U.S. patent application number 10/694457 was filed with the patent office on 2004-05-06 for gravity dependent pedicle screw tap hole guide.
Invention is credited to Gorek, Josef E..
Application Number | 20040087962 10/694457 |
Document ID | / |
Family ID | 28040312 |
Filed Date | 2004-05-06 |
United States Patent
Application |
20040087962 |
Kind Code |
A1 |
Gorek, Josef E. |
May 6, 2004 |
Gravity dependent pedicle screw tap hole guide
Abstract
A gravity dependent pedicle screw tap hole guide comprises a
guide shaft maintainable parallel to a drill bit during the
drilling of a pedicle screw tap hole; a level indicator associated
with a reference direction and responsive to gravity to provide
feedback regarding an angular difference between an acting
direction of gravity and the reference direction; and a mounting
attaching the indicator to the shaft and establishing a positional
relationship between the reference direction and the longitudinal
axis. Using the guide involves angulating the shaft about its
distal end adjacent the base of the superior articular process and
the base and middle of the transverse process until the guide
indicates that the angular orientation of the longitudinal axis
matches the previously determined pedicle axis orientation with
respect to the acting direction of gravity, and then drilling the
tap hole along a trajectory established by the longitudinal axis of
the shaft.
Inventors: |
Gorek, Josef E.; (Larkspur,
CA) |
Correspondence
Address: |
Joseph P. Errico
150 Douglas Road
Far Hills
NJ
07901
US
|
Family ID: |
28040312 |
Appl. No.: |
10/694457 |
Filed: |
October 27, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10694457 |
Oct 27, 2003 |
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10103079 |
Mar 21, 2002 |
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6638281 |
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Current U.S.
Class: |
606/96 |
Current CPC
Class: |
G01C 9/36 20130101; A61B
17/70 20130101; A61B 17/1757 20130101; A61B 90/06 20160201; A61B
17/90 20210801 |
Class at
Publication: |
606/096 |
International
Class: |
A61B 017/58 |
Claims
What is claimed is:
1. A gravity dependent pedicle screw tap hole guide, comprising: a
guide shaft having a proximal end, a distal end, and a longitudinal
axis, the guide shaft being maintainable parallel to a drill bit
during the drilling of a pedicle screw tap hole with the drill bit;
a level indicator associated with a reference direction and being
responsive to gravity to provide feedback regarding an angular
difference between an acting direction of gravity and the reference
direction; and a mounting by which the level indicator is attached
to the guide shaft, the mounting establishing a positional
relationship between the reference direction and the longitudinal
axis of the guide shaft.
2. The gravity dependent pedicle screw tap hole guide of claim 1,
wherein the guide shaft is fixed to the level indicator by the
mounting such that the longitudinal axis of the guide shaft is
parallel to the reference direction.
3. The gravity dependent pedicle screw tap hole guide of claim 1,
wherein the mounting is adjustable such that the longitudinal axis
of the guide shaft is angulatable with respect to the reference
direction.
4. The gravity dependent pedicle screw tap hole guide of claim 3,
wherein the mounting has at least one indicator that is viewable to
determine an angular difference between the longitudinal axis of
the guide shaft and the reference direction.
5. The gravity dependent pedicle screw tap hole guide of claim 3,
wherein the mounting comprises at least one rotational mounting
between the guide shaft and the level indicator, the rotational
mounting being engageable and disengageable at a plurality of
positions including a parallel position and a plurality of rotated
positions, the parallel position being a position at which the
longitudinal axis of the guide shaft is parallel to the reference
direction, each of the rotated positions being a respective
position at which the longitudinal axis of the guide shaft is
rotated with respect to the reference direction.
6. The gravity dependent pedicle screw tap hole guide of claim 5,
wherein the mounting comprises first and second rotational
mountings between the guide shaft and the level indicator, the
first rotational mounting providing rotation of the longitudinal
axis of the guide shaft relative to the reference direction in a
first plane, the second rotational mounting providing rotation of
the longitudinal axis of the guide shaft relative to the reference
direction in a second plane, the second plane being perpendicular
to the first plane, such that the parallel position of the first
rotational mounting is a position at which the longitudinal axis of
the guide shaft is parallel to the reference direction in the first
plane, and the parallel position of the second rotational mounting
is a position at which the longitudinal axis of the guide shaft is
parallel to the reference direction in the second plane, each of
the rotated positions of the first rotational mounting being a
respective position at which the longitudinal axis of the guide
shaft is rotated with respect to the reference direction in the
first plane, and each of the rotated positions of the second
rotational mounting being a respective position at which the
longitudinal axis of the guide shaft is rotated with respect to the
reference direction in the second plane.
7. The gravity dependent pedicle screw tap hole guide of claim 6,
wherein each of the first and second rotational mountings has angle
markers associated therewith that are viewable to determine an
angular difference between the longitudinal axis of the guide shaft
and the reference direction.
8. The gravity dependent pedicle screw tap hole guide of claim 1,
wherein the level indicator comprises a fluid chamber that is
partially filled with fluid such that a gas bubble is free to move
in the fluid chamber through a plurality of positions including a
position at which the reference direction is parallel to the acting
direction of gravity and a plurality of positions at which the
reference direction is angulated with respect to the acting
direction of gravity, the fluid chamber having a wall through which
the gas bubble is visible, the wall having a reference mark
indicating the parallel position.
9. The gravity dependent pedicle screw tap hole guide of claim 8,
wherein the fluid chamber comprises an enclosure having a convex
surface and having a central axis parallel to the reference
direction.
10. The gravity dependent pedicle screw tap hole guide of claim 8,
wherein the enclosure has a plurality of relative marks indicating
the angulated positions.
11. The gravity dependent pedicle screw tap hole guide of claim 10,
wherein the wall comprises a grid establishing the reference mark
and the relative marks.
12. The gravity dependent pedicle screw tap hole guide of claim 1,
wherein the level indicator comprises an accelerometer.
13. The gravity dependent pedicle screw tap hole guide of claim 12,
wherein the level indicator further comprises a readout adapted to
indicate the angular difference.
14. A method of drilling a pedicle screw tap hole, comprising:
determining a trajectory angle as an angle of a pedicle in a
reference plane relative to an acting direction of gravity;
positioning at least one of a distal end of a drill bit and a
distal end of a guide shaft of a gravity dependent pedicle screw
tap hole guide at a position adjacent the pedicle in a vicinity of
a base of a superior articular process of the pedicle and a base
and a middle of a transverse process of the pedicle, the guide
having the guide shaft and a level indicator associated with a
reference direction, the level indicator being responsive to
gravity to provide feedback regarding an angular difference between
an acting direction of gravity and the reference direction, the
guide having a mounting by which the level indicator is attached to
the guide shaft, the mounting establishing a positional
relationship between the reference direction and the longitudinal
axis of the guide shaft; angulating the guide shaft about the
distal end of the guide shaft until the gravity dependent pedicle
screw tap hole guide indicates that an angle between the
longitudinal axis of the guide shaft in the reference plane and the
acting direction of gravity matches the trajectory angle; and
rotating the drill bit into the pedicle along a trajectory
extending into the pedicle from the position at the trajectory
angle.
15. The method of drilling a pedicle screw tap hole of claim 14,
wherein the trajectory angle is a first trajectory angle and the
reference plane is a first reference plane, the method comprising:
determining the first trajectory angle as the angle of the pedicle
in the first reference plane relative to the acting direction of
gravity; determining a second trajectory angle as an angle of the
pedicle in a second reference plane relative to the acting
direction of gravity; positioning at least one of the distal end of
the drill bit and the distal end of the guide shaft at the
position; angulating the guide shaft about the distal end of the
guide shaft until the gravity dependent pedicle screw tap hole
guide indicates that the angle between the longitudinal axis of the
guide shaft in the first reference plane and the acting direction
of gravity matches the first trajectory angle, and that an angle
between the longitudinal axis of the guide shaft in the second
reference plane and the acting direction of gravity matches the
second trajectory angle; and rotating the drill bit into the
pedicle along a trajectory extending into the pedicle from the
position at the first trajectory angle and the second trajectory
angle.
16. The method of drilling a pedicle screw tap hole of claim 15,
wherein the first reference plane is a cephalad-caudad plane
defined by a vertebral body comprising the pedicle, and the second
reference plane is a medial plane defined by the vertebral
body.
17. The method of drilling a pedicle screw tap hole of claim 14,
comprising: determining the trajectory angle as the angle of the
pedicle in the reference plane relative to the acting direction of
gravity; positioning the distal end of the guide shaft at the
position; angulating the guide shaft about the distal end of the
guide shaft until the gravity dependent pedicle screw tap hole
guide indicates that the angle between the longitudinal axis of the
guide shaft in the reference plane and the acting direction of
gravity matches the trajectory angle; positioning the drill bit
coaxial with the longitudinal axis of the guide shaft; and rotating
the drill bit into the pedicle along the trajectory extending into
the pedicle from the position at the trajectory angle.
18. The method of drilling a pedicle screw tap hole of claim 14,
comprising: determining the trajectory angle as the angle of the
pedicle in the reference plane relative to the acting direction of
gravity; positioning the distal end of the drill bit at the
position; maintaining the longitudinal axis of the guide shaft
parallel to the drill bit while angulating the guide shaft about
the distal end of the guide shaft until the gravity dependent
pedicle screw tap hole guide indicates that the angle between the
longitudinal axis of the guide shaft in the reference plane and the
acting direction of gravity matches the trajectory angle; and
rotating the drill bit into the pedicle along the trajectory
extending into the pedicle from the position at the trajectory
angle.
19. The method of drilling a pedicle screw tap hole of claim 14,
wherein determining the trajectory angle comprises: establishing a
vertical orientation of a clamp having a longitudinal axis by
maintaining the longitudinal axis of the guide shaft parallel to
the longitudinal axis of the clamp while angulating the guide shaft
about the distal end of the guide shaft until the gravity dependent
pedicle screw tap hole guide indicates that the longitudinal axis
of the guide shaft is parallel to the acting direction of gravity;
attaching the clamp in the vertical orientation to a spinous
process of a vertebral body comprising the pedicle; generating an
image including the vertebral body while the clamp is attached; and
determining from the image an angular difference between the
orientation of the pedicle and the orientation of the clamp.
20. The method of drilling a pedicle screw tap hole of claim 19,
wherein determining the trajectory angle further comprises
obtaining at least one of an MRI image of the vertebral body, a CAT
image of the vertebral body, and a radiograph image of the
vertebral body.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] The present application is a divisional application of U.S.
patent application Ser. No. 10/103,079 (filed Mar. 21, 2002)
entitled "Gravity Dependent Pedicle Screw Tap Hole Guide".
FIELD OF THE INVENTION
[0002] This invention relates generally to devices and methods for
inserting pedicle screws into the spine, and more specifically to
devices and methods for accurately establishing a pedicle screw tap
hole drilling trajectory.
BACKGROUND OF THE INVENTION
[0003] The bones and connective tissue of an adult human spinal
column consist of more than 20 discrete bones coupled sequentially
to one another by a tri-joint complex which consist of an anterior
disc and the two posterior facet joints, the anterior discs of
adjacent bones being cushioned by cartilage spacers referred to as
intervertebral discs. These more than 20 bones are anatomically
categorized as being members of one of four classifications:
cervical, thoracic, lumbar, or sacral. The cervical portion of the
spine, which comprises the top of the spine, up to the base of the
skull, includes the first 7 vertebrae. The intermediate 12 bones
are the thoracic vertebrae, and connect to the lower spine
comprising the 5 lumbar vertebrae. The base of the spine is the
sacral bones (including the coccyx). The component bones of the
cervical spine are generally smaller than those of the thoracic and
lumbar spine.
[0004] The spinal column of bones is highly complex in that it
includes these more than 20 bones coupled to one another, housing
and protecting critical elements of the nervous system having
innumerable peripheral nerves and circulatory bodies in close
proximity. In spite of these complexities, the spine is a highly
flexible structure, capable of a high degree of curvature and twist
in nearly every direction. Genetic or developmental irregularities,
trauma, chronic stress, tumors, and disease, however, can result in
spinal pathologies which either limit this range of motion, or
which threaten the critical elements of the nervous system housed
within the spinal column. A variety of systems have been disclosed
in the art that achieve this immobilization by implanting
artificial assemblies in or on the spinal column. These assemblies
may be classified as anterior, posterior, or lateral implants. As
the classifications suggest, lateral and anterior assemblies are
coupled to the anterior portion of the spine, which is the sequence
of vertebral bodies. Posterior implants generally comprise pairs of
rods, which are aligned along the axis along which the bones are to
be disposed, and which are then attached to the spinal column by
either hooks which couple to the lamina or attach to the transverse
processes, or by screws which are inserted through the
pedicles.
[0005] The pedicles are the strongest parts of the vertebrae and
therefore provide a secure foundation for the screws to which the
rods are to be attached. In order to obtain the most secure anchor
for the pedicle screws, it is essential that the screws be threaded
in alignment with the pedicle axis and not be allowed to deviate
therefrom. Misalignment of the pedicle screws during insertion can
cause the screw body or its threads to break through the vertebral
cortex and be in danger of striking surrounding nerve roots. A
variety of undesirable symptoms can easily arise when the screws
make contact with nerves after breaking outside the pedicle cortex,
including dropped foot, neurological lesions, sensory deficits, or
pain.
[0006] Known surgical procedures to avoid misalignment of the
pedicle screws involve recognizing landmarks along the spinal
column for purposes of locating optimal tap hole entry points,
approximating tap hole trajectories, and estimating proper tap hole
depth. Some surgeons use a Kocher clamp applied to the vertebral
bone for a reference mark and/or view radiographs or other medical
images to better understand relative positions of the patient's
anatomy. X-ray exposures and/or fluoroscopy can sometimes be used
to monitor the advancement of a pedicle screws through the
vertebra. Unfortunately, these procedures are subject to surgeon
visual approximation errors, and anatomical landmarks are different
for each patient. Further, prolonged radiation exposure to a
patient is undesirable. U.S. Pat. No. 4,907,577 (Mar. 13, 1990)
discloses a jig that is described therein as providing a safe route
for drilling pedicle screw tap holes, by identifying a precise
location for drilling to prevent deviation from the drilling
direction so as to prevent injury during surgery to the nerve root
or spinal cord. However, the jig has a variety of moving parts that
must be adjusted and monitored simultaneously during the
adjustments, making operation of the jig difficult and time
consuming. Further, operation of the jig must occur during surgery,
as it must be held adjacent the vertebral body to determine the
proper adjustment settings. Finally, adjustment of the jig to the
proper settings requires precise visual approximation by the
surgeon, an activity that should be minimized to ensure that a
misaligned trajectory is not established in place of a safe
one.
[0007] More technologically advanced systems such as the
StealthStation.TM. Treatment Guidance System, the FluoroNav.TM.
Virtual Fluoroscopy System (both available from Medtronic Sofamor
Danek), and related systems, seek to overcome the need for surgeons
to approximate landmarks, angles, and trajectories, by assisting
the surgeons in determining proper tap hole starting points,
trajectories, and depths. However, these systems are extremely
expensive, require significant training, are cumbersome in
operation, are difficult to maintain, and are not cost effective
for many hospitals.
[0008] U.S. Pat. Nos. 5,474,558 (Dec. 12, 1995) and 5,196,015 (Mar.
23, 1993) propose a procedure in which a screw opening is started
in part of a skeletal region, e.g., a pedicle of a lumbar vertebra,
and an electric potential of a certain magnitude is applied to the
inner surface of the opening while the patient is observed for
nervous reactions such as leg twitching. The opening continues to
be formed while the electric potential is applied until a desired
hole depth is obtained in the absence of nervous reaction to the
potential. The direction in which the screw opening is being formed
is changed to a direction other than the last direction, after
observing patient reactions to the electric potential when the
screw opening was being formed in the last direction.
Unfortunately, this procedure is inherently reactive rather than
proactive, in that the surgeon becomes aware of the misalignment
after the patient exhibits a nervous reaction, and by that time the
misaligned hole has been drilled.
[0009] Therefore, there is a need for a simple device that eases
the difficulties associated with safely placing pedicle screws.
Specifically, there is a need for such a device that assists a
surgeon in making more accurate the surgeon's assessment of the
proper insertion trajectory of the pedicle screw. Further, there is
a need for such a device that does not require the surgeon to rely
on visual approximations. In addition, there is a need for such a
device that proactively determines the desirable drilling
trajectory rather than reactively informing the surgeon when an
improper trajectory has been used.
SUMMARY OF THE INVENTION
[0010] The needs identified above and other needs in the art are
achieved by the present invention that provides a gravity dependent
pedicle screw tap hole guide and methods of use thereof.
[0011] One embodiment of a gravity dependent pedicle screw tap hole
guide of the present invention has a shaft with a proximal end, a
distal end, a longitudinal axis, and a fluid chamber attached to
the shaft. A bubble in the fluid chamber indicates whether or not
the chamber is level and/or to what degree it is not level. The
translucent wall of the chamber has a reference mark positioned so
that that when the bubble is centered under the reference mark, the
longitudinal axis of the shaft is parallel to the acting direction
of gravity. The wall also has a grid that, when the bubble is not
centered under the reference mark, indicates an angular difference
(preferably in two perpendicular planes) between the longitudinal
axis of the shaft and the acting direction of gravity. Preferably,
the longitudinal axis of the shaft extends perpendicular to a plane
in which a platform holding the chamber extends. The chamber is
preferably a hemispherical enclosure with a central axis that is
parallel to the longitudinal axis of the shaft.
[0012] In operation of this embodiment, the surgeon first exposes a
vertebral bone and applies a Kocher clamp to the spinous process in
a vertical position (where the longitudinal axis of the clamp is
parallel to the acting direction of gravity) to his best visual
approximation. Preferably, the guide of this embodiment is used
here to make the vertical placement more accurate, by holding the
shaft parallel to the longitudinal axis of the Kocher clamp while
manipulating the shaft with the Kocher clamp so that when the
bubble is centered under the reference mark, the surgeon knows that
the Kocher clamp is in a vertical position.
[0013] Next, a lateral radiograph is taken and used to approximate
the cephalad-caudad declination of the pedicle of interest and the
medial angulation of the pedicle is determined from preoperative
transaxial MRI and/or CAT scan images. The surgeon then positions
the distal end of the shaft against the exposed vertebral bone in
the vicinity of the base of the superior articular process and the
base and middle of the transverse process (referred to herein as
the "preferred tap hole entry point"), and angulates the shaft
until the angular difference between the longitudinal axis of the
shaft and the acting direction of gravity matches the determined
cephalad-caudad declination (in the cephalad-caudad plane), and the
medial angulation (in the medial plane). During this angulation,
the surgeon can view the bubble's position relative to the grid
lines, to know when and in what direction additional angulational
adjustment of the shaft is necessary to bring the shaft to the
desired position.
[0014] Once the shaft has been placed in the desired position, the
surgeon can be confident that drilling into the vertebral bone
along the trajectory established by the longitudinal axis of the
shaft in the desired position will result in a pedicle screw tap
hole that is formed to maximize the stability of a pedicle screw
subsequently screwed thereinto. The shaft can be hollow to
accommodate a drill bit for this purpose, or, if the shaft is not
hollow, the distal end of the drill bit can be placed against the
preferred tap hole entry point of the exposed vertebral bone, and
the shaft can be held parallel to the longitudinal axis of the
drill bit so that the shaft and the drill bit can be angulated in
parallel together until the guide indicates the drill bit is at the
desired angle.
[0015] Another embodiment of a gravity dependent pedicle screw tap
hole guide of the present invention also has a shaft with an
attached fluid chamber housing a level-indicating bubble that rests
under a reference mark when the chamber is level. The chamber is
movably attached to the shaft and thereby positionable relative to
the shaft. Specifically, the degree of perpendicularity of the
longitudinal axis of the shaft relative to a plane defined by the
chamber can be varied in at least two planes. In this regard, the
movable attachment of the chamber to the shaft is achieved by two
rotatable mountings, the first being between the shaft and the
second rotatable mounting, and the second being between the first
rotatable mounting and the chamber. The first rotatable mounting
rotates about an axis extending perpendicular to the longitudinal
axis of the shaft, and the second rotatable mounting rotates about
an axis extending perpendicular to the plane defined by the
chamber. Each of the rotatable mountings can be secured at any
position to which it can be rotated. When each rotatable mounting
is in its zero position, the plane of the chamber is perpendicular
to the longitudinal axis of the shaft and, accordingly, when the
enclosure is oriented such that the bubble is under the reference
mark, the longitudinal axis of the shaft is parallel to the acting
direction of gravity. Marks on the mountings preferably indicate
the relative angle of rotation of the rotatable mounting with
respect to the zero position, such that if either or both of the
rotatable mountings are placed in a rotated position, the user can
read the marks to determine the angular difference between the
longitudinal axis of the shaft and the plane defined by the chamber
when the chamber is oriented so that the bubble is under the
circle.
[0016] In operation of this embodiment, the surgeon proceeds as
indicated above with regard to the first embodiment, but use of
this embodiment to make the Kocher clamp vertical placement more
accurate is as follows: The rotatable mountings are placed in their
respective zero positions, and the shaft is held parallel to the
longitudinal axis of the Kocher clamp while being manipulated with
the Kocher clamp until the bubble is centered under the reference
mark, at which time the surgeon knows that the Kocher clamp is in a
vertical position.
[0017] After determining the cephalad-caudad declination and medial
angulation of the pedicle of interest, the surgeon places the first
rotatable mounting into a rotated position at an angular offset
matching the cephalad-caudad declination, and places the second
rotatable mounting into a rotated position at an angular offset
matching the medial angulation. During these rotations, the surgeon
can view the marks to ensure that the mountings are rotated to the
desired angles. Then, the surgeon positions the distal end of the
shaft against the preferred tap hole entry point, and angulates the
shaft until the bubble is under the reference mark. The surgeon can
then safely drill the tap hole as desired along the trajectory
established by the longitudinal axis of the shaft. Again, the shaft
can be hollow and/or held in parallel to the drill bit as the drill
bit is angulated against the preferred tap hole entry point.
[0018] Yet another embodiment of a gravity dependent pedicle screw
tap hole guide of the present invention is similar to the first
embodiment discussed above, but uses an accelerometer instead of a
fluid chamber housing a level-indicating bubble. An accelerometer
is known in the art as an electronic device that can determine its
angular orientation relative to the acting direction of gravity,
and therefore can be used to determine, for any device in fixed
relation to the accelerometer, the angular orientation of that
device relative to the acting direction of gravity. The
accelerometer can be connected to an analog or digital readout
presenting the angular orientation of the accelerometer relative to
the acting direction of gravity. Preferably, the shaft is attached
in fixed relation to the accelerometer such that when the
accelerometer indicates that there is no angular difference between
the reference direction recognized by the accelerometer and the
acting direction of gravity, the longitudinal axis of the shaft is
parallel to the acting direction of gravity. Accordingly, as the
shaft is oriented freely in space, the accelerometer indicates the
angular difference (preferably in two planes) between the
longitudinal axis of the shaft and the acting direction of
gravity.
[0019] Operation of this embodiment proceeds as indicated with
regard to the first embodiment, with the accelerometer (rather than
the fluid-containing enclosure in the first embodiment) indicating
when the shaft is in the desired position, that is, when the
angular difference between the longitudinal axis of the shaft and
the acting direction of gravity matches the cephalad-caudad
declination (in the cephalad-caudad plane) and medial angulation
(in the medial plane) of the pedicle.
[0020] Still another embodiment of a gravity dependent pedicle
screw tap hole guide of the present invention is similar to that of
the second embodiment described above, except that the
fluid-containing enclosure of that embodiment is replaced with an
accelerometer similar to the accelerometer of the third embodiment
described above. Accordingly, when each rotatable mounting is in
its zero position, and the accelerometer reads level, the
longitudinal axis of the shaft is parallel to the acting direction
of gravity. And, accordingly, if either or both of the rotatable
mountings are placed in a rotated position, the user can, when the
accelerometer is oriented level, read the marks to determine the
angular difference between the longitudinal axis of the shaft and
the acting direction of gravity.
[0021] Operation of this embodiment proceeds as indicated with
regard to the second embodiment, with the accelerometer indicating
when the accelerometer is oriented level (and thus, if the
rotatable mountings have been rotated to match the cephalad-caudad
declination and medial angulation of the pedicle, that the shaft is
at the desired angulation).
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIGS. 1a-c are side, top, and perspective views of an
embodiment of a gravity dependent pedicle screw tap hole guide of
the present invention, the guide utilizing a fluid chamber housing
a level-indicating bubble.
[0023] FIGS. 2a-c are front, side, and top views of another
embodiment of a gravity dependent pedicle screw tap hole guide of
the present invention, the guide utilizing a fluid chamber housing
a level-indicating bubble and rotatable mountings.
[0024] FIGS. 3a-c are side, top, and perspective views of yet
another embodiment of a gravity dependent pedicle screw tap hole
guide of the present invention, the guide utilizing an
accelerometer.
[0025] FIGS. 4a-c are front, side, and top views of still another
embodiment of a gravity dependent pedicle screw tap hole guide of
the present invention, the guide utilizing an accelerometer and
rotatable mountings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0026] While the present invention will be described more fully
hereinafter with reference to the accompanying drawings, in which
particular embodiments and methods of implantation are shown, it is
to be understood at the outset that persons skilled in the art may
modify the invention herein described while achieving the functions
and results of this invention. Accordingly, the descriptions that
follow are to be understood as illustrative and exemplary of
specific structures, aspects and features within the broad scope of
the present invention and not as limiting of such broad scope. Like
numbers refer to similar features of like elements throughout.
[0027] Referring now to FIGS. 1a-c, an embodiment of a gravity
dependent pedicle screw tap hole guide of the present invention is
illustrated. The guide in this embodiment has a shaft 100 that has
a proximal end 101 and a distal end 102 and a longitudinal axis
105, and a fluid chamber 110 attached to the shaft 100. The fluid
chamber 110 is partially filled with fluid 120, and the fluid 120
is contained within the chamber 110, such that a bubble 130 is
present in the chamber 110. Because the gas in the bubble 130 is
lighter than the fluid in the chamber 110, the bubble 130 floats in
the chamber 110, seeking to travel in a direction opposite the
acting direction of gravity, but being prevented from leaving the
chamber 110 because the chamber 110 is closed.
[0028] The chamber 110 has a wall 135 through which the bubble 130
is visible. The wall 135 has a reference mark 160 positioned so
that that when the bubble 130 is centered under the reference mark
160, it is indicated that the longitudinal axis 105 of the shaft
100 is parallel to the acting direction of gravity.
[0029] Further, the translucent wall 135 has at least one relative
mark (grid 150) that can be read to determine the location of the
center of the bubble 130 relative to the reference mark 160 when
the bubble 130 is not centered under the reference mark 160, the
relative mark (grid 150) indicating an angular difference between
the longitudinal axis 105 of the shaft 100 and the acting direction
of gravity.
[0030] Preferably, as shown, the longitudinal axis 105 of the shaft
100 extends in a direction perpendicular to a plane in which a
platform 180 laterally attached to the shaft 100 extends. The
chamber 110 is preferably a transparent hemispherical enclosure 110
having a central axis 170 (the axis 170 passing through the center
top of the hemisphere 110 and being perpendicular to the platform
180) is parallel to the longitudinal axis 105 of the shaft 100.
[0031] Also preferably, the outer surface of the enclosure 110 is
marked with a guide grid 150 formed by grid lines as shown. Grid
lines in a first grid line set 140 are evenly spaced along the
curved surface of the enclosure 110 and extend in respective planes
parallel to the longitudinal axis 105 of the shaft 100. (Only one
grid line of this set is marked 140 merely for clarity in
presentation of the figures; the reference numeral 140 applies to
the entire set of grid lines). Grid lines in a second grid line set
142 are evenly spaced along the curved surface of the enclosure 110
and extend in respective planes parallel to the longitudinal axis
105 of the shaft 100 but perpendicular to the grid lines in the
first set 140. (Only one grid line of this set is marked 142 merely
for clarity in presentation of the figures; the reference numeral
142 applies to the entire set of grid lines). The central grid line
of each set intersects with the other to define the reference mark
160.
[0032] Accordingly, each grid line in the first set 140 indicates
(when the bubble 130 is under the line) a respective angular
difference between the longitudinal axis 105 of the shaft 100 and
the acting direction of gravity in a first plane, and each grid
line in the second set 142 indicates (when the bubble is under the
line) a respective angular difference between the longitudinal axis
105 of the shaft 100 and the acting direction of gravity in a
second plane perpendicular to the first plane. The lines are
preferably labeled to assist the surgeon in quantifying the angular
difference. In this embodiment, grid lines in the first set 140 are
labeled in degrees, in reference to the first plane, -40, -30, -20,
-10, 0, 10, 20, 30, 40, respectively. Also in this embodiment, grid
lines in the second set 142 are labeled in degrees, in reference to
the second plane, -40, -30, -20, -10, 0, 10, 20, 30, 40,
respectively. It should be understood that other labeling, with
greater or lesser angles, and/or greater or lesser increments, can
also be used.
[0033] In operation of this embodiment, the surgeon first exposes
the vertebral bone into which the pedicle screw is to be placed.
Next, the surgeon applies a clamp (e.g., a Kocher clamp) to the
spinous process of the exposed vertebral bone, placing the Kocher
clamp in a vertical position (parallel to the acting direction of
gravity) to his best visual approximation. Preferably, the gravity
dependent pedicle screw tap hole guide of this embodiment is used
at this point in the procedure to make more accurate the surgeon's
vertical placement of the Kocher clamp. That is, the shaft of the
guide can be held parallel to the longitudinal axis of the Kocher
clamp, manipulated with the Kocher clamp while being maintained in
said parallel position, so that when the bubble 130 is centered
under the reference mark 160, the surgeon knows that the Kocher
clamp is in the vertical position.
[0034] Once the Kocher clamp in attached to the spinous process in
the vertical position, a lateral radiograph is taken, and the
cephalad-caudad declination of the pedicle of interest is
determined by the surgeon to his best visual approximation using
the longitudinal axis of the Kocher clamp in the radiograph image
as the "zero" axis. Also, the medial angulation of the pedicle is
determined from preoperative transaxial MRI and/or CAT scan images.
Angular measurement devices known in the art can be used to make
these angular assessments more accurate. Once the cephalad-caudad
declination and the medial angulation have been determined, the
surgeon positions the distal end 102 of the shaft 100 against the
exposed vertebral bone in the vicinity of the base of the superior
articular process and the base and middle of the transverse process
(referred to herein as the "preferred tap hole entry point"), and
angulates the shaft 100 until the angular difference between the
longitudinal axis 105 of the shaft 100 and the acting direction of
gravity in the first plane matches the determined cephalad-caudad
declination, and the angular difference between the longitudinal
axis 105 of the shaft 100 and the acting direction of gravity in
the second direction matches the determined medial angulation. (It
should be understood that alternatively, the device can be used
with the grid lines in the set 140 begin use to match the medial
angulation, and the grid lines in the set 142 being used to match
the cephalad-caudad declination.) During this angulation, the
surgeon can view the position of the bubble 130 under the guide
grid 150, and particularly the bubble's position relative to the
grid lines, to know when and in what direction additional
angulational adjustment of the shaft 100 is necessary to bring the
shaft 100 closer to the desired position, and when the shaft 100
has reached the desired position.
[0035] Once the shaft 100 has been placed in the desired position,
the surgeon can be confident that drilling into the vertebral bone
along the trajectory established by the longitudinal axis of the
shaft 100 in the desire position will result in a pedicle screw tap
hole that is formed to maximize the stability of a pedicle screw
subsequently screwed thereinto. That is, the surgeon can be
confident that the drilling is unlikely to result in penetration of
the distal end of the drill bit to any outer surface of the
vertebral bone, and is likely to result in the walls of the tap
hole being relatively uniformly thick at any given cross-section.
Drilling into the vertebral bone along the trajectory established
by the longitudinal axis 105 of the shaft 100 in the desired
position can be accomplished in that the shaft 100 can be hollow,
as shown, with its internal diameter being sufficient to
accommodate a drill bit suitable for drilling the tap hole, and
with its length being shorter than the exposed length of the drill
bit (the amount of the drill bit protruding from the drill) by an
amount sufficient to allow the drill bit to go into the bone to the
clinically desired depth before the drill hits the proximal end of
the shaft 100. The drill bit can therefore be passed into the shaft
100, and can be rotated therein during the drilling, so that the
tap hole is drilled along an extension of the longitudinal axis of
the shaft 100 at the desired angle.
[0036] Alternatively, the distal end of the drill bit can be placed
against the preferred tap hole entry point of the exposed vertebral
bone, and the shaft 100 can be held parallel to the longitudinal
axis of the drill bit. (This parallel holding can be accomplished,
for example, by using suitable attachments or mountings for the
shaft against the drill.) The drill bit and the shaft 100 can be
angulated together (while being maintained in relative parallel
positions) until the angular difference between the longitudinal
axis 105 of the shaft 100 and the acting direction of gravity in
the first plane matches the determined cephalad-caudad declination,
and the angular difference between the longitudinal axis 105 of the
shaft 100 and the acting direction of gravity in the second plane
matches the determined medial angulation. (It should be understood
that alternatively, the device can be used with the grid lines in
the set 140 begin use to match the medial angulation, and the grid
lines in the set 142 being used to match the cephalad-caudad
declination.) During this angulation, the surgeon can view the
position of the bubble 130 under the guide grid 150, and
particularly the bubble's position relative to the grid lines, to
know when and in what direction additional angulational adjustment
of the drill bit (and parallel shaft 100) is necessary to bring the
drill bit closer to the desired position, and when the drill bit
has reached the desired position. Once the drill bit has been
placed in the desired position, the surgeon can be confident that
drilling into the vertebral bone along the trajectory established
the longitudinal axis of the drill bit in the desired position will
result in a pedicle screw tap hole that is formed to maximize the
stability of a pedicle screw subsequently screwed thereinto.
[0037] Referring now to FIGS. 2a-c, another embodiment of a gravity
dependent pedicle screw tap hole guide of the present invention is
illustrated. The guide in this embodiment has a shaft 200 that has
proximal end 201 and a distal end 202 and a longitudinal axis 205,
and a fluid chamber 210 attached to the shaft 200. The fluid
chamber 210 is partially filled with fluid 220, and the fluid 220
is contained within the chamber 210, such that a bubble 230 is
present in the chamber 210. Because the gas in the bubble 230 is
lighter than the fluid in the chamber 210, the bubble 230 floats in
the chamber 210, seeking to travel in a direction opposite the
acting direction of gravity, but being prevented from leaving the
chamber 210 because the chamber 210 is closed. Preferably, as
shown, the chamber 210 defines a plane 215 that is perpendicular to
the acting direction of gravity when the chamber 210 is held level.
The chamber 210 has a translucent wall 235 through which the bubble
230 is visible. The translucent wall 235 has a reference mark 260
positioned so that that when the chamber 210 is held level, the
bubble 230 is centered under the reference mark 260. The chamber
210 is movably attached to the shaft 200 and thereby positionable
relative to the shaft 200. Specifically, the degree of
perpendicularity of the longitudinal axis 205 of the shaft 200
relative to the plane 215 defined by the chamber 210 can be varied
in at least two planes.
[0038] Preferably, as shown, a platform 282 is laterally attached
to the shaft 200. The chamber 210 is a transparent cylindrical
enclosure 210 mounted on the platform 282, the bottom surface 215
of the chamber 210 defining the plane 215. Also preferably, an
upper surface 235 of the enclosure is centrally marked with a
circle 260. When the chamber 210 is oriented so that the bottom
surface 215 is held level, the bubble 230 is under the circle
260.
[0039] Also preferably, the movable attachment of the chamber 210
to the shaft 200 is achieved by two rotatable mountings 270, 280
between the chamber 210 and the shaft 200. The first rotatable
mounting 270 is between the shaft 200 and the second rotatable
mounting 280. The second rotatable 280 mounting is between the
first rotatable mounting 270 and the chamber 210. The first
rotatable mounting 270 rotates about an axis 275 extending
perpendicular to the longitudinal axis 205 of the shaft 200, and
the second rotatable mounting 280 rotates about an axis 285
extending perpendicular to the plane 215 defined by the chamber
210. Each of the rotatable mountings 270, 280 can be secured at any
position to which it can be rotated. In this embodiment, the
securing is accomplished in each rotatable mounting by a set screw
that when loose, permits rotation, and when tight, prevents
rotation by pressing the relatively moving surfaces of the
rotatable mounting against one another. Alternative or additional
securing mechanisms can be provided within the scope of the present
invention.
[0040] Also preferably, the angles of rotation that can be achieved
by the rotatable mountings are indicated by two sets 240, 242 of
angle marks associated respectively with each rotatable mounting
270, 280. Each set has a zero mark, each zero mark indicating a
zero position into which the associated rotatable mounting can be
placed. When each rotatable mounting 270, 280 is in its zero
position, the plane 215 of the enclosure 210 is perpendicular to
the longitudinal axis 205 of the shaft 200 and, accordingly, when
the enclosure 210 is oriented such that the bubble 230 is under the
circle 260, the longitudinal axis 205 of the shaft 200 is parallel
to the acting direction of gravity.
[0041] Additional marks in the set preferably indicate the relative
angle of rotation of the rotatable mounting with respect to this
zero position, such that if either or both of the rotatable
mountings are placed in a rotated position, the user can read the
marks to determine the angular difference between the longitudinal
axis 205 of the shaft 200 and the plane 215 when the enclosure 210
is oriented so that the bubble 230 is under the circle 260.
Preferably, each set marks 10 degree increments, e.g., -40, -30,
-20, -10, 0, 10, 20, 30, 40, with the first rotatable mounting
marks indicating the angular difference in a first plane, and the
second rotatable mounting marks indicating the angular offset in a
second plane parallel to the first plane. It should be understood
that other labeling, with greater or lesser angles, and greater or
lesser increments, can also be used.
[0042] In operation of this embodiment, the surgeon proceeds as
indicated above with regard to the first embodiment, applying a
Kocher clamp in a vertical position to the spinous process of the
vertebral bone into which the pedicle screw is to be placed. The
surgeon can again use his best visual approximation to apply the
Kocher clamp vertically, or can preferably use the gravity
dependent pedicle screw tap hole guide of this embodiment to make
the placement more accurate. That is, the rotatable mountings 270,
280 of the guide can be placed in their respective zero positions,
so that the plane 215 of the enclosure 210 is perpendicular to the
longitudinal axis 205 of the shaft 200, and the shaft 200 can then
be held parallel to the longitudinal axis of the Kocher clamp, and
manipulated with the Kocher clamp while being maintained in said
parallel position similar to the use of the first embodiment
discussed above, so that when the bubble 230 is centered under the
circle 260, the surgeon knows that the Kocher clamp is in a
vertical position.
[0043] Next, a lateral radiograph is taken and used to approximate
the cephalad-caudad declination of the pedicle of interest, and the
medial angulation of the pedicle is determined from preoperative
transaxial MRI and/or CAT scan images. The surgeon then places the
first rotatable mounting 270 into a rotated position at an angular
orientation matching the cephalad-caudad declination, and places
the second rotatable mounting 280 into a rotated position at an
angular orientation matching the medial angulation. During these
rotations, the surgeon can view the rotatable mounting marks 240,
242 to ensure that the mountings 270, 280 are rotated to the
desired angles.
[0044] Then, the surgeon positions the distal end 202 of the shaft
200 against the preferred tap hole entry point of the exposed
vertebral bone, and angulates the shaft 200 until the bubble 230 is
under the circle 260. When the bubble 230 is under the circle 260,
this indicates to the surgeon that the angulation of the shaft 200
matches the angulation of the pedicle with respect to the
vertical.
[0045] Once the shaft 200 has been placed in the desired position,
the surgeon can be confident that drilling into the vertebral bone
along the trajectory established by the longitudinal axis 205 of
the shaft 200 in the desired position will result in a pedicle
screw tap hole that is formed to maximize the stability of a
pedicle screw subsequently screwed thereinto. Drilling into the
vertebral bone along an extension of the longitudinal axis 205 of
the shaft 200 can be accomplished in that the shaft 200 can be
hollow, as discussed with regard to the first embodiment, and the
drill bit passed into and rotated in the shaft 200 during the
drilling. Alternatively, also as discussed with regard to the first
embodiment, if a hollow shaft is not used, the shaft 200 can be
held parallel to the longitudinal axis of the drill bit, and the
drill bit and the shaft 200 can be angulated together (while being
maintained in relative parallel positions) until the bubble 230 is
under the circle 260. When the bubble 230 is under the circle 260,
this indicates to the surgeon that the angular orientation of the
shaft 200 (and therefore the angular orientation of the drill bit)
matches the angular orientation of the pedicle with respect to the
vertical.
[0046] Referring now to FIGS. 3a-c, yet another embodiment of a
gravity dependent pedicle screw tap hole guide of the present
invention is illustrated. The guide in this embodiment has a shaft
300 that has a proximal end 301 and a distal end 302 and a
longitudinal axis 305, and an accelerometer 310 attached to the
shaft 300. The accelerometer 310 is an electronic device that can
determine its angular orientation relative to the acting direction
of gravity, and therefore can be used to determine, for any device
in fixed relation to the accelerometer 310, the angular orientation
of that device relative to the acting direction of gravity.
Although a variety of accelerometers exist and can be used with the
present invention, one example of an accelerometer that can be used
with the present invention has as its central functional mechanism
a computer chip that determines the angular orientation of a
reference direction relative to the acting direction of gravity,
and further can be connected to other electronic devices to provide
relevant data in that regard to such devices. A suitable
accelerometer is sold by Analog Devices, Inc. (Norwood, Mass.) as
product number ADXL202. Accordingly, and preferably as shown, an
analog or digital readout 320 in communication with the
accelerometer 310 is viewable to provide the angular orientation of
the accelerometer 310 relative to the acting direction of
gravity.
[0047] Preferably, as shown, the shaft 300 is attached in fixed
relation to the accelerometer 310 such that when the accelerometer
310 indicates that there is no angular difference between the
reference direction recognized by the accelerometer 310 and the
acting direction of gravity, the longitudinal axis 305 of the shaft
300 is parallel to the acting direction of gravity. Accordingly, as
the shaft 300 is oriented freely in space, the accelerometer 310
indicates the angular difference (preferably in two dimensions)
between the longitudinal axis 305 of the shaft 300 and the acting
direction of gravity.
[0048] Operation of this embodiment proceeds as indicated with
regard to the first embodiment, with the accelerometer 310 (rather
than the fluid-containing enclosure of the first embodiment)
indicating when the shaft 300 is in the desired position, that is,
when the angular difference between the longitudinal axis of the
shaft 300 and the acting direction of gravity matches the
cephalad-caudad declination (in the first plane) and medial
angulation (in the second plane) of the pedicle.
[0049] Referring now to FIGS. 4a-c, still another embodiment of a
gravity dependent pedicle screw tap hole guide of the present
invention is illustrated. The guide in this embodiment is similar
to that of the second embodiment described above, except that the
fluid-containing enclosure 210 of that embodiment is replaced with
an accelerometer 410 similar to the accelerometer 310 described in
the third embodiment described above. Elements in this fourth
embodiment that are similar to those in the second embodiment are
referenced with like numbers, but in the four hundreds rather than
the two hundreds. Accordingly, when each rotatable mounting 470,
480 is in its zero position, and the accelerometer 410 reads level,
the longitudinal axis 405 of the shaft 400 is parallel to the
acting direction of gravity. And, accordingly, if either or both of
the rotatable mountings are placed in a rotated position, the user
can read the marks in the mark sets 440, 442 to determine the
angular difference between the longitudinal axis 405 of the shaft
400 and the acting direction of gravity when the accelerometer 410
is oriented level.
[0050] Operation of this embodiment proceeds as indicated with
regard to the second embodiment, with the accelerometer 410
indicating when the accelerometer 410 is oriented level (and thus,
if the rotatable mountings 470, 480 have been rotated to match the
cephalad-caudad declination and medial angulation of the pedicle,
that the shaft 400 is at the desired angulation).
[0051] While there has been described and illustrated specific
embodiments of an intervertebral spacer device, it will be apparent
to those skilled in the art that variations and modifications are
possible without deviating from the broad spirit and principle of
the present invention. The invention, therefore, shall not be
limited to the specific embodiments discussed herein.
* * * * *