Note: Descriptions are shown in the official language in which they were submitted.
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P.C. 7172
SPINAL FIXATION DEVICE
The present invention relates to a spinal fixation
device and a method for fixation of that device between
two or more vertebrae. More particularly, it relates
5 to a fixation device that results in inherent
structural strength due to a unique method for
placement o and linkage between the pedicle screws.
One of the significant problems associated with
the design of a spinal fixation device is the need for
10 to localize the involvement of the spinal column. Such 5
a fixation device design should involve fixation r
directly at the site of instability rather than two or
three vertebrae away from it. The fixation device
should rely on bony tissue rather than intact soft
15 tissue to achieve stabilization and maximum patient
comfort, and to encourage rehabilitation. A splnal
fixation device should be fully internalized, with no
pins transfixing the skin or muscle. Further, it is
important that the device be easy to implant in an
20 accurate and consistent manner.
U.S. Patent No. 4,604,995 discloses a surgical
implant having a unitary rod with a generally
rectangular configuration formed by a pair of spaced
apart branches which are mirror image duplications of
25 one another and equally spaced along their entire
length.
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64680-436
U.S. Patent No. 4,078,559 discloses a straightening and
supporting device for the spinal column. The device comprises a
rod shaped supporting member at least the length of the spinal
column area to be treated and exerting a straightening and
supporting effect on the vertebrae of the spinal column.
U.S. Patent No. 4,003,376 discloses an apparatus for
straightening the spinal column. The apparatus includes an
elongated member securable forwardly of and against the spinal
column. A pair of fastening devices extend around the spinal
column from the elongated member to a pair of bands located
rearwardly of and adjacent the spinal column.
The prosthesis of the present invention overcomes
technical, surgical and practical shortcomings of the prior art.
Important features of the present invention are the ability to
provide three-dimensional stability adaptability which allows for
safer and more secure implantation of the device.
The device of the present invention combines all of
these features in one fixation device. These and other features
discussed hereinafter result in a device which is dynamically
stable and promotes a smooth and natural movement, while
accurately and consistently Eixing the spine.
The present invention seeks to provide a device for
internalized spinal fixation having three-dimensional
adjustability and requiring no violation of the spinal canal, said
device comprising: (a) a first and a second bone screw adapted to
be screwed at least into a first and a second pedicle,
respectively, of two vertebrae along one side of a spinal column
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and for anchoring the device posteriorly with respect to the
patient's body in the pedicle area of the spine, said first bone
screw to be screwed at least into a pedicle of a first vertebra
and said second bone screw to be screwed at least into a pedicle
of a second vertebra; (b) a rigid stabilizing rod; (c) a pair of
articulating clamps slidably and rotatably positionable at
opposite ends of said stabilizing rod, each of said clamps having
a securing means for fixedly but releasably attaching one of said
bone screws to the stahilizing rod, but without re~uiring said
bone screws to be parallel to each other, wherein said securing
means comprises radially arranged teeth located on the proximal
surface of a bone screw and corresponding intermeshable radially
arranged teeth located on a surface of an articulating clamp, and
(d) locking means to lock each bone screw to the articulating
clamp to which it is to be attached.
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The novel features and advantages of the present
invention will become apparent from a reading of the
following detailed description in conjunction with the
accompanying drawings wherein:
Fig. 1 is an exploded perspective view of a spinal
fixation prosthesis of the invention;
Fig. 2 is a cross-sectional view of the spinal
fixation prosthesis of Fig~ 1 taken along lines 2-2 of
Fig. l;
Fig. 3 is a front view of the spinal fixation
prosthesis in position in the spinal column; and
FigO 4 is a cross-sectional view taken along lines
4-4 of Fig. 3.
In Figs. 1-4 is illustrated a spinal fixation
15 device for immobilizing two or more vertebrae in the
spinal column of a patient. The spinal fixation device
generally indicated at 10 includes first and second
pedicle screw members 12, 13, respectively, two
articulating clamps 14, a stabilizing member 16, and
20 two clamp bolts 18.
The proximal ends 15 of the pedicle screw members
12, 13 are scored with radially arranged teeth 20. m
Preferably, the screws contain from about 10 to 100
teeth, most preferably 60 to 90 teeth. Each of the
25 articulating clamp 14 includes corresponding teeth 22
for securing the screw members 12, 13 to the
articulating clamp 14.
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Adjustment of the position of the screw members 12
and 13 relative to stabilizing member 16 is
I accomplished by (1) rotational motion of teeth 20 on
screw members 12 and 13 about teeth 22 on articulating
claimps 14, (2) rotational motion of articulating
clamps 14 about stabilizing member 16 and (3) sliding
motion of articulating clamps 14 along stabilizing
I member 16.
I The screw members 12, 13 are preferably from about
j 10 30mm to 60mm long, with the diameter of the pedicle
¦ screw member being preferably from about 2mms to 8mms,
and most preferably include a SpiralockTM thread which
is primarily used in aircraft and other high vibration
applications.
! 15 Arter adjustment, the position between screws 12
and 13 is locked by tightening clamp bolt 18, thus
' preventing the aforementioned rotational and sliding
motions. The threads 21 of the screw members 12, 13
' can be tightened and loosened repeatedly without
degradation and have an even load distribution along
the engaged threads.
The stabilizing member 16 is preferably a rod-
shaped member with a diameter of from about 2mm. to
lOmm. The rod should have a length appropriate for the
clinical application.
The threaded clamp bolt 18 preferably has a
hexagonal head with a major diameter of from about
` 2.0mm. to 8mm., and an overall length of from about
lOmm. to 20mms.
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Preferably, the stabilizing member, articulating
clamps, and first and second pedicle screw members are
made from titanium, cobalt chromium surgical implant
alloy or, most preferably, 316B strain hardened
stainless steel. Additionally, the articulating
clamps, stabilizing member and clamp bolts may be made
from biocompatible polymeric material.
The components of the spinal fixation device are
preferably manufactured by standard machining
techniques, for example drilling, burning, grinding,
milling and electric polishing.
The use of spinal fixation device 1 will be
described with reference to the fixation of the spine
at level T12 and into ~2.
The patient is anesthetized while lying on his/her
back, then turned onto his/her stomach, using an ~;
operating table which is radiolucent. The incision is
(midline) longitudinal over a vertebrae to be
instrumented (for example for an Ll burst fracturel.
20 Standard techniques are used for clearing soft tissue
off the posterior aspects of the bone out as far as the
tips of the transverse processes in a lateral
direction. An x-ray image intensifier is used to
ensure that the proper levels are dissected, and to
25 guide implantation throughout the procedure. The entry
site for the first drill hole is tenatively identified,
the drill guide is placed over this site and oriented
! so that by using the image intensifier, the drill guide
is centered over the pedicle. The proper sized
30 diameter drill is then used to begin the drill hole,
the image intensifier is rotated to show a lateral
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view, and the drill bit is advanced until the selected
depth is obtained, (but not so deep as to penetrate
through the anterior cortex). The drill bit is then
withdrawn, and a vertebral screw of appropriate length
and diameter (chosen ahead of time, usually based on
the ~T scan x-rays pre-operatively), is then threaded
into place. A similar procedure is performed at each
of the other three pedicles (four screws are used in
most common applications). The articulating mechanism
is then loosely attached to each screw head. ~ext, the
longitudinal rod is selected for proper length, so that
it just barely protrudes above the upper articulating
clamp and below the lower articulating clamp. If
movement of the vertebra needs to be produced, it is
now done at this time, using a special instrument that
grips onto the head of the vertebral screws. ~hile
this position is held, the clamp bolts are then
tightened using the clamp bolt wrench. At this point,
if desired (as is generally the case), a bone graft is
then put in place and the incision i9 closed.
