U.S. patent application number 09/861278 was filed with the patent office on 2002-11-21 for spinal fixation apparatus and methods for use.
Invention is credited to Howland, Robert S..
Application Number | 20020173789 09/861278 |
Document ID | / |
Family ID | 25335367 |
Filed Date | 2002-11-21 |
United States Patent
Application |
20020173789 |
Kind Code |
A1 |
Howland, Robert S. |
November 21, 2002 |
SPINAL FIXATION APPARATUS AND METHODS FOR USE
Abstract
An anchor screw assembly includes a screw having a threaded
portion and a head portion to which a swing bolt is pivotally
coupled. A clamp assembly includes lower and upper clamp portions
that are securable on the swing bolt by a fastener. The clamp
portions include noncircular first passages for receiving a
noncircular region of the swing bolt therethrough to prevent
rotation of the clamp assembly on the swing bolt, and cooperating
grooves that together define a second passage. The head portion of
the screw includes a shoulder, and the lower clamp portion
frictionally engages the shoulder when the clamp assembly is fully
secured on the swing bolt, thereby securing the swing bolt relative
to the screw. Multiple screw assemblies are screwed into adjacent
vertebrae, and a rod is secured within the second passages between
the anchor screw assemblies to stabilize the vertebrae.
Inventors: |
Howland, Robert S.; (Seal
Beach, CA) |
Correspondence
Address: |
LYON & LYON LLP
633 WEST FIFTH STREET
SUITE 4700
LOS ANGELES
CA
90071
US
|
Family ID: |
25335367 |
Appl. No.: |
09/861278 |
Filed: |
May 17, 2001 |
Current U.S.
Class: |
606/264 ;
606/278; 606/279 |
Current CPC
Class: |
A61B 17/7041 20130101;
A61B 17/7038 20130101 |
Class at
Publication: |
606/61 |
International
Class: |
A61B 017/70 |
Claims
1. An anchor screw assembly for a spinal fixation system,
comprising: a screw having a first threaded portion terminating in
a tip, and a second head portion opposite the tip comprising a
shoulder; a swing bolt pivotally coupled to the second portion of
the screw; a clamp assembly comprising a first passage therethrough
for receiving the swing bolt therethrough, the clamp assembly
comprising a second passage extending substantially transversely to
the first axis when received on the hub; and a fastener for
securing the clamp assembly on the swing bolt, the clamp assembly
substantially engaging the shoulder when the clamp assembly is
secured on the swing bolt, thereby preventing the swing bolt from
pivoting with respect to the screw.
2. The anchor screw assembly of claim 1, wherein the swing bolt
comprises a noncircular region, and wherein the first passage
through the clamp assembly has a noncircular cross-section similar
to the noncircular region.
3. The anchor screw assembly of claim 2, wherein the noncircular
region has a noncircular cross-section configured to be received in
the first passage to prevent rotation of the clamp assembly about
the first axis with respect to the swing.
4. The anchor screw assembly of claim 2, wherein the noncircular
cross-section comprises a generally circular cross-section having
one or more flattened regions.
5. The anchor screw assembly of claim 2, wherein the first passage
comprises an elongate slot, having a length substantially longer
than the noncircular region of the swing bolt, whereby the swing
bolt may be disposed in a plurality of locations along the slot
while preventing rotation of the clamp assembly with respect to the
swing bolt.
6. The anchor screw assembly of claim 1, wherein the swing bolt
comprises a threaded region opposite the screw, and wherein the
fastener comprises a nut threadable onto the threaded region.
7. The anchor screw assembly of claim 6, wherein the swing bolt
comprises a smooth walled region for slidably receiving the clamp
assembly thereon, the smooth walled region being located between
the threaded region and the screw.
8. The anchor screw assembly of claim 1, wherein the clamp assembly
comprising first and second clamp portions, each clamp portion
having a first passage therethrough for receiving the hub of the
swing bolt therethrough, the first and second clamp portions having
cooperating grooves therein, the cooperating grooves together
defining the second passage when the first and second clamp
portions are received on the hub.
9. The anchor screw assembly of claim 8, wherein the shoulder is
radiused, and wherein the first clamp portion comprises a recess
adjacent a lower surface of the first clamp portion that intersects
the first passage, the recess having a radiused shape for pivotally
receiving the shoulder therein before the clamp assembly is fully
secured on the swing bolt.
10. The anchor screw assembly of claim 9, wherein the first passage
comprises an elongate slot, having a length substantially longer
than the noncircular region of the swing bolt, whereby the swing
bolt may be disposed in a plurality of locations along the slot
while preventing rotation of the clamp assembly with respect to the
swing bolt, and wherein the first clamp portion comprises a
plurality of recesses adjacent the lower surface of the first clamp
portion that intersects the first passage for pivotally receiving
the shoulder in one of a plurality of locations before the clamp
assembly is fully secured on the swing bolt.
11. An anchor screw assembly for a spinal fixation system,
comprising: a screw having a first threaded portion, and a second
portion; a swing bolt pivotally coupled to the second portion of
the screw, the swing bolt defining a first axis and comprising a
noncircular region extending along the first axis, the noncircular
region having a noncircular cross-section; a clamp assembly
comprising first and second clamp portions, each clamp portion
having a noncircular first passage therethrough for receiving the
noncircular region of the swing bolt therethrough, the first and
second clamp portions having cooperating grooves therein, the
cooperating grooves together defining a second passage extending
substantially transversely to the first axis when the first and
second clamp portions are received on the swing bolt; and a
fastener for securing the clamp assembly on the swing bolt.
12. The anchor screw assembly of claim 11, wherein the second
portion of the screw comprises a shoulder, and wherein the clamp
assembly substantially engages the shoulder when the clamp assembly
is fully secured on the swing bolt, thereby preventing the swing
bolt from pivoting with respect to the screw.
13. The anchor screw assembly of claim 12, wherein the shoulder is
radiused, and wherein the first clamp portion comprises a recess
adjacent a lower surface of the first clamp portion that intersects
the first passage, the recess having a radiused shape for pivotally
receiving the shoulder therein before the clamp assembly is fully
secured on the swing bolt.
14. The anchor screw assembly of claim 13, wherein the first
passage comprises an elongate slot, having a length substantially
longer than the noncircular region of the swing bolt, whereby the
swing bolt may be disposed in a plurality of locations along the
slot while preventing rotation of the clamp assembly with respect
to the swing bolt, and wherein the first clamp portion comprises a
plurality of recesses adjacent the lower surface of the first clamp
portion that intersects the first passage for pivotally receiving
the shoulder in one of a plurality of locations before the clamp
assembly is fully secured on the swing bolt.
15. The anchor screw assembly of claim 11, wherein the noncircular
cross-section of the noncircular region and the first passage
prevents rotation of the clamp assembly with respect to the swing
bolt about the first axis when the noncircular region of the swing
bolt is received in the first passages.
16. The anchor screw assembly of claim 11, wherein the noncircular
cross-section of the noncircular region comprises a generally
circular shape having one or more flattened regions.
17. The anchor screw assembly of claim 11, wherein the noncircular
region comprises a generally cylindrical shape having at least one
flattened region extending along the noncircular region.
18. The anchor screw assembly of claim 11, wherein the swing bolt
further comprises a threaded region opposite the screw, and wherein
the fastener comprises a nut threadable onto the threaded region of
the swing bolt.
19. The anchor screw assembly of claim 18, wherein the noncircular
region comprises a smooth walled region for slidably receiving the
clamp assembly thereon, the smooth walled region being located
between the threaded region and the screw, the threaded region
having a cross-section smaller than the noncircular region.
20. The anchor screw assembly of claim 11, wherein the clamp
assembly defines a third axis extending along a centerline of the
clamp assembly between the first passage towards the second
passage, and wherein the third axis is substantially perpendicular
to the second axis.
21. The anchor screw assembly of claim 11, wherein the clamp
assembly defines a third axis extending along a centerline of the
clamp assembly between the first passage towards the second
passage, and wherein the third axis defines an acute angle with the
second axis.
22. A spinal fixation system, comprising: a first anchor screw
assembly comprising a first screw having a threaded portion, a
swing bolt pivotally coupled to the screw and comprising a
noncircular region extending along a first longitudinal axis of the
swing bolt, a first clamp assembly comprising a first passage for
receiving the first swing bolt therethrough, the noncircular region
and the first passage having similar cross-sections, and a fastener
for securing the first clamp assembly on the swing bolt, the first
clamp assembly comprising a second passage therethrough along a
second axis substantially transverse to the first axis; a second
anchor screw assembly comprising a second screw having a threaded
portion and a hub, a second clamp assembly receivable on the hub,
and defining a third passage therethrough along a third axis
substantially transverse to the first axis; and an elongate member
receivable through the second and third passages.
23. The spinal fixation system of claim 22, wherein the hub is
fixed to the second screw.
24. The spinal fixation system of claim 22, wherein the hub is
pivotally attached to the second screw.
25. The spinal fixation system of claim 24, wherein the hub is
pivotable about an axis that is substantially perpendicular to an
axis about which the swing bolt is pivotable when the elongate
member is received through the second and third passages.
26. The spinal fixation system of claim 22, wherein the noncircular
cross-section of the noncircular region and the first passage
prevents rotation of the first clamp assembly about the first axis
with respect to the swing bolt when the noncircular region is
received through the first clamp assembly.
27. The spinal fixation system of claim 22, wherein the swing bolt
comprises a threaded region opposite the first screw, and wherein
the fastener comprises a nut threadable onto the threaded region of
the swing bolt.
28. The spinal fixation system of claim 27, wherein the noncircular
region comprises a smooth walled region for slidably receiving the
first clamp assembly thereon, the smooth walled region being
located between the threaded region and the first screw.
29. The spinal fixation system of claim 22, wherein the first clamp
assembly comprises first and second clamp portions, each clamp
portion having a first passage therethrough for receiving the first
hub therethrough, the first and second clamp portions having
cooperating grooves therein, the cooperating grooves together
defining the second passage when the first and second clamp
portions are received on the swing bolt.
30. The spinal fixation system of claim 22, wherein the second and
third passages have noncircular cross-sections, and wherein the
elongate member has a similar noncircular cross-section.
31. The spinal fixation system of claim 22, wherein the first screw
comprises a shoulder adjacent the swing bolt, and wherein the first
clamp assembly substantially engages the shoulder when the first
clamp assembly is secured on the swing bolt, thereby preventing the
swing bolt from pivoting with respect to the first screw.
32. An anchor screw assembly for a spinal fixation system,
comprising: an anchor screw having a first threaded portion, and a
second head portion defining a longitudinal axis, the head portion
comprising a noncircular region extending along the longitudinal
axis, the noncircular region having a noncircular cross-section,
the threaded portion comprising a pull-out portion adjacent the
head portion; a clamp assembly comprising upper and lower clamp
portions, each clamp portion having a noncircular first passage
therethrough for receiving the noncircular region of the head
portion therethrough to prevent substantial rotation of the clamp
assembly with respect to the head portion about the longitudinal
axis, the first and second clamp portions having cooperating
grooves therein, the cooperating grooves together defining a second
passage extending along a second axis substantially transversely to
the first axis when the first and second clamp portions are
received on the swing bolt, the upper clamp portion comprising a
lower surface including one of the cooperating grooves therein, and
an upper surface including a raised shoulder above the one of the
cooperating groove and a recessed area adjacent the raised shoulder
and above the first passage; and a nut for securing the clamp
assembly on the head portion, the nut being received in the
recessed area, thereby minimizing a height profile of the anchor
screw assembly.
33. The anchor screw assembly of claim 32, wherein the noncircular
cross-section of the noncircular region comprises a generally
circular shape having one or more flattened regions.
34. The anchor screw assembly of claim 32, wherein the head portion
is pivotally fixed to the threaded portion.
35. The anchor screw assembly of claim 32, wherein the head portion
is nonpivotally fixed to the threaded portion.
36. The anchor screw assembly of claim 32, wherein the clamp
assembly defines a third axis extending along a centerline of the
clamp assembly between the first passage towards the second
passage, and wherein the third axis is substantially perpendicular
to the second axis.
37. The anchor screw assembly of claim 32, wherein the clamp
assembly defines a third axis extending along a centerline of the
clamp assembly between the first passage towards the second
passage, and wherein the third axis defines an acute angle with the
second axis.
38. A method for stabilizing vertebrae relative to one another
using a plurality of swing bolt anchor screws, each swing bolt
anchor screw comprising a swing bolt pivotally coupled to a
threaded portion, the vertebrae being disposed adjacent one another
along a central spinal axis, the method comprising: screwing a
threaded portion of a first swing bolt anchor screw into a first
vertebra until a first pivot axis of the first swing bolt anchor
screw has a predetermined orientation with respect to the spinal
axis; screwing a threaded portion of a second swing bolt anchor
screw into a second vertebra adjacent the first vertebra until a
second pivot axis of the second swing bolt anchor screw is
substantially transverse to the first pivot axis; adjusting an
angle of one or more swing bolts on the first and second swing bolt
anchor screws about the first and second pivot axes; placing lower
clamp portions on the swing bolts of the first and second swing
bolt anchor screws; placing a rod on the lower clamp portions, the
rod extending at least between the first and second anchor screws;
and securing upper clamp portions on the swing bolts of the first
and second swing bolt anchor screws, thereby securing the rod
between the upper and lower clamp portions.
39. The method of claim 38, further comprising: screwing a threaded
portion of a third anchor screw into a third vertebra adjacent the
first vertebra; placing a lower clamp portion on the third anchor
screw; placing the rod on the lower clamp portion of the third
anchor screw, the rod thereby also extending between the first
swing bolt anchor screw and the third anchor screw; and securing an
upper clamp portion on the third anchor screw, thereby securing the
rod between the upper and lower clamp portions on the third anchor
screw.
40. The method of claim 39, wherein the third anchor screw
comprises a third swing bolt anchor screw, wherein the threaded
portion of the third swing bolt anchor screw is screwed into the
third vertebra until a third pivot axis of the third swing bolt
anchor screw is substantially transverse to the first pivot axis,
and wherein the lower and upper clamp portions are placed on a
swing bolt of the third swing bolt anchor screw.
41. The method of claim 40, further comprising adjusting an angle
of the swing bolt of the third swing bolt anchor screw about the
third pivot axis.
42. The method of claim 39, wherein the third anchor screw
comprises a nonpivotable anchor screw.
43. The method of claim 38, wherein the threaded portions of the
first and second swing bolt anchor screws comprise head portions
including shoulders, the swing bolts being pivotally coupled to the
head portions, and wherein the upper clamp portions are secured on
the swing bolts until the lower clamp portions frictionally engage
the shoulders, thereby securing the swing bolts with respect to the
threaded portions.
44. The method of claim 38, wherein the swing bolts comprise
noncircular regions, and wherein the upper and lower clamp portions
comprise noncircular passages for engaging the noncircular regions
when received on the swing bolts, thereby preventing the upper and
lower clamp portions from rotating with respect to the swing
bolts.
45. The method of claim 38, wherein the swing bolts comprise
threaded regions, and wherein the upper clamp portions are secured
on the swing bolts by threading a fastener onto the threaded
regions.
46. The method of claim 38, further comprising bending the rod to a
predetermined configuration based upon anatomy encountered before
securing the upper clamp portions on the swing bolts.
47. The method of claim 38, wherein the predetermined orientation
of the first pivot axis is generally parallel to the spinal axis.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to apparatus and
methods for treating spinal disorders, and more particularly to
anchor screw assemblies, spinal fixation systems including such
anchor screw assembles, and methods for stabilizing, adjusting, or
otherwise fixing adjacent vertebrae using such spinal fixation
systems.
BACKGROUND
[0002] Various systems and methods have been suggested for treating
spinal disorders, such as degenerative discs, stenosis, trauma,
scoliosis, kyphosis, or spondylolisthesis. For example, U.S. Pat.
No. 5,545,166, naming the same inventor as the present application,
discloses a spinal fixation system that includes a plurality of
anchor screws, clamp assemblies, pivot blocks, clamp blocks, and
rods that are implanted along a patient's spine to fix two or more
adjacent vertebrae relative to one another. The system generally
includes a swing bolt anchor screw, a pivot block receivable on the
swing bolt, and a clamp block receiving a rod therethrough that is
pivotally attachable to the pivot block. In addition, the system
includes one or more fixed anchor screws, and clamp assemblies for
receiving the rod therein. The clamp assemblies and pivot block are
receivable on the anchor screws by spindles that thread along a
threaded portion of the anchor screws.
[0003] During use, vertebrae to be treated are surgically exposed,
and an arrangement of anchor screws and clamp accessories are
selected. For example, a fixed anchor screw may be screwed into
each of the vertebrae on either side of a first vertebra. A rod is
selected that may extend between the fixed anchor screws and that
may be bent to conform to the shape of the anatomy encountered. The
rod is inserted through a loose clamp block, and the rod is placed
in clamp assemblies that are received over the fixed anchor
screws.
[0004] A swing bolt anchor screw is then screwed into the first
vertebra adjacent the rod, and a pivot block is received on the
swing bolt screw. The clamp block and/or pivot block are adjusted
such that the clamp block may be engaged with a pivot on the pivot
block. A set screw may then be screwed into the clamp block to
secure the clamp block to the pivot. A pair of set screws are also
screwed into the clamp block to secure the rod within the clamp
block. Preferably, a pair of such systems are implanted on either
side of the vertebrae.
[0005] During the procedure, it may be desirable to adjust the
vertebrae relative to one another. Once the system(s) is(are)
connected as described above, the set screws may be loosened and
the rod(s), clamp block(s), and/or pivot block(s) may be adjusted,
e.g., by moving the spindle(s) to adjust the height of the pivot
block(s) and/or clamp assemblies on the anchor screws, by pivoting
the swing bolt anchor screw(s), and/or pivoting the clamp block(s)
relative to the pivot block(s). Once the vertebrae have been moved
into a desired position, the set screws may be tightened, and the
spindles secured in position by crimping the walls surrounding the
spindles.
[0006] An advantage of this system is that the swing bolt anchor
screw, pivot block, and clamp block arrangement allows adjustment
of the system about two axes, i.e., the axis of the swing bolt
anchor screw and the axis of the pivot on the pivot block. However,
because the system of the '166 patent is polyaxial, i.e., may pivot
about multiple axes, there is greater risk of the system coming out
of alignment when the patient resumes normal physical activity.
[0007] This system is also very complicated, involving six parts,
including three set screws, that are mounted on each swing bolt
anchor screw. In addition, because the swing bolt is threaded, an
intricate spindle device is required in order to allow the pivot
block and clamp assemblies to be threaded onto the swing bolt, and
still control their orientation about the axis of the swing bolt.
Thus, because of its complexity and many intricate parts, this
system may be expensive to manufacture and/or difficult to
implant.
[0008] Accordingly, apparatus and methods for stabilizing,
adjusting, and/or fixing vertebrae would be considered useful.
SUMMARY OF THE INVENTION
[0009] The present invention is directed to anchor screw
assemblies, spinal fixation systems including such anchor screw
assembles, and methods for stabilizing, adjusting, or otherwise
fixing adjacent vertebrae using such spinal fixation systems.
[0010] In accordance with one aspect of the present invention, an
anchor screw assembly is provided that includes a screw having a
first threaded portion, and a second head portion. A swing bolt is
pivotally coupled to the second portion of the screw. The swing
bolt defines a first axis, and includes a noncircular region
extending along the first axis, the noncircular region having a
noncircular cross-section and a substantially smooth wall. In
addition, the swing bolt may include a threaded region on its end
opposite the screw.
[0011] A clamp assembly is provided that includes first and second
clamp portions that are receivable on the swing bolt. Each clamp
portion has a noncircular first passage therethrough for receiving
the noncircular region of the swing bolt therethrough. Thus, the
noncircular region and the first passage have like cross-sections,
thereby preventing rotation of the clamp assembly with respect to
the swing bolt about the first axis when the noncircular region of
the swing bolt is received in the first passages.
[0012] In addition, the first and second clamp portions have
cooperating grooves therein, the cooperating grooves together
defining a second passage extending along a second axis
substantially transversely to the first axis when the first and
second clamp portions are received on the swing bolt. The clamp
assembly also defines a third axis extending along a centerline of
the clamp assembly, e.g., from the first passage towards the second
passage. The second axis, and consequently the second passage, may
extend substantially perpendicular to the third axis, or may define
an acute angle with the third axis.
[0013] A fastener is also provided for securing the clamp assembly
on the swing bolt. Preferably, the fastener is a nut, such as a
twelve (12) point nut or a hex nut, that may be threaded onto the
threaded region of the swing bolt to secure the clamp assembly on
the swing bolt.
[0014] In a preferred embodiment, the second portion of the screw
includes a shoulder, and the clamp assembly may substantially
engage the shoulder when the clamp assembly is fully secured on the
swing bolt, thereby preventing the swing bolt from pivoting with
respect to the screw. More preferably, the shoulder is radiused
about a pivot point on the second portion, and the lower clamp
portion includes a recess adjacent its lower surface that
intersects the first passage. The recess has a matching radiused
shape for slidably receiving the shoulder therein as the clamp
assembly pivots about the pivot point, i.e., before the clamp
assembly is fully secured on the swing bolt.
[0015] In accordance with another aspect of the present invention,
a spinal fixation system is provided that includes a first anchor
screw assembly, such as that described above. The first anchor
screw assembly includes a first screw having a threaded portion,
and a swing bolt pivotally coupled to the screw and including a
noncircular region. The spinal fixation system also includes a
plurality of clamp assemblies, including a first passage for
receiving the first swing bolt therethrough, and a second passage
for receiving an elongate member, e.g., a substantially rigid rod,
therethrough. The dimensions of each clamp assembly may be
different, e.g., including a second passage that is at one of a
plurality of distances from the first passage and/or that is
oriented at a predetermined angle along the clamp assembly.
[0016] For example, a first clamp assembly may include a first
passage for receiving the first swing bolt therethrough. The first
passage has a similar cross-section to the noncircular region of
the swing bolt. The first clamp assembly includes a second passage
therethrough along a second axis substantially transverse to the
first axis. A fastener may be used for securing the first clamp
assembly on the swing bolt. Thus, when the first clamp assembly is
received on the first swing bolt, the first clamp assembly is fixed
in a predetermined orientation with respect to a first pivot axis
of the first swing bolt.
[0017] The spinal fixation system also includes a second anchor
screw assembly including a second screw having a threaded portion
and a hub, and a second clamp assembly receivable on the hub. The
second screw may be a fixed screw or, preferably, a swing bolt
anchor screw, similar to that described above. The second clamp
assembly includes a third passage therethrough along a third axis.
The second screw assembly may be oriented, when implanted, such
that the third axis is substantially transverse to the first axis.
Optionally, additional anchor screw assemblies may also be
provided.
[0018] Finally, the spinal fixation system also include an elongate
member, such as a substantially rigid rod, that is receivable
through the second and third passages.
[0019] In accordance with another aspect of the present invention,
a method is provided for simple alignment or otherwise stabilizing
vertebrae relative to one another using a plurality of swing bolt
anchor screw assemblies, such as those described above. A threaded
portion of a first swing bolt anchor screw is screwed into a first
vertebra until a first pivot axis of the first swing bolt anchor
screw is generally parallel to the spinal axis. A threaded portion
of a second swing bolt anchor screw is screwed into a second
vertebra adjacent the first vertebra until a second pivot axis of
the second swing bolt anchor screw is substantially transverse to
the first pivot axis. If desired, a third anchor screw (or more)
may be screwed into other vertebra adjacent to the first
vertebra.
[0020] An angle of one or more swing bolts on the first and second
swing bolt anchor screws may be adjusted about the first and second
pivot axes. Lower clamp portions may be placed on the swing bolts
of the first and second swing bolt anchor screws, either before or
after the angle adjustments described above. A rod may be placed on
the lower clamp portions, e.g., when the grooves in the lower clamp
portions have been properly aligned with one another. Thus, the rod
may extend between the first and second anchor screws, and between
any additional anchor screws added generally in a straight line. In
addition, if desired, the rod may be bent, e.g., in a single plane,
to a predetermined configuration based upon anatomy encountered
before securing the rod on the swing bolts. Preferably, the rod is
bent and secured to the clamp assemblies such that it is curved in
the sagetal plane (the plane that may be seen from a lateral view
of the patient) and substantially straight in the coronal plane
(the plane that may be seen from an anterior or posterior view of
the patient).
[0021] Upper clamp portions may be secured on the swing bolts of
the first and second swing bolt anchor screws, thereby securing the
rod between the upper and lower clamp portions. For example, a nut
or other fastener may be threaded onto the swing bolt after the
upper and lower clamp portions, thereby securing the rod between
the upper and lower clamp portions and/or securing the clamp
assemblies on the swing bolts. These fasteners may also be loosened
to allow adjustment of the vertebrae relative to one another, and
then the fasteners may again be tightened to fix the vertebrae in
desired relative positions.
[0022] Other objects and features of the present invention will
become apparent from consideration of the following description
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1A is a perspective view of a preferred embodiment of
an anchor screw assembly, in accordance with the present
invention.
[0024] FIG. 1B is an exploded perspective view of the anchor screw
assembly of FIG. 1A.
[0025] FIGS. 2A and 2B are perspective and side views,
respectively, of a screw for the anchor screw assembly of FIGS. 1A
and 1B.
[0026] FIGS. 3A-3C are perspective and first and second side views,
respectively, of a swing bolt for the anchor screw assembly of
FIGS. 1A and 1B.
[0027] FIGS. 4A-4C are perspective and first and second side views,
respectively, of an assembled screw and swing bolt for the anchor
screw assembly of FIGS. 1A and 1B.
[0028] FIGS. 5A-5C are perspective and first and second side views,
respectively, of a first embodiment of a lower clamp portion for a
clamp assembly, in accordance with the present invention.
[0029] FIGS. 6A-6C are perspective and first and second side views,
respectively, of a first embodiment of an upper clamp portion for a
clamp assembly, in accordance with the present invention.
[0030] FIGS. 7A-7E are perspective views of alternative embodiments
of a lower clamp portion, in accordance with the present
invention.
[0031] FIGS. 8A-8E are perspective views of alternative embodiments
of an upper clamp portion, in accordance with the present
invention.
[0032] FIGS. 9A and 9B are perspective and side views,
respectively, of another embodiment of an anchor screw, in
accordance with the present invention.
[0033] FIGS. 10A-10C show a spinal fixation system being implanted
between vertebrae of a patient, in accordance with the present
invention.
[0034] FIG. 11 shows a pair of spinal fixation systems implanted
along a patient's spine.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] Turning now to the drawings, FIGS. 1-6 show a first
preferred embodiment of an anchor screw assembly 10, in accordance
with the present invention. Generally, the anchor screw assembly 10
includes a screw 12, a swing bolt 14 pivotally coupled to the screw
12 to provide an anchor screw 15, and a clamp assembly 16 securably
received on the swing bolt 14, as shown in FIGS. 1A and 1B. All of
the components of the anchor screw assembly 10 may be made from a
variety of biocompatible materials, e.g., metals, and preferably
from titanium or alloys including titanium.
[0036] With particular reference to FIGS. 2A and 2B, the screw 12
generally includes a first threaded portion 20 terminating in a tip
22, and a second head portion 24 opposite the tip 22. The threaded
portion 20 may include a helical thread 21 defining a thread
pattern, preferably configured for substantially securing the screw
12 into bone, such as a portion of a vertebra (not shown). The
thread spacing may be between about three to six threads per
centimeter (3-6 threads/cm), and preferably about 4.8 threads per
centimeter (about 12 threads per inch). The thread spacing may be
substantially constant between the tip 22 and the head portion 24
or may vary along the length of the threaded portion 20.
[0037] The leading and trailing edges of axially adjacent portions
of the thread 21 may define an inclusive angle "alpha" between them
of between about twenty to forty degrees (20-40.degree.), and
preferably about thirty degrees (30.degree.). Preferably, each
thread 21 tapers outwardly from the root diameter to the major
diameter of the thread 21, such that the leading and trailing edges
on either side of a portion of the thread 21 define tangent lines
that intersect one another adjacent the outer edge of the
respective portion of the thread 21. The thread 21 may have a
height of between about 0.50-3.00 millimeters, and preferably
between about 0.60-2.00 millimeters.
[0038] The threaded portion 20 may have desired dimensions to
accommodate threading into bone, such as a vertebra (not shown).
For example, the threaded portion 20 may have an outer diameter
between about 3.5-8.5 millimeters, preferably between about 5.8-8.5
millimeters, and a length between about 25-65 millimeters, and
preferably between about 35-65 millimeters. The threaded portion 20
may have a substantially uniform major and minor diameter along its
length. Alternatively, the threaded portion 20 may have a taper,
e.g., reducing in minor and/or major diameter from the head portion
24 towards the tip 22. The thread 21 may have a substantially
uniform height, or may become increasingly higher from the head
portion 24 towards the tip 22, e.g., if the threaded portion 20 is
tapered, to provide a substantially uniform outer diameter for the
threaded portion 20.
[0039] Preferably, the threaded portion 20 includes a pull-out
portion 21A. For example, the final two threads 21A before the head
portion 24 may include a minor diameter that gradually expands out
to the major diameter. In addition or alternatively, the final two
threads 21A may have a plateau on their outer edge. This pull-out
portion 21A may facilitate manufacturing of the anchor screw 12
and/or may improve engagement of the screw 12 with bone into which
the screw 12 is threaded. Other thread patterns and screw designs
that may be appropriate for use in an anchor screw assembly in
accordance with the present invention may be found in U.S. Pat.
Nos. 4,854,311, 5,034,011, and 5,226,766, the disclosures of which
are expressly incorporated herein by reference.
[0040] The head portion 24 generally has a cross-section larger
than the threaded portion 20 and includes a full-radius shoulder 28
opposite the threaded portion 20. The shoulder 28 includes a
predetermined radius about a pivot axis 35 to facilitate pivoting
of the swing bolt 14 and/or the clamp assembly 16 (not shown in
FIGS. 2A and 2B) with respect to the head portion 24, as explained
further below. The head portion 24 includes a slot 30 therein
extending generally parallel to a longitudinal axis 32 of the screw
12, thereby dividing the head portion 24 into ears 26. Pin holes 34
extend through the ears 26 along the pivot axis 35, i.e.,
substantially perpendicular to the longitudinal axis 32.
[0041] Turning to FIGS. 3A-3C, the swing bolt 14 includes an
elongate body 34 including a first looped region 36, a second
noncircular intermediate region 38, and a third threaded region 40
generally opposite the looped region 36. The looped region 36 may
be substantially narrower than the other regions of the swing bolt
14, i.e., having a width slightly smaller than a width of the slot
30 in the screw 12 such that the looped region 36 may be received
in the slot 30 between the ears 26, as shown in FIGS. 4A-4C. The
looped region 36 has a pin hole 37 therethrough that extends
substantially perpendicular to the longitudinal axis 32.
[0042] The noncircular region 38 of the swing bolt 14 is preferably
substantially smooth-walled and has a noncircular cross-section,
preferably for slidably receiving the clamp assembly 16 thereon
(see FIGS. 1A and 1B), while preventing rotation of the clamp
assembly 16 about longitudinal axis 33. In the preferred embodiment
shown in FIGS. 3A-3C, one or more flat walls 42, and preferably two
opposing flat walls, are formed along the no intermediate region
38. Thus, the cross-section may define a parallel side shape, a "D"
shape, or, alternatively, a hexagon, a square, a star, or other
geometric shape.
[0043] As shown in FIGS. 4A-4C, the looped region 36 of the swing
bolt 14 may be received in the slot 30 of the head portion 24, and
a pin 44 may be received through the pin holes 34, 37 to provide
anchor screw 15. The pin 44 may fix the swing bolt 14 to the screw
12, while allowing the swing bolt 14 and screw 12 to pivot with
respect to one another such that the longitudinal axes 32, 33
intersect, but define an angle "theta" greater than zero degrees,
as shown in phantom in FIG. 4B.
[0044] Turning to FIGS. 5A-6C, the clamp assembly 16 (shown in
FIGS. 1A and 1B) generally includes a first lower clamp portion 52
and a second upper clamp portion 72. The lower and upper clamp
portions 52, 72 have noncircular bolt passages 54, 74 that extend
entirely through them between lower surfaces 56, 76 and upper
surfaces 58, 78, respectively, thereby defining a first axis 60.
The bolt passages 54, 74 preferably have a cross-section similar to
the cross-section of the noncircular region 42 of the swing bolt 14
(see FIGS. 1B, 3A, 3B, 4A, and 4B). Thus, the bolt passages 54, 74
may accommodate receiving the swing bolt 14 therethrough, while
preventing rotation of the clamp assembly 16 on the swing bolt 14,
as explained further below.
[0045] In addition, the lower and upper clamp portions 52, 72 have
generally semi-cylindrical grooves 62, 82 therein that cooperate
with one another when the clamp assembly 16 is assembled to define
a rod passage 64, as shown in FIG. 1A. The rod passage 64 generally
extends along a second axis 66 that is substantially transverse to,
and preferably substantially perpendicular to, the first axis 60.
In the embodiment shown, the second axis 66 is also substantially
perpendicular to a third axis 70 that extends along a length of the
lower clamp portion 52 substantially perpendicular to both the
first and second axes 60, 66 (thus, the three axes 60, 66, 70 may
be orthogonal to one another). The rod passage 64 has a
cross-section similar to a rod (not shown) that may be received
therein. For example, the cross-section may be generally circular,
but preferably is noncircular, e.g., circular with one or more
flattened walls, such as wall 83 shown in the upper clamp portion
72 in FIGS. 6B and 6C. Alternatively, the rod passage 64 may have
other geometric shapes, similar to the bolt passages 54, 74,
described above. In a further alternative, one or both of the
grooves 62, 82 may include teeth or other serrations (not shown)
for enhancing engagement with a rod received in the rod passage 64,
either alone or in combination with one of the cross-sections
described above. Exemplary serrations are shown in U.S. Pat. No.
5,545,164, the disclosure of which is expressly incorporated herein
by reference.
[0046] With particular reference to FIGS. 6A-6C, the groove 82 in
the upper clamp portion 72 extends along the lower surface 76. The
upper surface 78 may be recessed above the bolt passage 174,
thereby accommodating a fastener (not shown) thereon, while
minimizing the profile of the resulting clamp assembly. For
example, the groove 82 may define a shoulder 79 that may be higher
than the upper surface 78. The shoulder 79 may have a height
similar to a nut or other fastener (not shown) that may be attached
to a swing bolt (also not shown) that is inserted through the bolt
passage 74. Thus, when the fastener engages the upper surface 78,
the upper surface of the fastener may define a height similar to
the shoulder 79, thereby substantially minimizing a profile of the
anchor screw assembly and/or reducing tissue irritation.
[0047] With particular reference to FIGS. 5A-5C, the groove 62 in
the lower clamp portion 52 extends along the upper surface 58. In
addition, the lower clamp portion 62 also includes a recess 68 in
the lower surface 56 that intersects the bolt passage 54. The
recess 68 preferably has a radius of curvature similar to the
shoulder 28 on the head portion 24 of the screw 12 (see FIGS.
4A-4C), as explained further below.
[0048] Returning to FIGS. 1A and 1B, the lower surface 76 of the
upper clamp portion 72 and the upper surface 58 of the lower clamp
portion 52 are substantially flat such that the lower and upper
clamp portions 52, 72 may substantially abut one another to provide
the rod passage 64. Alternatively, the upper and lower surfaces 58,
76 may include mating segments, e.g., cooperating tabs and slots or
other male/female connectors (not shown), that may positively
engage one another when the lower and upper clamp portions 52, 72
are disposed in the proper orientation.
[0049] The clamp assembly 16 may be received on the swing bolt 14,
e.g., by orienting the clamp assembly 16 such that the bolt
passages 54, 74 are properly aligned with the noncircular region of
the swing bolt. The lower clamp portion 52 may be directed over the
swing bolt 14 and then the upper clamp portion 72 may be received
over the swing bolt 14, i.e., through the bolt passages 54, 74,
respectively. A fastener, e.g., nut 18, may be threaded onto the
threaded region 40 of the swing bolt 14 until it engages upper
surface 78 of the upper clamp portion 72, thereby forcing the clamp
assembly 16 towards the head portion 24 of the screw 12.
Consequently, the lower clamp portion 52 may abut the head portion
24 such that the shoulder 28 is received in the recess 68 in the
lower surface 56.
[0050] Preferably, because of the mating shapes of the shoulder 28
and recess 68, the lower clamp portion 52 may slide along the
shoulder 28 as the swing bolt 14 is pivoted with respect to the
screw 12. Once a desired angle is obtained, the nut 18 may be
further tightened until the wall of the recess 68 frictionally
engages the shoulder 28, thereby substantially securing the swing
bolt 14 at the desired angle relative to the screw 12.
[0051] Turning to FIGS. 7A-8E, several alternative embodiments of
lower and upper clamp portions are shown that together may provide
clamp assemblies that may be received over the screw assembly 15 of
FIGS. 4A-4C. For example, the lower and upper clamp portions 152,
172 shown in FIGS. 7A and 8A are generally similar to that shown in
FIGS. 5A and 6A, except that the flat regions 155, 175 of the bolt
passages 154, 174 are offset ninety degrees from the previous
embodiment. The resulting clamp assembly (not shown) may be mounted
similar to the previous embodiment, but offset ninety degrees with
respect to the anchor screw (not shown).
[0052] Turning to FIGS. 7B and 8B, another set of lower and upper
clamp portions 252, 272 are shown that are similar to the to
embodiments of FIGS. 7A and 8A, except that the grooves 262, 282
are located further away from the bolt passages 254, 274 along the
third axis 270. The resulting clamp assembly from these embodiments
may be mounted on the anchor screw similar to the previous
embodiment. A rod received in the resulting rod passage, however,
will be disposed further from the anchor screw than the previous
embodiment.
[0053] Turning to FIGS. 7C and 8C, yet another set of lower and
upper clamp portions 352, 372 are shown that are similar to the
embodiments of FIGS. 7A and 8A, except that the bolt passages 354,
374 have an elongated elliptical shape extending along the third
axis 370. In addition, the lower surface 356 of the lower clamp
portion 352 includes adjacent recesses 368, 369 that intersect the
bolt passage 354 and may overlap one another. The resulting clamp
assembly from this embodiment may be secured to the anchor screw
such that either of the recesses 368, 369 slidably engages the
shoulder of the screw (not shown), thereby allowing a rod (also not
shown) received in the rod passage to be disposed at two possible
locations, e.g., distances, relative to the anchor screw.
optionally, more than two recesses (not shown) may be provided,
thereby allowing the rod passage to be disposed at multiple
distances from the anchor screw.
[0054] Turning to FIGS. 7D and 8D, still another set of lower and
upper clamp portions 452, 472 are shown that are similar to the
embodiments of FIGS. 5A and 6A, except that the grooves 462, 482
are aligned such that the second axis 466 defines an angle "beta"
with the third axis 470. Preferably, the angle "beta" is between
about ten and seventy degrees (10-75.degree.), and more preferably
between about forty five and sixty degrees (45-60.degree.). In
addition, the flattened wall regions 455, 475 are aligned
substantially parallel to the second axis 466, thereby also
defining an angle "beta" with respect to the third axis 470.
[0055] Turning to FIGS. 7E and 8E, another set of lower and upper
clamp portions 552, 572 are shown that are similar to the
embodiments of FIGS. 7D and 8D, except that the bolt passages 554,
574 and grooves 562, 582 are mirror opposites or opposite-hand of
those in the previous embodiment. Thus, it will be appreciated by
those skilled in the art that a variety of clamp assemblies may be
providing including a range of dimensions, e.g., lengths,
thicknesses, "beta" angles, and the like.
[0056] Turning to FIGS. 9A and 9B, another preferred embodiment of
an anchor screw 90 is shown that includes a threaded portion 92
terminating in a tip 93, and an enlarged head portion 94 including
a noncircular region 96 and a threaded region 98 opposite the tip
93. The threaded portion 92 may include any of the dimensions
described above for the anchor screw 12 of FIGS. 2A-2C, e.g.,
thread pattern, outer diameter, taper, and the like. Preferably,
the threaded portion 92 includes a pull-out portion 92A, similar to
the swing bolt anchor screw 12. The noncircular region 96 has a
cross-section similar to the previously described embodiments,
e.g., a generally circular cross-section with one or more flattened
wall regions 97. A raised ledge 95 may be provided between the
noncircular region 96 and the threaded portion 92.
[0057] The threaded region 98 may receive a fastener, such as the
nut described above (not shown), e.g., to substantially secure a
clamp assembly (also not shown) on the noncircular region 96,
similar to the embodiment described above. Thus, the anchor screw
90 may receive any of the clamp assemblies described above.
[0058] To provide a system for treating vertebrae of a patient, a
set of anchor screws, e.g. pivoting and/or fixed, clamp assemblies,
and fasteners may be selected based upon the specific vertebrae
being treated and/or based upon the anatomy encountered. A system
in accordance with the present invention provides a modularity that
may easily accommodate a variety of anatomy and patients.
[0059] Turning to FIGS. 10A-10C and 11, an exemplary system 1000 is
shown that includes a pair of rods 1002 that are each implanted
along a spinal column using three swing bolt anchor screws
1010-1014 and three clamp assemblies, 1016-1020. Alternatively, one
or more of the swing bolt anchor screws, such as the outside anchor
screws 1010, 1014, may be replaced with nonpivoting anchor screws
(such as that shown in FIGS. 9A and 9B). In a further alternative,
fewer or additional anchor screws may be implanted, e.g., to secure
a shorter or longer rod and/or to fix fewer or additional
vertebrae.
[0060] Preferably, the rods 1002 are implanted generally parallel
to the central spinal axis on either side of the spinous processes
902, as shown in FIG. 11. The system 1000 may be used to provide
adjustment of the vertebrae, e.g., to allow vertical or horizontal,
medial or lateral adjustment. Although an implantation procedure
for only one rod 1002 is described below, it will be appreciated
that a second rod (or even additional rods) may be implanted using
a similar procedure.
[0061] Turning first to FIG. 10A, the vertebrae, e.g., vertebrae
910, 920, 930, to be stabilized are exposed, e.g., using
conventional surgical procedures. The anchor screws 1010-1014 are
screwed into the vertebrae 910-930, respectively, e.g., into the
pedicles, generally in a substantially straight line. Preferably,
the anchor screws 1012-1014 are screwed in sufficiently to provide
a predetermined pivot axis with respect to a centerline spinal axis
of the patient. For example, the anchor screw 1012 may be screwed
until a pivot axis 1032 of the anchor screw 1012 is disposed
generally parallel to the centerline spinal axis. In contrast, the
other anchor screws 1010, 1014 may be screwed into their respective
vertebra until their respective pivot axes 1030, 1034 are disposed
substantially transverse to the first pivot axis 1032, and
preferably substantially perpendicular to the centerline spinal
axis.
[0062] Clamp assemblies 1016-1020 are selected based upon the
anatomy encountered. For example, the clamp assembly 1016 may be
similar to the clamp assembly 152, 172 shown in FIGS. 7A and 8A,
and the clamp assembly 1018 may be similar to the clamp assembly
252, 272 of FIGS. 7B and 8B, i.e., having a longer length than the
clamp assembly 1016. Finally, the clamp assembly 1020 may be
similar to the clamp assembly 552, 572 shown in FIGS. 7E and 8E,
i.e., having a groove 1028a (see FIG. 10A) that extends acutely
with respect to a centerline length of the clamp assembly 1020.
[0063] The lower clamp portions of the clamp assemblies 1016a-1020a
may be received over the noncircular regions (not shown) of the
anchor screws 1010-1014, as best seen in FIG. 10A. A rod 1002 may
be received in the grooves 1024a-1028a in the lower clamp portions
1016a-1020a, thereby extending between the anchor screws 1010-1014,
as shown in FIG. 10B. If desired, the rod 1002 may be bent to a
predetermined shape, as needed, to conform to the anatomy
encountered. Preferably, the rod 1002 is bent in only one plane,
e.g., the sagetal plane, while remaining substantially straight in
the coronal plane. "Sagetal" plane, as used herein, refers to the
plane that may be seen from a lateral view of the patient, e.g.,
that is disposed vertically when the patient is lying face-down.
"Coronal" plane refers to the plane that may be seen from an
anterior or posterior view of the patient, e.g., that is disposed
substantially horizontally when the patient is lying face-down.
[0064] In addition, if the rod 1002 includes one or more flattened
regions 1004, the flattened region(s) 1004 may be oriented so that
they may engage similar flattened regions (not shown) in the rod
passages 1024-1028 in the clamp assemblies 1016-1020 (e.g., in the
upper clamp portions 1016b-1020b).
[0065] One or more of the clamp assemblies 1016-1020 may be
adjusted at any time during the procedure. By adjusting the clamp
assemblies 1016-1020, the swing bolts on the anchor screws
1010-1014 may be pivoted about their respective pivot axes
1030-1034 with respect to the threaded portions that have been
threaded into the vertebrae 910-930. For example, the lower clamp
portions 1016a-1020a may be adjusted before and/or after the rod
100 is received in the grooves 1024a-1028a. Because the pivot axes
1030-1034 of the swing bolt anchor screws 1010-1014 are
substantially transverse with respect to one another, a uniaxial
device (i.e., pivoting in a single axis) may be used to provide
multiple degrees of freedom for moving the clamp assemblies
1016-1020 relative to the rod 1002. This may minimize the amount of
bending required of the rod 1002, preferably requiring bending in
only one plane (preferably, the sagetal plane), thereby
substantially maximizing the rigidity of the rod 1002.
[0066] As shown in FIG. 10C, upper clamp portions 1016b-1020b may
be placed on the lower clamp portions 1016a-1020a, i.e., received
on the swing bolts of the anchor screws 1010-1014. When properly
placed, the grooves (not shown) in the upper clamp portions
1016b-1020b substantially engage the rod 1002. Fasteners, such as
nuts 1022, may then by threaded onto the swing bolts, thereby
substantially securing the rod 1002 between the upper and lower
clamp portions 1016-1020.
[0067] Preferably, the nuts 1022 are twelve point jam nuts. The
nuts 1022 may have rounded upper edges, which may minimize tissue
irritation, e.g., of tissue overlying the nuts 1022 after
implantation of the system 1000. In addition, the nuts 1022 may
include a crimpable rim (not shown), which may be crimped when the
nuts are tightened to a desired torque, e.g., to prevent subsequent
loosening of the nuts. Alternatively, hex nuts or other fasteners
may be used.
[0068] Preferably, the lower clamp portions 1016a-1020a include
recesses (not shown) that intersect bolt passages through them and
the threaded portion of the anchor screws 1010-1014 include
radiused shoulders (not shown), as described above. Thus, as the
angles of the swing bolts are adjusted, the shoulders may pivotally
slide along the surfaces of the recesses of the lower clamp
portions 1016a-1020a. Once a desired configuration is obtained, the
nuts 1022 may be tightened, thereby causing the lower clamp
portions 1016a-1020a to frictionally engage the shoulders and
secure the swing bolts with respect to the threaded portions
without substantially moving one or more of the vertebrae out of
the desired position.
[0069] If it desired to adjust the vertebrae 910-930 with respect
to one another, the nuts 1022 may be loosened, and the vertebrae
910-930 adjusted, thereby possibly changing the angle of one or
more of the clamp assemblies 1016-1020 holding the rod 1002. Once a
desired arrangement is obtained, the nuts 1022 may be tightened,
thereby securing the clamp assemblies 1016-1020. Thus, with a
system in accordance with the present invention, each individual
clamp assembly is uniaxial, i.e., may only be pivoted about a
single axis. By setting the axes of the anchor screws substantially
transverse relative to one another, substantially flexibility may
be obtained without substantially compromising vertebra position.
Because of the uniaxial nature of the clamp assemblies, however,
the system may be less likely to become misaligned when the patient
resumes normal activity than a polyaxial system.
[0070] While the invention is susceptible to various modifications,
and alternative forms, specific examples thereof have been shown in
the drawings and are herein described in detail. It should be
understood, however, that the invention is not to be limited to the
particular forms or methods disclosed, but to the contrary, the
invention is to cover all modifications, equivalents and
alternatives falling within the spirit and scope of the appended
claims.
* * * * *