U.S. patent number RE46,371 [Application Number 14/830,247] was granted by the patent office on 2017-04-25 for bone fixation assembly and method.
This patent grant is currently assigned to Stryker European Holdings I, LLC. The grantee listed for this patent is Stryker European Holdings I, LLC. Invention is credited to Jerome David, Clifford B. Tribus.
United States Patent |
RE46,371 |
David , et al. |
April 25, 2017 |
Bone fixation assembly and method
Abstract
A bone fixation assembly and method of fixing bones including a
fixation element having a head portion, a unitary coupling element
and at least one locking element. The unitary coupling element
includes a first bore adapted to slidably receive the head portion
of the fixation element. A first locking element is adapted to
secure the head portion in the first bore.
Inventors: |
David; Jerome (Bordeaux,
FR), Tribus; Clifford B. (Madison, WI) |
Applicant: |
Name |
City |
State |
Country |
Type |
Stryker European Holdings I, LLC |
Kalamazoo |
MI |
US |
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Assignee: |
Stryker European Holdings I,
LLC (Kalamazoo, MI)
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Family
ID: |
1000002369818 |
Appl.
No.: |
14/830,247 |
Filed: |
August 19, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
10695849 |
Oct 29, 2003 |
7648522 |
Jan 19, 2010 |
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Foreign Application Priority Data
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Sep 26, 2003 [FR] |
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03 11291 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B
17/7035 (20130101); A61B 17/7041 (20130101) |
Current International
Class: |
A61B
17/70 (20060101) |
Field of
Search: |
;606/61,72,73,246,250-253,260,266,267,270,278,300,305,319,264,279,328,606
;403/76 ;74/617 ;81/132 ;269/76 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 933 065 |
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Aug 1999 |
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EP |
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1 254 640 |
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Nov 2002 |
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EP |
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2 781 663 |
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Feb 2000 |
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FR |
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02/34151 |
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May 2002 |
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WO |
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WO-02/34151 |
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May 2002 |
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WO |
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Primary Examiner: Wehner; Cary
Attorney, Agent or Firm: Lerner, David, Littenberg, Krumholz
& Mentlik, LLP
Claims
The invention claimed is:
1. A bone fixation assembly comprising: a unitary coupling element
having a first bore having an axis, the first bore adapted to
receive a head portion of a fixation element and to permit axial,
sliding movement of the coupling element relative to the fixation
element, the coupling element having a second bore adapted to
receive a spinal rod; a first locking element adapted to secure the
head portion of the fixation element in the first bore at any point
along the length of the head portion of the fixation element,
wherein the first locking element .[.comprises a.]. .Iadd.consists
essentially of an threaded .Iaddend.compressible ball ring; and a
second locking element adapted to secure the spinal rod in the
second bore.
2. The bone fixation assembly of claim 1, .[.wherein the first
locking element.]. further .[.comprises.]. .Iadd.comprising
.Iaddend.a locking nut .Iadd.for engaging the ball
ring.Iaddend..
3. The bone fixation assembly of claim 2, wherein the locking nut
contains external male threads that engage female threads formed in
the first bore.
4. The bone fixation assembly of claim 3, wherein the compressible
ball ring is seated within the first bore and at least a portion of
the locking nut circumferentially surrounds a portion of the ball
ring.
5. The bone fixation assembly of claim 4, wherein engagement of the
male threads of the locking nut with the female threads in the
first bore exerts radial force on the compressible ball ring to
secure the head .Iadd.portion .Iaddend.of the fixation element in
the first bore.
6. The bone fixation assembly of claim 5, wherein the locking nut
is in a locked position, and the compressible ball ring is in
contact with the coupling member and the locking nut.
7. The bone fixation assembly of claim 6, wherein the second
locking element includes a set screw.
8. The bone fixation assembly of claim 7, wherein the set screw is
permanently seated in the coupling member.
9. The bone fixation assembly of claim 8, wherein the locking nut
and compressible ball ring are permanently seated in the first
bore.
10. The bone fixation assembly of claim 8, wherein the locking nut
cannot be removed from said coupling element after connection
therewith.
11. The bone fixation assembly of claim 10, wherein a portion of
the first bore is tapered and the locking nut includes a tapered
opening to permit polyaxial motion between the fixation element and
the connector.
12. The bone fixation assembly of claim 11, wherein the taper in
the first bore and the taper in the locking nut extend in opposite
directions.
13. The bone fixation assembly of claim 12, wherein the fixation
element includes a screw.
14. The bone fixation assembly of claim 1, wherein the compressible
ball ring is at least partially split.
15. The bone fixation assembly of claim 1, wherein said second bore
has an axis transverse to the axis of the first bore.
16. The bone fixation assembly of claim 1, wherein said second
locking element is connected to said coupling element and cannot be
removed from said coupling element after connection therewith.
17. The bone fixation assembly of claim 16, wherein said second
locking element includes a flared lip that cooperates with a
shoulder associated with the coupling element to prevent
inadvertent removal of the second locking element.
18. The bone fixation assembly of claim 1, wherein the first
locking element is connected to said coupling element and cannot be
removed from said coupling element after connection therewith.
19. The bone fixation assembly of claim 1, further comprising a
fixation element having a head portion, wherein the head portion of
the fixation element is inserted in the first bore.
20. A bone fixation assembly comprising: a unitary coupling element
having a first bore adapted to slidingly receive a head portion of
a fixation element, and a second bore adapted to receive a spinal
rod; a first locking element pre-assembled with the coupling
element and adapted to secure the head portion of the fixation
element in the first bore at any point along the length of the head
portion of the fixation element, the first locking element
.[.including a.]. .Iadd.consisting essentially of an unthreaded
.Iaddend.compressible ball ring; and a second locking element
pre-assembled with the coupling element and adapted to secure the
spinal rod in the second bore.
21. The bone fixation assembly of claim 20, wherein the first bore
permits axial movement of the coupling element relative to the
fixation element.
22. The bone fixation assembly of claim 21, wherein the first bore
permits polyaxial movement of the coupling element relative to the
fixation element.
23. The bone fixation assembly of claim 22, wherein the first bore
has an axis, and the second bore has an axis transverse to the
first bore.
24. The bone fixation assembly of claim 21, .[.wherein the.].
.Iadd.further comprising a .Iaddend.locking nut .[.is.]. adapted to
exert radial force on the ball ring.
25. The bone fixation assembly of claim 20, wherein the
compressible ball ring is seated in the first bore and cooperates
with a locking nut threaded in the first bore.
26. The bone fixation assembly of claim 20, further comprising a
fixation element having a head portion, wherein the head portion of
the fixation element is inserted in the first bore.
27. The bone fixation assembly of claim 20, wherein said
compressible ball ring is at least partially split.
28. A bone fixation assembly comprising: a unitary coupling element
having a first bore adapted to slidingly receive a head portion of
a fixation element and to permit axial movement of the coupling
element relative to the fixation element; and a locking element
including .[.a.]. .Iadd.an unthreaded .Iaddend.ball ring and a
locking nut associated with the head portion of the fixation
element to exert a radial force on the ball ring such that the ball
ring exerts a compressive force on the head portion of the fixation
element to secure the head portion of the fixation element in the
coupling element at any point along the length of the head of the
fixation element.Iadd., the unthreaded ball ring including upper
and lower surfaces connected by a curved outer surface, and not
integrally connected to any other structure.Iaddend..
29. The bone fixation assembly of claim 28, further comprising a
fixation element having a head portion, wherein the head portion of
the fixation element is inserted in the first bore.
30. The bone fixation assembly of claim 28, wherein said ball ring
is at least partially split.
31. A bone fixation assembly comprising: a unitary coupling element
having a first bore adapted to slidingly receive a head portion of
a fixation element and to permit axial movement of the coupling
element relative to the fixation element; .[.a.]. .Iadd.an
unthreaded .Iaddend.compressible ball ring seated in the first bore
adapted to secure the head of the fixation element to the coupling
element when the ball ring is compressed at any point along the
length of the head of the fixation element.Iadd., the unthreaded
compressible ball ring including upper and lower surfaces connected
by a curved outer surface, and not integrally connected to any
other structure.Iaddend.; and means for exerting compressive radial
force on the ball ring.
32. The bone fixation assembly of claim 31, wherein the means for
exerting compressive radial force includes a locking nut.
33. The bone fixation assembly of claim 32, wherein the locking nut
contains external male threads adapted to engage internal female
threads in the first bore.
34. The bone fixation assembly of claim 31, further comprising a
fixation element having a head portion, wherein the head portion of
the fixation element is inserted in the first bore.
35. The bone fixation assembly of claim 31, wherein the
compressible ball ring is at least partially split.
36. A bone fixation assembly comprising: a unitary coupling element
having a first bore adapted to slidingly receive a head portion of
a fixation element and to permit axial movement of the coupling
element relative to the fixation element; and a first locking
element including a locking nut that engages the first bore and a
tapered opening adapted to allow polyaxial motion of the head
portion of the fixation element inserted therethrough, the first
locking .[.mechanism.]. .Iadd.element .Iaddend.further including
.[.a.]. .Iadd.an unthreaded .Iaddend.compressible ball ring for
locking the head portion of the fixation element at any position
along its length.Iadd., the unthreaded compressible ball ring
including upper and lower surfaces connected by a curved outer
surface, and not integrally connected to any other
structure.Iaddend..
37. The bone fixation assembly of claim 36, wherein the locking nut
cooperates with the compressible ball ring to exert force on the
head of the fixation element to lock the fixation element with
respect to the coupling element.
38. The bone fixation assembly of claim 36, wherein the
compressible ball ring is at least partially split.
39. A bone fixation assembly comprising: a fixation element having
a substantially cylindrical, smooth head portion; a unitary
coupling element having a first bore adapted to slidingly receive
the head portion of the fixation element and to permit axial,
sliding movement of the coupling element relative to the fixation
element, the coupling element having a second bore adapted to
receive a spinal rod; a first locking element including an
externally threaded locking nut adapted to cooperate with threads
in the first bore and exert radial compressive force on .[.a.].
.Iadd.an unthreaded .Iaddend.compressible ball ring slidably
mounted on the head portion of the fixation element pre-seated in
the first bore to secure the head portion of the fixation element
in the first bore at any point along the length of the head portion
of the fixation element, the locking nut permitting polyaxial
motion of the fixation element.Iadd., the unthreaded compressible
ball ring including upper and lower surfaces connected by a curved
outer surface, and not integrally connected to any other
structure.Iaddend.; and a second locking element pre-assembled with
the coupling member and adapted to secure the spinal rod in the
second bore.
40. The bone fixation assembly of claim 39, wherein the
compressible ball ring is at least partially split.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority of French Application No.
0311291 filed on Sep. 26, 2003, the contents of which are hereby
incorporated by reference in their entirety.
FIELD OF THE INVENTION
The invention relates to bone fixation devices, and in particular,
to pedicle fixation assemblies and methods used in spinal fixation
procedures.
BACKGROUND OF THE INVENTION
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 stacked vertebral bodies, 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 exerted upon the spinal column. A
vertebral canal containing the spinal cord and nerves is located
behind the vertebral bodies.
A surgical technique commonly referred to as spinal fixation uses
surgical implants for fusing together and/or mechanically
immobilizing two or more vertebral bodies of the spinal column.
Spinal fixation may also be used to alter the alignment of adjacent
vertebral bodies relative to one another to change the overall
alignment of the spinal column. Such techniques have been used
effectively to treat a wide variety of conditions and, in most
cases, to relieve pain.
One spinal fixation technique involves immobilizing the spine using
orthopedic stabilizing rods, commonly referred to as spine rods,
which run generally parallel to the spine. This technique involves
exposing the spine posteriorly and fastening bone screws to the
pedicles of vertebral bodies. The pedicle screws are generally
placed at least one 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 pedicle
screws. The aligning influence of the spine rods forces the spinal
column 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.
Most existing rod fixation systems require several components to
build the systems. Each additional component or instrument required
to assemble the fixation system adds to the complexity of the
surgical technique. A need has thus arisen for improved fixation
systems that minimize the assembly of small pieces of hardware
during the surgical procedure. Thus, there remains a need for
spinal fixation devices that facilitate simple and fast assembly of
attachment of a spinal rod to a spine. It would be desirable to
provide a device with pre-assembled components that will result in
less time in assembling the components in the operating room.
SUMMARY OF THE INVENTION
In accordance with one or more embodiments of the present
invention, a bone fixation assembly is provided comprising a
fixation element having a head portion, a unitary coupling element
having a first bore adapted to slidably receive the head portion of
the fixation element, and a first locking element adapted to secure
the head portion in the first bore. In certain embodiments, the
coupling element has a second bore adapted to receive a spinal rod
and a second locking element adapted to secure the spinal rod in
the second bore.
According to one or more further aspects of the present invention,
a bone fixation system assembly includes a fixation element having
a substantially cylindrical head portion; a unitary coupling
element having a first bore adapted to receive the head portion of
the fixation element and to permit axial movement of the coupling
element with respect to the fixation element, the coupling element
having a second bore adapted to receive a spinal rod; a first
locking element pre-assembled with the coupling member and adapted
to secure the head portion in the first bore; and a second locking
element pre-assembled with the coupling member and adapted to
secure the spinal rod in the second bore.
According to one or more further aspects of the present invention,
a bone fixation assembly includes: a fixation element having a head
portion; a unitary coupling element having a first bore adapted to
receive the head portion of the fixation element and to permit
axial movement of the coupling element with respect to the fixation
element; and a locking element including a ball ring and a locking
nut adapted to exert radial force on the ball ring such that the
ball ring exerts a compressive force on the head of the fixation
element to secure the head of the screw in the coupling
element.
According to still one or more further aspects of the present
invention, a bone fixation assembly includes: a fixation element
having a substantially cylindrical head portion; a unitary coupling
element having a first bore adapted to receive the head portion of
the fixation element and to permit axial, preferably polyaxial,
movement of the coupling element with respect to the fixation
element, and a first locking element including a locking nut that
engages the first bore and a tapered opening adapted to allow
polyaxial motion of the head of a fixation element inserted
therethrough.
In still another embodiment of the invention, a method of fixing a
bone in place is provided. The method comprises attaching a
fixation element having a head portion to a bone, sliding a first
bore of a unitary coupling element over the head portion, inserting
a rod through a second bore of the coupling element, tightening a
first locking element associated with the first bore to secure the
head portion to the coupling element, and tightening a second
locking element associated with the second bore.
According to one or more embodiments of the present invention, bone
fixation assemblies are provided to connect spinal rods without any
loose parts and very few steps (preferably only two steps) to lock
the fixation element to the coupling member and the spinal rod to
the coupling member. The assemblies of the present invention do not
require any additional locking mechanism, and they reduce the
assembly of small pieces of hardware during the surgical
procedure.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the subject matter of the present
invention and the various advantages thereof can be realized by
reference to the following detailed description in which reference
is made to the accompanying drawings in which:
FIG. 1 is a partial perspective view of a bone fixation assembly
with a spine rod secured thereto according to one or more
embodiments of the present invention;
FIG. 2 is a cross-sectional view taken along line 2-2 of FIG.
1;
FIG. 3 is a sectional view of a bone fixation assembly with a spine
rod and screw illustrating the manner in which the assembly is
connected with a vertebra;
FIG. 4 is a top perspective view of a coupling element according to
one or more embodiments of the present invention;
FIG. 5 is a side elevational view of a locking element for securing
a spine rod to a bone fixation assembly according to one or more
embodiments of the present invention;
FIG. 6 is a top view of the locking element shown in FIG. 5;
FIG. 7 is a perspective view of a locking nut for securing the head
of a fixation element according to one or more embodiments of the
invention;
FIG. 8 is a cross-sectional view of the locking nut taken along
line 8-8 in FIG. 7; and
FIG. 9 is a perspective view of a ball ring according to one or
more embodiments of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Before describing several exemplary embodiments of the invention,
it is to be understood that the invention is not limited to the
details of construction or process steps set forth in the following
description. The invention is capable of other embodiments and of
being practiced or carried out in various ways.
Referring now to the drawings and particularly to FIGS. 1-3, a bone
fixation assembly 10, in accordance with certain preferred
embodiments of the present invention, is shown. The bone fixation
assembly may be secured to the pedicles 11 of vertebral bodies of a
spinal column, as shown in FIG. 3. The fixation assembly includes a
coupling element 12, preferably made of a biologically inert
material, for example, any metal customarily used for surgical
devices and particularly those used for bone screws and pins, such
as titanium or stainless steel. Other suitable materials for the
coupling element include, but are not limited to, alloys, composite
materials, ceramics or carbon fiber materials.
The fixation assembly 10 includes a fixation element 16 having a
head portion 18. The head portion 18 is preferably cylindrical, and
preferably has a smooth outer surface to facilitate sliding on or
in connection with the head portion 18, as will be described below.
The head portion 18 can be constructed in other ways or in
connection with other components to facilitate sliding of the
coupling element with respect to the fixation element 16. The
fixation element 16 could be any suitable fixation element for
attachment to a bone, for example, a hook or a screw. In preferred
embodiments, the fixation element includes a screw fastener having
the head portion 18 and a threaded portion 20, and the threads are
adapted to be engaged in bone material. The end of the screw
fastener opposite the head portion 18 has a tip for insertion into
bone, and external screw threads 20 extend between the tip and the
head portion 18. The screw threads 20 have an inner diameter and an
outer diameter. The fixation element, including the screw threads
20 and head portion 18, are preferably made of a biologically inert
material, such as titanium or stainless steel.
In the embodiment shown in FIGS. 1-3, one end of the head portion
of the fixation element includes a tool engagement surface 22. In
the embodiment shown, the tool engagement surface 22 is in the form
of a hollow female hex head adapted to receive an end of a
hexagonal driver for turning the fixation element. It will be
understood, however, that other internal or external tool
engagement surfaces 22 can be used according to the present
invention.
Coupling element 12, which is shown in more detail in FIG. 4,
preferably comprises a unitary body and has at least a first bore
14 having a longitudinal axis adapted to receive the head portion
18 of the fixation element 16 and to permit axial, sliding movement
of the coupling element 12 along the axis of the head portion
.[.28.]. .Iadd.18 .Iaddend.with respect to the fixation element.
The fixation assembly further comprises a first locking element
adapted to secure the head portion 18 in the first bore 14.
According to one or more embodiments, the first locking element
includes at least a locking nut 24.
Further details on the locking nut 24 are shown in FIGS. 7 and 8.
Preferably, the locking nut 24 is hollow and has a bore 26
therethrough for receiving the head portion 18 of the fixation
element 16. The locking nut 24 includes a receiving end 28, and the
opening 26 at the receiving end 28 is flared or angled as shown in
FIG. 8. The flared or tapered opening permits polyaxial motion of a
fixation element inserted therethrough. In a preferred embodiment,
the first bore 14 includes a bottom portion 15 that is tapered or
flared in a direction opposite the taper or flared opening in the
locking nut 24. The oppositely extended flared openings permit
polyaxial movement between the fixation element and the coupling
member. Preferably, the fixation element can move polyaxially as
shown by the arrows "a" in FIG. 2. In preferred embodiments, the
fixation element can move by at least 20 degrees polyaxially, as
indicated by the arrows "a" in FIG. 2. The locking nut 24 further
includes a seating end 30, and according to at least one
embodiment, the seating end 30 includes an inner curved engagement
surface 32 for engaging a ball ring, which will be described in
more detail below. The ball ring, as seated in the inner curved
engagement surface 32, facilitates polyaxial movement of the
fixation element, and can do so in a controlled manner. The
receiving end 28 of the locking nut may further include a plurality
of flat surfaces 34 such that the receiving end 28 of the locking
nut is hexagonally shaped and adapted to receive a wrench or other
device adapted to turn the locking nut. According to certain
preferred embodiments, the exterior surface of the receiving end 28
further includes male threads for engagement with complementary
female threads on the interior of the first bore 14 of the coupling
element 12.
According to one or more embodiments, the coupling element 12
includes a second bore 36 adapted to provide an opening to receive
a spinal rod 38 through the bore. The second bore 36 has a
longitudinal axis that is substantially transverse to the
longitudinal axis of the first bore 14. In these embodiments, a
second locking element 40 is provided and is adapted to secure the
spinal rod in the second bore. FIGS. 5 and 6 show additional
details of the second locking element 40. The second locking
element 40 is preferably in the form of a set screw. The second
locking element 40 includes a hexagonal-shaped opening which is
adapted to receive an end of a hexagonal driver for turning the
second locking element 40. The second locking element 40 further
preferably includes external threads 42 for engagement with
complementary internal 43 threads on the surface of the second bore
36. The rod receiving opening and second locking element are thus
adapted to capture and seat an orthopedic stabilizing rod therein.
In preferred embodiments, both the first and second locking
elements 22, 40 are permanently seated in the coupling element 12
such that the locking elements cannot be inadvertently removed from
the coupling element. Inadvertent removal of the locking element 40
can be accomplished by providing a flared portion or lip 41 on the
end of the locking element opposite the tool engagement surface. A
shoulder 45 associated with the respective bore of the coupling
element prevents removal of the locking element 40. The flared
portion or lip 41 has a diameter that is greater than the threaded
portion of the locking element 40. The shoulder 45 associated with
the bore 36 provides an opening in the bore 36 that is greater than
the diameter of the threaded portion of the locking element 40, but
smaller than the diameter of the flared portion or lip 41 on the
locking element 40. Thus, when the locking element is turned in a
direction to back the locking element out of the bore 36, the
shoulder 45 and flared portion or lip 41 prevent the locking
element 40 from coming out of the bore 36. Although the shoulder 45
and flared portion or lip 41 are shown with respect to the second
bore 36, it will be understood that such a structure can be used
with respect to the first bore 14 to prevent inadvertent removal of
the locking nut 24 from the first bore. It will be understood, of
course, that other means and structures can be used to prevent
inadvertent removal or pre-assembly of the locking element 40 and
locking nut 24 in their respective bores. For example, the locking
element and/or locking nut could be press fit into the bores and
friction-locked to prevent inadvertent removal. Alternatively,
detents on the surfaces of the bores or the locking nut and locking
element could be utilized to prevent inadvertent removal of the
locking element or locking nut.
According to preferred embodiments of the invention, the first
locking element comprises a locking nut 24 that cooperates with a
ball ring 44 to lock the head portion 18 of the fixation element to
the coupling member 14. As shown in FIG. 2, the ball ring 44 is
seated within the first bore 14 and at least a portion of the
locking nut 24 circumferentially surrounds a portion of the ball
ring. In preferred embodiments, the ball ring 44 is pre-assembled
and permanently seated in the first bore of the coupling member. In
preferred embodiments, the curved engagement surface of the locking
nut 24 engages the exterior surface 46 of the ball ring 44. FIG. 9
shows a detailed view of the ball ring. The ball ring 44 shown in
FIG. 9 comprises a generally spherical outer surface having an
opening 48 through the body coaxial with the first bore and adapted
to receive the head portion 18 of the fixation element 16. As shown
in FIG. 9, the ball ring 44 includes a gap 50 in the outer surface,
allowing the ball ring 44 to be compressed such that the inner
diameter of the ball ring opening 48 is reduced when the ball ring
is compressed. The ball ring 44 and the gap 50 are designed such
that when the ball ring 44 is compressed, the diameter of the
opening 48 is less than the diameter of the head portion 18 of the
screw so that the head portion of the screw is securely and snugly
held in place. Compression of the ball ring occurs when the locking
nut 24 is tightened. Engagement of the male threads of the locking
nut with the female threads in the first bore causes the engagement
surface 32 of the locking nut to engage the outer surface 46 of the
ball ring 44, causing the ball ring to compress onto the head
portion 18 of the screw. This compression exerts a radial force on
the exterior surface of the ball ring 44. It is to be understood
that the ball ring 44 may be configured differently than shown in
FIG. 9. For example, instead of a single gap 50 in the outer
surface of the ring, the ring may include a plurality of split
openings that do not extend through the entire exterior surface of
the split ring.
Additionally, while the foregoing preferred structures facilitate
axial movement of the coupling element, other structures are also
available for this purpose. For example, a split collet could
surround a spherical head portion and the outer surface of the
collet could cooperate with the coupling element or other
components to permit axial sliding before being compressed around
the spherical head portion. Of course, in such a construction, the
extent of axial sliding may be limited by the size of the coupling
element, whereas in the preferred embodiment, the extent of sliding
may be limited by the length of the head portion of the fixation
element.
According to a preferred embodiment, a fixation assembly 10 is
provided in a package including the coupling element 12 having the
set screw 40, locking nut 24 and ball ring 44 permanently
pre-seated in the coupling element 12 to reduce the number of loose
parts and prevent any small loose parts from being lost, or from
having to be handled and manipulated during surgery, the ball ring
44 is generally kept in the interior of the coupling element by
virtue of the nut 24 being captured in connection with the coupling
element. As used herein, the terminology "permanently pre-seated"
means that the elements are prevented from being inadvertently
removed from their respective bores, as opposed to being loose in a
package and requiring assembly of the individual components. Such a
pre-seated construction helps to prevent the surgeon from losing or
dropping small loose parts during preparation for a surgical
procedure.
In use, the components are removed from the package, and a fixation
element such as a screw 16 having a generally smooth, cylindrical
head portion 18 is inserted into the first bore 14 of the coupling
element and through the coaxial openings in the ball ring 44 and
locking nut 24. A spinal rod 38 is inserted in the second bore of
the coupling member. The set screw 40 may be tightened to exert
force on the spinal rod and lock the spinal rod in place. The
fixation element 16 may then be inserted into a bone, preferably
into a previously drilled pilot hole in the bone. The fixation
element is then preferably screwed into the bone using a driver or
other appropriate device, advancing the fixation element along its
longitudinal axis into the bone. Prior to tightening the locking
nut 24, the angle of the fixation element is adjusted by moving it
in the tapered opening 26 in the locking nut and the oppositely
tapered opening of the first bore 14. Due to the opposite taper of
the first bore 14 of the coupling element and the taper of the
opening in the locking nut 24, the fixation assembly can be
manipulated to cover a broader range of angles for capturing an
orthopedic stabilizing rod. The range of angles that can be covered
is 20 degrees polyaxially about the head portion 18 of the fixation
element. After the proper angulation is determined, the locking nut
is tightened, exerting a compressive radial force on the ball ring
and locking the head portion of the fixation element in place.
Preferably, the connector is locked in the manner described above
in two steps. However, according to certain procedures, the locking
nut may be tightened on the head portion of the fixation element
first, and then the set screw may be tightened on the spinal rod
after the locking nut has been tightened. Achieving sufficient
angulation between anchoring elements while engaging the orthopedic
rod is essential for assemblies mounted in spines having abnormal
curvatures. Sufficient angulation is also important in the
cervicothoracic junction of the spine.
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. For example, the bores for
receiving the spinal rods or heads of the fixation elements may
have non-circular cross-sectional shapes, such as square,
pentagonal, elliptical, etc. 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 and their equivalents.
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