U.S. patent application number 13/190370 was filed with the patent office on 2011-11-17 for bone plate with rings.
This patent application is currently assigned to Zimmer Spine, Inc.. Invention is credited to Robert J. Jones, Erik J. Wagner.
Application Number | 20110282394 13/190370 |
Document ID | / |
Family ID | 26779790 |
Filed Date | 2011-11-17 |
United States Patent
Application |
20110282394 |
Kind Code |
A1 |
Wagner; Erik J. ; et
al. |
November 17, 2011 |
Bone Plate with Rings
Abstract
Embodiments disclosed herein provide a plating system including
a bone plate, a bone screw and a ring. The bone screw preferably
connects the bone plate to a bone, and the ring preferably fixes
the bone screw into a borehole of the bone plate such that the bone
screw extends from the bone plate at a selected angle. The ring is
preferably capable of swiveling within the borehole to allow the
bone screw to be angulated at a plurality of angles oblique to the
plate. The bone screw may have a head having a tapered, threaded
surface for engaging the ring. The ring preferably has threading on
its inner surface for mating with the threading on the head. The
inner surface of the ring may be tapered. Movement of the head
through the ring preferably expands the ring against the bone plate
to fix the bone screw at a selected angle relative to the bone
plate.
Inventors: |
Wagner; Erik J.; (Austin,
TX) ; Jones; Robert J.; (Austin, TX) |
Assignee: |
Zimmer Spine, Inc.
|
Family ID: |
26779790 |
Appl. No.: |
13/190370 |
Filed: |
July 25, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11148112 |
Jun 8, 2005 |
8007523 |
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13190370 |
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10036012 |
Dec 26, 2001 |
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11148112 |
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09089027 |
Jun 2, 1998 |
6454769 |
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10036012 |
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08905823 |
Aug 4, 1997 |
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09089027 |
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Current U.S.
Class: |
606/290 |
Current CPC
Class: |
A61B 17/7059 20130101;
A61B 17/8052 20130101; A61B 17/8047 20130101; A61B 17/8057
20130101 |
Class at
Publication: |
606/290 |
International
Class: |
A61B 17/80 20060101
A61B017/80 |
Claims
1. A bone plate system comprising: a plate having an opening
passing through the plate, wherein a portion of the plate forms a
wall of the opening; and a ring configured to fit within the
opening and to receive a fastener therethrough; wherein the
fastener is configured to couple the plate to a bone; wherein the
fastener comprises a head; wherein the ring surrounds at least a
portion of the fastener after the fastener is coupled to the ring;
wherein the wall of the opening is configured to inhibit backout of
the ring from the plate after the ring is placed in the opening;
wherein an outer surface of the ring is curved to permit the ring
to swivel within the opening after the ring is placed in the
opening and before the head of the fastener is screwed into the
ring; wherein an inner surface of the ring contains a ring
threading; wherein an outer surface of the head of the fastener
contains a head threading; wherein the head threading is
complementary to the ring threading; and wherein the ring has a
slot or gap.
2. A bone plate system according to claim 1, wherein as the head of
the fastener is screwed into the ring, the slot or gap of the ring
is widened as a result of force received from the head, wherein the
force exerted by the head of the fastener against the inner surface
of the ring creates a fixed connection between the fastener and the
plate.
3. A bone plate system according to claim 1, wherein the inner
surface of the ring is tapered.
4. A bone plate system according to claim 1, wherein the inner
surface of the ring is substantially untapered.
5. A bone plate system according to claim 1, wherein at least a
portion of the head of the fastener has a width greater than an
inner width of the ring.
6. A bone plate system according to claim 1, wherein the outer
surface of the head of the fastener comprises a substantially
untapered portion and a tapered portion.
7. A bone plate system according to claim 6, wherein the tapered
portion is proximate to an end of the head of the fastener.
8. A bone plate system according to claim 1, wherein the ring
threading has multiple starts to facilitate connection of the
fastener and the ring.
9. A bone plate system according to claim 1, wherein the ring
threading has a double start such that the head of the fastener can
be started into the ring threading at one of two orientations.
10. A bone plate system according to claim 9, wherein the two
orientations of the double start are offset by 180 degrees.
11. A bone plate system according to claim 1, wherein the ring
threading has a triple start such that the head of the fastener can
be started into the ring threading at one of three
orientations.
12. A bone plate system according to claim 11, wherein the three
orientations of the triple start are offset by 120 degrees.
13. A bone plate system according to claim 1, wherein the slot or
gap of the ring extends through the ring to allow the ring to
expand or contract.
14. A bone plate system according to claim 1, wherein the opening
is one of a plurality of openings passing through the plate.
15. A bone plate system according to claim 1, wherein the ring has
an outer width that is less than or about equal to a width of the
opening.
16. A bone plate system according to claim 1, wherein the fastener
further comprises a shank, wherein the shank comprises a bone
threading having a first pitch, and wherein the ring threading
comprises a second pitch, the second pitch of the ring threading
being smaller or substantially equal to the first pitch of the bone
threading.
17. A bone plate system according to claim 1, wherein swiveling of
the ring within the opening of the plate allows a shank of the
fastener to rotate in a substantially conical range of motion and
be inserted into bone at an oblique angle to the plate.
18. A bone plate system according to claim 1, wherein a lower
surface of the plate has a non-planar contour configured to be
positioned adjacent to a bony structure.
19. A bone plate system comprising: a plate having a plurality of
boreholes; and a fitting configured to fit within a first borehole
of the plurality of boreholes and to receive a bone screw
therethrough; wherein the bone screw is configured to couple the
plate to a bone; wherein the fitting surrounds at least a portion
of the bone screw after the bone screw is coupled to the fitting;
wherein the first borehole is configured to inhibit backout of the
fitting from the plate after the fitting is placed in the first
borehole; wherein an outer surface of the fitting is curved to
permit the fitting to swivel within the first borehole after the
fitting is placed in the first borehole and before a head of the
bone screw is screwed into the fitting; wherein the fitting is
configured for a threaded engagement with the head of the bone
screw; and wherein the fitting has a single slot or gap extending
through the fitting to allow the fitting to expand or contract
within the first borehole.
20. A bone plate system according to claim 19, wherein a lower
surface of the plate has a non-planar contour configured to be
positioned adjacent to a bony structure.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of U.S. patent
application Ser. No. 11/148,112, filed Jun. 8, 2005, now allowed,
which is a continuation of U.S. patent application Ser. No.
10/036,012, filed Dec. 26, 2001, abandoned, which is a continuation
of U.S. patent application Ser. No. 09/089,027, filed Jun. 2, 1998,
now U.S. Pat. No. 6,454,769, which is a continuation-in-part of
U.S. patent application Ser. No. 08/905,823, filed Aug. 4, 1997,
abandoned. All applications listed in this paragraph are fully
incorporated by reference herein.
TECHNICAL FIELD
[0002] The invention generally relates to bone plates. More
particularly, the invention relates to a plate system having a
mechanism for fixably attaching screws to a plate at a selected
angle.
DESCRIPTION OF RELATED ART
[0003] The use of spinal fixation plates for correction of spinal
deformities and for fusion of vertebrae is well known. Typically, a
rigid plate is positioned to span bones or bone segments that need
to be immobilized with respect to one another. Bone screws may be
used to fasten the plate to the bones. Spinal plating systems are
commonly used to correct problems in the lumbar and cervical
portions of the spine, and are often installed posterior or
anterior to the spine.
[0004] Spinal plate fixation to the cervical portion of the spine
can be risky because complications during surgery can cause injury
to vital organs, such as the brain stem or the spinal cord. When
attaching a fixation plate to a bone, bone screws are placed either
bi-cortically or uni-cortically through the bone. Uni-cortical
positioning of bone screws has grown in popularity because it is
inherently safer to use. Bi-cortical screws are intended to breach
the distal cortex for maximum anchorage into the bone; however,
this may place distal soft tissue structures at risk. Screw
placement is of particular importance in anterior cervical plate
procedures because of the presence of the spinal cord opposite the
distal cortex. Unfortunately, because of the soft texture of the
bone marrow, the uni-cortical screws may undergo movement from
their desired positions. In fact, the portion of the bone
surrounding such screws may fail to maintain the screws in their
proper positions, resulting in screw backout.
[0005] Screw backout is particularly a problem when a pair of
screws is implanted perpendicular to the plate. When the screws are
placed in such a manner, screw backout can occur as a result of
bone failure over a region that is the size of the outer diameter
of the screw threads. To overcome this problem, a different
configuration of the screws has been developed in which two screws
are angled in converging or diverging directions within the bone.
Advantageously, the amount of bone that is required to fail before
screw backout can occur is increased by this configuration as
compared to screws which are implanted in parallel. Although
positioning screws angled toward or away from each other in a bone
reduces the risk of a screw backout, such backouts can still
happen. The result of a screw backout can be damaging to internal
tissue structures such as the esophagus because a dislocated screw
may penetrate the surface of such structures.
[0006] In an attempt to reduce the risk of damage to internal
tissue structures, some cervical screw plate systems have been
devised in which uni-cortical screws are attached to the plate and
not just the bone. It is intended that if screw backout occurs, the
screw will remain connected to the plate so that it cannot easily
contact internal tissue structures. One such system is described in
U.S. Pat. No. 5,364,399 to Lowery et al. and is incorporated by
reference as if fully set forth herein. This plating system
includes a locking screw at each end of the plate which engages the
heads of the bone screws to trap them within recesses of the plate.
Since the locking screw is positioned over portions of the bone
screws, it may extend above the upper surface of the plate. Thus,
the locking screw may come into contact with internal tissue
structures, such as the esophagus. Unfortunately, breaches to the
esophageal wall may permit bacterial contamination of surrounding
tissues, including the critical nerves in and around the spinal
cord, which can be fatal.
[0007] Another plating system that includes a screw to plate ring
is the Aline.TM. Anterior Cervical Plating System sold by Smith
& Nephew Richards Inc. in Memphis, Tenn. A description of this
system can be found in the Aline.TM. Anterior Cervical Plating
System Surgical Technique Manual available from Smith & Nephew
Richards Inc. and is incorporated by reference as if fully set
forth herein. The bone screws of this system have openings within
each bone screw head for receiving a lock screw coaxially therein.
Each bone screw may be inserted into a bone such that the head of
the screw is positioned within a borehole of a plate placed
adjacent to the bone. The head of each bone screw is slotted such
that portions of the head may be deflected toward the plate during
insertion of the lock screw within the opening of the bone screw.
The bone screw may be thusly locked against the plate. However,
inserting the lock screw into and fixably positioning the lock
screw within the opening may be difficult since the lock screw is
very small. The surgeon may be unable to hold onto the lock screw
without dropping it. Unfortunately, once such a tiny screw falls
into the surgical wound, it may be unretrievable.
SUMMARY OF THE INVENTION
[0008] In accordance with the invention, a plating system is
provided that largely eliminates or reduces the aforementioned
disadvantages of conventional bone plating constructions. An
embodiment of the invention relates to an implant system that
includes a plate having end boreholes, midline boreholes, screws,
and expandable/contractible rings.
[0009] The end boreholes preferably extend from the upper surface
to the lower surface of the plate. The end boreholes may be
disposed in pairs at opposite ends of the plate. Each end borehole
is preferably sized to receive at least a portion of a head of a
screw therein. Each end borehole is also preferably spherical
shaped to permit the screw to be "obliquely angulated" relative to
the plate. Herein, "obliquely angulated" is taken to mean that the
screw may be positioned at a wide range of angles relative to the
plate, wherein the range of angles is preferably from 0 degrees to
about 15 degrees from an imaginary axis that is perpendicular to
the plate. Since the screws may be obliquely angulated with respect
to the plate, the occurrence of screw backout from a bone may be
significantly reduced.
[0010] The expandable/contractible rings are preferably sized so
that they may be positioned within each borehole between the plate
and each of the screw heads. The inner surface of each ring is
preferably shaped to mate with a screw head while the outer surface
is preferably shaped to mate with the plate. The outer surface of
each screw head may be tapered such that an upper portion of the
head is larger than a lower portion of the head. Each ring may also
have a gap that extends vertically through the ring to render it
expandable/contractible. Thus, during insertion of a screw head
within a bone, the ring preferably exerts a compressive force on
the screw head to fixably connect the screw to the plate. Since the
screw is attached to the plate, the screw may be prevented from
contacting tissue structures even when screw backout occurs.
[0011] The midline boreholes may be formed through the plate at
various locations along a midline axis extending across the plate.
The surface of the plate that surrounds each midline borehole is
preferably tapered. Further, the heads of screws that may be
positioned within the plates preferably have tapered outer surfaces
that are shaped to mate with the tapered surface of the plate.
Thus, when such a screw head is inserted into a midline borehole,
the shape of the plate causes the screw to become fixably attached
to the plate in a position that is substantially perpendicular to
the plate. Since the midline boreholes may be used when inserting
screws into bone graft, oblique angulation of screws positioned
within the midline boreholes is not required.
[0012] Prior to surgical implantation of a plating system disclosed
herein, the expandable/contractible rings may be placed within the
end boreholes of the plate. The plate may then be positioned
adjacent to a portion of a bone. Holes may be drilled and tapped
into a portion of the bone underlying each end borehole at the
desired angle. Screws may be inserted through the end boreholes
into the holes, and the heads of the screws may be positioned
within the boreholes such that the rings surround at least a
portion of the heads. Advantageously, during insertion of the
screws, the rings preferably lock the screws in place without
occupying regions outside of the boreholes. Further, since the
rings are pre-positioned within the end boreholes, surgeons do not
have to worry that they may drop the rings during insertion of the
screws.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Further advantages of the invention will become apparent to
those skilled in the art with the benefit of the following detailed
description of a preferred embodiments and upon reference to the
accompanying drawings in which:
[0014] FIG. 1 is a top plan view of one embodiment of a plating
system;
[0015] FIG. 2 is a cross-sectional view of the plating system along
plane I of FIG. 1;
[0016] FIG. 3 is a cross-sectional view of a screw within an end
borehole of a plate, wherein the screw is positioned according to
one embodiment of the invention;
[0017] FIG. 4 is a cross-sectional view of the screw, wherein the
screw is positioned according to another embodiment;
[0018] FIG. 5 is a cross-sectional view of the plating system along
plane II of FIG. 1, wherein a pair of screws extend in diverging
directions, according to one embodiment;
[0019] FIG. 6 is a cross-sectional view of the plating system along
plane II of FIG. 1, wherein the pair of screws extend in converging
directions, according to another embodiment;
[0020] FIG. 7 is a side view in partial cross-section of a fixation
system that includes a screw, a ring, and a plate;
[0021] FIG. 8 is a top view of an embodiment of the plate depicted
in FIG. 7;
[0022] FIG. 9 is a cross-sectional view of a tapered screwhead
connected to a tapered ring through a threaded engagement;
[0023] FIG. 10A is a cross-sectional view of a ring having a
tapered inner surface;
[0024] FIG. 10B is a cross-sectional view of a ring having a
non-tapered inner surface;
[0025] FIG. 11A is a cross-sectional view of a screw head having a
tapered outer surface;
[0026] FIG. 11B is a cross-sectional view of a screw head having a
non-tapered outer surface;
[0027] FIG. 12 depicts a side view of a ring having a plurality of
slots; and
[0028] FIG. 13 depicts a cross-sectional view of a screw head
positioned within a ring.
[0029] While the invention is susceptible to various modifications
and alternative forms, specific embodiments thereof are shown by
way of example in the drawings and will herein be described in
detail. The drawings may not be to scale. It should be understood,
however, that the drawings and detailed description thereto are not
intended to limit the invention to the particular form disclosed,
but on the contrary, the intention is to cover all modifications,
equivalents and alternatives falling within the spirit and scope of
the invention as defined by the appended claims.
DETAILED DESCRIPTION
[0030] FIG. 1 depicts a top plan view of an embodiment of a plating
system. In some embodiments, the plating system may be used to
correct problems in the lumbar and cervical portions of the spine.
For example, in some embodiments, the plating system may be
implanted into the occiput bone which is located at the base of the
skull. In some embodiments, the plating system may be preferably
installed anterior to the spine. In some embodiments, the plating
system preferably includes a plate 10 that may be placed adjacent
to a portion of the spine. In some embodiments, the length of plate
10 may be preferably chosen so that the plate may span between at
least two vertebrae. Plate 10 preferably includes a pair of end
boreholes 12 and 14 located at opposite ends 16 of plate 10. End
boreholes 12 and 14 are preferably formed vertically through plate
10 such that they extend from an upper surface to a lower surface
of the plate. End boreholes 12 and 14 are preferably spaced from a
longitudinal midline axis 21 of plate 10 by the same distance.
[0031] End boreholes 12 and 14 are preferably shaped to receive the
heads of bone screws 20. The plating system further includes rings
18 that may be disposed within each of the end boreholes 12 and 14
for fixedly attaching bone screws 20 to plate 10. A gap 19
preferably exists in each of the rings 18 to enable the rings to
contract or expand under pressure. The plating system may also
include midline boreholes 22 that extend vertically through plate
10 at some point along the midline axis 21 of plate 10. Preferably,
one of the midline boreholes 22 is located at the middle of plate
10 while the other midline boreholes are offset from the middle.
The head of screw 24 may be positioned within one of the midline
boreholes 22. This configuration of midline boreholes 22 may
provide a surgeon with more options as to the location of a screw
24 so that the screw may be placed in the most desirable location.
Such a screw 24 may be used to connect plate 10 to bone graft.
Those elements that make up the plating system are preferably
composed of steel, pure titanium, or of titanium alloys. Such
materials are generally nontoxic, biocompatible, strong, and
noncorrosive. Other materials which have these properties may also
be used to form the elements.
[0032] FIG. 2 illustrates a cross-sectional view of the plating
system along plane I of FIG. 1. Particularly, FIG. 2 shows how
screw 24 is attached to plate 10 within one of the midline
boreholes 22. Screw 24 preferably includes a head 26 and a shank 28
that extends from the base of head 26. The inner surface of a
portion 30 of plate 10 that surrounds borehole 22 is preferably
tapered, making borehole 22 larger at the top than at the bottom.
The outer surface of head 26 is also preferably tapered so that
head 26 may fit snugly within borehole 22. In fact, the shape of
plate 10 and head 26 preferably promotes attachment of screw 24 to
plate 10. During implantation of screw 24 into bone graft, the
shank of the screw is preferably screwed into a hole that has been
formed in the bone graft underlying borehole 22. Because the bottom
portion of borehole 22 is smaller than the upper portion of the
screw head 26, screw 24 may become locked into place within
borehole 22 once it has been screwed to a desired depth within the
bone graft. In the example of FIG. 2, the plate is also shown as
having a slight curvature to enhance its fixation to the bone.
[0033] FIG. 3 depicts a cross-sectional view of an embodiment of
one of the end boreholes 12 and 14 in which screw 20 is disposed.
Borehole 12 is preferably substantially spherical in shape so that
a head 32 of screw 20 may be rotated and moved to various positions
within borehole 12. Ring 18 is preferably sized to fit into
borehole 12 between plate 10 and head 32. The outer surface of ring
18 is preferably curved to permit movement of the ring within
borehole 12. The combination of ring 18 and borehole 12 is like
that of a ball and socket since ring 18 may be rotated both
horizontally and vertically in clockwise and counterclockwise
directions within borehole 12. Ring 18 may also be rotated in
directions that are angled away from the horizontal and vertical
directions. In FIG. 3, ring 18 at least partially surrounds head 32
of screw 20 which is positioned within borehole 12. A shank 34 of
bone screw 20 preferably has threading 36 to allow the screw to be
inserted into a bone when it is rotated in a clockwise direction.
Head 32 preferably includes a cavity 42 that extends from the top
of the head to an inner portion of the head. Cavity 42 may be
shaped to receive the end of any fastening device (e.g., a socket
wrench) that may be used to turn screw 20.
[0034] Screw 20 may be simultaneously screwed into a bone and moved
to its desired position. The inner surface of ring 18 and the outer
surface of head 32 are preferably tapered and shaped to mate with
each other. The bottom portion of head 32 is preferably smaller
than the upper portion of ring 18. As screw 20 is inserted into a
bone, head 32 preferably applies a radial force to ring 18, thereby
causing the ring to expand within the borehole and increase the
size of gap 19. An interference fit may form between screw head 32,
ring 18, and plate 10 in which these elements fit so tightly
together that they obstruct the movements of each other. The hoop
stress of ring 18 on head 32 may fixedly attach screw 20 to plate
10. Also during insertion of screw 20, screw head 32 and ring 18
may be positioned within borehole 12 such that their left sides are
at a higher elevation than their right sides. FIG. 3 shows that
positioning screw head 32 in this configuration may result in a
centerline 38 of shank 34 being obliquely angulated with respect to
plate 10. In fact, centerline 38 may be positioned where it is at
an angle ranging from 0 to 15 degrees with respect to an imaginary
axis 40 which is perpendicular to plate 10. FIG. 3 demonstrates
shank 34 of screw 20 being angled to the left of imaginary axis 40
while FIG. 4 demonstrates shank 34 being angled to the right of
imaginary axis 40. Screw 20 is not limited to these positions and
can be angled in various directions, such as into the page.
[0035] FIG. 5 and FIG. 6 depict different embodiments of the
plating system along plane II of FIG. 1. FIG. 5 shows that screws
20 may be positioned within end boreholes 12 and 14 such that they
extend in converging directions with respect to each other. The
screws 20 depicted in FIG. 6 are shown as being positioned such
that their shanks 34 extend in diverging directions with respect to
each other. Screws 20 may be moved to such positions as described
above. Since bone screws 20 may be placed in diverging or
converging directions through end boreholes 12 and 14 at both ends
of plate 10, screw backout may be greatly reduced. Further, the use
of rings 18 to fixedly attach screws 20 to plate 10 may prevent
damage to tissue structures by any screws that are able to escape
from the bone. Rings 18 preferably do not extend above the upper
surface of plate 10, and thus advantageously do not contact tissue
structures. Screw 20 may be placed in a uni-cortical position
within the bone since the problem of screw backout is greatly
reduced by the diverging or converging screw configurations.
[0036] According to one embodiment, the plating system of FIG. 1 is
prepared for surgical implantation by pre-positioning of rings 18
within end boreholes 12 and 14. During the actual surgical
procedure, holes may be drilled and tapped into the bones to which
plate 10 is to be attached. Plate 10 may then be positioned
adjacent to the bones. Each of the screws 20 may be screwed into
the bone holes while they are being positioned within their
corresponding boreholes 12 and 14. Each pair of screws 20 at
opposite ends 16 of plate 10 may be positioned so that shanks of
the screws are at oblique angles relative to the plate. The
insertion force of each screw 20 into each ring 18 preferably
causes the ring to exert a compressive force on the screw head,
thereby fixably connecting the screws to plate 10. If necessary,
screw 24 may be positioned in one of the midline boreholes 22 such
that screw 24 attaches to plate 10.
[0037] Each of the features of the embodiments discussed above may
be combined or used individually.
Further Improvements
[0038] The following additional embodiments may be used
individually or in combination with any of the embodiments
described above.
[0039] A side view of an embodiment of a plating system 100 is
shown in FIG. 7. Plating system 100 preferably includes a bone
screw 120, a ring 118, and a bone plate 110. Plate 110 may be used
to stabilize a bony structure to facilitate a bone fusion. The bone
screw 120 may be used to connect plate 110 to a bone. A vertebra
may be an example of a bone. Ring 118 preferably fixes bone screw
120 to plate 110 at a selected angle that depends upon the
patient's anatomy. Bone screw 120, ring 118, and bone plate 110 are
preferably capable of being used in similar applications as screw
20, ring 18, and plate 10 as previously described in FIGS. 1-6.
[0040] A top view of an embodiment of plate 110 is shown in FIG. 8.
Plate 110 preferably includes one or more boreholes 112 and may
function similarly to plate 10 as described above. Each borehole
112 preferably has a curvate inner surface 113 (shown in FIG. 7)
for engaging the outer surface 123 of ring 118. The inner surface
113 preferably has the shape of a portion of an outer surface of a
sphere. Borehole 112 has a width that is defined across the inner
surface 113 of the borehole. The width of the borehole may vary in
a direction axially through the borehole. In FIG. 7, for example,
the width of the boreholes preferably increases from a top surface
102 of the plate to about the middle of the plate. The width of the
borehole in FIG. 7 then preferably decreases from about the middle
of the plate to a lower surface 104 of the plate such that the
borehole has a maximum width near the midpoint between upper
surface 102 and lower surface 104 of the plate.
[0041] The outer surface 123 of ring 118 is preferably curvate for
engaging the inner surface 113 of the borehole. The shape of
surfaces 123 and 113 preferably allow ring 118 to swivel within the
borehole. The swiveling action may be similar to that of a ball and
socket joint. The ring preferably surrounds at least a portion of
the head 125 of a bone screw. The enlarged end 127 disposed on head
125 is optional and need not be included if it inhibits angulation
of the bone screw. The swiveling of the ring within the borehole
preferably enables the shank 135 of the bone screw 120 to rotate in
a substantially conical range of motion. In this manner, the head
is preferably movable within the borehole, and the shank is
adjustably positionable at a plurality of angles substantially
oblique to the plate.
[0042] In an embodiment, the surfaces 123 and 113 are preferably
shaped to provide a conical range of motion to the shank that is
within a preferred range of angles. The head is preferably movable
within the borehole such that the shank can be positioned at a
selected angle relative to an imaginary axis running perpendicular
to the plate proximate borehole 112. The selected angle is
preferably less than about 45 degrees, more preferably less than
about 30 degrees, and more preferably still less than about 15
degrees.
[0043] Ring 118 preferably has an outer width that is less than or
about equal to the width of borehole 112 at a location between
upper surface 102 and lower surface 104 of the plate. In this
manner, ring 118 may be positioned within borehole 112 proximate
the middle of the borehole to enable the bone screw 120 to extend
substantially perpendicularly from the bone plate 110. Prior to
surgery, rings 118 are preferably pre-positioned within boreholes
112 of plate 110. "Pre-positioned" is taken to mean that the rings
are capable of swiveling within the borehole but are preferably
inhibited from falling out of the borehole because of the reduced
width of the borehole proximate the upper and lower surfaces. The
width of the borehole proximate the upper and lower surfaces of
plate 110 is preferably less than or about equal to the outer width
of the ring to inhibit the ring from falling out of the borehole.
In this manner, the surgeon may use a plate 110 having rings 118
pre-positioned within the boreholes 112 such that the rings will
not fall into the surgical wound when plating system 100 is
installed.
[0044] Alternately, the rings 118 can be manually positioned within
the boreholes during surgery. Ring 118 preferably includes one or
more slots or gaps 19 (as shown in FIG. 1). The slot preferable
allows the ring to be contracted or expanded. Contraction of ring
118 may allow the ring to be positioned within the borehole during
surgery. Once positioned within the borehole the ring preferably
expands and is inhibited from falling out of the borehole.
[0045] The ring 118 is preferably capable of being swiveled such
that one portion of the ring is adjacent to upper surface 102 of
plate 110 while another portion of the ring lies adjacent to lower
surface 104 of plate 110. The ring is preferably sufficiently thin
to allow it to reside within the borehole without extending from
the borehole beyond the upper surface 102 or lower surface 104 of
the plate. Generally, it is preferred that the ring and screw head
remain within the borehole 112 to minimize the profile width of
plating system 100. In some embodiments, however, the bone screw
120 may be capable of being angulated relative to the plate 110
such that the ring 118 extends from the borehole 112 beyond a
surface of the plate 110.
[0046] The head 125 is preferably screwed into ring 118 to create a
fixed connection between bone screw 120 and plate 110 at a selected
angle. In an embodiment depicted in FIG. 9, screw head 125
preferably contains head threading 121 on its outer surface that is
complementary to ring threading 119 contained on the inner surface
of ring 118. The head threading 121 preferably mates with the ring
threading 119 to enhance the connection between the bone screw 120
and the ring 118. The head 125 preferably has a cavity 142 formed
on its upper surface for receiving a driving tool such as a screw
driver or an Allen wrench.
[0047] The outer surface of the head 125 is preferably tapered so
that screwing the head into the ring causes a change in width
(e.g., expansion) of the ring 118 to fix the bone screw 120 in
position relative to the plate 110. The inner surface of the ring
118 may also be tapered to substantially match the taper on the
outer surface of the head. At least a portion of the head 125
preferably has a width greater than the inner width of the ring
118. As the screw head is screwed into the ring 118, the ring
preferably expands outwardly from its inner surface to accommodate
the increasing width of the screw head 125. The ring 118 may
contain a slot or gap 19 (as shown in FIG. 1) as previously
described to facilitate expansion of the ring against the inner
surface 113 of the borehole 112. The slot is preferably widened as
a result of force received from head 125. The force exerted by head
125 against the inner surface of ring 118 preferably presses the
ring into a fixed engagement against inner surface 113 of borehole
112.
[0048] Alternatively, ring 118 may contain one or more partial
slots 145, as depicted in FIG. 12. Each partial slot 145 preferably
extends from a top 147 or bottom 149 of ring 118 into the ring.
Partial slots may extend up to about midpoint 148 of ring 118. In
one embodiment, a plurality of slots 145 may be oriented about the
ring such that alternate slots extend from the top 147 and/or the
bottom 149 of ring 118, as depicted in FIG. 12. These alternating
partial slots preferably facilitate the expansion and contraction
of ring 118.
[0049] Cross-sectional views of two embodiments of ring 118 are
shown in FIGS. 10A and 10B. The ring may contain an inner surface
that is tapered (as shown in FIG. 10A) or that is substantially
untapered (as shown in FIG. 10B). Cross sectional views of two
embodiments of screw 120 are shown in FIGS. 11A and 11B. The head
125 may have a substantially untapered outer surface (as shown in
FIG. 11A) or a substantially tapered outer surface (as shown in
FIG. 11B). It is to be understood that each of the heads of the
screws depicted in FIGS. 11A and 11B may be used in combination
with either of the rings 118 depicted in FIG. 10A or FIG. 10B. It
is also to be appreciated that the head of the screw may include an
outer surface having a substantially untapered portion along with a
tapered portion proximate its end for expanding the ring 118.
[0050] As described herein, a "ring" is taken to mean any member
capable of fitting between the inner surface 113 borehole and the
bone screw 120 to connect the bone screw to the bone plate 110. The
ring is preferably substantially circular to surround head 125, but
the ring may instead have a non-circular shape. The ring may be
made of a number of biocompatible materials including metals,
plastics, and composites.
[0051] It is believed that using a threading engagement between the
head 125 and ring 118 increases the hoop stress exerted on head
125, resulting in a stronger connection between the bone screw 120
and the plate 110. Moreover, if bone threading 136 becomes loose
within a bone, screw backout from plate 110 will tend to be
resisted by the threaded connection between the screw head 125 and
the ring 118. Thus, even if the shank 135 loosens within the bone,
the head will tend to remain within the borehole of the plate so as
not to protrude from the plate into surrounding body tissue.
[0052] As shown in FIG. 9, the head threading 121 on the head 125
and the ring threading 119 on the inner surface of ring 118 is
preferably substantially fine relative to the threading 136 on bone
screw 120. That is, the pitch of the head threading 121 and ring
threading 119 is preferably smaller than that on bone screw 120.
The ring threading 119 preferably has multiple starts to facilitate
connection of the bone screw and the ring. In one embodiment, the
ring threading 119 has a double start such that the head can be
started into the ring threading at either one of two orientations
offset by 180 degrees. In another embodiment, the ring threading
has a triple start such that the head can be started into the ring
threading at any one of three orientations offset by 120
degrees.
[0053] The ring threading 119 and head threading 121 are preferably
pitched to a substantially similar degree to the threading 136 on
the bone screw 120. Preferably, the ring threading 119 and head
threading 121 are pitched such that the head 125 causes expansion
of the ring 118 while the bone screw 120 is being inserted into the
bone.
[0054] During the surgical procedure for attaching the plate 110 to
a bone, holes may be drilled and tapped into the bones to which
plate 110 is to be attached. Plate 110 may then be positioned
adjacent to the bones. A ring 118 may be positioned within the
borehole. A bone screw 120 may be positioned through ring 118 such
that the head threading 121 of head 125 engages the ring threading
119 of ring 118. The bone screw 120 may then be rotated to insert
the bone screw into the bone. As the screw is rotated the head
threads and ring threads preferably interact such that the head is
moved into the ring. Movement of the head 125 into the ring 118
preferably causes the ring to expand such that the orientation of
the bone screw 120 relative to the plate 110 is fixed. Preferably,
the ring threading and head threading is pitched such the
orientation of the bone screw 120 is fixed after plate 110 engages
the bone.
[0055] The bone screws may be used in pairs to prevent screw
backout. The bone screws are preferably positioned into the bone in
substantially converging or substantially diverging directions
relative to one another.
[0056] In an embodiment, a stronger connection between the bone
screw 120 and the plate 110 may be formed by texturing either outer
surface 131 of head 125 of bone screw 120 or inner surface 133 of
ring 118, as depicted in FIG. 13. Preferably, both surfaces are
textured to inhibit movement of the bone screw with respect to the
plate. During typical manufacturing procedures, outer surface 131
of head 125 and inner surface 133 of ring 118 may be formed as
relatively smooth surfaces. While the friction between these smooth
surfaces tends to be sufficient to maintain bone screw 120 in a
fixed position with respect to plate 110, under stressful
conditions the bone screw may be forced out of ring 118. By
providing at least one textured surface, the coefficient of
friction of the surface may be increased so that a large amount of
force is needed to overcome the frictional connection between head
125 of bone screw 120 and ring 118. This increase in friction
between bone screw 120 and ring 118 may further inhibit screw
backout from plate 110.
[0057] A number of textured surfaces may be used to increase the
coefficient of friction between ring 118 and head 125 of bone screw
120. In general, any process which transforms a relatively smooth
surface into a roughened surface having an increased coefficient of
friction may be used. Methods for forming a roughened surface
include, but are not limited to: sanding, forming grooves within a
surface, ball peening processes, electric discharge processes, and
embedding of hard particles within a surface.
[0058] In one embodiment a plurality of grooves may be formed in
outer surface 131 of head 125 of bone screw 120 or inner surface
133 of ring 118. Preferably, a plurality of grooves is formed in
both outer surface 131 and inner surface 133. While it is preferred
that both outer surface 131 and the inner surface 133 be textured,
texturing of only one of the surfaces may be sufficient to attain
additional resistance to movement.
[0059] In another embodiment, the frictional surface may be created
by an electrical discharge process. An electrical discharge process
is based on the principle of removal of portions of a metal surface
by spark discharges. Typically a spark is generated between the
surface to be treated and an electrode by creating potential
differential between the tool and the electrode. The spark produced
tends to remove a portion of the surface disposed between the
electrode and the surface. Typically, the electrode is relatively
small such that only small portions of the surface are removed. By
moving the electrode about the surface numerous cavities may be
formed within the surface. Typically these cavities are somewhat
pyramidal in shape. Various patterns may be formed within the
surface depending on how the electrode is positioned during the
discharge. Electric discharge machines are well known in the art. A
method for forming a frictional surface within a metal surface
using an electric discharge process is described in U.S. Pat. No.
4,964,641 to Miesch et al. which is incorporated by reference as if
set forth herein.
[0060] A variety of patterns may be formed using an electric
discharge machine. Preferably a diamond pattern or a waffle pattern
is formed on either inner surface 133 of ring 118 or outer surface
131 of head 125 of bone screw 120.
[0061] In another embodiment, inner surface 131 of ring 118 and/or
outer surface 133 of head 125 of bone screw 120 may be textured by
the use of a shot peening process. A shot peening process for
forming a textured surface is described in U.S. Pat. No. 5,526,664
to Vetter which is incorporated by reference as if set forth
herein. In general, a shot peening process involves propelling a
stream of hardened balls, typically made of steel, at a relatively
high velocity at a surface. To create a pattern upon an area of the
surface the stream is typically moved about the surface. The speed
by which the stream is moved about the surface tends to determine
the type of textured surface formed.
[0062] Preferably, the stream is moved such that a pattern
resulting in a textured surface having ridges and valleys is formed
on inner surface 133 of ring 118 and outer surface 131 of head 125
of bone screw 120. When the textured inner surface 131 of ring 118
and the textured head 125 of bone screw 120 are coupled together
the ridges and valleys may interact with each other to provide
additional resistance to movement in either a longitudinal
direction or a direction perpendicular to the longitudinal
axis.
[0063] In another embodiment, the textured surface may be produced
by embedding sharp hardened particles in the surface. A method for
embedding sharp hardened particles in a metal surface is described
in U.S. Pat. No. 4,768,787 to Shira which is incorporated by
reference as if set forth herein. The method of Shira involves
using a laser or other high energy source to heat the surface such
that the surface melts in selected areas. Just before the molten
area re-solidifies, a stream of abrasive particles is directed to
the area. In this manner some of the particles tend to become
embedded within the molten surface. The particles typically have a
number of sharp edges that protrude from the surface after the
particles have been embedded within the surface.
[0064] Any of the above methods of texturing may be used in
combination with another method. For example, outer surface 131 of
head 125 of bone screw 120 may be textured using a pattern of
grooves. Inner surface of ring 118, however, may be textured using
an electrical discharge method. When coupled together the textured
surfaces of bone screw 120 and ring 118 may interact with each
other to provide additional resistance to movement in either a
longitudinal direction or a direction perpendicular to the
longitudinal axis.
[0065] Textured surfaces may also be formed on any of the other
surfaces of the plate system. The formation of textured surfaces
preferably increases the frictional resistance between the various
components of the plate system.
[0066] Further modifications and alternative embodiments of various
aspects of the invention will be apparent to those skilled in the
art in view of this description. Accordingly, this description is
to be construed as illustrative only and is for the purpose of
teaching those skilled in the art the general manner of carrying
out the invention. It is to be understood that the forms of the
invention shown and described herein are to be taken as the
presently preferred embodiments. Elements and materials may be
substituted for those illustrated and described herein, parts and
processes may be reversed, and certain features of the invention
may be utilized independently, all as would be apparent to one
skilled in the art after having the benefit of this description of
the invention. Changes may be made in the elements described herein
without departing from the spirit and scope of the invention as
described in the following claims.
* * * * *