 2B Depicted are Figure 2A facets of a representative equidistant modular intervertebral disc implant segment 200 in Figure 2A are reproduced in Figure 2B .

[0085] Figure 2C Depicted are Figure 2A multiple cross-sectional views of the equidistant modular intervertebral disc implant segment 200 in

[0086] Figure 2D Depicted are Figure 2AFIG. 6 is a plurality of cross-sectional views of opposite sides of an isometric modular intervertebral disc implant segment 200. According to this view, one embodiment of a male connector 206A in a connecting mechanism 206 is visible.

[0087] Figure 2E A representative manner of connecting two (or more) of the modular intervertebral disc implant segments 200A, 200B together is depicted. In one embodiment, the segments 200A, 200B are connected after the segment 200A has been inserted into the intervertebral disc space created by evacuating the existing nucleus pulposus material, and during insertion of the adjacent segment 200B into the intervertebral disc space. In the illustrated embodiment, the insertion portion 206A of the first modular intervertebral disc implant segment 200A slides over and along the groove 206B of the adjacent modular intervertebral disc implant segment 200B, such as in a sliding fit configuration. In one embodiment, the shape of the male connector 206A within the female connector 206B holds the two modular intervertebral disc implant segments 200A, 200B together. In other embodiments, a friction or interference fit can alternatively or additionally be implemented to hold the two modular intervertebral disc implant segments 200A, 200B in their desired relative position.

[0088] Figure 2F is an example of an intervertebral disc nucleus prosthesis 210 constructed from a plurality of connected modular intervertebral disc implant segments 200. In this embodiment, there are five modular intervertebral disc implant segments, including 3 interior modular intervertebral disc implant segments 200, and a first terminal modular intervertebral disc implant segment 201A and a second terminal modular intervertebral disc implant segment 201B. In one embodiment, the terminal modular intervertebral disc implant segments 201A, 201B differ in structural arrangement from the interior modular intervertebral disc implant segments 200, as they have only one open side in the illustrated embodiment. A cross-sectional view 211 of a representative intervertebral disc nucleus prosthesis 210 reveals the interior portion of the assembly of modular intervertebral disc implant segments, including the insertion facilitation mechanism male connector 206A and the female connector 206B in the connecting mechanism 206. As mentioned previously, the male connector 206A and the female connector 206B in the connecting mechanism 206 hold the modular intervertebral disc implant segments together to form the integral intervertebral disc nucleus prosthesis 210, functioning as a motion preserving device.

[0089] In one embodiment, the intervertebral disc nucleus prosthesis 210 is sized relative to the receiving target intervertebral disc space in the extracted nucleus pulposus material so as to eliminate or limit migration. For example, in one embodiment, the intervertebral disc nucleus prosthesis 210 is sized to be as large as or larger than the target intervertebral disc space (at least in some dimension). In other embodiments, the intervertebral disc nucleus prosthesis 210 can be smaller than the target intervertebral disc space, but preferably remains in place substantially with minimal internal migration capabilities.

[0090] Figure 2G depicts some of the faces of a representative intervertebral disc nucleus prosthesis 210. Figure 2F depicts some of the faces of a representative intervertebral disc nucleus prosthesis 210. Figure 2G depicts a perspective view, a side view, a top view, a front view, and a back view of each end modular intervertebral disc implant segment 201A, 201B. Figure 2G depicts a representative intervertebral disc nucleus prosthesis 210. When external pressure is applied to such an intervertebral disc nucleus prosthesis 210 (e.g., from lateral, forward, and / or rearward movement of the prosthesis-receiving patient), the pressure-bearing portion(s) in the intervertebral disc nucleus prosthesis 210 will deflect inward to absorb and respond to the applied pressure.

[0091] Figure 2H depicts exploded views of modular intervertebral disc implant segments 200, 201A, 201B of a five-component intervertebral disc nucleus prosthesis 210. Therein, the depiction indicates a representative manner of connecting the modular intervertebral disc implant segments, such as by male connectors 206A (in Figure 2H the receiving / female connectors 206B are not visible) in the connecting mechanisms 206. In one embodiment, the male connectors 206A slide over receiving grooves (not shown) on adjacent modular intervertebral disc implant segments. In one particular embodiment, the abutting modular intervertebral disc implant segments can then be locked together using, for example, fixation screws in the insertion facilitation device 204 (which can support the connection between the modular intervertebral disc implant segments), although in other embodiments no fixation screws or other additional connection devices are applied in addition to the physical mating of the connecting elements.

[0092] Figure 2I depicts another embodiment of an intervertebral disc nucleus prosthesis 210B configured from a plurality of connected modular intervertebral disc implant segments 200. In the illustrated embodiment, the intervertebral disc nucleus prosthesis 210B includes more Figure 2F and Figure 2GThe example shown has fewer modular disc implant segments. This illustration illustrates that the disc nucleus pulposus prosthesis described herein can have any number of sizes and any number of disc implant segments (including or excluding terminal modular disc implant segments); however, in the illustrated embodiment, the total number of modular disc implant segments is three. Specifically, the illustrative disc nucleus pulposus prosthesis 210B includes one modular disc implant segment 200 and two terminal modular disc implant segments 201A, 201B.

[0093] Figure 2J A representative terminal modular disc implant segment 201A is depicted. In this embodiment, the insertion facilitation mechanism 204 (e.g., an internally threaded hole) can be accessed through the access space 212A in the terminal modular disc implant segment 201A. In the illustration, the female connector 206B in the connection mechanism 206 is visible and in a state where it can receive the male connector 206A from adjacent modular disc implant segments to interconnect the segments. Furthermore, in addition to the structure of the terminal modular disc implant segment 201A thus entering the created structural space, the pivot hinges 212A and 212B can also facilitate deflection.

[0094] Figures 2A to 2J The examples depict representative modular connectable segments that can be assembled in situ with one or more other such modular connectable segments to ultimately provide an implanted intervertebral disc prosthesis; however, these modular connectable segments are constructed of a generally non-elastic material capable of compressing into one or more integrated spaces or voids. For example, in one embodiment, a modular intervertebral disc implant segment is provided, comprising one or more structural gaps, openings, slits, or other structural voids to allow the implant segment to compress in response to external forces, wherein the implant segment is configured to return to its original geometry in response to a reduction in the external force.

[0095] Figure 3A Another embodiment of a nucleus pulposus prosthesis 310 according to the principles of this disclosure is shown. This embodiment includes a first terminal modular disc implant segment 301A and a second terminal modular disc implant segment 301B, and three intermediate modular disc implant segments 300. Fixation screws 303 depict a representative manner in which the modular disc implant segments can be locked together. When the modular disc implant segments 300, 301A, and 301B are interconnected, they collectively form… Figure 3B The intervertebral disc nucleus pulposus prosthesis 310 is depicted in the text.

[0096] Figure 3CAnother representative configuration of structural voids in a modular intervertebral disc implant segment is depicted. In this embodiment, the structural voids are represented by slits or open channels that terminate at opposite ends of the modular intervertebral disc implant segment 300. These structural voids enable the arms 314A, 314B to flex in order to facilitate compression of the aggregated intervertebral disc nucleus prosthesis 310. As in other embodiments, this "leaf spring" arrangement appropriately balances absorption and resistance to the amount of compression that will ultimately be exerted by the spinal motion of a human recipient.

[0097] Figure 3D A representative modular intervertebral disc implant segment 300 is depicted in four faces. Figures 3A to 3C Figure 3D The position of the gaps 302A, 302B (structural voids) between the arms 314A, 314B relative to the interior body of the modular intervertebral disc implant segment 300 itself is depicted. Figure 3D Also shown is a connection mechanism that includes a male connector 306 that can be used to align and connect to another adjacent implant segment 300. In addition, Figure 3D Another embodiment of an insertion facilitation mechanism 404 is depicted to assist in the insertion of the implant segment 300 into the target intervertebral disc space. In the illustrated embodiment, the insertion facilitation mechanism 304 includes an internally threaded hole to receive a threaded instrument that can be used to guide and, in some embodiments, lock the modular intervertebral disc implant segment into the target intervertebral disc space. Figure 3E Additional details are depicted with respect to the embodiments described in Figures 3A to 3D

[0098] Figure 4 A representative manner in which the modular intervertebral disc implant segments can be implanted into the annulus fibrosis 401 is depicted. A representative implantation tool 400 can be coupled to the modular intervertebral disc implant segments 402 to guide them through an access aperture 404 created in the annulus fibrosis 401 and to facilitate interconnection and / or interlocking of adjacent modular intervertebral disc implant segments. In this manner, the target intervertebral disc space 406 can be equipped with an overall intervertebral disc nucleus prosthesis as described herein.

[0099] Figure 5 ​​A representative procedure is depicted in which a surgeon can implement the teachings herein to implant a whole disc nucleus prosthesis. In such an embodiment, the surgeon can use modular disc implant segments each having a structural void to enable the modular disc implant segment to compress in response to an external force, and wherein each modular disc implant segment is composed of a material configured to return to its original geometry in response to a reduction in the external force. The method includes implanting a first modular disc implant segment, and in conjunction with implanting a second modular disc implant segment, the surgeon can use a connection mechanism disposed on each of the first and second modular disc implant segments to connect the second modular disc implant segment to the first modular disc implant. Then, a last of the modular disc implant segments is implanted to form an aggregated disc prosthesis in situ in the patient.

[0100] The present disclosure addresses many of the problems of the prior art, including insertion and biomaterial issues. In one embodiment, a solution is provided by using a single well-known, biocompatible, thermoplastic material with a unique design that takes advantage of the superior flex fatigue properties of the material to provide a compression modulus similar to natural nucleus pulposus in all ranges of motion for a motion segment, while also having a compression modulus similar to bone material.

[0101] Such embodiments will allow the surgeon to reestablish normal disc height and re-tension the annulus fibers to create a physiologic load sharing between the annulus and the nucleus pulposus.

[0102] Embodiments set forth herein include a simple but robust attachment system to make module implantation quick, reproducible, easy to learn and secure.

[0103] As noted herein, the inventive information includes various representative embodiments disclosed herein, which are understood by those skilled in the art to be other embodiments in light of the teachings provided herein. Other representative / exemplary embodiments are set forth herein.

[0104] In one representative embodiment, an intervertebral disc nucleus replacement device is provided that implements a leaf spring arrangement to provide the necessary compressibility to mimic natural nucleus pulposus, allowing for motion between adjacent vertebral bodies.

[0105] In another particular embodiment, such an intervertebral disc nucleus replacement device (also referred to herein as an "implant") includes a non-elastic body material configured with one or more movable leaflets (connected but separate from the body of the implant through open channels), such that the implant as a whole is compressible. In a more particular representative embodiment, two or more leaflets are configured in each module. In another more particular embodiment, the material includes polyether ether ketone (PEEK), and in some embodiments, the material is made entirely of PEEK.

[0106] In yet another embodiment of such an intervertebral disc nucleus replacement device, the material includes a thermoplastic material, wherein in other embodiments, the material includes an elastomer, wherein in other embodiments, the material includes a composite of an elastomer and a thermoplastic. In still other embodiments, the material includes a metal, wherein in other embodiments, the material includes a composite of a metal and a polymer (e.g., an elastomer or a thermoplastic).

[0107] In another particular embodiment of such an intervertebral disc nucleus replacement device, the material has a stiffness or compressive modulus similar to bone.

[0108] In another particular embodiment, the implant includes two or more modules to allow insertion through a pathway in the annulus fibrosus. In a more particular embodiment, the modules include channels configured in a zig-zag configuration, wherein the open end of the upper channel faces posteriorly, and the open end of the lower channel faces anteriorly. In an alternative particular embodiment, the modules include channels configured in a zig-zag configuration, wherein the open end of the upper channel faces anteriorly, and the open end of the lower channel faces posteriorly. In yet another embodiment, the implant is inserted in sequence through a dilator and a retractor instrument, while in other embodiments, the open anterior channel ends in an enlarged, generally circular space at the posterior to increase compressibility of the leaflet elements. In another embodiment, the open posterior channel ends in an enlarged, generally circular space to increase compressibility of the leaflet elements.

[0109] In another embodiment, such an intervertebral disc nucleus replacement device is configured for insertion through a posterior lumbar interbody fusion (PLIF), transforaminal lumbar interbody fusion (TLIF), and for lateral approach.

[0110] Another embodiment includes an intervertebral disc nucleus replacement device including one or more structural voids within a substantially non-elastic body component, wherein the structural voids facilitate compressibility of the substantially non-elastic body component near the one or more structural voids when the one or more structural voids are disposed within a vertebral disc of a vertebra as a replacement for an original nucleus pulposus.

[0111] The foregoing description of representative embodiments has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the disclosure be limited only by the claims and equivalents thereof. Accordingly, the teachings of the specification and the drawings are to be considered illustrative only and not restrictive in nature.

[0112] The accompanying drawings, which form a part of this disclosure, are presented to aid in the understanding of the disclosed concepts. These drawings are not to be construed as limiting the disclosure in any manner. The specific embodiments of the disclosure are shown in the drawings, which are for illustrative purposes only.

[0113] For the sake of convenience, the embodiments in the innovation topic matter can be referred to herein in general as "the application," without intending to limit the scope of this application to any single embodiment or inventive concept. Thus, although specific embodiments have been shown and described herein, it is understood that a variety of modifications and variations are possible, as those skilled in the art having the benefit of this background teaching will appreciate. It is therefore intended that the disclosure be construed in keeping with the broadest interpretation of the appended claims and their equivalents.

Claims

1. An intervertebral disc nucleus replacement apparatus comprising: a plurality of modular intervertebral disc implant segments, wherein at least one of the plurality of implant segments includes one or more structural voids to facilitate compression of the at least one implant segment in response to an external force, and wherein the at least one implant segment is configured to return to an original geometry of the implant segment in response to the external force decreasing; an attachment mechanism on each of the plurality of implant segments to facilitate connecting each of the implant segments to at least one other of the implant segments; and wherein the intervertebral disc nucleus replacement apparatus includes a unit structure in the connected implant segments of the plurality of implant segments.

2. The intervertebral disc nucleus replacement apparatus of claim 1, wherein at least one of the structural voids is configured as a leaf spring having one or more open end gaps.

3. The intervertebral disc nucleus replacement apparatus of claim 1, wherein at least one of the structural voids is configured as a leaf spring having one or more closed interior spaces.

4. The intervertebral disc nucleus replacement apparatus of claim 1, wherein each of the plurality of modular intervertebral disc implant segments is composed of polyether ether ketone.

5. The intervertebral disc nucleus replacement apparatus of claim 1, wherein each of the plurality of modular intervertebral disc implant segments is composed of a titanium alloy.

6. The intervertebral disc nucleus replacement apparatus of claim 1, further comprising an implant segment connection mechanism configured to couple to an implant segment connection mechanism of at least one adjacent modular intervertebral disc implant segment.

7. The intervertebral disc nucleus replacement apparatus of claim 6, wherein the implant segment connection mechanism includes both a tongue element and a groove, and wherein the groove is configured to facilitate a snap-fit connection by receiving the tongue element from an adjacent one of the modular intervertebral disc implant segments.

8. The intervertebral disc nucleus replacement apparatus of claim 6, wherein the implant segment connection mechanism includes one of a tongue element or a groove, and wherein the tongue element or groove on a first one of the modular intervertebral disc implant segments is configured to facilitate a snap-fit connection by coupling to a matching one of a tongue element or groove in an adjacent one of the modular intervertebral disc implant segments.

9. The intervertebral disc nucleus replacement apparatus of claim 1, wherein each of the plurality of modular intervertebral disc implant segments includes a tool connection mechanism that is releasably connectable to an installation instrument.

10. The intervertebral disc nucleus replacement apparatus of claim 1, wherein the one or more structural voids are arranged in a symmetric manner within at least one of the modular intervertebral disc implant segments.

11. The intervertebral disc nucleus replacement device of claim 1, wherein the one or more structural voids are arranged in an asymmetric manner within at least one of the modular intervertebral implant segments.

12. The intervertebral disc nucleus replacement device of claim 1, wherein the one or more structural voids comprise a set of top structural voids and a set of bottom structural voids, the set of top structural voids and the set of bottom structural voids separated by a central portion of low compressibility.

13. The intervertebral disc nucleus replacement device of claim 1, further comprising a terminal modular intervertebral implant segment; the terminal modular intervertebral implant segment having a different arrangement of the one or more structural voids as compared to the at least one of the plurality of implant segments.

14. A method for implanting an intervertebral disc prosthesis in a patient, comprising: implementing a plurality of modular intervertebral implant segments, each modular intervertebral implant segment comprising a plurality of structural voids to facilitate compression of the modular intervertebral implant segment in response to an external force, and each modular intervertebral implant segment being comprised of a material that returns to an original geometry of the implant segment in response to a reduction in the external force; implanting a first one of the modular intervertebral implant segments; in connection with implanting a second one of the modular intervertebral implant segments, connecting the second one of the modular intervertebral implant segments to the first one of the modular intervertebral implant segments using a connecting mechanism provided on the first and second modular intervertebral implant segments; and implanting a last one of the modular intervertebral implant segments to form an aggregated intervertebral disc prosthesis in situ in the patient.

15. The method of claim 14, further comprising: between the first and last of the modular implant segments, implanting one or more additional modular intervertebral implant segments of the modular intervertebral implant segments via the respective connecting mechanisms of the implant segments.

16. The method of claim 14, wherein each of the modular intervertebral implant segments comprises polyether ether ketone.

17. The method of claim 14, further comprising: connecting an insertion tool to a connecting receptacle on the second modular intervertebral implant segment to facilitate insertion thereof into an intervertebral disc space within an annulus fibrosis; and disconnecting the insertion tool from the connecting receptacle on the second modular intervertebral implant segment when the second modular intervertebral implant segment has been connected to the first modular intervertebral implant segment via the respective connecting mechanisms of the implant segments.

18. An intervertebral disc nucleus replacement implant, comprising a leaf spring arrangement that provides the necessary compressibility to mimic a natural nucleus to allow for motion between adjacent vertebrae.

19. The intervertebral disc nucleus replacement implant of claim 18, comprising a non- elastomeric material configured with one or more moveable leaf springs connected to the body of the implant but separated from the body by an open channel such that the implant as a whole is compressible.

20. The intervertebral disc nucleus replacement implant of claim 19, wherein the open anterior channel ends in an enlarged, generally circular space to increase the compressibility of the leaf spring arrangement.

21. The intervertebral disc nucleus replacement implant of claim 19, wherein the open posterior channel ends in an enlarged, generally circular space to increase the compressibility of the leaf spring arrangement.

22. The intervertebral disc nucleus replacement implant of claim 18, wherein the leaf spring elements of the leaf spring arrangement of the implant remain connected to the body of the implant to form an open channel, but provide compressibility of the vertebral motion segment in flexion, extension, and lateral bending through a series of arcuate spring structures.

23. The intervertebral disc nucleus replacement implant of claim 18, wherein the leaf spring arrangement comprises a combination of open leaf spring elements and closed leaf spring elements configured to optimize the flexibility of the implant in all vertebral motions.

24. The intervertebral disc nucleus replacement implant of claim 18, wherein the material of the intervertebral disc nucleus replacement implant has a stiffness or compressive modulus similar to bone.

25. The intervertebral disc nucleus replacement implant of claim 18, wherein the intervertebral disc nucleus replacement implant is comprised of two or more modules to allow each of the two or more modules to be inserted separately through a path in the annulus fibrosis.

26. The intervertebral disc nucleus replacement implant of claim 19, wherein each of the modules has a channel in a Z-shaped configuration with a first open end on the upper channel facing posteriorly and a second open end on the lower channel facing anteriorly.

27. The intervertebral disc nucleus replacement implant of claim 19, wherein each of the modules has a channel in a Z-shaped configuration with a first open end on the lower channel facing posteriorly and a second open end on the upper channel facing anteriorly.

28. The intervertebral disc nucleus replacement implant of claim 19, wherein two or more leaf springs are configured in each of a plurality of modules that are connected to form the intervertebral disc nucleus replacement implant.

29. The intervertebral disc nucleus replacement implant of claim 19, wherein the material of the intervertebral disc nucleus replacement implant is polyether ether ketone (PEEK).

30. The intervertebral disc nucleus replacement implant of claim 19, wherein the material of the intervertebral disc nucleus replacement implant comprises a thermoplastic.

31. The intervertebral disc nucleus replacement implant of claim 19, wherein the material of the intervertebral disc nucleus implant comprises a composite of a metal and a polymer, wherein the polymer comprises an elastomer or a thermoplastic.

32. The intervertebral disc nucleus replacement implant of claim 19, wherein the material of the intervertebral disc nucleus replacement implant comprises an elastomer.

33. The intervertebral disc nucleus replacement implant of claim 19, wherein the material of the intervertebral disc replacement implant comprises a metal.

34. The intervertebral disc nucleus replacement implant of claim 19, wherein the material of the intervertebral disc replacement implant comprises a composite of a metal and an elastomeric or thermoplastic polymer.

35. The intervertebral disc nucleus replacement implant of claim 19, wherein the implant is configured for insertion through a posterior lumbar interbody fusion (PLIF), a transforaminal lumbar interbody fusion (TLIF), and for lateral approach.

36. The intervertebral disc nucleus replacement implant of claim 19, wherein the modules forming the intervertebral disc nucleus replacement implant are inserted in sequence using a dilator and a distraction instrument.

37. An apparatus for creating space between two adjacent vertebral bodies, the apparatus comprising a number of coaxially placed, progressively larger members to dilate the annulus fibrosis and exert a force on the vertebral endplates to effect increased distraction, wherein the final member in the sequence is sized to provide a desired endplate distraction and has an internal dimension for passage of an instrument and interbody implant modules.

38. An intervertebral disc nucleus replacement device comprising one or more structural voids within a substantially inelastic body member, wherein the structural voids facilitate compressibility of the substantially inelastic body member proximate to the one or more structural voids when the structural voids are disposed within the intervertebral space of the vertebrae as a replacement for the native nucleus material.

Images