Patent Description:
Surgical interbody fusion is often performed to fuse adjacent vertebrae to each other, thereby eliminating the spinal cord compression. Conventional surgical techniques include distraction of the vertebral bodies, spanning the disc space with an intervertebral spacer, typically made from polymethylmethacrylate (PMMA), and fixing the spacer in the disc space using screws or pins or the like. However, current surgical techniques risk complications, such as backing out of the screws or pins, cracking of the spacer, laceration of vertebral arteries, spinal nerves, nerve roots, and trauma to the spinal cord. Complications can further include improper placement of the pins or screws which are intended be bicortical, meaning that they are intended to thread into both a near cortex and a far cortex of the vertebral body. <CIT> teaches an intervertebral spacer implant with a retention mechanism to help alleviate expulsion and movement of the implant when placed in the spine while providing an implant that is easier to insert in the spine. The retention mechanism may comprise a keel on at least one of the inferior or superior faces of the spacer implant preferably extending in an anterior-posterior direction. <CIT> teaches an allogenic implant for use in intervertebral fusion, which is formed from one or more two pieces. The pieces are made from bone, and are joined together to form an implant having sufficient strength and stability to maintain a desired distance between first and second vertebrae in a spinal fusion procedure. The implant pieces may be formed of cortical bone and connected by dovetail joints, and at least one cortical bone pin may be provided to lock the pieces together and to add strength to the implant. Teeth are formed on the vertebra engaging surfaces of the implant prevent short-term slippage of the implant. <CIT> is directed to a spinal implant for insertion between vertebrae bodies. The implant may include an anterior surface, a posterior surface, first and second lateral surfaces extending therebetween, a superior surface for engaging one of the vertebrae bodies, an inferior surface for engaging the other vertebrae body, and a central bore which extends from the superior surface to the inferior surface. The central bore has a generally lobe-shaped footprint. The anterior surface of the implant may include a pair of vertical channels sized and configured to engage an insertion instrument and the superior surface preferably has a convexly curved surface extending substantially from the anterior surface to the posterior surface while the inferior surface has a substantially constant taper extending from the anterior surface to the posterior surface. <CIT> relates to a spinal implant. The spinal implant may be used for lateral insertion into an intervertebral disc space. For example, the spinal implant may include a spacer body to which a plate is fixed. The intervertebral spacer body may include a pair of opposite sides having pyramid-shaped teeth to fuse to bone. The plate defines at least one upper and lower borehole that each receives a screw. Each screw attaches the plate to a vertebral body between which the intervertebral spacer body is inserted. The boreholes may include locking threads that are adapted to lock the screws into place by engaging complementary locking threads of head of the screw. <CIT> discloses arcuate fixation members with varying configurations and/or features, along with additional components for use therewith in provided intervertebral implants. The arcuate fixation members may be of different lengths, cross sectional geometries, and/or cross-sectional areas. Applications of intervertebral implants utilizing arcuate fixation members are particularly suitable when a linear line-of-approach for delivering fixation members is undesirable.

What is therefore needed is an improved system for providing intervertebral fixation of a quadruped, and in particular of a canine.

In one example, an intervertebral implant is configured to be implanted in an intervertebral disc space of a quadruped, the intervertebral disc space defined by a cranial vertebral body and a caudal vertebral body. The implant can include a plate that defines a ventral plate end and a dorsal plate end spaced opposite the ventral plate end in a dorsal direction. The plate can further include a plurality of fixation apertures that extend through the plate from the ventral plate end to the dorsal plate end. The implant can further include a spacer that extends in the dorsal direction from the plate. The spacer can define a caudal surface and a cranial surface opposite the caudal surface in a cranial direction. The caudal and cranial surfaces can be configured to grip the caudal and cranial vertebral bodies, respectively. The cranial surface can be convex in a first plane that is oriented along the dorsal direction and the cranial direction, and the cranial surface is convex in a second plane that is oriented along the cranial direction and a lateral direction that is substantially perpendicular to each of the dorsal direction and the cranial direction. The caudal surface is substantially straight and liner in the first plane, and the caudal surface is concave in the second plane.

The foregoing summary, as well as the following detailed description of the preferred embodiments of the application, will be better understood when read in conjunction with the appended drawings. For the purposes of illustrating the preferred intervertebral implants of the present application, there is shown in the drawings preferred embodiments. It should be understood, however, that the application is not limited to the precise arrangements and instrumentalities shown. In the drawings:.

The present disclosure can be understood more readily by reference to the following detailed description taken in connection with the accompanying figures and examples, which form a part of this disclosure. It is to be understood that this disclosure is not limited to the specific devices, methods (not claimed), applications, conditions or parameters described and/or shown herein, and that the terminology used herein is for the purpose of describing particular embodiments by way of example only and is not intended to be limiting of the scope of the present disclosure. Also, as used herein, the singular forms "a," "an," and "the" include "at least one" and a plurality, unless otherwise indicated. Further, reference to a plurality as used herein includes the singular "a," "an," "one," and "the," and further includes "at least one" unless otherwise indicated. Further still, the term "at least one" can include the singular "a," "an," and "the," and further can include a plurality, unless otherwise indicated. Further yet, reference to a particular numerical value in the specification including the appended claims includes at least that particular value, unless otherwise indicated.

The term "plurality", as used herein, means more than one, such as two or more. When a range of values is expressed, another example includes from the one particular value and/or to the other particular value. The words "substantially" and "approximately" as used herein with respect to a shape, size, or other parameter or numerical value includes the stated shape, size, or other parameter or numerical value, and further includes plus and minus <NUM>% of the stated shape, size, or other parameter or numerical value.

Referring initially to <FIG>, an intervertebral implant <NUM> is configured to be implanted into the spine <NUM> of a quadruped, which can be a canine. The spine <NUM> of the quadruped includes a plurality of vertebrae <NUM> separated from each other by an intervertebral disc space <NUM> that contains disc material in a healthy quadruped. The vertebrae <NUM> include a first or cranial vertebral body <NUM> and an adjacent second or caudal vertebral body <NUM> separated from the cranial vertebral body <NUM> by a respective intervertebral disc space <NUM>. When the quadruped suffers from a condition that indicates fusion of the adjacent vertebral bodies <NUM> and <NUM>, the intervertebral implant <NUM> can be implanted into the disc space <NUM> that fuses the vertebral bodies <NUM> and <NUM> to each other following a discectomy procedure whereby some or all of the disc material is removed from the disc space <NUM>. In one example, the quadruped can be suffering from CSM, and thus the vertebral bodies <NUM> and <NUM> can be cervical vertebral bodies. While the intervertebral implant <NUM> can contain features that are designed for implantation in the cervical region of the spine as described below, it should be appreciated that the vertebral bodies <NUM> and <NUM> can alternatively be located in the thoracic or lumbar regions of the quadruped.

Referring also to <FIG>, the implant <NUM> can include a plate <NUM> and a spacer <NUM> that extends from the plate <NUM>. The spacer <NUM> is preferably configured and dimensioned for implantation into the intervertebral disc space <NUM> between the first and second vertebral bodies <NUM> and <NUM>. The spacer <NUM> is preferably sized and configured to maintain and/or restore a desired intervertebral disc height between the adjacent vertebral bodies <NUM> and <NUM>. The plate <NUM> can be configured to be fixed to the first and second vertebral bodies <NUM> and <NUM>.

The intervertebral implant <NUM> may be constructed of any suitable material or combination of materials including, but not limited to polymer (e.g. PEEK), titanium, titanium alloy, stainless steel, Nitinol, tantalum nitride (TaN), allograft bone, bioresorbable material, magnesium, composites, synthetic bone-welding polymers, etc. The plate <NUM> may be formed of a different material than the spacer <NUM>. For example, the plate <NUM> may be formed of a metallic material such as, for example, a titanium or a titanium alloy, and the spacer <NUM> may be formed of a non-metallic material such as, for example, an allograft, a polymer, a bioresorbable material, a ceramic, etc. Alternatively, the plate <NUM> and the spacer <NUM> may be formed from the same material. For example, the plate <NUM> and the spacer <NUM> may both be constructed of tantalum nitride (TaN) or any suitable alternative material as desired.

The spacer <NUM> may include a first or leading end <NUM> with respect to insertion into the disc space <NUM>, and a second or trailing end <NUM> that is opposite the leading end <NUM> along a longitudinal direction L. A forward or insertion direction into the disc space <NUM> can thus refer to a direction from the trailing end <NUM> toward the leading end <NUM>. A rearward direction opposite the forward direction can refer to a direction from the leading end <NUM> toward the trailing end <NUM>. The intervertebral implant <NUM> can be configured such that the insertion direction is oriented along any suitable approach as desired, including but not limited to a lateral approach. Thus, the leading end <NUM> can be referred to as a dorsal end, and the trailing end <NUM> can be referred to as a ventral end. Further, the forward or insertion direction can be referred to as a dorsal direction, and vice versa. The rearward direction can be referred to as a ventral direction, and vice versa. The ventral direction is opposite the dorsal direction. Accordingly, the term "longitudinal direction L" can be used interchangeably with a dorsal-ventral direction that either or both of the dorsal direction and the ventral direction, and vice versa. A ventral-dorsal direction includes each of the dorsal direction and the ventral direction.

The spacer <NUM> can extend along a central spacer axis <NUM>. The central spacer axis <NUM> can be oriented along the longitudinal direction L, and can bifurcate the spacer <NUM> into two substantially equally sized and shaped halves. The spacer <NUM> can include a first or cranial wall that defines an outer first or cranial surface <NUM>. The outer cranial surface <NUM> is configured to face the cranial direction when implanted. The spacer <NUM> can include a second or caudal wall that defines an outer second or caudal surface <NUM>. The outer caudal surface <NUM> is configured to face the caudal direction when implanted. Thus, the caudal surface <NUM> can face opposite the cranial surface <NUM> along a transverse direction T that is substantially perpendicular to the longitudinal direction L. The caudal surface <NUM> can further be said to be opposite the cranial surface <NUM> in a caudal direction. Similarly, the cranial surface <NUM> can further be said to be opposite the caudal surface <NUM> in a cranial direction Thus, the term "transverse direction T" can be used interchangeably with either or both of the cranial direction and the caudal direction, and vice versa. A caudal-cranial direction includes each of the caudal direction and the cranial direction.

The spacer <NUM> can further include first and second opposed lateral walls <NUM> and <NUM> that are opposite each other along a lateral direction A that is substantially perpendicular to each of the transverse direction T and the longitudinal direction L. The spacer can define a midplane <NUM> (see <FIG>) that is oriented along the longitudinal direction L and the transverse direction T, and includes the central spacer axis <NUM>. The midplane <NUM> can thus divide the spacer <NUM> into equal lateral halves. The midplane <NUM> can further divide the plate <NUM> into equal lateral halves. Further, the implant <NUM> can be substantially symmetrical about the midplane <NUM>.

With continuing reference to <FIG>, the cranial surface <NUM> can be configured to face the cranial vertebral body <NUM>, and the caudal surface <NUM> can be configured to face the caudal vertebral body <NUM> when the spacer <NUM> is disposed in the disc space <NUM>. Further, the cranial surface <NUM> can be configured to abut the cranial vertebral body <NUM>, and the caudal surface <NUM> can be configured to abut the caudal vertebral body <NUM> when the spacer <NUM> is disposed in the disc space <NUM>.

In one example, the cranial surface <NUM> can be configured to grip the cranial vertebral body <NUM>, and the caudal surface <NUM> can be configured to grip the caudal vertebral body <NUM> when the spacer <NUM> is disposed in the disc space <NUM>. The intervertebral implant <NUM> can include a plurality of teeth <NUM> that project out from the cranial and caudal surfaces <NUM> and <NUM>, respectively. The teeth <NUM> are configured to penetrate the vertebral endplates of the respective cranial and caudal vertebral bodies <NUM> and <NUM>. Thus, the intervertebral implant <NUM> can be configured to resist migration within the disc space <NUM> after implantation. The teeth <NUM> can be configured in any suitable manner as desired. In particular, the teeth <NUM> can include a leading surface <NUM> with respect to the insertion direction, and a trailing surface <NUM> opposite the leading surface <NUM>. The leading surface <NUM> can be convex, and the trailing surface <NUM> can be concave. The leading and trailing surfaces <NUM> and <NUM> can converge to a sharp pointed tip <NUM>. Distal ends of the leading and trailing surfaces <NUM> and <NUM> can extend along the rearward direction as they converge to the tip <NUM>.

Alternatively or additionally, the spacer <NUM> can include one or more windows <NUM> that are designed to receive bone graft material. The bone graft material can further fuse the intervertebral implant <NUM> to the first and second vertebral bodies <NUM> and <NUM>. The windows <NUM> can extend from the cranial surface <NUM> to the caudal surface <NUM>. The windows <NUM> can be configured to receive bone graft material so as to promote bone growth through the windows <NUM> following implantation of the intervertebral implant <NUM> into the disc space <NUM>. Alternatively or in addition, the spacer <NUM> may have one or more lateral channels extending through the spacer <NUM> from either or both of the lateral walls <NUM> for receiving bone graft material. The lateral channels can be open to the windows <NUM> in some examples. The spacer <NUM> can include a plurality of longitudinally oriented ribs <NUM> and laterally oriented ribs <NUM> that separate and define the windows <NUM>. The teeth <NUM> can extend out from the ribs <NUM> and <NUM>.

The spacer <NUM> can be shaped to substantially match the geometry of the vertebral endplates of the first and second vertebral bodies <NUM> and <NUM>. In one example shown in <FIG>, at least a portion up to an entirety of the cranial surface <NUM> can be curved as it extends in the insertion direction. For instance, a least a portion up to an entirety of the cranial surface <NUM> can be curved as it extends from the plate <NUM> to the leading end <NUM>. In particular, at least a portion up to an entirety of the cranial surface <NUM> can be convex as it extends from the plate <NUM> to the leading end <NUM>. Thus, the cranial surface <NUM> can be curved in a first plane that is oriented along the longitudinal direction L and the transverse direction T. For instance, the cranial surface <NUM> can be convex in the first plane that is oriented along the longitudinal direction L and the transverse direction T. The cranial surface <NUM> can be defined by a first radius of curvature in the first plane that can range from approximately <NUM> to approximately <NUM>. For instance, the first radius of curvature can range from approximately <NUM> to approximately <NUM>. In one example, the first radius of curvature can be approximately <NUM>. In another example, the first radius of curvature can be approximately <NUM>. Further, the first radius of curvature can be constant or variable along the length of the cranial surface 42in the first plane. Thus, a first portion of the cranial surface <NUM> can be defined by a radius of curvature of approximately <NUM>, and a second portion of the cranial surface <NUM> can be defined by a radius of curvature of approximately <NUM>. In one example, the cranial surface <NUM> can be convex in all first planes oriented along the longitudinal direction L and the transverse direction T and arranged from the first lateral wall <NUM> to the second lateral wall <NUM>.

With continuing reference to <FIG>, at least a portion up to an entirety of the caudal surface <NUM> can be substantially straight and linear as it extends in the insertion direction. For instance, a least a portion up to an entirety of the caudal surface <NUM> can be substantially straight and linear as it extends from the plate <NUM> to the leading end <NUM>. For instance, at least a portion up to an entirety of the caudal surface <NUM> can be substantially straight and linear as it extends from the plate <NUM> to the leading end <NUM>. According to the present invention, the caudal surface <NUM> is straight and linear in the first plane that is oriented along the longitudinal direction L and the transverse direction T. In one example, the cranial surface <NUM> can be substantially straight and linear in all first planes oriented along the longitudinal direction L and the transverse direction T and arranged from the first lateral wall <NUM> to the second lateral wall <NUM>.

Further, as shown in <FIG>, each of the cranial and caudal surfaces <NUM> and <NUM> can be curved in a plane that is oriented along the transverse direction T and the lateral direction A. In particular, at least a portion up to an entirety of the cranial surface <NUM> can be curved as it extends along the lateral direction A. For instance, a least a portion up to an entirety of the cranial surface can be curved as it extends from the first lateral wall <NUM> to the second lateral wall <NUM>. In particular, at least a portion up to an entirety of the cranial surface <NUM> can be convex as it extends from the first lateral wall <NUM> to the second lateral wall <NUM>. Thus, the cranial surface <NUM> can be curved in a second plane that is oriented along the lateral direction A and the transverse direction T. For instance, the cranial surface <NUM> can be convex in the second plane that is oriented along the lateral direction A and the transverse direction T. The cranial surface <NUM> can be defined by a second radius of curvature in the second plane that ranges from approximately <NUM> to approximately <NUM>. For instance, the second radius of curvature can range from approximately <NUM> to approximately <NUM>. In one example, the second radius of curvature can be approximately <NUM>. Further, the second radius of curvature can be constant or variable along the length of the cranial surface <NUM> in the second plane. Thus, the radius of curvature of the cranial surface <NUM> in the second plane can be greater than the first radius of curvature of the cranial surface <NUM> in the first plane. In one example, the cranial surface <NUM> can be convex in all second planes oriented along the lateral direction A and the transverse direction T and arranged from the first lateral wall <NUM> to the second lateral wall <NUM>. Thus, the cranial surface <NUM> can be geometrically configured to match a complementary geometry of the vertebral endplate of the cranial vertebral body <NUM>.

Similarly, with continuing reference to <FIG>, at least a portion up to an entirety of the caudal surface <NUM> can be curved as it extends along the lateral direction A. For instance, a least a portion up to an entirety of the caudal surface <NUM> can be curved as it extends from the first lateral wall <NUM> to the second lateral wall <NUM>. In particular, at least a portion up to an entirety of the caudal surface <NUM> can be concave as it extends from the first lateral wall <NUM> to the second lateral wall <NUM>. Thus, the caudal surface <NUM> can be curved in the second plane that is oriented along the lateral direction A and the transverse direction T. According to the present invention, the caudal surface <NUM> is concave in the second plane that is oriented along the lateral direction A and the transverse direction T. The caudal surface <NUM> can be defined by a radius of curvature in the second plane that ranges from approximately <NUM> to approximately <NUM>. For instance, the radius of curvature of the caudal surface <NUM> in the second plane can range from approximately <NUM> to approximately <NUM>. In one example, the radius of curvature of the caudal surface <NUM> in the second plane can be approximately <NUM>. Thus, the radius of curvature of the caudal surface <NUM> in the second plane can be less than the second radius of curvature of the cranial surface <NUM> in the second plane. In one example, the cranial surface <NUM> can be convex in all second planes oriented along the lateral direction A and the transverse direction T and arranged from the first lateral wall <NUM> to the second lateral wall <NUM>. Thus, the caudal surface <NUM> can be geometrically configured to match a complementary geometry of the vertebral endplate of the caudal vertebral body <NUM>. In one example, the cranial surface <NUM> and the caudal surface <NUM> can extend substantially parallel to each other in the second plane. While specific geometries of the cranial and caudal surfaces <NUM> and <NUM> have been described in one example, the geometries can vary as desired.

Referring now to <FIG>, the plate <NUM> can be monolithic with the spacer <NUM>. Alternatively, the plate <NUM> can be separate from and attached to the spacer <NUM>. The plate <NUM> can extend out with respect to both the first lateral wall <NUM> and the second lateral wall <NUM> of the spacer <NUM> along the lateral direction A. Further, the plate <NUM> can extend out with respect to the cranial surface <NUM> of the spacer <NUM> a first distance in the cranial direction. Further still, the plate <NUM> can extend out with respect to the caudal surface <NUM> of the spacer <NUM> a second distance in the caudal direction. In one example, the second distance can be greater than the first distance. Alternatively, the second distance can be substantially equal to or less than the first distance.

The plate <NUM> can define a first or dorsal plate end <NUM> and a second or ventral plate end <NUM> that is disposed opposite the dorsal plate end <NUM>. The ventral plate end <NUM> can face away from the spacer <NUM>. The dorsal plate end <NUM> is opposite the ventral plate end <NUM> in the dorsal direction. It should be appreciated that the anatomical terms "cranial," "caudal," dorsal," "ventral," and other anatomical directional terms as applied to the implant <NUM> can apply to the respective anatomical directions when the implant <NUM> is implanted. The anatomical terms can equally apply to the implant <NUM> when disposed outside the body as relative directional terms. A cranial portion <NUM> of the dorsal plate end <NUM> can extend out with respect to the cranial surface <NUM> of the spacer <NUM> in the cranial direction. A caudal portion <NUM> of the dorsal plate end <NUM> can extend out with respect to the caudal surface <NUM> of the spacer <NUM> in the caudal direction. The caudal portion <NUM> of the dorsal plate end <NUM> can extend out with respect to the caudal surface <NUM> of the spacer <NUM> a distance that is greater than the distance at which the cranial portion <NUM> of the dorsal plate end <NUM> extends out with respect to the cranial surface <NUM> of the spacer <NUM>.

Further, as shown in <FIG>, the cranial portion <NUM> of the dorsal plate end <NUM> and the cranial surface <NUM> of the spacer <NUM> can define a concavity <NUM> in the first plane at a cranial interface between the spacer <NUM> and the plate <NUM>. Thus, the implant <NUM> can include a cranial implant surface that is configured to be inserted into the intervertebral space and nest with anatomical geometry of the cranial vertebral body <NUM>. The cranial implant surface can include the cranial surface <NUM> and the cranial interface. Accordingly, the cranial implant surface, which can be defined by the cranial surface <NUM> of the spacer <NUM> and the cranial portion <NUM> of the dorsal plate end <NUM>, can define a concavo-convex geometry in the first plane that is oriented along the transverse direction T and the longitudinal direction L. The concavo-convex geometry can include the concavity defined at the interface between the cranial portion <NUM> of the dorsal plate end <NUM> and the cranial surface <NUM> of the spacer <NUM>. The convex portion of the concavo-convex geometry can be defined by the convex cranial surface <NUM> of the spacer <NUM>.

The caudal portion <NUM> of the dorsal plate end <NUM> and the caudal surface <NUM> of the spacer <NUM> can combine to define a caudal concavity <NUM> at a caudal interface between the spacer <NUM> and the plate <NUM> in the first plane. Thus, the implant <NUM> can define a caudal implant surface that is configured to be inserted into the intervertebral space and nest with anatomical geometry of the caudal vertebral body <NUM>. The caudal implant surface of the implant can include the caudal surface <NUM> of the spacer <NUM> and the caudal interface between the spacer <NUM> and the plate <NUM>. At least a portion of the caudal concavity <NUM> can be offset from the cranial concavity <NUM> in the ventral direction. Further, the caudal concavity <NUM> can have a greater curvature than the cranial concavity <NUM>. As shown in <FIG>, the cranial portion <NUM> of the dorsal plate end <NUM> can face or abut the cranial vertebral body <NUM>, and the caudal portion <NUM> of the dorsal plate end <NUM> can face or abut the caudal vertebral body <NUM>.

Referring now to <FIG>, the implant <NUM> can include at least one fixation aperture <NUM> such as a plurality of fixation apertures that extend through the plate <NUM>. In particular, the at least one fixation aperture <NUM> can extend from the ventral plate end <NUM> to the dorsal plate end <NUM>. The at least one fixation aperture <NUM> extends from the ventral plate end <NUM> to the dorsal plate end <NUM> along a central aperture axis. An intervertebral implant system can include the implant <NUM> and at least one bone fixation element <NUM> that is configured to be inserted through the at least one fixation aperture, respectively, and driven into an aligned one of the cranial and caudal vertebral bodies, thereby fixing the implant <NUM> to the respective vertebral body. The bone fixation element <NUM> can be configured as a bone screw <NUM> having a head <NUM> and a shaft <NUM> that extends out with respect to the head <NUM> and is configured to purchase with bone. The shaft <NUM> can include at least one thread <NUM> that is configured to threadedly purchase with bone. Thus, as the bone screw <NUM> is driven into the vertebral body, the threaded shaft <NUM> threadedly purchases with the vertebral body.

The at least one bone screw <NUM> can be configured as a locking screw that is configured to threadedly purchase with the implant in the respective at least one fixation aperture <NUM>. Thus, the head <NUM> can carry at least one thread <NUM>, and the implant <NUM> can carry at least one thread <NUM> in the at least one fixation aperture <NUM>. The thread of the bone screw head <NUM> can thus threadedly mate with the thread of the implant <NUM> as the bone screw <NUM> is driven into the vertebra.

Alternatively, the at least one bone screw <NUM> can be configured as a compression screw that applies a compressive force to the implant <NUM> against the vertebral body as the bone screw is driven into the vertebral body. The head <NUM> of the bone screw <NUM> can be thus unthreaded, and thus configured to apply a compressive force against the plate <NUM> in the respective at least one fixation aperture <NUM> as the shaft <NUM> is driven into the vertebral body. Thus, the at least one fixation aperture <NUM> can similarly be unthreaded, and receive the force from the head <NUM>, which in turn causes the implant <NUM> to compress toward or against the respective vertebral body.

In one example, the at least one fixation aperture <NUM> can include at least one cranial fixation aperture that extends along a cranial aperture axis. In particular, the at least one fixation aperture <NUM> can include a pair of cranial fixation apertures, including a first cranial fixation aperture <NUM> and a second cranial fixation aperture <NUM>. The first cranial fixation aperture <NUM> can define a first or dorsal opening 76a in the dorsal plate end <NUM> of the plate <NUM>, and a second or ventral opening 76b in the ventral plate end <NUM> of the plate <NUM>. The first cranial fixation aperture <NUM> can extend along a first cranial aperture axis <NUM>. The first cranial aperture axis <NUM> can thus extend centrally through each of the dorsal opening 76a and the ventral opening 76b. The first cranial aperture axis <NUM> can be straight and linear.

Referring now also to <FIG>, the first cranial fixation aperture <NUM> can be oriented along a trajectory that flares outward in the cranial direction as the first cranial fixation aperture <NUM> extends in the dorsal direction. Thus, the first cranial aperture axis <NUM> can flare outward in the cranial direction as the first cranial aperture axis <NUM> extends in the dorsal direction. It should therefore be appreciated that the center of the dorsal opening 76a can be offset in the cranial direction with respect to the central of the ventral opening 76b. It should be appreciated that the first cranial aperture axis <NUM> can define a cranial angle <NUM> with respect to a reference plane <NUM> that is oriented along the lateral direction A and the longitudinal direction L with respect to a view from the lateral direction A of the first cranial aperture axis <NUM> and the reference plane <NUM>. The angle <NUM> thus defines the extent that the first cranial aperture axis <NUM> flares in the cranial direction as it extends in the dorsal direction. The angle <NUM> can be any suitable angle as desired. In one example, the angle <NUM> can range from approximately <NUM> degrees to approximately <NUM> degrees. For instance the angle <NUM> can range from approximately <NUM> degrees to approximately <NUM> degrees. In one example, the angle <NUM> can range from approximately <NUM> degrees to approximately <NUM> degrees. For instance, the angle can be approximately <NUM> degrees.

Additionally, the first cranial aperture axis <NUM> can be spaced in the cranial direction from the cranial surface <NUM> of the spacer <NUM> both as the axis <NUM> exits the plate <NUM> and as the first cranial aperture axis <NUM> extends in the dorsal direction from the plate <NUM>. Further, an entirety of the first dorsal opening 76a can be offset from the cranial surface <NUM> of the spacer <NUM> in the cranial direction. Thus, when the bone screw <NUM> is inserted through the first cranial fixation aperture <NUM> an entirety of the bone screw shaft <NUM> that extends out from the first cranial fixation aperture <NUM> in the dorsal direction can be spaced from the cranial surface <NUM> of the spacer <NUM> in the cranial direction. Further, because the bone screw shaft <NUM> extends along the first cranial aperture axis <NUM>, the bone screw shaft <NUM> extends outward in the cranial direction as it extends in the dorsal direction.

Referring to <FIG>, the first cranial aperture axis <NUM> can further flare laterally inward (or medially) toward the midplane of the spacer <NUM> as the axis <NUM> extends in the dorsal direction through the plate <NUM>. Thus, the center of the dorsal opening 76a can be spaced a first distance from the midplane <NUM> along the lateral direction A, and the center of the ventral opening 76b can be spaced a second distance from the midplane <NUM> along the lateral direction that is greater than the first distance. The first cranial aperture axis <NUM> and the midplane <NUM> can define a cranial lateral angle <NUM> that can be any suitable angle as desired. In one example, the angle <NUM> can range from approximately <NUM> degrees to approximately <NUM> degrees. For instance, the angle <NUM> can range from approximately <NUM> degrees to approximately <NUM> degrees. In one particular example, the angle <NUM> can be approximately <NUM> degrees. The first cranial aperture axis <NUM> can intersect the midplane <NUM> at a location that is spaced in the dorsal direction from the leading end <NUM> of the spacer <NUM>, and thus outside the footprint of the spacer <NUM>.

The second cranial fixation aperture <NUM> can define a first or dorsal opening 84a in the dorsal plate end <NUM> of the plate <NUM>, and a second or ventral opening 84b in the ventral plate end <NUM> of the plate <NUM>. The second cranial fixation aperture <NUM> can extend along a second cranial aperture axis <NUM>. The second cranial aperture axis <NUM> can thus extend centrally through each of the dorsal opening 84a and the ventral opening 84b. The second cranial aperture axis <NUM> can be straight and linear.

As illustrated in <FIG>, the second cranial fixation aperture <NUM> can be oriented along a trajectory that flares outward in the cranial direction as the second cranial fixation aperture <NUM> extends in the dorsal direction. Thus, the second cranial aperture axis <NUM> can flare outward in the cranial direction as the second cranial aperture axis <NUM> extends in the dorsal direction. It should therefore be appreciated that the center of the dorsal opening 84a can be offset in the cranial direction with respect to the central of the ventral opening 84b. It should be appreciated that the second cranial aperture axis <NUM> can define the cranial angle <NUM> with respect to the reference plane <NUM> that is oriented along the lateral direction A and the longitudinal direction L with respect to a view from the lateral direction A of the first cranial aperture axis <NUM> and the reference plane <NUM>.

Additionally, the second cranial aperture axis <NUM> can be spaced in the cranial direction from the cranial surface <NUM> of the spacer <NUM> both as the axis <NUM> exits the plate <NUM> and as the axis <NUM> extends in the dorsal direction from the plate <NUM>. Further, an entirety of the dorsal opening 84a can be offset from the cranial surface <NUM> of the spacer <NUM> in the cranial direction. Thus, when the bone screw <NUM> is inserted through the second cranial fixation aperture <NUM>, an entirety of the bone screw shaft <NUM> that extends out from the second cranial fixation aperture <NUM> in the dorsal direction can be spaced from the cranial surface <NUM> of the spacer <NUM> in the cranial direction. Further, because the bone screw shaft <NUM> extends along the second cranial aperture axis <NUM>, the bone screw shaft <NUM> extends outward in the cranial direction as it extends in the dorsal direction.

Referring to <FIG>, the second cranial aperture axis <NUM> can further flare laterally inward (or medially) toward the midplane <NUM> of the spacer <NUM> as the axis <NUM> extends in the dorsal direction through the plate <NUM>. Thus, the center of the dorsal opening 84a can be spaced the first distance from the midplane <NUM> along the lateral direction A, and the center of the ventral opening 84b can be spaced the second distance from the midplane <NUM> along the lateral direction that is greater than the first distance. The second cranial aperture axis <NUM> and the midplane <NUM> can define the lateral angle <NUM> described above. The second cranial aperture axis <NUM> can intersect the midplane <NUM> at a location that is spaced in the dorsal direction from the leading end <NUM> of the spacer <NUM>, and thus outside the footprint of the implant <NUM>.

The first and second cranial fixation apertures <NUM> can be spaced substantially equidistantly from the midplane <NUM>, and positioned at opposed sides of the midplane <NUM>. Further, the first and second cranial aperture axes <NUM> and <NUM> can converge toward each other at an angle which can be approximately twice the lateral angle <NUM>. Further still, the lateral angle <NUM> can be less than the cranial angle <NUM>. Further still, the first and second cranial aperture axes <NUM> and <NUM> can flare outward in the cranial direction at the same angle as they extend in the dorsal direction.

Referring now to <FIG>, the at least one fixation aperture <NUM> can include at least one caudal fixation aperture that extends along a caudal aperture axis. In particular, the at least one fixation aperture <NUM> can include a pair of caudal fixation apertures, including a first caudal fixation aperture <NUM> and a second caudal fixation aperture <NUM>. The first and second caudal fixation apertures <NUM> and <NUM> can be offset laterally inward (or medially) with respect to the first and second cranial fixation apertures <NUM> and <NUM>. The first caudal fixation aperture <NUM> can define a first or dorsal opening 92a in the dorsal plate end <NUM> of the plate <NUM>, and a second or ventral opening 92b in the ventral plate end <NUM> of the plate <NUM>. The first caudal fixation aperture <NUM> can extend along a first caudal aperture axis <NUM>. The first caudal aperture axis <NUM> can thus extend centrally through each of the dorsal opening 92a and the ventral opening 92b. The first caudal aperture axis <NUM> can be straight and linear.

Referring to <FIG>, the first caudal fixation aperture <NUM> can be oriented along a trajectory that flares outward in the caudal direction as the first caudal fixation aperture <NUM> extends in the dorsal direction. Thus, the first caudal aperture axis <NUM> can flare outward in the caudal direction as the first caudal aperture axis <NUM> extends in the dorsal direction. It should therefore be appreciated that the center of the dorsal opening 92a can be offset in the caudal direction with respect to the central of the ventral opening 92b. It should further be appreciated that the first caudal aperture axis <NUM> can define a caudal angle <NUM> with respect to the reference plane <NUM> that is oriented along the lateral direction A and the longitudinal direction L with respect to a view from the lateral direction A of the first caudal aperture axis <NUM> and the reference plane <NUM>. The angle <NUM> thus defines the extent that the first caudal aperture axis <NUM> flares in the caudal direction as it extends in the dorsal direction. The angle <NUM> can be any suitable angle as desired. In one example, the angle <NUM> can range from approximately <NUM> degrees to approximately <NUM> degrees. For instance the angle <NUM> can range from approximately <NUM> degrees to approximately <NUM> degrees. In one example, the angle <NUM> can range from approximately <NUM> degrees to approximately <NUM> degrees. For instance, the angle can be approximately <NUM> degrees. Thus, the caudal angle <NUM> can be greater than the cranial angle <NUM>. For instance, the caudal angle <NUM> can be approximately double the cranial angle <NUM>.

Additionally, the first caudal aperture axis <NUM> can be spaced in the caudal direction from the caudal surface <NUM> of the spacer <NUM> both as the axis <NUM> exits the plate <NUM> and as the axis <NUM> extends in the dorsal direction from the plate <NUM>. Further, an entirety of the first dorsal opening 92a can be offset from the caudal surface <NUM> of the spacer <NUM> in the caudal direction. Thus, when the bone screw <NUM> is inserted through the first caudal fixation aperture <NUM> an entirety of the bone screw shaft <NUM> that extends out from the first caudal fixation aperture <NUM> in the dorsal direction can be spaced from the caudal surface <NUM> of the spacer <NUM> in the caudal direction. Further, because the bone screw shaft <NUM> extends along the first caudal aperture axis <NUM>, the bone screw shaft <NUM> extends outward in the caudal direction as it extends in the dorsal direction.

Referring now to <FIG>, the first caudal aperture axis <NUM> can further flare laterally outward away from the midplane of the spacer <NUM> as the axis <NUM> extends in the dorsal direction through the plate <NUM>. Otherwise stated, the first caudal aperture axis <NUM> can flare laterally inward toward the midplane of the spacer <NUM> as the axis <NUM> extends in the ventral direction. Further, the center of the dorsal opening 92a can be spaced a first distance from the midplane <NUM> along the lateral direction A, and the center of the ventral opening 92b can be spaced a second distance from the midplane <NUM> along the lateral direction that is less than the first distance. The first caudal aperture axis <NUM> and the midplane <NUM> can define a caudal lateral angle <NUM> that can be any suitable angle as desired. In one example, the angle <NUM> can range from approximately <NUM> degrees to approximately <NUM> degrees. For instance, the angle <NUM> can range from approximately <NUM> degrees to approximately <NUM> degrees. In one particular example, the angle <NUM> can be approximately <NUM> degrees. The first caudal aperture axis <NUM> can intersect the midplane <NUM> at a location that is spaced in the ventral direction from the ventral plate end <NUM> of the plate <NUM>, and thus outside the footprint of the implant <NUM>. Alternatively, the first caudal aperture axis <NUM> can extend in the dorsal direction substantially parallel to the midplane <NUM>.

The second caudal fixation aperture <NUM> can define a first or dorsal opening 98a in the dorsal plate end <NUM> of the plate <NUM>, and a second or ventral opening 98b in the ventral plate end <NUM> of the plate <NUM>. The first and second caudal fixation apertures <NUM> and <NUM> extend through the plate <NUM> a distance from the respective dorsal opening to the respective ventral opening that is less than the distance that the cranial fixation apertures <NUM> and <NUM> extend from the respective dorsal opening to the respective ventral opening. The second caudal fixation aperture <NUM> can extend along a second caudal aperture axis <NUM>. The second caudal aperture axis <NUM> can thus extend centrally through each of the dorsal opening 98a and the ventral opening 98b. The second caudal aperture axis <NUM> can be straight and linear.

As illustrated in <FIG>, the second caudal fixation aperture <NUM> can be oriented along a trajectory that flares outward in the caudal direction as the second caudal fixation aperture <NUM> extends in the dorsal direction. Thus, the second caudal aperture axis <NUM> can flare outward in the caudal direction as the second caudal aperture axis <NUM> extends in the dorsal direction. It should therefore be appreciated that the center of the dorsal opening 98a can be offset in the caudal direction with respect to the central of the ventral opening 98b. It should further be appreciated that the second caudal aperture axis <NUM> can define the caudal angle <NUM> described above with respect to the reference plane <NUM> with respect to a view from the lateral direction A of the second caudal aperture axis <NUM> and the reference plane <NUM>.

Additionally, the second caudal aperture axis <NUM> can be spaced in the caudal direction from the caudal surface <NUM> of the spacer <NUM> both as the axis <NUM> exits the plate <NUM> and as the axis <NUM> extends in the dorsal direction from the plate <NUM>. Further, an entirety of the first dorsal opening 98a can be offset from the caudal surface <NUM> of the spacer <NUM> in the caudal direction. Thus, when the bone screw <NUM> is inserted through the second caudal fixation aperture <NUM>, an entirety of the bone screw shaft <NUM> that extends out from the first caudal fixation aperture <NUM> in the dorsal direction can be spaced from the caudal surface <NUM> of the spacer <NUM> in the caudal direction. Further, because the bone screw shaft <NUM> extends along the second caudal aperture axis <NUM>, the bone screw shaft <NUM> extends outward in the caudal direction as it extends in the dorsal direction.

Referring to <FIG>, the second caudal aperture axis <NUM> can further flare laterally outward away from the midplane <NUM> of the spacer <NUM> as the axis <NUM> extends in the dorsal direction through the plate <NUM>. Otherwise stated, the second caudal aperture axis <NUM> can flare laterally inward toward the midplane <NUM> of the spacer <NUM> as the axis <NUM> extends in the ventral direction. Thus, the first and second caudal aperture axes <NUM> and <NUM>, respectively, can be sloped opposite the first and second cranial aperture axes <NUM> and <NUM>, respectively. Thus, the center of the dorsal opening 98a can be spaced a first distance from the midplane <NUM> along the lateral direction A, and the center of the ventral opening 98b can be spaced a second distance from the midplane <NUM> along the lateral direction that is less than the first distance. The second caudal aperture axis <NUM> and the midplane <NUM> can define the lateral angle <NUM> described above. Thus, the second caudal aperture axis <NUM> can intersect the midplane <NUM> at a location that is spaced in the ventral direction from the ventral plate end <NUM> of the plate <NUM>, and thus outside the footprint of the implant <NUM>. Alternatively, the second caudal aperture axis <NUM> can extend in the dorsal direction substantially parallel to the midplane <NUM>.

The first and second caudal fixation apertures <NUM> and <NUM> can be spaced substantially equidistantly from the midplane <NUM>, and positioned at opposed sides of the midplane <NUM>. Further, as the first and second caudal aperture axes <NUM> and <NUM> extend along the dorsal direction, the axes <NUM> and <NUM> can diverge away from each other at an angle which can be approximately twice the lateral angle <NUM>. Further still, the lateral angle <NUM> can be less than the caudal angle <NUM>. Further still, the first and second caudal aperture axes <NUM> and <NUM> can flare outward in the caudal direction at the same angle as they extend in the dorsal direction.

While the plate <NUM> has been described as including the first and second cranial fixation apertures <NUM> and <NUM> and the first and second caudal fixation apertures <NUM> and <NUM>, it will be appreciated that the plate <NUM> can include any one or more fixation apertures configured to receive the bone fixation elements <NUM> such as, for example, one or more bone screws <NUM>, respectively, for securing the intervertebral implant <NUM> to the adjacent vertebral bodies <NUM> and <NUM>. The plate <NUM> may include any number of fixation apertures arranged in any number of combinations. For example, the plate <NUM> may include two, three, four or more fixation apertures for receiving, preferably, an equal number of bone screws <NUM>. Moreover, the fixation apertures can alternatively repeatedly alternate with one another, whereby one fixation aperture is angled cranially so as to define a cranial fixation aperture, and an adjacent fixation aperture is angled caudally so as to define a caudal fixation aperture. Thus, a cranial fixation aperture can be surrounded on both lateral sides by a caudal fixation aperture. Further, a caudal fixation aperture can be surrounded on both lateral sides by a cranial fixation aperture.

Referring again to <FIG>, the intervertebral implant <NUM> can have any suitable dimensions as desired. For instance, the spacer <NUM> can have a spacer length along the longitudinal direction L from the leading end <NUM> to the trailing end <NUM> that is in the range from approximately <NUM> to approximately <NUM>. The spacer <NUM> can have a spacer width along the lateral direction from the first lateral wall <NUM> to the second lateral wall <NUM> that is in the range from approximately <NUM> to approximately <NUM>. For instance, the spacer width can range from approximately <NUM> to approximately <NUM>. The plate <NUM> can have a plate length along the longitudinal direction L from the dorsal end <NUM> to the ventral end <NUM> that is in the range from approximately <NUM> to approximately <NUM>. In one example, the plate length can be approximately <NUM>.

During operation, and referring generally to <FIG>, the plate <NUM> can be inserted into the intervertebral disc space <NUM> between the adjacent vertebral bodies <NUM> and <NUM>, such that the cranial portion <NUM> of the dorsal plate end <NUM> of the plate <NUM> faces the cranial vertebral body <NUM> and the caudal portion <NUM> of the dorsal plate end faces the caudal vertebral body <NUM>. In one example, the cranial portion <NUM> of the dorsal plate end <NUM> of the plate <NUM> can abut the cranial vertebral body <NUM>, and the caudal portion <NUM> of the dorsal plate end can abut the caudal vertebral body <NUM>. The concavo-convex geometry of the cranial surface of the implant <NUM> can geometrically nest with an anatomical geometry of the cranial vertebral body <NUM>. The caudal surface of the implant <NUM> can geometrically nest with the anatomical geometry of the cranial vertebral body <NUM>.

Next, a plurality of bone screws <NUM> can be inserted through respective ones of the cranial and caudal fixation apertures <NUM>, <NUM>, <NUM>, and <NUM>, respectively. The bone screws <NUM> inserted into the cranial fixation apertures <NUM> and <NUM> can be driven into the cranial vertebral body <NUM>. The respective trajectories of the first and second cranial aperture axes <NUM> and <NUM> can cause the bone screws <NUM> to purchase in dense cortical bone of the cranial vertebral body <NUM>. Thus, a reliable fixation to the cranial vertebral body <NUM> can be achieved. Similarly, the bone screws <NUM> inserted into the caudal fixation apertures <NUM> and <NUM> can be driven into the caudal vertebral body <NUM>. The respective trajectories of the first and second caudal aperture axes <NUM> and <NUM> can cause the bone screws <NUM> to purchase in dense cortical bone of the caudal vertebral body <NUM>. Thus, a reliable fixation to the cranial vertebral body <NUM> can be achieved.

Referring now to <FIG>, the intervertebral implant <NUM> can be constructed as described above, but as an alternative to the windows <NUM> and ribs <NUM> and <NUM>, the implant <NUM> can include a bone graft cavity <NUM> that is configured to receive bone graft material that can further fuse the intervertebral implant <NUM> to the first and second vertebral bodies <NUM> and <NUM>. In particular, the bone graft cavity <NUM> can have a first open end <NUM> that is configured to receive bone graft material, such as allograft, autograft, or the like. The open end <NUM> can extend through the leading end <NUM> of the spacer <NUM> along the longitudinal direction L in one example. It is appreciated that the open end <NUM> is not limited to the leading end of the spacer <NUM>. For instance, the open end <NUM> can alternatively extend through one of the first and second lateral walls <NUM> and <NUM>, respectively.

In one example, the bone graft cavity <NUM> can extend in the rearward direction from the open end <NUM> to a wall <NUM> that defines a closed end of the bone graft cavity <NUM>. The wall <NUM> can be defined by the spacer <NUM>, or can alternatively be defined by the plate <NUM>. The cavity <NUM> can also be partially defined by one or more up to all of the cranial wall, the caudal wall, and one or both of the first and second lateral walls. For instance, the cranial wall can include a cranial lattice structure <NUM> that defines a cranial end of the bone graft cavity <NUM>. In this regard, it should be appreciated that the spacer <NUM> defines a plurality of openings that extend through the cranial wall and are open to the bone graft cavity <NUM>. The openings can be defined by the cranial lattice structure <NUM>, or can be otherwise defined as desired. The caudal wall can include a caudal lattice structure <NUM> that defines a caudal end of the bone graft cavity <NUM>. In this regard, it should be appreciated that the spacer <NUM> defines a plurality of openings that extend through the caudal wall and are open to the bone graft cavity <NUM>. The openings can be defined by the caudal lattice structure <NUM>, or can be otherwise defined as desired. The cranial lattice structure <NUM> and the caudal lattice structure <NUM> can be spaced from each other along the transverse direction T.

The first lateral wall can include a first and second lateral lattice structures <NUM> that define the first and second lateral ends of the bone graft cavity <NUM>, respectively. Thus, the first and second lateral lattice structures <NUM> can be spaced from each other along the lateral direction A. In this regard, it should be appreciated that the spacer <NUM> defines a plurality of openings that extend through the first and second lateral walls and are open to the bone graft cavity <NUM>. The openings can be defined by the lateral lattice structures <NUM>, or can be otherwise defined as desired.

During operation, bone graft material can be inserted through the open end <NUM> and into the bone graft cavity <NUM>. The bone graft material can thus extend through one or more up to all of the openings in the cranial, caudal, and lateral walls. Thus, the bone graft material can extend through openings in the cranial lattice structure <NUM> and can contact the cranial vertebral body. Similarly, the bone graft material can extend through openings in the caudal lattice structure <NUM> and can contact the caudal vertebral body. Further still, the bone graft material can extend through openings in the first and second lateral lattice structures <NUM>, and can fuse with bony ingrowth that grows around the intervertebral implant <NUM>.

Claim 1:
An intervertebral implant (<NUM>) configured to be implanted in an intervertebral disc space (<NUM>) of a quadruped, the intervertebral disc space (<NUM>) defined by a cranial vertebral body (<NUM>) and a caudal vertebral body (<NUM>), the implant (<NUM>) comprising:
a plate (<NUM>) defining a ventral plate end (<NUM>) and a dorsal plate end (<NUM>) spaced opposite the ventral plate end (<NUM>) in a dorsal direction, and a plurality of fixation apertures (<NUM>) that extend through the plate (<NUM>) from the ventral plate end (<NUM>) to the dorsal plate end (<NUM>); and
a spacer (<NUM>) that extends in the dorsal direction from the plate (<NUM>), wherein the spacer (<NUM>) defines a caudal surface (<NUM>) and a cranial surface (<NUM>) opposite the caudal surface (<NUM>) in a cranial direction, the caudal and cranial surfaces (<NUM>, <NUM>) configured to grip the caudal and cranial vertebral bodies (<NUM>, <NUM>), respectively, characterized in that
the cranial surface (<NUM>) is convex in a first plane that is oriented along the dorsal direction and the cranial direction, and the cranial surface (<NUM>) is convex in a second plane that is oriented along the cranial direction and a lateral direction that is substantially perpendicular to each of the dorsal direction and the cranial direction, and
the caudal surface (<NUM>) is substantially straight and linear in the first plane, and the caudal surface (<NUM>) is concave in the second plane.