U.S. patent application number 10/933155 was filed with the patent office on 2005-02-17 for systems and methods for fixation of adjacent vertebrae.
Invention is credited to Mathews, Hallett H..
Application Number | 20050038434 10/933155 |
Document ID | / |
Family ID | 25313692 |
Filed Date | 2005-02-17 |
United States Patent
Application |
20050038434 |
Kind Code |
A1 |
Mathews, Hallett H. |
February 17, 2005 |
Systems and methods for fixation of adjacent vertebrae
Abstract
A method for internal fixation of vertebra of the spine to
facilitate graft fusion includes steps for excising the nucleus of
an affected disc, preparing a bone graft, instrumenting the
vertebrae for fixation, and introducing the bone graft into the
resected nuclear space. Disc resection is conducted through two
portals through the annulus, with one portal supporting resection
instruments and the other supporting a viewing device. The fixation
hardware is inserted through small incisions aligned with each
pedicle to be instrumented. The hardware includes bone screws,
fixation plates, engagement nuts, and linking members. In an
important aspect of the method, the fixation plates, engagement
nuts and linking members are supported suprafascially but
subcutaneously so that the fascia and muscle tissue are not
damaged. The bone screw is configured to support the fixation
hardware above the fascia. In a further aspect of the invention, a
three component dilator system is provided for use during the bone
screw implantation steps of the method.
Inventors: |
Mathews, Hallett H.;
(Richmond, VA) |
Correspondence
Address: |
WOODARD, EMHARDT, MORIARTY, MCNETT & HENRY LLP
BANK ONE TOWER/CENTER
111 MONUMENT CIRCLE
SUITE 3700
INDIANAPOLIS
IN
46204-5137
US
|
Family ID: |
25313692 |
Appl. No.: |
10/933155 |
Filed: |
September 2, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10933155 |
Sep 2, 2004 |
|
|
|
09519295 |
Mar 6, 2000 |
|
|
|
6793656 |
|
|
|
|
09519295 |
Mar 6, 2000 |
|
|
|
09042910 |
Mar 17, 1998 |
|
|
|
6033406 |
|
|
|
|
09042910 |
Mar 17, 1998 |
|
|
|
08677135 |
Jul 9, 1996 |
|
|
|
5728097 |
|
|
|
|
08677135 |
Jul 9, 1996 |
|
|
|
08437523 |
May 9, 1995 |
|
|
|
5569248 |
|
|
|
|
08437523 |
May 9, 1995 |
|
|
|
08116351 |
Sep 2, 1993 |
|
|
|
08116351 |
Sep 2, 1993 |
|
|
|
07938708 |
Sep 1, 1992 |
|
|
|
07938708 |
Sep 1, 1992 |
|
|
|
07852577 |
Mar 17, 1992 |
|
|
|
5171279 |
|
|
|
|
Current U.S.
Class: |
606/86A ;
606/247; 606/279; 606/301; 606/53; 606/60; 606/916 |
Current CPC
Class: |
A61B 17/7049 20130101;
A61F 2002/30329 20130101; A61F 2220/0025 20130101; A61F 2002/2839
20130101; A61F 2002/2835 20130101; A61F 2002/449 20130101; A61B
17/70 20130101; A61B 17/86 20130101; A61B 17/7007 20130101; A61F
2/442 20130101; A61F 2/4455 20130101; A61F 2002/448 20130101; A61B
17/7059 20130101 |
Class at
Publication: |
606/061 ;
606/060; 606/053 |
International
Class: |
A61F 005/04; A61B
017/56; A61F 002/30 |
Claims
What is claimed is:
1. A method for internal fixation of the spine comprising the steps
of: a) inserting a guide pin into a pedicle of at least two
vertebrae to be instrumented for internal fixation; b) making an
incision in the skin at the entry site for each guide pin; c)
dissecting subcutaneous suprafascial tissue between each entry
site; d) initially advancing a bone screw over each guide pin
through each incision and into each pedicle, the bone screw having
bone engaging threads and machine threads for engaging a nut; e)
elevating the skin between each entry site; f) inserting a fixation
plate into the subcutaneous suprafascial space and supporting the
plate on and between at least two bone screws with the machine
threaded portion projecting above the plate; and g) clamping the
fixation plate to the bone screws using nuts engaging the machine
threaded portions of the bone screws with the fixation plate
supported above the fascia and muscle tissue but beneath the skin
of the patient.
2. The method for internal fixation of the spine of claim 1,
further comprising the following steps between the plate insertion
and clamping steps: loosely engaging a nut on the nut threaded
portion of each of the bone screws; and further advancing each bone
screw deeper into the respective pedicle until the fixation plate
lies immediately adjacent the fascia.
3. The method for internal fixation of the spine of claim 1,
wherein: each of the steps (a)-(g) is repeated on opposite sides of
the spinous process for bilateral instrumentation of each pedicle
of each vertebrae.
4. The method for internal fixation of the spine of claim 3,
further comprising the steps of: dissecting subcutaneous
suprafascial tissue between the ipsilateral and contralateral bone
screws at each level of instrumentation of the vertebrae; and after
the step of inserting the fixation plate, inserting a linking
member between bilateral bone screws at the same level of
instrumentation with the machine threaded portion of the bone
screws projecting above the linking member.
5. The method for internal fixation of the spine of claim 1,
wherein the step of advancing the bone screw includes the steps of:
advancing a cannulated drill bit over each guide pin; and using the
drill bit, drilling into the pedicle to a predetermined depth less
than the length of the bone engaging threads of the bone screw.
6. The method for internal fixation of the spine of claim 6,
wherein: in the drilling step the predetermined depth is about
one-third of the pedicle depth; and in the step of initially
advancing the bone screw, the bone screw is advanced into at least
one-half of the pedicle depth.
7. The method for internal fixation of the spine of claim 1,
wherein the step of advancing the bone screw includes the steps
of:. dilating the tissue at each entry site using three dilators
having successively larger diameters; removing the smallest
dilator; advancing a cannulated drill bit over each guide pin
through an intermediate dilator; and using the drill bit, drilling
into the pedicle to a predetermined depth less than the length of
the bone engaging threads of the bone screw.
8. The method for internal fixation of the spine of claim 7,
wherein the step of advancing the bone screw further includes the
subsequent steps of: removing the intermediate dilator, leaving the
largest diameter dilator; and advancing the bone screw over the
guide pin and through the largest dilator.
9. A method for percutaneously resecting the nucleus of a spinal
disc, comprising the steps of: a) introducing a pair of cannulae
bilaterally into the disc space of the affected disc; b)
perforating the disc annulus at each cannula insertion site; c)
inserting a cutting instrument into one cannula and a viewing
instrument into the other cannula; d) resecting the disc nuclear
material through the one cannula under direct vision through the
other cannula; e) transposing the cutting instrument and viewing
instrument between cannulae and resecting the remaining disc
nuclear material through the other cannula.
10. The method for percutaneously resecting the nucleus of a spinal
disc of claim 9, wherein, in the step of introducing the pair of
cannulae the entry points for the cannulae are nominally ten
centimeters bilaterally from the midline of the spinous process and
the cannulae are introduced below the transverse processes of the
adjacent vertebra.
11. The method for percutaneously resecting the nucleus of a spinal
disc of claim 9, further comprising the step of verifying the
anatomy under each cannulae using a visualization scope prior to
perforating the disc annulus.
12. The method for percutaneously resecting the nucleus of a spinal
disc of claim 9, wherein the step of resecting the disc material
includes terminating resection through the one cannula when the
cutting instrument can be seen under direct vision through the
other cannula.
13. The method for percutaneously resecting the nucleus of a spinal
disc of claim 9, wherein the step of resecting the disc material
includes ablating the disc end plates using an ablating instrument
introduced through the cannula.
14. A method for introducing bone graft material into an
intervertebral disc space comprising the steps of: a) creating
bilateral cannulated portals into an affected disc; b) removing the
nucleus of the disc; c) inserting a viewing instrument into the
first portal; d) introducing bone graft material into the second
portal; e) advancing the graft material through the second portal
into the empty disc space; and f) verifying the entry of the graft
material through the viewing instrument in the first portal.
15. The method for introducing bone graft material into an
intervertebral disc space of claim 14, wherein the step of
advancing the graft material includes using an obturator to push
the material through the portal into the empty disc space.
16. The method for introducing bone graft material into an
intervertebral disc space of claim 14, comprising the additional
subsequent steps of: g) removing the viewing instrument from the
first portal; and h) advancing graft material through the first
portal into the disc space.
17. A bone screw for internal fixation of the spine, comprising: a
distal threaded shank having threads for engagement within a
vertebra; a proximal threaded stem having machine threads for
engagement with a threaded nut; and a smooth shank intermediate
said threaded shank and said threaded stem, said smooth shank
having a hub near said threaded stem, said hub defining a support
surface for supporting a fixation plate engaged to the bone screw
over said proximal stem, wherein said smooth shank has a length
from said threaded shank to said hub that is approximately equal to
distance from the pedicle to the the muscle fascia of a patient, so
that said hub is situated above the muscle fascia when said distal
threaded shank is engaged in a vertebra of the patient.
18. A three component dilator system for use in implantation of a
bone screw into a vertebra, comprising: a first tubular dilator
having a tapered end, a first length and a first diameter; a second
tubular dilator having a tapered end, a second length and a second
diameter; a third tubular dilator having a tapered end, a third
length and a third diameter; wherein said first diameter is greater
than said second diameter which is greater than said third
diameter, and wherein said first length is shorter than said second
length which is shorter than said third length.
19. The three component dilator system of claim 18, wherein: said
second tubular dilator has a second end opposite said tapered end,
said second dilator having a knurled outer surface adjacent said
second end; and said third tubular dilator has a second end
opposite said tapered end, said third dilator having a knurled
outer surface adjacent said second end.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention concerns a method for internal
fixation of vertebra of the spine.
[0002] It has long been known that internal fixation is an adjunct
to fusion, such as a transverse process fusion. In early prior art
techniques, a surgeon made an incision in the patient's back and
separated tissue and muscle in order to expose a wide area of the
spine in which the procedure was to take place. The fusion and
fixation in one prior art process is by grafting bone segments
between opposing transverse processes of adjacent vertebrae.
However, this technique resulted in gross destruction of normal
anatomy as well as high blood loss. Moreover, this surgical
technique did not completely stabilize the vertebra since there was
no direct connection between the vertebral bodies.
[0003] In more recent times, a surgical technique known as dowel
interbody fusion has been developed. In this technique, bores are
formed in disc tissue through either open surgery or percutaneous
surgery. A dowel is made to fit into the bores formed in the disc
tissue in still a further technique, all disc tissue is removed
between adjacent vertebrae, as well as the disc plates. Large
surface area bone grafts are then placed within the clean space to
form a graft between the opposing vertebral bodies. In each of
these latter two prior art processes it still remains necessary to
provide some means for fixation to facilitate fusion of the large
area bone graft or the dowel to the vertebrae.
[0004] Many types of instrumentation for performing spinal fixation
are known in the art. For instance, spine instrumentation developed
by Harrington incorporates a hook and rod configuration.
Implantation of the Harrington spinal instrumentation requires
subperiosteal stripping of the spine to avoid injury to the
muscular nerves and vessels. Dissection of the muscle tissue is
also required. In some aspects of the early Harrington techniques,
the spine was stripped clean of the supraspinous and intraspinous
ligaments.
[0005] Later developed techniques involve hardware which is placed
through the skin and through the muscle into the bone. Some of the
fixation hardware remains outside the body, but is removed after
the fusion has been completed. Techniques of this sort are
characterized by high risk of pin tract infection and incisional
morbidity.
[0006] Thus far, each of the prior art spinal fixation and/or
fusion techniques have been characterized by excessive invasion
into the patients spine and back region, What is needed is a
technique which allows for adequate stabilization of the spine, yet
decreases the chance of infection as well as patient morbidity.
There is further a need for such a method which permits
percutaneous removal of the fixation hardware as an outpatient
procedure after fusion has been completed.
SUMMARY OF THE INVENTION
[0007] The present invention contemplates a percutaneous fusion
technique using subcutaneous suprafascial internal fixation. More
particularly, the minimally invasive technique of the present
invention permits anterior fusion of the disc space of the lumbar
spine following appropriate disc resection and bone grafting. The
fixation process is suprafascial, that is above the muscle fascia,
but subcutaneous, that is beneath the surface of the skin. Thus,
none of the muscle tissue is destroyed and the subcutaneous nature
of the procedure greatly decreases the risk of pin tract secretions
or infections, or the potential of osteomyelitis.
[0008] In more specific aspects of the invention, the technique
contemplates first resecting the intranuclear cavity of a damaged
disc, including ablation of the superior and inferior end plates.
Bone graft material is prepared for introduction into the vacated
disc space. Prior to introduction of the bone graft into the empty
disc nuclear space, fixation instrumentation is implanted. In
general, this fixation hardware can include self-tapping cannulated
bone screws, fixation plates and linking members for laterally
fixing plates on opposite sides of the spinous process.
[0009] In the preferred method, guide wires are inserted
bilaterally in line with and into the pedicle. Pedicle screws are
advanced over the guide wire and engaged into a predrilled bore in
the pedicle. After the guide wire is removed, the skin is elevated
and tissue in the suprafascial subcutaneous space is dissected to
permit insertion of the fixation plates. The appropriate plates are
first engaged over the ipsilateral screws and then the procedure is
repeated for the contralateral bone screws at each level of
hardware, that is at each vertebra to be stabilized. The bilateral
fixation plates can be laterally connected by dissecting across the
midline between corresponding screws and then positioning a linking
member between the screws using a top-loading insertion mechanism.
A nut is also top-loaded on to each successive screw to secure the
linking members to the plate and to secure the plate to the pedicle
screws.
[0010] In the inventive method, the nuts engaging the pedicle
screws are initially loosely threaded onto the screws. The bone
screws are then advanced into the vertebral body until the hardware
resides below the level of the skin, but suprafascially in the
subcutaneous space at each level of the instrumentation. The nuts
are then tightened when they fixation hardware is in its final
resting spot. Once the fixation instrumentation is in position, the
bone graft material is introduced through a cannula to the disc
space and moved into position by an obturator. With the bone graft
in place and the spinal fixation hardware engaged to the
appropriate vertebrae, the subcutaneous tissue is then irrigated
and closed.
[0011] In another aspect of the invention, a cannulated fixation or
bone screw is provided which is well suited for use with the
inventive method. More specifically, the screw includes a distal
threaded shank and a proximal nut threaded stem which terminates in
a driving hub. The distal threaded shank includes self-tapping bone
engaging threads. Intermediate the threaded shank and the stem is a
smooth shank of sufficient length so that only the smooth shank
contacts muscle tissue when the fixation instrumentation is in
place. Near the stem end of the smooth shank is a mounting hub
which supports the fixation plate before the nut is engaged on the
threaded stem. The smooth shank preferably accounts for about
one-half of the length of the screw as measured from the tip of the
bone engaging threaded shank to the underside of the mounting
hub.
[0012] In a further aspect of the invention, a three component
dilator system is provided to facilitate instrumentation of the
vertebrae. In particular, the dilator system includes three
concentrically disposed hollow dilator tubes, each tapered at its
respective end for atraumatic introduction into the patient. Each
of the three dilators is successively smaller in diameter but
larger in length. The intermediate and smallest dilator tubes have
knurled ends to grasp for removal during steps of the method.
[0013] It is one object of the present invention to provide a
method for internal fixation of the spinal column which is
minimally invasive and which poses a minimal health risk to the
patient. Another object is to provide such a technique which
further permits subcutaneous removal of the temporarily implanted
hardware in an out-patient procedure.
[0014] A further object of the invention is realized by the present
technique which contemplates subcutaneous but suprafascial fixation
to avoid damage to the spinal musculature and ligaments. Further
objects and certain advantages of the present invention will become
apparent from the following description of the invention.
DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1. is a section view through the spinal column of a
patient shown after implantation of fixation instrumentation using
the method of the present invention.
[0016] FIG. 2 is a side view of a bone strew adapted for use in the
method of the present invention.
[0017] FIG. 3 is a posterior view of the spinal column of the
patient after implantation of fixation instrumentation using the
method of the present invention, showing bilateral fixation with
linking members across the spinal midline, as viewed beneath the
skin but with the muscle tissue removed to expose details of the
underlying vertebrae.
[0018] FIGS. 4A-C are side views of the components of a three
component dilator system for use with the method of the present
invention during steps for implanting the bone screw into a
vertebra.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0019] For the purposes of promoting an understanding of the
principles of the invention, reference will now be made to the
embodiment illustrated in the drawings and. specific language will
be used to describe the same. It will nevertheless be understood
that no limitation of the scope of the invention is thereby
intended, such alterations and further modifications in the
illustrated device, and such further applications of the principles
of the invention as illustrated therein being contemplated as would
normally occur to one skilled in the art to which the invention
relates.
[0020] The present invention first contemplates steps for a
percutaneous fusion technique, such as may be used to fuse adjacent
vertebrae after disc tissue has been removed. According to the
preferred embodiment of the invention, the method is conducted on
lumbar vertebrae, although it is believed to be adaptable to other
portions of the spine. The patient, after appropriate preparation,
is positioned prone on a radiolucent padded frame which allows for
both AP (anterior/posterior) and lateral fluoroscopic visualization
during the entire procedure. An initial AP fluoroscopic view is
taken with an external guide pin placed parallel to the plane of
the end-plates of the affected disc to assure the proper
orientation of the procedure relative to the disc space. A
guideline is drawn on the AP radiograph along the guidepin image to
demarcate the plane of entry.
[0021] In the preferred embodiment of the fusion technique of the
present method, a bi-portal approach is utilized to clean out the
disc nuclear space. Entry points for local anesthesia are located
bilaterally from the midline, nominally about tell centimeters
bilaterally from the radiograph guideline (varying between 8
centimeters for a smaller patient to 12 centimeters for a larger
patient).
[0022] After the fascia and intrafascia musculature are
appropriately anesthetized, discography is performed using a
two-needle technique bilaterally. Pursuant to the preferred method,
the initial needle entry point to the disc annulus is located on
the mid-pedicle line on the AP radiograph, which is defined by the
line created by the midportion of the pedicle above and below the
disc space being instrumented. Both needles are advanced into the
posterior central portion of the nucleus and triangulation is
begun. The discography is performed to confirm the nature of the
disc disease and the contained verses the uncontained condition of
the involved disc structure. (An uncontained disc is a disc which
has ruptured through the posterior longitudinal ligament and/or
annulus, which therefore allows a free flow of dye from the
intranuclear space into the epidural space.)
[0023] The procedure of the preferred method continues with the
introduction of cannulae into the disc space. The hubs of the
discogram needles can be removed and then serve as guide wires for
the cannulae. Dilating probes are place over the guide wires
bilaterally into the annulus of the disc. Sheaths are placed over
the probes over which progressively larger cannulae can then be
advanced to dilate the annulus to an appropriate diameter for
intradiscal work. Again, this prior procedure is performed
bilaterally at the two entry points described above, and is
repeated for each affected disc.
[0024] In one aspect of the method, a visualization scope is place
through each cannula to verify the annulus and to confirm the
anatomy under the cannula. If no nerve tissue is observed and the
annular tissue is present, a trephine is introduced after the
visualization scope has been removed. The annulus is perforated and
successively sized trephines are used to open an annular hole of
adequate dimension for the purpose of disc removal and extra-discal
visualization.
[0025] Once the trephine operation is complete at each bilateral
entry point, two portals are provided. Disc resection can be
conducted through one portal while a verifying scope can be placed
at the other portal. Triangulation of the disc material through one
portal is considered achieved when direct visualization of the disc
resecting instrument occurs through the viewing portal. The
intranuclear cavity of the affected disc is completely resected and
the superior and inferior end-plates are ablated using cutting and
sucking instruments or through the use of laser-assisted probes.
The instruments may be removed from each portal and transposed for
complete resection of the disc nucleus. Rapid disc removal
instruments for the nucleus and rapid burring devices for the
end-plates can be used to resect the tissues in preparation for
fusion. The instruments may also be used to resect the posterior
ligamentus structures and the interannular ring to create an
adequate cavity for introduction of the bone graft. Acceptable
devices include burrs, laser, curettes and gauges for the ablation
of the end-plate tissues to the state of bleeding bone. Both rigid
and flexible scopes can be used for the verification of the
complete resection of the intranuclear cavity. Once the disc
material has been completely cleared out of the cavity and the
end-plates completely ablated, and obturator is placed in each
cannula to prevent contamination during this succeeding portions of
the procedure.
[0026] At this point of the preferred technique of the present
invention, bone graft harvesting is undertaken. The bone graft
harvesting can be accomplished according to any known techniques
suitable for this purpose. In one specific embodiment of the
inventive method, after appropriate anesthesia and analgesia, a
small incision is made over either posterior superior iliac crest
to expose the outer crest for bone harvesting. The bone is procured
from the corticocancellous table and prepared for the grafting
process. The bone graft is fashioned to be accommodated within the
inner diameter of the largest outer cannula employed during the
disc resection described above. The bone may be mixed with other
components, including osteoinductive proteins or morphogenic
materials. The bone harvest cite is then irrigated, dried and
closed over a small drain.
[0027] The next step of the inventive process, the instrumentation
step, occurs under direct fluoroscopy. Under AP fluoroscopic view,
a guide wire (preferably a 0.062 guide wire is introduced with the
sharp end of the guide wire being inserted into the skin at a
position slightly offset from the area to be cannulated. In one
specific embodiment, the guide wire is introduced one centimeter
lateral to the area to be cannulated. The position of the guide pin
is verified by fluoroscopy angled to 15 degrees in line with the
pedicle. The guide pin is used to palpate the cortex over the
pedicle and is then secured by tapping with a mallet to prevent
movement of the pin until further advancement is desired. After the
guide pin has been locked into the cortex, tissue dilators are
applied to protect the surrounding muscle tissue. The guide pin is
then advanced, under lateral fluoroscopic view, into the pedicle
and within the vertebral body. The position of the pin is confirmed
using both AP and fluoroscopy views. This procedure is repeated for
each pedicle o the vertebra. Thus, for each vertebra to be
instrumented, a pair of guide pins are positioned at about a
15.degree. angle from the midline and along each pedicle of the
vertebra.
[0028] After the guide pin insertion process is complete, an
incision is made at the guide pin insertion site, which, in one
specific embodiment, is about 2.0 cm. in length. Then, using
pick-ups and Metzenbaum scissors, subcutaneous tissue is dissected
suprafascially. Metzenbaum scissors are also used to dissect the
suprafascial subcutaneous tissues from the ipsilateral pin across
the midline to the contralateral guide pin. Dissection of this
tissue provides space for connection of pedicle screws in
subsequent steps of the method.
[0029] In the next step of the inventive method, a three component
tissue dilator system is used to dilate the tissue at each guide
pin to accept first a cannulated drill bit and then a larger
diameter cannulated self-tapping bone screw. The dilator system
comprises three tapered tubes of increasing diameter and decreasing
length. The tubes are introduced successively from smallest
diameter to largest diameter to provide adequate access through the
tissue for later steps of the method. After the three component
tissue dilator system has been inserted, the smallest of the
internal dilators is removed allowing for insertion of the drill
bit along the guide pin. The bit is used to drill into the initial
one-third of the pedicle. The bit is removed and the intermediate
tissue dilator is then removed, leaving the largest dilator still
in place. The self-tapping bone screw is inserted through the
largest dilator over the guide wire until it is advanced to at
least 50% depth of the pedicle. After the position of the bone
screw has been confirmed by lateral fluoroscopy, the guide wire is
removed and the screw advanced until the proximal tip of the screw
is at the level of the skin incision. This procedure is repeated
for each pedicle in each successive vertebra until all the bone
screws are in place for the final internal fixation
instrumentation.
[0030] In one specific embodiment, the cannulated drill bit has an
outer diameter of 4.5 mm, while, the cannulated bone screw can have
a diameter between 5.5-8.5 mm. Thus, in this specific embodiment,
the intermediate dilator of the three component dilator system has
an internal diameter of at least 4.5 mm, and preferably 5.2 mm to
receive the drill bit therethrough. Likewise, the largest dilator
has an internal diameter at least larger than the bone screw, and
preferably 9.6 mm to accommodate a range of bone screw
diameters.
[0031] Pick-ups are again used to elevate the skin and Metzenbaum
scissors arc used to dissect any remaining subcutaneous
suprafascial tissue as required to accommodate insertion of an
elongated fixation plate. An appropriately sized fixation plate is
inserted using forceps through the 2.0 cm. incisions. It is
understood that the fixation plates are sized to fit over bone
screws engaged in the pedicles of adjacent vertebrae to provide
adequate fixation at each side of the spinous process. The fixation
plates for tie ipsilateral screws are first inserted by forceps and
then the procedure is repeated for the contralateral side at each
vertebral level requiring instrumentation. In addition, linking
members are inserted through the incision at the ipsilateral guide
pin and passed across the midline in the subcutaneous space to
engage the ipsi- and contra-lateral bone screws to accomplish
trans-lateral linkage. The linking member can be of the type sold
by Danek Medical, Inc., assignee of the present invention, as its
CROSSLINK.TM. product. Once each of the fixation plates and linking
members have been engaged over the appropriate bone screws, a nut
is applied in a top-loaded fashion to loosely secure the hardware
together.
[0032] After each nut is initially threaded onto its corresponding
screw, the bone screws are advanced as necessary so that all of the
fixation hardware lies subcutaneously, but suprafascially, at each
level of the instrumentation. Once each of the bone screws has
reached its final resting place within the vertebra, and once all
the instrumentation, including the fixation plates and linking
members, is within the appropriate suprafascial subcutaneous space,
the nuts are tightened, while the bone screws are held, at each
successive level, thus creating a firm interlock between all of the
components of the fixation system. AP and lateral fluoroscopic
views can document the final position of the hardware to the
satisfaction of the operating surgeon.
[0033] Once the fixation instrumentation has been inserted, each
bone screw insertion cite is thoroughly irrigated as well as the
subcutaneous space which has accepted the fixation components. The
incisions are dried and hemostasis verified followed by closure of
the incision with subcutaneous absorbable sutures.
[0034] With the fixation hardware in place, attention is returned
to the prior portals through which the disc resection was
conducted. In this step of the method of the present invention, the
obturator are removed from the portals and the previously harvested
bone graft material is introduced through one cannula into the disc
space. A visualizing scope is extended through the cannula in the
other portal for confirmation of entry of the bone graft into the
disc space. A smooth obturator is inserted into the cannula to
facilitate advancement of the bone graft material through the
cannula into the empty disc nuclear space. After the ipsilateral
portal has been completely filled with bone graft material, the
same procedure is performed at the contralateral portal. Visual
verification of the grafting procedure in the contralateral portal
is not possible because the first portal has been filled by graft
material. However, fluoroscopy can be used to identify the
introduction of the obturator into the disc nuclear cavity, thereby
confirming the location of the bone graft material. Upon completion
of the grafting process, the cannulae are removed, the subcutaneous
tissue irrigated and the discography entry points are closed with
absorbable sutures.
[0035] With the foregoing description of the inventive method in
mind, attention is directed to the figures. In FIG. 1, a
cross-sectional view of a vertebral region of a patient shows a
vertebra 10 having pedicle portions 11. In this superior section
view, a disc is shown with its annulus 15 intact but with an empty
nuclear space 16 after the disc tissue has been resected. Fixation
hardware is shown at only one side of the midline ML defined by the
spinous process of the vertebra 10. However, as depicted in FIG. 3,
fixation instrumentation is implanted on either side of the midline
ML. FIG. 3 further shows fixation between adjacent vertebrae,
identified as vertebra 10 and 10', with corresponding body
portions. 10a, transverse processes 10b and 10c, spinous processes
10d, and laminae 10e.
[0036] The entry sites 25a and 25b shown in FIG. 1 are used in the
disc resection steps of the method. FIGS. 1 and 3 show the location
of the portals 26a and 26b through which the disc annulus is
removed and the bone graft material introduced. As described above,
the entry sites 25a and 25b are nominally 10.0 cm bilaterally from
the midline ML. The portals 26a and 26b are oriented so that the
disc resection tools can be inserted below the transverse processes
10c of the vertebra at the level of the nerve root.
[0037] Referring again to FIG. 1, the skin 20 of the patient is
shown dissected from the fascia 22 protecting muscle tissue 23 to
provide a suprafascial subcutaneous space 25. An incision 27 is
shown through which the fixation hardware is inserted in accordance
with the method described above. The fixation hardware includes a
bone screw 30, which is preferably a pedicle screw. A fixation
plate 40 is mounted on the screw 30, held in place by a nut 42. In
the posterior view of FIG. 3, the fixation hardware is also shown
as including linking members 44 spanning across the midline between
corresponding bone screws 30.
[0038] As can be seen most clearly in FIG. 1, the method of the
present invention provides a technique for instrumenting adjacent
vertebra to facilitate fusion. Implantation of the fixation
instrumentation according to the inventive method causes minimal
invasion to the patient, with the insertion occurring through a
single incision, like incision 27, aligned with each pedicle. Most
significantly, the hardware resides within the suprafascial
subcutaneous space 25 so that destruction of muscle tissue is not
required. With this method, patient morbidity rates are reduces,
while healing rates are improved. Since the fixation hardware
resides above the muscle layer, removal can be conducted in an
out-patient procedure under a local anesthetic.
[0039] Referring now to FIG. 2, the details of a bone screw
particularly adapted for the present method is shown. The screw 30
includes a distal threaded shank 31, which in the preferred
embodiment is configured as a self-tapping pedicle screw in
accordance with known technology. The proximal end of the screw 30
includes a machine threaded stem 34, which is threaded for
engagement with the nut 42 used to fix the fixation plate 40 and
linking member 44. The stem 34 terminates in a driving hex recess
35 which is engaged by an appropriate screw driving tool as known
in the art. (Alternatively, a hex projection can be used in lieu of
the recess 35, with an appropriate change in the screw driving
tool.)
[0040] Intermediate the distal shank 31 and proximal stem 34 is a
smooth shank portion 32. The smooth shank portion 32 defines a hub
33 near the proximal threaded stem 34. The hub 33 includes a
surface 33a configured to support the fixation plate 40. When the
nut 42 is tightened onto the proximal stem 34, the fixation plate
40 is locked between the nut and the hub surface 33a. The hub 33
supports the fixation plate to keep it within the suprafascial
space 25. The surface 33a is preferably slightly curved to fit
within a scalloped fixation plate of known design in the art. The
screw 30 is cannulated along its entire length, as represented by
the bore 36 provided for guidewire insertion.
[0041] The smooth shank portion 32 provides a non-irritating
surface for contacting the fascia and muscle tissue. The length of
the smooth shank portion 32 is determined by the muscle thickness
around the instrumented vertebra, and is generally equal in length
to the length of the bone engaging threaded shank 31. In one
specific embodiment, the screw 30 has a length measured from the
tip of tie bone engaging shank 31 to the underside of the mounting
hub 33 of 65-75 mm. The bone engaging distal shank 31 has a nominal
length of 35 mm which provides optimum engagement with the
vertebra. The smooth shank portion 32 accounts for the remainder of
the 65-75 mm length, or between 30-40 mm. The machine threaded stem
34 has a length, as measured from surface 33a of the mounting hub
33, that is sufficient to accommodate the fixation plate 40, a nut
42 and a linking member 44. In the specific embodiment, the length
of the machine threaded stem 34 is 10-15 mm so that very little of
the stem projects beyond the nut. The bone screw 30 can have a
diameter of between 5.5-8.5 mm as required for the patient and
fixation procedure. It is understood, of course, that the specific
dimensions are illustrative of a nominal bone screw configuration.
These dimensions can be varied as required for a particular patient
or procedure, while still adhering to the basic concepts of the
present invention.
[0042] Referring now to FIGS. 4A-C, the components of a three
component dilator system 50 are shown. As described above, the
dilator system is used to facilate implantation of the bone screw
30 into the vertebrae of the patient. The system 50 includes three
successively smaller and longer dilator tubes 51, 56 and 61. Each
dilator tube is tapered at its respective tip 53, 58 and 63 for
atraumatic introduction of the tubes through the skin and tissue of
the patient. Each of the tubes is cannulated or hollow as
represented by respective bores 52, 57 and 62 therethrough. The
bore 52 in the thinnest dilator tube 51 has a diameter sufficient
to accept a guidewire therethrough. The bore 57 in the intermediate
diameter dilator tube 56 has a diameter slightly larger than the
outer diameter of the dilator tube 51. Likewise, the bore 62 in the
largest diameter dilator tube 61 is slightly larger than the outer
diameter of the dilator tube 56.
[0043] The ends of the smallest and intermediate diameter tubes 51
and 56, ends 54 and 59 respectively, are knurled to provide a
gripping surface for removal of the tubes. The lengths of the tubes
are graduated so that the smallest diameter tube 51 has the
greatest length, while the intermediate tube 56 has is longer than
the outermost larger diameter dilator tube 61. This length
differential also facilitates sequential removal of The tubes 51
and 56, just prior to and just after the vertebra has been drilled
in the instrumentation step of the method.
[0044] In one specific embodiment of the three component dilator
system 50 of the present invention, the smallest diameter dilator
tube 51 has an outer diameter of about 5 mm, a length of 152.5 mm,
and a cannulated bore diameter of about 2 mm. The intermediate
dilator tube 56 has an outer diameter of 9.4 mm, a length of about
140.0 mm, and a cannulated bore diameter of 5.15 mm (leaving 0.15
mm clearance for insertion of the tube 51). The final dilator tube
61, through which the bone screw 30 is inserted has an outer
diameter of 11.1 mm, a length of 127.0 mm and a cannulated bore
diameter of 9.58 mm to receive the intermediate dilator tube 56, as
wed as the bone screw 30, therethrough.
[0045] While the invention has been illustrated and described in
detail in the drawings and foregoing description, the same is to be
considered as illustrative and not restrictive in character, it
being understood that only the preferred embodiment has been shown
and described and that all changes and modifications that come
within the spirit of the invention are desired to be protected.
* * * * *