U.S. patent application number 12/012437 was filed with the patent office on 2008-10-16 for bone cutting device.
This patent application is currently assigned to Karlin Technology, Inc.. Invention is credited to Gary Karlin Michelson.
Application Number | 20080255564 12/012437 |
Document ID | / |
Family ID | 22121653 |
Filed Date | 2008-10-16 |
United States Patent
Application |
20080255564 |
Kind Code |
A1 |
Michelson; Gary Karlin |
October 16, 2008 |
Bone cutting device
Abstract
Apparatus and a method of inserting spinal implants is disclosed
in which an intervertebral space is first distracted, a hollow
sleeve having teeth at one end is then driven into the vertebrae
adjacent that disc space. A drill is then passed through the hollow
sleeve removing disc and bone in preparation for receiving the
spinal implant which is then inserted through the sleeve.
Inventors: |
Michelson; Gary Karlin;
(Venice, CA) |
Correspondence
Address: |
MARTIN & FERRARO, LLP
1557 LAKE O'PINES STREET, NE
HARTVILLE
OH
44632
US
|
Assignee: |
Karlin Technology, Inc.
Sofamor Danek Holdings, Inc.
SDGI Holdings, Inc.
Warsaw Orthopedic, Inc.
|
Family ID: |
22121653 |
Appl. No.: |
12/012437 |
Filed: |
February 1, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10223916 |
Aug 20, 2002 |
7399303 |
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12012437 |
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08586950 |
Jan 16, 1996 |
6436098 |
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10223916 |
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08074781 |
Jun 10, 1993 |
5484437 |
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08586950 |
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Current U.S.
Class: |
606/79 ; 606/86A;
606/90 |
Current CPC
Class: |
A61B 17/025 20130101;
Y10T 407/1964 20150115; A61B 2017/0256 20130101; A61B 17/1757
20130101; Y10S 623/908 20130101; A61B 17/1671 20130101 |
Class at
Publication: |
606/79 ; 606/90;
606/86.A |
International
Class: |
A61B 17/00 20060101
A61B017/00; A61B 17/58 20060101 A61B017/58; A61F 5/00 20060101
A61F005/00 |
Claims
1. A bone-cutting device adapted for use in forming an implantation
space in between and at least in part into two adjacent vertebral
bodies where adjacent a disc space formed by the removal of disc
material from a disc between the adjacent vertebral bodies of a
human spine, said bone-cutting device comprising: a shaft having a
distal end and a proximal end; a forward projecting portion
proximate said distal end of said shaft being configured to fit
into the disc space, said forward projecting portion being adapted
to contact each of the adjacent vertebral bodies from within the
disc space; and a cutting portion proximate said distal end of said
shaft and proximate said forward projecting portion, said cutting
portion having at least two opposed sharpened cutting surfaces
adapted to cut bone from each of the adjacent vertebral bodies
during advancement of said cutting portion into the spine behind
said projecting portion, said forward projecting portion and said
cutting portion being fixed relative to one another to permit
simultaneous advancement of said forward projecting portion and
said cutting portion into the spine.
2. The bone-cutting device of claim 1, wherein said forward
projecting portion adapted to contact each of the adjacent
vertebral bodies from within the disc space includes opposed upper
and lower surfaces configured to urge apart the adjacent vertebral
bodies.
3. The bone-cutting device of claim 1, wherein said forward
projecting portion adapted to contact each of the adjacent
vertebral bodies from within the disc space includes opposed upper
and lower surfaces configured to align the adjacent vertebral
bodies.
4. The bone-cutting device of claim 1, wherein said cutting
surfaces are adapted to simultaneously cut bone from each of the
adjacent vertebral bodies.
5. The bone-cutting device of claim 1, wherein said forward
projecting portion has a reduced cross sectional dimension at its
most distal aspect to facilitate introduction of said bone-cutting
device into the disc space.
6. The bone-cutting device of claim 1, wherein said forward
projecting portion is adapted to be self-centering along a
mid-longitudinal axis of said device.
7. The bone-cutting device of claim 1, wherein said forward
projecting portion is one of an alignment member, a distractor, a
centering post, a maximum thickness of resected bone limiter, and a
means for controlling maximum thickness of bone to be resected.
8. The bone-cutting device of claim 1, wherein said shaft has a
longitudinal axis and said cutting portion has a maximum dimension
measured from an outer aspect of one of said cutting surfaces to an
outer aspect of the opposed one of said cutting surfaces that is
greater than a maximum dimension measured between where said
forward projecting portion contacts each of the adjacent vertebral
bodies along a plane perpendicular to the longitudinal axis of said
shaft.
9. The bone-cutting device of claim 1, wherein said shaft has an
enlarged portion between said cutting portion and said proximal end
to limit the depth of penetration of said cutting portion into the
spine.
10. The bone-cutting device of claim 1, further comprising a power
unit operatively connected to said shaft for providing power to
said bone-cutting device.
11. The bone-cutting device of claim 1, in combination with a guard
member having an opening for providing protected access to the disc
space and the adjacent vertebral bodies and for guiding said
bone-cutting device into contact with the adjacent vertebral
bodies.
12. The bone-cutting device of claim 1, in combination with a
spinal insert adapted for insertion at least in part into the
implantation space formed by said bone-cutting device.
13. The bone-cutting device of claim 12, in combination with an
implant driver configured to insert said spinal insert into the
implantation space formed by said bone-cutting device.
14. The bone-cutting device of claim 1, in combination with an
instrument for removing from the spine the bone cut by said
bone-cutting device.
15. The bone-cutting device of claim 1, wherein at least one of
said cutting surfaces has a portion parallel to a mid-longitudinal
axis of said shaft and an angled portion converging toward said
parallel portion away from the mid-longitudinal axis of said
shaft.
16. A bone-cutting device adapted for use in forming an
implantation space in between and at least in part into two
adjacent vertebral bodies where adjacent a disc space formed by the
removal of disc material from a disc between the adjacent vertebral
bodies of a human spine, said bone-cutting device comprising: a
shaft having a distal end and a proximal end; and a working end
attached to said distal end of said shaft, said working end
comprising a forward projecting portion being configured to fit
into the disc space, said forward projecting portion being adapted
to contact each of the adjacent vertebral bodies from within the
disc space, said working end further comprising a cutting portion
proximate said forward projecting portion, said cutting portion
having at least two opposed sharpened cutting surfaces adapted to
cut bone from each of the adjacent vertebral bodies during
advancement of said cutting portion into the spine behind said
forward projecting portion, said forward projecting portion and
said cutting portion being fixed relative to one another to permit
simultaneous advancement of said forward projecting portion and
said cutting portion into the spine.
17. The bone-cutting device of claim 16, wherein said forward
projecting portion adapted to contact each of the adjacent
vertebral bodies from within the disc space includes opposed upper
and lower surfaces configured to urge apart the adjacent vertebral
bodies.
18. The bone-cutting device of claim 16, wherein said forward
projecting portion adapted to contact each of the adjacent
vertebral bodies from within the disc space includes opposed upper
and lower surfaces configured to align the adjacent vertebral
bodies.
19. The bone-cutting device of claim 16, wherein said cutting
surfaces are adapted to simultaneously cut bone from each of the
adjacent vertebral bodies.
20. The bone-cutting device of claim 16, wherein said forward
projecting portion has a reduced cross sectional dimension at its
most distal aspect to facilitate introduction of said bone-cutting
device into the disc space.
21. The bone-cutting device of claim 16, wherein said forward
projecting portion is adapted to be self-centering along a
mid-longitudinal axis of said device.
22. The bone-cutting device of claim 16, wherein said forward
projecting portion is one of an alignment member, a distractor, a
centering post, a maximum thickness of resected bone limiter, and a
means for controlling maximum thickness of bone to be resected.
23. The bone-cutting device of claim 16, wherein said shaft has a
longitudinal axis and said cutting portion has a maximum dimension
measured from an outer aspect of one of said cutting surfaces to an
outer aspect of the opposed one of said cutting surfaces that is
greater than a maximum dimension measured between where said
forward projecting portion contacts each of the adjacent vertebral
bodies along a plane perpendicular to the longitudinal axis of said
shaft.
24. The bone-cutting device of claim 16, wherein said shaft has an
enlarged portion between said cutting portion and said proximal end
to limit the depth of penetration of said cutting portion into the
spine.
25. The bone-cutting device of claim 16, further comprising a power
unit operatively connected to said shaft for providing power to
said bone-cutting device.
26. The bone-cutting device of claim 16, in combination with a
guard member having an opening for providing protected access to
the disc space and the adjacent vertebral bodies and for guiding
said bone-cutting device into contact with the adjacent vertebral
bodies.
27. The bone-cutting device of claim 16, in combination with a
spinal insert adapted for insertion at least in part into the
implantation space formed by said bone-cutting device.
28. The bone-cutting device of claim 27, in combination with an
implant driver configured to insert said spinal insert into the
implantation space formed by said bone-cutting device.
29. The bone-cutting device of claim 16, in combination with an
instrument for removing from the spine the bone cut by said
bone-cutting device.
Description
[0001] This application is a divisional of application Ser. No.
10/223,916, filed Aug. 20, 2002; which is a continuation of
application Ser. No. 08/586,950, filed Jan. 16, 1996, now U.S. Pat.
No. 6,436,098; which is a continuation of application Ser. No.
08/074,781, filed Jun. 10, 1993, now U.S. Pat. No. 5,484,437; all
of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to artificial fusion implants
to be placed into the intervertebral space left remaining after the
removal of a damaged spinal disc and specifically to the apparatus
for and method of, inserting the implants.
[0004] 2. Description of the Prior Art
[0005] For the purpose of achieving long term stability to a
segment of injured spine, a fusion (the joining together of two or
more bones via a continuous bridge of incorporated bone) may be
performed. Well-known to those skilled in such art is the interbody
fusion wherein the disc is partially excised and bone placed within
that space previously occupied by that disc material (between
adjacent vertebrae) for the purpose of restoring a more normal
spatial relationship, and to provide for stability; short term by
mechanical support, and long term by the permanent cross bonding of
bone from vertebra to vertebra. For fusion to occur within the disc
space, it is necessary to prepare the vertebrae to be fused by
breaking through, or cutting into, the hardened outside plates of
bone (the endplates) to allow the interposed bone graft to come
into direct contact with the more vascular cancellous (spongy)
bone, and to thereby trick the body into attempting to heal this
induced, but controlled, "fracturing" by both bone production and
the healing of the grafts to both opposed vertebral surfaces such
that they become one continuous segment of bone.
[0006] The purpose of the present invention is to provide an
implant, and the apparatus and method of inserting the implant
within the intervertebral space left after the removal of the disc
material and permanently eliminate all motion at that location. To
do so, the device of the present invention is space occupying
within the disc interspace, rigid, self-stabilizing to resist
dislodgement, stabilizing to the adjacent spinal vertebrae to
eliminate local motion, and able to intrinsically participate in a
vertebra to vertebra bony fusion so as to assure the permanency of
the result.
[0007] At present, following the removal of a damaged disc, either
bone or nothing is placed into the remaining space. Placing nothing
into this space allows the space to collapse which may result in
damage to the nerves; or the space may fill with scar tissue and
eventually lead to a reherniation. The use of bone to fill the
space is less than optimal in that bone obtained from the patient
requires additional surgery and is of limited availability in its
most useful form, and if obtained elsewhere, lacks living bone
cells, carries a significant risk of infection, and is also limited
in supply as it is usually obtained from accident victims.
Furthermore, regardless of the source of the bone, it is only
marginal structurally and lacks a means to either stabilize itself
against dislodgement, or to stabilize the adjacent vertebrae.
a. Prior Art Implants
[0008] There have been an extensive number of attempts to develop
an acceptable disc prosthesis (an artificial disc). Such devices by
design would be used to replace a damaged disc and seek to restore
the height of the interspace and to restore the normal motion of
that spinal joint. No such device has been found that is medically
acceptable. This group of prosthetic or artificial disc
replacements, seeking to preserve spinal motion and so are
different from the present invention, would include:
[0009] U.S. Pat. No. 3,867,728 to STUBSTAD--describing a flexible
disc implant.
[0010] U.S. Pat. No. 4,349,921 to KUNTZ--describing a flexible disc
replacement with file-like surface projections to discourage device
dislocation.
[0011] U.S. Pat. No. 4,309,777 to PATIL--describing a motion
preserving implant with spiked outer surfaces to resist dislocation
and containing a series of springs to urge the vertebrae away from
each other.
[0012] U.S. Pat. No. 3,875,595 to FRONING--describing a motion
preserving bladder-like disc replacement with two opposed stud-like
projections to resist dislocation.
[0013] U.S. Pat. No. 2,372,622 to FASSIO (France)--describing a
motion preserving implant comprising complimentary opposed convex
and concave surfaces.
[0014] In summary, these devices resemble the present invention
only in that they are placed within the intervertebral space
following the removal of a damaged disc. In that they seek to is
preserve spinal motion, they are diametrically different from the
present invention which seeks to permanently eliminate all motion
at that spinal segment.
[0015] A second related area of prior art includes those devices
utilized to replace essentially wholly removed vertebrae. Such
removal is generally necessitated by extensive vertebral fractures,
or tumors, and is not associated with the treatment of disc
disease. While the present invention is to be placed within the
disc space, these other vertebral devices cannot be placed within
the disc space as at least one vertebra has already been removed
such that there no longer remains a "disc space". Furthermore,
these devices are limited in that they seek to perform as temporary
structural members mechanically replacing the removed vertebrae
(not a removed disc), and do not intrinsically participate in
supplying osteogenic material to achieve cross vertebrae bony
fusion. Therefore, unlike the present invention which provides for
a source of osteogenesis, use of this group of devices must be
accompanied by a further surgery consisting of a bone fusion
procedure utilizing conventional technique. This group consisting
of vertebral struts rather than disc replacements would include the
following:
[0016] U.S. Pat. No. 4,553,273 to WU--describing a turnbuckle-like
vertebral strut.
[0017] U.S. Pat. No. 4,401,112 to REZAIAN--describing a
turnbuckle--like vertebral strut with the addition of a long
stabilizing staple that spans the missing vertebral body.
[0018] U.S. Pat. No. 4,554,914 to KAPP--describing a large
distractible spike that elongates with a screw mechanism to span
the gap left by the removal of an entire vertebra and to serve as
an anchor for acrylic cement which is then used to replace the
missing bone (vertebrae).
[0019] U.S. Pat. No. 4,636,217 to OGILVIE--describing a vertebral
strut mechanism that can be implanted after at least one vertebrae
has been removed and consists of a mechanism for causing the
engagement of screws into the vertebrae above and the vertebrae
below the one removed.
[0020] In summary, this second group of devices differs from the
present invention in that they are vertebral replacements struts,
do not intrinsically participate in the bony fusion, can only be
inserted in the limited circumstances where an entire vertebra has
been removed from the anterior approach, and are not designed for,
or intended to be used for the treatment of disc disease.
[0021] A third area of prior art related to the present invention
includes all devices designed to be applied to one of the surfaces
of the spine. Such devices include all types of plates, struts, and
rods which are attached by hooks, wires and screws. These devices
differ significantly from the present invention in that they are
not inserted within the disc space and furthermore do not
intrinsically participate in supplying osteogenic material for the
fusion.
[0022] Therefore, where permanent spinal immobilization is desired,
an additional surgery, consisting of a spinal fusion performed by
conventional means or the use of supplemental methylmethacrylate
cement is required. Such devices applied to the spine, but not
within the disc space, would include the following:
[0023] U.S. Pat. No. 4,604,995 to STEPHENS--describing a "U" shaped
metal rod attached to the posterior elements of the spine with
wires to stabilize the spine over a large number of segments.
[0024] U.S. Pat. No. 2,677,369 to KNOWLES--describing a metal
column device to be placed posteriorly along the lumbar spine to be
held in position by its shape alone and to block pressure across
the posterior portions of the spinal column by locking the spine in
full flexion thereby shifting the maximum weight back onto the
patient's own disc.
[0025] Other devices are simply variations on the use of rods (e.g.
Harrington, Luque, Cotrel-Dubosset, Zielke), wires or cables
(Dwyer), plates and screws (Steffee), or struts (Dunn,
Knowles).
[0026] In summary, none of these devices are designed to be nor can
be used within the disc space. Moreover, these devices do not
replace a damaged disc, and do not intrinsically participate in the
generation of a bony fusion.
[0027] Another area of related prior art to be considered is that
of devices designed to be placed within the vertebral interspace
following the removal of a damaged disc, and seeking to eliminate
further motion at that location.
[0028] Such a device is contained in U.S. Pat. No. 4,501,269 issued
to BAGBY which describes an implantable device and limited
instrumentation. The method employed is as follows: a hole is bored
transversely across the joint and a hollow metal basket of larger
diameter than the hole is then pounded into the hole and then the
hollow metal basket is filled with the bone debris generated by the
drilling.
[0029] While the present invention (device, instrumentation, and
method) may appear to bear some superficial resemblance to the
BAGBY invention, it is minimal, while the differences are many fold
and highly significant. These differences include the
following:
[0030] 1. Safety--The present invention provides for a system of
completely guarded instrumentation so that all contiguous vital
structures (e.g. large blood vessels, neural structures) are
absolutely protected. The instrumentation of the present invention
also makes overpenetration by the drill impossible. Such
overpenetration in the cervical spine, for example, would result in
the total paralysis or death of the patient. In the thoracic spine,
the result would be complete paraplegia. In the lumbar spine, the
result would be paraplegia or a life-threatening perforation of the
aorta, vena cava, or iliac vessels.
[0031] The present invention is atraumatically screwed into place
while the BAGBY device, in contradistinction, is pounded into
position. BAGBY describes that its implant is significantly larger
in size than the hole drilled and must be pounded in. This is
extremely dangerous and the pounding occurs directly over the
spinal cord which is precariously vulnerable to percussive injury.
Furthermore, while it is possible, for example in the lumbar spine,
to insert the present invention away from the spinal cord and
nerves, the BAGBY device must always be pounded directly towards
the spinal cord.
[0032] Furthermore, since the BAGBY device is pounded into a smooth
hole under great resistance, and lacking any specific design
features to secure it, the device is highly susceptible to forceful
ejection which would result in great danger to the patient and
clinical failure. The present invention, in contradistinction, is
securely screwed into place, and possesses highly specialized
locking threads to make accidental dislodgement impossible. Because
of the proximity of the spinal cord, spinal nerves, and blood
vessels, any implant dislodgement as might occur with the BAGBY
device might have catastrophic consequences.
[0033] 2. Broad applicability--The BAGBY device can only be
inserted from the front of the vertebral column, however, in
contrast, the present invention can be utilized in the cervical,
thoracic, and lumbar spine, and can be inserted from behind
(posteriorly) in the lumbar spine. This is of great importance in
that the purpose of these devices is in the treatment of disc
disease and probably greater than 99 percent of all lumbar
operations for the treatment of disc disease are performed from
behind where the present invention can easily be utilized, but the
BAGBY device, as per BAGBY'S description, cannot.
[0034] 3. Disc removal--The BAGBY invention requires the complete
removal of the disc prior to the drilling step, whereas the present
invention eliminates the laborious separate process of disc removal
and efficiently removes the disc and prepares the vertebral end
plates in a single step.
[0035] 4. Time required--The present invention saves time over the
BAGBY invention since time is not wasted laboring to remove the
disc prior to initiating the fusion. Also, with the present
invention the procedure is performed through a system of guarded
instrumentation, time is not wasted constantly placing and
replacing various soft tissue retractors throughout the
procedure.
[0036] 5. Implant stability--Dislodgement of the implant would be a
major source of device failure (an unsuccessful clinical result),
and might result in patient paralysis or even death. As discussed,
the BAGBY device lacks any specific means of achieving stability
and since it is pounded in against resistance to achieve vertebral
distraction, and is susceptible to forceful dislodgement by the
tendency of the two distracted vertebrae, to return to their
original positions squeezing out the device. The present invention,
however, is screwed into place. As there is no unscrewing force
present between the vertebrae, compression alone cannot dislodge
the implant. The implant is inherently stable by its design.
Furthermore, the threads of the present invention are highly
specialized in that they are periodically interrupted so that the
tail ends of each of the tabs so formed are blunted and twisted so
as to resist accidental unscrewing. The removal of an implant with
such "locking threads" requires the use of a special extractor
included within the instrumentation. The stability of the present
invention is still further enhanced, again in contradistinction to
the BAGBY device, by the presence of a "bone ingrowth" surface
texturing, which both increases the friction of the fit and allows
for the direct growth of the vertebral bone into the casing of the
implant itself.
[0037] 6. Spinal stability--The present invention is not only
self-stabilizing, it also provides stability to the adjacent
vertebrae in at least three ways that the BAGBY device cannot.
First, the BAGBY device is placed transversely across the joint in
the center, leaving both vertebrae free to rock back and forth over
this round barrel shaped axis, much like a board over a barrel,
being used for a seesaw.
[0038] Secondly, as the BAGBY device lacks any specific design
features to resist sliding, it may actually behave as a third body
allowing the translation of the vertebrae relative to the device
and to each other.
[0039] Thirdly, any device can only provide stability if it remains
properly, seated. The present invention is inherently stable, and
therefore assures that it will stabilize the adjacent vertebrae,
rather than, as with the BAGBY, the instability of the spine to be
treated may cause a dislocation of the BAGBY implant, is with
further loss of spinal stability.
[0040] 7. The collapse of the interspace--While both the present
invention and the BAGBY device can be fabricated to withstand the
compression forces within the interspace, the interspace may
nevertheless collapse under the superincumbent body weight as the
implant settles into the vertebral bone. This is related to the
load per unit area. Again the present invention is superior to the
BAGBY device in at least four ways.
[0041] First, the present invention offers considerably greater
surface area to distribute the load. Secondly, while the BAGBY
device is placed centrally, the present device is placed
bilaterally where the bone tends to be more cortical and much
stronger out towards the rim. Thirdly, the present invention
supports the load achieving an "I" beam effect, whereas the BAGBY
implant does not. Fourthly, it is not pressure alone that causes
the collapse of the bone adjacent to the implant, but also bony
erosion that is caused by the motion under pressure of the implant
against the bone. As discussed in item 6 above, the present
invention alone is highly resistant to such motion, again
diminishing the likelihood of erosion and interspace collapse.
[0042] 8. Bone ingrowth surface texturing--The present invention
has a surface treatment of known and conventional technology to
induce the growth of bone from the vertebrae directly into the
casing material of the implant itself. The BAGBY device has no
similar feature.
[0043] 9. Fusion mass--The BAGBY invention calls for removing the
disc and then drilling a hole between the adjacent vertebrae. The
bony debris so generated is then put into the device. The present
invention takes a core of pure bone producing marrow from the iliac
crest, and then by use of a special press, forcibly injects the
implant device with an extremely dense compressed core of that
osteogenic material until the material itself virtually extrudes
from every cell of the implant.
[0044] 10. The probability of achieving fusion--The fusion rate
within the spine is known to be related directly to the amount of
exposed vascular bone bed area, the quality and quantity of the
fusion mass available, and the extent of the stabilization obtained
with all other factors being half constant. It would then be
anticipated, that the fusion rate would be superior with the
present invention as compared to the RAGBY device, because of
optimal implant stability (#5), optimal spinal stability (#6), bone
ingrowth surface treatment (#8), superior fusion mass (#9), and the
greater exposed vertebral bony surface area (#7).
[0045] The last area of prior art possibly related to the present
invention and therefore, to be considered related to "bony
ingrowth", are patents that either describe methods of producing
materials and or materials or devices to achieve the same. Such
patents would include:
[0046] U.S. Pat. No. 4,636,526 (DORMAN), No. 4,634,720 (DORMAN),
No. 4,542,539 (ROWE), No. 4,405,319 (COSENTINO), No. 4,439,152
(SMALL), No. 4,168,326 (BROEMER), No. 4,535,485 (ASHMAN), No.
3,987,499 (SCHARBACH), No. 3,605,123 (HAHN), No. 4,655,777 (DUNN),
No. 4,645,503 (LIN), No. 4,547,390 (ASHMAN), No. 4,608,052 (VAN
KAPEN), No. 4,698,375 (DORMAN), No. 4,661,536 (DORMAN), No,
3,952,334 (BOKROS), No. 3,905,047 (LONG), No. 4,693,721 (DUCHEYNE),
No. 4,070,514 (ENTHERLY).
[0047] However, while the implant of the present invention would
utilize bone ingrowth technology, it would do so with conventional
technology.
b. Prior Art Instrumentations And Methods
[0048] The following is a history of the prior art apparatus and
methods of inserting spinal implants:
[0049] In 1956, Ralph Cloward developed a method and instruments
which he later described for preparing the anterior aspect (front)
of the cervical spine, and then fusing it. Cloward surgically
removed the disc to be fused across and then placed a rigid drill
guide with a large foot plate and prongs down over an aligner rod
and embedded said prongs into the adjacent vertebrae to maintain
the alignment so as to facilitate the reaming out of the bone
adjacent the disc spaces. As the large foot plate sat against the
front of the spine, it also served as a fixed reference point to
control the depth of drilling. The reaming left two opposed
resected arcs, one each, from the opposed vertebral surfaces. The
tubular drill guide, which was placed only preliminary to the
drilling, was thereafter completely removed. A cylindrical bony
dowel, significantly larger in diameter than the hole formed, was
then pounded into the hole already drilled. Cloward's method of
instrumentation was designed for, and limited to, use on the
anterior aspect and in the region of the cervical spine only. The
hole was midline, which would preclude its use posteriorly where
the spinal cord would be in the way.
[0050] As the bone graft to be inserted in Cloward's method was
necessarily larger in diameter than the hole drilled, the graft
could not be inserted through the drill guide. This mandated the
removal of the drill guide and left the graft insertion phase
completely unprotected. Thus Cloward's method and instrumentation
was inappropriate for posterior application.
[0051] In addition, the failure to provide continuous protection to
the delicate neural structures from the instruments, as well as the
bony and cartilaginous debris generated during the procedure, made
Cloward's method inappropriate for posterior application. Also, the
drill guide described by Cloward could not be placed posteriorly
within the spinal canal, as the foot plate would crush the nerves.
Modifying Cloward's drill guide by removing the foot plate
completely, would still leave the instrument unworkable as it would
then lack stability, and would not be controllable for depth of
seating.
[0052] Nevertheless, Wilterberger, (Wilterberger, B. R., Abbott, K.
H., "Dowel Intervertebral Fusion as Used in Lumbar Disc Surgery,"
The Journal of Bone and Joint Surgery, Volume 39A, pg. 234-292,
1957) described the unprotected drilling of a hole from the
posterior into the lumbar spine between the nerve roots and across
the disc space, and then inserting a stack of button-like dowels
into that space. While Wilterberger had taken the Cloward concept
of circular drilling and dowel fusion and applied it to the lumbar
spine from a posterior approach, he had not provided for an
improved method, nor had he advanced the instrumentation so as to
make that procedure sufficiently safe, and it rapidly fell into
disrepute.
[0053] Crock (Crock, H. V., "Anterior Lumbar Interbody
Fusion--Indications for its Use and notes on Surgical Technique,"
Clinical Orthopedics, Volume 165, pg. 157-163, 1981) described his
technique and instrumentation for Anterior Interbody Fusion of the
lumbar spine, wherein he drilled two large holes side by side
across the disc space from anterior to posterior essentially
unprotected and then pounded in two at least partially cylindrical
grafts larger than the holes prepared.
[0054] A review of the prior art is instructive as to a number of
significant deficiencies in regard to the method and
instrumentation for the performance of Interbody Spinal Fusion
utilizing drilling to prepare the endplates.
[0055] As the great majority of spinal surgery is performed in the
lumbar spine and from posteriorly, a review of the prior art
reveals a number of deficiencies in regard to the spine in general,
and to the posterior approach to the lumbar spine specifically.
These deficiencies include the:
[0056] 1. Failure to protect the surrounding tissues throughout the
procedure, specifically, prior to drilling and until after the
insertion of the graft;
[0057] 2. Failure to contain the debris, bony and cartilaginous,
generated during the procedure;
[0058] 3. Failure to optimize the contact of the cylindrical drill
hole and bone graft, the mismatch in their diameters resulting in
incongruence of fit;
[0059] 4. Failure to determine the optimal drill size prior to
drilling;
[0060] 5. Failure to determine the optimal amount of distraction
prior to drilling;
[0061] 6. Inability to optimize the amount of distraction so as to
restore the-normal spatial relationships between adjacent
vertebrae;
[0062] 7. Inability to create sufficient working space within the
spinal canal (between the nerve roots and the dural sac) to make
the procedure safe;
[0063] 8. Absent a foot plate on the drill guide, as necessitated
by the close tolerances posteriorly, the inability to reliably
insure that the drilling is parallel to the vertebral
endplates;
[0064] 9. The inability to insure equal bone removal from the
opposed vertebral surfaces; and
[0065] 10. The inability to determine within the spinal canal, the
proper side by side positioning for dual drill holes.
SUMMARY OF THE INVENTION
[0066] The present invention comprises a series of artificial
implants, the purpose of which is to participate in, and directly
cause bone fusion across an intervertebral space following the
excision of a damaged disc. Such implants are structurally load
bearing devices, stronger than bone, capable of withstanding the
substantial forces generated within the spinal interspace. The
devices of the present invention have a plurality of macro sized
cells and openings, which can be loaded with fusion promoting
materials, such as autogenous bone, for the purpose of materially
influencing the adjacent vertebrae to perform a bony bond to the
implants and to each other. The implant casing may be surface
textured or otherwise treated by any of a number of known
technologies to achieve a "bone ingrowth surface" to further
enhance the stability of the implant and to expedite the
fusion.
[0067] The devices of the present invention are configured and
designed so as to promote their own stability within the vertebral
interspace and to resist being dislodged, and furthermore, to
stabilize the adjacent spinal segments.
[0068] The apparatus and method of the present invention for
preparing the vertebrae for insertion of the implant allows for the
rapid and safe removal of the disc, preparation of the vertebrae,
performance of the fusion, and internal stabilization of the spinal
segment.
[0069] The present invention is a method for Interbody Spinal
Fusion utilizing novel instrumentation, whereby a protective
tubular member is placed prior to the drilling part of the
procedure and is left in place until the graft is fully seated.
[0070] In the preferred embodiment two distractors are used to
separate two adjacent vertebrae to a preferred distance. A hollow
Outer Sleeve having teeth at one end is driven into the adjacent
vertebrae on one side to hold the vertebrae in position when the
distractor is removed, a diameter reducing hollow Inner Sleeve is
introduced into the Outer Sleeve, a drill having a drill stop is
passed through the hollow Inner Sleeve to drill a hole to a desired
depth, and an implant is inserted in the hole. The method is
repeated on the other side of the disc.
[0071] In summary then, the present invention, instrumentation, and
method, provides for a single surgery providing for an integrated
discectomy, fusion, and interbody internal spinal fixation.
Discussion of the Instrumentation
[0072] The apparatus and method of the present invention provide
the following advantages:
[0073] 1. The present invention is safer by providing protection of
the surrounding tissues. An Outer Sleeve places all of the delicate
soft tissue structures, nerves, blood vessels, and organs outside
of the path of the various sharp surgical instruments and the
implant. Further, it is an improvement upon hand held retractors in
that it occupies the least possible amount of area, avoids the
stretching associated with manual retraction, provides for the
retraction and shielding of the surrounding tissues in all
directions circumferentially and simultaneously, and it does so
exclusively with smooth, curved surfaces.
[0074] 2. The present invention is safer by providing protection
against the danger of instrument or implant overpenetration.
[0075] 3. The present invention is safer as the surgical site and
wound are protected from the debris generated during the
procedure.
[0076] 4. The present invention is safer because the method
provides for absolute protection to the soft tissues directly and
from indirect injury by overpenetration. It makes safe the use of
power instrumentation which is both more effective and
efficient.
[0077] 5. The present invention maintains the vertebrae to be fused
rigid throughout the procedure.
[0078] 6. The present invention holds the vertebrae to be fused
aligned throughout the procedure.
[0079] 7. The present invention holds the vertebrae to be fused
distracted throughout the procedure.
[0080] 8. The present invention assures that all instruments
introduced through the Outer Sleeve are coaxial and equally
centered through the disc space and parallel the endplates.
[0081] 9. The present invention facilitates the implant insertion
by countering the high compressive forces tending to collapse the
interspace, which if left unchecked would resist the introduction
and advancement of the implant and make stripping more likely.
[0082] 10. The present invention extends the range and use of the
procedure and similarly the interbody spinal implant itself by
making the procedure safe throughout the spine.
[0083] 11. The present invention increases the ability to use a
specifically sized implant.
[0084] 12. In the present invention the end of all the penetrating
instrumentation is blunt faced.
[0085] 13. In the present invention all of the instruments have
been stopped at a predetermined depth to avoid overpenetration.
[0086] 14. The design of the Outer Sleeve in the present invention
conforms to the spacial limitations of the specific surgical
site.
[0087] 15. The design and use of a second or Inner Sleeve in the
present invention allows for the difference in size between the
inside diameter of the Outer Sleeve, and the outside diameter of
the drill itself. This difference being necessary to accommodate
the sum of the distraction to be produced, and the depth of the
circumferential threading present of the implant.
[0088] 16. In the present invention a specially designed drill bit
with a central shaft recess allows for the safe collection of the
drilling products, which can then be removed without disturbing the
Outer Sleeve by removing the drill bit and Inner Sleeve as a single
unit.
[0089] 17. In the present invention a specially designed trephine
for removing a core of bone slightly smaller in diameter than the
internal diameter of the implant cavity itself, however of a
greater length.
[0090] 18. In the present invention a specially designed press for
forcefully compressing and injecting the long core of autogenous
bone into the implant, such that it extrudes through the implant
itself.
[0091] 19. In the present invention a specially designed driver
extractor, which attaches to the implant and allows the implant to
be either inserted or removed without itself dissociating from the
implant, except by the deliberate disengagement of the
operator.
[0092] 20. In the present invention predistraction increases the
working space.
[0093] 21. The Distractor in the present invention is
self-orienting acting as a directional finder.
[0094] 22. The Distractor in the present invention is
self-centralizing between the opposed vertebral surfaces acting as
a centering post for the subsequent bone removal.
[0095] 23. In the present invention predistraction assures the
equal removal of bone from the adjacent vertebral surfaces.
[0096] 24. In the present invention predistraction assures the
exact congruence between the hole drilled-and the device.
[0097] 25. In the present invention predistraction assures that the
drilling is parallel to the vertebral endplates.
[0098] 26. In the present invention predistraction allows for the
determination of the optimal distraction prior to drilling.
[0099] 27. In the present invention predistraction allows for the
verification of the correct prosthesis size prior to drilling.
[0100] 28. In the present invention predistraction facilitates
device insertion by relieving the compressive loads across the
interspace which would resist implantation.
[0101] 29. In the present invention predistraction decreases the
likelihood of stripping the bone during insertion.
[0102] 30. In the present invention predistraction provides for the
side by side positioning, spacing, and parallelism required prior
to the irrevocable event of drilling.
[0103] 31. In the present invention predistraction provides for the
rigid stabilization of the vertebrae opposed to the disc space
throughout the surgical procedure.
[0104] 32. In the present invention predistraction provides for an
implant easier to insert as the compressive loads of the opposed
vertebrae are held in check so that the device itself need not
drive the vertebrae apart to be inserted.
[0105] 33. In the present invention predistraction allows for the
insertion of a more effective implant as more of the implant can be
dedicated to its intended purpose and be full diameter, whereas
without the benefit of predistraction and the ability to maintain
the same, a significant portion of the forward end of the implant
would need to be dedicated to the purpose of separating the
opposing vertebrae.
[0106] 34. The present invention allows for the use of an implant
with a sharper thread or surface projections as there is no danger
to the surrounding tissues.
[0107] 35. The present invention allows for the implant to be fully
preloaded as provided to the surgeon, or for the surgeon to load it
with the material of his choice at the time of surgery.
[0108] 36. The present invention allows for the loading of a spinal
implant outside of the spinal canal and prior to implantation.
OBJECTS OF THE PRESENT INVENTION
[0109] It is an object of the present invention to provide an
improved method of performing a discectomy, a fusion, and an
internal stabilization of the spine, and specifically, all three of
the above simultaneously and as a single procedure.
[0110] It is another object of the present invention to provide an
improved method of performing a discectomy, a fusion, and an
internal stabilization of the spine, which is both quicker and
safer than is possible by previous methods.
[0111] It is another object of the present invention to provide an
improved method of performing a discectomy, a fusion and an
internal stabilization of the spine, to provide for improved
surgical spinal implants.
[0112] It is another object of the present invention to provide an
improved method of performing a discectomy, a fusion, and an
internal stabilization of the spine, which provides for an improved
system of surgical instrumentation to facilitate the performance of
the combined discectomy, fusion, and internal spinal
stabilization.
[0113] It is another object of the present invention to provide an
improved method of performing a discectomy, a fusion, and an
internal stabilization of the spine procedures.
[0114] It is an object of the present invention to provide
instrumentation and a method of spinal interbody arthrodesis that
is faster, safer, and more efficacious than prior methods, and can
effectively be performed in the cervical, thoracic, and lumbar
spine anteriorly, as well as in the lower lumbar spine
posteriorly.
[0115] It is a further object of the present invention to provide a
means for inserting a spinal implant between adjacent vertebrae
while maintaining their optimal spacing, positioning, and
alignment.
[0116] These and other objects of the present invention will be
apparent from review of the following specification and the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0117] FIG. 1 is a side view of the Long Distractor, of the present
invention inserted into the intervertebral space.
[0118] FIG. 2 is a side view of a Convertible Distractor assembly
in relation to the spine.
[0119] FIG. 3 is a perspective view of a high retention Short
Distractor of FIG. 2.
[0120] FIG. 3A is a side view of the high retention Short
Distractor of FIG. 2.
[0121] FIG. 3B is a side view of an alternative Short Distractor
with circumferential forward facing ratcheting.
[0122] FIG. 3C is a top view of the alternative Short Distractor of
FIG. 3B.
[0123] FIG. 3D is a perspective view of an alternative embodiment
of a Short Distractor.
[0124] FIG. 3E is a top view of the alternative distractor of FIG.
3D.
[0125] FIG. 3F is a side view of a further alternative
rectangularized Short Distractor with knurled surfaces.
[0126] FIG. 4 is a perspective view of a spinal segment (two
vertebrae and an interposed disc) with a Short Distractor in place,
with a portion of the upper vertebrae and disc cut away to show the
Short Distractor on one side of the spine and the Long Distractor
about to be placed contralaterally.
[0127] FIG. 5 shows a side view of the Outer Sleeve in place over
the Long Distractor, and about to receive the Driver Cap in
preparation for being seated.
[0128] FIG. 6 shows the Long Distractor, Outer Sleeve, and Driver
Cap following the proper seating of the Outer Sleeve into the two
adjacent vertebrae.
[0129] FIG. 7A is a side view of the cervical Outer Sleeve being
placed over a Long Distractor which is in place within the disc
space anteriorly.
[0130] FIG. 7B is a bottom view of the single Outer Sleeve of FIG.
7A.
[0131] FIG. 7C is a bottom view of a Dual Outer Sleeve.
[0132] FIG. 7D is an enlarged side view of the proximal portion of
FIG. 7C.
[0133] FIG. 7E is a bottom view of a Dual Driver Cap for driving
two distractors.
[0134] FIG. 7F is a side sectional view showing the Dual Outer
Sleeve of FIGS. 7C and 7D, Distractors and Dual Cap of FIG. 7E
seated.
[0135] FIG. 8 is a side view of the Outer Sleeve of FIG. 7A
centered on the Long Distractor and fully seated on the anterior
aspect of the cervical spine.
[0136] FIG. 9 is a perspective view of the Distractor Puller.
[0137] FIG. 10 is a cutaway partial side view of the Proximal
Puller engaging the extraction ring of the Long Distractor over the
end of the Outer Sleeve.
[0138] FIG. 10A is a side view of the Puller coupled to the Long
Distractor just prior to its extraction.
[0139] FIG. 10B is a posterior view of the proximal Outer Sleeve
and a Short Distractor in place in regard to the vertebrae, disc
and nerves.
[0140] FIG. 11A is a side sectional view of the Drill and Inner
Sleeve within the Outer Sleeve and drilling across the
intervertebral space and cutting partially cylindrical arcs from
the adjacent vertebrae.
[0141] FIG. 11B is a sectional side view of preparation of the
intervertebral space by the alternative "Trephine Method" showing
the Distractor, Trephine, Inner Sleeve, and Outer Sleeve in
place.
[0142] FIG. 11C is a sectional side view as in FIG. 11A, but
showing the use of an alternative drilling conformation wherein the
extended proximal portion is both distracting and
self-centering.
[0143] FIG. 11D is a side view of an instrument for removing arcs
of bone from vertebrae following drilling.
[0144] FIG. 12 is a perspective view of the surgical Tap.
[0145] FIG. 13 is a side view of the Outer Sleeve and the surgical
Tap fully threaded within the interspace.
[0146] FIG. 14A is a side view of the bone harvesting Trephine and
motor adapter.
[0147] FIG. 14B is a perspective view of the implant Bone Loading
Device.
[0148] FIG. 14C is a perspective view of the Corkscrew.bone freeing
and extracting instrument.
[0149] FIG. 15 is a partial perspective view of the Bone Loading
Device in operation.
[0150] FIG. 16 is a perspective view of the Implant Driver about to
engage the spinal implant.
[0151] FIG. 17 is a side view of the spinal implant being fully
seated within the intervertebral space by means of the Driver
apparatus in place within the Outer Sleeve.
[0152] FIG. 18 is a side view of the lumbar spine showing the end
result of the device implantation via the posterior route.
DETAILED DESCRIPTION OF THE DRAWINGS
[0153] The following discussion will be in regard to application in
the lumbar spine via the posterior approach. In its simplest form,
the method of the present invention involves the following steps.
The patient is placed on a spinal surgery frame, which allows for
the distraction and alignment of the disc space to be fused. A
bilateral posterior exposure of the interspace, with or without
partial discectomy is then performed. Utilizing distractors the
disc space is distracted, and a hollow Outer Sleeve is fitted over
one of the distractors. The end of the Outer Sleeve has teeth for
engaging the two adjacent vertebrae. The Outer Sleeve is driven
into the vertebrae and the distractor is then removed. A hollow
Inner Sleeve is then inserted into the Outer Sleeve and a stopped
Drill is utilized to prepare the opposed vertebral surfaces. The
Drill and the Inner Sleeve are removed as a single unit. The space
is tapped if so required. The prepared spinal implant is then
inserted via the Outer Sleeve utilizing a stopped inserter. The
instruments are then removed and the procedure repeated on the
contralateral side of the spine.
[0154] Step 1a. Prior to surgery, translucent implant templates
appropriately adjusted for scale are superimposed on AP, lateral,
and axial images of the interspace to be fused, for the purpose of
selecting the optimal implant size and to determine the desired
distraction.
[0155] Step 1b. The patient is preferably placed onto a spinal
surgery frame capable of inducing both distraction and vertebral
alignment.
[0156] Step 2. In the preferred embodiment, a standard bilateral
(partial) discectomy is performed and any posterior lipping of the
vertebral bodies adjacent the interspace is removed. Alternatively,
no disc material need be removed. In the preferred embodiment, the
interspace is exposed by performing bilateral paired
semihemilaminotomies and resecting the inner aspects of the facet
joints adjacent the spinal canal while preserving the supra and
interspinous ligaments.
[0157] Step 3. Beginning on the first side, the dural sac and
traversing nerve root at that level are retracted medially and a
Long Distractor then inserted and impacted flush to the posterior
vertebral bodies adjacent that interspace. Long Distractors with
working ends of increasing diameter are then sequentially inserted
until the optimal distraction is obtained. This optimal distraction
not only restores the normal height of the interspace, but further
achieves a balance wherein the tendency for the space to collapse
is resisted, which in urging the vertebral bodies apart is being
equally resisted by the powerful soft tissue structures about the
spinal segment including the outer casing of the disc (the annulus
fibrosus), various ligaments, capsular structures, as well as the
muscles and other soft-tissue structures. This balanced distraction
not only provides for the spatial restoration of the height of the
interspace, but for considerable stability as the space now resists
further distraction or collapse.
[0158] In the preferred embodiment, as the desired distraction is
approached, the use of the solid bodied Long Distractors is
terminated and a disassemblable Convertible Distractor is placed
with tactile and/or radiographic confirmation of ideal distraction.
The Convertible Distractor is then disassembled such that the Short
Distractor portion is left in place and the ultra-low profile head
portion being positioned adjacent to the canal floor and safely
away from the neural structures. To insure that the Short
Distractor remains in place until its removal is desired, various
embodiments of the Short Distractor are available with varying
degrees of resistance to dislodgment. In the preferred embodiment
of the procedure, attention is then directed to the contralateral
side of the spine.
[0159] Step 4. On the contralateral side of the same interspace the
Long Distractor having at its working end the diameter matching the
Short Distractor already in place, is then inserted. If however,
due to an asymmetrical collapse of the interspace it is then
determined that greater distraction is required on the second side
to achieve the optimal stability, then the appropriate Short
Distractor would be placed on the second side. Then the Short
Distractor would be removed from the first side and replaced with a
larger Long Distractor so as to bring the interspace into
balance.
[0160] In an alternative embodiment, the entire procedure is
performed on the one side of the spine utilizing only the Long
Distractor prior to repeating the procedure on the contralateral
side of the spine. While this method can be performed in accordance
with the remaining steps as described in the preferred embodiment,
when utilized it is best performed using a Trephine which allows
the Long Distractor to remain in place, thereby allowing for
interspace distraction otherwise provided in the first method by
the Short Distractor. This alternative method then requires the use
of a Trephine over the Long Distractor in lieu of a reamer and is
therefore called the "Trephine Method", which will be discussed in
detail later.
[0161] Step 5. With the Short Distractor in place on the first side
of the spine, and the matching Long Distractor in place on the
second side of the spine, and with the dural sac and traversing
nerve root safely retracted, the Outer Sleeve is placed over the
Long Distractor and firmly impacted to its optimal depth using the
Impaction Cap and a mallet. The Long Distractor is then
removed.
[0162] Step 6. An Inner Sleeve is then placed within the Outer
Sleeve, and the interspace is then prepared on that side by
utilizing a Drill, Endmill, Reamer, or Trephine to drill, ream, or
cut out the bone to be removed to either side, as well as any
remaining interposed discal material. In the preferred method,
utilizing a specially designed Endmill-Drill, it and the Inner
Sleeve are removed as a unit, safely carrying away the bone and
disc debris trapped within them from the spinal canal.
[0163] Step 7. If required, a thread forming Tap with penetration
limiting means to control the depth of insertion, is then inserted
through the Outer Sleeve.
[0164] Step 8. The prepared implant is then inserted utilizing the
specialized Driver unit. It should be noted that the implant may be
coated with, made of, and/or loaded with substances consistent with
bony fusion. However, in the preferred embodiment, the implant is
treated with bone promoting and inducing substances, but is loaded
with materials suitable for participating in a fusion.
[0165] While substances both natural and artificial are covered by
the present invention, the preferred embodiment is in regard to the
use of the patient's own bone by the following method. A hollow
Trephine is utilized to harvest a core of bone from the posterior
superior aspect of the iliac crest adjacent the sacroiliac joint.
This core of bone is at its outside diameter, slightly smaller than
the inside diameter of the spinal implant to be loaded, but longer
than the spinal implant. Utilizing an instrument designed for that
purpose, the core of bone is then injected from within the Trephine
into the central cavity of the implant causing a superabundance of
the bone material within the implant such that the bone material
tends to press out through the openings communicating with the
outside surface of the implant.
[0166] Step 9. Using the Driver Extractor instrument, the prepared
implant is threaded into the prepared interspace. The
instrumentation is removed from that side of the spine and
attention is then redirected to the first side of the spine. A
small retractor is utilized to move the dural sac and traversing
nerve root medially and to protect them and allowing the direct
visualization of the retained Short Distractor unit. Without
removing the Short Distractor, it is reassembled to its shaft
portion, essentially reconstituting itself into a Long Distractor.
With the inserted implant now acting as the distractor on the
opposite side, the Long Distractor is utilized to guide the Outer
Sleeve down where it is impacted as described in Step 5.
[0167] Steps 6 & 7 are then repeated, completing the procedure
at that level. The wound is then irrigated and closed in the
routine manner.
Representative Example of the Preferred Method
[0168] Through preoperative templating of the patient's anterior
posterior, lateral, and axially imaged MRI scan in conjunction with
translucent overlays of the various sized implants, the correct
implant diameter and length are accurately assessed, as well as the
correct amount of distraction needed to restore the interspace to
its premorbid height. The patient is then properly positioned and a
bilateral partial discectomy performed via paired
semihemilaminotomies.
[0169] For the purpose of this example, it will be assumed that by
preoperative assessment it was determined that the correct implant
would have an external diameter of 18 mm and be 26 mm long.
Further, the distraction necessary to restore the height of the
interspace would be approximately 10 mm. The dural sac and
traversing nerve root would then be retracted medially and
protected, while a Long Distractor having an outside diameter to
the barrel portion corresponding to the implant to be inserted,
that is 18 mm, and having a diameter at the working end of perhaps
8 mm, would be inserted. This then being found to be slightly
smaller than optimal by direct observation, a Convertible
Distractor having in its barrel portion an 18 mm outside diameter,
but having in its working portion a 10 mm diameter would then be
inserted. Direct observation and/or x-ray then confirming the ideal
distraction, the Convertible Distractor would then be disassembled,
the barrel and head portion removed, and the Short Distractor
portion left deeply embedded and with its flanged head flat against
the canal floor and deep to the neural structures. It would then be
safe to allow the dural sac and nerve root to return to their
normal positions, which would be superficial to the flanged portion
of the Short Distractor.
[0170] Attention would then be directed to the contralateral side.
The dural sac and nerve root would then be retracted medially on
this second side, and a Long Distractor with an 18 mm diameter
barrel portion and a 11 mm working portion would then be inserted
into the interspace and driven flush to the bone if necessary, such
impaction imploding any osteophytes not already removed, and
assuring that the shoulder portion of the barrel comes to lie flat
against the posterior aspects of the adjacent bodies. With the
dural sac and nerve root still safely retracted, the Outer Sleeve
would then be placed over the Long Distractor and utilizing the
Driver Cap and a mallet, seated to the optimal depth.
[0171] In the preferred embodiment, the Long Distractor is then
removed and the Inner Sleeve is inserted into the Outer Sleeve.
Since the purpose of the Inner Sleeve is to support the drill and
allow for the increased size of the implant over the size of the
drill, thus making it possible for the insertion of the implant to
occur through the Outer Sleeve, the Inner Sleeve therefore measures
18 mm in its outside diameter, and 16.6 mm in its inside diameter.
This allows it to fit within the Outer Sleeve, the diameter of
which is 18.1 mm and to admit the drill bit which is 16.5 mm in
diameter.
[0172] Following the drilling procedure, the Drill and Inner Sleeve
are removed as a single unit with the trapped interposed
cartilaginous and bony debris. The depth of drill penetration is
preset and limited by the fixed rigid column of the Outer Sleeve.
In this example, the space will be prepared to a depth of 28 mm in
anticipation of countersinking a 26 mm long implant at least 2 mm.
If a Tap were to be utilized, it would be inserted at this time and
be appropriate to the minor and major diameters of the implant to
be inserted and as with the Drill, controlled for its depth of
penetration. The spinal implant would then be prepared for
implantation by utilizing a Trephine to harvest a core of posterior
iliac bone greater than 30 mm long and approximately 14.5 mm in
diameter.
[0173] Using the Bone Loading Device, this core of bone would be
forcefully injected into the internal chamber of the spinal implant
which would then be capped. Cap end forward, the fully loaded
implant would then be attached to the Insertion Driver, down the
Outer Sleeve and screwed into place with the depth of penetration
limited by the Insertion instrument. The Insertion Driver is then
unscrewed from the implant and removed from the Outer Sleeve. With
the dural sac and nerve root retracted and protected, the Outer
Sleeve would then be removed. This would complete the fusion
procedure on that side, and then as described, the procedure would
be repeated on the other (first) side of the same interspace.
Alternative Methods
[0174] An alternative and extremely useful method is the "Trephine
Method". Its advantages include that it may be used in conjunction
with the preferred embodiment substituting the use of a hollow,
tubular cutter, called a Trephine for the use of the Drill in Step
5 of the preferred embodiment. Additionally, it may be utilized so
as to obviate the need for the placement of the Short Distractor
and to allow the procedure to be effectively performed from start
to finish on one side prior to initiating the procedure on the
opposite side, and while nevertheless maintaining distraction at
the site of the bone removal.
[0175] The following is a description of the "Trephine Method".
Having completed the exposure of the interspace on at least one
side, the dural sac and nerve root are retracted. A Long Distractor
differing from the Long Solid Bodied Distractor of the preferred
embodiment only in that the barrel portion is of a precisely lesser
diameter than the spinal implant. As in the preferred embodiment,
the Outer Sleeve has an inner diameter only slightly greater than
the implant to be inserted. Therefore, at this time, a first Inner
Sleeve is inserted into the Outer Sleeve to make up the difference
between the outside diameter of the Long Distractor and the inside
diameter of the Outer Sleeve. With the Outer Sleeve and first Inner
Sleeve thus assembled, they are placed over the Long Distractor and
the Outer Sleeve is optimally seated using the Impaction Cap. The
Cap and first Inner Sleeve are removed, but the Long Distractor and
Outer Sleeve are left in place.
[0176] With the Long Distractor maintaining optimal distraction and
with the Outer Sleeve locking the vertebrae together so as to
resist any movement of the vertebrae, a hollow, tubular cutter
known as a Trephine is then inserted over the Long Distractor and
its barrel portion and within the Outer Sleeve. The Trephine, which
is stopped out to the appropriate depth, can then be utilized to
cut equal arcs of bone from the opposed vertebral endplates.
[0177] Alternatively, a second Inner Sleeve may be placed within
the Outer Sleeve prior to placing the Trephine over the Long
Distractor and within that second sleeve. This second Inner Sleeve
would be just greater in its internal diameter than the Long
Distractor and just smaller in its outside diameter than the inner
diameter of the Outer Sleeve. While it would provide enhanced
stability to the Trephine, provision would then need to be made in
is the way of large flutes passing longitudinally or obliquely
along the outer surface of the Distractor to its barrel portion to
accommodate the bony and cartilaginous debris generated during the
cutting procedure.
[0178] Following the use of the Trephine to the appropriate depth
by either of these methods, the Trephine, the Long Distractor, and
the second Inner Sleeve, if utilized, are all removed. Since the
Trephine cuts two arcs of bone but does not ream them out, a
shafted instrument with a perpendicular cutting portion at its
working end is then inserted parallel to the disc space and then
rotated through an arc of motion cutting the bases of the two
longitudinally cut arcs, thus freeing them for removal through the
Outer Sleeve. The space may then be tapped if required, and the
implant is inserted as per the preferred method. As already
mentioned, the "Trephine Method" can be used with or without the
use of the Short Distractor on the contralateral side.
Applications of Method in Other Areas of the Spine
[0179] The following method is the preferred embodiment for
performing anterior interbody fusion in the thoracic and lumbar
spines. It is also appropriate in the cervical spine when the width
of the spine anteriorly is sufficient so that it is possible to
place two implants side by side and such that each intrudes at
least several millimeters into the substance of the opposed
vertebrae and for the length of the implants.
[0180] The interspace to be fused is adequately exposed and the
soft tissues and vital structures retracted and protected to either
side. Visualization of the broad width of the interspace anteriorly
is made possible by the absence of the neurological structures in
relation to this aspect of the spine. The center line of the
anterior aspect of the interspace is noted and marked. The disc is
removed using first a knife and then curettes and rongeurs as
needed. Alternatively, the disc may be left intact to be removed
during the drilling stage of the procedure. However, as per the
preferred embodiment of the procedure, having removed the great
mass of the nucleus and the greater portion of the annulus
anteriorly, Long Distractors with progressively increasing
diameters to their working ends are inserted into the interspace at
a point midway between the central marking line and the lateral
extent of the anterior aspect of the spine as visualized.
[0181] The Dual Outer Sleeve with its common Foot Plate and
Retention Prongs is then inserted over either a singly placed Long
Distractor and then the second Distractor placed, or is placed over
both Distractors if already placed. The Dual Outer Sleeve is then
seated firmly against the anterior aspect of the spine. Any spurs
which would interfere with the flush seating of the Foot Plate to
the anterior aspect of the spine should be removed prior to
inserting the Long Distractors. Once the Outer Sleeve has been
optimally seated, one of the Long Distractors is removed and in its
place is inserted an Inner Sleeve and drill bit. The drill bit has
as its outside diameter the minor diameter of the implant to be
inserted. The Inner Sleeve is essentially equal in thickness to the
difference between the minor and major diameters of the threaded
implant.
[0182] A Stopped Drill is then utilized to prepare the opposed
vertebral surfaces and to remove any remaining disc material
interposed. If required, a Stopped Tap may be inserted through the
Outer Sleeve and into the interspace to create a thread form. The
properly prepared implant is then affixed to the Insertion Driver
and passed through the Outer Sleeve down into the interspace and
inserted until its depth of penetration is limited by the stop on
the Insertion Driver. With the implant itself now in a position to
act as a distractor, the Long Distractor is then removed from the
contralateral side and the procedure repeated. When both implants
are firmly in place, the outer sleeve may then be removed. The
amount of countersinking of the implants may then be adjusted under
direct vision.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT METHOD AND
INSTRUMENTATION
[0183] In the preferred embodiment, the disc (D) between adjacent
vertebrae (V) is approached via bilateral paired
semihemilaminotomies of the adjacent vertebrae. In the preferred
embodiment the supraspinous ligament, the interspinous ligament,
the spinous process, portions of the lamina, and most of the facet
joints are preserved. However, while less desirable, these
structures may be removed.
[0184] In the preferred method, a bilateral partial nuclear
discectomy is then performed through bilateral openings created
through the posterior aspect of the annulus fibrosus. While
considered less desirable, disc excision can be delayed and
performed simultaneously with the vertebral bone resection during
the drilling procedure. Starting on the first side a dural nerve
root retractor is placed such that the dural sac and lower nerve
root are retracted medially allowing exposure to one side of a
portion of two adjacent vertebral bodies and the interposed disc
posteriorly.
[0185] Referring now to FIG. 1, preferably after removing some
portion of nuclear disc material, a Long Distractor 100 is inserted
under direct vision into the intervertebral space. The disc
penetrating portion 102 is essentially cylindrical with a
bullet-shaped front end 103 and a shoulder portion 104 where the
penetrating portion 102 extends from barrel 106. The penetrating
portion 102 urges the vertebral bodies apart, facilitating the
introduction of the instruments. Long Distractors with sequentially
increasing diameter penetrating portions 102 are then introduced.
As the optimal diameter of penetrating portion 102 is achieved, the
vertebral bodies to either side are forced into full congruence and
thus become parallel, not only to the penetrating portion 102, but
to each other. At this time, any remaining excrescences of bone of
the posterior vertebral bodies adjacent the posterior disc which
have not already been removed are flattened flush to the vertebral
body by the forced impaction, such as by hitting with a hammer flat
surface 109 of crown 110, driving the shoulder 104 against the
lipped portions of vertebrae V. Because of the forced opposition of
the vertebral endplates to portion 102 with optimal distraction,
unit 100 will then come to lie absolutely perpendicular to the
plane of the posterior bodies and absolutely parallel to the
vertebral endplates, allowing optimal alignment for the procedure
to be performed.
[0186] Penetrating portion 102 is available in various diameters,
but all are of a constant length, which is less than the known
depth of the interspace. This combined with the circumferential
shoulder 104, which is too large to fit within the interspace,
protects against the danger of overpenetration. Barrel 106 is of
the same diameter as the external diameter of the device to be
implanted. A recessed portion 108 below the crown 110 allows for
the Long Distractor 100 to be engaged by an extractor unit shown in
FIG. 9.
[0187] In the preferred embodiment, a Convertible Long Distractor
113 is used on the first side of the spine. As shown in FIG. 2, the
Convertible Long Distractor 113 has a barrel portion 152 separable
from the Short Distractor portion 120. While the initial
distraction may be performed with a solid Long Distractor, as the
optimal distraction is approached the appropriate Convertible Long
Distractor is utilized. The Convertible Long Distractor 113
consists of a Short Distractor portion 120 and a barrel 152 having
a rectangular projection 134 at one end. The Short Distractor 120
has an increased diameter head 128, a rectangular slot 118 and an
internal threaded opening 114. The barrel 152 is hollow and has an
internal shaft 111 terminating in a large diameter hexagonal crown
115 at one end and a reduced diameter portion 112. The crown has a
detent portion 117 in its flat surface. The other end of the shaft
111 has a threaded small member 116 that corresponds to threaded
opening 114. The shaft 111 is prevented from removal from the
barrel 152 by set pin 119 passing through the wall of barrel 152 in
a convenient manner. The Short Distractor portion 120 is removably
attached to the barrel portion 152 via the mating of female
rectangular slot 118 and the male mating member 134. The mating
held together by utilizing is knob 136 to drive the crown 110
connected to interior shaft 111 having a threaded working end screw
116 that threads into the female aperture 118 of the Short
Distractor portion 120.
[0188] Cap 136 has an open socket 138 for fitting around crown 115
and engages the reduced diameter hexagonal portion 112 so as to
permit the rotation of shaft-111 and threaded male member 116. A
detent ball 150 in the inside of the socket 138 engages detent 117
in the crown 115, holding them together.
[0189] The Short Distractor portion 120 of FIGS. 2, 3, and 3A-3F
are designed to provide for high stability when temporarily
situated so as to resist inadvertent migration while the surgeon is
working on the second side. To that end, the embodiment of the
Short Distractor 120 shown in FIGS. 3 and 3A has a pair of sharp
pegs 126, to embed into the opposing vertebral bodies and forward
facing ratchetings 124, that further resist backward movement.
FIGS. 3B and 3C, which show the preferred embodiment, are side and
top views of an alternative embodiment of the distractor portion
such that the distractor portion to be interposed between the
vertebrae is essentially cylindrical, but with circumferential
forward facing ratchetings 124.
[0190] A further alternative embodiment is shown in FIGS. 3D and
3E. This is a more rectangularized design, with forward facing
ratchetings, without the sharp prongs 126 of FIG. 3. FIG. 3F is a
side view of a further embodiment of the Short Distractor 120 shown
with knurling, to increase the interference with the bone surface
so as to add stability to the unit and to resist dislodgment. To
this end, it is apparent that the working ends of both the Long and
Short Distractors can have a variety of configurations consistent
with their purpose, and that surface irregularities as well as the
shape of the ends themselves, with or without prongs 126, may be
utilized to make the Short Distractor 120 more resistant to
migration.
[0191] Once the ideal distraction has been achieved on the first
side of the spine, the Convertible Distractor is dissociated,
leaving Short Distractor 120 in place with its rounded external end
128, safely on the canal floor and deep to the dural sac and nerve
root.
[0192] As shown in FIG. 4, the surgeon then moves to the other side
of the spine at the same disc (D) level, and retracts the dural sac
and nerve root medially, exposing the disc on that side. Long
Distractors 100 are then sequentially inserted into the disc space
until the diameter of the distractor on the second side is at least
as big as that on the first side. If because of some asymmetry of
the interspace a larger diameter distractor is required on the
second side to achieve the ideal distraction as compared to the
first side, then the second side is fitted with a Short Distractor
of the larger diameter, and the surgeon would then return back to
the first side. In that event, the first side Short Distractor
would then be removed and the Long Distractor 100 corresponding to
the increased diameter of the already placed Short Distractor 120
would then be inserted. In either event, the operation is continued
by working on the one side where the Long Distractor is in place.
In this regard, it should be noted, that by the use of such a
device as the Michelson Spinal Surgery Frame, it may be possible to
obtain adequate distraction preoperatively such that the surgeon is
either disinclined to use a distractor, or to simply place the
correct Long Distractor on the first side and then proceed with the
surgical procedure on that side before moving to the opposite side.
These variations are within the scope of the present invention.
[0193] The Long Distractor now serves as both a centering post and
an alignment rod for the hollow Outer Sleeve 140 shown in FIG. 5
which is fitted over the Long Distractor 100, shown by phantom
lines 101 in FIG. 5. The Outer Sleeve 140 is metal and has a sharp
toothed front end 142 that is capable of penetrating into and
holding fast the two adjacent vertebrae (V). Interrupting the
circumferential sharp teeth of 142 are flat, planar areas 152 which
serve to resist the further insertion of the sharp teeth into the
vertebral bodies. The toothed front end 142 of the Outer Sleeve 140
is a continuation of the tubular shaft 144, which in turn is
connected to circumferentially enlarged tubular back end 146 having
a knurled outer surface 148 for easier manipulation. An alternative
embodiment of an Outer Sleeve incorporates an expansile key hole
and slot configuration 154 to either side of shaft 144 along the
mid-plane of the interspace and parallel to it such that the end
142 resists the collapse of the vertebrae (V) to either side of the
disc (D), but may nevertheless allow for their further distraction,
in the event the only diameter or the root diameter of the implant
is larger than the hole drilled.
[0194] A Driver Cap 160 in-the form of an impaction cap has at its
far end a flat, closed-back surface 162 and at its other end a
broad, circular opening. The Driver Cap 160 fits over both the
Outer Sleeve 140 and the Long Distractor 100. As the Driver Cap 160
is seated, interior surface 170 circumferentially engages portion
146 of the Outer Sleeve until the back end 172 engages the internal
shoulder 164. As mallet blows are applied to surface 162, that
force is transmitted via the internal shoulder 164 to the Outer
Sleeve 140 via its far end 172, seating teeth 142 into the
vertebral bodies adjacent the disc space D and to the depth of the
teeth 142 to the flat portions 152. As the Outer Sleeve 140 is
advanced forward, crown portion 110 of the Long Distractor is
allowed to protrude within the Driver Cap 160 unobstructed until it
contacts the interior flat surface 168. Once crown 110 comes into
contact with the flat interior surface 168, then further taps of
the mallet will not advance the Outer Sleeve, any further motion
being resisted by the flat shoulder portion 104 of the Long
Distractor abutting the hard surfaces of the posterior vertebral
bodies. In this way, the Outer Sleeve 140 is safely and assuredly
inserted to its optimal depth and rigidly securing the two opposed
vertebrae as shown in FIG. 6.
[0195] The Cap 160 is then removed and the Distractor Puller 200 of
FIG. 9 utilized to remove the Long Distractor 100 from the spine
leaving the Outer Sleeve 140 in place. The Distractor Puller 200
has front portion 202, a mid portion 204, and a back handle portion
206. At the front portion 202 of the Distractor Puller 200, a
socket 208 is connected to one end of shaft 210 which at its far
end is connected to back handle portion 206. The socket 208 has
defined within it a cavity 212 that is open at its front end and
funnelized on the interior aspect of its sides. The cavity 212 is
constructed so that the head of the Distractor Puller 200 and the
partially circumferential flange 218 engages the circumferential
recess 108 of the Distractor 100. The entrance to cavity 212 is
slightly funnelized, and the leading edges of flange 218 slightly
rounded to facilitate the engagement of recess 108 and head 110 of
Distractor 100, which is further facilitated in that the Driver Cap
160 leaves portion 108 of Distractor 100 precisely flush with the
back surface 172 of the Outer Sleeve 140. This provides a large,
flat surface 172 to precisely guide surface 230 of socket 208, and
open portion 212 around head 110 while flange 218 engages recess
108. The springloaded detent ball 228 engages hemispherical
depression 112 in the crown 110, shown in FIG. 2. This springloaded
detent 228 in engagement with complimentary indent 218 protects
against the inadvertent dissociation of the Long Distractor from
the Puller 200 after the Distractor has been removed from within
the Outer Sleeve 140 and prior to its removal from the wound. Once
out of the body, the two instruments are easily disassociated by
freeing the crown portion 110 from cavity 212 by a manual force
applied perpendicular to their relative long axes at this
location.
[0196] A cylindrical and free removable weight 216 is fitted around
shaft 210 between the front portion 202 and the rear handle portion
206. Gently, but repeatedly sliding the weight 216 along shaft 210
and driven rearwardly against flat surface 228, transmits a
rearward vector to proximal end 202 and thereby to the Long
Distractor 100 to which it is engaged.
[0197] Paired extended handle 224 and 226, allow the surgeon to
resist any excessive rearward motion as the instrument is used to
liberate the Long Distractor 100. Paired handles 224 and 226 are
also useful in that they allow a rotational directing of portion
208, via the shaft 210. This allows the surgeon to control and
manipulate rotationally the orientation of the opening of cavity
212 to facilitate its application, to the head 110 of the
distractor 100.
[0198] The Distractor Puller 200 is a significant improvement over
the alternatives of striking a remover instrument with an
independent hammer over the exposed surgical wound, or manually
extracting the distractor by forcefully pulling. The use of a free
hammer over the open wound is dangerous because the neural
structures can be impacted on the back swing which is made even
more likely by the effects of gravity on the mallet head. Manual
extraction by pulling is dangerous because of the significant
interference fit of portion 102 within the spine such that
significant force would be required to remove the Distractor 100,
and if force were not coaxial then the Outer Sleeve might be
dislodged or misaligned. Further, once the flat portion 102 became
free of the interspace, all resistance to withdrawal would be lost
and in the face of the considerable force necessary to free it, the
Distractor 100 might easily become projectile imparting injury to
the patient and/or the surgeon.
[0199] Once the Long Distractor 100 has been fully removed from the
Outer Sleeve 140, the toothed end 142 of the Outer Sleeve 140,
working in conjunction with the Short Distractor 120 on the
contralateral side rigidly maintains the relative position of the
adjacent vertebrae V. Further, since the remainder of the procedure
on that side of the spine occurs entirely through the protective
Outer Sleeve 140, and as the nerves and dural sac are external to
that Outer Sleeve and superficial to the toothed end 142 of the
Outer Sleeve 140, which is firmly embedded into the adjacent
vertebrae V, the Outer Sleeve 140 serves to insure the safety of
these delicate neural structures. Further, since the Outer Sleeve
140 is of a fixed length and rigid, its flat rearward surface 172
may be used as a stop to the advancement of all instruments placed
through the Outer Sleeve 140, thus protecting against accidental
overpenetration. Further, the Outer Sleeve 140 assures that the
further procedure to be performed will occur coaxial to the disc
space D and further, be symmetrical in regard to each of the
opposed vertebral surfaces.
[0200] FIG. 10B is a posterior view of the spine at this stage of
the procedure, showing a Short Distractor 120 in place on one side
of the spine and the bottom portion of Outer Sleeve 140 in place on
the opposite side of the spine.
[0201] Referring to FIG. 11A, an Inner Sleeve 242 is inserted from
the rear within the Outer Sleeve 140. This Inner Sleeve has a
collar portion 244 of a known thickness which seats against the top
edge surface 172 of Outer Sleeve 140. The cylindrical barrel
portion of Inner Sleeve 242 comes to approximate the posterior
aspect of the vertebral bodies interior the Outer Sleeve when fully
seated. A Drill 240, having a known selected length is then
introduced through the rearward aperture of the Inner Sleeve 242
and utilized to ream out the arcs of bone which it engages from the
opposed vertebral endplates as well as any discal material within
its path down to its predetermined and limited depth. The Drill
240, has a narrow engagement portion 246, which allows it to be
affixed to a drill mechanism which may be either a manual or a
power unit. A circumferential collar 248 of an increased diameter
serves to limit the depth of penetration of the drill 240 and may
be fixed, or lockably adjustable.
[0202] Not shown here, but well known to those skilled in the art,
are various mechanisms to lockably adjust such instruments as
drills. Such mechanisms include, but are not limited to, the use of
collets, threaded shafts with lock nuts, and flanges engaging
grooves forced therein by either a cap pulled over the flanges or
screwed down upon them.
[0203] In the preferred embodiment, the forward cutting edge 252 of
Drill 240 is a modification of a large fluted drill design such
that the end resembles an end cutting mill which may contain any
workable number of cutting surfaces, but preferably four or more,
and such cutting surfaces being relatively shallow such that the
advancement of the instrument occurs more slowly. The outside
diameter of the Drill 240 corresponds to the minor diameter of the
threaded spinal implant. The Inner Sleeve 242 has an inner diameter
slightly greater than that dimension and its outer diameter is
slightly smaller than the inside diameter of the Outer Sleeve 140
which has the same outer diameter as the major diameter of the
threaded implant.
[0204] The drill shaft of drill 240 comprises an upper portion 243,
a central recessed portion 256 of a smaller diameter and a lower
cutting drill portion 250. The upper portion 243 and lower portion
256 of the drill 240 have the same outside diameter.
[0205] The Inner Sleeve 242 serves many functions. First, it
provides a more intimate drill guide for drill 240 in the event a
smaller diameter hole is to be drilled than that of the inside
diameter of the Outer Sleeve 140. Second, since it now guides the
Drill, it allows for the Outer Sleeve 140 to have an internal
diameter large enough to admit the threaded spinal implant, which
is indeed considerably larger in diameter than the Drill 240
itself.
[0206] If a larger Outer Sleeve 140 were utilized absent the Inner
Sleeve 242, then the Drill 240 would be free to wander within the
confines of that greater space and would not reliably make parallel
cuts removing equal portions of bone from the adjacent vertebrae V.
Further, the bone removal not only needs to be equal, but must be
correctly oriented in three dimensions. That is, the path of the
Drill 240 must be equally centered within the disc space, parallel
the endplates, and parallel to the sagittal axis dissecting the
interspace.
[0207] A further purpose of the Inner Sleeve 242 is that it may be
removed simultaneously with the Drill 240, thereby trapping the
debris, both cartilaginous and bony generated during the drilling
procedure, which are guided rearward by the large flutes 251 of
Drill portion 250, where they are collected around recessed portion
256 between the recessed portion 256 and the inner wall of the
Inner Sleeve 242 are there contained therein. Thus, by removing the
Drill 240 in conjunction with the Inner Sleeve 242, all of the
debris generated by the reaming procedure is safely removed from
the spinal canal and wound area.
[0208] Further, if the disc tissue in the area to be reamed has
been removed previously, as per the preferred method, then the
patient's own bone of good quality and useful within the operation
will then be contained between the Inner Sleeve 242 and the shaft
portion 256. Once away from the surgical wound, this material may
be used to load the spinal implant or placed deep within the
interspace to participate in the fusion.
[0209] The method of actually producing the surgical hole within
the spine is variable. As shown in FIG. 1C, in an alternative
embodiment Drill end 250 has a forward projecting nipple 260, which
itself is bullet-shaped in its leading aspect so as to ease its
entrance into the disc space and to urge the vertebrae apart.
Nipple 260 is distracting, stabilizing as it resists any tendency
of the vertebrae to move together, is self-centering to the Drill
portion 250 when working in conjunction with Sleeves 140 and 242,
and virtually assures the symmetrical resection of bone from the
opposed vertebral surfaces.
[0210] The alternative "Trephine Method" referred to earlier in
this application, is shown in FIG. 11B. In this alternative, a Long
Distractor 100 is left in place after the Outer Sleeve 140 is
seated. The Long Distractor 100 in this case differs from the Long
Distractor of the preferred embodiment in that its outside diameter
of the barrel 106 is of a smaller diameter than in the prior
version. This is made necessary because regardless of the method,
the hole to be formed corresponds to the minor diameter of the
spinal implant. Trephine 270, a hollow, tubular member with sharp
cutting teeth 251 at its proximal end, has a wall thickness and
since the outside diameter of that trephine 270 must correspond to
the root diameter of the implant, then the wall thickness of the
trephine 270 must be allowed for by a corresponding reduction in
the diameter of the Long Distractor 100.
[0211] A further modification of the Long Distractor 100 to the
"Trephine Method" would use longitudinal grooves (not shown) along
the barrel surface 106 for the purpose of transmitting any debris
generated during the cutting procedure, rearward. Since the cutting
element is both centered and aligned by the Long Distractor, the
use of the Inner Sleeve 242 is not mandatory, but may once again be
useful in controlling the path of the debris. To that end, little
debris is generated in the "Trephine Method" as the bony arcs are
not so much being reamed out and removed as they are simply being
cut into the bone where these arcs of bone are left connected at
their far ends. Thus, when the Trephining Method has been completed
and the Trephine 270 and Inner Sleeve 242 removed, unlike in the
preferred embodiment where the hole is drilled out, it remains
necessary to remove both the two arcs of bone, and any interposed
material. Nevertheless, this is very easily performed by various
means, one of which is depicted in FIG. 11D.
[0212] Instrument 272 consisting of a shaft 276 attached off center
to the lower surface 273 handle 274. The shaft 274 terminates in a
cutting arm 278. The instrument 272 is inserted through Outer
Sleeve 140 where the lower surface 273 of handle 274 abuts the top
172 of the Outer Sleeve 140, both stopping downward motion of
instrument 272 and precisely placing the perpendicularly cutting
arm 278 of instrument 272 so that as handle portion 274 is rotated,
the cutting arm 278 is also rotated, cutting the arcs of bone and
liberating them from their last attachments. These portions of bone
are then removed utilizing this instrument or a long forceps, and
then placed within the implants or otherwise used to participate in
the fusion.
[0213] While in the preferred embodiment of the present invention
the spinal implant 1, is essentially self-tapping, if the bone is
unusually hard it may be desirable to form the thread pattern
within the interspace prior to the insertion of the implant I. To
that end, as shown in FIG. 12, Tap 280 has a thread-cutting portion
282 connected by a shaft 286 to a handle portion 292, which has
been designed to give mechanical advantage to the rotation of the
instrument for the purpose of cutting threads. The lower portion of
handle 290 has a forward facing flat surface 288 too large to fit
through the opening of Outer Sleeve 140 which thus safely limits
the depth of penetration of the cutting element 282. This tap 280
is further made safe by blunt end 294 which will engage the uncut
portions of the vertebral bone just prior to the engagement of
shoulder 288 against surface 172. This feature allows the surgeon
to appreciate a less harsh resistance as the blunt nose 294
encounters the remaining unresected bone for the drill hole and
prior to the sudden increase in resistance caused by the seating of
shoulder 288 against top edge 172, which first resistance serves as
a warning to the surgeon to discontinue the tapping procedure.
Thus, the surgeon has both visual (as shoulder 288 approaches top
edge 172) and tactile warnings to avoid stripping the thread form.
Tap end 282 is highly specialized for its specific purpose.
Rearward to the specialized blunt tip 294 is a truncated
bullet-shaped area 298 which ramps up to the constant diameter
intermediate the cutting ridges 296. Ramp portion 298 urges the
opposed vertebral bodies apart, which motion is resisted by Outer
Sleeve 140, thus progressively driving the sharp leading edges of
thread forms 296 into the vertebral bodies. The periodic
longitudinal grooves 284 interrupting the thread forms, which may
number 1 to 8, but preferably 4, function to accumulate the bony
material which is removed during the thread cutting process. In
that regard, in the ideal embodiment, the thread cutting form is
designed to compress the bone to be formed rather than to trough
through it. Further, while both the major and minor diameters of
the Tap 280 may be varied, in the preferred embodiment, the minor
diameter corresponds to the minor diameter of the implant I, but
the major diameter is slightly less than the major diameter of the
implant.
[0214] With Tap 280 now removed, and Sleeve 140 still in place, the
surgical site is now fully prepared to receive the spinal implant
I. In the preferred embodiment of the spinal implant, the implant
has been enhanced by the use of, application to, and filling with
fusion promoting, enhancing, and participating substances and
factors. Thus, the implant may be fully prepared for insertion as
provided to the operating surgeon. However, at the present time,
human bone is most commonly used as the graft material of choice,
with the patient's own bone being considered the best source.
[0215] FIG. 14a shows a trephine 300 with an exceedingly sharp
front cutting edge 302 for quickly and cleanly coring into the
patient's posterior iliac crest, or any other bony tissue, and for
the purpose of producing a core of bone then contained within the
hollow 304 of the trephine 300. Trephine 300 has a rear portion 306
with a pair of diametrically opposed slots 310, and disposed
clockwise from their longitudinally oriented rearward facing
openings so as to engage diametrically and opposing members 312 of
Drive unit 308, by which trephine 300 may be attached to either a
hand or power drill. It can be appreciated that engagement
mechanism 312 is stable during the clockwise cutting procedure, and
yet allows for the rapid disconnection of the two components once
the cutting is completed.
[0216] Because of the high interference between the graft and the
inner wall of hollow portion 304, and the relative weakness of the
cancellous bone being harvested, it is possible to remove the
Trephine 300 while still drilling, and to have it extract the core
of bone with it. However, in the highly unlikely event that the
core of bone would remain fixed at its base, then with the drive
mechanism 308 removed, a corkscrew 408 shown in FIG. 14C is
introduced though the central opening of rear portion 306 and
threaded down and through the core of bone within 304 and to the
depth of teeth 302. The tip 318 of the corkscrew 408, which extends
substantially on line with the outer envelope of the corkscrew,
then cuts radially through the base of the bone core. As the handle
portion 314 of the corkscrew 408 abuts the flat, rearward surface
of portion 306 and it can no longer advance. As corkscrew 408 is
continued to be turned further, it will cause the core of bone to
be pulled rearward, as in removing a cork from a wine bottle.
Trephine 300 has a barrel portion 304 continuous with sharp toothed
portion 302 having an inner diameter just less than the inner
diameter of the spinal implant I to be loaded.
[0217] The Trephine 300 with its core of harvested bone is then
placed as shown in FIG. 14B, through opening 340 of Implant Bone
Loading device 320, where the barrel portion 304 then passes
through and is stopped by circular flange 344. The plunger shaft
326 of instrument 320 is then prepared for attachment by rotating
knob 332 counterclockwise such that the plunger 372 is pulled via
the long threaded shaft portion 328 back to the base of collar 330
at its proximal end. In this position, knob 332 is considerably
extended rearward from collar 330. With plunger shaft 326 in this
position, the plunger head 372 is inserted into the central hollow
of portion 306 of Trephine 300 as the proximal cylindrical portion
of collar 330 then follows it, such that the plunger 372 then
occupies the rearward portion of barrel 304 and the proximal
cylindrical portion of collar 330 occupies the central hollow of
portion 306. A pair of diametrically opposed radially projecting
arms 346 on collar 330 are then advanced longitudinally into
diametrically opposed paired L slots 340 and then rotated clockwise
to complete this assembly.
[0218] At the other end of instrument 320, a spinal implant I is
engaged through its female rectangular slot 364 by a rectangular
protruding bar extending from rearward facing surface of end plug
324, (not shown) and secured there by knob 334 which extends as a
rod through a central aperture within end plug 324 to extend at the
far end as a small bolt which threads to a female aperture centered
within the female slot 364 of the spinal implant. With the spinal
implant I secured to end plug 324 and the opposite end of the
implant I presenting as a hollow, tubular opening, end plug 324 is
advanced into device 320 where it is secured by rotationally
engaging diametrically opposed L- shaped slots 321. With device 320
fully assembled, end 302 of trephine 300 lies coaxial and opposed
to the open end of implant I.
[0219] As shown in FIG. 15, as knob 332 is then rotated clockwise,
the plunger 372 proximal the threaded shaft 328 is then forcibly,
but controllably driven forward down the barrel 304 ejecting the
bone graft directly into the spinal implant I. As the bone graft is
greater in length than the interior of the spinal implant, with
further compression the bone is forced into the radially disposed
apertures through the wall of the device communicating from the
central cavity to the exterior.
[0220] End plug 324 is then removed from apparatus 320. Using end
plug 324 as a handle, end cap 374 shown in FIG. 16 is secured to
the open end of the spinal implant I. The implant is then
disassociated from end plug 324 by rotating knob 334
counterclockwise.
[0221] FIG. 16 shows an Implant Driver instrument which may be used
to either insert or to remove said implant 1. Driver 350 has at its
far end 362, a rectangular protrusion 398, which protrusion
intimately engages the complimentary rectangular slot 364 of
implant I. Protruding from slot 398 of end 362 is threaded portion
353, which extends as a rod through hollow shaft 358 and hollow
hand barrel 360 to knob 354 where it can be rotationally
controlled. Threaded portion 353 screws into a female aperture
central slot 364, urging 353 into 364, and binding them together
such that instrument 350 can be rotated via paired and
diametrically opposed extending arms 366 and in either direction
while maintaining contact with the implant.
[0222] Affixed to the Driver 350, the implant is then introduced
through the Outer Sleeve 140 and screwed into the interspace
opposed between the two prepared vertebrae V until such time as the
leading edge of the Implant Cap 374 reaches the depth of the
prepared hole at which time its forward motion is impeded by the
bone lying before it which had not been drilled out. This allows
for a progressive feel to the surgeon as the implant is screwed
home.
[0223] As described previously, with the use of the Tap 280, this
terminal resistance to further seating provides significant tactile
feedback to the surgeon. Again, as with the Tap 280, visual
monitoring of the depth of insertion of the implant is provided to
the surgeon by observing the progressive approximation of the
forward surface 370, of barrel portion 360, as it approaches the
rearward facing-surface 172 of Outer-Sleeve 140. Nevertheless, a
final safety mechanism, when the full depth of insertion has been
achieved, surface 370 of instrument 350 will abut surface 172 of
the Outer Sleeve 140, prohibiting any further installation of the
spinal implant.
[0224] Once the implant has been fully installed, the Driver 350 is
dissociated from the implant by turning knob 354 in a
counterclockwise direction. The Driver 350 is then withdrawn from
the outer sheath, then the Outer Sleeve 140 is removed. This leaves
the implant fully installed and inset to the determined depth as
shown in FIG. 18.
[0225] Attention is then redirected to the other, or first, side of
the spine. A dural nerve root retractor is used to retract the
neural structures medially, bringing into full view the head 128 of
the Short Distractor 120, lying flush on the canal floor. Utilizing
apparatus 152, extended screw portion 116 is inserted into the
female threaded portion 114 of the Short Distractor 120 as the
extended rectangular portion 134 of apparatus 152 is engaged to the
female rectangular portion 118 of the Short Distractor 120. Then
turning rearward facing portions 108 and 110, utilizing the knob
136 of FIG. 2, the Long Distractor configuration is restored.
[0226] With the dural sac and nerve roots still retracted and
protected, the Outer Sleeve 140 is slipped over the reconstituted
Long Distractor and seated using the Driver Cap 162. The entire
sequence of events as described for the implantation of the spinal
implant I as already placed, is then repeated such that both spinal
implants come to lie side by side within the interspace. Though not
necessary, circlage or other internal fixation of the levels to be
fused may additionally be performed, and then the wound is closed
in the routine manner.
Brief Discussion with Reference to the Drawings of the Preferred
Method and Instrumentation for Anterior Interbody Fusion
Incorporating Intercorporeal Predistraction and Utilizing a Guarded
Sleeve System Is Disclosed
[0227] Because of the absence of the spinal cord and nerve roots,
it is generally possible to visualize in one instance the entire
width of the disc space from side to side throughout the cervical,
thoracic, or lumbar spine. In the preferred embodiment of the
anterior interbody fusion, implants are placed side by side from
anterior to posterior parallel to the interspace and extending
through into the adjacent vertebral bodies. Where the transverse
width of the disc space is insufficient to allow for the use of two
implants, each of which would be large enough to protrude to the
required depth into the adjacent vertebrae, then a singular and
significantly larger implant may be placed centrally. With this in
mind, and in light of the very detailed description of the
technique and instrumentation already provided in regard to the
method of posterior lumbar interbody fusion, a brief discussion of
anterior spinal interbody fusion with dual implant installation
will suffice, and the method for installation of a large, singular
midline graft will become obvious.
[0228] The interspace to be fused is exposed anteriorly. The soft
tissues are withdrawn and protected to either side, and if
necessary, above and below as well. It is then possible to
visualize the entire width of the vertebrae anteriorly adjacent
that interspace. As discussed above, the surgeon has already
templated the appropriate patient radiographs to determine the
requisite distraction and optimal implant size. In the preferred
method, the surgeon then broadly excises the great bulk of the
nuclear disc portion. (Alternatively, the disc can be left to be
removed via the drill later.) The surgeon then notes and marks a
point midway from side to side anteriorly. He then inserts Long
Distractor 100 centering it on a point midway between the point
just noted and the lateral extent of the intervertebral space
visualized anteriorly. The outer barrel portion 106 of the
Distractor 100 utilized, will correspond to the outside diameter of
the implants to be installed. The Distractor tips 102 inserted are
sequentially larger in diameter until the optimal distraction is
achieved. This optimal distraction, although suggested by the
initial templating, may be visually and tactilely confirmed as
performed. When the optimal distraction is achieved, the vertebral
endplates will come into full congruence and parallel to the
forward shaft portion 102 of the Distractor 100, causing an
alteration in the alignment of the vertebrae and a significant
increase in the interference fit and pressurization at the tip,
such that the instrument becomes exceedingly stable.
[0229] There is a sensation imparted to the surgeon of the tissues
having moved through their elastic range to the point where the two
adjacent vertebrae V begin to feel and move as if a single solid.
These changes are easily appreciated visually as the vertebrae
realign to become congruent to tip 102, and can also easily be
appreciated via lateral Roentgenography. However, should the
surgeon fail to appreciate that optimal distraction has been
achieved and attempt to further distract the interspace, he would
find that extremely difficult to do because of the increased
resistance as the tissues are moved beyond their range of elastic
deformation. Further, there would be no elasticity left to allow
the vertebrae to move further apart and the sensation to the
surgeon should he attempt to gently tap the oversized Distractor
forward with a mallet, would be one of great brittleness.
[0230] Returning now to the procedure, when the correct
intercorporeal Distractor 100 producing the ideal interspace
distraction having its barrel portion 106 corresponding to the
implant to be installed has been inserted, then its exact duplicate
is inserted anteriorly equidistant to the other side of the spine.
As the barrel portion 106 of Long Distractor 100 is exactly of the
same major diameter as the spinal implant I looking coaxially on
end, the surgeon can then assess the anticipated side by side
relationship of the dual implants when implanted.
[0231] As shown in FIGS. 7C and 7D, a Dual Outer Sleeve 340
consisting of a pair of hollow tubes is then introduced over the
side by side Long Distractors protruding anteriorly from the spine.
The Dual Outer Sleeve 340 is comprised of two hollow tubular
members identical in size displaced from each other ideally the sum
of the difference between the minor and major diameters of both
implants combined, but not less than that difference for one
implant, as it is possible to have the threads of one implant nest
interposed to the threads of the other, such that they both occupy
a common area between them. However, while the preferred embodiment
is slightly greater than two times the difference between the major
and minor diameters of the implant (the sum of both) the distance
may be considerably greater. Whereas in the preferred embodiment
extending tubular portions 348 of instrument 340 are parallel, when
the area between them 350, is sufficiently great, these elements
may be inclined or declined relative to each other such that they
either converge or diverge at their proximal ends. Paired tubular
structures 348, may be bridged in part or wholly throughout their
length, but are rigidly fixed by Foot Plate 344. In its preferred
embodiment, a top view shows the Foot Plate to be essentially
rectangular, but without sharp corners.
[0232] Other shapes can be utilized. In side view 7D it can be
appreciated, that Foot Plate 344 is contoured so as to approximate
the shape of the vertebrae anteriorly. Extending forward from Foot
Plate 344 are multiple sharp prongs 342 sufficiently long to affix
them to the vertebrae. The prongs 342 are limited in length so as
to not penetrate too far posteriorly and number from 2 to 10, but
preferably 6. As the Dual Outer Sleeve 340 is driven forward
utilizing Dual Driver Cap 420, of FIG. 7E, engaging the rearward
end 352, the prongs 342 extending from Foot Plate 344 are embedded
into the opposed vertebral bodies until their forward motion is
inhibited by the curved Foot Plate 344 becoming congruent to and
being stopped by, the anterior aspect of the vertebral bodies.
[0233] As already taught in FIG. 5, the Dual Driver Cap 420 is of
the same design as Single Driver Cap 160, in that there is a recess
354 as per 168, allowing the Outer Sleeve to be fully seated
without impeding the rearward projection of the Long Distractor
unit. However, unlike in Cap 160, area 354 is more relieved as it
is unnecessary for the Dual Cap 420 to contact the Long Distractor
through portion 110 to inhibit its forward motion, as the Foot
Plate 344 functions to that effect. Further, the Dual Cap 420 for
the Dual Outer Sleeve 340 is correspondingly dual itself and
engages the rearward facing dual tubular portion 352. Once the Dual
Outer Sleeve has been fully seated, the vertebrae adjacent the
interspace to be fused are rigidly held via Foot Plate 344 and the
prongs 342. Thus, it is possible to remove either one, or if
desired, both of the Long Distractor rods utilizing Long Distractor
puller 200, as per the method already described. It is then the
surgeon's choice to work on one or both sides of the spine. As per
previous discussion, the surgeon may drill the interspace utilizing
the Inner Sleeve 242 or leave the Long Distractors in place as per
the "Trephine Method".
[0234] Tapping, if necessary, and the insertion of the implants
then occurs through the protective Outer Sleeve 340. Once the
implants have been fully inserted, the Outer Sleeve is removed.
[0235] Having utilized the Drill method, or "Trephine Method", with
or without an Inner Sleeve to prepare the fusion site, it is the
preferred embodiment to leave the Outer Sleeve 340 in place as it
provides for the ideal placement and alignment of the Tap 280 and
implant I.
[0236] It is anticipated that the surgeon wishing to work deep
within the interspace, or preferring the ability to directly
visualize the tap being used, or the implant being inserted, may
choose to remove the Outer Sleeve after the insertion of the first
prosthesis to maintain stability, or prior to that, which while not
the preferred embodiments, are nevertheless within the scope of the
present invention.
Alternative Methods to the Preferred Embodiment for Method of
Anterior Interbody Fusion
[0237] As previously described for the posterior lumbar spine,
alternatively, one can employ the "Trephine Method" as has been
described in detail.
[0238] As a further alternative, it should be noted that the key
element in the anterior method is the use of the predistraction
principle, where such distraction is maintained by the Outer Sleeve
with or without the Long Distractor. Therefore, once the
preparation of the interspace has been completed, while not the
preferred embodiment, it is nevertheless within the scope of this
invention that one could remove the Outer Sleeve as there are no
neural structures requiring protection, and insert the implants
directly rather than through the Outer Sleeve.
[0239] As yet a further alternative of this method, where the
height of the distracted interspace is such that the diameter of
the implant required to span that height and to embed with
sufficient depth into the opposed vertebral bodies is such that it
is not possible to place two such implants side by side, then only
a single implant which may be of significantly increased diameter,
is used and placed centrally within the interspace rather than to
either side. The placement of a singular central graft via the
present invention method and instrumentation is in keeping with the
methods already described and can be performed using either a drill
or the "Trephine Method".
[0240] Referring to FIGS. 16-18, a cylindrical embodiment of the
spinal implant I of the present invention is shown. In FIG. 16 the
implant I is shown attached to the insertion device 350. In FIGS.
17 and 18 the implant I is shown installed in the disc space D,
between the adjacent vertebrae.
[0241] The cylindrical implant I comprises a hollow tubular member
which in the preferred embodiment is made of an ASTM surgically
implantable material, preferably Titanium. The cylindrical implant
I is closed at one end and open at the other end covered by a cap
394. The cylindrical implant I has a series of macro-sized openings
390 through the side walls of the cylindrical implant I. A series
of external threads 392 are formed on the circumference of the
cylindrical implant I. Any variety of threads may be used on the
implant. The cap 374 has a hexagonal is opening 394 for tightening
the cap 374.
[0242] While the present invention has been described in
association with the implant of a threaded spinal implant, it is
recognized that other forms of implants may be used with the
present method. For example, dowels, made from bone or artificial
materials, knurled or irregularly shaped cylinders or spheres, or
any other shaped implants that can be introduced through the outer
sleeve may be used. Being able to perform the procedure through the
outer sleeve permits the procedure to be performed safely and
quickly, and more accurately.
* * * * *