Note: Descriptions are shown in the official language in which they were submitted.
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OSTEOGENIC FUSION DEVICES
This application claims the benefit of U.S. Provisional Application
Serial No. 60/233,563 filed September 19, 2001, which is hereb;
incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
The present invention relates to an implant to be placed into
the intervertebral space left after the removal of a damaged spinal
disc. Specifically, the invention concerns an osteogenic fusion
device that enhances arthrodesis or fusion between adjacent
vertebrae while also maintaining the normal spinal anatomy at the
instrumented vertebral level.
In many cases, low back pain originates from damages or
defects in the spinal disc between adjacent vertebrae. The disc can
be herniated or can be affected by a variety of degenerative
conditions. In many cases, these pathologies affecting .the spinal
disc can disrupt the normal anatomical function of the disc. In
some cases, this disruption is significant enough that surgical
intervention is indicated.
In one such surgical treatment, the affected disc is essentially
removed and the adjacent vertebrae are fused together. In this
treatment, a discectomy procedure is conducted to remove the disc
nucleus while retaining the annulus. Since the disc material has
been removed, a body must be placed within the intervertebral
space to prevent the space from collapsing.
In early spinal fusion techniques, bone material, or bone
osteogenic fusion devices, were simply disposed between adjacent
vertebrae, typically at the posterior aspect of the vertebrae. In the
early history of these osteogenic fusion devices, the osteogenic
fusion devices were formed of cortical-cancellous bone which was
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not strong enough to support the weight of the spinal column at the
instrumented level. Consequently, the spine was stabilized by way
of a plate or a rod spann,ng the affected vertebrae. With this
technique, once fusion occurred across and incorporating the bone
osteogenic fusion device, the hardware used to maintain the
stability of the spine became superfluous.
Following the successes of the early fusion techniques, focus
was directed to modifying the device placed within the intervertebral
space. Attention was then turned to implants, or interbody fusion
devices, that could be interposed between the adjacent vertebrae,
maintain the stability of the disc interspace, and still permit fusion
or arthrodesis. These interbody fusion devices have taken many
forms. For example, one prevalent form is a cylindrical hollow
implant or "cage". The outer wall of the cage creates an interior
space within the cylindrical implant that is filled with bone chips,
for example, or other bone growth-inducing material. Implants of
this type are represented by the patents to Bagby, No. 4,501,269;
Brantigan, No. 4,78,915; Ray, No. 4,961,740; and Michelson, No.
5,015,247. In some cases, the cylindrical implants included a
threaded exterior to permit threaded insertion into a tapped bore
formed in the adjacent vertebrae. Alternatively, some fusion
implants have been designed to be impacted into the intradiscal
space.
Experience over the last several years with these interbody
fusion devices has demonstrated the efficacy of these implants in
yielding a solid fusion. Variations in the design of the implants
have accounted for improvements in stabilizing the motion segment
while fusion occurs. Nevertheless, some of the interbody fusion
devices still have difficulty in achieving a complete fusion, at least
without the aid of some additional stabilizing device, such as a rod
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or plate. Moreover, some of the devices are not structurally strong
enough to support the heavy loads and bending moments applied at
certain levels of the spine, namely those in the lumbar spine.
Even with devices that do not have these difficulties, other
less desirable characteristics exist. Recent studies have suggested
that the interbody fusion implant devices, or cages as they are
frequently called, lead to stress-shielding of the bone within the
cage. It is well known that bone growth is enhanced by stressing or
loading the bone material. The stress-shielding phenomenon
relieves some or all of the load applied to the material to be fused,
which can greatly increase the time for complete bone growth, or
disturb the quality and density of the ultimately formed fusion
mass. In some instances, stress-shielding can cause the bone
chips or fusion mass contained within the fusion cage to resorb or
evolve into fibrous tissue rather than into a bony fusion mass.
A further difficulty encountered with many fusion implants is
that the material of the implant is not radiolucent. Most fusion
cages are formed of metal, such as stainless steel, titanium or
porous tantalum. The metal of the cage shows up prominently in
any radiograph (x-ray) or CT scan. Since most fusion devices
completely surround and contain the bone graft material housed
within the cage, the developing fusion mass within the metal cage
between the adjacent vertebrae cannot be seen under traditional
radiographic visualizing techniques and only with the presence of
image scatter with CT scans. Thus, the spinal surgeon does not
have a means to determine the progress of the fusion, and in some
cases cannot, ascertain whether the fusion was complete and
successful.
The field of spinal fusion can be benefited by an intervertebral
fusion device that can support bone growth material within the
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intervertebral space, while still maintaining the normal height of the
disc space. The device would beneficially eliminate the risk of
stress-shielding the fusion mass, and would also provide for
visualization of the fusion mass as the arthrodesis progresses.
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SUMMARY OF INVENTION
To address the current needs with respect to interbody fusion
devices, the present invention contemplates an osteogenic fusion
device that is configured to place as much of the bone growth-inducing
material as possible into direct contact with the adjacent bone. In one
embodiment, the osteogenic fusion device includes an elongated body
having opposite first and second end pieces separated by an integral
central element. The central element has a significantly smaller
diameter than the two end pieces. The osteogenic fusion device thus
forms an annular pocket between the end pieces and around the
central element.
In accordance with one aspect of the present invention, a bone
growth-inducing material is disposed within the annular pocket
around the central element of the osteogenic fusion device. In one
specific embodiment, the bone growth-inducing material can constitute
a sheet of a pharmaceutically suitable carrier for a bone growth factor,
such as a bone morphogenetic protein. In this embodiment, the sheet
can be a collagen sheet that is soaked with the BMP and then
subsequently wrapped in spiral fashion around the central element of
the osteogenic fusion device.
In one feature of the present invention, the osteogenic fusion
device can be implanted in a bi-lateral approach. Specifically, two
such osteogenic fusion devices can be inserted into prepared bores
formed in the endplates of adjacent vertebrae after completion of a
discectomy. The spinal loads are borne by the two end pieces that are
in direct contact with the adjacent vertebral bodies. Preferably, the
osteogenic fusion device has a length sufficient to allow the end pieces
to at least partially contact the harder bone at the apophysis of the
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adjacent vertebrae. With the osteogenic fusion device thus inserted,
the bone growth-inducing material is in direct contact with the
adjacent vertebral bodies. In addition, bone growth-inducing material
can be placed within the bi-lateral space separating the two osteogenic
fusion devices. When fusion occurs, a substantial fusion mass is
produced that is virtually uninterrupted by the material of the
osteogenic fusion device itself
Several alternative embodiments of the osteogenic fusion device
are presented, all retaining the capability of supporting bone growth-
inducing material so that it is in direct contact with the adjacent
vertebrae. In some embodiments, additional elements of the central
element are provided, while in another embodiment, an intermediate
piece is provided for further support across the disc space. In one
embodiment, osteogenic fusion devices are provided wherein at least
one of the opposite end pieces includes a truncated surface. In yet
another embodiment, the truncated surface advantageously includes
opposite faces, such as opposite edges, that define an entrance to a
cutout region. The cutout region is typically defined by the truncated
surface and the truncated surface is preferably concave. Such
implants are advantageously configured to nest within another fusion
device, such as the fusion device of the present invention.
Another embodiment of the present invention provides an implant
system including at least two load bearing members as described
above adapted to be bilaterally placed between adjacent vertebrae,
wherein at least one of the load bearing members has a truncated
surface configured to nest within the other load bearing member.
Yet another embodiment .of the invention provides an implant
system for promoting fusion bone growth in the space between
adjacent vertebrae which includes at least first and second load
bearing members adapted to be bilaterally placed between adjacent
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vertebrae, wherein the load bearing members are connected to one
another so as to resist lateral separation. In particular, a preferred
embodiment provides a first of the load bearing members including a
male member, and a second of the load bearing members including a
female member. The male and female members cooperate to resist
lateral separation of said devices. In another preferred embodiment,
the load bearing members can be connected by a connecting member
such as a plate spanning the two load bearing members.
In other embodiments of the invention, methods of promoting
fusion bone growth in the space between adjacent vertebrae are
provided. The methods include providing load bearing members or
implant systems as described above, preparing adjacent vertebrae to
receive the load bearing members or implant systems in an
intervertebral space between adjacent vertebrae and placing the load
bearing members or implant systems into the intervertebral space after
the preparing step.
The present invention also contemplates an insertion tool and
certain modifications to the osteogenic fusion device to accommodate
the tool. In one preferred embodiment, the tool is essentially an
elongated shank having opposite prongs extending therefrom. The
prongs can engage truncated side walls of one of the end pieces. In
addition, the opposite end piece can be formed with notches to receive
the tips of the two prongs. With this design, the osteogenic fusion
device can be a push-in or a threaded type osteogenic fusion device.
It is one object of the present invention to provide an interbody
fusion device that allows the greatest possible contact between the
adjacent vertebrae and the bone growth-inducing material supported
by the osteogenic fusion device. It is a further object to provide such a
osteogenic fusion device that is capable of supporting the loads
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generated throughout the spine without stress-shielding developing
bone within the osteogenic fusion device.
Another object of the invention is achieved by features that
~nimi~e the radiopacity of the device. This results in a benefit to the
surgeon of being able to more readily assess the progress of a spinal
fusion.
Yet another object of the invention is to provide an interbody
fusion device whereby enough lateral exposure is present to place two
large devices side-by-side to distract the disc space and facilitate
fusion.
It is yet another object of the invention to provide an interbody
fusion device which can be placed closer to another interbody fusion
device and which will require no or minimal resection of facet joints.
Yet a further object of the invention is to provide an implant
system which is placed in the intervertebral space with minimal
retraction of the spinal cord to lessen the chance of neurological
complications or damage.
Other objects and benefits of the present invention can be
discerned from the following written description and accompanying
figures.
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DESCRIPTION OF THE FIGURES
FIG. 1 is a top elevational view of an osteogenic fusion device in
accordance with one embodiment of the present invention.
FIG. 2 is an end elevational view of one end of the osteogenic
fusion device shown in FIG. 1.
FIG. 3 is a top elevational view of an alternative embodiment of the
osteogenic fusion device utilizing exterior threads.
FIG. 4 is a top cross-sectional view of an osteogenic fusion device
as shown in FIG. 1 with a bone growth-inducing material supported by
the osteogenic fusion device.
FIG. 5 is an cross-sectional view of the osteogenic fusion device
and bone growth material shown in FIG. 4 taken along line 5-5 as
viewed in the direction of the arrows.
FIG. 6 is a plan view of a sheet for a bone growth-inducing
material used with the osteogenic fusion device shown in FIG. 4.
FIG. 7 is an end elevational view of one end of a osteogenic fusion
device, such as the osteogenic fusion device of FIG. 1, modified to
include apertures.
FIG. S is an end elevational view of one end of a osteogenic fusion
device, such as the osteogenic fusion device of FIG. 1, modified to
include apertures.
FIG. 9 is a side, partially cross-sectional view of an intervertebral
disc space with a osteogenic fusion device according to FIG. 1
implanted between adjacent vertebrae.
FIG. 10 is a top elevational view of the superior aspect of the
instrumented vertebral level shown in FIG. 9, depicting bilateral
placement of osteogenic fusion devices according to the present
invention.
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FIG. 11 is a cross-sectional view of the instrumented vertebral
segment shown in FIG. 10, taken along line 11-11 as viewed in the
direction of the arrows.
FIG. 12 is a top elevational view of a osteogenic fusion device, such
as shown in FIG. 1, with features to permit insertion of the osteogenic
fusion device.
FIG. 13 is an end elevational view of the osteogenic fusion device
shown in FIG. 12.
FIG. 14 is a side elevational view of an insertion tool according to
one embodiment of the present invention.
FIG. 15 is a top elevational view of the insertion tool shown in FIG.
14.
FIG. 16 is a top elevational view of a osteogenic fusion device for
restoring the lordotic angle between adjacent vertebrae according to a
further embodiment of the present invention.
FIG. 17 is a top elevational view of a osteogenic fusion device
according to a further embodiment of the present invention.
FIG. 18 is a top elevational view of a osteogenic fusion device
according to a still further embodiment of the present invention.
FIG. 19 is an end elevational view of the osteogenic fusion device
shown in FIG. 18.
FIG. 20 is a top elevational view of a osteogenic fusion device
according to another embodiment of the present invention.
FIG. 21 is an end elevational view of the osteogenic fusion device
shown in FIG. 20
FIG. 22 is a top elevational view of a osteogenic fusion device
according to yet another embodiment of the present invention.
FIG. 23 is an end elevational view of the osteogenic fusion device
shown in FIG. 22.
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FIG. 24 is a top elevational view of a osteogenic fusion device
according to a further embodiment of the present invention.
FIG. 25 is an end elevational view of the osteogenic fusion device
shown in FIG. 25.
FIG. 26 is a top elevational view of a pair of fusion devices
according to FIGS. 24-25 disposed in a bilateral configuration in the
lumbar spine.
FIG. 27 is a top elevational view of a fusion device according to
FIGS. 24-25 disposed in the cervical spine.
FIG. 28 is an end elevational view of osteogenic fusion devices of
the present invention within a surgical window showing how such
fusion devices of particular sizes may not fit entirely within the
surgical window.
FIG. 29 is an end elevational view similar to that of FIG. 28 and
depicting one embodiment of the implant system of the present
invention.
FIG. 30 is a side elevational view of a osteogenic fusion device in
accordance with an alternative embodiment of the present invention.
FIG. 31 is an end elevational view of one end of the osteogenic
fusion device shown in FIG. 30.
FIG. 32 is an end elevational view of the other end of the
osteogenic fusion device depicted in FIG. 31.
FIG. 33 is a perspective view of an alternative embodiment of the
osteogenic fusion device of the present invention.
FIG. 34 is a top elevational view of an alternative embodiment of
the implant system of the present invention.
FIG. 35 is an end elevational view of one end of the implant system
depicted in FIG. 34.
FIG. 36 is an end elevational view of the other end of the implant
system depicted in FIG. 35.
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FIG. 37 is an end elevational view of an alternative embodiment of
the implant system of the present invention.
FIG. 38 is a perspective view of an alternative embodiment of the
implant system of the present invention.
FIG. 39 is a perspective view of yet a further alternative
embodiment of the implant system of the present invention.
FIG. 40 is an end elevational view of mated osteogenic fusion
devices of the invention.
FIG. 41 is a perspective view of one of the osteogenic fusion devices
depicted in FIG. 40.
FIG. 42 is a perspective view of another of the osteogenic fusion
devices depicted in FIG. 40.
FIG. 43 is a perspective view of an osteogenic fusion device of the
invention including a stop member.
FIG. 44 is an end elevational view of mated osteogenic fusion
devices connected by a connecting plate in accordance with the
invention.
FIG. 45 is a side elevational view of a spinal implant of the
invention.
FIG. 46 is an end elevational view of the spinal implant of FIG. 45.
FIG. 47 is a side elevational view of a spinal implant of the
invention.
FIG. 48 is an end elevational view of the spinal implant of FIG. 47.
FIG. 49 is a top elevational view of the spinal implant of FIG. 47.
FIG. 50 is a side elevational view of another spinal implant of the
invention.
FIG. 51 is a side elevational view of another spinal implant of the
invention.
FIG. 52 is a side elevational view of another spinal implant of the
invention.
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FIG. 53 is an end elevational view of the spinal implant of FIG. 52.
FIG. 54 is a top elevational view of a spinal implant of the
invention having dual central elements.
FIG. 55 is an end elevational view of the spinal implant of FIG. 54.
FIG. 56 is a top elevational view of a spinal implant of the
invention.
FIG. 57 is an end elevational view of the spinal implant of FIG. 56.
FIG. 58 is a side elevational view of the spinal implant of FIG. 56.
FIG. 59 is a top elevational view of another spinal implant of the
invention.
FIG. 60 is an end elevational view of the spinal implant of FIG. 59.
FIG. 61 is a side elevational view of the spinal implant of FIG. 59.
FIG. 62 is a top elevational view of a further spinal implant of the
invention.
FIG. 63 is an end elevational view of the implant of FIG. 62.
FIG. 64 is a top elevational view of another spinal implant of the
invention.
FIG. 65 is a top elevational view of a further spinal implant of the
invention having a central support member.
FIG. 66 is an end elevational view of the spinal implant of FIG. 65.
FIG. 67 is a perspective view of another spinal implant of the
invention.
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DESCRIPTION OF THE PREFERRED EMBODIMENTS
For the purposes of promoting an understanding of the principles
of the invention, reference will now be made to the embodiments
illustrated in the drawings and specific language will be used to
describe the same. It will nevertheless be understood that no
limitata.on of the scope of the invention is thereby intended, such
alterations and further modifications in the illustrated device, and
such further applications of the principles of the invention as
illustrated therein being contemplated as would normally occur to one
skilled in the art to which the invention relates.
The present invention contemplates osteogenic fusion devices for
use as interbody fusion devices. The osteogenic_ fusion devices include
opposite end pieces that are configured to span the intervertebral disc
space and engage the adjacent vertebral bodies. The inventive
osteogenic fusion devices include a central element separating the two
end pieces and substantially spanning the anterior-posterior length of
the disc space. The invention further contemplates that a bone
growth-inducing material be disposed about the central element and
between the opposite end pieces. When the inventive osteogenic fusion
device is implanted within a patient, the bone growth-inducing
material is in direct contact with the adjacent vertebral bodies. The
end pieces are formed of a material sufficient to withstand the spinal
loads generated at the instrumented vertebral level.
In accordance with one embodiment of the invention, an
osteogenic fusion device 10, depicted in FIGS. 1-2, includes a first end
piece 11 and a second end piece 12. The end pieces are separated by a
central element 13. The first end piece 11 could be substantially
cylindrical or any geometrical shape and includes an outer bone
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contacting surface 15. The end piece 11 also defines an inwardly
facing retaining surface 17. The central element I3 integrally extends
from the retaining surface 17 of the first end piece I 1.
The second end piece 12 also defines a bone contacting surface 20
that, in this embodiment, does not extend entirely around the end
piece. The bone contacting surface 20 could be any geometrical shape,
preferably circular and is defined at a radius equal to the radius of the
outer surface 15 of the first end piece. Thus, as depicted in FIG. 2, the
bone contacting surface 20 of the second end piece 12 is generally
coincident with portions of the outer surface 15 of the first end piece
11 when the osteogenic fusion device is viewed along the longitudinal
axis of its central element 13. The second end piece 12 also includes
opposite truncated surfaces 21 that are disposed between the circular
bone contacting surfaces 20. Preferably, the truncated surfaces 21 are
generally flat and can be configured to be engaged by an insertion tool.
The insertion tool preferably has arms that contact the flat truncated
surfaces 21, yet still fall within the envelope defined by the outer
surface 15 of the first end piece 11.
The second end piece 12 also defines a second retaining surface 22
that faces the first retaining surface 17 of the first end piece 11.
Again, the central element 13 is preferably integral with and projects
outwardly from the second retaining surface 22. Alternatively, the
central element can be in the form of a central rod that is engaged
within colinear bores formed in the two end pieces. In this variation,
the engagement between the central rod and the end pieces can be
threaded.
The central element 13 includes an outer central surface 23.
Preferably, the central element 13 is substantially cylindrical along its
length. In one aspect of the invention, the first end piece 11 defines a
diameter Di, while the central element 13 defines a diameter Dz. The
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diameter D 1 is at least equal to the height of the intervertebral space
within which the osteogenic fusion device 10 is to be interposed. Most
preferably, the diameter D1 corresponds to the diameter of a cylindrical
channel cut into the endplates of the adjacent vertebrae. In this
instance, the diameter D i will be somewhat larger than the
intervertebral disc space height. Moreover, the diameter D1 is
significantly larger than the diameter D2 of the central element 13.
This diameter differential creates an annular pocket 24 surrounding
the central element 13.
The osteogenic fusion device 10 has a length Li between the
opposite ends of the osteogenic fusion device. This length Ll is
preferably selected to be slightly less than the anterior-posterior length
of the intervertebral disc space, although the length can be calibrated
to the lateral dimension of the space. Most preferably, the length Li is
sized so that the first and second end pieces 11, 12 can contact at
least a portion of the apophysis or harder cortical bone at the
perimeter of the vertebral endplates. The osteogenic fusion device 10
further defines a length L2 which is essentially the length of the central
element 13. The length L2 is calibrated so that the end pieces 11 and
12 are sufficiently wide to provide adequate support between the
adjacent vertebrae. Conversely, the length I~ is sufficiently long so
that the annular pocket 24 has the capacity for retaining a substantial
quantity of bone growth-inducing material.
In a modification of the osteogenic fusion device 10, the second
end piece can be configured with threads. For example, as depicted in
FIG. 3 an end piece 25 includes external bone engaging threads 26
extending from the outer surface 27. _ In accordance with this
embodiment, the second end piece 25 can be cylindrical, like the first
end piece 11, or the threads can be formed between truncated
surfaces, such as truncated surfaces 21 in the prior embodiment. At
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any rate, the threaded end piece 25 is configured to be threadedly
advanced into a drilled and tapped channel within the adjacent
vertebral bodies. The first end piece 11 can also be threaded to
facilitate insertion and to reduce the chance of expulsion.
In a further aspect of the invention, a bone growth-inducing
material 30 is provided for support by the osteogenic fusion device 10.
Preferably the material 30 is in the form of a sheet. In a specific
example, the carrier sheet 30 can be a collagen sheet that is soaked
with a solution containing a bone growth-inducing substance, or a
bone morphogenetic protein (BMP). In accordance with the invention,
the carrier sheet 30 can be formed of a variety of materials other than
collagen, provided the materials are capable of containing a
therapeutically effective quantity of a bone growth-inducing substance
or BMP. Moreover, the material 30, whether in sheet form or not, is
most preferably susceptible to manipulation to be disposed within the
annular pocket 24 of the fusion device 10.
In accordance with the specific embodiment, the carrier sheet 30 is
wound around the outer surface 23 of the central element 13 (see FIG
5). The carrier sheet 30 is held between the retaining surface 17 of the
first end piece 11 and the retaining surface 22 of the second end piece
12. In accordance with one specific embodiment, the retaining surface
22 is curved or convex. In this way, the carrier sheet 30 can project
into the convexity to serve as a sort of anchor to hold the carrier sheet
within the annular pocket 24 of the osteogenic fusion device 10. In
25 addition, the convex surface 22 conforms better with the anterior
portion of the vertebral body profile when the fusion device is
implanted.
In the illustrated embodiment, the carrier sheet 30 can be provided
as a single sheet, as shown in FIG. 6. The inner end 31 of the sheet is
30 disposed against the central outer surface 23 of the central element
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13. The sheet can be wound in a spiral fashion about the central
element 13 until its outer end 32 is disposed adjacent the outer
surface 15 of the first end piece 11. The carrier sheet 30 has width W
that is preferably slightly larger than the length I,~ between the first
and second end pieces to allow a portion of the carrier sheet 30 to
project into the concave retaining surface 22 of the second end piece
12. The overall length of the sheet 30 between ends 31 and 32
depends upon its thickness and the difference in diameters D i and D2.
For example, in one embodiment the diameter D2 is about one-fourth
( 1 /4) the diameter D 1. Preferably, the length is sufficient so that the
carrier sheet 30 can be tightly wound about the central element 13
and fill the annular pocket 24. One important object of the present
invention is that the carrier sheet 30 or bone growth-inducing material
reside in direct contact with the adjacent vertebral bone.
Consequently, the sheet 30 is preferably wound so that its outer end
32 is at least slightly outside the envelope of the outer surface 15 of
the first end piece 11.
The carrier sheet 30 of FIGS. 4-6 illustrates one specific
embodiment of bone growth-inducing material usable with the
osteogenic fusion device of the present invention. It is also
contemplated that the carrier can be in the form of a sponge, paste, gel
or a settable osteogenic material. The osteogenic material must be
provided in some form that can be generally retained about the central
element 13 and within the annular pocket 24 of the osteogenic fusion
device 10. Put differently, the present invention contemplates an
osteogenic material that does not need to be contained in the
traditional manner of the hollow cylindrical cages of the prior art. In
these prior art devices, cancellous bone chips have been contained
within a hollow cage. In one preferred form, bone chips contained
within a bone paste or a gel may be utilized with the osteogenic fusion
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device 10, provided that the paste or gel have a consistency sufficient
to hold the bone growth-inducing material on and within the
osteogenic fusion device 10.
In accordance with one specific embodiment, the end pieces 11
and 12 are solid and circular in configuration. Alternative end piece
configurations are shown in FIGS. 7 and 8. For example, end piece 11'
can have a plurality of generally circular apertures 34 disposed
circumferentially about the end piece, as shown in FIG. 7. The end
piece 11" shown in FIG. 8 includes a plurality of pie-shaped apertures
35 so that the end piece gives the appearance of a spoked wheel. The
second end piece 12 of the osteogenic fusion device 10 can have
similar apertures defined therethrough. The apertures 34 and 35 in
the end pieces 11', 11" provide a further avenue for facilitating fusion
bone growth. The apertures themselves can be filled with an
osteogenic material, such as a gel or a paste. Moreover, once the
osteogenic fusion device 10 is implanted within an intervertebral disc
space, osteogenic material can be packed around the osteogenic fusion
device within the disc space. These additional apertures in the end
pieces 11, 12 provide further avenues for the formation of a bony
bridge between adjacent vertebrae. Additionally, these or other
apertures may be used as a portals) for the insertion of osteogenic
material into the implant site after the implant is in place, for example
by injecting an osteogenic material through the apertures) in sufficient
amount to fill the pocket formed between the implant and its
surrounding environment.
The end pieces 11,12, etc. can also have non-circular shapes. For
instance, the . end pieces can be rectangular or other mufti-sided
shapes. If the osteogenic fusion device resides within a channel
prepared in the endplates, the channel shape can be modified to
conform to the bone engaging surfaces 15, 20 of the end pieces.
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FIGS. 9-11 depict a pair of osteogenic fusion devices 10 implanted
in a bi-lateral configuration between adjacent vertebral bodies Vi and
V2. As depicted, the disc annulus A is retained but at least one portal
must be defined in the annulus A to permit insertion of the osteogenic
fusion devices 10. The present invention also contemplates insertion
of each osteogenic fusion device 10 through its own portal formed in
the disc annulus A. Alternatively, in conformance with other known
procedures, a single portal can be provided through which each
osteogenic fusion device 10 is successively inserted. Further in
accordance with the present invention, the osteogenic fusion devices
10 can be positioned within the intervertebral disc space according to
known posterior or postern-lateral techniques.
According to the present invention, the osteogenic fusion device 10
is inserted into the disc space S with the first end piece 11 proceeding
first into the space. Preferably, a channel C is bored into the vertebral
endplates E to a preferred depth of insertion of the osteogenic fusion
device 10, in accordance with known techniques. If the osteogenic
fusion device to be implanted is of the type shown in FIG. 3 with the
threaded second end piece 25, the channels C can be appropriately
drilled and tapped to accommodate the bone engaging threads 26. In a
modification of this embodiment, the first end piece 11 can also carry
external threads.
The preferred embodiment contemplates a generally cylindrical
osteogenic fusion device placed within circular channels. Alternatively,
the osteogenic fusion devices can operate as spacers that directly
contact the endplates, without a prepared channel. In this instance,
the bone engaging surfaces of the end pieces can be modified to
conform to the vertebral endplate geometry.
As depicted in FIGS. 9-11, the osteogenic material 30 is disposed
in direct contact with the adjacent vertebral endplates E. Moreover,
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the placement of osteogenic fusion devices 10 can present a medial
space 37 between the two osteogenic fusion devices. Osteogenic
material can then be placed within the medial space 37, again in direct
contact with the osteogenic material 30 situated around the central
elements 13 of each of the osteogenic fusion devices 10. Once
complete fusion occurs, new bone growth will substitute the carrier
material 30 to form a solid bony bridge spanning the adjacent
vertebrae Vl, Vz. As can be seen from FIGS. 9-11, the region of
continuous bone growth is very substantial and is not interrupted by
the structure of the fusion device itself.
It is understood, of course, that the end pieces 11 and 12 provide
sufficient support for the vertebral loads passing between the adjacent
vertebrae. At the same time, this load bearing capacity is concentrated
outside the middle regions of the vertebral endplates E. It is known
that the central region of the endplates is very rich in blood flow and
has a high capacity for new bone growth. Thus, the elimination of
structural material of the osteogenic fusion device 10 from that region
provides for a faster and more complete arthrodesis than may have
been possible with prior fusion cages.
Referring next to FIGS. 14, 15, an insertion tool 50 is depicted fox
inserting a osteogenic fusion device 10 according to the present
invention. The insertion tool 50 includes a solid shank 51 to which a
knob or handle 52 is affixed. The knob 52 is configured for manual
grasping and manipulation during insertion of the osteogenic fusion
device. In the case where the osteogenic fusion device is not threaded,
the insertion tool 50 simply acts as a pushing device. On the other
hand, in the instance where the osteogenic fusion device includes
threaded end pieces such as shown in FIG. 3, the insertion tool 50
must be rotated as the end piece is threaded into the prepared channel
between the adjacent endplates.
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The insertion tool 50 includes a pair of prongs 53 that are
disposed apart to define an end piece recess 54. For insertion of the
osteogenic fusion device 10 shown in FIG. 1, the end piece recess 54 is
configured so that the prongs 53 are in tight contact with the
truncated surfaces 21 of the second end piece 12. The outer surface of
the prongs 53 can conform to a portion of the outer surface 15 of the
first end piece 11.
The insertion tool 50 depicted in FIGS. 14-15 also includes tapered
tips 55 at the ends of each of the prongs 53. These tapered tips are
configured to be received within driving notches 41 in a modified first
end piece 40, as depicted in FIGS. 12-13. The osteogenic fusion device
depicted in FIGS. 12-13 is substantially similar to the osteogenic
fusion device 10 shown in FIG. 1, with the exception of the added
driving notches. The insertion tool 50 is configured so that the tips 55
project into the notches 41 while the prongs 53 directly contact the
truncated surfaces 21 of the second end piece 12. This particular
configuration of the insertion tool is particularly useful for threaded
insertion of the osteogenic fusion device. Preferably, the prongs 53
have an effective outer diameter that is approximately equal to the
diameter Di. Moreover, the prongs 53 can have an arc segment
configuration to complement the truncated surfaces 21. If the end
piece 12 is threaded (see FIG. 3), the prongs 53 can include
complementary threads along their length.
The present invention also contemplates a osteogenic fusion device
for restoring the normal lordotic angle of an intexvertebral segment.
Specifically, a lordotic osteogenic fusion device 60 includes a first end
piece 61 and a second end piece 62 as shown in FIG. 16. As with the
prior embodiments, a central element 63 is provided to connect the two
end pieces. The outer surface 65 of the first end piece 61 is in the
form of a frusto-conical surface. The outer surface 65 tapers toward
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the second end piece 62 at a preferred lordotic angle. Similarly, the
outer surface 66 of the second end piece 62 is also tapered at a similar
lordotic angle. Alternatively, the second end piece 62 can include
threads formed on the outer surface 66. While the threads 66 at the
smaller second end piece 62 may not contact the vertebral endplates at
the larger insertion end, the threads will contact the endplates at the
anterior end of the intradiscal space and will act as an anchor to resist
expulsion of the lordotic osteogenic fusion device 60.
The present invention contemplates several modifications to the
basic osteogenic fusion device 10. For example, the osteogenic fusion
device 70 shown in FIG. 17 includes first and second end pieces 71, 72
and a center piece 73 disposed between the two end pieces. First and
second central elements 74 and 75 connect each of the end pieces 71,
72 to the center piece 73. In this instance, the center piece 73 will
contact the interior of the disc endplates E. Osteogenic material, such
as carrier sheets 30, can be disposed or wound around each of the
central elements 74, 75 until the end of the bone growth-inducing
material is exposed at the outer surface of the osteogenic fusion device
70.
In a further modification, a osteogenic fusion device 80 depicted in
FIG. 18 includes first and second end pieces 81 and 82 that are
connected by a plurality of central beams 83. In the illustrated
embodiment as shown in FIG. 19, four such beams 83 are provided;
however, other arrangements and numbers of beams are
contemplated. Important aspects of the present invention are retained
by the osteogenic fusion device 80 because osteogenic material can be
supported by the several beams 83 between the first and second end
pieces 81, 82, with the bone growth-inducing material in direct contact
with the adjacent vertebral bodies.
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The two embodiments of FIGS. 20-21 and FIGS. 22-23 pose a
slight deviation from the general concept of the osteogenic fusion
device 10. In these two embodiments, the smaller diameter central
element 13 is replaced by a wall. In the embodiment of FIGS. 20-21, a
osteogenic fusion device 85 includes first and second ends 86, 87
separated by a central element 88. The first and second ends 86 and
87 can be in the form of short cylindrical sections, such as the first
end piece 11 of the osteogenic fusion device 10 in FIG. 1. While the
central element 88 can be in the form of a solid wall, the osteogenic
fusion device 85 preferably includes a number of apertures or slots 89
defined through the central element 88. In accordance with the
specific embodiment, the slots extend along substantially the entire
length of the central element 88. While the osteogenic fusion device 85
deviates somewhat from the concept of the osteogenic fusion device 10,
this latter osteogenic fusion device 85 retains the broad beneficial
feature of the present invention, namely provision for direct contact
between osteogenic material supported by the osteogenic fusion device
85 and the vertebral endplates. In the present instance, the osteogenic
material can be situated on opposite sides of the central element 88.
In addition, the material can be passed through the slots 89.
Preferably, the osteogenic fusion device 85 will be oriented within
the intervertebral disc space with the central element 88, or wall,
spanning between the adjacent vertebrae. This central element 88,
then, will provide additional structure and load bearing capability for
sustaining the spinal loads at the instrumented level.
The osteogenic fusion device 90 of FIGS. 22-23 operates on a
similar concept to the osteogenic fusion device 85. However, in this
instance, the first and second end pieces are in the form of arc
segments, rather than shortened cylinders. Specifically, the osteogenic
fusion device 90 includes upper and lower first arc segments 91u and
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91L, and upper and lower second arc segments 92u and 92L. The
osteogenic fusion device 90 also includes a central element 93 that is
again in the form of a wall connecting the first and second end pieces.
As can be seen most clearly in FIG. 23, the arc segments 91, 92 and
central element 93 define a pair of cavities 96 for containing osteogenic
material. In this embodiment, the osteogenic material can be
contained completely from end to end of the osteogenic fusion device
90. In the prior embodiments, the osteogenic material is contained
within retaining surfaces of the opposite end pieces. In accordance
with a specific embodiment, the osteogenic fusion device 90 includes a
plurality of apertures 94 defined in each of the upper and lower first
and second arc segments 91u, 91L, 92u and 92L. Similarly, a plurality
of apertures 95 can be defined through the central element 93. In this
manner, the apertures provide the maximum capacity for bone
ingrowth not only around, but also through the osteogenic fusion
device 90.
A osteogenic fusion device 100 shown in FIGS. 24-25 again
presents a slightly different concept. This osteogenic fusion device 100
includes a first end plate 101, a second end plate 102 and a central
element 103 that are similar to the like-named components of the
osteogenic fusion device 10. However, the osteogenic fusion device 100
also includes a side piece 104 spanning between the first and second
end pieces 101, 102. Moreover, unlike the osteogenic fusion device 10,
the first and second end pieces 101, 102 are not generally circular in
configuration, but are generally rectangular in configuration. In one
specific embodiment, the end pieces 101, 102 can include cutouts 105
at . opposite sides of the end pieces to provide further avenues for the
formation of a bony bridge between adjacent vertebrae. As with the
prior embodiments, the osteogenic fusion device 100 provides means
for adequately containing osteogenic material, such as in the form of
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the carrier sheet 30. In this embodiment, the carrier sheet 30 can be
wound around the central element 103, in the manner described
above. This particular embodiment of the invention, namely osteogenic
fusion device 100, is preferably adapted for use in the lumbar spine as
illustrated in FIG. 26 and in the cervical spine illustrated in FIG. 27,
and is consequently sized accordingly.
In many situations, it is preferable to use two fusion devices in a
posterior lumbar interbody fusion technique (PLIF) but there is not
enough lateral exposure to place two devices side-by-side. This
problem can be visualized, for example, by reference to FIG. 28. Two
osteogenic fusion devices, such as osteogenic fusion device 10, may be
placed side-by-side within a surgical window depicted by the dotted
Iine. As seen in FIG. 28, the two devices do not fit within the surgical
window presented. In many such cases, the facet joints must be
removed to make the surgical window larger, which may lead to spinal
instability.
In order to address this problem, at least one end piece of an
osteogenic fusion device may have a truncated surface, such as a
circular cutout, as depicted in FIG. 29. As seen in FIG. 29, two fusion
devices placed together thereby nest ar interleave and reside within the
operative window, and thus require no or minimal resection of the
facet joints during posterior insertion of the devices.
As more fully shown in FIGS. 30-32, osteogenic fusion device 110
is in many respects similar to osteogenic fusion device 10 depicted in
FIGS. 1 and 2 and includes, for example, opposite end pieces including
first end piece 111 and second end piece 112 and central element 113.
Each end piece defines two opposing surfaces as similarly described
for osteogenic fusion device 10. For example, first end piece 111
defines a bone contacting surface 114 and second end piece 112
defines a bone contacting surface 115. Bone contacting surface 115,
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in this embodiment, does not extend entirely around end piece 112.
Moreover, the bone contacting surface of second end piece 112 is
generally coincident with portions of the outer surface 114 of first end
piece 111 when the device is viewed along the longitudinal axis of its
central element I3. Second end piece 112 also includes two opposite
truncated surfaces 117 that are disposed between bone contacting
surfaces Z 15. Additionally, first end piece 111 includes external face
118 and internal face 119 whereas second end piece 112 includes
external face 120 and internal face 121. Osteogenic fusion device 110
is configured to nest with another osteogeni.c fusion device, including
other devices of the present invention. In the embodiment depicted in
FIGS. 30-32, the configuration of the osteogenic fusion device 110
includes a first end piece 111 having opposite faces, including opposite
edges I23, that define an entrance 124 to a cutout region 122. Cutout
region 122 is defined by truncated surface 1I6. Truncated surface
116, in this embodiment, is concave. As best seen in FIG. 31, first end
piece 111 has a minimum lateral dimension Ds transverse to a
maximum vertical dimension D4 between the two opposite surfaces
114. In the illustrated device, maximum vertical dimension D4 is
generally larger than minimum lateral dimension Ds. Vertical
dimension D4 has a height approximating the desired separation of the
adjacent vertebrae.
FIG. 33 depicts another embodiment, in which load bearing
member 130 has a first end piece 131 with a truncation adapted for
nesting and a second generally cylindrical end piece 132 having no
cutout regions.
The above-described osteogenic fusion devices configured to nest
may also bear modifications similar to those shown in FIGS. 3-13 and
I6-21, and their accompanying descriptions in the text above. For
example, osteogenic fusion devices having threaded end pieces, end
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pieces with apertures, and such devices having either center pieces, a
plurality of central elements and a central element defining a wall may
also be incorporated into osteogenic fusion devices such as those
described in conjunction with FIGS. 30-33. In devices with center
pieces, the center pieces may be substantially cylindrical with no
cutout regions or may be shaped with a cutout region as described
above. Moreover, the device can also include a bone growth-inducing
material as described above which may be wound around the central
elements of the devices, and if desired also shaped to allow for or
facilitate the nesting arrangement.
It is to be noted that the shapes of the opposing end pieces of the
load bearing members described above are preferably cylindrical and
may include a concave truncated surface. However, opposite end
pieces and truncated surfaces having any suitable geometrical shape
are contemplated as forming a part of the present invention.
The present invention also contemplates an implant system
including at least two load bearing members as described above and
wherein at least one load bearing member is configured to nest within
the other load bearing member. FIGS. 34-36 depict one embodiment
of the implant system including load bearing member 110 and load
bearing member 10 (as shown in FIGS. 1 and 2) having a substantially
cylindrical first end piece 11. First end piece 11 of load bearing
member 10 is nested within first end piece 11 I of load bearing member
110. In this particular embodiment as best seen in FIG. 36, width wi
of second end piece 112 of load bearing member 1 IO and width wz of
second end piece 12 of Load bearing member 10, when added together,
must be such that will not prevent first end piece 11 of load bearing
member 10 from nesting within first end piece 111 of first Ioad bearing
member I10.
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In yet a further embodiment, the load bearing members in a
nesting implant system may have an identical shape. For example,
FIG. 37 depicts a perspective view of two load bearing members 110
wherein first end piece 111 of one of the load bearing members is
nested within an identical end piece 111 of the other load bearing
member 110.
FIG. 38 shows implant system 150 of the invention which includes
load bearing member 160 and load bearing member 170. Load bearing
member 160 is similar to load bearing member 130 except that second
end piece 162 of load bearing member 160 is substantially cylindrical
with a cutout portion (i.e., it has the shape of first end piece 131 of
load bearing member 130). Load bearing member 170 is similar to Ioad
bearing member 130 except that first end piece 171 of load bearing
member 170 is substantially cylindrical, with no cutout regions. FIG.
38 further depicts first end piece 171 of load bearing member 170
nested within first end piece Z 61 of load bearing member 160 and
second end piece 172 of load bearing member 170 is nested within
second end piece 162 of load bearing member 160.
It is to be appreciated that the implant system may include first
and second load bearing members with end pieces arranged in a
variety of ways to achieve the nesting arrangement. For example, the
first and second load bearing members may each include one
truncated and one non-truncated end piece, such as that illustarated in
FIG. 33. In such an embodiment, the two devices can be used in
inverted relationship with respect to one another to achieve a nesting
relationship. For example, in implant system 180 shown in FIG. 39,
first end piece 191 of first load bearing member 190 and second end
piece 202 of second load bearing member 200 are truncated. Non-
truncated first end piece 201 of load bearing member 200 is nested
within first end piece 191 of load bearing member 190 and non-
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truncated second end piece 192 of load bearing member 190 is nested
within second end piece 202 of second load bearing member 200.
With reference now to FIGS. 40-42, shown is an implant system of
the invention including mated fusion devices and wherein the devices
are configured to connect to one another so as to resist lateral
separation of the devices. In preferred systems, such connection may
also provide increased resistance to expulsion due to the cooperation
of the two devices. In particular, the system 210 includes a first fusion
device 211 and a second fusion device 212. First fusion device 211
includes end pieces 213 having openings 214 serving as female
members. Second fusion device 212 includes end pieces 215 having
mating members 216 sized correspondingly to fit within openings 214
of device 212 and serve as male members. In this fashion, when
devices 211 and 212 are assembled as depicted in FIG. 40, the two
devices are connectedly mated so as to resist lateral separation from
one another and/or expulsion, desirably acting more as a single unit
when implanted in a patient. In this regard, devices 211 and 212 may
be mated prior to implantation and implanted as a single unit;
however, it is contemplated as preferred to implant a first of the
devices, e.g. device 211, and then to implant the second device, e.g.
212, by pushing or sliding the second device in next to the first
implanted device along the long axis, such that mating members 216
are received within openings 214 thus connecting the two devices to
one another. As illustrated, devices 211 and 212 are also configured
to nest to present a reduced lateral profile generally as described above
for certain devices. Thus, device 212 includes concave shoulder
portions 217, with mating member 216 located therebetween with its
outward end 218 extending radially outward to a distance which
allows the nesting relationship. In device 212, outward end 218
extends radially outward no further than the radius r of the
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predominant cylindrical shape of end piece 215. Devices 211 and 212
can optionally having outer surfaces configured to resist expulsion
from the space between adjacent vertebrae, for example threads,
ratchets, grooves or other like features. In one mode, one of the fusion
devices may include threads that facilitate controlled insertion, and
that device may be implanted first. The other fusion device of the
system can be of the push-in type, having no expulsion-resisting
features or those features commonly used for push-in devices, for
example ratchets or similar proturbances, or grooves. Still further, at
least one of the fusion devices can include a stop member to
controllably stop insertion of the second device by contact between the
two devices. For example, illustrated in FIG. 43 is a device 220 similar
to device 211, except including a stop member 221 positioned to be
contacted by mating member 216 of device 212, for example in a
procedure in which device 220 is implanted first with end piece 222
occurring distally, and device 212 is thereafter pushed in and mated
with device 220.
With reference now to FIG. 44, illustrated in another implant
system of the invention in which two adjacent fusion devices are
connected to one another. In particular, system 230 includes a first
fusion device 10 and a second fusion device 110 as described above.
In addition, system 230 includes a relatively thin connecting plate 231
spanning the end pieces of devices 10 and 110. Connectors 232, for
example screws, pins or the like, extend through plate 231 and into
the end pieces of devices 10 and 110. In this case, such end pieces
can include corresponding means for receiving connectors 232, for
example a threaded hole in the case. where connectors 232 are screws.
Implant system 230 having devices 10 and 110 connected in this
fashion at one or both ends will thus also desirably act more as a
single unit within the patient, desirably adding torsional resistance. It
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is contemplated that the devices 10 and 110 may be connected prior to
or after implant. In one mode, for example, devices 10 and 110 may be
implanted separately in the nested relationship, and only a single plate
231 used to connect the proximal (more accessible) end pieces.
Use of two large devices side-by-side in accordance with the
invention facilitates engagement of the devices into the vertebral body
endplates to distract the disc space and facilitate fusion. The larger
diameter devices provide other advantages over the use of two small
diameter devices. For example, the deeper the devices are placed into
the endplates, the more bleeding bone is exposed and the better the
chance for new bone formation. Moreover, the smaller diameter devices
do not get adequate distraction or stabilization in the end plate bone
allowing for motion which inhibits new bone formation. The larger
diameter devices are advantageously used in situations requiring less
lateral exposure to implant two devices side-by-side (i.e., bilaterally).
The design of the above-described devices that have cylindrical end
pieces with cutout regions can be used in current fusion cages that act
as containers, or baskets, for holding autograft chips and in allograft
bone dowels. Such a design allows for threading-in of the devices
much closer together as desired for a PLIF procedure. Moreover, the
instruments that indicate the correct vertical orientation of the cage for
bone thru-growth can also assist in orienting the cage cutout on the
medial side for mating with a second cage.
The present invention contemplates osteogenic fusion devices that
are formed of a material that is sufficiently strong to support the
adj acent vertebrae and to maintain the disc height of the instrumented
intervertebral space. For example, the osteogenic fusion devices, such
as osteogenic fusion device 10, can be formed of a biocompatible
sterilizable metal, such as stainless steel or titanium. Of course, other
medical grade materials are contemplated, such as certain ceramics,
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polymers, etc., as well as allograft and xenograft bone, provided the
materials axe sufficiently strong. The overall dimensions of each of the
osteogenic fusion devices described above depends upon the
instrumented level. For example, an osteogenic fusion device for use
in the cervical spine must necessarily be smaller than a osteogenic
fusion device used in the lumbar spine. Moreover, the relative
dimensions of the components of the osteogenic fusion devices may be
altered depending upon the vertebral level to be instrumented. For
example, a osteogenic fusion device, such as osteogenic fusion device
10, for use in the lumbar spine, may require a central element I3
having a diameter D2 that is more than one fourth of the outer
diameter D1 of the outer surface 15 of the first end piece 11. In some
instances, the lumbar spine may generate bending moments across a
osteagenic fusion device, such as osteogenic fusion device 10, that
would require a stronger central element 13.
In accordance with the present invention, the illustrated
osteogenic fusion devices can be of the push-in or threaded-in type. Of
course, the end pieces, such as end pieces 11, 12 of osteogenic fusion
device 10, and end pieces 111, 112 of osteogenie fusion device 110,
can include various surface characteristics known in the art for
enhancing the degree of fixation of the osteogenic fusion device
between the adjacent vertebrae. For example, the end pieces can
include certain macro surface features for penetrating the vertebral
endplates to resist expulsion of the osteogenie fusion devices.
Likewise, the surfaces, such as outer surface 15 and 114 and bone
contacting surface 20 and 115 can be provided with bane ingrowth
coatings so that a certain amount of bone , ingrowth occurs even
between the end pieces and the adjacent vertebral bodies.
With reference now to Figures 45 and 46, shown is another spinal
implant of the invention. Implant 240 includes two generally
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cylindrical end pieces, 241 and 242, and a central element 243
interconnecting the end pieces 241 and 242. Implant 240 is adapted
for implantation with central element 243 extending in the anterior-
posterior direction. End pieces 241 and 242 include features adapted
to resist expulsion of device 240 from the intervertebral space. These
features include directional teeth 244, which resist migration greater
in one direction than in an opposite direction. The illustrated device
would more readily be inserted with end piece 241 first, followed by
end piece 242. Teeth 244 would then resist migration in the opposite
direction, i.e. in the direction reverse to insertion. In this fashion, a
convenient, push-in device is provided, which can be forced into the
implant site manually or with the aid of an impact device.
Teeth 244 of implant 240 are formed as the edges of a plurality of
generally frusto-conical sections 245 of end pieces 241 and 242.
Implant 240 also includes a threaded tool-engaging hole 246, and a
tool-engaging slot 247, for cooperation with corresponding components
upon an insertion tool.
Figures 47-49 depict another inventive implant 250, having end
pieces 251 and 252 and a cylindrical central element 253. End pieces
251 and 252 are generally rectangular in shape, and include upper
surfaces 254 and 255 and lower surfaces 256 and 257 for contacting
respective upper and lower vertebral bodies. Upper surface 254 and
lower surface 255 of end piece 251 each include a series of directional
teeth 258 adapted to resist expulsion. Teeth 258 are formed as the
edges of elongate wedges 259 extending across the width of end piece
251 on its upper and lower surfaces 254 and 256. Each elongate
wedge 259 includes a first wall 259A and a second wall 259B
intersecting one another at an acute angle, preferably less than 80°
and more preferably about 60°C or less. Implant 250 may also include
a tool-engaging hole and a tool-engaging slot on the outer surface of its
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trailing end piece 252 as illustrated, similar to implant 240 of Figs. 45-
46.
Fig. 50 illustrates a spinal implant similar to that depicted in Figs.
47-49, except having directional teeth on the trailing end piece. In this
fashion, removal and adjustment of the implant after only partial
implantation is facilitated because fewer or none of the directional
teeth will yet be engaged between the vertebral bodies.
Illustrated in Fig. 51 is another implant 260 of the present
invention. Implant 260 is has the same features as implant 250
discussed above, except that implant 260 has directional teeth on the
upper and lower surfaces of each of its end pieces 261 and 262.
Figs. 52-53 illustrate another implant 270 in accordance with the
invention, which is similar in design to implants 250 and 260, except
that implant 270 lacks directional teach ar other surface proturbances
for resisting expulsion from the intervertebral space. Thus, the upper
and lower surfaces 271-274 of end pieces 271 and 272 are
substantially smooth surfaces for contact with adjacent vertebral
bodies.
With reference to Figs. 54-55, shown is another implant 280 of the
invention. Implant 280 includes end pieces 281 and 282 and central
elements 283 and 284, and as shown is adapted for push-in or
impacted insertion with these central elements extending in the
anterior-posterior direction, although modification for lateral
implantation is also contemplated within the invention. Implant 280 is
designed as a unitary spinal implant, as opposed to an implant
adapted for bilateral placement with another similar implant. Thus,
generally rectangular end pieces 281 and 282 of implant, 280 have a
width which is greater than their height, such width is sufficient to
extend substantially across the lateral dimension of the vertebral
bodies between which the implant will reside. End piece 281 provides
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upper surface 285 and a corresponding lower surface for contact with
adjacent vertebral bodies, and end piece 282 similarly provides upper
surface 286 and lower surface 287 for contact with the vertebral
bodies. Implant 280 also includes a centrally located tool-engaging
S hole 288 and a tool-engaging slot 289 generally as in other implants
discussed herein. Implant 280 may also have directional teeth on the
upper and/or lower surfaces of its end pieces 281 and 282 as
discussed for other implants herein.
Illustrated in Figs. 56-66 are additional spinal implants adapted
for unitary implantation in the spine. Such spinal implants can be
adapted for implantation with central elements extending laterally or in
the anterior-posterior direction in the patient. Thus, the central
elements will be of a length sufficient to position the end pieces to
contact the hard cortical bone of the apophysis on the lateral ends of
the vertebral endplates or at the anterior and posterior portions of the
vertebral endplates.
Referring now particularly to Figs. 56-58, shown are views of
spinal implant 290. Implant 290 has end pieces 291 and 292
interconnected by central element 293. End pieces 291 and 292 have
upper surfaces 294 and 295 and lower surfaces 296 and 297 for
contacting the vertebral endplates. In the device illustrated in Figs.
55-57, these surfaces are substantially smooth. Shown in Figs. 59-60
is an implant 300 similar to implant 290, except having surface
proturbances in the form of directional teeth 309 for resisting
expulsion. If desired, implants 290 and 300 can incorporate tool-
engaging holes (e.g. threaded) and/or tool-engaging slots on their
respective end pieces and/or on central elements thereof.
End pieces 29I and 292 of implant 290 and end pieces 301 and
302 of implant 300 each include a first, generally straight portion to
which the central elements are attached, terminating on each end into
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a curved portion forming an inwardly-extending arm extending
inwardly of the central element-end piece attachment point. In this
fashion a pocket is formed between the end pieces, configured to
contain an osteogenic material.
With reference to Figs. 62-63, shown is an implant 310 similar to
implants 290 and 300, except having generally arcuate end pieces 311
and 312 connected by central element 3I3. Arcuate end pieces 311
and 312 are sized and configured to substantially follow the contour of
the perimeter of the vertebral endplates, and have portions extending
inwardly of the central element-end piece attachment point and
forming a pocket between the end pieces 311 and 312 for containing
an osteogenic material.
Fig. 64 shows a device 320 similar to device 310, except
incorporating two central elements. Figs. 65-66 illustrate an implant
330 also similar to implant 310, except also incorporating a central
cylindrical support element 335 having a height substantially equal to
that of the end pieces 331 and 332, thus also contacting and
supporting the adjacent vertebral bodies.
Referring to Fig. 67, shown is another inventive implant 340
having generally cylindrical end pieces 341 and 342 connected by
generally cylindrical central element 343. Implant 340 is adapted for
threaded insertion, having a first set of threads 344 on end piece 341
and a second set of threads 345 on end piece 342. First threads 344
and second threads 345 are preferably discontinuous with respect to
one another. Thus, upon threaded insertion of implant 340, the
trailing end piece (e.g. 342) will follow a different thread path than the
leading end piece, thus facilitating securement of the implant 340
within the inter~rertebral space and resisting expulsion therefrom.
The present invention also provides methods of promoting fusion
bone growth in the space between adjacent vertebrae. The method
CA 02422710 2003-03-18
WO 02/24121 PCT/USO1/29349
-38-
advantageously includes providing the load bearing members or
implant systems described above, preparing adjacent vertebrae to
receive the load bearing member or implant system and placing the
load bearing member or implant system into the intervertebral space
after the preparing step. The load bearing members and implant
system may also include an osteogenic material within the pocket of
the devices that is arranged to contact the adjacent vertebrae when the
vertebrae are supported by the opposite end pieces of the device as
described more fully above.
While the invention has been illustrated and described in detail in
the drawings and foregoing description, the same is to be considered
as illustrative and not restrictive in character, it being understood that
only the preferred embodiments have been shown and described and
that all changes and modifications that come within the spirit of the
invention are desired to be protected.
