U.S. patent number RE44,392 [Application Number 12/985,997] was granted by the patent office on 2013-07-23 for spinal fixation system and related methods.
This patent grant is currently assigned to Warsaw Orthopedic, Inc.. The grantee listed for this patent is Richard A. Hynes. Invention is credited to Richard A. Hynes.
United States Patent |
RE44,392 |
Hynes |
July 23, 2013 |
**Please see images for:
( Certificate of Correction ) ** |
Spinal fixation system and related methods
Abstract
Pedicle screws are secured in two columns, one along each side
of the spine. Cross support rods have ends connected to pedicle
screw heads. A longitudinally extending rod is supported on the
cross supports and recessed in the cavity created by removal of
portions of spinous processes, providing a reduced profile of the
installed construct. Several types of cross supports are shown such
as: arms from the screws inward to rings or yokes connecting the
longitudinal rod; cross rods with ends connected to the screws and
having centrally-located yokes for the longitudinal rod; cross rods
with articulating longitudinal rod portions fixed or swiveled to
them. These cross rods may have end portions angled posterior
toward anterior to accommodate lateral positioned pedicle screws,
but shorter cross rods without angled end portions enable
medialized pedicle screw orientation.
Inventors: |
Hynes; Richard A. (Melbourne,
FL) |
Applicant: |
Name |
City |
State |
Country |
Type |
Hynes; Richard A. |
Melbourne |
FL |
US |
|
|
Assignee: |
Warsaw Orthopedic, Inc.
(Warsaw, IN)
|
Family
ID: |
38049518 |
Appl.
No.: |
12/985,997 |
Filed: |
January 6, 2011 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
10099797 |
Mar 15, 2002 |
7220262 |
|
|
|
60276706 |
Mar 16, 2001 |
|
|
|
Reissue of: |
11132972 |
May 19, 2005 |
7473269 |
Jan 6, 2009 |
|
|
Current U.S.
Class: |
606/279;
606/250 |
Current CPC
Class: |
A61B
17/7023 (20130101); A61B 17/7034 (20130101); A61B
17/7043 (20130101); A61B 17/7038 (20130101); A61B
17/7011 (20130101); A61B 17/7025 (20130101); A61B
17/7005 (20130101); A61B 17/7013 (20130101); A61B
17/7041 (20130101); A61B 17/7071 (20130101); A61B
17/7014 (20130101) |
Current International
Class: |
A61B
17/88 (20060101); A61B 17/70 (20060101) |
Field of
Search: |
;606/279,250,276,264,278,265 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
0 465 158 |
|
Jan 1997 |
|
EP |
|
2 624 720 |
|
Jun 1989 |
|
FR |
|
WO 01/54597 |
|
Aug 2002 |
|
WO |
|
Primary Examiner: Philogene; Pedro
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
.[.The present invention.]. .Iadd.This application is a reissue of
U.S. Pat. No. 7,473,269 issued on Jan. 6, 2009, which is hereby
incorporated by reference, as if fully set forth herein. U.S. Pat.
No. 7,473,269 matured from application Ser. No. 11/132,792 which
.Iaddend.is a divisional of application Ser. No. 10/099,797, filed
on Mar. 15, 2002, now U.S. Pat. No. 7,220,262, which claims the
benefit of priority of U.S. Provisional Application No. 60/276,706,
filed Mar. 16, 2001.
Claims
What is claimed is:
1. A method of .[.instrumentation for patients undergoing spinal
treatment and.]. .Iadd.inserting pedicle screws in posterior
vertebrae in a medialized orientation, the method
.Iaddend.comprising: at a first motion segment of the spine,
placing a first pedicle screw entering the cephalad border of the
pars interarticularis at the junction of the caudal aspect of the
inferior facet at one side of the spine; at said first motion
segment, placing a second pedicle screw entering the cephalad
border of the pars interarticularis at the junction of the caudal
aspect of the inferior facet at the other side of the spine; at a
second motion segment of the spine, placing a third pedicle screw
entering the cephalad border of the pars interarticularis at the
junction of the caudal aspect of the inferior facet at the one side
of the spine; .Iadd.and .Iaddend. at the said second motion
segment, placing a fourth pedicle screw entering the cephalad
border of the pars interarticularis at the junction of the caudal
aspect of the interior facet at the other side of the spine.[.;
connecting a first cross support to the first and second pedicle
screws; connecting a second cross support to the third and fourth
pedicle screws; connecting a longitudinal support to said first and
second cross supports; adjusting the relationship of the cross
supports relative to each other; and fixing the cross supports to
the pedicle screws and to the longitudinal support.]..Iadd.,
wherein each of said pedicle screws has a medialized orientation
and a trajectory from medial to lateral.Iaddend..
.[.2. The method of claim 1 and comprising: adjusting the
relationship of the cross supports by changing the distance between
the cross supports..].
.[.3. The method of claim 1 and comprising: adjusting the
relationship of the cross supports by changing the angle of the
first cross support relative to the second cross support in a
plane..].
.[.4. The method of claim 1 and comprising: adjusting the
relationship of the first cross support relative to the second
cross support by rotating the first cross support relative to the
second cross support about a longitudinal axis of said longitudinal
support..].
.[.5. The method of claim 1 and comprising: prior to connecting
said cross supports to said pedicle screws, removing of portions of
spinous processes adjacent said motion segments to establish a
valley at said motion segments; and locating said longitudinal
support in said valley..].
.[.6. The method of claim 5 and further comprising: manipulating
the supports in association with the valley at levels of the spinal
region associated with said motion segments..].
.[.7. The method of claim 6 and further comprising: manipulating
the supports by rotating one of said cross supports relative to the
other cross support about a longitudinal axis of said longitudinal
support..].
.[.8. The method of claim 6 and further comprising: manipulation of
the supports by pivoting one of said cross supports relative to
said other cross support in a plane containing said other cross
support..].
9. The method of claim 1, wherein said step of placing a first
pedicle screw includes orienting a head of said first pedicle screw
in a medialized orientation, and said step of placing a second
pedicle screw includes orienting a head of said second pedicle
screw in a medialized orientation.
10. The method of claim 9, wherein said step of placing a third
pedicle screw includes orienting a head of said third pedicle screw
in a medialized orientation, and said step of placing a fourth
pedicle screw includes orienting a head of said fourth pedicle
screw in a medialized orientation.
11. The method of claim 1, further comprising the step of exposing
at least one of said motion segments only to the facet joints.
.[.12. A method of instrumentation for patients undergoing spinal
treatment and comprising: at a first motion segment of the spine,
placing a first pedicle screw entering the cephalad border of the
pars interarticularis at the junction of the caudal aspect of the
inferior facet at one side of the spine; at said first motion
segment, placing a second pedicle screw entering the cephalad
border of the pars interarticularis at the junction of the caudal
aspect of the inferior facet at the other side of the spine; at a
second motion segment of the spine, placing a third pedicle screw
entering the cephalad border of the pars interarticularis at the
junction of the caudal aspect of the inferior facet at the one side
of the spine; at the said second motion segment, placing a fourth
pedicle screw entering the cephalad border of the pars
interarticularis at the junction of the caudal aspect of the
interior facet at the other side of the spine; connecting a first
cross support to the first and second pedicle screws; connecting a
second cross support to the third and fourth pedicle screws;
connecting a longitudinal support to said first and second cross
supports; fixing the cross supports to the pedicle screws and to
the longitudinal support; and manipulating the supports by moving
telescoping portions of the longitudinal support to provide desired
compression and distraction at vertebral bodies associated with
said motion segments..].
13. The method of claim .[.12.]. .Iadd.1.Iaddend., further
comprising making a laminectomy dissection.
14. The method of claim .[.12.]. .Iadd.1.Iaddend., further
comprising removal of an inferomedial portion of the inferior
facet.
.[.15. The method of claim 12, wherein said manipulating includes
rotating a portion of said longitudinal support relative to another
portion of said longitudinal support..].
16. A method of .[.instrumentation for patients undergoing spinal
treatment and.]. .Iadd.inserting pedicle screws in posterior
vertebrae in a medialized orientation, the method
.Iaddend.comprising: .[.removing some bone from spinous processes
of vertebral bodies adjacent selected motion segments of the spine
to provide cavities at the posterior of the spine;.]. securing a
plurality of pairs of pedicle screws in .[.said.]. vertebral
bodies, one screw of each pair being in a first column at one side
of the spinal foramen, the other screw of each pair being in a
second column at the other side of the spinal foramen, said pedicle
screws having .Iadd.a medialized orientation and .Iaddend.a
trajectory from posterior medial to anterior lateral.[.; using a
plurality of cross supports, each of which cross supports has first
and second opposite ends, and connecting said cross supports to
said pairs by connecting the first end of each cross support to one
screw of one of said pairs, and connecting the second end of said
cross support to the other screw of said one pair; placing in said
cavities, a longitudinal support connected to said cross supports;
manipulating said supports to positions to correct relationship of
some of said vertebral bodies relative to others of said vertebral
bodies; and locking said supports in said positions.]..
17. The method of claim 16 and further comprising: installing said
pedicle screws with trajectory from posterior lateral to anterior
medial.
.[.18. The method of claim 17 and further comprising: projecting
ends of said cross supports from posterior forward around facets to
connect to said pedicle screws..].
19. The method of claim 16 and further comprising: installing said
pedicle screws entering the cephalad border of the pars
interarticularis at the junction of the caudal aspect of the
interior facet, at opposite sides of the spine.
.[.20. The method of claim 16 and wherein: manipulating said
supports includes deforming said longitudinal support..].
.[.21. The method of claim 16 and wherein: manipulating said
supports includes swiveling at least one of said cross supports
relative to said longitudinal support..].
.[.22. The method of claim 21 and wherein: manipulating said
supports includes swiveling more than one of said cross supports
relative to said longitudinal support..].
.[.23. The method of claim 16 and wherein: manipulating said
supports includes changing the length of said longitudinal
support..].
24. The method of claim 16, further comprising the step of
orienting heads of at least one of the pairs of pedicle screws in a
medialized orientation.
25. The method of claim 24, wherein said step of orienting heads
includes orienting the heads of at least two of the pairs of
pedicle screws in a medialized orientation.
26. The method of claim 16, further comprising the step of exposing
at least one of said motion segments only to the facet joints.
.[.27. A method of instrumentation for patients undergoing spinal
treatment and comprising: removing some bone from spinous processes
of vertebral bodies adjacent selected motion segments of the spine
to provide cavities at the posterior of the spine; securing a
plurality of pairs of pedicle screws in said vertebral bodies, one
screw of each pair being in a first column at one side of the
spinal foramen, the other screw of each pair being in a second
column at the other side of the spinal foramen; using a plurality
of cross supports, each of which cross supports has first and
second opposite ends, and connecting said cross supports to said
pairs by connecting the first end of each cross support to one
screw of one of said pairs, and connecting the second end of said
cross support to the other screw of said one pair; placing in said
cavities, a longitudinal support connected to said cross supports;
manipulating said supports to positions to correct relationship of
some of said vertebral bodies relative to others of said vertebral
bodies; and locking said supports in said positions; wherein
manipulating said supports includes rotating a portion of said
longitudinal support relative to another portion of said
longitudinal support..].
28. The method of claim .[.27.]. .Iadd.16.Iaddend., further
comprising .Iadd.the step of .Iaddend.making a laminectomy
dissection.
29. The method of claim .[.27.]. .Iadd.16.Iaddend., further
comprising .[.removal.]. .Iadd.the step .Iaddend.of .Iadd.removing
.Iaddend.an inferomedial portion of the inferior facet.
.[.30. The method of claim 27, wherein said manipulating further
includes moving telescoping portions of the longitudinal support to
provide desired compression and distraction at vertebral bodies
associated with said motion segments..].
31. A method of .[.instrumentation for patients undergoing spinal
treatment and.]. .Iadd.inserting pedicle screws in posterior
vertebrae in a medialized orientation, the method
.Iaddend.comprising: at a first motion segment of the spine,
placing a first pedicle screw having a head, said head of said
first pedicle screw being oriented in a medialized orientation; at
said first motion segment, placing a second pedicle screw having a
head, said head of said second pedicle screw being oriented in a
medialized orientation.[.; at a second motion segment of the spine,
placing a third pedicle screw; at said second motion segment,
placing a fourth pedicle screw, wherein said third and fourth
pedicle screws each have a head, said heads of said third and
fourth pedicle screws being oriented in a medialized orientation;
connecting a first cross support to the first and second pedicle
screws; connecting a second cross support to the third and fourth
pedicle screws; connecting a longitudinal support to said first and
second cross supports; and fixing the cross supports to the pedicle
screws and to the longitudinal support.]..Iadd., and said pedicle
screws each have a trajectory from posterior medial to anterior
lateral.Iaddend..
.[.32. The method of claim 31, further comprising the step of
adjusting the relationship of the cross supports relative to each
other..].
.[.33. The method of claim 32, wherein said adjusting step includes
at least one of distraction, compression and rotation..].
.[.34. A method of instrumentation for patients undergoing spinal
treatment and comprising: removing bone from spinous processes of
vertebral bodies adjacent selected motion segments of the spine;
securing a plurality of pairs of pedicle screws in said vertebral
bodies, one screw of each pair being in a first column, the other
screw of each pair being in a second column; using a plurality of
cross supports, each of which cross supports has first and second
opposite ends, and connecting said cross supports to said pairs by
connecting the first end of each cross support to one screw of one
of said pairs, and connecting the second end of said cross support
to the other screw of said one pair; placing a longitudinal support
connected to said cross supports; manipulating at least said
longitudinal support to correct a relationship of some of said
vertebral bodies relative to at least another of said vertebral
bodies, said manipulating including at least one of rotating a
portion of said longitudinal support relative to another portion of
said longitudinal support and moving telescoping portions of the
longitudinal support..].
.Iadd.35. A method for implanting a bone anchor in a vertebra in a
medialized orientation, comprising the steps of: exposing a
posterior portion of the vertebra; locating a starting position on
a medial inferior portion of the vertebra relative to a superior
facet; and angling the bone anchor from the starting position along
a trajectory extending laterally away from a midportion of the
vertebra as the bone anchor protects anteriorly from the posterior
portion of the vertebra. .Iaddend.
.Iadd.36. The method of claim 35, wherein the exposing step further
comprises the step of performing a laminectomy exposure.
.Iaddend.
.Iadd.37. The method of claim 35, wherein the locating step further
comprises the step of identifying the cephalad border of the pars
interarticularis at the junction of the caudal aspect of the
inferior facet. .Iaddend.
.Iadd.38. The method of claim 35, further comprising the step of
angling the bone anchor in a cephalad direction. .Iaddend.
.Iadd.39. The method of claim 38, wherein the angling the bone
anchor in the cephalad direction step includes angling the bone
anchor approximately 20.degree.. .Iaddend.
.Iadd.40. The method of claim 35, further comprising the step of
drilling a small opening in cortical bone along the trajectory
extending laterally away from the midportion of the vertebra as the
bone anchor projects anteriorly from the posterior portion of the
vertebra. .Iaddend.
.Iadd.41. The method of claim 40, further comprising the step of
tapping the small opening. .Iaddend.
.Iadd.42. The method of claim 35, wherein the bone anchor has a
length of 25 to 30 mm. .Iaddend.
.Iadd.43. The method of claim 35 wherein the trajectory crosses
cortical bone such that the bone anchor bicortically purchases in
the vertebra. .Iaddend.
.Iadd.44. The method of claim 35, wherein the starting point for a
cephalad level is inferior to the starting position for a caudal
level. .Iaddend.
.Iadd.45. A method of implanting a bone anchor in a vertebra in a
medialized orientation, comprising the steps of: performing a
laminectomy exposure to expose a posterior portion of the vertebra;
and angling the bone anchor along a trajectory extending laterally
away from a midportion of the vertebra as the bone anchor projects
anteriorly from the posterior portion of the vertebra.
.Iaddend.
.Iadd.46. The method of claim 45, further comprising the step of
locating a starting position for the bone anchor, wherein the
starting position is the cephalad border of the pars
interarticularis at the junction of the caudal aspect of the
inferior facet. .Iaddend.
.Iadd.47. The method of claim 45, further comprising the step of
angling the bone anchor in a cephalad direction. .Iaddend.
.Iadd.48. The method of claim 47, wherein the angling the bone
anchor in the cephalad direction step includes angling the bone
anchor approximately 20.degree.. .Iaddend.
.Iadd.49. The method of claim 45, further comprising the step of
drilling a small opening in cortical bone along the trajectory
extending laterally away from the midportion of the vertebra as the
bone anchor projects anteriorly from the posterior portion of the
vertebra. .Iaddend.
.Iadd.50. The method of claim 49, further comprising the step of
tapping the small opening. .Iaddend.
.Iadd.51. The method of claim 45, wherein the bone anchor has a
length of 25 to 30 mm. .Iaddend.
.Iadd.52. The method of claim 45 wherein the trajectory crosses
cortical bone such that the bone anchor bicortically purchases in
the vertebra. .Iaddend.
Description
FIELD OF THE INVENTION
The present invention relates to medical devices, and, more
particularly, to spinal fixation systems and related methods.
BACKGROUND OF THE INVENTION
Spinal fixation systems may be used to correct and stabilize the
position of vertebral segments within a patient's spine. Such
correction may be necessary as a result of accidents, degenerative
diseases, etc. Typical spine fixation systems in use today include
pedicle screws attached to the posterior of a patient's vertebrae
in a vertical column along either one or both sides of the spine. A
rod is connected to the heads of each pedicle screw in a column to
provide support for the spine. Examples of such prior art devices
may be seen in U.S. Pat. No. 5,741,255 entitled "Spinal Column
Retaining Apparatus" to Krag et al. and U.S. Pat. No. 6,187,005
entitled "Variable Angle Spinal Fixation System" to Brace et
al.
Unfortunately, when the above prior art systems are inserted in a
patient, the pedicle screws are typically positioned such that the
head of each pedicle screw angles outward away from the center of
the spine (i.e., in a lateral orientation). Because of this screw
angle and the fact that the support rods are mounted at about the
same height as the pedicle screw heads, there is a significant
amount of trauma to the back muscles when this system is installed.
This, in turn, leads to a significant amount of pain after the
surgery as well as a long recovery time.
Another spinal fixation system is disclosed in U.S. Pat. No.
5,628,740 entitled "Articulating Toggle Bolt Bone Screw" to
Mullane. This spinal fixation system is designed for anterior
attachment to a patient's spine and includes two columns of screws
on either side of the spine with a single support rod as
therebetween attached to the screws by clamps, as may be seen in
FIG. 5 of the patent. However, while such anterior spinal fixation
systems may not cause as severe trauma to back muscles (since they
are installed on the opposing side of the spine from the back
muscles), it may not be possible to install such devices at certain
positions on the spine.
Another limitation of the above systems is that their support rods
are typically formed as a unitary piece. Even though such support
rods typically have some degree of flexibility, they may not be
able to accommodate spines that require correction in multiple
directions.
SUMMARY OF THE INVENTION
The invention involves apparatus and method for minimizing the
height of profile of spinal implants employed for correcting and
stabilizing the position of vertebral segments within a patient's
spine. Fasteners are secured in two columns, one on each side of
the center of the spine. Cross members are connected to the
fasteners and support a spinal rod in space provided by removal of
portions of spinous processes involved in the treatment of the
patient. In some embodiments, the spinal rod is a one-piece item,
and in other embodiments it is a multi-piece assembly with cross
supports fixed to longitudinal portions at certain locations and
cross supports swiveled to longitudinal portions at other
locations. The spinal rod also has portions longitudinally slidable
for selectively increasing or decreasing spacing between cross
supports. Rotatable or swivel joints are provided according to
other features of the invention to enable relative rotation between
cross supports about axes of spinal rod portions connecting such
cross supports.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of one embodiment of apparatus
according to the present invention.
FIG. 2 is an exploded view of one of the combinations of pedicle
screw, connector arm and ring assembly of the embodiment of FIG.
1.
FIG. 2A is a fragmentary view showing a yoke-type pivoting end on
the connector arm instead of the ring-type in FIG. 2.
FIG. 3 is a perspective view similar to FIG. 1 but of apparatus
according to another embodiment using a different type of pedicle
screw and mounting brackets for the support rods.
FIG. 4 is a posterior view of the lumbar region of the spine with
articulating apparatus according to still another embodiment of the
present invention secured thereon.
FIG. 5 is an enlarged perspective view of a portion of a typical
component used the embodiment of FIG. 4.
FIG. 6 is a posterior view of a scoliotic spine and employing the
instrumentation using the construct of the type shown in FIG.
5.
FIG. 7 is a posterior view of the spine of FIG. 6 after using the
constructs for rotation.
FIG. 8 is a posterior view of the spine ready to complete the
straightening.
FIG. 9 is a posterior view of the spine following completion of
straightening.
FIG. 10 is a perspective view of the FIG. 5 type of construct with
the interfitting telescopic tubing portions of the articulating rod
assembly extended to increase spacing between the cross rods
(tubes) at an intervertebral location between spinal segments.
FIG. 11 is a view like FIG. 10 but with the tubing portions
retracted as for compression.
FIG. 12 is an example where the cross rods are at a distance
intermediate those of FIGS. 10 and 11 but rotated 90 degrees
relative to each other about the colinear axes of the telescoping
tubing portions.
FIG. 13 is an arrangement in which the cross rods are centered at
essentially the same distance as in FIG. 12 and co-planar but
oriented at converging angles in the same plane.
FIG. 14 is a view like FIG. 4 but showing another embodiment
wherein the cross rods are formed in an anterior direction near
their ends to enable pedicle screw installation from posterior
lateral to anterior medial.
FIG. 15 is an enlarged perspective view of the support construct
for the embodiment of FIG. 14.
FIG. 16 shows a technique in which the loose, segmented construct
of the previous illustrations is supported by a temporary rod
during manipulation of the cross rods to correct a deformity.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
Turning now to FIGS. 1-2, one embodiment of a spinal fixation
system according to the present invention includes two columns 21,
22 of pedicle screws along each side of a patient's spine and a
single support rod 23 positioned between the two columns (i.e.,
substantially in the center of the spine) and connected to each of
the pedicle screws. An example of the connection is shown in the
exploded view of FIG. 2 where the pedicle screw 24 has a yoke at
the top receiving a proximal end of connector arm 26 retained in
the yoke by hinge pin 27, received through aperture 28 in the arm
and fixed there by locking screw 29. At the distal end 26D of the
arm 26, a ring 31 is connected by multi-axial hinge at 32 and
through which the rod 23 is received as shown in FIG. 1 and secured
in place by a locking screw 34. FIG. 2A is an example in which a
multi-axial screw head 31A on stem 32A with locking screw 34A is
substituted for ring 31 of FIGS. 1 and 2. Screw head and stem are
of the Medtronic Sofamor Danek, Inc. (MSD) M-8 type mentioned
below, but without stem threads.
One advantage of this configuration is that the support rod may
protrude less than with typical prior art systems. This is due
partly to the fact that the pedicle screws may be angled so the
heads of the screws are angled in toward the center of the spine
(i.e., a medialized orientation), causing less interference with
the back muscles. Also, during the installation of spinal fixation
systems, and as shown in FIG. 4, for example, some bone structure
may be removed in the center of the vertebrae, which creates a
cavity or valley 36. According to the invention, the rod may be
recessed within this cavity to further reduce the profile of the
device once installed.
As mentioned above, poly-axial hinges may be used to attach the
pedicle screws to the support rods. More particularly, a pin 27 and
locking screw 29 may be used to attach the poly-axial hinge to the
screw head, as seen in FIG. 2. In yet another embodiment
illustrated in FIG. 3, M-8 type locking pedicle screws 37 as shown
in U.S. Pat. No. 6,280,442 and manufactured by the Medtronic
Corporation (MSD), for example, may be used with cross-supports 39
extending therebetween. The support rod 41 may be carried by
mounting brackets 42 attached to the cross-supports, which may
preferably be aligned with the center of the spine. This embodiment
may too incorporate the medialized pedicle screw orientation. Of
course, those of skill in the art will appreciate that the various
embodiments described herein may advantageously use either the
current laterally positioned screws or the medialized
orientation.
Still other embodiments of the invention may be understood with
reference to FIGS. 4-16. These embodiments are directed to
articulating spinal fixation systems which may be particularly
useful for controlled segmental correction. For example, the
centralized articulating system may be used for applications such
as deformity of the adult lumbar spine, e.g., scoliosis and
possibly for applications toward idiopathic scoliosis, in addition
to traditional applications.
The articulating spinal fixation systems illustrated in FIGS. 4-16
may include medialized columns of pedicle screws 37 on either side
of the spine, cross rods 46, 47 (FIG. 5) extending between adjacent
pedicle screws in each column, and an articulating rod 48 carried
by the cross rods. The articulating rod may advantageously provide
distraction (FIG. 10) compression (FIG. 11) in the cephalad-caudal
plane, rotational correction (FIG. 13) in the coronal plane, and
rotational correction in the cross sectional plane (FIG. 12), as
will be appreciated by those of skill in the art. For correction of
degenerative scoliosis and its associated deformity, correction in
all three of these planes may be achieved according to the present
invention. The articulating system of the present invention may
allow this to occur in the lumbar spine over several segments
(FIGS. 4 and 14).
A key feature of the articulating system according to the invention
is that it provides controlled correction at each segment (FIG. 6).
The surgical approach for installing this system may include
installing the screws 37 and cross bars with the associated central
linking articulating system components of FIG. 5. Then, at each
segment (FIG. 6), compression (L4-L5) distraction (L1-L2) rotation
(L2-L4) may be performed to facilitate a final controlled segmental
correction.
If there were no correction of deformity required, the articulating
system could easily be allowed to lock by lock screw 51 (FIGS. 5
and 15), or the illustrated hinge or ball-in-socket mechanisms at
52 may be locked or omitted. A distraction and compression
mechanism (telescoping tube portions 53 and 54 with position lock
screw 51) of the articulating system may be used to increase
intervertebral distance for neural foraminal patency. This is
advantageous over dual-rod prior art systems such as those
described above in that stresses are applied to all four screws
simultaneously, thus decreasing the stress at any one or two of the
screws in distraction and compression. This may have a specific
benefit in osteoporotic bone.
Again, as shown in FIG. 14 with construct componentry of FIG. 15,
the articulating system may advantageously be used with the current
lateralized position screws 37 for those surgeons who do not wish
to consider a medialized orientation or for special applications
which may require such an orientation. For example, for very severe
deformities such as Grade III or Grade IV spondylolisthesis, the
aberrant anatomy is such that it may be best in these circumstances
to either leave the screws higher to cross over the dura or to go
to a longitudinal construct.
It will be appreciated by those of skill in the art that the
articulating system of the present invention allows surgeons
greater control in soft bone for degenerative spines. It may
further allow greater capture of the pedicle screws in cortical
bone for osteopenic patients with less screw pull out. This may
allow greater manipulation of deformity in the elderly spine. This
may be particularly difficult with prior art systems because of the
weakness of the bone which may cause the pedicle screws to cut
through or pull out.
Medial orientation of the pedicle screws may also allow coverage
over the muscle to be significantly enhanced. Thus, dissection over
the posterolateral recess may not be necessary for lateral grafting
with a posterior lumbar interbody fusion (PLIF) approach,
especially with the advent of bone morphogenetic protein (BMP).
Further, the present invention facilitates the concept of a
posterior tension band with anterior column fusion and may also
have significant application with regard to absorbable systems, as
will be appreciated by those of skill in the art.
Traditional methods for placement of pedicle screw instrumentation
in the lumbar and thoracic spine involve identifying bony landmarks
and following a trajectory from posterior lateral to anterior
medial, as will be understood by those of skill in the art. A
method aspect of the present invention is directed to a method
which starts more medially and follows a lateral trajectory for
pedicle screw insertion (i.e., posterior medial to anterior
lateral). The method of present invention provides several
advantages over prior art methods. For example, narrower exposure
may be required. That is, traditional methods call for dissection
to the tips of the transverse process. This may result in a wide
band of muscle that is stripped from the bone, de-innervated, and
potentially experiences compromised blood supply. By only exposing
to the facet joints, this limitation may be dramatically
reduced.
Yet another advantage is that the implant mass may be moved to the
midline. Medialized instrumentation places the bulk of the mass
more toward the midline where massive structures (like the spinous
process) are typically found anyway. This permits the muscles to
reapproximate naturally back into position once the instrumentation
is placed. Additionally, improved biomechanical control and
correction of spinal deformity is facilitated.
Traditionally, lateral positioned pedicle screws have been utilized
historically for the past 15 or 20 years. The positioning of the
screw involves a starting point at the midportion of the transverse
process at the lateral wall midportion of the superior facet. The
trajectory really begins anywhere from 30 to 40 degrees lateral to
a medial position and in the pedicle, transversing toward the
midline of the vertebral body along the cephalad border. This
progresses up to the lumbar spine to about a 20 degree position or
so at the higher lumbar levels.
The method of medialized pedicle screw instrumentation according to
the present invention may improve surgical outcome in the use of
instrumentation for patients undergoing lumbar stabilization
procedures, for example. It has been identified that the dorsal
cortex of the transverse process is a critical area of maintenance
of bony structure to facilitate holding of the pedicle screw
laterally.
The medialized approach of the present invention involves entering
the bony construct from the medial inferior portion on the facet,
rather than a lateral position. That is, it involves a different
trajectory than with prior art systems. Advantages of this method
may include ease of insertion, harder and more abundant cortical
bone for fixation of screws, smaller screw sizes, potentially less
metal in the spine, more favorable trajectory from medial to
lateral to reduce the potential for injury of the neural
structures, better muscle coverage, easy metal removal and better
muscle physiology.
According to the present invention, a laminectomy dissection may be
required, i.e., not a typical lateral dissection for posterolateral
screw placement, for example. This facilitates reduced stripping of
the paravertebral muscles from the transverse processes and reduced
denervation of paravertebral muscles. It has been noted in the past
that a typical laminectomy incision is less painful and less
debilitating than a typical exposure for a lumbar posterolateral
fusion. This represents a marked advantage for patient outcome,
recovery and postoperative healing.
An initial starting point is identified at the cephalad border of
the pars interarticularis at the junction of the caudal aspect of
the inferior facet. Along the pars interarticularis at the cephalad
border approximately at the perpendicular midportion of transverse
process, the pedicle may be identified. This may be visualized
after laminectomy, especially from the medial position. The
egressing nerve roots beneath the pedicle from cephalad to an
inferolateral direction may easily be identified along with the
pedicle cortical medial wall.
Two points of entry are possible, for example. Through standard
laminectomy the inferomedial portion of the inferior facet may be
removed to prevent any abutment against the screw. This does not
necessarily involve any more removal of facet than is done with a
typical laminectomy. Using a drill, a small starting point may be
made in the cortical bone with the direction approximately neutral
to 10 degrees medial and the drill may be directed approximately 10
degrees cephalad. The uppermost screw position may be directed more
cephalad based on the preoperative CT scan after approximating the
angle of the vertebral body endplate compared to the
perpendicular.
Using the drill lightly, a small opening may be made in the
cortical bone drilling in the appropriate trajectory. Next,
appropriate, sharp bone taps may be used because of the greater
content of cortical bone in this region. Forces are preferably
directed away from the cauda equina in the trajectory. To avoid any
facet impingement, by starting the entry, slight caudal pointing to
the above starting point at the cephalad border of the pars
interarticularis and then angling in the cephalad direction
approximately 20 degrees may be performed. This may create a
cephalad angulation of the screw and thereby alleviate abutment of
the inferior articulating facet.
The lower levels to be included in the fusion need not be of
concern, since these facet joints may be included in the fusion
mass itself. By way of example, 5.5 mm and 6.5 mm screws can fit in
this trajectory fairly well. With anterior column support, such as
allograft or cage, smaller size screws may be used, such as 4.0 or
4.5 mm, for example. Of course, other screw sizes may also be used
in accordance with the present invention. Generally, the smaller
the screw size, the easier the insertion and the greater the range
for placement of the screw.
Because of the above trajectory and because of the significant
increased amount of cortical bone, the typical 40 to 45 mm length
screws used for lateral position may not be required. For example,
it has been found that 25 mm screws facilitate excellent hold in
this position because of the increased cortical bone. Yet, screws
longer than 25 to 30 millimeters are not preferred for secondary to
possible lateral exit or penetration of the vertebral body margin.
Bicortical purchase, of course, is an option of the surgeon and
certainly can be accomplished with careful technique, as will be
appreciated by those of skill in the art.
Once the pedicle screws are positioned bilaterally, it is noted
that the articulating heads of the M-8 system, for example, may be
more centralized and approximate the area of the spinous process
rather than lateral to the facet obstructing the paravertebral
muscles. This facilitates greater ease of instrumentation. The
surgeon may not be required to pull the paravertebral muscles
laterally trying to access a lateral starting point. In patients
with very deep spine dissections, this may facilitate a much
greater ease of the instrumentation because the instrumentation is
placed centrally and the surgeon can work from one side of the
table.
The rods may be placed in the usual fashion with a typical
medialized approach or a central construct system. The central mass
of metal is now in a natural physiologic position (spinous process
mass) thereby being recognized as a normal physiologic position to
the paravertebral muscles. Next, the rods may be placed from
cephalad to caudad or transversely based on a new concept of the
central construct system.
Cross rods or links may also be utilized in a more rigid fashion
with an inverted "V" relationship of the screws to the spine. Once
again, the mass of metal may remain centralized. The paravertebral
muscle may easily reapproximate with a low profile system, such as
that of the present invention. There is a normal physiological
position over the facet with the ease of closure of the wound.
Normal tension of the paravertebral muscles may be recreated, which
is not possible with a lateral position screw system.
Furthermore, there may be less "dead space" for wound healing
beneath the spinal fixation systems of the present invention
compared to a lateral construct. Again, this facilitates less
postoperative drainage, seroma and other possible complications of
hematoma. The initial recovery is facilitated to a significant
degree due to the method and systems of the present invention. The
above method may be used in conjunction with the PLIF technique
with anterior construct and/or a facet fusion from a medialized
approach rather than a posterolateral fusion.
It is believed that there will be a learning curve to developing
the appropriate surgical technique to facilitate the above methods,
and it is recommended appropriate instruction be done with
cadaveric work before instrumentation with patients. This method
for medialized pedicle instrumentation according to the present
invention differs from the classic lateral position screw technique
in that: 1. Paravertebral muscle mass stripping may not be required
which results in much less dissection and thus reduces denervation
of the paravertebral muscles, facilitating postoperative recovery
and closure of the wound; 2. In deep spine patients with difficult
exposure, the medial approach allows ease of placement of
instrumentation with forces directed away from the neural elements,
thus reducing neurological injury; 3. Placement in significant
cortical bone facilitates greater control and deformity correction
in osteoporotic and elderly spinal patients with degenerative
spondylosis; 4. In thin patients with very poor coverage of
hardware, medialization of the hardware allows better coverage than
posterolateral screw positioning; and 5. Removal of hardware (which
may need to be done for various surgical reasons) is facilitated by
the medial approach because the rods and screws are all
centralized. Thus, much less dissection is required in the removal
of the instrumentation of the present invention than in typical
prior art lateral spinal fixation systems.
If the surgeon elects to continue with posterolateral
intertransverse process fusion, the medial approach allows for
significant exposure of the posterior bony areas for fusion
compared to the typical lateral constructs. The medialized approach
potentially represents a marked advantage and improvement over the
standard technique of lateral positioning for the care of patients
with lumbar disorders and facilitates minimal access to the
clinical surgical approach to the lumbar spine. The construct of
FIGS. 14 and 15 facilitates this, and in this case, the end
portions of the cross bars 146 and 147 are provided with a slight
posterior to anterior orientation as at location 146A and 147A to
go around the facets and enable the lateral trajectory of the bone
screws 37 from the outside to the inside. So in this embodiment the
cross bars are slightly longer from end-to-end than in the FIGS. 4
and 5 embodiment, but the telescoping tube portions 153 and 154 are
the same and can use a swivel of the pin-type 52 or the ball and
socket type, located as in the FIGS. 4 and 5 embodiment.
Referring to FIG. 16 for an example, a loose (locking screws not
tight) segmental construct as in FIG. 5, or as in FIG. 15, is
placed at a spinal site with the ends of the cross bars attached to
the heads of the pedicle screws. A solid rod 56 is temporarily
attached to cross rods 46 and 47 with eyebolts 57 and 58. Then the
rods 46 and 47 are rotated (arrow 59) relative to each other to
correct a deformity. Then locking screws are tightened to tighten
the construct. Then the temporary rod 56 and eyebolts 57 and 58 are
removed.
Many modifications and other embodiments of the invention will come
to the mind of one skilled in the art having the benefit of the
teachings presented in the foregoing descriptions and the
associated drawings. Therefore, it is to be understood that the
invention is not to be limited to the specific embodiments
disclosed, and that other modifications and embodiments are
intended to be included within the scope of the invention as
defined by the appended claims, in some of which the term "motion
segment" is to be understood as a location in the spine where
motion is achieved through a combination of two vertebral bodies
with an intervertebral disc in-between.
* * * * *