U.S. patent number RE42,932 [Application Number 11/303,091] was granted by the patent office on 2011-11-15 for pedicle screw assembly and methods therefor.
This patent grant is currently assigned to Stryker France. Invention is credited to Yves Crozet, William J. Kelly, Greg Martin.
United States Patent |
RE42,932 |
Martin , et al. |
November 15, 2011 |
**Please see images for:
( Certificate of Correction ) ** |
Pedicle screw assembly and methods therefor
Abstract
A method for stabilizing a spine includes providing a coupling
element having upper and lower ends, a rod receiving opening
adapted to receive an elongated stabilizing rod, a bore extending
through the lower end and a conical-shaped seat surrounding the
bore adjacent the lower end; providing a fastener having upper and
lower ends, a head having a radial surface, and at least one
anchoring element between the lower end of the fastener and the
head; assembling the fastener with the coupling element so that the
lower end of the fastener passes through the bore of the coupling
element and the radial surface of the head engages the
conical-shaped seat. The method also includes anchoring the
fastener to bone; moving the coupling element relative to the
fastener for capturing the elongated stabilizing rod in the rod
receiving opening; and urging the captured stabilizing rod toward
the head of the fastener so that the rod contacts the head and
forces the radial surface of the head against the conical-shaped
seat of the coupling element for locking the coupling element from
further movement relative to the fastener.
Inventors: |
Martin; Greg (Encinitas,
CA), Crozet; Yves (Ramsey, NJ), Kelly; William J.
(Montville, NJ) |
Assignee: |
Stryker France
(FR)
|
Family
ID: |
25040890 |
Appl.
No.: |
11/303,091 |
Filed: |
December 15, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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09755846 |
Jan 5, 2001 |
6488681 |
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Reissue of: |
10197092 |
Jul 17, 2002 |
6858030 |
Feb 22, 2005 |
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Current U.S.
Class: |
606/278; 606/86A;
606/279 |
Current CPC
Class: |
A61B
17/7037 (20130101); G06Q 10/107 (20130101); A61B
2017/564 (20130101); A61B 17/7032 (20130101); A61B
17/7082 (20130101) |
Current International
Class: |
A61B
17/58 (20060101) |
Field of
Search: |
;606/61,60,70,71,72,73,86A,278,279 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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195 42 116 |
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Nov 1995 |
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DE |
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19542116 |
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Nov 1995 |
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DE |
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19542116 |
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May 2007 |
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DE |
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96/08206 |
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Mar 1996 |
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WO |
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00/72769 |
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Dec 2000 |
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WO |
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Other References
European Search Report, EP 07 12 3729. cited by other.
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Primary Examiner: Philogene; Pedro
Attorney, Agent or Firm: Lerner, David, Littenberg, Krumholz
& Mentlik, LLP
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation of application Ser. No.
09/755,846 filed Jan. 5, 2001, now U.S. Pat No 6,488,681.
Claims
What is claimed is:
1. A method for stabilizing a spine comprising: providing a
coupling element having upper and lower ends, a rod receiving
opening adapted to receive an elongated stabilizing rod, a bore
extending through the lower end and a conical-shaped seat
surrounding said bore adjacent the lower end.[.; providing.].
.Iadd.and .Iaddend.a fastener having upper and lower ends, a head
having a radial surface, and at least one anchoring element between
the lower end of said fastener and the head.[.;
assembling.]..Iadd., wherein .Iaddend.said fastener .Iadd.is
assembled .Iaddend.with said coupling element so that the lower end
of said fastener passes through the bore of said coupling element
and the radial surface of said head engages the conical-shaped
seat; anchoring said fastener to bone; moving said coupling element
relative to said fastener for capturing said elongated stabilizing
rod in the rod receiving opening; urging said captured stabilizing
rod toward the head of said fastener so that said rod contacts said
head and forces the radial surface of said head against the
conical-shaped seat of said coupling element for locking said
coupling element from further movement relative to said
fastener.
2. The method as claimed in claim 1, wherein the urging step
comprises: providing a locking element associated with said
coupling element; using said locking element in cooperation with
said coupling element to apply a force upon said stabilizing rod
positioned in said rod receiving opening.
3. The method as claimed in claim 2, wherein said coupling element
has threads extending from the upper end thereof toward the lower
end thereof and said locking element has threads adapted for mating
with the threads of said coupling element during the urging
step.
4. The method.[.,.]. as claimed in claim 3, wherein said coupling
element has internal threads formed on an interior surface thereof
and said locking element has external threads.
5. The method as claimed in claim 3, wherein said coupling element
has external threads formed on an external surface thereof and said
locking element has internal threads.
6. The method as claimed in claim 1, wherein said coupling element
and said fastener are made from a material selected from the group
consisting of titanium and stainless steel.
7. The method as claimed in claim 1, wherein said fastener is a
screw fastener and the at least one anchoring element comprises
screw threads extending between the upper and lower ends
thereof.
8. The method as claimed in claim 1, wherein the at least one
anchoring element comprises a hook at the lower end of said
fastener.
9. A method of stabilizing a spinal column comprising: providing a
fastener including a bone anchoring element and a head having a
first radial surface with a first radius at an underside thereof
and a second radial surface with a second radius at a top side
thereof, wherein the first radius at the underside is greater than
the second radius at the top side.[.; providing.]. .Iadd.and
.Iaddend.a coupling element having upper and lower ends, a rod
receiving opening adapted to receive an elongated rod, a bore
extending through the lower end of said coupling element, and a
conical-shaped seat.[.; assembling said fastener with said coupling
element so that.]..Iadd., wherein .Iaddend.said fastener
.[.passes.]. .Iadd.is sized to pass .Iaddend.through said bore with
the first radial surface at the underside of said head opposing the
conical-shaped seat; anchoring said fastener to bone; after the
anchoring step, moving said coupling element for capturing said
elongated rod in the rod receiving opening; urging said elongated
rod against said head of said fastener for forcing the first radial
surface of said head against the conical-shaped seat of said
coupling element for locking said coupling element from further
movement relative to said fastener.
10. The method as claimed in claim 9, wherein said coupling element
includes an exterior surface having one or more notches formed
therein, and wherein the moving step includes engaging said notches
with a gripping tool.
11. The method as claimed in claim 9, wherein the urging step
includes using a locking element in association with said coupling
element for forcing said stabilizing rod against the second radial
surface of said head which in turn forces the first radial surface
of said head against.[.,.]. the conical-shaped seat of said
coupling element for preventing said coupling element and said
fastener from pivoting and rotating relative to one another.
12. The method as claimed in claim 9, wherein said fastener
includes screw threads extending between upper and lower ends
thereof.
13. The method as claimed in claim 9, wherein said fastener
includes a hook.
14. A method of stabilizing a vertebral column comprising:
providing a coupling element having upper and lower ends, a rod
receiving opening adapted for receiving an elongated stabilizing
rod, an exterior surface, an interior surface defining a central
bore extending through the lower end thereof, and a conical-shaped
seat adjacent the lower end.[.; providing.]..Iadd., and .Iaddend.a
fastener having upper and lower ends, at least one anchoring
element between the upper and lower ends, and a head at the upper
end having a radial surface .[.and assembling said fastener with
said coupling element so that the radial surface of said head
engages the conical-shaped seat and the.]. .Iadd.to engage to
conical-shaped seat and the .Iaddend.lower end of said fastener
.[.passes.]. .Iadd.is sized to pass .Iaddend.through said central
bore; anchoring the lower end of said fastener to vertebral bone;
after the anchoring step, moving said coupling element to capture
said stabilizing rod in the rod receiving opening; utilizing a
locking element in association with said coupling element to urge
said stabilizing rod into direct engagement with the head of said
fastener for forcing the radial surface of said head against the
conical-shaped seat of said coupling element for preventing further
movement of said coupling element and said fastener relative to one
another.
15. The method as claimed in claim 14, wherein said fastener is a
screw fastener and said anchoring element comprises screw
threads.
16. The method as claimed in claim 14, wherein said coupling
element and said fastener are made of materials selected from the
group consisting of titanium and stainless steel.
17. The method as claimed in claim 15, wherein said coupling
element has threads extending from the upper end toward the lower
end thereof and said locking element has threads adapted for
meshing with the threads of said coupling element.
18. The method as claimed in claim 14, wherein the head of said
fastener includes at least one groove extending from the top
surface toward the underside thereof, said at least one groove
being adapted for receiving a driver for inserting said fastener
into bone.
19. The method as claimed in claim 18, wherein said at least one
groove includes a plurality of grooves spaced apart from one
another.
20. The method as claimed in claim 19, wherein the anchoring step
comprises: providing a driver having a shaft with a lower end and a
plurality of prongs extending from the lower end; inserting the
prongs into the grooves of said head; rotating said driver for
driving said fastener into the vertebral bone.
.Iadd.21. A stabilizing assembly comprising: a fastener having an
upper end and a lower end, a head at the upper end, and at least
one anchoring element between the upper and lower ends thereof;
said head including a center, an underside including a first radial
surface and a top side including a second radial surface, wherein
said first radial surface defines a first radius from the center of
said head and said second radial surface defines a second radius
from the center of said head; and a coupling element having an
upper end and a lower end, said coupling element including a rod
receiving opening adapted to receive a stabilizing rod, a bore
extending through the lower end of said coupling element for
receiving said fastener, a seat adjacent the lower end of said
coupling element, and an annular lip having a diameter less than
twice the first radius of said head between the upper end and the
seat of said coupling element, wherein the annular lip prevents the
fastener from passing into the upper end, and wherein the
stabilizing rod contacts the top side of said head so that the
stabilizing rod forces the underside of said head against the seat
of said coupling element..Iaddend.
.Iadd.22. The stabilizing assembly as claimed in claim 21, wherein
the first radius of the first radial surface of said head is
greater than the second radius of the second radial
surface..Iaddend.
.Iadd.23. The stabilizing assembly as claimed in claim 21, wherein
the seat of said coupling element includes inwardly tapering
conical-shaped sidewalls..Iaddend.
.Iadd.24. The stabilizing assembly as claimed in claim 21, wherein
said coupling element includes one or more cuts between the
rod-receiving opening and the exterior surface
thereof..Iaddend.
.Iadd.25. The stabilizing assembly as claimed in claim 24, wherein
one or more notches are formed on the exterior surface of said
coupling element..Iaddend.
.Iadd.26. The stabilizing assembly as claimed in claim 25, wherein
the anchoring element of said fastener comprises screw threads and
said fastener includes a neck having a reduced diameter between the
head and the screw threads..Iaddend.
.Iadd.27. A stabilizing assembly comprising: a fastener having an
upper end and a lower end, a head at the upper end, and at least
one anchoring element between the upper and lower ends thereof,
said head including a center and an underside defining a first
radius from the center of said head; a coupling element having an
upper end and a lower end, said coupling element including a rod
receiving opening adapted to receive a stabilizing rod, a bore
extending through the lower end of said coupling element for
receiving said fastener, a seat adjacent the lower end of said
coupling element, and an annular lip located between the upper end
of said coupling element and the seat of said coupling element,
said annular lip having a diameter less than twice the first radius
of said head, wherein the annular lip prevents the fastener from
passing into the upper end, and wherein said coupling element
includes one or more cuts between the rod-receiving opening and the
exterior surface thereof for minimizing the width of said coupling
element..Iaddend.
.Iadd.28. The stabilizing assembly as claimed in claim 27, wherein
the underside of said head includes a first radial surface and a
top side of said head includes a second radial surface, wherein
said first radial surface defines the first radius from the center
of said head and the second radial surface defines a second radius
from the center of said head..Iaddend.
.Iadd.29. The stabilizing assembly as claimed in claim 28, wherein
the first radius of the first radial surface of said head is
greater than the second radius of the second radial surface of said
head..Iaddend.
.Iadd.30. The stabilizing assembly as claimed in claim 27, wherein
the stabilizing rod contacts a top side of said head so that the
stabilizing rod forces an underside of said head against the seat
of said coupling element..Iaddend.
.Iadd.31. A stabilizing assembly comprising: a fastener having an
upper end and a lower end, a head at the upper end, and at least
one anchoring element between the upper and lower ends thereof;
said head including a center, an underside including a first radial
surface, wherein said first radial surface defines a first radius
from the center of said head; and a coupling element having an
upper end and a lower end, said coupling element including a rod
receiving opening adapted to receive a stabilizing rod, a bore
extending through the lower end of said coupling element for
receiving said fastener, a conical-shaped seat adjacent the lower
end of said coupling element, and one or more cuts between the
rod-receiving opening and the exterior surface thereof for
minimizing the width of said coupling element, and wherein the
stabilizing rod contacts the top side of said head so that the
stabilizing rod forces the underside of said head against the seat
of said coupling element..Iaddend.
.Iadd.32. A method for stabilizing a spine comprising: providing a
coupling element having upper and lower ends, a rod receiving
opening adapted to receive an elongated stabilizing rod, a bore
extending through the lower end and a conical-shaped seat
surrounding said bore adjacent the lower end, and an annular lip,
and a fastener having upper and lower ends, a head having a radial
surface, and at least one anchoring element between the lower end
of said fastener and the head, the lower end of said fastener is
sized to pass through the bore of said coupling element and the
radial surface of said head engages the conical-shaped seat,
wherein said annular lip having a diameter less than twice the
first radius of said head between the upper end and the seat of
said coupling element, wherein the annular lip prevents the
fastener from passing into the upper end; anchoring said fastener
to bone; moving said coupling element relative to said fastener for
capturing said elongated stabilizing rod in the rod receiving
opening; urging said captured stabilizing rod toward the head of
said fastener so that said rod contacts said head and forces the
radial surface of said head against the conical-shaped seat of said
coupling element for locking said coupling element from further
movement relative to said fastener..Iaddend.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to spinal fixation devices
and more specifically relates to a pedicle screw assembly having a
low profile and having an improved screwhead/coupling element
interface for locking the assembly.
The spinal column is a highly complex system of bones and
connective tissues that provides support for the body and protects
the delicate spinal cord and nerves. The spinal column includes a
series of vertebrae stacked one atop the other, each vertebral body
including an inner or central portion of relatively weak cancellous
bone and an outer portion of relatively strong cortical bone.
Situated between each vertebral body is an intervertebral disc that
cushions and dampens compressive forces experienced by the spinal
column. A vertebral canal containing the spinal cord and nerves is
located behind the vertebral bodies.
There are many types of spinal column disorders including scoliosis
(abnormal lateral curvature of the spine), kyphosis (abnormal
forward curvature of the spine, usually in the thoracic spine),
excess lordosis (abnormal backward curvature of the spine, usually
in the lumbar spine), spondylolisthesis (forward displacement of
one vertebra over another, usually in a lumbar or cervical spine)
and other disorders caused by abnormalities, disease or trauma,
such as ruptured or slipped discs, degenerative disc disease,
fractured vertebra, and the like. Patients that suffer from such
conditions usually experience extreme and debilitating pain, as
well as diminished nerve function.
The present invention generally involves a technique commonly
referred to as spinal fixation whereby surgical implants are used
for fusing together and/or mechanically immobilizing vertebrae of
the spine. Spinal fixation may also be used to alter the alignment
of adjacent vertebrae relative to one another so as to change the
overall alignment of the spine. Such techniques have been used
effectively to treat the above-described conditions and, in most
cases, to relieve pain suffered by the patient. However, as will be
set forth in more detail below, there are some disadvantages
associated with current fixation devices.
One spinal fixation technique involves immobilizing the spine by
using orthopedic rods, commonly referred to as spine rods, that run
generally parallel to the spine. This may be accomplished by
exposing the spine posteriorly and fastening bone screws to the
pedicles of the appropriate vertebrae. The pedicle screws are
generally placed two per vertebra and serve as anchor points for
the spine rods. Clamping elements adapted for receiving a spine rod
therethrough are then used to join the spine rods to the screws.
The aligning influence of the rods forces the spine to conform to a
more desirable shape. In certain instances, the spine rods may be
bent to achieve the desired curvature of the spinal column.
U.S. Pat. No. 5,129,388 to Vignaud et al. discloses a spinal
fixation device including a pedicle screw having a U-shaped head
rigidly connected to an upper end of the screw. The U-shaped head
includes two arms forming a U-shaped channel for receiving a spine
rod therein. The U-shaped head is internally threaded so that a set
screw having external threads may be screwed therein. After the
pedicle screw has been inserted into bone and a spine rod
positioned in the U-shaped channel, the set screw is threaded into
the internal threads of the U-shaped channel for securing the spine
rod in the channel and blocking relative movement between the spine
rod and the pedicle screw. The fixation device also includes a cap
covering an upper portion of the U-shaped head to prevent the arms
from spreading upon threading the set screw into the internal
threads of U-shaped head.
Surgeons have encountered considerable difficulty when attempting
to insert spinal fixation devices such as those disclosed in the
above-mentioned '388 patent. This is because the U-shaped heads of
adjacent screws are often out of alignment with one another due to
curvature in spines and the different orientations of the pedicles
receiving the screws. As a result, spine rods must often be bent in
multiple planes in order to pass the rods through adjacent U-shaped
channels. These problems weaken the strength of the assembly and
result in significantly longer operations, thereby increasing the
likelihood of complications associated with surgery.
In response to the above-noted problems, U.S. Pat. No. 5,733,286 to
Errico et al., U.S. Pat. No. 5,672,176 to Biedermann et al., and
U.S. Pat. No. 5,476,464 to Metz-Stavenhagen disclose polyaxial
spinal fixation devices wherein the anchoring element fixed to the
bone has a spherically-shaped head. The fixation devices in the
above-identified patents also have orthopedic rod capturing
assemblies for securing orthopedic rods in the capturing assemblies
and connecting the rods with the anchoring elements. The
spherically-shaped heads of the anchoring elements permit movement
of the anchoring elements relative to the orthopedic rod capturing
assemblies. However, the above-mentioned patents do not solve all
of the deficiencies of fixation devices such as those described in
the Vignaud '388 patent because the respective spinal fixation
devices may shift following insertion. This is due primarily to the
fact that there is insufficient surface area contact between the
spherically-shaped heads of the anchoring elements and the rod
capturing assemblies. In addition, the devices are complex, include
many parts, and are difficult to manufacture.
In certain preferred embodiments of commonly assigned U.S. patent
application Ser. No. 09/414,272, filed Oct. 7, 1999, the disclosure
of which is hereby incorporated by reference as if fully set forth
herein, a pedicle screw assembly includes a fastener having a tip
end for insertion into bone and an expandable head at the opposite
end of the fastener. The expandable head has an outer surface
including a convex portion, a recess having an inner surface and
defining an inner dimension, and at least one slot extending
between the inner and outer surfaces thereof for allowing expansion
of the head. The assembly also has an insert which can be
positioned at least partially in the recess, the insert having an
outer surface and defining an outer dimension that is greater than
the inner dimension of the recess. The assembly includes a coupling
element having a rod receiving opening, a bore for receiving the
fastener, and a seat for receiving the head of the fastener, the
seat including a concave portion for receiving the convex underside
of the head and allowing the fastener to pivot and rotate relative
to the coupling element before being locked therein. After an
orthopedic rod has been positioned within the coupling element, a
locking element associated with the coupling element locks the
orthopedic rod in the rod-receiving opening. The locking element is
adapted to be forced against an orthopedic rod arranged in the rod
receiving opening, to in turn force the insert into the recess of
the expandable head so that the outer dimension of the insert bears
against the inner dimension of the head, thereby expanding the
outer surface of the head against the concave seat of the coupling
element for locking the fastener from further pivotal movement
relative to the coupling element. In other preferred embodiments,
the head is expandable by virtue of the material of which it is
made, such as carbon fiber.
In spite of the above-mentioned devices, there remains room for
improvement of prior art spinal fixation devices in the manner of
locking the screwhead, the complexity of use, difficulty in
properly positioning the orthopedic rod and the rod-capturing
assemblies, the required manipulation of the many parts associated
with some complex devices and post-operative movement of the
rod-capturing assemblies relative to the bone anchoring elements
due to the weak interfaces between the two.
SUMMARY OF THE INVENTION
In accordance with certain preferred embodiments of the present
invention, a stabilizing assembly used for stabilizing a spinal
column includes a fastener having an upper end and a head at the
upper end, and at least one anchoring element between the upper and
lower ends thereof. The head of the fastener preferably includes a
center, an underside including a first radial surface and a top
side including a second radial surface, the first radial surface
defining a first radius from the center of the head and the second
radial surface defining a second radius from the center of the
head, the first radius being greater than the second radius.
Although the present invention is not limited by any particular
theory of operation, it is believed that utilizing a fastener head
having a dual-radius outer surface will provide a stabilizing
assembly having a lower overall silhouette, thereby enhancing the
compactness of the assembly. The lower silhouette results, in part,
from the lower height of the second radial surface at the top of
the head.
The pedicle screw assembly also preferably includes a coupling
element that couples together the fastener and a stabilizing rod
inserted into the coupling element. The coupling element desirably
includes an upper end and a lower end, a rod receiving opening
adapted to receive a stabilizing rod, a bore extending through the
lower end of the coupling element for receiving the fastener, and a
seat adjacent the lower end of the coupling element adapted to
engage the first radial surface of the head when the fastener is
positioned in the bore. In certain preferred embodiments the seat
is a conical-shaped seat having side walls that taper inwardly
toward the lower end of the coupling element. In certain preferred
embodiments, the rod-receiving opening begins at the upper end of
the coupling element and extends toward the lower end of the
coupling element, the lower end of the rod-receiving opening
preferably terminating at U-shaped channels on opposite sides of
the coupling element.
The stabilizing assembly also preferably includes a locking element
associated with the coupling element, the locking element being
adapted to apply a force upon a stabilizing rod positioned in the
rod receiving opening, whereby the stabilizing rod in turn applies
a force upon the second radial surface of the head for forcing the
first radial surface of the head against the conical-shaped seat
for preventing further pivotal and rotational movement of the
fastener and the coupling element relative to one another. The
locking element may include a set screw having external threads for
threadably engaging internal threads of the coupling element.
However, in other embodiments, the coupling element preferably
includes external threads formed on an exterior surface of the
coupling element and the locking element includes a nut having
internal threads threadable onto the external threads of the
coupling element.
In certain preferred embodiments, the fastener is a screw fastener
having a longitudinal axis extending between the upper and lower
ends thereof, and includes a screwhead having at least one groove
extending from the top surface of the screwhead toward the
underside of the screwhead, the at least one groove being adapted
to receive a driver for inserting the fastener into bone. The at
least one groove preferably extends in a direction substantially
parallel to the longitudinal axis of the fastener. Moreover, the at
least one groove desirably includes a plurality of grooves that are
equally spaced apart from one another about the head. The fastener
also preferably includes a neck portion having a reduced diameter
for facilitating pivotal movement of the coupling element and the
fastener relative to one another. The neck of the fastener may also
have a concave surface so as to broaden the pivotal range of the
fastener relative to the coupling element.
The fastener may be inserted into bone using a driver including a
shaft having a lower end and a plurality of prongs extending from
the lower end of the shaft. The prongs are preferably adapted for
being inserted into the grooves of the head. The shaft of the
driver may include external threads that are adapted for engaging
the internal threads of the coupling element.
In operation, the coupling element is anchored in place by
anchoring the screw fastener into bone, such as vertebral bone. A
pilot hole may be formed in the bone before the fastener is
anchored to the bone. After the coupling element is anchored in
place, a gap preferably remains between the lower end of the
coupling element and the bone so that the coupling element is free
to pivot and rotate relative to the fastener and bone. This
pivoting and rotary action facilitates the positioning of an
orthopedic stabilizing rod within the rod-receiving opening of the
coupling element.
After a stabilizing rod has been positioned in the rod-receiving
opening of the coupling element, the locking element, i.e., an
externally threaded set screw, is threaded into the internal
threads of the coupling element. As the set screw is tightened, the
underside of the set screw abuts the orthopedic rod to apply a
downward force through the rod onto the second radial surface of
the head. As used herein, the term "downward force" means a force
directed toward the lower end of the coupling element. The downward
force applied to the second radial surface of the head forces the
first radial surface of the head into the conical-shaped seat of
the coupling element. Engagement of the first radial surface of the
screwhead with the conical-shaped seat locks the coupling element
relative to the screwhead, thereby preventing further pivotal and
rotary movement of the coupling element. As a result, the
likelihood of post-operative shifting and/or movement of a spine
rod or coupling element relative to one or more of the bone
fasteners is significantly reduced. Thus, the present invention
provides for a more reliable spinal fixation device and overcomes
the post-operative shifting problems seen in prior art devices.
Moreover, the pedicle screw assembly of the present invention has
fewer parts. As a result, implantation operations are greatly
simplified and the possibility of a component being dropped inside
a patient's body greatly reduced.
In certain preferred embodiments, the fastener may have one or more
holes therein for receiving bone graft material as disclosed in
U.S. Pat. No. 4,484,570 to Sutter. Instead of using a screw for
securing the screw to bone, in other preferred embodiments the
fastener may include a hook-shaped anchoring element as disclosed
in the above-mentioned U.S. Pat. No. 5,476,464 to Metz-Stavenhagen.
The fastener may also be a structure having barbs on an outer
surface thereof, whereby the fastener is forced into bone and the
barbs prevent the fastener from being withdrawn from the bone.
In certain preferred embodiments, the top surface of the fastener
head may include a socket adapted to receive a driver, such as a
screwdriver or a hexagonal wrench. In this embodiment, the fastener
is attached to bone by inserting the driver into the socket, and
then turning the driver to rotate the fastener in either a
clockwise or counterclockwise direction.
The coupling element may also have one or more impressions or
grooves formed therein for receiving a controlling device, such as
a persuader instrument for seating the rod in the coupling element.
In some embodiments, the impressions or grooves generally extend in
a direction substantially perpendicular to the longitudinal axis of
the coupling element. The groove or blind holes may be formed in
the exterior surface of the coupling element.
The interior surface of the coupling element at the lower end
thereof preferably defines the seat adapted for engaging the first
radial surface at the underside of the head and for allowing the
head to pivot relative to the coupling element before being locked
in place. The seat is preferably provided adjacent the lower end of
the coupling element. The seat may define a conical shape or a
convex shape. In particular preferred embodiments, the seat is a
conical-shaped seat. The walls of the conical-shaped seat
preferably taper inwardly toward one another so that the diameter
of the walls at the lower end thereof is less than the outer
diameter of the head.
During assembly of the above-mentioned stabilizing device, a
portion of the fastener is passed through the bore of the coupling
element until the underside of head is positioned adjacent the
conical-shaped seat of the coupling element. During a spinal
fixation operation, after the fastener has been anchored in bone,
the coupling element remains free to pivot relative to the
fastener. Moreover, a gap preferably exists between the bottom of
the coupling element and bone, the presence of the gap facilitating
pivoting movement of the coupling element. The neck portion of the
fastener, preferably having a concave surface with a diameter less
than the diameter of the threaded portion of the fastener, enables
the coupling element to pivot through a broader range of angles
relative to the fastener. Thus, a spine rod may be more easily
positioned within the rod receiving opening of the coupling
element. After the rod has been positioned within the rod receiving
opening, a locking element is threaded into the threads of the
coupling element. As the locking element tightens down upon the
rod, the rod, in turn, exerts a downward force onto the second
radial surface of the head. The downward force applied to the
second radial surface of the head forces the first radial surface
of the head into the conical-shaped seat of the coupling element.
Engagement of the first radial surface of the head with the
conical-shaped seat locks the coupling element relative to the
head, thereby preventing further pivotal and rotary movement of the
coupling element. As a result, the likelihood of post-operative
shifting and/or moving of the pedicle screw assembly is greatly
reduced, thereby minimizing the occurrence of post-operative
complications for spinal implant patients.
The present invention also preferably includes a tool for securing
or anchoring the fastener in bone. The tool is preferably a driver
having a rotatable shaft and one or more prongs extending from an
end of the shaft for engaging grooves in the head. In preferred
embodiments, the driver has one prong for each groove in the head
of the fastener. The driver may also have external threads at a
lower end of the shaft. The external threads are preferably adapted
for engaging the internal threads of the coupling element when a
fastener is being anchored to the bone. The engagement of the
external threads of the driver and the internal threads of the
coupling element generally stabilizes the assembly when the
fastener is secured to bone. Specifically, the engagement of the
threads prevents the coupling element from moving relative to the
fastener when driving the fastener into bone, thereby simplifying
installation of the fasteners.
These and other objects, features and advantages of the present
invention will be more readily apparent from the detailed
description of preferred embodiments set forth below, taken in
conjunction with the accompanying drawings.
In other preferred embodiments, a coupling element for a
stabilizing assembly desirably includes an upper end and a lower
end, a rod receiving opening adapted to receive a stabilizing rod,
a bore extending through the lower end of the coupling element for
receiving a fastener having a head with a first radial surface of a
first diameter, and a seat adjacent the lower end of the coupling
element adapted to engage an underside of the head of the fastener.
The coupling element preferably includes threads extending from the
upper end toward the lower end of the coupling element, and an
annular lip between the threads and the seat of the coupling
element, whereby the annular lip has a second diameter that is less
than the first diameter of the first radial surface of the
head.
In still other preferred embodiments, a coupling element for a
stabilizing assembly includes an upper end and a lower end remote
therefrom, and a rod receiving opening adapted to receive a
stabilizing rod. The coupling element preferably has an exterior
surface and an interior surface defining a central bore extending
through the lower end of the coupling element. A seat adjacent the
lower end of the coupling element is desirably adapted to engage an
underside of a head of the fastener, whereby the coupling element
includes one or more cuts between the rod-receiving opening and the
exterior surface thereof for minimizing the width of the coupling
element. Although the present invention is not limited by any
particular theory of operation, it is believed that providing cuts
at the edge of the rod receiving opening reduces the width of the
coupling element so that more coupling elements may be fit onto a
given length of a stabilizing rod. The cuts also minimize the sharp
edges on the coupling element, thereby reducing the chance that the
coupling element will irritate a patient's tissue and/or cutting a
surgeon's glove.
These and other objects, features and advantages of the present
invention will be more readily apparent from the detailed
description of preferred embodiments set forth below, taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a front elevation view of a fastener for a stabilizing
assembly, in accordance with certain preferred embodiments of the
present invention.
FIG. 2 shows a plan view of the fastener shown in FIG. 1.
FIG. 3A shows a fragmentary, cross-sectional view of the fastener
shown in FIG. 2 taken along line IIIA--IIIA of FIG. 2.
FIG. 3B shows an expanded view of a portion of the fastener shown
in FIG. 3A.
FIG. 4 shows a perspective view of a coupling element for a
stabilizing assembly, in accordance with certain preferred
embodiments of the present invention.
FIG. 5 shows a fragmentary, cross-sectional view of the coupling
element shown in FIG. 4.
FIGS. 6A and 6B show a method of assembling the fastener of FIGS.
1-3B with the coupling element of FIGS. 4 5, in accordance with
certain preferred embodiments of the present invention.
FIG. 7 shows a perspective view of the assembly shown in FIG.
6B.
FIG. 8 shows a perspective view of a driver for engaging the
assembly of FIG. 7 for driving the fastener into bone, in
accordance with certain preferred embodiments of the present
invention.
FIG. 9A shows the assembly of FIG. 7 after the fastener has been
anchored in bone.
FIG. 9B shows an expanded view of a portion of FIG. 9A with the
coupling element being pivoted to receive a stabilizing rod.
FIG. 9C shows a stabilizing rod secured to the coupling element by
a set screw, in accordance with certain preferred embodiments of
the present invention.
FIG. 10 shows a cross-sectional view of a coupling element, in
accordance with further preferred embodiments of the present
invention.
FIG. 11 shows a fragmentary view of the coupling element shown in
FIG. 10.
FIG. 12 shows a fragmentary view of a fastener, in accordance with
certain preferred embodiments of the present invention.
FIGS. 13A and 13B show a method of assembling the fastener to a
coupling element, in accordance with certain preferred embodiments
of the present.
FIG. 14 shows a perspective view of a coupling element, in
accordance with further preferred embodiments of the present
invention.
FIG. 15 shows a front elevation view of the coupling element of
FIG. 14.
FIG. 16 shows a plan view of the coupling element shown in FIGS. 14
and 15.
FIG. 17 shows a front elevation view of a screw fastener coupled
with a coupling element, in accordance with further preferred
embodiments of the present invention.
FIG. 18 shows a fastener for a stabilizing assembly in accordance
with further preferred embodiments of the present invention.
FIG. 19 shows a coupling element having external screw threads in
accordance with another preferred embodiment of the present
invention.
DETAILED DESCRIPTION
Referring to FIG. 1, in accordance with certain preferred
embodiments of the present invention, a pedicle screw assembly
includes a fastener 20, such as a screw fastener having a tip end
22 for insertion into bone and a head 24 at an upper end thereof.
The screw fastener 20 preferably has external screw threads 26 that
extend between the tip end 22 and screwhead 24. The screw threads
26 terminate at a neck 28 preferably located between screwhead 24
and an upper end of the screw threads 26. The neck 28 desirably has
a concave surface having a diameter that is less than the diameter
of the screw threads. The reduced diameter neck 28 allows the screw
fastener 20 to pivot and rotate through a broader range of motion,
as will be described in more detail below. The screw fastener,
including the external threads 26, neck 28 and screwhead 24, are
preferably made of a non-organic material that is durable and that
can be implanted in a human body, such as titanium or stainless
steel.
Referring to FIGS. 1 and 2, screwhead 24 preferably has an
underside 30 defining a first radial surface and a top side 32
defining a second radial surface. Screwhead 24 also desirably
includes one or more grooves 34 that extend in a direction
substantially parallel to the longitudinal axis of screw fastener
24. Referring to FIG. 2, in one preferred embodiment, screwhead 24
includes a plurality of grooves 34 evenly spaced from one another
and extending around the outer perimeter of screwhead 24. The top
surface 32 of screwhead 24 is preferably centered on the plurality
of grooves 34.
Referring to FIGS. 3A and 3B, screwhead 24 includes a center 36,
whereby the underside 30 of screwhead 24 defines the first radial
surface having a radius R.sub.1 from center 36. Screwhead 24
includes top surface 32 having second radial surface at a second
radius R.sub.2 from center 36. The plurality of grooves 34 are
preferably adapted to receive prongs of a driver used to screw the
screw fastener into bone, as will be described in more detail
below.
Referring to FIGS. 4 and 5, pedicle screw assembly also includes a
coupling element 40 for coupling an orthopedic stabilizing rod with
the screw fastener shown in FIGS. 1 3B. Coupling element 40 is
preferably made of an inert material such as titanium or stainless
steel. Coupling element 40 has an upper end 42, a lower end 44, and
a longitudinal axis C--C extending between the upper and lower
ends. Coupling element 40 also preferably has an outer surface 46
including a convex surface at the lower end 44 thereof and a
cylindrical surface at the upper end thereof. Outer surface 46 also
preferably includes one or more grooves 48 formed therein so that
coupling element 40 may be grasped and/or maneuvered using a
securing element or tool, such as a persuader instrument used to
seat the orthopedic rod in the pedicle screw assembly. The grooves
48 preferably extend in directions substantially perpendicular to
the longitudinal axis C--C of coupling element 40.
The coupling element 40 has a bore 50 for receiving the screw
fastener, the bore extending along the longitudinal axis C--C of
coupling element 40. The bore 50 defines an inner surface of
coupling element 40 and has internal threads 44 extending from the
upper end 42 of the coupling element toward a cavity 52 adjacent
lower end 44. The lower end of cavity 52 preferably has a
conical-shaped seat 54 including sidewalls tapering inwardly toward
the lower end 44. In other embodiments, the threads on the coupling
element may be external threads.
FIGS. 6A and 6B show one preferred method for assembling screw
fastener 20 with coupling element 40. Referring to FIG. 6A, tip end
22 of screw fastener 20 is passed through bore 50 of coupling
element 40 from the upper end 42 toward the lower end 44 of the
coupling element so that the threaded portion of screw fastener
passes through bore 50. The threaded portion 26 of screw fastener
20 is able to pass freely through bore 50 because the threaded
portion 26 has an outer diameter that is less than the internal
diameter of the internal threads 44 of coupling element 40.
Referring to FIG. 6B, screw fastener 20 continues to be inserted
toward the lower end of coupling element 40 until screwhead 24 is
disposed within cavity 52 of coupling element 40 and the underside
of screwhead engages the seat of coupling element.
Referring to FIG. 7, after the screw fastener 20 has been assembled
with coupling element 40, the neck 28 of screw fastener 20 is free
to pivot and rotate relative to coupling element. As mentioned
above, neck 28 preferably has a reduced diameter and may also have
a concave outer surface so that the screw fastener 20 and coupling
element, may pivot relative to one another over a broader range of
angles.
After screw fastener 20 and coupling element, have been assembled
together, the subassembly is ready to be inserted into bone 60. In
a first step, the screw fastener 20 may be anchored to bone 60 by
drilling a pilot hole into the bone. The tip end (not shown) of
screw fastener 20 may then be placed in the pilot hole and the
screw fastener screwed into bone 60 using a driver or tool. One
preferred driver 62 for driving screw fastener 20 into bone 60
includes a rotatable shaft 64 having a lower end 66 with a
plurality of downwardly extending prongs 68. The prongs 68 are
sized for fitting into the grooves 34 of the screwhead (not shown)
of screw fastener 20. Upon rotation of shaft 64, prongs 68 engage
grooves 34 of screw fastener 20 for rotating screw fastener 20 and
screwing the fastener into bone 60. Driver 62 may also include
external threads 70, preferably between shaft 64 and prongs 68.
External threads 70 are designed for threadably mating with the
internal threads 44 of coupling element 40 (FIGS. 4 5). The mating
engagement of the external threads 70 of driver 62 and the internal
threads 44 of coupling element 40 generally stabilizes the pedicle
screw assembly when driving the screw fastener 20 into bone 60.
Referring to FIGS. 9A and 9B, after screw fastener 20 is anchored
in bone 60, coupling element 40 remains free to pivot and rotate
relative to the screw fastener so that an orthopedic stabilizing
rod 72 may be positioned within the rod receiving opening 74 of
coupling element 40. Rod receiving opening 74 preferably includes a
U-shaped opening extending from the top 42 of coupling element 40.
Moreover, after screw fastener 20 has been fully inserted into
bone, a gap exists between the lower end 44 of coupling element 40
and bone 60. The gap facilitates pivotal and rotational movement of
coupling element 40 relative to screw fastener 20. The coupling
element 40 may then be moved (e.g. pivoted) by engaging grooves 48
with a tool or by grasping the outer body portion of the coupling
element. Coupling element 40 would then be pivoted and/or rotated
so that an orthopedic rod 72 can be positioned in the rod receiving
opening 74, as shown in FIG. 9B.
Referring to FIG. 9C, after stabilizing rod 72 has been positioned
within coupling element 40, a set screw 76 having external threads
(not shown) is screwed into the internal threads 44 of coupling
element 40. Set screw 76 continues to be threaded into the internal
threads 44 until an underside 78 of set screw 76 abuts against
stabilizing rod 72. Set screw 76 is then further rotated into
internal threads 44 for locking stabilizing rod 72 in rod receiving
channel 74. The tightened set screw 76 applies a downward force
through rod 72 onto the second radial surface at the top side 32 of
screwhead 24. The downward force applied to the second radial
surface of screwhead 24 forces the first radial surface at the
underside 30 of screwhead 24 into the conical-shaped seat 54 of
coupling element 40. Engagement of the first radial surface at the
underside 30 of screwhead 24 with the conical-shaped seat 54
creates a spherical surface/conical surface friction lock that
locks the coupling element 40 relative to the screwhead 24, thereby
preventing further pivotal and rotary movement of coupling element
40 and screw fastener 20 relative to one another. Although the
present invention is not limited by any particular theory of
operation, it is believed that the engagement of the spherical
surface of the screwhead with the conical seat of the coupling
element dramatically improves the locking force exerted at the
interface of the screwhead and the coupling element.
Referring to FIG. 10, in accordance with other preferred
embodiments of the present invention, a coupling element 140 for a
stabilizing assembly includes an upper end 142 and a lower end 144.
Coupling element 140 also includes an outer surface 146 extending
between upper and lower ends 142, 144, the outer surface 146
including one or more grooves 148. Coupling element also includes a
centrally located bore 150 extending between the upper end 142 and
lower end 144 along longitudinal axis C--C. Bore 150 is surrounded
by interior threads 151 extending from the upper end 142 toward the
lower end 144. Coupling element 140 also includes a cavity 152
adjacent lower end 144, the cavity including a conical-shaped seat
154 having sidewalls that taper inwardly toward the lower end 144
of coupling element 140. Coupling element 140 also preferably
includes an interior wall 153 having diameter D.sub.w between
interior threads 151 and cavity 152, and a lip 155 between interior
wall 153 and cavity 152. The lip 155 has a diameter D.sub.L that is
less than the diameter D.sub.w of interior wall 153. As shown in
FIG. 12, the outer diameter D.sub.s of the first radial surface 130
of screwhead 124 is greater than the diameter D.sub.L of the lip
155 of coupling element. As a result, lip 155 serves as a detent
that holds fastener 120 in the cavity 152 of coupling element 140
after the screwhead of fastener 120 has been assembled with the
coupling element 140.
FIG. 11 shows a magnified view of a portion of the coupling element
140 shown in FIG. 10. As described above, coupling element 140
includes bore 150 extending from an upper end (not shown) toward
lower end 144 thereof, and an interior wall 153 extending between
internal threads 151 and cavity 152. Cavity 152 includes
conical-shaped seat 154 having inwardly tapering sidewalls 154.
Coupling element 140 includes lip 155 positioned between interior
wall 153 and cavity 152. Lip 155 has a diameter D.sub.L that is
less than the diameter D.sub.w of the interior wall 153 of coupling
element 140.
FIG. 12 shows screw fastener 120 having screwhead 124 at an upper
end thereof, the screwhead including a first radial surface 130 at
an underside thereof and a second radial surface 132 at a top side
of screwhead 124. Screwhead 124 includes a center 136, a first
radial surface 130 from center 136 having a radius R.sub.1 and a
second radial surface 132 from center 136 having a second radius
R.sub.2, whereby R.sub.1 is greater than R.sub.2. The first radial
surface of screwhead 124 defines an outer diameter D.sub.s that is
two times the length of R.sub.1.
FIGS. 13A and 13B show screw fastener 120 being assembled with the
coupling element 140 shown in FIGS. 10 and 11. As mentioned above,
coupling element 140 includes lip 155 having a diameter D.sub.L
that is less than the diameter D.sub.s of the first radial surface
130 of screwhead 124, however, the outer diameter D.sub.s of the
first radial surface 130 of screwhead 124 is less than the inner
diameter of inner wall 153.
Referring to FIGS. 13A and 13B, during assembly of screw fastener
120 to coupling element 140, the screw fastener 120 is passed
through bore 150 so that screw threads 126 pass through the opening
at lower end 144 of coupling element 140. Because the outer
diameter D.sub.s of screwhead 124 is less than the inner diameter
of inner wall 153, screwhead 124 passes easily through bore 150
until first radial surface 130 engages lip 155. Because the inner
diameter D.sub.L of lip 155 is less than the outer diameter D.sub.s
of the first radial surface 130 of screwhead 124, the lip 155 acts
as a detent and the screwhead must be forced through the reduced
diameter of lip 155. Referring to FIG. 13B, after the outer
diameter D.sub.s of screwhead 124 has passed by lip 155, the
screwhead is retained within cavity 152 by lip 155, with coupling
element 140 pivotable relative to screwhead 124 for capturing a
stabilizing rod. After stabilizing rod is captured within the
U-shaped opening of coupling element 140, a set screw (not shown)
may be threaded into internal threads 151 of coupling element 140
for capturing the stabilizing rod within the U-shaped opening. The
set screw is then preferably tightened for exerting a downward
force upon the stabilizing rod which, in turn, applies a force to
the second radial surface 132 of screwhead 124. The downward force
on the second radial surface 132 forces the first radial surface
130 into the conical-shaped seat of coupling element for locking
the screwhead and coupling element relative to one another.
FIGS. 14 16 show a coupling element 240 in accordance with further
preferred embodiments of the present invention. Coupling element
240 includes upper end 242, lower end 244 and outer wall 246
extending between upper and lower ends 242, 244. The outer surface
246 of coupling element 240 includes grooves 248 on opposing arms
thereof. Coupling element 240 has central bore 150 extending
between upper and lower ends thereof. Coupling element 240 has a
first arm 261A and a second arm 261B on either side of U-shaped
rod-receiving opening 174, the U-shaped rod-receiving opening being
adapted to receive a stabilizing rod (not shown). The edges of the
U-shaped opening include cuts 263 formed therein. The cuts 263
reduce the profile or width of the coupling element, thereby
minimizing interference with other coupling elements when a series
of coupling elements are connected with a stabilizing rod. The cuts
263 allow the coupling elements 240 to be packed more tightly
together and to be secured over each vertebrae, thereby improving
fusion of a spinal segment. Although the present invention is not
limited by any particular theory of operation, it has been observed
that some patients have relatively small vertebrae, making it
difficult to secure a coupling element over each vertebrae. As a
result, some of the vertebrae may not have a section of the
stabilizing assembly attached thereto, a situation that may
adversely affect stabilization and fusion of a spine segment
because the entire portion of the spine segment is not being
stabilized. In addition, the cuts 263 minimize the occurrence of
sharp edges on the coupling element that may irritate a patient's
tissue or cut through a surgeon's surgical glove.
FIG. 17 shows a front elevation view of the coupling element 240 of
FIGS. 14 16 assembled with screw fastener 220. Coupling element 240
includes internal threads (not shown) for receiving set screw 276.
Coupling element 240 includes cuts 263 for minimizing the profile
of the coupling element and reducing the occurrence of sharp
edges.
FIG. 18 shows a fastener 320 in accordance with another embodiment
of the present invention. Fastener 320 includes head 324 having a
first radial surface 330 having radius R.sub.1 from center 336 and
second radial surface 332 having radius R.sub.2 from center 336.
The first radius, R.sub.1, is greater than the second radius
R.sub.2. Fastener 320 includes hook 370 for securing the fastener
to bond (not shown).
FIG. 19 shows an assembly in accordance with another embodiment of
the present invention including a coupling element 440 having
external threads 444 extending from an upper end thereof. The
assembly also includes a locking element 476 having internal
threads 477 adapted to thread onto the external threads 444 of
coupling element 440.
Although the invention herein has been described with reference to
particular embodiments, it is to be understood that these
embodiments are merely illustrative of the principles and
applications of the present invention. It is therefore to be
understood that numerous modifications may be made to the
illustrative embodiments and that other arrangements may be devised
without departing from the spirit and scope of the present
invention as defined by the appended claims.
* * * * *