Interbody spinal fusion implant with trailing end adapted to receive bone screws

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DESCRIPTION

Rear end vertebral fusion implant adapted to receive bone screws.

Background of the invention

Implants adapted for use in the lumbar and thoracic spine are found to be much less usable in the cervical spine due to anatomical differences. In the lumbar spine, the intervertabral disc spaces are approximately 25% of the height of the vertebral bodies (that is, the vertebral bodies are generally four times taller than the intervening intervertrebral disc space). In the cervical spine, the disc space can be 50% of the height of the vertebral bodies. Disc spaces in the cervical spine are generally no higher than 7 to 8 mm in height in most people.

The screws generally used to fix an implant in the cervical spine typically have a diameter between 4 and 5 mm. If two bone screws were to be inserted, each within each of the adjacent cervical vertebral bodies; and if you tried to oppose these two bone screws vertically, that would not be possible because the sum of the screw diameters would exceed the implant height. Such vertically aligned bone screws would require at least 10mm of combined height for themselves, plus sufficient implant structure and enough additional height to surround and retain them. Thus, in total, the two bone screws and the surrounding implant would have to have a combined height that would substantially exceed the height of the intervertebral disc space and an implant adapted to fit within.

Alternatively, one could try to place a plurality of bone screws more horizontally (side to side) to avoid the previously described problems associated with vertical alignment. To achieve the preferred implant stability provided by the use of paired screws (two within each of the adjacent vertebral bodies), four bone screws could be aligned horizontally on the implant equator with two of the screws directed toward one of the cervical vertebral bodies and two of the bone screws directed toward the other of the adjacent cervical vertebral bodies. The four horizontally aligned bone screws, each with a head diameter of 5mm, would require at least 20mm, just for the screw heads. Also, with sufficient implant structure surrounding each of these screw heads, the width of the implant would be a minimum of approximately 24 mm, which would exceed the desirable width of the implant for most spaces in the implants. cervical intervertebral discs. Staggered placement of the bone screw receiving holes would provide some benefit, but in itself would not be a satisfactory solution to the problem described in which it is desirable to maintain some symmetry of the screws with each other, the vertebrae, and the implant.

A prior art solution to the aforementioned problem proposes extending the height of the rear end of the implant to make it taller than the disc space. An example of this is a flanged implant. The flanged implant makes it possible to position the screws in such a way that they can be vertically aligned and that the implant has sufficient structure to retain them. The flanged portion of the implant, however, extends beyond the disc space, which may not be desirable in all circumstances. Also, these flanged implants may not be usable when multiple levels of the spine need to be fused.

Accordingly, there is a need for a vertebral implant adapted to provide the advantages of a flanged implant for the placement and orientation of bone screws associated therewith but without the flanged portion, or the need for the implant to extend. outside the intervertebral disc space.

US Patent No. 5,674,296 discloses a vertebral disc stent having a resilient body made of one or more materials whose stiffness can vary from a relatively rigid outer annular gasket portion to a relatively ductile central core portion. Concave-convex elements at least partially surround the core portion to retain the core portion and the joint between adjacent vertebral bodies of a patient's spine.

International Patent Application WO 00/66045 A1 describes a vertebral arthrodesis implant that has a front end, a rear end, and an extension between them, and opposing upper and lower portions adapted to contact each of the adjacent vertebral bodies. . Each of the lower and upper portions has at least one opening adapted to communicate with each of the adjacent vertebral bodies and to communicate with each other to allow regrowth of bone from the vertebral body to the adjacent body through the implant. Each of the upper and lower portions has at least one screw hole that passes through those near the rear end.

Summary of the invention

The present invention relates to an intervertebral spinal implant, such as - without implying limitation - an intervertebral arthrodesis implant, some spacers, some motion preservation implants, or others. The spinal intervertebral implant of the present invention is characterized in independent claim 1. Preferred embodiments of the present invention are characterized in the dependent claims.

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The implant has opposing upper and lower surfaces each of which contacts each of the opposing vertebral bodies adjacent a space of an intervertebral disc. The implant is adapted to cooperatively receive at least two opposing bone screws, at least one of which is intended for insertion into each of the vertebral bodies adjacent to the intervertebral disc space. The spinal intervertebral implant is adapted to receive the bone screws through its rear end and to allow the forward end of the bone screws to pass through at least a portion of the implant and exiting the upper or lower surfaces. opposite bottom of the implant, respectively, each of them. Bone screws have a front end, a shaft, a threading on the shaft, and a rear end. The implant and the rear end of the bone screw are adapted to cooperatively engage with each other to prevent further advancement of the bone screws through the implant. At least a portion of the perimeter of the rear ends of at least some of the bone screws project beyond at least one of the opposite upper and lower surfaces of the implant.

The rear end is configured to allow a portion of the head of at least one of the bone screws to project beyond the height of the perimeter of the rear end. The rear end of the implant includes at least one bone screw receiving opening or hole that has a clearance at its perimeter to allow at least a portion of the rear end of a bone screw to project beyond the surfaces. of the opposing upper and lower vertebral bodies. The clearance interrupts the perimeter of the bone screw receiving hole so that the bone screw receiving hole has an incomplete or C-shaped perimeter. The size of the clearance is such that it is less than half screw diameter. By allowing each screw to project over one of the upper or lower edges of the rear end of the implant, the upper or lower screws can be positioned so that the maximum height of the rear end of the implant is less than the sum of the diameter Maximum of two bone screws adapted to be inserted into the bone screw receiving holes. This allows the use of larger bone screws at the rear end of the implant than would otherwise be possible. Also, although not limited in this regard, the present invention allows optimal diameter bone screws to be inserted into and in part through the implant and into adjacent vertebral bodies without the need for a portion of the implant itself to be inserted. extend beyond the intervertebral disc space and out of the spine.

The rear end of the implant is configured to allow insertion of the bone screws into each of the adjacent vertebrae to be angled relative to each other, with the rear end of the implant and with the upper and lower surfaces. implant. The opposing bone screws preferably pull the anterior faces of the vertebral bodies toward the implant together. The bone screws preferably penetrate a portion of the vertebral body closest to the disc space within which the implant is being installed so as not to interfere with bone screws from a second implant being installed in a disc space. adjacent where consecutive levels of the column are merging. In a preferred embodiment, the rear end is configured to coat the bone screws to compress the vertebral bodies together and to load the interface of the vertebral bodies of the implant to promote fusion.

In certain preferred embodiments, the screws subtend an angle to the upper and lower surfaces to keep them confined to the lower half of the vertebral body above or to the upper half of the vertebral body below the disc space to be fused. .

In other preferred embodiments, the rear end of the implant is configured to enable screws originating at or near the vertical midline of the rear end of the implant to be directed outwardly, or divergently oriented, and to screws originating beyond the vertical line of the rear end of the implant are directed inward or convergently oriented. Screws that are oriented convergently are directed toward one vertebral body and screws that are oriented divergently are directed toward the other adjacent vertebral body. Said arrangement allows said implants, when inserted into the spaces of the adjacent discs, to have convergently oriented screws from one implant and divergently oriented screws from the other implant, to be screwed into the same vertebral body and ensure that the screws do not interfere with each other. This configuration allows screws from different implants to intersect within a vertebral body where both spaces of the adjacent discs are to be fused.

In any of these embodiments it is preferred, although not required, that the screws be retained within the implant by "locking mechanisms" which may include any of those known to those of skill in the art, including, but not limited to , those disclosed by the applicant, for example, in US Patent Nos. 6,139,550, 6,193,721 and 6,558,423. The rear end of the implant can be configured to receive bone screws in such a way that they are constrained within the bone screw receiving holes (i.e., fixing the path of each bone screw), or held without constriction within the bone screw receiving holes to allow variable angles of the bones. If a locking mechanism is used, the screws can start from an initial constrained state within the bone screw receiving holes and remain so when locked. Alternatively, the screws may start from a free state prior to locking and, after locking, can be constrained by the screw keeper or kept unconstrained by the screw keeper. Examples of this are described below.

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If the bone screws are desired to be constrained within the bone screw receiving holes, then the bone screw receiving holes must be adapted to capture the screws. Preferably, an interference fit is provided between the wall of the bone screw receiving hole and the screw to prevent the screws from moving within the bone screw receiving hole.

The screws may also be self-locking with the matching threads cooperating between the screw head and the bone screw receiving hole. A preferred example of a self-locking bone screw can be found in Applicant's US Patent No. 6,558,423.

If the bone screws are desired to be unconstrained, then the bone screws may have a rounded head portion and / or a reduced neck diameter to allow displacement of the bone screws to allow angle between the implant and the bone screw is variable.

If it is desired to lock the bone screw, the locking mechanism can be adapted to allow the bone screw to be constrained or unconstrained by adapting the inner surface of the locking mechanism accordingly. For example, the end of a screw fastener that faces a screw head can be concave to accommodate a round screw head, thereby allowing an unconstrained screw to become locked with the implant, although the angles of the screws can still be modified. screws relative to the implant. Alternatively, the locking mechanism can be configured to constrain an unconstrained bone screw causing the stylet to bear force on the screw head.

Although bone screw fasteners are preferred, the invention is not limited in this regard. Bone screws do not need to be locked within the implant, but may simply have, for example, a stop or shoulder to stop the advancement of a bone screw through an implant beyond a certain point along the implant. length of bone screw extension.

The bone screw heads are preferably, but not necessarily, flush with or slightly below the outer surface of the rear end of the implant when fully installed so as not to substantially protrude therefrom and penetrate delicate anatomical structures that may be located close to the outer surface of the rear end of the implant.

The implant of the present invention may be useful throughout the entire spine, including the cervical, thoracic, and lumbar portions and, depending on the location, may be inserted from the anterior, posterior, or lateral aspects of the spine.

Many of the preferred embodiments of the present invention offer one or more of the following advantages over the prior art. An advantage is a slightly inclined screw angle between the screw and the implant. A slightly inclined screw angle gives the screws additional anchoring force. The ability of the screw to anchor into the bone is proportional to the amount of threaded surface area. When the screw goes further, its grip is better. Consequently, a lower screw angle allows the screw to stay longer within a short height body.

Another advantage is that by starting with the screw close to the implant surface and having the screw come out of the implant earlier, less of the screw will be in the implant, thereby providing more space inside the implant for fusion promoting substances. other desired content.

An additional benefit is the accommodation of the rear ends of the bone screws within the depth of the disc space to reduce the risk of damage to delicate adjacent structures, including, but not limited to, proximal neurological and vascular structures within the interior of the disc. body. Implant parts that extend beyond the depth of the disc space can pose a risk of damage to these delicate adjacent structures. It should be understood that accommodation of the rear ends of the bone screws within the depth of the disc space is only a preferred embodiment and that the invention is not limited in this regard.

An additional advantage is the ability of the bone screws to exit the implant more quickly and engage with an adjacent vertebral body. A rear end of a bone screw that is closer to the equator of the implant (that is, to the horizontal midline of the rear end) and further away from the opposite lower or upper surfaces of the implant, determines that the threaded portion of the screw spend more time leaving the implant. In contrast, the present invention, in one or more preferred embodiments, enables the threaded portion of a bone screw to protrude prior to implantation at a shallow angle, thereby having an additional threaded length than that in Another case would be obtained if a larger part of the threaded portion were within the rear end of the implant.

Although the configurations described above are preferred due to their various advantages, they in no way limit the scope of the present invention, which is limited only by the claims.

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Brief description of the drawings

FIG. 1 is a rear end perspective view of one embodiment of the vertebral implant of the present invention.

Fig. 2 is a top plan view of the vertebral implant of Fig. 1.

Fig. 3 is a side elevation view of the vertebral implant of Fig. 1.

Fig. 4 is an elevational view of the rear end of the vertebral implant of Fig. 1.

Fig. 5 is a side elevation view of one embodiment of the vertebral implant of the present invention shown at the time of being inserted into an implant space formed through the intervertebral disc space between two adjacent vertebral bodies. of the spine shown in partial cross section.

FIG. 6 is a side elevational view of a drill and drill guide for constituting bone screw receiving openings within adjacent vertebral bodies corresponding to existing bone screw receiving holes in the rear end of the vertebral implant of the present invention implanted between two adjacent vertebral bodies shown in partial cross section.

Fig. 7 is a top plan view of the vertebral implant of Figs. 1 to 4 in the inserted position with the bone screws installed and showing one of the adjacent vertebral bodies.

Fig. 8 is a rear end elevational view of the vertebral implant of Figs. 1 to 4 installed between two adjacent vertebral bodies shown in dotted line with the locking mechanisms in the unlocked position.

Fig. 9 is an exploded view of the vertebral implant of Fig. 8 and a driving retention instrument and locking tool for installing and locking the implant.

Fig. 10 is a partial cross-sectional top plan view of the vertebral implant of Fig. 8 and the bone screws installed between two adjacent vertebral bodies with the driving retention instrument and locking tool locking one of the implant locking instruments in the inserted position, showing one of the adjacent vertebral bodies.

FIG. 11 is a rear end elevational view of the vertebral implant of FIG. 8, showing the locking mechanisms locking the four bone screws to the implant.

Detailed description of the preferred embodiments

Reference will now be made in detail to the presently preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Similar reference numerals, such as "102, 202" will be used throughout the drawings to refer to similar portions of different embodiments of the present invention.

As shown in Figs. 1 to 4, a preferred embodiment of the vertebral implant of the present invention is designated generically by the number 100. As used herein the term "implant" includes any device adapted for insertion between two adjacent vertebral bodies, only for example, spacers, bone studs, spinal fusion implants. The implant 100 has a leading end 102, an opposite trailing end 104, and sides 106 and 108 between those for connecting, clamping, or joining, the ends 102, 104.

In a preferred embodiment, the leading end 102 can be a portion of a circle and the width of the implant can be equal to that portion of the circle, or if it is a half circle, then the diameter of that circle. Alternatively, the front end 102 may be at least partially straight and, for example, the straight portion may be arranged at an approximately right angle to the sides 106, 108 to form a generally rectangular or square profile. The configuration of the leading end of the implant of the present invention can be adapted to match the configuration of an implant space formed through the disc space and within adjacent vertebral bodies in accordance with U.S. Patent No. 6,159,214 and with Applicant's US Patent No. 6,224,607.

Implant 100 incorporates an upper vertebral body engaging surface 110 and an opposite lower vertebral body engaging surface 112. In a preferred embodiment, the upper and lower surfaces 110,112 may be convergent towards each other such that the implant 100 is capable of positioning the adjacent vertebral bodies in angular relation to one another, for example, in a lordosis. Upper and lower surfaces 110,112 may incorporate at least one opening 114 therethrough to allow regrowth of bone from an adjacent vertebral body to another adjacent vertebral body through implant 100.

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Both ends 102 and 104 may include openings, such as those indicated at 116, to allow bone regrowth and vascular access through them. Similarly, the sides 106, 108 may include openings, such as those indicated at 118, for similar or other purposes. The implant 100 preferably has an open interior 120 between the sides 106, 108 to allow regrowth of bone from an adjacent vertebral body to another adjacent vertebral body therethrough. The implant itself 100, any of its different surfaces, the open interior 120 and / or any of its openings, such as those indicated with the numerals 114, 116, 118, may be coated with, or contain, growth-promoting materials. bone, including, but not limited to, bone, bone morphogenetic proteins, hydroxyapatite, genes encoding bone production, or any other material that intrinsically participates in the regrowth of bone from one of the adjacent vertebral bodies to the other of the adjacent vertebral bodies at the point of fusion.

In a preferred embodiment, the rear end 104 has an outer surface 122 and an inner surface 124. At least the outer surface 122 may be curved to accommodate at least a portion of the natural curvature of the anterior face of the vertebral bodies. : For example, the outer surface 122 may be concave in a horizontal plane, in a vertical plane, or biconcave in both the vertical and horizontal planes. Outer surface 122 may, but is not required, correspond to the configuration of inner surface 124. In the preferred embodiment, outer surface 122 is configured to eliminate sharp edges or corners to protect adjacent delicate neurological and vascular structures from the inside the body. For example, the outer surface 122 may be tapered at the outer edges and may have rounded corners. The shape of the rear end 104 itself can be generally quadrangular, circular, or in any other way useful for the intended purpose.

Rear end 104 includes bone screw receiving holes 126 to receive bone screws 128 to secure implant 100 to adjacent vertebral bodies. The bone screw receiving holes 126 include clearance 130 in the perimeter of the bone screw receiving holes 126 to allow at least a portion of the bone screw 128 to protrude beyond the perimeter 132. of the rear end 104. The rear end 104 can be straight, curved, or anatomically contoured. The clearance 130 interrupts the perimeter of the bone screw receiving holes 126 so that the bone screw receiving holes 126 have an incomplete or C-shaped perimeter. At least one of the bone screw receiving holes 126 is adapted to cooperatively engage the rear end of the bone screw 128 to enable at least a portion of the rear end perimeter of at least one of the The bone screws protrude beyond at least one of the opposite upper and lower surfaces of the implant.

As used herein, the rear end of a bone screw includes not less than that portion of the bone screw at the end opposite the front end of the screw adapted to engage in cooperation with the implant to prevent its passage through. through him. The rear end may include the head and / or the stem proximal to the head, eg, the stem 134 and the head 138, as shown in FIG. 1. The bone screw heads are preferably, but not necessarily, level with or slightly below the outer surface of the rear end of the implant when fully installed so that they do not protrude from the implant inside anatomical structures that may exist near the outer surface of the rear end of the implant.

The rear end of the implant is adapted to receive the bone screws so that they are constrained within the bone screw receiving holes (i.e., fixing the path of each bone screw), or remain unconstrained. within bone screw receiving holes to allow variable screw angles. Preferably, for a constrained configuration, an interference fit is provided between the wall of the bone screw receiving hole and the screw to prevent the screws from moving within the bone screw receiving hole. Constrained screws may also be self-locking with the mating threads cooperating between the screw head and the bone screw receiving hole.

If the bone screws are desired to be unconstrained, then the bone screws should have a rounded head portion and / or a reduced neck diameter to allow for displacement of the bone screws to allow for variation. the angle between the implant and the bone screw.

The bone screws do not need to be locked within the implant, but can simply incorporate, for example, a shoulder to stop the advancement of a bone screw through the implant beyond a certain point along the length of the bone screw. bone. It is appreciated that all of the bone screws described herein can be self-tapping. Bone screw receiving holes 126 preferably contain a recessed portion 136 to accommodate screw head 138 so that screw head 138 does not protrude outside the rear end. Clearance 130 is sized precisely to be less than half the diameter of screw 128. By allowing the screws 128 to protrude from the edges 140, 142 of the rear end 104, the upper and lower screws can be positioned so that the maximum height H of the rear end 104 is less than the sum of the maximum diameter of two bone screws. adapted to be inserted into bone screw receiving holes 126.

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Bone screw receiving holes 126 must be adapted to capture screws 128, thereby constraining the screws within rear end 104. Alternatively, rear end 104 may also include at least one locking mechanism 144 to locking bone screws within implant 100. Although the application of bone screw fasteners is preferred, the invention is not limited in this regard.

In various embodiments of the present invention, locking mechanisms 144 and rear end 104 may be configured to either rigidly capture bone screws 128 so that their positions are fixed, or alternatively, enabling the screw angles to be variable in an unconstrained state in which case the screw angles can remain variable once locked.

The locking mechanism 144 may consist of a screw or rivet having a head of contact and fixation of the bone screws with the implant 100. The locking mechanism 144 may be capable of being rotatably displaced with respect to the rear end 104. The locking mechanism 144 includes a useful engaging portion 146 for moving the locking mechanism 144 from an unlocked position to a locked position.

As best shown in Figs. 1 and 4, the locking mechanism 144 also includes cut-out portions 148 that allow the installation of bone screws within the bone screw receiving holes 126 while the locking mechanism 144 is in the unlocked position. In a preferred embodiment, the locking mechanisms 144 can be rotated 180 degrees to be fully tightened. The locking mechanisms 144 can rotate in the same direction or in the opposite direction relative to each other. The lower portion of the head of the locking mechanism 144 may be of various configurations and, for example, may be ramped or concave. Likewise, as disclosed in the Applicant's Application with serial number 09 / 565,392 entitled "Spinal Implant with Vertebral Endplate Engaging Anchor", the present invention it can be adapted to receive self-locking screws.

The fasteners 144 can function either to constrain the screws 128 by fixing their positions, or alternatively, preventing the screws 128 from moving back without fixing the position of the screws so that the screws can allow adjustment of the disk space (Dynamization ).

It is appreciated that the present invention includes the use of other screw locking mechanisms and devices than could be used in other plate / screw or implant / screw devices and which are known to those skilled in the art.

As shown in FIG. 9, rear end 104 also includes alignment holes 150, 152 and threaded engagement hole 153 for mating alignment of pins 154 and threaded driver 155, respectively, connected to a driving instrument described later. Any other means of engaging the implant to aid insertion, as known in the art, is within the scope of the present invention.

A preferred origin and trajectory of bone screw receiving hole 126 is where a surgeon may (but need not) be able to insert bone screws 128 through holes 126 to an optimal or desired depth. without these bone screws crossing a plane that bisects the height of the adjacent vertebral body. An alternative embodiment may include upper and lower screws that are asymmetrically positioned so as to be offset from each other so that screws from said implants inserted into adjacent disc spaces intersect within an intermediate vertebral body but without colliding with each other. For example, an implant may incorporate two bone screws at the rear end towards the outer sides and project through the upper surface and one bone screw located at the middle of the rear end project through the bottom surface. .

As shown in FIG. 5, implant 100 is inserted into the implantation space formed through the disc space within adjacent vertebral bodies. Implant 100 is installed with leading end 102 inserted first into the disc space.

As shown in FIG. 6, bone screw receiving holes 126 may be formed within adjacent vertebral bodies with a drill 156 and drill guide 158, an awl, or other device. The drill 156 has a bone termination end 160 and a shaft 162. The drill guide 158 has a forward end 164 adapted for insertion into one of the bone screw receiving holes 126 of the rear end 104. The forward end 164 has a minor dimension 166, a major dimension 168 and a shoulder 170 corresponding to the reduced dimension portions of the bone screw receiving holes 126 that are configured to receive the head portion of the screws 128 for the bone. Drill guide 158 has an inner gauge (not shown) that, in a preferred embodiment, is aligned with the longitudinal axis of bone screw receiving holes 126 when forward end 164 is properly seated in its interior. If it is desired to modify the angle of drill guide 158 relative to bone screw receiving holes 126, the tip of drill guide 158 can be rounded. Alternatively, the drill guide may be screwed into the bone screw receiving hole or it may be attached to the implant by any other method known in the art. Likewise, the

Openings made within the bone can be formed with a point or other device, or the screws can be inserted without first forming the gauges into the bone.

When the drill guide 158 is seated within the bone screw receiving hole 126, the drill 156 passes through the bore to form a bone screw receiving opening within the bone of the corresponding adjacent vertebral bodies in alignment with receiving holes 126 of the bone screws. In the preferred embodiment, the bone screw receiving openings 126 are formed within the bone, located at or near the junction of the two cortices of the vertebral bodies.

In the vertebral implant of the present invention, the bone screws may be oriented in angular relationship to one another so that they diverge along the vertical plane of the implant once installed within adjacent vertebral bodies. The preferred angular divergence from the implant surface is preferably 25 ° to 40 °, but any angle useful for the required purpose is within the scope of the present invention. In a preferred embodiment, screws 128 are angled such that they do not extend beyond half the height of the adjacent vertebral body. This ensures that the screws of an implant will not contact the screws of the implant inserted into a neighboring intervertebral disc space.

In the implant of the present invention, if lag screws are used or if there is a veneering implant in relation to the screws, then the adjacent vertebral bodies are pulled into the implant 100 when the bone screws 128 are installed within the vertebral bone to create a compressive load on the implant. Also, the angulation of the bone screws 128 holds the anterior portion of the adjacent vertebral bodies together during the spinal extension movement as would occur when a patient is bent backward. Among the many advantages of the present invention, the anterior portions of the implant 100 from the adjacent vertebral bodies do not separate when held in position by the bone screws 128 inserted through the rear end 104, the rear of the implant is not pushed into the vertebral bodies with spinal extension, and the compressive load is safely distributed along the entire intervertebral length of the implant.

Fig. 7 shows a plan view of the implant 100 inserted into the disc space between two adjacent vertebral bodies and bone screws 128 installed at the rear end 104. In a preferred embodiment, the screws 128 for the bone are located converging to each other. It is appreciated that, however, the bone screws 128 need not be in a convergent position, but may be in parallel, diverging, or otherwise have any desired orientation with each other. It is also appreciated that only one screw or three or more screws can be used to fix the implant to each of the adjacent vertebral bodies in place of the two screws shown in Fig. 7.

FIG. 8 is a rear end elevational view of vertebral implant 100 installed between two adjacent vertebral bodies with locking mechanisms 144 shown in the unlocked position and bone screws 128 in position. The upper bone screws 128 are converging, while the lower bone screws 128 are diverging. If two implants of the indicated type were located within consecutive disc spaces, the converging upper bone screws 128 of one implant and the diverging lower bone screws 128 of the other implant would not interfere with each other, due to the difference in angulation of the respective bone screw.

As shown in Fig. 9, the implant 100 can be installed with a driver instrument 172 both to retain the implant so that it can be useful in insertion and to prevent torque from being inflicted on the implant when the fasteners remain. fixed in the locked position. The driver instrument 172 has a locking portion 174 to cooperatively engage the rear end 104 of the implant 100. The blocker 174 has a forward arcuate surface 176 that may be configured to conform, at least in part, to the contour of the rear end 104. The pusher instrument 172 incorporates a shaft 178 extending from the blocker 174 with an inner bore 180 through it. along the longitudinal axis of the tree 178. Extending from the blocker 174 are a pair of alignment pins 154 and a threaded shaft 155 of the drive instrument to cooperatively lock alignment holes 150, 152 and threaded hole 153, respectively, at rear end 104. Blocker 174 incorporates openings 182 that are coaxially aligned with locking mechanisms 144. Apertures 182 are configured to receive a locking tool 184 through those for accessing and acting on locking mechanisms 144. Instrument 172 enables the surgeon to tighten locking mechanisms 144 against locking device 174 rather than torque. on the patient's spine.

The driver instrument 172 and the blocker 174 are shown as an example of insertion tools with the understanding that any blocker, or any combined inserter and blocker known to those skilled in the art and useful for the intended purpose are included in the scope of the present invention.

Fig. 10 shows a partial cross-sectional top plan view of the vertebral implant 100 installed between two adjacent vertebral bodies and engaged to the driver instrument 172 with the tool 184 (e.g., a screwdriver) shown locking the locking mechanism 144 (a rivet) to secure bone screws 128 to rear end 104. It is appreciated that locking mechanism 144 could be a rivet, screw, or the like.

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Fig. 11 is a rear end elevational view of a vertebral implant 100 installed between two adjacent vertebral bodies with the locking mechanisms 144 shown in the locked position in the direction of the arrows to lock the bone screws 128 within the rear end 104. It should be understood that any clockwise or counter-clockwise rotational direction can be used to lock the screws 128.