U.S. patent application number 13/815669 was filed with the patent office on 2013-10-17 for polyaxial bone screw assembly.
The applicant listed for this patent is Roger P. Jackson. Invention is credited to Roger P. Jackson.
Application Number | 20130274805 13/815669 |
Document ID | / |
Family ID | 64901148 |
Filed Date | 2013-10-17 |
United States Patent
Application |
20130274805 |
Kind Code |
A1 |
Jackson; Roger P. |
October 17, 2013 |
Polyaxial bone screw assembly
Abstract
A polyaxial bone screw assembly for capturing a rod includes a
receiver, a threaded shank body having an upper capture portion
mated with a retaining and articulating structure, a compression
insert and a closure having a domed bottom. The closure captures
and fixes the rod within the receiver between the domed bottom and
the compression insert, the insert pressing on the retaining and
articulating structure to fix such structure against the
receiver.
Inventors: |
Jackson; Roger P.; (Prairie
Village, MO) |
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Applicant: |
Name |
City |
State |
Country |
Type |
Jackson; Roger P. |
Prairie Village |
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MO |
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|
Family ID: |
64901148 |
Appl. No.: |
13/815669 |
Filed: |
March 14, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12924260 |
Sep 23, 2010 |
8403962 |
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13815669 |
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11385957 |
Mar 21, 2006 |
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12924260 |
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11178854 |
Jul 11, 2005 |
7789896 |
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11385957 |
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11140343 |
May 27, 2005 |
7776067 |
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12924260 |
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60655239 |
Feb 22, 2005 |
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Current U.S.
Class: |
606/264 ;
606/278 |
Current CPC
Class: |
A61B 2090/037 20160201;
A61B 17/864 20130101; A61B 17/8685 20130101; A61B 17/7037 20130101;
A61B 17/7028 20130101; A61B 17/7032 20130101; A61B 17/8625
20130101; A61B 17/7035 20130101 |
Class at
Publication: |
606/264 ;
606/278 |
International
Class: |
A61B 17/70 20060101
A61B017/70 |
Claims
1. A closure for a bone screw assembly including a shank for
implanting in a bone and a receiver joined with the shank and
having an upper channel formed between a pair of arms each having a
first inwardly facing helically wound flange form; the closure
comprising: a) a generally cylindrical body with a bottom; b) a
driving structure for rotating the body; c) a second outwardly
facing helically wound flange form on the body sized and shaped to
rotatably mate with the first flange forms on the receiver; and d)
the bottom of the closure having a downwardly projecting dome.
2. The closure according to claim 1 wherein the dome extends across
the entire closure bottom.
3. The closure according to claim 1 in combination with the shank,
receiver and rod.
4. The closure according to claim 3 wherein the shank and receiver
are separate and polyaxially joined during positioning and
thereafter locked by downward advancement of the closure relative
to the receiver.
5. A polyaxial bone screw assembly adapted to hold a rod and
comprising: a) a shank having a lower threaded portion for
implantation in a bone and an upper capture portion; b) a receiver
having an inner cavity operably and polyaxially receiving the shank
upper portion during positioning; the receiver also having a pair
of upstanding arms that have inwardly facing and helically wound
first flange form guide and advancement structure forming a channel
therebetween adapted to receive the rod; and c) a closure having a
cylindrical body with a helically wound second flange form guide
and advancement structure thereon that is sized and shaped to
operably mate with the first flange form guide and advancement
structure upon rotation and to advance the closure downwardly
through the channel so as to be adapted to apply downward pressure
to the rod, the closure including a drive mechanism for operably
rotating the closure, the closure body having a bottom that has a
downwardly facing dome adapted for engaging the rod.
6. The assembly according to claim 5 including a retainer for
joining with and polyaxially rotating with the shank upper portion
in the cavity during positioning and holding the shank in the
receiver; and a pressure insert positioned between the rod and the
shank upper portion and transferring downward force from the rod to
the shank so as to lock a position of the shank relative to the
receiver when the closure is fully advanced.
7. A polyaxial bone screw adapted to receive a rod and comprising:
a) a shank having a lower threaded portion for implanting in a bone
of a patient and an upper capture portion; b) a receiver having an
internal cavity that operably receives the shank capture portion;
the receiver also having a pair of spaced upstanding arms forming a
rod receiving channel therebetween and having inwardly facing first
guide and advancement structures thereon; c) a compression
structure operably positioned above the shank and including a
cradle having a U-shaped seating surface sized and shaped to
receive the rod; the seating surface having a lowest rod receiving
linear portion that remains perpendicular to a central vertical
axis of the receiver as the compression structure moves vertically
relative to the receiver, whereby the rod is received in the
receiver so as to be perpendicular to the central axis of the
receiver; and d) a closure having a generally cylindrical body and
a bottom with a second guide and advancement structure thereon that
rotatably mates with the first guide and advancement structure on
the receiver arms; the closure bottom having a downwardly facing
and rod engaging dome.
8. The bone screw assembly according to claim 7 including a
retainer that joins with the shank capture portion in the receiver
to polyaxially rotate with the shank in the receiver during
positioning and that holds the shank in the receiver, the
compression structure engaging and applying downward locking force
directly to the retainer and not directly to the shank as the
closure is advanced downwardly between the arms and against the
rod.
9. The bone screw according to claim 8 wherein the shank and the
retainer both polyaxially rotate together relative to both the
compression structure and the receiver during positioning.
10. A spinal bone anchor assembly for cooperation with a rod having
a radius, the assembly comprising: a) a shank having a lower
portion for implanting into bone and an upper portion; b) a
receiver communicating with the shank, the receiver having an inner
cavity operably and polyaxially receiving the shank upper portion
during positioning, the receiver also having a pair of upstanding
arms, each arm having a partial inwardly facing first helical guide
and advancement structure thereon, the arms forming a rod receiving
channel; c) a compression structure located within the receiver
cavity and movable therein during positioning, the compression
structure having a seating surface with a second radius sized and
shaped for receiving the rod at the first radius; and d) a closure
having an outer second helically wound guide and advancement
structure thereon sized and shaped for operably mating with the
first guide and advancement structure upon rotation of the closure
between the receiver arms and into the rod receiving channel, the
closure having a downwardly directed domed rod engaging surface,
the closure rod engaging surface operatively pressing downwardly on
the rod and fixing the rod between the closure and the compression
structure seating surface.
11. In a bone anchor assembly having a shank pivotal with respect
to a head defining a cavity and a lower opening, the shank further
having a bone implanting portion integral with an upper portion,
the bone implanting portion extending through the head lower
opening, the upper portion located within the head cavity and
moveable with respect to the head during positioning of the shank
with respect to the head prior to fixing an angle of orientation of
the shank with respect to the head, the head further having opposed
upright arms defining a channel for receiving a length of a rod,
the channel communicating with the cavity, the upright arms having
an inner first helically wound guide and advancement structure
thereon, the assembly further having a compression structure
located within the cavity and a closure structure having a second
guide and advancement structure thereon for rotating mating
engagement with the first guide and advancement structure, the
improvement wherein: a) the closure structure has a base with a
downwardly directed domed surface; and b) the compression structure
has an outer cylindrical surface defined by an outer diameter, the
compression structure further comprising a rod seating surface, the
seating surface having a width substantially equal to the outer
diameter, the seating surface width extending in a direction along
the length of the rod, the compression structure being movable
within the head cavity during positioning of the shank with respect
to the head prior to fixing of the angle of the shank with respect
to the head, the closure structure domed surface pressing
downwardly on the rod and fixing the rod against the compression
structure seating surface when the angle of the shank is fixed with
respect to the head.
12. In a bone anchor assembly having a shank connected to a head
defining a cavity and a lower opening, the shank further having a
bone implanting portion integral with an upper portion, the bone
implanting portion extending through the head lower opening, the
upper portion located within the head cavity, the head further
having opposed upright arms defining a channel for receiving a
length of a rod, the channel communicating with the cavity, the
upright arms having an inner first helically wound guide and
advancement structure thereon, the assembly further having a
compression structure located within the cavity and a closure
structure having a second guide and advancement structure thereon
for rotating mating engagement with the first guide and advancement
structure, the improvement wherein: a) the closure structure has a
base with a downwardly directed domed surface; and b) the
compression structure has opposed outer peripheral surfaces defined
by a width in the direction of the length of the rod, the
compression structure further comprising a rod seating surface, the
seating surface having a width substantially equal to the width
between the outer peripheral surfaces, the seating surface width
thereby more fully supporting the length of the rod, the
compression structure being movable within the head cavity during
positioning of the shank with respect to the head prior to fixing
of the rod with respect to the head, the closure structure domed
surface pressing downwardly on the rod and fixing the rod against
the entire width of the compression structure seating surface when
the rod is fixed with respect to the head.
13. In a polyaxial bone screw having a shank for implanting in a
bone, a receiver with a cavity that operably receives an upper
portion of the shank and upward extending first arms forming a
channel therebetween adapted to receive a connecting member, the
first arms having top surfaces, a compression insert operably
positioned above and in direct contact with an upper end of the
shank and including upward extending second arms that extend around
and above the connecting member when the connecting member is in
the channel, the improvement wherein the closure comprises: a) an
outer fastener having a through bore with an internal surface guide
and advancement thread; b) an inner set screw having an outer
surface guide and advancement thread and a bore with a central axis
opening onto a top surface of the inner set screw, the bore
terminating at a bottom tool engagement abutment surface, said
abutment surface having a central axis secondary bore communicating
with the exterior terminating on a bottom surface of the inner set
screw, the inner set screw being threadedly received in the outer
fastener; c) the inner set screw in a final position located
beneath the top surfaces of the receiver arms.
14. The improvement according to claim 13, wherein the outer
fastener engages the compression insert second arms to provide for
downward application of force to the shank from the insert to allow
independent locking of the shank relative to the receiver without
locking the position of the connecting member relative to the
receiver.
15. The improvement according to claim 13, wherein the closure
outer fastener has a top surface that is substantially flush with a
top surface of the upright arms of the receiver.
16. The improvement according to claim 13, wherein the inner set
screw in the final position is positioned extends below a bottom
surface of the outer fastener.
17. In a polyaxial bone screw having a shank for implanting in a
bone, a receiver with a cavity that operably receives an upper
portion of the shank and upward extending first arms forming a
channel therebetween adapted to receive a connecting member, the
first arms having top surfaces, a compression insert operably
positioned above and in direct contact with an upper end of the
shank and including upward extending second arms that extend around
and above the connecting member when the connecting member is in
the channel, the improvement wherein the closure comprises: a) an
outer fastener having a through bore with an internal surface guide
and advancement thread and being positioned entirely within the
arms of the receiver such that a top surface of the outer fastener
is flush with the top surfaces of the receiver first pair of arms;
b) an inner set screw having an outer surface guide and advancement
thread and a bore with a central axis opening onto a top surface of
the inner set screw, the bore terminating at a bottom tool
engagement abutment surface, said abutment surface having a central
axis secondary bore communicating with the exterior terminating on
a bottom surface of the inner set screw, the inner set screw being
threadedly received in the outer fastener; c) the inner set screw
in a final position located beneath the top surfaces of the
receiver arms.
18. The improvement according to claim 17, wherein the outer
fastener engages the compression insert second arms to provide for
downward application of force to the shank from the insert to allow
independent locking of the shank relative to the receiver without
locking the position of the connecting member relative to the
receiver.
19. The improvement according to claim 17, wherein the inner set
screw further comprises a bottom surface, and wherein in the final
position, the inner set screw bottom surface extends below a bottom
surface of the outer fastener.
20. The improvement according to claim 19, wherein the bottom
surface of the inner set screw is flat.
21. In a polyaxial bone screw having a shank for implanting in a
bone, a receiver with a cavity that operably receives an upper
portion of the shank and upward extending first arms forming a
channel therebetween adapted to receive a connecting member, the
first arms having top surfaces, a compression insert operably
positioned above and in direct contact with an upper end of the
shank and including upward extending second arms that extend around
and above the connecting member when the connecting member is in
the channel, the improvement wherein the closure comprises: a) an
outer fastener having a through bore with an internal surface guide
and advancement thread and being positioned entirely within the
arms of the receiver such that a top surface of the outer fastener
is flush with the top surfaces of the receiver first pair of arms;
b) an inner set screw having an outer surface guide and advancement
thread, the inner set screw being threadedly received in the outer
fastener; c) the inner set screw in a final position located
beneath the top surfaces of the receiver arms and the top surface
of the outer fastener.
22. The closure according to claim 21, wherein the outer fastener
engages the compression insert second arms to provide for downward
application of force to the shank from the insert to allow
independent locking of the shank relative to the receiver without
locking the position of the connecting member relative to the
receiver.
23. The closure according to claim 21, wherein the inner set screw
further comprises a bottom surface, and wherein in the final
position, the inner set screw bottom surface extends below a bottom
surface of the outer fastener.
24. The closure according to claim 23, wherein the bottom surface
of the inner set screw is flat.
25. The closure according to claim 23, wherein the bottom surface
of the inner set screw is dome shaped.
26. A medical implant bone screw including: a) a shank adapted to
be implanted in a bone at a lower end and having an upper end; b) a
receiver structure located at the shank upper end; the receiver
having a first pair of upright arms forming a channel therebetween
adapted to receive a connecting member, the upright arms having a
top surface; c) a lower compression member positioned below and
around the connecting member and having a second pair of upright
arms that are sized and shaped to extend above the connection
member; the lower compression member engaging the shank; and d) a
closure having an outer ring that is positioned entirely within and
threadably securable to an inner side of the receiver first pair of
upright arms; the closure having an inner set screw threadably
secured and advanced in the outer ring and relative to the
receiver, wherein the inner set screw is positioned beneath the top
surface of the receiver.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/924,260, filed Sep. 23, 2010 that was a
continuation-in-part of U.S. patent application Ser. No.
11/385,957, filed Mar. 21, 2006, that was a continuation-in-part of
U.S. patent application Ser. No. 11/178,854 filed Jul. 11, 2005,
now U.S. Pat. No. 7,789,896, that claimed the benefit of U.S.
Provisional Application No. 60/655,239 filed Feb. 22, 2005 and Ser.
No. 12/924,260 also was a continuation-in-part of U.S. patent
application Ser. No. 11/140,343, now U.S. Pat. No. 7,776,067, all
of the noted prior applications are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] The present invention is directed to polyaxial bone screws
for use in bone surgery, particularly spinal surgery.
[0003] Bone screws are utilized in many types of spinal surgery,
such as for osteosynthesis, in order to secure various implants to
vertebrae along the spinal column for the purpose of stabilizing
and/or adjusting spinal alignment. Although both closed-ended and
open-ended bone screws are known, open-ended screws are
particularly well suited for connections to rods and connector
arms, because such rods or arms do not need to be passed through a
closed bore, but rather can be laid or urged onto the open receiver
channel of an open ended bone screw.
[0004] Typical open-ended bone screws include a threaded shank with
a pair of parallel projecting branches or arms which form a yoke
with a U-shaped slot or channel to receive a rod. Hooks and other
types of connectors, as are used in spinal fixation techniques, may
also include open ends for receiving rods or portions of other
structure.
[0005] A common mechanism for providing vertebral support is to
implant bone screws into certain bones which then in turn support a
longitudinal structure such as a rod, or are supported by such a
rod. Bone screws of this type may have a head or receiver that
receives the rod or other structure that is fixed relative to a
shank thereof. In the fixed bone screws, the fixed receiver cannot
be moved relative to the shank and the rod must be favorably
positioned in order for it to be placed within the receiver. This
is sometimes very difficult or impossible to do. Therefore,
polyaxial bone screws are commonly preferred.
[0006] Open-ended polyaxial bone screws allow rotation of a rod
receiver with respect to the shank until a desired rotational
position of the receiver is achieved relative to the shank. A rod
is inserted into the receiver and eventually the receiver is locked
or fixed in a particular position relative to the shank.
[0007] There are a variety of ways in which the rod may be captured
within an open polyaxial bone screw. Some sort of closure structure
or plug is required so as to block the channel opening once the rod
is inserted therein and, also preferably urge the rod into a seated
and locked position relative to the receiver. A substantial amount
of torque is required to seat the plug against the rod which in
turn seats the rod in the receiver channel so as to prevent
relative motion between the rod and the bone screw. Consequently,
the need to highly torque a plug disposed between the arms of an
open bone screw functions counter to the need to prevent the bone
screw arms from splaying.
[0008] Certain prior art plug type closures have been threadably
received between the opposed arms of the bone screw receiver using
conventional V-shaped thread forms which has resulted in a
significant amount of radially outward pressure or force being
applied to the arms of the bone screw receiver. Such outward force
may result in splaying of the arms, after which the closure becomes
loose which may either result in a failure of the implant by
allowing the rod to slip relative to the bone screw or the closure
may even come completely out of the receiver of the bone screw for
total failure of the implant. In order to help relieve this
problem, certain of the prior art has added structure to the rod
engaging lower surface of the closure. Such structure has included
adding a central or axial point or ring designed to penetrate into
the rod and help lock the rod into place. Surface finish on the
plug, such as knurling, has also been utilized.
[0009] At a side of the rod opposite of the closure plug, various
compression spacers or insertable compression structures have been
developed that are operably disposed adjacent the rod and within
the bone screw receiver. Such compression structures have been used
to frictionally link the rod with the bone screw shank and to aid
in snugly seating the rod in the open bone screw, thus aiding in
preventing relative motion between the rod and the bone screw.
Prior art bone screw compression inserts have typically been
utilized with top-loaded bone screw shanks, having substantially
spherical heads that are integral with the shank body. Such
compression inserts include those that contact an upper spherical
portion of the bone screw shank and others that extend
substantially around such a spherical surface. Such compression
inserts may also include a curved upper surface or surfaces for
receiving the rod.
[0010] Bone screw compression inserts may desirably reduce relative
motion between the rod and the bone screw, but may be undesirable
in practice as they may also require separate insertion during
surgery, after implantation of the bone screw shank, and may be
small and thus difficult to handle. Alternatively, compression
inserts loaded in a bone screw prior to implantation may obstruct
bone screw features utilized for driving the threaded bone screw
shank into bone, or require less than desirable modifications in
the bone screw, decreasing strength and/or requiring specialized
driving tools.
SUMMARY OF THE INVENTION
[0011] A polyaxial bone screw assembly according to the invention
includes a shank having an upper portion and a body for fixation to
a bone. The shank upper portion has a width or diameter smaller
than a diameter of a lower opening of a cooperating receiver that
also includes an open channel for receiving a rod or other elongate
structure. The assembly further includes an independent
non-integral retaining and articulating structure for attachment to
the shank upper portion within the receiver. Furthermore, a
compression structure is operably disposed between the retaining
and articulating structure and the rod. The shank is connected to
the receiver by the retaining and articulating structure that is
operably slidably mated with an inner surface of the receiver,
allowing the shank body to be swivelable with respect to the
receiver.
[0012] According to one aspect of the invention, a closure member
having a flangeform thereon is mateable with cooperating
flange-form structure on inner arms of an upper portion of the
receiver. The closure member further includes a dome-shaped lower
surface for operably pressing against the rod or other structural
member. The rod in turn contacts and presses on the compression
structure and the compression structure contacts and presses on the
retaining and articulating structure which fixes the retaining and
articulating structure against an inner seating surface of the
receiver.
[0013] According to another aspect of the invention, a bone screw
shank upper portion is sized and shaped to be insertable through a
lower opening of a receiver. The shank upper portion includes a
helical thread and in some embodiments a lateral projection. In a
particular embodiment the projection is in the form of a cylinder
forming a buttress stop. The retaining and articulating structure
includes a through-bore defined in part by a helical thread sized
and shaped to mate with the helical thread of the shank capture
structure. The retaining and articulating structure also includes
structure, such as a cooperating buttress stop sized and shaped to
abut against the projection when fully installed on the shank upper
portion, stopping the retaining and articulating structure from
further rotation down the shank upper portion. The retaining and
articulating structure could have a vertical slit and thus be
down-loadable or up-loadable into the receiver.
[0014] According to another aspect of the invention, the shank
upper portion that is insertable in the receiver lower opening
includes a driving formation at a top surface thereof. The driving
formation is sized and shaped to receive an end of a driving tool.
A further aspect of the invention includes a compression structure
or insert that is pre-loadable in the bone screw receiver and
includes a central through bore, allowing for the driving of the
shank into bone with the insert loaded in the bone screw receiver.
The insert in some embodiments can be down-loaded or up-loaded into
the receiver, in particular the insert and the retaining structure
could both be up-loaded into the receiver.
OBJECTS AND ADVANTAGES OF THE INVENTION
[0015] Therefore, objects of the present invention include:
providing an improved spinal implant assembly for implantation into
vertebrae of a patient; providing such an assembly that includes a
receiver with an open channel, a shank pivotally connected to the
receiver, a rod or other structural element, and a compression
structure disposed between the shank and the rod for holding the
shank at a desired angle of inclination or articulation with
respect to the receiver; providing such an assembly that has a low
profile after final installation; providing such an assembly in
which the compression structure may be inserted into a bone screw
receiver prior to installing the bone screw into bone; providing
such an assembly in which an upper shank portion of the bone screw
includes a non-slip feature for driving the shank into bone;
providing such an assembly in which an upper portion of the bone
screw shank has a maximum diameter or width that is smaller than a
diameter or width of a lower opening of the bone screw receiver and
further includes an independent retaining and articulating
structure fixable to the shank upper portion within the bone screw
receiver; and providing such an assembly that is easy to use,
especially adapted for the intended use thereof and wherein the
implant assembly components are comparatively inexpensive to
produce.
[0016] Other objects and advantages of this invention will become
apparent from the following description taken in conjunction with
the accompanying drawings wherein are set forth, by way of
illustration and example, certain embodiments of this
invention.
[0017] 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
[0018] FIG. 1 is an exploded perspective view of an assembly
according to the invention including a shank with a capture
structure at one end thereof, a receiver, a retaining and
articulating structure and a compression structure.
[0019] FIG. 2 is an enlarged front elevational view of the
compression structure of FIG. 1.
[0020] FIG. 3 is an enlarged top plan view of the compression
structure of FIG. 1.
[0021] FIG. 4 is an enlarged bottom plan view of the compression
structure of FIG. 1.
[0022] FIG. 5 is an enlarged, exploded front elevation of the shank
and retaining and articulating structure of FIG. 1.
[0023] FIG. 6 is a partial cross-sectional view of the shank and
retaining and articulating structure taken along the line 6-6 of
FIG. 5.
[0024] FIG. 7 is an enlarged and partial view of the shank and
retaining and articulating structure of FIG. 6.
[0025] FIG. 8 is an enlarged and partial cross-sectional view of
the receiver taken along the line 8-8 of FIG. 1 and showing a first
stage of insertion of the compression structure.
[0026] FIG. 9 is an enlarged and partial cross-sectional view of
the receiver similar to FIG. 8 and showing a fully installed
compression structure.
[0027] FIG. 10 is a top plan view of the bone screw receiver,
shank, retaining and articulating structure and compression
structure of FIG. 9.
[0028] FIG. 11 is a cross-sectional view of the receiver, shank,
retaining and articulating structure and compression structure,
shown being driven into a vertebra with an Allen-type tool.
[0029] FIG. 12 is a partial cross-sectional view similar to FIG. 11
further showing a rod and a partially installed closure structure,
also in cross-section.
[0030] FIG. 13 is a partial cross-sectional view similar to FIG. 12
showing a break-off head of the closure structure removed.
[0031] FIG. 14 is an enlarged and partial cross-sectional view
taken along the line 14-14 of FIG. 13.
DETAILED DESCRIPTION OF THE INVENTION
[0032] 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.
[0033] With reference to FIGS. 1-14, the reference numeral 1
generally designates a polyaxial bone screw assembly according to
the present invention. The assembly 1 includes a shank 4 that
further includes a body 6 integral with an upwardly extending,
substantially cylindrical end or capture structure 8; a receiver or
head 10; a retaining and articulating structure 12; and a
compression structure 14. The shank 4, the receiver 10, the
retaining and articulating structure 12 and the compression
structure 14 are preferably assembled prior to implantation of the
shank body 6 into a vertebra 15, which procedure is shown in FIG.
11 and will be discussed more fully below.
[0034] FIGS. 12-14 further show a closure structure generally 18,
of the invention for capturing a longitudinal member such as a rod
21 within the receiver 10. Upon installation, which will be
described in detail below, the closure structure 18 presses against
the rod 21 that in turn presses against the compression structure
14 that presses against the retaining and articulating structure 12
that is threadably mated to the capture structure 8. The
compression structure 14 biases the retaining and articulating
structure 12 into fixed frictional contact with the receiver 10, so
as to fix the rod 21 relative to the vertebra 15. The receiver 10,
shank 4, retaining and articulating structure 12 and compression
structure 14 cooperate in such a manner that the receiver 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
receiver 10 with the shank 4 until both are locked or fixed
relative to each other.
[0035] The shank 4, best illustrated in FIGS. 1 and 5-7, is
elongate, with the shank body 6 having a helically wound, radially
outwardly extending bone implantable thread 22 axially extending
from near a tip 24 of the body 6 to near a slanted or sloped
surface 26 that is adjacent to a lateral projection illustrated as
a smooth cylindrical surface 28 located adjacent to the capture
structure 8. As will be described more fully below, the laterally
projecting cylindrical surface 28 includes a buttress stop feature
30 for frictional engagement with and placement of the retaining
and articulating structure 12. During use, the body 6 utilizing the
thread 22 for gripping and advancement is implanted into the
vertebra 15 leading with the tip 24 and driven down into the
vertebra 15 with an installation or driving tool so as to be
implanted in the vertebra 15 to near the sloped surface 26, as
shown in FIGS. 12-14, 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.
[0036] The sloped surface 26 extends radially outward and axially
upward from the shank body 6 to the cylindrical projection 28.
Further extending axially from the projection 28 is the capture
structure 8 that provides a connective or capture apparatus
disposed at a distance from the threaded shank body 6 and thus at a
distance from the vertebra 15 when the body 6 is implanted in the
vertebra 15.
[0037] The capture structure 8 is configured for connecting the
shank 4 to the receiver 10 and capturing the shank 4 in the
receiver 10. The capture structure 8 has an outer substantially
cylindrical surface 34 having a helically wound guide and
advancement structure thereon which in the illustrated embodiment
is a V-shaped thread 36 extending from adjacent the cylindrical
surface 28 to adjacent an annular upper surface 38. The upper
surface 38 is disposed substantially perpendicular to the axis of
rotation A. A diameter of the cylindrical surface 34 measured
between roots of the thread 36 is smaller than a diameter of the
projected cylindrical surface 28. A diameter measured between
crests of the thread 36 is illustrated equal to and may be smaller
than the diameter of the cylindrical surface 28. Although a simple
thread 36 is shown in the drawings, it is foreseen that other
structures including other types of threads, such as buttress,
square and reverse angle threads, and non threads, such as
helically wound flanges with interlocking surfaces, may be
alternatively used in place of the thread 36 in alternative
embodiments of the present invention.
[0038] With particular reference to FIG. 7, the buttress stop
feature 30 disposed near a base or bottom of the thread 36 is
defined in part by the cylindrical surface 28 and in part by an
upper shoulder 40 disposed perpendicular to the surface 28 and
extending inwardly radially toward the thread 36. In a preferred
embodiment, a buttress stop feature 42 disposed on the retaining
and articulating structure 12 cooperates with the feature 30 as
will be described more fully below to stop the advancement of the
structure 12 along the thread 36 and provide for a desired
placement of the structure 12 with respect to the capture structure
8.
[0039] A driving formation 44 extends from the upper surface 38
into the capture structure 8. The illustrated formation 44 includes
six walls or facets 46 disposed parallel to the axis A and a
hex-shaped seating surface or base 48 disposed perpendicular to the
axis A. The driving formation 44 is sized and shaped to cooperate
with a hex-driver for rotating and driving the shank body 6 into
bone. It is foreseen that other driving features or apertures, such
as slotted, tri-wing, hexalobular (such as the 6-point star shaped
pattern sold under the trademark TORX), spanner, or the like may
also be utilized according to the invention.
[0040] In the illustrated embodiment, the shank 4 is cannulated
with a small central bore 49 extending an entire length of the
shank along axis A. The bore 49 is coaxial with the threaded body 6
and the capture structure outer surface 34, providing a passage
through the shank interior for a length of wire or pin inserted
into the vertebra 15 prior to the insertion of the shank body 6,
the wire or pin providing a guide for insertion of the shank body 6
into the vertebra 15.
[0041] Referring to FIGS. 1, and 8-10, the receiver 10 has a
generally cylindrical outer profile with a substantially
cylindrical base 50 integral with a pair of opposed upstanding arms
52 that extend from the base 50 to a top surface 54. The arms 52
form a U-shaped cradle and define a U-shaped channel 56 between the
arms 52 and include an upper opening 57 and a lower seat 58 having
substantially the same radius as the rod 21 for operably snugly
receiving the rod 21.
[0042] Each of the arms 52 has an interior surface 60 that defines
an 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
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 buttress thread, a square 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 18 downward between the arms
52 and having such a nature as to resist splaying of the arms 52
when the closure top 18 is advanced into the U-shaped channel
56.
[0043] Tool engagement apertures 64 are formed on outer
substantially cylindrical surfaces 66 of the arms 52 which may be
used for holding the receiver 10 with a holding tool (not shown)
having projections that are received within the apertures 64 during
implantation of the shank body 6 into the vertebra 15. The
apertures 64 may also cooperate with a holding tool during bone
screw assembly and during subsequent installation of the rod and
closure top. The illustrated apertures 64 are circular and disposed
centrally on each arm 52. However, it is foreseen that the
apertures may be configured in a variety of shapes and sizes and
include undercut surfaces and be disposed at other locations on the
arms 52, including near the top surfaces 54. Also, the holding tool
(not shown) and respective apertures 64 may be configured to
provide for a variety of ways to install the holding tool in the
apertures, including a twist on/twist off engagement with the
receiver, a twist on/snap off engagement or a flexible snap on/snap
off engagement wherein the holding tool has legs which splay
outwardly to position the tool for engagement in the apertures 64
or a combination thereof.
[0044] Communicating with the U-shaped channel 56 and located
within the base 50 of the receiver 10 is a chamber or cavity 78
partially defined by an inner cylindrical surface 80, the cavity 78
opening upwardly into the U-shaped channel 56. In the illustrated
embodiment, the cylindrical surface 80 has a diameter equal to an
inner diameter between the arms 52 measured between crests of the
guide and advancement structure 62. In the illustrated embodiment,
the cylindrical inner surface 80 terminates at a ledge or lower
shoulder 81 that is disposed perpendicular to an axis of rotation B
of the receiver. The shoulder 81 is adjacent to a partial internal
spherical seating surface 82 having a first radius. The surface 82
is sized and shaped for mating with the retaining and articulating
structure 12, as described more fully below. It is foreseen that
the surface 82 may be partially spherical or conical, or the like,
and may include a high friction surface.
[0045] The base 50 further includes a restrictive neck 83 adjacent
the seating surface 82. The neck 83 defines 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 the rotational axis B of
the receiver 10. The bore 84 may be conically counterbored or
beveled in a region 87 to widen the angular range of the shank 4.
The neck 83 and associated bore 84 are sized and shaped to be
smaller than a radial dimension of a fixed or fully expanded
retaining and articulating structure 12, as will be discussed
further below, so as to form a restriction at the location of the
neck 83 relative to the retaining and articulating structure 12, to
prevent the structure 12 from passing from the cavity 78 and out
into the lower exterior 86 of the receiver 10 when the retaining
and articulating structure 12 is seated on the seating surface 82.
Again, it is foreseen that the retaining and articulating structure
could be compressible (such as where such structure has a missing
section) and could be loaded through the neck 83 and then allowed
to expand and fully seat in the spherical seating surface 82.
[0046] The retaining and articulating structure 12, best
illustrated by FIGS. 1 and 5-7, has an operational central axis
that is the same as the elongate axis A associated with the shank
4, but when the structure 12 is separated from the shank 4, the
axis of rotation is identified as an axis C. The retaining and
articulating structure 12 has a central bore 90 that passes
entirely through the structure 12 from a top surface 92 to a bottom
surface 94 thereof. An inner cylindrical surface 96 defines a
substantial portion of the bore 90, the surface 96 having a
helically wound guide and advancement structure thereon as shown by
a v-shaped helical rib or thread 98 extending from adjacent the top
surface 92 to near the bottom surface 94. 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 the thread 98 are configured to mate
under rotation with the capture structure outer surface 34 and
helical guide and advancement structure or thread 36, as described
more fully below.
[0047] The buttress stop formation 42 of the retaining and
articulating structure 12 that is sized and shaped to mate with the
stop 30 located on the shank 4 is located axially between the
helical rib 98 and the bottom surface 94 of the structure 12. The
formation 42 includes a lower shoulder 100 extending radially from
the thread 98 and towards the structure 12 and a cylindrical wall
102 disposed perpendicular to the lower shoulder 100. The lower
shoulder 100 is sized and shaped to mate and abut with the upper
shoulder 40 and the cylindrical wall 102 is sized and shape to mate
with the cylindrical projection 28. Thus, as will be described in
more detail below, when the retaining and articulating structure 12
is rotated and mated with the capture structure 8 and fully
installed thereon, the lower shoulder 100 of the structure 12 abuts
the upper shoulder 40 of the stop 30. The retaining and
articulating structure 12 and the capture structure 8 are
configured such that when the buttress stop 30 abuts the buttress
stop 42, the top surface 92 of the structure 12 is flush with the
upper surface 38 of the capture structure 8. A sloped surface or
chamfer 103 runs between the cylindrical wall 102 and the bottom
surface 94 of the retaining and articulating structure 12.
[0048] It is foreseen that other types of geometrical orientation
or structure may be utilized to engage or mate the capture
structure and the retaining and articulating structure. For
example, the capture structure may have an outer surface that is
frusto-conical and the retaining and articulating structure may be
a split ring with an inner surface sized and shaped to frictionally
engage the frusto-conical capture structure. Also, the capture
structure may have an inverted polyhedral or conical geometry and
the mating retaining and articulating structure may be a plurality
of pieces, the geometry of the pieces corresponding and cooperating
with the polyhedral or conical geometry of the capture structure to
frictionally envelope the retaining and articulating structure
between the capture structure and an internal surface defining a
cavity of the receiver.
[0049] The illustrated retaining and articulating structure 12 has
a radially outer partially spherically shaped surface 104 sized and
shaped to mate with the partial spherically shaped seating surface
82 of the receiver and having a radius approximately equal to the
radius associated with the surface 82. The retaining and
articulating structure radius is larger than the radius of the neck
83 of the receiver 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.
[0050] It is also foreseen that the retaining and articulating
structure outer surface may be elliptical or ellipsoid in shape
rather than spheroid in shape. Such an elliptical surface would be
sized and shaped to contact and seat within a substantially
spherical seating surface, such as the seating surface 82. Such an
ellipsoid structure may be attachable to the shank upper portion by
threads, a pin, compression, or the like as previously described
with respect to the substantially spherical retaining and
articulating structure 12. Furthermore, it is foreseen that an
ellipsoid retaining structure may be integral with the bone screw
shank and may include threads that allow the ellipsoid to be
threadably received into a base of a bone screw receiver.
[0051] The illustrated retaining and articulating structure top
surface 92 extends from the central bore 90 to the outer surface
104. The top surface 92 is disposed perpendicular to the axis of
rotation C of the structure 12. The bottom surface 94 extends from
the chamfer 103 to the outer surface 104 and also is disposed
perpendicular to the axis of rotation C.
[0052] 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 smooth, outer cylindrical surface 108
of uniform diameter. The rod 21 is preferably sized and shaped to
snugly seat near the bottom of the U-shaped channel 56 of the
receiver 10 and, during normal operation, is positioned slightly
above the bottom of the channel 56 at the lower seat 58.
[0053] The compression structure 14 is best illustrated in FIGS.
1-4. In the embodiment shown, the compression structure 14 includes
a body 110 of substantially circular cross-section integral with a
pair of upstanding arms 112. The body 110 and arms 112 form a
generally U-shaped, open, through-channel 114 having a
substantially U-shaped bottom seating surface 116 having a radius
substantially conforming to a radius of the rod 21 and thus
configured to operably snugly engage the rod 21. The arms 112
disposed on either side of the channel 114 each included a top
surface 118 that is parallel to an annular bottom surface 120. The
compression structure 14 includes a substantially cylindrical outer
surface 122 and an inner cylindrical wall 124 defining a central
through-bore 125 extending along a central axis D of the
compression structure 14. The top surface 118 and the bottom
surface 120 are disposed perpendicular to the axis D. Extending
between the inner cylindrical wall 124 and the bottom surface 120
is a curved or spherical surface 126 sized and shaped to
frictionally engage and mate with the outer spherical surface 104
of the retaining and articulating structure 12. The cylindrical
surface 122 has a diameter slightly smaller than a diameter between
crests of the guide and advancement structure 62 allowing for top
loading of the compression structure 14 as illustrated in FIGS.
8-10. The cylindrical surface 122 diameter and a height of the
compression structure 14 measured from the top surface 118 to the
bottom surface 120 are sized such that the compression structure 14
is received within the cylindrical surface 80 of the receiver 10
below the guide and advancement structure 62, but the bottom
surface 120 thereof does not engage the ledge 81 when fully
installed on the retaining and articulating structure 12. There is
thus a space between the bottom surface 120 and the ledge 81 in any
angular position of the shank 4 with respect to the receiver 10.
When fully installed, the compression structure 14 does not contact
the bone screw shank capture structure 8, but engages only with the
retaining and articulating structure 12. When pressed upon by the
rod 21, the surface 126 of the compression structure 14
frictionally engages the surface 104 of the retaining and
articulating structure 12, which in turn presses upon the seating
surface 82 of the receiver 10. In some embodiments, the compression
structure could be up-loaded into the receiver, followed by
up-loading of the retaining structure into the receiver.
[0054] With particular reference to FIGS. 12-14, the closure
structure 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 of the receiver
10. The closure structure 18 is rotatable between the spaced arms
52. The illustrated structure 18 includes a cylindrical base 140
and a break-off head 142. Helically wound about the base 140 is a
guide and advancement structure in the form of a flange form 144.
The illustrated guide and advancement structure 144 operably joins
with the guide and advancement structure 62 disposed on the
interior 60 of the arms 52. The flange form 144 includes a root 146
and a crest 148. Furthermore, the flange form 144 also has a
trailing surface 150 and a leading surface 152 which are relative
to the forward movement of the closure 18 as it is rotated
clockwise about the central axis B of the bone screw receiver and
joined therewith. Located on the trailing surface 150 or the
leading surface 152 or both is a projection which protrudes
rearwardly or frontwardly with respect to the width of the flange
form 144 at the root 146 and which interlocks with the guide and
advancement mating structure 62 of the receiver 10.
[0055] In the illustrated embodiment, the flange form 144 has a
protrusion 154 that projects rearwardly from the trailing surface
150. The flange form 144 utilized in accordance with the present
invention may be any structure which effectively locks the closure
18 to the structure within which it is set so as to prevent
splaying of the structure upon which mating guide and advancement
structure is mounted. Various flange form structures which can be
used alternatively are illustrated in applicant's U.S. Pat. No.
6,726,689, which is incorporated herein by reference. As stated
herein with respect to the flange form guide and advancement
structure 62, it is also foreseen that according to the invention
the guide and advancement structure 144 could alternatively be a
buttress thread, a square head, a reverse angle thread or other
thread like or non-thread like helically wound advancement
structure for operably guiding under rotation and advancing the
closure 18 downward between the arms 52 and having such a nature as
to resist splaying of the arms 52 when the closure top 18 is
advanced into the U-shaped channel 56.
[0056] The base 140 of the closure structure 18 includes a lower
surface 156 having a dome 158 located thereon. The dome 158 extends
greatest from the base 140 along a central axis E that is operably
coaxial with the receiver axis B. The dome 158 in the present
embodiment is spherical in shape and, in particular, is a partial
sphere that has a uniform or constant radius of generation.
[0057] However, it is foreseen that in certain embodiments the
radius may vary depending upon the needs and desires of the
particular structure and the dome 158 may have shape that is only
partly a spherical curved surface or some other shape. The dome 158
may be a simple curved surface that allows greatest projection
along the axis. That is, the dome surface could be radiused at the
location of greatest projection and feathered along the periphery
so as to not have a continuous uniform radius of generation
throughout, but rather a continually changing radius of generation
along at least the length thereof. Preferably, the dome 158 is
smoothly curved where the dome 158 intersects with the axis E. It
is also foreseen that the lower surface 156 could be flat or have a
point and rim geometry.
[0058] The closure structure 18 break off head 142 is secured to
the base 140 by a break off region 160 that is designed to allow
the head 142 to break from the base 140 at a preselected torque,
for example, 70 to 140 inch pounds. The break off head 142 has an
external radial outward surface with six planar facets 162 so as to
form a structure designed to be received within a socket of a
driving type tool (not shown) with a similar receiving shape. The
break off head 142 has a central bore 164 that may also include
driving formations suitable for engagement by a tool (not
shown).
[0059] During installation, the dome 158 engages the rod 21 at an
apex 166 as seen in FIGS. 13 and 14. The closure structure 18 is
torqued until a preselected pressure is reached at which point the
closure 18 at the apex 166 abuts the rod 21 which in turn is urged
toward but not completely to the lower seat 58 of the channel 56.
In turn, the rod 21 braces against the compression structure 14
which urges the retaining and articulating structure 12 to fixedly
seat in the cavity 78. Thereafter, the receiver 10 is no longer
rotatable relative to the shank 4, but rather is locked in
position.
[0060] 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 168 disposed in the
base 140, as shown in FIG. 13. The hex aperture 168 is accessible
after the break-off head 142 breaks away from the base 140. The
aperture 168 is coaxial with the helically wound guide and
advancement structure 144 and is designed to receive a hex tool, of
an Allen wrench type, into the aperture 168 for rotating the
closure structure base 140 subsequent to installation so as to
provide for removal thereof, if necessary. Although a hex-shaped
aperture 168 is shown in the drawings, the tool engagement
structure may take a variety of tool-engaging forms and may include
more than one aperture of various shapes, such as a pair of spaced
apertures, a left hand threaded bore, an easy out engageable step
down bore or the like.
[0061] With reference to FIG. 1, prior to the polyaxial bone screw
assembly 1 being implanted in the vertebra 15, the retaining and
articulating structure 12 is typically first inserted or
top-loaded, into the receiver U-shaped channel 56, and then into
the cavity 78 to dispose the structure 12 adjacent the inner
surface 80 of the receiver 10. The structure 12 may be loaded with
the axis C coaxial with the receiver axis B or turned or rotated
such that the axis C is perpendicular to the axis B of the receiver
10 during insertion of the structure 12 into the receiver 10. Then,
after the retaining and articulating structure 12 is within the
cavity 78, the retaining and articulating structure 12 is rotated
approximately 90 degrees such that the axis C is coaxial with the
axis B of the receiver 10, and then the structure 12 is seated in
sliding engagement with the seating surface 82 of the receiver
10.
[0062] The shank capture structure 8 is preloaded, inserted or
bottom-loaded into the receiver 10 through the bore 84 defined by
the neck 83. The retaining and articulating structure 12, now
disposed in the receiver 10 is coaxially aligned with the shank
capture structure 8 so that the helical v-shaped thread 36
rotatingly mates with the thread 98 of the retaining and
articulating structure 12.
[0063] With reference to FIGS. 5-7, the shank 4 and/or the
retaining and articulating structure 12 are rotated to fully mate
the structures 36 and 98 along the respective cylindrical surfaces
34 and 96, fixing the capture structure 8 to the retaining and
articulating structure 12, until the lower shoulder 100 of the
buttress stop 42 abuts the upper shoulder 40 of the stop 30.
[0064] With reference to FIGS. 8-10, at this time the shank 4 is in
slidable and rotatable engagement with respect to the receiver 10,
while the capture structure 8 and the lower aperture or neck 83 of
the receiver 10 cooperate to maintain the shank body 6 in
rotational relation with the receiver 10. According to the
illustrated embodiment, only the retaining and articulating
structure 12 is in slidable engagement with the receiver spherical
seating surface 82. Both the capture structure 8 and threaded
portion of the shank body 6 are in spaced relation with the
receiver 10. The shank body 6 can be rotated through a substantial
angular rotation relative to the receiver 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 receiver 10.
[0065] In the embodiment shown, the compression structure 14
illustrated in FIGS. 1-4 is then loaded into the receiver 10 as
illustrated in FIGS. 8-10. With particular reference to FIG. 8, the
insert U-shaped channel 114 is aligned with the receiver 10
U-shaped channel 56 and the compression structure 14 is initially
top or down-loaded into the receiver 10 until the arms 112 are
disposed adjacent to the surface 80 and the bottom spherical
surface 126 is in contact with the surface 104 of the retaining and
articulating structure 12. To ready the assembly 1 for implantation
into bone, the shank 4, receiver 10 and compression structure 14
axes A, B and D, respectively are aligned, providing access to the
hex-shaped formation 44 on the shank capture structure 8 through
the bore 125 of the compression structure 14. Such placement allows
for unrestricted rotation of the shank body 6 with respect to the
receiver 10.
[0066] With reference to FIG. 11, the assembly 1 is typically
screwed into a bone, such as the vertebra 15, by rotation of the
shank 4 using a driving tool with an Allen type driving formation
175 that operably drives and rotates the shank 4 by engagement
thereof with the shank at the driving formation 44, a base 177 of
the tool 175 abutting and engaging the driving formation 44 at the
base 48 thereof. It is foreseen that in other embodiments according
to the invention, the hex-shaped driving formation 44 may be
replaced by other types of foot print type tool engaging formations
or recesses. Through the driving formation aperture, the retaining
structure and the shank can be crimped together so as to not come
apart with rotation.
[0067] Typically at least two and up to a plurality of bone screw
assemblies 1 are implanted into vertebrae for use with the rod 21.
Each vertebra 15 may be pre-drilled to minimize stressing the bone.
Furthermore, when a cannulated bone screw shank is utilized, each
vertebra will have a guide wire or pin (not shown) inserted therein
that is shaped for the bone screw cannula 49 of the bone screw
shank and provides 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. The shank body 6 is then driven into the vertebra 15,
by rotation of the driving tool 175.
[0068] With reference to FIGS. 12-14, the rod 21 is eventually
positioned within the receiver U-shaped channel 56, and the closure
structure is then inserted into and advanced between the arms 52.
The compression structure 14 is pressed downwardly into engagement
with the retaining and articulating structure outer surface 104 to
set the angle of articulation of the shank body 6 with respect to
the receiver 10 by pressure from the rod 21 that in turn is being
pressed upon by the dome 158 of the closure structure 18. The rod
21 is seated on the compression structure 14 and the fastener 18 is
initially placed between the arms 52 and rotated using an
installation tool (not shown) engaged with the surfaces 162 of the
break-off head 142 until the guide and advancement structure 144 is
fully mated with the receiver guide and advancement structure 62.
With reference to FIG. 13, the break-off head 142 is then twisted
to a preselected torque, for example 70 to 140 inch pounds, also
utilizing the installation tool in engagement with the faceted
outer surface 162 of the break-off head 142, with or without
bending of the rod 21 in order to achieve and maintain a desired
alignment of the spine. As illustrated in FIGS. 13 and 14, upon
final installation, a stable fixation of the rod 21 is accomplished
with one area of contact provided at the apex 166 of the closure
top dome 158 and two areas of contact provided between the rod 21
and the compression structure 14.
[0069] If removal of the assembly 11 is necessary, or if it is
desired to release the rod 21 at a particular location, disassembly
is accomplished by using an Allen type tool (not shown) with the
hex-shaped driving formation 168 located on the closure structure
base 140 to rotate and remove the closure structure base 140 from
the receiver 10. Disassembly of the assembly 1 is accomplished in
reverse order to the procedure described previously herein for
assembly. Again, it is foreseen that a non-break off closure could
be used which is inserted and removed with the same driving
formation.
[0070] 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.
* * * * *