U.S. patent application number 16/806059 was filed with the patent office on 2020-09-10 for spinal implant system and method.
The applicant listed for this patent is Gregory Poulter. Invention is credited to Gregory Poulter.
Application Number | 20200281629 16/806059 |
Document ID | / |
Family ID | 1000004737320 |
Filed Date | 2020-09-10 |
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United States Patent
Application |
20200281629 |
Kind Code |
A1 |
Poulter; Gregory |
September 10, 2020 |
Spinal Implant System and Method
Abstract
A spinal construct is based on a fixed contour rod and modified
bone screws configured to account for different height and angular
offsets between the rod and the spinal anatomy. The rod contour is
adapted for percutaneous introduction thereby eliminating the need
for open spinal surgery for multi-level constructs.
Inventors: |
Poulter; Gregory;
(Zionsville, IN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Poulter; Gregory |
Zionsville |
IN |
US |
|
|
Family ID: |
1000004737320 |
Appl. No.: |
16/806059 |
Filed: |
March 2, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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62815669 |
Mar 8, 2019 |
|
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|
62914424 |
Oct 12, 2019 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 17/7032 20130101;
A61B 17/7013 20130101 |
International
Class: |
A61B 17/70 20060101
A61B017/70 |
Claims
1. A bone screw for fixation in a vertebral body of a spine,
comprising: an elongated shank having bone engaging threads and
defining a longitudinal axis; and a rod-engaging portion connected
to one end of said elongated shank, said rod-engaging portion
defining a channel for receiving a spinal rod therein, wherein said
channel is defined at a non-perpendicular angle relative to said
longitudinal axis of said shank.
2. The bone screw of claim 1, further comprising a set screw
threaded into said rod-engaging portion, said set screw including a
tip arranged to engage the spinal rod received within said channel
to clamp the rod within the rod-engaging portion, wherein said tip
is conical and defined at said non-perpendicular angle.
3. The bone screw of claim 1, wherein said non-perpendicular angle
is between 5.degree. and 45.degree. measured from a line that is
perpendicular to said longitudinal axis.
4. A kit for use in forming a spinal construct, comprising a
plurality of screws according to claim 3, each having said channel
defined at a different non-perpendicular angle.
5. The kit of claim 4, wherein said plurality of screws have
non-perpendicular angles provided in 5.degree. increments.
6. A bone screw for fixation in a vertebral body of a spine,
comprising: an elongated shank having bone engaging threads and
defining a longitudinal axis; and a rod-engaging portion connected
to one end of said elongated shank, said rod-engaging portion
defining a vertical axis and a channel for receiving a spinal rod
therein oriented perpendicular to said vertical axis, wherein said
rod-engaging portion is connected to said elongated shank so that
said longitudinal axis is not colinear with said vertical axis.
7. The bone screw of claim 6, further comprising a set screw
threaded into said rod-engaging portion to engage the spinal rod
received within said channel to clamp the rod within the
rod-engaging portion.
8. The bone screw of claim 6, wherein said longitudinal axis is
oriented at an angle relative to said vertical axis, wherein said
angle is between 5.degree. and 45.degree..
9. A kit for use in forming a spinal construct, comprising a
plurality of screws according to claim 8, each having said angle
different from the other screws.
10. The kit of claim 9, wherein said plurality of screws have
angles provided in 5.degree. increments.
11. A bone screw for fixation in a vertebral body of a spine,
comprising: an elongated shank having bone engaging threads and
defining a longitudinal axis; a rod-engaging portion defining a
channel for receiving a spinal rod therein oriented perpendicular
to said vertical axis; and an intermediate portion connecting said
rod-engaging portion to said elongated shank, said intermediate
portion having a height along said longitudinal axis of at least
0.5 mm.
12. The bone screw of claim 11, further comprising a set screw
threaded into said rod-engaging portion to engage the spinal rod
received within said channel to clamp the rod within the
rod-engaging portion.
13. The bone screw of claim 11, wherein said height is less than 30
mm.
14. A kit for use in forming a spinal construct, comprising a
plurality of screws according to claim 13, each having different
heights ranging from 0.5 mm to 30 mm.
15. The kit of claim 14, wherein said plurality of screws are
provided with heights at 0.5 mm increments.
16. A kit for forming a spinal construct for correcting a number of
vertebral levels of a patient's spine, comprising: an elongated rod
defining a fixed curved contour adapted for percutaneous
introduction along a patient's spine, said fixed curved contour
being offset from the patient's spine by different offsets at
different vertebral levels; and a plurality of bone screws having;
an elongated shank with bone engaging threads and defining a
longitudinal axis; and a rod-engaging portion defining a channel
for receiving the spinal rod therein, wherein said rod-engaging
portion is attached to said elongated shank at different heights
along said longitudinal axis, each of said different heights
corresponding to each of said different offsets.
17. A kit for forming a spinal construct for correcting a number of
vertebral levels of a patient's spine, comprising: an elongated rod
defining a fixed curved contour adapted for percutaneous
introduction along a patient's spine, said fixed curved contour
being non-perpendicular relative to an optimum insertion angle for
a bone screw into vertebral bodies at different vertebral levels;
and a plurality of bone screws having; an elongated shank with bone
engaging threads and defining a longitudinal axis; and a
rod-engaging portion defining a channel for receiving the spinal
rod therein, wherein said elongated shank is attached to said
rod-engaging portion at different non-perpendicular angles to align
with the optimum insertion angle for a bone screw at each of the
different vertebral levels.
Description
PRIORITY CLAIM
[0001] This application is a utility filing form and claims
priority to co-pending U.S. Provisional No. 62/815,669, filed on
Mar. 8, 2019, and to co-pending U.S. Provisional No. 62/914,424,
filed on Oct. 12, 2019. The disclosures of both provisionals, along
with the appendices filed with the provisional applications, are
incorporated herein by reference.
BACKGROUND
[0002] Spinal surgery and spinal implants have advanced
considerably over the last half-century, resulting in an increased
number of fusion surgeries performed each year. The current
generation of spinal implants and procedures are designed to allow
the safe application of spinal fixation with a great amount of
customization to accommodate significant patient to patient
variation in anatomy and alignment. However, in some respects, the
flexibility allowed by current designs sacrifices the ability of
these implants to control spinal alignment. In fusion surgery,
achieving the correct spinal alignment is critical to achieve
improved patient outcomes. The current state of the art use of rod
and screw constructs to control spinal alignment involves one of
two techniques. The first involves placing rods that are contoured
to the patient's spine and then manipulating the rods by bending
them or compressing/distracting on screws to effect alignment. The
other technique involves creating rods from a preoperative plan
that are custom shaped to the patient's desired alignment and then
bringing the patients spine into alignment by reducing the screws
to the rods in surgery.
[0003] The first minimally invasive surgeries were generally
limited to discectomies and fusions at one or two vertebral levels.
Rod fixation for correcting spinal deformities were more
problematic for minimally invasive techniques due to the need to
introduce a long, curved rod spanning multiple vertebral levels.
Early techniques were developed for minimally invasive lumbar
fixation using shorter curved rods that can easily be placed over a
short segment of the spine. Attempts to expand these minimally
invasive techniques to larger fusions has been limited as the
geometry of the human spine necessitates a rod contour that cannot
be introduced using a minimally invasive technique. To date,
current rods, whether they are hand bent or pre-contoured, are
designed to match the desired spinal curvature and thus are limited
in their application of minimally invasive surgery.
[0004] Instrumentation for minimally invasive fusion systems
include modifications of the standard pedicle screws and rods that
allow them to be placed through small incisions in the skin.
Placing a connecting rod through the tops of the screws requires
that the screws line up with the shape of the rod that is being
placed. This requirement for precise alignment has limited the
application of minimally invasive techniques to fusions of only a
small number of levels. In recent years, computer aided
pre-surgical planning systems have allowed greater precision. This
precision stems from the ability to develop a detailed
pre-operative plan and the ability to precisely place the implants
according to that plan. This technology has expanded the
capabilities of both standard and minimally invasive techniques by
allowing the minimally invasive placement of screws and rods from
the lower thoracic spine, across the lumbar spine to the pelvis.
Even though the pre-surgical planning systems have addressed one of
the primary limitations of minimally invasive deformity surgery,
the current procedures are still limited by the curved shape of the
rod.
[0005] In a typical procedure, the rod is pre-shaped or is manually
bent at the time of surgery to a lordotic curve that matches the
desired lordotic shape of the spine. This, however, can create
extreme difficulty in placing the rod, particularly for correcting
an extremely deformed spine. Another problem is that bending the
spinal rod inherently weakens the rod to some degree at the bend
points. A further difficulty arises from a rod bent to a lordosis
matching the spine in which the rod is too curved to pass easily
through the soft tissue of the patient when attempting to perform
procedures spanning several vertebral levels. In cases that include
fusions of multiple levels, particularly those spanning the lower
lumbar spine, a minimally invasive insertion of the rods is not
possible and necessitates an opening of the spine with a large
incision. Although pre-planning screw and rod placements and
advances in rod bending techniques have greatly improved spinal
surgery, there is still a significant need for a spinal construct
and surgical technique that can overcome the detriments noted
above.
SUMMARY OF THE DISCLOSURE
[0006] The technology of the present disclosure differs
substantially from the pre-existing techniques as it involves using
rods that are of standard dimensions and controlling the shape of
the spine by controlling the relationship between the spine and
rods by a combination of screw placement and angular control of the
spine with implants that are rigid in the sagittal plane. This
technique first involves creating a computerized 3-dimensional
model of spines desired shape. Then preexisting rods are added to
the model of the spine. The variation between the two is bridged by
precise screw placement. This technique works for longer fusion
constructs of multiple levels. Shorter constructs require the
screws and rods to interact with each other at precise angles to
establish the desired angular relationships. This requires the use
of implants that are constrained in the sagittal plane to control
the sagittal alignment for short constructs. Larger constructs may
have their alignment controlled both by a combination of screws
placement as well as fixed angular relationships between the rods
and screws.
[0007] One difference between the method disclosed herein and
current techniques is that the proposed system uses rods of a
predefined shape and plans the screw depth and angular relationship
to the rods. The goals of the system are to provide control of the
patient's spinal alignment in fusion surgery for both long and
short fusion constructs utilizing standardized (not patient
specific implants) in both minimally invasive and open
applications. Current rod/screw constructs are also limited in
their application of minimally invasive surgery in long constructs
that span the lumbar spine.
[0008] Accordingly, in one aspect of the disclosure, a bone screw
for fixation in a vertebral body of a spine is provided that
comprises an elongated shank having bone engaging threads and
defining a longitudinal axis, and a rod-engaging portion connected
to one end of the elongated shank. The rod-engaging portion defines
a channel for receiving a spinal rod therein, wherein the channel
is defined at a non-perpendicular angle relative to the
longitudinal axis of the shank. In particular, the channel can be
defined at an angle of between 5.degree. and 45.degree.. A kit can
be provided that includes a plurality of such screws with different
non-perpendicular angle so that the surgeon can select an optimum
screw for a particular vertebral level.
[0009] In another aspect, another bone screw for fixation in a
vertebral body of a spine includes a rod-engaging portion that is
connected to the elongated shank so that the longitudinal axis of
the shank is not colinear with a vertical axis through the
rod-engaging portion. In particular, the longitudinal axis can be
oriented at an angle relative to the vertical axis of between
5.degree. and 45.degree.. A kit can be provided that includes a
plurality of such screws with different angles so that the surgeon
can select an optimum screw for a particular vertebral level.
[0010] In another feature of the present disclosure, a bone screw
for fixation in a vertebral body of a spine is provided that
includes an elongated shank having bone engaging threads and
defining a longitudinal axis, a rod-engaging portion defining a
channel for receiving a spinal rod therein oriented perpendicular
to the vertical axis, and an intermediate portion connecting the
rod-engaging portion to the elongated shank. The intermediate
portion has a height along the longitudinal axis of between 0.5 mm
and 30 mm. A kit can be provided that includes a plurality of such
screws, each having different heights so that the surgeon can
select an optimum screw for a particular vertebral level.
[0011] The kits can include an elongated rod defining a fixed
curved contour adapted for percutaneous introduction along a
patient's spine. The fixed curved contour will ordinarily be offset
from the patient's spine by different height and angular offsets at
different vertebral levels. The surgeon can select among the screws
described above to achieve coronal and sagittal correction of the
patient's spine. The devices, kits and methods disclosed herein can
be used for a wide range of spinal procedures and across any number
of vertebral levels. Thus, while the present disclosure
demonstrates the use of the devices, kits and methods in the
correction of scoliosis, this disclosure is merely for illustrative
purposes. The same devices, kits and methods can be used for shorer
constructs, spanning only one or two vertebral levels.
DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is an X-ray image of a spine showing a conventional
spinal rod for fixation and a modified rod according to the present
disclosure.
[0013] FIG. 2 is a representation of the spine in the sagittal
plane showing the modified rod of the present disclosure.
[0014] FIG. 3 is diagram of the curvature of the modified rod of
the present disclosure.
[0015] FIG. 4 is a representation of the spine in the sagittal
plane with the modified rod and bone screws of the present
disclosure.
[0016] FIG. 5 is a view of a bone screw according to one aspect of
the present disclosure.
[0017] FIG. 6 is a view of a bone screw according to another aspect
of the present disclosure.
[0018] FIG. 7 is a view of a bone screw according to a further
aspect of the present disclosure.
DETAILED DESCRIPTION
[0019] For the purposes of promoting an understanding of the
principles of the disclosure, 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 disclosure is thereby intended. It
is further understood that the present disclosure includes any
alterations and modifications to the illustrated embodiments and
includes further applications of the principles disclosed herein as
would normally occur to one skilled in the art to which this
disclosure pertains.
[0020] The present disclosure addresses these problems by providing
a rod system incorporating a novel rod that has a lesser lordotic
curve that can be easily passed under the tissues in a minimally
invasive fashion. This concept of a rod designed to specifically
allow minimally invasive placement in the treatment of long lumbar
fusions is demonstrated by the rod 10' in the X-ray image of FIG.
1, as it is much less curved than the rod 10 that is representative
of current rod shape strategies. As can be appreciated the
conventionally rod 10 has a significant curvature to match the
patient's anatomy but this curvature prevents the rod from being
placed in a minimally invasive fashion. It is noted that the rod
10' can be formed by conventional means, such as by bending, or can
be formed in a 3D printing process akin to the UNiD rod of
Medicrea.
[0021] The present disclosure provides devices and methods to
accommodate the lesser curved pre-bent rod to the patient's
anatomy. Thus, as depicted in FIG. 2, the method contemplates
introducing a rod 10' having an excursion or offset E' or bend that
is less than offset E the patient's anatomy in order to facilitate,
and achieve, percutaneous placement. A rod with reduced lumbar
lordosis also has applications in open surgery as planning tulip
screws that are proud of the bone surface can allow for control of
spinal alignment. As shown in FIG. 2, the rod generally follows the
thoracic vertebrae but begins to deviate from the surface of the
lumbar vertebrae, finishing generally even (level) with the second
sacral vertebra. The reduced curvature of the rod allows for
subcutaneous cranial introduction. It can be appreciated that the
rod 11' can be pre-bent or pre-formed into the reduced curvature
configured shown in FIG. 2. More particularly, as illustrated in
FIG. 3, the rod 10' can be sized to extend from S2 to T10. In this
instance, the rod 10' includes two sections--caudal and
cranial--each formed at a circular arc of radius R. The arc at the
caudal portion provides the lordotic curvature and spans 60% of the
total length of the rod from T10 to S2 (the T10-S2 length). The
radius R is sized so that the anterior displacement A at the caudal
(lordotic) portion is 9-11% of the total T10-S2 length of the rod.
The rod 10' can include a cranial end portion 11 that can be
trimmed and/or bent by hand as required for the particular patient
anatomy. The end portion 11 can be provided with markings, such as
laser etched markings, indicating the length from S2, to facilitate
trimming the rod to the proper length. For instance, for a T10-S2
length of 45 cm, the anterior displacement A for the caudal
(lumbar) portion is 4-5 cm and the length of the caudal portion (L1
to S2) is 27 cm. The radius R can be calculated using the equation:
((L1-S2 length).sup.2/8A)+A/2, so in the specific example the
radius R is 20.7 cm. It can be appreciated from the appearance of
the rod 10' in FIG. 3 that the rod is well-suited to percutaneous
introduction adjacent the vertebral levels to be instrumented. It
should also be appreciated that a rod prepared and used according
to the present disclosure does not need to span the seven vertebral
levels of the rod 10' in the present example. The rod can be
shorter or longer, depending on the desired treatment.
[0022] When placing a rod with a decreased lordotic bend, there is
a risk of inducing a flat back deformity in the patient's spinal
alignment. To allow the lumbar spine to achieve a proper anterior
offset and suitable lordotic angles, precise placement of the
pedicle screws and a modified pedicle screw is provided according
to the present disclosure. In particular, in order to accept the
lesser curved spinal rod 10', the present disclose contemplates
bone fasteners, such as bone screws 12a-12e, having a lengthened
intermediate portion between the bone-engaging threads and the
rod-receiving tulip portion, as shown in FIG. 4. It can be
appreciated form FIG. 4 that the cranial side screw 12a in the
fixation construct can be conventional bone screws that are
threaded into the bone with the rod-interface portion abutting the
surface of the bone. However, the bone screws 12b-12d engaged to
the lower lumbar vertebrae exhibit an increasing height from the
threaded shank and the rod-engaging portion. In order to address
this height differential, the present disclosure contemplates a
bone screw 12 shown in FIG. 5. The bone screw 12 includes a shank
20 with bone-engaging threads, and an intermediate portion 18 that
terminates in a tulip portion 14 that defines a U-shaped channel
14a to receive the rod. The end of the tulip portion 14 can be
threaded to receive a conventional set screw 16 or other set screw
construct suitable for clamping the spinal rod within the channel
14a. The bone screw 12 is configured to be threaded into vertebral
bone until the base 15 of the intermediate portion 18 contacts the
surface of the bone. In one aspect of the present disclosure, the
bottom of the channel 14a is situated at a height H from the base
15 of the intermediate portion 18, as measured along the
longitudinal axis L of the shank 20. This height H varies depending
upon the position of the bone screw in the construct. Thus, as
shown in construct depicted in FIG. 4, the height H is greater in
screw 12d than screw 12c, and the height of screw 12c is greater
than the height of screw 12b. In one aspect of the present
disclosure, the bone screws can have intermediate portions 18
provided in a range of discrete heights, such as ranging from 0.5
mm to 30 mm in 0.5 mm increments.
[0023] The selection of the bone screws is preferably made in the
planning stage, and most preferably using software operable to
evaluate X-rays, CT scans and other advanced imaging techniques
capable of accurately displaying the patient's spinal anatomy, in
order to determine an optimum spinal construct. The software can
assist in determining the spinal curvature, an acceptable curvature
of the spinal rod for simplified introduction, and ultimately the
amount of offset at each level of instrumentation--i.e., the gap
between the reduced curvature rod and the desired position of the
spinal level. The software can then assist in selecting the bone
screw with the optimum height H for each level. The goal of this
screw selection is that the tulip 14 of each bone screw is exactly
aligned along the path of introduction of the reduced curvature
spinal rod 10' so that the rod is solidly seated within each tulip
by the time the rod reaches its caudal extent during percutaneous
insertion. With this feature of the bone screws, the entire
construct can be designed prior to the surgery, with the curvature
of the rod being defined in the planning stage. The rod can then be
pre-bent or pre-formed, as described above, and provided with a
pre-determined collection of bone screws 10'.
[0024] The tulip portion 14 of the bone screw can be of any desired
configuration, including fixed, uni-planar and poly-axial. The
intermediate portion 18 can be uniform with the outer dimensions of
the tulip portion along the extended height H and can merge into
the threaded shank 20 in a conventional manner for bone screws,
thereby preserving the structural integrity of the bone screw.
[0025] In another feature of the present disclosure, a bone screw
is provided that optimally creates a pre-defined sagittal
relationship between the bone screw and the fixation rod. As
described above, the rod 10' of the present disclosure has a fixed
pre-determined curved contour that is configured for optimal
correction of a patient's spinal deformity. Since the rod has a
fixed contour, the interface between the rod and a particular
vertebral body may not lend itself to the strict perpendicular
interface required by prior fixed bone screws. In prior spinal
constructs, poly-axial screws have been provided to address this
angular misalignment, albeit at the cost of coronal correction.
According to one aspect of the present disclosure, a bone screw 30
is provided as shown in FIG. 6. The bone screw 30 includes a
threaded shank 32 and a tulip portion 34. A typical tulip portion
of a bone screw includes a partially circular or U-shaped channel
(such as channel 14' in FIG. 5), in which the channel extends along
a line that is perpendicular to the longitudinal axis of the
threaded shank. In one aspect of the present disclosure, the
channel 36 of the tulip portion 34 is oriented at a
non-perpendicular angle 37 relative to the longitudinal axis L of
the threaded shank 32. More particularly, the angle 37 is measured
relative to a line that is perpendicular to the longitudinal axis.
A set screw 38, or suitable set screw construct, is threaded into
the tulip portion 34 to clamp the spinal rod within the channel 36.
In one aspect of the present disclosure, the set screw includes a
tip 40 that is conical and defined at the same angle 37 relative to
the longitudinal axis of the set screw. The combination of the
angled channel 36 and the angled set screw tip 40 ensures a solid
contact and fixation of the spinal rod traversing the tulip portion
at an angle. The bone screw 30 can thus be a fixed screw, at least
in the sagittal plane, in order to mate with a rod that is at an
angle relative to the particular vertebral level. Several bone
screws can be provided with channels 36 at pre-defined angles 37,
such as between 5.degree. and 45.degree. in 5.degree.
increments.
[0026] The angled channel feature of the screw 30 can be integrated
into an enhanced height screw, such as the screws 12b-12e described
above. It can be appreciated that range of angles can be more
limited for bone screws having a greater height H since the angular
orientation of the rod relative the vertebral body would be less
dramatic where the rod is farther away from the true curvature of
the patient's anatomy.
[0027] As with the variable height feature of the bone screws, the
angle of the channel 36 can be determined in the pre-operative
planning. Once the shape of the fixation rod and the location of
the bone screws is known, the desired angle of the rod relative to
the bone screw at each vertebral level can be determined. The
planning software can thus assist in the selection of the bone
screw having the optimum height H and optimum angle of the channel
36. The planning software can also assist in optimization of both
height and angle to control lordosis or kyphosis in a fusion
construct. Providing a bone screw with an optimum sagittal angle
allows the screw to be introduced at a precise predetermined
optimum angle with respect to vertebral body or endplates. Subtly
adjusting the angle between the pedicle screws and vertebra allows
for fine tuning of the spinal alignment. This is an important
feature of precise control of sagittal alignment with pedicle
screws that is not possible with the prior art technique of placing
screws at an uncontrolled angle.
[0028] In another embodiment, a screw 45, shown in FIG. 7, includes
a threaded shank 47 that is arranged at an angle 52 relative to the
rod-engaging portion 48. The rod-engaging portion 48 may be in the
form of a tulip, as described above, or another suitable feature
capable of rod fixation. The rod-engaging portion 48 defines a
channel 49 similar to the channel 14a in that the channel is
perpendicular to the vertical axis V of the rod-engaging portion,
as is known in the art. The rod-engaging portion is also configured
to receive a conventional set screw or set screw construct for
clamping the rod within the channel, such as the set screw 16 in
FIG. 5. The interface 50 between the tulip 48 and the threaded
shank 47 defines the angle 52. In particular, the threaded shank 47
defines a longitudinal axis L that is not colinear with the
vertical axis V through the rod-engaging portion 48, and more
particularly oriented at the angle 52. As with the typical bone
screw, an insertion tool interface 54 is provided that can be
engaged by a tool to thread the screw 45 into the vertebral bone in
a known manner. However, unlike the conventional tool interface,
the interface 54 is provided at the angle 52 relative to the
longitudinal axis extending through the tulip 48. The tool is thus
aligned with the threaded shank 47 for proper introduction of the
screw into the bone. The tulip 48 can be otherwise configured as a
conventional tulip rod-engaging portion. As with the bone screw 30
of FIG. 6, the bone screw 45 of FIG. 7 can be provided with
pre-defined angles 52, such as between 5.degree. and 45.degree. in
5.degree. increments. The angled shank 47 can be likewise
integrated into an enhanced height screw, such as the screws
12b-12e described above.
[0029] It is contemplated that the bone screws 30, 45 accommodate
angular deviations between the rod-engaging portion and the rod
from the conventional perpendicular orientation. More specifically,
the angular deviations are in the sagittal plane to accommodate the
tulip configuration of the rod-engaging portions 34, 48. These
"sagittally-biased" screws can be provided in several standard
angles to account for the majority of spinal deformities. In
contrast to conventional poly-axial screws, the screws of the
present disclosure are rigid which facilitates sagittal alignment
of the spine as the screws are tightened onto the contoured rod.
Thus, the spinal construct disclosed herein achieves both coronal
and sagittal correction of the spine in a minimally-invasive
percutaneous procedure.
[0030] It should be understood that the bone screws disclosed
herein can be used in a wide range of spinal constructs. For
instance, the screws 12b-12e, 30 or 45 may be beneficial in a
shorter construct with shorter rods. The same planning process can
be used to assign a proper curvature to the shorter rod and to
select the bone screws having the necessary height H, angled
channel 36 and/or angled shank 47. These bone screws can be used
with any shaped rod--straight or curved.
[0031] One differentiating feature of the rod 10' and bone screws
12b-12e, 30 or 45 is that the planning to achieve alignment of the
spine is based on knowing the exact geometry of the rod ahead of
time and using this known rod geometry as the foundation of the
spinal alignment. This approach also allows selecting the
appropriate bone screws ahead of time, secure in the knowledge that
if the screws are implanted according to the predetermined plan the
reduced curvature rod 10' can be easily introduced percutaneously
into all of the rod-engaging portions of the bone screws. For
instance, in a method for treating degenerative lumbar fusions, the
pedicle screws of the present disclosure can be placed with a
defined orientation relative to the vertebral endplates and with a
pre-planned degree of bias. The rod can be passed percutaneously
beneath the soft tissue and navigated into the tulips of the
pedicle screws. Tightening the set screws corrects the spine to the
desired segmental lordosis. As needed, the screws can "walk" along
the rod to move the axis of rotation anteriorly prior to
tightening.
[0032] The implant procedure starts with modeling the patient's
spine using known software. A model of the modified rod disclosed
herein is overlaid onto the spine model. As explained above, the
rod has a fixed contour that is configured to facilitate
percutaneous placement. The rod contour can be determined based on
the dimensions of the patient's spine, as described above. The rod
model is aligned with the spine model to achieve the desired
correction, with the understanding that the excursion or offset
from the rod to a particular vertebral body will vary along the
length of the rod. Models of the bone screws are overlaid onto the
models of the spine and rod, bridging the space between rod and
spine and oriented at an optimum sagittal angle for proper fixation
within the bone. The height from the rod to the bone surface and
the angle of the threaded shank relative to the rod are determined
and this information is used to select a bone screw modified as
disclosed herein. The selected bone screws are precisely placed in
the spine with the rod-engaging portion, or tulip, exactly aligned
to accept the fixed contour rod. The rod is passed percutaneously
into the aligned tulips and tightened onto the bone screws in a
conventional manner.
[0033] It is contemplated that the rod 10' and the bone screws 12,
30 and 45 described herein are formed of medical grade materials
suitable for use in spinal implant constructs. The rod and bone
screws can be manufacture in a conventional manner for the
fabrication of spinal implants.
[0034] The present disclosure should be considered as illustrative
and not restrictive in character. It is understood that only
certain embodiments have been presented and that all changes,
modifications and further applications that come within the spirit
of the disclosure are desired to be protected.
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