U.S. patent application number 09/729398 was filed with the patent office on 2002-06-06 for posterior expandable fusion cage.
Invention is credited to Jackson, Roger P..
Application Number | 20020068976 09/729398 |
Document ID | / |
Family ID | 24930850 |
Filed Date | 2002-06-06 |
United States Patent
Application |
20020068976 |
Kind Code |
A1 |
Jackson, Roger P. |
June 6, 2002 |
POSTERIOR EXPANDABLE FUSION CAGE
Abstract
An interbody device for use between a pair of adjacent vertebrae
includes a body and at least one expansion member. The body has
upper and lower walls that are joined by a rear wall that functions
as a spring hinge. The walls have anterior or distal ends that are
supported in a non-expanded configuration by spaced feet that
project out from the walls. The expansion member is elongate and
has a threaded portion that is threadably received in the rear
wall. Each expansion member also includes a head having an anterior
wedge portion that engages the anterior ends of the walls and
forces the walls apart as the expansion member is screwed into the
body. A surface engages the expansion member after expansion and
supports the walls during usage. Preferably, the expansion member
is only one of a plurality of expansion members found in a kit
which vary with respect to the diameter of the head thereof.
Inventors: |
Jackson, Roger P.; (Mission
Hills, KS) |
Correspondence
Address: |
John C. McMahon
PO Box 30069
Kansas City
MO
64112
US
|
Family ID: |
24930850 |
Appl. No.: |
09/729398 |
Filed: |
December 4, 2000 |
Current U.S.
Class: |
623/17.15 |
Current CPC
Class: |
A61F 2002/30507
20130101; A61F 2002/448 20130101; A61F 2002/30556 20130101; A61F
2002/30789 20130101; A61F 2250/0006 20130101; A61F 2230/0017
20130101; A61F 2/30744 20130101; A61F 2002/30593 20130101; A61F
2002/2835 20130101; A61F 2002/30904 20130101; A61F 2310/00023
20130101; A61F 2220/0025 20130101; A61F 2/4455 20130101; A61F
2002/30785 20130101; A61F 2310/00017 20130101; A61F 2250/0009
20130101; A61F 2002/30616 20130101; A61F 2002/30777 20130101; A61F
2002/30538 20130101; A61F 2/442 20130101; A61F 2002/30143 20130101;
A61F 2002/30774 20130101; A61F 2/447 20130101 |
Class at
Publication: |
623/17.15 ;
606/61 |
International
Class: |
A61F 002/44; A61B
017/58 |
Claims
What is claimed and desired to be secured by Letters Patent is as
follows:
1. A posterior interbody device that is anteriorly variably
expandable; said device comprising: a) a U-shaped body having an
upper wall and a bottom wall hingeably joined by rear wall; said
rear wall having a threaded bore, said upper and lower walls having
a non-expanded configuration; b) said upper and lower walls each
having an anterior mating region that face each other; c) an
elongate expansion member; said expansion member being threaded and
being operably threadedly received in said rear wall bore; d) said
expansion member having a wedge that is sized, shaped and
positioned to engage said upper and lower anterior mating regions
as said expansion member is threadedly advanced into said bore such
that anterior ends of upper and lower walls are urged into an
expanded configuration wherein said upper and lower walls become
spaced greater than said non-expanded configuration.
2. The device according to claim 1 wherein: a) said expansion
member has an axis of rotation; and b) said wedge is cylindrical
shaped and is coaxial with said axis of rotation.
3. The device according to claim 1 wherein: a) said expansion
member includes a support surface adjacent and anterior of said
mating region.
4. The device according to claim 3 wherein: a) said expansion
member is a first expansion member; and including in a set a second
expansion member such that said first and second expansion members
have cylindrical surfaces of different diameters so that said first
and second expansion members can be selectively individually used
with said body to produce different degrees of expansion of the
anterior end of said body.
5. The device according to claim 1 wherein: a) said expansion
member has an axis of rotation; b) said expansion member has a
threaded region near a posterior end thereof that is screwable into
a thread in said rear wall bore; c) said expansion member has a
head near an anterior end thereof; said head including said wedge
in the shape of a cylinder; said body including a supporting
surface anterior of said mating region that is sized, shaped and
positioned to engage and support said upper and lower walls when
said expansion member is fully inserted into said body; so that as
said expansion member is threadedly advanced into said body, said
wedge engages said upper and lower wall wedge mating regions and
vertically spreads the anterior ends of said upper and lower walls
while said walls hinge at a posterior end thereof and, thereafter
said support surface engages and supports anterior ends of said
upper and lower walls in a preselected anterior spaced
configuration.
6. The device according to claim 5 wherein: a) said expansion
member includes a stop located to limit advancement of said
expansion member into said body and to position said expansion
member in said body.
7. The device according to claim 6 wherein: a) said stop is
adjacent and posterior to said threaded region of said expansion
member and has a greater diameter than said threaded region.
8. The device according to claim 1 wherein: a) said body is
generally rectangular in cross-section.
9. The device according to claim 1 wherein: a) said upper and lower
walls each include a window positioned to allow growth of bone
therethrough during usage.
10. The device according to claim 1 wherein: a) said upper and
lower walls have anterior surfaces that engage when in a
non-expanded configuration such that said device is adapted to be
utilized alternatively as an expanded or non-expanded fusion
cage.
11. The device according to claim 1 wherein: a) said upper and
lower walls each include an anterior pair of spaced feet that
respectively engage and rest against feet of the opposite wall when
in the non-expanded configuration.
12. The device according to claim 1 wherein: a) when fully
inverted, said expansion member extends longitudinally through said
body from a posterior end thereof in said threaded bore to near an
anterior end thereof.
13. In an expandable posterior interbody fusion cage; the
improvement comprising: a) said cage having a U-shaped body having
upper and lower walls each with anterior mating regions near an
anterior end thereof; and b) an elongate expansion member that is
threadedly received in said body; said expansion member having a
head with an anterior wedge for operably engaging said body mating
regions and expanding an anterior end of said cage as said
expansion member advances into said body.
14. In a posterior expandable fusion cage; the improvement
comprising: a) an expansion kit including at least a pair of
interchangeable expansion members; each of said expansion members
being cooperatively mateable with said cage to provide a different
degree of anterior expansion of said cage.
15. The cage according to claim 14 wherein: a) said kit includes a
non-expansion plug.
16. The cage according to claim 15 wherein: a) at least one of said
non-expansion plug and expansion members includes a threaded region
for being threaded into a bore in a rear wall of said cage and said
threaded region includes a passageway therethrough to allow
insertion of matrix material into said cage after installation of
said one of said non-expansion plug and expansion members.
Description
BACKGROUND OF THE INVENTION
[0001] The present application is directed to an expandable
interbody device which is inserted from a posterior approach
between adjacent vertebrae in the spine of a patient and which is
also selectively anteriorly expandable.
[0002] Fusion cages, as well as other related interbody devices,
are frequently utilized in spinal surgery between vertebrae of a
patient. In particular, one or a pair of interbody devices are
placed between the vertebrae to provide support and promote fusion
between vertebrae where such is necessary due to disease, injury,
general deterioration or a congenital problem.
[0003] Frequently, the anterior sides or fronts of the vertebrae
also require additional spacing in comparison to posterior sides to
correct curvature of the spine. Therefore, it is often desirable to
use an anteriorly expandable interbody device so that the vertebrae
are spread or spaced more on the anterior sides thereof than on the
posterior sides thereof. It is seldom if ever desirable to space
the posterior sides of the vertebrae more than the anterior sides
thereof. Interbody devices which provide for anterior greater
expansion are generally referred to as interbody expansion devices
or expansion fusion cages. They are specifically expandable on the
anterior end thereof such that the fronts of the adjacent vertebrae
are more greatly spaced than the rears.
[0004] It is noted that interbody devices, such as fusion cages,
may be inserted into the intervertebral space anteriorly or
posteriorly. That is, in some instances the surgery is performed
from the front and sometimes from the rear of the patient. The
present application is directed to types of devices that are
inserted posteriorly or from the rear of the patient and are
generally referred to as posterior interbody devices or posterior
fusion cages.
[0005] Interbody devices typically must be very strong along the
entire length of the top and bottom walls of the device that engage
the vertebrae. In particular, in the turning and twisting of
everyday life, substantial forces can be exerted against the
interbody devices and, in particular, against the anterior end
thereof. This is even more so when the devices are subjected to
unusual forces during an accident or the like. Some types of
interbody devices in the prior art have provided for anterior
expansion, but have not well supported the anterior end of the
upper and lower walls. Such prior art devices have provided some
kind of a wedge or rod that is urged rearward along a ramp of the
device in such a way as to expand the anterior portion subsequent
to it being placed between the vertebrae. Because the wedge moves
rearwardly or posteriorly toward the back wall of the device in
order to spread the walls, a lever arm of unsupported wall is
formed between the front edge of each wall and the position where
the wedge engages the walls. Substantial forces can act on this
lever arm. The interbody devices poorly supported along the
unsupported wall can fail due to forces exerted along the lever arm
in the region.
[0006] Secondly, it is desirable for the interbody devices to not
expand sideways, while the devices are expanding vertically. This
need arises because it is often necessary to put interbody devices
in close proximity to one another in side by side relationship.
Sideways expansion may prevent desirable positioning of the
interbody devices and may also interfere with positioning of bone
chips for grafting between the interbody devices. Some prior art
devices expand radially which expands the devices vertically, but
also sideways.
[0007] When installing interbody devices, such as fusion cages, a
surgeon may also find that it is necessary to have more anterior
expansion than was initially anticipated in order to correct spinal
curvature. Consequently, it is often desirable to be able to
increase the expansion in increments that allow the surgeon to
determine whether expansion is sufficient after each incremental
advance in expansion and then further increase the expansion, if
necessary. Therefore, it is desirable to have a kit that provides
for alternative expansion devices, especially where such modular
expansion devices can each be screwed into and secured in place in
the cage so as to resist inadvertent removal during use.
[0008] Interbody devices, such as fusion cages, are quite expensive
to produce in general. This is because the body of the devices must
be made to very high tolerances in order to provide reproducible
results and to provide the strength necessary to support the spine
of the person. Because the surgeon is not always certain exactly
which expansion size interbody device will be required until the
surgery site is opened, it has been necessary for the surgeon to
have on hand many different sizes of fusion cages and, in some
cases, different types of fusion cages, such as expandable and
non-expandable, so as to insure that the necessary item will be
present when the surgery is performed.
[0009] Consequently, it is also desirable to be able to provide an
interbody device that is modular in nature and easily adjusted to
many degrees of expansion and that it may be used as efficiently
with no expansion as with expansion, so that the same body can be
used with different degrees of expansion. Many of the expandable
types of prior art fusion cages cannot be used as non-expandable
type cages.
[0010] Further, it is desirable for a single fusion cage body to be
utilized for virtually any degree of expansion desired or
foreseeable by simply providing a set of comparatively much less
expensive expansion members in a kit, any of which expansion
members may be used in conjunction with the body to provide for
various and different degrees of expansion and each of which may be
removed after insertion into a fusion cage body and replaced with a
different expansion member without removing the cage body from
between vertebrae.
SUMMARY OF THE INVENTION
[0011] A posterior interbody device or fusion cage for use between
a pair of adjacent vertebrae in order to provide support and/or
promote growth between the vertebrae that have been destabilized
due to injury, illness or the like. The interbody device includes a
body which may be rectangular in shape in which case the device is
slid or driven between the vertebrae or generally cylindrical in
shape and often threaded, in which case the device is screwed
between the vertebrae. The body has an upper wall and a lower wall
that are connected by a rear or posterior wall in a somewhat
U-shaped configuration. The body is hinged about the rear wall by
utilization of a material of construction that is flexible, such as
stainless steel or titanium, so that the rear wall functions like a
spring in conjunction with the upper and lower walls, so that the
upper and lower walls are able to pivot relative to each other at
the rear, when a spreading force is applied to the walls, which
causes the anterior ends of the upper and lower walls rotate from
an initial non-expanded configuration anteriorly to an expanded
configuration anteriorly. In particular, the upper and lower walls
are initially in a non-expanded state wherein the upper and lower
walls are generally parallel and subsequently may be expanded by a
plurality of expansion members to various expanded states wherein
the upper and lower walls are at angles relative to each other
which angles increase with expansion.
[0012] The upper and lower walls also have legs on either side of
the anterior end thereof that face toward similarly positioned legs
on the other wall and which abut against each other when the device
is in the non-expanded configuration thereof, so the cage can be
utilized operably in a non-expanded configuration. An aperture is
formed between the legs and preferably extends through the body in
such a manner as to form an interior chamber suitable for receiving
bone chips or other growth promoting media. The body also
preferably has upper and lower windows which communicate with the
chamber and open onto the surface of the vertebrae, when in use, so
as to promote growth of bone through the interbody device. The rear
wall of the body includes a threaded bore.
[0013] An expansion member, preferably having a shape similar to a
large headed bolt, is utilized to apply spreading force to the
upper and lower walls so as to expand the body anterior end. The
expansion member includes an elongate shaft having a rear portion
threaded so as to be operably and threadably received in the rear
wall bore and has a head at an opposite end. The shank includes a
stop, preferably adjacent the threaded rear portion abutting the
rear wall and being of enlarged diameter compared to and adjacent
to the threaded rear portion, which insures that the expansion
member is properly positioned during use.
[0014] The expansion member head varies in diameter depending on
the expansion desired. The expansion head is sized, and shaped in
position so as to engage a wedge mating or ramp surface located
anteriorly on facing surfaces of each of the lower and upper walls.
In particular, the expansion head first engages the mating surfaces
on the walls near the posterior end of the ramp surface and then
the mating surface slides along the ramp surface as the expansion
member is screwed into the rear wall bore. Alternatively, the ramp
may be associated with the wall and the expansion member then has
an edge or surface that mates with and slides along such a ramp in
the wall. In this manner the anterior end of the body is forced to
spread or space vertically until a forward or anterior end of the
ramp surface is reached. The ramp surface is adjacent to a support
surface that is generally parallel to an axis of rotation of the
expansion member and transfers the support of the upper and lower
walls to the support surface as the expansion member is further
rotated clockwise and advanced into the rear wall bore. Continued
advancement of the expansion member to the stop causes the head to
pass between the anterior ends of the upper and lower walls and to
be fully supported by opposed surfaces to thereafter provide
support to the upper and lower walls at the anterior ends thereof
and keep the upper and lower walls in a preselected spaced
relationship relative to each other.
[0015] Finally, in use each interbody device is normally provided
with a set or kit of expansion members wherein each member of the
set provides a different degree of spacing of the anterior end of
the interbody device, for example, with one half or one millimeter
differences in spacing between each size. In this manner, a surgeon
can utilize the interbody device without an expansion member or can
alternatively select from a number of expansion members with
different sized heads to provide appropriate expansion of the
anterior end of the interbody device. Normally, the surgeon would
start with no or minimal expansion and then increase incrementally
toward greater expansions until the surgeon is satisfied with the
expansion provided.
OBJECTS AND ADVANTAGES OF THE INVENTION
[0016] Therefore, the objects of the present invention are: to
provide a posterior interbody device or fusion cage for use between
a pair of vertebrae that is expandable; to provide such an
interbody device that has a body and at least one expansion member
wherein the expansion member includes a head that engages an
anterior portion of upper and lower walls of the body so as to
spread the body from the anterior end thereof; to provide such a
device wherein a single body may be utilized either without an
expansion member or in conjunction with any of an alternative group
of modular expansion members, each producing a different degree of
expansion and contained in a kit of expansion members; to provide
such a device wherein an expansion member that produces one degree
of expansion can be screwed into the body such that the body
expands and thereafter the expansion member can be removed and
another expansion member producing a greater degree of expansion
can be subsequently inserted; to provide such a device wherein the
expansion members include an anterior or frontward head that rests
on opposed anterior surfaces of the upper and lower body walls
subsequent to full insertion of the expansion member; to provide
such a device wherein the device expands vertically and not
horizontally or side to side; to provide such a device including a
central cavity and windows to allow for packing with bone chips or
other growth media so as to promote fusion between adjacent
vertebrae exposed to the windows; to provide such a device wherein
a single body may be alternatively utilized with a number of
different expansion members, such that multiple different sized
bodies are not required to be maintained in stock during a surgical
operation; to provide such a device that does not cantilever the
walls over a wedge that is medially located with respect to the
body, but rather positions the expansion head, ramp surfaces and
the support surfaces at or near the anterior end of the body at all
times during expansion, so as to continuously provide support to
anterior ends of the walls; and to provide such a device which is
relatively inexpensive to produce, extremely easy to use and
especially well adapted for the intended usage thereof.
[0017] Other objects and advantages of this invention will become
apparent from the following description taken in conjunction with
the accompanying drawings wherein are set forth, by way of
illustration and example, certain embodiments of this
invention.
[0018] The drawings constitute a part of this specification and
include exemplary embodiments of the present invention and
illustrate various objects and features thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a perspective and exploded view of an expandable,
posteriorly inserted interbody fusion device, illustrating a body
of the device in a non-expanded configuration and a plurality of
alternative expansion members.
[0020] FIG. 2 is a top plan view of the body in the non-expanded
configuration.
[0021] FIG. 3 is a cross-sectional view of the body, taken along
line 3-3 of FIG. 2.
[0022] FIG. 4 is a cross-sectional view of the body, taken along
line 4-4 of FIG. 2, and a non expanding member.
[0023] FIG. 5 is a cross-sectional view of the body, similar to the
view taken along line 4-4 of FIG. 2, with the non-expansion member
inserted therein and located between two vertebrae.
[0024] FIG. 6 is a cross-sectional view of the body, similar to the
view taken along line 4-4 of FIG. 2, with a first expansion member
partially inserted therein prior to expansion and located between
the vertebrae.
[0025] FIG. 7 is a cross-sectional view of the body, similar to the
view taken along line 4-4 of FIG. 2, with the first expansion
member fully inserted so that the body is expanded and located
between the vertebrae.
[0026] FIG. 8 is a front elevational view of the body with the
first expansion member fully inserted therein.
[0027] FIG. 9 is a cross-sectional view of the body similar to the
view taken along line 4-4 of FIG. 2, with a second expansion member
partially inserted therein prior to expansion and located between
the vertebrae.
[0028] FIG. 10 is a cross-sectional view of the body similar to the
view taken along line 4-4 of FIG. 2, with the second member fully
inserted therein and located between the vertebrae.
[0029] FIG. 11 is a cross-sectional view of the body similar to the
view taken along line 4-4 of FIG. 2, with a third expansion member
partially inserted therein prior to expansion and located between
the vertebrae.
[0030] FIG. 12 is a cross-sectional view of the body similar to the
view taken along line 4-4 of FIG. 2, with the third expansion
member partially inserted therein with partial expansion of the
body and located between the vertebrae.
[0031] FIG. 13 is a cross-sectional view of the body similar to the
view taken along line 4-4 of FIG. 2, with the third expansion
member fully inserted such that the body is anteriorly expanded and
located between the vertebrae.
[0032] FIG. 14 is a perspective view of a pair of the fusion
devices located between the vertebrae and being anteriorly
expanded.
DETAILED DESCRIPTION OF THE INVENTION
[0033] As required, detailed embodiments of the present invention
are disclosed herein; however, it is to be understood that the
disclosed embodiments are merely exemplary of the invention, which
may be embodied in various forms. Therefore, specific structural
and functional details disclosed herein are not to be interpreted
as limiting, but merely as a basis for the claims and as a
representative basis for teaching one skilled in the art to
variously employ the present invention in virtually any
appropriately detailed structure.
[0034] The reference numeral 1 generally designates an interbody
device or fusion cage in accordance with the present invention
having a body 5. The device 1 also includes a non-expansion member
6 and a set of expansion members, including expansion members 7, 8
and 9. The non-expansion member 6 and the expansion members 7, 8
and 9 are used individually and interchangeably or modularly in the
body 5, but only one at a time. The expansion member 9 is the
largest of the set and is seen in FIGS. 1 through 5 as well in
FIGS. 8 and 8a. The expansion member 7 is the smallest of the group
and is seen in FIGS. 6 and 6a. Although only three expansion
members are shown in the present embodiment and together with the
body 5 and non-expansion member 6 form a kit for use in spinal
surgery, it is foreseen that a much larger group of expansion
members, each having a different head diameter, could be included
in the kit with smaller size increments between the size thereof.
For example, the expansion members could each differ by one half,
one, or two millimeters in diameter or by other dimensions as
desired with additional larger sizes also as desired. Or in some
situations the kit may include only two expansion members.
[0035] The body 5 includes a top or upper wall 15, a bottom or
lower wall 16 and a posterior or rear wall 17. The upper wall 15
and lower wall 16 are joined near the posterior ends thereof to the
rear wall 17. As used herein posterior and anterior pertain to
configurations in the human body and posterior would be to the left
in FIG. 2, while anterior would be to the right in FIG. 2. The
upper wall 15 and lower wall 16 are initially in substantially
parallel relationship to one another and are urged to retain that
position or configuration by the springy or resilient nature of
materials of construction thereof which maintain the non-expanded
shape thereof unless force is applied to change that shape through
expansion members 7, 8 or 9.
[0036] Preferably the body 5 is constructed of a bio-compatible
metal, such as stainless steel or titanium or other material, and
the rear wall acts as a spring to try to maintain the upper wall
and lower wall 15 and 16 in parallel relationship while also
functioning as a hinge, when the upper and lower walls 15 and 16
are anteriorly forced apart by application of spreading force to
the walls 15 and 16.
[0037] The upper and lower walls 15 and 16 have bone engaging outer
surfaces 20 and 21 respectively which are serrated in such a manner
as to bite into the bone of vertebrae 24 and 25 respectively, after
being placed therebetween. The upper and lower walls 15 and 16 also
have fenestrations or windows 28 and 29 respectively. Although the
present embodiment is shown with a pair of each of the windows 28
and 29, it is foreseen in some circumstances that no windows would
be provided and in other circumstances different members of windows
may be provided in the walls 15 and 16.
[0038] Near anterior ends 30 and 31 of each of the walls 15 and 16
are legs 32 and 33 respectively. The legs 32 and 33 of each of the
walls 15 and 16 extend toward one another and abut or almost abut
when the body 5 is in a non-expanded configuration thereof, such as
is shown in FIG. 1, so as to maintain the non-expanded
configuration of the walls 15 and 16 when a load is applied
thereto. In this manner the front or anterior ends 30 and 31 of the
walls 15 and 16 are supported by the legs 32 and 33 in the
non-expanded configuration. Located on each wall 15 and 16 and
located behind each leg 32 and 33 is a ramp 38 and 39 respectively.
Each ramp 38 and 39 has a semicircular cross-section (see FIG. 3)
and slopes from the facing sides of walls 15 and 16 to facing
support surfaces 41 and 42 on the facing sides of the legs 32 and
33. The support surfaces 41 and 42 shown in the illustrated
embodiment are generally flat, but it is foreseen that the support
surfaces could have a central depression or the like to help guide
and stabilize the expansion member 7, 8 and 9. Immediately located
along and between the walls 15 and 16 are a pair of side windows 45
and 46.
[0039] The rear wall 17 includes a centrally located threaded bore
50. A bone chip receiving cavity 51 is located between the walls
15, 16 and 17.
[0040] The non-expansion member 6 has a plug body 53 with a
threaded outer surface 54 sized and shaped to be received in the
threaded bore 50. The plug body 53 also has a rear flange that is
larger in diameter than the surface 54 and operably functions as a
stop limiting penetration of the plug body relative to the threaded
bore 50. Extending into the rear of the plug body 53 is a hexagonal
shaped bore 56 sized and shaped to receive an Allen wrench tool or
the like (not shown) for operably rotating and driving the
non-expansion member 6 into the threaded bore 50.
[0041] Each of the expansion members 7, 8 and 9 include an elongate
shank 60 having a threaded posterior portion 61 that is sized and
shaped to be received in the rear wall threaded bore 50 and that is
similar in size and shape to the plug body 53. In the illustrated
embodiment the posterior portion 61 has a larger diameter than the
remainder of the shank 60 which reduces the space occupied by the
remainder of the shank 60, but both can be the same size in certain
embodiments. Also the posterior portion 61 may have an axial
extending opening to allow for inserting bone fragments into the
body 5 through the posterior portion 61. Each shank 60 also has a
stop 64 that is effectively a region of increased diameter located
at the posterior end of the threaded posterior portion 61 thereof.
The stops 64 insure that the expansion members 7, 8 and 9 will be
properly positioned when fully installed. Each of the expansion
members 7, 8 and 9 also include a head 66, 67 and 68
respectively.
[0042] The heads 66, 67, and 68 each include an outer cylindrical
shaped surface 69, 70 and 71 respectively coaxially attached to the
shank 60 thereof. During installation of the expansion members 7, 8
or 9 into the body 5, one of the cylindrical shaped surfaces 69, 70
or 71 as the case may be first engages the ramps 38 and 39 on the
anterior ends of the walls 15 and 16. While the present embodiment
surfaces 69, 70 and 71 have a forward edge, it is foreseen that an
angled conical shaped surface could function for this purpose also
in which case the ramps 38 and 39 could be more edge like in
nature. The cylindrical surfaces 69, 70 or 71 ultimately engage and
rest on the support surfaces 41 and 42.
[0043] As seen in FIG. 1, the heads 66, 67 and 68 of each of the
expansion members 7, 8 and 9 increase progressively in diameter. In
this manner the expansion members 7, 8 and 9 provide increasing
expansion of the anterior ends 30 and 31 of the body 5, as is seen
in FIGS. 7, 10 and 13 respectively, when fully inserted into the
body 5. A hexagonal bore 73, 74 or 75 is provided in the rear of
each of the members 7, 8 and 9 and is sized and shaped to mate with
an Allen wrench driver for rotating and torquing the members 7, 8
and 9.
[0044] In use the pad or disc located between a pair of vertebrae
24 and 25 is removed or partially removed and a pair of the bodies
5 are inserted by a posterior approach between the vertebrae 24 and
25. Once the bodies 5 have been positioned between the vertebrae 24
and 25 the surgeon checks to determine whether additional anterior
expansion is desirable. If additional expansion is desired,
normally the expansion member having the smallest expansion head
diameter, in this case expansion member 7, is inserted in each of
the bodies 5 and screwed into place. As the members 7 are screwed
inwardly, the heads 69 thereof engage the ramp surfaces 38 and 39
of the upper and lower walls 15 and 16 and space the anterior ends
30 and 31 of the upper and lower walls 15 and 16 respectively. The
surgeon then determines whether or not additional anterior
expansion is required. If further expansion is needed, the first
expansion member 7 is removed from each of the bodies 5 and the
second expansion member 8 of somewhat larger diameter is installed.
This process is continued until the surgeon is satisfied that the
proper expansion has been achieved. If no expansion is initially
needed the non-expansion member 6 is installed in the bore 50.
[0045] It is to be understood that while certain forms of the
present invention have been illustrated and described herein, it is
not to be limited to the specific forms or arrangement of parts
described and shown.
* * * * *