Claims

I claim:

1. An orthopedic implant for use in human body, said implant comprising: a leading portion adapted to be placed toward and in contact with a bone of the human body; a trailing portionopposite said leading portion, said trailing portion having an exterior surface and an outer perimeter with an upper edge and a lower edge, said trailing portion having a maximum height as measured from said upper edge to said lower edge; and at leastfirst and second bone screw receiving holes, said first bone screw receiving hole having an entrance and an exit proximate said upper edge of said outer perimeter, said entrance of said first bone screw receiving hole having a single gap therein forpermitting a portion of a trailing end of a bone screw to protrude over said upper edge of the outer perimeter of said trailing portion within a plane of said trailing portion, said second bone screw receiving hole having an entrance and an exitproximate said lower edge of said outer perimeter, said entrance of said second bone screw receiving hole having a single gap therein for permitting a portion of a trailing end of another bone screw to protrude over said lower edge of the outer perimeterof said trailing portion within a plane of said trailing portion, each of said gaps being sufficient to retain the trailing end of the respective bone screw.

2. The implant of claim 1, wherein a plane of said trailing portion of said implant is curved.

3. The implant of claim 1, wherein at least one of said first and second bone screw receiving holes passes through said exterior surface and one of said edges and is C-shaped in cross section.

4. The implant of claim 1, wherein said trailing portion of said implant is relieved to allow for a head of a bone screw inserted into one of said first and second bone screw receiving holes to be at least partially recessed.

5. The implant of claim 1, wherein said first and second bone screw receiving holes are at different distances from the mid-longitudinal axis of said implant.

6. The implant of claim 1, wherein said first and second bone screw receiving holes are adapted to orient bone screws to be received therein at an angle to a horizontal mid-longitudinal plane of said implant passing through said leading andtrailing portions of said implant.

7. The implant of claim 1, wherein each of said first and second bone screw receiving holes is configured to position a bone screw therein at an angle to a vertical mid-longitudinal plane of said implant passing through said leading andtrailing portions of said implant.

8. The implant of claim 1, wherein said bone screw receiving holes include a pair of bone screw receiving holes along said upper edge and a pair of bone screw receiving holes along said lower edge, one of said pair of bone screw receiving holesbeing adapted to position bone screws in a convergent relationship to one another.

9. The implant of claim 1, wherein said bone screw receiving holes include a pair of bone screw receiving holes along said upper edge and a pair of bone screw receiving holes along said lower edge, one of said pair of bone screw receiving holesbeing adapted to position bone screws in a divergent relationship to one another.

10. The implant of claim 1, further comprising at least one lock for retaining a bone screw to said implant.

11. The implant of claim 10, wherein said at least one lock is adapted to retain at least two bone screws to said implant.

12. The implant of claim 1, wherein said implant has an interior surface and a hollow defined therein, said hollow being capable of containing bone growth promoting material.

13. The implant of claim 1, in combination with a fusion promoting substance.

14. The implant of claim 13, wherein said fusion promoting substance is at least one of bone, bone morphogenetic protein, hydroxyapatite, and genes coding for the production of bone.

15. The implant of claim 1, wherein said first and second bone screw receiving holes each have a mid-longitudinal axis passing through said entrance and said exit of said first and second bone screw receiving holes, respectively, themid-longitudinal axis of said first bone screw receiving hole passing through said exit at a point above a point where the mid-longitudinal axis of said first bone screw receiving hole passes through said entrance, the mid-longitudinal axis of saidsecond bone screw receiving hole passing through said exit at a point below a point where the mid-longitudinal axis of said second bone screw receiving hole passes through said entrance.

16. The implant of claim 1, wherein said first and second bone screw receiving holes each have a mid-longitudinal axis, the mid-longitudinal axes of said first and second bone screw receiving holes being in an angular relationship to and notintersecting a horizontal mid-longitudinal plane of said implant between said leading and trailing portions of said implant.

17. An orthopedic implant for use in a human body, said implant comprising: a leading portion adapted to be placed toward and in contact with a bone of the human body; a trailing portion opposite said leading portion, said trailing portionhaving an exterior surface and an outer perimeter with an upper edge and a lower edge, said trailing portion having a maximum height as measured from said upper edge to said lower edge; at least one bone screw having a leading end for placement in thebone and a trailing end opposite said leading end adapted to cooperatively engage said implant so as to prevent further advancement of said at least one bone screw into the bone; and a plurality of bone screw receiving holes in said trailing portion, atleast first and second of said bone screw receiving holes being adapted to only partially circumferentially surround said trailing end of said at least one bone screw adapted to be received therein, said first bone screw receiving hole having an entranceand an exit proximate said upper edge of said outer perimeter, said second bone screw receiving hole having an entrance and an exit proximate said lower edge of said outer perimeter, said first bone screw receiving hole passing through said exteriorsurface and said upper edge and said second bone screw receiving hole passing through said exterior surface and said lower edge so as to permit said trailing end of said at least one bone screw to protrude beyond one of said upper and lower edges,respectively, and at least in part contact the bone when said at least one bone screw is inserted into a respective one of said first and second bone screw receiving holes, said first and second bone screw receiving holes being adapted to position bonescrews in a divergent relationship to one another.

18. The implant of claim 17, wherein a plane of said trailing portion of said implant is curved.

19. The implant of claim 17, wherein said outer perimeter of said trailing portion of said implant has at least one gap therein for permitting a portion of at least an outer diameter of said at least one bone screw to protrude beyond said outerperimeter of said trailing portion, said gap dimensioned to be less than the outer diameter of said at least one bone screw.

20. The implant of claim 17, wherein said first bone screw receiving hole interrupts said upper edge of said perimeter of said trailing portion of said implant and said second bone screw receiving hole interrupts said lower edge of saidperimeter of said trailing portion of said implant.

21. The implant of claim 17, wherein at least one of said first and second bone screw receiving holes passing through said exterior surface and one of said edges is C-shaped in cross section.

22. The implant of claim 17, wherein said trailing portion of said implant is relieved to allow for a head of said at least one bone screw inserted into one of said first and second bone screw receiving holes to be at least partially recessed.

23. The implant of claim 17, wherein said first and second bone screw receiving holes are at different distances from the mid-longitudinal axis of said implant.

24. The implant of claim 17, wherein said first and second bone screw receiving holes are adapted to orient bone screws to be received therein at an angle to a horizontal mid-longitudinal plane of said implant passing through said leading andtrailing portions of said implant.

25. The implant of claim 17, wherein each of said first and second bone screw receiving holes is configured to position said at least one bone screw therein at an angle to a vertical mid-longitudinal plane of said implant passing through saidleading and trailing portions of said implant.

26. The implant of claim 17, wherein said plurality of bone screw receiving holes includes a pair of bone screw receiving holes along said upper edge and a pair of bone screw receiving holes along said lower edge, one of said pair of bone screwreceiving holes being adapted to position bone screws in a convergent relationship to one another.

27. The implant of claim 17, further comprising at least one lock for retaining said at least one bone screw to said implant.

28. The implant of claim 27, wherein said at least one lock is adapted to retain at least two bone screws to said implant.

29. The implant of claim 17, wherein said implant has an interior surface and a hollow defined therein, said hollow being capable of containing bone growth promoting material.

30. The implant of claim 17, in combination with a fusion promoting substance.

31. The implant of claim 30, wherein said fusion promoting substance is at least one of bone, bone morphogenetic protein, hydroxyapatite, and genes coding for the production of bone.

32. The implant of claim 17, wherein said first and second bone screw receiving holes each have a mid-longitudinal axis passing through said entrance and said exit of said first and second bone screw receiving holes, respectively, themid-longitudinal axis of said first bone screw receiving hole passing through said exit at a point above a point where the mid-longitudinal axis of said first bone screw receiving hole passes through said entrance, the mid-longitudinal axis of saidsecond bone screw receiving hole passing through said exit at a point below a point where the mid-longitudinal axis of said second bone screw receiving hole passes through said entrance.

33. The implant of claim 17, wherein said first and second bone screw receiving holes each have a mid-longitudinal axis, the mid-longitudinal axes of said first and second bone screw receiving holes being in an angular relationship to and notintersecting a horizontal mid-longitudinal plane of said implant between said leading and trailing portions of said implant.

34. An orthopedic implant for use in a human body, said implant comprising: a leading portion adapted to be placed toward and in contact with a bone of the human body, said leading portion being at least in part convex; a trailing portionopposite said leading portion, said trailing portion having an exterior surface and an outer perimeter with an upper edge and a lower edge, said trailing portion having a maximum height as measured from said upper edge to said lower edge; and aplurality of bone screw receiving holes in said trailing portion, at least first and second of said bone screw receiving holes being adapted to only partially circumferentially surround a trailing end of a bone screw adapted to be received therein,respectively, said first bone screw receiving hole having an entrance and an exit proximate said upper edge of said outer perimeter, said second bone screw receiving hole having an entrance and an exit proximate said lower edge of said outer perimeter,said first bone screw receiving hole passing through said exterior surface and said upper edge and said second bone screw receiving hole passing through said exterior surface and said lower edge so as to permit the trailing end of the bone screw toprotrude over one of said upper and lower edges, respectively, within a plane of said trailing portion; and at least one bone screw, said at least one bone screw having: a leading end for placement in the bone; and a trailing end opposite said leadingend, said trailing end of said bone screw adapted to cooperatively engage said implant so as to prevent further advancement of said at least one bone screw into the bone and to be retained within said implant, said trailing end of said at least one bonescrew protruding over one of said upper and lower edges, respectively, within a plane of said trailing portion of said implant when inserted into a respective one of said first and second bone screw receiving holes.

35. The implant of claim 34, wherein a plane of said trailing portion of said implant is curved.

36. The implant of claim 34, wherein said outer perimeter of said trailing portion of said implant has at least one gap therein for permitting a portion of at least an outer diameter of said at least one bone screw to protrude beyond said outerperimeter of said trailing portion, said gap dimensioned to be less than the outer diameter of said at least one bone screw.

37. The implant of claim 34, wherein said first bone screw receiving hole interrupts said upper edge of said perimeter of said trailing portion of said implant and said second bone screw receiving hole interrupts said lower edge of saidperimeter of said trailing portion of said implant.

38. The implant of claim 34, wherein at least one of said first and second bone screw receiving holes passing through said exterior surface and one of said edges is C-shaped in cross section.

39. The implant of claim 34, wherein said trailing portion of said implant is relieved to allow for said head of said at least one bone screw inserted into one of said first and second bone screw receiving holes to be at least partiallyrecessed.

40. The implant of claim 34, wherein said first and second bone screw receiving holes are at different distances from the mid-longitudinal axis of said implant.

41. The implant of claim 34, wherein said first and second bone screw receiving holes are adapted to orient bone screws to be received therein at an angle to a horizontal mid-longitudinal plane of said implant passing through said leading andtrailing portions of said implant.

42. The implant of claim 34, wherein each of said first and second bone screw receiving holes is configured to position said at least one bone screw therein at an angle to a vertical mid-longitudinal plane of said implant passing through saidleading and trailing portions of said implant.

43. The implant of claim 34, wherein said plurality of bone screw receiving holes includes a pair of bone screw receiving holes along said upper edge and a pair of bone screw receiving holes along said lower edge, one of said pair of bone screwreceiving holes being adapted to position bone screws in a convergent relationship to one another.

44. The implant of claim 34, wherein said plurality of bone screw receiving holes includes a pair of screw receiving holes along said upper edge and a pair of screw receiving holes along said lower edge, one of said pair of bone screw receivingholes being adapted to position bone screws in a divergent relationship to one another.

45. The implant of claim 34, further comprising at least one lock for retaining said at least one bone screw to said implant.

46. The implant of claim 45, wherein said at least one lock is adapted to retain at least two bone screws to said implant.

47. The implant of claim 34, wherein said implant has an interior surface and a hollow defined therein, said hollow being capable of containing bone growth promoting material.

48. The implant of claim 34, in combination with a fusion promoting substance.

49. The implant of claim 48, wherein said fusion promoting substance is at least one of bone, bone morphogenetic protein, hydroxyapatite, and genes coding for the production of bone.

50. The implant of claim 34, wherein said first and second bone screw receiving holes each have a mid-longitudinal axis passing through said entrance and said exit of said first and second bone screw receiving holes, respectively, themid-longitudinal axis of said first bone screw receiving hole passing through said exit at a point above a point where the mid-longitudinal axis of said first bone screw receiving hole passes through said entrance, the mid-longitudinal axis of saidsecond bone screw receiving hole passing through said exit at a point below a point where the mid-longitudinal axis of said second bone screw receiving hole passes through said entrance.

51. The implant of claim 34, wherein said first and second bone screw receiving holes each have a mid-longitudinal axis, the mid-longitudinal axes of said first and second bone screw receiving holes being in an angular relationship to and notintersecting a horizontal mid-longitudinal plane of said implant between said leading and trailing portions of said implant.

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Description BACKGROUND OF THE INVENTION

Implants adapted for use in the lumbar spine and the thoracic spine become much less usable in the cervical spine because of differences in anatomy. In the lumbar spine, the disc spaces are about 25% as tall as the vertebral bodies (i.e., thevertebral bodies are generally four times taller than the intervening disc space). In the cervical spine, the disc space can be 50% of the height of the vertebral bodies. The disc spaces in the cervical spine are generally not greater than 7 or 8 mmtall in most people.

Screws generally used to secure an implant in the cervical spine typically have a diameter of between 4 and 5 mm. If two bone screws were to be inserted one each into each of the adjacent cervical vertebral bodies; and if one were to attempt tovertically oppose those two bone screws, this would not prove possible because the sum of the screw diameters would exceed the height of the implant. Such vertically aligned bone screws would require at least 10 mm of combined height for themselves plussufficient implant structure and further height sufficient to surround and retain them. Thus, altogether the two bone screws and the surrounding implant would have to have a combined height that would substantially exceed the height of the disc spaceand an implant adapted to fit therein.

Alternatively, one could try to place a number of bone screws more horizontally (side-by-side) so as to avoid the problems described above associated with vertical alignment. To provide for the preferred implant stability that the use of pairedscrews would provide (two each into each of the adjacent vertebral bodies), one could horizontally align four bone screws on the equator of the implant with two of the bone screws directed toward one of the cervical vertebral bodies and two of the bonescrews directed toward the other of the adjacent cervical vertebral bodies. Four such horizontally aligned bone screws having a head diameter of 5 mm each would require at least 20 mm for the screw heads alone. Further, with sufficient implantstructure to surround each of those screw heads, the implant width would at a minimum be about 24 mm, which would exceed the desirable implant width for most cervical disc spaces. Staggering the bone screw receiving holes would be of some benefit, butof itself not an adequate solution to the problem described where it is desirable to maintain some symmetry of the screws to each other, the vertebrae, and the implant.

One prior art solution to the aforementioned problem teaches extending the height of the trailing 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 placescrews so that they can be vertically aligned and have sufficient structure of the implant to retain them. The flanged portion of the implant, however, extends outside of the disc space which may not be desirable in all circumstances. Further, theseflanged implants may not be usable when it is needed to fuse multiple levels of the spine.

Accordingly, there exists a need for a spinal implant adapted to provide the advantages of a flanged implant for placement and orientation of bone screws associatated therewith but without the flanged portion, or the necessity of the implantextending outside of the disc space.

SUMMARY OF THE INVENTION

The present invention is directed to an interbody spinal implant, such as but not limited to a spinal fusion implant, spacers, motion preserving implants, or others. The implant has opposed upper and lower surfaces, one each for contacting eachof the opposed vertebral bodies adjacent a disc space. The implant is adapted to cooperatively receive at least two opposed bone screws, at least one screw each for insertion into each of the vertebral bodies adjacent a disc space. The interbody spinalimplant is adapted to receive the bone screws through its trailing end and to allow for the passage of the leading end of the bone screws through at least a portion of the implant and out of the opposed upper or lower implant surfaces, one eachrespectively. The bone screws have a leading end, a shaft, threading upon the shaft, and a trailing end. The implant and the trailing end of the bone screw are adapted to cooperatively engage each other so as to prevent the further advance of the bonescrews through the implant. At least a portion of the perimeter of the trailing ends of at least some of the bone screws protrude beyond at least one of the opposed upper or lower implant surfaces.

In one preferred embodiment, the trailing end is configured to permit a portion of the head of at least one bone screw to protrude beyond the height of the perimeter of the trailing end. The trailing end of the implant includes at least onebone screw receiving opening or hole that has a gap in the perimeter thereof for permitting at least a portion of the trailing end of a bone screw to protrude beyond the opposed upper or lower vertebral body engaging surfaces. The gap interrupts theperimeter of the bone screw receiving hole, so that the bone screw receiving hole has an incomplete perimeter or C-shape. The gap is sized such that it is less than half the diameter of the screw. By allowing the screws to each protrude over either theupper or lower edges of the implant trailing end, the upper and lower screws may be placed such that the maximum height of the implant trailing end is less than the sum of the maximum diameter of two bone screws adapted to be inserted in the bone screwreceiving holes. This permits the use of larger bone screws in the trailing end of the implant than would otherwise be possible. Further, though not so limited, the present invention allows bone screws of the optimal diameter to be inserted into and inpart through the implant and into the adjacent vertebral bodies without the necessity of a portion of the implant itself extending beyond the disc space and outside of the spine.

The trailing end of the implant is configured to permit the bone screws for insertion into each of the adjacent vertebrae to be angled relative to each other, the implant trailing end, and to the implant upper and lower surfaces. The opposedbone screws preferably pull the anterior aspects of the vertebral bodies together toward the implant. The bone screws preferably penetrate into a portion of the vertebral body closest to the disc space into which the implant is being installed so as notto interfere with bone screws from a second implant being installed in an adjacent disc space where consecutive levels of the spine are being fused. In a preferred embodiment, the trailing end is configured to lag the bone screws so as to compress thevertebral bodies together and to load the vertebral body implant interface to promote fusion.

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

In other preferred embodiments, the trailing end of the implant is configured to allow screws that are originating at or close to the vertical midline of the trailing end of the implant to be directed outward, or divergently oriented; and screwsthat originate further from the vertical midline of the trailing end of the implant to be directed inward, or convergently oriented. The screws that are convergently oriented are directed to one vertebral body and the screws that are divergentlyoriented are directed to the other adjacent vertebral body. Such an arrangement permits such implants when inserted into adjoining disc spaces to have convergently oriented screws from one implant and divergently oriented screws from the other implantto be screwed into the same vertebral body and ensure that the screws do not interfere with one another. Such a configuration allows screws from different implants to pass each other within a vertebral body where both adjacent disc spaces are to befused.

In any of these embodiments it is preferred though not required that the screws be retained to the implant by “locking mechanisms” which may include any of those known to those skilled in the art including, but not limited to, those taught byapplicant, for example, U.S. Pat. No. 6,139,550, titled “Skeletal Plating System,” U.S. application Ser. No. 09/022,293 titled “Anterior Cervical Plating System, Instrumentation, and Method of Installation,” and U.S. application Ser. No. 09/565,392titled “Interbody Spinal Fusion Implants with Opposed Locking Screws”, all of which are incorporated herein by reference. The trailing end of the implant may be configured to receive bone screws such that they are constrained within the bone screwreceiving holes (i.e., fixing the trajectory of each bone screw), or left unconstrained within the bone screw receiving holes for allowing variable screw angles. If a locking mechanism is used, the screws may start out constrained within the bone screwreceiving holes and remain so when locked. Alternatively, the screws may start out unconstrained prior to locking them, and upon being locked, may be constrained by the screw lock or left unconstrained by the screw lock. Examples are described below.

If it is desired to have the bone screws constrained in the bone screw receiving holes then the bone screw receiving holes may be adapted to capture the screws. Preferably, an interference fit is formed between the wall of the bone screwreceiving hole and the screw to prevent the screws from moving within the bone screw receiving hole.

The screws may also be self-locking with cooperative mating threads between the screw head and the bone screw receiving hole. An example of a preferred self-locking bone screw may be found in applicant’s application Ser. No. 09/565,392 titled”Spinal Implant with Vertebral Endplate Engaging Anchor” incorporated herein by reference.

If it is desired that the bone screws are unconstrained then the bone screws may have a rounded head portion and/or a reduced neck diameter to permit movement of the bone screws so as to allow the angle between the implant and the bone screw tobe variable.

If it is desired to lock the bone screw, the locking mechanism may be adapted to leave the bone screw constrained or unconstrained by adapting the interior surface of the locking mechanism accordingly. For example, the end of a screw lockfacing a screw head may be concave to accommodate a round screw head, thereby allowing an unconstrained screw to be locked to the implant, yet still permit variable screw angles relative to the implant. Alternatively, the locking mechanism may beconfigured to constrain an unconstrained bone screw by having the lock forcefully bear upon the screw head.

Although bone screw locks are preferred, the invention is not so limited. Bone screws need not be locked to the implant, but simply may have, for example, a stop or shoulder for stopping the progress of a bone screw through the implant beyond acertain point along the bone screw length.

The bone screw heads are preferably but not necessarily flush or slightly below the exterior surface of the trailing end of the implant when fully installed so as not to substantially protrude therefrom as into delicate anatomical structuresthat may be present proximate the exterior surface of the trailing end of the implant.

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

Many of the preferred embodiments of the present invention have one or more of the following advantages over the prior art. One advantage is a more shallow screw angle between the screw and the implant. A more shallow screw angle provides thescrews with additional anchoring force. The ability of the screw to anchor in the bone is proportional to the amount of threaded surface area. As the screw gets longer, its bite gets better. Therefore, a more shallow screw angle permits the screw tostay in a short height body longer.

Another advantage is that by starting with the screw close to the implant surface and having the screw exit the implant sooner, less of the screw will be in the implant, thereby providing more space within the implant for fusion promotingsubstances or other desired contents.

A further advantage is the accommodation of the trailing ends of bone screws within the depth of the disc space to reduce the risk of damage to adjacent delicate structures, including but not limited to proximate vascular and neurologicalstructures within the body. Parts of implants extending beyond the depth of the disc space may have a risk of damaging these adjacent delicate structures. It should be understood that the accommodation of the trailing ends of bone screws within thedepth of the disc space is a preferred embodiment only and that the invention is not so limited.

A further advantage is the ability of the bone screws to exit the implant quicker and engage an adjacent vertebral body. A trailing end of a bone screw that is closer to the equator of the implant (i.e., the horizontal mid-line of the trailingend) and further from the opposed upper or lower surfaces of the implant takes longer for the threaded portion of the screw to leave the implant. In contrast, the present invention in one or more preferred embodiments allows the threaded portion of abone screw to leave the implant sooner at a shallower angle and to thereby have additional threaded length than otherwise would be achieved if more of the threaded portion were within the trailing end of the implant.

While the above-described configurations are preferred for various advantages they do not in any way limit the breadth of the present invention, which is limited only by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a trailing end perspective view of an embodiment of the spinal implant of the present invention.

FIG. 2 is a top plan view of the spinal implant of FIG. 1.

FIG. 3 is a side elevation view of the spinal implant of FIG. 1.

FIG. 4 is a trailing end elevation view of the spinal implant of FIG. 1.

FIG. 5 is a side elevation view of an embodiment of the spinal implant of the present invention shown being inserted into an implantation space formed across the disc space between two adjacent vertebral bodies of the spine shown in partialcross-section.

FIG. 6 is a side elevation view of a drill and drill guide for forming bone screw receiving openings into adjacent vertebral bodies corresponding to bone screw receiving holes in the trailing end of the spinal implant of the present inventionimplanted between two adjacent vertebral bodies shown in partial cross-section.

FIG. 7 is a top plan view of the spinal implant of FIGS. 1-4 in the inserted position with bone screws installed and one of the adjacent vertebral bodies shown.

FIG. 8 is a trailing end elevation view of the spinal implant of FIGS. 1-4 installed between two adjacent vertebral bodies shown in hidden line with the locking mechanisms in the unlocked position.

FIG. 9 is an exploded view of the spinal implant of FIG. 8 and a driver holder instrument and locking tool for installing and locking the implant.

FIG. 10 is a top plan view in partial cross-section of the spinal implant of FIG. 8 and bone screws installed between two adjacent vertebral bodies with the driver holder instrument and locking tool locking one of the locking mechanisms of theimplant in the inserted position with one of the adjacent vertebral bodies shown.

FIG. 11 is a trailing end elevation view of the spinal implant of FIG. 8 with the locking mechanisms shown locking all four bone screws to the implant.

DETAILED DESCRIPTION OF THE DRAWINGS

Reference will now be made in detail to the present preferred embodiments of this invention, examples of which are illustrated in the accompanying drawings. Similar reference numbers such as “102, 202” will be used throughout the drawings torefer to similar portions of different embodiments of the present invention.

As shown in FIGS. 1-4, a preferred embodiment of the spinal implant of the present invention is generally referred to by the numeral 100. As used herein, the term “implant” includes any device adapted for insertion between two adjacentvertebral bodies, for example only, spacers, bone dowels, and spinal fusion implants. Implant 100 has a leading end 102, an opposite trailing end 104, and sides 106 and 108 therebetween for connecting, spanning, or joining, ends 102, 104.

In a preferred embodiment, leading end 102 can be a portion of a circle and the implant width can be equal to that portion of the circle, or if a half circle, then the diameter of that circle. Alternatively, leading end 102 may be straight atleast in part, and for example the straight part can be at an approximately right angle to sides 106, 108 to form a generally rectangular or square shape. The configuration of the leading end of the implant of the present invention may be adapted tomatch the configuration of an implantation space formed across the disc space and into the adjacent vertebral bodies in accordance with U.S. Pat. No. 6,159,214 titled “Milling Instrumentation and Method for Preparing a Space Between Adjacent VertebralBodies” and applicant’s co-pending patent application Ser. No. 09/490,901 titled “Instrument and Method for Creating an Intervertebral Space for Receiving an Implant,” both of which are incorporated by reference herein.

Implant 100 has a vertebral body engaging upper surface 110 and an opposite vertebral body engaging lower surface 112. In a preferred embodiment, upper and lower surfaces 110, 112 may be convergent toward one another such that implant 100 isable to place the adjacent vertebral bodies in angular relationship to each other, for example, in lordosis. Upper and lower surfaces 110, 112 may have at least one opening 114 therethrough for permitting the growth of bone from adjacent vertebral bodyto adjacent vertebral body through implant 100.

Both ends 102 and 104 may include openings such as 116 so as to permit for the growth of bone and vascular access therethrough. Similarly, sides 106, 108 can include openings such as 118 for similar or other purposes. Implant 100 preferablyhas an open interior 120 between sides 106, 108 to permit for the growth of bone from adjacent vertebral body to adjacent vertebral body therethrough. The implant 100 itself, any of its various surfaces, open interior 120 and/or any of its openings suchas 114, 116, 118, for example, can be coated with, or contain bone growth promoting materials, including but not limited to, bone, bone morphogenetic proteins, hydroxyapatite, genes coding for the production of bone, or any other material thatintrinsically participates in the growth of bone from one of the adjacent vertebral bodies to the other of the adjacent vertebral bodies at the fusion site. Implant 100 may also be combined with a chemical substance to inhibit scar formation.

In a preferred embodiment, trailing end 104 has an exterior surface 122 and an interior surface 124. At least exterior surface 122 may be curved to conform to at least a portion of the natural curvature of the anterior aspect of the vertebralbodies. For example, exterior surface 122 may be concave in a horizontal plane, in a vertical plane, or biconcave in both the vertical and horizontal planes. Exterior surface 122 may, but need not, correspond to the configuration of interior surface124. In the preferred embodiment, exterior surface 122 is configured to eliminate sharp edges and corners to protect the adjacent delicate vascular and neurological structures within the body. For example, exterior surface 122 can be tapered at itsexterior edges and can have rounded corners. The shape of trailing end 104 itself may be generally quadrilateral, circular, or any other shape useful for the intended purpose.

Trailing end 104 includes bone screw receiving holes 126 for receiving bone screws 128 for securing implant 100 to the adjacent vertebral bodies. Bone screw receiving holes 126 include a gap 130 in the perimeter of bone screw receiving holes126 for permitting at least a portion of bone screw 128 to protrude beyond perimeter 132 of trailing end 104. Trailing end 104 may be straight, curved, or anatomically contoured. Gap 130 interrupts the perimeter of bone screw receiving holes 126, sothat bone screw receiving holes 126 have an incomplete perimeter or C-shape. At least one of the bone screw receiving holes 126 is adapted to cooperatively engage the trailing end of bone screw 128 to allow at least a portion of the perimeter of thetrailing end of at least one of the bone screws to protrude beyond at least one of the opposed upper and lower implant surfaces.

As used herein, the trailing end of a bone screw includes not less than that portion of the bone screw at the end opposite the leading end of the screw adapted to cooperatively engage the implant to prevent its passage therethrough. Thetrailing end may include the head and/or shaft proximate to the head, for example, shaft 134 and head 138 as shown in FIG. 1. The bone screw heads are preferably but not necessarily flush or slightly below the exterior surface of the trailing end of theimplant when fully installed so as not to protrude therefrom into anatomical structures that may be present proximate the exterior surface of the trailing end of the implant.

The trailing end of the implant may be configured to receive bone screws such that they are constrained within the bone screw receiving holes (i.e., fixing the trajectory of each bone screw), or left unconstrained within the bone screw receivingholes for allowing variable screw angles. Preferably, for a constrained configuration an interference fit is formed 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 cooperative mating threads between the screw head and the bone screw receiving hole.

If it is desired that the bone screws are unconstrained then the bone screws may have a rounded head portion and/or a reduced neck diameter to permit movement of the bone screws so as to allow the angle between the implant and the bone screw tobe variable.

Bone screws need not be locked to the implant, but simply may have, for example, a shoulder for stopping the progress of a bone screw through the implant beyond a certain point along the bone screw length. It is appreciated that all the bonescrews described herein may 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 substantially protrude away from the trailing end. Gap 130 is sized suchthat it is less than half the diameter of screw 128. By allowing screws 128 to protrude over edges 140, 142 of trailing end 104, upper and lower screws may be placed such that the maximum height H of trailing end 104 is less than the sum of the maximumdiameter of two bone screws adapted to be inserted in bone screw receiving holes 126.

Bone screw receiving holes 126 may be adapted to capture screws 128, thereby constraining the screws within trailing end 104. Alternatively, trailing end 104 can further include at least one locking mechanism 144 for locking the bone screws toimplant 100. Although bone screw locks are preferred, the invention is not so limited.

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

Locking mechanism 144 can be in the form of a screw or a rivet having a head for contacting and securing the bone screws to implant 100. Locking mechanism 144 may be capable of rotational movement relative to trailing end 104. Lockingmechanism 144 includes a tool-engaging portion 146 for moving locking mechanism 144 from an unlocked to a locked position.

As best shown in FIGS. 1 and 4, locking mechanism 144 further includes removed portions 148 permitting the installation of bone screws into bone screw receiving holes 126 while locking mechanism 144 is in the unlocked position. In a preferredembodiment, locking mechanisms 144 can turn 180 degrees to be fully tightened. Locking mechanisms 144 can turn in the same direction or counter to one another. The bottom of the head of locking mechanism 144 can be of various shapes and, for example,can be ramped or concave. Further, as taught in applicant’s application Ser. No. 09/565,392 titled “Spinal Implant with Vertebral Endplate Engaging Anchor”, the present invention may be adapted to receive self-locking screws.

Locks 144 can work either to constrain screws 128 by fixing their positions, or in the alternative by preventing screws 128 from backing out without fixing the screws position so that the screws can allow for settling of the disc space(dynamization).

It is appreciated that the present invention includes the use of other screw locking mechanisms and devices such as would be used in other plate/screw or implant/screw devices and as would be known to one of ordinary skill in the art.

As shown in FIG. 9, trailing end 104 further includes alignment holes 150, 152 and threaded engagement hole 153 for engaging alignment pegs 154 and threaded driver 155, respectively from a driver instrument described below. Any other means ofengaging the implant to assist in its insertion as would be known in the art is within the scope of the present invention.

A preferred origin and trajectory of bone screw receiving hole 126 is such that a surgeon can (but does not necessarily have to be able to) insert bone screws 128 through holes 126 to an optimal or desired depth without those bone screwscrossing a plane bisecting the height of the adjacent vertebral body. An alternative embodiment may include top and bottom screws that are placed asymmetrically so as to be offset from one another so that the screws from such implants inserted intoadjacent disc spaces pass each other in an intermediate vertebral body without hitting one another. For example, an implant may have two bone screws in the trailing end toward the outer sides and projecting through the upper surface and one bone screwin the middle of the trailing end projecting through the lower surface.

As shown in FIG. 5, implant 100 is inserted into an implantation space formed across the disc space into the 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 into the adjacent vertebral bodies with a drill 156 and a drill guide 158, an awl, or other device. Drill 156 has a bone removing end 160 and a shaft 162. Drill guide 158 has aleading end 164 adapted for insertion into one of bone screw receiving holes 126 of trailing end 104. Leading end 164 has a smaller dimension 166, a larger dimension 168, and a shoulder 170 corresponding to the reduced dimension portions of bone screwreceiving holes 126 that are configured to receive the head portion of bone screws 128. Drill guide 158 has an inner bore (not shown) that in one preferred embodiment is aligned with the central longitudinal axis of the bone screw receiving holes 126when leading end 164 is properly seated therein. If it is desired to vary the angle of drill guide 158 to bone screw receiving holes 126, the tip of drill guide 158 may be rounded. In the alternative, the drill guide may screw into the bone screwreceiving hole, or may attach to the implant by any other technique known in the art. Further, the openings into the bone may be formed with a spike or other device, or the screws may be inserted without first forming bores into the bone.

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

In the spinal implant of the present invention, the bone screws can be oriented in an angular relationship to each other so as to be divergent along the vertical plane of the implant when installed into the adjacent vertebral bodies. Thepreferred angular divergence from the implant surface is preferably 25.degree.-40.degree., but any angle useful for the intended purpose is within the scope of the present invention. In a preferred embodiment, screws 128 are angled such that they do notextend beyond half the height of the adjacent vertebral body. This ensures that screws of one implant will not contact the screws of an implant inserted in a neighboring disc space.

In the implant of the present invention, if lag screws are utilized or if there is a lagging implant to screw relationship, then the adjacent vertebral bodies are pulled toward implant 100 as bone screws 128 are installed into the vertebral boneto create a compressive load on the implant. Further, the angling of bone screws 128, keeps the anterior portion of the adjacent vertebral bodies together during extension movement of the spine such as would occur when a patient leans backwards. Amongthe many advantages of the present invention, the anterior portions of the vertebral bodies adjacent implant 100 do not move apart as they are held in place by bone screws 128 inserted through trailing end 104, the back of the implant is not driven intothe vertebral bodies with spinal extension, and the compressive load is safely distributed over the entire length of the interbody portion of the implant.

FIG. 7 shows a top plan view of implant 100 installed within the disc space between two adjacent vertebral bodies and bone screws 128 installed in trailing end 104. In a preferred embodiment, bone screws 128 are toed-in toward each other. Itis appreciated, however, that bone screws 128 need not be toed-in but may be parallel, diverging, or have any other desired orientation to one another. It is further appreciated that only a single screw or three or more screws can be used to secure theimplant to each of the adjacent vertebral bodies instead of the two screws shown in FIG. 7.

FIG. 8 is a trailing end elevation view of spinal implant 100 installed between two adjacent vertebral bodies with locking mechanisms 144 shown in the unlocked position and bone screws 128 in place. Upper bone screws 128 are converging whilelower bone screws 128 are diverging. If two such implants are placed into consecutive disc spaces, converging upper bone screws 128 of one implant and diverging lower bone screws 128 of the other implant would not interfere with each other because ofthe difference in angulation of the respective bone screws.

As shown in FIG. 9, implant 100 can be installed with driver instrumentation 172 for both holding the implant so as to be useful for insertion and for preventing torquing of the implant when the locks are secured in their locked position. Driver instrumentation 172 has a blocker portion 174 for cooperatively engaging trailing end 104 of implant 100. Blocker 174 has a leading arcuate surface 176 that may be configured to conform at least in part to the contour of trailing end 104. Driverinstrumentation 172 has a shaft 178 extending from blocker 174 with of an inner bore 180 along the longitudinal axis of shaft 178. Extending from blocker 174 are a pair of alignment pegs 154 and threaded driver shaft 155 for cooperatively engagingalignment holes 150, 152 and threaded hole 153, respectively, in trailing end 104. Blocker 174 has openings 182 that are coaxially aligned with locking mechanisms 144, respectively. Openings 182 are configured to receive a locking tool 184 therethroughfor accessing and operating locking mechanisms 144. Instrumentation 172 allows the surgeon to tighten locking mechanisms 144 against the blocker 174 instead of torquing the spine of the patient.

Driver instrument 172 and blocker 174 are shown as an example of insertion instrumentation with the understanding that any inserter or a blocker or combined inserter and blocker known to one of ordinary skill in the art and useful for theintended purpose is within the scope of the present invention.

FIG. 10 shows a top plan view in partial cross-section of spinal implant 100 installed between two adjacent vertebral bodies and coupled to the driver instrumentation 172 with tool 184 (such as a screw driver) shown locking the locking mechanism144 (a rivet) to secure bone screws 128 to trailing end 104. It is appreciated that locking mechanism 144 could be a rivet, screw, or the like.

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

Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered asexemplary only, with a true scope and spirit of the invention being indicated by the following claims.