Note: Descriptions are shown in the official language in which they were submitted.
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VARIABLE ANGLE SPINAL IMPLANT CONNECTION ASSEMBLY
Background of the Invention
The present invention relates generally to the field of spinal implant
systems,
and particularly to systems that employ elongated spinal implants, such as rod
and
plates, connected at various locations along the spinal column. More
particularly, the
invention concerns a connection assembly that provides variable angle
adjustability to
the elongated spinal implant relative to a bone fastener engaged to the spine.
Several spinal fixation systems have been developed for use in correcting and
stabilizing sections of the spinal column and facilitating spinal fusion. In
one such
system, a bendable elongated spinal implant, such as a rod, is longitudinally
disposed
adjacent the vertebral column and then secured to various vertebrae along the
length
of the column by way of a number of bone fasteners of fixation elements. A
variety
of bone fasteners can be utilized, such as hooks or bone screws, which are
configured
to engage specific portions of a vertebra.
An example of one such system is the TSRH Spinal System of Sofamor
Danek Group, Inc. In this system, various hooks and bone screws are engaged to
a
spinal rod by way of eyebolts. In early versions of the TSRH" Spinal System,
the
vertebral hooks and bone screws were attached to the spinal rod at a fixed
orientation,
usually projecting perpendicularly below the rod. At the time, the TSRH
Spinal
System presented a significant advance over prior systems in its VERSATILITY,
strength of fixation, and ease of implantation.
However, one drawback faced by the original TSRH" Spinal System, as well
as the other prevalent fixation systems, was that the surgeon was required to
make
significant adjustments to the contour of the bendable rod so that the bone
fasteners
could solidly engage the vertebra bodies. What was needed, then, was a bone
fastener
that could be connected to the spinal cord a variable angle. In order to
address this
need, the TSRH Variable Angle Screw was developed, as described in U.S.
Patent
No. 5,261,909. This Variable Angle Screw utilized the same TSRH~' eyebolt to
achieve a connection to a spinal rod. In addition, the Variable Angle System
incorporated a washer that fit over the eyebolt, engaged the spinal rod within
a groove
in one surface of the washer, and provided a radially splined surface facing
the bone
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fastener. The bone fastener had a complementary splined surface so that the
fastener
could be situated at variable angular orientations relative to the spinal rod.
A nut
threaded onto the post of the eyebolt clamped all the components together to
complete
the assembly.
The Variable Angle Screw system of the '909 Patent presented a significant
advance over prior rod-based implant systems. The system of the '909 Patent
was
relatively compact and required a minimal number of parts, yet was able to
accomplish a solid fixation of the bone fasteners to the rod at a wide range
of angular
orientations. One drawback of the system was that the eyebolt-nut combination
required side tightening of the nut to clamp the system together. This side-
tightening
aspect required a larger surgical site about the spine so that a wrench could
be
manipulated. To address this difficulty, a top-tightening assembly was
developed as
disclosed in U.S. Patent No. 5,282,801. The clamp assembly depicted in the
'801
Patent replaced the eyebolt and nut with a clamp body having a T-bar against
which
the head of the variable angle bone fastener was clamped. In addition, while
the
original TSRH System relied upon tightening a nut against the variable angle
bone
screw, the top-tightening approach of the '801 Patent utilized a set screw
that acted
against the spinal rod to push the spinal rod into the interlocking washer,
and
ultimately against a complementary spline face of the variable angle screw.
With this
system, the variable angle capability was retained, while a top-tightening
feature was
added.
With the addition of the top-tightening capability, the more recent TSRH
Spinal System has provided surgeons with a great deal of flexibility in the
placement
and orientation of bone fasteners, such as hooks and screws, relative to a
spinal rod.
The variable angle coinponents greatly reduce the need to manipulate and bend
the
spinal rod to conform to the patient's anatomy. Even with the great
improvements
presented by the TSRH" Spinal System, a certain amount of shaping or
contouring of
the spinal rod has still been required. Specifically, the rod must be shaped
so that the
point of attachment of the bone fastener to the rod is the same distance from
the
vertebral body as the splined or interdigitating portion of the bone fastener.
This
vertical or height adjustment is necessary so that the variable angle
components are
properly aligned for accurate connection when the assembly is clamped to
together.
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In order to address this difficulty, later systems were developed that
provided
for a certain degree of vertical adjustability. By vertical or height
adjustability, it is
meant adjustment along the length of the bone fastener. Adjustment in this
dimension
allows the rod to be situated at varying distances from the spine, or oriented
with a
pre-set contour regardless of the location of the fastener.
One approach to achieving vertical adjustability has been to adapt a Schantz-
type bone fastener to the variable angle and top-tightening TSRH System, such
as
described in the above-mentioned '801 Patent. A Schantz-type fastener includes
an
elongated smooth shank portion. Adapting this type of fastener to the TSRH
System required the addition of a split clamp that fit over the T-bar of the
connector.
The split clamp defined a bore to receive the shank of the Schantz-type
fastener, in
which the bore diameter is effectively reduced around the shank as the split
clamp
halves are pressed together. One of the clamp halves included an
interdigitating
feature to engage the variable angle washer. As with the system described in
the'801,
the top-tightening setscrew is tightened against the rod, which pushes the
washer
against the split clamp to compress the clamp halves between the washer and
the T-
bar.
This split clamp has allowed use of a Schantz-type bone fastener, such as a
bone screw, to introduce vertical adjustability to the angular adjustability
present in
the TSRH System. In addition, the split clamp can be adapted to the top-
tightening
aspect of the TSRH System as reflected in the '801 Patent. One difficulty
that
remains is that the overall construct still embodies a certain amount of
"fiddle factor"
to implant and connect together. In addition, the addition of the split clamp
does not
reduce the overall prominence of the construct. There remains a need for a
connector
assembly that can accommodate a Schantz-type bone fastener while addressing
the
drawbacks of these prior systems.
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Summary of the Invention
To address this need, the present invention contemplates a connector assembly
that includes a variable angle clamp configured to engage the shank of a
Schantz-type
bone fastener. In one embodiment, the clamp includes a pair of clamp halves
forming
a slot therebetween that intersects a clamping bore configured to receive the
bone
fastener. Thus, the clamp can be in the form of a split clamp in which the
clamp
halves are compressed together to reduce the bore and provide a clamping force
on
the shank of the bone fastener within the bore.
In one important feature of this embodiment of the invention, the clamp halves
define an open channel that is configured to receive the stem portion of a
connector
that provides a link to an elongated spinal implant, such as a spinal rod. In
certain
preferred embodiments, the clainp and open channel can be configured to be
mounted
on a variable angle top-tightening connector of the type described in U.S.
Patent No.
5,282,901. However, the clamp halves and open channel can alternatively be
configured to mate with other connectors that provide a means to connect the
clamp,
and ultimately the bone fastener, to an elongated implant.
Each of the clamp halves includes an outer surface against which a clamping
force is applied to compress the split clamp against the bone-engaging
fastener. The
outer surface of one or U9,th clamp halves is provided with a variable angle
feature. In
a preferred embodiment, this feature can include radiating splines that are
configured
to interdigitate with similar radiating splines on a component of the variable
angle
connector. The outer surface of the other clamp half can provide a pressure
surface
and need not, but may, include similar variable angle features.
In accordance with certain features of the invention, the variable angle clamp
can be mounted on the shank of a bone-engaging fastener with the open channel
exposed. A connector mounted on an elongated implant, such as a spinal rod,
can be
manipulated to engage the channel of the clamp. The clamp is juxtaposed with
the
connector at whatever orientation is assumed by the bone-engaging fastener.
The
entire assembly is tightened so that the clamp halves are compressed to lock
the clamp
about the fastener.
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In a further embodiment, the clamp can include a body having a screw
receiving portion with a bore configured to receive the shank of a Schantz-
type screw
therein. The body also defines an open channel that is configured to receive
the stem
portion of a connector that provides a link to an elongated spinal implant,
such as a
spinal rod. In certain preferred embodiments, the clamp and open channel can
be
configured to be mounted on a variable angle top-tightening connector of the
type
described in U.S. Patent No. 5,282,901. However, the clamp halves and open
channel
can alternatively be configui-ed to mate with other connectors that provide a
means to
connect the clamp, and ultimately the bone fastener, to an elongated implant.
A first outer surface of the body of this embodiment can be provided with a
variable angle feature. In a preferred embodiment, this feature can include
radiating
splines that are configured to interdigitate with similar radiating splines on
a variable
angle washer coinponent of the connector. The opposite outer surface of the
body can
provide a pressure surface and need not, but may, include similar variable
angle
features.
In an important feature of this embodiment of the invention, the body defines
a
notch tllrough the screw engaging portion that communicates with the screw
bore.
The notch is aligned with the first outer surface of the body so that when the
variable
angle washer component contacts the first outer surface a portion of the
washer
component extends through the notch into contact with the screw shank within
the
screw bore.
In accordance with certain features of the invention, the variable angle clamp
can be mounted on the shanlc of a bone-engaging fastener with the open channel
exposed. A coiuiector mounted on an elongated implant, such as a spinal rod,
can be
manipulated to engage the channel of the clainp. The clainp is juxtaposed with
the
variable angle washer of the connector at whatever orientation is assumed by
the
bone-engaging fastener. When the connector is tightened, pressure on the
variable
angle washer is transmitted through the portion projecting through the notch
to
provide a pressure force against the screw shank.
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According to an aspect of the present invention,
there is provided an assembly for connecting a bone-engaging
fastener to an elongated spinal implant configured to span a
length of the spine, the bone engaging fastener having an
elongated shank, comprising: a connector having a body
configured for engagement to the elongated spinal implant
and a stem projecting from said body; a first surface
associated with said connector; a second surface associated
with said stem; and a clamp having a clamping portion
defining a bore for receiving the elongated shank
therethrough and including a pair of clamp halves forming a
slot therebetween that intersects said bore, said clamp
halves movable toward each other to substantially close said
slot, each of said pair of clamp halves defining an open
channel configured for receiving said stem therein with said
clamp halves disposed between said first and second
surfaces.
According to another aspect of the present
invention, there is provided a spinal fixation assembly
comprising: an elongated rod sized to span a length of the
spine; at least one bone engaging fastener having an
elongated shank; and a connector assembly associated with
each said at least one bone-engaging fastener including; a
connector having a body defining a bore for receiving said
elongated rod therethrough and a stem projecting from said
body; a first surface associated with said connector; a
second surface associated with said stem; and a clamp having
a clamping portion defining a bore for receiving the
elongated shank therethrough and including a pair of clamp
halves forming a slot therebetween that intersects said
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bore, said clamp halves movable toward each other to
substantially close said slot, each of said pair of clamp
halves defining an open channel configured for receiving
said stem therein with said clamp halves disposed between
said first and second surfaces.
According to still another aspect of the present
invention, there is provided a clamp for use with a spinal
implant assembly, the assembly having a spinal rod
configured to span a length of the spine, a bone-engaging
fastener having an elongated shank, and a variable angle
connector having a body defining an opening configured to
receive the spinal rod therethrough, a washer mounted on the
body having a first surface having a variable angle feature,
and a stem projecting from the body, the stem terminating in
a T-bar having a second surface facing the first surface,
said clamp comprising: a clamping portion defining a bore
therethrough configured to receive the elongated shank of
the bone-engaging fastener therein; a pair of clamp halves
forming a slot therebetween that intersects said bore, said
clamp halves movable toward each other to substantially
close said slot and reduce said bore around the elongated
shank; an outer surface of one of said clamp halves defining
a variabie angle feature configured for interengagement with
the first surface of the washer, and the outer surface of
the other of said clamp halves configured for pressure
contact with the second surface of the T-bar; and an open
channel defined in said clamp halves, said open channel
configured to receive the stem of the variable angle
connector therein when the shank of the bone-engaging
fastener extends through said bore.
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According to yet another aspect of the present
invention, there is provided an assembly for connecting a
bone-engaging fastener to an elongated spinal implant
configured to span a length of the spine, the bone engaging
fastener having an elongated shank, comprising: a connector
having a body configured for engagement to the elongated
spinal implant and a stem projecting from said body; a
washer mounted on said stem and defining a first clamping
surface; a second clamping surface associated with said
stem; and a clamp having a body defining a bore for
receiving the elongated shank therethrough, said body
further defining a channel configured for receiving said
stem therein with said body disposed between said first and
second surfaces, said body further defining a notch
extending through said body and intersecting said bore, said
notch configured to receive a portion of said washer
therethrough so that said portion engages the elongated
shank of the bone screw when the shank extends through said
bore.
According to a further aspect of the present
invention, there is provided a spinal fixation assembly
comprising: an elongated rod sized to span a length of the
spine; at least one bone engaging fastener having an
elongated shank; and a connector assembly associated with
each said at least one bone-engaging fastener including; a
connector having a body defining a bore for receiving said
elongated rod therethrough and a stem projecting from said
body; a washer mounted on said stem and defining a first
clamping surface; a second clamping surface associated with
said stem; and a clamp having a body defining a bore for
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receiving the elongated shank therethrough, said body
further defining a channel configured for receiving said
stem therein with said body disposed between said first and
second surfaces, said body further defining a notch
extending through said body and intersecting said bore, said
notch configured to receive a portion of said washer
therethrough so that said portion engages the elongated
shank of the bone screw when the shank extends through said
bore.
According to yet a further aspect of the present
invention, there is provided a clamp for use with a spinal
implant assembly, the assembly having a spinal rod
configured to span a length of the spine, a bone-engaging
fastener having an elongated shank, and a variable angle
connector having a body defining an opening configured to
receive the spinal rod therethrough, a washer mounted on the
body having a first surface having a variable angle feature,
and a stem projecting from the body, the stem terminating in
a T-bar having a second surface facing the first surface,
said clamp comprising: a clamping portion defining a bore
configured to receive the elongated shank of the bone
engaging fastener therethrough; a clamp body defining a
channel configured for receiving the stem of the variable
angle connector therein with said clamp body disposed
between the variable angle connector body and the T-bar;
said clamp body further defining a notch extending
therethrough and intersecting said bore, said notch
configured to receive a portion of the washer therethrough
so that the portion of the washer engages the elongated
shank of the bone screw when the shank extends through said
bore.
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One object of the invention is to provide a
variable angle clamp assembly for use with a bone-engaging
fastener having a shank, such as a Schantz-type fastener.
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Another object is achieved by features that reduce the "fiddle factor"
associated with
completing a spinal fixation construct.
One benefit of the present invention is that it can be readily used to engage
a
bone fastener to a spinal rod, for instance. A further benefit is that the
inventive
variable angle clainp can assume various orientations to facilitate overall
assembly of
the clamp, connector, spinal rod and bone-engaging fastener. Yet another
benefit is
that the body of the variable angle clamp assembly can have reduced profile.
Other objects and benefits of the invention will become apparent from the
following written description taken together with the accompanying figures.
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Description of the Figures
FIG. 1 is a side elevational view of a top-tightening variable angle connector
assembly according to a prior system disclosed in U.S. Pat. No. 5,282,801.
FIG. 2 is a side perspective view of a known variable angle bone screw for
use with the connector assembly shown in FIG. 1.
FIG. 3 is a variable angle connector assembly modified from the assembly
shown in FIG. 1 to accommodate a Schantz screw.
FIG. 4 side elevational view of a portion of a Schantz screw for use with the
connector assembly shown in FIG. 3.
FIG. 5 is a transverse elevational view of the clamp assembly shown in FIG.
3.
FIG. 6 is a top perspective view of a variable angle connector assembly
according to one embodiment of the present invention.
FIG. 7 is a top elevational view of a clamp of the connector assembly shown
in FIG. 6.
FIG. 8 is a transverse elevational view of the clamp shown in FIG. 7, with the
stem of a connector depicted in phantom lines..
FIG. 9 is a transverse elevational view of the opposite side of the clamp
shown in FIGS. 7 and 8, with the clamp in a different orientation.
FIG. 10 is a top elevational view of a modified clamp according to a further
embodiment of the invention that can be used with the connector assembly shown
in
FIG. 6.
FIG. 11 is a top elevational view of a modified clamp according to another
embodiment of the invention that can be used with the connector assembly shown
in
FIG. 6.
FIG. 12 is a transverse elevational view of a modified clamp in accordance
with yet another embodiment of the invention that can be used with the
connector
assembly shown in FIG. 6.
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FIG. 13 is a top elevational view of a variable angle clainp in accordance
with
yet another embodiment of the invention that can be used with the connector
assembly shown in FIG. 6.
FIG. 14 is a front elevational view of the variable angle clamp shown in FIG.
13.
FIG. 15 is a top elevational view of the variable angle clamp shown in FIGS.
13 and 14 engaged to a connector assembly, such as the connector assembly
shown in
FIG. 6.
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Description of the Preferred Embodiments
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 described in the following written specification. It is understood that no
limitation to the scope of the invention is thereby intended. It is further
understood
that the present invention includes any alterations and modifications to the
illustrated
embodiments and includes further applications of the principles of the
invention as
would normally occur to one skilled in the art to which this invention
pertains.
Although the present invention lias broad applicability, it may be best
understood with reference to prior spinal implant connection assemblies, and
particularly variable angle connection assemblies. For instance, a
representative top-
tightening variable angle clamp asseinbly is depicted in FIG. 1. The connector
assembly 10 can be constructed as described in U.S. Pat. No. 5,282,801.
In particular, the connector assembly includes a connector
body 11 that defines an elongated channel 12 for
receiving a spinal rod therethrough. A pair of fixation screw bores 13 are
defined in
opposite top and bottom surfaces of the body and intersect the elongated
channel rod
12. A setscrew 14 can be threaded into one of the screw bores 13 to bear
against a rod
disposed within the channel.
The top-tightening connector 10 also includes a stem 16 that projects from the
body 11. 'The stem terminates in a T-bar 17 which forms a clamping surface 18.
The variable angle capability of the connector assembly 10 is accomplished by
a variable angle washer 20. The washer 20 fits over a portion of the body 11
and can
be slid over the T-bar 17 and stem 16 to its operative position. The washer 20
defines
a splined surface 21 that can mate with a corresponding splined surface on a
spinal
fixation element. One such element is depicted in FIG. 2. Specifically, a
variable
angle screw 25 includes a threaded shank 26 adapted for engagement into a
vertebra.
The head 27 of the screw 25 defines a yol{e opening 28 that is configured to
receive
the stein 16 of the top-tightening connector of body 11. The head 27 also
defines the
splined surface 29 that is arranged for mating engagement or interdigitation
with the
splined surface 21 of the variable angle washer.
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The use and application of the top-tightening connector 10 and the variable
angle screw 25 is described in more detail in U.S. Pat. No. 5,282,801.
Briefly, the variable angle screw 25 can be engaged in a spinal
element, such as a vertebra, with the head 27 projecting
therefrom. A top-tightening connector 20 can be threaded onto the spinal rod
prior to
implantation. The connector 10 can be oriented on the rod immediately adjacent
the
variable angle screw 25, and more particularly with the stem 16 extending
through the
yolce opening 28 of the screw. The variable angle washer 20 can contact the
splined
surface 29 of the screw at whatever angular orientation exists between the
connector
10 and screw 25. When the setscrew 14 is tightened, it pushes the spinal rod
against
one side of the washer, which causes the splined surface to press against the
variable
angle screw. The screw is then trapped between the splined surface 21 of the
washer
and the clamping surface 18 of the T-bar 17. With this approach, the variable
angle screw is solidly affixed to the spinal rod at whatever angular
orientation exists
15 between the two components.
While the top-tightening variable angle aspect of the system described in
the'801 patent was an important advancement, it was generally limited to bone
fixation elements, such as the screw 25, having a head such as the head 27
configured
as shown in FIG. 2. In certain applications, a Schantz-type screw may be
preferable.
20 In order to address this type of fixation element, an alternative connector
or clamp
assembly was developed as shown in FIG. 3. In particular, the same top-
tightening
connector 10 can be mounted on a spinal rod R. In addition, the same variable
angle
washer 20 can be mounted on the connector body. However, instead of mating
directly with the head of a variable angle screw, this prior art system
utilized a clamp
35 configured to be mounted over stem 16 of the coiuiector 10. In particular,
the
clamp included opposite clamp halves 36 and 37. A stem bore 38 is formed
through
each of the clamp halves 36 and 37 to allow the clamp 35 to be mounted onto
the stem
16 of the connector 10.
The clainp 35 further includes a clamping portion 40 that is configured to 30
receive and engage the shank of a Schantz screw, sucli as a screw 45 shown in
FIG. 4.
The Schantz screw 45 includes bone engaging thread 46 and a clamping shank 47.
The clamping portion 40 of the clamp 35 defines a bore 41 therethrough adapted
to
receive the clamping shanlc 47 of the screw 45.
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The clamp 35 does not alter the operation of the top-tightening connector 10
from what was described previously. However, as the setscrew is tightened to
push
the rod R against the washer 20, the washer compresses the two clamp heads 36
and
37 toward each other. When the halves are pushed together, they tend to reduce
the
diameter of the screw bore 41, which creates an engagement or fixation force
against
the clamping shank 47 of the Schantz screw 45. Thus, the same top-tightening
feature, along with the variable angle engagement feature, can be utilized to
engage a
Schantz screw clamp, such as clamp 35.
One problem with the Schantz screw clamp 35 may be best understood with
reference to FIG. 5. In particular, in order to be mounted over the T-bar 17,
the
clamp 35, and more particularly each of the clainp halves 36 and 37, must
include a
stem bore 38 that is sized to fit over the T-bar 17. Thus, in the illustrated
assembly
the T-bar 17 has a generally rectangular configuration, so the stem bore 38
has a
commensurate rectangular configuration. The clamp 35, just as with the
variable
angle washer 20, is first mounted over the T-bar 17 with the stem bore 38
oriented
parallel to the long axis of the T-bar. Then, when in use the clamp 35 is
rotated 90
so that the clamp 35 is trapped against the T-bar and engaged over the stem
16.
As can be appreciated, this configuration of the clamp 35 increases the
profile
or prominence of the clamp because a sufficient material must surround the
stem bore
38 to ensure the strength of the clamp. In addition, the bore 38 may require
significant manipulation of the clamp 35 to engage the clamp on the T-bar. As
discussed in more detail in the '801 patent, the variable angle washer 20 can
be
preassembled and staked onto the top-tightening connector body 11. Thus, the
connector and washer are provided as a single piece during the implantation
surgery.
The clamp 35 is preferably provided as a separate piece and then engaged onto
both
the Schantz screw 45 and the stem 16 of the top-tightening connector 10 in
situ. The
closed opening of the stem bore 38 provides a great deal of the security of
the
fixation, but also increases the "fiddle factor" associated with completing
the variable
angle assembly.
In order to address this problem, the present invention contemplates a
variable
angle clamp 50, such as the clamp depicted in FIG. 6. Again, the clamp 50 is
preferably configured to work with both the top-tightening connector 10 and
the
variable angle washer 20, although the clamp can also be assembled with a TSRH
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eyebolt as well. As shown in FIG. 6, the variable angle clamp 50 includes
opposing
clamp halves 52 and 54 that form a slot 55 therebetween so that the clamp can
be in
the form of a split clamp. The clamp half 54 defines a splined surface 56
configured
for engagement or interdigitation with the splined surface of the variable
angle washer
20. The opposite clamp half 52 defines an outer clamping surface 58 that is
configured for engagement with the clamping surface 18 of the T-bar 17. In the
illustrated embodiment, the surface 58 is generally smooth; however, the
surface can
be configured to enhance engagement with the clainping surface 18. Moreover, a
variable angle feature can be incorporated between the surfaces 18 and 58, or
a
splined surface like surface 56 could be applied to surface 58 so that clamp
could be
assembled in opposite directions.
In contrast to the clamp 35 depicted in FIGS. 3 and 5, the variable angle
clamp 50 according to the preferred embodiment of the present invention
defines a
yoke channe160 and 62 through each corresponding clamp half 52, 54. Thus, as
shown in FIG. 6, each yoke channels 60, 62 is open so that the stem 16 of the
top-
tightening connector 10 can readily slide into the channel.
The variable angle clamp 50 further includes a clamping portion 64. The
clamping portion defines a screw bore 66 that is sized to receive the shank of
a
Schantz screw, such as the screw 45 depicted in FIG. 4. As with the clamp 35,
the
screw bore 66 initially has a diameter that is slightly larger than the
diameter of the
clamping shank 47 of the screw 45. However, when the variable angle clamp 50
is
engaged within the top-tightening connector, and more particularly between the
T-bar
17 and the variable angle washer 20, the two clamp halves 52, 54 are driven
together,
reducing the slot 55 and the diameter of the screw bore 66 to compress or
clamp
against the shank 47.
Certain benefits of the variable angle clamp 50 can be appreciated upon
consideration of the opposite side views of FIGS. 8 and 9. As shown in FIG. 8,
the
stem 16 of the top-tightening connector can be readily and easily slid into
the yoke
channels 60, 62. With this approach, the clamp 50 need not be preloaded onto
the T-
bar, but instead can be mounted first onto the screw 45, with the shank 47
extending
through the screw bore 66. With the variable angle clainp 50 arranged as shown
in
FIGS. 6 and 8, that is with the yoke channels 60, 62 facing upward, a top-
tightening
connector can be slid along the spinal rod R immediately adjacent the clamp
50. The
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connector can then be rotated about the rod R so that the stem 16 rotates and
slides
into the yolce channels 60, 62, until the stem is situated at the base of the
channel as
depicted in phantom lines in FIG. 8. With this feature - i.e., the open yoke
channel -
the T-bar 17 of the top-tightening connector 10 does not interfere with or
complicate
the engagement of the variable angle clamp 50 to the connector.
Moreover, as illustrated in FIG. 9 the variable angle clamp 50 can be situated
essentially upside down. In other words, the clamp can be mounted on the stem
16
from above so that the openings of the yoke channels 60, 62 face downward.
With
this approach, a variable angle clamp 50 can be mounted essentially
simultaneously
over both the clamping shank 47 of the screw 45 and the stem 16 of the top-
tightening
connector 10. Thus, it can be appreciated that the variable angle clamp 50
provides a
greater degree of flexibility in creating a support scaffold for the spine
using a spinal
rod construct.
It can also be appreciated that the variable angle clamp 50 of the present
invention allows flexibility in the placement of the bone fastener, such as
the screw
45. For instance, the screw 45 can be threaded into a spinal element, such as
a
vertebra, while the clamping shank 47 extends through the screw bore 66 of the
clamp
50. The screw 45 can be provided with a driving feature 48 in the clamping
shank 47
to allow rotation of the screw. This driving feature 48 can be an internal
feature for
engagement by a driving bit such as a hex tool, or can be an external feature,
such as
an external hex configuration, for engagement by a wrench. In addition, the
driving
feature 48 can include a torque-limiting aspect in which the upper portion of
the shanlc
47 is severed from the remainder of the shank at a pre-deterinined torque.
Preferably,
the shank of the screw 45 extends only a minimal amount beyond the variable
angle
clamp 50, thereby reducing the overall profile of the construct.
Additional embodiments of the variable angle clamp of the present invention
are shown in FIG. 10 - 12. In one alternative embodiment, a clamp 70 can be
provided in which the screw bore 71 includes a fixation feature 72. For
instance, the
fixation feature can be knurling or splines arranged to provide a solid
engagement
with the clamping shank 47.
In the initial embodiment depicted in FIG. 7, the two clamp halves 52 and 54
form a slot 55. This slot 55 intersects the clatnping bore 66 to form the
split clamp
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feature. Most preferably, the bore 66 is symmetric about the slot 55 so that
an even
clamping force is exerted on the shank 47 extending through the bore when the
clamp
halves are compressed together. In this preferred embodiment, the center of
the bore
66 is oriented along the midline M of the clamp 50. In addition, in this
preferred
embodiment, the clainp halves 52, 54 are generally symmetric. With symmetric
clamp halves, the bore in this preferred embodiment is substantially
symmetrically
disposed between the outer engagement surfaces of the clamp halves.
In an alternative embodiment shown in FIG. 11, a variable angle clamp 75 can
include an offset clamping portion 76. More particularly, the portion can be
offset so
that the screw bore 77 is offset by a dimension 0 from the midline M of the
clamp.
With this configuration, the clamp halves 78 and 79 are preferably non-
symmetric.
Specifically, one clamp half 78 is thicker than the opposite clamp half 79.
However,
both clamp halves 78 and 79 operate in the same way to perform the clamping
function. Of course, it is understood that the offset clamping portion 76 can
be
configured so that the bore 77 is offset toward the clamp half 78 and away
from the
variable angle surface 80. With this embodiment, then, the clamping bore is
asymmetrically disposed between the outer engagement surfaces of the clamp
halves.
As a further alternative, a variable angle clamp 85 can be provided in which
the yoke channel opens in a different orientation from the clamp 50. The clamp
85 as
illustrated in FIG. 12 includes a clamping portion 86 that defines a clamping
bore 87
therethrough. The clamp also includes a yoke channe188 that is oriented at a
generally perpendicular angle to the clamping bore 87. This orientation is in
contrast
to the substantially parallel arrangement of the yoke channels 60, 62 relative
to the
clamping bore 66 of the clainp 50 shown in FIGS. 6-9. Again, the yol<e channel
88 is
configured to receive the stem of a connector, such as connector 10; however,
the T-
bar of the connector should be rotated, such as the T-bar 17' shown in FIG. 12
to
provide solid engagement with the clamp 85.
The variable angle clamp 85 of the embodiment in FIG. 12 can include
features similar to those described above, the only difference since the clamp
is
essentially side-loaded onto the stem of the connector. This side loading
capability is
made possible by the open channel feature of the inventive variable angle
clamp.
With this embodiment, the clamp 85 can be mounted on the shank 45 of a bone
fastener with the open channel 88 facing along the length of the spinal rod R.
A pre-
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loaded connector 10 can be slid along the length of the bar until the stein of
the
connector is lodged within the yoke channel 88.
In a further embodiment of the invention shown in FIGS. 13-15, a variable
angle clamp 100 includes a body 102 that defines a bone engaging portion 114.
More
particularly, the bone engaging portion 114 defines a bore 116 sized to
receive the
shank of a bone screw, such as the shank 47 of the Schantz-type bone screw 45
shown
in FIG. 4. A first outer surface 106 can include a variable angle feature,
such as the
splines discussed above. Preferably, the first outer surface 106 can include
interdigitating splines that mate with the splined surface of a variable angle
washer
component, such as the washer 20 of a connector assembly 10. The opposite
outer
surface 108 is configured for engagement by the T-bar of a connector assembly,
such
as the T-bar 17 of the connector assembly 10. As with the variable angle
clamps in
the previous embodiments, the clamp 100 can include a channel 110 configured
to
receive a portion of a connector assembly.
As can be seen from FIGS. 13 and 14, the screw engaging portion 114 is
completely closed - i.e., there are no split clamp halves of the type included
in the
clamp shown in FIGS. 7-12. Thus, the bore 116 completely encircles the shank
of the
bone screw, as shown in FIG. 15. In order to fix the bone screw shank within
the
bore, a notch 120 is cut through the screw engaging portion 114 to define a
generally
crescent shaped opening 122 in the bore 116. The purpose of the notch 120 can
be
appreciated on consideration of FIG. 15.
In FIG. 15, the variable angle clamp 100 is engaged to a connector assembly
10' that is substantially similar to the connector assembly 10 shown in FIG.
6. The
connector assembly 10' is configured to engage a spinal rod R with a top-
tightening
set screw 14'. The connector includes a stem 16' that can be disposed within
the
channel 110 in the clamp body 102. The stem 16' terminates in a T-bar 17' that
bears
against the opposite outer surface 108 of the clamp body 102.
The connector assembly 10' also includes a variable angle washer 20' that is
configured to engage the first outer surface 106 of the clamp body. The washer
20'
includes a portion 125 that projects through the notch 120 and into the screw
bore 116
to engage the shank of the bone screw 47 passing through the bore. As the set-
screw
14' is tightened, it bears against the spinal rod R, which in turn pushed
against the
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washer 20' to trap the clamp body 102 between the washer 20' and the T-bar
17'. The
relative angular position of the clamp 100 and rod R is established by this
engagement.
As the set screw is tightened further, the washer 20' is pressed further into
the
clamp body so that the portion 125 extends into the notch 120. Further
pressure on
the washer causes the portion 125 to bear against the screw 47 to thereby
clamp the
screw within the screw bore 116. The radiating splines of the variable angle
washer
20' can enhance the fixation between the two components. In addition, the
inner
surface of the bore 116 can include a surface treatment to enhance the
clamping force
on the bone screw. Preferably, any surface treatinent of clamping features
will be
formed at a portion 117 that is diametrically opposite the notch 120 and
opening 122
(FIG. 13) to follow the line of force from the washer portion 125.
The screw clamp 100 of this embodiment provides the same variable angle
features of the previous einbodiments. In addition, shlce the clainp 100 does
not rely
upon split clamp halves for generating the screw clamping force, the body 102
of the
clamp 100 can be made thinner, thereby reducing the overall profile of the
clamp.
Modifications to the connector assembly can readily accommodate the reduced
thiclcness of the clamp 100.
In the illustrated embodiments, the bone fastener is a Schantz screw 45. Of
20. course, it is understood that other types of spinal fasteners are
contemplated for use
with the clamps 50, 70, 75, 85 and 100 of the present invention. For instance,
a spinal
hook can be provided with a clamping shank, such as the shank 47 illustrated
in FIG.
6. Other elements of a spinal fixation scaffolding can also be adapted for
engagement
by the variable angle clamp 50. In addition, while the top tightening
connector 10 has
been illustrated for use with the clamps of the present invention, other rod-
engagement connectors can be utilized.
It should be understood that the clamps 50, 70, 75, 85 and 100 are all formed
of a medical grade and strength material sufficient for implantation as part
of a spinal
fixation system. It should also be appreciated that the clamps should be
formed of the
saine or compatible material or metal as the variable angle connector, such as
titanium, stainless steel, or fiber reinforced composite.
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While the invention has been illustrated and described in detail in the
drawings
and foregoing description, the same should be considered as illustrative and
not
restrictive in character. It is understood that only the preferred embodiments
have
been presented and that all changes, modifications and further applications
that come
within the spirit of the invention are desired to be protected.
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