US20100070041A1 - Expandable spinal implant and associated instrumentation - Google Patents

Abstract

An expandable spinal implant including an implant body transitionable between an initial configuration and an expanded configuration. The implant body includes first and second axial walls spaced apart along a transverse axis, with at least one of the walls including first and second axial wall portions laterally offset from one another. An expansion member co-acts with the first wall portion to outwardly displace the first wall portion relative to the second wall portion to transition the implant body to the expanded configuration. In another embodiment, the first wall portion defines a recessed region relative to the second wall portion when the implant body is in the initial configuration, and wherein the recessed region is outwardly expanded as the implant to body is transitioned to the expanded configuration. In a further embodiment, the first wall portion is movable while the second wall portion remains substantially stationary.

Description

CROSS REFERENCE TO RELATED APPLICATIONS
• The subject patent application is related to a U.S. Patent Application entitled “Expandable Intervertebral Implant and Associated Instrumentation” filed on the same day as the subject patent application, the contents of which are hereby incorporated by reference.
FIELD OF THE INVENTION
• The present invention relates generally to the field of spinal implants, and more particularly relates to an expandable spinal implant and associated instrumentation.
BACKGROUND
• There have been numerous attempts to develop intervertebral implants to replace a damaged or degenerated natural spinal disc and to maintain sufficient stability of the disc space between adjacent vertebrae, at least until arthrodesis is achieved. Intervertebral implants can either be solid, sometimes referred to as a spacer or plug, or can define a hollow interior designed to permit bone in-growth, sometimes referred to as a fusion device or fusion cage. The interior of a fusion device may be filled with a bone growth inducing substance to facilitate or promote bone growth into and through the device to achieve a more rapid and stable arthrodesis.
• Various types, shapes and configurations of intervertebral implants are known in the art. For example, one of the more prevalent designs includes intervertebral implants having a cylindrical shape and defining external threads to facilitate insertion into the disc space. As a result, reaming and tapping of the adjacent vertebral bodies is required to form a threaded passage for receiving the threaded implant. However, these techniques generally involve over-reaming of the posterior portion of the adjacent vertebral bodies, thereby resulting in excessive removal of load bearing vertebral bone which may lead to instability of the portion of the spinal column being treated. Other types of intervertebral implants have a generally rectangular configuration having planar upper and lower outer surfaces for engagement with adjacent vertebral bodies. However, the planar upper and lower outer surfaces may not adequately conform to the shape of the vertebral endplates, thereby resulting in non-uniform and inconsistent engagement between the implant and the adjacent vertebral bodies.
• Additionally, most intervertebral implant designs have a predetermined, fixed height that approximates the natural height of the disc space. Insertion of an intervertebral implant having a fixed height usually requires distraction of the disc space to an insertion height somewhat greater than the natural height of the disc space. Attempts have also been made to develop various types of expandable intervertebral implants that are configured to expand along the height of the disc space. These types of expandable implants typically include multiple arms or branches having proximal end portions that extend from a fixed base, and distal end portions that remain unconnected and free to move independently of one another. A wedge is displaced between the arms to separate or splay the distal end portions of the arms apart to transition the implant to an expanded configuration defining a taper and having a maximum implant height adjacent the distal end portion of the implant. Notably, positioning of the wedge adjacent the distal end portions of the arms fails to provide support along the mid-portion of the implant to resist compression forces exerted onto the implant by the adjacent vertebral bodies. Additionally, the expansion wedge may occupy a significant portion of the inner chamber of the implant, thereby reducing the capacity of the implant to receive bone growth inducing material therein.
• Moreover, some intervertebral implant designs include upper and lower bearing surfaces that are engaged against upper and lower vertebral endplates to maintain a select disc space height. These implants sometimes include teeth or other types of surface projections extending from the upper and lower bearing surfaces to aid in gripping the adjacent vertebral endplates to substantially prevent migration of the implant and possible expulsion of the implant from the disc space. However, the inclusion of teeth or other types of surface projections increases the overall height of the implant. As a result, the adjacent vertebrae to must be spread apart a distance sufficient to establish a disc space height that is at least as great as the overall height of the implant, including the height of the teeth. Spreading the adjacent vertebrae apart to accommodate for the overall height of the implant may result in over distraction of the disc space. Additionally, insertion of the implant into the disc space may be impeded by the teeth or other surface projections that extend beyond the upper and lower bearing surfaces.
• Thus, there is a general need in the industry to provide an improved expandable spinal implant and associated instrumentation. The present invention satisfies this need and provides other benefits and advantages in a novel and unobvious manner.
SUMMARY
• The present invention relates generally to an expandable spinal implant and associated instrumentation. While the actual nature of the invention covered herein can only be determined with reference to the claims appended hereto, certain forms of the invention that are characteristic of the preferred embodiments disclosed herein are described briefly as follows.
• In one form of the present invention, an expandable spinal implant is provided, including an implant body having a longitudinal axis and being transitionable between an initial configuration and an expanded configuration, with the implant body including first and second to axial walls spaced apart along a transverse axis, and with at least one of the axial walls including first and second axial wall portions laterally offset from one another. The implant further includes an expansion member that co-acts with the first wall portion to outwardly displace the first wall portion relative to the second wall portion generally along the transverse axis to transition the implant body from the initial configuration to the expanded configuration.
• In another form of the present invention, an expandable spinal implant is provided, including an implant body having a longitudinal axis and being transitionable between an initial configuration and an expanded configuration, with the implant body including first and second axial walls spaced apart along a transverse axis, and with at least one of the axial walls including first and second axial wall portions laterally offset from one another. The first wall portion defines a recessed region relative to the second wall portion when the implant body is in the initial configuration. The implant further includes an expansion member that co-acts with the first wall portion to transition the implant body from the initial configuration to the expanded configuration wherein the recessed region is outwardly expanded generally along the transverse axis.
• In another form of the present invention, an expandable spinal implant is provided, including an implant body having a longitudinal axis and being transitionable between an initial configuration and an expanded configuration, with the implant body including first and second axial walls spaced apart along a transverse axis, and with at least one of the axial walls including a movable wall portion and a substantially stationary wall portion laterally offset from one another. The implant further includes an expansion member that co-acts with the movable wall portion to outwardly displace the movable wall portion relative to the stationary wall portion generally along the transverse axis to transition the implant body from the initial configuration to the expanded configuration.
• It is one object of the present invention to provide an improved expandable spinal implant and associated instrumentation. Further objects, features, advantages, benefits, and aspects of the present invention will become apparent from the drawings and description contained herein.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a perspective view of an expandable intervertebral implant according to one form of the present invention.
• FIG. 2 is a side elevational view of an expandable implant body according to one embodiment of the present invention for use in association with the expandable intervertebral implant illustrated inFIG. 1.
• FIG. 3 is a top plan view of the expandable implant body illustrated inFIG. 2.
• FIG. 4 is an end elevational view of the expandable implant body illustrated inFIG. 2.
• FIG. 5 is an end elevational view of an expansion member according to one embodiment of the present invention for use in association with the expandable intervertebral implant illustrated inFIG. 1.
• FIG. 6 is a side elevational view of the expansion member illustrated inFIG. 5.
• FIG. 7 is a side elevational view of the expandable intervertebral implant illustrated inFIG. 1, as shown in an initial, non-expanded state within an intervertebral disc space.
• FIG. 8 is a side elevational view of the expandable intervertebral implant illustrated inFIG. 1, as shown in a fully expanded state within the intervertebral disc space.
• FIG. 9 is a top plan view of a pair of the expandable intervertebral implants illustrated inFIG. 1, as shown in a fully expanded state within the intervertebral disc space.
• FIG. 10 is a side elevational view of an expandable spinal implant according to another form of the present invention, as shown in an initial, non-expanded state.
• FIG. 11 is an end elevational view of the expandable spinal implant illustrated inFIG. 10, as shown in the initial, non-expanded state.
• FIG. 12 is a side elevational view of the expandable spinal implant illustrated inFIG. 10, as shown in a fully expanded state.
• FIG. 13 is an end elevational view of the expandable spinal implant illustrated inFIG. 10, as shown in the fully expanded state.
• FIG. 14 is a side elevational view of the expandable spinal implant illustrated inFIG. 10, as shown in a fully expanded state within an intervertebral disc space.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
• For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is hereby intended, and that alterations and further modifications to the illustrated devices and/or further applications of the principles of the invention as illustrated herein are contemplated as would normally occur to one skilled in the art to which the invention relates.
• Referring toFIG. 1, shown therein is an expandableintervertebral implant20 according to one form of the present invention. Theintervertebral implant20 extends along a longitudinal axis L and is generally comprised of anexpandable implant body22 and anexpansion member24. As will be discussed in greater detail below, theexpansion member24 serves to transition theimplant body22 from an initial non-expanded state (as shown inFIG. 7) to an expanded state (as shown inFIG. 8) wherein expansion of theimplant body22 occurs generally along a transverse axis T. Theexpansion member24 may also allow theimplant body22 to be retracted from the expanded state back toward the initial, non-expanded state. Further details regarding the features and operation of the expandableintervertebral implant20 will be set forth below.
• The components of the expandableintervertebral implant20 are formed of a bio-compatible material. In one embodiment of the invention, the components of theintervertebral implant20 are formed of a metallic material such as, for example, stainless steel and stainless steel alloys, titanium and titanium alloys, shape-memory alloys, cobalt chrome alloys, or any other suitable metallic material. In another embodiment of the invention, the components of theintervertebral implant20 are formed of a non-metallic material such as, for example, a polymeric material, a ceramic material, a reinforced composite material, bone, a bone substitute material, or any other suitable non-metallic material.
• Referring collectively toFIGS. 1-4, shown therein are further details regarding theexpandable implant body22. In the illustrated embodiment of the invention, theimplant body22 is configured as an expandable fusion cage including features that facilitate or promote bone growth into and/or through theimplant20 to achieve arthrodesis between the adjacent vertebral bodies, the details of which will be discussed below. However, it should be understood that in other embodiments of the invention, theimplant body22 may be configured as an expandable spacer or plug.
• In one embodiment of the invention, theexpandable implant body22 comprises of upper andlower walls30,32 extending generally along the longitudinal axis L, and a pair ofend walls34,36 extending transversely between and interconnecting opposing end portions of the upper andlower walls30,32. The upper and loweraxial walls30,32 and thetransverse end walls34,36 cooperate to define aninner chamber40 extending generally along the longitudinal axis L. In the illustrated embodiment of theimplant body22, theaxial walls30,32 and thetransverse walls34,36 provide theimplant body22 with a generally rectangular axial cross-section. However, it should be understood that other shapes and configurations of theimplant body22 are also contemplated as falling within the scope of the present invention.
• In one aspect of the invention, the upper andlower walls30,32 are coupled to theend walls34,36 in a manner that allows the upper andlower walls30,32 to be outwardly displaced relative to one another via theexpansion member24. In another aspect of the invention, theexpansion member24 co-acts with the upper andlower walls30,32 to flexibly deform the upper andlower walls30,32 in an outward direction relative to one another to provide for outward expansion of theimplant body22 generally along the transverse axis T from the non-expanded state illustrated inFIG. 7 to the expanded state illustrated inFIG. 8. Such outward deformation is primarily attributable to the flexible nature of the upper andlower walls30,32 and/or the flexible interconnection between the upper andlower walls30,32 and theend walls34,36. In one embodiment of the invention, the upper andlower walls30,32 are formed integral with theend walls34,36 to define a unitary, single-piece implant body22. However, it is also contemplated that the upper andlower walls30,32 and theend walls34,36 may be formed separately and connected together to form a multi-piece expandable body assembly. As shown inFIG. 2, in a further embodiment, the points of connection between the upper andlower walls30,32 and theend walls34,36 include roundedinner surfaces38 to provide increased flexibility to facilitate outward deformation of the upper andlower walls30,32 during expansion of theimplant body22. Additionally, the points of connection between the upper andlower walls30,32 and theend walls34,36 include roundedouter surfaces39 to provide rounded proximal and distal ends which aid in the insertion of theimplant body22 between adjacent vertebral bodies and into the disc space, and also facilitate the possible removal of theimplant body22 from the intervertebral disc space.
• In a further aspect of the invention, when in the non-expanded state (FIG. 7), the outer surfaces of the upper andlower walls30,32 define a recessed region extending inwardly along the transverse axis T. In the illustrated embodiment, the recessed region defined by the upper andlower walls30,32 comprises an inwardly extending concave curvature. However, other types and configurations of recessed regions are also contemplated as falling within the to scope of the present invention. As will be discussed in greater detail below, the recessed region or concave curvature provides theintervertebral implant20 with a lower overall vertical profile to facilitate insertion of theimplant20 into the disc space without having to distract the adjacent vertebrae apart to accommodate for the additional height that would otherwise be presented by teeth or other surface projections extending from the upper andlower walls30,32. However, as shown inFIG. 8, once theintervertebral implant20 is inserted into the disc space, expansion of theimplant body22 causes outward deformation of the upper andlower walls30,32 wherein the recessed region or concave curvature is outwardly expanded generally along the transverse axis T. In the illustrated embodiment, expansion of theimplant body22 provides each of the upper andlower walls30,32 with an outwardly extending convex curvature relative to the longitudinal axis L. As will be discussed below, the convex curvature defined by each of the upper andlower walls30,32 when theimplant20 is transitioned to the expanded state corresponds to a concave surface curvature defined by each of the adjacent vertebral bodies.
• The upper andlower walls30,32 of theimplant body22 define upper and lower engagement surfaces50,52. In one embodiment of the invention, the upper and lower engagement surfaces50,52 in turn define upper bearing surfaces54a,54band lower bearing surfaces56a,56badjacent theend walls34,36. As will be discussed below, the upper and lower bearing surfaces54a,54band56a,56bcontact and bear against the cortical rim/apophyseal ring region of the respective upper and lower vertebral bodies V_U, V_L(FIGS. 7-9) to provide support and resistance to a substantial amount of the compressive forces exerted onto theimplant body22. In the illustrated embodiment of the invention, the upper and lower bearing surfaces54a,54band56a,56bare substantially smooth and devoid of any steps, protrusions, projections or irregularities. However, it should be understood that in other embodiments, the upper and lower bearing surfaces may define anchoring features to aid in engaging and gripping vertebral bone.
• In a further embodiment of the invention, the upper and lower engagement surfaces50,52 of theimplant body22 include a number of anchor elements positioned axially between the upper and lower bearing surfaces54a,54band56a,56b.The anchor elements are adapted for engagement with the adjacent vertebral bodies V_U, V_Lto prevent or inhibit movement of theimplant body22 and/or to facilitate bone growth onto theimplant body22 subsequent to implantation within the intervertebral disc space. In one embodiment, the anchor elements comprise a number of teeth orsurface protrusions60 projecting from the upper and lower engagement surfaces50,52. In another embodiment, the anchor elements comprise a number ofgrooves62 cut into the upper and lower engagement surfaces50,52. However, it should be understood that other combinations and/or configurations of anchor elements are also contemplated for use in association with theimplant body22, including other features or elements extending from the upper and lower engagement surfaces50,52 such as, for example, spikes, threads, ridges, bumps, surface roughening, or any other element or feature suitable for anchoring to vertebral tissue. It should also be understood that in other embodiments of the invention, the upper and lower engagement surfaces50,52 of theimplant body22 need not necessarily include any anchor elements, but may alternatively define a substantially smooth configuration devoid of any surface projections or surface irregularities.
• As shown inFIG. 2, theupper surfaces54a,54badjacent theend walls34,36 are positioned along a first plane P₁, and thelower surfaces56a,56badjacent theend walls34,36 are positioned along a second plane P₂. The distance between the first and second planes P₁, P₂defines the maximum initial, non-expanded height h₁of theimplant body22. As discussed above, when theimplant body22 is in the initial, non-expanded state, the outer surfaces of the upper andlower walls30,32 define an inwardly extending concave curvature. Due to this concave curvature, the teeth60 (or other types of surface protrusions) projecting from the upper and lower engagement surfaces50,52 are at least partially positioned inward of the first and second planes P₁, P₂which define the maximum non-expanded height h₁of theimplant body22. In the illustrated embodiment of the invention, theteeth60 are positioned entirely inward of the first and second planes P₁, P₂.
• Since theteeth60 preferably do not protrude or extend beyond the first and second planes P₁, P₂when theimplant body22 is in the initial, non-expanded state, theteeth60 do not interfere with the upper and lower vertebral bodies V_U, V_Land potentially impede placement of theimplant20 during insertion into the disc space. Accordingly, distraction of the upper and lower vertebral bodies V_U, V_Lto accommodate for the height of theteeth60 above the upper and lower surfaces of thewalls30,32 is substantially avoided. Additionally, theimplant body22 may be provided with teeth60 (or other types of surface projections) having a greater height than would otherwise be allowed for if the upper andlower walls30,32 did not define a concave curvature when in the initial, non-expanded state. Although the illustrated embodiment of theimplant body22 contemplates that the planes P₁and P₂are arranged substantially parallel to one another, it should be understood that in other embodiments of the invention, the planes P₁and P₂may be angled or tapered relative to one another. As should be appreciated, theimplant body22 may be configured such that the planes P₁and P₂are angled relative to one another to provide theimplant body22 with a tapered configuration that corresponds to the lordotic angle between the upper and lower vertebral bodies V_U, V_L.
• In the illustrated embodiment of theimplant body22, theteeth60 are arranged in rows extending laterally across acentral portion22cof theimplant body22. Although theimplant body22 is shown as having two rows ofteeth60 extending from the upper and lower engagement surfaces50,52, it should be understood that the inclusion of a single row of teeth or three or more rows of teeth are also contemplated. Additionally, it should be understood that theteeth60 may be orientated in other directions such as, for example, in a direction parallel with the longitudinal axis L or arranged at an oblique angle relative to the longitudinal axis L. It should also be understood that one or more rows ofteeth60 may extend from other portions of the upper and lower engagement surfaces50,52, including theend portions22a,22bof theimplant body22. In one embodiment, theteeth60 have a triangular-shaped configuration; however, other shapes and configurations of teeth are also contemplated as falling within the scope of the present invention. As shown inFIG. 8, upon transitioning of theimplant body22 to an expanded configuration, theteeth60 are engaged/impacted into the vertebral endplates of the adjacent vertebral bodies V_U, V_Lto prevent or inhibit movement of theimplant body22 and possible expulsion from the disc space.
• In the illustrated embodiment of theimplant body22, thegrooves62 are arranged in rows extending laterally across theend portions22a,22bof theimplant body22. Although theimplant body22 is shown as having tengrooves60 formed into each of the upper and lower engagement surfaces50,52, it should be understood that any number ofgrooves60 may be included. Additionally, it should be understood that thegrooves62 may be orientated in other directions such as, for example, in a direction parallel with the longitudinal axis L or arranged at an oblique angle relative to the longitudinal axis L. It should also be understood that grooves may be cut into other portions of theimplant body22, including thecentral portion22c.
• In one embodiment of the invention, thegrooves62 are formed by cutting swales or channels into the upper and lower engagement surfaces50,52 which are spaced apart so as to define lands or plateaus64 that are substantially co-planar with the upper and lower engagement surfaces50,52. Edges orcorners66 are defined at the point where thegrooves62 and thelands64 meet. In one embodiment, thegrooves62 are configured to have a groove width and a groove depth that is greater than the width of thelands64. However, other configurations of thegrooves62 are also contemplated. Additionally, in the illustrated embodiment, thegrooves62 have a substantially circular configuration defining a substantially uniform radius or curvature. However, other shapes and configurations of thegrooves62 are also contemplated such as, for example, arcuate or bow-shaped grooves, V-shaped or U-shaped grooves, or any other suitable groove shape or configuration. As illustrated inFIG. 8, upon transitioning of theimplant body22 to an expanded configuration, thelands64 engage the vertebral endplates of the adjacent vertebral bodies V_U, V_Lso as to position thegrooves62 in close proximity thereto to receive bone tissue therein and/or to facilitate bone growth onto theimplant body22. Additionally, theedges66 formed between thegrooves62 and thelands64 aid in preventing or otherwise inhibiting movement of theimplant body22 and possible expulsion from the disc space.
• As shown most clearly inFIGS. 1 and 3, in one embodiment of the invention, theimplant body22 defines a bone in-growth opening orslot80 extending transversely therethrough in communication with theinner chamber40 and opening onto the upper and lower engagement surfaces50,52 of thewalls30,32. In the illustrated embodiment, theslot80 extends along substantially the entire length l of theimplant body22 and defines a pair of longitudinally extending and oppositely facing side surfaces82a,82bwhere theslot80 extends through the upper andlower walls30,32. As should be appreciated, the bone in-growth slot80 permits bone growth from the adjacent vertebral bodies and into and potentially through theimplant body22. Additionally, theslot80 is also sized to receive a portion of theexpansion member24 therein, between the opposing side surfaces82a,82b,to aid in guiding theexpansion member24 generally along the longitudinal axis L to substantially prevent side-to-side displacement as theexpansion member24 is axially displaced through theimplant body22 during expansion of theintervertebral implant20.
• Although theimplant body22 is illustrated as having a single bone in-growth slot80 extending transversely through and along substantially the entire length l of theimplant body22, it should be understood that theimplant body22 may be configured to have any number of bone in-growth slots, including two or more bone in-growth slots or openings positioned at various locations along the length of theimplant body22. Additionally, although the bone in-growth slot80 is illustrated as having a generally rectangular configuration having a slot length l_sextending along substantially the entire length l of theimplant body22, and a slot width w_sextending across about one-third of the width w of theimplant body22, it should be understood that other shapes, configurations and sizes of bone in-growth openings are also contemplated. It should further be understood that although the bone in-growth slot80 is illustrated and described as communicating with theinner chamber40, in other embodiments, theslot80 need not necessarily extend entirely through the upper andlower walls30,32.
• As shown most clearly inFIGS. 1 and 4, in the illustrated embodiment of theimplant body22, anaxial opening84 extends through each of theend walls34,36 in communication with theinner chamber40. As will be discussed in further detail below, theaxial openings84 are sized to receive an end portion of an instrument therein for engagement with theexpansion member24 to facilitate transitioning of theimplant body22 to an expanded configuration. Additionally, theaxial openings84 also permit bone growth from the adjacent vertebral bodies into theinner chamber40 of theimplant body22 from posterior and anterior directions. In the illustrated embodiment of the invention, theaxial openings84 have a generally rectangular configuration and have a relatively large size which encompasses almost all of theend walls34,36. However, it should be understood that other sizes, shapes and configurations of theaxial openings84 are also contemplated as falling within the scope of the present invention. It should also be understood that in other embodiments of the invention, only one of theend walls34,36 defines anaxial opening84, with the other end wall having a substantially solid configuration to close off the end of theimplant body22 opposite theaxial opening84.
• As illustrated inFIGS. 1 and 2, in one embodiment of the invention, theinner chamber40 includes a number of distinct compartments or sections positioned along the length l of theimplant body22. In the illustrated embodiment of theimplant body22, theinner chamber40 includes end compartments90aand90bpositioned adjacent theend portions22aand22bof theimplant body22, and an intermediate orcenter compartment90cpositioned adjacent thecentral portion22cof theimplant body22. However, it should be understood that theinner chamber40 may include any number of compartments, including a single compartment, two compartments, or four or more compartments. In the illustrated embodiment of the invention, each of the chamber compartments90a,90b,90cextends laterally through the entire width w of theimplant body22, thereby providing increased flexibility for expansion of theimplant body22 and also providing theimplant body22 with open sides to permit bone growth into theinner chamber40 from lateral directions.
• In the illustrated embodiment of theimplant body22, the end compartments90a,90beach have a tapered region wherein the inner surfaces of the upper andlower walls30,32 adjacent theintermediate compartment90ctaper inwardly toward one another to define a pair of opposing rampedsurfaces92a,92b.The center compartments90chas an arcuate configuration, with the inner surfaces of the upper andlower walls30,32 defining a pair of opposingconcave surfaces94a,94bhaving substantially the same curvature as the upper and lower arcuate engagement surfaces120a,120bdefined by the expansion member24 (FIGS. 5 and 6), the details of which will be discussed below. The point of intersection between the ramped surfaces92a,92bof the end compartments90a,90band theconcave surfaces94a,94bof thecenter compartment90cdefines opposing apices orvertices96a,96band98a,98bpositioned on either side of thecenter compartment90c.Although the illustrated embodiment of theimplant body22 depicts theinner chamber40 and thecompartments90a,90band90cas having a particular shape and configuration, it should be understood that other suitable shapes and configurations are also contemplate as falling within the scope of the present invention. In one embodiment of the invention, the end compartments90a,90bare substantially symmetrical to one another relative to the transverse axis T, the purpose of which will be discussed below.
• Referring toFIGS. 5 and 6, shown therein is theexpansion member24 according to one embodiment of the present invention. In the illustrated embodiment, theexpansion member24 includes a centralmain body portion100 and a pair ofside portions102a,102bprojecting laterally from thecentral portion100 and arranged generally along alateral axis104.
• In one embodiment of the invention, thecentral portion100 of theexpansion member24 has a generally rectangular or square cross section that defines substantially flat or planar side surfaces106a,106bfrom which theside portions102a,102bextend. However, it should be understood that other shapes and cross sections of thecentral portion100 are also contemplated such as, for example, hexagonal or polygonal cross sections, or circular or elliptical cross sections, with the side surfaces106a,106bhaving a curved or arcuate configuration, or any other shape or configuration that would occur to one of skill in the art. At least the upper andlower segments108a,108bof thecentral portion100 define a width w_ebetween the side surfaces106a,106bthat closely corresponds to the width w_sof theslot80 extending through theimplant body22. As will be discussed below, the upper andlower segments108a,108bof thecentral portion100 are displaced through theslot80 and along the opposing side surfaces82a,82bas theexpansion member24 is axially displaced through theinner chamber40 during transitioning of theimplant body22 toward the expanded configuration illustrated inFIG. 8.
• In the illustrated embodiment, thecentral portion100 defines apassage110 having a diameter d_l. Thepassage110 extends entirely through thecentral portion100 and is arranged generally along the longitudinal axis L when theexpansion member24 is positioned within theimplant body22. Thepassage110 is sized to receive a distal end portion of a surgical instrument200 (FIG. 7) which is configured to axially displace theexpansion member24 through theinner chamber40 during transitioning of theimplant body22 to an expanded configuration, the details of which will be discussed below. In one embodiment, thepassage110 has a generally circular cross section and includesinternal threads112 that define a continuous thread pattern through theaxial passage110 which are adapted for engagement with a threaded distal end portion of thesurgical instrument200. However, it should be understood that other shapes and configurations of theaxial passage110 are also contemplated for use in association with the present invention.
• In a further embodiment of the invention, theside portions102a,102bof theexpansion member24 each have a generally circular cross section relative to thelateral axis104 and define an outer diameter d₂. As shown inFIG. 5, the diameter d₁of theaxial passage110 extending through thecentral portion100 of theexpansion member24 is greater than the outer diameter d₂of theside portions102a,102b.As should be appreciated, absent the enlargedcentral portion100, the maximum diameter d₁of theaxial passage110 extending through theexpansion member24 would be somewhat less than the outer diameter d₂of theside portions102a,102b.As will be discussed below, providing thepassage110 with a relatively large diameter d₁facilitates the passage of graft material (or other types of material) through theexpansion member24 and into one of the end compartments90a,90bdefined by theinner chamber40 of theimplant body22. Additionally, providing thepassage110 with a relatively large diameter d₁also provides more stable and secure engagement with the distal end portion of thesurgical instrument200.
• In the illustrated embodiment, each of theside portions102a,102bof theexpansion member24 has a generally circular cross section which defines upper and lower engagement surfaces120a,120bhaving a curved or arcuate configuration. However, it should be understood that other shapes and cross sections of theside portions102a,102band the upper and lower engagement surfaces120a,120bare also contemplated. For example, in other embodiments of the invention, theside portions102a,102bmay have triangular, rectangular, hexagonal or polygonal cross sections with the upper and lower engagement surfaces120a,120bhaving angled or substantially flat or planar configurations, or any other shape or configuration that would occur to one of skill in the art. Theside portions102a,102bprovide theexpansion member24 with an overall width that is less than or equal to the overall width of theimplant body22 so that theside portions102a,102 do not extend laterally beyond the side surfaces of theimplant body22. As will be discussed in greater detail below, the upper and lower engagement surfaces120a,120bof theside portions102a,102bslide along the ramped surfaces92a,92bof the upper andlower walls30,32 as theexpansion member24 is axially displaced through theinner chamber40 during transitioning of theimplant body22 to the expanded configuration illustrated inFIG. 8.
• Referring now toFIG. 7, shown therein is theintervertebral implant20 positioned within the disc space between the upper and lower vertebral bodies V_U, V_Lin an initial, non-expanded configuration. As discussed above, the maximum initial height h₁of theimplant body22 when in the initial, non-expanded state is the distance between the upper and lower end surfaces54a,56aand54b,56badjacent theend walls34,36, respectively, which in the illustrated embodiment is the distance between the first and second planes P₁, P₂. In order to minimize distraction of the upper and lower vertebral bodies V_U, V_Land avoid over distraction of the disc space, the initial height h₁of theimplant body22 is preferably selected to correspond to the natural disc space height. In one embodiment, the initial height h₁of theimplant body22 closely corresponds to the natural disc space height adjacent the cortical rim/apophyseal ring region adjacent the anterior/posterior portions of the upper and lower vertebral bodies V_U, V_L. However, other initial heights h₁of theimplant body22 are also contemplated as falling within the scope of the present invention. As also discussed above, due to the inwardly extending configuration of the upper andlower walls30,32, the teeth60 (or other types of surface projections) extending from the upper andlower walls30,32 do not protrude or extend beyond the first and second planes P₁, P₂, thereby avoiding interference between theteeth60 and the upper and lower vertebral bodies V_U, V_Lwhich could otherwise impede insertion of theimplant20 into the intervertebral disc space.
• Asurgical instrument200 according to one embodiment of the invention is engaged to theintervertebral implant20 to aid in the insertion of theimplant20 into the disc space and to transition theimplant body22 to the expanded configuration illustrated inFIG. 8. In one embodiment, thesurgical instrument200 generally includes anouter sleeve202 engagable with theimplant body22, and aninner drive shaft204 positioned within theouter sleeve202 and engagable with theexpansion member24. Although a specific configuration of thesurgical instrument200 has been illustrated and described herein, it should be understood that other suitable types and configurations of surgical instruments are also contemplated for use in association with the present invention, and that the elements and operation thereof may differ from the embodiment of thesurgical instrument200 illustrated and described herein. For example, another type of instrument suitable for use in association with the present invention is illustrated and described in U.S. Pat. No. 6,436,140 to Liu et al., the entire contents of which are hereby incorporated herein by reference.
• Thesurgical instrument200 may include a first handle (not shown) attached to theouter sleeve202 to aid in the manipulation and handling of theintervertebral implant20, and a second handle (not shown) attached to theinner drive shaft204 to aid in actuation of thedrive shaft204 to expand theimplant20. In one embodiment, the handle associated with theouter sleeve202 may be configured as a counter torque-type handle that is easily grasped by the surgeon during manipulation and handling of the implant20 (e.g., during insertion of theimplant20 into the disc space), and which may also be used to oppose any torque forces that may be exerted onto theouter sleeve202 during actuation or expansion of the implant20 (e.g., during displacement of theexpansion member24 through theinner chamber40 of the implant body22). In another embodiment, the handle associated with theinner drive shaft204 may be configured as a T-handle that is manipulated by the surgeon to impart a rotational force onto thedrive shaft204, which in turn displaces theexpansion member24 through theinner chamber40 of theimplant body22 to expand theimplant20 subsequent to insertion into the disc space. However, it should be understood that other suitable types and configurations of handles are also contemplated for use in association with theinstrument200, and that the elements and operation thereof may differ from the embodiment of thesurgical instrument200 illustrated and described herein.
• Theouter sleeve202 of thesurgical instrument200 has adistal end portion202aadapted for engagement with theimplant body22. In one embodiment of the invention, thedistal end portion202adefines an engagement surfaces206 formed by the distal end of thesleeve202, or by a shoulder or boss that can be abutted or compressed against either of theend walls34,36 of theimplant body22, the purpose of which will be discussed below. In another embodiment, theinstrument200 and theimplant body22 may include features that cooperate with one another to prevent rotation of theimplant body22 relative to theouter sleeve202. In a specific embodiment, one or more projections associated with thedistal end portion202aof theouter sleeve202 may be inserted into a recessed area formed in either of theend walls34,36 of theimplant body22. For example, one or more pins associated with thedistal end portion202amay be inserted into openings or recesses formed in theend walls34,36 of theimplant body22. In another specific embodiment, the distal-most end portion of theinstrument200 may be provided with an outer profile that closely corresponds to the inner profile of theaxial opening84 formed through theend walls34,36 of theimplant body22. In yet another specific embodiment, theinstrument200 may include a pair of prongs (not shown) extending axially from thedistal end portion202aof thesleeve202 and including transverse flanges extending inwardly toward one another in an opposing manner. As should be appreciated, positioning of the transverse flanges into either of theend compartment90a,90bof theimplant body22 would function to secure theouter sleeve202 to theimplant body22 and to prevent rotation of theimplant body22 relative to theouter sleeve202. It should be understood that other types of engagement features between thesleeve202 and theimplant body22 are also contemplated as would occur to one of skill in the art including, for example, threaded engagement, clamping engagement, keyed engagement, tongue-and-groove engagement, frictional engagement, or any other suitable means for engagement.
• Theinner drive shaft204 of thesurgical instrument200 is positioned within theouter sleeve202 in a manner which allows rotation of thedrive shaft204 within thesleeve202 while constraining axial displacement of thedrive shaft204 through thesleeve202. Thedrive shaft204 includes adistal end portion204athat extends through theaxial opening84 in theend wall36 of theimplant body22 and into engagement with theexpansion member24. In one embodiment, at least thedistal end portion204aof thedrive shaft204 includesexternal threads210 adapted for threading engagement with theinternal threads112 formed along thepassage110 in thecentral portion100 of theexpansion member24 to thereby engage thedrive shaft204 to theexpansion member24. However, it should be understood that other types of engagement between thedrive shaft204 and theimplant body22 are also contemplated, such as, for example, abutting engagement, clamping engagement, keyed engagement, tongue-and-groove engagement, frictional engagement, or any other suitable means for engagement.
• As shown inFIG. 7, in one embodiment of the invention, theexpansion member24 is initially positioned in theend compartment90aadjacent thedistal end22aof theimplant body22 and, as will be discussed below, expansion of theimplant20 is accomplished by pulling theexpansion member24 toward theproximal end22bof theimplant body22 until theexpansion member24 is positioned within thecenter compartment90c.In another to embodiment of the invention, theexpansion member24 may be initially positioned in theend compartment90badjacent theproximal end22bof theimplant body22, with expansion of theimplant20 resulting from pushing theexpansion member24 toward thedistal end22auntil theexpansion member24 is positioned within thecenter compartment90c.However, the initial positioning theexpansion member24 in thedistal end compartment90aand pulling theexpansion member24 into thecenter compartment90cresults in the relatively simpler overall design of a “pull” style instrument, such as thesurgical instrument200 illustrated and described herein. For example, with regard to the pull-style instrument200, engagement between theouter sleeve202 and theimplant body22 can be accomplished via non-positive, abutting engagement since pulling of theexpansion member24 toward theproximal end22bof theimplant body22 compresses theproximal end wall36 against the distal end portion of theouter sleeve204. Accordingly, positive locking engagement between theouter sleeve202 and theimplant body22 is not required, as would be the case with a “push” style instrument. Additionally, a pull-style instrument also tends to provide a greater degree of control over the forces required to expand theimplant20 compared to that of a push-style instrument.
• As shown inFIG. 7, thedistal end portion202aof theouter sleeve202 is engaged against theproximal end wall36, with the threadeddistal portion204aof theinner drive shaft204 extending through theaxial opening84 in theend wall36 and into threading engagement with the threadedpassage110 in thecentral portion100 of theexpansion member24. As should be appreciated, since thedrive shaft204 is axially constrained relative to the outer sleeve202 (and hence relative to the implant body22), rotation of thedrive shaft204 in a direction of rotation R will threadingly engage thedistal end portion204aof thedrive shaft204 along the threadedpassage110, which will in turn result in theexpansion member24 being drawn in the direction of arrow A toward thecenter compartment90cof theimplant body22.
• Although a specific instrument and technique for displacing theexpansion member24 relative to theimplant body22 has been illustrated and described herein, it should be understood that other instruments and techniques are also contemplated as falling within the scope of the present invention. For example, thedrive shaft204 may be axially displaced relative to theouter sleeve202 via threading engagement between thedrive shaft204 and theouter sleeve202, as illustrated, for example, in U.S. Pat. No. 6,436,140 to Liu et al. In this manner, rotation of thedrive shaft204 would result in axial displacement of thedrive shaft204, which would in turn result in axial displacement of theexpansion member24 relative to theimplant body22. In other embodiments, thedrive shaft204 may simply be pulled in the direction of arrow A, which would in turn result in axial displacement of theexpansion member24 toward thecenter compartment90cof theimplant body22. Additionally, although the illustrated embodiment of the invention contemplates the use of linear displacement of theexpansion member24 relative to theimplant body22 to expand theimplant20, it should be understood that in other embodiments of the invention, theimplant body22 and theexpansion member24 may be configured such that transverse, rotational and/or pivotal displacement of theexpansion member24 relative to implantbody22 serves to expand theimplant body22 along the transverse axis T. For example, in an alternative embodiment of the invention, theexpansion member24 may be configured to have an oblong or cam-like configuration such that rotation of theexpansion member24 within thecenter compartment90cresults in expansion of theimplant body22.
• As should be appreciated, axial displacement of theexpansion member24 in the direction of arrow A will correspondingly transition theimplant body22 toward the fully expanded configuration shown inFIG. 8. More specifically, axial displacement of theexpansion member24 from thedistal end compartment90atoward thecenter compartment90cslidably engages the upper andlower engagement surface120a,120bdefined by theside portions102a,102bof theexpansion member24 along the opposing rampedsurfaces92a,92bdefined by theimplant body22. As a result, the upper andlower walls30,32 of theimplant body22 are driven away from one another and are outwardly deformed along the transverse axis T to transition theimplant body22 from the initial, non-expanded configuration illustrated inFIG. 7 toward the expanded configuration illustrated inFIG. 8. Theexpansion member24 is further displaced in an axial direction until positioned within thecenter compartment90cof theinner chamber40, with theside portions102a,102bof theexpansion member24 positioned within the recessed areas formed by the opposingconcave surfaces94a,94band captured between the opposing apices/vertices96a,96band98a,98b.
• It should be appreciated that positioning of theside portions102a,102bof theexpansion member24 within the opposingconcave surfaces94a,94band between the opposing apices/vertices96a,96band98a,98bretains theexpansion member24 within thecenter compartment90cand resists or inhibits further axial displacement of theexpansion member24 to thereby maintain theimplant body22 in the expanded configuration shown inFIG. 8, even after thedrive shaft204 is detached from theexpansion member24. It should also be appreciated that during expansion of theimplant body22, once theexpansion member24 is positioned beyond the pair of opposing apices/vertices96a,96band enters or “clicks” into thecenter compartment90c,the amount of linear driving force or rotational torque exerted onto thedrive shaft204 of theinstrument200 will significantly and abruptly decrease. This abrupt drop-off in driving force or torque provides the surgeon with a perceptible indication that theexpansion member24 is properly positioned within thecenter compartment90cand that the desired amount of expansion has been attained.
• Additionally, as indicated above, the upper andlower segments108a,108bof theexpansion member24 define a width w_ebetween the side surfaces106a,106b(FIG. 5) that closely corresponds to the width w_sof theslot80 extending through the implant body22 (FIG. 3). Accordingly, as theexpansion member24 is displaced through theinner chamber40 of theimplant body22 to transition theimplant body22 toward an expanded configuration, the upper andlower segments108a,108bof thecentral portion100 are displaced through theslot80, with the side surfaces106a,106bbeing displaced along the opposing side surfaces82a,82bof theslot80. Displacement of the upper andlower segments108a,108bof thecentral portion100 through theslot80 aids in guiding theexpansion member24 through theinner chamber40 during expansion of theimplant body22. Additionally, the relatively close fit between the side surfaces106a,106bof theexpansion member24 and the opposing side surfaces82a,82bof theslot80 provides additional support and rigidity to theimplant body22, and particularly resists side-to-side or lateral forces exerted onto theimplant20 by the upper and lower vertebral bodies V_U, V_L.
• As shown inFIG. 8, expansion of theimplant body22 increases the overall height of theimplant body22 adjacent the central portion of the implant to an expanded height h₂that is substantial equal to the height adjacent the central portion of the disc space. As should be appreciated, the difference between the initial height h₁and the expanded height h₂of theimplant body22 corresponds to the difference between the diameter d₁(or height) of theside portions102a,102bof the expansion member24 (FIGS. 5 and 6) and the non-expanded distance d₂between theconcave surfaces94a,94bof thecenter compartment90cof the implant body22 (FIG. 2). Accordingly, expansion of theimplant body22 can be easily and accurately controlled by providing theexpansion member24 withside portions102a,102bhaving a select diameter d₁(or height) and/or by providing thecenter compartment90cwith a configuration having a select non-expanded distance d₂between theconcave surfaces94a,94b.
• When theimplant body22 is transitioned to the expanded configuration, the upper andlower walls30,32 are outwardly deformed away from one another along the transverse axis T to increase the overall height h₂of theimplant body22. Since the end portions of the upper andlower walls30,32 are integrally connected to theend walls34,36, the end portions of the upper andlower walls30,32 remain relatively stationary and expansion of theimplant body22 adjacent theend portions22a,22bis limited. However, since the central portions of the upper andlower walls30,32 are not interconnected, expansion of theimplant body22 occurs primarily along the central portion of theimplant body22. As a result, upon expansion of theimplant body22, the upper andlower walls30,32 each form an outwardly extending convex curvature relative to the longitudinal axis L. The convex curvature of the outwardly deformed upper andlower walls30,32 preferably substantially corresponds to the anterior-to-posterior surface curvature C defined by the vertebral endplates of the adjacent vertebral bodies V_U, V_L. Additionally, expansion of theimplant body22 generally along the transverse axis T imbeds or impacts theteeth60 extending from the upper and lower engagement surfaces50,52 into the vertebral endplates to resist migration and possible expulsion of theimplant body22 from the disc space. Following expansion of theimplant body22, thesurgical instrument200 is disengaged from theexpansion member24 and removed from the patient. In the illustrated embodiment, this may be accomplished by simply rotating the drive shaft in a direction opposite the initial direction of rotation R until the threadeddistal end portion204ais disengaged from the threadedpassage110.
• If removal of the expandedimplant20 from the disc space is required due to non-optimal placement of theimplant20 or for other reasons, due to the symmetrical nature of the end compartments90a,90b,theimplant body22 can be transitioned from the expanded configuration (FIG. 8) back toward the initial, non-expanded configuration (FIG. 7) by simply repositioning theexpansion member24 from thecenter compartment90cto theproximal end compartment90b.As should be appreciated, further axial displacement of theexpansion member24 is accomplished by rotating thedrive shaft204 in a direction of rotation R, which will in turn draw theexpansion member24 in the direction of arrow A until theside portions102a,102bof theexpansion member24 are removed from theconcave surfaces94a,94bof thecenter compartment90cand positioned within theproximal end compartment90bof theimplant body22. Such repositioning will in turn cause theflexible implant body22 to retract toward the initial, non-expanded configuration illustrated inFIG. 7 wherein theteeth60 will once again be inwardly recessed relative to the planes P₁, P₂so as to avoid interfering with the upper and lower vertebral bodies V_U, V_Lwhich may otherwise impede removal of theimplant20 from the disc space. Theimplant20 may then be removed from the disc space and reintroduced therein using the insertion and expansion procedures outlined above to reposition theimplant20 into a revised position within the disc space.
• In a further aspect of the invention, following the insertion and expansion of theimplant20 within the disc space, a bone growth promoting material130 (FIGS. 8 and 9) is loaded into theinner chamber40 of theimplant body22 to facilitate or promote bone growth from the upper and lower vertebral bodies V_U, V_L, through theslot80 extending through the upper andlower walls30,32, and into and possibly through theimplant body22. In one embodiment, the bonegrowth promoting material130 comprises of a bone graft material, a bone morphogenic protein (BMP), or any other suitable bone growth promoting material or substance, including but not limited to bone chips or bone marrow, a demineralized bone matrix (DBM), mesenchymal stem cells, and/or a LIM mineralization protein (LMP). It should be understood that the bonegrowth promoting material130 can be used with or without a suitable carrier.
• In one embodiment of the invention, the bonegrowth promoting material130 is loaded or packed into theinner chamber40 via theaxial opening84 in theend wall36 subsequent to insertion and expansion of theimplant body22. However, in an alterative embodiment, a portion of the bonegrowth promoting material130 may be pre-loaded into theinner chamber40 prior to insertion and expansion of theimplant body22. As indicated above, the size of thepassage110 in thecentral portion100 of theexpansion member24 is relatively large. As a result, the bonegrowth promoting material130 may be conveyed through thelarge passage110 in theexpansion member24 and into thedistal end compartment90aof theinner chamber40. Once thedistal end compartment90ais fully loaded, additional bonegrowth promoting material130 may be loaded into theproximal end compartment90bof theinner chamber40. As should be appreciated, due to the inclusion of the relativelylarge passage110 in theexpansion member24, the bonegrowth promoting material130 need not be preloaded into thedistal end compartment90aprior to insertion and expansion of theimplant20 within the disc space. Additionally, conveying the bonegrowth promoting material130 through the relativelylarge passage110 in theexpansion member24 allows the entireinner chamber40 to be tightly packed with the bonegrowth promoting material130. Additionally, bone graft, morselized autograft bone or a similar type of material may be positioned laterally adjacent the expandedimplant body22 to further promote fusion with the adjacent vertebral bodies V_U, V_L.
• Having illustrated and described the elements and operation of theintervertebral implant20, reference will now be made to a technique for implanting theintervertebral implant20 within a disc space according to one embodiment of the invention. However, it should be understood that other implantation techniques and procedures are also contemplated, and that the following technique in no way limits the scope of the present invention.
• In one embodiment of the invention, access to the spinal column and insertion of theintervertebral implant20 into the disc space is accomplished via a posterior surgical approach. However, it should be understood that access and insertion of theintervertebral implant20 into the disc space may be accomplished via other surgical approaches such as, for example, an anterior approach or a lateral approach. In another embodiment of the invention, theintervertebral implant20 is used to treat the lumbar region of the spine, with the upper and lower vertebral bodies V_U, V_Lcomprising lumbar vertebral bodies. However, it should be understood that the present invention is also applicable to other portions of the spine such as, for example, the cervical, thoracic or sacral regions of the spinal column.
• Initially, the portion of the spinal column to be treated is identified and accessed from a posterior approach using known surgical techniques. At least a portion of the natural intervertebral disc is removed via a total or partial discectomy to provide an opening for receiving theintervertebral implant20 between the upper and lower vertebral bodies V_U, V_L. The disc space is then distracted to a height substantially equal to the natural disc space height. Prior to insertion of theintervertebral implant20, the disc space and the endplates of the upper and lower vertebral bodies V_Uand V_Lmay be prepared using various cutting tools and/or other types of surgical instruments (e.g., curettes, chisels, etc.). One example of a cutting instrument suitable for preparing the vertebral bodies V_U, V_Lis illustrated and described in U.S. Pat. No. 6,610,089 to Liu et al., the contents of which have been incorporated herein by reference. However, it should be understood that other types and configurations of cutting instruments are also contemplated for use in association with the present invention.
• In one embodiment of the present invention, the cutting instrument used to prepare the vertebral bodies V_U, V_Lis adapted to cut and remove bone tissue from the vertebral endplates while substantially retaining the natural concave curvature of the endplates and avoiding cutting into the cortical rim/apophyseal ring region adjacent the anterior/posterior portions of the vertebral endplates. The cutting instrument may also be configured to collect bony debris or chips generated during the cutting operation for subsequent insertion into theinner chamber40 of theimplant body22 to promote arthrodesis. As illustrated inFIGS. 7 and 8, each of the prepared vertebral endplates defines a recessed area or surface curvature C that is generally concave in an anterior-to-posterior direction. As should be appreciated, the recessed area or surface curvature C defined by the vertebral bodies V_U, V_Lreceives the outwardly deformed upper andlower walls30,32 of the expandedimplant body22 so as to position the upper and lower engagement surfaces50,52 of theimplant body22 and thebone growth material130 positioned therein in close proximity to the spongy cancellous bone tissue of the vertebral bodies V_U, V_Lto promote fusion. Following preparation of the vertebral endplates, theimplant20 is inserted into the disc space using a suitable insertion technique such as, for example, impaction or push-in type insertion. Notably, since theintervertebral implant20 is inserted into the disc space while in a non-expanded configuration having an initial maximum height h₁that is somewhat less than the disc space height, over distraction of the disc space is avoided and neural distraction is minimized.
• In a further embodiment of the invention, theintervertebral implant20 may be inserted into the disc space in a minimally invasive manner (i.e., through a small access portal) via the use of endoscopic equipment, a small diameter tube or cannula, or by other minimally invasive surgical techniques. However, it should be understood that theimplant20 may be inserted into the disc space using conventional surgical methods and techniques. Following insertion of theimplant20 into the disc space, theimplant body22 is expanded to the configuration illustrated inFIG. 8 (having an expanded height h₂) to restore and/or maintain a desired disc space height. As discussed above, transitioning of theimplant body22 to the expanded configuration results in outward deformation of the upper andlower walls30,32 from the inwardly curved or concave configuration illustrated inFIG. 7 to the outwardly curved or convex configuration illustrated inFIG. 8.
• As should be appreciated, a vertebra is comprised of a hard cortical bone material extending about the outer region of the vertebral body, and a softer cancellous or spongiose bone material within of the cortical bone material. As illustrated inFIGS. 8 and 9, the upper and lower anterior/posterior bearing surfaces54a,54band56a,56bof theimplant body22 are positioned to bear against the cortical rim/apophyseal ring region of the respective upper and lower vertebral bodies V_U, V_Lto resist the compressive forces exerted onto theimplant body22 and to reduce the likelihood of subsidence into the relatively softer cancellous or spongiseum bone tissue. Additionally, transitioning of theintervertebral implant20 to the expanded configuration illustrated inFIG. 8 imbeds or impacts theteeth60 extending from the upper and lower engagement surfaces50,52 into the vertebral endplates to resist migration and possible expulsion of theimplant body22 from the disc space. Moreover, positioning of the outwardly deformed upper andlower walls30,32 within the concave surface curvature C defined by the upper and lower vertebral bodies V_U, V_Ltends to increase stability of theimplant body22 and also reduces the likelihood of migration and possible expulsion of theimplant body22 from the disc space. Furthermore, positioning of the outwardly deformed upper andlower walls30,32 in close proximity to or in direct contact with the cancellous or spongiseum bone tissue of the upper and lower vertebral bodies V_U, V_Lfacilitates bone growth into thegrooves62 and/or through theslot80 and into theinner chamber40.
• In a further aspect of the invention, positioning of theexpansion member24 within thecenter compartment90cof theinner chamber40 provides additional support and rigidity to the upper andlower walls30,32 of theimplant body22 to resist compression loads from the vertebral bodies V_U, V_L, particularly near thecentral portion22cof theimplant body22 which is otherwise devoid of internal support members. Additionally, as discussed above, the relatively close fitting engagement of the upper andlower segments108a,108bof theexpansion member24 within theslot80 in the upper andlower walls30,32 also provides additional support and rigidity to theimplant body22, and particularly resists side-to-side or lateral forces exerted onto theimplant20 by the upper and lower vertebral bodies V_U, V_L. Although theintervertebral implant20 is maintained in the expanded configuration solely via engagement between theexpansion member24 and the upper andlower walls30,32 of theimplant body22, it should be understood that one or more supplemental internal fixation elements may also be used to provide further support to theimplant body22, particularly in instances involving excessive vertebral loading and/or instability. It should also be understood that supplemental external intravertebral fixation elements and/or stabilization techniques may also be used if excessive residual instability is encountered following insertion and expansion of one or more of theimplants20 within the disc space.
• Referring toFIG. 9, in a further embodiment of the invention, a pair ofintervertebral implants20a,20bmay be positioned side-by-side in a bilateral arrangement within the disc space. However, it should be understood that unilateral placement or central placement of a singleintervertebral implant20 within the disc space is also contemplated as falling within the scope of the present invention. Bone graft, morselized autograft bone, or a bone growth promoting substance may be positioned within the area between theimplants20a,20bto further facilitate fusion between the upper and lower vertebral bodies V_U, V_L.
• Referring toFIGS. 10-13, shown therein is an expandablespinal implant320 according to another form of the present invention. Thespinal implant320 extends along a longitudinal axis L and is generally comprised of animplant body322 and anexpansion member24. Theexpansion member24 is substantially identical to the expansion member illustrated inFIGS. 5 and 6 and described above with regard to the expandableintervertebral implant20. However, it should be understood that other types and configurations of to expansion members are also contemplated for use in association with thespinal implant320. Theexpansion member24 serves to transition theimplant body322 from an initial, non-expanded state (as shown inFIGS. 10 and 11) to an expanded state (as shown inFIGS. 12 and 13), wherein expansion of theimplant body322 occurs generally along a transverse axis T. Theexpansion member24 may also allow theimplant body322 to be retracted from the expanded state back toward the initial, non-expanded state. Further details regarding the features and operation of the expandablespinal implant320 will be set forth below.
• The components of the expandablespinal implant320 are formed of a bio-compatible material. In one embodiment of the invention, the components of thespinal implant320 are formed of a metallic material such as, for example, stainless steel and stainless steel alloys, titanium and titanium alloys, shape-memory alloys, cobalt chrome alloys, or any other suitable metallic material. In another embodiment of the invention, the components of thespinal implant320 are formed of a non-metallic material such as, for example, a polymeric material, a ceramic material, a reinforced composite material, bone, a bone substitute material, or any other suitable non-metallic material. In the illustrated embodiment of the invention, theimplant body322 is configured as an expandable fusion cage including features that facilitate or promote bone growth into and through theimplant320 to achieve arthrodesis between the adjacent vertebral bodies, the details of which will be discussed below. However, it should be understood that in other embodiments of the invention, theimplant body322 may be configured as an expandable spacer or plug.
• In one embodiment of the invention, theimplant body322 is comprised of upper andlower walls324,326 extending generally along the longitudinal axis L, and a pair ofend walls334,336 extending transversely between and interconnecting opposing end portions of the upper andlower walls324,326. In the illustrated embodiment of the invention, the upperaxial wall324 includes acentral wall portion329 and a pair ofouter wall portions330a,330bpositioned on either side of thecentral wall portion329. Similarly, the loweraxial wall326 includes acentral wall portion331 and a pair of lowerouter wall portions332a,332bpositioned on either side of thecentral wall portion331. As will be discussed in greater detail below, in the illustrated embodiment of the invention, theexpansion member24 co-acts with the upper and lower pairs ofouter wall portions330a,330band332a,332bto displace the outer wall portions in an outward direction relative to one another to provide for outward expansion of theimplant body322 generally along the transverse axis T from the initial, non-expanded state illustrated inFIGS. 10 and 11 to the expanded state illustrated inFIGS. 12 and 13, with the central upper andlower wall portions329,331 remaining in a substantially undeformed and stationary configuration.
• However, other embodiments of the invention are also contemplated wherein theexpansion member24 co-acts with the upper and lowercentral wall portions329,331 to displace thecentral wall portions329,331 in an outward direction relative to one another to provide for outward expansion of theimplant body322 generally along the transverse axis T, with the upper and lower pairs ofouter wall portions330a,330band332a,332bremaining in a substantially stationary position. In still other embodiments of the invention, the upperaxial wall324 may include a single movable wall portion330 positioned laterally adjacent thestationary wall portion329, and the loweraxial wall326 may include a single movable wall portion332 positioned laterally adjacent thestationary wall portion331. Additionally, it should be understood that other arrangements and configurations of movable and stationary wall portions are also contemplated as falling within the scope of the present invention. It should also be understood that the term “stationary” does not necessarily require that the stationary wall portion remains in an absolute stationary position, but only requires that the stationary wall portion remain in a substantially stationary position, or that the stationary wall portion is outwardly displaced or expanded to a lesser degree compared to that of an adjacent movable wall portion.
• In the illustrated embodiment of the invention, the upper and loweraxial walls324,326 and thetransverse end walls334,336 cooperate to define aninner chamber340 extending generally along the longitudinal axis L. In one embodiment of theimplant body322, the upper and loweraxial wall portions324,326 and thetransverse end walls334,336 provide theimplant body322 with a generally rectangular axial cross-section. However, it should be understood that other shapes and configurations of theimplant body322 are also contemplated as falling within the scope of the present invention. In one aspect of the invention, the upper and lower pairs ofmovable wall portions330a,330band332a,332bare coupled to thetransverse end walls334,336 in a manner that allows the upper and lower movable wall portions to be outwardly deformed relative to one another via theexpansion member24. In one embodiment, such outward deformation is primarily attributable to the flexible nature of the upper and lower pairs ofmovable wall portions330a,330band332a,332band/or the flexible interconnection between the movable wall portions and thetransverse end walls334,336.
• In one embodiment of the invention, the upper and loweraxial walls324,326 are formed integral with thetransverse end walls334,336 to define a unitary, single-piece implant body322. However, it is also contemplated that one or more portions of theaxial walls324,326 and thetransverse end walls334,336 may be formed separately and connected together to form a multi-piece expandable implant body assembly. As shown inFIG. 10, in a further embodiment of the invention, the interconnection location between the upper and lower pairs of themovable wall portions330a,330band332a,332band thetransverse end walls334,336 include roundedinner surfaces337 to provide increased flexibility to facilitate outward deformation of the movable wall portions during expansion of theimplant body322. Additionally, the upper and loweraxial walls324,326 and the leading orfront end wall334 cooperate with one another to define a rounded or bullet-shapeddistal end portion338 to facilitate insertion of theimplant body322 between adjacent vertebral bodies and into the intervertebral disc space. The interconnection location between the upper and loweraxial walls324,326 and the trailingend wall336 also definerounded corners339 to aid in possible removal of theimplant body322 from the intervertebral disc space and/or to minimize injury or trauma to adjacent tissue.
• In a further aspect of the invention, as illustrated most clearly inFIG. 10, when in an initial, non-expanded state, the upper and lower pairs ofmovable wall portions330a,330band332a,332bare recessed below theouter surfaces344,346 of the upper and loweraxial walls324,326 (e.g., positioned below the outer surfaces of the upper and lowerstationary wall portions329,331). Accordingly, when in the non-expanded state, themovable wall portions330a,330band332a,332bdefine recessedregions348 that extend inwardly along the transverse axis T relative to theouter surfaces344,346. In the illustrated embodiment, the recessedregions348 provided by themovable wall portions330a,330band332a,332bdefine outwardly extending convex curvatures. However, in other embodiments of the to invention, the recessedregions348 may define inwardly extending concave curvatures or may take on substantially planar configurations. Other suitable configurations and arrangements of theimplant body322 are also contemplated wherein the upper and lower pairs ofmovable wall portions330a,330band332a,332bare recessed or positioned below theouter surfaces344,346 of the upper and loweraxial walls324,326.
• As will be discussed in greater detail below, the recessedregions348 defined by the upper and lower pairs ofmovable wall portions330a,330band332a,332b(relative to the upper and lowerstationary walls329,331) provide thespinal implant320 with a lower overall vertical profile to facilitate insertion of theimplant320 into the intervertebral disc space without having to distract the adjacent vertebrae apart to accommodate for the additional height that would otherwise be presented by teeth or other surface projections extending from the pairs ofmovable wall portions330a,330band332a,332b.However, once thespinal implant320 is inserted into the disc space, expansion of theimplant body322 causes outward deformation of the upper and lowermovable wall portions330a,330band332a,332bwherein the recessedregions348 are outwardly expanded generally along the transverse axis T.
• In the illustrated embodiment, expansion of theimplant body322 provides each of the upper and lowermovable wall portions330a,330band332a,332bwith a convex curvature that substantially corresponds to the convex curvature of the upper andlower surfaces344,346 defined by thestationary wall portions329,331. In other words, as illustrated inFIG. 12, when thespinal implant320 is transitioned to the expanded state, the upper andlower surfaces345,347 of the movable wall portions are substantially aligned with the upper andlower surfaces344,346 of the stationary wall portions to provide theimplant body322 with upper and lower engagement surfaces350,352. However, other configurations are also contemplated as falling within the scope of the present invention. As will be discussed below, when thespinal implant320 is transitioned to the expanded state, the convex curvature defined by the upper and lower engagement surfaces350,352 substantially corresponds to a concave surface curvature C defined by the endplates of the adjacent vertebral bodies (FIG. 14).
• In one embodiment of the invention, the end portions of theimplant body322 define a pair of upper bearing surfaces354a,354band a pair of lower bearing surfaces356a,356badjacent thetransverse end walls334,336. As will be discussed below, the upper and lower bearing surfaces354a,354band356a,356bcontact and bear against the cortical rim/apophyseal ring region of the respective upper and lower vertebral bodies V_U, V_L(FIG. 14) to provide support and resistance to a substantial amount of the compressive forces exerted onto theimplant body322. In the illustrated embodiment of the invention, the upper and lower bearing surfaces354a,354band356a,356bare substantially smooth and devoid of any steps, protrusions, projections or irregularities. However, it should be understood that in other embodiments, the upper and lower bearing surfaces may define anchoring features to aid in engaging and gripping vertebral bone.
• In a further embodiment of the invention, the upper and lowermovable wall portions330a,330band332a,332bdefine a number of anchor elements positioned between the upper and lower bearing surfaces354a,354band356a,356b.The anchor elements are adapted for engagement with the adjacent vertebral bodies V_U, V_Lto prevent or inhibit movement of theimplant body322 and/or to facilitate bone growth onto theimplant body322 subsequent to implantation within the intervertebral disc space (FIG. 14). In one embodiment, the anchor elements comprise a number of teeth orsurface protrusions360 projecting outwardly from the upper and lowermovable wall portions330a,330band332a,332b.However, other types and configurations of anchor elements are also contemplated including, for example, spikes, threads, ridges, bumps, surface roughening, or any other element or feature suitable for anchoring to vertebral tissue. Additionally, anchor elements comprising grooves or surface depressions formed in the upper andlower surfaces345,347 of the movable wall portions are also contemplated as falling within the scope of the present invention. It should also be understood that in other embodiments of the invention, the upper andlower surfaces345,347 need not necessarily include any anchor elements, but may alternatively have a substantially smooth configuration. Moreover, although the upper andlower surfaces344,346 of thestationary wall portions329,331 are illustrated as having a substantially smooth configuration (i.e., devoid of any surface projections or surface depressions), it should be understood that in other embodiments of the invention, the upper andlower surfaces344,346 may be provided with one or more types of anchor elements adapted for engagement with the adjacent vertebral bodies.
• As indicated above, when theimplant body322 is in the initial, non-expanded state shown inFIG. 10, the upper and lowermovable wall portions330a,330band332a,332bdefine recessedregions348 that extend inwardly along the transverse axis T so as to position the tips orpeaks362 of theteeth360 at or below theouter surfaces344,346 of the upper and lowerstationary walls329,331. However, other embodiments are also contemplated wherein the recessedregions348 position theteeth360 partially below theouter surfaces344,346 of the upper and lowerstationary walls329,331, with the tips orpeaks362 of theteeth360 remaining above theouter surfaces344,346. The recessed positioning of theteeth360 provides thespinal implant320 with a lower overall vertical profile to facilitate insertion into the intervertebral disc space. However, as shown inFIG. 14, upon transitioning of theimplant body322 to the expanded configuration, theteeth360 are engaged/impacted into the vertebral endplates of the adjacent vertebral bodies V_U, V_Lto prevent or inhibit movement of theimplant body322 and possible expulsion from the disc space.
• As should be appreciated, when theimplant320 is in the initial, non-expanded state (FIG. 10), the maximum non-expanded height h₁of theimplant body322 is defined by the distance between theouter surfaces344,346 of the upper and lowerstationary walls329,331. In order to minimize distraction of the upper and lower vertebral bodies V_U, V_Land avoid over distraction of the disc space, the maximum non-expanded initial height h₁of theimplant body322 is preferably selected to correspond to the natural disc space height. In one embodiment, the non-expanded initial height h₁of theimplant body322 closely corresponds to the natural disc space height adjacent the cortical rim/apophyseal ring region adjacent the anterior/posterior portions of the upper and lower vertebral bodies V_U, V_L. However, other non-expanded initial heights h₁of theimplant body322 are also contemplated as falling within the scope of the present invention.
• Since theteeth360 preferably do not protrude or extend beyond theouter surfaces344,346 of thestationary wall portions329,331, theteeth360 do not interfere with the upper and lower vertebral bodies V_U, V_Lwhich could potentially impede placement of theimplant320 during insertion into the intervertebral disc space. Additionally, distraction of the upper and lower vertebral bodies V_U, V_Lto accommodate for the additional height of theteeth360 above theouter surfaces344,346 is substantially avoided. Specifically, the upper and lower vertebral bodies V_U, V_Lonly need to be spread apart a distance to provide a disc space height h_dthat is equal to or slightly greater than the maximum non-expanded height h₁of theimplant body322. Additionally, the recessed positioning of theteeth360 allow theimplant body322 to be provided with teeth360 (or other types of surface projections) having a greater height than would otherwise be allowed for if theteeth360 were not at least partially recessed below the stationaryouter surfaces344,346 when theimplant320 is in the initial, non-expanded state.
• In the illustrated embodiment of theimplant body322, theteeth360 are arranged in rows extending laterally across the width of themovable wall portions330a,330band332a,332b.Although theimplant body322 is shown as having eight rows ofteeth360 associated with each of the movable wall portions, it should be understood that the inclusion of a single row of teeth or any number of rows of teeth are also contemplated. Additionally, it should be understood that theteeth360 may be orientated in other directions such as, for example, in a direction parallel with the longitudinal axis L or arranged at an oblique angle relative to the longitudinal axis L. In one embodiment, theteeth360 have a triangular-shaped configuration; however, other shapes and configurations of teeth are also contemplated as falling within the scope-of the present invention. Furthermore, in the illustrated embodiment of the invention, theouter teeth360 located fartherest from the central transverse axis T have a somewhat lesser height than theintermediate teeth360 located adjacent the central transverse axis T. As should be appreciated, this variation in height ensures that each of theteeth360 are recessed below the convexly curvedouter surfaces344,346 defined by the upper and lowerstationary walls329,331. However, it should be understood that other sizes and arrangements of theteeth360 are also contemplated as falling within the scope of the present invention.
• As shown inFIG. 11, in one embodiment of the invention, theimplant body322 defines a bone in-growth opening or slot380 extending transversely therethrough in communication with theinner chamber340 and opening onto theouter surfaces344,346 of the upper and lowerstationary wall portions329,331. In the illustrated embodiment, theslot380 extends along substantially the entire length of theimplant body322 and defines a pair of longitudinally extending and oppositely facing side surfaces382a,382bat the location where theslot380 extends through each of thestationary wall portions329,331. As should be appreciated, the bone in-growth slot380 permits bone growth from the adjacent vertebral bodies and into and potentially through theimplant body322. Additionally, theslot380 is also sized to receive a portion of theexpansion member24 therein, between the opposing side surfaces382a,382b,to aid in guiding theexpansion member24 generally along the longitudinal axis L to substantially prevent side-to-side displacement as theexpansion member24 is axially displaced through theimplant body322 during expansion of thespinal implant320.
• Although theimplant body322 is illustrated as having a single bone in-growth slot380 extending transversely through and along substantially the entire length l of theimplant body322, it should be understood that theimplant body322 may be configured to have any number of bone in-growth slots, including two or more bone in-growth slots or openings positioned at various locations along the length of theimplant body322. Additionally, although the bone in-growth slot380 is illustrated as having a generally rectangular configuration having a slot length extending along substantially the entire length of theimplant body322, and a slot width w_sextending across about one-third of the width w of theimplant body322, it should be understood that other shapes, configurations and sizes of bone in-growth openings are also contemplated. It should further be understood that although the bone in-growth slot380 is illustrated and described as communicating with theinner chamber340, in other embodiments, theslot380 need not necessarily extend entirely through the upper and lowerstationary wall portions329,331, but may instead extend partially therethrough.
• As shown inFIG. 11, in the illustrated embodiment of theimplant body322, anaxial opening384 extends through the trailingend wall336 and into communication with theinner chamber340. However, the rounded leadingend wall334 is preferably solid or closed off. Nevertheless, in other embodiments of the invention, an axial opening may also extend through theleading end wall334 and into communication with theinner chamber340. Theaxial opening384 extending through the trailingend wall336 is sized to receive an end portion of an instrument therein for engagement with theexpansion member24 to facilitate transitioning of theimplant body322 to an expanded configuration. In the illustrated embodiment of the invention, theaxial opening384 has a generally rectangular configuration and has a relatively large size which encompasses a substantially portion of the trailingend336. However, it should be understood that other sizes, shapes and configurations of theaxial opening384 are also contemplated as falling within the scope of the present invention.
• As illustrated inFIG. 10, in one embodiment of the invention, theinner chamber340 includes a number of distinct compartments or sections positioned along the length of theimplant body322. In the illustrated embodiment of theimplant body322, theinner chamber340 includes end compartments390aand390bpositioned adjacent theend portions322aand322bof theimplant body322, and an intermediate orcenter compartment390cpositioned adjacent thecentral portion322cof theimplant body322. However, it should be understood that theinner chamber340 may include any number of compartments, including a single compartment, two compartments, or four or more compartments. In the illustrated embodiment of the invention, each of the chamber compartments390a,390b,390cextends laterally through the entire width w of theimplant body322, thereby providing increased flexibility for expansion of theimplant body322 and also providing theimplant body322 with open sides to permit bone growth into theinner chamber340 from lateral directions.
• In the illustrated embodiment of theimplant body322, the end compartments390a,390beach have a tapered region wherein the inner surfaces of the upper and lowermovable wall portions330a,330band332a,332badjacent theintermediate compartment390ctaper inwardly toward one another to define a pair of opposing rampedsurfaces392a,392b.The center compartments390chas an arcuate configuration, with the inner surfaces of themovable wall portions330a,330band332a,332bdefining a pair of opposingconcave surfaces394a,394bhaving substantially the same curvature as the upper and lower arcuate engagement surfaces120a,120bdefined by theexpansion member24, the details of which will be discussed below. The point of intersection between the rampedsurfaces392a,392bof the end compartments390a,390band theconcave surfaces394a,394bof thecenter compartment390cdefines opposing apices orvertices396a,396band398a,398bpositioned on either side of thecenter compartment390c.Although the illustrated embodiment of theimplant body322 depicts theinner chamber340 and thecompartments390a,390band390cas having a particular shape and configuration, it should be understood that other suitable shapes and configurations are also contemplate as falling within the scope of the present invention.
• As indicated above, theexpansion member24 is identical to the expansion member illustrated inFIGS. 5 and 6 and as described above with regard to theintervertebral implant20. In general, theexpansion member24 includes acentral portion100 having a generally rectangular or square cross section, and a pair ofside portions102a,102bprojecting laterally from thecentral portion100 and having a generally circular cross section. At least the upper andlower segments108a,108bof thecentral portion100 define a width w_ebetween the side surfaces106a,106bthat closely corresponds to the width w_sof theslot380 extending through theimplant body322. The upper andlower segments108a,108bof thecentral portion100 are displaceable through theslot380 and along the opposing side surfaces382a,382bas theexpansion member24 is axially displaced through theinner chamber340 during transitioning of theimplant body322 toward the expanded configuration illustrated inFIGS. 12 and 13. Thecentral portion100 defines apassage110 having a diameter d₁and which is sized to receive a distal end portion of a surgical instrument therein such as, for example, thesurgical instrument200 shown inFIG. 7 and described above.
• In the illustrated embodiment of the invention, each of theside portions102a,102bof theexpansion member24 defines upper and lower engagement surfaces120a,120bhaving a curved or arcuate configuration. The curved engagement surfaces120a,120bfacilitate sliding movement along the rampedsurfaces392a,392bof the upper and lowermovable wall portions330a,330band332a,332bof theimplant body322 as theexpansion member24 is axially displaced through theinner chamber340 during transitioning of theimplant body322 to the expanded configuration. Additionally, theside portions102a,102bprovide theexpansion member24 with an overall width that is less than or equal to the overall width w of theimplant body322 so that theside portions102a,102bdo not extend laterally beyond the side surfaces of theimplant body322.
• In one embodiment of the invention, thesurgical instrument200 illustrated inFIG. 7 and described above in association with theexpandable implant20 is also used to aid in the insertion of theimplant320 into the disc space and to transition theimplant body322 to the expanded configuration illustrated inFIGS. 12 and 13. However, it should be understood that other suitable types and configurations of surgical instruments are also contemplated for use in association with the present invention. Thesurgical instrument200 cooperates with thespinal implant320 in a manner very similar to that described above with regard to thespinal implant20. Accordingly, the specific details regarding use of thesurgical instrument200 in association with thespinal implant320 need not be discussed herein.
• As shown inFIG. 10, in one embodiment of the invention, theexpansion member24 is initially positioned in theend compartment390aadjacent the leading ordistal end322aof theimplant body322, and expansion of theimplant body322 is accomplished by pulling theexpansion member24 toward the trailing orproximal end322bof theimplant body322 until theexpansion member24 is positioned within thecenter compartment390c.In another embodiment of the invention, theexpansion member24 may be initially positioned in theend compartment390badjacent theproximal end322b,with expansion of theimplant320 resulting from pushing theexpansion member24 toward thedistal end322auntil theexpansion member24 is positioned within thecenter compartment390c.However, the initial positioning theexpansion member24 in thedistal end compartment390aand pulling theexpansion member24 into thecenter compartment390cresults in the relatively simpler overall design of a “pull” style instrument, such as thesurgical instrument200 illustrated inFIG. 7 and described above.
• As should be appreciated, axial displacement of theexpansion member24 in the direction of arrow A will correspondingly transition theimplant body322 toward the fully expanded configuration illustrated inFIGS. 12 and 13. More specifically, axial displacement of theexpansion member24 from thedistal end compartment390atoward thecenter compartment390cslidably engages the upper andlower engagement surface120a,120bdefined by theside portions102a,102bof theexpansion member24 along the opposing rampedsurfaces392a,392bdefined by theimplant body322. As a result, the upper and lowermovable wall portions330a,330band332a,332bof theimplant body322 are driven away from one another and are outwardly deformed along the transverse axis T to transition theimplant body322 from the initial, non-expanded configuration illustrated inFIGS. 10 and 11 toward the expanded configuration illustrated inFIGS. 12 and 13. The expansion member to24 is further displaced in an axial direction until positioned within thecenter compartment390cof theinner chamber340, with theside portions102a,102bof theexpansion member24 positioned within the recessed areas formed by the opposingconcave surfaces394a,394band captured between the opposing apices/vertices396a,396band398a,398b.
• It should be appreciated that positioning of theside portions102a,102bof theexpansion member24 within the opposingconcave surfaces394a,394band between the opposing apices/vertices396a,396band398a,398bretains theexpansion member24 within thecenter compartment390cand resists or inhibits further axial displacement of theexpansion member24 to thereby maintain theimplant body322 in the expanded configuration shown inFIGS. 12 and 13, even after thesurgical instrument200 is detached from theexpansion member24. It should also be appreciated that during expansion of theimplant body322, once theexpansion member24 is positioned beyond the pair of opposing apices/vertices396a,396band enters or “clicks” into thecenter compartment390c,the amount of linear driving force required to displace theexpansion member24 will significantly and abruptly decrease. This abrupt drop-off in driving force provides the surgeon with a perceptible indication that theexpansion member24 is properly positioned within thecenter compartment390cand that the desired amount of expansion has been attained.
• Additionally, as indicated above, the upper andlower segments108a,108bof theexpansion member24 define a width w_ebetween the side surfaces106a,106bthat closely corresponds to the width w_sof theslot380 extending through theimplant body322. Accordingly, as theexpansion member24 is displaced through theinner chamber340 of theimplant body322 to transition theimplant body322 toward the expanded configuration, the upper andlower segments108a,108bof thecentral portion100 are displaced through theslot380, with the side surfaces106a,106bbeing slidably displaced along the opposing side surfaces382a,382bof theslot380. Displacement of the upper andlower segments108a,108bof thecentral portion100 through theslot380 aids in guiding theexpansion member24 through theinner chamber340 during expansion of theimplant body322. Additionally, the relatively close fit between the side surfaces106a,106bof theexpansion member24 and the opposing side surfaces382a,382bof theslot380 provides additional support and rigidity to theimplant body322, and particularly resists side-to-side or lateral forces exerted onto theimplant320 by the upper and lower vertebral bodies V_U, V_L.
• As shown inFIGS. 12 and 13, expansion of theimplant body322 increases the overall height of the upper and lowermovable wall portions330a,330band332a,332badjacent thecentral portion322cto an expanded height that is substantial equal to the height adjacent the central portion of the intervertebral disc space. As should be appreciated, the difference between the initial and expanded heights of the movable wall portions corresponds to the difference between the diameter d₁(or height) of theside portions102a,102bof the expansion member24 (FIGS. 5 and 6) and the non-expanded distance between theconcave surfaces394a,394bof thecenter compartment390cof the implant body322 (FIG. 10). Accordingly, expansion of theimplant body322 can be easily and accurately controlled by providing theexpansion member24 withside portions102a,102bhaving a select diameter d₁(or height) and/or by providing thecenter compartment390cwith a configuration having a select non-expanded distance between theconcave surfaces394a,394b.
• When theimplant body322 is transitioned to the expanded configuration, the upper and lowermovable wall portions330a,330band332a,332bare outwardly deformed away from one another along the transverse axis T to increase the overall height thereof. Since the end portions of the upper and lowermovable wall portions330a,330band332a,332bare integrally connected to theend walls334,336, the end portions of the movable wall portions remain relatively stationary, and expansion of theimplant body322 adjacent theimplant end portions322a,322bis limited. However, since the central portions of the upper and lowermovable wall portions330a,330band332a,332bare not interconnected, expansion of theimplant body322 occurs primarily along thecentral portion322cof theimplant body322. As a result, upon expansion of theimplant body322, the upper and lowermovable wall portions330a,330band332a,332beach form an outwardly extending convex curvature relative to the longitudinal axis L. As illustrated inFIG. 14, the convex curvature of the outwardly deformedmovable wall portions330a,330band332a,332bpreferably substantially corresponds to the anterior-to-posterior surface curvature defined by the vertebral endplates of the adjacent vertebral bodies V_U, V_L. Additionally, expansion of theimplant body322 generally along the transverse axis T imbeds or impacts theteeth360 extending from the upper and lower movable wall portions into the vertebral endplates to resist migration and possible expulsion of theimplant body322 from the intervertebral disc space. Following expansion of theimplant body322, thesurgical instrument200 is disengaged from theexpansion member24 and removed from the patient.
• If removal of the expandedimplant320 from the disc space is required due to non-optimal placement of theimplant320 or for other reasons, theimplant body322 can be transitioned from the expanded configuration (FIG. 12) back toward the initial, non-expanded configuration (FIG. 10) by simply repositioning theexpansion member24 from thecenter compartment390cto theproximal end compartment390b.Such repositioning will in turn cause theflexible implant body322 to retract toward the initial, non-expanded configuration illustrated inFIG. 10, wherein theteeth360 will once again be at least partially inwardly recessed relative to theouter surfaces344,346 of the upper and lowerstationary wall portions329,331 so as to avoid interfering with the upper and lower vertebral bodies V_U, V_Lwhich may otherwise impede removal of theimplant320 from the intervertebral disc space. Theimplant320 may then be removed from the disc space and reintroduced therein using the insertion and expansion procedures outlined above to reposition theimplant320 into a revised position within the disc space.
• In a further aspect of the invention, following the insertion and expansion of theimplant320 within the disc space, a bone growth promoting material130 (FIG. 14) is loaded into theinner chamber340 of theimplant body322 to facilitate or promote bone growth from the upper and lower vertebral bodies V_U, V_L, through theslot380 extending through the upper and lowerstationary wall portions329,331, and into and possibly through theimplant body322. In one embodiment of the invention, the bonegrowth promoting material130 is loaded or packed into theinner chamber340 via theaxial opening384 in therear end wall336 subsequent to insertion and expansion of theimplant body322. However, in an alterative embodiment, a portion of the bonegrowth promoting material130 may be pre-loaded into theinner chamber340 prior to insertion and expansion of theimplant body322.
• As indicated above, the size of thepassage110 in thecentral portion100 of theexpansion member24 is relatively large. As a result, the bonegrowth promoting material130 may be conveyed through thelarge passage110 in theexpansion member24 and into thedistal end compartment390aof theinner chamber340. Once thedistal end compartment390ais fully loaded, additional bonegrowth promoting material130 may be loaded into theproximal end compartment390bof theinner chamber340. As should be appreciated, due to the inclusion of the relativelylarge passage110 in theexpansion member24, the bonegrowth promoting material130 need not be preloaded into thedistal end compartment390aprior to insertion and expansion of theimplant320 within the disc space. Additionally, conveying the bonegrowth promoting material130 through the relativelylarge passage110 in theexpansion member24 allows the entireinner chamber340 to be tightly packed with the bonegrowth promoting material130. Additionally, bone graft, morselized autograft bone or a similar type of material may be positioned laterally adjacent the expandedimplant body322 to further promote fusion with the adjacent vertebral bodies V_U, V_L.
• Having illustrated and described the elements and operation of thespinal implant320, reference will now be made to a technique for implanting thespinal implant320 within an intervertebral disc space according to one embodiment of the invention. However, it should be understood that other implantation techniques and procedures are also contemplated, and that the following technique in no way limits the scope of the present invention.
• In one embodiment of the invention, access to the spinal column and insertion of thespinal implant320 into the disc space is accomplished via a posterior surgical approach. However, it should be understood that access and insertion of thespinal implant320 into the disc space may be accomplished via other surgical approaches such as, for example, an anterior approach or a lateral approach. In another embodiment of the invention, thespinal implant320 is used to treat the lumbar region of the spine, with the upper and lower vertebral bodies V_U, V_Lcomprising lumbar vertebral bodies. However, it should be understood that the present invention is also applicable to other portions of the spine such as, for example, the cervical, thoracic or sacral regions of the spinal column. Initially, the portion of the spinal column to be treated is identified and accessed from a posterior approach using known surgical techniques. At least a portion of the natural intervertebral disc is removed via a total or partial discectomy to provide an opening for receiving thespinal implant320 between the upper and lower vertebral bodies V_U, V_L. The disc space is then distracted to a height substantially equal to the natural disc space height. Prior to insertion of thespinal implant320, the disc space and the endplates of the upper and lower vertebral bodies V_U, V_Lmay be prepared using various cutting tools and/or other types of surgical instruments (e.g., curettes, chisels, etc.).
• In a further embodiment of the present invention, the cutting instrument used to prepare the vertebral bodies V_U, V_Lis adapted to cut and remove bone tissue from the vertebral endplates while substantially retaining the natural concave curvature of the endplates and avoiding cutting into the cortical rim/apophyseal ring region adjacent the anterior/posterior portions of the vertebral endplates. The cutting instrument may also be configured to collect bony debris or chips generated during the cutting operation for subsequent insertion into theinner chamber340 of theimplant body322 to promote arthrodesis. As illustrated inFIG. 14, each of the prepared vertebral endplates defines a recessed area or surface curvature that is generally concave in an anterior-to-posterior direction. As should be appreciated, the recessed area or surface curvature defined by the vertebral bodies V_U, V_Lreceives the upper and lowerstationary wall portions329,331 of the expandedimplant body322 so as to position thebone growth material130 positioned therein in close proximity to the spongy cancellous bone tissue of the vertebral bodies V_U, V_Lto promote fusion. Following preparation of the vertebral endplates, theimplant320 is inserted into the disc space using a suitable insertion technique such as, for example, impaction or push-in type insertion. Notably, since thespinal implant320 is inserted into the disc space while in a non-expanded configuration having an initial maximum height h₁that is somewhat less than the disc space height, over distraction of the disc space is avoided and neural distraction is minimized.
• Following insertion of theimplant320 into the intervertebral disc space, theimplant body322 is expanded to the configuration illustrated inFIG. 14 to restore and/or maintain a desired disc space height. Additionally, transitioning of thespinal implant320 to the expanded configuration illustrated inFIG. 14 imbeds or impacts theteeth360 into the vertebral endplates to resist migration and possible expulsion of theimplant body322 from the disc space. Moreover, positioning of the outwardly deformed upper and lowermovable wall portions330a,330band332a,332bwithin the concave surface curvature defined by the upper and lower vertebral bodies V_U, V_Ltends to increase stability of theimplant body322 and also reduces the likelihood of migration and possible expulsion of theimplant body322 from the disc space. Furthermore, positioning of the upper and lowerstationary wall portions329,331 in close proximity to or in direct contact with the cancellous or spongiseum bone tissue of the upper and lower vertebral bodies V_U, V_Lfacilitates bone growth through theslot380 and into theinner chamber340. The upper and lower anterior/posterior bearing surfaces354a,354band356a,356bof theimplant body322 are positioned to bear against the cortical rim/apophyseal ring region of the respective upper and lower vertebral bodies V_U, V_Lto resist the compressive forces exerted onto theimplant body322 and to reduce the likelihood of subsidence into the relatively softer cancellous or spongiseum bone tissue.
• In a further aspect of the invention, positioning of theexpansion member24 within thecenter compartment390cof theinner chamber340 provides additional support and rigidity to the upper and lowermovable wall portions330a,330band332a,332bof theimplant body322 to resist compression loads from the vertebral bodies V_U, V_L, particularly near thecentral portion322cof theimplant body322 which is otherwise devoid of internal support members. Additionally, as discussed above, the relatively close fitting engagement of the upper andlower segments108a,108bof theexpansion member24 within theslot380 in the upper and lowerstationary wall portions329,331 also provides additional support and rigidity to theimplant body322, and particularly resists side-to-side or lateral forces exerted onto theimplant320 by the upper and lower vertebral bodies V_U, V_L. Although thespinal implant320 is maintained in the expanded configuration solely via engagement between theexpansion member24 and the upper and lower wall portions of theimplant body322, it should be understood that one or more supplemental internal fixation elements may also be used to provide further support to theimplant body322, particularly in instances involving excessive vertebral loading and/or instability. It should also be understood that supplemental external intravertebral fixation elements and/or stabilization techniques may also be used if excessive residual instability is encountered following insertion and expansion of one or more of theimplants320 within the disc space.
• In a further embodiment of the invention, a pair of the expandablespinal implants320 may be positioned side-by-side in a bilateral arrangement within the disc space in a manner similar to that shown inFIG. 9. However, it should be understood that unilateral placement or central placement of a singlespinal implant320 within the disc space is also contemplated as falling within the scope of the present invention. Bone graft, morselized autograft bone, or a bone growth promoting substance may be positioned within the area between thebilateral implants320 to further facilitate fusion between the upper and lower vertebral bodies V_U, V_L.
• While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.

Claims (26)

1.-45. (canceled)

46. An expandable spinal implant, comprising:

an implant body having a longitudinal axis and being transitionable between an initial configuration and an expanded configuration, said implant body including an implant length extending between first and second ends and including first and second axial walls extending along said implant length and spaced apart along a transverse axis extending along a height of said implant body, at least one of said axial walls including first and second axial wall portions laterally offset from one another and extending continuously and substantially entirely along said implant length; and

an expansion member co-acting with said first wall portion to outwardly displace said first wall portion relative to said second wall portion generally along said transverse axis to transition said implant body from said initial configuration to said expanded configuration.

47. The implant ofclaim 46, wherein said second axial wall portion remains substantially stationary relative to said first axial wall portion as said implant body is transitioned from said initial configuration to said expanded configuration.

48. The implant ofclaim 46, wherein said first axial wall portion is positioned laterally adjacent said second axial wall portion.

49. The implant ofclaim 46, wherein said implant body includes first and second transverse end walls interconnecting opposite end portions of said first axial wall with opposite end portions of said second axial wall.

50. The implant ofclaim 46, wherein said first axial wall portion defines a recessed region relative to said second axial wall portion when said implant body is in said initial configuration; and

wherein said recessed region is outwardly expanded generally along said transverse axis as said implant body is transitioned from said initial configuration to said expanded configuration.

51. The implant ofclaim 46, wherein said at least one of said axial walls includes a third axial wall portion laterally offset from said second axial wall portion with said first and third axial wall portions positioned on opposite sides of said second axial wall portion; and

wherein said expansion member co-acts with each of said first and third wall portions to outwardly displace said first and third wall portions relative to said second wall portion generally along said transverse axis to transition said implant body from said initial configuration to said expanded configuration; and

wherein said second axial wall portion remains substantially stationary relative to said first and third axial wall portions as said implant body is transitioned from said initial configuration to said expanded configuration.

52. The implant ofclaim 46, wherein said first axial wall portion includes a first outer surface that is inwardly recessed relative to a second outer surface of said second axial wall portion when said implant body is in said initial configuration.

53. The implant ofclaim 52, wherein said first outer surface of said first axial wall portion is substantially aligned with said second outer surface of said second axial wall portion when said implant body is transitioned to said expanded configuration.

54. The implant ofclaim 52, wherein said first axial wall portion includes a number of surface protrusions projecting outwardly from said first outer surface, at least a portion of said surface protrusions being inwardly recessed relative to said second outer surface of said second axial wall portion when said implant body is in said initial configuration.

55. The implant ofclaim 54, wherein said surface protrusions are entirely inwardly recessed relative to said second outer surface of said second axial wall portion when said implant body is in said initial configuration.

56. The implant ofclaim 54, wherein said surface protrusions are at least partially positioned outward of said second outer surface of said second axial wall portion when said implant body is transitioned to said expanded configuration.

57. The implant ofclaim 46, wherein said first axial wall portion of said at least one of said axial walls is flexibly deformed during transitioning of said implant body to said expanded configuration to outwardly displace said first axial wall portion relative to said second axial wall portion generally along said transverse axis to transition said implant body from said initial configuration to said expanded configuration.

58. An expandable spinal implant, comprising:

an implant body having a longitudinal axis and being transitionable between an initial configuration and an expanded configuration, said implant body including an implant length extending between first and second ends and including first and second axial walls extending along said implant length and spaced apart along a transverse axis extending along a height of said implant body, at least one of said axial walls including first and second axial wall portions laterally offset from one another and extending continuously and substantially entirely along said implant length, said first axial wall portion defining a recessed region relative to said second axial wall portion when said implant body is in said initial configuration; and

an expansion member co-acting with said first wall portion to transition said implant body from said initial configuration to said expanded configuration wherein said recessed region is outwardly expanded generally along said transverse axis.

59. The implant ofclaim 58, wherein said second axial wall portion remains substantially stationary relative to said first axial wall portion as said implant body is transitioned from said initial configuration to said expanded configuration.

60. The implant ofclaim 58, wherein the first axial wall portion is positioned laterally adjacent said second axial wall portion.

61. The implant ofclaim 58, wherein said implant body includes first and second transverse end walls interconnecting opposite end portions of said first axial wall with opposite end portions of said second axial wall, said recessed region extending along substantially an entire length of said at least one of said axial walls between said pair of opposite end portions.

62. The implant ofclaim 58, wherein said recessed region defined by said first axial wall portion comprises a convex curvature extending outwardly along said transverse axis and along substantially an entire length of said at least one of said axial walls.

63. The implant ofclaim 58, wherein said first axial wall portion includes a first outer surface that is inwardly positioned relative to a second outer surface of said second axial wall portion when said implant body is in said initial configuration to define said recessed region.

64. The implant ofclaim 63, wherein said first axial wall portion includes a number of surface protrusions projecting outwardly from said first outer surface, at least a portion of said surface protrusions being inwardly recessed relative to said second outer surface of said second axial wall portion when said implant body is in said initial configuration.

65. An expandable spinal implant, comprising:

an implant body having a longitudinal axis and being transitionable between an initial configuration and an expanded configuration, said implant body including an implant length extending between first and second ends and including first and second axial walls extending along said implant length and spaced apart along a transverse axis extending along a height of said implant body, at least one of said axial walls including a movable wall portion and a substantially stationary wall portion laterally offset from one another and extending continuously and substantially entirely along said implant length; and

an expansion member co-acting with said movable wall portion to outwardly displace said movable wall portion relative to said stationary wall portion generally along said transverse axis to transition said implant body from said initial configuration to said expanded configuration.

66. The implant ofclaim 65, wherein said movable wall portion defines a recessed region relative to said stationary wall portion when said implant body is in said initial configuration; and

wherein said recessed region is outwardly expanded generally along said transverse axis as said implant body is transitioned from said initial configuration to said expanded configuration.

67. The implant ofclaim 65, wherein the movable wall portion is positioned laterally adjacent said stationary wall portion.

68. The implant ofclaim 65, wherein said at least one of said axial walls includes a pair of said movable wall portions positioned on opposite sides of said stationary wall portion; and

wherein said expansion member co-acts with each of said movable wall portions to outwardly displace said movable wall portions relative to said stationary wall portion generally along said transverse axis to transition said implant body from said initial configuration to said expanded configuration.

69. The implant ofclaim 65, wherein said movable wall portion includes a first outer surface that is inwardly recessed relative to a second outer surface of said stationary wall portion when said implant body is in said initial configuration.

70. The implant ofclaim 65, wherein said movable wall portion is flexibly deformed during transitioning of said implant body to said expanded configuration to outwardly displace said movable wall portion relative to said stationary wall portion generally along said transverse axis to transition said implant body from said initial configuration to said expanded configuration.

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