Patent Description:
The spine or vertebral column comprises a plurality of separate vertebrae. The vertebrae are movable relative to one another, and separated from one another by fibrocartilage called inter-vertebral discs.

In its entirety, the spinal column is highly complex in that it houses and protects critical elements of the nervous system which have innumerable peripheral nerves and arterial and venous bodies in close proximity. In spite of these complexities, the spine is a highly flexible structure, capable of a high degree of curvature and twist through a wide range of motion. The intervertebral discs provide mechanical cushion between adjacent vertebrae. Genetic or developmental irregularities, trauma, chronic stress, tumours, and disease, however, can result in spinal pathologies which either limit this range of motion, or which threaten the critical elements of the nervous system housed within the spinal column. A variety of systems have been disclosed in the art which achieve immobilization by implanting artificial assemblies in or on the spinal column.

In order to treat certain injuries or conditions of the spinal column an intervertebral device may be placed in the intervertebral disc space to fuse or promote fusion of adjacent vertebrae. Such fusion devices are often used in combination with stabilisation systems wherein a metal rod that is bendable to match the natural curvature of the spine is mechanically attached at strategically selected vertebrae, allowing the rod to be rigidly fixed to the spine. This provides a rigid support to the spinal column. For this, screws located in the bone structure are typically fixed to a specially designed clamp to attach to a spinal rod. A problem with these stabilisation systems if used in the cervical spine of small animals is that the space in this area is very limited and the quality of the underlying bone section is such that it is very difficult to achieve good fixation using cortical bone screws. There is the additional risk of screws being close to or damaging the nerves that are very close to the bone. A safer implant placement can be achieved from the ventral side where there is more bone structure for cortical screw placement. A fusion system that can be used in small animals, in particular for a ventral approach is needed, wherein confined spaces make conventional rod anchoring systems unsuitable. <CIT> discloses a spinal implant system for fusing one or more vertebral joints of a subject's spine.

According to the invention there is provided a spinal implant system for fusing one or more vertebral joints of a subject's spine, the spinal implant system comprising: a first intervertebral device for installation in a spinal disc space separating two adjacent vertebrae, a first elongate member, a first connector adapted to be secured to a first vertebra and a second connector adapted to be secured to a second vertebra adjacent the first vertebra, each comprising a body portion being adapted to couple thereto at least a first bone screw for installation in a vertebra, the body portion further being adapted for coupling said first elongate member thereto, the first connector further comprising an extension portion extending from the body portion of the first connector, the extension portion being adapted for coupling thereto said first intervertebral device for securing the connector to the spinal disc space, wherein the extension portion has a longitudinal axis which is configured to extend substantially parallel with the longitudinal axis of the subject's spine when installed, the extension portion being sized with a length to span longitudinally across the spinal disc space between the first intervertebral device when installed in the spinal disc space and the body portion of the first connector when installed at the first vertebra; said first intervertebral device being coupled in use to the extension portion of the first connector at or near the distal end of the extension portion, the first and second connectors being coupled together in use by said first elongate member.

The spinal implant system may be used to fuse two adjoining vertebrae together, with an intervertebral device for installation in a spinal disc space between. The extension portion has means for selectively coupling the intervertebral device thereto, the intervertebral device being for insertion in an intervertebral space separating two adjacent vertebrae. The connectors of the present invention, when used as part of a spinal fusion system, advantageously allows gradual build-up of the fusion system, piece by piece, making it easy to align and assemble the pieces in the confined space of the neck of a subject.

Advantageously, the first connector is adapted so that it can be coupled to the intervertebral device after the intervertebral device has been installed in a subject (rather than requiring assembly to the intervertebral device before it is installed in the subject). This is because the first connector is adapted to simply affix to the proximal end of the intervertebral device. Suitably each connector has means for holding the or each bone screw captive during installation of the bone screws in a subject.

The body portion of each connector is preferably configured to seat on the exterior surface of a vertebra when installed.

As used herein the term spinal disc space or intervertebral disc space refers to the space between adjacent vertebrae, which may or may not be occupied by an intervertebral disc.

The intervertebral device and at least one bone screw each have a longitudinal axis which is parallel to their direction of insertion in the spine. The first connector is preferably configured to hold the longitudinal axis of the intervertebral device and at least one bone screw coupled thereto at a predetermined angle with respect to one another. The first connector is preferably adapted to hold the longitudinal axis of the intervertebral device and at least one bone screw coupled thereto at a predetermined angle with respect to one another at least during and after installation in a subject. The predetermined angle can be selected or set depending on the particular vertebral geometry at the vertebral joint. This allows the intervertebral device to be anchored to an adjacent vertebra using the at least one bone screw, with the at least one bone screw stably anchored in the bone and with the body portion seated on said vertebra when installed, to provide a stable coupling. The predetermined angle may be varied by adjustment by the user or by selecting a connector from a set including connectors adapted to hold the longitudinal axes of the intervertebral device and at least one bone screw at differing angles relative to one another. Said predetermined angle is preferably adjustable.

Preferably at least part of the extension portion is bendable. This allows for adjustment of the angle that the longitudinal axes of the intervertebral device and the at least one bone screw will extend at with respect to one another when assembled to the first connector. By means of the extension portion being bendable, this assists during installation in that a connector can be secured to an intervertebral device that has been installed in an intervertebral disc space and then the extension portion can be bent by the surgeon to place the bone screw or bone screws assembled to the connector stably into the adjacent vertebra whilst ensuring that the body portion is stably in contact with the vertebral bone underneath once the bone screws are installed. The extension portion is preferably bendable about an axis which is substantially parallel to the medio-lateral axis when the first connector is installed. At least a portion of the extension portion is pivotable with respect to the body portion about an axis substantially parallel with the medio-lateral axis. The extension portion is preferably bendable such that with the distal end of the extension portion secured to the spine, the body portion of the first connector can be bent towards or away from the spine. Alternatively, or in addition, a plurality of connectors can be provided to the installer as part of a modular kit in which connectors having extension portions at least a portion of which is bent at different angles relative to the body portion are provided and the user can select the connector which suits the vertebral geometry at the particular vertebral joint that the connector is being installed at. If using a modular kit of connectors providing differing angles for projection of the intervertebral device and at least one bone screw when assembled to the connector, at least a portion of the extension portion may be bendable to allow for fine adjustment of the angle between the intervertebral device and at least one bone screw prior to installation.

The extension portion is sized with a length to span between an implanted intervertebral device and the body portion of the first connector implanted in an adjacent vertebra. Suitably the lateral width of the body portion of the first connector is greater than that of the extension portion. This means that one or two elongate members can be assembled to the body portion of the first connector to be positioned to one or both sides of the extension portion, substantially parallel with the extension portion, to couple the first connector to the second connector, to strengthen the bridge across the intervertebral space.

Preferably the extension portion is adapted to couple with the intervertebral device at or near the distal end of the extension portion. As used herein, the term distal or distally refers to location away from the point of attachment/connection of the corresponding piece with the remainder of the connector or assembly. As used herein, the term proximal or proximally refers to a location towards the point of attachment/connection of the corresponding piece with the remainder of the connector or assembly. At one end of the extension portion (the proximal end) is the body portion and at or near the other end (the distal end) of the extension portion is means for securing the extension portion to an intervertebral device.

Preferably the extension portion is an elongate plate. The connector is preferably configured such that the extension portion aligns substantially parallel with the coronal plane when installed. In an unbent configuration, the extension portion is planar. The planar extension portion can be bent out of the planar configuration by the installer or during manufacture.

Preferably the extension portion has an aperture for receiving a locking member for securing an intervertebral device to the extension portion. The aperture is preferably at or near the distal end of the extension portion. In preferred embodiments, the extension portion has a single aperture such that the extension portion is configured to couple to a single intervertebral device.

Preferably the extension portion is integral with the body portion. Alternatively the extension portion is attachable to the body portion. If so, the extension portion can be supplied pre-assembled to the body portion.

Preferably the body portion of each connector is adapted to couple thereto a second bone screw for installation in a vertebra. The body portion of each connector is adapted such that the second bone screw will be installed laterally from the first bone screw, both screws being installed in the vertebra. Preferably the body portion of each connector has a first aperture for receiving a first bone screw. Preferably the body portion of each connector has a second aperture for receiving a second bone screw.

Preferably the body portion of each connector has a lower surface adapted to face a vertebra when installed and an upper surface opposite said lower surface, the or each aperture for receiving a corresponding bone screw extending through the body portion from said upper surface to said lower surface, forming a bore for receiving at least a portion of the bone screw.

Preferably the body portion of each connector is adapted to couple thereto the or each bone screw at a predetermined angle relative to the body portion. The or each corresponding bore that receives the bone screw may be appropriately inclined relative to the body portion such that the bone screw will be correspondingly inclined when assembled to the body portion.

Preferably the body portion of each connector is adapted to couple thereto first and second bone screws, each at a predetermined angle relative to the body portion, the predetermined angles being such that the bone screws diverge from one another when installed. The bone screws preferably diverge from one another substantially in the transverse plane. Alternatively the bone screws can be installed such that they are convergent to one another. The body portion of each connector is preferably also adapted such that the first and second bone screws couple thereto with a predetermined spacing between the bone screws. Typically for a given type of animal, the desired angle of incline and lateral spacing for the first and second bone screws will not differ from one animal to another as the lateral geometry of vertebra in the cervical spine is typically quite consistent from one animal to the next.

Preferably the body portion of each connector has a first recess for receiving the first elongate member. Preferably the body portion of each connector has a second recess for receiving a second elongate member. The or each recess may be a groove. Alternatively, the or each recess may be a partially spherical shaped depression.

Preferably the body portion of each connector has a lower surface adapted to face a vertebra when installed and an upper surface opposite said lower surface, at least part of the lower surface of the body portion having a concave curvature. The concavely curved lower surface of the body portion of each connector is configured to conform to at least a portion of a subject's vertebra. The typical curvature of vertebra for a particular type of subject can be ascertained such that connectors with suitably curved body portions can be manufactured. Alternatively, custom-made body portions can be manufactured to suit a particular subject's vertebrae.

Preferably the spinal implant system further comprises at least one bone screw for securing the first connector to a first vertebra. The or each bone screw couples to the body portion when assembled as explained above. Bone screws for installation in vertebrae are well-known. Any suitable bone anchoring screws may be employed. Suitably at least part of the or each bone screw is externally threaded. Suitably the or each bone screw has a thin profile.

Also described herein are means for coupling a connector to a connector of another spinal implant assembly.

Preferably the elongate member comprises a rod. Preferably the rod is bendable. Preferably the rod has first and second ends, one or both ends having an enlarged head. Preferably the or each enlarged head is a substantially spherical head. The body portion preferably includes at least one spherical shaped recess, the or each recess for receiving a spherical head of said rod therein. Preferably the radius of curvature of the recess is smaller than the radius of curvature of the corresponding spherical head of the rod to be received therein such that the body portion makes a circular line of contact with the spherical head when assembled.

The intervertebral device is for securing the first connector to a spinal disc space. When assembled, the intervertebral device is adapted to secure the connector to a spinal disc space adjacent the first vertebra that the bone screw is to be installed in.

Preferably at least part of the intervertebral device is externally threaded. Typically the or each bone screw will be narrower in profile than the intervertebral device, the or each bone screw being sized and shaped to install into bone and the intervertebral device being sized and shaped to install into intervertebral disc space. The intervertebral device will preferably have a hollow bore communicating with at least one aperture in its side. This allows for bone ingrowth into the intervertebral device when installed, thus improving the stability of the anchorage. Preferably at least part of the intervertebral device is hydroxyapatite coated.

Preferably the spinal implant system further comprises a locking member for securing the intervertebral device to the extension portion. Preferably the locking member is adapted to secure the intervertebral device to the extension portion via a threaded connection. Preferably at least part of the locking member is externally threaded. Preferably the intervertebral device has a hollow bore. Preferably the locking member has a head portion and a shank portion, the shank portion being at least partially externally threaded, the intervertebral device having a bore with a first open end, the bore being at least partially internally threaded, the internal threads of the bore corresponding with the external threads of the shank portion of the locking member such that the locking member is attachable to the intervertebral device, with the extension portion retainable therebetween. The locking member may be releasably attachable to the intervertebral device. The locking member suitably retains the intervertebral device to the connector by means of the extension portion being clamped between the intervertebral device and the locking member when the pieces are assembled.

Preferably the spinal implant system further comprises a clamp member for non-movably securing the or each elongate member to the first connector. The clamp member acts as a compression member for securing the elongate member to the connector. Preferably the assembly further comprises a clamp locking member for non-movably securing the clamp member to the body portion. Suitably the clamp member is releasably attachable to the body portion. Preferably the clamp locking member is a locking screw, the locking screw having a shank, at least part of the shank being externally threaded, the body portion having a locking screw receiving bore with a first open end, the bore being internally threaded, the external threads of the bore corresponding with the external threads of the shank of the locking screw, the clamp member having a bore connecting first and second open ends, the locking screw being receivable in the bore of the clamp member and threadedly receivable in the bore of the body portion.

Preferably the clamp member has a lower surface adapted to face the connector when assembled and an upper surface opposite said lower surface, the lower surface including a first recess for receiving the elongate member therein when assembled. Preferably the lower surface has a second recess for receiving the elongate member therein when assembled. Suitably the recess(es) in the clamp member overlie corresponding recess(es) in the body portion when assembled, such that the or each pair of corresponding recesses can hold an elongate member captive therebetween. The or each recess in the clamp member may be a groove. The or each recess in the clamp member may alternatively by a spherical shaped depression. The or each spherical shaped depression in the clamp member is configured for receiving a spherical head of said elongate member therein. Preferably the radius of curvature of the or each spherical depression in the clamp member is smaller than the radius of curvature of the or each spherical head of the elongate member such that the clamp member makes a circular line of contact with the spherical head when assembled, to enhance fixation of the elongate member relative to the connector when the clamp member is non-movably secured to the connector.

Also described herein is a spinal implant system further comprising a distal end assembly adapted to be installed in a subject distally to the distal end of the extension portion of a first connector as described above, the distal end assembly adapted to be coupled to said connector, the distal end assembly being adapted to be installed with its extension portion extending towards the extension portion of the connector, the extension portion of the distal end assembly being adapted to couple with the extension portion of the connector. Suitably the extension portion of the distal end assembly is shorter than that of the standard connector. The extension portion of the distal end connector is sufficiently long to couple with the extension portion of the connector installed on an adjacent vertebra. An intervertebral device suitably couples to the extension portion of the first connector and the distal end assembly when assembled.

In the spinal implant system the first connector may be described as a spinal implant assembly. Preferably the system comprises a first spinal implant assembly and a second spinal implant assembly comprising a distal end assembly, wherein first implant assembly is adapted to be secured to a first vertebra and the second spinal implant assembly is adapted to be secured to a second vertebra adjacent the first vertebra, and the intervertebral device of the first implant assembly is adapted to be secured in the spinal disc space between the first and second vertebrae, and wherein the first and second spinal implant assemblies are configured to be coupled together using the elongate member. The elongate member is suitably clamped at or near one end to the first implant assembly and clamped at or near the other end to the second implant assembly. The elongate member is positioned on the left or right lateral side of the intervertebral disc device when the assembly is installed. Where the second implant assembly is a distal end assembly, the extension portion of the distal end assembly couples with the extension portion of the adjacent spinal implant assembly when assembled.

Preferably the system comprises a plurality of spinal implant assemblies, the spinal implant assemblies adapted to be assembled in a row with each spinal implant assembly secured to a vertebra of a row of successive vertebrae when installed and with the intervertebral device of each spinal implant assembly secured in the spinal disc space adjacent the corresponding vertebra such that the intervertebral devices are secured in a row of successive disc space when installed, the extension portions of the spinal implant assemblies extending substantially in the same direction as one another when the system is installed and wherein the spinal implant assemblies are adapted to be coupled together using an elongate member between each connector and the next connector. For example, each spinal implant assembly may be installed such that the proximal-distal axis of the extension portions substantially align with the cranial-caudal axis of the subject's spine. Of course, the row of assemblies need not be straight, and can be arranged to align with desired curvature of the fused vertebral region.

Preferably the system further comprises a distal end assembly for coupling to the spinal implant assembly at the distal end of the row of spinal implant assemblies relative to the direction of the extension portions thereof. This provides a stable end connection when assembling across one or more vertebrae pairs. Preferably the elongate members that couple the spinal implant assemblies together when assembled are arranged on alternate sides of the spine. In other words, a first elongate member may be on the left lateral side, then the next will be on the right lateral side, the next on the left lateral side and so on or vice versa. Instead of the elongate members being arranged alternately, elongate members can be assembled to couple a first spinal assembly to a second spinal assembly on both the right lateral and left lateral sides. In preferred embodiments, the elongate member for coupling a first spinal implant assembly to a second spinal implant assembly is sized such that the length of the elongate member is adapted to couple only two connectors together. In this way, spinal implant assemblies can be coupled together in a row, a pair at a time. Alternatively a longer elongate member which can couple more than two connectors together can be used to couple more than two connectors together, or to be cut down to size during installation to couple only two connectors together. Advantageously the system may comprise two space-filling elongate members, one to be installed in each spinal implant assembly of a pair of assemblies or in each terminating spinal implant assembly of a row of assemblies. Each space-filling elongate member is sufficiently long to overlie the opening to the bone screw receiving bore in the body portion. Advantageously this fills the void where an elongate member for coupling to another connector could go and helps to prevent the underlying bone screw from loosening.

Also described herein is a kit for assembly into a spinal implant assembly or system, wherein the kit comprises the parts of the system according to any previous aspect of the invention. Instructions for assembly may be provided as part of the kit.

A modular kit can be provided wherein differing connectors are provided. Connectors having body portions of differing lateral dimension can be provided, connectors having body portions with differing curvature of the lower surface can be provided. In particular, a range of connectors may be provided in a kit, the connectors having differing spacing between the bores for receiving first and second bone screws and/or differing angles of inclination of the bone screw bores such that the first and second bone screws diverge/converge from one another at differing angles. A plurality of each of the different connectors can be provided to allow for variations in bone geometry, entry approach etc..

Also described herein is a computer program embodied on a computer readable medium for manufacturing a spinal implant system according to any previous aspect of the invention.

Also described herein is a method of installing a spinal implant system, the method comprising the steps of providing at least first and second implant assemblies; implanting the intervertebral device of the first spinal implant assembly between adjacent vertebrae; coupling the intervertebral device to the extension portion of the connector of the first spinal implant assembly and securing the body portion to a vertebra adjacent the implanted intervertebral device; and coupling the connector to the second spinal implant assembly using an elongate member. This method does not form part of the claimed invention.

The term subject as used herein can be a human or animal subject. The terms lateral, ventral, dorsal, cranial, caudal as used herein have the usual meanings in relation to veterinary anatomy. For installation in a human subject, it will be understood that the terms ventral/dorsal as used herein can be substituted with the terms anterior/posterior. Anatomical directional terms used herein in relation to the connector, assembly or system refer to anatomical directions when the connector, assembly or system is installed in a subject. It will be understood that components of the invention can be positioned in a number of different orientations, the directional terminology being used for purposes of illustration and being in no way limiting.

A preferred embodiment of the present invention will now be more particularly described by way of example only with reference to the accompanying drawings, wherein:.

The present embodiments represent currently the best ways known to the applicant of putting the invention into practice. But they are not the only ways in which this can be achieved. They are illustrated, and they will now be described, by way of example only.

Referring to <FIG>, this shows a spinal implant system <NUM> according to the invention. This system can be used to fuse two or more vertebrae together, in order to provide stabilisation of the spine. The system of <FIG> comprises a plurality of individual spinal implant assemblies <NUM> which are assembled together in a series, end to end, with each assembly configured to secure to a vertebra and to an adjacent disc space of a successive row of vertebra. The system is particularly suited to achieving fusion of the cervical spine via a ventral approach, however it will be understood that it can be used at different regions of the spine and/or via a dorsal approach. The present invention is particularly suited for installation in small animals, where the confined space makes pre-existing systems unsuitable, however it will be understood that the present invention is also suitable for installation in humans.

<FIG> show a shorter system of only two spinal implant assemblies <NUM>, <NUM>' for fusing two adjoining vertebrae. <FIG> show a standard spinal implant assembly <NUM> on the right and a distal end assembly <NUM>' shown on the left.

The standard spinal implant assembly <NUM> will now be described and will be referred to in the specification. The standard spinal implant assembly <NUM>, shown on the right of <FIG>, comprises a connector <NUM>, means for installation into vertebral bone comprising first and second bone screws <NUM>, means for installation into the adjacent intervertebral disc space comprising an intervertebral device, and means <NUM> for coupling the connector <NUM> with another connector of another spinal implant assembly. In this embodiment the means for coupling the connector <NUM> with another connector is an elongate rod <NUM>.

The connector <NUM> has a body portion <NUM> and an extension portion <NUM> extending from the body portion <NUM>. The body portion <NUM> forms a saddle configured to contact the vertebra to which it is to be secured. The body portion has a lower surface 32a adapted to face a vertebra when installed and an upper surface 32b opposite said lower surface, at least part of the lower surface 32a of the body portion having a concave curvature configured to conform to at least a portion of a subject's vertebra.

The extension portion <NUM> is an elongate plate having an upper surface 40b adapted to face away from the spine when installed and a lower surface (not visible in the figures) opposite said upper surface. The extension portion <NUM> is preferably integral with the body portion <NUM> of the connector <NUM>. The extension portion <NUM> is bendable such that during installation the connector <NUM> can be adjusted so that the body portion <NUM> can be stably seated on the vertebra relative to a coupled intervertebral device <NUM> that has already been installed in the disc space. The extension portion <NUM> is made from a suitable material that is sufficiently malleable to allow the extension portion <NUM> to be bent by the surgeon during installation, whilst retaining rigidity and strength once the connector <NUM> is fully installed.

The assembly <NUM> includes means for coupling the intervertebral device <NUM> to the extension portion <NUM>, said means in this embodiment comprising a locking member <NUM> which is engageable with the intervertebral device <NUM> such that the extension portion <NUM> can be clamped therebetween. The locking member <NUM> has a head portion and 43b a shank portion 43a, at least part of which is externally threaded. The extension portion <NUM> has an aperture <NUM> at or near its distal end (i.e. the end furthest from the point at which the extension portion <NUM> meets the body portion <NUM> of the connector <NUM>). The intervertebral device <NUM> has a hollow bore communicating with a first open end <NUM> in its proximal end (the end which secures to the extension portion <NUM>), the bore being at least partially internally threaded such that the shank portion 43a of the locking member <NUM> can be threadedly secured to the intervertebral device <NUM>. The locking member <NUM> is receiveable through the aperture <NUM> in the extension portion and then securable in the first open end <NUM> of the intervertebral device <NUM> to secure the intervertebral device to the extension portion <NUM>.

The body portion <NUM> has first and second bores <NUM> for receiving first and second bone screws <NUM> respectively. The bone screws <NUM> are preferably cortical screws. Each bore <NUM> extends from an aperture in the upper surface 32b to an aperture in the lower surface 32a of the body portion <NUM>, forming a bore for receiving a corresponding bone screw <NUM>. At least part of each bone screw <NUM> is externally threaded. The threading toward the distal end of each bone screw <NUM> will secure each bone screw <NUM> into vertebral bone when installed. Threading toward the proximal end of each bone screw corresponds with internal threading within each corresponding bore <NUM>, such that the bone screws <NUM> lock securely relative to the connector <NUM> when installed. In alternative embodiments, the bone screws <NUM> may not be threadedly fastenable to the connector <NUM>. Each bore <NUM> is inclined at a predetermined angle relative to the connector <NUM> such that when installed, the corresponding bone screw extends at a predetermined angle relative to the connector <NUM>. In this particular embodiment the incline of the bores relative to the lateral axis of the connector <NUM> has been selected so that the first and second bone screws <NUM> of assembly <NUM> diverge from one another. Connectors can be provided with different spacings between the first and second bores <NUM> in the body portion <NUM> and with different inclines relative to the connector <NUM>, so as to suit different vertebral bone geometry in different types of animal.

The connector <NUM> has means for non-movably securing the rod <NUM> for coupling the connector <NUM> with another connector of another spinal implant assembly. Said means comprises a clamp member <NUM> for clamping the rod <NUM> to the connector <NUM>. The clamp member <NUM> has a lower surface 70a adapted to face the connector <NUM> when assembled and an upper surface 70b opposite the lower surface. The lower surface 70a has first and second grooves <NUM> shaped for receiving a rod thereunder. Similarly, the upper surface 32b of the body portion <NUM> of the connector <NUM> has corresponding first and second grooves <NUM> shaped for receiving a rod therein, each groove <NUM> extending across the upper open end of a bone screw receiving bore <NUM>. The first and second grooves <NUM> of the clamp member <NUM> overlie the corresponding first and second grooves <NUM> of the connector <NUM> when assembled, allowing each pair of corresponding grooves to receive a rod <NUM> therebetween in the cylindrical space formed therein. The clamp member <NUM> is non-movably fastened to the connector <NUM> using a locking screw <NUM> (although other clamp locking means could be used). The locking screw <NUM> has a head portion 75b and a shank portion 75a, at least part of the shank portion 75a being externally threaded. The clamp member <NUM> has a bore <NUM> passing through it from an opening in the upper surface 70b to an opening in the lower surface 70a. During assembly, the shank portion 75a of the locking screw is received through bore <NUM> in the clamp member <NUM> and into an internally threaded bore <NUM> in the body portion <NUM>, having a first opening in the upper surface 32b of the body portion <NUM>, to threadedly secure the clamp member <NUM> to the connector <NUM>. If a rod <NUM> is placed in the first or second cylindrical space formed by grooves <NUM>, <NUM>, and the clamp member <NUM> then tightly fastened to the connector <NUM>, the rod <NUM> will be clamped to the connector <NUM>.

As can be seen from <FIG>, several vertebral joints can be fused using a series of connectors <NUM>, the connectors <NUM> being coupled to one another using rods <NUM> to strengthen the system. Starting at the right hand-side of <FIG>, there is a first connector <NUM> coupled distally to a second connector <NUM> (i.e. the second connector <NUM> is arranged distally of the distal end of the extension portion <NUM> of the first connector). The second connector <NUM> is coupled proximally to the first connector and distally to a third connector and so on.

In a spinal implant system of the present invention, any connector <NUM> which is not coupled distally to a further connector <NUM> of a standard spinal implant assembly is preferably coupled to a distal end assembly <NUM>' in order to stablilise the intervertebral device <NUM> at the distal end of the system. For example, a distal end assembly <NUM>' is assembled at the left-hand side of the row of implant assemblies in <FIG> and a distal end assembly <NUM>' is preferably assembled to any standard spinal implant assembly used to fuse a single vertebral joint (for example, as shown in <FIG>).

A distal end assembly <NUM>', as shown on the left of <FIG>, will now be described. The distal end assembly <NUM>' is very similar to the standard spinal implant assembly <NUM> shown on the right of <FIG>, except that the distal end assembly <NUM>' has a connector <NUM>' with a shorter extension portion <NUM>' than that of the standard assembly <NUM> and the distal end assembly <NUM>' does not include its own intervertebral device for installation in the next disc space as the extension portion <NUM>' of the distal end assembly <NUM>' secures to the intervertebral device <NUM> associated with the adjacent standard spinal implant assembly <NUM> when assembled.

The distal end assembly <NUM>' has a connector <NUM>' having a body portion <NUM>' and a short extension portion <NUM>' extending therefrom. The body portion <NUM>' is substantially similar to that of the standard spinal implant assembly <NUM> described above, said body portion <NUM>' including first and second bores <NUM> for receiving first and second corresponding bone screws <NUM> for securing the connector <NUM>' to a vertebra, first and second grooves <NUM> extending across each of the upper open ends of the bone screw bores <NUM> in the upper surface of the body portion <NUM>', each able to receive a rod, and including a similar clamp member <NUM> and locking screw <NUM> adapted to clamp one or two rods against the connector <NUM>'.

The extension portion <NUM>' of the distal end connector <NUM>' is a short plate-like piece having an upper surface adapted to face away from the spine when installed and a lower surface opposite the upper surface, adapted to face towards the spine when installed. The extension portion <NUM>' has an aperture <NUM>' passing through from the upper surface to the lower surface. The aperture <NUM>' is sized to receive the shank portion 43a of the locking member <NUM> therethrough. The distal end connector <NUM>' of the distal end assembly <NUM>' is arranged distally of the standard spinal implant assembly <NUM> it is to couple to, with the extension portions <NUM>, <NUM>' of each connector <NUM>, <NUM>' pointing towards one another. In order to couple the connector <NUM> and distal end connector <NUM>', extension portion <NUM>' is placed over the distal end of extension portion <NUM>, with the apertures <NUM>', <NUM> aligned and the shank portion 43a of the locking member <NUM> is received through aperture <NUM>', then through aperture <NUM> and secured in the threaded bore of the intervertebral device <NUM>. Alternatively the distal end of extension portion <NUM> can be placed over extension portion <NUM>' before connectors <NUM> and <NUM>' are fastened together.

Similar to the connector <NUM> of a standard implant assembly <NUM>, the extension portion <NUM>' of the distal end connector <NUM>' is bendable relative to the body portion <NUM>' of the connector <NUM>' so that the bone screws <NUM> received in body portion <NUM>' can be placed into the vertebral bone with the lower surface of body portion <NUM>' in stable contact with the bone.

An advantage of clamping the rod <NUM> which couples one connector to another to overlie the upper open end of bone screw receiving bore <NUM> is that this helps to prevent the bone screws <NUM> from unscrewing and therefore helps to prevent the bone screws from loosening from the bone. Referring to <FIG>, preferably each pair of implant assemblies <NUM>, <NUM>' is coupled together using a single rod <NUM>, which is long enough to span the vertebral joint and to couple a connector installed in one vertebra to an adjacent connector installed in an adjacent vertebra. When a series of connectors are assembled end to end, the rods are preferably arranged on alternate sides of the system (for example, in the system of <FIG>, the first connector shown at the right hand side is coupled to the second connector by a rod arranged on the right lateral side of the spine and the second connector is coupled to the third connector by a rod arranged on the left lateral side and so on). In this arrangement one end of a rod <NUM> is received in the grooves <NUM>, <NUM> in the body component <NUM>, <NUM>' and clamping member <NUM> on one side of the body portion <NUM>, <NUM>' and the other end of the rod is received in the grooves <NUM>, <NUM> on the same side of the body component <NUM>, <NUM>' on the next connector.

Any connector <NUM>, <NUM>' which is only coupled to one other connector preferably has a short rod <NUM> assembled within the groove <NUM> which is not used for coupling to another connector. The system of <FIG> shows a pair of implant assemblies <NUM>, <NUM>' having a short rod <NUM> assembled within a groove <NUM> of each connector. The short rods <NUM> serve to prevent the bone screws <NUM> from unscrewing, in the same way that rod <NUM> of the system does.

Referring to <FIG>, the system of <FIG> is shown installed on the ventral side of a subject's spine <NUM>. The vertebrae are labelled and as can be seen, starting from the right hand side, the bone screws of the first spinal implant assembly are installed at vertebra C2, with its intervertebral device installed in the disc space between vertebrae C2 and C3, the bone screws of the second spinal implant assembly are installed in vertebra C3, with its intervertebral device installed in the disc space between vertebrae C3 and C4 etc. The seventh assembly is a distal end assembly <NUM>', having its bone screws installed in vertebra T1 and its extension portion extending towards vertebra C7.

Referring to <FIG>, various different connectors are shown. In <FIG> a connector <NUM> is shown wherein the distal end of its extension portion <NUM> is bent relative to the longitudinal axis of the extension portion. The extension portion <NUM> extends from the body portion <NUM> such that the longitudinal axis of the extension portion <NUM> is perpendicular to that of the bone screws <NUM> when installed (i.e. the longitudinal axis of the extension portion <NUM> extends from the body portion <NUM> with the longitudinal axis of the extension portion <NUM> perpendicular to that of the bores for the bone screws). The distal end of the extension portion <NUM> is bent in a direction towards the spine when installed, such that the distal end of the intervertebral device <NUM> points towards the bone screws <NUM>. A notional angle between the intervertebral device <NUM> and the bone screws <NUM> in the sagittal plane is an acute angle (i.e. the distal ends of the intervertebral device <NUM> and the bone screws <NUM> are convergent).

In <FIG> a connector <NUM> is shown wherein the distal end of its extension portion <NUM> is bent relative to its connection with the body portion <NUM>, towards the spine, however it is bent by a smaller angle than the connector <NUM> of <FIG>. The extension portion <NUM> of the variant in <FIG> is also shorter than the extension portion <NUM> of the <FIG>, connector <NUM>. A connector <NUM> for a standard spinal implant assembly <NUM> preferably is bendable such that only the distal, apertured part, of the extension portion <NUM> bends relative to the body portion <NUM>.

<FIG> show a connector <NUM>' for a distal end assembly <NUM>', the extension portion <NUM>' being angled away from the spine about its connection with the body portion <NUM>', such that a notional angle between the intervertebral device <NUM> and the bone screws <NUM> in the sagittal plane is an obtuse angle (i.e. the distal ends of the intervertebral device <NUM> and the bone screws <NUM> are divergent).

<FIG> show another example connector <NUM>' for a distal end assembly <NUM>', the extension portion <NUM>' being angled away from the spine about its connection with the body portion <NUM>', but with the extension portion <NUM>' angled at a greater angle relative to the bores for the bone screws <NUM> than in the connector <NUM>' of <FIG>, such that the intervertebral device <NUM> and the bone screws <NUM> are diverge by a larger angle in <FIG>.

The rods <NUM> for coupling one connector to another are preferably bendable so that the installer can bend the rods during assembly.

In operation, in order to install a system according to the present invention an intervertebral device <NUM> is inserted in between two adjoining vertebrae by drilling through the intervertebral disc. A spinal implant assembly <NUM> is then placed on top of the intervertebral device <NUM> and the intervertebral device <NUM> is secured to the distal end of the extension portion <NUM> of the connector <NUM>. The connector <NUM> is then secured to a vertebra adjacent the disc space. The extension portion <NUM> can be bent to place the bone screws <NUM> through the vertebral body into each pedicle whilst making sure the lower surface of the body portion <NUM> makes stable contact with the bone underneath. The spinal implant assembly can be coupled to an adjacent spinal implant assembly that has been installed distally using one or two rods <NUM> to strengthen the bridge formed across the vertebral joint. By installing several spinal implant assemblies in series in this manner, several vertebral joints can be used and linked using an alternate arrangement of rods.

In operation to install a distal end assembly <NUM>' (i.e. in situations where only a single vertebral joint is to be fused by a standard spinal implant assembly <NUM> and a distal end assembly <NUM>' or in situations where several vertebral joints are to be fused and a distal end assembly is required to stabilise the distal end of the row of connectors), a distal end assembly <NUM>' is placed adjacent a standard spinal implant assembly <NUM>, each overlying an adjacent vertebra, and the extension portions <NUM>, <NUM>' of each are secured to an intervertebral device installed in the disc space between. Then each connector <NUM>, <NUM>' is secured to its corresponding vertebra using bone screws and the connectors <NUM>, <NUM>' are coupled using a rod <NUM>.

Preferably the intervertebral device <NUM> is a specially designed device, such as a disc screw, disc bolt or other spacer for installation between two adjoining vertebrae. In the presently described embodiment the intervertebral device <NUM> is externally threaded and these threads on the external surface cut into the tissue during insertion. The intervertebral device <NUM> has a hollow bore. The intervertebral device <NUM> has at least one elongate slot communicating with the hollow bore, the or each slot having a longitudinal axis running parallel with the longitudinal axis of the intervertebral device <NUM>. The outer surface of the intervertebral device <NUM> may have a hydroxyapatite coating to stimulate bone ingrowth. The hollow bore of the intervertebral device <NUM> can be impregnated with bone graft before installation in the subject. The subject's bone will ingrow, through the elongate slot(s), and attach with the bone graft inside the hollow section. This further anchors the device in the subject. Even if no bone graft is inserted in the hollow of the device before implantation, cutting of the subject's bone by the external threads as the device is implanted will create bone debris that will accumulate, via the elongate slot(s), in the hollow bore. The subject's bone will ingrow, through the elongate slots(s) and attach with the accumulated bone debris, further anchoring the device against rotation.

As well as the lower surface of the body portion <NUM>, <NUM>' of a connector <NUM>, <NUM>' being concavely curved or at least partially concavely curved in the transverse plane, the lower surface may be convexly curved in the coronal plane for optimal seating over a range of bony geometries.

Instead of being bendable by the user during installation, the extension portion <NUM>,<NUM>' of a connector <NUM>, <NUM>' can be provided as part of a kit in which connectors having extension portions bent at different angles relative to the body portion are provided and the user can select the connector which suits the vertebral geometry at the particular vertebra that the connector is being installed at.

Referring to <FIG>, a further embodiment of a spinal implant assembly is shown. <FIG> show a standard spinal implant assembly <NUM> like standard spinal implant assembly <NUM> of <FIG> (i.e. a standard spinal implant assembly that can be coupled to a series of other standard spinal implant assemblies installed longitudinally along a subject's spine, as shown for example in <FIG>). The same reference numerals have been used in the Figures for features which are substantially the same as features of other embodiments. The standard spinal implant assembly <NUM> of <FIG> is similar to that of <FIG> except for certain differences which will be described.

The spinal implant assembly <NUM> includes a connector <NUM> having a body portion <NUM> that receives first and second bone screws <NUM>. The extension portion <NUM> is an elongate plate which extends from the body portion <NUM> and which differs from that of the <FIG> embodiment in that the extension portion <NUM> is wider than that of the <FIG> embodiment and extension portion <NUM> is provided manufactured in a pre-bent form wherein the plate is curved in the sagittal plane such that the plate is hump shaped. The extension portion <NUM> is a thin plate of substantially uniform thickness having a lower surface adapted to face the spine when installed and an upper surface opposite said lower surface, the upper surface being convexly curved in the sagittal plane and the lower surface being concavely curved in the sagittal plane.

The extension portion <NUM> has an aperture <NUM> at or near its distal end for coupling an intervertebral device <NUM> (shown in <FIG>) to the connector <NUM>. The extension portion <NUM> has slot <NUM> therein, which in the present embodiment is an elongate slot having an elongate axis parallel with the sagittal plane, but which may be other shapes. The slot <NUM> decreases the stiffness of extension portion <NUM> compared to an extension portion without any slot, therefore making it easier for a user to bend the extension portion <NUM> to vary the curvature of extension portion <NUM> from that shown in <FIG> in order to selectively increase or decrease the angle between the longitudinal axes of the bone screws <NUM> and intervertebral device relative to one another when assembled such that the bone screws <NUM> and intervertebral device are angled relative to one another to suit the geometry at the vertebral joint where the assembly is to be installed. The curvature of extension portion <NUM> in the sagittal plane also provides space to accommodate vertebral bone beneath it when installed, thus allowing the assembly to be installed on the spine without the need to cut large amounts of vertebral bone to accommodate the connector <NUM>.

In this embodiment the means for coupling the connector <NUM> with another connector is an elongate rod <NUM> like that of the previous embodiments except that the elongate rod <NUM> has a ball end <NUM> at each end of the rod, each ball end <NUM> being substantially spherical.

Like the connector of the <FIG> embodiment, the spinal implant assembly <NUM> has means for securing the rod <NUM> to the connector <NUM>, said means being a clamp member <NUM> for clamping the rod <NUM> to the connector <NUM>. The clamp member <NUM> has a lower surface 370a adapted to face the connector <NUM> when assembled and an upper surface 370b opposite the lower surface. The lower surface 370a has first and second recesses <NUM> each for receiving the spherical end <NUM> of a rod <NUM> thereunder. Similarly the upper surface 332b of the body portion <NUM> of the connector <NUM> has corresponding first and second recesses <NUM> for receiving the spherical end <NUM> of a rod <NUM> therein. The first and second recesses <NUM> of the clamp member <NUM> overlie the corresponding first and second recesses <NUM> of the connector <NUM> when the clamp member <NUM> is assembled thereto, allowing each pair of corresponding recesses to receive a spherical end <NUM> in the space formed therebetween. The clamp member <NUM> is non-movably fastenable to the connector <NUM> using a locking screw <NUM> (although other clamp locking means could be used). The locking screw <NUM> has a head portion 375b and a shank portion 375a, at least part of the shank portion 375a being externally threaded and receivable in a bore <NUM> passing through the clamp member <NUM> and an internally threaded bore <NUM> in the connector <NUM> to threadedly secure the clamp member <NUM> to the connector <NUM> with the end of a rod <NUM>, or two rod ends, clamped therebetween.

Whereas the connector and clamp member of the <FIG> embodiment had cylindrical grooves for receiving rods, the recesses <NUM>, <NUM> in the connector <NUM> and clamp member <NUM> in the <FIG> embodiment are preferably part-spherical depressions. The recesses <NUM>, <NUM> in the connector and clamp member are each concavely curved and the curvature of each recess <NUM>, <NUM> is substantially the same as one another. The curvature of each recess <NUM>, <NUM> may closely match that of the spherical end <NUM> of the rod <NUM> to be received therein. Preferably however the curvature of the recesses <NUM>, <NUM> does not match the spherical end <NUM> to be received therein and instead the radius of curvature of the recesses <NUM>, <NUM> is slightly less than the radius of curvature of the spherical end <NUM> of the rod. This non-conformance between the radius of curvature of each substantially spherical end <NUM> of the rod and the concave recesses <NUM>, <NUM> provides an edge contact between the spherical rod end <NUM> and the edge of the recess <NUM>, <NUM>. The edge contact between the edge of each recess and a corresponding spherical end <NUM> of the rod comprises a circular line of contact, which enhances the fixation of the rod <NUM> relative to the connector <NUM> and reduces loosening. For example, the radius of curvature of the recesses <NUM>, <NUM> may be around <NUM> less than the radius of curvature of the spherical end <NUM> of rod <NUM>.

Between the first and second recesses <NUM> of the upper side of the body portion of the connector <NUM> is a wall portion <NUM> in which bore <NUM> is located. There is a corresponding wall portion <NUM> on the lower surface 370a of the clamp member <NUM> in which bore <NUM> is located. Wall portions <NUM> and <NUM> preferably do not engage one another when the clamp member <NUM> is clamped relative to the connector <NUM> in order to clamp at least one spherical end <NUM>, and preferably a small gap is maintained between wall portions <NUM> and <NUM>. The clamp member <NUM> has first and second lateral side walls <NUM> which extend away from the main body of the clamp member <NUM> and towards the spine when installed. On the inner side of each lateral side wall <NUM> is a shoulder <NUM> which preferably does not engage the upper surface 332b of the body portion <NUM> of the connector <NUM> when the clamp member <NUM> is assembled to the connector <NUM> with at least one spherical end <NUM> clamped therebetween. When the clamp member <NUM> is assembled to the assembly as shown in <FIG>, the lateral side walls <NUM> of clamp member <NUM> overhang the side of the body portion of connector <NUM>. By means of the the lateral side walls <NUM> overhanging the connector <NUM>, this helps the user to locate the clamp member <NUM> into the correct position with respect to the connector <NUM>.

As can be seen in <FIG>, there is a first notch <NUM> (i.e. a cut-out) extending proximally and a second notch <NUM> extending distally away from each recess <NUM> in the connector. Similarly, there are corresponding notches <NUM> extending proximally and distally from each recess <NUM> in the clamp member <NUM>. The notches <NUM>, <NUM> allow for the rod <NUM> to be angled at a greater range of angles relative to the connector <NUM>.

Each rod <NUM> has a length such that it will span between a first connector <NUM> to be installed in a first vertebra and a second connector <NUM> to be installed in an adjacent vertebra. A set of matching rods <NUM> may be supplied having a length predetermined based on the subject the assembly is to be installed in. Alternatively a kit may be supplied with rods <NUM> of differing discrete lengths. The rods <NUM> are preferably bendable to conform to the natural curvature of the spine. Slight bending of the rod <NUM> also provides a small reduction in length between the two spherical ends <NUM> of a rod <NUM> to precisely position the spherical ends <NUM> into the corresponding recesses <NUM> and <NUM> of the two adjacent standard assemblies <NUM>.

Referring to <FIG>, a further embodiment of a spinal implant assembly <NUM> is shown which is intended for implantation at the vertebral joint that forms the transition between the cervical and thoracic regions of the spine (i.e. for implantation across the joint between the C7 and T1 vertebrae). The assembly <NUM> is somewhat like the bridge formed by the standard spinal implant assembly <NUM> and the distal end assembly <NUM>' as shown in <FIG>, except that in the <FIG> embodiment the bridge is formed by a single connector <NUM> which is secured to both adjacent vertebrae spanning the vertebral joint to be fused, rather than by two connectors which are coupled together across the vertebral joint by one or more rods. The connector <NUM> comprises a first body portion <NUM> and a second body portion <NUM>' which are coupled by an extension portion <NUM>. In this embodiment the extension portion <NUM> is integral with the first and second body portions <NUM>, <NUM>', however the components may be initially separate and affixed together in a suitable manner. The first body portion <NUM> has means for installation into vertebral bone, which in this embodiment is via means of two bone screws <NUM> each receivable in a corresponding bore <NUM> in the first body portion <NUM>. Similarly the second body portion <NUM>' has two bores <NUM>', each for receiving a bone screw <NUM> to be implanted in the adjacent vertebral bone.

Like the extension portion of the <FIG> assembly, the extension portion <NUM> of the <FIG> assembly is an elongate plate. Preferably the extension portion <NUM> is provided in a pre-bent form as shown in <FIG> wherein the plate is curved in the sagittal plane such that the plate is hump shaped. The extension portion <NUM> has a smaller thickness than the body portions <NUM>, <NUM>' and the extension portion <NUM> also includes a slot <NUM> therein, both of which allow for the extension portion <NUM> to be malleable so that it can be bent to change the curvature of the extension portion <NUM> and to change the angle at which the proximal bone screws <NUM> extend relative to the distal bone screws <NUM>. The extension portion <NUM> includes an aperture <NUM> therein for receiving the intervertebral device <NUM> so that the intervertebral device <NUM> can be securely engaged with the connector <NUM>. The aperture <NUM> for receiving the intervertebral device <NUM> is nearer the distal end of the device than the proximal end, i.e. nearer the second body portion <NUM>' than the first body portion <NUM>. Like the <FIG> assembly, the curved extension portion <NUM> provides space for vertebral bone to reside underneath so that the assembly can be installed without removing excessive amounts of bone.

The spinal implant assembly <NUM> is adapted for securing at least a first rod <NUM> to the connector <NUM>. The upper surface of the first body portion <NUM> is configured like that of the upper surface of the body portion of the <FIG> embodiment (i.e. including first and second recesses <NUM> for receiving the spherical end of a rod <NUM>). In this embodiment, the second body portion <NUM> does not include any recesses on its upper surface and is therefore not configured to couple any rods thereto. The assembly <NUM> includes a clamp member <NUM> for clamping a rod <NUM> to the connector <NUM>. The clamp member <NUM> differs from that of the <FIG> embodiment in that the clamp member <NUM> is configured for clamping only one rod <NUM> to the connector <NUM>. At one lateral end, the clamp member <NUM> has a single recess <NUM> in its lower surface 470a adapted to face the connector <NUM> for receiving the spherical end of a rod <NUM> thereunder. At the other lateral end there is a protrusion <NUM> extending away from the lower surface 470a of the clamp member <NUM>, intended to seat over the recess <NUM> in the connector <NUM> which does not receive a rod <NUM> in use. The clamp member <NUM> includes a bore <NUM> for receiving a locking screw <NUM> for securing the clamp member <NUM> to the connector <NUM> to clamp the rod <NUM> therebetween. The assembly <NUM> may be coupled to a spinal implant assembly such as the type shown in <FIG> using a rod <NUM>, or alternatively the assembly <NUM> may be installed at the C7-T1 joint without coupling the assembly <NUM> to any other spinal implant assemblies. Of course, this connector <NUM> could of course alternatively be used to couple two rods thereto by using a clamp member <NUM> as shown in <FIG> instead of clamp member <NUM>, whereby both rods run side by side to join assembly <NUM> to an adjoining standard assembly <NUM>. This assembly with single connector <NUM> for installation at the C7-T1 joint provides a stable device for fusion of the joint.

Claim 1:
A spinal implant system (<NUM>) for fusing one or more vertebral joints of a subject's spine, the spinal implant system comprising:
a first intervertebral device (<NUM>) for installation in a spinal disc space separating two adjacent vertebrae,
a first elongate member (<NUM>, <NUM>, <NUM>),
a first connector (<NUM>, <NUM>', <NUM>, <NUM>, <NUM>, <NUM>) adapted to be secured to a first vertebra and a second connector (<NUM>, <NUM>', <NUM>, <NUM>, <NUM>, <NUM>) adapted to be secured to a second vertebra adjacent the first vertebra, each comprising a body portion (<NUM>, <NUM>',<NUM>, <NUM>, <NUM>, <NUM>) being adapted to couple thereto at least a first bone screw (<NUM>) for installation in a vertebra, the body portion further being adapted for coupling said first elongate member (<NUM>, <NUM>, <NUM>) thereto,
the first connector (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) further comprising an extension portion (<NUM>, <NUM>', <NUM>, <NUM>, <NUM>, <NUM>) extending from the body portion of the first connector, the extension portion being adapted for coupling thereto said first intervertebral device (<NUM>) for securing the connector to the spinal disc space,
wherein the extension portion (<NUM>, <NUM>', <NUM>, <NUM>, <NUM>, <NUM>) has a longitudinal axis which is configured to extend substantially parallel with the longitudinal axis of the subject's spine when installed, the extension portion being sized with a length to span longitudinally across the spinal disc space between the first intervertebral device when installed in the spinal disc space and the body portion of the first connector when installed at the first vertebra;
said first intervertebral device (<NUM>) being coupled in use to the extension portion (<NUM>, <NUM>', <NUM>, <NUM>, <NUM>, <NUM>) of the first connector at or near the distal end of the extension portion,
the first and second connectors being coupled together in use by said first elongate member (<NUM>, <NUM>, <NUM>).