U.S. patent number RE42,545 [Application Number 11/256,914] was granted by the patent office on 2011-07-12 for polyaxial pedicle screw having a threaded and tapered compression locking mechanism.
This patent grant is currently assigned to Warsaw Orthopedic, Inc.. Invention is credited to Joseph P. Errico, Thomas J. Errico, James D. Ralph.
United States Patent |
RE42,545 |
Ralph , et al. |
July 12, 2011 |
Polyaxial pedicle screw having a threaded and tapered compression
locking mechanism
Abstract
A polyaxial orthopedic device for use with rod implant apparatus
includes a screw having a curvate head, a two-piece interlocking
coupling element which mounts about the curvate head, and a rod
receiving cylindrical body member having a tapered socket into
which both the screw and the interlocking coupling element are
securely nested. The interlocking coupling element includes a
socket portion which is slotted and tapered so that when it is
radially compressed by being driven downwardly into the tapered
socket in the cylindrical body it crush locks to the screw. The
securing of the rod in the body member provides the necessary
downward force onto the socket portion through a contact force on
the top of the cap portion. Prior to the rod being inserted,
therefore, the screw head remains polyaxially free with respect to
the coupling element and the body. In a preferred embodiment, the
cap portion and the socket portion are formed and coupled in such a
way that when the cap portion is compressed toward the socket
portion, there is an additional inward radial force applied by the
cap portion to the socket portion, thereby enhancing the total
locking force onto the head of the screw.
Inventors: |
Ralph; James D. (Seaside Park,
NJ), Errico; Thomas J. (Summit, NJ), Errico; Joseph
P. (Green Brook, NJ) |
Assignee: |
Warsaw Orthopedic, Inc.
(Warsaw, IN)
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Family
ID: |
27357187 |
Appl.
No.: |
11/256,914 |
Filed: |
October 24, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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09992612 |
Nov 13, 2001 |
Re. 39089 |
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09774915 |
Jan 30, 2001 |
Re. 37665 |
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08843972 |
Apr 17, 1997 |
5888204 |
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08632560 |
Apr 15, 1996 |
5725588 |
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08421087 |
Apr 13, 1995 |
5520690 |
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08835909 |
Apr 10, 1997 |
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08663383 |
Jun 13, 1996 |
5669911 |
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08559196 |
Nov 13, 1995 |
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08421087 |
Apr 13, 1995 |
5520690 |
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Reissue of: |
09002535 |
Jan 2, 1998 |
5882350 |
Mar 16, 1999 |
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Current U.S.
Class: |
606/266;
606/246 |
Current CPC
Class: |
A61B
17/7037 (20130101); A61F 2/4611 (20130101); A61F
2/30744 (20130101); A61F 2/34 (20130101); A61B
17/70 (20130101); A61F 2002/3021 (20130101); A61F
2002/30594 (20130101); A61F 2002/3401 (20130101); A61F
2220/0033 (20130101); A61F 2002/30787 (20130101); A61F
2002/30329 (20130101); A61F 2230/0067 (20130101); A61F
2002/30495 (20130101); A61F 2310/00023 (20130101); A61B
17/7032 (20130101); A61F 2002/30378 (20130101); A61F
2220/0025 (20130101); A61F 2310/00017 (20130101); A61F
2002/30332 (20130101) |
Current International
Class: |
A61B
17/56 (20060101); A61B 17/70 (20060101) |
Field of
Search: |
;606/246,264-274,301,305,308 ;403/9,83,90,110,135,136,409.1
;411/147,148,541 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Robert; Eduardo C
Assistant Examiner: Comstock; David
Parent Case Text
CROSS-REFERENCE TO PRIOR APPLICATION
This application is a .Iadd.continuation of U.S. patent application
Ser. No. 09/992,612, filed on Nov. 13, 2001, which is a
continuation of U.S. patent application Ser. No. 09/774,915, filed
on Jan. 30, 2001, now U.S. Pat. RE 37,665, which is a reissue of
U.S. Pat. No. 5,882,350 issued from U.S. patent application Ser.
No. 09/002,535 filed on Jan. 2, 1998, which is a
continuation-in-part of U.S. patent application Ser. No. 08/843,972
filed on Apr. 17, 1997, now U.S. Pat. No. 5,888,204, which is a
continuation-in-part of U.S. patent application Ser. No. 08/632,560
filed on Apr. 15, 1996, now U.S. Pat. No. 5,725,588, which is a
continuation-in-part of U.S. patent application Ser. No. 08/421,087
filed Apr. 13, 1995, now U.S. Pat. No. 5,520,690. U.S. patent
application Ser. No. 09/002,535 filed on Jan. 2, 1998, now U.S.
Pat. No. 5,882,350 is also a continuation of U.S. patent
application Ser. No. 08/835,909 filed Apr. 10, 1997, now abandoned,
which is a .Iaddend.continuation-in-part of prior application U.S.
Ser. No. 08/663,383, entitled "A Polyaxial Pedicle Screw", filed
Jun. 13, 1996, now U.S. Pat. No. 5,669,911 .Iadd.which is a
continuation-in-part of U.S. patent application Ser. No. 08/559,196
filed Nov. 13, 1995, now abandoned, .Iaddend.and which, in turn,
was a continuation-in-part of Ser. No. 08/421,087, filed Apr. 13,
1995, now issued U.S. Pat. No. 5,520,690, entitled "An Anterior
Spinal Polyaxial Locking Screw Plate Assembly". .Iadd.The
disclosure of each of these prior applications is hereby
incorporated by reference in their entirety..Iaddend.
Claims
We claim:
.[.1. A polyaxial screw and coupling element assembly for use with
orthopedic rod implantation apparatus, comprising: a screw having a
semi-spherical head; a cylindrical body including an axial bore
defining a bottom chamber portion at a bottom end thereof and a rod
receiving channel at a top end thereof, said bottom chamber portion
further defining a tapered lower portion and a constant diameter
upper chamber portion, and said top end having a threading thereon;
a two-piece interlocking coupling element including a socket
portion having a semi-spherical interior volume for receiving
therein the head of said screw, upper and lower sections, and
vertical slots formed in said upper and lower sections, at least
one of said slots rendering said interior volume expandable and
contractable, said lower section having a tapered exterior surface
for nesting in said tapered lower chamber portion of said
cylindrical body such that forceable advancement of socket portion
along the tapered lower chamber portion of the axial bore causes
the at least one of said slots to narrow such that the
semi-spherical interior volume contract, and a cap portion having
an opening in a bottom thereof and an interior chamber extending
upwardly therefrom for joining with, and slideably retaining
therein, the upper section of said socket portion, said cap portion
initially seating with a portion thereof extending into a bottom
portion of said rod receiving channel; and a top locking nut,
mateable with said threading, for locking a rod in said channel and
for applying therethrough a downward force onto said cap portion,
wherein said semi-spherical head portion is rotationally freely
mounted within the semi-spherical interior volume of the socket
portion prior to said socket portion being forceably advanced into
the tapered lower chamber portion of the axial bore, and whereby
downward compression of a rod in said channel portion of said body
member, by said top locking nut, onto the cap portion causes the
forceable advancement of the socket portion into the tapered lower
chamber portion of the axial bore, and locks the screw, coupling
element and body relative to one another..].
.[.2. The polyaxial screw as set forth in claim 1, wherein said
semi-spherical head of said screw further includes a recess formed
therein for receiving therein a screwdriving tool such that said
screw may be threadably advanced into a vertebral bone..].
.[.3. The polyaxial screw as set forth in claim 1, wherein said
threading on said top end is on the interior surface of said
channel..].
.[.4. The polyaxial screw as set forth in claim 3, wherein said cap
portion further includes a threading and wherein said cap portion
needs to be threadably advanced along the threading to be seated in
the bore into its initial position..].
.[.5. The assembly as set forth in claim 1, wherein said socket
portion further comprises a substantially constant diameter upper
section having an outwardly annular extending lip at an extreme end
thereof, wherein said opening in the bottom of the cap portion
comprises an inwardly directed annular lip, and wherein at least
one of said vertical slots in the upper section of said socket
portion renders the upper section thereof to be expandable and
contractable such that the upper section of the socket portion may
be forceably inserted into the opening in the bottom of the cap
portion so that it may be retained in the interior chamber therein
by mutual interference engagement of the inwardly directed annular
lip of the cap portion and the outwardly extending annular lip of
the socket portion..].
.[.6. The assembly as set forth in claim 5, wherein the interior
chamber of the cap portion comprises a tapered surface such that
advancement thereof into the hole causes an inwardly directed force
against the upper section of the socket portion, therein causing
the at least one of said vertical slots in the upper section to
narrow and causes the upper section to contract and further lock
the head of the screw within the interior semi-spherical volume of
the socket portion..].
.[.7. An orthopaedic implant apparatus having a rod and a plurality
of screw and coupling element assemblies, comprising: at least one
screw having a semi-spherical head; at least one cylindrical body
including an axial bore defining a bottom chamber portion at a
bottom end thereof and a rod receiving channel at a top end
thereof, said bottom chamber portion further defining a tapered
lower portion and a constant diameter upper chamber portion, and
said top end having a threading thereon; at least one corresponding
two-piece interlocking coupling element including a socket portion
having a semi-spherical interior volume for receiving therein the
head of said corresponding screw, upper and lower sections, and
vertical slots formed in said upper and lower sections, at least
one of said slots rendering said interior volume expandable and
contractable, said lower section having a tapered exterior surface
for nesting in said corresponding tapered lower chamber portion of
said cylindrical body such that forceable advancement of socket
portion along the tapered lower chamber portion of the axial bore
causes the at least one of said slots to narrow such that the
semi-spherical interior volume contract, and a cap portion having
an opening in a bottom thereof and an interior chamber extending
upwardly therefrom for joining with, and slideably retaining
therein, the upper section of said socket portion, said cap portion
initially seating with a portion thereof extending into a bottom
portion of said rod receiving channel; and at least one
corresponding top locking nut, mateable with said threading, for
locking a rod in said channel and for applying therethrough a
downward force onto said cap portion, wherein said semi-spherical
head portion is rotationally freely mounted within the
semi-spherical interior volume of the socket portion prior to said
socket portion being forceably advanced into the tapered lower
chamber portion of the axial bore, and whereby downward compression
of a rod in said channel portion of said body member, by said top
locking nut, onto the cap portion causes the forceable advancement
of the socket portion into the tapered lower chamber portion of the
axial bore, and locks the screw, coupling element and body relative
to one another..].
.[.8. The apparatus as set forth in claim 7, wherein said threading
on said top end is on the interior surface of said channel..].
.[.9. The apparatus as set forth in claim 8, wherein said cap
portion further includes a threading and wherein said cap portion
needs to be threadably advanced along the threading to be seated in
the bore into its initial position..].
.[.10. The apparatus as set forth in claim 7, wherein said socket
portion further comprises a substantially constant diameter upper
section having an outwardly annular extending lip at an extreme end
thereof, wherein said opening in the bottom of the cap portion
comprises an inwardly directed annular lip, and wherein at least
one of said vertical slots in the upper section of said socket
portion renders the upper section thereof to be expandable and
contractable such that the upper section of the socket portion may
be forceably inserted into the opening in the bottom of the cap
portion so that it may be retained in the interior chamber therein
by mutual interference engagement of the inwardly directed annular
lip of the cap portion and the outwardly extending annular lip of
the socket portion..].
.[.11. The apparatus as set forth in claim 10, wherein the interior
chamber of the cap portion comprises atapered surface such that
advancement thereof into the hole causes an inwardly directed force
against the upper section of the socket portion, therein causing
the at least one of said vertical slots in the upper section to
narrow and causes the upper section to contract and further lock
the head of the screw within the interior semi-spherical volume of
the socket portion..].
.Iadd.12. An orthopedic device for securing immobilizing structures
to sequences of bones, comprising: a screw having a semi-spherical
head and a threaded shaft; a coupling element having an axial hole
extending therethrough, a portion of the axial hole defining an
interior volume for receiving therein the semi-spherical head of
the screw such that the threaded shaft may be moved through a
variety of angles relative to the axial hole, the coupling element
further including at least one slot rendering at least the interior
volume deformable, the coupling element further including a tapered
exterior surface; a receiving member including a through hole
having an interior wall surface, a portion of the interior wall
surface of the through hole being shaped to receive the coupling
element and the screw when the semi-spherical head of the screw is
mounted within the coupling element; and wherein advancement of the
screw through the through hole relative to the receiving member
when the exterior surface of the coupling element engages the
interior wall surface of the through hole prevents the coupling
element from further advancement through the hole, preventing the
semi-spherical head of the screw from advancing further through the
through hole, and causing locking of the screw relative to both the
coupling element and to the receiving member thereby locking the
angle of the screw relative to the axial hole..Iaddend.
.Iadd.13. The assembly as set forth in claim 12, wherein the
semi-spherical head of the screw further includes a recess formed
therein for receiving therein a screwdriving tool such that the
screw may be advanced into a vertebral bone..Iaddend.
.Iadd.14. An orthopedic implant apparatus comprising: a fixation
element having a semi-spherical head and a shaft extending
therefrom; a receiving member including an axial bore defined by an
interior surface wall, a portion of the axial bore having a tapered
portion; a socket portion having a semi-spherical interior volume
for receiving therein the semi-spherical head, and an exterior
surface capable of nesting against the interior surface wall of the
tapered portion, the socket portion being located in the axial bore
of the receiving member; wherein the semi-spherical head is
rotationally freely mounted within the semi-spherical interior
volume of the socket portion prior to the socket portion being
forcibly advanced against the interior surface wall of the tapered
portion, and whereby advancement of the socket portion causes the
fixation element, the socket portion and the receiving member to be
locked relative to one another..Iaddend.
.Iadd.15. The assembly as set forth in claim 14, wherein the
semi-spherical head of the fixation element further includes a
recess formed therein for receiving therein a screwdriving tool
such that the fixation element may be advanced into a vertebral
bone..Iaddend.
.Iadd.16. A pedicle screw and rod coupling member assembly wherein
said rod coupling member and screw are capable of being selectively
positioned and locked at a plurality of angles relative to one
another, said assembly comprising: a bone screw having a curvate
head; a locking collar disposed around said curvate head and having
a slot; and a rod coupling member having a bore therethrough for
receiving said curvate head and locking collar, said bore having an
interior surface and a pair of upwardly extending members forming a
rod-receiving U-shaped channel, said upwardly extending members
having threads thereon for receiving a locking device, wherein said
pedicle screw and rod coupling member assembly assume a first
position such that said rod coupling member and screw are capable
of assuming a variety of angles relative to each other and a second
position with a rod member disposed in said rod-receiving U-shaped
channel and said locking device tightened on said threads such that
said locking collar engages said rod coupling member interior
surface to lock the angle of the screw relative to the rod coupling
member..Iaddend.
.Iadd.17. The orthopedic device as set forth in claim 16, wherein
the curvate head of the screw further includes a recess formed
therein for receiving therein a screwdriving tool such that the
screw may be advanced into a vertebral bone..Iaddend.
.Iadd.18. The orthopedic device as set forth in claim 16, wherein
the rod coupling member interior surface includes a lower portion
that is inwardly tapered, and which engages said locking collar to
crush lock the locking collar to the curvate head of the
screw..Iaddend.
.Iadd.19. The orthopedic device as set forth in claim 16, wherein
the rod coupling member interior surface includes a lower portion
that is inwardly tapered, and the exterior surface of the locking
collar is tapered to engage said inwardly tapered
surface..Iaddend.
.Iadd.20. An orthopedic implant and bone anchoring member assembly
wherein said bone anchoring member is selectively positionable and
lockable at any one of a plurality of angles relative to said
implant, said assembly comprising: a bone anchoring member having a
curvate head and a threaded shaft; a rod coupling member having a
bore extending therethrough for receiving said curvate head in a
lower portion thereof, said bore having an interior surface; a rod
positioned in an upper portion of said bore; and a locking ring
positioned in the lower portion of the bore between said curvate
head and said interior surface, wherein axial translation of said
rod relative to said bore urges said curvate head into locking
engagement with said locking ring to lock the angle of the screw
relative to rod coupling element..Iaddend.
.Iadd.21. The assembly of claim 20, wherein said curvate head is
semi-spherical..Iaddend.
.Iadd.22. The assembly of claim 20, wherein said bore includes at
least two portions having different diameters..Iaddend.
.Iadd.23. The assembly of claim 22, wherein said locking ring is
positioned at least partially within one of said portions having
different diameters..Iaddend.
.Iadd.24. The assembly as set forth in claim 20, wherein said
locking ring circumferentially retains the curvate
head..Iaddend.
.Iadd.25. The assembly as set forth in claim 20, further comprising
a locking device for engaging said rod to urge said rod to
translate axially relative to said bore..Iaddend.
.Iadd.26. The assembly as set forth in claim 25, wherein said
locking device comprises a nut engageable with threads on said
orthopedic implant..Iaddend.
.Iadd.27. The assembly of claim 20, wherein the bore includes a
tapered portion and the locking ring contacts against the interior
surface of the tapered portion..Iaddend.
.Iadd.28. An orthopedic device for securing structures to bone,
comprising: a screw having a curvate head and a threaded shaft; a
coupling element having an axial hole extending therethrough, a
portion of the axial hole defining an interior volume for receiving
therein the curvate head of the screw such that the threaded shaft
may be moved through a variety of angles to the axial hole, the
coupling element further including at least one slot rendering at
least the interior volume deformable, the coupling element further
including a tapered exterior surface; a receiving member including
a through hole having an interior wall surface, a portion of the
interior wall surface of the through hole being shaped to receive
the coupling element and the screw when the curvate head of the
screw is mounted within the coupling element; and wherein
advancement of the screw through the through hole relative to the
receiving member when the exterior surface of the coupling element
engages the interior wall surface of the through hole prevents the
coupling element from further advancement through the hole, and
causing locking of the screw relative to both the coupling element
and to the receiving member thereby locking the angle of the screw
relative to the axial hole..Iaddend.
.Iadd.29. The assembly as set forth in claim 28, wherein the
curvate head of the screw further includes a recess formed therein
for receiving therein a screwdriving tool such that the screw may
be advanced into a vertebral bone..Iaddend.
.Iadd.30. An orthopedic implant apparatus comprising: a fixation
element having a curvate head and a shaft extending therefrom; a
receiving member including an axial bore defined by an interior
surface wall, a portion of the axial bore having a tapered portion;
a socket portion having a curved interior volume for receiving
therein the curvate head, and an exterior surface capable of
nesting against the interior surface wall of the tapered portion,
the socket portion being located in the axial bore of the receiving
member, the socket portion including a slot with the interior
volume being deformable when the socket portion moves along the
tapered portion; wherein the curvate head is rotationally freely
mounted within the curved interior volume of the socket portion
prior to the socket portion being forcibly advanced against the
interior surface wall of the tapered portion, and whereby
advancement of the socket portion causes the fixation element, the
socket portion and the receiving member to be locked relative to
one another..Iaddend.
.Iadd.31. The assembly as set forth in claim 30, wherein the
curvate head of the fixation element further includes a recess
formed therein for receiving therein a screwdriving tool such that
the fixation element may be advanced into a vertebral
bone..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a polyaxial screw and coupling
apparatus for use with orthopedic fixation systems. More
particularly, the present invention relates to a screw for
insertion into spinal bone, and a coupling element polyaxially
mounted thereto, via a two-piece interlocking coupling element
having a socket portion and a threaded compression member, for
coupling the screw to an orthopedic implantation structure, such as
a rod, therein enhancing the efficacy of the implant assembly by
providing freedom of angulation among the rod, screw and coupling
element.
2. Description of the Prior Art
The bones and connective tissue of an adult human spinal column
consists of more than 20 discrete bones coupled sequentially to one
another by a tri-joint complex which consist of an anterior disc
and the two posterior facet joints, the anterior discs of adjacent
bones being cushioned by cartilage spacers referred to as
intervertebral discs. These more than 20 bones are anatomically
categorized as being members of one of four classifications:
cervical, thoracic, lumbar, or sacral. The cervical portion of the
spine, which comprises the top of the spine, up to the base of the
skull, includes the first 7 vertebrae. The intermediate 12 bones
are the thoracic vertebrae, and connect to the lower spine
comprising the 5 lumbar vertebrae. The base of the spine is the
sacral bones (including the coccyx). The component bones of the
cervical spine are generally smaller than those of the thoracic and
lumbar spine. For the purposes of this disclosure, however, the
word spine shall refer only to the cervical region.
Referring now to FIGS. 1, 2, and 3, top, side, and posterior views
of a vertebral body, a pair of adjacent vertebral bodies, and a
sequence of vertebral bodies are shown, respectively. The spinal
cord is housed in the central canal 10, protected from the
posterior side by a shell of bone called the lamina 12. The lamina
12 includes a rearwardly and downwardly extending portion called
the spinous process 16, and laterally extending structures which
are referred to as the transverse processes 14. The anterior
portion of the spine comprises a set of generally cylindrically
shaped bones which are stacked one on top of the other. These
portions of the vertebrae are referred to as the vertebral bodies
20, and are each separated from the other by the intervertebral
discs 22. The pedicles 24 comprise bone bridges which couple the
anterior vertebral body 20 to the corresponding lamina 12.
The spinal column of bones is highly complex in that it includes
over twenty bones coupled to one another, housing and protecting
critical elements of the nervous system having innumerable
peripheral nerves and circulatory bodies in close proximity. In
spite of these complexities, the spine is a highly flexible
structure, capable of a high degree of curvature and twist in
nearly every direction. Genetic or developmental irregularities,
trauma, chronic stress, tumors, and disease, however, can result in
spinal pathologies which either limit this range of motion, or
which threaten the critical elements of the nervous system housed
within the spinal column. A variety of systems have been disclosed
in the art which achieve this immobilization by implanting
artificial assemblies in or on the spinal column. These assemblies
may be classified as anterior, posterior, or lateral implants. As
the classifications suggest, lateral and anterior assemblies are
coupled to the anterior portion of the spine, which is the sequence
of vertebral bodies. Posterior implants generally comprise pairs of
rods, which are aligned along the axis which the bones are to be
disposed, and which are then attached to the spinal column by
either hooks which couple to the lamina or attach to the transverse
processes, or by screws which are inserted through the
pedicles.
"Rod assemblies" generally comprise a plurality of such screws
which are implanted through the posterior lateral surfaces of the
laminae, through the pedicles, and into their respective vertebral
bodies. The screws are provided with upper portions which comprise
coupling elements, for receiving and securing an elongate rod
therethrough. The rod extends along the axis of the spine, coupling
to the plurality of screws via their coupling elements. The
rigidity of the rod may be utilized to align the spine in
conformance with a more desired shape.
It has been identified, however, that a considerable difficulty is
associated with inserting screws along a misaligned curvature and
simultaneously exactly positioning the coupling elements such that
the rod receiving portions thereof are aligned so that the rod can
be passed therethrough without distorting the screws. Attempts at
achieving proper alignment with fixed screws is understood to
require increased operating time, which is known to enhance many
complications associated with surgery. Often surgical efforts with
such fixed axes devices cannot be achieved, thereby rendering such
instrumentation attempts entirely unsucessful.
The art contains a variety of attempts at providing instrumentation
which permit a limited freedom with respect to angulation of the
screw and the coupling element. These teachings, however, are
generally complex, inadequately reliable, and lack long-term
durability. These considerable drawbacks associated with prior art
systems also include difficulty properly positioned the rod and
coupling elements, and the tedious manipulation of the many small
parts in the operative environment.
It is, therefore, the principal object of the present invention to
provide a pedicle screw and coupling element assembly which
provides a polyaxial freedom of implantation angulation with
respect to rod reception.
In addition, it is an object of the present invention to provide
such an assembly which comprises a reduced number of elements, and
which correspondingly provides for expeditious implantation.
Accordingly it is also an object of the present invention to
provide an assembly which is reliable, durable, and provides long
term fixation support.
Other objects of the present invention not explicitly stated will
be set forth and will be more clearly understood in conjunction
with the descriptions of the preferred embodiments disclosed
hereafter.
SUMMARY OF THE INVENTION
The preceding objects of the invention are achieved by the present
invention which is a polyaxial locking screw and coupling element
for use with rod stabilization and immobilization systems in the
spine. More particularly, the polyaxial screw and coupling element
assembly of the present invention comprises a bone screw having a
head which is curvate in shape, for example semi-spherical, and a
two-piece interlocking coupling element mounted thereto. This
combination is mounted inside the bottom of an internal channel of
a cylindrical body member.
More specifically, with respect to the cylindrical body member, the
tubular body comprises a rod receiving channel formed in the upper
portion thereof, with a threading formed on the remaining upper
elements so that a rod securing nut and/or set screw may be
threaded thereon once a rod has been placed in the channel. The
body further includes an axial bore which includes extends from the
rod receiving channel through to the bottom of the cylinder. The
portion of the axial bore which is below the channel forms a
receiving chamber, the upper portion thereof having a constant
diameter, and the lower portion of the chamber being inwardly
tapered. The inner surface of the upper portion of the chamber
and/or the inner surface of the portion of the axial bore which is
above the chamber may further include a threading.
The two-piece interlocking coupling element comprises and socket
portion and a cap portion. The socket portion is designed with an
interior semi-spherical volume, so that it may receive the
semi-spherical head of a corresponding bone screw. The interior
volume of the socket portion is open at both axial ends thereof.
The exterior surface of the socket portion, at the bottom thereof,
includes a first set of slots which extend upwardly from the
opening so that the interior semi-spherical volume may be expanded
or contracted by the application of a radial force. In addition,
the exterior surface at the bottom is tapered so that it is
narrower at the bottom than at a midpoint. This taper is designed
to mate with and nest in the tapered lower portion of the socket
portion of the axial bore of the body member.
The upper exterior surface of the socket portion comprises a second
set of slots, directed axially along the element to the midpoint,
such that the upper opening of the socket element may expand and
contract in accordance with the application of a radial force
thereon. The exterior surface of this upper section of the socket
portion is not tapered and is narrower than the widest taper
position of the bottom of the socket portion. The upper section,
however, does further include an outwardly extending annular lip at
the uppermost axial position. This upper section is designed to be
inserted into, and joined with, the cap portion of the coupling
element.
The cap portion has a generally cylindrical shape, having an open
bottom. The open bottom is inwardly tapered, forming an inwardly
extending annular lip, so that as the upper end of the socket
portion is inserted, its upper slots are narrowed. Once axially
inserted beyond this taper, the upper section of the socket portion
expands outward over the inwardly extending annular lip. The
inwardly extending annular lip engages the outwardly extending lip
of the socket portion so as to prevent disengagement of the two
pieces. The socket portion is then permitted to slide into the cap
portion, until the larger diameter of the tapered lower portion of
the socket contacts the entrance of the cap portion.
The exterior surface of the cap portion may be threaded, so that it
may engage a threading of the upper portion of the socket portion
and/or the inner surface of the axial bore which is above the
socket portion. In addition, the top of the cap includes an opening
so that a screw driving tool may directly engage the top of the
screw.
The assembly of the entire device begins with the joining of the
socket portion to the cap portion of the two-piece interlocking
coupling element. This is achieved by the slideable interlocking
mating of the two elements. Next, the semi-spherical head of the
screw is inserted into the socket portion through the lower
expandable opening in the taper portion. Once these parts have been
assembled the screw and coupling element should be polyaxially
rotateable relative to one another. The screw and coupling element
are then inserted through the axial bore of the body (which may
require the threading the cap portion of the coupling element along
the threading on the inner surface of the axial bore and/or the
threading of the cap along the threading of the upper portion of
the chamber) until the socket portion nests in the tapered lower
portion of the axial bore. If the upper portion of the chamber
includes a threading it should not extend beyond the point of the
initial nesting of the coupling element in the chamber. This is
important because the cap portion must be able to move relative to
the socket portion.
In this initial position, the top of the cap portion should rest
above the bottom of the rod receiving channel so that a rod, when
placed therein, seats directly onto the top of the cap. This direct
contact provides the downward force necessary to compress the
coupling element into the chamber so that the socket portion is
compressed in the tapered portion and locks to the head of the
screw.
In a preferred variation of this embodiment, the interior surface
of the cap portion includes a slight narrowing taper so that as the
cap is compressed downward by the rod, the upper slots of the
socket portion are also narrowed, further increasing the crush
locking effect on the head of the screw.
The implantation of this screw by a surgeon may proceed first by
the assembly of the screw into its initial state. The shaft of the
screw is then driven into the vertebral bone at the desired
angulation. A rod is then introduced into the rod receiving
channel, and the body is angulated into the most ideal position for
receiving the rod. A nut and/or set screw is then used to secure
the rod in the channel, and simultaneously to provide a sufficient
downward translational force to cause the socket portion to be
driven into the tapered portion of the chamber in the axial bore,
and further to cause the cap portion to drive downwardly also (this
further compression locking the screw head in the embodiment
wherein the sliding of the cap portion toward the socket portion
provides an additional compression on the top of the socket portion
and therefore onto the head of the screw).
In a preferred variation, the locking nut comprises a cap nut which
has a central post which is designed to provide additional
structural support to the inner walls of the element at the top
thereof, as well as providing a central seating pressure point for
locking the rod in the channel. In either variation, the locking
nut seats against the rod and prevents it from moving
translationally, axially and rotationally.
Multiple screw assemblies are generally necessary to complete the
full array of anchoring sites for the rod immobilization system,
however, the screw assembly of the present invention is designed to
be compatible with alternative rod systems so that, where
necessary, the present invention may be employed to rectify the
failures of other systems when the surgery may have already
begun.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a top view of a human vertebra, which is representative
of the type for which the present invention is useful for coupling
thereto a rod apparatus;
FIG. 2 is a side view of a pair of adjacent vertebrae of the type
shown in FIG. 1;
FIG. 3 is a posterior view of a sequence of vertebrae of the type
shown in FIGS. 1 and 2;
FIG. 4 is a side view of a screw having a curvate head which is an
aspect of the present invention;
FIG. 5 is a side view of a two-piece interlocking coupling element
of present invention;
FIG. 6 is a side view of a two-piece interlocling coupling element
of present invention mounted around the head of a screw of the type
shown in FIG. 4;
FIG. 7 is a side cross-sectional view of a cylindrical body having
a chamber for receiving the two-piece interlocking coupling element
and the screw of the present invention;
FIG. 8 is a side cross-sectional view of a top locking nut which is
an aspect of the present invention;
FIG. 9 is a side cross-sectional view of an embodiment of the
present invention in its fully assembled disposition having a rod
securely locked therein; and
FIG. 10 is a side view of an alternative embodiment of the present
invention in its fully assembled disposition having a rod securely
locked therein.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
While the present invention will be described more fully
hereinafter with reference to the accompanying drawings, in which
particular embodiments and methods of implantation are shown, it is
to be understood at the outset that persons skilled in the art may
modify the invention herein described while achieving the functions
and results of this invention. Accordingly, the descriptions which
follow are to be understood as illustrative and exemplary of
specific structures, aspects and features within the broad scope of
the present invention and not as limiting of such broad scope.
Referring now to FIG. 4, a side view of the screw portion of the
present invention, comprising a curvate head, is shown. The screw
120 comprises a head portion 122, a neck 124, and a shaft 126. In
FIG. 4, the shaft 126 is shown as having a tapered shape with a
high pitch thread 128. It shall be understood that a variety of
shaft designs are interchangeable with the present design. The
specific choice of shaft features, such as thread pitch, shaft
diameter to thread diameter ratio, and overall shaft shape, should
be made be the physician with respect to the conditions of the
individual patient's bone, however, this invention is compatible
with a wide variety of shaft designs.
The head portion 122 of the screw 120 comprises a semi-spherical
shape, which has a recess 130 in it. It is understood that the
semi-spherical shape is a section of a sphere, in the embodiment
shown the section is greater in extent than a hemisphere, and it
correspondingly exhibits an external contour which is equidistant
from a center point of the head. In a preferred embodiment, the
major cross-section of the semi-spherical head 122 (as shown in the
two dimensional illustration of FIG. 4) includes at least 270
degrees of a circle.
The recess 130 defines a receiving locus for the application of a
torque for driving the screw 120 into the bone. The specific shape
of the recess 122 may be chosen to cooperate with any suitable
screw-driving tool. For example, the recess 130 may comprise a slot
for a screwdriver, a hexagonally shaped hole for receiving an alien
wrench, or most preferably, a threading for a correspondingly
threaded post. It is further preferable that the recess 130 be
co-axial with the general elongate axis of the screw 120, and most
particularly with respect to the shaft 126. Having the axes of the
recess 130 and the shaft 126 co-linear facilitates step of
inserting the screw 120 into the bone.
The semi-spherical head portion 122 is connected to the shaft 126
at a neck portion 124. While it is preferable that the diameter of
the shaft 126 be less than the diameter of the semi-spherical head
122, it is also preferable that the neck 124 of the screw 120 be
narrower than the widest portion of the shaft 126. This preferable
dimension permits the screw to swing through a variety of angles
while still being securely joined to the locking collar (as set
forth more fully with respect to FIGS. 5, 8-9).
Referring now to FIG. 5, the two elements which form the two-piece
interlocking coupling element of the present invention are shown in
a side cross-section view. Phantom lines show the interior
structure of the elements along the diametrical cross section. With
specific reference to the socket portion 132, the coupling element
comprises a roughly cylindrical shape having an interior volume 134
in which the semi-spherical head 122 of the screw 120 is disposed.
The interior volume 134 is open at the top 136 of the socket
portion 132 and at the bottom thereof 138. The lower section 131 of
the socket portion 132 comprises a set of slots 133 which extend
vertically from the bottom 138 of the socket portion 132 to a
position above the maximum diameter of the semi-spherical interior
volume 134. These slots 133 permit the interior volume to expand
and contract in accordance with the application of a radial force
thereon. The external surface 135 of the lower section 131 of the
socket portion 132 is tapered such that the narrowest part of the
lower section 131 is at the bottom 138.
The upper section 139 of the socket portion 132 has a generally
constant diameter, which is less than the diameter at the uppermost
position 137 of the taper of the lower section 131. A second set of
vertical slots 141 are provided in this upper section 139 so that
it may also expand and contract in accordance with radial forces
applied thereto. In addition, the uppermost end of this upper
section 139 comprises an outwardly extending annular lip 140.
The cap portion 142 of the coupling element comprises an opening
143 in the bottom thereof, having an inwardly tapered entrance
surface conformation 144. As the upper section 139 of the socket
portion 132 is inserted into the opening 143 in the cap portion
142, the taper 144 of the opening 143 provides an inwardly directed
force which causes the upper section 139 to contract (causes the
slots 141 to narrow). This tapered entrance 144 opens to form an
annular lip 145 which is useful for engaging and retaining the
annular lip 140 of the upper section 139 of the socket portion 132.
The interior surface 146 of the cap portion has a constant
diameter, therein permitting the inserted upper section 139 of the
socket portion 132 to slide and rotate relative to the cap portion
142.
The exterior surface of the cap portion 142 comprises a threading
147 which is designed to engage threadings 211 disposed in the
axial bore of the rod receiving body member (see FIG. 7). In
addition, the cap portion 142 comprises an axial hole 148 through
which a surgeon may insert a screw driving tool to access the head
of the screw which is positioned in the interior volume 134 of the
socket portion 132.
More particularly, with respect to the disposition of the head 122
of the screw 120 in the socket portion 132, and with reference to
FIG. 6, a partially assembled screw 120 and coupling element is
shown in a side cross-section view. The top 136 of the socket
portion 132 is inserted into the opening in the cap portion 142
until the annular lip 140 of the socket 132 seats into the cap 142.
The screw 120 is loosely held within the socket 132, which is, in
turn, loosely retained within the cap 142.
Referring now to FIG. 7, the rod receiving body member 200 of the
present invention is shown in a side view, wherein critical
features of the interior of the element are shown in phantom. The
body member 200, which comprises a generally cylindrical tubular
body having an axial bore 201 extending therethrough, may be
conceptually separated into a chamber portion 202 at the bottom of
the axial bore 201, and an upper rod receiving channel portion 204,
each of which shall be described more fully hereinbelow.
The upper rod receiving channel portion 204 of the body 200
includes a channel 206 formed therein, having rounded bottom
surfaces 207. The channel 206, in turn, divides the walls of the
cylindrical body of the upper portion 204 into a pair of upwardly
extending members 214a, 214b. As shown in the embodiment
illustrated in FIG. 7, the vertical distance from the top 208 of
the channel to the curvate bottom 207 thereof, is larger than the
diameter of the rod which is to be provided therein. This distance
is necessarily larger than the diameter of the rod (see FIGS. 9 and
10) so that the rod may be fully nested in the channel 206. In
addition, the depth of the bottom curvate surface 207 of the
channel is such that the cap portion 142 of the two-piece
interlocking coupling element initially seats above the curvate
bottom 207 of the body 200.
The upwardly extending members 214a, 214b further have, disposed
thereon, a threading 216 (which may be provided on the inner and/or
outer circumferential surfaces, but which is shown in FIGS. 7, 9
and 10 as being on the inner circumferential surface). This
threading 216 is ideally suited for receiving a top locking nut
(see FIG. 8).
Referring now to the lower portion of the body, the chamber portion
202 can further be subdivided into a lower chamber portion 203
which includes an inwardly tapered surface, and an upper chamber
portion 205 which has a constant diameter. The inwardly tapered
portion 203 defines a nesting volume into which the socket portion
132 may nest. Prior to its being fully driven into this nesting
volume, the socket portion 132 and the screw 120 disposed therein
may be angulated relative to one another, and the screw 120 may be
angulated relative to the body 200. Once driven fully into the
tapered lower chamber portion 203, however, the taper of the axial
bore 201 provides the necessary inwardly directed radial force to
cause the socket portion 132 to crush lock to the head 122 of the
screw 120.
The force which causes the socket portion 132 to be driven
downwardly into the tapered lower chamber portion 203 is provided
by the cap portion 142. More specifically, as stated above, when
the initially assembled screw 120 and coupling element combination
132 and 142 (see FIG. 6) is advanced into the bottom of the axial
bore 201 of the body 200, and the socket portion 132 nests in the
lower chamber portion 203, the top of the cap portion 142 is
positioned to receive the rod (see FIGS. 9 and 10) directly
thereon. The locking of the rod in the channel 206 of the body 200
causes the cap portion 142 to be forced downwardly onto the socket
portion 132, which in turn drives the socket portion 132 into the
tapered lower chamber portion 203 and causes it of compression lock
to the head 122 of the screw 120.
Referring now to FIG. 8, a top locking nut 185 is shown in side
cross-section view. The nut 185 comprises post portion 186 and a
flange portion 187, each of which is rotafionally free, relative to
the other. The post portion 186 includes a threading 188 thereon,
for engaging and advancing along a threading 216 on the inner
surface of the upwardly extending members 214a, 214b of the upper
portion 204 of the body 200. The bottom surface 189 of the flange
portion 187 (which does not rotate relative to the body as the post
portion 186 is rotationally advanced) is intended to seat against
the top surface of the rod 250.
Referring now to FIG. 9, in which the fully assembled and body
member 200, screw 120, coupling element portions 132 and 142, rod
250 and locking nut 185 are shown in side cross-section views, the
implantation of this embodiment is described. First, the screw 120
and the two portions 132 and 142 of the coupling element are
assembled into their initial association (see FIG. 6). The
combination of the screw 120 and the two coupling element portions
132 and 142 are then advanced down the axial bore 201 of the body
200 until the socket portion 132 nests in the lower chamber 203 and
the top of the cap portion 142 seats above the bottom 207 of the
channel 206. (This insertion of the subassembly of the screw 120
and coupling element portions 132 and 142 into the axial bore 201
of the body 200 may require the threaded advance of the cap portion
142 along the interior threads 216 of the body.)
The shaft of the screw 120 is then inserted and driven downward
into the vertebral bone at the desired angle. Once properly
positioned, the body 200 is rotated into the ideal rod receiving
position. The rod 250 is then inserted into the channel 206 and the
top locling nut 185 is threaded onto the threading 216 and
compresses the rod 250 to securely lock it in the channel 206. This
downward force of the nut 185 and the rod 250 onto the cap portion
142 causes the cap portion to translate downward thus causing the
socket portion 132 to translate downward in the tapered chamber 203
and contract to crush against the head 122 of the screw 120. The
assembly is thereby fully locked in position.
Referring to FIG. 10, a variation of the above device is shown in a
similar cross-section view. In this embodiment, the inner surface
146' of the cap portion 142 is tapered inwardly in the vertical
direction so that the downward translation of the cap portion 142
causes the annular lip 140 of the socket portion 132 to be
compressed inwardly. This causes the slots 141 of the upper section
139 of the socket portion 132 to narrow. This may be utilized to
further clamp the interior volume 134 against the head 122 of the
screw 120.
While there has been described and illustrated embodiments of a
polyaxial screw and coupling element assembly for use with
posterior spinal rod implantation apparatus, it will be apparent to
those skilled in the art that variations and modifications are
possible without deviating from the broad spirit and principle of
the present invention. The present invention shall, therefore, be
limited solely by the scope of the claims appended hereto.
* * * * *