U.S. patent application number 10/134463 was filed with the patent office on 2002-08-29 for anterior cervical plating system and method.
Invention is credited to Herkowitz, Harry N., Needham, Dusty Anna, Poyner, Jeffrey Wade, Zdeblick, Thomas A..
Application Number | 20020120273 10/134463 |
Document ID | / |
Family ID | 23653880 |
Filed Date | 2002-08-29 |
United States Patent
Application |
20020120273 |
Kind Code |
A1 |
Needham, Dusty Anna ; et
al. |
August 29, 2002 |
Anterior cervical plating system and method
Abstract
The present invention is directed to a system for anterior
fixation of the spine that utilizes an elongated fixation plate.
The plating system stabilizes the spine and promotes fusion and
incorporation of a graft or implant in a portion of the spinal
column. In one aspect of the invention, the fixation plate has a
first end with a pair of holes. Bone screws extend through the
holes to rigidly secure the plate to a first vertebra. The second
end of the plate is provided with a pair of slots through which
bone screws extend for engagement with a second vertebra. The
screws extending through the slots are translatable in the slot to
maintain compression of the spinal column portion. The plating
system includes a retainer assembly that prevents screw back out.
Methods and instruments relating to the plating system are also
described.
Inventors: |
Needham, Dusty Anna;
(Lakeland, TN) ; Poyner, Jeffrey Wade; (Atoka,
TN) ; Herkowitz, Harry N.; (West Bloomfield, MI)
; Zdeblick, Thomas A.; (Middleton, WI) |
Correspondence
Address: |
STERNE, KESSLER, GOLDSTEIN & FOX PLLC
1100 NEW YORK AVENUE, N.W., SUITE 600
WASHINGTON
DC
20005-3934
US
|
Family ID: |
23653880 |
Appl. No.: |
10/134463 |
Filed: |
April 30, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10134463 |
Apr 30, 2002 |
|
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|
09417402 |
Oct 13, 1999 |
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Current U.S.
Class: |
606/281 ;
606/247; 606/282; 606/287; 606/289; 606/295; 606/296; 606/86B;
623/17.11 |
Current CPC
Class: |
A61B 17/1757 20130101;
A61B 17/808 20130101; A61B 17/1728 20130101; A61B 17/8042 20130101;
A61B 17/7059 20130101; A61B 17/8014 20130101; A61B 17/8019
20130101; A61B 17/8866 20130101 |
Class at
Publication: |
606/61 |
International
Class: |
A61B 017/58 |
Claims
What is claimed is:
1. A bone fixation system for a portion of the spinal column,
comprising: a plate having a length along a central axis extending
longitudinally between a first end and a second end, and a top
surface and a bottom surface along said length, and said plate
having a plurality of first openings and a plurality of second
openings between said surfaces, wherein: at least one of said
plurality of first openings is positioned adjacent said first end,
said one first opening defining a circular hole having a first
diameter adjacent said bottom surface; at least one of said
plurality of second openings is positioned adjacent said second
end, said one second opening defining a slot having a first width
and a first length adjacent said bottom surface; bone engaging
fasteners extending through said first and second openings, each
bone engaging fastener having an elongated shank defining bone
engaging threads thereon and an enlarged head, said shank having a
substantially cylindrical portion with a third diameter less than
said first diameter so said bone engaging fastener can be inserted
through said one first opening and said cylindrical portion
contacts said plate in said one first opening so that said bone
engaging fastener assumes a fixed orientation relative to said
plate, said cylindrical portion third diameter also less than said
second width so said bone engaging fastener can be inserted through
said one second opening from said top surface of said plate and
said head of said bone engaging fastener is translatable along the
length of said at least one second opening to maintain compression
of the spinal column portion.
2. The bone fixation system of claim 1, wherein said second
openings include a ramp that guides said bone engaging fastener as
it is inserted into said one second opening to provide a dynamic
compression load to the spinal column portion.
3. The bone fixation system of claim 1, whereby each of said at
least one first and second openings define a recess adjacent said
top surface and said enlarged head defines a partially spherical
surface complementary to said recess of said at least one first and
second openings.
4. The bone fixation system of claim 3, wherein said head of said
fastener includes a truncated top surface.
5. The bone fixation system of claim 3, further comprising a
retainer assembly for retaining said heads of said number of bone
engaging fasteners within said at least one first opening and said
at least one second opening.
6. The bone fixation system of claim 5, wherein said retainer
assembly includes: a first fastener bore defined in said plate
adjacent said at least one first opening and a second fastener bore
defined in said plate adjacent said at least one second opening; a
washer having at least a first aperture adjacent said at least one
first opening and a second aperture adjacent said at least one
second opening and a countersink portion communicating with each of
said apertures, said washer further having a body with portions
overlapping said at least one first and second opening when said
washer is in a first position relative to said at least one first
and second openings, said body portions being arranged so that bone
engaging fasteners can be inserted through said at least one first
opening and said at least one second opening when said washer is in
a second position relative to said at least one first and second
openings; and a locking fastener for each of said apertures having
a head configured to be at least partially recessed within said
countersink portion of said washer and having an elongated shank
extending through said aperture and configured to engage said
fastener bore of said plate.
7. The bone fixation system of claim 6, wherein said plate further
defines a groove in said top surface extending longitudinally along
said plate, said groove being overlapping said at least one first
and second openings, said first and second fastener bores being
positioned within said groove.
8. The bone fixation system of claim 5, wherein said retainer
assembly includes a washer having a contact surface for contacting
said head of said bone engaging fastener in said one first opening
and an outer surface for overlapping said heads of said bone
engaging fasteners in said one second opening.
9. The bone fixation system of claim 1, further comprising a
retainer assembly including: a first fastener bore defined in said
plate adjacent said at least one first opening and a second
fastener bore defined in said plate adjacent said at least one
second opening; a washer having at least a first aperture adjacent
said at least one first opening and a second aperture adjacent said
at least one second opening and a countersink communicating with
each of said apertures, said washer further having a surface
configured to contact said head of said bone engaging fastener
extending through said at least one first opening; and a locking
fastener for each of said apertures having a head configured to be
at least partially recessed within said countersink portion of said
washer and an elongated shank extending through said aperture
configured to engage said fastener bore of said plate.
10. The bone fixation system of claim 9, wherein said washer has an
outer surface that overlaps said head of said bone engaging
fastener extending through said at least one second hole without
contacting said head.
11. The bone fixation system of claim 9, wherein said plate further
defines a groove in said top surface extending longitudinally along
said plate, said groove overlapping said at least one first and
second openings, said first and second fastener bores being
positioned within said groove.
12. The bone fixation system of claim 1, wherein said elongated
plated defines a plurality of vertebral nodes at longitudinally
spaced location along the plate.
13. The bone fixation system of claim 12, wherein there are
provided a pair of said first openings at one said vertebral nodes
adjacent said first end of said plate and a pair of said second
openings at one of said vertebral nodes adjacent said second end of
said plate.
14. The bone fixation system of claim 13, wherein said openings of
said pair of first openings are symmetrically positioned about said
central axis and said openings of said pair of second openings are
symmetrically positioned about said central axis.
15. A bone fixation system for a portion of the spinal column,
comprising: a plate having a length along a central axis extending
longitudinally between a first end and a second end, a top surface
and a bottom surface along said length, said plate further defining
a plurality of first openings and a plurality of second openings
between said surfaces, wherein: at least two of said first openings
are circular, having a first diameter, and are positioned adjacent
said first end; at least two of said second openings are slotted,
having a first width and a first length, and are positioned
adjacent said second end of said plate; bone engaging fasteners
extending through said first and second openings, each bone
engaging fastener having an elongated shank having bone engaging
threads thereon and an enlarged head, said bone engaging fasteners
configured for insertion into said first and second openings from
said top surface; and means retaining said heads of said bone
engaging fasteners in said first and second openings, said
retaining means translatable from a first position allowing bone
engaging fastener insertion into said first and second openings to
a second position retaining said bone engaging fasteners in said
first and second openings.
16. The bone fixation system of claim 15, wherein said two first
openings have a recess portion adjacent said top surface and said
two second openings have a recess portion adjacent said top
surface.
17. The bone fixation system of claim 16, wherein said heads of
said bone engaging fasteners are configured to be at least
partially recessed in said two first and second openings.
18. The bone fixation system of claim 15, wherein said two first
and second openings each include a recess adjacent said top surface
and said enlarged head has a partially spherical surface
complementary to said recess of said two first and second
openings.
19. The bone fixation system of claim 18, wherein said plate
further defines a groove in said top surface extending
longitudinally along said plate for receiving said retaining means
therein, said groove overlapping said recesses.
20. The bone fixation system of claim 15, wherein said head of said
bone engaging fastener has an inclined surface and said retaining
means has a contact surface to contact said inclined surface of
said bone engaging fasteners extending through said two first
openings.
21. The bone fixation system of claim 15, wherein retaining means
includes: a first fastener bore defined in said plate adjacent said
two first openings and a second fastener bore defined in said plate
adjacent said two second openings; a washer having a body defining
at least a first aperture adjacent said two first openings and a
second aperture adjacent said two second openings and a countersink
portion communicating with each of said apertures, said washer
further having a contact surface configured to contact said head of
said bone engaging fastener extending through said two first
openings; and a locking fastener for each of said apertures having
a head configured to be at least partially recessed within said
countersink portion of said washer and an elongated shank extending
through said aperture and configured to engage said fastener bore
of said plate.
22. The bone fixation system of claim 21, wherein said apertures of
said washer each form a slot having a length extending
longitudinally with the plate.
23. The bone fixation system of claim 22, wherein at least one of
said aperture countersink portion is tapered along said length of
said slot and has a width that increases along said length of said
aperture from said second end towards said first end.
24. The bone fixation system of claim 22, wherein said at least one
aperture is positioned adjacent said two second openings.
25. The bone fixation system of claim 15, wherein said retaining
means includes: a first fastener bore defined in said plate
adjacent said two first openings and a second fastener bore defined
in said plate adjacent said two second openings; a washer having at
least a first aperture adjacent said two first openings and a
second aperture adjacent said two second openings and a countersink
portion communicating with each of said apertures, said washer
further having a body with portions overlapping said two first
openings and said two second openings when said washer is in a
first position relative to said two first and second openings, said
body portions being arranged so that bone engaging fasteners can be
extended through said two first openings and said two second
openings when said washer is in a second position relative to said
two first and second openings; and a locking fastener for each of
said apertures having a head configured to be at least partially
recessed within said tapered portion of said washer and an
elongated shank extending through said aperture and configured to
engage said fastener bore of said plate.
26. The bone fixation system of claim 25, wherein said apertures of
said washer form slots having a length extending in the direction
of the length of the plate.
27. The bone fixation system of claim 26, where said countersink
communicating with each of said apertures has a width that
increases along the length of said aperture in a direction from
said second end towards said first end.
28. A bone fixation system for a portion of the spinal column,
comprising: four bone engaging fasteners, each having an enlarged
head and a threaded shank; and an elongated plate having a length
extending between a first end and a second end and sized to span
between at least two vertebrae, said plate defining a one pair of
adjacent holes adjacent said first end and one pair of adjacent
slots adjacent said second, each of said holes and said slots
configured to receive said threaded shank of a corresponding one of
said bone engaging fasteners therethrough, wherein said bone
engaging fasteners extending through said pair of holes fix said
plate to said first vertebra and said bone engaging fasteners
extend through said slots to secure said plate to said second
vertebra, and said bone engaging fasteners received in said slots
are enabled to translate in said slots in a direction of the length
of the plate to maintain compression on the spinal column
portion.
29. The bone fixation system of claim 28, wherein said plate has a
top surface and a bottom surface and said holes and said slots each
further include a recess adjacent said top surface.
30. The bone fixation system of claim 28, further including a
retainer assembly having a washer configured to overlap each of
said holes and slots and retain said bone engaging fasteners
extending through said holes and slots.
31. The bone fixation system of claim 30, wherein said head of each
of said bone engaging fasteners has an inclined surface and said
washer has a contact surface configured to contact said inclined
surface of said bone engaging fasteners extending through said pair
of holes.
32. The bone fixation system of claim 30, wherein said plate
includes a first fastener bore defined in said plate between said
pair of holes and a second fastener bore defined in said plate
between said pair of slots, and said retainer assembly further
includes: said washer has at least a first aperture adjacent said
holes and a second aperture adjacent said slots and a countersink
portion communicating with each of said apertures; and a locking
fastener for each of said apertures, said locking fastener having a
head configured to be recessed within said recess of said washer
and an elongated shank extending through said aperture and
configured to engage said fastener bore of said plate.
33. The bone fixation system of claim 32, wherein said elongated
shank of said locking fastener terminates in a sharp point for
penetrating a vertebral body.
34. The bone fixation system of claim 33, wherein said head of said
locking fastener defines a lower conical surface for contacting
said washer.
35. A bone fixation system for a portion of a spinal column,
comprising: six bone engaging fasteners, each having an enlarged
head and a threaded shank; and an elongated plate having a length
extending between a first end and a second end and sized to span
between at least three vertebrae, said plate defining one pair of
holes over a first vertebra, one pair of intermediate slots over a
second vertebra, and one pair of slots over a third vertebra, each
of said holes and said slots configured to receive said threaded
shank of a corresponding one of said bone engaging fasteners
therethrough, wherein said bone engaging fasteners extending
through said pair of holes fix said plate to said first vertebra
and said bone engaging fasteners extend through said slots to
secure said plate to said second vertebra, and said bone engaging
fasteners received in said slots are enabled to translate in said
slots in a direction of the length of the plate to maintain
compression on the spinal column portion.
36. The bone fixation system of claim 35, further including a
retainer assembly having a washer configured to overlap each of
said holes and slots and retain said bone engaging fastener
extending through said holes and slots in said plate.
37. A fastener retainer assembly for an elongated plate having a
length extending between at least two vertebrae, the plate defining
a number of openings therethrough for insertion of bone engaging
fasteners to attach the plate to the at least two vertebrae, said
retainer assembly comprising: a first fastener bore defined in said
plate adjacent at least one of the openings positioned over the
first vertebra and a second fastener bore defined in said plate
adjacent at least one the openings positioned over the second
vertebra; a washer defining at least a first aperture adjacent said
at least one opening positioned over the first vertebra and a
second aperture adjacent said at least one opening positioned over
the second vertebra, said washer configured to retain said bone
engaging fasteners extending through said openings in said plate;
and a locking fastener for each of said apertures, said locking
fastener having an elongated shank extending through said aperture
and configured to engage said fastener bore of said plate, said
openings in said plate being positioned and configured wherein said
washer is movable between a first position enabling insertion of
said bone engaging fasteners into said at least one openings and a
second position wherein said washer retains said inserted bone
engaging fasteners in said plate.
38. The retainer assembly of claim 37, wherein said apertures of
said washer form slots having a length extending in the direction
of the length of the plate.
39. The retainer assembly of claim 38, wherein each of said
apertures include a countersink portion communication with said
slot.
40. The retainer assembly of claim 39, wherein said countersink
portion of at least one of said apertures is tapered and has a
width that increases along the length of said aperture from a
second end to a first end.
41. A fastener retainer assembly for an elongated plate extending
between at least two vertebrae, the plate defining a number of
openings for insertion of bone engaging fasteners therethrough to
secure the plate to the at least two vertebrae, and the plate
defining at least one fastener bore, said retainer assembly
comprising: a washer having a central axis and defining at least a
firs aperture in communication with said at least one fastener
bore, said washer further configured to retain said heads of at
least two bone engaging fasteners extending through certain ones of
said openings in said plate; and a locking fastener for said first
aperture having an elongated shank extending through said aperture
and configured to engage said fastener bore of said plate, said
washer being movable along said central axis between a first
position whereby said at least two bone engaging fasteners are
insertable into certain ones of said openings and a second position
whereby washer retains said at least two bone engaging fasteners in
said plate.
42. The retainer assembly of claim 41, wherein said apertures of
said washer form slots having a length extending in the direction
of the length of the plate.
43. The retainer assembly of claim 42, wherein each of said
apertures include a countersink portion communication with said
slot.
44. The retainer assembly of claim 42, wherein said countersink
portion of at least one of said apertures is tapered and has a
width that increases along the length of said aperture from a
second end to a first end.
45. A method for applying a compressive load to a portion of the
spinal column, the spinal column portion including at least a first
vertebra and a second vertebra, the method comprising: engaging a
pin to the second vertebra; placing a sleeve over the pin;
providing a plate having a length extending between a first end and
a second end, the plate including a notch on the second end, and a
number of openings through the plate; placing the plate on the
spinal column portion with the sleeve nested in the radius of the
plate; fixing the first end of the plate to the first vertebra with
bone engaging fasteners extending through the openings positioned
over the first vertebra; removing the sleeve from the pin to form a
gap between the pin and the notch; connecting a compression tool to
the pin and the plate; and applying a compression load to the
spinal column portion with the compression tool until the pin
contacts the notch.
46. The method according to claim 45, wherein engaging a pin to the
second vertebra includes: providing a template having a guide
surface and a notch; positioning the template on the second
vertebra with the guide surface on an endplate of the second
vertebra to locate the notch on the body of the second vertebra;
inserting a pin through the notch of the template into the body of
the second vertebra; and removing the template;
47. The method according to claim 45, further comprising providing
a plate with holes positioned over the first vertebra and slots
positioned over the second vertebra.
48. The method according to claim 45, further comprising retaining
the bone engaging fasteners in the plate with a retainer
assembly.
49. A method for allowing graft settling in a portion of a spinal
column, comprising: providing a plate having a length between a
first end and a second end sized to span at least two vertebra, the
plate having a pair of holes at the first end positioned over the
first vertebra and a pair of slots at the second end positioned
over the second vertebra; fixing the first end of the plate to the
first vertebra with bone engaging fasteners extending through the
pair of holes; securing the second end of the plate to the second
vertebra with bone engaging fasteners extending through the pair of
slots; and translating the bone engaging fasteners in the slots to
allow settling of the spinal column portion.
50. The method according to claim 49, further comprising retaining
the bone engaging fasteners in the plate with a retainer
assembly.
51. The method according to claim 50, wherein the retainer assembly
includes a washer having a length substantially corresponding to
the length of the plate.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to the field of
instrumentation and systems for the spine, and more particularly to
instrumentation and systems for use in treatment of various
pathologies of the cervical spine.
[0002] As with any bony structure, the spine is subject to various
pathologies that compromise its load bearing and support
capabilities. Such pathologies of the spine include, for example,
degenerative diseases, the effects of tumors and, of course,
fractures and dislocations attributable to physical trauma. Spinal
surgeons have addressed these problems using a wide variety of
instrumentation in a broad range of surgical techniques. The use of
elongated rigid plates has been helpful in the stabilization and
fixation of the lower spine, most particularly in the thoracic and
lumbar spine. These same plating techniques have found some level
of acceptance by surgeons specializing in the treatment of the
cervical spine.
[0003] The cervical spine can be approached either anteriorly or
posteriorly, depending upon the spinal disorder or pathology to be
treated. Many well-known surgical exposure and fusion techniques of
the cervical spine are described in the publication entitled Spinal
Instrumentation, edited by Drs. Howard An and Jerome Coter. This
text also describes instrumentation that has been developed in
recent years for the cervical spine. Plating systems have become
predominant for providing internal instrumentation in techniques
that achieve fusion of the cervical spinal from an anterior
approach.
[0004] During the development of cervical plating systems,
particularly for the anterior approach, various needs have been
recognized. For example, the system should provide strong
mechanical fixation that can control movement of each vertebral
segment. The system should be able to withstand axial loading and
continuity with each of the three columns of the spine. The system
should also be able to maintain stress levels below the endurance
limits of the plate material, while at the same time exceeding the
strength of the anatomic structures or vertebrae to which the
plating system is engaged. The thickness of the system should be
small to lower its prominence, particularly at the smaller spaces
of the cervical spine. Also, the screws used to connect the plate
to the vertebrae must not loosen over time or back out from the
plate.
[0005] While the plating system should satisfy certain mechanical
requirements, the system should also satisfy certain anatomic and
surgical considerations. For example, the cervical plating system
should minimize the intrusion into the patient and reduce the
trauma to the surrounding soft tissue. This is particularly
important in such procedures that relate to the cervical spine
because the complications can be very devastating, such as injury
to the brain stem, spinal cord, or vertebral arteries. It has also
been found that the optimum plating system permits placement of
more than one screw in each of the instrumented vertebrae. Also,
the system should be designed to contact the vertebrae for greater
stability.
[0006] Many spinal plating systems have been developed in the last
couple of decades to address some of the needs and requirements for
cervical fixation systems. However, even with the more refined
plating system designs, there still remains a need for a system
that effectively addresses the requirements for such a system.
[0007] There is also a need for a plating system that addresses
procedures designed to achieve fusion of the cervical spine. In
cases where a graft or implant is implanted to maintain a disc
space and/or replace one or more diseased vertebral bodies, it is
desirable to increase the rate of fusion and incorporation of the
graft or implant into the spine. A plating system that allows
pre-loading of the graft or implant and/or provides continual
loading thereafter is preferred.
[0008] While the prior art plating systems relating to cervical
plating systems are steps in the right direction, there remains a
need for additional improvements. The present invention is directed
to satisfying these needs, among others.
SUMMARY OF THE INVENTION
[0009] The present invention contemplates a system for anterior
fixation of the spine that utilizes an elongated fixation plate. In
one aspect of the invention, the plating system promotes fusion and
incorporation of a graft or implant in a spinal column portion. The
plating system provides continual loading of the graft or interbody
implant. In another aspect, the plating system allows a compressive
load to be applied to the spinal column portion. This preloading
and continual loading avoids stress-shielding and promotes fusion
and incorporation of the graft or implant into the spinal column
portion.
[0010] In one aspect of the invention, the fixation plate has a
first end with a pair of holes. Bone engaging fasteners extend
through the holes to rigidly secure the plate to a first vertebra.
A second end of the plate is provided with a pair of slots through
which bone engaging fasteners extend for engagement with a second
vertebra. The bone engaging fasteners extending through the slots
are translatable in the slots to allow settlement and compression
of the second vertebra with respect to the first vertebra. In a
preferred embodiment, the plating system includes a retainer
assembly that prevents fastener back out.
[0011] According to another aspect of the invention, a bone
fixation system for a spinal column segment is provided. The bone
fixation system includes a plate with a central axis, a length
between a first end and a second end, and top and bottom surfaces.
The plate defines a plurality of first openings and a plurality of
second openings between the top and bottom surfaces. At least one
of the plurality of first openings is positioned adjacent the first
end of the plate and defines a circular hole though the plate. At
least one of the plurality of second openings is positioned
adjacent the second end of the plate and defines a slotted hole
having a first width and a first length adjacent the bottom
surface. A number of bone engaging fasteners extend through the
first and second openings. Each bone engaging fastener has a
threaded shank and an enlarged head. The fastener has a
substantially cylindrical portion with a third diameter that
interfaces with the plate in the first opening such that the
fastener inserted in the first opening assumes a fixed orientation
with the plate. The head of said bone engaging fastener inserted
into the second opening is translatable along the length of the
second opening to maintain compression of the spinal column
portion.
[0012] In another aspect of the invention, a bone fixation system
for a spinal column portion is provided. The bone fixation system
includes a plate with a length along a central axis that extends
between a first end and a second end. The plate has a top surface
and a bottom surface and defines a plurality of first and second
openings between the surfaces. At least a pair of the first
openings is positioned adjacent the first end, and the first
openings define a circular opening having a first diameter. At
least a pair of the second openings is positioned adjacent the
second end, and the second openings define a slot having a first
width and a first length. A number of bone engaging fasteners with
an elongated threaded shank and an enlarged head are provided. The
bone engaging fasteners extend through the first and second holes
from the top surface. A retainer assembly retains the bone engaging
fasteners in the first and second openings. In one form, the
retainer assembly includes a washer having a length that
substantially corresponds to the length of the plate.
[0013] In yet another aspect of the invention, a bone fixation
system for a spinal column segment is provided. The system includes
four bone engaging fasteners that have an enlarged head and a
threaded shank. An elongated plate has a length extending between a
first end and a second end sized to span between at least two
vertebrae. The plate defines one pair of holes adjacent the first
end and one pair of slots adjacent the second end. Each of the
holes and the slots are configured to receive the threaded shank of
a corresponding one of the bone engaging fasteners therethrough to
engage the plate to the vertebrae. The bone engaging fasteners
extend through the pair of holes to fix the plate to the first
vertebra. Bone engaging fasteners extend through the pair of slots
to secure the plate to the second vertebra. The bone engaging
fasteners axially translate in the slots to maintain compression on
the spinal column portion.
[0014] In a further aspect of the invention, a bone fixation system
for a spinal column portion is provided. The system includes six
bone engaging fasteners that each have an enlarged head and a
threaded shank. An elongated plate extending between a first end
and a second end has a length sized to span between at least three
vertebrae. The plate defines one pair of holes over a first
vertebra, one pair of slots over a second vertebra, and one pair of
intermediate slots over a third vertebra intermediate the first and
second vertebrae. The holes and the slots are configured to receive
the threaded shank of the bone engaging fasteners therethrough. The
bone engaging fasteners extend through the pair of holes to fix the
plate to the first vertebra The bone engaging fasteners extend
through the slots to secure the plate to the second vertebra. The
bone engaging fasteners axially translate in the slots to maintain
compression on the spinal column portion. The surgeon can
optionally place bone engaging fasteners in the intermediate slots
to engage the plate to the third vertebra.
[0015] In another aspect of the invention, there is provided a
retainer assembly for an elongated plate that extends between at
least two vertebrae. The retainer assembly includes a washer having
at least one tapered aperture. The washer is translatable between a
locked position and an unlocked position by threading a locking
fastener into the tapered aperture.
[0016] In another aspect of the invention, there is provided a
retainer assembly for an elongated plate that extends between at
least two vertebrae. The plate defines a number of openings for
insertion of bone engaging fasteners to attach the plate to the at
least two vertebrae. The plate further includes a first fastener
bore in the plate adjacent at least one of the openings positioned
over the first vertebra and a second fastener bore in the plate
adjacent at least one of the openings positioned the second
vertebra The retainer assembly includes a washer that defines at
least a first aperture adjacent the at least one opening positioned
over the first vertebra and a second aperture adjacent the at least
one opening positioned over the second vertebra. A locking fastener
for each of the apertures in the washer has an elongated shank
extending through the aperture configured to engage the fastener
bore of the plate. The washer is movable between a first position
where the bone engaging fasteners are insertable into each of the
at least one openings and a second position where the washer has a
surface configured to contact the head of a bone engaging fastener
extending through the at least one opening positioned over the
first vertebra and overlap the head of a bone engaging fastener
extending through the at least one opening positioned over the
second vertebra.
[0017] In another aspect of the invention, a retainer assembly for
an elongated plate is provided. The plate extends between at least
two vertebrae and defines a number of openings for insertion of
bone engaging fasteners to secure the plate to the at least two
vertebrae. The plate includes at least one first fastener bore. The
retainer assembly includes a washer that defines at least a first
aperture positioned in communication with the at least one fastener
bore. A locking fastener extends through the first aperture and has
an elongated shank to engage the fastener bore of the plate. The
washer is movable along its central axis between a first position
where the at least two bone engaging fasteners are inserted through
the openings to engage the first and second vertebrae and a second
position where a surface of the washer contacts at least the head
of the bone engaging fasteners engaged to the first vertebra.
[0018] In another aspect of the present invention, a method for
applying a compressive load to a number of vertebrae including at
least a first vertebra and a second vertebra is provided. The
method includes: (a) providing a template having a guide surface
and a notch; (b) positioning the template on the second vertebra
with the guide surface on an endplate of the second vertebra to
locate the template notch on the body of the second vertebra; (c)
inserting a pin through the notch of the template into the body of
the second vertebra; (d) removing the template; (e) placing a
sleeve over the pin; (f) providing a plate having a length
extending between a first end and a second end, the plate including
a notch on the second end and a number of openings therethrough;
(g) placing the plate on the vertebral segment with the sleeve
nested in the notch of the plate; (h) fixing the first end of the
plate to the first vertebra with bone engaging fasteners extending
through the openings positioned over the first vertebra; (i)
removing the sleeve from the pin to form a gap between the pin and
the notch in the plate; (j) connecting a compression tool to the
pin and the plate; and (k) applying a compression load to the
vertebral segment with the compression tool until the pin contacts
the notch. In one embodiment, the plate includes holes positioned
over the first vertebra and slots positioned over the second
vertebra. In another embodiment, the method further includes the
step of retaining the bone engaging fasteners in the plate with a
retainer assembly.
[0019] In another aspect of the present invention, there is
provided a method for maintaining compression of a spinal column
portion. The method includes: (a) providing a plate having a length
between a first end and a second end sized to span at least two
vertebra, the plate having a pair of holes at the first end
positioned over the fist vertebra and a pair of slots at the second
end positioned over the second vertebra; (b) fixing the first end
of the plate to the first vertebra with bone engaging fasteners
extending through the pair of holes; (c) securing the second end of
the plate to the second plate with bone engaging fasteners
extending through the pair of slots; and (d) translating the bone
engaging fasteners in the slots to allow settling of the spinal
column segment. In one embodiment, the method further includes
retaining the bone engaging fasteners in the plate with a retainer
assembly.
[0020] These and other forms, embodiments, aspects, features,
objects of the present invention will be apparent from the
following description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a top perspective view of an anterior plating
system according to the present invention.
[0022] FIG. 2 is a top perspective view of the anterior plating
system of FIG. 1 with the bone screws locked in place.
[0023] FIG. 3 is a top perspective view of the anterior plating
system of FIG. 1 with bone screws translated in a slot of the
plate.
[0024] FIGS. 4(a)-4(f) are top plan views of fixation plates of the
present invention provided in different sizes and
configurations.
[0025] FIGS. 5(a)-5(f) are top plan views of washers of the present
invention provided in sizes and configurations corresponding to the
plates in FIGS. 5(a)-5(f).
[0026] FIG. 6 is a side elevational view of a bone screw according
to one aspect of the present invention.
[0027] FIG. 7 is a side elevational view of a locking fastener
according to another aspect of the present invention.
[0028] FIGS. 8(a)-8(k) are various views and sections of washers
according to the present invention.
[0029] FIG. 9 is a top plan view of a first end of the fixation
plate of the present invention.
[0030] FIG. 10 is a cross-sectional view taken through line 10-10
of FIG. 9.
[0031] FIG. 11 is an end elevational view of the plate of FIG.
9.
[0032] FIG. 12 is a top plan view of a second end of the fixation
plate of the present invention.
[0033] FIG. 13 is a cross-sectional view taken along line 13-13 of
FIG. 12.
[0034] FIG. 14 is an enlarged cross-sectional view taken through
line 14-14 of FIG. 12.
[0035] FIG. 15 is a top plan view of an intermediate portion of the
fixation plate of the present invention.
[0036] FIG. 16 is a cross-sectional view taken through line 16-16
of FIG. 15.
[0037] FIG. 17 is an enlarged cross-sectional view taken through
line 17-17 of FIG. 15.
[0038] FIG. 18 is an enlarged cross-sectional view taken through
line 18-18 of FIG. 15.
[0039] FIG. 19a is a partial sectional view of the anterior plate
assembly of the present invention with the screws disposed through
the holes at the first end of the plate and engaged in a
vertebra.
[0040] FIG. 19b is a partial sectional view of the anterior plate
assembly of the present invention with the screws disposed through
the slots of the plate and engaged in a vertebra.
[0041] FIGS. 20(a)-20(f) illustrate various instruments and steps
of a method according to another aspect to the present
invention.
[0042] FIGS. 21(a)-21 (c) are various perspective views of a
compression tool according to yet another aspect of the present
invention.
[0043] FIGS. 22(a)-22(b) are side elevational views of the arms of
an alternate embodiment compression tool.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0044] For the purposes of promoting an understanding of the
principles of the invention, reference will now be made to the
embodiments illustrated in the drawings and specific language will
be used to describe the same. It will nevertheless be understood
that no limitation of the scope of the invention is thereby
intended. Any alterations and further modifications in the
illustrated devices, and any further applications of the principles
of the invention as illustrated herein, are contemplated as would
normally occur to one skilled in the art to which the invention
relates.
[0045] A plating system 30 having application in an anterior
approach to the cervical spine is depicted in FIGS. 1-3. The
portion of the spine is shown schematically in FIG. 1 to include a
first vertebra V1, a second vertebra V2, and intermediate vertebrae
V3 and V4. Preferably, first vertebra V1 is the inferior or bottom
vertebra in the portion of the spinal column and the second
vertebra V2 is the superior or top vertebra of the portion of the
spinal column. However, it is also contemplated herein that first
vertebra V1 is the superior vertebra and that second vertebrae V2
is the inferior vertebra. It should also be understood that as
described below, the present invention has application with spinal
column portions that include vertebrae ranging in number from two
to six vertebrae. One or more implants I may be placed into one or
more of the disc spaces between adjacent vertebrae as needed.
Implant I may be a bone graft, fusion device, or any other type of
interbody device that is insertable into a disc space and promotes
fusion between adjacent vertebrae.
[0046] In accordance with the present invention, the plating system
30 includes an elongated plate 31 having a number of openings
therethrough and a number of bone engaging fasteners, shown in the
form of bone screws 50, that are insertable through the openings.
In a preferred form, each bone engaging fastener is in the form of
a bone screw. Plate 31 has a longitudinal axis L extending along
the length of the plate at its centerline. Bone engaging fasteners
or bone screws 50 are held in plate 31 by way of a retainer
assembly 33 positioned along axis L. The openings of elongated
plate 31 include a pair of holes 34 at first node 36 adjacent a
first end of plate 31. First node 36 is positioned over first
vertebra V1. Plate 31 also includes a pair of slots 35 at a second
node 37 adjacent a second end of plate 31. Second node 37 is
positioned over second vertebra V2. In some forms of plate 31,
several intermediate nodes 38 are provided along the length of the
plate 31 between first node 36 and second node 37. Each
intermediate node 38 includes a pair of intermediate slots 32
positioned over a corresponding one of the intermediate vertebrae
V3 and V4. Plating system 30 can be fabricated from any type of
biocompatible material.
[0047] It is preferred that holes 34 are paired with one of the
holes of the pair on one side of the longitudinal axis L and the
other hole of the pair on the opposite side of axis L. Slots 32 and
35 are similarly arranged in pairs. It is also preferred that
paired holes 34 are identical in shape and size, and are located
symmetrically about the axis L. Paired slots 35 are also identical
in shape and size, and are located symmetrically about the axis L.
The paired slots 32 at intermediate nodes 38 are also identical in
shape and size, and are located symmetrically about the axis L.
Plate 31 includes recesses between each of nodes 36, 37, 38 to
reduce the outer contouring size of the plate. In addition, the
recesses between each of the nodes provides an area of reduced
material, allowing additional bending of the plate by the surgeon
as may be required by the spinal anatomy. Plate 31 has a length
selected by the surgeon with nodes 36, 37, and, if needed, nodes 38
to register with the patient vertebrae.
[0048] Plate 31 preferably includes a rounded upper surface 41 that
is in contact with the soft tissue surrounding the spine when the
plate is engaged to the spine. Rounded surface 41 reduces the
amount of trauma that would be experienced by the surrounding soft
tissue. The bottom surface 42 of plate 31 is preferably configured
to contact the vertebral bodies of the spine at each of the
instrumented levels. In one embodiment, at least a portion of
bottom surface 42 can be textured along the length of the plate to
enhance its grip on a vertebral body.
[0049] Holes 34 include a recess 45 adjacent the top surface of
plate 31 that allow the head of the bone engaging fastener, such as
bone screw 50, to be countersunk in plate 31. Similarly,
intermediate slots 32 include a recess 46 around each slot 32
adjacent top surface of the plate, and slots 35 include a recess 47
around each slot 35 adjacent the top surface of the plate.
Preferably, slots 35 include a ramp 60 that, as described further
below, allows a dynamic compression load to be applied to the
spinal column portion upon insertion of screw 50 at second end 43
of slot 35. Recesses 46, 47 also allow the head of screw 50 to be
countersunk in plate 31 when inserted through a corresponding one
of the slots 32, 35. A groove 39 extends along axis L of plate 31
and intersects with each of recesses 45, 46, 47 along the length of
groove 39. The end of plate 31 at second node 37 includes a notch
40, which is preferably rounded with a radius R4 centered on axis L
(FIG. 12.)
[0050] Retainer assembly 33 includes a washer 90 having a length
that substantially corresponds to the length of plate 31. Washer 90
defines a plurality of apertures 91. Each aperture 91 is provided
at a body portion 93, 94, 95 that corresponds to vertebral nodes
36, 37,38, respectively. A connecting portion 98 extends between
and connects body portions 93, 94, 95. Each of the apertures 91 has
a countersink 92 extending therearound adjacent to the top surface
of washer 90. As described more fully below, countersink 92 is
tapered from a first width at the first end of aperture 91 to a
second width at the second end of aperture 91, the first width
being greater than the second width. Locking fasteners, shown in
the form of screws 85, are positionable, each through a
corresponding one of the apertures 91, to engage a fastener bore 70
(see FIGS. 4(a)-4(f)) in plate 31 and couple washer 90 to plate
31.
[0051] Consequently, retainer assembly 33 retains screws 50 placed
into the vertebral bodies at each of the instrumented levels.
Washer 90 is translatable from an unlocked position (FIG. 1) for
bone screw insertion to a locked position (FIG. 2) after screw
insertion to contact the head of the bone screws in holes 34 and
overlap the heads of bone screws in slots 32, 35. Preferably,
washer 90 does not contact the heads of bone screws in slots 32,
35, thus allowing translation of the bone screws in the slots.
Back-out of the bone screws in slots 32, 35 is prevented when the
bone screw backs out from its seated position a sufficient amount
to contact washer 90. Preferably, washer 90 resides almost entirely
within groove 39 of plate 31 to minimize the overall height of the
construct.
[0052] As shown in FIG. 1, retainer assembly 33 is in an unlocked
condition with screws 85 at the second end of apertures 90. In the
unlocked condition, body portions 93, 94, 95 of washer 90 do not
overlap holes 34 and a portion of slots 32, 35, and enable
insertion of the bone screws 50 therein. Narrowed portions 98 of
washer 90 allow bone screws 50 to be placed through holes 34 and
slots 35 to secure plate 31 to the vertebrae V1 and V2. If desired,
the surgeon can also place bone screws 50 in intermediate slots 32
to secure plate 31 to vertebrae V3 and V4 as deemed necessary.
Plate 31 and bone screws 50 preferably interface in holes 34 such
that rigid fixation of plate 31 to the first vertebra V1 is
achieved. Slots 35 are positioned over second vertebra V2, and
include a second end 43 and a first end 44. As shown in FIG. 1,
screw 50 is initially is inserted at second end 43 of slot 35,
allowing subsequent translation of screw 50 in slot 35 from second
end 43 to first end 44. For the purposes of clarity, only a single
screw 50 is shown in slot 35; however, it is contemplated that bone
screws are inserted in both slots 35. Bone screws 50 inserted in
intermediate slots 32 also translate from the second end 48 to
first end 49 (FIG. 15) of slot 32.
[0053] Once screws 50 are placed through holes 34 and in slots 32
and 35, washer 90 of retainer assembly 33 may be translated to its
locked condition shown in FIG. 2. In the locked condition, body
portions 93, 94, 95 of washer 90 retain the heads of the inserted
screws 50 in holes 34 and slots 32, 35 and prevent the screws from
backing out of plate 31. In order to translate the retainer
assembly 33 to its locked condition, locking screw 85 is threaded
into a corresponding fastener bore 70 in plate 31. This downward
threading of locking screw 85 causes the tapered countersink 92 of
washer 90 to ride along the head of locking screw 85 until locking
screw 85 contacts the first end of aperture 91. This translates
washer 90 along axis L to its locked condition, where the washer 90
retains bone screws 50 in plate 31.
[0054] Bone screws 50 are allowed to translate within slots 35 and
intermediate slots 32 from the second end of the slots to the first
end of the slots while retainer assembly 33 retains bone screws 50
in plate 31 and prevents screw backout. As shown in FIG. 3, the
screw positioned in slot 35 has translated from second end 43 to
first end 44. The translation of screw 50 is limited by contact of
screw 50 with first end 44. The amount of translation may also be
controlled by providing bone screws in intermediate slots 32. Thus,
the amount of translation of the spinal column segment can be
limited by the length of slots 32, 35.
[0055] Referring now to FIGS. 4(a)-4(f) and FIGS. 5(a)-5(f),
several embodiments of elongated plate 31 and washer 90 are
depicted. It is understood that the anterior plating system 30
according to the present invention can be readily adapted for
fixation to several vertebrae by modifying the length of plate 31
and the number and arrangements of holes 34, second slots 35, and
intermediate slots 32. Paired slots 32, 35 and paired holes 34 at
each of the vertebrae provide, at a minimum, for at least two bone
screws 50 to be engaged into each respective vertebrae. The
placement of two or more screws in each vertebral body improves the
stability of the construct. It is one object of the present
invention not only to provide for multiple screw placements in each
vertebral body, but also to provide means for retaining the bone
screws in plate 31 to prevent back out or loosening of the screws.
The present invention contemplates various specific embodiments for
a plate 31 that is provided in lengths that range from 19
millimeters (hereinafter "mm") to 110 mm, and an overall width of
about 17.8 mm. However, other dimensions for the length and width
of plate 31 are also contemplated herein.
[0056] The plate 31 of FIGS. 1-3 is sized to span four vertebrae
and includes a first node 36, a second node 37, and two
intermediate nodes 38. In FIGS. 4(a) and 5(a), plate 31a and washer
90a are sized span two vertebrae. Plate 31a has holes 34a at first
node 36a and holes 34a at second node 37a Plate 31a is provided
with washer 90a that resides in groove 39a and is translatable to
retain bone screws in holes 34a. In this embodiment, plate 31a
provides rigid fixation at each vertebra. A modification of plate
31a is depicted FIGS. 4(b) and 5(b). The holes at the second
vertebral node are replaced with slots 35b at second node 37b. A
washer 90b resides in groove 39b and is translatable to retain bone
screws in holes 34b and slots 35b.
[0057] Plate 31c and washer 90c of FIGS. 4(c) and 5(c) similarly
provide for instmentation at two vertebrae. Plate 30c has a recess
portion between nodes 36c and 37c. Washer 90c resides in groove 39c
and is translatable to retain lock screws in holes 34c and slots
35c. It should be noted that the plates of FIGS. 4(a)-4(c) span two
vertebrae, and preferably do not include notch 40 on the second end
of that plate as do the plates sized to span three or more
vertebrae.
[0058] Plate 31d and washer 90d of FIGS. 4(d) and 5(d) are provided
for instrumentation at three vertebrae. Plate 31d has first
vertebral node 36d, second vertebral node 37d, and intermediate
node 38d. Washer 90d resides in groove 39d and is translatable to
retain bone screws in holes 34d and slots 32d, 35d. Plate 31e and
washer 90e of FIGS. 4(e) and 5(e) are provided for instrumentation
at five vertebrae. Plate 31e has first vertebral node 36e, second
vertebral node 37e, and three intermediate nodes 38e. Washer 90e
resides in groove 39e and is translatable to retain bone screws in
holes 34e and slots 32e, 35e. Plate 31f and washer 90f of FIGS.
4(f) and 5(f) are provided for instrumentation at six vertebrae,
Plate 3 if has first vertebral node 36f, second vertebral node 37f,
and four intermediate nodes 38f. Washer 90f resides in groove 39f
and is translatable to retain bone screws in holes 34f and slots
32f, 35f.
[0059] Referring now to FIG. 6, the details of bone engaging
fastener or screw 50 are shown. Bone screw 50 is preferably
configured for engagement in the cervical spine, and includes
threaded shank 51 that is configured to engage a cancellous bone of
the vertebral body. The threaded shank may be provided with
self-tapping threads, although it is also contemplated that the
threads can require prior drilling and tapping of the vertebral
body for insertion of screw 50. It is preferred that the threads on
shank 51 define a constant outer diameter d2 along the length of
the shank. It is also preferred that shank 51 has a root diameter
that is tapered along a portion of the length of the shank and
increases from the tip of shank 51 to a diameter d1 at an
intermediate or cylindrical portion 52.
[0060] Intermediate portion 52 extends between shank 51 and a head
54 of screw 50. The threads on shank 51 extend into portion 52 by a
thread run out 53. According to standard machining practices,
cylindrical portion 52 includes a short segment that does not bear
any threads This segment of cylindrical portion 52 interfaces or
contacts with a plate thickness at hole 34 or slot 32, 35 through
which bone screw 50 extends. This short segment has an outer
diameter d1. The head 54 of screw 50 includes a tool recess 55
configured to receive a driving tool. In one specific embodiment,
tool recess 55 is a hex recess, or in the alternative, any type of
drive recess as would occur to those skilled in the art. Head 54
includes a truncated or flattened top surface 56 having a diameter
d4. A spherical surface 57 extends from cylindrical portion 52 to a
shoulder 59. Shoulder portion 59 has a diameter d5. An inclined
surface 58 extends between shoulder 59 and truncated top surface
56. Inclined surface 58 forms an angle A.sub.1 with top surface
56.
[0061] It is contemplated that screw 50 may be provided with shank
51 having a length that varies from about 10 mm to about 24 mm. In
one specific embodiment of screw 50, the threads have diameter d2
of about 4.5 mm. In another specific embodiment, the diameter d2 is
about 4.0 mm. In both specific embodiments, cylindrical portion 52
has a diameter d1 of about 4.05 mm. Cylindrical portion 52 has an
unthreaded segment with a height h1 that is determined by standard
machining practices for thread run-out between a shank and screw
head. Height h1 and diameter d1 of cylindrical portion 52 are sized
to achieve a snug fit between screw 50 and plate 31 in hole 34 or
slot 32, 35 through which screw 50 is placed. Head 54 is provided
with height h2, outer diameter d5 at shoulder 59, diameter d4 at
top surface 56, and inclined surface 54 angle A.sub.1 such that the
head 54 is nested within its corresponding slot 32, 35 or hole 34
and recessed below the top surface of the plate. Although reference
has been made to specific dimensions in this specific embodiment,
it should be understood that the present invention also
contemplates other dimensions and configurations for screw 50. It
should also be understood that bone screws used to secure plate 31
can each have a different length and diameters associated
therewith, and need not correspond exactly to the other bone
engaging fasteners used in the construct.
[0062] The details of locking screw 85 are provided in FIG. 7.
Locking screw 85 includes a shank 86 having machine threads
thereon. In one specific embodiment, locking screw 85 terminates in
a sharp point 88 that permits penetration into the vertebral body
when locking screw 85 is secured in threaded fastener bore 70. Head
87 includes a lower conical surface 89 configured to mate with
aperture 91 of washer 90. Head 87 further includes a tool recess
87a for receiving a driving tool therein.
[0063] Further details and embodiments of washer 90 of retainer
assembly 33 are provided in FIGS. 8(a)-8(k). Washer 90 includes
second body portion 95, first body portion 93, and if necessary,
one or more intermediate body portions 94. A connecting portion 98
extends between and connects each of the body portions 93, 94, 95.
Washer 90 has a top surface 100a and a bottom surface 100b. Each
body portion 94, 95 defines an aperture 91 extending between top
surface 100a and bottom surface 100b. Aperture 91 has a tapered
countersink portion 92 therearound adjacent top surface 100b.
Aperture 91 allows passage of shank 86 of locking screw 85
therethrough, and countersink 92 is preferably configured to mate
with conical surface 89 and seat locking screw 85 at various
positions along the length of aperture 91. Preferably, countersink
portion 92 is sloped toward bottom surface 100b from second end 97
to first end 96. The mating conical features between locking screw
85 and aperture 91 provide a self-translating capability for washer
90 relative to plate 31 as locking screw 85 is tightened into
fastener bore 70 of plate 31.
[0064] Body portions 93, 94, 95 have a width W1 that is greater
than a width W2 of connecting portion 98. The width W1 and length
of body portions 93, 94, 95 are configured so that the body
portions overlap with recess 45 of holes 34 and recesses 46, 47 of
slots 32, 35. The body portions 93, 94, 95 retain the heads of bone
screws extending through the holes and slots of plate 31 when
washer 90 resides in groove 39 and is in the locked condition of
FIG. 2. The width W2 and the length of the connecting portions 98
are configured to allow insertion of screws in holes 34 and slots
32, 35 when washer 90 is in the unlocked condition of FIG. 1.
[0065] In FIGS. 8(a) and 8(b) there is shown second body portion 95
of washer 90. Aperture 91 has countersink portion 92 that is
tapered along the length of aperture 91. Aperture 91 has a width W3
at bottom surface 100b of washer 90. Countersink portion 92 has a
width that varies along the length of aperture 91 and is greater
than width W3. Countersink portion 92 has a radius R1 at second end
97 and a radius R2 at first end 96 at top surface 100a. It is
preferred that R1 is less than R2 and the width of countersink
portion 92 increases from second end 97 towards first end 96.
Aperture 91 has a chord length S1 extending between the center of
radius R1 and the center of radius R2. Body portion 95 further
includes a transition portion 99 that extends between connecting
portion 98 and body portion 95.
[0066] Intermediate body portion 94 of FIGS. 8(c) and 8(d) is
similar in many respects to second body portion 95 of FIGS. 8(a)
and 8(b), and also includes an aperture 91 having a tapered
countersink portion 92. However, intermediate body portion 94 has a
connecting portion 98 extending in both directions therefrom. A
second transition portion 98a extends between second connecting
portion 98 and body portion 94. Body portion 94 has a chord length
S1 between the center of radius R1 and the center of radius R2.
[0067] Tapered countersink 92 of aperture 91 provides a
self-translating capability of the washer 90. This is because the
washer 90 is translated relative to plate 31 as the locking screw
85 is threaded into threaded bore 70. The camming conical surface
89 of screw 85 advances downward along the tapered portion of the
wall of countersink portion 92 of aperture 91.
[0068] FIGS. 8(e) and 8(f) show first body portion 93. First body
portion 93 is also similar to second body portion 95. However, in
one embodiment, first body portion 93 includes an aperture 91'
having a countersink portion 92' that is not tapered along its
length to provide a self-translating capability for washer 90 like
the countersink portions 92 of body portions 94 and 95. Rather,
after washer 90 is translated relative to plate 31 as described
above, locking screw 85 will already be positioned at first end
96', and may thereafter be threaded into bore 70 and seated within
countersink portion 92'. Alternatively, the surgeon may slide the
washer by hand or with a tool to its translated position, and lock
the washer in its translated position by seating locking screw 85
into countersink 92' at first end 96'. Countersink 92' has a
definite location at second end 96' for seating locking screw 85,
providing a reference for the surgeon to confirm that washer 90 has
been translated to its locked position. It should be understood,
however, that it is also contemplated herein that body portion 93
could also be provided with aperture 91 like body portions 94 and
95 as shown in FIGS. 1-3.
[0069] Referring now to FIG. 8(g), a cross-sectional view of washer
90 is provided through aperture 91 of body portion 94, 95. Washer
90 has an outer surface 104 configured to overlap bone screws 50 in
slots 32, 35 without contacting inclined surface 58 of screws 50
when retainer assembly 33 is in its locked condition. Outer surface
104 extends from bottom surface 100b to a shoulder 103. Shoulder
103 extends between inclined surface 104 and top surface 100a.
Inclined surface 104 forms an angle A.sub.2 with respect to bottom
surface 100b. Washer 90 defines a thickness t1 between top surface
100a and bottom surface 100b, and a shoulder height of t2 from
bottom surface 100b. Washer 90 has a width W7 along bottom surface
100b at aperture 91.
[0070] Referring now to FIG. 8(h), a cross-sectional view of washer
90 is provided through aperture 91 or 91' of body portion 93.
Washer 90 has contact surface 106 configured to contact inclined
surface 58 of screws 50 when retainer assembly 33 is in its locked
condition. Contact surface 106 extends from bottom surface 100b to
a shoulder 105. Shoulder 105 extends between contact surface 106
and top surface 100a. Contact surface 106 forms an angle A.sub.3
with respect to bottom surface 100b that is configured to mate with
and provide surface contact with inclined surface 58 of bone screw
50. Washer 90 defines a thickness t3 between top surface 100a and
bottom surface 100b, and a shoulder height of t4 from bottom
surface 100b.
[0071] In one specific embodiment of the washer 90, the body
portions have a width W1 and connecting portion have width W2 that
is based on the spacing between the centerlines of the paired slots
and holes of the plates and the overall width of the plate. The
width W3 of aperture 91 in the specific embodiment is sized to
accommodate the shank 86 of locking screw 85 without head 87
passing therethrough. The length of body portions 94 and 95 varies
based on the length and spacing between slots 32, 35 and holes 34
in plate 31. Preferably, the body portions 94, 95 have a length
sufficient to overlap substantially the entire length of slot 32,
35 when retainer assembly 33 is in its locked position. The tapered
countersink portion 92 of aperture 91 has radius R1 that
transitions to radius R2 along the chord length S1. Thickness t1 is
less than thickness t3, and shoulder height t4 is less than
shoulder height t2. Body portion 93 has a width W8 along bottom
surface 100b that is greater than width W7 of body portions 94, 95.
Angle A.sub.2 is preferably less that angle A1. The dimensions of
washer 90 are preferably arranged so that body portions 94, 95 do
not contact the screw heads nested in slots 32, 35 to facilitate
translation of the screws in slots 32, 35. Body portion 93 contacts
the screw heads nested in holes 34 to further enhance the fixed
orientation between screws 50 and plate 31 in holes 34. Although
reference has been made to the dimensional attributes of this
specific embodiment, it should be understood that the present
invention also contemplates other orientations and dimensional
relationships for washer 90.
[0072] The present invention also contemplates a retainer assembly
in which individual washers are provided at each node for retaining
screws in holes 34 and slots 32, 35 of plate 31. Referring now to
FIGS. 8(i) and 8(j), a slot washer 195 and a hole washer 193 are
provided. Slot washer 195 is similar to body portion 95 of washer
90 and hole washer 193 is similar to body portion 93 of washer 90,
both of which are described above. Elements that are alike bear the
same reference number as the corresponding element of body portions
95, 93. Slot washer 195 and hole washer 193 do not have a
connecting portion 98 extending to another washer. Slot washer 195
has a body portion 198 with a length S2 that varies and is sized to
correspond to the length of the adjacent slot 32, 35 when washers
195 are positioned on plate 31. Slot washer 195 does not have a
connecting portion 98 extending to another washer. Hole washer 193
has a body portion 199 with a length S3 that varies and is sized to
correspond to the length of the plate adjacent hole 34 when washer
is positioned on plate 31.
[0073] In FIG. 8(k) an alternate embodiment of washers 193 and 195
is provided and designated at 193', 195' respectively. Washers
193', 195' are the same as washers 193, 195 described above, except
for aperture 191. Aperture 191 does not have a tapered countersink,
but rather has a semi-circular countersink portion 192 only at
first end 196. Countersink portion 192 provides a single position
for locking screw 85 to lock the washer 193', 195' to plate 31
after the washer 193', 195' has been translated relative to plate
31 by the surgeon. Washers 193', 195' have body portion 198', 199'
with length S4 that varies as described above with respect to
length S2 and S3.
[0074] Referring now to FIGS. 9-18, further details of plate 31
will be discussed with reference to illustrations of first node 36,
second node 37, and intermediate node 38. In FIGS. 9-11, first node
36 of plate 31 is depicted. It is preferred that holes 34 are
identical and symmetrical about axis L. Hole 34 includes recess 45
adjacent top surface 41. Holes 34 include a cylindrical bore 77
having generally vertical sidewalls adjacent bottom surface 42.
Cylindrical bore 77 extends between recess 45 and bottom surface 42
of plate 31, and has a diameter D1. Cylindrical bore 77 has axis
72b that is offset at angle A.sub.5 from an axis 72a that extends
normal to plate 31 as shown in FIG. 10. Recess 45 has a partial
spherical portion 45a defined about a central axis 72b. Axis 72b is
offset from axis 72a by angle A.sub.5. Offset angle A.sub.5 directs
bone screws inserted into holes 34 toward the first end of plate
31. Furthermore, as shown in FIG. 11, axes 72a converge below the
bottom surface 42 of plate 31 at angle A.sub.4 with respect to an
axis 72c that extends along the centerline of plate 31
perpendicular to axis L. Recess 45 intersects groove 39 at
intersecting portion 45c. Spherical portion 45a is configured to
mate with spherical surface 57 of bone screw 50, allowing at least
a portion of head 54 to be recessed below top surface 41 of plate
31.
[0075] To facilitate insertion of drill guides, drills and the bone
screws 50, recess 45 also includes a flared portion 45b that
extends in a superior direction from axis 72b. In one embodiment,
recess 45 includes a wall that parallels bore 77 and extends
between between spherical portion 45a and flared portion 45b to
further facilitate insertion and maintenance of a drill guide in
recess 45.
[0076] In one specific embodiment, spherical portion 45a has a
diameter that mates with the diameter of spherical surface 57 of
screw 50, and is slightly larger than diameter d5 of head 54 of
bone screw 50. The cylindrical bore 77 of hole 34 has a diameter D1
of 4.1 mm, which is slightly larger than the diameter d1 of
intermediate portion 52 of screw 50. This portion of the screw
contacts bore 77 and assumes a fixed orientation with respect to
plate 31. In this specific embodiment, offset angle A.sub.5 is
about 12.6 degrees and convergence angle A.sub.4 is about 6 degrees
relative to axis 72c. Although reference has been made to the
dimensional attributes of this specific embodiment, it should be
understood that the present invention also contemplates other
dimensions.
[0077] Referring now to FIGS. 12-14, second vertebral node 37 is
depicted. Vertebral node 37 includes slots 35 that are preferably
identical and symmetrical about axis L. Slot 35 includes slotted
bore 78 adjacent bottom surface 42 of plate 31 having generally
vertical sidewalls extending between second end 43 and first end
44. Slotted bore 78 extends between bottom surface 42 and recess 47
adjacent top surface 42. Bore 78 has a width W5 and a chord length
S4, and has a central axis 75b extending through plate 31. Recess
47 has a spherical portion 47a about central axis 75b that extends
around slot 35. As shown in FIG. 13, central axis 75b is offset
from axis 75a that extends normal to plate 31 by angle A.sub.5.
Offset angle A.sub.5directs bone screws inserted into slot 35
towards the second end of plate 31. It should be noted that slot 35
allows insertion of a bone screw at angles less than A.sub.5 in
slot 35, and bone screw 50 may be positioned within slot 35 at any
location between ends 43 and 44. However, retaining assembly 33
provides for insertion of bone screws 50 at second 43 as would be
clinically desirable for settling. Furthermore, as shown in FIG.
14, axes 75b converge below the bottom surface 42 of plate 31 at
angle A.sub.5 with respect to axis 72c.
[0078] Spherical portion 47a is configured to mate with spherical
surface 57 of bone screw 50, allowing at least a portion of head 54
to be recessed below top surface 41 of plate 31. To facilitate
insertion of drill guides, drills and the bone screws 50, recess 47
also includes a flared portion 47b that extends around spherical
portion 47a. In one embodiment, it is contemplated that recess 47
include a wall that parallels bore 78 extending between spherical
portion 47a and flared portion 47b to further facilitate
maintenance and insertion of a drill guide in recess 47. Recess 47
intersects groove 39 at overlap portion 47c, as shown in FIG. 14.
The second end of second node 37 includes notch 40 having radius R4
centered about axis L. It is also contemplated herein that plate 31
is provided without notch 40, as shown in FIGS. 4(a)-4(c).
[0079] In a preferred embodiment, slot 35 includes ramp 60
extending between bore 78 and flared portion 47b at second end 43.
Ramp 60 is not configured to allow spherical surface 57 of screw 50
to seat therein, but has an orientation that causes second end 43
of slot 35 and screw 50 to separate as screw 50 is threaded into
slot 35. Spherical surface 57 of head 54 provides camming action
along the ramp 60 until head 54 seats in recess 47 at a position
spaced a distance from second end 43. This camming action applies a
dynamic compression load to the spinal column portion. The amount
of compression applied to the spinal column portion is controlled
by the length of ramp 60 from second 43 to the position in slot 35
where screw 50 seats in recess 47. It should be understood that
slot 35 may also be provided without ramp 60.
[0080] In one specific embodiment, spherical portion 47a has a
diameter sized to mate with spherical surface 57 of screw 50, and
is slightly larger than diameter d5 of head 54 of bone screw 50.
Slotted bore 78 has a width W5 of about 4.1 mm, which is slightly
larger than the diameter d1 of intermediate portion 52 of screw 50.
The cylindrical portion 52 of bone screw 50 contacts plate 31 in
bore 78 and prevents rotation of screw 50 transverse to axis 72c.
The chord length S4 varies depending upon the length of the slot 35
needed for the particular application of plate 31 and patient
anatomy. In this specific embodiment, offset angle A.sub.5 is about
12.6 degrees and convergence angle A.sub.4 is about 6 degrees
relative to an axis 72c. Although reference has been made to the
dimensional attributes of this specific embodiment, it should be
understood that the present invention also contemplates other
dimensions.
[0081] Referring now to FIGS. 15-17, various views of intermediate
node 38 are depicted. Vertebral node 38 includes slots 32 that are
preferably identical and symmetrical about axis L. Slot 32 includes
slotted bore 79 adjacent bottom surface 42 of plate 31 having
generally vertical sidewalls extending between a second end 48 and
a first end 49. Slotted bore 79 extends between bottom surface 42
and recess 46 adjacent top surface 42. Bore 79 has a width W5 and a
chord length S5, and has a central axis 76a extending through plate
31. Recess 46 has a spherical portion 46a that extends around slot
35. As shown in FIG. 16, central axis 76a generally extends normal
to plate 31. However, as shown in FIG. 17, the axes 76a converge
below the bottom surface 42 of plate 31 at angle A.sub.4 with
respect to axis 72c. It should be noted that slot 32 allows
insertion of bone screws 50 at various angles with respect to axis
76a.
[0082] Spherical portion 46a is configured to mate with spherical
surface 57 of bone screw 50, allowing at least a portion of head 54
to be recessed below top surface 41 of plate 31. To facilitate
insertion of drill guides, drills and bone screws 50, recess 46
also includes a flared portion 46b that extends around spherical
portion 46a. In one embodiment, a wall paralleling bore 79 extends
between spherical portion 46a and flared portion 46b to further
facilitate insertion and maintenance of a drill guide in recess 46.
Screw 50 may be placed within intermediate slot 32 between ends 48
and 49. However, it is preferred that the screw is inserted
initially at second end 48, thus allowing compression loading of
the spinal column segment. Recess 46 intersects groove 39 at
overlap portion 46c, as shown in FIG. 17.
[0083] In one specific embodiment, spherical portion 46a has a
diameter sized to mate with spherical surface 57 of screw 50, and
is slightly larger than diameter d5 of head 54 of bone screw 50.
The slotted bore 79 has a width W5 of about 4.1 mm, which is
slightly larger than the diameter d1 of intermediate portion 52 of
screw 50. Cylindrical portion 52 of bone screw 50 interfaces with
plate 31 in bore 79 such that angular adjustment of screw 50
transverse to axis 72c is prevented. The chord length S5 varies
depending upon the length of slot 35 needed for the particular
application of plate 31 and patient anatomy. In this specific
embodiment convergence angle A.sub.4 is about 6 degrees relative to
an axis 72c. Although reference has been made to the dimensional
attributes of this specific embodiment it should be understood that
the present invention also contemplates other dimensions.
[0084] Referring now to FIG. 18, a cross-sectional view of plate 31
is provided through line 18-18 of FIG. 15. Groove 39 has a width W6
at top surface 41 of plate 31. Groove 39 has bottom surface 73
extending between inclined sidewalls 74. Sidewalls 74 extend
between bottom surface 73 of groove 39 and top surface 41 of plate
31. It is contemplated that the groove 39 has a depth sufficient to
accommodate the washer 90 so as to minimize protrusion of washer 90
above top surface 41 of plate 31.
[0085] To accommodate the anterior application of the fixation
plate assembly 30, the plate is curved in two degrees of freedom.
Specifically, the bottom surface 42 of the plate can be curved
along a large radius R, centered in a vertebral plane containing
central axis L, as shown schematically in FIG. 16, to accommodate
the lordotic curvature of the cervical spine. In addition, bottom
surface 42 forms a medial/lateral curvature C, as shown in FIG. 18,
to correspond to the curvature of the vertebral body. It is
understood that plate 31 can also be bent as needed to accommodate
the particular spinal anatomy and vertebral pathology.
[0086] Referring now to FIG. 19a, a partial sectional view of
fixation plate assembly 30 at holes 34 is provided with screws 50
engaged to vertebra V1 and retainer assembly 33 in the locked
position. A pair of screws 50 are disposed within the respective
holes 34 so that the threaded shanks 51 project beyond the lower
surface 42 of plate 31 into the vertebral body V1. The intermediate
portion 52 of screw 50 extends through the bore 77 of the hole 34.
Spherical surface 57 of head 54 contacts recess 45 of hole 34 when
screw 50 is seated therein. The intermediate portion 52 provides a
snug fit for screw 50 in the bore 77 so that screw 50 is not able
to pivot with respect to plate 31.
[0087] Referring to FIG. 19b, a partial sectional view of fixation
plate assembly 30 at slots 32 or 35 is provided with screws 50
engaged to vertebra V1 and retainer assembly 33 in the locked
position. A pair of screws 50 are disposed within respective slots
32, 35 so that threaded shanks 51 project beyond lower surface 42
of plate 31 into the corresponding vertebral body V2, V3, or V4.
Cylindrical portion 52 of screw 50 extends through bores 78, 79 of
slots 35 and 32, respectively. Spherical surface 57 of head 54
contacts recesses 46, 47 of slots 32, 35 when screw 50 is seated
therein. Cylindrical portion 52 provides a snug fit for screw 50 in
bores 78, 79 so that screw 50 is not able to pivot or translate
with respect to axis 72c of plate 31. Of course, screws 50 inserted
into slots 32 or 35 are able to translate along the length of slots
32, 35 as described above. It should be understood that the present
invention also contemplates various embodiments of plate 31 that
use variable angle screws capable of assuming universal angular
orientation with respect to plate 31 in slots 32, 35 and holes
34.
[0088] In order to ensure screws 50 are retained within plate 31,
retainer assembly 33 is moved to its locked position where it
contacts the heads 54 of bone screws 50 in holes 34. Locking screw
85 is threaded into threaded fastener bore 70 of plate 31 to
translate washer 90 from its unlocked position to its locked
position, as described above, and to draw contact surface 106 into
contact with inclined surface 58 of screw 50 as shown in FIG.
19aContact surface 106 preferably applies a downward force onto
head 54 to firmly seat the screw heads within the plate recesses
and further fix screw 50 in hole 34. In a preferred embodiment,
this downward force is exacted by washer 90 as surface 106 contacts
inclined surface 58. As shown in FIG. 19b, outer surface 104 of
washer 90 does not contact the heads of bone screws 50 in slots 32,
25. Outer surface 104 overlaps the bone screws 50 to retain bone
screws in slots 32, 35. Outer surface 104 will contact the heads of
the bone screws if the bone screws backout from slots 32, 35. It is
preferred that bottom surface 100b of washer 90 does not contact
bottom surface 73 of groove 39.
[0089] In a further aspect of the invention, the retainer assembly
33 may be loosely fixed on plate 31 so the surgeon need not fiddle
with applying retainer assembly 33 to plate 31 during surgical
procedures. The locking fasteners 85 are pre-inserted through
apertures 91 of washer 90 and partially threaded into fastener
bores 70. Washer 90 is initially positioned such that the second
end of each aperture 91 is positioned adjacent locking screw 85.
After positioning screws 50 through the holes and slots of plate
31, locking fasteners 85 are advanced further into bores 70 and
along tapered portions 92 of apertures 91 to translate washer 90 to
a locked condition and retain bone screws 50 in plate 31.
[0090] As previously mentioned, sharp point 88 of locking screw 85
is preferably configured to penetrate the cortical bone. In one
embodiment, sharp point 88 will penetrate the vertebra when plate
31 is initially positioned on the bone. In this instance, locking
screw 85 helps locate and temporarily stabilize the plate on the
vertebra as the bone screws 50 are engaged to the vertebra. This
temporary location feature provided by locking screw 85 can also be
used to maintain the position of plate 31 on the vertebra as a
drill guide is used to drill and tap the vertebrae to receive bone
screws 50.
[0091] According to another aspect of the invention, there are
provided instruments and techniques for securing plate 31 to
vertebrae of a spinal column segment and for applying a compression
load to a graft or implant placed in the spinal column segment.
Referring to FIGS. 20(a)-20(f), a guide 150 includes a handle 152,
a template 154, and arm 153 extending therebetween. Preferably, arm
153 extends outward from the spine and is bent so that handle 152
parallels the spine, positioning handle 152 out of the way of the
surgeon. Template 154 includes a second end 155 that defines a
notch 158. Template 154 also includes first end 156 having a
projection 156a extending downward therefrom towards vertebral body
V2. Template 154 further defines a pair of slots 157 between second
end 159 and first end 156.
[0092] The surgeon selects a guide 150 with a template 154 sized to
position notch 158 at the desired location on vertebra V2 and
places guide instrument 150 on vertebral body V2. Notch 158 is
located on vertebra V2 by placing projection 156a in abutting
contact with the endplate of vertebra V2 in disc space D. Slots 157
provide a visual indication to the surgeon of the range of
positions available for screw insertion into the vertebral body
through slots 35 of plate 31. If desired, the surgeon can obtain a
desired position or location of notch 158 and the desired available
range of bone screw positions on vertebra V2 by selecting a guide
having a different sized template 154.
[0093] Referring now to FIG. 20(b), after the notch is in the
desired position on vertebra V2, a compression pin 170 is placed
into vertebra V2 guided by notch 158. Pin 170 includes a lower end
171 having a threaded portion (not shown) for attaching pin 170 to
vertebra V2. The attachment portion is preferably threaded to screw
into vertebra V2, but may also be smooth with a spiked tip for
insertion into the vertebra. Pin 170 also includes tool engagement
portion 172 to facilitate installation of pin 170 to the vertebral
body. It is also contemplated that the surgeon can place pin 170 on
the vertebral body spaced away from notch 158 if desired and the
vertebral anatomy so allows.
[0094] After pin 170 is engaged to vertebra V2, guide 150 is
removed and a sleeve 180 is placed over pin 170 as shown in FIG.
20(c). Sleeve 180 has a hollow body 181 extending between a first
end 186 adjacent vertebra V1 and a second end 184. A second end 174
of pin 170 preferably extends from second end 184 of sleeve 180,
allowing access to pin 170. Sleeve 180 includes enlarged portion
184 to facilitate placement and removal of sleeve 180. It is
contemplated that sleeve 180 has hollow interior and an internal
configuration that provides secure attachment to pin 170. Body 181
includes cylindrical outer surface 182 with an outer diameter
d6.
[0095] With sleeve 180 in its proper position, plate 31 is
positioned with notch 40 in abutting contact with outer surface 182
of sleeve 180, as shown in FIG. 20(d). The diameter d6 of sleeve
180 slightly less than the twice the radius of notch 40 so that
notch 40 is nested around sleeve 180. Plate 31 is then secured to
vertebra V1 by inserting screws 50 through holes 34.
[0096] With plate 31 secured to the vertebra V1, sleeve 180 is
removed from pin 170, as shown in FIG. 20(e), forming a gap 177
between pin 170 and notch 40. In a preferred embodiment, it is
contemplated that gap 177 is about 2 mm. However, other sizes for
gap 177 are contemplated herein based on the desired compression to
be applied.
[0097] Referring now to FIG. 20(f), a compression tool 290 is
secured to pin 170 and to slots 32 of plate 31. It is also
contemplated that the compression tool can be secured to plate 31
other than at slots 32 by, for example, engaging the sides of plate
31. Compression tool 290 has a first arm 291 with a first foot 294
connected to pin 170. Second arm 292 is connected to the second end
of slots 32 via extensions 297 extending from second foot 296.
First arm 291 and second arm 292 are manipulated by the surgeon to
apply a compression load to the spinal column segment. The amount
of applied load is limited by gap 177 between pin 170 and notch 40.
For example, in the specific embodiment where gap 177 is 2 mm, the
spinal column portion is compressed 2 mm.
[0098] Bone screws 50 are inserted into slots 35 with compression
tool 290 maintaining the compression load. With ramp 60 at second
43 of slot 35, an additional amount of dynamic compression is
achieved with screw insertion in slots 35, as described above. With
screws 50 seated at end 43 of slots 35, compression tool 290 may be
removed without release of the compression load. Additional bone
screws may be inserted into intermediate slots 32. Washer 90 may
then be translated as described above to retain bone screws 50 in
plate 31. It should be note that it is contemplated herein that
compression tool 290 and pin 170 are preferably only used with
plates providing instrumentation at three or more vertebra.
However, utilization of a compression tool configured to engage a
plate for providing instrumentation at two vertebrae is not
precluded.
[0099] Referring now to FIGS. 21(a)-21(c), further details of
compression tool 290 are provided. Tool 290 has first arm 291
having first foot 294 extending therefrom. First foot 294 defines
recess 293 for receiving the pin 170. Second arm 292 has second
foot 296 extending therefrom. Second foot 296 includes extensions
297 extending downward therefrom configured to engage intermediate
slots 32 of plate 31. Extensions 297 preferably include recesses
307 that are configured contact the second ends of intermediate
slots 32. It is also contemplated that extensions 297 have a curved
bottom surface 308 that corresponds to the medial lateral curvature
of the vertebral bodies.
[0100] First arm 291 has a reduced thickness portion 299 extending
through a passage 295 formed in second arm 292, and is pivotally
coupled to second arm 292 with pin 299. First arm 291 has curved
handle portion 306 having a projection 303 extending therefrom.
Second arm 292 has a handle 305. A ratchet bar 301 is pivotally
coupled to second arm 292 via coupling 302. Preferably, ratchet bar
301 is spring-biased towards projection 303. Serrations 304 formed
on the bottom side of ratchet mechanism 301 provide for selective
engagement with projection 303 on first arm 291.
[0101] The first and second arms are compressed towards one another
to apply the compressive load to the vertebral segment. Projection
303 engages the serrated bottom of ratchet bar 301 to prevent
relaxation of the arms and allows the surgeon to maintain the
compression load during insertion of bone screws 50 within slots
35. Ratchet bar 301 may be lifted against its spring bias away from
arm 291 to disengage ratchet bar 301 from projection 303. Arms 291,
292 may then be moved away from one another to release compression
tool 290 from pin 170 and plate 31.
[0102] While compression tool 290 has been illustrated and
described in detail, the present invention also contemplates other
tools capable of being secured between pin 170 and plate 31 to
provide a compression load to the spinal column segment. For
example, referring now to FIGS. 22(a) and 22(b), it is contemplated
that a compression tool may include one or more angular
modifications to first arm 391 and second arm 392 to facilitate
access to plate 31 and pin 170 at the surgical site. First arm 391
has a lower portion 391a forming angle B1 with first foot 396.
First foot 396 has extensions 397 extending therefrom that are
similar to extensions 297 of tool 290. First arm has an upper
portion 391c that terminates with curved handle 406. Curved handle
406 has projection 403 extending therefrom to engage a ratchet bar
extending from second arm 392. Arm 391 has a vertical extension
391b extending between lower portion 391a and upper portion 391c.
Angle B2 is formed between lower portion 391a and vertical portion
391b. Angle B1 is formed between vertical portion 391b and upper
portion 391c. Vertical portion 391b as a region of reduced
thickness 399 for connection with second arm 392.
[0103] Second arm 392 has a lower portion 392a forming angle B1
with second foot 394. Second foot 394 has a recess (not shown) for
receiving pin 170 and is similar to recess 293 of tool 290
described above. Second arm 392 has an upper portion 392c that
terminates with handle 405. Upper portion 392c has ratchet bar 401
with serrations 404. Ratchet bar 401 is pivotally coupled to arm
392 and spring-biased towards projection 403. Ratchet bar 401 is
similar to ratchet bar 301, but is preferably curved along its
length to accommodate the angular offsets in arms 391, 392 while
maintaining engagement between ratchet bar 401 and projection 403.
Arm 392 has a vertical extension 392b extending between lower
portion 392a and upper portion 392c. Angle B2 is formed between
lower portion 392a and vertical portion 392b. Angle B1 is formed
between vertical portion 392b and upper portion 392c. Vertical
portion 392b as a slot 395 of receiving reduced thickness portion
399 of vertical portion 391b, where first and second arms are
pivotally coupled via a pin (not shown.)
[0104] In one specific embodiment of compression tool 290 and 390,
angle B1 is about 120 degrees and angle B2 is about 150 degrees.
However, other angular offsets in first and second arms of
compression tools 190, 290 are also contemplated herein as would
occur to those skilled in the art.
[0105] While the invention has been illustrated and described in
detail in the drawings and foregoing description, the same is to be
considered as illustrative and not restrictive in character, it
being understood that only the preferred embodiment has been shown
and described and that all changes and modifications the come
within the spirit of the invention are desired to be protected.
* * * * *