INTERBODY FUSION IMPLANT AND SCREW GUIDE

Abstract

An interbody fusion implant fits between adjacent vertebrae for fixation during fusion thereof. Upper bores extend into a cephalid surface of the implant and preferably include threads therein. A guide tool is removably attachable to the implant which supports guide bores along centerlines aligned with the upper bores in the implant. A drill can pass along these guide bores to form holes in a vertebra adjacent the cephalid surface of the implant which is precisely aligned with the upper bores. A hybrid screw then passes through these holes in the vertebra adjacent the cephalid surface and threads into the upper bores to secure the implant to the adjacent cephalid vertebra. Bone screws can also be used to secure the implant to caudal vertebra by passing through bores passing through the implant, such that the implant is securely mechanically fastened to both cephalid and caudal vertebrae adjacent the implant.

Claims

1: A method for securing an implant to an adjacent structure, including the steps of: identifying an implant having an anterior surface and a cephalid surface opposite a caudal surface, the implant having at least one bore extending into the cephalid surface thereof along a bore centerline extending from the cephalid surface toward the caudal surface and away from the anterior surface and wherein the at least one bore extending into the cephalid surface includes female threads thereon; identifying a hybrid screw with a proximal end opposite a distal end, said proximal end having a head with a torque applying interface thereon and the distal end having male threads thereon, the hybrid screw having a bone engaging structure on a proximal side of the male threads and spaced from the male threads for engagement of a vertebra adjacent the cephalid surface of the implant; selecting a guide having a guide bore extending therethrough, the guide being removably attachable to the implant; placing the implant at an implant location with an adjacent structure covering the bore into the cephalid surface; attaching the guide to the implant with the guide bore aligned with the centerline of the bore into the cephalid surface; cutting a hole through the adjacent structure along the centerline to the bore, using the guide bore; placing the hybrid screw with the male threads matching the female threads in the bore through the hole in the adjacent structure formed during said cutting step with the male threads engaging the female threads; and threading the screw into the bore in the implant until the adjacent structure is secured to the implant by the bone engagement structure.

2: The method of claim 1 wherein said screw has both the male threads and bone threads, with the male threads closer to a distal end of the screw than the bone threads, and the bone threads providing at least a portion of the bone engagement structure securing the adjacent structure to the implant as part of said threading step.

3: The method of claim 1 wherein said cutting step includes the step of drilling a hole through the adjacent structure, the hole having a diameter large enough to allow the screw to pass through the hole during said placing a screw step.

4: The method of claim 1 wherein said identifying an implant step includes said implant having at least one additional bore extending into the cephalid surface of the implant along a separate bore centerline oriented non-parallel with said bore centerline of said at least one bore, wherein said selecting a guide step includes the guide having at least one additional guide bore with the at least one additional guide bore aligned with the separate bore centerline for at least one additional bore extending into the cephalid surface of the implant, wherein said cutting step includes cutting at least one additional hole through the adjacent structure aligned with the at least one additional bore in the implant, and wherein said placing step includes placing at least one additional screw into the at least one additional hole formed in the adjacent structure during said cutting step, and threaded into the at least one additional bore in the cephalid surface of the implant.

5: The method of claim 4 wherein said identifying step includes the implant having throughbores extending from said anterior surface through said caudal surface, and at least one bone screw sized to pass through said throughbore from said anterior surface through to said caudal surface with threads on the bone screw engaging a structure adjacent the caudal surface of the implant and with the bone screw also engaging at least a portion of the implant for attachment of the implant to the structure adjacent the caudal surface of the implant.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 is a side elevation view of the lumbar spine of a human including the sacrum and illustrating a spine exhibiting spondylolisthesis, and showing an L5/S1 joint which is a candidate for fusion utilizing the implant of this invention and according to the method of this invention.

[0020] FIG. 2 is a side elevation view of a portion of that which is shown in FIG. 1 after a disk has been removed from the L5/S1 joint and the implant according to this invention has been placed therein, and with portions of vertebrae adjacent the implant cut away and with the cage implant shown in full section to reveal interior structures of the implant and operation of the guide tool and alignment of various screws for secure attachment of the cage implant to the L5 vertebra and to the S1 sacrum.

[0021] FIG. 3 is a side elevation exploded view of the implant, tool and screws of FIG. 2, but shown without the spine portions present, and without the guide block and associated guide bores, and with interior structures of the implant shown in broken lines.

[0022] FIG. 4 is a side elevation view of a hybrid screw for use according to this invention to secure the L5 vertebra (or other structure adjacent a cephalid side of the implant) to the implant. FIG. 4 also shows in broken lines a variation on the hybrid screw where threads are only provided at a distal end and a head having a greater diameter than a shaft is provided instead of or in addition to bone threads for engagement of an adjacent upper vertebral structure.

[0023] FIG. 5 is a side elevation view similar to that which is shown in FIG. 4, but for an embodiment of the screw which includes a self-tapping cutting groove therein, and illustrating pitch angles for the various threads.

[0024] FIG. 6 is a top plan view of the implant and tool and attachment threads with broken lines depicting paths of the guide bores in the guide tool and a tool port within the implant for removable attachment of a coupling tip of the guide tool thereto.

[0025] FIG. 7 is a side elevation view similar to that which is shown in FIG. 2, but with the tool removed and after completion of the interbody fusion procedure, with the interbody fusion cage fastened to both the cephalid L5 vertebra and the caudal S1 sacrum.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0026] Referring to the drawings, wherein like reference numerals represent like parts throughout the various drawing figures, reference numeral 10 is directed to a cage implant for use in a vertebral interbody fusion procedure (FIGS. 2 and 7), according to a preferred embodiment of this invention. The implant 10 is utilized as part of a system 100 which includes a guide tool 60, drill 70 or other hole forming tool and bone screws 30 and hybrid screws 50 for securing of the implant 10 to adjacent structures such as the L5 vertebra and the S1 sacrum adjacent the implant, when used at the L5/S1 joint. Following the system 100 of this invention, the implant 10 is mechanically secured to both cephalid and caudal adjacent structures for secure fixation of the implant 10 during fusion of the adjacent vertebral structures together. While depicted primarily for interbody vertebral fusion, and especially fusion of portions of the lumbar spine S, and in particular the L5/S1 joint, the implant 10 and system 100 of this invention could be utilized for fusion of other bones or other structures together with modification of size and shape to match varying anatomy for such other uses.

[0027] In essence, and with particular reference to FIGS. 1 and 2, basic details of the implant 10 of this invention and other portions of the system 100 are described, according to this preferred embodiment. The implant 10 is a rigid cage structure sized to fit within an interbody space between adjacent structures to be fused together, such as adjacent vertebrae, and in this example the L5 vertebrae and the S1 sacrum. The implant 10 can have any of a variety of different geometries and configurations known for interbody fusion cages, with the implant 10 depicted herein having a generalized shape. The implant 10 includes standard bores passing entirely through the implant 10. These standard bores are oriented to allow standard bone screws to pass into the standard bores and thread into the sacrum S1 or other structure adjacent a caudal side of the implant 10. The standard bone screw 30 is thus utilized to secure the implant 10 to the sacrum S1.

[0028] Upper bores 40 are provided extending into a cephalid surface of the implant 10. A hybrid screw 50 is provided to secure the L5 vertebra or other structure adjacent a cephalid side of the implant 10 to the implant 10 through the upper bores 40. To allow this hybrid screw 50 to pass into the upper bores 40, holes H must first be formed in the L5 vertebra, or other structure adjacent the cephalid side of the implant 10, which are precisely aligned with the upper bores 40. A guide tool 60 is provided which is removably attachable to the implant 10. This guide tool 60 includes guide bores 68 which are aligned with the upper bores 40 in the implant 10. A drill 70 or other cutting tool can pass through the guide bores 68 to form the holes H aligned with the upper bores 40 in the implant 10. The hybrid screws 50 can then pass through these holes H and be threaded into the upper bores 40, so that the implant 10 can be securely attached to the L5 vertebra or other vertebra on a cephalid side of the implant 10. In this way, the implant 10 is securely attached to adjacent structures, such as the L5 vertebra and the S1 sacrum, on either side of the implant 10 for secure holding of the L5 vertebra and S1 sacrum or other adjacent vertebrae together during the fusion process.

[0029] More specifically, and with particular reference to FIGS. 2, 3, 6 and 7, details of the implant 10 are described, according to this most preferred embodiment. Interbody fusion cages such as the implant 10 come in a variety of different sizes, shapes and configurations, and exhibiting a variety of different surfaces and attributes, to optimize placement within an intervertebral space and fixation of adjacent vertebrae during a fusion procedure. The implant 10 of this invention can be utilized with a variety of such cages, so that the implant 10 generally references some form of cage or other interbody implant without particular requirement of any details of this cage implant 10.

[0030] Generally, the implant 10 includes a cephalid surface 14 opposite a caudal surface 16, which are spaced apart generally by a height of the implant 10. An anterior surface 12 is provided generally extending between the cephalid surface 14 and the caudal surface 16. This anterior surface 12 generally defines a portion of the implant 10 which is on an anterior side of the implant 10. These surfaces 12, 14, 16 could have a variety of different contours including generally flat, curving, or with other geometries or surface attributes as are known in the spinal fusion cage arts.

[0031] The implant 10 includes a tool port 18, preferably in the anterior surface 12. This tool port 18 is most preferably in the form of a threaded blind bore extending into the anterior surface 12 perpendicular to the anterior surface 12. This tool port 18 is provided for secure but removable attachment of the guide tool 60 thereto. The tool port 18 could have a configuration other than that of a threaded blind bore, with the primary function of the tool port 18 being secure removable attachment of the guide tool 60 to the implant 10 in a precise alignment between the guide tool 60 and the implant 10.

[0032] Most preferably, when the tool port 18 is in the form of a blind threaded bore, threads are formed and the bore formed so that the coupling tip 64 of the guide tool 60 which threads into this tool port 18 bottoms out within a bottom of the tool port 18 before the threads wedge the coupling tip 64 too tightly into the tool port 18. In this way, the guide tool 60 stops at a reliable rotational orientation relative to the implant 10, such that guide bores 68 associated with the guide tool 60 are reliably aligned precisely with the upper bores 40 in the implant 10. As a further alignment aid, a stop could be placed within or adjacent the tool port 18 which acts on the guide tool 60 to stop and hold its orientation where desired after coupling to the tool port.

[0033] The implant 10 preferably has both standard bores 20 and upper bores 40. In alternative embodiments, the implant 10 could be provided merely with the upper bores 40. Also, it is conceivable that only one standard bore 20 would be provided, or that more than two standard bores 20 would be provided into the implant 10. Similarly, while two upper bores 40 are provided extending along non-parallel centerlines, only one upper bore 40 could be provided or more than two upper bores 40 could be provided according to alternatives to this invention. The standard bores 20 and the upper bores 40 could be oriented parallel to each other when viewed from the side (FIGS. 2, 3 and 7) or could be otherwise oriented. Such a generally parallel orientation minimizes the area needed by a surgeon outside the surgical site to utilize the drill 70 or other cutting tool and to place the screws 30, 50 into the implant 10.

[0034] The standard bores 20 preferably pass entirely through the implant 10, extending in this preferred embodiment from the anterior surface 12 through the caudal surface 16 along bone screw axis B. Preferably, two such standard bores 20 are provided. These standard bores 20 thus have an entrance 22 adjacent the anterior surface 12 and a exit 26 adjacent the caudal surface 16. The entrance 22 can be near a junction between the anterior surface 12 and the cephalid surface 14, or conceivably slightly onto the cephalid surface 14, but near the anterior surface 12.

[0035] A step 24 is preferably provided between the entrance 22 and the exit 26 in the standard bores 20. This step 24 provides a shelf against which a bone screw head 32 of a standard bone screw 30 can abut when the standard bone screw 30 has been passed through the standard bore 20 and threaded into the S1 sacrum or other vertebrae or other structure on a caudal side of the implant 10. Preferably, the standard bone screw 30 includes the bone screw head 32 opposite a tip 36 with bone screw threads 34 adjacent the tip 36 and extending up toward the bone screw head 32. These bone screw threads 34 are cancellous threads or otherwise threads formed for engagement with bony structures such as within the S1 sacrum. These bone screw threads 34 can be configured to tap complementary threads in the sacrum S1.

[0036] As an alternative, a tapping tool can be utilized and a drill utilized to first drill a hole in the sacrum S1 and then form threads in the hole formed in the sacrum S1, so that the bone screw 30 does not need to form a hole and/or form threads in the sacrum S1, or other vertebrae or other structure, but rather merely is threaded into such a hole. As another alternative, the standard bone screw 30 could be a cannulated bone screw which is configured to follow a guide wire which has been previously fitted into the sacrum S1, such as with the assistance of a fluoroscope to ensure precise orientation of the standard bone screws 30. Most preferably, the standard bone screws 30 are oriented non-parallel to each other, for maximum mechanical coupling of the implant 10 to the sacrum S1 or other vertebrae or other structure adjacent the caudal surface 16 of the implant 10.

[0037] As shown in FIG. 2, portions of the tool 60 can conceivably block the standard bores 20 in the implant 10. The standard bone screws 30 can be placed into the standard bores 20 when the guide tool 60 is detached from the implant 10, or the guide tool 60 can be provided with holes or a shape which leaves the standard bores 20 substantially open so that the guide tool 60 can be attached to the implant 10 when the standard bone screws 30 are attached to the implant 10 and to the sacrum S1 or other vertebrae or other structure on a caudal side of the implant 10. As the standard bone screws 30 are tightened, the bone screw head 32 abuts against the step 24 and the implant 10 is drawn tight against the sacrum S1 or other vertebral structure adjacent the caudal surface 16 of the implant 10.

[0038] The upper bores 40 preferably are blind bores which extend from an entrance 42 and terminate within an interior of the implant 10. Female machine threads 44 are formed on these upper bores 40. As an alternative, the upper bores 40 could pass entirely through the implant 10 out the caudal surface 16, and with the entrance 42 still located in the cephalid surface 14. If the upper bores 40 are in the form of such throughbores, the upper bores 40 could optionally have no threads therein.

[0039] Before the upper bores 40 can be utilized, holes H are formed in the L5 vertebra or other vertebral structure adjacent the cephalid surface 14 of the implant 10. Once such a hole H has been formed, a hybrid screw 50 can be passed through this hole H and with male machine threads 57 on a distal end 56 of the hybrid screw 50 sized to match the female machine threads 44 in the upper bore 40 for securing of the hybrid screw 50 to the implant 10.

[0040] The hybrid screws 50 are configured to engage both the implant 10 and the L5 vertebra or other vertebral structure adjacent the cephalid surface 14 of the implant 10. In the preferred embodiment, the hybrid screw 50 includes a proximal end 52 opposite a distal end 56. A hybrid screw head 54 is provided at the proximal end 52. A torque applying structure is associated with the hybrid screw head 54, such as a allen wrench recess formed in the hybrid screw head 54. Such a recess is shown in broken lines in FIGS. 4 and 5.

[0041] Bone threads 55 are provided adjacent the proximal end 52 and with male machine threads 57 provided adjacent the distal end 56. The male machine threads 57 are referred to as machine threads because they are configured to thread into the female machine threads 44 pre-formed in the upper bores 40, with precise matching of pitch angles and major and minor diameters for secure attachment of the male machine threads 57 with the female machine threads 44 in the upper bores 40.

[0042] The bone threads 55 are configured to engage walls of the hole H formed in the L5 vertebra or other vertebral structure adjacent the cephalid surface 14 of the implant 10. In one embodiment, the hole H has a diameter similar to a minor diameter of the hybrid screw 50. The bone threads 55 thus thread into walls of the hole H as the hybrid screw 50 is advanced along a centerline of the hole H and the upper bores 40. As the hybrid screw 50 advances, the male machine threads 57 adjacent the distal end 56 engage the female machine threads 44 and the hybrid screw 50 is then coupled through both the male machine threads 57 engaging the female machine threads 44 in the upper bores 40 of the implant 10, as well as the bone threads 55 simultaneously engaging walls of the hole H in the L5 vertebra or other vertebral structure adjacent the cephalid surface 14 of the implant 10. The bone threads 55 can be self-tapping, such as by including a self-tapping cutting groove 160 in the alternative hybrid screw 150 depicted in FIG. 5.

[0043] Also in FIG. 5, pitch angles for the male machine threads 57 and the bone threads 55 are depicted. Angle depicts a pitch angle for the male machine threads 57. Angle depicts the pitch angle for the bone threads 55. Preferably, the pitch angle for the male machine threads 57 and the pitch angle for the bone threads 55 are substantially identical. Because the male machine threads 57 in this embodiment are finer than the bone threads 55, the male machine threads 57 can be compound threads to allow the pitch angles , to match each other. As another alternative, the male machine threads 57 could be provided no finer than the bone threads 55.

[0044] In one embodiment, a slight differential is provided between the pitch angle and the pitch angle , with the pitch angle being slightly steeper than the pitch angle . In this way, portions of the hybrid screw 50 adjacent the distal end 56 advance at a greater rate per turn of the hybrid screw 50 than portions of the screw 50 adjacent the proximal end 52, so that the implant 10 is drawn toward the L5 vertebra or other vertebral structure adjacent the cephalid surface 14 of the implant 10. With such a configuration, an initially somewhat loose threading of the hybrid screw 50 through the hole H and into the upper bore 40 becomes a tight fit as the hybrid screw 50 continues to be rotationally advanced into the upper bores 40 and this differential in the pitch angles of the male machine threads 57 and bone threads 55 cause a tightening of the L5 vertebra or other vertebral structure adjacent the cephalid surface 14 of the implant 10 to be drawn tightly against the cephalid surface 14 of the implant 10.

[0045] In another alternative depicted in FIG. 4 in broken lines, a further alternative hybrid screw 250 is depicted which has no bone threads thereon. Rather, an alternative hybrid screw head 254 is provided which has a diameter greater than that of an alternative hybrid screw shaft 253. In this embodiment, the hole H would be provided with a step therein, such as midway between an anterior side of the L5 vertebra and a surface of the L5 vertebra adjacent the cephalid surface 14 of the implant 10. The alternative hybrid screw head 254 would abut this shelf and then apply a compressing force on the L5 vertebra compressing it against the implant 10 as further turning of the hybrid screw 50 and further engagement of the male machine threads 57 of the hybrid screw 50 with the female machine threads 44 in the upper bores 40 of the implant 10 draws the hybrid screw 50 further down into the implant 10.

[0046] To form such a stepped hole in the L5 vertebra, or other vertebral structure adjacent the cephalid surface 14 of the implant 10, a drill bit can be utilized which has a stepped character. As another alternative, two separate drill bits having different sizes can be sequentially utilized. A first smaller drill bit would follow a centerline C entirely through the L5 vertebra to form the hole H. Then a second larger drill bit would be advanced only partway along the same centerline C, with perhaps a stop on the drill bit or other technique to precisely control a depth of the larger diameter portion of the hole H.

[0047] Hybrid screws 50 having such an alternative hybrid screw head 254 and without bone threads (or optionally with both the alternative hybrid screw head 254 and bone threads 55) could be provided with different lengths in small increments, so that if the hybrid screw 50 is found to be too long or too short, a separate hybrid screw can be selected which has an appropriate length to maximize secure attachment of the L5 vertebra (or other vertebral structure adjacent the cephalid surface 14 of the implant 10) to the upper bores 40 of the implant 10.

[0048] With particular reference to FIGS. 2, 3 and 6, details of the guide tool 60, according to one embodiment of the system 100 of this invention, are described. In operating the system 100 and method of this invention it is important that the hole H be precisely formed that is aligned with the centerline C of the upper bores 40 in the implant 10. To achieve this precise alignment, the guide tool 60 is provided. The guide tool 60 is removably attachable securely to the implant 10 so that guide bores 68 in the guide tool 60 can be precisely aligned with the upper bores 40 in the implant 10 along the common centerline C.

[0049] In the preferred embodiment, this guide tool 60 includes a handle 62 coupled to one end of a guide tool shaft 63 with a coupling tip 64 at an opposite end of the guide tool shaft 63. This coupling tip 64 is threaded to thread into the tool port 18 in the anterior surface 12 of the implant 10. As an alternative, some other form of rigid removable coupling can exist between the guide tool 60 and the implant 10 for secure attachment of the guide tool 60 to the implant 10. Importantly, this attachment not only provides for elimination of movement between the implant 10 and the guide tool 60, but also provides for precise orientation of guide bores 68 of the guide tool 60 relative to the implant 10.

[0050] The guide tool shaft 63 in this embodiment supports a guide block 66 extending therefrom. Multiple guide bores 68 pass through this guide block 66 which guide bores 68 are aligned with the upper bores 40 in the implant 10 when the coupling tip 64 of the guide tool 60 is coupled to the implant 10. Once so attached, the drill 70 can be utilized passing through the guide bores 68 to form the holes H through which the hybrid screws 50 pass, for secure attachment to the upper bores 40 of the implant 10.

[0051] While the guide tool 60 is described in this manner, a variety of different guides could be provided, so long as guide bores are oriented where required and precisely aligned with the centerline C of the upper bores 40 of the implant 10, so that a drill 70 or other cutting tool can be precisely passed along this centerline C to cut a hole through the L5 vertebra or other vertebral structure adjacent the cephalid surface 14 of the implant 10, to form the hole H precisely aligned with the upper bores 40 in the implant 10. In one embodiment, the guide tool 60 is attached to multiple locations on the anterior surface 12 or other portions of the implant 10, to ensure very precise alignment of the guide bores 68 associated with the guide tool 60 with the centerlines C of the upper bores 40 in the implant 10.

[0052] This disclosure is provided to reveal a preferred embodiment of the invention and a best mode for practicing the invention. Having thus described the invention in this way, it should be apparent that various different modifications can be made to the preferred embodiment without departing from the scope and spirit of this invention disclosure. When structures are identified as a means to perform a function, the identification is intended to include all structures which can perform the function specified. When structures of this invention are identified as being coupled together, such language should be interpreted broadly to include the structures being coupled directly together or coupled together through intervening structures. Such coupling could be permanent or temporary and either in a rigid fashion or in a fashion which allows pivoting, sliding or other relative motion while still providing some form of attachment, unless specifically restricted.