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BACKGROUND
The present invention relates to an artificial fusion implant to be placed
into the intervertebral space left after the removal of a damaged spinal
disc.
The purpose of the present invention is to provide an implant to be placed
within the intervertebral disc space and provide for the permanent
elimination of all motion at that location. To do so, the device is space
occupying within the disc space, rigid, self-stabilizing to resist
dislodgement, stabilizing to the adjacent spinal vertebrae to eliminate
local motion, and able to intrinsically participate in a vcrtebral to
vertebra bony fusion so as to assure the permanency of the result.
At present, following the removal of a damaged disc, either bone or nothing
is placed into the space left. Placing nothing in the 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 is less than optimal in that the 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 review of related prior art will demonstrate the novelty of the present
invention.
There have been an extensive number of attempts to develop an acceptable
disc prothesis (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:
U.S. Pat. No. 3,867,728 STUBSTAD--describing a flexible disc implant.
U.S. Pat. No. 4,349,921 KUNTZ--describing a flexible disc replacement with
file like surface projections to discourage device dislocation.
U.S. Pat. No. 4,309,777 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.
U.S. Pat. No. 3,875,595 FRONING--describing a motion preserving bladder
like disc replacement with two opposed stud-like projections to resist
dislocation.
U.S. Pat. No. 2,372,622 (Fassio)--describing a motion preserving implant
comprising complimentary opposed convex and concave surfaces.
In summary then, 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 preserve spinal motion, they are
diametrically different from the present invention which seeks to
permanently eliminate all motion at that spinal segment.
A second related area of prior art includes those devices utilized to
replace essentially wholly removed vertebra. 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 vertebra
(not a removed disc), and do not intrinsically participate in supplying
osteogenic material to achieve cross vertebra bony fusion. Therefore,
again 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:
U.S. Pat. No. 4,553,273 WU--describing a turnbuckle like vertebral strut.
U.S. Pat. No. 4,401,112 REZAIAN--describing a turnbuckle like vertebral
strut with the addition of a long stabilizing staple that spans the
missing vertebral body.
U.S. Pat. No. 4,554,914 KAPP--describing a large distractible spike that
elongates with a screw mechanism to span the gap left by the removal of a
entire vertebra and to serve as an anchor for acrylic cement which is then
used to replace the missing bone (vertebra).
U.S. Pat. No. 4,636,217 OGILVIE--describing a vertebral strut mechanism
that can be implanted after at least one vertebra has been removed and
which device consists of a mechanism for causing the engagement of screws
into the vertebra above and the vertebra below the one removed.
In summary then, this 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.
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.
Therefore, with these devices 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:
U.S. Pat. No. 4,604,995 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.
U.S. Pat. No. 2,677,369 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.
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).
In summary, none of these devices are designed or can be used within the
disc space, do not replace a damaged disc, and do not intrinsically
participate in the generation of a bony fusion.
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.
Such a device is contained in U.S. Pat. No. 4,501,269 BAGBY--describing an
implantable device and limited instrumentation. The method employed is as
follows: a hole is bored transversely across the joint and then a hollow
metal basket of larger diameter than the hole is then pounded into the
hole and then filled with the bone debris generated by the drilling.
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:
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. Said
instrumentation 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. The present invention is atraumatically screwed into place
while the BAGBY device, in contradistinction, is pounded into position.
BAGBY describes that the 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.
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 a 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.
2. Broad applicability--The BAGBY device can only be inserted from the
front of the vertebral column, however, 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 his
description, cannot.
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.
4. Time required--The present invention saves time over the BAGBY invention
in that time is not wasted laboring to remove the disc prior to initiating
the fusion. Also, since 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.
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, it is susceptible to forceful
dislodgement by the tendency of the two distracted vertebra, 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 vertebra and 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 such 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.
6. Spinal stability--The present invention is not only self-stabilizing, it
also provides stability to the adjacent vertebra in at least three way
that the BAGBY device cannot. First, the BAGBY device is placed
transversely across the joint in the center, leaving both vertebra free to
rock back and forth over this round barrel shaped axis, much like a board
over a barrel, being used for a seesaw.
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 vertebra relative to the device and to each other.
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 vertebra; rather than, as with the
BAGBY device, where the instability of the spine to be treated may instead
cause a dislocation of the implant, with further loss of spinal stability.
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. 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.
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 vertebra directly into the casing material of the implant
itself. Th BAGBY device has no similar feature.
9. Fusion mass--The BAGBY invention calls for removing the disc and then
drilling a hole between the adjacent vertebra. 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 device with an extremely dense
compressed core of that osteogenic material until the material itself
virtually extrudes from every cell of the implant.
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 hold
constant. It would then be anticipated, that the fusion rate would be
superior with the present invention as compared to the BAGBY 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).
The last area of prior art possibly related to the present invention and
therefore, to be considered related to "BONY INGROWTH", and patents either
describe methods of producing materials and or materials or devices to
achieve the same. Such patents would include:
U.S. Pat. No. 4,636,526 (DORMAN), U.S. Pat. No. 4,634,720 (DORMAN), U.S.
Pat. No. 4,542,539 (ROWE), U.S. Pat. No. 4,405,319 (COSENTINO), U.S. Pat.
No. 4,439,152 (SMALL), U.S. Pat. No. 4,168,326 (BROEMER), U.S. Pat. No.
4,535,485 (ASHMAN), U.S. Pat. No. 3,987,499 (SCHARBACH), U.S. Pat. No.
3,605,123 (HAHN), U.S. Pat. No. 4,655,777 (DUNN), U.S. Pat. No. 4,645,503
(LIN), U.S. Pat. No. 4,547,390 (ASHMAN), U.S. Pat. No. 4,608,052 (VAN
KAMPEN), U.S. Pat. No. 4,698,375 (DORMAN), U.S. Pat. No. 4,661,536
(DORMAN), U.S. Pat. No. 3,952,334 (BOKROS), U.S. Pat. No. 3,905,047
(LONG), U.S. Pat. No. 4,693,721 (DUCHEYNE), U.S. Pat. No. 4,070,514
(ENTHERLY).
However, while the present invention would utilize bone ingrowth
technology, it would do so with conventional technology.
In summary t hen, the present invention, instrumentation, and method, alone
provides for a one stage discectomy, fusion, and interbody internal spinal
fixation; that being performed more quickly, with greater safety, and more
affectively, for all of the aforementioned reasons than is possible with
any other known art.
BRIEF SUMMARY OF THE INVENTION
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. Such devices 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
vertebra to form 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.
Further, said devices are so 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.
The apparatus for preparing the vertebra for insertion of the implant is
also disclosed, such instrumentation and method allowing for the rapid and
safe removal of the disc, preparation of the vertebra, performance of the
fusion, and internal stabilization of the spinal segment.
DISCUSSION OF THE INSTRUMENTATION
The concept of performing various aspects of this surgery are not entirely
new. Drills are frequently placed through hollow, tubular guards to
protect the adjacent soft tissues. A set of instruments developed by Ralph
Cloward utilizes such a tubular drill guard on a larger scale, for the
purpose of drilling into the cervical spine. However, this inventor is
unaware of any set of instruments, system, or procedure designed to allow
the entire surgical procedure beyond the initial exposure, to be performed
blindly and with complete safety through a fixed sheath apparatus.
Specific design features which combine to make this uniquely possible are
as follows:
1. The availability of the specific implant.
2. The end of all the penetrating instrumentation is blunt faced.
3. All of the instruments have been stopped out at a predetermined depth to
avoid overpenetration.
4. The design of the external sheath conforms to the spacial limitations of
the specific surgical site.
5. The design and use of a second or inner sheath allows for the difference
in size between the inside diameter of the outer sheath, 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 on the implant.
6. 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 sheath by removing the drill bit and inner
sheath as a single unit.
7. A specially designed trephine for removing a oore of bone slightly
smaller in diameter than the internal diameter of the implant cavity
itself, however of a greater length.
8. 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.
9. 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.
OBJECTS OF THE PRESENT INVENTION
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.
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.
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.
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.
These and other objects of the present invention will be apparent from
review of the following specifications and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial view of the vertebra structure with the driver and
outer sheath assembly of the present invention.
FIG. 1 is a perspective view of the driver and sheath and its orientation
to a vertebral structure.
FIG. 1A is a perspective view of the driver member for the outer sheath.
FIG. 2 is a perspective view of the outer sheath being inserted into the
vertebra structure.
FIG. 3 is a perspective view of the outer sheath and inner sheath assembly,
with the drill bit of the present invention.
FIG. 3A is a side sectional view of the collar and drill bit of FIG. 3.
FIG. 4 is a perspective view of a cylindrical implant and vertebra
structure.
FIG. 4A is a perspective view of one preferred embodiment of the implant.
FIG. 4B is a cross sectional view of the implant of FIG. 4A.
FIG. 4C is the driving and insertion equipment for the implant of FIG. 4A.
FIG. 4d is a side sectional view of the driver and implant between
vertebra.
FIG. 5 is a sectional view of the vertebra structure, taken along lines
5--5 of FIG. 4.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring to FIG. 1 a vertebra structure comprising two vertebra V and a
disc D between the two vertebra, is shown. A hollow tubular drill sleeve
10 has teeth 12 at its lower end. The sleeve 10 has an enlarged diameter
upper portion 14.
A driver 16, shown in FIG. 1A, consists of a solid tubular member 18 and an
increased diameter head 20. The external diameter of the solid tubular
member 18 is slightly smaller than the inside diameter of the hollow
tubular drill sleeve 10 and has a length that is substantially shorter tha
the overall length of the hollow tubular drill sleeve 10.
The drill sleeve 10 is made of metal in order to be driven into the
vertebra V and be held in place by the teeth 12 of the drill sleeve 10.
Referring to FIG. 2 the drill sleeve 10 with the driver 16 installed is
shown being driven into two vertebra V on either side of a disc D by
hammer H.
Referring to FIG. 3 and 3a the drill assembly is shown. In FIG. 3 the drill
sleeve 10 is illustrated in the two vertebra V, straddling the disc D.
The retaining sleeve 15 has an outside diameter slightly smaller than the
inside diameter of the drill sleeve 10, and a length substantially the
same length as the drill sleeve 10. The retaining sleeve 15 has a collar
17 at its upper end for engaging the top of the drill sleeve 10.
The drill 22 comprises an upper portion 24, a central recessed portion 26
and a lower cutting drill portion 28. The upper 24 and lower portion 28 of
the drill 22 have the same outside diameter. The drill 24 has a collar 30
attached to the upper portion 24 of the drill 22.
The outside diameter of the drill 22 is slightly smaller than the inside
diameter of the retaining sleeve 15. The length of the drill, from the
collar 30 to the end of the drill bit, is such that a predetermined
portion of the drill bit 22 extends beyond the end 29 of the sleeve when
fully inserted.
Referring to FIG. 4, a cylindrical embodiment of the present invention is
shown, one implant positioned in the opening in the vertebra and disc
formed by the drill 22, and a second implant shown prior to implantation.
The cylindrical implant 50 comprises a hollow tubular member which in the
preferred embodiment is made of an ASTM surgically implantable material,
and preferably Titanium. The cylindrical implant 50 is closed at on end 52
and open at the other end 54. The outer cylindrical implant 50 has a
series of macro-sized openings 56 through the side walls of the
cylindrical member 50. A series of external threads 53 are formed on the
circumference of the cylindrical implant 50. The threads 53 are locking
threads having a series of interjections, the ends of which are blunted
and twisted so as to resist unscrewing.
The open end 54 of the cylindrical implant 50 has an internal thread 51 for
receiving a complementary cap 52 which has an external thread 58 for
engaging the internal threads 51 of the cylindrical member 50. The cap 52
has a hexagonal opening 59 for use with an allen wrench for tightening the
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