Note: Descriptions are shown in the official language in which they were submitted.
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POLYAXIAL BONE FIXATION ELEMENT
CROSS REFERNCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional Application No.
60/950,995, filed on July 20, 2007, entitled "TOP-LOADING POLYAXIAL PEDICLE
SCREW," and the benefit of U.S. Provisional Application No. 60/988,584, filed
on
November 16, 2007, entitled "BONE SCREW WITH AN INSTRUMENT
INTERFACE," the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] It is often necessary due to various spinal disorders to surgically
correct and
stabilize spinal curvatures, or to facilitate spinal fusion. Numerous systems
for treating
spinal disorders have been disclosed.
[0003] One method involves a pair of elongated members, typically spinal rods,
longitudinally placed on the posterior spine on either side of spinous
processes of the
vertebral column. Each rod is attached to various vertebrae along the length
of the spine
by way of pedicle screws. The pedicle screws each may include a body having a
U-
shaped rod-receiving channel for receiving a portion of the longitudinal
spinal rod
therein. Moreover, the body often interacts with a locking cap to clamp and
secure the
position of the spinal rod within the rod-receiving channel.
[0004] To facilitate insertion of the spinal rod into the rod-receiving
channels and to
provide additional flexibility in the positioning of the spinal rods and the
pedicle screws,
pedicle screws have been developed wherein the body is pivotable with respect
to the
bone anchor (commonly known as polyaxial pedicle screws).
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[0005] It is desirable to develop a pedicle screw that is simple for a surgeon
to use,
provides for polyaxial rotation and is able to securely mount the rod to the
selected
vertebra.
SUMMARY OF THE INVENTION
[0006] A preferred embodiment of the present invention is directed to a
polyaxial
bone fixation element for use in a spinal fixation procedure. The polyaxial
bone fixation
element preferably includes a bone anchor having an enlarged head portion
(e.g., a bone
screw), a collet (e.g., an insert member), a body having an axial bore for
receiving the
collet and the enlarged head portion of the bone anchor. The body also
includes a rod-
receiving channel and threads for threadably receiving a locking cap (e.g., an
externally
threaded set screw). The polyaxial bone fixation element preferably enables in-
situ
assembly. That is, the polyaxial bone fixation element is preferably
configured so that in
use, the bone anchor may be secured to the patient's vertebra prior to being
received
within the body. Accordingly, the polyaxial bone fixation element preferably
enables a
surgeon to implant the bone anchor without the body and collet to maximize
visibility
and access around the anchoring site. Once the bone anchor has been secured to
the
patient's vertebra, the body can "pop-on" to the bone anchor. The bone anchor
may also
include an instrument interface so that a surgical instrument can be directly
coupled to the
bone anchor.
[0007] In one preferred embodiment, the polyaxial bone fixation element
includes a
bone anchor, a body, a collet and a locking cap. The bone anchor preferably
includes an
enlarged head portion. The head portion preferably includes a drive surface
for engaging
a first surgical instrument and an instrument interface for engaging a second
surgical
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instrument. The body preferably includes a longitudinal axis, an upper end
with an upper
opening, a lower end with a lower opening, a bore extending between the upper
opening
and the lower opening wherein the bore has a first diameter, and a rod-
receiving channel
for receiving the spinal rod. The rod-receiving channel has a channel axis
that is oriented
substantially perpendicular to the longitudinal axis. The body preferably also
includes a
lower edge portion adjacent the lower opening. The lower edge portion has a
second
diameter smaller than the first diameter. The collet preferably includes a
first end, a
second end and one or more slots extending from the second end, wherein the
slots define
a plurality of flexible arms. The collet is preferably movably positioned
within the bore
of the body. The locking cap is preferably removably engageable with the body.
The
locking cap is movable from an unlocked position to a locked position, wherein
movement of the locking cap from the unlocked position to the locked position
urges the
rod against the collet and the flexible arms against the lower edge portion to
secure a
position of the bone anchor relative to the body.
[0008] In another preferred embodiment, the polyaxial bone fixation element
includes
a body sized and configured to snap onto a head portion of an implanted bone
anchor.
The body preferably includes a longitudinal axis, an upper end with an upper
opening, a
lower end with a lower opening, a bore extending between the upper and lower
openings
wherein the bore has a first diameter, and a rod-receiving channel extending
from the
upper end toward the lower end and positioned on a channel axis that is
oriented
substantially perpendicular to the longitudinal axis. The bore preferably
includes a lower
edge portion terminating proximate the lower end and an enlarged diameter
portion
disposed adjacent to the lower edge portion and between the lower edge portion
and the
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upper end. The lower edge portion preferably has a second diameter while the
enlarged
diameter portion has a third diameter, wherein the third diameter is
preferably larger than
the first diameter, which is larger than the second diameter. The collet
preferably
includes a first end, a second end and one or more slots extending from the
second end,
wherein the slots define a plurality of flexible arms. The flexible arms
preferably each
have a root end, a terminal end and a generally spherical, external surface
proximate the
terminal end. The flexible arms render the collet expandable to accept the
head of the
bone anchor and compressible to secure the head of the bone anchor relative to
the collet.
The flexible arms are preferably positioned proximate the enlarged diameter
portion in a
loading position and at least a portion of the external surface of the
flexible arms contact
the lower edge portion in a locked position.
[0009] In an alternate preferred embodiment, the polyaxial bone fixation
element
preferably includes a bone anchor, a body and a collet. The bone anchor
preferably
includes a head portion, wherein the head portion includes a drive surface for
engaging a
first surgical instrument and an instrument interface for engaging a second
surgical
instrument. The body preferably includes a longitudinal axis, an upper end
with an upper
opening, a lower end with a lower opening, a bore extending between the upper
and
lower openings, and a rod-receiving channel extending from the upper end
toward the
lower end and positioned on a channel axis that is oriented substantially
perpendicular to
the longitudinal axis. The bore preferably also includes a lower edge portion
proximate
the lower end and an enlarged diameter portion adjacent to the lower edge
portion and
between the lower edge portion and the upper end. The collet is preferably
movably
positioned within the bore of the body. The collet preferably includes a first
end, a
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second end and one or more slots extending from the second end, wherein the
slots define
a plurality of flexible arms. The flexible arms preferably render the collet
expandable to
accept the head of the bone anchor and compressible to secure the head of the
bone
anchor relative to the collet. The collet preferably further includes a cavity
extending
from the second end. The flexible arms of the collet are preferably positioned
in general
vertical alignment with the enlarged diameter portion in a loading position so
that the
head of the bone anchor can be received in the cavity formed in the collet. At
least a
portion of the flexible arms preferably contact the lower edge portion in a
locked position
so that the head of the bone anchor is secured with respect to the collet. In
the locked
position, the contact is generally a line contact between the collet and the
body.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0010] The foregoing summary, as well as the following detailed description of
a
preferred embodiment of the application, will be better understood when read
in
conjunction with the appended drawings. The preferred embodiment of the
polyaxial
bone fixation element is shown in the drawings for the purposes of
illustration. It should
be understood, however, that the application is not limited to the precise
arrangements
and instrumentalities shown. In the drawings:
[0011] Fig. 1 illustrates an exploded, perspective view of a preferred
embodiment of
a polyaxial bone fixation element;
[0012] Fig. 2A illustrates a front elevational view of a portion the polyaxial
bone
fixation element shown in Fig. 1, mounted in a patient's vertebra;
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[0013] Fig. 2B illustrates a side elevational view of the portion of the
polyaxial bone
fixation element shown in Fig. 1, mounted in the patient's vertebra;
[0014] Fig. 3 illustrates a partial, cross-sectional view of the polyaxial
bone fixation
element shown in Fig. 1, taken along line 3-3 of Fig. 2B;
[0015] Fig. 4A illustrates a magnified cross-sectional view of a head portion
of a
bone anchor used in connection with the polyaxial bone fixation element shown
in Fig. 1;
[0016] Fig. 4B illustrates a top plan view of the bone anchor shown in Fig.
4A;
[0017] Fig. 5A illustrates a front elevational view of a collet used in
connection with
the polyaxial bone fixation element shown in Fig. 1;
[0018] Fig. 5B illustrates a side elevational view of the collet shown in Fig.
5A;
[0019] Fig. 5C illustrates a cross-sectional view of the collet shown in Fig.
5A, taken
along line 5C-5C of Fig. 5B;
[0020] Fig. 6A illustrates a front elevational view of a first preferred
embodiment of a
body used in connection with the polyaxial bone fixation element shown in Fig.
1;
[0021] Fig. 6B illustrates a side elevational view of the body shown in Fig.
6A;
[0022] Fig. 6C illustrates a cross-sectional view of the body shown in Fig.
6A, taken
along line 6C-6C of Fig. 6B;
[0023] Fig. 6D illustrates a magnified, cross-sectional view of a lower end of
the
body shown in Fig. 6A, taken from within circle 6D of Fig. 6C;
[0024] Fig. 6E illustrates a magnified, cross-sectional view of the lower end
of the
body shown in Fig. 6D and a collet and head of a bone anchor of the polyaxial
bone
fixation element shown in Fig. 1;
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[0025] Fig. 6F illustrates a magnified, cross-sectional view of a second
preferred
embodiment of a lower end of a body of the polyaxial bone fixation element
shown in
Fig. 1;
[0026] Fig. 6G illustrates a magnified, cross-sectional view of the lower end
of the
body shown in Fig. 6F;
[0027] Fig. 7A illustrates a top plan view of a locking cap used in connection
with the
polyaxial bone fixation element shown in Fig. 1;
[0028] Fig. 7B illustrates a cross-sectional view of the locking cap shown in
Fig. 7A,
taken along line 7B-7B of Fig. 7A;
[0029] Fig. 8A illustrates a side perspective view of a preferred embodiment
of a
screw driver and a sleeve coupled to a portion of the polyaxial bone fixation
element of
Fig. 1;
[0030] Fig. 8B illustrates a cross-sectional view of the screw driver and
sleeve
coupled to the portion of the polyaxial bone fixation element of Fig. 1, taken
along line
8B-8B of Fig. 8A;
[0031] Fig. 9A illustrates a cross-sectional view of a syringe assembly and
the sleeve
coupled to a portion of the polyaxial bone fixation element of Fig. 1; and
[0032] Fig. 9B illustrates a magnified, cross-sectional view of the syringe
assembly
and sleeve shown in Fig. 9A, taken from within the circle 9B of Fig. 9A.
DETAILED DESCRIPTION OF THE INVENTION
[0033] Certain terminology is used in the following description for
convenience only
and is not limiting. The words "right", "left", "lower" and "upper" designate
directions
in the drawings to which reference is made. The words "inwardly" and
"outwardly" refer
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to directions toward and away from, respectively, the geometric center of the
polyaxial
bone fixation element, the described instruments and designated parts thereof.
The
words, "anterior", "posterior", "superior", "inferior" and related words
and/or phrases
designate preferred positions and orientations in the human body to which
reference is
made and are not meant to be limiting. The terminology includes the above-
listed words,
derivatives thereof and words of similar import.
[0034] Certain exemplary embodiments of the invention will now be described
with
reference to the drawings. In general, such embodiments relate to a preferred
polyaxial
bone fixation element, and related instruments by way of non-limiting example
and a
polyaxial bone fixation element for use in spinal fixation to facilitate
insertion of a
longitudinal spinal rod in a rod-receiving channel formed in the body of the
polyaxial
bone fixation element. The invention may have other applications and uses and
should
not be limited to the structure or use described and illustrated.
[0035] Referring to Figs. 1-7B, a preferred polyaxial bone fixation element 10
includes a bone anchor 20 (shown as a bone screw), a collet 150, a body 200,
and a
locking cap 300 (shown as an externally threaded set screw). As will be
described in
greater detail below, the polyaxial bone fixation element 10 preferably
enables in-situ
assembly. That is, preferably, the polyaxial bone fixation element 10 is
configured so
that in use, the bone anchor 20 may be secured to a patient's vertebra 700
prior to being
received within the body 200. The polyaxial bone fixation element 10
preferably enables
a surgeon to implant the bone anchor 20 without the body 200 and collet 150
pre-
assembled to the bone anchor 20. By enabling the surgeon to implant the bone
anchor 20
only, the polyaxial bone fixation element 10 maximizes visibility and access
around the
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anchoring site. Once the bone anchor 20 has been secured to the patient's
vertebra 700,
the body 200 and collet 150 may "pop-on" to the bone anchor 20. Accordingly,
the
preferred polyaxial bone fixation element 10 is typically considered a bottom
loading
device, because the bone anchor 20 enters the body 200 through a lower or
bottom end
204. Alternatively, the polyaxial bone fixation element 10 may be provided pre-
assembled using identical components as described herein or may be configured
for top
loading with minor modifications, as would be apparent to one having ordinary
skill in
the art. Further, the collet 150 and body 200 assembly may be popped-off of
the bone
anchor 20 in-situ by arranging the collet 150 relative to the body 200 in a
loading
position, after the fixation element 10 has been arranged in the locked
position, and
removing the assembly from the bone anchor 20, as will be described in greater
detail
below.
[0036] While the polyaxial bone fixation element 10 will be described as and
may
generally be used in the spine (for example, in the lumbar, thoracic or
cervical regions),
those skilled in the art will appreciate that the polyaxial bone fixation
element 10 may be
used for fixation of other parts of the body such as, for example, joints,
long bones or
bones in the hand, face, feet, extremities, cranium, etc.
[0037] As will be described in greater detail below, several polyaxial bone
fixation
elements 10 may be used to secure a longitudinal spinal rod 250 to several
vertebrae 700.
It should be understood that the spinal rod 250 may include, but is not
limited to, a solid
rod, a non-solid rod, a flexible or dynamic rod, etc. It should be understood
that the
polyaxial bone fixation element 10 is not limited in use to any particular
type of spinal
rod 250.
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[0038] Referring to Figs. 1-4B, the bone anchor 20 preferably is in the form
of a bone
screw 22. Alternatively, however, the bone anchor 20 may be, for example, a
hook or
other fastener such as, a clamp, an implant, etc.
[0039] The bone screw 22 preferably includes an enlarged, curvate head portion
24
and an externally threaded shaft portion 26 for engaging the patient's
vertebra 700. The
specific features of the shaft 26 including, for example, thread pitch, shaft
diameter, shaft
shape, etc. are interchangeable, and it would be apparent to one having
ordinary skill in
the art that the bone screw 22 is not limited to any particular type of shaft
26. The bone
screw 22 may or may not be cannulated (See Figs. 9A and 9B). The bone screw 22
may
also include a reduced diameter neck portion 28 between the head portion 24
and the
shaft portion 26, which accommodates the polyaxial nature of the bone fixation
element
10. The bone screw 22 may further be cannulated and fenestrated (not
shown)such that
openings extend outwardly from a central hollow channel in a cannulated screw
to urge
fluid out of the screw during injection or draw fluid into the central hollow
channel from
sides of the screw during extraction of material adjacent the screw.
[0040] Referring to Figs. 3-4B and 8A-9B, the enlarged curvate head portion 24
preferably has a curvate or semi-spherical shape to facilitate rotation with
respect to the
collet 150, as will be described in greater detail below. The head portion 24
also
preferably includes a drive surface 30 for receiving a corresponding tip 501
formed on a
drive tool, such as a screw driver 500 (Figs. 8A and 8B) for rotating the bone
screw 22
into engagement with the patient's vertebra 700. The drive surface 30 may have
any
form now or hereafter known including, but not limited to, an external
hexagon, a star
drive pattern, a Phillips head pattern, a slot for a screw driver, a threading
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correspondingly threaded post, etc. Preferably, as shown, the drive surface 30
is
comprised of a first tool interface or an internal recess 32, but is not so
limited and may
be comprised of an external drive feature that engages a female-type driver
(not shown).
The specific shape of the drive surface 30 or first tool interface 32 may be
chosen to
cooperate with the corresponding drive tool.
[0041] The head portion 24 may also include a second tool interface or a
sleeve
interface 40. The second tool interface 40 may be in any form now or hereafter
known
including, but not limited to, an internal or external thread, an external
hexagon, a star
drive pattern, a Phillips head pattern, a slot for a screw driver, a groove, a
slot, etc.
Preferably, however, the second tool interface 40 includes a plurality of
threads 42 for
threadably engaging a surgical instrument, such as a sleeve 600 (Figs. 8A-9B),
bone
augmentation instrumentation, aspiration instrumentation, reduction tool for
sagittal
reduction or other reduction, coronal rotation tool, soft tissue retraction
tool, kyphosis
and lordosis correction tool, etc. The second tool interface 40 of the
preferred
embodiment permits application of forces to the bone anchor 20 along a
longitudinal axis
of the bone anchor 20, as well as along or at angles to the axis. In the
preferred
embodiment, the sleeve 600 is adaptable for use in combination with at least
the screw
driver 500 and an injection assembly 650. The surgical instrument may
alternatively be
any surgical instrument now or hereafter used in connection with a spinal
fixation
procedure including, but not limited to, a compressor, a distractor, minimally
invasive
instrumentation, etc. By incorporating the second tool interface 40 into the
head portion
24 of the bone anchor 20, the sleeve 600 is able to directly engage the bone
anchor 20
thus eliminating the need for the sleeve 600 to engage the body 200 of the
polyaxial bone
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fixation element 10 and thereby, limiting toggling between the sleeve 600,
screw driver
500 and/or bone anchor 20 in a working configuration, as will be described in
greater
detail below. In addition, the preferred second tool interface 40 permits
application of
forces to the bone anchor 20 through the sleeve 600 or another tool that mates
with the
second tool interface 40 to manipulate the bone anchor 20 and potentially the
bone that
the bone anchor 20 is mounted in.
[0042] Referring to Figs. 3-4B, 8B and 9B, the second tool interface 40 and
the first
tool interface 32 are preferably formed in a head interface cavity 41 exposed
from the top
end of the head 24. Exposing both the second tool interface 40 and the first
tool interface
32 at the top end of the head 24 permits simultaneous engagement of
instruments with the
second tool interface 40 and first tool interface 32 for manipulating the bone
anchor 20.
Both the second tool interface 40 and the first tool interface 32 may be
engaged
individually or simultaneously by an instrument prior to mounting the collet
150 and
body 200 to the head 24 or after the collet 150 and body 200 are mounted to
the head 24
(See Figs. 8B and 9B).
[0043] Referring to Figs. 3 and 5A-5C, the collet 150 preferably includes a
first or
upper end 152 sized and configured to contact at least a portion of the spinal
rod 250
(schematically depicted in Fig. 5A) when the spinal rod 250 is received within
a rod-
receiving channe1208 formed in the body 200 and a second or lower end 154
sized and
configured to contact at least a portion of the head portion 24 of the bone
anchor 20.
More preferably, the upper end 152 of the collet 150 includes a seat 160 sized
and
configured to receive at least a portion of the spinal rod 250 when the spinal
rod 250 is
received within the rod-receiving channe1208 of the body 200. The lower end
154 of the
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collet 150 preferably includes an interior cavity 165 for receiving and
securing the head
portion 24 of the bone anchor 20 so that, as will be generally appreciated by
one of
ordinary skill in the art, the bone anchor 20 can polyaxially rotate through a
range of
angles with respect to the collet 150 and hence with respect to the body 200.
The cavity
165 formed in the collet 150 preferably has a curvate or semi-spherical shape
for
receiving the curvate or semi-spherical head portion 24 of the bone anchor 20
so that the
bone anchor 20 can polyaxially rotate with respect to the collet 150 and hence
with
respect to the body 200. Furthermore, at least a portion of the outer surface
of the collet
150 is comprised of a curvate or spherical, convex surface 151 having a radius
of
curvature r5 for contacting the inner surface 211 of the body 200, preferably
the lower
edge portion 218, as will be described in greater detail below.
[0044] The collet 150 preferably also includes one or more slots 170 (shown as
a
plurality of slots) extending from the lower end 154 thereof so that at least
a portion of
the collet 150 is: (i) radially expandable so that the head portion 24 of the
bone anchor 20
can be inserted through the lower end 154 and into the cavity 165 of the
collet 150 and
(ii) radially compressible to compress or crush-lock against the head portion
24 of the
bone anchor 20, in accordance with the application of radial forces applied
thereto. In the
preferred embodiment, the slots 170 define a plurality of flexible arms 172.
Preferably
each flexible arm 172 includes a root end 173 and a terminal end 174. The
outer surface
of the flexible arms 172 preferably include the curvate or spherical convex
surface 151 of
the collet 150 for defining a line-contact with the inner surface 211 of the
body 200,
preferably the first undercut 218a, as will be described in greater detail
below.
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[0045] The collet 150 may also include one or more grooves 175 formed on the
outer
surface thereof for engaging a projection or dimple 216a formed in the inner
surface 211
of the body 200. As will be described in greater detail below, the collet 150
is permitted
to float within the axial bore 206 formed in the body 200 between a loading
position and
a locked position. That is, the collet 150 is preferably movably positioned
within the
body 200 in an assembled configuration. Interaction between the one or more
grooves
175 and the projection or dimples 216a prevents the collet 150 from moving out
of the
upper end 202 of the body 200 when in the loading position.
[0046] The collet 150 also includes a bore 156 extending from the upper end
152 to
the lower end 154 with an upper opening at the upper end 152 so that, for
example, a
drive tool, such as, for example, a screw driver 500, can be inserted through
the collet
150 and into engagement with the bone anchor 20 so that the bone anchor 20 may
be
rotated into engagement with the patient's vertebra 700. The upper opening at
the upper
end 152 of the collet 150 also permits simultaneous insertion of the screw
driver 500 and
a second tool, such as the sleeve 600, therethrough to engage the head 24
(Figs. 8B and
9B).
[0047] The collet 150 may also include one or more provisional rod-locking
features
so that the spinal rod 250 may be provisionally coupled to the collet 150, and
hence with
respect to the body 200. The provisional rod-locking features may be any
mechanism
now or hereafter developed for such purpose.
[0048] Referring to Fig. 5C, the collet 150 includes one or more inwardly
projecting
ledges 184, 186 disposed on an inner surface 161 of the seat 160 adjacent the
upper end
152 of the collet 150. The ledges 184, 186 may be engaged by a tool (not
shown) to
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apply a force between the collet 150 and the body 200 to move the collet 150
relative to
the body 200. For example, the body 200 may be urged downwardly toward the
bone
anchor 20 relative to the collet 150 when the collet 150, body 200 and bone
anchor 20 are
in the locked position. Such application of a force may move the collet 150
from the
locked position into the loading position, in situ, such that the flexible
arms 172 are able
to flex outwardly within an enlarged diameter portion 220 to permit the head
24 to move
out of the cavity 165. Accordingly, the ledges 184, 186 may be utilized to
disassemble
the collet 150 and body 200 from the bone anchor 20 after the collet 150 and
body 200
have been locked to the head 24.
[0049] Referring to Figs. 6A-6D and 7A-7B, the body 200 may generally be
described as a cylindrical tubular body having a longitudinal axis 201, an
upper end 202
having an upper opening 203, a lower end 204 having a lower opening 205, and
an axial
bore 206 substantially coaxial with the longitudinal axis 201 of the body 200.
The axial
bore 206 extends from the upper opening 203 to the lower opening 205. The
axial bore
206 preferably has a first diameter portion Di proximate the upper end 202.
The body
200 also includes a substantially transverse rod-receiving channe1208 (shown
as a top
loading U-shaped rod-receiving channel) defining a pair of spaced apart arms
209, 210.
The inner surface 211 of the spaced apart arms 209, 210 preferably includes a
plurality of
threads 212 for engaging a locking cap 300. Alternatively, the body 200 and,
in
particular, the spaced apart arms 209, 210 may have nearly any mounting
receiving
structure for engaging the locking cap 300 including, but not limited to,
external threads,
cam-lock, quarter lock, clamps, etc. The outer surface 213 of the spaced apart
arms 209,
210 may each include a recess 214 for engaging one or more surgical
instruments such
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as, for example, rocker forceps, a compressor, a distractor, a sleeve,
minimally invasive
instrumentation, etc.
[0050] Referring to Figs. 5A-6E, the axial bore 206 preferably has the first
diameter
portion Di proximate the upper end 202. The inner surface 211 of the axial
bore 206
preferably also includes a lower end portion 218 proximate the lower end 204
thereof.
The lower end portion 218 defines a second diameter portion D2, which is
comprised of
the smallest diameter portion of the axial bore 206. The second diameter
portion D2 is
preferably defined by a first spherical undercut 218a adjacent the lower end
204 of the
body 200. The first spherical undercut 218a preferably has a second radius of
curvature
r2 that is centered on the longitudinal axis 201 of the body 200. The second
diameter
portion D2 is preferably smaller than the first diameter portion Di of the
axial bore 206
such that the collet 150 may be inserted through the upper end 202 into the
axial bore
206, but generally preventing the collet 150 from being inserted into the
lower end 204 or
from falling out of the lower end 204 once inserted into the axial bore 206.
[0051] The first spherical undercut 218a is preferably defined as a curvate or
spherical concave surface for accommodating the outer curvate or spherical
convex
surface 151 of the collar 150. The first spherical undercut 218a and the
spherical convex
surface 151 preferably have a different radius of curvature such that line
contact is
defined between the surfaces 151, 218 when the collet 150 is positioned
proximate the
lower end 204. The second diameter portion D2 is preferably sized and
configured so that
the enlarged head portion 24 of the bone anchor 20 may be passed through the
lower
opening 205 of the body 200, but is prevented from passing therethrough once
the head
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portion 24 of the bone anchor 20 is received within the interior cavity 165 of
the collar
150.
[0052] The inner surface 211 of the axial bore 206 preferably includes an
enlarged
portion 220 that is located toward the lower end 204 relative to the first
diameter portion
Di. The enlarged portion 220 preferably defines a third diameter D3 comprised
of a
curvate, preferably spherical, radially outwardly recessed portion. In the
enlarged portion
220 of the axial bore 206, the third diameter D3 is larger than the first
diameter Di of the
axial bore 206. In addition, the third diameter D3 is larger than the second
diameter D2.
In the preferred embodiment, the third diameter D3 is defined by a second
spherical
undercut 220a.
[0053] The enlarged portion 220 is preferably located in between the upper end
202
and the lower end portion 218 and accommodates expansion of the flexible arm
172
therein when the head 24 is loaded into the collet 150, as will be described
in greater
detail below. The enlarged portion 220 is preferably in the form of a curvate
or spherical
concave surface having a third radius of curvature r3, which defines the third
diameter D3
at the largest diameter within the axial bore 206. The third radius of
curvature r3 defines
the spherical nature of the second spherical undercut 220a. The enlarged
portion 220 is
sized and configured so that when the collet 150 is placed in general
alignment with the
curvate or spherical concave surface of the enlarged portion 220, the flexible
arms 172 of
the collet 160 are permitted to radially expand within the axial bore 206 of
the body 200
so that the head portion 24 of the bone anchor 20 can be inserted through the
lower
opening 205 formed in the body 200 and into the cavity 165 formed in the
collet 150.
More preferably, the enlarged portion 220 is sized and configured so that the
outer
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curvate or spherical convex surface 151 of the collet 150 does not touch or
contact the
enlarged portion 220 of the body 200 when the head 24 is loaded into the
collet 150.
That is, the enlarged portion 220 formed in the body 200 is preferably sized
and
configured so that a gap remains between the outer curvate or spherical convex
surface
151 of the collet 150 and the enlarged portion 220 of the body 200 even when
the flexible
arms 172 radially expand to accept the head portion 24 of the bone anchor 20.
The
enlarged portion 220 is not limited to constructions comprised of the
preferred curvate or
spherical undercut defined by the third radius of curvature r3 and may be
constructed of
nearly any undercut having nearly any shape that permits expansion of the
collet 150
therein in the loading position to accept the head 24. For example, the
enlarged portion
220 may be defined by a rectangular slot or groove on the inner surface 211
that results in
the third diameter D3 being larger than the first and second diameters Di, D2.
[0054] In the preferred embodiment, the second radius of curvature r2 of the
first
spherical undercut 218a is preferably different than an outer radius of
curvature r5 of the
outer curvate or spherical convex surface 151 of the collet 150 so a line
contact results
between the first spherical undercut 218a and the outer convex surface 151
when the
collet 150 is positioned adjacent the lower end portion 218. That is, by
providing non-
matching radius of curvatures between the first spherical undercut 218a and
the collet
150, only line contact occurs between the first spherical undercut 218a of the
body 200
and the outer curvate or spherical convex surface 151 of the collet 150. The
line contact
between the body 200 and the collet 150 effectively pinches the lower ends of
the flexible
arms 172 onto the lower end of the head 24 below the greatest diameter of the
head 24 to
direct the lower end 154 beneath the largest diameter of the head 24,
effectively locking
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the bone anchor 20 to the collet 150 in the locked position. In addition, the
line contact
between the collet 150 and body 200 permits disengagement of the collet 150
from the
body 200 after the collet 150 and body 200 are engaged in the locked position
or
popping-off of the body 200 and collet 150 from the bone anchor 20, in situ.
[0055] Referring to Figs. 5A-5C, 6F and 6G, the second and third diameters D2,
D3
may be formed by a single internal radius of curvature r4 that undercuts the
body 200 in
the axial bore 206. The single internal radius of curvature r4 preferably
permits
expansion of the collet 150 to accept the head 24, insertion of the collet 150
into the axial
bore 206 from the upper end 202 but not the lower end 204 and line contact
between the
outer curvate or spherical convex surface 151 of the collet and the lower end
portion 218
when the collet 150 is in facing engagement with the lower end portion 218. In
this
configuration, the second diameter portion D2 is smaller than the first
diameter portion
Dl, which is smaller than the third diameter portion D3.
[0056] Referring to Figs. 1-3 and 5A-6C, the body 200 and collet 150 also
preferably
include a collet retention feature 50 so that once the collet 150 has been
inserted into the
bore 206 formed in the body 200 and, if necessary, the collet retention
feature 50 has
been engaged, the collet retention feature 50 inhibits the collet 150 from
passing back
through the upper opening 203 formed in the body 200, but permits some degree
of
vertical translation or floating of the collet 150 with respect to the body
200. That is,
once inserted into the axial bore 206 of the body 200, the collet 150 is sized
and
configured to float or move within the axial bore 206 between a loading
position and a
locking position. The collet retention feature 50 preferably prevents the
collet 150 from
moving out of the upper opening 203 of the body 200. Preferably the collet
retention
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feature 50 permits the flexible arms 172 to align with the enlarged portion
220 in the
loading position when the lower edge of the grooves 175 come into contact with
the
dimples 216a. In addition, the collet 150 is preferably permitted to float
between the
loading position and the locking position prior to locking of the head 24 in
the collet 150.
Specifically, the collet 150 may float between the loading position where the
dimples
216a are in contact with the lower edge of the grooves 175 and the locking
position
wherein the outer curvate or spherical convex surface 151 is in line contact
with the
lower end portion 218. The collet retention feature 50 preferably limits
rotation of the
collet 150 with respect to the body 200, because the dimples 216a slide within
the
grooves 175, so that the seat 160 formed in the collet 150 is aligned with the
rod-
receiving channe1208 formed in the body 200. However, the retention feature 50
is not
limited to limiting rotation of the collet 150 with respect to the body 200
and may be
configured to permit unlimited rotation of the collet 150 relative to the body
200 by
eliminating the grooves 175 from the collet 150 and forming a shelf (not
shown) around
the collet 150 at the bottom end of the grooves 175 such that the dimples 216a
engage the
shelf to limit removal of the collet 150 out of the upper end 202 of the body
200, but
permit unlimited rotation of the collet 150 relative to the body 200 in the
assembled
configuration.
[0057] The collet retention feature 50 may be any feature now or hereafter
known for
such purpose including, but not limited to, for example, an inwardly
protruding shoulder
or detent formed on the collet 150 for engaging corresponding indentations
formed on the
inner surface 211 of the body 200. In the preferred embodiment, the body 200
includes
one or more partial passageways 216 formed therein so that once the collet 150
has been
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received within the axial bore 206 of the body 200, a force may be applied to
the partial
passageways 216 formed in the body 200 deforming the remaining portion of the
partial
passageway 217 into the dimple or projection 216a formed in the inner surface
211 of the
body 200. That is, once the collet 150 has been received within the bore 206
of the body
200, an external force may be applied to the partial passageways 216 formed in
the body
200 transforming the passageways 216 into the projections or dimples 216a that
extend
inwardly from the inner surface 211 of the spaced apart arms 209, 210 and into
the bore
206 formed in the body 200. The dimples or projections 216a are preferably
sized and
configured to interact with the longitudinal groove 175 formed in the outer
surface of the
collet 150 so that the collet 150 is permitted to move with respect to the
body 200 at least
along the longitudinal axis 201, but inhibited from moving back through the
upper
opening 203 formed in the body 200. The collet 150 is also preferably
partially inhibited
from rotational movement with respect to the body 200. Movement of the collet
150 with
respect to the body 200 toward the upper end 202 is preferably inhibited by
the
projections or dimples 216a contacting the bottom and/or lateral surfaces of
the grooves
175. Limiting rotational movement of the collet 150 with respect to the body
200 permits
alignment of the rod-receiving channe1208 and the seat 160 for receiving the
rod 250, as
will be described in greater detail below.
[0058] In use, positioning the collet 150 in general alignment with the
curvate or
spherical concave surface of the enlarged portion 220 in the loading position
preferably
enables the flexible arms 172 of the collet 150 to radially expand within the
axial bore
206 of the body 200 so that the head portion 24 of the bone anchor 20 can be
inserted
through the lower opening 205 formed in the body 200 and into the cavity 165
formed in
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the collet 150. The enlarged portion 220 formed in the body 200 is preferably
sized and
configured so that a gap remains between the outer curvate or spherical convex
surface
151 of the collet 150 and the enlarged portion 220 of the body 200 even when
the flexible
arms 172 radially expand to accept the head portion 24 of the bone anchor 20.
Thereafter, movement of the collet 150 into general alignment and engagement
with the
first spherical undercut 218a of the lower end portion 218 causes a radial
inward force to
be applied to the flexible arms 172, which in turn causes the flexible arms
172 to
compress against the head portion 24 of the bone anchor 20, thereby securing
the position
of the bone anchor 20 with respect to the collet 150 and hence with respect to
the body
200. The lower end portion 218 and the outer curvate or spherical convex
surface 151 of
the collet 150 have non-matching radii of curvature r2, r4, r5 so that only
line contact
occurs between these components.
[0059] The head portion 24 of the bone anchor 20 and interaction of the
dimples 216
with the grooves 175 preferably moves the collet 150 into alignment with the
enlarged
portion 220 as the head portion 24 is inserted through the lower opening 205
and into the
axial bore 206. Moreover, the collet 150 is preferably moved into alignment
and
engagement with the lower edge portion 218 via engagement of the locking cap
300, as
will be described in greater detail below.
[0060] Referring to Figs. 7A and 7B, the locking cap 300 is preferably an
externally
threaded set screw 302 for threadably engaging the threads 212 formed on the
inner
surface 211 of the body 200. The externally threaded set screw 302 generally
provides
flexibility when inserting a spinal rod 250 into the body 200 such that the
spinal rod 250
does not have to be completely reduced or seated within the body 200 prior to
22
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engagement of the cap 300. Incorporation of a threaded set screw 302 also
enables the
set screw 302 to reduce the spinal rod 250 during tightening of the locking
cap with
respect to the body 200. The locking cap 300 may be any locking cap now or
hereafter
developed for such purpose including, but not limited to, an externally
threaded cap, a
quarter-turn or partial-turn locking cap, two-piece set screw, etc.
[0061] As shown, the externally threaded set screw 302 preferably includes a
drive
surface 304 for engaging a corresponding drive tool for securing (e.g.,
threading) the set
screw 302 onto the body 200. The drive surface 304 may take on any form now or
hereafter developed for such purpose, including, but not limited to, an
external hexagon,
a star drive pattern, a Phillips head pattern, a slot for a screw driver, a
threading for a
correspondingly threaded post, etc. The drive surface 304 is preferably
comprised of an
internal recess. The specific shape of the internal recess may be chosen to
cooperate with
the corresponding drive tool. The drive surface 304 may also be configured to
include
the first and second tool interfaces 40, as were described above.
[0062] The externally threaded set screw 302 preferably also includes a saddle
310
operatively coupled thereto. The saddle 310 includes a transverse recess 312
formed
therein for contacting at least a portion of the spinal rod 250. The rod-
contacting surface
of the recess 312 may include a surface finish (not shown) that adds
roughness, such as,
for example, a knurl, bead blasting, grooves, or other textured finish that
increases
surface roughness and enhances rod push through strength.
[0063] The saddle 310 may be coupled to the set screw 302 by any means now or
hereafter developed for such purpose including, but not limited to, adhesion,
mechanically fastening, etc. The set screw 302 preferably includes a bore 306
for
23
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receiving a stem 316 formed on a top surface 311 of the saddle 310. In use,
the saddle
310 is preferably coupled to the set screw 302 but is free to rotate with
respect to the set
screw 302 so that the saddle 310 can self-align with the spinal rod 250 while
the set
screw 302 is being rotated with respect to the body 200.
[0064] In one particularly preferred embodiment, the threads formed on the
externally threaded set screw 302 may incorporate inclined load flanks forming
an angle
with respect to the longitudinal axis 201 of the body 200. The load flanks may
be
converging so that the top surface of the thread and the bottom surface of the
thread
converge. The angle may be about five degrees (5 ), although, as will be
generally
appreciated by one of ordinary skill in the art, the threads may take on any
other form
now or hereafter known for such purpose including, negative load threads,
perpendicular
threads flanks, buttress threads, etc.
[0065] Referring to Figs. 1-7B, the polyaxial bone fixation element 10 is
preferably
provided to the user in a kit including at least (1) bone anchors, (2) locking
caps, and (3)
pre-assembled collet/body subassemblies. The pre-assembled collet/body
subassemblies
are preferably assembled by inserting the collet 150 into the axial bore 206
formed in the
body 200 through the upper opening 203 formed in the body 200. The flexible
arms 172
may flex inwardly as the collet 150 is inserted into the axial bore 206, if
the greatest
diameter of the flexible arms 172 is larger than the first diameter D l. Such
a
configuration generally results in the collet 150 being retained within the
axial bore 206,
even before the collet retention feature 50 is engaged. Once the collet 150 is
positioned
within the axial bore 206 such that the flexible arms 172 are positioned
proximate the
enlarged portion 220, a force is applied to a distal end of the partial
passageway 216
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formed in the body 200 so that a projection or dimple 216a is formed, which
extends into
the bore 206 of the body 200. The projection or dimple 216a is positioned
within the
longitudinal groove 175 formed in the collet 150 so that the collet 150 is
free to vertically
translate or float within the bore 206 with respect to the body 200, but
generally
prevented from passing back up through the upper opening 203 formed in the
body 200
and limited in its ability to rotate relative to the body 200.
[0066] The kit is preferably shipped to the user for use in spinal surgery.
During
surgery, the surgeon preferably identifies a level of the spine where the
surgery will take
place, makes and incision to expose the selected area and implants the bone
anchors 20
into the desired vertebrae 700. The body/collet subassemblies are preferably
popped-on
to the bone anchors 20 by urging the head 24 through the lower opening 205.
Accordingly, the collet/body subassembly may be engaged with the head portion
24 of
the bone anchor 20 in situ. Specifically, as the head 24 moves into the lower
opening
205, the collet 150 is urged toward and into the loading position wherein the
lower end of
the longitudinal grooves 175 contact the dimples 216a. In the loading
position, the outer
curvate or spherical convex surface 151 of the collet 150 is in general
vertical alignment
with the enlarged curvate or spherical concave surface of the enlarged portion
220
formed in the axial bore 206 of the body 200. Alignment of the enlarged
portion 220
with the collet 150 enables the collet 150 to radially or outwardly expand so
that the head
portion 24 of the bone anchor 20 can be received within the cavity 165 formed
in the
collet 150.
[0067] Once the head 24 is positioned in the cavity 165, the head portion 24
of the
bone anchor 20 and the collet 150 are both preferably constrained within the
body 200.
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The bone anchor 20 is preferably able to polyaxially rotate with respect to
the collet 150
and the body 200 in this configuration. The spinal rod 250 is inserted into
the rod-
receiving channe1208 formed in the body 200 and onto the inner surface 161 of
the seat
160. The spinal rod 250 is preferably positioned in facing engagement with the
inner
surface 161 of the seat 160. The set screw 302 is preferably threaded into
engagement
with the threads 212 formed in the body 200 to urge the spinal rod 250 and
collet 150
toward the lower end 204.
[0068] Rotation of the set screw 302 causes the bottom surface of the set
screw 300,
preferably the saddle 310, to contact the top surface of the spinal rod 250,
which in turn
causes the spinal rod 250 and the collet 150 to move downwards with respect to
the body
200. Downward movement of the collet 150 with respect to the body 200 causes
line
contact between the outer curvate or spherical convex surface 151 of the
collet 150 and
the first spherical undercut 218a of the lower end portion 218. Additional
tightening of
the set screw 300 and downward movement of the spinal rod 250 and collet 150
results in
an inwardly directed compressive force to the flexible arms 172, causing the
flexible
arms 172 to pivot inwardly toward the head portion 24 at their terminal ends
174 about
the root ends 173. In a locking position, the flexible arms 172 engage the
head 24 of the
bone anchor 20 securing the position of the bone anchor 20 with respect to the
collet 150
and the body 200. Specifically, the flexible arms 172 of the collet 150
radially compress
against the head portion 24 of the bone anchor 20, which secures the position
of the bone
anchor 20 with respect to the body 200. The line contact between the collet
150 and body
200 proximate the terminal ends 174 direct the radial inward force on the
flexible arms
172 at a location preferably below the largest diameter of the head 24 to
efficiently urge
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the terminal ends 174 beneath the curved outer surface of the head 24 in the
locked
position. In addition, the spinal rod 250 is sandwiched between the set screw
302 and the
collet 150 in the locking position, thereby securing the position of the
spinal rod 250 with
respect to the body 200 and the bone anchor 20.
[0069] Referring to Figs. 3 and 5A-6E, the collet 150 and body 200 may be
popped-
off of the bone anchor 20, in situ, after the bone fixation element 10 is
engaged in the
locked configuration. Specifically, the set screw 300 may be removed from the
body 200
and the spinal rod 250 may be extracted from the rod-receiving channe1208 and
the seat
160. A tool (not shown) engages the ledges 184, 186 and the body 200 and
applies a
force between the collet 150 and the body 200 to move the body 200 downwardly
toward
the body anchor 20. The line contact between the body 200 and the collet 150
is released
and the collet 150 is urged into the loading position. In the loading
position, the flexible
arms 172 flex outwardly within the enlarged portion 220 to permit popping-off
of the
body 200 and collet 150 from the head 24 of the bone anchor 20. The collet 150
and
body 200 may then be popped back onto the bone anchor 20.
[0070] Referring to Figs. 4A, 4B and 8A-9B, the head portion 24 of the bone
anchor
20 preferably includes a drive surface 30 in the form of an internal drive
recess or a first
tool interface 32 and a second tool interface 40. The second tool interface 40
preferably
includes a plurality of threads 42 for threadably engaging the sleeve 600. The
sleeve 600
preferably accommodates a variety of surgical instruments now or hereafter
known
including, but not limited to, the screw driver 500, a fluid delivery device
such as the
injection assembly 650, a compressor, a distractor, minimally invasive
instrumentation,
etc. By incorporating the second tool interface 40 into the head portion 24 of
the bone
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anchor 20, the surgical instruments are able to directly engage the bone
anchor 20, thus
eliminating the need for the surgical instruments and/or the sleeve 600 to
engage the body
200 or collet 150 of the polyaxial bone fixation element 10. In addition, once
the sleeve
600 is engaged with the second tool interface 40, toggling between the screw
driver 500
or another instrument inserted through an internal bore in the sleeve 600 and
the bone
anchor 20 is limited. In the preferred embodiment, the sleeve 600 is utilized
to draw the
screw driver 500 into the first tool interface 32 to limit toggling between
the screw driver
500 and the bone anchor 20. The second tool interface 40 is described herein
as
interacting or engaging the sleeve 600, but is not so limited and may be
configured to
interact or engage with nearly any tool or instrument that preferably is
utilized to
positively engage the head 24 and apply forces to the bone anchor 20 for
manipulating
the bone anchor 20, vertebra 700 mounted to the bone anchor 20 or any other
structure
that is mounted to the bone anchor 20.
[0071] In order to facilitate implantation of the polyaxial bone fixation
elements 10
and to perform, for example, one or more steps in a surgical procedure, it is
advantageous
to limit or remove "toggling" between the polyaxial bone fixation elements 10
and any
surgical instruments that are utilized with the bone fixation elements 10. By
incorporating the second tool interface 40 into the head portion 24 of the
bone anchor 20,
the sleeve 600 and, indirectly, the surgical instrument, for example, the
screw driver 500,
are directly connected to the bone anchor 20. The sleeve 600 includes a
threaded distal
portion 602 for threadably engaging the threads 42 of the second tool
interface 40. In this
manner, the sleeve 600 is directly coupled and secured to the bone anchor 20.
Through
this engagement, toggling is limited between the sleeve 600 and the bone
anchor 20. In
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addition, having a close tolerance between in internal surface of the bore in
the sleeve
600 and the screw driver 500 or other instrument significantly limits toggling
between the
screw driver 500 or other instrument and the bone anchor 20.
[0072] During the surgical procedure, the direct connection of the sleeve 600
with the
bone anchor 20 facilitates protection of the polyaxial locking mechanism (the
collet 150
and the body 200) of the polyaxial bone fixation element 10 and provides a
more stable
distraction, because the forces applied to the sleeve 600 are transferred
directly to the
bone anchor 20 via the second tool interface 40 and into the vertebra 700, as
opposed to
acting through these elements as well as the collet 150 and/or the body 200,
which may
distort some of the forces and cause toggling. In addition, instruments, such
as the screw
driver 500 or the injection assembly 650 may be securely positioned in
engagement with
the bone anchor 20 to drive the bone anchor 20 with the screw driver 500,
inject bone
cement or other fluid into and through the bone anchor 20 or otherwise conduct
a
procedure with the bone anchor 2, without operating through the body 200
and/or collet
150.
[0073] The second tool interface 40 preferably does not obstruct access to the
drive
recess 32, because the second tool interface 40 is preferably located above
and radially
outwardly relative to the drive recess 32. However, the second tool interface
40 is not
limited to being located above and radially outwardly relative to the drive
recess or first
tool interface 32 and may be located below and radially inwardly relative to
the first tool
interface 32, as long as tools or instruments are able to engage the first and
second tool
interfaces 32, 40 simultaneously. Specifically, the second tool interface 40
may be
comprised of a threaded recess in the bone anchor 20 having a smaller diameter
and
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located below the first tool interface 32. Moreover, as best shown in Figs. 9A
and 9B,
the sleeve 600 preferably includes the longitudinal bore so that the screw
driver 500, for
example, may engage the drive recess 32 formed in the head portion 24 of the
bone
anchor 20. In this manner, the sleeve 600 engages the bone anchor 20 via the
second tool
interface 40 while the screw driver 500 simultaneously engages the drive
recess 32.
[0074] Referring to Figs. 8A and 8B, the sleeve 600 is preferably associated
with a
slip sleeve 800 that surrounds the sleeve 600 in a working configuration. The
sleeve 600
and the screw driver 500 are rotatable relative to the slip sleeve 800 such
that a surgeon
may grasp the slip sleeve 800 while turning a handle 502 on a distal end of
the screw
driver 500 to screw the bone anchor 20 into or out of the vertebra 700. When
the surgeon
rotates the handle 502, the sleeve 600, screw driver 500 and bone anchor 20
each rotate
relative to the slip sleeve 800.
[0075] In an anchor driving position (Fig. 8B), external threads 602 on the
sleeve 600
are fully threaded into the threads 42 of the second tool interface 40,
thereby limiting any
toggling between the sleeve 600 and bone anchor 20. The top 501 of the screw
driver
500 is also fully engaged with the drive recess 32 of the bone anchor 20 in
the anchor
driving position. When a surgeon has completed manipulating the bone anchor 20
with
the screw driver 500, the screw driver 500 may be removed from the sleeve 600
and
another instrument may be utilized with the sleeve 600 to gain access to the
bone anchor
20.
[0076] Referring to Figs. 9A and 9B, the injection assembly 650 may be
utilized with
the sleeve 600 to inject bone cement or other flowable materials into a
cannulated bone
anchor 20'. Once the bone anchor 20' is mounted in the vertebra 700 and the
sleeve 600
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is mounted on the bone anchor 20', a cannula 652 of the injection assembly 650
is
inserted into the sleeve 600. The cannula 652 is associated with a syringe 654
at a
proximal end and includes a blunt tip 656 at a distal end. The cannula 652
preferably
includes an engagement mechanism 656 proximate the proximal end to engage a
proximal end of the sleeve 600 to secure the cannula 652 to the sleeve 600. In
addition,
the engagement mechanism 656 preferably urges the blunt tip 656 of the cannula
652 into
engagement with a shelf 32a at the bottom of the first tool interface 32 such
that a flow
channe134 of the cannula 652 is in communication with a flow channe1652a of
the
cannula and a seal is created between the blunt tip 656 and the shelf 32a. In
the preferred
embodiment, the engagement mechanism 656 is comprised of a threaded joint that
may
be tightened to secure the cannula 652 relative to the sleeve 600 and securely
seal the
blunt tip 656 to the shelf 32a, thereby generally preventing leakage of bone
cement or
other flowable fluid into the first tool interface 32. Bone cement is
preferably injected
into the flow channe1652a with the injection assembly 650 and into the
vertebra 700 to
securely mount the bone anchor 20' to the vertebra 700, particularly in
generally weak,
brittle and/or osteoporotic bone. The bone anchor 20' may also be fenestrated
to inject
bone cement toward the sides of the bone anchor 20' or to generally
directionally
dispense the bone cement or other fluid. Further, the bone anchor 20' may be
utilized to
extract material from the vertebra 700 or other bone that the bone anchor 20'
is engaged
with by drawing the material into the flow channe1652a, by, for example,
creating a
vacuum in the flow channe1652a. For example, the bone anchor 20' may be
utilized to
extract bone marrow from the bone. Further, the bone anchor 20' may be
utilized to aid
in bone graft extension, as would be apparent to one having ordinary skill in
the art.
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[0077] It should be understood that while the bone anchor 20 is being
described
herein as preferably including the second tool interface 40, the second tool
interface 40 is
optional. Furthermore, it should be understood that the bone anchor 20
including the
second tool interface 40 may be used in any other type of bone screw
application such as,
for example, long bone fixation, fracture fixation, or in connection with
securing a bone
plate, vertebral spacer, dental implant, etc.
[0078] The polyaxial bone fixation element 10 including the bone anchor 20,
the
collet 150, the body 200 and the locking cap 300 may be made from any
biocompatible
material now or hereafter known including, but not limited to, metals such as,
for
example, titanium, titanium alloys, stainless steel, Nitinol, etc.
[0079] As will be appreciated by those skilled in the art, any or all of the
components
described herein may be provided in sets or kits so that the surgeon may
select various
combinations of components to perform a fixation procedure and create a
fixation system
which is configured specifically for the particular needs/anatomy of a
patient. It should
be noted that one or more of each component may be provided in a kit or set.
In some
kits or sets, the same device may be provided in different shapes and/or
sizes.
[0080] While the foregoing description and drawings represent the preferred
embodiment of the present invention, it will be understood that various
additions,
modifications, combinations and/or substitutions may be made therein without
departing
from the spirit and scope of the present invention as defined in the
accompanying claims.
In particular, it will be clear to those skilled in the art that the present
invention may be
embodied in other specific forms, structures, arrangements, proportions, and
with other
elements, materials, and components, without departing from the spirit or
essential
32
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WO 2009/015100 PCT/US2008/070670
characteristics thereof. One skilled in the art will appreciate that the
invention may be
used with many modifications of structure, arrangement, proportions,
materials, and
components and otherwise, used in the practice of the invention, which are
particularly
adapted to specific environments and operative requirements without departing
from the
principles of the present invention. In addition, features described herein
may be used
singularly or in combination with other features. The presently disclosed
embodiments
are, therefore, to be considered in all respects as illustrative and not
restrictive, the scope
of the invention being indicated by the appended claims and not limited to the
foregoing
description.
[0081] It will be appreciated by those skilled in the art that changes could
be made to
the embodiments described above without departing from the broad inventive
concept
thereof. It is understood, therefore, that this invention is not limited to
the particular
embodiments disclosed, but it is intended to cover modifications within the
spirit and
scope of the present invention, as defined by the appended claims.
33
