U.S. patent application number 12/220466 was filed with the patent office on 2009-02-05 for polyaxial bone screw with helically wound capture connection.
Invention is credited to Roger P. Jackson.
Application Number | 20090036935 12/220466 |
Document ID | / |
Family ID | 36317306 |
Filed Date | 2009-02-05 |
United States Patent
Application |
20090036935 |
Kind Code |
A1 |
Jackson; Roger P. |
February 5, 2009 |
Polyaxial bone screw with helically wound capture connection
Abstract
A polyaxial bone screw assembly includes a threaded shank body
having an upper capture structure, a head and a closed retainer
ring. The external capture structure surface and retainer ring
internal bore surface are both threaded for rotatable attachment
within a cavity of the head. The head has a U-shaped cradle
defining a channel for receiving a spinal fixation rod. The head
channel communicates with the cavity and further with a restrictive
opening that allows for loading the capture structure into the head
but prevents passage of the closed retainer ring out of the head.
The retainer ring has an external substantially spherical surface
that mates with an internal surface of the head, providing a ball
joint, enabling the head to be disposed at an angle relative to the
shank body. The threaded capture structure or the closed retainer
structure includes a tool engagement formation and gripping
surfaces for non-slip engagement by a tool for driving the shank
body into bone.
Inventors: |
Jackson; Roger P.; (Prairie
Village, KS) |
Correspondence
Address: |
John C. McMahon
P.O. Box 30069
Kansas City
MO
64112
US
|
Family ID: |
36317306 |
Appl. No.: |
12/220466 |
Filed: |
July 24, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10986377 |
Nov 10, 2004 |
|
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12220466 |
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Current U.S.
Class: |
606/301 ;
606/302; 606/305 |
Current CPC
Class: |
A61B 17/7037 20130101;
A61B 17/7011 20130101; A61B 17/7032 20130101 |
Class at
Publication: |
606/301 ;
606/302; 606/305 |
International
Class: |
A61B 17/04 20060101
A61B017/04 |
Claims
1. A polyaxial bone screw assembly method comprising: (a) inserting
a closed ring-like retainer structure through a channel and into a
cavity of a head, the retainer structure having an inner surface
with a first helically wound advancement structure thereon; (b)
inserting a capture structure of a bone screw shank through a shank
receiving opening of the head and into the cavity thereof, the
capture structure being integral with an elongate threaded shank
body and having an outer surface with a second helically wound
advancement structure thereon, the head channel opening outwardly
and adapted to receive a rod within the channel, the head cavity
being disposed between and communicating with both the channel and
the shank receiving opening; (c) attaching the capture structure to
the retainer structure within the cavity by mating the first and
second helically wound advancement structures.
2. The method of claim 1 further comprising: (d) driving the shank
body into bone by rotating the shank body with a tool engaged with
a tool engagement formation disposed on at least one of the capture
structure and the retainer structure.
3. The method of claim 3 further comprising: (e) subsequently
inserting a rod into the channel; and (f) biasing the rod against
the capture structure by inserting a closure structure into the
channel.
4. A method of assembling a polyaxial bone screw comprising the
steps of: (a) providing a bone screw shank, head and closed
ring-like retainer structure; (b) providing the shank with an upper
threaded capture structure; (c) providing the retainer structure
with a closed threaded bore; (d) providing the head with a central
cavity and a shank receiving bore connecting the cavity with an
underside of the head; (e) loading the retainer structure into the
cavity; (f) uploading the shank capture structure into the cavity
through the shank receiving bore; and (g) screwing the shank
capture structure into the retainer structure threaded bore while
within the head.
5. The method according to claim 4 including the steps of: (a)
providing the head with an upwardly open channel that communicates
with the cavity; and (b) downloading the retainer structure through
the channel into the cavity.
6. In a shank for a bone screw having a projection near an upper
end thereof adapted for operably mating with a tool to drive the
shank into a bone; the improvement comprising: (a) the projection
includes a base and the shank includes a recess surrounding the
base adapted to receive the tool.
7. The shank according to claim 6 wherein: (a) said recess has an
outer wall opposite the projection that is sized and shaped to be
adapted to fit the contour of an outer surface of the tool.
8. The shank according to claim 7 wherein: (a) the outer wall is
hexagonal.
9. The shank according to claim 7 wherein: (a) the outer wall is
multi faceted in shape.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 10/986,377, filed Nov. 10, 2004.
BACKGROUND OF THE INVENTION
[0002] The present invention is directed to polyaxial bone screws
for use in bone surgery, particularly spinal surgery. Such screws
have a head that can swivel about a shank of the bone screw,
allowing the head to be positioned in any of a number of angular
configurations relative to the shank.
[0003] Many spinal surgery procedures require securing various
implants to bone and especially to vertebrae along the spine. For
example, elongate rods are often utilized that extend along the
spine to provide support to vertebrae that have been damaged or
weakened due to injury or disease. Such rods must be supported by
certain vertebrae and support other vertebrae.
[0004] The most common mechanism for providing vertebral support is
to implant bone screws into certain bones which then in turn
support the rod or are supported by the rod. Bone screws of this
type may have a fixed head relative to a shank thereof. In the
fixed bone screws, the head cannot be moved relative to the shank
and the rod must be favorably positioned in order for it to be
placed within the head. This is sometimes very difficult or
impossible to do. Therefore, polyaxial bone screws are commonly
preferred.
[0005] Polyaxial bone screws allow rotation of the head about the
shank until a desired rotational position of the head is achieved
relative to the shank. Thereafter, a rod can be inserted into the
head and eventually the head is locked or fixed in a particular
position relative to the shank.
[0006] A variety of polyaxial or swivel-head bone screw assemblies
are available. One type of bone screw assembly includes an open
head that allows for placement of a rod within the head. A closure
top or plug is then used to capture the rod in the head of the
screw.
[0007] Because such implants are for placement within the human
body, it is desirable for the implant to have as little effect on
the body as possible. Consequently, heavy, bulky implants are
undesirable and lighter implants with a relatively small profile
both in height and width are more desirable. However, a drawback to
smaller, lighter implants is that they may be more difficult to
rigidly fix to each other and into a desired position. Lack of bulk
may also mean lack of strength, resulting in slippage under high
loading. Also, more component parts may be required to rigidly fix
the implant in a desired position. A further drawback of smaller
components is that they may be difficult to handle during surgery
because of their small size, failing to provide adequate driving or
gripping surfaces for tools used to drive the shank into bone.
[0008] One undesirable attribute of some of the swivel-head
implants is the need for a multitude of components that may loosen
or even disassemble within the body. It is most undesirable for
components to be free to move around in the body after the
completion of surgery. Loosening of components relative to each
other may result in related undesirable movement of the bone or
vertebra that the implant was intended to stabilize.
SUMMARY OF THE INVENTION
[0009] It is an object of the invention to overcome one or more of
the problems described above. Further objects of the invention
include: providing a polyaxial bone screw with features that
provide adequate frictional or gripping surfaces for bone
implantation tools and may be readily, securely fastened to each
other and to bone. Also, if the implant should slip or become loose
for some reason, an object of the invention is to provide an
implant wherein all of the parts remain together and do not
separate. Furthermore, it is an object of the invention to provide
a lightweight, low profile polyaxial bone screw that assembles in
such a manner that the components cooperate to create an overall
structure that prevents unintentional disassembly.
[0010] A polyaxial bone screw assembly of the present invention
includes a shank having a body for fixation to a bone. Integral
with the shank and extending axially upwardly and outwardly
therefrom is a capture structure. The capture structure has a
radially projecting outer surface that is substantially cylindrical
and that further includes a helically wound structure, such as a
thread. The upper end of the shank is convexly curved.
[0011] The bone screw assembly further includes a head having a top
portion and a base. The top portion is open and has a channel. The
base also is upwardly open and includes an inner seating surface
partially defining a cavity and has a lower aperture or opening.
The channel of the top portion communicates with the cavity, which
in turn communicates with an exterior of the base of the head
through the base opening. The base opening is sized and shaped to
receive the capture structure of the shank into the head
cavity.
[0012] The bone screw assembly also includes an integral one piece
contiguously closed ring-like retainer structure that has an
internal surface with a helically wound structure thereon, such as
a thread. The thread of the retainer structure is sized and shaped
to mate with the thread of the shank capture structure when the
retainer structure and the capture structure are coaxially aligned
within the head cavity, thereby securing the retainer structure to
the capture structure.
[0013] The external surface of the retainer structure is configured
to be in slidable mating engagement with the surface defining the
cavity of the head. Preferably, the retainer structure external
surface and the mating head inner surface are substantially
spherical. However, it is noted that the mating surfaces may be of
another shape, such as conical or tapered, especially for the head
cavity inner surface. The cooperating shapes of the retainer
external surface and the head inner surface enable selective
angular positioning of the shank body with respect to the head.
[0014] In one embodiment according to the invention, the capture
structure includes a tool engagement formation that extends or
projects from the capture structure and is located between the
curved upper end and the threaded cylindrical portion thereof. In
another embodiment of the invention, the closed ring-like retainer
structure includes a tool engagement formation. In both
embodiments, the tool formation is for non-slip engagement by a
tool for driving the shank into bone and may also be cooperatively
used for attaching the retainer structure to the capture
structure.
[0015] Also according to the invention are tool seating surfaces
that may be disposed on one or both of the capture structure and
the retainer structure. In one embodiment, the shank capture
structure includes tool engagement surfaces that are positioned and
shaped to receive a socket type tool and a planar, tool seating
surface extending radially from the lower end of the tool
engagement surfaces. The seating surface is disposed coaxially with
the shank body. The retainer structure has mating seating surfaces
that cooperate with the shank capture structure seating surface.
The tool seating surfaces and the tool engagement surfaces
partially define a recess for receiving a driving tool mating with
the tool engagement surfaces. When engaged, the driving tool is in
contact with the capture structure tool seating surface, providing
greater mating surface to the capture structure tool engagement
surfaces so as to provide additional surface for frictional
gripping when the shank body is driven into bone, especially harder
bone.
[0016] In certain embodiments a tool seating and partially
surrounding surface may be disposed on the retainer structure
according to the invention such that when the retainer structure is
mated with the capture structure, the retainer structure seating
surface extends radially from the lower end of the tool engagement
surfaces and is disposed coaxially with respect to the shank
body.
[0017] In certain embodiments, both the capture structure and the
retainer structure may include tool seating surfaces that extend
radially in the same plane when the capture structure and the
retainer structure are mated. In such embodiments, the two tool
seating surfaces and the shank tool engagement surfaces partially
define a recess for receiving a driving tool engaged with the tool
engagement surfaces. When engaged, the driving tool is in contact
with both tool seating surfaces, thereby seating the tool lower
relative to the tool engagement surfaces and providing additional
frictional gripping surface when the shank body is driven into
bone.
[0018] A polyaxial bone screw assembly method according to the
invention includes inserting an independent closed ring-like
retainer into a head cavity, inserting a capture structure of a
bone screw shank through a shank receiving opening of the head and
into a cavity thereof; and attaching the capture structure to the
retainer structure within the head.
[0019] A method according to the invention further includes driving
the shank body into bone by rotating the shank body with a tool
engaged with a tool engagement formation, such as a pair of aligned
and spaced slots, disposed on the capture structure or the retainer
structure. Further assembly steps according to the invention
include inserting a rod into the channel; and biasing the rod
against a top of the bone screw shank capture structure by
rotatably inserting a closure member structure within or onto a
mating structure of the rod receiving channel structure.
[0020] It is to be understood that while certain forms of the
present invention have been illustrated and described herein, it is
not to be limited to the specific forms or arrangement of parts
described and shown.
[0021] Other objects and advantages of this invention will be
apparent to those skilled in the art from the following description
taken in conjunction with the drawings and the appended claims.
[0022] The drawings constitute a part of this specification and
include exemplary embodiments of the present invention and
illustrate various objects and features thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is an exploded perspective view of a polyaxial bone
screw assembly according to the present invention having a shank
with a capture structure at one end thereof, a head, and a closed
ring-like retainer structure and further showing a rod and closure
structure.
[0024] FIG. 2 is an enlarged top plan view of the retainer
structure of FIG. 1.
[0025] FIG. 3 is an enlarged cross-sectional view of the retainer
structure of FIG. 2, taken along line 3-3 of FIG. 2.
[0026] FIG. 4 is an enlarged top plan view of the shank of FIG.
1.
[0027] FIG. 5 is an enlarged cross-sectional view of the shank,
taken along line 5-5 of FIG. 4.
[0028] FIG. 6 is an enlarged cross-sectional view of the head,
taken along the line 6-6 of FIG. 1, and showing the retainer
structure seated in the head (in solid lines) and illustrating the
retainer structure being inserted into the head (in dashed
lines).
[0029] FIG. 7 is an enlarged cross-sectional view of the head and
retainer structure similar to FIG. 6, showing the shank capture
structure partially threaded into the retainer structure.
[0030] FIG. 8 is an enlarged cross-sectional view of the head and
retainer structure similar to FIG. 7, illustrating the fully
assembled shank and retainer structure pivoted to a selected angle
relative to the head.
[0031] FIG. 9 is an enlarged cross-sectional view of a vertebra,
and head and retainer similar to FIG. 7, showing the shank being
implanted into the vertebra using a driving tool mounted on the
shank capture structure.
[0032] FIG. 10 is an enlarged, fragmentary cross-sectional view of
the head, rod and vertebra, similar to FIG. 8 and further showing
the closure member structure in contact with the rod and the rod in
contact with the capture structure.
[0033] FIG. 11 is a fragmentary and enlarged perspective view of
the assembly of FIG. 1 shown completely assembled.
[0034] FIG. 12 is an exploded perspective view of an alternative
embodiment of a polyaxial bone screw assembly according to the
present invention having a shank with an upper capture structure, a
head, and a closed ring-like retainer structure.
[0035] FIG. 13 is an enlarged top plan view of the retainer
structure of FIG. 12.
[0036] FIG. 14 is an enlarged cross-sectional view of the retainer
structure of FIG. 13, taken along line 14-14 of FIG. 13.
[0037] FIG. 15 is an enlarged top plan view of the shank of FIG.
12.
[0038] FIG. 16 is an enlarged cross-sectional view of the shank of
FIG. 12, taken along line 16-16 of FIG. 15.
[0039] FIG. 17 is an enlarged cross-sectional view of the head of
FIG. 12 showing the retainer structure seated in the head, taken
along line 17-17 of FIG. 12.
[0040] FIG. 18 is an enlarged cross-sectional view of the head and
retainer structure similar to FIG. 17, showing the shank capture
structure partially assembled with respect to the retainer
structure.
[0041] FIG. 19 is an enlarged cross-sectional view of the head and
retainer structure, similar to FIG. 18, illustrating the shank and
retainer structure being pivotable to selected angles relative to
the head in solid and phantom lines.
[0042] FIG. 20 is an enlarged and fragmentary perspective view,
similar to FIG. 19, illustrating the use of a punch tool to lock
the position of the retainer structure relative to the capture
structure.
[0043] FIG. 21 is an enlarged and partial view similar to FIG. 20
showing a thread of the capture structure deformed to rigidly
secure the retainer structure to the capture structure.
[0044] FIG. 22 is an enlarged cross-sectional view of a vertebra,
and the head and retainer structure of FIG. 12, showing the shank
being implanted into the vertebra using a driving tool mounted on
the shank capture structure and the retainer structure.
[0045] FIG. 23 is an exploded fragmentary, partially
cross-sectional view of the embodiment of FIG. 12, showing a rod in
contact with the domed upper extension of the capture structure and
illustrating a two-piece closure member structure and driving tool
for biasing the rod against the domed upper extension of the
capture structure.
[0046] FIG. 24 is an enlarged cross-sectional view of the assembly
of FIG. 23 shown completely assembled.
[0047] FIG. 25 is an enlarged perspective view of the assembly of
FIG. 23 shown completely assembled.
DETAILED DESCRIPTION OF THE INVENTION
[0048] As required, detailed embodiments of the present invention
are disclosed herein; however, it is to be understood that the
disclosed embodiments are merely exemplary of the invention, which
may be embodied in various forms. Therefore, specific structural
and functional details disclosed herein are not to be interpreted
as limiting, but merely as a basis for the claims and as a
representative basis for teaching one skilled in the art to
variously employ the present invention in virtually any
appropriately detailed structure.
[0049] In FIGS. 1-11 the reference number 1 generally represents a
first embodiment of a polyaxial bone screw apparatus or assembly
according to the present invention. The assembly 1 includes a shank
4 that further includes a body 6 integral with an upwardly
extending capture structure 8; a head 10; and a closed integral
retainer structure or ring 12. The shank 4, head 10 and retainer
structure 12 preferably are assembled prior to implantation of the
shank body 6 into a vertebra 15, which procedure is shown in FIG.
9.
[0050] FIG. 1 further shows a closure structure 18 of the invention
for biasing a longitudinal member such as a rod 21 against the
capture structure 8 which biases the ring 12 into fixed frictional
contact with the head 10, so as to fix the rod 21 relative to the
vertebra 15. The head 10 and shank 4 cooperate in such a manner
that the head 10 and shank 4 can be secured at any of a plurality
of angles, articulations or rotational alignments relative to one
another and within a selected range of angles both from side to
side and from front to rear, to enable flexible or articulated
engagement of the head 10 with the shank 4 until both are locked or
fixed relative to each other near the end of an implantation
procedure.
[0051] The shank 4, best illustrated in FIGS. 1 and 5, is elongate,
with the shank body 6 having a helically wound bone implantable
thread 24 extending from near a neck 26 located adjacent to the
capture structure 8 to a tip 28 of the body 6 and extending
radially outward therefrom. During use, the body 6 utilizing the
thread 24 for gripping and advancement is implanted into the
vertebra 15 leading with the tip 28 and driven down into the
vertebra 15 with an installation or driving tool 31, so as to be
implanted in the vertebra 15 to near the neck 26, as shown in FIG.
9, and as is described more fully in the paragraphs below. The
shank 4 has an elongate axis of rotation generally identified by
the reference letter A. It is noted that any reference to the words
top, bottom, up and down, and the like, in this application refers
to the alignment shown in the various drawings, as well as the
normal connotations applied to such devices, and is not intended to
restrict positioning of the assembly 1 in actual use.
[0052] The neck 26 extends axially outward and upward from the
shank body 6. The neck 26 is of reduced radius as compared to an
adjacent top 32 of the body 6. Further extending axially and
outwardly from the neck 26 is the capture structure 8 that provides
a connective or capture apparatus disposed at a distance from the
body top 32 and thus at a distance from the vertebra 15 when the
body 6 is implanted in the vertebra 15.
[0053] The capture structure 8 is configured for connecting the
shank 4 to the head 10 and capturing the shank 4 in the head 10.
The capture structure 8 has an outer substantially cylindrical
surface 34 having a helically wound advancement structure thereon
which in the illustrated embodiment is a V-shaped thread 36
disposed adjacent to a seating surface 38 and extending to a
location near a rim 37. The rim 37 is adjacent to the neck 26.
Although a simple thread 36 is shown in the drawings, it is
foreseen that other structures including other types of threads,
such as buttress and reverse angle threads, and non threads, such
as helically wound flanges with interlocking surfaces, may be
alternatively used in alternative embodiments of the present
invention. The cylindrical surface 34 could be truncated giving a
non-contiguous helically wound structure.
[0054] The shank 4 further includes a tool engagement structure 40
disposed near a top end surface 42 thereof for engagement of the
driving tool 31 shown in FIG. 9 which includes a driving structure
in the form of a socket. The tool 31 is configured to fit about the
tool engagement structure 40 so as to form a socket and mating
projection for both driving and rotating the shank body 6 into the
vertebra 15. Specifically in the embodiment shown in FIGS. 1-11,
the tool engagement structure 40 is in the shape of a hexagonally
shaped extension head coaxial with both the threaded shank body 6
and the threaded capture structure 8.
[0055] The top end surface 42 of the shank 4 is preferably curved
or dome-shaped as shown in the drawings, for contact engagement or
positive mating engagement with the rod 21, when the bone screw
assembly 1 is assembled, as shown in FIGS. 10 and 11 and in any
alignment of the shank 4 relative to the head 10. In certain
embodiments, the surface 42 is smooth. While not required in
accordance with practice of the invention, the surface 42 may be
scored or knurled to further increase frictional positive mating
engagement between the surface 42 and the rod 21.
[0056] The shank 4 shown in the drawings is cannulated, having a
small central bore 44 extending an entire length of the shank 4
along the axis A. The bore 44 is defined by an inner cylindrical
wall 45 of the shank 4 and has a first circular opening 46 at the
shank tip 28 and a second circular opening 48 at the top surface
42. The bore 44 is coaxial with the threaded body 6 and the capture
structure outer surface 34. The bore 44 provides a passage through
the shank 4 interior for a length of wire (not shown) inserted into
the vertebra 15 prior to the insertion of the shank body 6, the
wire providing a guide for insertion of the shank body 6 into the
vertebra 15.
[0057] Referring to FIGS. 1 and 6 through 10, the head 10 has a
generally U-shaped appearance with a partially cylindrical inner
profile and a faceted outer profile; however, the outer profile
could also be partially cylindrical. The head 10 includes a
somewhat spherical base 50 integral with a pair of upstanding arms
52 and 54 forming a U-shaped cradle and defining a U-shaped channel
56 between the arms 52 and 54 with an upper opening 57 and a lower
seat having substantially the same radius as the rod 21 for
operably snugly receiving the rod 21.
[0058] Each of the arms 52 and 54 has an interior surface that
defines the inner cylindrical profile and includes a partial
helically wound guide and advancement structure 62. In the
illustrated embodiment, the guide and advancement structure 62 is a
partial helically wound interlocking flangeform configured to mate
under rotation with a similar structure on the closure top 18, as
described more fully below. However, it is foreseen that the guide
and advancement structure 62 could alternatively be a V-shaped
thread, a buttress thread, a reverse angle thread or other thread
like or non-thread like helically wound advancement structures for
operably guiding under rotation and advancing the closure top
downward between the arms 52 and 54.
[0059] Tool engaging apertures 64 and 65 are formed within the arms
52 and 54, respectively which may be used for holding the head 10
during assembly with the shank 4 and the retainer structure 12 and
also during the implantation of the shank body 6 into a vertebra
15.
[0060] Communicating with the apertures 64 and 65 are respective
upwardly projecting, hidden inner recesses 68 and 69. The holding
tool (not shown) is sized and shaped to have structure to mate with
and to be received in the apertures 64 and 65 and locked into place
by pulling the holding tool slightly axially upward relative to the
base 50 and toward the upper opening 57 of the channel 56 formed by
the arms 52 and 54. The holding tool and respective apertures 64
and 65 can be configured for a flexible snap on/spring off
engagement wherein the holding tool has flexible legs which splay
outwardly to position the tool for engagement in the apertures 64
and 65. It is noted that the apertures 64 and 65 and the
cooperating holding tool may be configured to be of a variety of
sizes and locations along any of the surfaces of the arms 52 and
55, for example, extending into a face 75 or disposed only at a
single face or facet.
[0061] Communicating with and located beneath the U-shaped channel
56 of the head 10 is a chamber or cavity 78 substantially defined
by an inner surface 80 of the base 50, the cavity 78 opens upwardly
into the U-shaped channel 56. The inner surface 80 is substantially
spherical, with at least a portion thereof forming a partial
internal spherical seating surface 82 having a first radius. The
surface 82 is sized and shaped for mating with the retainer
structure 12, as described more fully below.
[0062] The base 50 further includes a restrictive neck 83, having a
second radius R and defining a bore 84 communicating with the
cavity 78 and a lower exterior 86 of the base 50. The bore 84 is
coaxially aligned with respect to a rotational axis B of the head
10. The neck 83 and associated bore 84 are sized and shaped to be
smaller (the second radius) than a radial dimension of the retainer
structure 12 (the first radius), as will be discussed further
below, so as to form a restriction at the location of the neck 83
relative to the retainer structure 12, to prevent the retainer
structure 12 from passing from the cavity 78 and out into the lower
exterior 86 of the head 10 when the retainer structure 12 is
seated.
[0063] The inner surface 80 further defines an elongate upper
loading recess 87 for accommodating and loading the retainer
structure 12 into the cavity 78. The loading recess 87 is generally
vertically disposed in the head 10, extending between and
communicating with both the channel 56 and the cavity 78, allowing
for ease in top loading the retainer structure 12 into the cavity
through the upper opening 57 and otherwise allowing for the
spherical wall 80 of the head 10 to have a comparatively enlarged
radius to allow for increased thickness and strength of the head
base 50; however, the loading recess 87 is not always
necessary.
[0064] The retainer structure or ring 12 is used to retain the
capture structure 8 of the shank 4 within the head 10. The retainer
structure 12, best illustrated by FIGS. 1-3 and 6-8, has an
operational central axis that is the same as the elongate axis A
associated with the shank 4, but when the retainer structure 12 is
separated from the shank 4, the axis of rotation is identified as
axis C, as shown in FIG. 3. The retainer structure 12 has a central
bore 90 that passes entirely through the retainer structure 12 from
a top surface 92 to a bottom surface 94 thereof. A first inner
cylindrical surface 96 defines a substantial portion of the bore
90, the surface 96 having a helically wound advancement structure
thereon as shown by a helical rib or thread 98 extending from
adjacent the bottom surface 94 to adjacent a flat, seating surface
99 disposed perpendicular to the inner surface 96.
[0065] Although a simple helical rib 98 is shown in the drawings,
it is foreseen that other helical structures including other types
of threads, such as buttress and reverse angle threads, and non
threads, such as helically wound flanges with interlocking
surfaces, may be alternatively used in an alternative embodiment of
the present invention. The inner cylindrical surface 96 with
helical rib 98 are configured to mate under rotation with the
capture structure outer surface 34 and helical advancement
structure or thread 36, as described more fully below.
[0066] The retainer structure 12 further includes a second inner
wall or cylindrical surface 102, coaxial with the first inner
cylindrical surface 96. The surface 102 is disposed between the
seating surface 99 and the top surface 92 of the retainer structure
12 and has a diameter greater than that of the cylindrical surface
96. As will be described more fully below, the cylindrical surface
102 in cooperation with the seating surface 99 and the surface 38
of the retainer structure 12, provide a recess about the base of
the tool engagement structure 40 and a stable seating surface for
the tool 31, as shown in FIG. 9. The wall 102 which is the outer
wall of the recess may be shaped to fit an outer surface of the
tool 31 and may be faceted or especially hexagonal in shape to
better grip the tool 31.
[0067] The retainer structure or ring 12 has a radially outer
partially spherically shaped surface 104 sized and shaped to mate
with the partial spherical shaped seating surface 82 of the head
and having a third radius approximately equal to the first radius
associated with the surface 82. The retainer structure third radius
is larger than the second radius R of the neck 83 of the head 10.
Although not required, it is foreseen that the outer partially
spherically shaped surface 104 may be a high friction surface such
as a knurled surface or the like.
[0068] The elongate rod or longitudinal member 21 that is utilized
with the assembly 1 can be any of a variety of implants utilized in
reconstructive spinal surgery, but is normally a cylindrical
elongate structure having a cylindrical surface 106 of uniform
diameter and having a generally smooth surface. The rod 21 is
preferably sized and shaped to snugly seat near the bottom of the
U-shaped channel 56 of the head 10 and, during normal operation, is
positioned slightly above the bottom of the channel 56 at the lower
seat 58. In particular, the rod 21 normally directly or abutingly
engages the shank top surface 42, as shown in FIG. 10 and is biased
against the dome shank top surface 42, consequently biasing the
shank 4 downwardly in a direction toward the base 50 of the head 10
when the assembly 1 is fully assembled. For this to occur, the
shank top surface 42 must extend at least slightly into the space
of the channel 56 when the retainer structure 12 is snugly seated
in the lower part of the head cavity 80. The shank 4 and retainer
structure 12 are thereby locked or held in position relative to the
head 10 by the rod 21 firmly pushing downward on the shank top
surface 42.
[0069] With reference to FIGS. 1, 10 and 11, the closure structure
or closure top 18 can be any of a variety of different types of
closure structures for use in conjunction with the present
invention with suitable mating structure on the upstanding arms 52
and 54. In the embodiment shown, the closure top 18 is rotatably
received between the spaced arms 52 and 54.
[0070] The illustrated closure top 18 has a generally cylindrical
shaped base 108 with an upwardly extending break-off head 110. The
base 108 includes a helically wound guide and advancement structure
111 that is sized, shaped and positioned so as to engage and
interlock with the guide and advancement structure 62 on the arms
52 and 54 to provide for rotating advancement of the closure
structure 18 into the head 10 when rotated clockwise and, in
particular, to cover the top or upwardly open portion of the
U-shaped channel 56 to capture the rod 21, preferably without
splaying of the arms 52 and 54. The closure structure 18 also
operably biases against the rod 21 by advancement and applies
pressure to the rod 21 under torquing, so that the rod 21 is urged
downwardly against the shank top end surface 42 that extends up
into the channel 56. Downward biasing of the shank top surface 42
operably produces a frictional engagement between the rod 21 and
surface 42 and also urges the retainer structure 12 toward the base
50 of the head 10, so as to frictionally seat the retainer
structure external spherical surface 104 fixedly against the
partial internal spherical seating surface 82 of the head 10, also
fixing the shank 4 and retainer structure 12 in a selected, rigid
position relative to the head 10.
[0071] In the embodiment shown, the closure structure includes a
break-off head 110 secured to the base 108 at a neck 114 that is
sized and shaped so as to break away at a preselected torque that
is designed to properly seat the retainer structure 12 in the head
10. The break-off head 110 includes an external faceted surface 115
that is sized and shaped to receive a conventional mating socket
type head of a driving tool (not shown) to rotate and torque the
closure structure 18. The break-off head 110 also includes a
central bore 117 and grooves 118 for operably receiving
manipulating tools.
[0072] The closure structure 18 also includes removal tool
engagement structure which in the present embodiment is in the form
of a hex-shaped and axially aligned aperture 116 disposed in the
base 108, as shown in FIGS. 10 and 11. The hex aperture 116 is
accessible after the break-off head 110 breaks away from the base
108. The aperture 116 is coaxial with the helically wound guide and
advancement structure 111 and is designed to receive a hex tool, of
an Allen wrench type, into the aperture 116 for rotating the
closure structure base 108 subsequent to installation so as to
provide for removal thereof, if necessary. Although a hex-shaped
aperture 116 is shown in the drawings, the tool engagement
structure may take a variety of tool-engaging forms and may include
one or more apertures of various shapes, such as a pair of spaced
apart apertures, or a left hand threaded bore, or an easyout
engageable step down bore, or a Torx aperture, or a multi-lobular
aperture or the like.
[0073] Prior to the polyaxial bone screw assembly 1 being placed in
use according to the invention, the ring-like retainer structure 12
is typically first inserted or top-loaded, into the head U-shaped
channel 56, as is shown in dotted lines in FIG. 6, and then into
the cavity 78 through the vertical loading recess 87 to dispose the
structure 12 within the inner surface 80 of the head 10. Then, the
retainer structure 12 is rotated approximately 90 degrees so as to
be coaxial with the head 10 and then seated in sliding engagement
with the seating surface 82 of the head 10, also shown in FIG.
6.
[0074] With reference to FIG. 7, the shank capture structure 8 is
then inserted or bottom-loaded into the head 10 through the bore 84
defined by the neck 83. The retainer structure 12, now disposed in
the head 10 is coaxially aligned with the shank capture structure 8
so that the helical advancement structure 36 rotatingly mates with
the helical advancement structure 98 of the retainer structure
12.
[0075] The shank 4 and or the retainer structure 12 are rotated to
fully mate the structures 36 and 98 along the respective
cylindrical surfaces 34 and 96, as shown in FIG. 7, fixing the
capture structure 8 to the retainer structure 12, until the seating
surface 38 and the seating surface 99 are contiguous and disposed
in the same plane and the rim 37 abuts the surface 94 of the
retainer structure 12 as shown in FIG. 8. Permanent, rigid
engagement of the capture structure 8 to the retainer structure 12
may be further ensured and supported by the use of adhesive, a spot
weld, deforming one or both threads with a punch or the like.
[0076] As shown in FIG. 8, at this time the shank 4 is in slidable
and rotatable engagement with the head 10, while the capture
structure 8 and the lower aperture or neck 83 of the head 10
cooperate to maintain the shank body 6 in rotational relation with
the head 10. According to the embodiment of the invention shown in
FIGS. 1-11, only the retainer structure 12 is in slidable
engagement with the head spherical seating surface 82. Both the
capture structure 12 and threaded portion of the shank body 6 are
in spaced relation with the head 10.
[0077] It is believed that an advantage to this embodiment is that,
although the shank 6 could engage the head lower aperture or neck
83 when rotated fully relative to the head 10 as best illustrated
in FIG. 8, upper shank body 6 does not contact the lower spherical
seating surface 82, so that rotational stresses between the capture
structure 8 and the retainer structure 12 are lessened, making it
less likely that the retainer structure 12 would loosen from the
capture structure 8 or that the capture structure would fail or
break when the assembly 1 is implanted and loaded.
[0078] An extent of rotation is shown in FIG. 8 where it is
illustrated that the shank body 6 can be rotated through a
substantial angular rotation relative to the head 10, both from
side to side and from front to rear so as to substantially provide
a universal or ball joint wherein the angle of rotation is only
restricted by engagement of the neck 26 of the shank body 6 with
the neck or lower aperture 83 of the head 10.
[0079] With reference to FIG. 9, the assembly 1 is then typically
screwed into a bone, such as the vertebra 15, by rotation of the
shank 4 using the driving tool 31 that operably drives and rotates
the shank 4 by engagement thereof with the hexagonally shaped
extension head 40 of the shank 4. Preferably, when the driving tool
31 engages the head 40, an end portion 118 thereof is disposed in a
recess defined by the head 40, the seating surface 38, the
contiguous seating surface 99 and the inner cylindrical surface
102, with a bottom surface 119 of the tool 31 contacting and
frictionally engaging both the seating surface 38 and the seating
surface 99. Some frictional engagement between an outer surface 120
of the tool 31 with the cylindrical surface 102 may also be
achievable during rotation of the driving tool 31.
[0080] It is foreseen that in other embodiments according to the
invention, the tool engaging recess may be defined by only one of
the seating surface 38 or the seating surface 99. For example, a
retainer structure might not include a seating surface, so a
driving tool might seat or mate only with a seating surface or an
internal aperture of a shank capture structure. Alternatively, the
tool engaging end of a capture structure might be of a size and
shape that a driving tool substantially seats on a seating surface
of a retainer structure or ring and not the capture structure.
[0081] Typically, the head 10 and the retainer structure 12 are
assembled on the shank 4 before inserting the shank body 6 into the
vertebra 15, but in certain circumstances, the shank body 6 can be
first partially implanted in the bone with the capture structure 8
extending proud to allow assembly with the head 10 utilizing the
retainer structure 12. Then the shank body 6 can be further driven
into the vertebra 15.
[0082] With reference to FIGS. 1 and 5 as well as FIG. 9, the
vertebra 15 may be pre-drilled to minimize stressing the bone and
have a guide wire (not shown) that is shaped for the cannula 44
inserted to provide a guide for the placement and angle of the
shank 4 with respect to the vertebra 15. A further tap hole may be
made using a tap with the guide wire as a guide. Then, the assembly
1 or the solitary shank 4, is threaded onto the guide wire
utilizing the cannulation bore 44 by first threading the wire into
the bottom opening 46 and then out of the top opening 48. The shank
4 is then driven into the vertebra 15, using the wire as a
placement guide.
[0083] With reference to FIGS. 1, 10 and 11, the rod 21 is
eventually positioned within the head U-shaped channel 56, and the
closure structure or top 18 is then inserted into and advanced
between the arms 52 and 54 so as to bias or push against the rod
21. The break-off head 110 of the closure structure 18 is twisted
to a preselected torque, for example 90 to 120 inch pounds, to urge
the rod 21 downwardly. The shank top end surface 42, because it is
rounded to approximately equally extend upward into the channel 56
approximately the same amount no matter what degree of rotation
exists between the shank 4 and head 10 and because the surface 42
is sized to extend upwardly into the U-shaped channel 56, the
surface 42 is engaged by the rod 21 and pushed downwardly toward
the base 50 of the head 10 when the closure structure 18 biases
downwardly toward and onto the rod 21. The downward pressure on the
shank 4 in turn urges the retainer structure 12 downward toward the
head seating surface 82, with the retainer structure seating
surface 99 in frictional engagement with the head seating surface
82. As the closure structure 18 presses against the rod 21, the rod
21 presses against the shank and the retainer structure 12 that is
now rigidly attached to the shank 4 which in turn becomes
frictionally and rigidly attached to the head 10, fixing the shank
body 6 in a desired angular configuration with respect to the head
10 and rod 21.
[0084] FIG. 10 illustrates the polyaxial bone screw assembly 1 and
including the rod 21 and the closure structure 18 positioned in a
vertebra 15. The axis A of the bone shank 4 is illustrated as not
being coaxial with the axis B of the head 10 and the shank 4 is
fixed in this angular locked configuration. Other angular
configurations can be achieved, as required during installation
surgery due to positioning of the rod 21 or the like.
[0085] If removal of the assembly 1 and associated rod 21 and
closure structure 18 is necessary, disassembly is accomplished by
using a driving tool of an Allen wrench type (not shown) mating
with the aperture 116 and turned counterclockwise to rotate the
base 108 and reverse the advancement thereof in the head 10. Then,
disassembly of the assembly 1 is accomplished in reverse order to
the procedure described previously herein for assembly.
[0086] With reference to FIGS. 12-25, the reference number 201
generally represents a second or alternative embodiment of a
polyaxial bone screw apparatus or assembly according to the present
invention. As shown in FIG. 12, the assembly 201 includes a shank
204 that has a body 206 integral with a capture structure 208, a
head 210, and a retainer structure 212. The shank 204, head 210 and
retainer structure 212 are typically assembled prior to
implantation of the shank body 206 into a vertebra 215, as shown in
FIGS. 18-22.
[0087] FIG. 23 further shows a closure assembly 218 of the
invention for biasing a longitudinal member such as a rod 221
against the capture structure 208 so as to fix the rod 221 relative
to the vertebra 215.
[0088] Similar to the embodiment shown in FIGS. 1-11, the
alternative embodiment of the invention 201 provides for the head
210 and shank 204 to cooperate in such a manner that the head 210
and shank 204 can be secured at any of a plurality of obtuse
angles, relative to one another and within a selected range of
angles both side to side and front to rear, to enable flexible
engagement of the assembly 201 with the rod 221, as shown in FIG.
19, and will be described in more detail below. That is the two
elements, the head 210 and the shank 204, are articulatable or
rotatable relative to each other within a preselected range of
movement until locked in a fixed configuration at the end of the
procedure.
[0089] The shank 204, best illustrated in FIGS. 12 and 16 is
elongate, with the shank body 206 having a helically wound bone
implantable thread 224 extending from near a neck located adjacent
to the capture structure 208 to a tip of the body 206 and extending
radially outward therefrom. During use, the body 206 utilizing the
thread is implanted into the vertebra 215 leading with the tip 228
and driven down into the bone with an installation tool 231 to
adjacent the neck 226 as shown in FIG. 22, described more fully in
the paragraphs below. The shank 204 has an elongate axis of
rotation generally identified by the reference letter A'.
[0090] The neck 226 extends axially outward and upward from the
shank body 206. The neck 226 constricts to a reduced radius as
compared to an adjacent top 232 of the body 206. Further extending
axially and outwardly from the neck 226 is the capture structure
208 that provides a connective or capture apparatus disposed at a
distance from the shank body top 232 and thus at a distance from
the vertebra 215 when the body 206 is implanted in the vertebra
215. The capture structure 208 is configured for connecting the
shank 204 with the head 210 and the retainer structure 212.
[0091] The capture structure 208 includes an outer substantially
cylindrical surface 234 contiguous to the neck 226 and coaxial with
the shank body 206. The cylindrical surface 234 is also contiguous
and disposed substantially perpendicular to a seating surface 236.
The seating surface 236 is also coaxial with the shank body 206 and
the cylindrical surface 234. Both the cylindrical surface 234 and
the seating surface 236 are configured to come into frictional
engagement with the retainer structure 212, as described more fully
below.
[0092] Perpendicular to and contiguous with the seating surface 236
is a second cylindrical surface 238 having a helically wound
advancement structure thereon as shown by a helical rib or thread
240 extending from adjacent the seating surface 236 to adjacent a
rod engagement dome 242. Although a simple helical rib 240 is shown
in the drawings, it is foreseen that other helical structures
including other types of threads, such as buttress and reverse
angle threads, and non threads, such as helically wound flanges
with interlocking surfaces, may be alternatively used in an
alternative embodiment of the present invention.
[0093] The top end surface or dome 242 of the shank 204 is
preferably convex, domed or curved as shown in the drawings, and
sized and positioned for positive engagement with the rod 221 when
the bone screw assembly 201 is assembled, as shown in FIGS. 24 and
25. If desired, the dome 242 may be scored or knurled. In certain
embodiments, the purpose of the dome 242 is simply to be engaged by
the rod 221 during assembly and be biased downwardly in such a
manner as to frictionally engage the retainer structure 212, which
is secured to the shank 206 at this time, within the head 210, as
described below. The dome 242 may be radiused so that the dome 242
engages the rod 221 at generally the same level or height relative
to the head channel lower surface 258, even as the head 210 is
swiveled relative to the shank 204. However in other embodiments
the dome 242 can have other shapes.
[0094] In the embodiment shown in FIGS. 12-25, the shank body 206
and capture structure 208 components are integral. Furthermore the
shank 204 is cannulated, having a small cylindrical central bore
244 extending an entire length of the shank 204 along the axis A'.
The bore 244 is defined by an inner cylindrical wall 245 of the
shank 204 and has a first circular opening 246 at the shank tip 228
and a second circular opening 248 at the dome top surface 242. The
bore 244 is coaxial with the threaded body 206 and capture
structure outer cylindrical surfaces 234 and 238. The bore 244
provides a passage through the shank 204 interior for a length of
wire (not shown) inserted into the vertebra 215 prior to the
insertion of the shank body 206, the wire providing a guide for
accurate insertion of the shank body 206 into the vertebra 215.
[0095] Referring to FIGS. 12, 17 and 18, the head 210 is
substantially cylindrical in external profile and includes a base
portion 250 integral with a pair of upstanding arms 252 and 254
forming a U-shaped channel 256 between the arms 252 and 254 with an
upper opening 257 and the lower surface 258 having substantially
the same radius as the rod 221. In operation, the rod 221
preferably is located just above the channel lower surface 258.
[0096] Each of the arms 252 and 254 has an interior surface 260
that defines an inner cylindrical profile and includes a partial
helically wound guide and advancement structure 262. Similar to the
guide and advancement structure 62 shown with respect to FIGS.
1-11, the guide and advancement structure 262 is a partial
helically wound flangeform configured to mate and interlock under
rotation about an axis B' with a similar structure disposed on the
closure top assembly 218, as described more fully below. However,
it is foreseen that the guide and advancement structure 262 could
alternatively be a V-shaped thread, a buttress thread, a reverse
angle thread or other thread like or non-thread like helically
wound advancement structures for operably guiding under rotation
and advancing the closure top between the arms 252 and 254. Also,
it is foreseen that this mating advancement structure could be
located on the cylindrical external surfaces of the arms 252 and
254.
[0097] The head 210 includes external, closed end grip bores 264
and 265 disposed on the respective arms 252 and 254 for positive
engagement by a holding tool (not shown) to facilitate secure
gripping of the head 210 during assembly of the head 210 with the
shank 204 and retainer structure 212. Furthermore, the grip bores
264 and 265 may be utilized to hold the head 210 during the
implantation of the shank body 206 into the vertebra 215. The bores
264 and 265 are centrally located on the respective arms 252 and
254. However, it is noted that the bores 264 and 265 may be
configured to be of a variety of sizes and locations along outer
surfaces of the arms 252 and 254.
[0098] Communicating with the U-shaped channel 256 of the head 210
is a chamber or cavity 268 substantially defined by an inner
surface 270 of the base 50, the cavity 268 opening upwardly into
the U-shaped channel 256. The inner surface 270 is substantially
spherical, with at least a portion thereof forming a partial
internal spherical seating surface 272 having a first radius, the
surface 272 for mating with the retainer structure 212, as
described more fully below.
[0099] The base 250 further includes a restrictive aperture,
opening or neck 274, having a second radius R' and partially
defining a bore 276 communicating with the cavity 268 and a bottom
exterior 278 of the base 50. The bore 276 is coaxial with a
rotational axis B' of the head 210. A bevel 280 extends between the
neck 274 and the bottom exterior 278. The neck 274 and associated
bore 276 are sized and shaped to be smaller than a radial dimension
of the retainer structure 212, as will be discussed further below,
so as to form a restriction at the location of the neck 274
relative to the retainer structure 212, to prevent the structure
212 from passing between the cavity 268 and the bottom exterior 278
of the head 210, when fully seated. The bevel 280 widens the
angular range of the shank 204 when assembled with the head
210.
[0100] The retainer structure or ring 212 is used to retain the
capture structure 208 of the shank 204 within the head 210. The
retainer structure 212, best illustrated by FIGS. 12-14, has an
operational central axis that is the same as the elongate axis A'
associated with the shank 204, but when the retainer structure 212
is separated from the shank 204, the axis of rotation is identified
as axis C', as shown in FIG. 14. The retainer structure 212 has a
central bore 282 that passes entirely through the retainer
structure 212 from a top surface 284 to a bottom surface 285
thereof. A first inner cylindrical surface 286 defines a
substantial portion of the bore 282, the surface 286 having a
helically wound advancement structure thereon as shown by a helical
rib or thread 288 extending from adjacent the top surface 284 to
adjacent a seating surface 290 disposed perpendicular to the inner
surface 286.
[0101] Although a simple helical rib 288 is shown in the drawings,
it is foreseen that other helical structures including other types
of threads, such as buttress and reverse angle threads, and non
threads, such as helically wound flanges with interlocking
surfaces, may be alternatively used in an alternative embodiment of
the present embodiment. The first inner cylindrical surface 286
with helical rib 288 are configured to mate under rotation with the
capture structure outer surface 238 and helical advancement
structure or thread 240, as described more fully below.
[0102] The retainer structure 212 further includes a second inner
cylindrical surface 292, coaxial with the first inner cylindrical
surface 286. The surface 292 is disposed between the seating
surface 290 and the bottom surface 285 of the retainer structure
212 and has a diameter greater than that of the cylindrical surface
286. As will be described more fully below, the cylindrical surface
292 in cooperation with the seating surface 290, provide a recess
for insertion of the shank 204 thereinto and the seating surface
290 provides a frictional contact or seating surface for the
seating surface 236 of the capture structure 108 as shown in FIGS.
18 and 19.
[0103] The retainer structure or ring 212 has a radially outer
partially spherically shaped surface 294 sized and shaped to mate
with the partial spherical shaped seating surface 272 of the head
and having a third radius approximately equal to the first radius
associated with the surface 272. The retainer structure third
radius is larger than the second radius R' of the restrictive neck
274 of the head 210.
[0104] The retainer structure 212 shown in FIG. 13 further includes
a transverse slot 296 formed in the top surface 284 thereof for
engagement of the driving tool 231 shown in FIG. 22. It is foreseen
that a retainer structure according to the present invention may
include two or more slots in the retainer top surface, or other
types of apertures for engaging with a cooperating driving tool.
The slot 296 is defined by a pair of spaced, parallel walls 298
perpendicular to a base 300. The slot 296 extends out to the outer
spherical surface 294 from each side of the central bore 282. A
plane aligned with the center of the slot 296 intersects the
rotational axis C'. The tool 231 includes a pair of spaced slot
engaging extensions 302 sized and shaped to seat in the slot 296 on
either side of the central bore 282 and with the region
therebetween configured to clear the rod-engagement dome 242 during
assembly and while driving and rotating the shank body 206 into the
vertebra 215.
[0105] With reference to FIGS. 20 and 21, the slot 296 is
preferably sized such that, after the shank 204, head 210 and
retainer structure 12 have been assembled, a tool such as the
illustrated punch 304 may be inserted into the slot 296 to deform
the helical rib 240 of the capture structure 208 by causing a nick
or deformity 305 thereon, thereby preventing relative rotation
therebetween and rigidly fixing the rib 240 against the helical rib
288 of the retainer structure 212, ensuring a fixed relation
between the shank capture structure 208 and the retainer structure
212.
[0106] The elongate rod or longitudinal member 221 that is utilized
with the assembly 201 can be any of a variety of implants utilized
in reconstructive spinal surgery, but is normally a cylindrical
elongate structure having a cylindrical surface 306 of uniform
diameter. The rod 221 is preferably sized and shaped to snugly seat
at the lower channel seat 258 near the bottom of the U-shaped
channel 256 of the head 210, and, during normal operation, is
positioned slightly above the bottom of the channel 256. In
particular, the rod 221 normally engages the shank top surface or
dome 242, as shown in FIG. 24 and is biased against the dome 242,
consequently biasing the shank 204 downwardly in a direction toward
the base 250 of the head 210 when the assembly 201 is fully
assembled.
[0107] With reference to FIGS. 23-25, the closure or top assembly
218 can be any of a variety of different types of closure
structures for use in conjunction with the present invention with
suitable mating structure internally or externally on the
upstanding arms 252 and 254. The illustrated closure top assembly
218 includes a cylindrical closure plug 310 and a cylindrical inner
set screw or plug 312. The inner plug 312 includes a pointed rod
engaging projection or point 314 at a bottom surface thereof and a
tool engagement aperture 315 disposed in an opposite or top surface
thereof, illustrated in FIGS. 24 and 25 as a hex aperture. However,
the tool engagement structure 315 may take a variety of
tool-engaging forms and may include more than one aperture, such as
a pair of spaced apertures or other shapes such as Torx or the
like.
[0108] The closure plug 310 includes an outer helically wound guide
and advancement structure 316 that is sized, shaped and positioned
so as to engage the guide and advancement structure 262 on the arms
252 and 254 to provide for the rotation of the closure plug 310
into the head 210 and, in particular, to enclose the top of the
U-shaped channel 56 to capture the rod 221, preferably without
splaying of the arms 252 and 254. The closure plug 310 is a hollow
cylinder and also includes an inner threaded cylindrical wall 317
sized and shaped to receive and rotatingly mate with an outer
threaded surface 318 of the inner plug or set screw 312. As shown
in FIG. 25, the closure plug 310 further includes a pair of
transverse slots 319 in perpendicular relation, the slots 319 for
engagement with a driving tool (not shown). The hex aperture 315,
closure plug inner wall 317, inner plug wall 318, and arms 252 and
254 are configured so as to be coaxial upon assembly. A hex driving
tool 320 can be inserted into the aperture 315 of the inner plug
312 to drive and rotate both the inner plug 312 into the closure
plug 310 and the closure plug 310 into the head arms 252 and 254.
Preferably, the closure plug 310 is first driven and rotated into
the arms 252 and 254 by engaging a tool with the slots 319,
followed by the inner plug 312 being rotated individually into the
closure plug 312 by engagement with the tool 320.
[0109] The closure assembly 218 operably biases against the rod
221, with the projection 314 frictionally engaging and abrading the
rod surface 306 and thereby applying pressure to the rod 221 under
torquing, so that the rod 221 is urged downwardly against the
rod-engagement dome 242. Downward biasing of the dome 242 operably
produces a frictional engagement between the rod 221 and the dome
242 and also urges the retainer structure 212 toward the base 250
of the head 210, so as to frictionally seat the retainer structure
external spherical surface 294 fixedly or in a locked configuration
against the partial internal spherical seating surface 272 of the
head 210, also fixing the shank 204 and retainer structure 212 in a
selected, rigid angular position relative to the head 210.
[0110] If necessary, the hex tool 320 may be used to loosen the
assembly subsequent to installation, and for removal of the plugs
310 and 312.
[0111] When the polyaxial bone screw assembly 201 is placed in use
according to the invention, the closed ring-like retainer structure
212 is typically first inserted or top-loaded, into the head
U-shaped channel 256 and then into the cavity 268 within the inner
surface 270 of the head 210. Although not shown, the inner surface
270 may include a loading recess similar to the recess 87 disclosed
with respect to the first embodiment assembly 1, and may be loaded
into the head 210 in similar fashion. The retainer structure 212 is
then seated with the surface 294 in sliding engagement with the
spherical seating surface 272 of the head 210, as shown in FIG. 17.
Although not required, both the retainer structure and head
surfaces 294 and 272, respectively maybe high friction surfaces,
such as knurled surfaces, or the like.
[0112] With reference to FIGS. 17 and 18, the shank capture
structure 208 is inserted or bottom-loaded into the head 210
through the bore 276 defined by the neck 274. The retainer
structure 212, now disposed in the head 210 is coaxially aligned
with the shank capture structure 208 so that the helical
advancement structure 240 of the capture structure 208 rotatingly
mates with the helical advancement structure 288 of the retainer
structure 212. The shank 204 and or the retainer structure 212 are
rotated to fully mate the structures 240 and 288 along the
respective cylindrical surfaces 238 and 286, as shown in FIG. 18,
securing or fixing the capture structure 208 to the retainer
structure 212, until the seating surface 236 and the seating
surface 290 are in frictional contact, as shown in FIG. 19.
[0113] With reference to FIGS. 20 and 21, permanent, fixed or rigid
engagement of the capture structure 208 to the retainer structure
212 may be further enhanced by deforming the helical advancement
structure or thread 240 by inserting the pointed tool 304 into the
slot 296 and marring or nicking the helical rib 240 with the tool
304, resulting in the nick or deformity 305, as is shown in FIG.
21. The deformity 305 causes the rib 240 to abut against the
helical rib 288 of the retainer structure 212, thereby resisting
unscrewing and ensuring a fixed relation between the shank capture
structure 208 and the retainer structure 212. As with the assembly
1, the fixed relation between the rib 240 and the rib 288 may also
be accomplished by the use of an adhesive, or spot weld or the
like, in any area of the retainer structure cylindrical surface
238, especially where exposed by the slot 296.
[0114] As shown in FIG. 19, the shank 204 with integral capture
structure 208 and attached retainer structure 212 are in pivotable
engagement with the head 210. The capture structure 208 and the
neck 274 of the head 210, connecting the shank 204 to the head 210
and after locking the retainer structure 212 keeping the shank body
206 in fixed rotational relation with the head 210.
[0115] According to the embodiment of the invention shown in FIGS.
12-25, only the retainer structure 212 is in slidable engagement
with the head spherical seating surface 272. The capture structure
208 and threaded portion of the shank body 206 are in spaced
relation with the head 210, although the shank outer neck 226 could
engage the head restrictive neck 274 at a full rotation, as best
illustrated in FIG. 24.
[0116] An extent of rotation is shown in FIG. 19 in phantom lines
where it is illustrated that the shank body 206 can be rotated
through a substantial angular rotation relative to the head 210,
both from side to side and from front to rear so as to
substantially provide a universal or ball joint wherein the angle
of rotation is only restricted by engagement of the neck 226 of the
shank body 206 with the neck 274 of the head 210.
[0117] With reference to FIG. 22, the assembly 201 is then
typically screwed into a bone, such as the vertebra 215, by
rotation of the shank 204 using the driving tool 231 that operably
drives and rotates the shank 204 by engagement thereof with the
transverse slot 296 of the retainer structure 212. Preferably, when
the driving tool 231 engages the retainer structure 212, each of
the tool prong like extensions 302 are disposed in a recess defined
by the slot walls 298 and the base of the slot 300, with the tool
extensions 302 seated upon and driving against the slot base
300.
[0118] The head 210 and the retainer structure 212 are assembled on
the shank 204 before inserting the shank body 206 into the vertebra
215. With reference to FIG. 16 and FIG. 22, the vertebra 215 may be
pre-drilled to minimize stressing the bone, as well as the
connection between the retainer ring and capture structure, and a
guide wire inserted to provide a guide for the placement and angle
of the shank 204 with respect to the vertebra 215 (not shown). A
bone screw shaped tap hole may be made utilizing a tap. Then, the
assembly 201 or the solitary shank 204, is threaded onto the guide
wire utilizing the cannulation bore 244 by first threading the wire
into the bottom opening 246 and then out of the top opening 248.
The shank 204 is then driven into the vertebra 215, using the wire
as a screw placement guide and the wire is then removed.
[0119] With reference to FIGS. 23-25, the rod 221 is eventually
positioned within the head U-shaped channel 256, and the closure
assembly 218 is then inserted into and advanced between the arms
252 and 254 so as to bias or push against the rod 221.
Specifically, a driving tool (not shown, but could be the same tool
231 shown in FIG. 22) is inserted into the slots 319 of the closure
plug 310 to drive and rotate the closure plug 310 into the head
arms 252 and 254. Subsequently, the hex driving tool 320 is
inserted into the aperture 315 of the inner plug 312 to drive and
rotate the inner plug 312 into the closure plug 310.
[0120] The shank top end surface or dome 242, because it is rounded
and sized to extend upwardly into the U-shaped channel 256, is
engaged by the rod 221 and pushed downwardly toward the base 250 of
the head 210 when the outer closure structure and inner plug
projection 314 bias downwardly toward and onto the rod 221. The
downward pressure on the shank 204 in turn urges the retainer
structure 212 downward toward the head seating surface 272, with
the retainer structure seating surface 294 into frictional
engagement with the head seating surface 272. As the outer plug and
inner set screw 312 press against the rod 221, the rod 221 presses
against the shank and rigidly attached retainer structure 212,
which in turn becomes rigidly and frictionally attached to the head
210, fixing the shank body 206 in a desired angle with respect to
the head 210 and rod 221.
[0121] FIGS. 24 and 25 illustrate the polyaxial bone screw assembly
201, the rod 221 and the closure assembly 218 positioned in the
vertebra 215. The axis A' of the bone shank 204 is illustrated as
not being coaxial with the axis B' of the head 210 and the shank
204 is fixed in this angular locked configuration. Other angular
configurations can be achieved, as required during installation
surgery due to positioning of the rod 221 or the like.
[0122] If removal of the assembly 201 and associated rod 221 and
closure assembly 218 is necessary, disassembly is accomplished by
using the driving tool 320 mating with the aperture 315 to rotate
the inner plug or set screw 312 and reverse the advancement thereof
in the outer closure plug 310. Subsequently, the outer plug 310 is
loosened by mating the slots 319 with a driver (not shown) to
reverse the advancement of the plug 310 in the arms 252 and 254. It
may be possible to loosen both the inner plug 312 and the closure
plug 310 with the tool 320, thus loosening the closure plug 310
from the head arms 252 and 254, as the outer plug 310 and inner
plug 312 may be joined together by threads at the lower ends
thereof becoming deformed by engagement with the rod 221. Then,
disassembly of the assembly 1 is accomplished in reverse order to
the procedure described previously herein for assembly. For
disassembly, it is preferred that the retaining structure 312 be
strongly secured to the shank 310 by deformation of the threads 238
and 288 or by other locking structure such as welding or pins so
that both are assured of being removed as a single unit.
[0123] It is to be understood that while certain forms of the
present invention have been illustrated and described herein, it is
not to be limited to the specific forms or arrangement of parts
described and shown.
* * * * *