U.S. patent application number 09/918332 was filed with the patent office on 2003-02-06 for methods and devices for interbody spinal stabilization.
Invention is credited to Mathews, Hallett H..
Application Number | 20030028251 09/918332 |
Document ID | / |
Family ID | 36641633 |
Filed Date | 2003-02-06 |
United States Patent
Application |
20030028251 |
Kind Code |
A1 |
Mathews, Hallett H. |
February 6, 2003 |
Methods and devices for interbody spinal stabilization
Abstract
Methods and instruments for preparing a disc space and for
forming interbody devices therein are provided. The instruments
include distractors having enlargeable portions positionable in the
disc space for distracting the disc space. The enlargeable portions
can also provide form about or against which an interbody device of
a first material is placed. A second material may be placed in the
disc space in the space previously occupied by the distractors.
Inventors: |
Mathews, Hallett H.;
(Williamsburg, VA) |
Correspondence
Address: |
Douglas A. Collier
Woodard, Emhardt, Naughton, Moriarty and McNett
Bank One Center/Tower
111 Monument Circle, Suite 3700
Indianapolis
IN
46204-5137
US
|
Family ID: |
36641633 |
Appl. No.: |
09/918332 |
Filed: |
July 30, 2001 |
Current U.S.
Class: |
623/17.16 ;
623/23.62 |
Current CPC
Class: |
A61M 25/10 20130101;
A61B 2017/00261 20130101; A61F 2002/444 20130101; A61B 2017/0256
20130101; A61F 2310/00353 20130101; A61F 2/4601 20130101; A61F
2/4455 20130101; A61F 2002/2835 20130101; A61F 2/4611 20130101;
A61B 17/025 20130101; A61F 2002/4627 20130101; A61F 2002/30004
20130101; A61F 2002/2817 20130101; A61B 17/8855 20130101; A61B
2017/00243 20130101; A61F 2250/0014 20130101; A61B 17/8805
20130101; A61M 2210/02 20130101; A61B 2017/00557 20130101 |
Class at
Publication: |
623/17.16 ;
623/23.62 |
International
Class: |
A61F 002/44 |
Claims
What is claimed is:
1. A method for performing spinal surgery, comprising: accessing a
disc space between adjacent vertebrae; performing a discectomy in
the interspace; inserting an enlargeable portion of a distractor
into the disc space; enlarging the enlargeable portion of the
distractor to distract the disc space to a desired disc space
height, wherein the enlarged enlargeable portion is sized to form a
void in the disc space between the annulus and an exterior surface
of the enlarged enlargeable portion; and placing a material into
the void.
2. The method of claim 1, further comprising: curing the material;
reducing the size of the enlargeable portion of the distractor
after the material is cured; and removing the reduced enlargeable
portion of the distractor from the disc space.
3. The method of claim 2, further comprising: placing a second
material in the space previously occupied by the enlargeable
portion.
4. The method of claim 3, wherein the cured material and the
vertebral endplates substantially encapsulate the second
material.
5. The method of claim 3, wherein the second material is bone
growth material.
6. The method of claim 1, wherein the material is a cement.
7. The method of claim 1, wherein enlarging the enlargeable portion
of the distractor includes inflating the enlargeable portion of the
distractor.
8. The method of claim 7, wherein the enlarged portion of the
distractor is deflated to remove the enlargeable portion from the
disc space.
9. The method of claim 1, further comprising: removing
cartilaginous material from the vertebral endplates before
inserting the enlargeable portion of the distractor; and removing a
portion of the inner wall of the annulus before inserting the
enlargeable portion of the distractor.
10. The method of claim 1, further comprising selecting a
distractor including an enlargeable portion having a predetermined
vertebral endplate contact area.
11. The method of claim 1, further comprising inserting an
enlargeable portion of a second distractor in the disc space with
the enlargeable portion of the distractor.
12. The method of claim 11, further comprising enlarging the
enlargeable portion of the second distractor, wherein an inner wall
of an annulus encompassing the disc space, the enlarged enlargeable
portion of the distractor and the enlarged enlargeable portion of
the second distractor form the void.
13. The method of claim 12, further comprising: curing the
material; reducing the size of the enlargeable portion of the
distractor after the material is cured; removing the reduced
enlargeable portion of the distractor from the disc space; and
placing material into the space previously occupied by the enlarged
enlargeable portion of the distractor with the enlargeable portion
of the second distractor remaining in disc space.
14. The method of claim 13, further comprising: curing the material
placed in the space; reducing the size of the enlargeable portion
of the second distractor; withdrawing the enlargeable portion of
the second distractor from the disc space; and placing a second
material in the space previously occupied by the enlargeable
portion of the second distractor.
15. The method of claim 11, wherein the enlargeable portion of the
distractor is positioned at a first lateral location in the disc
space and the enlargeable portion of the second distractor is
centrally positioned in the disc space.
16. The method of claim 11, wherein the enlargeable portion of the
distractor is positioned at a first lateral location in the disc
space and the enlargeable portion of the second distractor is
positioned at a second lateral location in the disc space.
17. The method of claim 1, wherein accessing the disc space
includes: forming a first access port at a first postero-lateral
location of the spine; and forming a second access port at a second
postero-lateral location of the spine.
18. The method of claim 1, wherein accessing the disc space
includes accessing the disc space from an uni-portal approach.
19. The method of claim 1, wherein accessing the disc space
includes accessing the disc space from a foraminal approach.
20. The method of claim 1, wherein the enlargeable portion of the
distractor is configured to establish lordosis of the disc
space.
21. A method for performing spinal surgery in an interspace between
adjacent vertebrae, comprising: providing a distractor having an
inflatable distal end portion defining upper and lower vertebral
endplate contact surfaces having a predetermined area; inserting
the inflatable distal end portion of the distractor into the
interspace; inflating the distal end portion of the distractor to
distract the interspace to a desired interspace height, wherein a
void is formed in the interspace between the annulus and the
inflated portion; and placing material into the void.
22. A method for performing spinal surgery, comprising: accessing a
disc space between adjacent vertebrae; performing a discectomy in
the interspace; inserting an enlargeable portion of a distractor
into the disc space; enlarging the enlargeable portion of the
distractor to distract the disc space to a desired disc space
height, wherein the enlarged enlargeable portion is sized to form a
void in the disc space between the annulus and an exterior surface
of the enlarged enlargeable portion; placing a material into the
void; reducing the size of the enlargeable portion of the
distractor after the material is placed; and removing the reduced
enlargeable portion of the distractor from the disc space.
23. A method for performing spinal surgery in an interspace between
adjacent vertebrae, comprising: providing a distractor having an
inflatable distal end portion defining upper and lower vertebral
endplate contact surfaces having a predetermined area; inserting
the inflatable distal end portion of the distractor into the
interspace; inflating the distal end portion of the distractor to
distract the interspace to a desired interspace height, wherein a
void is formed in the interspace between the annulus and the
inflated portion; placing material into the void. reducing the size
of the enlargeable portion of the distractor after the material is
placed; and removing the reduced enlargeable portion of the
distractor from the disc space
24. A method for performing spinal surgery in the disc space
between adjacent vertebrae, comprising: providing a first
distractor having an inflatable distal end portion defining upper
and lower vertebral endplate contact surfaces; accessing the disc
space from at least one access port; inserting the inflatable
distal end portion of the first distractor into the disc space
through the at least one access port; inserting the inflatable
distal end portion of the second distractor into the disc space
through the at least one access port; and inflating the first and
second distal end portions to distract the disc space.
25. The method of claim 24, wherein a void is formed in the disc
space between the inflated first and second inflatable distal end
portions and the annulus; and further comprising placing material
into the void.
26. The method of claim 24, wherein the inflatable distal end
portion of the first distractor has a distraction height that
differs from a distraction height of the inflatable distal end
portion of the second distractor.
27. The method of claim 24, wherein: the inflatable distal end
portions of the first and second distractors each define a banana
shape; accessing the disc space includes accessing the disc space
with opposite first and second postero-lateral access ports; the
first distractor is positionable through the first access port with
its banana shaped distal end portion positioned along a first
portion of the apophyseal ring of the vertebral endplates; and the
second distractor is positionable through the second access port
with its banana shaped distal end portion positioned along a second
portion of the apophyseal ring of the vertebral endplates.
28. The method of claim 27, wherein the inflatable distal end
portion of the first distractor has a distraction height that
differs from a distraction height of the inflatable distal end
portion of the second distractor.
29. The method of claim 24, wherein the at least one access port
provides a postero-lateral approach to the disc space.
30. A method for performing spinal surgery, comprising: preparing a
spinal disc space for insertion of a form; positioning the form in
the spinal disc space wherein a void is formed around the form;
placing a first material in the void and in contact with the
vertebral endplates on either side of the spinal disc space;
removing the form; and placing a second material in the position
that was occupied by the removed form.
31. The method of claim 30, wherein the first material has a fluid
state while placing the first material and after placing the first
material changes to a second condition after wherein the first
material provides a solid interbody device extending between the
vertebral endplates.
32. The method of claim 30, wherein the form is an enlargeable
portion of a distractor.
33. The method of claim 30, wherein preparing the spinal disc space
includes: accessing the spinal disc space from a pair of opposite
ports each inserted from a postero-lateral approach; and performing
a discectomy through at least one of the ports.
34. A method for performing spinal surgery, comprising: preparing a
spinal disc space for placement of a first material therein;
forming a void in the spinal disc space; placing a first material
in the void and in contact with vertebral endplates on either side
of the spinal disc space and in contact with an inner annulus wall;
forming a cavity in the first material; and placing a second
material in the cavity.
35. The method of claim 34, wherein forming the void includes:
inserting an enlargeable portion of a distractor into the disc
space in a reduced-size configuration; and enlarging the
enlargeable portion of the distractor in the disc space.
36. The method of claim 35, wherein enlarging the distractor
distracts the disc space to a desired disc space height.
37. A spinal surgical instrument for distracting a disc space,
comprising: a shaft extending between a proximal end and a distal
end; and an inflatable portion adjacent said distal end, said
inflatable portion having a reduced size configuration for
insertion into the disc space and an enlarged inflated
configuration, wherein when in said inflated configuration said
inflatable portion defines an upper vertebral endplate contacting
surface and an opposite lower vertebral endplate contacting
surface, each of said upper and lower vertebral endplate contacting
surfaces having a vertebral endplate contacting area in the range
of 0.1 square inches to 0.5 square inches.
38. The instrument of claim 37, wherein said shaft defines an
inflation lumen in communication with said inflatable portion.
39. The instrument of claim 37, wherein each of said vertebral
endplate contacting surfaces has an oval shape.
40. The instrument of claim 37, wherein each of said vertebral
endplate contacting surfaces has a circular shape.
41. The instrument of claim 37, wherein each of said vertebral
endplate contacting surfaces has a generally rectangular shape.
42. The instrument of claim 37, wherein each of said vertebral
endplate contacting surfaces has a first contacting node and a
second contacting node and said inflatable portion includes a
concave surface extending between said first and second contacting
nodes.
43. The instrument of claim 42, wherein when in said inflated
configuration said inflatable portion is sized to contact vertebral
endplates adjacent the disc space and restore the disc space to a
desired disc space height, said inflatable portion is further sized
and shaped in the anterior, posterior and lateral directions to
occupy the disc space with a void formed between the inflatable
portion and an inner wall of an annulus surrounding the disc space
annulus.
44. A spinal surgical device implantable in a disc space,
comprising: a shaft extending between a proximal end and a distal
end; and an inflatable portion adjacent said distal end, said
inflatable portion having a reduced size configuration for
insertion into the disc space and an enlarged inflated
configuration, wherein when in said inflated configuration said
inflatable portion is sized to contact vertebral endplates adjacent
the disc space and restore the disc space to a desired disc space
height, said inflatable portion is further sized and shaped in the
anterior, posterior and lateral directions to occupy the disc space
with a void formed between the inflatable portion and an inner wall
of an annulus surrounding the disc space annulus; and a first
material in the void.
45. The device of claim 44, wherein said shape is selected from the
group consisting of: a vertically-oriented cylinder, a
horizontally-oriented cylinder, a sphere, a center cylinder with
frusto-conically tapered ends, a banana, and a pear.
46. The device of claim 44, wherein when inflated said inflatable
portion defines an upper vertebral endplate contacting surface and
an opposite lower vertebral endplate contacting surface, each of
said upper and lower vertebral endplate contacting surfaces having
a vertebral endplate contacting area in the range of 0.1 square
inches to 0.5 square inches.
47. The device of claim 44, wherein said shaft defines an inflation
lumen in communication with said inflatable portion.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to instruments and
devices for spinal surgery, more particularly to methods and
devices for spinal disc space preparation and interbody spinal
stabilization.
BACKGROUND OF THE INVENTION
[0002] There are prior art interbody devices that are fabricated
prior to implantation and then inserted into the patient's spinal
disc space during surgery. It is also known to insert one or more
pre-fabricated devices from anterior, antero-lateral, lateral,
postero-lateral, transforaminal, posterior, posterior mid-line or
any other known approach to the disc space. These pre-fabricated
devices can require the surgeon to modify the interbody device, the
vertebral bodies, and/or the vertebral endplates to achieve a
desired fit between the spinal anatomy and the interbody device.
While some pre-fabricated devices can be modified before and during
surgery by the surgeon, this is a time consuming task and also does
not always result in a desired or optimum fit with the natural or
altered spinal anatomy. Further, the various approaches and
instruments required to insert pre-fabricated devices can be
invasive and traumatic to the nervature, vasculature, and tissue
between the skin and the disc space.
[0003] What is therefore needed are methods and devices for
providing interbody devices in a disc space between vertebral
bodies that allow the surgeon to achieve a desired or optimum fit
between the device and the natural or altered spinal anatomy. What
is also needed are devices and methods for preparing a disc space
for an interbody device while minimizing invasion into the tissue
between the skin and the subject disc space. What is further needed
are improved devices and methods for performing spinal surgery.
What is also needed are methods and devices for providing interbody
fusion utilizing minimally invasive approaches and instruments. The
present invention is directed toward meeting these needs, among
others.
SUMMARY OF THE INVENTION
[0004] According to one aspect of the present invention, there is
provided a form positionable in a spinal disc space and an
interbody device made from material that has a first condition
allowing placement around the form and in contact with the
vertebral endplates and thereafter the material has a second
condition that provides structural support between the
endplates.
[0005] According to another aspect of the invention, there is
provided a distractor for a disc space that has a reduced-size
configuration for insertion into a disc space and an enlarged
configuration for distracting the disc space and for defining a
void between the enlarged portion and the inner wall of the disc
space annulus.
[0006] According to yet another aspect of the invention, a spinal
disc space distractor provides an intradiscal form around which an
interbody device is placed.
[0007] According to a further aspect of the invention, a spinal
disc space distractor having an enlargeable portion is
provided.
[0008] According to a further aspect of the invention, a spinal
disc space distractor having an enlargeable portion with upper and
lower vertebral endplate contact surfaces with predetermined areas
is provided.
[0009] According to another aspect of the invention, a surgeon
inserts a distractor in a spinal disc space and places a first
material around the distractor and between the vertebral endplates.
When the first material cures, the distractor is withdrawn and a
second material is placed in the disc space in the space that was
occupied by the distractor.
[0010] According to a further aspect of the invention, multiple
distractors having enlargeable distracting portions are inserted in
the disc space to form a void for receiving a first material
[0011] According to another aspect of the invention, a disc space
is bi-laterally distracted by inserting an enlargeable portion of a
first distractor at a first lateral disc space location and an
enlargeable portion of a second distractor at a second lateral disc
space location. Scoliosis can be addressed by providing the
enlargeable portions with different distraction heights.
[0012] According to a further aspect of the invention, a spinal
disc space distractor having an enlargeable portion of a
predetermined shape is provided. The predetermined shape is
selected from one of the following: vertically-oriented cylinder,
horizontally-oriented cylinder, sphere, cylindrical center portion
with frusto-conical tapered ends; banana-shaped, and pear
shaped.
[0013] These and other aspects, forms, features and advantages will
be apparent from the following description of the illustrated
embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is diagrammatic illustration in the axial plane of a
spinal disc space with instruments positioned therein for
performing a discectomy procedure.
[0015] FIG. 2a is a diagrammatic illustration of the disc space of
FIG. 1 with a distractor having an enlargeable portion positioned
therein.
[0016] FIG. 2b is a diagrammatic illustration looking in the
direction transverse to the sagittal plane of the spinal column
segment encompassing the disc space and the distractor of FIG.
2a.
[0017] FIG. 3a is a diagrammatic illustration of the disc space of
FIG. 2a with the distractor disposed therein along with a material
delivery instrument.
[0018] FIG. 3b is a diagrammatic illustration of the disc space of
FIG. 3a with a first material being delivered around the enlarged
portion of the distractor.
[0019] FIG. 3c is a sectional view of an alternate embodiment
enlargeable distractor and material delivery instrument according
to the present invention.
[0020] FIG. 4 is a diagrammatic illustration of the disc space of
FIG. 3b after the first material has cured and the enlargeable
portion of the distractor in a reduced size configuration for
removal from the disc space.
[0021] FIG. 5 is a diagrammatic illustration of the disc space of
FIG. 4 with a second material in the disc space within the cured
material.
[0022] FIG. 6 is a diagrammatic illustration of in partial section
through line 6-6 of FIG. 5.
[0023] FIG. 7 is a diagrammatic illustration of the partial
sectional view of FIG. 7 showing posterior stabilization
instrumentation secured to the spinal column segment across the
disc space.
[0024] FIG. 8 is a diagrammatic illustration in the axial plane of
a spinal disc space having a pair of distractors having enlargeable
portions for bi-lateral distraction of the disc space.
[0025] FIG. 9 is a diagrammatic illustration of a spinal disc space
having another arrangement for dual distractors along with a first
material positioned at a first lateral location in the disc
space.
[0026] FIGS. 10a-10c show a side view, an end view and a plan view,
respectively, of one embodiment of an inflatable distractor.
[0027] FIGS. 11a-11c show a side view, an end view and a plan view,
respectively, of another embodiment inflatable distractor.
[0028] FIGS. 12a-12c show a side view, an end view and a plan view,
respectively, of another embodiment inflatable distractor.
[0029] FIGS. 13a-13c show a side view, an end view and a plan view,
respectively, of another embodiment inflatable distractor.
[0030] FIGS. 14a-14c show a side view, an end view and a plan view,
respectively, of another embodiment inflatable distractor.
[0031] FIGS. 15a-15c show a side view, an end view and a plan view,
respectively, of another embodiment inflatable distractor.
[0032] FIGS. 16a-16c show a side view, an end view and a plan view,
respectively, of another embodiment inflatable distractor.
[0033] FIGS. 17a-17c show a side view, an end view and a plan view,
respectively, of another embodiment inflatable distractor.
[0034] FIG. 18 is a graphical representation of the load applied to
the vertebral endplates versus inflation pressure for inflatable
distractors having various vertebral endplate contact areas.
DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0035] 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 limitation of the scope of the invention is thereby
intended. Any such alterations and further modifications in the
illustrated devices, and any such further applications of the
principles of the invention as illustrated herein are contemplated
as would normally occur to one skilled in the art to which the
invention relates.
[0036] The present invention provides techniques for forming
interbody devices in a disc space of the spinal column. It is
contemplated that techniques of the present invention utilize
minimally invasive endoscopic instruments and methods for
performing discectomy and other disc space preparatory procedures.
However, open surgical techniques and other visualization
instruments and techniques are also contemplated. In techniques
where the interbody device is part of a spinal fusion procedure,
percutaneous stabilization and fixation techniques through the
pedicles or facets are also possible after completing insertion of
the interbody device. The present invention further provides
minimally invasive techniques for segmental stabilization of a
spinal disc space to repair a spinal disc space due to, for
example, disc space collapse or progressive mono-segmental
instability which are normally repaired via discectomy procedures
that do not include interbody fusion. The present invention has
application from any approach to any disc space along the spinal
column, including L5-S1. Further, the present invention has
application in a bi-portal, postero-lateral approach to one or disc
spaces in the lumbar region of the spine.
[0037] Reference will now be made to FIGS. 1-7 to describe methods,
instruments and materials according to the present invention to
provide an interbody device formed in situ in the disc space that
conforms with the patient's vertebral endplate anatomy. FIG. 1
shows an outline in plan view of a spinal disc space and lower
vertebral body 10b in plan view during a discectomy procedure. The
anterior aspect of the spinal column is indicated by "A" and the
posterior side is indicated by "P." The lateral aspects of the
spinal column extend between A and P on each side the spinal
column. As shown further in FIG. 2b, the subject spinal disc space
is located between an upper vertebra 10a having an inferior
endplate 11a and a lower vertebral 10b having a superior endplate
11b. The disc space has a nucleus 12 that is surrounded by an
annulus 14. First and second pedicles 16a extend posteriorly from
upper vertebral body 10a, and first and second pedicles 16b extend
posteriorly from lower vertebral body 10b. The spinal cord or dura
17 extends along the posterior aspect of vertebrae 10a, 10b.
[0038] In FIG. 1 there are shown instruments inserted via a
bi-portal approach to the disc space that are useful in completing
a nucleotomy or a discectomy of the spinal disc. The instruments
for performing this procedure can include a scope 20 and a
discectomy instrument 22. In the illustrated embodiment, discectomy
instrument 22 and scope 20 are inserted through first access port
18 and second access port 19, respectively, in a postero-lateral
approach to the disc space. Access ports 18, 19 can each be a
working channel cannula to provide a protected first and second
postero-lateral access ports to the disc space. It is to be
understood that aspects of the present invention contemplate
approaches and combinations of approaches to the disc space other
than a postero-lateral approach, such as a lateral approach,
anterior approach, or antero-lateral approaches. It should be
understood that uni-portal disc space access is contemplated, as
well as bi-portal disc space access from the same side of the
spinal disc space or from differing approaches, such as a lateral
approach and a postero-lateral approach. It is further contemplated
that open surgical procedures could be utilized for the
discectomy.
[0039] In one specific surgical technique used with the present
invention, the disc space in the lumbar region of the spine is
accessed endoscopically via a foraminal or postero-lateral,
bi-portal approach. Cannulas and dilators can be used for access
ports 18, 19 and catheters inserted therethrough for visualization,
discectomy procedures, distraction, and material delivery. In these
approaches, the outer cannulas can have an outside diameter of up
to 7.5 millimeters and more typically in the range of about 6.5
millimeters. However, any sized cannula is contemplated so long as
there is an acceptable level of trauma to the tissue and nerve
structures.
[0040] To provide access ports 18, 19 in this specific technique,
insertion begins 9 to 13 centimeters from the midline with a
guidewire or discogram needle. The facet joint at the dome of the
facet is initially targeted and palpated by the tip of the needle.
The needle is withdrawn and re-angulated to go inside the dome,
thus missing the exiting nerve root. The posterior vertebral
bodyline is imaged fluoroscopically to document its resting
position. The fluoro machine is then moved to an A-P position and
the resting zone is either on the mid or lateral pendicular
starting position for a postero-lateral approach or the medial
pendicular midline for a foraminal approach. Needle insertion into
the disc space can be completed simultaneously on the left and
right hand sides. The needles can be triangulated to touch one
another in the posterior central portion of the disc space or
alignment can be adjusted and conformed via discography.
[0041] One or more dilators of increasing diameter are then
sequentially placed over each of the needles to the annulus, and a
cannula is placed over each of the final dilators to land on the
annulus. The final dilators are removed and a trephine used through
each cannula to cut holes in the annulus to allow for entry into
the disc space. An endoscope can be used at any time throughout the
procedure to document the presence of nerve roots or to observe the
annulus prior to cutting. The final dilator is then re-inserted
into each of the cannulas and impacted through the hole in the
annulus and into the disc space. The final dilator thus secures the
cannula into position and obstructs the annulus opening to ensure
material is delivered into the disc space without excursion out of
the disc space. The cannulas and dilators are then used as access
portals to the disc space for completion of the remaining
procedures, and also allow for the interchange of instruments
between the left and right sides. Either one of the access ports
18, 19 can then be used for endoscopic visualization and the other
access portal 18, 19 can be used for disc material removal with
manual, automated, ultrasonic, laser, or any other disc material
removal instruments desired by the surgeon.
[0042] After discectomy there is a prepared disc space 24. It can
also be desired by the surgeon to expose and gently remove endplate
cartilage and to remove all soft tissue and debris from within the
disc space to expose the inner wall of the annulus. Inner portions
of a minimally appropriate amount of the inner wall laminates of
annulus 14 surrounding the removed nucleus can be removed to
increase the lateral and anterior-posterior extent of the prepared
disc space 24. The remaining portion of the annulus remains intact
except for the access holes cut for instrument entry locations. An
endoscope can be placed in one of the access portals to check disc
material removal and to also check the annulus to ensure there are
no wall defects requiring repair. In cases where interbody fusion
is desired, the endplates can be prepared by eburnating the
apophyseal ring to prepare it for bony fusion, and the vertebral
endplates can be scraped or abraded to reduce them to bleeding
bone. Right angle curettes or probes can also be inserted to make
small protrusions or abrasions into the endplates to further
facilitate fusion if so desired.
[0043] After disc space access and discectomy, the disc space will
typically still be in a collapsed state, and the only distraction
that has been completed at this point has been the result of
insertion of the final dilator into the disc space. The disc space
must now be further distracted to the desired disc space height and
also to establish lordosis if desired or necessary. Referring now
to FIGS. 2a-2b, a distractor 30 is inserted into the prepared disc
space 24. Distractor 30 has a shaft 32 extending between a distal
end 36 and a proximal end 38 situated outside the disc space.
Adjacent distal end 36 there is an enlargeable portion 34
positionable in prepared disc space 24. Enlargeable portion 34 is
inserted into the disc space in a reduced size configuration, and
after proper positioning in prepared disc space 12 is confirmed
endoscopically, fluoroscopically or via any other visualization
technique, is thereafter enlarged to contact endplates 11a, 11b and
distract the disc space to the desired height.
[0044] Enlargeable portion 34 is sized with respect to prepared
disc space 24 such that a void 26 is formed between the enlarged
portion 34, inner wall of annulus 14, and the endplates 11a, 11b
generally in the location of the apophyseal ring as shown in FIG.
3a. In one form, enlargeable portion 34 is an inflatable balloon or
cuff-type structure that is inserted into the disc space in a
deflated condition and thereafter inflated via an inflation lumen
through shaft 32 to a predetermined pressure with air, gas, or
liquid from an inflation source 39. A valve 37 can be provided on
shaft 32 to block the lumen therethrough and maintain the inflation
pressure in enlargeable portion 34. It is further contemplated that
enlargeable portion 34 could be made from any material capable of
assuming a reduced sized for insertion and withdrawal from the
prepared disc space and enlargeable for disc space distraction,
such as an elastomer, polymer, shape memory material or spring
steel. Examples of various types of inflatable devices are
described further below with respect to FIGS. 10-17.
[0045] In any event, enlargeable portion 34 is sized in the
cephalad-caudal directions sufficiently to distract the spinal disc
space to a desired normal disc space height and sized in the
lateral and anterior-posterior directions to provide void 26 when
enlarged. A single centrally placed enlargeable distractor 30 could
utilize endplate geometry to create lordosis.
[0046] In addition to a single distractor having an enlargeable
portion inserted into the disc space as shown above with respect to
FIGS. 1-7, other distraction instruments and techniques are
contemplated. For example, if the enlargeable portion of the
distractor is inflatable, then the enlargeable portion 34 can be
provided with dual chambers of differing heights to establish a
lordotic effect. In another example, multiple distractors having
different height enlargeable portions 34 can be inserted and
positioned at the appropriate locations in the disc space and be
enlarged together to provide the desired endplate angulation.
[0047] As further shown in FIGS. 3a and 3b, with distractor 30
enlarged and maintaining disc space distraction, a material
delivery instrument 40 is inserted into the disc space in the
access port opposite the distractor access port. Material delivery
instrument 40 includes a working channel 42 through which a first
material 50 can be delivered through a distal opening 44 and into
void 26. First material 50 has a first condition that allows it to
be selectively placed, injected, flowed, moved or otherwise
migrated around the enlargeable portion 34 in void 26 such that all
or substantially all of void 26 is occupied by first material 50.
First material 50 thereafter changes, cures or transforms from its
first condition into a second condition in which it forms a solid
or semi-solid interbody device 50' in space 26, as shown in FIG. 4,
capable of structurally supporting the vertebrae at the desired
disc space height. Interbody device 50' thus conforms to the
patient's vertebral endplate anatomy and also conforms to the shape
of void 26 between enlargeable portion 34 and annulus 14.
[0048] It is contemplated that first material 50 can be a cement,
poly(methyl methacrylate), or any other bio-compatible material
that has the structural capabilities to withstand the spinal column
loads applied thereto. It is further contemplated that first
material 50 can be delivered in a first condition through an
instrument channel or lumen of instrument 40 and thereafter changed
to a second condition via any natural or chemically induced or
enhanced reaction to form an interbody device 50'. First material
50 can further be static or include bio-active material to promote
bone growth.
[0049] While delivery instrument 40 is illustrated as an instrument
separate from distractor 30, it is also contemplated that
distractor 30 could be provided with a working channel for delivery
of first material 50 to void 26 or second material 60 to central
space 52'. For example, as shown in FIG. 3c, distractor 30' has a
shaft 32' and an inflatable enlargeable portion 34'. Shaft 32'
defines an inflation lumen 32a' in communication with the interior
of enlargeable portion 34'. Shaft 32' further include a material
delivery lumen 32b' extending through enlargeable portion 34' and
opening at distal end 36'. After distraction with enlargeable
portion 34', first material 50 can be delivered through lumen 32b'
into void 26. Such an instrument could be employed for uni-portal
material delivery and disc space distraction, or used in
combination with material delivery instrument 40 or another
distractor 30' in the opposite access port to provide bi-portal
material delivery. It is further contemplated that delivery
instrument 40 can be a flexible cannula or catheter that can be
moved or manipulated around void 26 in order to deliver first
material 50 to all portions thereof. Material delivery instrument
40 can further be provided with endoscopic capabilities to allow
visualization and direct viewing of material delivery.
[0050] In another form, one or more flexible material delivery
catheters can be placed over a guide wire extending through one of
the access portals and into the disc space around enlargeable
portion 34 and at various locations in void 26. The flexible
catheter(s) can be placed through only one or both of the access
portals 18, 19. With the desired distraction achieved and the
material delivery catheters positioned as desired, the guide wires
are removed and first material 50 delivered through the flexible
catheter(s). First material 50 can be delivered sequentially
through the catheters or simultaneously through the catheters to
provide an interbody device 50' that is completely formed about
enlargeable portion 34 except for an entry port to central cavity
52'. Interbody device 50' thus provides balanced spinal load
support on the apophyseal ring. Second material 60 can then be
placed centrally into the interbody device in the central cavity
52' previously occupied by the withdrawn enlargeable portion 34 of
distractor 30.
[0051] One specific technique for placement of first material 50
via bi-portal, postero-lateral access ports was completed as
follows. The material delivery instrument 40 included first and
second material delivery catheters each placed in a respective one
of the first and second access ports 18 and 19. First material 50
was delivered through one catheter through the first access port
under low pressure until the presence of first material 50 was
detected at the distal end of the first access port or the second
access port. The catheter was then slowly pulled back through the
first access port until first material 50 was delivered to the
distal end of the first access port housing the first delivery
catheter. Thereafter the first material delivery catheter was
withdrawn. First material 50 was then delivered through the second
material delivery catheter positioned in the second access port
until first material 50 was detected at the distal end of either of
the second access port or the first access port. The second
material delivery catheter was then pulled back through the second
access port, thereby completely filling the void 26 with first
material 50.
[0052] Several factors are to be considered in placing first
material 50 in the disc space. For example, if first material 50
were a cement, factors to consider include the liquidity of the
cement, the cure temperature of the cement and the insertion
pressure of the cement. If the cement has a relatively cool
temperature, then more time is required for the cement to cure
which increase operating room time. Curing time can also be
affected by adding other substances to it, such as growth factors,
antibiotics and/or barium tracer. The injection pressure of first
material 50 can affect whether it will leak out of small tears in
the annulus or infiltrate interstices and nutrient canals of the
vertebral endplates. It is also desirable that placement procedures
for first material be carried out under fluoroscopy with a tracer
such as barium in first material 50 to allow monitoring of material
excursion and its presence in the disc space. Monitoring of the
placement of first material 50 to confirm its proper positioning in
the disc space can be accomplished by AP and lateral fluoroscopy or
bi-planar fluoroscopy. The presence of material excursion could
signify a significant annulus or other anatomical or surgically
created defect or void. Such monitoring provides a safety measure
to ensure first material 50 is not placed into inappropriate
anatomic locations during formation of interbody device 50'.
[0053] Referring further to FIG. 4, enlargeable portion 34 is
returned to its reduced size configuration so it can be removed
from interbody device 50' and the disc space. This leaves a central
cavity 52' surrounded by interbody device 50'. An endoscope 20 can
be used to monitor distractor withdrawal and to check the integrity
of interbody device 50'. Material delivery instrument 40 can then
be repositioned, if necessary, in one of the access portals and
used to deliver a second material 60 to central cavity 52' as shown
in FIG. 5. Second material 60 can be artificial disc material,
bioactive substance, rhBMP, autograft, or bioactive or
osteoconductive carrier for bony fusion. In situations where second
material 60 is fusion material, bony fusion can occur centrally
while interbody device 50' provides stability of the disc space
during fusion. It is further contemplated that in situations where
fusion is desired, the endplates 11a, 11b could be reduced to
bleeding bone via scraping, cutting, or reaming prior to placement
of second material 60.
[0054] Referring now to FIG. 6, there is shown a partial section
view of the spinal column segment having interbody device 50'
formed in a disc space as described above. Interbody device 50'
conforms with the shape of endplates 11a, 11b and constrains second
material 60 therein. In FIG. 7, there are shown posterior screws
46a, 46b secured to pedicles 16a, 16b and a rod 48 extending
between and secured thereto. It is further contemplated that
posterior stabilization could be provided with screws at the facet
joints, or via a posterior plate secured to the vertebrae. Anterior
or lateral stabilization plates secured to the vertebrae are also
contemplated. Such supplemental fixation and stabilization devices
are known in the art and will not be described further herein.
[0055] Referring now to FIG. 8, there is shown another technique
for forming an interbody device in a spinal disc space. The
instruments used in the technique of FIG. 8 include a left side
lateral distractor 70a and a right side lateral distractor 70b that
is substantially identical to left side distractor 70a. Lateral
distractors 70a, 70b each include shafts 72a, 72b and an
enlargeable portion 74a, 74b, respectively, adjacent a distal end
of the respective shaft. If enlargeable portions 74a, 74b were
inflatable, shafts 72a, 72b would also define an inflation lumen.
After completing procedures to form a prepared disc space as
discussed above, lateral distractors 70a, 70b are positioned
through bi-portal access ports 18, 19 and into the disc space 24.
Enlargeable portions 74a, 74b each have a concavo-convex or
banana-shaped configuration so that each can be positioned along
the inner annulus wall and the apophyseal ring of the upper and
lower vertebrae 10a, 10b while leaving the central portion of the
disc space open. Further, the apophyseal ring in its most anterior
portion between the distal tips of enlargeable portions 74a, 74b
remains open for placement of material 50 and also remains open
along its most posterior portion between the distal ends of
enlargeable portions 74a, 74b. For example, as shown in FIG. 8,
first material 50 has been placed in the anterior portion of the
disc space by a material delivery instrument or catheter inserted
through one of the access portals 18, 19 alongside the distractor
to form a first interbody device segment 50" when cured. First
material 50 could also be placed in the posterior portion to form a
second interbody device segment (not shown). Additional interbody
segments or pillars could be formed in the disc space, and second
material 60 could then be placed or packed between the interbody
segments.
[0056] There are several distraction and material placement
techniques afforded by use of lateral distractors as shown in FIG.
8. For example, after sequential bi-lateral distraction of the disc
space, one of the lateral distractors could be reduced in size and
withdrawn and this same side of the disc space could be provided
with first material 50 from delivery instrument 40 to form a first
lateral interbody device segment 50a as shown in FIG. 9. A single
central distractor 30 can be used to block the central portion of
the prepared disc space 24 while second lateral distractor 70b
blocks the right lateral side of the disc space. Second lateral
distractor 70b can then be withdrawn and additional first material
50 is provided to form a second interbody device segment (not
shown) using enlargeable portion 34 as a form. After completion of
the interbody device segments, second material 60 can be delivered
into the space between the interbody device segments. Further,
sequential distraction can be done in such a way that two lateral
distractors 70a, 70b are left in prepared disc space 24 and second
material 60 can be placed between the lateral distractors 70a, 70b.
Second material 60 can then be used alone or in combination with
one of the lateral distractors 70a, 70b as a form for placement of
first material 50.
[0057] It is further contemplated that the placement location for
first material 50 can be varied at any location about the
apophyseal ring by using combinations of lateral distractors,
anterior and posterior distractors, and central distractors.
Further, it is contemplated first material 50 could be placed at
multiple, discrete locations about the apophyseal ring to provide a
number of columnar or segmented interbody devices in the disc
space. These segmented interbody devices could be formed adjacent
to and in contact with one another or formed with gaps
therebetween. It is further contemplated that the positioning of
the various interbody devices could be varied to accommodate the
approach desired for material placement, including both uni-lateral
injection or a bi-lateral placement.
[0058] In another embodiment, the banana-shaped lateral distractors
70a, 70b can be tapered in height to provide angulation between the
vertebral endplates. For example, lordosis could be established by
providing the enlargeable portions 74a, 74b with a greater height
posteriorly than anteriorly. Further, the lateral distractors 70a,
70b can be provided with differing heights in order to distract one
side of the disc space more than the other side, reducing or
eliminating scoliosis. Alternatively, identical inflatable devices
could be provided in which the inflatable portions have a height
that corresponds to the internal inflation pressure supplied
thereto. One of the lateral distractors could be inflated to a
greater pressure than the contra-lateral side to provide
differential distraction heights for each side. The same lateral
distractor could be employed bi-laterally to change the lateral
angulation of the disc space by varying the inflation pressure
supplied to the enlargeable portion thereof.
[0059] After repairing scoliosis by providing the appropriate
distraction and interbody devices, the disc space occupied by the
enlargeable portions of the distractor is available for placement
of bone growth material. For example, if two banana-shaped
inflatable devices are used, a central cavity encompassed by the
enlargeable portions remains after the portions are enlarged.
Second material can then be placed in this central cavity.
Additional first material can then be placed in the space
previously occupied by the enlarged portions to provide structural
peripheral support. Thus, this specific example contemplates
initially central placement of a first material, such as bone
growth material, and then the enlargeable distractors can be
sequentially or simultaneously withdrawn from the disc space and a
second material, such as a cement, placed around the central core
of first material and against the enlargeable distractor portion,
if any, remaining in the disc space to provide structural support
of the disc space.
[0060] As discussed above, enlargeable portion 34 of the distractor
30 can be an inflatable device. In FIGS. 10-17, there are provided
various embodiments of inflatable devices that can be used to
perform disc space distraction. By providing inflatable devices of
various shapes and sizes, different vertebral endplate contact
areas can be formed thereby providing selection of the optimal
inflatable device based on vertebral endplate load resistance,
required distraction force, and the structural integrity of the
pressurized inflated device. It should be understood, however, that
the contact surface areas provided below are estimated based on a
distraction height of 14 millimeters. The contact surface area of
each balloon will vary depending on the degree to which the balloon
is inflated. For distraction heights less than 14 millimeters, the
contact are will be greater than 0.2 square inches. For distraction
heights greater than 14 millimeters, the contact are will be less
than 0.2 square inches. It should be further understood that the
contact area for each balloon can be varied by changing the lateral
and/or anterior-posterior dimensions of the balloon while retaining
the same balloon shape.
[0061] Referring now to FIGS. 10a-10c, there is shown a first
embodiment an inflatable device in the form of a balloon 100 having
the shape of a center cylinder with frusto-conically tapered ends
extending therefrom. Balloon 100 is in communication with an
inflation lumen 102 and has upper vertebral endplate contacting
surface 104 and opposite lower vertebral endplate contacting
surface 106. As shown in FIG. 10b, surfaces 104, 106 have an oval
shape with the rounded end portions of the oval positioned
laterally of a longitudinal axis extending through inflation lumen
102 and balloon 100. Surfaces 104, 106 contact endplates 11a, 11b
of the upper and lower vertebrae 10a, 10b, respectively, as shown
in FIG. 10c. Balloon 100 has a central cylindrical portion 108
which defines contact surfaces 104, 106, and opposite
frusto-conical portions 110, 112 distally and proximally extending
therefrom, respectively, and tapered at an angle that avoids
contact with the vertebral endplates. In one specific embodiment,
it is estimated that balloon 100 has a contact surface area of
about 0.2 square inches for each of the upper and lower contact
surfaces 104, 106 when balloon 100 is expanded to distract the disc
space to a height of 14 millimeters.
[0062] Referring now to FIGS. 11a-11c, there is shown another
embodiment of an inflatable device in the form of a balloon 120
having a shape of a center cylinder with a pair of frusto-conically
tapered ends extending from each end thereof. Balloon 120 is in
communication with inflation lumen 122 and has upper vertebral
endplate contacting surface 124 and opposite lower vertebral
endplate contacting surface 126. As shown in FIG. 11b, surfaces
124, 126 have an oval shape with the rounded portions oriented
distally and proximally along a longitudinal axis extending through
inflation lumen 122 and balloon 120. Surfaces 124, 126 contact
endplates 11a, 11b of the upper and lower vertebrae 10a, 10b,
respectively, as shown in FIG. 11c. Balloon 120 has a central
cylindrical portion 128 which defines a portion of contact surfaces
124, 126. Balloon 120 further includes first frusto-conical
portions 130, 132 extending distally and proximally therefrom,
respectively, which define the remaining portions of contact
surfaces 124, 126. Frusto-conical portions 130, 132 are only
tapered slightly and generally match the curvature of the vertebral
endplates in order to provide additional contact area as compared
to balloon 100. In one specific embodiment, balloon 120 has a
contact surface area of about 0.3 square inches for each of the
upper and lower contact surfaces 124, 126. Distal frusto-conical
portion 134 and proximal frusto-conical portion 136 extend to the
distal end of balloon 120 and to inflation lumen 122, respectively,
and generally do not contact the vertebral endplates unless the
balloon is sufficiently inflated to create such contact.
[0063] Referring to FIGS. 12a-12c, there is shown another
embodiment an inflatable device in the form of a balloon 140 having
a vertically oriented cylindrical shape. Balloon 140 is in
communication with an inflation lumen 142 and has upper vertebral
endplate contacting surface 144 and opposite lower vertebral
endplate contacting surface 146. Surfaces 144, 146 contact
endplates 11a, 11b of the upper and lower vertebrae 10a, 10b,
respectively, as shown in FIG. 12c. Balloon 140 has a cylindrical
body 148 which has circular upper and lower ends 150, 152 that
define circular contact surfaces 144, 146 as shown in FIG. 12b. In
one specific embodiment, balloon 140 has a contact surface area of
about 0.5 square inches for each of the upper and lower contact
surfaces 144, 146.
[0064] Referring now to FIGS. 13a-13c, there is shown another
embodiment an inflatable device in the form of a balloon 160 having
a horizontally oriented cylindrical shape. Balloon 160 in
communication with an inflation lumen 162 and has a cylindrical
body 168 with distal end 170 and opposite proximal end 172. Balloon
160 further includes upper vertebral endplate contacting surface
164 and opposite lower vertebral endplate contacting surface 166.
As shown in FIG. 13b, contact surfaces 164, 166 have a
substantially rectangular shape formed by the contact between the
cylindrical sidewalls of cylindrical body 168 and endplates 11a,
11b of the upper and lower vertebrae 10a, 10brespectively. In one
specific embodiment, balloon 160 has a contact surface area of
about 0.24 square inches for each of the upper and lower contact
surfaces 164, 166.
[0065] Referring to FIGS. 14a-14c, there is shown another
embodiment an inflatable device in the form of a balloon 180 having
a horizontally oriented cylindrical shape. Balloon 180 is in
communication with inflation lumen 182 and has a cylindrical body
188 with distal end 190 and opposite proximal end 192. Balloon 180
further includes upper vertebral endplate contacting surface 184
and opposite lower vertebral endplate contacting surface 186. As
shown in FIG. 14b, contact surfaces 184, 186 have a rectangular
shape formed by the contact between the cylindrical sidewalls of
cylindrical body 188 and endplates 11a, 11b of the upper and lower
vertebrae 10a, 10b, respectively. In one specific embodiment,
balloon 180 has a contact surface area of about 0.3 square inches
for each of the upper and lower contact surfaces 184, 186. Balloon
180 is similar in shape to balloon 160, but has a shorter length
between its distal and proximal ends to allow balloon 180 to extend
further laterally in the disc space than balloon 160 and thus
increasing the vertebral endplate contact area.
[0066] Referring to FIGS. 15a-15c, there is shown another
embodiment an inflatable device in the form of a balloon 200 having
a spherical shape. Balloon 200 is in communication with an
inflation lumen 202 and has upper vertebral endplate contacting
surface 204 and opposite lower vertebral endplate contacting
surface 206. Surfaces 204, 206 are formed on spherical body 208 and
have a circular shape in contact with endplates 11a, 11b of the
upper and lower vertebrae 10a, 10b, respectively. Spherical body
208 has opposite distal and proximal ends 210, 212 respectively. In
one specific embodiment, balloon 200 has a diameter of 22
millimeters which provides a contact surface area of about 0.35
square inches for each of the upper and lower contact surfaces 204,
206.
[0067] In FIGS. 16a-16c there is shown another embodiment
spherically shaped balloon 220 having a spherical body 228 in
communication with inflation lumen 222. Spherical body 228 includes
contact surfaces 224, 226 forming a circular contact surface with
endplates 11a, 11b. In this embodiment, balloon 220 has a diameter
of 24 millimeters and the endplate contact surface areas of
surfaces 224, 226 are each 0.45 square inches.
[0068] Referring now to FIG. 17, there is shown an inflatable
device having a pear shaped balloon 240 in fluid communication with
an inflation shaft 242. Balloon 240 includes upper surface 244 and
an opposite lower surface 246. Upper surface 244 has first
vertebral endplate contacting node 244a, a second vertebral
endplate contacting node 244b and a concave portion 244c extending
therebetween. Similarly, lower surface 246 has first vertebral
endplate contacting node 246a, a second vertebral endplate
contacting node 246b and a concave portion 246c extending
therebetween. Balloon 240 is shaped such that the contacting nodes
are positionable at the apophyseal ring and the concave surfaces
span weaker bony material at the central portion of the vertebral
endplate. It is further contemplated that such a shape could be
provided to establish lordosis by, for example, providing the
anteriorly positioned node with a height less than the posteriorly
oriented node.
[0069] In addition to the above-described shapes, other shapes for
the enlargeable portion 34 of distractor 30 are also contemplated.
For example, the enlargeable portion can have a shape that
corresponds to the shape of the vertebral endplates, such as a
kidney bean shape, or can have a square or rectangular cuboid
shape. It is also desirable that first material 50 does not adhere
to the enlargeable portion 34 while it is curing. Thus, various
coatings can be applied to the exterior surface of enlargeable
portion 34 such as, for example, Teflon spray or silicone oil.
Other coatings are also contemplated, so long as they prevent the
adhesion of first material 50 and enlargeable portion 34. For
embodiments in which enlargeable portion 34 is an inflatable
device, the device should also be made from a tough yet elastic
material that can withstand the inflation pressures applied thereto
while also retaining the capability to return to a reduced size
configuration for insertion and withdrawal from the disc space and
through the access port.
[0070] The inflatable devices of the present invention can be
designed to accommodate the patient anatomy. One factor considered
in such a design is the force required to distract the disc space
to the desired disc space height. The ability of the vertebral
endplates to resist contact pressure has been found to decrease
with patient age. For example, one study found those persons in the
range of 20-30 years have a vertebral endplate resistance
capability of 1500 pounds per square inch, those persons in the
range of 40-60 year olds have a vertebral endplate resistance
capability of 1050 pounds per square inch, and those persons over
60 year olds have a vertebral endplate resistance capability of 594
pounds per square inch. In order to distract the disc space with an
inflatable device, sufficient pressure must be exerted to overcome
the tension from the muscles and ligaments that have become
accustomed to the collapsed condition of the disc space. However,
the pressure on the vertebral endplates must remain within
acceptable limits.
[0071] Based on the contact area of the balloon, the load the
balloon will exert on the vertebral endplates to distract the disc
space can be determined. The pressure exerted on the vertebral
endplates can also be determined and the balloon sized so that the
contact pressure does not exceed the vertebral endplate resistance
capability of the patient. The following table presents the maximum
allowable load for various balloon contact areas based on the
vertebral endplate resistance for the patient ranges provided
above:
1 Maximum Allowable Endplate Load Contact Area 20-30 yr olds 40-60
yr olds 60+ yr olds 0.5 sq. in. 750 lbs 525 lbs 297 lbs 0.4 sq. in.
600 lbs 420 lbs 238 lbs 0.3 sq. in. 450 lbs 315 lbs 178 lbs 0.2 sq.
in. 300 lbs 210 lbs 119 lbs 0.1 sq. in. 150 lbs 105 lbs 59 lbs
[0072] As shown in FIG. 18, a graphical representation is provided
to represent the relationship between the balloon pressure and the
load exerted by the balloon for various sizes of contact areas for
the balloons ranging between 0.1 square inches to 0.5 square
inches. From this information, a balloon contact area size and
pressure can selected that is within the maximum allowable load for
a particular patient. For example, if 100 pounds is required to
distract the vertebrae to the desired height, then a balloon having
contact surface areas of 0.5 square inches would apply a vertebral
endplate load of about 100 pounds at an inflation pressure of 200
psi. The distraction load of 100 pounds for the 0.5 square inch
contact area is well below the maximum allowable endplate load for
each of the patient age ranges provided above.
[0073] 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 embodiment has been shown
and described and that all changes and modifications that come
within the spirit of the invention are desired to be protected.
* * * * *