U.S. patent application number 09/089027 was filed with the patent office on 2001-08-16 for system and method for stabilizing the human spine with a bone plate.
Invention is credited to JONES, ROBERT, WAGNER, ERIK J..
Application Number | 20010014807 09/089027 |
Document ID | / |
Family ID | 26779790 |
Filed Date | 2001-08-16 |
United States Patent
Application |
20010014807 |
Kind Code |
A1 |
WAGNER, ERIK J. ; et
al. |
August 16, 2001 |
SYSTEM AND METHOD FOR STABILIZING THE HUMAN SPINE WITH A BONE
PLATE
Abstract
A spinal plate system and method for fixation of the human spine
is provided. In an embodiment, the system includes 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; (AUSTIN, TX) |
Correspondence
Address: |
ERIC B MEYERTONS
CONLEY ROSE & TAYON
P O BOX 398
AUSTIN
TX
787670398
|
Family ID: |
26779790 |
Appl. No.: |
09/089027 |
Filed: |
June 2, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09089027 |
Jun 2, 1998 |
|
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|
08905823 |
Aug 4, 1997 |
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Current U.S.
Class: |
606/279 |
Current CPC
Class: |
A61B 17/7059 20130101;
A61B 17/8047 20130101; A61B 17/8052 20130101; A61B 17/8057
20130101 |
Class at
Publication: |
606/61 |
International
Class: |
A61B 017/58 |
Claims
What is claimed is:
1. A spinal fixation system, comprising: a plate for stabilizing a
spine, the plate comprising a borehole; a bone screw comprising a
head and a shank for coupling the plate to a bone, the head being
movable within the borehole during use such that the shank is
adjustably positionable at a plurality of angles substantially
oblique to the plate; and a ring for coupling the bone screw to the
plate, the ring being positionable within the borehole between the
plate and the bone screw during use, the ring comprising ring
threading for engaging the bone screw during use.
2. The system of claim 1, wherein the ring is configured to
substantially surround the head during use.
3. The system of claim 1, wherein the head comprises an outer
surface having head threading disposed thereon, the head threading
being complementary to the ring threading.
4. The system of claim 1, wherein the head is movable within the
borehole such that the shank is rotatable in a substantially
conical range of motion to allow the shank to be positioned at a
selected angle relative to the plate.
5. The system of claim 1, wherein the ring threading has multiple
starts to facilitate connection of the bone screw and the ring
during use.
6. The system of claim 1, wherein the ring threading has a double
start to facilitate connection of the bone screw and the ring
during use.
7. The system of claim 1, wherein the ring threading has a triple
start to facilitate connection of the bone screw and the ring
during use.
8. The system of claim 1, wherein the shank comprises bone
threading having a first pitch, and wherein the ring threading
comprises a second pitch, the second pitch being substantially
equal to the first pitch.
9. The system of claim 1, wherein the shank comprises bone
threading having a first pitch, and wherein the ring threading
comprises a second pitch, the second pitch being substantially
equal to the first pitch, and wherein the pitch is predetermined to
allow the plate to contact the bone when the bone screw is inserted
within the bone and coupled to the ring.
10. The system of claim 1, wherein the head comprises a tapered
outer surface for expanding the ring to fix the bone screw in
position during use.
11. The system of claim 1, wherein the ring comprises an inner
surface where the ring threading is disposed, the inner surface
being tapered to cause the ring to expand during use to fix the
bone screw in position.
12. The system of claim 1, wherein the head comprises a tapered
outer surface, and wherein the ring comprises an inner surface
containing the ring threading, the inner surface being tapered to
mate with the tapered outer surface of the head, and wherein the
head is adapted to exert force against the ring during use to
substantially expand the ring and thereby substantially fix the
position of the screw relative to the plate during use.
13. The system of claim 1, wherein the ring comprises one or more
slots to allow it to expand.
14. The system of claim 1, wherein the ring comprises one or more
slots to allow it to contract.
15. The system of claim 1, wherein the borehole comprises an inner
surface and a width across the borehole, the inner surface being
curved such that the width varies in a direction axially along the
borehole.
16. The system of claim 1, wherein the borehole comprises a
substantially curvate inner surface, and wherein the ring further
comprises a substantially curvate outer surface, the curvate outer
surface being shaped to engage the curvate inner surface to allow
the ring to swivel within the borehole.
17. The system of claim 1, wherein the plate comprises an upper
surface and lower surface, and wherein the ring comprises an outer
surface and an outer ring width, and wherein the borehole comprises
a substantially curvate inner surface and a width defined across
the inner surface, the width of the borehole varying in a direction
axially along the borehole, and wherein the width of the borehole
is greater than about the outer ring width at a location between
the upper and lower surface, and wherein the width of the borehole
is not greater than the outer ring width proximate the upper and
lower surfaces.
18. The system of claim 1, wherein the plate comprises an upper
surface and a lower surface, and wherein the borehole extends
between the upper and lower surfaces, the borehole comprising a
width that varies in a direction axially along the borehole, and
wherein the ring is disposed within the borehole, the ring further
comprising an outer ring width that is greater than about the width
of the borehole proximate the upper and lower surfaces, the outer
ring width being sized relative to the width of the borehole
proximate the upper and lower surfaces to substantially inhibit the
ring from being removed from the borehole.
19. The system of claim 1, wherein the ring is configured to reside
within the borehole without extending above an upper surface of the
plate during use.
20. The system of claim 1, wherein the ring substantially surrounds
the head of the bone screw, and wherein the bone screw is capable
of being angulated relative to the plate during use such that the
ring extends from the borehole beyond a surface of the plate.
21. The system of claim 1, wherein the plate comprises a second
borehole, and the system further comprises: a second bone screw
comprising a second head and a second shank for coupling the plate
to a bone, the second head being movable within the second borehole
during use such that the second shank is adjustably positionable at
a plurality of angles substantially oblique to the plate; and a
second ring for coupling the second bone screw to the plate, the
second ring being positionable within the second borehole between
the plate and the second bone screw during use, the second ring
comprising second ring threading for engaging the second bone screw
during use; and wherein the first bone screw and the second bone
screw are positionable to extend into the bone in substantially
converging or substantially diverging directions relative to one
another during use.
22. The system of claim 21, wherein the first shank is positioned
at a first oblique angle relative to the plate during use, and
wherein the second shank is positioned at a second oblique angle
relative to the plate during use, and wherein the first shank and
the second shank extend in diverging directions relative to each
other during use.
23. The system of claim 21, wherein the first shank is positioned
at a first oblique angle relative to the plate during use, and
wherein the second shank is positioned at a second oblique angle
relative to the plate during use, and wherein the first shank and
the second shank extend in converging directions relative to each
other during use.
24. The system of claim 1, wherein the head is movable within the
borehole such that the shank is rotatable in a substantially
conical range of motion to allow the shank to be positioned at a
selected angle of less than about 15 degrees relative to a plane
substantially perpendicular to the plate.
25. The system of claim 1, wherein the ring comprises a plurality
of slots extending from a bottom and a top of the ring to a middle
portion of the ring.
26. A method for stabilizing a spine, comprising: positioning a
plate adjacent to a bone, the plate comprising a borehole; moving a
bone screw through a ring positioned within the borehole, the bone
screw comprising a head having an outer surface with head threading
disposed thereon, the ring comprising an inner surface having ring
threading disposed thereon that mates with the head threading;
engaging the ring threading with the head threading; and screwing
the bone screw into the bone to connect the plate to the bone,
wherein screwing the bone screw into the bone simultaneously moves
the head through the ring such that an outer surface of the ring is
forced against an inner surface of the borehole to substantially
fix the bone screw relative to the plate.
27. The method of claim 26, wherein forcing the ring against the
inner surface of the borehole comprises expanding the ring.
28. The method of claim 26, wherein the bone screw is fixed in a
position whereby it extends from the plate at a substantially
oblique angle.
29. The method of claim 26, wherein the ring comprises one or more
slots, and wherein the slot is widened when the head is moved
through the ring.
30. The method of claim 26, further comprising drilling and/or
tapping an opening into the bone that is shaped to receive the bone
screw prior to screwing the bone screw into the bone.
31. The method of claim 26, further comprising screwing a second
bone screw into the bone, the second bone screw extending through a
second borehole in the plate such that the two bone screws extend
in diverging directions relative to each other.
32. The method of claim 26, further comprising screwing a second
bone screw into the bone, the second bone screw extending through a
second borehole in the plate such that the two bone screws extend
in converging directions relative to each other.
33. The method of claim 26, wherein the head is movable within the
borehole such that the bone screw is rotatable in a substantially
conical range of motion, and further comprising positioning the
bone screw at a selected angle oblique to the plate.
34. The method of claim 26, wherein the ring threading has multiple
starts to facilitate engagement of the ring threading with the head
threading.
35. The method of claim 26, wherein the head comprises a tapered
outer surface, and further comprising expanding the ring by forcing
the tapered outer surface against the inner surface of the ring,
thereby substantially fixing the bone screw in position.
36. The method of claim 26, wherein the head comprises a tapered
outer surface, and wherein the inner surface of the ring is tapered
to complement the tapered outer surface of the head, and further
comprising expanding the ring by forcing the tapered outer surface
against the inner surface of the ring, thereby substantially fixing
the bone screw in position.
37. The method of claim 26, wherein the borehole comprises a
substantially curvate inner surface, and wherein the ring further
comprises a substantially curvate outer surface, and further
comprising angulating the bone screw by swiveling the outer surface
of the ring across the inner surface of the borehole to position
the bone screw prior to fixing the bone screw relative to the
plate.
38. The method of claim 26, further comprising manually inserting
the ring within the borehole prior to moving the bone screw through
the ring.
39. The method of claim 26, wherein the borehole is shaped to
substantially inhibit the ring from being removed from the
borehole, and further comprising swiveling the ring about the
borehole to position the bone screw.
40. The method of claim 26, wherein the ring does not extend from
the borehole beyond a surface of the plate after the bone screw is
substantially fixed relative to the plate.
41. The method of claim 26, wherein the head is movable within the
borehole such that a shank of the bone screw is rotatable in a
substantially conical range of motion to allow the shank to be
positioned at a selected angle of less than about 15 degrees
relative to a plane substantially perpendicular to the plate.
42. A spinal fixation system, comprising: a plate for stabilizing a
spine, the plate comprising a borehole; a bone screw comprising a
head and a shank for coupling the plate to a bone, the head
comprising a tapered outer surface and being movable within the
borehole during use such that the shank is adjustably positionable
at a plurality of angles substantially oblique to the plate; and a
ring for coupling the bone screw to the plate, the ring being
positionable within the borehole between the plate and the bone
screw during use, the ring comprising an inner surface having ring
threading disposed thereon for engaging the bone screw during use,
the inner surface of the ring being tapered; and wherein movement
of the tapered outer surface of the head along the inner surface of
the ring causes the ring to substantially expand against the
borehole during use to substantially fix the shank at a selected
angle relative to the plate during use.
43. A spinal fixation system, comprising: a plate for stabilizing a
spine, the plate comprising a borehole; a bone screw for coupling
the plate to a bone, the bone screw comprising a head, the head
comprising threading and being positionable within the borehole
during use; and a ring for coupling the bone screw to the plate,
the ring being positionable within the borehole between the plate
and the head during use, the ring comprising an inner surface
having ring threading disposed thereon for engaging the threading
on the head during use, the ring being expandable during use to
form a fixable connection between the bone screw and the plate.
44. A spinal fixation system, comprising: a plate for stabilizing a
spine, the plate comprising a borehole; a bone screw comprising a
head and a shank for coupling the plate to a bone, the head being
movable within the borehole during use such that the shank is
adjustably positionable at a plurality of angles substantially
oblique to the plate, wherein the head comprises a substantially
textured surface; and a ring comprising an inner surface, the ring
configured to couple the bone screw to the plate, wherein the ring
is positionable within the borehole between the plate and the bone
screw during use; and wherein the textured surface of the head
engages an inner surface of the ring during use such that movement
of the bone screw with respect to the plate is substantially
inhibited during use.
45. The system of claim 44, wherein the ring is configured to
substantially surround the head during use.
46. The system of claim 44, wherein the head is movable within the
borehole such that the shank is rotatable in a substantially
conical range of motion to allow the shank to be positioned at a
selected angle relative to the plate.
47. The system of claim 44, wherein the head comprises a tapered
outer surface for expanding the ring to fix the bone screw in
position during use.
48. The system of claim 44, wherein the inner surface of the ring
is tapered to cause the ring to expand during use to fix the bone
screw in position.
49. The system of claim 44, wherein the head comprises a tapered
outer surface, and wherein the inner surface of the ring is tapered
to mate with the tapered outer surface of the head, and wherein the
head is adapted to exert force against the ring during use to
substantially expand the ring and thereby substantially fix the
position of the screw relative to the plate during use.
50. The system of claim 44, wherein the ring comprises one or more
slots to allow it to expand.
51. The system of claim 44, wherein the ring comprises one or more
slots to allow it to contract.
52. The system of claim 44, wherein the borehole comprises an inner
surface and a width across the borehole, the inner surface being
curved such that the width varies in a direction axially along the
borehole.
53. The system of claim 44, wherein the borehole comprises a
substantially curvate inner surface, and wherein the ring further
comprises a substantially curvate outer surface, the curvate outer
surface being shaped to engage the curvate inner surface to allow
the ring to swivel within the borehole.
54. The system of claim 44, wherein the plate comprises an upper
surface and lower surface, and wherein the ring comprises an outer
surface and an outer ring width, and wherein the borehole comprises
a substantially curvate inner surface and a width defined across
the inner surface, the width of the borehole varying in a direction
axially along the borehole, and wherein the width of the borehole
is greater than about the outer ring width at a location between
the upper and lower surface, and wherein the width of the borehole
is not greater than the outer ring width proximate the upper and
lower surfaces.
55. The system of claim 44, wherein the plate comprises an upper
surface and a lower surface, and wherein the borehole extends
between the upper and lower surfaces, the borehole comprising a
width that varies in a direction axially along the borehole, and
wherein the ring is disposed within the borehole, the ring further
comprising an outer ring width that is greater than about the width
of the borehole proximate the upper and lower surfaces, the outer
ring width being sized relative to the width of the borehole
proximate the upper and lower surfaces to substantially inhibit the
ring from being removed from the borehole.
56. The system of claim 44, wherein the ring is configured to
reside within the borehole without extending above an upper surface
of the plate during use.
57. The system of claim 44, wherein the ring substantially
surrounds the head of the bone screw, and wherein the bone screw is
capable of being angulated relative to the plate during use such
that the ring extends from the borehole beyond a surface of the
plate.
58. The system of claim 44, wherein the inner surface of the ring
is substantially textured.
59. A spinal fixation system, comprising: a plate for stabilizing a
spine, the plate comprising a borehole; a bone screw comprising a
head and a shank for coupling the plate to a bone, the head being
movable within the borehole during use such that the shank is
adjustably positionable at a plurality of angles substantially
oblique to the plate; and a ring for coupling the bone screw to the
plate, the ring being positionable within the borehole between the
plate and the bone screw during use; and wherein at least one of a
surface of an inner surface of the ring and an outer surface of the
head is substantially textured such that a frictional engagement is
formed between the head and the inner surface of the ring during
use, and wherein the frictional engagement inhibits movement of the
bone screw with respect to the plate during use.
60. A spinal fixation system, comprising: a plate for stabilizing a
spine, the plate comprising a first pair of boreholes, a second
pair of boreholes, and a midline borehole, the midline borehole
positioned between the first and the second pairs of boreholes; a
plurality of bone screws, each of the bone screws comprising a head
and a shank for coupling a portion of the plate to a bone, the head
being movable within the borehole during use such that the shank is
adjustably positionable at a plurality of angles substantially
oblique to the plate; and a plurality of rings for coupling the
bone screws to the plate, each of the rings being positionable
within one of the boreholes between the plate and one of the bone
screws during use, wherein each of the rings comprises ring
threading for engaging one of the bone screws during use.
61. A spinal fixation plate, comprising: a borehole extending
between an upper surface and a lower surface of the plate, the
borehole comprising a width that varies in a direction axially
along the borehole; and a ring disposed within the borehole, the
ring further comprising an outer ring width that is greater than
about the width of the borehole proximate the upper and lower
surfaces, the outer ring width being sized relative to the width of
the borehole proximate the upper and lower surfaces to
substantially inhibit the ring from being removed from the
borehole.
62. The system of claim 61, wherein the ring comprises ring
threading on an inner surface of the ring.
63. The system of claim 61, wherein the ring comprises a textured
inner surface.
64. The system of claim 61, wherein the ring comprises a slot to
allow it to expand.
65. The system of claim 61, wherein the ring comprises a slot to
allow it to contract.
66. The system of claim 61, wherein the ring comprises a plurality
of partial slots extending from top and bottom surfaces of the
ring.
67. The system of claim 61, wherein the borehole comprises a
substantially curvate inner surface, and wherein the ring further
comprises a substantially curvate outer surface, the curvature of
the outer surface being shaped to engage the curvate inner surface
to allow the ring to swivel within the borehole.
68. The system of claim 61, wherein the ring is configured to
reside within the borehole without extending above an upper surface
of the plate during use.
69. A spinal screw system, comprising: a ring, the ring comprising
at least one slot to allow expansion of the ring; and a bone screw
comprising a head and a shank; wherein the head of the bone screw
is sized to be contained within the ring, and wherein the head is
positionable within the ring such that the ring is substantially
expanded.
70. The system of claim 69, wherein the ring comprises an inner
surface, the inner surface comprising ring threading, and wherein
the head comprises an outer surface, the outer surface comprising
head threading, the head threading being complementary to the ring
threading.
71. A spinal fixation plate, comprising a borehole extending
between an upper surface and a lower surface of the plate, the
borehole comprising a width that varies in a direction axially
along the borehole.
72. The plate of claim 71, further defined as comprising a
plurality of boreholes disposed to form at least two pairs of bore
holes positioned proximate opposite edges of the plate.
73. A method of making a spinal fixation plate, comprising forming
a borehole through an upper and lower surface of the plate, wherein
the formed borehole comprises a width that varies in a direction
axially along the borehole.
74. A system for fixation of the human spine, comprising: an
elongated plate comprising an upper surface, a lower surface, and a
first borehole extending from the upper surface to the lower
surface; a first screw comprising a first shank and a first head,
wherein the first borehole is shaped to receive at least a portion
of the first head, and wherein the first borehole is shaped to
permit the first screw to be obliquely angulated relative to the
plate during use; and a first ring sized to fit within the first
borehole between the plate and the first head, the first ring being
adapted to fixably connect the first screw to the plate during
use.
75. The system of claim 74, wherein the first ring comprises a gap
to render it substantially contractible.
76. The system of claim 74, wherein the first ring comprises a gap
to render it substantially expandable.
77. The system of claim 74, wherein the first ring is shaped to at
least partially surround the first head during use.
78. The system of claim 74, wherein the first borehole is
substantially spherical shaped.
79. The system of claim 74, wherein the first ring comprises an
outer surface that is substantially curvate to permit the first
ring to mate with the plate while positioned within the first
borehole.
80. The system of claim 74, wherein the first head comprises a
substantially tapered outer surface, and wherein the first ring
comprises a substantially tapered inner surface that is shaped to
mate with the outer surface during use.
81. The system of claim 74, wherein the first head comprises an
upper portion and a lower portion, and wherein the upper portion is
substantially larger than the lower portion, and wherein the first
ring comprises an inner surface that is shaped to mate with the
first head during use.
82. The system of claim 74, wherein the first shank comprises
external threads adapted to engage bone during use.
83. The system of claim 74, wherein the first head comprises a
cavity adapted to receive an end of a fastening device, the
fastening device being adapted to rotate the first screw during
use.
84. The system of claim 74, wherein the first ring is adapted to
reside within the first borehole without extending above the upper
surface of the plate during use.
85. The system of claim 74, wherein the first head comprises a
first side opposite to a second side, and wherein the first screw
is positioned such that the first side is elevated above the second
side within the first borehole during use.
86. The system of claim 74, wherein the first head comprises a
first side opposite to a second side, and wherein the first screw
is positioned such that the second side is elevated above the first
side within the first borehole during use.
87. The system of claim 74, wherein the plate comprises a first end
opposite to a second end, and wherein the first borehole is
positioned proximate one of the first and second ends.
88. The system of claim 74, wherein the plate comprises a first end
opposite to a second end and a second borehole extending from the
upper surface to the lower surface, and wherein the first borehole
and the second borehole are located a spaced distance apart
proximate one of the first and second ends.
89. The system of claim 74, wherein the plate comprises a second
borehole extending from the upper surface to the lower surface a
spaced distance from the first borehole, and further comprising: a
second screw comprising a second shank and a second head, wherein
the second borehole is shaped to receive at least a portion of the
second head, and wherein the second borehole is shaped to permit
the second screw to be obliquely angulated relative to the plate
during use; and a second ring sized to fit within the second
borehole between the plate and the second head, said second ring
being adapted to fixably connect the second screw to the plate
during use.
90. The system of claim 89, wherein the first shank is positioned
at a first oblique angle relative to the plate during use, and
wherein the second shank is positioned at a second oblique angle
relative to the plate during use, and wherein the first shank and
the second shank extend in diverging directions relative to each
other during use.
91. The system of claim 89, wherein the first shank is positioned
at a first oblique angle relative to the plate during use, and
wherein the second shank is positioned at a second oblique angle
relative to the plate during use, and wherein the first shank and
the second shank extend in diverging directions relative to each
other during use.
92. The system of claim 89, wherein the plate comprises a midline
axis and a third borehole extending from the upper surface to the
lower surface at the midline axis, and further comprising a third
screw comprising a third shank and a third head, and wherein the
plate comprises a tapered inner surface that substantially
surrounds the third borehole, and wherein the third head is sized
to fit within the third borehole during use, and wherein the inner
surface is adapted to fixably connect the third screw to the plate
during use.
93. The system of 74, wherein the first screw is positioned within
the first borehole during use such that the first shank is at
approximately a first angle of about 15 degrees or less than about
15 degrees relative to an imaginary axis that is substantially
perpendicular to the plate.
94. The system of claim 89, wherein the second screw is positioned
within the first borehole during use such that the second shank is
at approximately a second angle of about 15 degrees or less than
about 15 degrees relative to an imaginary axis that is
substantially perpendicular to the plate.
95. A method for surgically implanting a spinal plate system,
comprising: positioning a substantially flexible first ring within
a first borehole that extends from an upper surface to a lower
surface of a plate; positioning the plate adjacent to a bone; and
screwing a first shank of a first screw into the bone while
simultaneously positioning a first head of the first screw within
the first borehole such that the first ring substantially surrounds
a portion of the first head, wherein the step of screwing causes
the first ring to exert a compressive force on the first head to
fixably connect the first screw to the plate.
96. The method of claim 95, wherein the step of positioning the
first head comprises moving the first screw to a position where the
first screw is at an oblique angle relative to the plate.
97. The method of claim 95, wherein the step of positioning the
first head comprises moving the first screw to a position where the
first shank is at approximately an angle of about 15 degrees or
less than about 15 degrees relative to an imaginary axis that is
substantially perpendicular to the plate.
98. The method of claim 95, wherein the first ring is positioned
within the first borehole such that the ring is disposed within the
first borehole without extending above the upper surface of the
plate.
99. The method of claim 95, wherein the first ring comprises a gap
to render it contractible and expandable.
100. The method of claim 95, wherein the first ring comprises a gap
to render it contractible and expandable, and wherein the step of
screwing causes the gap to increase in size such that the ring is
compressed against the plate.
101. The method of claim 95, wherein the first borehole is
substantially spherical shaped.
102. The method of claim 95, wherein the first ring comprises an
outer surface that is shaped to mate with the plate while
positioned within the first borehole.
103. The method of claim 95, wherein the first head comprises a
substantially tapered outer surface, and wherein the first ring
comprises a substantially tapered inner surface that is shaped to
mate with the outer surface.
104. The method of claim 95, wherein the first head comprises an
upper portion and a lower portion, wherein the upper portion is
substantially larger than the lower portion, and wherein the first
ring comprises an inner surface that is shaped to mate with the
first head.
105. The method of claim 95, wherein the first shank comprises
external threads that engage the bone during the step of screwing
the bone.
106. The method of claim 95, wherein the step of screwing comprises
placing an end of a fastening device within a cavity of the first
head and rotating the fastening device to rotate the first
screw.
107. The method of claim 95, further comprising drilling an opening
into the bone that is shaped to receive the first shank, prior to
the step of screwing the first shank.
108. The method of claim 95, wherein the first head comprises a
first side opposite to a second side, and wherein the first screw
is positioned such that the first side is elevated above the second
side within the first borehole.
109. The method of claim 95, wherein the first head comprises a
first side opposite to a second side, and wherein the first screw
is positioned such that the second side is elevated above the first
side within the first borehole.
110. The method of claim 95, wherein the plate comprises a first
end opposite to a second end, and wherein the first borehole is
positioned proximate one of the first and second ends.
111. The method of claim 95, wherein the plate comprises a first
end opposite to a second end and a second borehole extending from
the upper surface to the lower surface, wherein the first borehole
and the second borehole are located a spaced distance apart
proximate one of the first and second ends.
112. The method of claim 95, further comprising: positioning a
substantially flexible second ring within a second borehole that
extends from the upper surface to the lower surface a spaced
distance from the first borehole, prior to the step of positioning
the plate; and screwing a second shank of a second screw into the
bone while simultaneously positioning a second head of the second
screw within the second borehole such that the second ring
substantially surrounds a portion of the second head, wherein the
step of screwing the second shank causes the first ring to exert a
compressive force on the second head to fixably connect the second
screw to the plate.
113. The method of claim 112, wherein the steps of positioning the
first head and the second head comprise moving the first screw and
the second screw to respective positions where the first shank and
the second shank extend in diverging directions relative to each
other.
114. The method of claim 112, wherein the steps of positioning the
first head and the second head comprise moving the first screw and
the second screw to respective positions where the first shank and
the second shank extend in converging directions relative to each
other.
115. The method of claim 112, wherein the step of positioning the
second head comprises moving the first screw to a position where
the second shank is at approximately an angle of about 15 degrees
or less than about 15 degrees relative to an imaginary axis that is
substantially perpendicular to the plate.
116. The method of claim 112, wherein the plate comprises a midline
axis and a third borehole extending from the upper surface to the
lower surface at the midline axis.
117. The method of claim 112, further comprising screwing a third
shank of a third screw into the bone while simultaneously
positioning a third head of the third screw within a third borehole
that extends from the upper surface to the lower surface at a
midline axis of the plate, wherein the step of screwing causes a
substantially tapered surface of the plate to exert a compressive
force on the third head to fixably connect the third screw to the
plate.
118. A system for fixation of the human spine, comprising: an
elongated plate comprising an upper surface, a lower surface, and a
first borehole extending from the upper surface to the lower
surface; a substantially flexible first ring sized to fit within
the first borehole during use; and a first screw comprising a first
shank and a first head, the first head being adapted to engage the
first ring, wherein the first ring is adapted to fixably connect
the first screw to the plate during use.
119. A system for fixation of the human spine, comprising: an
elongated plate comprising an upper surface, a lower surface, and a
first borehole extending from the upper surface to the lower
surface; a first screw comprising a first shank and a first head,
wherein the first borehole is shaped to receive at least a portion
of the first head, and wherein the first borehole is substantially
spherically shaped to permit the first screw to be obliquely
angulated relative to the plate during use; and; a first ring sized
to fit within the first borehole between the plate and the first
head, the first ring being adapted to fixably connect the first
screw to the plate during use.
120. A system for fixation of the human spine, comprising: an
elongated plate comprising an upper surface, a lower surface, and a
first borehole extending from the upper surface to the lower
surface; a first screw comprising a first shank and a first head,
wherein the first borehole is shaped to receive at least a portion
of the first head, and wherein the first borehole is shaped to
permit the first screw to be obliquely angulated relative to the
plate during use; and a first ring sized to fit within the first
borehole between the plate and the first head, wherein the first
ring comprises a gap to render the first ring substantially
expandable and contractible, and wherein the first ring is adapted
to fixably connect the first screw to the plate during use.
121. A method for surgically implanting a spinal plate system,
comprising: positioning a substantially flexible first ring within
a first borehole that extends from an upper surface to a lower
surface of a plate; positioning the plate adjacent to a bone; and
screwing a first shank of a first screw into the bone while
simultaneously positioning a first head of the first screw within
the first borehole such that the first ring substantially surrounds
a portion of the first head, wherein the step of screwing causes
the first ring to exert a compressive force on the first head to
fixably connect the first screw to the plate, and wherein the step
of positioning comprises moving the first screw to a position where
the first screw is at an oblique angle relative to the plate.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 08/905,823, filed Aug. 4, 1997.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention The
[0003] present invention generally relates to spinal fixation
systems and the like. More particularly, the present invention
generally relates to a spinal plate system that includes a
mechanism for fixably attaching screws to a plate.
[0004] 2. Description of the Related Art
[0005] 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.
[0006] 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 (i.e., entirely through the vertebrae such that a
portion of the screw extends into the spinal cord region) or
uni-cortically (i.e., the screw extends into but not through the
vertebrae). Uni-cortical positioning of bone screws has grown in
popularity because it is generally safer to use. Bi-cortical screws
are intended to breach the distal cortex for maximum anchorage into
the bone; however, this placement of the screws 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,
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.
[0007] Screw backout is particularly a problem when a pair of
screws are implanted perpendicular to the plate. When the screws
are placed in such a manner, screw backout may 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.
[0008] 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.
[0009] Another plating system that includes a screw to plate
locking mechanism 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 by Foley, K. T.
et al., available from Smith & Nephew Richards Inc., September
1996, pp. 1-16 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. 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 screw falls into the
surgical wound, it is typically difficult to retrieve. In some
instances it may be unretrievable.
SUMMARY OF THE INVENTION
[0010] An embodiment of the invention relates to an implant system
for fixation of the human spine that includes a plate having end
boreholes, midline boreholes, screws, and expandable/contractible
rings.
[0011] 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. Herein, "screw" is taken to mean any elongated
member, threaded or non-threaded which is securable within a bone.
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.
[0012] 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. The screw
may be prevented from contacting tissue structures that are
protected by the spine even when screw backout occurs since the
screw is attached to the plate.
[0013] 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.
[0014] Prior to surgical implantation of the spinal plate system,
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 the spine that requires spinal fixation. 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.
[0015] In another embodiment, the head is preferably screwed into
the ring to create a fixed connection between bone screw and plate
at a selected angle. The screw head preferably contains head
threading on its outer surface that is complementary to ring
threading contained on the inner surface of the ring. The head
threading preferably mates with the ring threading to enhance the
connection between the bone screw and the ring. The head preferably
has a cavity formed on its upper surface for receiving a driving
tool such as a screw driver or an allen wrench.
[0016] The outer surface of the head is preferably tapered so that
screwing the head into the ring causes a change in width of the
ring to fix the bone screw in position relative to the plate. The
inner surface of the ring may also be tapered to substantially
match the taper on the outer surface of the head. At least a
portion of the head preferably has a width greater than the inner
width of the ring. As the screw head is screwed into the ring, the
ring preferably expands outwardly from its inner surface to
accommodate the increasing width of the screw head. The ring may
contain one or more slots or gaps as previously described to
facilitate expansion of the ring against the inner surface of the
borehole.
[0017] It is believed that using a threading engagement between the
head and ring increases the hoop stress exerted on the head,
resulting in a stronger connection between the bone screw and the
plate. Moreover, if bone threading becomes loose within a bone,
screw backout from plate will tend to be resisted by the threaded
connection between the screw head and the ring. Thus, even if the
shank 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Further advantages of the present invention will become
apparent to those skilled in the art with the benefit of the
following detailed description of preferred embodiments and upon
reference to the accompanying drawings in which:
[0019] FIG. 1 is a top plan view of one embodiment of a spinal
plating system that may be used for fixation of the human
spine;
[0020] FIG. 2 is a cross-sectional view of the spinal plating
system along plane I of FIG. 1;
[0021] 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 present invention;
[0022] FIG. 4 is a cross-sectional view of the screw, wherein the
screw is positioned according to another embodiment;
[0023] FIG. 5 is a cross-sectional view of the spinal plating
system along plane II of FIG. 1, wherein a pair of screws extend in
converging directions, according to one embodiment;
[0024] FIG. 6 is a cross-sectional view of the spinal plating
system along plane II of FIG. 1, wherein the pair of screws extend
in diverging directions, according to another embodiment;
[0025] FIG. 7 is a side view in partial cross-section of a spinal
fixation system that includes a screw, a ring, and a plate;
[0026] FIG. 8 is a top view of an embodiment of the plate depicted
in FIG. 7;
[0027] FIG. 9 is a cross-sectional view of a tapered screwhead
connected to a tapered ring through a threaded engagement;
[0028] FIG. 10A is a cross-sectional view of a ring having a
tapered inner surface;
[0029] FIG. 10B is a cross-sectional view of a ring having a
non-tapered inner surface;
[0030] FIG. 11A is a cross-sectional view of a screw head having a
non-tapered outer surface;
[0031] FIG. 11B is a cross-sectional view of a screw head having a
tapered outer surface;
[0032] FIG. 12 is a side view of a ring having a plurality of
slots;
[0033] FIG. 13 is a cross-sectional view of a screw head positioned
within a ring.
[0034] 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. 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 present
invention as defined by the appended claims.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] Turning to FIG. 1, a top plan view of a spinal plating
system is depicted according to an embodiment of the present
invention. The spinal plating system may be used to correct
problems in the lumbar and cervical portions of the spine. For
example, the plating system may be implanted into the occiput bone
which is located at the base of the skull. The plating system is
preferably installed anterior to the spine. The spinal plating
system preferably includes a plate 10 that may be placed adjacent
to a portion of the spine. The length of plate 10 is preferably
chosen so that the plate may span between at least two vertebrae.
Plate 10 preferably includes two pairs 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.
[0036] End boreholes 12 and 14 are preferably shaped to receive the
heads of bone screws 20 during spinal implantation. The spinal
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 spinal plating system may also include one or more
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 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 spinal plating system are preferably
composed of steel (e.g, stainless steel), pure titanium, steel
alloys or titanium alloys because such materials are generally
nontoxic, biocompatible, strong, and non-corrosive. Other materials
which have these properties may also be used to form the
elements.
[0037] FIG. 2 illustrates a cross-sectional view of the spinal
fixation 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. The plate is also shown as having a slight curvature to
enhance its fixation to the spine.
[0038] 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 arcuate or 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 screw 20 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
hexagonal wrench, that may be used to turn screw 20.
[0039] 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 (or vice versa). 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.
[0040] FIG. 5 and FIG. 6 depict different embodiments of the spinal
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. Screws 20 may also be moved to positions such that the
screws are non-planar with respect to a latitudinal plane extending
through plate 10. For example one screw 20 may be positioned out of
the page and the other screw 20 may be positioned into the page.
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.
[0041] According to one embodiment, the spinal fixation 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 are preferably moved to positions
where they are at an oblique angle 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 becomes fixedly attached to plate 10.
[0042] Each of the features of the embodiments discussed above may
be combined or used individually.
FURTHER IMPROVEMENTS
[0043] The following additional embodiments may be used
individually or in combination with any of the embodiments
described above.
[0044] A side view of an embodiment of a spinal plate system 100 is
shown in FIG. 7. Spinal plate system 100 preferably includes a bone
screw 120, a ring 118, and bone plate 110. Plate 110 may be used to
stabilized a bony structure such as the spine to facilitate a bone
fusion (e.g., a spinal fusion). The bone screw 120 may be used to
connect plate 110 to a bone such as a vertebra. 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.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] 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 spinal system 100 is
installed.
[0049] 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.
[0050] 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
spinal 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.
[0051] 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.
[0052] 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.
[0053] 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.
[0054] 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.
[0055] 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.
[0056] 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.
[0057] 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.
[0058] 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.
[0059] 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.
[0060] 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.
[0061] 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 between head 125 of bone screw 120 and ring 118 may be
increased. This increase in friction between bone screw 120 and
ring 118 may further inhibit screw backout from plate 110.
[0062] 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.
[0063] 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.
[0064] 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.
[0065] 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.
[0066] 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.
[0067] 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.
[0068] 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.
[0069] 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.
[0070] 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.
[0071] 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.
* * * * *