Note: Descriptions are shown in the official language in which they were submitted.
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METHODS AND DEVICES FOR MINIMALLY INVASIVE
SPINAL FIXATION ELEMENT PLACEMENT
FIELD OF THE INVENTION
This application relates to tools for use in spinal surgery, and in particular
to
minimally invasive methods and devices for introducing a spinal fixation
element to one
or more spinal anchor sites within a patient's spine.
BACKGROUND OF THE INVENTION
For a number of known reasons, spinal fixation devices are used in orthopedic
surgery to align and/or fix a desired relationship between adjacent vertebral
bodies.
Such devices typically include a spinal fixation element, such as a relatively
rigid
fixation rod, that is coupled to adjacent vertebrae by attaching the element
to various
anchoring devices, such as hooks, bolts, wires, or screws. The fixation
elements can
have a predetermined contour that has been designed according to the
properties of the
target implantation site, and once installed, the instrument holds the
vertebrae in a
desired spatial relationship, either until desired healing or spinal fusion
has taken place,
or for some longer period of time.
Spinal fixation elements can be anchored to specific portions of the
vertebrae.
Since each vertebra varies in shape and size, a variety of anchoring devices
have been
developed to facilitate engagement of a particular portion of the bone.
Pedicle screw
assemblies, for example, have a shape and size that is configured to engage
pedicle
bone. Such screws typically include a threaded shank that is adapted to be
threaded into
a vertebra, and a head portion having a rod-receiving element, usually in the
form of a
U-shaped slot formed in the head. A set-screw, plug, or similar type of
fastening
mechanism is used to lock the fixation element, e.g., a spinal rod, into the
rod-receiving
head of the pedicle screw. In use, the shank portion of each screw is threaded
into a
vertebra, and once properly positioned, a rod is seated through the rod-
receiving member
of each screw and the rod is locked in place by tightening a cap or other
fastener
mechanism to securely interconnect each screw and the fixation rod.
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Recently, the trend in spinal surgery has been moving toward providing
minimally invasive devices and methods for implanting spinal fixation devices.
One
such method, for example, is disclosed in U.S. Patent No. 6,530,929 of Justis
et al. and it
utilizes two percutaneous access devices for implanting an anchoring device,
such as a
spinal screw, into adjacent vertebrae. A spinal rod is then introduced through
a third
incision a distance apart from the percutaneous access sites, and the rod is
transversely
moved into the rod-engaging portion of each spinal screw. The percutaneous
access
devices can then be used to apply closure mechanisms to the rod-engaging heads
to lock
the rod therein. While this procedure offers advantages over prior art
invasive
techniques, the transverse introduction of the rod can cause significant
damage to
surrounding tissue and muscle. Moreover, the use of three separate access
sites can
undesirably lengthen the surgical procedure, and increase patient trauma and
recovery
time.
Accordingly, there remains a need for improved minimally invasive devices and
methods for introducing a spinal fixation element into a patient's spine.
SUMMARY OF THE INVENTION
Disclosed herein are minimally invasive methods and devices for delivering a
spinal fixation element to one or more spinal anchor sites in a patient's
spinal column.
In one embodiment, a minimally invasive surgical method is provided that
includes
forming an incision through tissue located adjacent to a vertebra in a
patient's spinal
column, and inserting a blunt tip of a tool through the incision while
manipulating the
tool along the muscle plane extending between the incision and the vertebra to
separate
the muscles. The blunt tip preferably has a substantially planar
configuration, or it
includes at least one surface that is substantially planar. In an exemplary
embodiment,
the blunt tip of the tool is adapted to separate the longissimus thoracis and
multifidus
muscles. The method can also include inserting a guide wire through a lumen
extending
through the tool. The guide wire is preferably positioned such that it extends
into the
vertebra. Once properly positioned, the tool can be removed leaving the guide
wire in
position to receive a spinal implant, such as a spinal anchor, which is
preferably
delivered to the vertebra along the guide wire. The aforementioned method can
be
repeated to deliver one or more additional implants to adjacent vertebrae. A
spinal
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fixation element, such as a spinal rod, can then be delivered along one of the
pathways
extending to a vertebral body, and it can be coupled to the implant implanted
within the
adjacent vertebrae. In an exemplary embodiment, the fixation element may be
inserted
through one of the pathways in an orientation substantially parallel to a
longitudinal axis
of the 'first pathway. In certain exemplary embodiments, the spinal fixation
element may
be delivered through a cannula that extends along the pathway from the tissue
surface to
one of the vertebra.
In another exemplary embodiment, a medical device kit for use in spinal
surgery
may include a tissue dissection tool have a blunt member formed on a distal
end thereof
and adapted to separate muscles along a muscle plane without causing damage to
the
muscles. The exemplary tissue dissection tool may include a lumen extending
therethrough. The kit may also include at least one guide wire that is adapted
to be
disposed through the lumen in the tissue dissection tool, and at least one
spinal anchor
that is adapted to be implanted in a vertebral body. The kit can may also
include at least
one cannula that is adapted to provide a pathway from a tissue surface to a
vertebral
body for delivering a spinal anchor to the vertebral body, and/or at least one
spinal
fixation element that is adapted to couple to and extend between at least two
spinal
anchors.
In yet another embodiment of the present invention, a spinal anchor is
percutaneously delivered to a vertebral body having a percutaneous access
device mated
thereto and having a lumen extending therethrough and defining a longitudinal
axis. A
spinal fixation element is then advanced through the lumen in the percutaneous
access
device in a first, lengthwise orientation in which the fixation element is
substantially
parallel to the longitudinal axis of the percutaneous access device. The
spinal fixation
element can then be manipulated to extend in a second orientation, such that
the fixation
element is angled with respect to the first orientation, to position the
spinal fixation
element in relation to the spinal anchor. The method can also include the step
of
percutaneously delivering a second spinal anchor to a vertebral body with a
second
percutaneous access device mated thereto. The spinal fixation element thus
preferably
extends between the first and second spinal anchors in the second orientation.
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In an exemplary embodiment, the percutaneous access device is in the form of
an elongate, generally cylindrical tube that is adapted for percutaneous
delivery and
that is mated to a spinal anchor. The tube can include a proximal and a distal
end with
a lumen extending therebetween. The lumen is adapted to transport a spinal
fixation
element therethrough in a first, lengthwise orientation that is substantially
parallel to a
longitudinal axis of the percutaneous access device, and to deliver the spinal
fixation
element to a spinal anchor site in a second orientation that is angled with
respect to
the first orientation, and more preferably that is substantially parallel to a
patient's
spinal column. The percutaneous access device can also include at least one
sidewall
opening extending from the distal end of the elongate, generally cylindrical
tube
through at least a portion thereof for facilitating transition of a spinal
fixation element
from the first orientation to the second orientation. In one embodiment, the
device
includes opposed sidewall openings formed therein adjacent to the distal end
thereof.
The device can also optionally or alternatively include a guide member formed
within
the lumen that is adapted to direct a spinal fixation element disposed therein
from the
first orientation to the second orientation. The guide member can be, for
example, a
sloped shelf formed within the lumen of the percutaneous access device.
In another embodiment of the present invention, a minimally invasive method
for delivering a spinal fixation element to a spinal anchor site in a
patient's spinal
column is provided. The method includes the step of introducing a spinal
fixation
element into a lumen of a percutaneous access device. The lumen preferably
forms a
pathway to a spinal anchor disposed in a patient's vertebra. In an exemplary
embodiment, the percutaneous access device has an outer diameter that is
substantially the same as or less than a largest width of the spinal anchor to
which it is
attached. A person skilled in the art will appreciate that the outer diameter
of the
percutaneous access device can optionally be greater than the outer diameter
of the
spinal anchor to which it is attached. The method further includes the steps
of
advancing the spinal fixation element distally through the lumen in a first,
lengthwise
orientation that is substantially parallel to a longitudinal axis of the
percutaneous
access device, and manipulating the spinal fixation element into a second
orientation
that is substantially parallel to the patient's spinal column. The spinal
fixation element
can then be positioned relative to one or more spinal anchors.
In other aspects of the present invention, a minimally invasive surgical
method
is provided that includes the steps of making a first percutaneous incision in
a patient,
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and creating a first pathway from the first percutaneous incision to an anchor
site on a
first vertebral body. Preferably, the pathway is a minimally invasive pathway
such
that it leads only to a single anchor site, rather than multiple anchor sites.
This can be
achieved, for example, by a percutaneous access device that has a
substantially
uniform width from the first percutaneous incision to a first anchor site on a
first
vertebral body. In an exemplary embodiment, the first pathway has a width that
is
substantially equal to or less than a width of the first percutaneous
incision, and/or
that is substantially equal to or less than a width of a first anchor. The
method also
includes the steps of placing a first anchor through the first percutaneous
incision,
advancing the first anchor along the first pathway to the single anchor site,
and
placing a fixation element through the first pathway in an orientation
substantially
parallel to a longitudinal axis of the first pathway.
In a further embodiment, a second percutaneous incision can be made in a
patient, and a second minimally invasive pathway can be created from the
second
percutaneous incision to a second anchor site on a second vertebral body. A
second
anchor is then advanced along the second pathway to the second anchor site on
the
second vertebral body.
Additional methods and devices for introducing a spinal fixation element to
one or more spinal anchor sites are also provided.
Another embodiment of the present invention is a dissection tool for
separating muscles, comprising:
a rigid elongate tube adapted for percutaneous delivery and including a
proximal handle and a distal end;
a lumen extending between the proximal and distal ends of the tube and sized
to receive a guide wire, the lumen defining a longitudinal axis; and
a blunt member formed on the distal end of the tool and extending along the
longitudinal axis, the blunt member being configured to separate muscles along
a
muscle path while minimizing trauma to the muscles.
Another embodiment of the present invention is a use of the percutaneous
access device described above for introducing a spinal fixation element into a
patient's body.
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A further embodiment of the present invention is a use of the dissection
tool described above for separating muscles.
A still further embodiment of the present invention is a use of the
medical device kit described above for implanting at least one spinal anchor
in
a vertebral body.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. I is a perspective view of a percutaneous access device coupled to an
anchor according to one embodiment of the present invention;
FIG. 2 is a cross-sectional view taken along the longitudinal axis of the
percutaneous access device shown in FIG. 1;
FIG. 3A is a partially cut-away view of another embodiment of a percutaneous
access device having a guide member formed therein;
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FIG. 3B is a partially cut-away view of the percutaneous access device shown
in
FIG. 3A having a sleeve disposed there around and a spinal anchor mated
thereto;
FIG. 4A is a posterior view of three percutaneous incisions formed in the
thoracolumbar fascia of a patient's back;
FIG. 4B is a posterior view of six percutaneous incisions formed in the
thoracolumbar fascia of a patient's back;
FIG. 5A is an end view showing a blunt dissection of the muscles surrounding a
patient's vertebra;
FIG. 5B is an end view of the vertebra shown in FIG. 5A showing a technique
using a finger for separating the muscles along the dissected muscle plane to
gain access
to the vertebra;
FIG. 5C is an end view of the vertebra shown in FIG. 5A showing another
embodiment of a technique using a tool for separating the muscles along the
dissected
muscle plane to gain access to the vertebra;
FIG. 5D is an end view of the vertebra shown in FIG. 5C showing the tool
further inserted along the dissected muscle plane;
FIG. 5E is an end view of the vertebra shown in FIG. 5C showing placement of a
guide wire through the tool and into the patient's vertebra;
FIG. 5F is a side view of the tool shown in FIGS. 5C-5E;
FIG. 5G is a cross-sectional view of the tool shown in FIG. 5F taken along
line
A-A;
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FIG. 6 is an end view of the vertebra shown in FIG. 4 showing placement of a
guide wire through the incision and into the patient's vertebra;
FIG. 7 is an end view of the vertebra shown in FIG. 6 having an obturator and
several dilators disposed over the guide wire to dilate the tissue and
muscles;
FIG. 8 is perspective view of a first spinal anchor implanted in a vertebra
and
having a percutaneous access device coupled thereto and extending through a
percutaneous incision formed in the patient's tissue surface, and a second
spinal anchor
being implanted into an adjacent vertebra and having a percutaneous access
device
coupled thereto with a driver tool extending therethrough;
FIG. 9 is a perspective view of two percutaneous access devices attached to
spinal anchors that are disposed within adjacent vertebrae in a patient's
spinal column;
FIG. 10 illustrates a method for introducing a spinal fixation element through
a
partially cut-away view of one of the percutaneous access devices shown in
FIG. 9;
FIG. 11 is a perspective view of the spinal fixation element shown in FIG. 10
being advanced in toward the spinal anchors using a pusher device;
FIG. 12 is a perspective view of the spinal fixation element shown in FIG. 11
after it is frilly positioned within receiver heads of the adjacent spinal
anchors;
FIG. 13 illustrates a method for introducing a spinal fixation element through
a
partially cut-away view of the percutaneous access device shown in FIGS. 3A
and 3B;
FIG. 14 is a perspective view of the spinal fixation element shown in FIG. 13
being advanced toward the spinal anchors using a pusher device;
FIG. 15 is a perspective view of the spinal fixation element shown in FIG. 14
advanced further toward the receiver heads of the adjacent spinal anchors;
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FIG. 16 is a perspective view of the spinal fixation element shown in FIG. 15
about to be disposed within the receiver heads of the adjacent spinal anchors;
and
FIG. 17 is a perspective view of a compression tool positioned around the
percutaneous access devices shown in FIG. 12 and compressing the devices
toward one
another, and a closure mechanism being applied through one of the percutaneous
access
devices to lock the spinal fixation element in relation to the spinal anchor.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides minimally invasive methods and devices for
introducing a spinal fixation element into a surgical site in a patient's
spinal column. In
general, the method involves advancing a spinal fixation element in a
lengthwise
orientation along a minimally invasive pathway that extends from a minimally
invasive
percutaneous incision to a spinal anchor site. In an exemplary embodiment, a
percutaneous access device is used to create the minimally invasive pathway
for
receiving the spinal fixation element and for delivering the fixation element
to a spinal
anchor site. The spinal fixation element is preferably inserted through a
lumen in the
percutaneous access device in a lengthwise orientation, such that the spinal
fixation
element is oriented substantially parallel to a longitudinal axis of the
percutaneous
access device. As the spinal fixation element approaches or reaches the distal
end of the
pathway, the spinal fixation element can be manipulated to orient it at a
desired angle
with respect to the percutaneous access device, preferably such that the
spinal fixation
element is substantially parallel to the patient's spinal column. The spinal
fixation
element can then optionally be positioned to couple it, either directly or
indirectly, to
one or more spinal anchors. A fastening element or other closure mechanism, if
necessary, can then be introduced into the spinal anchor site to fixedly mate
the spinal
fixation element to the anchor(s).
The methods and devices of the present invention are particularly advantageous
in that they can be achieved using one or more minimally invasive percutaneous
incisions for accessing the spinal column. Such incisions minimize damage to
intervening tissues, and they reduce recovery time and post-operative pain.
The present
invention also advantageously provides techniques for delivering spinal
fixation
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elements and anchors along a minimally invasive pathway, thus eliminating the
need to
create a large working area at the surgical site.
While a variety of devices can be used to perform the methods of the present
invention, FIGS. I and 2 illustrate an exemplary embodiment of a percutaneous
access
device 12 that is mated to a spinal anchor 50 (FIG. 1) to form a spinal
implant assembly
10. As shown, the device 12 is in the form of a generally elongate,
cylindrical tube
having an inner lumen 12c formed therein and defining a longitudinal axis L
that extends
between proximal and distal ends 12a, 12b. The size of the access device 12
can vary
depending on the intended use, but it should have a length I that allows the
proximal end
12a of the access device 12 to be positioned outside the patient's body, while
the distal
end 12b of the access device 12 is coupled to, or positioned adjacent to, a
spinal anchor,
e.g., anchor 50, that is disposed in a vertebra in a patient's spine. The
access device 12
is also preferably adapted to provide a minimally invasive pathway for the
delivery of a
spinal fixation element, and in particular, the percutaneous access device 12
should also
be adapted to be implanted through a minimally invasive percutaneous incision,
which is
a relatively small incision that typically has a length that is less than a
diameter or width
of the device being inserted therethrough.
In an exemplary embodiment, the device 12 has an inner diameter d, that is
sufficient to allow a spinal fixation element to be introduced therethrough,
preferably in
a lengthwise orientation. The inner diameter d, can also optionally be
configured to
allow a driver mechanism to be introduced therethrough for applying a closure
mechanism to lock the spinal fixation element in relation to a spinal anchor.
The outer
diameter d,, of the access device 12 can also vary, and it can be the same as,
less than, or
greater than an outer diameter d,= of the spinal anchor. In the illustrated
embodiment, the
access device 12 has an outer diameter d0 that is substantially the same as an
outer
diameter d,. of the spinal anchor, which, as illustrated in FIG. 1, is the
receiver head 52
of a spinal screw 50. This is particularly advantageous in that the size of
the incision
does not need to be any larger than necessary. The matching outer diameters
do, d,. of
the access device 12 and the anchor 50 also allow the access device 12 and/or
the anchor
50 to be introduced through a cannula. If the access device 12 is mated to the
anchor 50,
the matching outer diameters d,,, d,. also allows a sleeve or other device to
be slidably
disposed there around to prevent disengagement between the access device 12
and the
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anchor 50. In another, exemplary embodiment, the outer diameter do of the
access
device 12 can be slightly greater than the outer diameter d,. of the spinal
anchor. By way
of non-limiting example, where a receiver head of the spinal anchor has an
outer
diameter d,. that is about 13 min, the access device 12 preferably has an
outer diameter do
that is about 15 mm.
The percutaneous access device 12 also preferably includes at least one
sidewall
opening or slot 14 formed therein, and more preferably it includes two opposed
sidewall
openings (only one opening 14 is shown) formed therein and extending
proximally from
the distal end 12b thereof. The openings 14 allow a spinal fixation element to
be
introduced through the device 12 in a first, lengthwise orientation, in which
the spinal
fixation element is substantially parallel to the longitudinal axis L of the
access device
12. The spinal fixation element can then to be manipulated to extend at an
angle with
respect to the first orientation, such that the fixation element extends in a
direction
substantially transverse to the longitudinal axis L of the access device 12,
for example,
in a direction that is substantially parallel to the patient's spine. Since
the length L of the
spinal fixation element will necessarily be greater than the inner diameter d;
of the
access device 12, the openings 14 allow the spinal fixation element to pass
therethrough
while being transitioned from the first, lengthwise orientation to the second
orientation.
A person skilled in the art will appreciate that the exact position of the
spinal fixation
element with respect to the longitudinal axis L will of course vary depending
on the
configuration of the spinal fixation element.
The shape and size of each opening 14 can vary, but the opening(s) 14 should
be
effective to allow movement of the spinal fixation element from the first
orientation to
the second orientation. In an exemplary embodiment, the openings 14 extend
over about
half of the length, or less than half of the length, of the percutaneous
access device 12.
The shape of each slot 14 can be generally elongate, and they should each have
a width
iv that is sufficient to accommodate the diameter of the spinal fixation
element. A
person skilled in the art will appreciate that the percutaneous access device
12 can
include any number of sidewall openings having any shape that is sufficient to
allow a
spinal fixation element to be moved from the first orientation to the second
orientation.
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In another embodiment of the present invention, shown in FIGS. 3A-3B, the
percutaneous access device 112 can also optionally include a guide member 120
formed
within the distal end 112b of the lumen 112c to help guide the spinal fixation
element
from the first orientation to the second orientation. The guide member 120 can
have a
variety of configurations, but it should be effective to guide the spinal
fixation element
from the first orientation toward the anchor 50 attached to, or positioned
adjacent to, the
access device 112, and optionally toward anchor(s) implanted in adjacent
vertebrae. In
an exemplary embodiment, as shown, the guide member 120 is in the form of a
sloped
shelf formed within the inner lumen 112c of the access device 112 and
preferably
positioned opposite to a single sidewall slot 114 formed in the access device
112. The
sloped shelf 120 can vary in shape and size depending on the type of fixation
element
being used and/or the geometry of the access device. In use, as the leading
end of a
spinal fixation element, such as a spinal rod, contacts the shelf 120, the
shelf 120 begins
to direct the spinal fixation element into the second orientation, thereby
causing the
spinal fixation element to extend in a direction that is substantially
transverse to the axis
L of the device 112, and that is preferably substantially parallel to the
patient's spinal
column. The spinal fixation element can then be manipulated to position it in
relation to
one or more spinal anchors, as will be discussed in more detail below.
Referring back to FIG. 1, in use, the percutaneous access device 12 can be
adapted to attach to a spinal anchor 50. Accordingly, the distal end 12c of
the
percutaneous access device 12 can include one or more mating elements 18
formed
thereon or therein for engaging the anchor 50. Suitable mating elements
include, for
example, threads, a twist-lock engagement, a snap-on engagement, or any other
technique known in the art, and in an exemplary embodiment the mating elements
are
formed on opposed inner surfaces of the distal end 12b of the access device
12. A
sleeve 100 (partially shown in FIG. 3B) or other device, preferably having
sidewall
openings (not shown) that correspond with the sidewall openings 14 formed in
the
percutaneous access device 12, can also be placed over the percutaneous access
device
12, and optionally over the implant 50 as well, to prevent disengagement of
the access
device 12 from the implant 50 during use. Exemplary techniques for mating the
percutaneous access device 12 to an anchor are disclosed in a patent
application entitled
"Percutaneous Access Devices and Bone Anchor Assemblies," filed concurrently
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herewith. A person skilled in the art will appreciate that a variety of other
techniques
can be used to removably mate the percutaneous access device to an anchor.
For reference purposes, FIG. 1 illustrates an exemplary spinal anchor for use
with the methods and devices of the present invention. A person skilled in the
art will
appreciate that a variety of anchors can be used with the devices and methods
of the
present invention, including, for example, spinal screws, hooks, bolts, and
wires. FIG. I
illustrates a spinal screw that includes a distal, bone-engaging portion,
e.g., a threaded
shank 54, and a proximal, U-shaped, receiver head 52 that is adapted to seat a
spinal
fixation element, preferably a spinal rod (not shown). The threaded shank 54
can be
fixedly attached to the receiver head 52 to form a monoaxial screw, or
alternatively the
shank 54 can be configured as a polyaxial screw, as shown, that is rotatably
disposed
through an opening formed in the distal end of the receiver head 52 to allow
rotation of
the shank 54 with respect to the receiver head 52. A variety of techniques can
be used to
allow rotation of the head 52 with respect to the shank 54.
FIGS. 4A-17 show a minimally invasive method of implanting a spinal fixation
element. While the method is shown and described in connection with the
percutaneous
access device 12 and spinal screw 50 disclosed herein, a person skilled in the
art will
appreciate that the method is not limited to use with such devices, and that a
variety of
other devices known in the art can be used. Moreover, while only two access
devices
12, 12' and two anchors 50, 50' are shown in FIGS. 4-14, the method of the
present
invention can be performed using any number of access devices and anchors. The
method can also be performed using only some of the method steps disclosed
herein,
and/or using other methods known in the art.
The procedure preferably begins by forming a minimally invasive percutaneous
incision through the tissue located adjacent to the desired implant site.
While the
location, shape, and size of the incision will depend on the type and quantity
of spinal
anchors being implanted, FIG. 4A illustrates three midline minimally invasive
percutaneous incisions 62a-c formed on one side of three adjacent vertebra in
the
thoracolumbar fascia in the patient's back, and FIG. 4B illustrates three
additional
midline minimally invasive percutaneous incisions 62d-f formed on the opposite
side of
the three adjacent vertebra in the thoracolumbar fascia in the patient's back.
Each
incision 62a-f is a stab incision that has a diameter of about 10-20 mm in
diameter,
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however this can vary depending on the procedure. In an exemplary embodiment,
each
incision 62a-f has a diameter that is equal to or less than a largest diameter
of the anchor
and/or the percutaneous access device being inserted therethrough.
While probably not necessary, once the percutaneous incisions 62a-f are
formed,
blunt finger dissection can optionally be used, as shown in FIG. 5A-5B, to
separate the
longissimus thoracis and multifidus muscles, thereby exposing the facet and
the junction
of the transverse process and superior articular process.
FIGS. 5C-5E illustrate another exemplary technique for separating the
longissimus thoracis and multifidus muscles using a blunt tool 200, which is
shown in
more detail in FIGS. 5F-5G. Referring first to FIGS. 5F-5G, the tool 200
generally
includes a rigid elongate shaft 202 having proximal and distal ends 202a,
202b. The
shaft 202 also includes a lumen 202c extending therethrough between the
proximal and
distal ends 202a, 202b for receiving a guide wire, such as a k-wire. The lumen
202c
may be sized to receive a guidewire 202c delivered through the lumen 202c. The
proximal end 202a may include a handle 204 formed therein to facilitate
grasping of the
tool 200. The handle 204 can have virtually any shape and size. For example,
as shown
in FIGS. 5F-5G, the handle 204 in the exemplary embodiment has a generally
elongate
cylindrical shape and it includes ridges 204a formed thereon to facilitate
gripping of the
device.
The distal end 202b of the tool 200 includes a blunt member 206 formed
thereon.
The blunt member 206 may be adapted, e.g., sized and shaped, to separate
muscles along
a muscle plane while concomitantly minimizing trauma to the separated muscles.
While
the shape of the blunt member 206 can vary, in an exemplary embodiment, as
shown,
the blunt member 206 has a substantially elongate rectangular shape with
opposed front
and back surfaces 206a, 206b. The width between the front and back surfaces
206a,
206b may taper or decreases in a distal direction such that the distal-most
width w62 is
less than the proximal-most width Wbi. Such an exemplary configuration
facilitates
insertion of the blunt member 206 between tissue, e.g., muscle, to allow the
tissue to be
separated. The width ii,, extending between opposed side edges of the front
and back
surfaces 206a, 206b can also vary, but in an exemplary embodiment, as shown,
the
width 1-iws remains constant along the length of the front and back surfaces
206a, 206b.
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While not shown, the tool 200 can also optionally include an inner tube
disposed
within the elongate shaft 202 for preparing the vertebra. In particular, the
inner tube can
be slidably disposed within the elongate shaft 202 to allow the inner tube to
be moved
distally into bone to create a divot in the vertebra, thereby preparing the
bone for an awl
or tap. The tool 200 can also optionally serve as a drill guide. In
particular, the elongate
shaft 202 can have an inner diameter that is adapted to receive a drill
therethrough to
guide the drill toward and into the vertebra. The shaft 202 also serves as a
protective
cannula for the drill, inhibiting contact between the drill and the muscles
surrounding the
tool 200. A person having ordinary skill in the art will appreciate that the
tool 200 can
have a variety of other configurations, and that the tool 200 can be adapted
for a variety
of other uses.
Referring now to FIGS. 5C-5E, the exemplary tool 200 is shown in use. As
shown, after the percutaneous incisions 62a-f are formed, as previously
described, the
blunt member 206 of the dissection tool 200 may be inserted through an
incision 62.
The incision 62 may be deep enough to allow the fat layer between the
longissimus
thoracis and multifidus muscles to be located. Once located, the tool 200 may
be
manipulated to separate or split the longissimus thoracis and multifidus
muscles, thereby
exposing the facet and the junction of the transverse process and superior
articular
process. Once the tool 200 is positioned adjacent to or against the vertebra
60, as shown
in FIG. 5D, a guide wire, e.g., a k-wire 64, can be inserted through the lumen
202c in the
tool 200 to position a distal end of the k-wire 64 at or within the vertebra
60, as shown in
FIG. 5E. Fluoroscopy or other imaging may be used to facilitate proper
placement of
the k-wire 64. The tool 200 can then be removed from the k-wire 64, leaving
the k-wire
64 to serve as a guide for various other devices, which will be described in
more detail
below. This procedure can be repeated at each incision 62a-f to facilitate
placement of
multiple spinal anchors.
Where tool 200 is not used, a guide wire, e.g., k-wire 64, can be implanted,
either
prior to or after formation of the incision, at each spinal anchor implant
site. As shown
in FIG. 6, the k-wire 64 preferably extends between the muscles and into the
vertebra at
the desired entry point of the spinal anchor. Fluoroscopy can be used to
facilitate proper
placement of the k-wire 64.
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The opposed ends of the incision can then be dilated to provide a pathway for
delivery of a spinal anchor to each implant site. FIG. 7 illustrates dilation
at one end of
the incision 62 using an obturator 66a having several dilators 66b, 66c of
increasing size
placed there over. The dilators 66b, 66c are delivered over the obturator 66a
and k-wire
64 to essentially stretch the skin around the incision 62 and to expand the
pathway to the
anchor site.
Once the incision 62 is dilated to the proper size, an anchor can be delivered
to
each anchor site, as shown in FIG. 8. This procedure typically involves
preparation of
the vertebra 60 using one or more bone preparation instruments, such as
drills, taps,
awls, burrs, probes, etc. While not always necessary, one or more cannulae can
be used
to provide a pathway from the incision 62 to the anchor site for insertion of
the bone
preparation instruments and/or the anchor. In an exemplary embodiment, a
relatively
small cannula is used to introduce bone preparation instruments into the
surgical site.
The incision 62 can then be further dilated, and the small cannula can be
replaced with a
larger cannula that is adapted to receive or mate to the anchor.
Once the vertebra 60 is prepared, a spinal anchor can be implanted at each
implant site. An access device 12, 12' can be mated to each anchor 50, 50'
after insertion
of the anchor 50, 50' into bone 60, 60', but more preferably each percutaneous
access
device 12, 12' is attached to the anchor 50, 50' prior to insertion of the
anchor 50, 50'
into bone 60, 60' to provide a passageway for a driver tool for driving the
anchor 50 into
bone 60, 60'. FIG. 8 illustrates anchor 50 implanted in a first vertebra 60
and having
access device 12 attached thereto. While not shown, the anchor 50 is
preferably
cannulated to allow the k-wire 64 to extend through the anchor 50 and the
access device
12 to guide the devices 50, 12 toward the implant site. FIG. 8 further
illustrates a second
anchor 50' having an access device 12' mated thereto. As shown, the screw 50'
is about
to be implanted in a second vertebra 60' that is adjacent to the first
vertebra 60. Once the
screw 50' is positioned adjacent to the vertebra 60', a driver tool 90 can be
positioned
through the access device 12' and coupled to the receiver head 52' of the
screw 50' to
drive the screw 50' into the vertebra 60'.
In another embodiment, a sleeve can be placed over each access device 12, 12',
either prior to or after the devices 12, IT, 50, 50' are implanted, to prevent
the devices
12, 12' from becoming disengaged from the anchors 50, _50' to which they are
attached.
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The sleeve 100, which is partially illustrated in FIG. 3B, is preferably in
the form of a
cannula that has substantially the same configuration as each access device
12, 12'. The
use of a sleeve is particularly desirable where the access devices 12, 12'
utilize pin
members that engage corresponding detents formed on an outer surface of each
screw
head 52, 52', as the sleeve will prevent the pin members from becoming
disengaged
from the detents. The sleeve can also optionally serve as an access device,
allowing
access devices 12, 12' to be detached and removed from the anchors 50, 50'.
After the anchors 50, 50' are implanted, a spinal fixation element 70 is
delivered
to the anchor site. This can be achieved by introducing the spinal fixation
element 70
through one of the percutaneous access devices 12, 12' that is attached to the
anchor 50,
50', or through some other percutaneous access device that provides a pathway
to the
anchor(s) 50, 50'. As shown in FIG. 9, a spinal fixation element, e.g., a
spinal rod 70, is
introduced into device 12 in a first, lengthwise orientation, such that the
spinal fixation
element 70 is substantially parallel to the longitudinal axis L of the access
device 12.
Where the fixation element has a curved orientation or it has some other
configuration, it
is understood that the fixation element is in the "substantially parallel"
orientation when
it is positioned lengthwise through the percutaneous access device.
The spinal fixation element 70 is then moved distally toward the distal end
12b
of the percutaneous access device 12, as shown in FIGS. 10 and 11. Movement of
the
spinal fixation element 70 can be achieved using a manipulator device 80. The
manipulator device 80 can have a variety of configurations, but it should be
effective to
allow controlled movement of the fixation element 70. A person skilled in the
art will
appreciate that a variety of other techniques can be used to guide the spinal
fixation
element 70 through the percutaneous access device 12 and to position the
spinal fixation
element 70 in relation to one or more anchors 50, 50'. Moreover, the spinal
fixation
element 70 can have a variety of configurations to facilitate insertion
through a
percutaneous access device. By way of non-limiting example, a patent
application
entitled "Flexible Spinal Fixation Elements," and filed concurrently herewith,
discloses
a spinal fixation element that can be flexed as it is passed through a
percutaneous access
device, thereby allowing the spinal fixation element to transition from the
first
orientation to the second orientation. The application also discloses
techniques for
delivering the spinal fixation element along a guide wire or cable, thus
eliminating the
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need for a manipulator device. Other spinal fixation elements suitable for use
with the
present invention, in addition to mechanical and flexible fixation elements,
include, for
example, inflatable fixation elements such as those disclosed in U.S. Patent
Publication
No. 2002/0068975, entitled "Formable Orthopedic Fixation System with Cross
Linking"
by Teitelbaum et al., U.S. Patent Publication No. 2002/0082600, entitled
"Formable
Orthopedic Fixation System" by Shaolian et al., and U.S. Patent Publication
No.
2002/0198526, entitled "Formed In Place Fixation System With Thermal
Acceleration"
by Shaolian et al.
Referring now to FIGS. 11 and 12, as the spinal fixation element 70 approaches
the distal end 12b of the access device 12, the spinal fixation element 70 can
be
manipulated to cause the spinal fixation element 70 to-assume a second
orientation that
is different from the first orientation, and more preferably that is
substantially parallel to
the patient's spinal column and/or transverse to the first orientation. It is
understood that
the angle of the fixation element 70 in the second orientation will vary
depending on the
type of fixation device being implanted, as well as the orientation of the
access device
12, which can vary throughout the surgical procedure since the access device
12 can be
positioned at several angles with respect to the patient's spinal column.
During transition of the spinal fixation element 70 from the first orientation
to
the second orientation, a leading end of the spinal fixation element 70 should
be
subcutaneously positioned. Where the access device 12 includes slots or
openings (only
one opening 14 is shown), the opening(s) 14 can be used to facilitate movement
of the
spinal fixation element 70 into the second orientation as they will allow the
spinal
fixation element 70 to extend therethrough during rotation. This may not be
necessary,
however, depending on the length of the openings 14, the length of the spinal
fixation
element 70, and/or the configuration of the spinal fixation element 70. As
shown in
FIGS. 1 I and 12, only the leading end 70a of the spinal fixation element 70
exits the
percutaneous access device 12 through one of the openings 14.
Referring to FIG. 12, manipulation of the spinal fixation element 70 is
continued
until the spinal fixation element 70 is positioned in relation to one or more
spinal
anchors. Depending on the type of spinal anchor used, the fixation element can
be
positioned to be directly or indirectly mated to the spinal anchor. As shown
in FIG. 12;
the fixation element 70 is fully seated in the receiver heads 52, 52' of the
adjacent spinal
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anchors 50, 50'. The manipulator device 80, if used, can then be removed fi=om
the
access device 12.
In another embodiment, the percutaneous access device 112 shown in FIGS. 3A
and 3B can be used to facilitate introduction of a spinal fixation element
into a surgical
anchor site. As previously stated, access device 112 includes a guide member
20 formed
therein to direct the spinal fixation element 70 from the first orientation to
the second
orientation. This is illustrated in FIGS. 13-16. As shown, as the spinal
fixation element
70 is moved distally to come into contact with the guide member 120, the guide
member
120 causes the spinal fixation element 70 to rotate and extend toward the
opening 114 in
the percutaneous access device 112. As a result, the spinal fixation element
70 is
directed into the second orientation, whereby it can be positioned in or
adjacent to the
receiver heads 52, 52' of the adjacent spinal implants 50, 50'.
Referring back to FIG. 12, once the spinal fixation element 70 is fully seated
in
the receiver heads 52, 52' of the adjacent spinal anchors 50, 50', the pusher
shaft 80, if
used, can then be removed or detached from the spinal fixation element 70, and
a closure
mechanism can be applied to one or both receiver heads 52, 52' to retain the
spinal
fixation element 70 therein. In an exemplary embodiment, however, a
compression tool
100 is used to compress the access devices 12, 12' toward one another prior to
applying
a closure mechanism to each anchor 50, 50'. The closure mechanism(s) can,
however,
be partially applied before compression.
An exemplary compression tool 300 is shown in FIG. 17, and in general it
includes opposed arms 302, 304 that are pivotally coupled to one another at a
substantial
mid-point thereof such that each arm 302, 304 includes a distal portion 302b,
304b that
is adapted to be disposed around a percutaneous access device 12, 12', and a
proximal,
handle portion 302a, 304a. The device 300 can also include a fulcrum (not
shown) that
is disposed between the arms 302, 304 to facilitate controlled movement of the
arms
302, 304 with respect to one another. In use, the distal portion 302b, 304b of
each arm
302, 304 is placed around an access device 12, 12', preferably around the
distal end 12b,
12b' of each device 12, 12' and/or around the head 52, 52' of each anchor 50,
50'. The
proximal, handle portions 302a, 304a are then brought toward one another to
move the
access devices 12, 12' toward one another, preferably while maintaining
relative spacing
therehetween, as shown in FIG. 17.
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Once properly positioned, a closure mechanism can be applied, preferably via
the
access devices 12, 12', to each anchor head 50, 50' to retain the spinal
fixation element
70 within the receiver heads 52, 52'. A variety of closure mechanisms and
tools for
delivering closure mechanisms are known in the art and they can be used with
the
present invention. By way of non-limiting example, FIG. 13 illustrates driver
tool 90
disposed through access device 12 for applying a closure mechanism, such as a
set
screw, to the receiver head 52 of the spinal anchor 50 to lock the spinal
fixation element
70 with respect to the spinal anchor 50. This step can be repeated for the
adjacent spinal
anchor(s).
A person skilled in the art will appreciate that the spinal fixation element
70 does
not need to be directly attached to each anchor 50, 50', and that it can be
indirectly
attached to the anchors 50, 50' using, for example, a band clamp, or slotted
or offset
connectors.
Once the fixation element 70 is secured in relation to the implants 50, 50',
the
access devices 12, 12' can be removed from the implants 50, 50', leaving only
minimally
invasive percutaneous incisions in the patient where each access device 12,
12' was
introduced. This is particularly advantageous in that it reduces the amount of
trauma
caused to the patient, and it minimizes the damage to muscle surrounding the
surgical
site.
As previously stated, a person skilled in the art will appreciate that the
method
can be performed in any sequence using any of the steps. Moreover, the access
devices
of the present invention can be used to deliver multiple spinal fixation
elements
simultaneously or sequentially, and/or to perform a variety of other surgical
procedures
not illustrated or described herein.
One skilled in the art will appreciate further features and advantages of the
invention based on the above-described embodiments. Accordingly, the invention
is not
to be limited by what has been particularly shown and described, except as
indicated by
the appended claims,
