U.S. patent application number 12/138217 was filed with the patent office on 2008-12-18 for system and method for polyaxially adjustable bone anchorage.
This patent application is currently assigned to ROBERT REID, INC.. Invention is credited to Joshua A. Butters, Joseph Q. Marietta.
Application Number | 20080312697 12/138217 |
Document ID | / |
Family ID | 40133053 |
Filed Date | 2008-12-18 |
United States Patent
Application |
20080312697 |
Kind Code |
A1 |
Butters; Joshua A. ; et
al. |
December 18, 2008 |
System and Method for Polyaxially Adjustable Bone Anchorage
Abstract
An implantable bone anchor assembly for fixing an elongated
member such as a spinal rod may include a bone anchor, a coupling
head configured to receive the bone anchor and the elongated
member, and a locking mechanism. The locking mechanism may provide
compressive force to simultaneously fix the position of the
elongated member and lock out polyaxial rotation of the bone anchor
relative to the coupling head. The locking mechanism may include an
engagement member with an oblique surface configured to slide along
an oblique surface of the coupling head into engagement with the
elongated member. The bone anchor may comprise a head portion and a
threaded portion which may be coupled with the coupling head and
joined together during manufacture. The assembly may further
include a pin and/or a collar to retain the bone anchor. The bone
anchor may be side-loaded into the coupling head.
Inventors: |
Butters; Joshua A.;
(Chandler, AZ) ; Marietta; Joseph Q.; (Hyde Park,
UT) |
Correspondence
Address: |
MEDICINELODGE INC.
180 SOUTH 600 WEST
LOGAN
UT
84321
US
|
Assignee: |
ROBERT REID, INC.
Tokyo
JP
|
Family ID: |
40133053 |
Appl. No.: |
12/138217 |
Filed: |
June 12, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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60944321 |
Jun 15, 2007 |
|
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|
61029467 |
Feb 18, 2008 |
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61031276 |
Feb 25, 2008 |
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Current U.S.
Class: |
606/272 ;
29/428 |
Current CPC
Class: |
Y10T 29/49826 20150115;
A61B 17/7032 20130101; A61B 17/7037 20130101; A61B 17/8685
20130101; A61B 17/8605 20130101 |
Class at
Publication: |
606/272 ;
29/428 |
International
Class: |
A61B 17/70 20060101
A61B017/70; B23P 11/00 20060101 B23P011/00 |
Claims
1. A bone anchor assembly securable to an elongated member, the
bone anchor assembly comprising: a bone screw comprising a threaded
portion and a head portion, wherein the threaded portion and the
head portion are formed as separate pieces, each of which comprises
a fitting feature, wherein the fitting features mate together to
facilitate joining of the head portion and the threaded portion; a
coupling member having a channel shaped to receive the elongated
member and a bore comprising a seat shaped to polyaxially
adjustably receive the head portion; and a locking member that is
actuatable to lock the elongated member in a fixed position
relative to the coupling member and restrict polyaxial
adjustability of the bone screw relative to the coupling
member.
2. The bone anchor assembly of claim 1, wherein the bore comprises
a minimum diameter that is smaller than a maximum diameter of the
threaded portion.
3. The bone anchor assembly of claim 2, wherein the seat comprises
a concave semispherical seat, wherein the head portion comprises a
complementary convex semispherical shoulder capable of resting
against the concave semispherical seat in any of a plurality of
relative orientations, wherein the minimum diameter of the bore is
immediately distal to the seat.
4. The bone anchor assembly of claim 1, wherein the fitting feature
of the head portion comprises a shaft and the fitting feature of
the threaded portion comprises an aperture sized to receive the
shaft.
5. The bone anchor assembly of claim 4, wherein the aperture is
sized to receive the shaft with some degree of interference to
provide a press fit between the shaft and the aperture.
6. The bone anchor assembly of claim 1, wherein the bone screw
comprises a lumen extending through its entire length.
7. The bone anchor assembly of claim 1, wherein the channel is
flanked by a first support wall and a second support wall that
cooperate to define a U-like shape of the channel, wherein each of
the first and second support walls comprises interior threads that
face toward the other of the first and second support walls,
wherein the locking member comprises a set screw with exterior
threads that engage the interior threads of the first and second
support walls to enable threaded advancement of the set screw into
the channel.
8. The bone anchor assembly of claim 7, wherein the channel is
positioned proximal to the bore, the bone anchor assembly further
comprising an elongated member comprising an attachment portion
shaped to be received by the channel.
9. A bone anchor assembly securable to an elongated member, the
bone anchor assembly comprising: a bone screw comprising a distal
threaded portion shaped to engage bone and a proximal head portion;
a coupling member having a channel shaped to receive elongated
member and a bore comprising a seat shaped to polyaxially
adjustably receive the head portion; and a locking member
configured to be actuated to lock the position of the elongated
member in a fixed position relative to the assembly and restrict
polyaxial adjustability of the bone screw relative to the coupling
member; wherein a minimum diameter of the bore is less than a
maximum diameter of the threaded portion.
10. The bone anchor assembly of claim 9, wherein the seat comprises
a concave semispherical seat, wherein the head portion comprises a
complementary convex semispherical shoulder capable of resting
against the concave semispherical seat in any of a plurality of
relative orientations, wherein the minimum diameter of the bore is
immediately distal to the seat.
11. The bone anchor assembly of claim 9, wherein each of the head
portion and the threaded portion comprises a fitting feature,
wherein the fitting features are matable together to provide a
press fit between the head portion and the threaded portion.
12. The bone anchor assembly of claim 9, wherein the bone screw
comprises a lumen extending through its entire length.
13. The bone anchor assembly of claim 9, wherein the channel is
flanked by a first support wall and a second support wall that
cooperate to define a U-like shape of the channel, wherein each of
the first and second support walls comprises interior threads that
face toward the other of the first and second support walls,
wherein the locking member comprises a set screw with exterior
threads that engage the interior threads of the first and second
support walls to enable threaded advancement of the set screw into
the channel.
14. The bone anchor assembly of claim 13, wherein the channel is
positioned proximal to the bore, the bone anchor assembly further
comprising an elongated member comprising an attachment portion
shaped to be received by the channel.
15. A method of manufacturing a bone anchor assembly, the method
comprising: forming a head portion of a bone screw; forming a
threaded portion of the bone screw; forming a coupling member
comprising a channel shaped to receive an elongated member and a
bore comprising a seat shaped to polyaxially adjustably receive the
head portion; positioning the head portion at least partially
within the bore; and joining the threaded portion to the head
portion with the head portion positioned at least partially within
the bore.
16. The method of claim 15, wherein forming the coupling member
comprises forming the bore with a minimum diameter that is smaller
than a maximum diameter of the threaded portion.
17. The method of claim 16, wherein the seat comprises a concave
semispherical seat and the head portion comprises a complementary
convex semispherical shoulder, wherein positioning the head portion
at least partially within the bore comprises resting the convex
semispherical shoulder against the concave semispherical seat,
wherein forming the bore comprises providing the minimum diameter
of the bore immediately distal to the seat.
18. The method of claim 15, wherein each of the head portion and
the threaded portion comprises a fitting feature, wherein the
fitting features mate together to facilitate joining of the head
portion and the threaded portion.
19. The method of claim 18, wherein the fitting feature of the head
portion comprises a shaft and the fitting feature of the threaded
portion comprises an aperture, wherein joining the threaded portion
to the head portion comprises inserting the shaft into the
aperture.
20. The method of claim 19, wherein the aperture is sized to
receive the shaft with some degree of interference such that
inserting the shaft into the aperture comprises providing a press
fit between the shaft and the aperture.
21. The method of claim 15, wherein providing the head portion and
the threaded portion comprises providing a lumen through each of
the head portion and the threaded portion such that, after joining
of the threaded portion to the head portion, a lumen extends
through the entire length of the bone screw.
22. The method of claim 15, wherein the channel is flanked by a
first support wall and a second support wall that cooperate to
define a U-like shape of the channel, wherein forming the coupling
member comprises forming interior threads in each of the first and
second support walls such that the interior threads of each support
wall face toward the other of the first and second support
walls.
23. The method of claim 22, further comprising forming a set screw
with exterior threads that engage the interior threads of the first
and second support walls to enable threaded advancement of the set
screw into the channel.
24. The method of claim 15, wherein the channel is positioned
proximal to the bore, the method further comprising forming an
elongated member comprising an attachment portion shaped to be
received by the channel.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of the following, which
are incorporated herein by reference:
[0002] Pending prior U.S. Provisional Patent Application No.
60/944,321, filed Jun. 15, 2007, which carries Applicants' docket
no. REI-01 PROV, and is entitled WEDGE CLAMP POLYAXIAL PEDICLE
SCREW;
[0003] Pending prior U.S. Provisional Patent Application No.
61/029,467, filed Feb. 18, 2008, which carries Applicants' docket
no. REI-2 PROV, and is entitled MODULAR POLYAXIAL PEDICLE SCREW;
and
[0004] Pending prior U.S. Provisional Patent Application No.
61/031,276, filed Feb. 25, 2008, which carries Applicants' docket
no. REI-3 PROV, and is entitled SIDE LOADING POLYAXIAL PEDICLE
SCREW.
BACKGROUND OF THE INVENTION
The Field of the Invention
[0005] The present invention relates to orthopaedics, and more
particularly, to systems and methods for implantable bone anchor
and rod assemblies to provide spinal support.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] Various embodiments of the present invention will now be
discussed with reference to the appended drawings. It is
appreciated that these drawings depict only typical embodiments of
the invention and are therefore not to be considered limiting of
its scope.
[0007] FIG. 1 illustrates a perspective view of a bone anchor
assembly comprising a bone anchor, a coupling head, an engagement
member, and a locking member, and a spinal rod clamped in the bone
anchor assembly;
[0008] FIG. 2 illustrates an exploded perspective view of the bone
anchor of FIG. 1;
[0009] FIG. 3A illustrates a perspective view of the coupling head
of FIG. 1; and FIG. 3B illustrates a cross-sectional view of the
coupling head of FIG. 1;
[0010] FIG. 4A illustrates a posterior view of the engagement
member of FIG. 1; FIG. 4B illustrates a side view of the engagement
member of FIG. 1; FIG. 4C illustrates a perspective posterior view
of the engagement member of FIG. 1; and FIG. 4D illustrates a
perspective side view of the engagement member of FIG. 1;
[0011] FIG. 5 illustrates an exploded perspective view of the bone
anchor assembly and spinal rod of FIG. 1;
[0012] FIG. 6 illustrates a partial side view of the bone anchor
assembly and spinal rod of FIG. 1 with the engagement member in
partial engagement with the coupling head and the spinal rod;
[0013] FIG. 7 illustrates a partial side view of the bone anchor
assembly and spinal rod of FIG. 6 with the engagement member in
engagement with the coupling head and the spinal rod;
[0014] FIG. 8 illustrates a partial cross-sectional view of the
bone anchor assembly and spinal rod of FIG. 7;
[0015] FIG. 9 illustrates a perspective view of an alternative
embodiment of a bone anchor assembly comprising a bone anchor, a
coupling head, and a locking member, and a spinal rod clamped in
the bone anchor assembly;
[0016] FIG. 10 illustrates an exploded perspective view of the bone
anchor and coupling head of FIG. 9;
[0017] FIG. 11 illustrates a cross-sectional view of the coupling
head of FIG. 10;
[0018] FIG. 12 illustrates a partially exploded perspective view of
the bone anchor assembly and spinal rod of FIG. 9;
[0019] FIG. 13 illustrates a cross-sectional view of the bone
anchor assembly and spinal rod of FIG. 9;
[0020] FIG. 14 illustrates a perspective view of an alternative
embodiment of a bone anchor assembly and a spinal rod clamped in
the bone anchor assembly, the bone anchor assembly comprising a
bone anchor, a coupling head, a compression member and a
collar;
[0021] FIG. 15A illustrates a perspective view of the coupling head
of FIG. 14; FIG. 15B illustrates a posterior view of the coupling
head of FIG. 14; FIG. 15C illustrates a cross-sectional view of the
coupling head of FIG. 14; and FIG. 15D illustrates a
cross-sectional view of the coupling head of FIG. 14;
[0022] FIG. 16 illustrates a perspective view of the bone anchor
and coupling head of FIG. 14, coupled together;
[0023] FIG. 17A illustrates a perspective view of the collar of
FIG. 14; and FIG. 17B illustrates a cross-sectional view of the
collar of FIG. 17A;
[0024] FIG. 18 illustrates a cross-sectional view of the bone
anchor assembly and spinal rod of FIG. 14;
[0025] FIG. 19 illustrates a perspective view of an alternative
embodiment of a bone anchor assembly and a spinal rod clamped in
the bone anchor assembly, the bone anchor assembly comprising a
bone anchor, a coupling head, a compression member and a
collar;
[0026] FIG. 20 illustrates an exploded perspective view of the bone
anchor assembly and spinal rod of FIG. 19;
[0027] FIG. 21 illustrates a perspective view of an alternative
embodiment of a bone anchor assembly and a spinal rod clamped in
the bone anchor assembly, the bone anchor assembly comprising a
bone anchor, a coupling head, and a compression member;
[0028] FIG. 22 illustrates an enlarged perspective view of the bone
anchor and coupling head of FIG. 21;
[0029] FIG. 23 illustrates a perspective view of a bone anchor and
an alternative embodiment of a coupling head;
[0030] FIG. 24 illustrates a perspective view of an alternative
embodiment of a bone anchor assembly and a spinal rod clamped in
the bone anchor assembly, the bone anchor assembly comprising a
bone anchor, a coupling head, and a compression member; and
[0031] FIG. 25 illustrates a cross-sectional view of the coupling
head and bone anchor of FIG. 24.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] The present invention relates to systems and methods for
bone anchor and rod assemblies for providing spinal support. Those
of skill in the art will recognize that the following description
is merely illustrative of the principles of the invention, which
may be applied in various ways to provide many different
alternative embodiments. This description is made for the purpose
of illustrating the general principles of this invention and is not
meant to limit the inventive concepts in the appended claims.
[0033] One embodiment of the present invention includes a bone
anchor having a threaded section and an at-least partially
spherical head, a rod coupling member that has polyaxial
adjustability with the spherical bone anchor head, a compression
element, an engagement member, and a elongated member, which may be
a spinal rod. A method of clamping to the spinal rod consists of a
set screw located laterally in the pedicle screw assembly with
respect to the implant rod, but still within the rod coupling head.
This screw acts on a wedge-shaped clamping engagement member that
rests on an inclined plane feature on one side of the top of the
rod coupling head. The act of tightening the set screw provides a
mechanically advantaged force that drives the wedge-shaped clamp
into the implant rod, which in turn, transmits a force to the bone
anchor head, which presses against the spherical cavity in the rod
coupling head. This action secures the rod in place while also
locking the position/orientation of the rod coupling head relative
to the bone anchor head. Locating the clamping member/set screw
laterally may greatly reduce the posterior profile of the pedicle
screw implant located above the rod.
[0034] FIGS. 1-8 illustrate an embodiment of a bone anchor assembly
with a wedge-shaped clamping engagement member, and a spinal rod.
Referring to FIG. 1, bone anchor assembly 100 includes a bone
anchor 102, a coupling head 104, a wedge-shaped clamping member
106, and a locking member which is a set screw 108. A spinal rod
110 is received by the coupling head 104 and rigidly clamped by the
clamping member 106. In addition to the spinal rod 110 illustrated,
other rod-like elongated members may be received and clamped by the
assembly 100, including facet joint replacement components, spinal
fusion devices, or other orthopaedic devices with a rod-like
attachment portion shaped to be received in a coupling member such
as coupling head 104 or other coupling heads disclosed within.
[0035] Referring to FIG. 2, bone anchor 102 comprises a threaded
portion 112 and a head portion 114. The threaded portion 112
includes threads 116 which may extend entirely or partially along
the threaded portion 1 12. A first fitting feature 118 is located
on the threaded portion 112, and shaped to mate with a second
fitting feature 120 situated on the head portion 114. A maximum
diameter 122 of the threaded portion 112 is measured normal to the
longitudinal axis of the threaded portion, from the maximum lateral
extension of the thread on one side to the maximum lateral
extension of the thread on the opposite side. The head portion 114
further comprises a head 124 which may be at least semispherical,
comprising a semispherical shoulder 126 and a crown 128. A
"semispherical" surface is a concave or convex surface that
contains at least some three dimensional portion of the outer
surface of a sphere.
[0036] The first and second fitting features 118, 120 are shaped to
be joined by press fitting, welding, brazing, or other methods well
known in the art, thus joining the independent head 114 and
threaded 112 portions into a single, permanently joined piece. The
bone anchor 102 may be cannulated throughout such that a lumen
extends through its entire length. Advantageously, during
manufacture the head portion 114 may be assembled with the coupling
head 104 such that the second fitting feature 120 extends distal of
the coupling head 104. The second fitting feature 120 is coupled
with the first fitting feature on the threaded portion 118, and
joined as described. Thus assembled the bone anchor 102 and
coupling head 104 form a partial bone anchor assembly 101.
[0037] FIG. 3A is a perspective view of coupling head 104, while
FIG. 3B is a transverse cross-section of the member. Coupling head
104 may be monolithic and may be generally U-shaped, with a first
support body wall and a second support wall 131 flanking a channel
130. The channel 130 is semi-cylindrical and shaped to receive the
spinal rod 110 (seen in FIG. 1). A first bore 132, encircled by a
bore surface 134, extends through the member 104, perpendicular to
the channel 130. The first bore 132 is shaped to receive the bone
anchor 102, and includes a proximal bore portion 136 and a distal
bore portion 138 which are delimited by a ridge 140 which protrudes
from the bore surface 134. A semispherical seat 142 is formed in
the proximal bore portion 136 and is immediately proximal to the
ridge 140. The proximal bore portion encircles a spherical cavity
143. A minimum diameter 144 of the first bore 132 is measured
normal to the longitudinal axis of the first bore 132, from one
location on the ridge 140 directly across the bore to the opposite
side. A maximum diameter 145 of the spherical cavity 143 is
measured normal to the longitudinal axis of the first bore 132,
from the widest part of the spherical cavity across to the widest
part on the opposite side. The bore 132 is shaped to receive the
bone anchor 102 such that the head 124 is contained in the proximal
bore portion 136, and the semispherical shoulder 124 may rest
against the semispherical seat 142 in a plurality of relative
orientations. The proximal 136 and distal 138 bore portions are
sized and shaped so that when the head 124 is contained in the
proximal bore portion 136, but before tightening of the set screw
108, the bone anchor 102 may polyaxially rotate relative to the
coupling head 104.
[0038] A second bore 152, independent and offset from the first
bore 132, extends through the second support wall 131 of the
coupling head 104. The second bore 152 may be parallel to the first
bore 132 and perpendicular to the channel 130. The second bore 152
is encircled by a threaded surface 154 and is configured to receive
the set screw 108. A second oblique surface 156 occupies a proximal
side of the second support wall 131.
[0039] Referring to FIGS. 4A-C, several views of the clamping
member 106 are shown. Clamping member 106, in combination with set
screw 108, can form a locking mechanism which can be actuated to
lock the spinal rod in a fixed position relative to the coupling
head 104. The clamping member 106 is generally wedge-shaped and may
also be termed an engagement member. The clamping member 106 is
configured to slide along the second oblique surface 156 of the
coupling head 104 into engagement with the spinal rod 110, when the
set screw 108 is actuated. The clamping member 106, coupling head
104 and set screw 108 are sized and shaped to create a low profile
spinal rod connection. By locating the set screw 108 in a lateral
position relative to the rod a reduced posterior profile may be
created in comparison to an assembly with a proximally positioned
set screw.
[0040] Clamping member 106 comprises a wedge body 160 with a first
body wall 162 and a second body wall 164. The body walls 162, 163
flank a recessed area 166 with a recessed surface 167. Extending
distally from the recessed surface 167 is an aperture 168. Distal
to the walls 162, 164 and aperture 168 is a first oblique surface
170. At the junction of the first oblique surface 170 and the walls
162, 164 is an engagement surface 172, which may be curved to fit
around a portion of the spinal rod 1 10. The aperture 168 is
substantially oval in shape and sized to receive the set screw 108.
The first oblique surface 170 may be shaped to complement the
second oblique surface 156 of the coupling head 104.
[0041] FIGS. 5-7 illustrate one method of assembling spinal rod 110
with bone anchor assembly 100. Referring to FIG. 5, a partially
exploded view of bone anchor assembly 100 and spinal rod 110 are
shown. As previously set forth, during manufacture bone anchor 102
may be assembled with coupling head 104, to form partial bone
anchor assembly 101. Following bone preparation, which may include
placement of a guide wire or other guiding feature, the threaded
portion 116 of partial bone anchor assembly 101 is anchored in the
bone. Coupling head 104 may be polyaxially adjusted relative to the
head portion 114 of the bone anchor 102 to attain a preferred
orientation.
[0042] Referring also to FIG. 6, an attachment portion 111 of the
spinal rod 110 is placed in the channel 130. The attachment portion
111 contacts the head 124 of the bone anchor 102. A threaded
portion 180 of set screw 108 is received through the aperture 168
of the wedge member 106. After passing through the aperture 168,
the threaded portion 180 is received in the second bore 152, and
the threads engage with the threaded wall 154. As the set screw 108
is actuated by turning, a head 182 of the set screw 108 engages the
recessed surface 167 of the wedge member 106, urging the wedge
member toward the spinal rod 110. The wedge member 106 is drawn
transverse to the axis of the set screw 108, and the first oblique
surface 170 of the wedge member 106 moves transversely along the
second oblique surface 156 of the coupling head 104. As seen in
FIGS. 7 and 8, actuation of the set screw 108 may continue until
the engagement surface 172 presses against the spinal rod 110,
rigidly clamping the rod 110 in the channel 130. The spinal rod
transmits a force to the head 124 of the bone anchor 102, and the
semispherical shoulder 126 is pressed against the semispherical
seat 142 of the coupling head 104. Thus, the position and
orientation of both the spinal rod 110 and the bone anchor 102
relative to the coupling head 104 are locked out.
[0043] FIG. 8 is an enlarged cross-sectional view of the bone
anchor assembly 100 locked to the spinal rod 110. As set forth
previously, during manufacture the head 114 and threaded portions
116 of bone anchor 102 may be coupled with coupling head 104 and
joined such that the head portion 114 is retained proximal to the
ridge 140 of the first bore 132, and the threaded portion extends
distal to the bore 132. Since the bone anchor 102 and coupling head
104 are thus pre-assembled, during implantation the bone anchor 102
need not be top- or bottom- loaded into the coupling head 104. As a
result, the maximum diameter 122 of the threaded portion 116 of the
bone anchor 102 may be greater than the minimum diameter 144 of the
first bore. Similarly, a maximum diameter 174 of the head portion
114 of the bone anchor 102 may be greater than the minimum diameter
144 of the first bore. The maximum diameter 174 of the head portion
114 of the bone anchor 102 may be less than the maximum diameter
122 of the threaded portion 116. The maximum diameter 145 of the
spherical cavity 143 may be less than the maximum diameter 122 of
the threaded portion 116.
[0044] Another embodiment of the present invention includes a bone
anchor having a threaded section and an independent at-least
partially spherical head configured to be joined to the threaded
section, a rod coupling head that has polyaxial adjustability with
the spherical bone anchor head, a compression element, and an
implant rod. During manufacture, the bone anchor is assembled with
the rod coupling head such that the bone anchor head is received by
the rod coupling head, and joined to the threaded section so that
the threaded section extends distally of the rod coupling head. A
method of clamping to the implant rod consists of a set screw
located superior in the pedicle screw assembly with respect to the
implant rod. This screw acts on directly on the implant rod. The
act of tightening the set screw provides a mechanically advantaged
force that drives the inferior set screw surface into the implant
rod, which in turn, transmits a force to the bone anchor head,
which presses against the spherical cavity in the rod coupling
head. This action secures the rod in place while also locking the
position and/or orientation of the rod coupling head relative to
the bone anchor head. This assembly allows the threaded portion of
the bone anchor to be bottom-loaded during manufacture and
therefore the spherical head is not required to be larger in
diameter than the screw threads, and accordingly, the matching
spherical cavity in the rod coupling head can be smaller. This may
provide substantial reduced profile advantages for the rod coupling
head and overall pedicle screw assembly.
[0045] FIGS. 9-12 illustrate an alternative embodiment of a bone
anchor assembly configured to hold an elongated member in a fixed
position. Referring to FIG. 9, a bone anchor assembly 200 is shown
with a spinal rod 210. Bone anchor assembly 200 comprises a bone
anchor 202, coupling head 204, and compression member, or set
screw, 206. Bone anchor 202 is configured to be anchored in a
pedicle of a vertebra, or in another bone. Coupling head 204 may be
coupled with the bone anchor 202 during manufacture, and is shaped
to receive a spinal rod 210 or other elongated rod-like member. Set
screw 206 is configured to be actuated to engage with the coupling
head 204 to provide force on the spinal rod 210 and in turn the
bone anchor 202, to lock out polyaxial motion between the bone
anchor 202 and the coupling head 204, and to fix the position of
the spinal rod 210 relative to the assembly 200.
[0046] Referring to FIG. 10, bone anchor 202 comprises a threaded
portion 208 and a head portion 209. The threaded portion 208 may be
partially or entirely threaded. The head portion 209 comprises an
elongated neck 212 and a head 214. The head 214 further comprises a
semispherical shoulder 216 and a crown 218. One or more driver
features 220 may be included in the head 214 to cooperate with a
driver or other tool configured to grip, drive or otherwise
manipulate the bone anchor 202. The bone anchor 202 may be
cannulated throughout.
[0047] Referring to FIG. 11, coupling head 204 is generally
tulip-shaped, with a semispherical base 228, and a first support
wall 230 and a second support wall 232 flanking a U-shaped channel
234. Distal and perpendicular to the channel 234, a bore 236
extends through the semispherical base 228. The bore 236 is shaped
to receive the bone anchor 202, and includes a proximal bore
portion 237 and a distal bore portion 239 which are delimited by a
ridge 240 which is an annular protrusion from the semispherical
base 228 and defines a location of minimum diameter of the bore
236. A semispherical seat 238 is formed in the proximal bore
portion 237 and is immediately proximal to the ridge 240. The
proximal bore portion 237 encircles a spherical cavity 243. A
minimum diameter 244 of the bore 236 is measured normal to the
longitudinal axis of the bore 236, from one location on the ridge
240 directly across the bore to the opposite side. A maximum
diameter 245 of the spherical cavity 243 is measured normal to the
longitudinal axis of the bore 236, from the widest part of the
spherical cavity across to the widest part on the opposite side. A
portion of the interior surfaces of the first 230 and second 232
support walls are threaded to receive the set screw 206 (not
shown).
[0048] Referring to FIGS. 10 and 11, head portion 209 is configured
to be coupled with coupling head 204 and joined to threaded portion
208 during the manufacturing process. Head portion 209 may be
received by bore 236 in coupling head 204 such that head 214 is
retained proximal of a location of minimum diameter of the bore,
and neck 212 extends through the bore and distal to the bore. Neck
212 is coupled with the threaded portion 208 distal to the bore
236, and permanently joined to the threaded portion by means which
may include welding, grazing, press-fit, or other methods. After
joining but before lockout of the assembly, bone anchor 202 may
freely polyaxially rotate relative to the coupling head 204.
[0049] Referring to FIGS. 11 and 12, bone anchor 202, coupled with
coupling head 204 as set forth previously, may be anchored in a
pedicle of a vertebra or another bone. Coupling head 204 may be
polyaxially rotated to a preferred orientation relative to the bone
anchor 202. Spinal rod 210 or another elongated rod-like portion of
an implant may be positioned in the channel of the coupling head
204. Set screw 206 is actuated to engage with the threaded surfaces
of support walls 230, 232. As the set screw 206 is turned it is
driven into contact with the spinal rod 210, and the spinal rod in
turn transmits a force to the head 214, which presses against the
semispherical seat 238 in the bore 236. The spinal rod 210 is thus
secured in position relative to the coupling head 204 and the
orientation of the coupling head 204 relative to the bone anchor
202 is fixed.
[0050] Referring to FIG. 13, a cross-sectional view of the bone
anchor assembly 200 assembled with a spinal rod 210 is shown.
Because the bone anchor 202 is pre-assembled with the coupling head
204, the bone anchor does not have to be top-loaded into coupling
head, and a maximum diameter 246 of the head portion 209 may be
less than a maximum diameter 248 of the threaded portion 208.
Similarly, the maximum diameter 248 of the threaded portion 208 may
be greater than the minimum diameter 244 of the bore 236. The
maximum diameter 246 of the head portion 209 may be greater than a
minimum diameter 244 of the bore 236. Also, the maximum diameter
245 of the spherical cavity 243 may be less than the maximum
diameter 248 of the threaded portion 208.
[0051] Another embodiment of the present invention includes a bone
anchor having a threaded section and an at-least partially
spherical head, a rod coupling head that has polyaxial
adjustability with the spherical bone anchor head, a compression
element, and a spinal rod. A collar or ring component may be used
to further strengthen the rod coupling head after assembly with the
bone anchor and can be fixed via a press fit, weld, threads or any
other means well known in the art. The rod coupling head may
include a keyhole-shaped slot which allows the bone anchor to be
side-loaded into the rod coupling head. The method of clamping to
the spinal rod consists of a set screw located superior in the
pedicle screw assembly with respect to the implant rod. This screw
acts on directly on the implant rod. The act of tightening the set
screw provides a mechanically advantaged force that drives the
inferior set screw surface into the implant rod, which in turn,
transmits a force to the bone anchor head, which presses against
the spherical cavity in the rod coupling head. This action secures
the rod in place while also locking the position/orientation of the
rod coupling head relative to the bone anchor head. Using a
side-loaded bone anchor element does not require the spherical head
to be larger in diameter than the screw threads, and accordingly,
the matching spherical cavity in the rod coupling head can be
smaller. This may provide substantial reduced profile advantages
for the rod coupling head and overall pedicle screw assembly.
[0052] Referring to FIG. 14, a bone anchor assembly 300 is shown
rigidly coupled with a spinal rod 310. Bone anchor assembly 300
comprises a bone anchor 302, a coupling head 304, a collar 306 and
a compression element which is a set screw 308. Bone anchor 302 is
configured to be anchored in a pedicle of a vertebra, or in another
bone. Coupling head 304 is shaped to couple with bone anchor 302,
and is shaped to receive a spinal rod 210 or other elongated
rod-like member. Collar 306 may assist in retaining bone anchor 302
within the coupling head 304 and provide additional structural
support to the coupling head 304. Set screw 308 is configured to be
actuated to engage with the coupling head 304 to provide force on
the spinal rod 310 and in turn the bone anchor 302, to lock out
polyaxial motion between the bone anchor 302 and the coupling head
304, and to fix the position of the spinal rod 310 relative to the
assembly 300.
[0053] Coupling head 304 is shown in greater detail in FIGS. 15A-D.
Coupling head 304 is generally tulip-shaped, and comprises a
semi-circular base portion 312, a first support wall 314 and a
second support wall 316 positioned generally opposite the first
support wall. A channel 318 shaped to receive the spinal rod 310 is
positioned between the first and second support walls 314, 316. The
base portion 312 is not fully circular but discontinuous,
comprising a gap 320. Proximal to and continuous with the gap 320,
a cutout 322 is formed in a portion of the first support wall 314.
Together, the gap 320 and cutout 322 form a keyhole-shaped slot 324
sized to allow passage of a proximal end of the bone anchor 302. In
the embodiment depicted in FIGS. 15A-D, the slot 324 is
perpendicular to the channel 318; however in other embodiments of
the invention the slot may be parallel, oblique or at another
orientation relative to the channel, and may extend partway or all
the way through the coupling head. Additionally, the slot 324 may
comprise other shapes such as rectangular or circular, among
others.
[0054] A bore 330 extends through the base portion 312, lined by a
bore wall 332. A ridge 334 protruding from the bore wall defines a
minimum diameter of the bore 330. Proximal to the ridge 334, a
semispherical seat 336 encircles the bore, and is sized to retain a
head portion of the bone anchor 302. A spherical cavity 338 sized
and shaped to receive the head portion of the bone anchor is
proximal to the semispherical seat 336. The slot 324 is in a
transverse position relative to the bore 330, allowing side-loading
of the bone anchor 302 into the bore.
[0055] Referring to FIG. 16, the bone anchor 302 may be coupled
with the coupling head 304. The bone anchor 302 comprises a
threaded portion 340 and a head portion 342. The head portion 342
is semi-spherical and may comprise a plurality of driving features
344 and a semispherical shoulder 346. The bone anchor 302 may be
formed as one piece or may comprise head and threaded portions
which have been permanently joined together. The bone-anchor 302
may be side-loaded into the coupling head 304 with the head portion
342 guided through the slot 324, and the coupling head 304 and bone
anchor 302 may be polyaxially adjusted relative to one another,
such that the semispherical shoulder 346 of the head portion is
able to rest at any of a plurality of relative orientations between
the semispherical shoulder 346 and the semispherical seat 336.
[0056] Because the bone anchor 302 may be side-loaded into the
coupling head 304 and need not be top-loaded, a maximum diameter of
the head portion 342 may be less than a maximum diameter of the
threaded portion 340. Similarly, the maximum diameter of the
threaded portion 340 may be greater than a minimum diameter of the
bore 330. The maximum diameter of the head portion 342 may be
greater than the minimum diameter of the bore 330. Also, a maximum
diameter of the spherical cavity 338 may be less than the maximum
diameter of the threaded portion 340.
[0057] Once the bone anchor 302 has been loaded into the coupling
head 304, the collar 306 may be coupled to the base portion 312 of
the coupling head 304, to further retain the bone anchor 302. The
collar may be further secured by press-fitting, threads, welding,
or other means. The collar 306 is only one of many different
retention members that may be used to keep the bone anchor 302 in
place. If desired, such retention members may have features
designed to interlock with or otherwise engage corresponding
features of the coupling head 304. The collar 306 has a shape that
generally complements that of the coupling head 304 to complete the
interior wall of the bore 330.
[0058] Referring to FIGS. 17A and 17B, collar 306 is generally
ring-shaped. An outer wall 350 of the collar 306 may be rounded
and/or chamfered or otherwise shaped to attain a preferred profile.
A collar bore 352 extends through the collar, the collar bore 352
having an inner bore wall 354. A projection 356 which protrudes
inwardly from the inner bore wall 354 is shaped to fill the gap 320
in the coupling head 304 (not shown) when the collar 306 is secured
to the coupling head 304. The projection 356 includes a portion of
the semispherical seat 336 and the ridge 334.
[0059] Referring to FIG. 18, a cross-sectional view of bone anchor
assembly 300 assembled with spinal rod 310 is shown. Prior to
implantation, bone anchor 302 may be side-loaded into coupling head
304, and collar 306 secured to coupling head 304. Bone anchor 302
may be driven into the pedicle of a vertebra, or another bone,
using a driving tool (not shown). The coupling head 304 and collar
306 may be polyaxially rotated relative to the bone anchor 302 such
that the semispherical shoulder 346 of the head portion 342 is able
to rest at any of a plurality of relative orientations between the
semispherical shoulder 346 and the semispherical seat 336. The
spinal rod 310 or other elongated member may be top-loaded into the
channel, and the set screw 308 threaded into the coupling head 304
to form a locking mechanism. As the set screw 308 is actuated, an
inferior surface of the set screw is pressed against the implant
rod 310, which in turn, transmits a force to the bone anchor head
portion 342, which presses against the semispherical seat 336 in
the coupling head 304 and collar 306. This action secures the rod
in place while also locking the position/orientation of the rod
coupling head relative to the bone anchor head.
[0060] Referring to FIGS. 19 and 20, an alternative embodiment of a
bone anchor assembly with a transverse opening that extends all the
way across the coupling head is shown. Bone anchor assembly 400 is
shown coupled with a spinal rod 410, and comprises a bone anchor
402, a coupling head 404, a collar 406, and a set screw 408.
Coupling head 404 is similar to coupling head 304, except that
coupling head 404 comprises two slots 412, 414 oriented opposite
one another to form a single transverse opening 416 which extends
all the way across a base portion 418 of the coupling head 404. As
a result, a head portion 420 of bone anchor 402 may be inserted
into the coupling head through either slot 412, 414 during assembly
of the bone anchor assembly 400. Collar 406 is ring-shaped and
sized to encircle the base portion 418 of the coupling head 404, to
prevent withdrawal of bone anchor 402 from the coupling head.
[0061] Referring to FIGS. 21 and 22, an alternative embodiment of a
bone anchor assembly with a base portion configured to accept a pin
is shown. Bone anchor assembly 500 is shown coupled with a spinal
rod 510, and comprises a bone anchor 502, a coupling head 504, and
a set screw 506. The bone anchor 502 may be side-loaded into the
coupling head 504 through a slot 507, similar to bone anchor
assembly 300. The coupling head 504 has a semi-circular base
portion 508. At a first end 512 of the base portion 508 is a first
hole 514, and at a second end 516 of the base portion is a second
hole 518. Holes 514, 518 are opposably oriented such that a pin
(not shown) may extend through and between the holes to prevent
withdrawal of the bone anchor 502. A channel 520, sized to receive
spinal rod 510 extends across the coupling head 504 perpendicular
to the slot 507. A collar (not shown) may optionally be secured
onto the base portion to retain the pin and further retain the bone
anchor.
[0062] Referring to FIG. 23, a portion of another alternative
embodiment of a bone anchor assembly is shown. Bone anchor 602 is
shown received in coupling head 604. Coupling head 604 is similar
to coupling head 504, with the exception that a channel 606 shaped
to receive a spinal rod extends parallel to a slot 608. Coupling
head 604 further comprises holes 610, 612 shaped to receive a pin
(not shown) which may prevent withdrawal of the bone anchor 602
from the coupling head 604. A collar (not shown) such as collar 406
may optionally be secured onto the base portion to retain the pin
and further retain the bone anchor.
[0063] Referring to FIGS. 24 and 25, another alternative embodiment
of a bone anchor assembly is shown. Bone anchor assembly 700
comprises a bone anchor 702, coupling head 704, set screw 706, and
a collar (not shown) such as collar 406. Coupling head 704
comprises a slot 712 allowing the bone anchor 702 to be side-loaded
into the coupling head. A base portion 714 comprises a first hole
716 and a second hole 718 located on opposing side of the base
portion, each hole extending through the base portion and in
communication with a spherical cavity 720. A head portion 722 of
the bone anchor 702 may be side-loaded through the slot 712 into
the spherical cavity 720. A semispherical shoulder 724 of the head
portion 722 may be engaged in the holes 716, 718, retaining the
head portion 722 in the semispherical cavity and allowing a
threaded portion 726 to extend distal of the coupling head 704. The
collar is secured around the base portion 714 to further retain the
bone anchor 702.
[0064] Bone anchor assemblies 400, 500, 600 and 700 may be
assembled and implanted similarly to the method described for bone
anchor assembly 300. In all four assemblies, the bone anchor may be
side loaded into the coupling head. A collar and/or pin may be
secured to the coupling head to prevent withdrawal of the bone
anchor. The bone anchor may be anchored into a bone, and the
coupling head and bone anchor polyaxially rotated relative to one
another to a preferred orientation. A spinal rod may be loaded into
the channel of the coupling head in a preferred position, and the
set screw fastened into the coupling head. As the set screw is
actuated, it presses on the spinal rod, which in turn presses on
the head of the bone anchor, seating the bone anchor head against
the coupling head at the preferred orientation. The position of the
spinal rod and the position and orientation of the bone anchor
relative to the coupling head are thus locked down.
[0065] The present invention may be embodied in other specific
forms without departing from its spirit or essential
characteristics. For example, above are described various
alternative examples of pedicle screw and rod coupling systems for
providing spinal support. It is appreciated that various features
of the above-described examples can be mixed and matched to form a
variety of other alternatives. It is also appreciated that this
system should not be limited creating access to the intervertebral
space. This arcuate access system may be used to obtain access to
any portion of the spine. As such, the described embodiments are to
be considered in all respects only as illustrative and not
restrictive. The scope of the invention is, therefore, indicated by
the appended claims rather than by the foregoing description. All
changes which come within the meaning and range of equivalency of
the claims are to be embraced within their scope.
* * * * *