Note: Descriptions are shown in the official language in which they were submitted.
WO 2010/123879 PCT/US2010/031725
INTRAMEDULLARY NAIL TARGETING DEVICE
Alfred A. Durham
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority under 35 USC 119(e) to U.S. Provisional
Patent
Application 61/214,060 filed April 20, 2009, and is a continuation-in-part
under 35 USC
120 of U.S. Patent Application 12/552,726 filed September 2, 2009, which
claims
priority under 35 USC 119(e) to U.S. Provisional Patent Application
61/190,709 filed
September 2, 2008 and is a continuation-in-part under 35 USC 120 of U.S.
Patent
Application 10/679,166 filed October 3, 2003, which claims priority under 35
U.S.C.
119(e) to U.S. Provisional Patent Application 60/415,952 filed October 3,
2002, all of
which are incorporated herein by reference in their entirety.
FIELD OF THE INVENTION
The present invention is directed to a targeting device in general and
specifically relates to an intramedullary nail targeting device and method for
positioning locking screws for intramedullary nails.
BACKGROUND
Devices for targeting of distal holes or openings in orthopedic hardware such
as
intramedullary nails include mechanical targeting devices and magnetic
targeting devices.
Examples of conventional mechanical targeting devices for intramedullary nails
include those described in U.S. Patent Nos. 4,622,959 to Marcus; 4,913,137 to
Azer et al.;
5,281,224 to Faccioli et al.; 6,039,739 to Simon; 7,060,070 to Anastopoulos et
al.;
7,077,847 to Pusnik et al.; 7,147,642 to Robioneck et al.; 7,311,710 to
Zander; 7,232,443
to Zander et al.; and 7,549,994 to Zander et al. These devices typically
include rigid arms
that extend from the intramedullary nail that guide a drill bit toward an
opening in the
intramedullary nail. However, these devices fail to provide the degree of
accuracy
required for locating and drilling openings in intramedullary nails due to the
inherent
flexure in these devices. Furthermore, the flexure increases as the length of
the arm
increases, which renders them impractical for drilling distal openings in the
nails. These
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devices can be deflected as much as a centimeter or more off the distal
openings of an
intramedullary nail.
The earliest successful magnetic targeting was accomplished by Durham et al.
and
was described in a succession of patents covering a mechanical magnetic
targeting system
using a mechanically balanced cannulated magnet (U.S. Patent Nos. 5,049,151;
5,514,145; 5,703,375; and 6,162,228). Hollstien et al. (U.S. Patent No.
5,411,503)
followed with an electrically based system of stacked flux finders connected
to a PC
display. These devices, however, operate at the level of the skin. The magnets
used in
these devices may not be strong enough to accurately position the drill bit as
even the
fields of the strongest magnets diminish to that of the earth's magnetic field
at distance of
about 10 cm.
As a result, all of the prior devices have yet to be practical in surgical
use.
SUMMARY OF THE INVENTION
The present invention provides an intramedullary nail targeting apparatus.
A preferred version of the targeting apparatus includes a nail extension. The
nail
extension is capable of being connected to an end of an intramedullary nail
and includes a
targeting arm configured to extend along a longitudinal axis of the
intramedullary nail
when connected thereto. The targeting arm on the nail extension includes one
or more
bores.
The targeting apparatus also includes a magnetic targeting device capable of
detecting a magnet for attaching to the targeting arm. The targeting arm
provides support
and stability for the magnetic targeting device. The magnetic targeting device
includes a
support member having a proximal end and a distal end and is structured to fit
through at
least one of the bores in the targeting arm, a sensor array disposed on the
distal end of the
support member, and a positional indicator. The support member has a length
sufficient to
place the sensor array against a bone comprising the intramedullary nail when
the nail
extension is connected to the intramedullary nail and the magnetic targeting
device is
connected to the targeting arm.
The targeting apparatus also includes a magnet member disposed in fixed
relation
to the intramedullary nail. Targeting of the magnetic targeting device to the
magnet
member in the intramedullary nail aligns the targeting arm on which the
magnetic
targeting device is supported with the intramedullary nail. This, in turn,
aligns bores in
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the targeting arm with screw openings in the intramedulary nail. The bores can
then be
used for accurate drilling of the bone to secure the intramedullary nail
thereto.
A preferred version of the invention further includes a magnet member that
produces a radial magnetic field. This includes, for example, a magnet member
comprising individual magnets in a "bucking configuration," wherein the magnet
member
includes a first magnet and a second magnet arranged coaxially with like poles
placed
head-to-head. In other versions of the invention, the magnet member includes a
third
magnet interposed between the first and the second magnets and oriented
orthogonally to
the first and the second magnets.
Some versions of the invention further include an orthogonal targeting guide
for
targeting and drilling orthogonal screw openings in intramedullary nails. A
preferred
version of the orthogonal targeting guide includes a lateral support base for
attaching to
the targeting arm or other support structures, orthogonal support arms
extending from the
lateral support base, and a mechanical targeting arm with orthogonal guide
bores for use
in drilling the orthogonal screw openings. The orthogonal targeting guide also
preferably
includes a straight-edge guide for aligning the orthogonal guide bores over
the orthogonal
screw openings.
The invention also provides a method of targeting screw openings in an
intramedullary nail for the internal fixation of a bone within a limb, wherein
the
intramedullary nail includes first and second screw openings. In a preferred
version, the
method includes placing the intramedullary nail in a medullary cavity of the
bone,
wherein the intramedullary nail includes a magnet member positioned at a
known, fixed
position relative to the second screw opening, attaching a nail extension
comprising at
least a first bore and a second bore to a proximal end of the intramedullary
nail, attaching
a magnetic targeting device to the targeting arm, aligning the magnetic
targeting device
with the magnet member, drilling a first hole in the bone at a position of the
first screw
opening, stabilizing the targeting arm to the first screw opening, and
drilling a second
hole in the bone at a position of the second screw opening. In this version,
the second
screw opening is targeted with the magnetic targeting device inserted through
the second
bore while the first screw opening is drilled using the first bore.
In some versions, the targeting arm is stabilized to the first and second
screw
openings after drilling the second hole. The targeting arm is preferably
stabilized to the
screw openings with drill guides. The stabilizing is followed by attaching an
orthogonal
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targeting guide to the stabilized targeting arm and drilling holes in the bone
through the
orthogonal targeting guide.
Other versions further include un-stabilizing the targeting arm after drilling
the
second hole, rotating the nail extension orthogonally, targeting orthogonal
openings in the
intramedullary nail with the magnetic targeting device, and drilling holes in
the bone
through the orthogonal openings.
The invention further provides a bone plate targeting apparatus for targeting
a
bone plate including holes. The apparatus comprises a magnet member disposed a
defined
distance from at least one of the holes in the bone plate, and a magnetic
targeting device.
The invention further provides a method of targeting holes in a bone plate for
the
external fixation of a bone within a limb. The method comprises placing the
bone plate
against the bone, placing a magnetic targeting device against the bone plate,
aligning the
magnet member with a sensor array in the magnetic targeting device, wherein
aligning the
magnet member with the sensor array aligns the lower opening of the drill
guide with the
at least one of the holes, and drilling a hole in the bone through the hole in
the bone plate.
The present invention advantageously provides magnet members that provide
larger magnetic fields in the same space confines, a targeting system that is
unaffected by
incidental rotation of a magnet member within an intramedullary nail, the
ability to use
smaller sensor arrays that can be used percutaneously while still attaining
accurate
targeting, a targeting system that can be used for a variety of bone sizes and
intramedulary nail sizes, and a stable system that minimizes erroneous degrees
of
freedom while targeting and drilling.
The objects and advantages of the invention will appear more fully from the
following detailed description of the preferred embodiments of the invention
made in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of the magnetic targeting device of the present
invention.
FIG. 2 is a cross-sectional view of the magnetic targeting device of FIG. 1
taken
along lines 2 - 2 of FIG. 1.
FIG. 3 is a cross-sectional view of the sensor foot of the magnetic targeting
device of FIG. 1 taken along lines 3 - 3 of FIG. 2.
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FIGS. 4A and 4B are partial side plan views of the magnetic targeting device
of
FIG. 1 comprising a hinged sensor foot.
FIG. 5 is a side plan view of the magnetic targeting device illustrating its
operation with respect to a long bone.
FIG. 6 is a top view of the intramedullary nail of the present invention.
FIG. 7 is a top plan view of the magnetic targeting device of FIG. 1 with the
cover (i.e., upper body portion) removed.
FIG. 8 is a block diagram illustrating the operation of the magnetic targeting
device of the present invention.
FIG. 9 is a top plan view of the magnetic targeting device of FIG. 1
illustrating
the display.
FIG. 10 is a diagram illustrating the amplitude output of the sensors.
FIG. 11 is a diagram illustrating the flux density of the magnetic field at
various
distances from the magnet.
FIG. 12A is a side cutaway view of a magnet member on a magnet insertion rod
in a "bucking" configuration within an intramedullary nail.
FIG. 12B is a cross-sectional view taken across line 12B - 12B of FIG. 12A.
FIG. 12C is a side cutaway view of a magnet member comprising both
longitudinally and orthogonally oriented magnets on a magnet insertion rod.
FIG. 13 is a perspective view of a magnetic targeting device mounted on a nail
extension of the present invention.
FIG. 14 is a perspective view of a magnetic targeting device mounted on a nail
extension with an orthogonal targeting guide mounted on the nail extension.
DETAILED DESCRIPTION OF THE INVENTION
Definitions
Unless explicitly stated otherwise, "x axis," "y axis," and "z axis" used in
reference to the intramedullary nail 60 or the magnet member 70 inserted in
the
intramedullary nail 60 are defined relative to the intramedullary nail 60
having screw
openings 64,66,68 shown in FIGS. 5 and 6. "X axis" refers to an axis defined
by the long
axis of the intramedullary nail 60. "Y axis" refers to an axis defined by the
central axis of
screw opening 68, which is substantially orthogonal to the long axis of the
intramedullary
nail 60 and to screw openings 64,66. "Z axis" refers to an axis defined by the
central axis
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of screw openings 64,66, which are substantially orthogonal to the long axis
of the
intramedullary nail 60 and to screw opening 68. Thus, in FIGS. 5 and 6, the x
axis runs
the length of the depicted intramedullary nail 60 from its left-hand side to
its right-hand
side; the y axis runs perpendicular to the length of the depicted
intramedullary nail 60
through screw opening 68; and the z axis runs perpendicular to the length of
the depicted
intramedullary nail 60 through screw openings 64,66.
Magnetic Targeting Device 10
Referring now to FIG. 1, the present invention includes a magnetic targeting
device 10 which, in an exemplary version, includes a body 12 with a handle
portion 22, a
support member 14, a button 20, a sensor foot 16 connected to a distal end of
the support
member 14, a display 18, and a drill sleeve 26 constituting or extending
through the
support member 14. The magnetic targeting device 10 places the sensor foot 16
of the
support member 14 directly on the bone 100, illustrated in FIG. 5, for more
accurate
reading.
Body 12
The body 12 can be made of a variety of materials known to the medical arts,
including plastic and metal as appropriate for durability and reusability of
the magnetic
targeting device 10. As illustrated in FIG. 1, the body 12 is designed to be
handheld and
comfortable with finger grips 24 in the handle portion 22. The body 12 also
holds the
battery 32, the comparator circuit 86 and the display 18, as illustrated in
FIGS. 2 and 7.
The magnetic targeting device 10 can operate on two AAA batteries, have
rechargeable
cells, or be wired for electrical operation.
The body 12 of the magnetic targeting device 10 is amenable to several non-
limiting design variations, each with various advantages.
In some versions, the body 12 and support member 14 are provided as a single
unit.
In the exemplary version, the body 12 and support member 14 are provided as
separate units and are separable, for example, at line 38 (see FIGS. 1 and 2).
Connecting
elements are known in the art for joining the support member 14 to the body 12
in a
manner to enable the electrical connection between the two units. In the
exemplary
version, the body 12, which contains the electronic circuitry (such as the
comparator
circuit 86), may be provided in a sterile bag (not illustrated) and would not
have to be
sterilized prior to use. During use, the plastic bag containing the body 12
could be
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perforated by the sensor-support member 14 portion of the device to connect to
the
electronic circuitry in the body 12 to render the magnetic targeting device 10
ready for
use. Alternatively, the electronics can be made to withstand sterilization,
including but
not limited to gas sterilization, autoclaving, CIDEX disinfecting solutions
(Johnson &
Johnson Corporation, New Brunswick, NJ) or other similar chemical soaks, or
any
equivalent thereof. This permits the support member 14 to attach to the body
12 at line 38
and be used without a sterile bag.
Having the support member 14 and the body 12 as separate units also allows for
different interchangeable support member 14 options for the same body 12. One
advantage of having different support member 14 options is that they can be
used for
different applications such as humeral or tibial nail-locking, which might use
smaller
diameter locking screws and require narrower drill sleeves 26. A second
advantage is that
support members 14 having different lengths may be used. Shorter support
members 14
would allow more efficient use of the magnetic targeting device 10 when deep
soft tissues
do not have to be avoided. A third advantage is that different sensor array 33
configurations (see below) may be used for different applications. The ability
to use
different support member 14 options therefore prevents the necessity of making
a
different magnetic targeting device 10 for each application.
Providing the body 12 and support member 14 as separable units also permits
the
support member 14 to be made of disposable materials for simple disposal after
use.
In another version, the magnetic targeting device 10 is connected wirelessly
between the sensor foot 16 and the display 18 to transfer targeting or display
information
wherever needed. The sensing information may be transmitted by radio,
infrared, or
equivalent thereof from the sensor foot 16 to the display 18. The display 18
may be
separate from the body 12 and can comprise any medium, including virtual
projections,
heads-up glasses, a personal computer, or a television screen. Such a display
18 can be
made from any compatible non-magnetic material.
The body 12 may also be separable along line 39, as shown in FIG. 2, to divide
the body 12 into an upper body portion 12A and a lower body portion 12B. The
upper and
lower body portions 12A,B, may be connected by screws 13A that insert into
threaded
holes 13B, the latter of which extend from the lower body portion 12B into the
upper
body portion 12A. Other mechanisms of connecting the upper and lower body
portions
12A,B may be used. The ability to separate the upper and lower body portions
12A,B
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allows the user to access internal parts of the device 10, such as the battery
32 and the
comparator circuit 86.
The body 12 may be provided with or without a handle portion 22.
The button 20 is provided generally on the top surface of the body 12 at a
convenient location for the surgeon to power and calibrate the device 10. The
button may
also turn off the device 10. The button 20 is positioned for comfortable use.
There may be
a button 20 on either side of the handle portion 22 activating the same
functions, to allow
for left- or right-handed use.
Support Member 14 and Sensor Foot 16
The preferred design of the present invention includes a support member 14
about
10 cm in length. While the length of the support member 14 is variable, a
length of 10 cm
incorporates most distal femoral soft tissue sleeves. For tibial and humeral
applications,
the support member 14 can be as short as 3-4 cm.
The sensor foot 16 is preferably disposed on a distal end of the support
member
14 and comprises the sensor array 33. In a version shown in FIG. 3, the sensor
foot 16
resembles a foot wherein the toe portion 17 contains the sensor array 33 and
the heel
portion 19 contains the lower opening 30 of the drill sleeve 26. In another
version, the
sensor foot 16 comprises the same shape as the distal end of the support
member 14. A
smaller sized sensor foot 16 on the support member 14 is more practical to
use.
In some versions, the sensor foot 16 can be separated from the support member
14. This enables sensor feet 16 having different sensor arrays 33 to be used
on the support
member 14.
As shown in FIGS. 4A and 4B, some versions of the sensor foot 16 include a
swivel design wherein the sensor foot 16 is hingedly attached to the support
member 14
by means of a hinge unit 40. This configuration eases insertion of the sensor
foot 16 into
the soft tissues at the point of insertion. The hinge unit 40 can be made of a
number of
materials and designs to incorporate the swivel functioning of the unit. Prior
to insertion
into an opening in a limb for positioning next to a bone 100, the sensor foot
16 is rotated
by means of the hinge 40 and pointed in parallel alignment with the support
member 14
for ease of movement toward the bone 100, as illustrated in FIG. 4A. As the
toe portion
17 comes in contact with the bone 100, the foot 16 will rotate in an arc
approximating
arrow 42 until the sensor foot 16 rests on the bone 100 approximately
perpendicular to the
support member 14, as illustrated in FIG. 4B.
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Sensor array 33
The sensor array 33 is preferably included within the sensor foot 16 of the
support
member 14 near the lower opening 30 of the drill sleeve 26 (see FIG. 3). In
one version
of the invention, the sensor array 33 is dimensioned and configured such that
each sensor
34 in the array 33 is capable of being excited by the same magnitude and angle
of flux
when centered about the magnet member 70. As used herein, "angle of flux"
refers to the
angle of the magnetic field 74 flux lines 78 relative to the orientation of
the sensor 34 and
does not refer to the direction through which the flux lines 78 run through
the sensor 34.
For example, sensors 34 positioned equidistantly from and on either side of a
center line
of flux 75 extending from a magnet member 70 would have the same magnitude and
angle of flux even though the flux lines 78 would extend through the sensors
34 in
opposite directions. An exemplary version of an array 33 that is excited by
the same
magnitude and angle of flux when centered about the magnet member 70 is shown
in
FIG. 3. The sensor array 33 in this version includes four magnetic sensors 34
arranged in
a substantially planar, symmetrical array. Other exemplary substantially
planar arrays
include those described in U.S. Pub. No. 2005/0075562 to Szakelyhidi et al.
Other sensor arrays 33 may be symmetrical about the magnetic field 74 but not
planar. For example, the sensor array 33 may include a pyramidal arrangement.
Such an
arrangement may include one or two additional, "z-axis" sensors positioned
equidistantly
from sensors 34 arranged in a planar, symmetrical arrangement. The z-axis
sensors may
be placed anywhere along an axis running through the center of the planar,
symmetrical
arrangement of sensors 34. In one version, the sensor array 33 includes one z-
axis sensor
positioned outside the plane defined by the sensors 34 arranged in the planar,
symmetrical
arrangement. In a second version, the sensor array 33 includes a first z-axis
sensor
positioned outside the plane defined by the sensors 34 in the planar
arrangement and a
second z-axis sensor positioned within the plane defined by the sensors 34 in
the planar
arrangement. The z-axis sensor positioned outside the plane in these versions
is
preferably disposed on a side of the planar sensors 34 opposite the magnet
member 70. A
sensor array 33 in a pyramidal arrangement provides both translational and
rotational
positional information with respect to the magnet member 70. When the sensor
array 33
is aligned over the field, the z-axis sensors detect the field at maximum
strength.
In sensor array 33 configurations comprising z-axis sensors, a magnet 72
placed at
a distance from the sensor foot 16 may dispose the z-axis sensors between
collinear flux
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lines 78. Targeting in such a case may be achieved when the sensors detect
flux lines 78
parallel to the magnetic field 74.
The sensor array 33 may include any number of sensors 34 in any configuration,
provided that each sensor 34 in the array 33, in combination with other
elements of the
invention, is capable of detecting the magnetic field 74 in a manner that
predictably
indicates the translational and/or rotational position of the magnetic
targeting device 10
relative to the magnet member 70. For example, in preferred versions, the
system permits
translational alignment in either the x-y and/or x-z planes in addition to
rotational
alignment about the x, y, and z axes.
The individual sensors 34 in the sensor array 33 are preferably polarized
sensors.
As used herein, "polarized sensors" are sensors 34 capable of detecting the
magnetic field
74 in all three dimensions (as defined by the sensor), thereby providing a
readout of the
magnitude and direction of the flux lines 78 comprising the magnetic field 74
at a given
position. A preferred example of a polarized sensor that may be used in the
sensor array
33 is a Honeywell HMC 1052 (Morristown, NJ) magneto resistive sensor. Magneto
resistive sensors advantageously have an internal magnetic reset function that
can reverse
the magnetizing effect of a permanent magnet when brought too close to the
sensor array
33. This feature works well and is used to reset the sensors 34 upon every
calibration
operation (described below). The sensor reset driver pushes a large current
pulse through
all sensors at once to perform the reset.
The sensor array 33 is connected to the comparator circuit 86 in the body 12
by
printed circuit wiring, wires 36 extending within the support member 14 beside
the drill
sleeve 26 (see FIG. 2), or through wireless communication. In the exemplary
version
shown in FIG. 2, the sensor array 33 is molded in a plastic support member 14
with the
wires 36 from the sensor array 33 ascending the support member 14 to the
comparator
circuit 86 and linked to a display 18.
The magnetic targeting device 10 is preferably configured such that each
individual sensor 34 in the sensor array 33 detects multiple flux lines 78 for
high
resolution in targeting. This is a difficult hurdle in conventional magnetic
intramedullary
nail targeting devices. All magnets obey the inverse square rule, wherein the
strength of
the magnetic field drops off at the square of the distance. Doubling the
distance decreases
the magnetic field strength to 25%. If the distance between a sensor and a
magnet is 10
cm, the magnetic field is 1% the strength and field density of a sensor array
1 cm from the
WO 2010/123879 PCT/US2010/031725
magnet. Conversely, the strength of the magnetic field at 1 cm from the magnet
would be
100 times stronger than the same magnetic field measured at 10 cm.
As shown in FIG. 11, the lines of flux 78 of a magnetic field 74 are so
diffuse at a
distance of 10 cm 80 from a magnet member 70 that a sensor would detect only
one or
fewer flux lines 78 at a time. This is insufficient for accurately locating
the center of a 5
mm hole. At a distance of 1.5 cm 82 or other distances closer to the magnet
member 70,
multiple flux lines 78 can be detected and translated into targeting
information. This
applies even for relatively small sensors.
Disposing the sensor array 33 on the sensor foot 16 in the present invention
allows
the sensor array 33 to be placed at the surface of the bone 100 and in close
proximity to
the magnet member 70. As a non-limiting example, a sensor array 33 suitable
for
detecting multiple flux lines 78 in the current system includes individual
sensors 34 1-2
mm square and arranged in an array 33 about 5-8 mm across and 2-5 mm thick. A
preferred distance between the sensor array 33 and the magnet member 70 is a
distance of
about 1.5 cm, typically the average thickness of the side of the bone 100. At
that distance,
the field density is about 30 times the density at a distance of 10 cm. Other
acceptable
distances include about 1 cm, about 2 cm, about 3 cm, about 4 cm, about 5 cm,
about 6
cm, or more. The center line of flux 75 of the magnetic field 74 can be offset
as little as 6-
10 mm from the center axis of the hole to be drilled. To date the most
difficult distal
targeting goal has been the distal femur. The working distances from the
annular cavity
62 of an intramedullary nail 60 in a distal femur to the surface of the bone
is typically no
more than 3 cm and is usually 1-2 cm. Thus, the magnetic targeting device 10
described
herein is capable of accurately targeting the distal femur. This makes
targeting nearly any
other bone, i.e., the tibia, humerus, or any other long bone, even easier with
the magnetic
targeting device 10 described herein because of smaller cortex to nail
distances.
In a preferred version, the sensors 34 in the array 33 are positioned so that
they are
perpendicular to the maximum density flux lines when the array 33 is centered
over the
magnet member 70.
Intramedullary Nail 60
Referring to FIG. 5, the magnetic targeting device 10 is illustrated in
association
with a long bone 100, such as a broken femur, tibia, or humerus bone. Within
the bone
100, there is illustrated an intramedullary nail 60, known in the art.
Examples of
intramedullary nails are prevalent in the prior art. For example, reference is
made to U.
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S. Patent 6,503,249 to Krause and the patents to Durham (cited herein), the
contents
of which are incorporated herein for a description of intramedullary nail and
manners
of use. The intramedullary nail 60 is an elongated metal rod typically having
an
annular cavity 62; although, as described with respect to the intramedullary
nail 60 in
FIG. 6, the intramedullary nail 60 may also be a solid body. The
intramedullary nail 60
typically includes a first, proximal screw opening 64 and a second, distal
screw
opening 66. The screw openings 64,66 of typical intramedullary nails 60 are
transverse, i.e., having center axes about ninety degrees to the long axis of
the nail 60,
as illustrated in FIGS. 5 and 6. However, intramedullary nails 60 may contain
non-
transverse or oblique screw openings, i.e., having center axes at angles other
than at
about ninety degrees in relation to the long axis of the intramedullary nail
60.
Intramedullary nails 60 also typically include one or more screw openings 68
positioned orthogonally to both the longitudinal axis of the nail 60 and screw
openings 64,66, as illustrated in FIG. 6. As used herein, screw openings 64,66
are
referred to as "lateral" screw openings 64,66, and screw opening 68 is
referred to as
an "orthogonal" screw opening 68.
Prior to placement of the intramedullary nail 60 within a bone 100, a reaming
rod known to the art is worked through the medullary cavity 101 of the bone
100, such
as a broken femur, tibia, or humerus bone. The intramedullary nail 60 is then
placed
within the medullary cavity 101 for securing within the bone 100 by means of
cross-
locking screws or bolts positioned through the screw openings 64,66,68.
Magnet Member 70
The magnetic targeting device 10 of the present invention targets an
intramedullary nail 60 by aligning the sensor array 33 on the magnetic
targeting device 10
with a magnet member 70 in fixed relation to the intramedullary nail 60. The
magnet
member 70 comprises one or more individual magnets 72.
In a version of the invention shown in FIG. 12A, the magnet member 70 is
attached to a magnet insertion rod 73 or other like device. The magnet
insertion rod 73 is
inserted into the annular cavity 62 of the intramedullary nail 60, typically
in a specified
orientation, to a locking point at a set distance from at least one of the
screw openings
64,66,68. A reaming rod, known in the art, can be adapted for use as a magnet
insertion
rod 73. The adaptation requires a mechanism for attaching the magnet member 70
to the
distal end of the rod 73, with provisions for maintaining correct depth,
rotation, and
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centering of the magnet member 70 within the intramedullary nail 60. Such an
attachment
mechanism can include threads on a proximal end of the magnet insertion rod 73
that
connect to a threaded portion of the annular cavity 60. The magnet insertion
rod 73 can
also be secured to an end of a nail extension 110 (see below). Magnet
insertion rods 73 of
different lengths can be included for placement of the magnet member 70
relative to
different screw openings 64,66,68 along the length of the nail.
In another version of the invention, as illustrated in FIGS. 5 and 6, the
intramedullary nail 60 has magnet members 70 embedded directly on the surface
of the
intramedullary nail 60. An intramedullary nail 60 with a magnet member 70
embedded
therein does not require an annular cavity 62 and can be solid.
In another version (not shown), a magnetic ring is placed around the periphery
of
the screw openings 64,66,68 or to placed in the center of the screw opening
64,66,68 as a
displaceable "bull's-eye."
In yet another version (not shown), the magnet member 70 can be located at the
screw opening 64,66,68 on a swivel that retracts when the drill enters the
screw opening
64,66,68. The magnet member 70 is centered within the intramedullary nail 60
by a
circular spring mechanism or equivalent.
In order to align and advance a drill bit 96 through the bone 100 accurately,
a
surgeon must have accurate knowledge of the position of the lower opening 30
of the drill
sleeve 26 in relation to the axes of the screw openings 64,66,68. The magnetic
targeting
device 10 described herein accomplishes this by employing magnet member-sensor
array
30-34 combinations that provide translational and/or rotational positioning
information.
For example, the magnet member-sensor arrays 30-34 described herein provide
translational positioning alignment along planes orthogonal to the targeted
screw
openings 64,66,68, together with rotational positioning alignment about the
central axis
defined by the screw openings 64,66,68. Alternatively, the magnetic targeting
device 10
employs magnet member-sensor array 30-33 combinations together with additional
elements, such as a nail extension 110 (see below), to provide this alignment
for
targeting.
One version of the magnet member 70, shown in FIG. 11, employs a polarized
magnet 72 with either its north or south pole facing an axis orthogonal to the
x axis of the
intramedullary nail 60 such that it projects a magnetic field 74 having a
central line of
flux 75 parallel to the axis of one of the screw openings 64,66,68. Such a
magnet 70 may
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be dimensioned and configured to produce either circular or non-circular flux
lines. Non-
circular flux lines produce a non-circular field shape that uniquely defines
each axis. This
produces a field shape and polarity that potentially affords unique targeting
information in
all possible planes, such as the three-dimensional orientation of the
intramedullary nail's
60 x-axis, y-axis, and z-axis. See U.S. Pub. No. 2005/0075562 to Szakelyhidi
et al.
regarding non-circular flux lines.
Another version of the magnet member 70, shown in FIGS. 12A and 12B,
includes two individual magnets 72 with like poles placed head-to-head in a
"bucking"
arrangement. For example, a north pole of a first magnet 72 is connected to a
north pole
of a second magnet 72, and south poles of the first and second magnets 72
extend
coaxially therefrom. The same arrangement can be achieved by placing the south
poles
head-to-head. The magnet member 70 in such an arrangement is preferably
longitudinally
oriented within the annular cavity 62 along the longitudinal axis (x axis) of
the
intramedullary nail 60. The bucking arrangement is advantageous in that it
compresses
the flux lines and produces a radial magnetic field 74 projecting orthogonally
to the long
axis of the intramedullary nail 60. Because the magnetic field 74 is radially
projected, it
always has a component perpendicular to the targeted screw openings 64,66,68,
regardless of the amount of rotational deflection while inserting the magnet
member 70 in
the annular cavity 62 of the intramedullary nail 60. The condensed, radially
projected
magnetic field 74 also permits the sensor array 33 to be compressed, which, in
turn,
permits a smaller-sized sensor foot 16. This allows for placement of the
sensor foot 16
directly against the bone 100 with less damage to surrounding tissue. Another
advantage
of the bucking arrangement is that the central lines of flux 75 emanating from
the like
poles of the magnet member 70 (FIGS. 12A and 12B) are at least twice the
strength of
central lines of flux 75 emanating from a magnet member 70 with its pole
aligned
orthogonally to the longitudinal axis of the intramedullary nail 60 (FIG. 11).
This
increases the strength of the magnetic field 74 at any given position on the z
axis of the
intramedullary nail 60.
The magnets 72 used in the bucking arrangement have cross-sectional dimensions
and shapes that enable them to fit within the annular cavity 62 of the
intramedullary nail
60. Most intramedullary nails 60 have an annular cavity 62 about 3-4 mm in
diameter.
The magnet 70 used in the bucking arrangement therefore are preferably sized
with about
3 mm in cross-sectional width (i.e., diameter of a cylindrical-shaped magnet)
and
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preferably no more than about 4 mm in cross-sectional width. This provides an
optimal
strength while still fitting in the annular cavity 62 of the intramedullary
nail 60. However,
it is within the scope of the present invention to use any size of magnet 72,
as long as the
magnet 72 can fit within the annular cavity 62 of the intramedullary nail 60.
Other magnet configurations for producing radially oriented magnetic fields 74
that can be used in the present invention are provided by U.S. Patent No.
5,028,902 to
Leupold et al. and U.S. Patent No. 5,865,970 to Stelter.
Another version of the magnet member 70 is shown in FIG. 12C. This version
comprises at least three magnets 72 disposed along a longitudinal axis, for
example, the x
axis of the intramedullary nail 60. Two of the magnets 72, comprising the ends
of the
magnet member 70, are disposed with both the north and south poles aligned
along the
longitudinal axis of the magnet member 70. These longitudinally oriented
magnets are
oriented with their like poles (i.e., north-north or south-south) facing each
other, similar
to the arrangement in the bucking configuration. A third, orthogonally
oriented magnet 72
is interposed between the longitudinally oriented end magnets with its axis
and central
line of flux 75, parallel to the axis of one of the screw openings 64,66,68.
In the preferred
version of this magnet member 70, the longitudinally oriented magnets contact
the
orthogonally oriented magnet. However, the magnets may be separated by a short
distance as well. As with the other magnet member 70 configurations, the
magnet
member 70 configuration shown in FIG. 12C can be attached co-axially along the
longitudinal axis to a magnet insertion rod 73 for insertion in an annular
cavity 62 of an
intramedullary nail 60. The magnets 72 are each sized to fit within the
annular cavity 62.
The magnet member 70 in the configuration shown in FIG. 12C produces a
magnetic field 74 substantially similar in shape to a magnet member 70
comprising an
orthogonally oriented magnet 72 alone (see FIG. 11). However, the presence of
the
longitudinally oriented end magnets tightens and further projects the magnetic
field 74
along the axis defined by the orthogonally oriented magnet 72. The
orthogonally oriented
magnet 72 captures and redirects the "bucking" field preferentially toward the
sensor
array 33. The magnetic field produced by this configuration permits greater
resolution in
targeting at distances further away from the magnet member 72.
Several mechanisms can be employed to increase the sensitivity of the magnetic
targeting device 10 with respect to the magnetic field 74 . One mechanism
includes
superimposing a fluctuating magnetic field upon the static magnetic field 74
produced by
WO 2010/123879 PCT/US2010/031725
the magnet member 70. Another mechanism includes placing a ferromagnetic
material
within the support member 14 between the sensor array 33 and the proximal end
of the
support member 14 on an axis running through the center of the sensor array
33. When in
the presence of the magnetic field 74, the flux lines 78 concentrate on the
ferromagnetic
material, which extends the magnetic field 74 in the direction of the device
10.
Any type of magnet 72 may be used in the current device 10, including
permanent
magnets, solenoids, and electromagnets (i.e., iron core solenoids). A
preferred version of
the magnetic targeting device 10 includes a neodymium iron boron (NdFeB) bar
magnet.
Display 18
As illustrated in FIG. 9, the display 18 is preferably graphical in nature and
provides a crosshair 92 in combination with a target icon 90. The crosshair 92
and target
icon 90 indicate the amount of misalignment of the sensor array 33 with
respect to the
magnet member 70 in or on the intramedullary nail 60. Referring to FIG. 9,
when the
target icon 90 is centered on the crosshair 92, the sensor array 33 is
centered over the
magnet member 70. Depending on the version of the invention, this may indicate
that the
lower opening 30 of the drill sleeve 26 is centered over a screw opening
64,66,68 for
accurate drilling. An advantage of this type of display is that it has sub-
millimeter
resolution. In addition, visualization of the position of the sensor array 33
relative to the
magnet member 70 in the display 18 permits the surgeon to ultimately decide
when
drilling is appropriate. It is preferred that the display 18 includes a liquid
crystal display
(LCD) screen.
In addition to moving the target icon 90 with respect to the crosshairs 92,
more
accurate information can be attained by enlarging the target icon 90 in
response to the
strength of the magnetic field 74 being sensed. Being able to detect the
strength of the
magnetic field 74 at various locations ensures that the magnetic targeting
device 10 is not
sensing a symmetrical set of magnetic field 74 flux lines 78 around the magnet
member
70 or a flux pattern created between two or more magnet members 70 which may
be
embedded into the side of a solid intramedullary nail 60.
Some versions of the magnetic targeting device 10 may include other types of
positional indicators in addition to or as an alternative to the display 18
with crosshairs 92
and a target icon 90. These positional indicators may indicate positional
information of
the magnetic targeting device 10 relative to the intramedullary nail 60 and/or
the magnet
member 70 via any modality, including variable LED, audio output, color
change, or
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vibration. In a version employing audio output, the magnetic targeting device
10 provides
intermittent sounds such as beeps when the magnetic targeting device 10
detects a magnet
field, with intervals between the intermittent sounds becoming shorter as the
magnetic
targeting device 10 becomes centered over the magnet member 70. In version
employing
a vibration modality, the magnetic targeting device 10 vibrates as the
magnetic targeting
device 10 first detects a magnetic field 74. The vibration grows in intensity
as the
magnetic targeting device 10 centers over the magnet member 70. Any of the
display
modalities described herein may be combined in any combination. For example, a
magnetic targeting device 10 employing a visual display 18 may beep and/or
provide a
short vibration pulse upon the target icon 90 being centered on the crosshairs
92.
In other versions, the display 18 can operate in the manner described in U.S.
Pub.
No. 2005/0075562 to Szakelyhidi et al., which is incorporated herein by
reference.
Some versions of the invention are capable of detecting positional information
of
the magnetic targeting device 10 relative to the intramedullary nail 60 and/or
the magnet
member 70 in three-dimensions, i.e., by detecting the position of the magnetic
targeting
device 10 relative to the x, y, and z axes of the intramedullary nail 60
and/or the magnet
member 70. Such versions may provide positional indicators that reflect the
three-
dimensional position and orientation of the sensor array 33 relative to the
magnet member
70. In one version, the positional indicator reflects the position of the
magnetic targeting
device 10 using two outputs. A first output displays the position with respect
to a plane
orthogonal to the targeted screw opening 64,66,68 (e.g., the x-y plane), and a
second
output displays the position with respect to a central axis defined by the
screw opening
64,66,68 (e.g., the z axis). An example of a first output for such a
positional indicator is
as shown in FIG. 9. The translational positioning of the magnetic targeting
device 10 on
the x-y plane relative to the magnet member 70 is indicated by the positioning
of the
target icon 90 relative to the crosshairs 92. The rotational positioning of
the magnetic
targeting device 10 on the x-y plane relative to the magnet member 70 is
indicated by
rotation of the sides of the target icon 90 relative to the crosshairs 92. An
example of a
second output for such a positional indicator includes a line with a hash mark
indicating
the center of the line and a target icon positioned along the length of the
line. Positioning
of the rotational target icon along the line either to one side or the other
of the hash mark
would indicate rotational misalignment of the magnetic targeting device 10
relative to the
z axis of the magnet member 70. Positioning of the rotational target icon on
the hash
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mark would indicate alignment. The positional information afforded by such a
positional
indicator permits translational and/or rotational positioning with respect to
the x-y plane
and rotational position with respect to the z axis. This prevents off-axis
drilling of the
nail.
Internal Operation of Device 10
Reference is now made to FIGS. 7 and 8 for a description of the internal
operation
of the device 10. In action, the microcontroller powers a single sensor 34 in
turn, using
the switch 103 to connect it to the high gain amplifier 104. The
microcontroller 102 then
sets the digital voltage generator 106 to a predetermined value. The
microcontroller 102
waits for the sensor 34 and amplifier 104 to settle and then reads the voltage
from the
amplifier 104. This voltage is proportional to the applied magnetic field 74
but also
contains some environmentally generated noise and noise which is inherent in
the sensors
34. The microcontroller 102 selects the four sensors 34 in sequence, measuring
their
outputs and saving them for targeting computations. A complete set of
measurements is
made typically 20 to 50 times per second. As with any high gain sensor system,
small
errors can be multiplied by factors of 1000 or more, resulting in problems
making the
required measurements. The sensors 34 are no different and have offset errors
in their
outputs that make measurements difficult without some adjustment. The
amplifier 104
introduces errors as well. The digital voltage generator 106 is used during
the calibration
process to null out these errors.
When the magnetic targeting device 10 is powered on by the button 20, the
magnetic targeting device 10 immediately begins a calibration sequence. This
involves
selecting each sensor 34 in turn and determining the value from the digital
voltage
generator 106 that is required to bring the amplifier 104 into its linear
amplifying region
of operation. This operation takes only a couple seconds. Thereafter, as each
sensor 34 is
selected, the digital voltage generator 106 is loaded with the particular
value for that
sensor 34, resulting in nullification of static errors for that sensor's
measurement. The
circuit also features a two-step amplifier gain selection, though the software
may use only
the high gain setting. Such a system allows use of the magnetic targeting
device 10 for
various thicknesses of human bone 100 without software changes. This design
uses one
amplifier 104 and an inexpensive commodity solid state switch 103 to select
which sensor
34 to read. Another feature not shown is that the microcontroller 102 does not
leave all
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WO 2010/123879 PCT/US2010/031725
sensors 34 powered continuously, but rather turns them on in sequence, saving
power
consumption.
The microcontroller 102 uses a vector algorithm to determine how to position
the
target icon 90 on the display 18. The position of each sensor 34 is assigned a
vector
direction depending on its position in the array 33. The amplitude of the
output of each
sensor 34 provides the magnitude of each vector 35. Addition of the magnitudes
of the
vectors 35 provide a resultant vector 71 that determines the position of the
magnetic
targeting device 10 relative to the magnet member 70, which is represented as
a two-
dimensional position of a target icon 90 on the display 18 (see FIG. 9). FIG.
10, for
example, shows a center box representing the magnet member 70 and four other
boxes
representing the magnetic sensors 34. The vector lines 35 attached to each
sensor 34,
respectively, indicate the strength of the field at each sensor. The resultant
vector 71 is the
sum of the vector lines 35 and indicates the direction the sensor array 33
should be moved
to center it over the magnet member 70. The magnet member 70 in FIG. 10
corresponds
with the target icon 90 in FIG. 9.
The circuitry in the present invention compares and displays information about
the
magnetic field 74 in real time for rapid and accurate positioning of the
targeting arm 120
while drilling.
Referring back to FIG. 8, the thermal cutoff 108 is present in case the
magnetic
targeting device 10 is accidentally run through a sterilizer cycle. The
thermal cutoff 108
activates at 82 Celsius and disables operation of the magnetic targeting
device 10
permanently. Without the thermal cutoff 108, it is likely that the magnetic
targeting
device 10 would work somewhat after being exposed to such heat, but reliable
operation
could not be guaranteed. A low battery indicator is implemented that warns the
user of
low batteries 32 on the display 18 and also prevents the magnetic targeting
device 10
from operating.
User Operation
The button 20 is used to turn on the magnetic targeting device 10, and the
magnetic targeting device 10 immediately performs a calibration cycle. If the
button 20 is
pressed briefly thereafter, another calibration cycle is initiated. The
display 18 indicates to
the user that calibration is in progress. It is not possible to turn on the
magnetic targeting
device 10 without initiating a calibration cycle. To turn off the magnetic
targeting device
10, the button 20 is held down for a couple seconds until the display 18 goes
off. The
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WO 2010/123879 PCT/US2010/031725
magnetic targeting device 10 also powers off after two minutes to prevent the
batteries 32
from draining.
To perform targeting, the magnetic targeting device 10 is held in the same
orientation as it will be used. The magnetic targeting device 10 is raised 10-
12 inches
above the targeting magnet member 70 and the button 20 is pressed to start a
calibration
cycle. It is important that the magnetic targeting device 10 be oriented
approximately as it
will be used in order to properly null the magnetic field of the earth. Once
the magnetic
targeting device 10 completes its calibration operation, it is lowered to the
work area and
moved to achieve an on-target indication.
Nail extension 110
In a version of the invention as shown in FIG. 13, the magnetic targeting
device
10 is included on a nail extension 110 of an intramedullary nail, the latter
of which
includes a nail connector 111 and a targeting arm 120. The nail extension 110
may be a
continuous unit, or may be comprised of separate but attachable nail connector
111 and
targeting arm 120 members.
The nail connector 111 is capable of being connected to a proximal end of an
intramedullary nail 60 in a fixed rotational orientation around the x axis of
the nail. The
nail connector 111 may be connected to the nail by a threaded connection or in
any other
manner, all of which are well-known in the art. To maintain the fixed
orientation, the nail
connector 111 preferably includes diametrically aligned lugs 113 projecting
from a
surface of the nail connector 111 that interfaces with the intramedullary nail
60. The lugs
113 are shaped and sized to fit closely in respective recesses 114 in the
proximal end of
the intramedullary nail 60. Insertion of the lugs 113 within the recesses 114
during
attachment of the nail connector 111 to the intramedullay nail 60 prevents
rotation of the
nail connector 111 with respect to the intramedullary nail 60 around the x
axis.
The nail connector 111 further includes an annular cavity (not shown). When
the
nail connector 111 is connected to the intramedullary nail, the annular cavity
of the nail
connector 111 is co-axial and continuous with the annular cavity 62 of the
nail. The
annular cavity of the nail connector 111 and the annular cavity 62 of the nail
are
dimensioned and configured to accept a magnet insertion rod 73 therein. In a
one version,
a distal end of the annular cavity of the nail connector 111 and the annular
cavity 62 at the
proximal end of the nail are both threaded, and the magnet insertion rod 73
for insertion
in these annular cavities 62 is externally threaded. The nail connector 111 is
fastened to
WO 2010/123879 PCT/US2010/031725
the nail 60 by threading the magnetic insertion rod 73 through both the
annular cavity of
the nail connector 111 and the annular cavity 62 of the nail 60. This threaded
system
permits the magnet member 70 on the end of the magnet insertion rod 73 to be
placed at a
known location at the distal end of the nail.
The nail connector 111 further includes a targeting-arm connector 116 that
enables connection of the targeting arm 120 to the nail connector 111. In a
preferred
version, the targeting-arm connector 116 comprises a portion extending
substantially
parallel to the longitudinal axis of the nail. The distance between the nail
60 and the
extended targeting arm 120 is preferably greater than the amount of tissue
surrounding a
patient's bone. This distance may be adjustable by a variety of mechanisms. In
an
exemplary version, the targeting-arm connector 116 is slidable along an
orthogonally
oriented portion 115 of the targeting arm 120 and secured thereto with a
compression
screw mechanism 119. The support member 14 preferably has a length sufficient
to place
the sensor array an appropriate distance from the magnet member 70 (see above)
given
the distance between the nail 60 and the extended targeting arm 120. The
targeting-arm
connector 116 preferably includes one or more connector holes for attaching
the targeting
arm 120 to the nail connector 111.
In one version of the invention, the nail connector 111 and targeting-arm
connector 116 comprise the systems described in U.S. Patent 7,232,433 and U.S.
Patent
7,549,994 to Zander et al., which are incorporated herein by reference.
The targeting arm 120 is preferably connected to the nail connector 111 via
the
targeting-arm connector 116 and extends substantially parallel to the
longitudinal axis of
the intramedullary nail 60. In the exemplary version, the targeting arm 120
may be
fastened to the targeting-arm connector 116 with bolts 121 that insert through
the
targeting arm 120 and through the connector holes in the targeting-arm
connector 116.
The targeting arm 120 includes a plurality of bores 123A,B. The targeting arm
120 preferably includes a corresponding bore 123A,B for each screw opening
64,66 in the
nails 60 that are intended to be used with the targeting arm 120. The bores
123A,B are
preferably coaxial with the corresponding screw openings when the targeting
arm 120 is
aligned with the intramedullary nail 60. 0 ne or more of the bores 12 3A,B ma
y be
dimensioned and configured to accommodate a support member 14, and one or more
bores 123A,B may be dimensioned and configured to accommodate a drill sleeve
125. In
the preferred version, the bores 123A,B are grouped in pairs comprising a
proximal bore
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123A and a distal bore 123B, wherein the proximal bore 123A accommodates a
support
member 14 and the distal bore 123B accommodates a drill sleeve.
The proximal bore 123A places the sensor foot directly over the magnet member
70 in the intramedullary nail 60 when the targeting arm 120 and the
intramedullary nail
60 are aligned along the y and z axes. The fit of the support member 14 in the
proximal
bore 123A is snug enough to prevent lateral movement of the support member 14
in the
proximal bore. This prevents misalignment of the targeting arm 120 relative to
the
intramedullary nail when the sensor foot 16 is aligned with the magnet member
70.
A proximal bore 123A with a magnetic targeting device 10 inserted therethrough
may be used for magnetic targeting only or may also be used for drilling. When
used for
magnetic targeting and drilling, the proximal bore 123A is positioned on the
targeting arm
120 such that alignment of the sensor foot 16 with respect to the magnet
member 70 in
the intramedullary nail 60 places the lower opening 30 of the drill sleeve 26
of the support
member 14 directly over the corresponding screw opening, such as the proximal
screw
opening 64.
The distal bore 123B is configured to place a drill sleeve 125B directly over
the
corresponding screw opening, such as the distal screw opening 66, when the
targeting
arm 120 is aligned with the intramedullary nail 60. The fit of the drill
sleeve 125B in the
distal bore 123B is snug enough to prevent lateral movement of the drill
sleeve 125B in
the distal bore 123B. This permits accurate drilling through the distal bore
123B when the
targeting arm 120 is aligned with the intramedullary nail 60.
In some versions of the invention, the targeting arm 120 has more than one
proximal bore 123A and/or distal bore 123B. This permits targeting and
drilling of each
screw opening of intramedullary nails of difference sizes. A targeting arm 120
having
more than one proximal bore 123A and/or distal bore 123B preferably has
indicia along
the length of the targeting arm 120 indicating the correct positions for
targeting and
drilling for a nail 60 of a particular size.
The support member 14 and the drill sleeve 125B preferably have substantially
the
same cross-sectional shapes and dimensions in the areas where each nests in
the bores
123A,B. This permits all of the bores 123A,B in the targeting arm 120 to have
the same
dimensions and to accommodate either the support member 14 or the drill sleeve
125B
therein. This allows different combinations of the bores 123A,B to be used for
targeting
and/or drilling. Alternatively, the support member 14 and the drill sleeve
125B are
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differently dimensioned and fit in bores 123A,B specifically designed to
accommodate
each.
It is preferable that the distal bore 123B is located on the targeting arm 120
far
enough away from the proximal bore 123A so that the metal in the drill bit 96
while
drilling through the distal bore 123B does not interfere with the magnetic
field 74
generated by the magnet member 70. However, for purposes of drilling accuracy,
it is
important that the distal bore 123B is not placed too far from the proximal
bore 123A.
Because the intramedullary nail 60 and the targeting arm 120 are connected at
their
proximal ends, a small amount of misalignment at the position of a more
proximal bore
123A results in a larger amount of misalignment at the position of a more
distal bore
123B. Placing the proximal bore 123A just out of the range of interference
induced by the
drill bit 96 in the distal bore 123B minimizes such an amplification of
misalignment.
The medullary cavity 101 of the femur is curved. Intramedullary nails 60 are
therefore typically curved along their longitudinal axes for insertion in the
medullary
cavity 101. The targeting arm 120 may comprise a curvature that corresponds
with the
curvature of the intramedullay nail 60 such that each bore 123A,B in the
targeting arm
120 is axially aligned with the screw openings in the nail 60 at approximately
the same
distance from the intramedullary nail.
During targeting and drilling, it is preferable to attach the magnetic
targeting
device 10 to the targeting arm 120 in some manner to prevent movement of the
magnetic
targeting device 10 with respect to the targeting arm 120. Such attachment is
minimally
achieved by virtue of inserting the support member 14 through the proximal
bore 123A.
Additional mechanisms of attachment may include snap-fit protrusions extending
from
the bottom of the nail connector 111 to fit into additional bores along the
length of the
targeting arm 120, zip ties, straps with "VELCRO"-brand hook-and-loop
fasteners, and/or
other fasteners. The targeting arm 120 may further include indented portions
to nest the
body of the device therein.
The nail extension 110 is preferably comprised of carbon fiber for maximum
strength and minimum weight.
Y- and Z-Axis Alignment of Bores 123A,B in Nail Extension 110 with Radial
Magnetic Field 74
The nail extension arm 110 does not admit of flexure along longitudinal axis
of
the targeting arm 120, i.e., "stretching." Therefore, the targeting arm 120 is
substantially
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fixed with respect to the x axis of the nail 60. However, the nail extension
arm 110 does
admit of flexure across the longitudinal axis of the targeting arm 120. In
other words, the
targeting arm 120 will yield slightly to forces having a z or y vector
component. Because
the targeting arm 120 is anchored via the nail connector 111 to the
intramedullary nail 60,
purely translational displacement of the sensor array 33 with respect to the
magnet
member 70 does not occur. Any flexure of the targeting arm 120 will therefore
induce
rotational misalignment with respect to the magnetic field 74. The rotational
misalignment is read as an imbalance by the sensor array 33. This is true even
when a
symmetrical, planar array 33 of four sensors 34 and a magnet member 70
producing a
radial magnetic field 74 is used. The detected imbalance can be corrected by
positional
adjustment of the targeting arm 120 relative to the intramedullary nail 60.
Orthogonal Targeting Guide 130
As shown in FIG. 14, some versions of the invention further include an
orthogonal targeting guide 130, which is configured for use with the nail
extension 110.
The magnetic targeting device 10 is used to attach two parallel, mechanically
stabilized
drill sleeves 125A,125B against a lateral portion of the bone 100. The drill
sleeves
125A,125B are stabilized at one end by the targeting arm 120 and at another
end with set
screws that fasten into holes drilled at the screw openings 64,66,68.
Fastening the drill
sleeves 125A,125B generates a stable, substantially rectangular construct
comprising the
stabilized drill sleeves 125A,125B, the targeting arm 120, the nail connector
111, and the
intramedullary nail 60.
The orthogonal targeting guide 130 includes a lateral support base 131,
orthogonal
support arms 132, a mechanical targeting guide 133, and, optionally, a
straight-edge guide
134. The lateral support base 131 attaches to the two parallel, mechanically
stabilized
drill sleeves 125A,125B, preferably by clamping thereto. The orthogonal
support arms
132 extend from the lateral support base 131 to either the anterior or
posterior side of the
intramedullary nail 60 being targeted in a manner that clears soft tissues
surrounding the
bone 100. The orthogonal support arms 132 include the mechanical targeting
guide 133
slidingly engaged thereto, such that the mechanical targeting guide 133 is
capable of
sliding on the orthogonal support arms 132 along the y axis of the
intramedullary nail 60.
The mechanical targeting guide 133 includes one or more orthogonal guide bores
135 that
correspond to the position of the orthogonal screw openings 68 along the x
axis, in
addition to a locking screw 136 that restricts movement of the mechanical
targeting guide
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133 on the orthogonal support arms 132 along the y axis. The straight-edge
guide 134 is
mounted on the nail extension 110 and projects a physical or visual indicator
of the
midline of the intramedullary nail 60 for alignment of the orthogonal guide
bores 135 on
the mechanical targeting guide 133 with respect to the orthogonal screw
openings 68 in
the nail 60. In the exemplary version of the invention, the strait-edge guide
134 is a laser
137 that projects a visual indicator of the midline of the intramedullary nail
60. The laser
137 may be used with or without a mirror 138 also mounted on the nail
extension 110.
The orthogonal targeting guide 130 aligns the orthogonal guide bores 135 with
the
underlying orthogonal screw openings 68 in the intramedullary nail 60 for
accurate
drilling.
As an alternative to anterior-posterior targeting with an orthogonal targeting
guide
130, the nail extension 110 may be configured to rotate to either an anterior
or posterior
position for targeting and drilling. In this version, the targeting arm 120
further includes
bores positioned along the length of the targeting arm 120 to correspond to
the position of
the orthogonal screw openings 68 along the length of the intramedullary nail
60.
Orthogonal recesses for accepting the lugs 113 are also included in the
proximal portion
of the nail 60 for maintaining the orientation of the targeting arm 120 in the
xy plane.
Intramedullary Nail 60 Targeting
In a preferred version of the invention, the proximal screw opening 64 is
targeted
while the distal screw opening 66 is drilled. This prevents magnetic
interference from the
drill bit 96 from disrupting targeting. The intramedullary nail 60 is placed
in the marrow
of the bone 100 and urged through the bone 100 as described in Szakelyhidi et
al. The
proximal opening 64 in the intramedullary nail 60 to be targeted has a magnet
member 70
placed at a reproducible distance therefrom. The magnet member 70 is either
embedded
in the surface of the intramedullary nail 60 as illustrated in FIG. 6 or is
inserted in the
annular cavity 62 of the intramedullary nail 60 with a magnet insertion rod 73
and locked
in place. A nail extension 110 with a nail connector 111 and a targeting arm
120 is
attached to the intramedullary nail 60. The indicia on the targeting arm 120
indicate the
end of the intramedullary nail 60, the approximate location of the openings
64, 66 in the
intramedullary nail 60 in the bone 100, and the proximal bore 123A and the
distal bore
123B in the targeting arm 120 that correspond with the proximal opening 64 and
distal
opening 66, respectively. An incision is made in the limb in the vicinity of
the openings
64,66 according to the positions of the indicia. An oval trochar can be used
to make a
WO 2010/123879 PCT/US2010/031725
path for the support member 14 down to the surface of the bone 100. The
support member
14 is inserted through the proximal bore 123A, and the sensor foot 16 is
placed on the
surface of the bone 100. In addition, a drill sleeve 125B is inserted through
the distal bore
123B and placed directly on the bone 100. A drill bit 96 is then inserted into
the drill
sleeve 125B. A star-point drill prevents the drill from "walking" on the
slippery curved
surface of the bone and is therefore preferred.
While the distal bore 123B in the nail extension 110 places the drill sleeve
125B
in the general vicinity of the distal opening 66, targeting at the magnet
member 70 in the
general vicinity of the proximal opening 66 corrects the final 2-3 mm
misalignments
resulting from the flexure of the nail extension 110. The sensor array 33 is
activated to
locate the magnet member 70, which then determines the location of the
proximal
opening 64. The display 18 is activated by the action of the button 20. A
signal is sent to
the sensor array 33 to zero the sensors 34. When the sensor array 33 is moved
across the
surface of the bone 100, the sensor information appears on the display 18,
generally in the
form of a target icon 90 and crosshairs 92 as illustrated in FIG. 9. If the
sensor
configuration affords z axis alignment information, a target icon 90 on a z-
axis line in the
display 18 also appears. The positioning of the target icon 90 in the center
of the targeting
grid 92 and positioning of the target icon 90 in the center of the z-axis line
indicates
correct placement of the magnetic targeting device 10 for drilling.
As soon as the target icons 90 align at the center of the crosshairs 92 and/or
the t-
axis line, the drill 96 is drilled through the distal opening 66 to the
opposite cortex. The
drill is far enough from the magnet member 70 and sensor foot that it does not
produce
magnetic interference.
Once the drill has passed through the bone cortex surrounding the distal
opening
66, it is left in place. A modified drill sleeve 125B with a set screw is
pushed against the
cortex of the bone. The set screw is tightened, making a stable, substantially
rectangular
construct comprising the stabilized drill sleeve 125B, the targeting arm 120,
the nail
connector 111, and the intramedullary nail 60. With the distal opening 66
successfully
targeted and stabilized, all proximal holes are aligned with the targeting arm
120. Drilling
the proximal opening 64 occurs either by drilling through the drill sleeve 26
in the
support member 14 of the magnetic targeting device 10 or by replacing the
magnetic
targeting device 10 in the proximal bore 123A with a separate drill sleeve
125A and
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drilling therethrough. Any other openings on the proximal side of the drilled
and
stabilized opening 66 are similarly drilled.
The user has two options for targeting and drilling orthogonal openings 68, if
drilling of such openings is desired. In a first option, the stabilized drill
sleeve 125B at
opening 66 is removed. The nail extension 110 is rotated 90 degrees about the
x axis of
the intramedullary nail 60. If using a magnet member 70 with its pole aligned
orthogonally to the longitudinal axis of the nail 60, the magnet insertion rod
73 is also
rotated 90 degrees about the x axis of the intramedullary nail 60. If using a
magnet
member 70 in a bucking arrangement, no rotation is required. If using a magnet
member
70 embedded in the surface of the nail 60, the magnet member is pre-positioned
for
targeting and drilling. The orthogonal openings 68 are then targeted and
drilled through
orthogonal guide bores 135 corresponding with the orthogonal openings 68 in
the same
manner in which the lateral openings 64,66 were drilled.
In a second option, a second stabilized drill sleeve 125A is constructed at
the
proximal opening 64 such that there are two parallel, mechanically stabilized
drill sleeves
125A,125B braced by the nail extension 110 and the intramedullary nail 60. An
orthogonal targeting guide 130 is attached to the stabilized drill sleeves
125A,125B with
the orthogonal support arms 132 directed to the desired side for drilling. A
straight-edge
guide 134, such as a laser 137, is mounted on the nail extension 110, and the
anterior-
posterior guide bores 135 are aligned with the straight-edge guide 134 to
indicate the
position of the underlying orthogonal openings 68 along the y axis of the nail
60. The
orthogonal openings 68 are then drilled via mechanical targeting of the
orthogonal
targeting guide 130.
In some applications it is advantageous to insert a locking screw through the
drilled opening 64,66,68 directly after targeting and drilling. A calibration
on the drill
measures the depth of the drilled hole at the upper opening 28 of the support
member 14.
Alternatively, after drill removal, the magnetic targeting device 10 can
remain against the
bone 100. A depth gauge is used to measure the length of the screw to be
inserted. Once
measured, the screw of the appropriate length is loaded onto a screw driver
and inserted
across the openings 64,66,68 of the intramedullary nail 60. Self tapping
screws are used
in the preferred embodiment.
An aiming device is always more accurate if it has two references in space to
align
it. In the present invention, a first reference to provide accuracy comes from
the bores
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123A,B on the targeting arm 120, which indicate the entry point on the skin
directly over
the opening 64,66,68 to be targeted in the intramedullary nail 60. The
targeting arm 120
shows the correct entry point over each opening and stabilizes the device
perpendicular to
the longitudinal axis of the intramedullary nail 60. A second reference is
provided by the
magnetic targeting device 10, which is placed directly on the surface of the
bone 100 to
be targeted. The targeting of the magnetic targeting device 10 at the surface
of the bone
100 corrects the final 2-3 mm misalignments resulting from the tolerances of
the nail
extension 110. The importance of being able to rest the magnetic targeting
device 10 on
the surface of the bone 100 during use cannot be over-emphasized. The accuracy
needed
for drilling and stabilizing intramedullary nails 60 within a broken bone is
on the order of
1 mm. Use of either a magnetic targeting device 10 or mechanical targeting arm
120
alone is not as accurate as using both in combination.
Bone Plates and Bone Plate Targeting
Versions of the device described herein can be extended to subcutaneous bone
plating. Bone plates are generally solid, rigid plates with holes that attach
to the outer
surface of a bone, particularly a broken bone, to stabilize it. Bone plates
are well known
in the art. Examples include those described in U.S. Patent No. 7,635,365 to
Ellis et al.
Bone plates used in the art are modified to include a magnet member 70 for
targeting. In
one version, a magnet member 70 is embedded in the surface of the plate
proximal to a
hole to be targeted for drilling the underlying bone 100. Preferably, the most
distal drill
hole of every plate has a 2 mm magnet member 70 embedded into the plate just
proximal
to the hole. In another version, a ring magnet is embedded around the hole. In
either case,
the magnet members 70 included in the bone plates are disposed on the outside
of the
bone 100. This enables the sensor foot to be placed in a percutaneous manner
in the direct
vicinity of the magnet member. Because the targeting distances are so small, a
sensor foot
16 including a single sensor 34 can be used for targeting.
For targeting and drilling bone plating holes, the magnetic targeting device
10 is
used either with or without an intramedullary nail 60 and nail extension 110.
To target the
bone plate with the device 10, a drill sleeve 26 is inserted in the support
member 14, and
the sensor foot 16 of the support member 14 is placed in the vicinity of the
distal hole to
be drilled. When the sensor foot 16 is aligned with the magnet member 70, the
display is
centered, and the distal hole is drilled. A modified Cleco spring fastener
(Cleco Industrial
Fasteners, Inc., Harvey IL, USA) is inserted in the drilled hole to provide
temporary
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fixation and stability. If the location of the drilled hole is correct after
reduction of the
fracture, the Cleco spring fastener is replaced by a screw. The Cleco spring
fastener
allows easy repositioning and drilling if minor adjustments in position of the
plate are
needed.
In an alternate version, drill holes in a subcutaneous bone plate are located
by
detecting threaded magnet members 70 that are screwed into holes pre-selected
for use.
The magnets 72 comprising the magnet members 70 are preferably NbFeBoron
magnets
for maximum strength. The magnet members 70 preferably have a hex drive.
Because the
most advantageous hole to locate during bone plating is the most distal
subcutaneous hole
of the plate, a magnet member 70 is inserted in the most distal hole. The
magnets
members 70 are sensed through the soft tissues by a sterile magnetic compass.
Once
located, the skin is marked and excised. The pre-positioned magnet members 70
in the
screw holes are located by a magnetic screwdriver of the opposite polarity
that locks into
the hex head of the magnet member. Once the targeted hole is located, a hole
is drilled,
and a Cleco plate holder is inserted for immediate temporary fixation. If x-
rays show that
the reduction is satisfactory, other critical holes are located in a similar
fashion. The distal
Cleco plate holder is then removed and replaced by a locking screw. If the
position of the
plate is not ideal, the Cleco plate holder allows rapid repositioning of the
distal end of the
plate. The magnet-to-magnet location of the screw holes provides simplicity,
low cost,
and reliability in locating bone plating holes.
Plates made by Synthes, Inc. (West Chester, PA, USA) have a combination of
holes that are immediately adjacent to each other. In targeting such plates,
one of the
holes is modified to include a magnet member 70 and is used for targeting. A
second hole
is drilled through an adjacent parallel drill sleeve stabilized by the
targeting arm 120. For
single-hole plate designs, a magnet member placed in a small recess in the
plate would
allow a drill sleeve with a magnetic material to locate and lock into position
for drilling.
Any version of any component or method step of the invention may be used with
any other component or method step of the invention. The elements described
herein can
be used in any combination whether explicitly described or not.
All combinations of method steps as used herein can be performed in any order,
unless otherwise specified or clearly implied to the contrary by the context
in which the
referenced combination is made.
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As used herein, the singular forms "a," "an," and "the" include plural
referents
unless the content clearly dictates otherwise.
Numerical ranges as used herein are intended to include every number and
subset
of numbers contained within that range, whether specifically disclosed or not.
Further,
these numerical ranges should be construed as providing support for a claim
directed to
any number or subset of numbers in that range. For example, a disclosure of
from 1 to 10
should be construed as supporting a range of from 2 to 8, from 3 to 7, from 5
to 6, from 1
to 9, from 3.6 to 4.6, from 3.5 to 9.9, and so forth.
All patents, patent publications, and peer-reviewed publications (i. e.,
"references") cited herein are expressly incorporated by reference in their
entirety to the
same extent as if each individual reference were specifically and individually
indicated as
being incorporated by reference. In case of conflict between the present
disclosure and the
incorporated references, the present disclosure controls.
The devices and methods of the present invention can comprise, consist of, or
consist essentially of the essential elements and limitations described
herein, as well as
any additional or optional steps, ingredients, components, or limitations
described herein
or otherwise useful in the art.
It is understood that the invention is not confined to the particular
construction
and arrangement of parts herein illustrated and described, but embraces such
modified
forms thereof as come within the scope of the following claims.
