U.S. patent application number 10/848588 was filed with the patent office on 2005-04-21 for customized surgical fixture.
This patent application is currently assigned to Neutar L.L.C., a Maine corporation. Invention is credited to Franck, Joel I., Franklin, Ronald J., Haer, Frederick C..
Application Number | 20050085719 10/848588 |
Document ID | / |
Family ID | 22331074 |
Filed Date | 2005-04-21 |
United States Patent
Application |
20050085719 |
Kind Code |
A1 |
Franklin, Ronald J. ; et
al. |
April 21, 2005 |
Customized surgical fixture
Abstract
A customized surgical fixture (400) is formed by scanning a body
to form a three-dimensional image of the body, and then identifying
in the image a target (310) in the body, and mounting points or
structures (330) on the body. A model, such as a computer solid
model, of the fixture (400) is specified in accordance with the
locations of the target (310) and mounting structures (330) or
points. The fixture (400) is formed in accordance with the model of
the fixture (400), for example using a rapid prototyping and
tooling machine. When attached to the body, the fixture (400) can
be used to guide a surgical instrument (610) into the body, for
example, by using a mechanical guide (600) attached to the fixture
(400) or using a remote sensing device (1300) that tracks the
relative position of the customized fixture (400) and the surgical
instrument.
Inventors: |
Franklin, Ronald J.;
(Bowdoinham, ME) ; Franck, Joel I.; (Durharm,
ME) ; Haer, Frederick C.; (Brunswick, ME) |
Correspondence
Address: |
FISH & RICHARDSON PC
225 FRANKLIN ST
BOSTON
MA
02110
US
|
Assignee: |
Neutar L.L.C., a Maine
corporation
|
Family ID: |
22331074 |
Appl. No.: |
10/848588 |
Filed: |
May 18, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10848588 |
May 18, 2004 |
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09869551 |
Dec 4, 2002 |
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6738657 |
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09869551 |
Dec 4, 2002 |
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PCT/US99/15006 |
Jul 2, 1999 |
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09869551 |
Dec 4, 2002 |
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09110070 |
Jul 6, 1998 |
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6327491 |
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Current U.S.
Class: |
600/424 ;
128/920; 606/130 |
Current CPC
Class: |
A61B 2034/2072 20160201;
A61B 2034/256 20160201; A61B 2034/105 20160201; A61B 90/11
20160201; A61B 34/20 20160201; A61B 90/14 20160201; A61B 2090/3983
20160201; B33Y 80/00 20141201; A61B 90/39 20160201; A61B 2090/363
20160201; A61B 2034/107 20160201; B33Y 10/00 20141201; A61B
2034/2055 20160201; B33Y 50/02 20141201 |
Class at
Publication: |
600/424 ;
606/130; 128/920 |
International
Class: |
A61B 019/00; A61B
005/05 |
Claims
What is claimed is:
1-19. (canceled)
20. A method for designing a customized medical fixture comprising:
(a) locating a first plurality of devices attached to a body from a
scanned image of the body; (b) determining desired locations for a
second plurality of devices relative to the locations of the first
plurality of devices; (c) computing a digital model of the shape of
medical fixture wherein the shape of the fixture is adapted for
placement on the body in a predetermined location relative to the
first plurality of devices, the shape of the fixture includes
structures for attaching the second plurality of devices, and the
shape of the fixture being such that when the second plurality of
devices are attached to the medical fixture at said structures and
the fixture is placed at said predetermined location, the second
plurality of devices are at the desired locations of the second
plurality of devices relative to the locations of the first
plurality of device.
21. The method of claim 20 wherein the second plurality of devices
includes a plurality of bone anchors attached to bone structures of
the body.
22. The method of claim 21 wherein the first plurality of devices
includes a plurality of tracking markers.
23. The method claim 21 wherein the shape of the fixture is adapted
for attachment to the bone anchors.
24. A method for stereotactic surgery comprising: locating a first
plurality of devices attached to a body from a scanned image of the
body; fabricating a medical fixture customized for the body, the
fixture including a plurality of structures for attaching a second
plurality of devices, the fixture being adapted for placement on
the body in a predetermined location relative to the first
plurality of devices such that when the fixture is placed in said
predetermined location the structures of attaching the second
plurality of devices are in a known geometry relative to the first
plurality of devices; attaching the second plurality of devices at
the plurality of structures on the fixture; positioning the
customized medical fixture on the body at the predetermined
location; tracking locations of the second plurality of devices;
and computing a location of the body based on the tracked locations
of the second plurality of devices, the known geometry, and
locations of the first plurality of devices attached to the body.
Description
BACKGROUND
[0001] The invention relates to customized surgical fixtures.
[0002] Many types of surgical procedures rely on precisely guiding
an instrument into the body. This is the case in stereotactic
surgery in which a target point within a body, for example, within
a brain, is identified in a three-dimensional scanned image of the
body. A detailed survey of stereotactic surgery can be found in
Textbook of Stereotactic and Functional Neurosuraery, P. L.
Gildenberg and R. R. Tasker (eds.), McGraw-Hill, June 1997 (ISBN:
0070236046). In a typical approach to stereotactic surgery, a frame
is attached to the body prior to scanning. After scanning, the
target point in the body is identified in the scanned image with
reference to the frame. Then, during surgery, an adjustable
instrument guide is attached to the frame. The guide is adjusted to
align with the target point. A related approach to stereotactic
surgery is described in copending U.S. patent application Ser. No.
09/063,658 filed 21 Apr. 1998, which is incorporated herein by
reference. In that approach applied to brain surgery, an adjustable
instrument guide is attached directly to the skull. Once attached,
it is adjusted to align with the target point.
[0003] These previous approaches to stereotactic surgery require
adjustment of an instrument guide in order that the instrument can
be driven accurately to the target point within the body.
SUMMARY
[0004] Adjusting an instrument guide to align with a target point
within the body can be complex and time consuming. In some
procedures multiple points must be targeted. For example, in spinal
sterotactic surgery, multiple targets on different spinal segments
are used. In a general aspect of the invention, rather than
targeting an adjustable instrument guide, a customized fixture is
fabricated for a particular patient, such that targeting is
unnecessary or greatly simplified. A fixed instrument guide
attached to the customized fixture can be used to guide a surgical
instrument to the desired point without adjustment.
[0005] In one aspect, the invention features a method for forming a
surgical fixture for attaching to a body and providing a reference
structure for precisely locating a target within the body, such as
a particular point or an anatomical structure within the body. The
method includes processing a three-dimensional scanned image of the
body, for example a CT or MRI scan. The scanned image includes the
target within the body, for example a point or region of the body,
and a mounting location of the body. The method also includes
determining a structure of the surgical fixture such that when
attached at the mounting location of the body the fixture provides
a reference structure in a determined location and orientation with
respect to the target within the body.
[0006] The method can include one or more of the following
features.
[0007] Multiple mounting points can be identified in the scanned
image. The geometric relationship between corresponding mounting
points on the fixture and the reference structure can then be
determined. The method can further include attaching mounting
anchors to the body prior to scanning the body. Scanning markers
are attached to the anchors. The identified mounting points are
then the locations of the scanning markers in the three-dimensional
image.
[0008] The mounting location for the fixture can be an anatomical
structure on the body. A contour of a surface of the fixture is
determined to mate with the anatomical structure.
[0009] The method can include identifying the target in the scanned
image. Also, a trajectory for reaching the target can be
identified. The location and orientation of the reference structure
is then determined with respect to the identified trajectory.
[0010] The structure of the fixture can be determined in terms of a
solid model of the fixture which defines the volume enclosed by the
surface of the fixture. The method can then also include
fabricating the fixture according to the solid model.
[0011] The method can include attaching the surgical fixture to the
body and guiding an instrument to the target with reference to the
attached surgical fixture.
[0012] The method can include attaching the surgical fixture to the
body and attaching multiple tracking markers to the surgical
fixture. For example, the multiple tracking markers, such a
light-emitting diodes, can be attached to a tracking fixture that
is then attached to the surgical fixture. The method then includes
tracking locations of the tracking markers relative to a remote
sensing device, such as a camera array or a laser tracker. The
method can further include tracking a location of a surgical
instrument relative to the remote sensing device, for example by
tracking locations of tracking markers attached to the instrument,
and computing a relative position of the surgical instrument to the
surgical fixture using the tracked location of the tracking markers
and the surgical instrument relative to the remote sensing
device.
[0013] The method can also include attaching a second surgical
fixture at a second mounting location of the body, and attaching
multiple tracking markers to the second surgical fixture. For
example, the two surgical fixtures are attached at two mounting
points on an articulated portion of the body, for example, on two
bones coupled at a skeletal joint. The method then includes
tracking locations of the tracking markers attached to the second
surgical fixture relative to the remote sensing device and
computing a relative position of the two mounting locations of the
body from the tracked locations of the tracking markers attached to
both surgical fixtures. For example, a configuration of a skeletal
joint can be determined from the computed relative position of the
mounting locations.
[0014] The body can include a spine and the mounting location can
include a spinal segment. The method can also include forming a
model of the spine. The method can further include forming a
corrected model of the spine in a corrected configuration. The
determined structure of the surgical fixture is such that when
attached, the fixture provides a second reference structure in a
determined location and orientation with respect to the target in
the corrected configuration of the spine.
[0015] The method can include selecting a model of a standard
fixture and deforming the model of the standard fixture in order to
match the standard model to the target and the mounting
location.
[0016] In another aspect, the invention features a surgical fixture
formed from a computer model using a rapid prototyping and tooling
technique. The fixture includes multiple mounting sections for
attaching the fixture to a body at a predetermined mounting
location on a body and a reference structure coupled to the
mounting sections for guiding a surgical instrument into the body.
When the fixture is attached to the body at the mounting location
the reference structure is at a predetermined location and
orientation to a target within the body. The fixture can include an
instrument guide mounted on the reference structure for driving the
instrument into the body.
[0017] In another aspect, the invention features software stored on
a computer readable medium for causing a computer to perform the
functions of processing a three-dimensional scanned image of a
body, the scanned image including the target within the body and a
mounting location of the body and determining a structure of a
surgical fixture such that when attached at the mounting location
of the body the fixture provides a reference structure in a
determined location and orientation with respect to a target within
the body.
[0018] Advantages of the invention include avoiding the need for
targeting of an adjustable guidance fixture based on the location
of target points within the body. This reduces the time required
for surgery, and can increase the accuracy and precision of
targeting.
[0019] Another advantage is that the customized fixture can provide
a mounting base in a precise location relative to the body. This
avoids a manual registration procedure of stereotactic surgery in
which a correspondence between the scanned image and the physical
body is established. The manual registration procedure can be time
consuming and inaccurate.
[0020] Another advantage is that tracking markers, such as light
sources or reflectors, can be attached at predetermined locations
relative to the body, without requiring that mounting points, such
as bone anchors, are in a particular configuration, and without
requiring a manual registration step after the tracking markers are
attached to the body. This provides flexibility in the choice of
where to mount the fixture and reduces the time required before
surgery can begin and provides improved accuracy compared to that
typically achieved using manual registration and avoids errors
inherent in a manual registration step.
[0021] Another advantage is that the customized fixture is easily
attached to the body, for instance by mating the fixture to a set
of anchors attached to the body prior to scanning, or in another
instance, mating the fixture to the particular anatomy of the
patient.
[0022] Another advantage is that the customized fixture can be
repeatedly reattached to permanently implanted anchors in the body
allowing follow-up or repeated procedures.
[0023] Another advantage of the invention is that the detailed
fixture design can be based on a desired configuration of a
configurable portion of the body, such as the spine, rather than
solely on the configuration during scanning. This allows the
fixture to be used not only to guide instruments into the body, but
when attached to the body, to constrain the configuration of the
body, such as correcting a spinal or orthopedic bone deformity or
complex fracture.
[0024] Other features and advantages of the invention will be
apparent from the following description, and from the claims.
DESCRIPTION OF THE DRAWINGS
[0025] FIGS. 1a-b show scanning markers and bone anchors used to
attached the scanning markers to a skull;
[0026] FIG. 2 illustrates a scanning phase;
[0027] FIG. 3 illustrates a scanned image and located image
points;
[0028] FIG. 4 illustrates a customized fixture;
[0029] FIGS. 5a-c illustrate another customized fixture, attached
to a head, and viewed along a target trajectory and from the
side;
[0030] FIG. 6 is a side view of a fixture supporting an instrument
guide;
[0031] FIG. 7 is a side view of a fixture supporting an adjustable
instrument guide;
[0032] FIG. 8 illustrates a head-mounted fixture which mates with
the contours of the skull;
[0033] FIGS. 9a-b illustrate a customized fixture for spinal
surgery;
[0034] FIGS. 10a-b illustrate a spinal fixture used to modify the
curvature of the spine;
[0035] FIG. 11 illustrates a computer implementation of the fixture
design procedure;
[0036] FIG. 12 illustrates attachment of tracking markers to a
customized fixture;
[0037] FIG. 13 illustrates sensor-tracked image guidance of a
surgical instrument relative to tracking markers attached to a
skull with a customized fixture; and
[0038] FIG. 14 illustrates multiple customized fixtures supporting
tracking markers used to track the position of a femur relative to
a pelvis.
DESCRIPTION
[0039] An approach to stereotactic surgery according to the
invention involves four phases.
[0040] Scanning and Surgical Planning. A three-dimensional scanned
image of a patient is taken. A surgeon identifies a target point or
volume within the body and determines coordinates of the target in
the image.
[0041] Fixture Design. Based on the scanned image and the
identified target point, a computer "solid model" of a customized
fixture is computed. The solid model is computed so that the
resulting fixture can be precisely attached to the body. The
fixture is further designed to include an integral instrument
guide, or a mounting base for a removable guide, for accurately
positioning a surgical instrument at the target point when the
fixture is attached to the body.
[0042] Fixture Fabrication. Based on the computed solid model, the
customized fixture is fabricated using a computer controlled rapid
prototyping and tooling (RPT) technique.
[0043] Surgery. The fabricated customized fixture is attached to
the patient, and a surgical instrument is guided to the target
point using the fixture.
[0044] Brain Surgery
[0045] A first embodiment of the invention is directed to brain
surgery. Several alternative embodiments, described below, are also
directed to brain surgery. Additional related embodiments are also
applicable to other types of surgery, including spinal surgery. The
first embodiment, which is directed to brain surgery, is described
below following the four phases summarized above.
[0046] Scanning and Surgical Planning Phase
[0047] Referring to FIG. 1a, in the first phase, the scanning and
surgical planning phase, a set of bone anchors 120 is attached to
the skull 100 prior to scanning the patient. In the illustrative
example shown in FIG. 1, three bone anchors 120 are attached to the
skull. A greater or smaller number of anchors can also be used.
During the later surgical phase, bone anchors 120 will be the
attachment points for the fabricated fixture.
[0048] Referring to FIG. 1b, each of the bone anchors 120 has a
threaded opening for accepting threaded bolts or other threaded
attachments. In particular, prior to scanning, each threaded
opening is used to accept a scanning marker 122. Each scanning
marker 122 includes a threaded section 124 attached to a marker
portion 126. Marker portion 126 includes a material that will
result in a visible image in the scanned image. Various types of
scanning techniques can be used, including CT, PET, MRI, SPECT, and
laser. The material in the marker portions 126 is chosen depending
on the scanning technique that will be used.
[0049] Referring to FIG. 2, after scanning markers 122 are attached
to bone anchors 120, the patient is scanned in a scanner 210
(illustrated schematically) producing a three-dimensional image
230. This image is transferred to a computer 220 where it is
stored.
[0050] After the scanning process is complete, scanning markers 122
are removed from the patient, but bone anchors 120 are left firmly
in place. In a typical situation, because the surgical phase of the
process will not begin for several hours, or even several days, the
patient is allowed to walk around or even allowed to return home at
this point.
[0051] Referring to FIG. 3, a surgeon plans the upcoming surgery
using a computer display of image 230 using well-known techniques
in stereotactic surgery. The surgeon identifies a target image
point 310 in image 230 corresponding to a target point in the body.
The three dimensional coordinates of the target image point in the
coordinate system of image 230 are stored on the computer. The
surgeon also identifies an entry image point 320 defining a
straight-line trajectory by which a surgical instrument can reach
the target point while avoiding critical structures in the brain.
The coordinates of the entry image point are also stored.
[0052] Referring still to FIG. 3, marker image points 330 in image
230 correspond to the marker portions 126 of scanning markers 122
(FIG. 1b). The surgeon can locate these points using the computer
display in a similar manner to locating the target and entry
points. Alternatively, an automated algorithm is implemented on
computer 220 to locate marker image points 330 based on the image
characteristics, such as brightness or shape, of the points. In
either case, the coordinates in the image of marker image points
330 are stored.
[0053] At this point, based on a known correspondence of the
scanned image to the physical body, the locations of the actual
target and entry points on the body with respect to the locations
of the scanning markers are computed and stored on the computer.
This computation is based on the stored coordinates of the
corresponding marker, target, and entry image points.
[0054] A representation of the surface of the skull can be computed
directly from the scanned image using well-known image processing
techniques. This surface representation can be used to ensure that
a designed fixture will properly fit over the skull, or to
determine other characteristics of the skull that may be used to
design the fixture.
[0055] This completes the scanning and surgical planning stage.
[0056] Fixture Design Phase
[0057] The next phase of the process involves design and
fabrication of the fixture itself. The design requirements of the
fixture can be understood by referring to FIG. 4 which shows how a
fabricated fixture 400 will be attached to bone anchors 120 in the
surgical phase. In this embodiment, fixture 400 is attached to bone
anchors 120 using bolts 432 which pass through openings 430 in
fixture 400. When attached to the bone anchors, mounting points of
fixture 400 are located at the prior locations of the marker
portions 126 of scanning markers 122.
[0058] A planned actual trajectory 460 passes through an actual
entry point 420 to an actual target point 410 corresponding to the
planned entry image point 320 and target image point 310 (FIG. 3).
Trajectory 460 passes through fixture 400 when attached to the
skull.
[0059] Fixture 400 includes a way of mounting an instrument guide
onto it to guide a surgical instrument along trajectory 460. In
this embodiment, fixture 400 includes a mounting base 450 for
attaching an instrument guide. Mounting base 450 has a flat surface
with a central opening. When fixture 400 is attached to the skull,
trajectory 460 passes through the central opening of the mounting
base and the flat surface of mounting base 450 is perpendicular to
trajectory 460. The distance between target point 410 and the
mounting base is also determined before the surgical phase, for
example by designing the fixture so that this distance is a
standard distance related to the type of instrument that will be
used.
[0060] The design of fixture 400 for a particular patient and
surgical procedure must satisfy several constraints including one
or more of the following:
[0061] mounting base 450 is centered on the planned trajectory and
oriented perpendicular to the trajectory,
[0062] the mounting points of fixture 400 mate with bone anchors
120,
[0063] the distance between target point 410 and the mounting base
must be an exact distance or within a particular range related to
the surgical instrument and guide that will be used,
[0064] the orientation of the fixture at each of the mounting
points must be appropriate for the orientation of the corresponding
bone anchors, and
[0065] the fixture must provide sufficient clearance above the
skull when mounted.
[0066] Referring to FIGS. 5a-c, an second exemplary fixture 500 is
shown attached to the patient's head (FIG. 5a) and shown in a view
along the planned trajectory (FIG. 5b) and in cross section (FIG.
5c). Fixture 500 is designed to attach to four bone anchors.
Fixture 500 has a central mounting base 550 in a center section
520. Four "legs" 510 extend from the center section to four
mounting pads 530 with mounting holes 540 through which fixture 500
is attached to the bone anchors.
[0067] The procedure for satisfying the constraints identified
above uses an algorithmic approach. The approach can be understood
with reference to FIGS. 5b-c. Referring to FIG. 5c, mounting base
550 is centered on planed trajectory 460. In this example, the
distance between target point 410 and the center point 562 of the
mounting base is set to a predetermined fixed distance.
[0068] Referring still to FIG. 5c, two of the mounting points 532
are illustrated along with the axes of the bone anchors. Mounting
pads 530 are designed as planar sections to lie over the mounting
points and to be perpendicular to the axes of the bone anchors.
Legs 510 are then designed as planar sections that join mounting
pads 530 and center section 520.
[0069] In FIG. 5c, the surface of the skull 534 is illustrated
along with entry point 420. The mounting pads, legs, and center
section are design to lie above and provide sufficient clearance
above the skull.
[0070] In order to orient mounting pads 530 perpendicularly to the
axes of the bone anchors, this approach to designing fixture 500
relies on knowledge of the orientations as well as the locations of
the bone anchors. In the approach described above, as shown in FIG.
1b, a single marking portion 126 is attached in scanning marker 122
to each bone anchor 120. Therefore only the location of each bone
anchor is determined by locating the marker images of the scanning
markers.
[0071] One of several alternative approaches to determining the
orientation of the bone anchors can be used. First, alternative
scanning markers 122 can be used. The alternative scanning markers
have two marking portions 126 separated along the axis of the
scanning marker. Locating the images of both the marking portions
determines the orientation of the bone anchor. A second alternative
is to use a normal direction to a surface models of the skull. The
surface model of the skull can be computed directly from the
scanned image using well known image processing techniques. A third
alternative is to approximate the orientation of the bone anchors
by fitting a surface through the locations of the scanning markers,
and optionally through the entry point. A fourth alternative is to
not rely on the mounting pads being normal to the axes of the bone
anchors, relying instead on a mounting approach that is less
sensitive to the orientation or the anchors. For instance, a ball
can be mounted on each bone anchor and the fixture can have
corresponding sockets which mate with the balls.
[0072] Fixture 500 shown in FIGS. 5a-c is made up of essentially
planar sections. Alternative algorithmic design approaches can be
used to design curved structures. For instance, the shape of the
fixture can be determined using a surface spline with the mounting
points and the mounting base being points at which constraints on
the coefficients of the splines are determined.
[0073] The design of the customized fixture is converted into a
computerized specification of a solid model. A solid model is a
computer representation of a volume enclosed by a surface
surrounding the entire volume. Various types of computer
representations of the volume can be used. A common format is an
".stl" file that is used by many computer aided design (CAD)
systems. The .stl file includes a set of representations of surface
patches that together define a complete surface that encloses the
volume. The .stl file for the designed fixture is then used as the
specification for fabrication of the fixture.
[0074] Fixture Fabrication
[0075] The solid model file is transferred to a rapid prototyping
and tooling (RPT) machine. The file can be transferred on a
physical medium, such as a magnetic disk, sent over a data network,
or used directly on the computer on which is was computed.
[0076] A variety of RTP techniques can be used to fabricate the
fixture. In this embodiment, a Fused Deposition Modeling (FDM)
machine, such model FMD2000 manufactured by Stratasys, Inc. of Eden
Prairie Minn., is used to make the three dimensional fixture from
the .stl file. The FDM machine essentially robotically lays down a
long ribbon of extruded material thereby slowly building up the
modeled fixture. As material is laid down, it fuses with the
previously laid down material making a homogeneous solid. The
process results in a highly accurate fixture, within 5 mil of the
specification in the .stl file. Various materials can be used for
the fixture. In the embodiment, medical grade ABS is used.
[0077] After fabrication in the FDM machine, some further machining
may be needed for some fixture designs. For instance, the ABS
material can be drilled and tapped to provide mounting points at
which an instrument guide is attached.
[0078] Surgery
[0079] The completed fixture is returned to the surgeon. The
patient returns, with the bone anchors still intact, for the
surgical phase. The fixture is sterilized and then the surgeon
attaches the sterilized fixture to the bone anchors in the
patient's skull and begins the surgical phase.
[0080] The surgical phase for brain surgery involves several steps,
including opening a burr hole, and the inserting of an instrument
in the burr hole. The burr hole can be drilled prior to attaching
the fixture, or can be drilled using the fixture. In the latter
case, a drill guide is attached to the mounting base and a drill is
inserted through the drill guide to drill the burr hole at the
planned entry point.
[0081] Referring to FIG. 6, to insert a surgical instrument into
the brain to reach the planned target point, fixture 400 is used to
support an instrument guide 600. In the illustrative example shown
in FIG. 6, instrument guide 600 supports an insertion tube 620
through which an instrument 610, such as a recording electrode, is
passed. The instrument is attached to a drive 630 on instrument
guide 600 for manually or automatically driving the instrument to
target point 410. Since the separation of target point 410 and
mounting base 450 is specified when the fixture is designed, if the
length of the surgical instrument is predetermined, then the
instrument guide can be calibrated to precisely insert the
instrument to the target point. For instance, if the instrument is
known to have a standard length, the separation of the target point
and the mounting base on the fixture can be designed such that when
the instrument drive is in its fully inserted position, the
instrument has reached the planned target point.
[0082] Alternative instrument guides can be used in conjunction
with a custom fabricated fixture. Referring to FIG. 7, an
adjustable instrument guide 700 is attached to mounting base 450.
The instrument guide is adjustable allowing the actual trajectory
of instrument 610 to fall within a cone with an apex at entry point
420. For instance, an adjustable guidance fixture such as one
described in copending U.S. patent application Ser. No. 09/063,658
filed 21 Apr. 1998 or Provisional Application 60/096,384 filed 12
Aug. 1998 can be used. Both of these copending applications are
incorporated herein by reference.
[0083] Note that since adjustable instrument guide 700 is attached
in a precise relationship to target point 410 and entry point 420,
a "registration" step of the type typically carried out in
stereotactic surgery, used to conformally map a physical coordinate
system to an image coordinate system, is not needed. Furthermore,
instrument guide 700 can include encoders that generate signals
which encode the adjustment of the actual trajectory relative to
the planned trajectory, allowing precise visual feedback to be
computed and displayed to a surgeon. Instrument guide can also be
actuated allowing remote or robotic control of the instrument and
the guide.
[0084] Alternative Approaches
[0085] In the embodiment described above, the fabricated fixture is
attached to bone anchors. Alternative embodiments attach the
fixture to the body in different ways. For instance, other types of
inserts or bone anchors can be attached to the skull. Also, rather
than attaching the fixture to a bone anchor, the fixture can be
designed to precisely clamp onto the patient's head. For example,
referring to FIG. 8, two mating halves 810, 820 of a fixture 800
match the contours of cheek bones and forehead, and the contours of
the back of the head, respectively. The contours of the patients
head are derived from the a model of the skull that is computed
automatically from the scanned image.
[0086] In the embodiments described above, the design (i.e., the
solid model) of the fixture is determined algorithmically from the
locations and orientations of points, including the mounting
points, the target point and the entry point. An alternative
approach to design of the fixture involves interaction with the
surgeon. Rather than having to specify a detailed design for the
fixture, the surgeon has control over a limited number of
deformations of a standard fixture.
[0087] A particular implementation of this deformation procedure
uses a relational geometry approach. U.S. Pat. No. 5,627,969 issued
17 Mar. 1995 to John S. Letcher, Jr., describes such a relational
geometry approach and software architecture to implement the
approach.
[0088] A set of "standard" fixtures are used as the basis of the
procedure. Each of the standard fixtures is described using a
"logical model" in which geometric relationships of various
elements of the fixture are explicitly identified. Examples of
constraints described in the logical model include the shape of the
mounting base (which is not deformed), and the connections of
sections such as the mounting legs and central section.
[0089] In the fixture design phase, the surgeon selects one of the
standard fixtures. Using a computer aided graphic design (CAGD)
tool, the surgeon views both a representation of the body and a
representation of the fixture. Initially, the standard fixture does
not satisfy any of the design constraints. Using the CAGD tool, the
surgeon adjusts the fixture design so that the fixture will mate
with the bone anchor, and so that the mounting base will have the
correct location and orientation with respect to the entry and
target points. Furthermore, the surgeon can adjust other aspects of
the design, for example, deforming the fixture to allow sufficient
clearance for an ear.
[0090] Spinal Surgery
[0091] Another embodiment of the invention is directed to spinal
surgery. As in the brain surgery approach, a three-dimensional
scanned image is taken of the patient, in this case of his or her
spine. In this embodiment, no anchor points or scanning markers are
necessarily applied to the spine, however.
[0092] Referring to FIG. 9a, using techniques well known in
stereotactic spinal surgery, the surgeon identifies target points
934 in the image of a spine 920, for example, points at which
screws are to be inserted into the spine. The surgeon also plans
trajectories 932 to reach the target points, for example
determining the angles at which the screw holes will be
drilled.
[0093] Using well-known image analysis and modeling techniques, a
computer model of the segments of the spine 920 is formed from the
scanned image.
[0094] The surgeon identifies two segments 922 to which a
customized fixture 900 is to be attached. Referring to FIG. 9b, the
models of segments 922 are used to form clamp sections which mate
with the contours of the segments. A portion 910 of the clamp
section is formed in one piece with the main section of the
fixture. A second portion 912 of each clamp section is formed as a
separate component. The two portions of the clamp section are drawn
together to attach the fixture to the spinal segments. Fixture 900
is formed to match the curvature of spine 920 as it is scanned. For
instance, the separation of segments 922 matches the separation in
the scanned image.
[0095] For each of the target points, a separate instrument guide
930 is formed in fixture 900. For example, each instrument guide
can be a elongated hole into which a drill is inserted. The
instrument guides can be designed so that not only the orientation
but also the depth of the holes drilled into the spinal segments
are precisely determined by the instrument guides.
[0096] After attaching the fixture, the surgeon proceeds with the
operations on each of the spinal segments that are involved in the
overall surgery without repositioning fixture 900.
[0097] In an alternative embodiment directed to spinal surgery,
previously applied anchors and scanning markers in spinal segments
or bony structures are used to define the geometry of a customized
fixture so that it mates with these anchors.
[0098] Another embodiment directed to spinal surgery not only
addresses operations to be performed on the spine in the
configuration that it was scanned, but also address manipulating
the spine to a desired curvature different from that in the scanned
image. In addition to forming a computer model of the spine as it
is scanned, a modified spinal model is also derived. The modified
model represents the desired curvature of the spine. A second
fixture is designed according to the modified model. After the
first fixture is removed, the second fixture is attached to achieve
the desired curvature of the spine.
[0099] A related embodiment is illustrated schematically in FIG.
10a-b. This embodiment also uses the modified spinal model.
However, rather than forming a second fixture, additional guides
1010 are formed in the first fixture for the purpose of
manipulating the spine into the desired configuration. For example,
in addition to guides 1020 which are formed along the orientations
1022 to drill the segments, additional guides 1010 are formed in
the fixture corresponding to the orientations 1012 of the drilled
holes after modification of the curvature, and screws inserted into
the holes can be forced to lie in the desired orientations. Similar
embodiments can be applied to correction and repair of orthopedic
bone or joint deformity or fracture.
[0100] Other Surgical Procedures
[0101] The embodiments presented above are described in the context
of stereotactic brain or spine surgery. Similar approaches are
applicable to other types of stereotactic surgery.
[0102] Similar customized fixtures are also applicable to other
types of surgical procedures in which a device must be precisely
attached to a body. For instance, a precise instrument guide can be
mounted with reference to facial features for eye surgery.
[0103] Sensor-Tracked Image Guidance
[0104] In other alternative embodiments, one or more customized
fixtures are used to support tracking markers that are used in
sensor-tracked image-guided stereotactic surgery. Referring to FIG.
12, in an exemplary embodiment in which tracking markers are used,
bone anchors 120 are attached to a body. In a procedure of the type
described above, scanning markers are attached to the bone anchors,
and the precise location of the bone anchors relative to the body
are determined from a scanned image.
[0105] Referring still to FIG. 12, a customized fixture 1200 is
fabricated so that it has a known geometry relative to the mounting
points which mate with bone anchors 120. In this embodiment, a
tracking fixture 1210 is attached to customized fixture 1200.
Tracking fixture 1210 has a number of tracking markers 1215
attached to it. These markers are tracked during surgery. Tracking
markers 1215 light-emitting diodes, or other emitters or reflectors
of energy, whose three-dimensional location can be tracked using a
remote sensing device, such as a camera array or a laser
tracker.
[0106] Referring to FIG. 13, tracking fixture 1210 is shown rigidly
mounted to the body through bone anchors 120. The locations of bone
anchors relative to the body is determined from the scanned image.
The geometry of customized fixture 1200 is determined in the
fixture design phase. The location of tracking markers 1215 on
tracking fixture 1210 are known from the predetermined geometry of
the tracking fixture. The locations of tracking markers 1215
relative to bone anchors 120 are then computed from the geometry of
the customized fixture and the geometry of the tracking fixture
attached to it, in what is essentially a "computed registration"
step.
[0107] Referring still to FIG. 13, a surgical instrument 1310, for
example a manually positioned probe, also includes multiple
tracking markers 1315. A tracking system, which includes a remote
sensing device 1300, in this case a camera array, is used to track
the three-dimensional locations of tracking markers 1215 and 1315.
Using a predetermined geometry of surgical instrument 1310,
including the locations of tracking markers 1315 on the instrument,
and the determined locations of tracking markers 1215 relative to
the bone anchors. The tracking system is used to compute the
relative position of the surgical instrument to the body. The
tracking system displays a representation of surgical instrument
1310 on display system 1320 in a proper position and orientation
relative to an image of the body.
[0108] Note that a manual registration phase of the type generally
performed prior to conventional image-guided stereotactic surgery
is not needed to determine the relative position of the instrument
to the body. However, the computed registration step described
above can be validated or double-checked using a manual procedure,
for example, by touching the end of the surgical instrument to
predetermined locations, such as the locations of the bone anchors,
and verifying that the tracking system correctly calculates the
locations. Furthermore, remote sensing device 1300 does not have to
remain in a fixed location relative to the body, and in fact, both
the body and sensing device 1300 can be freely moved around while
continually tracking the location of the surgical instrument
relative to the body.
[0109] Referring to FIG. 14, in another alternative embodiment,
multiple tracking fixtures 1210 are used. Tracking fixtures 1210
are rigidly attached to segments of an articulated portion of the
body to track the relative positions of those segments. In one
exemplary use of multiple tracking fixtures, as shown in FIG. 14,
one tracking fixture 1210 is attached to a pelvis 1410 using a
first customized fixture 1420, while a second tracking fixture 1210
is attached to a femur 1430 using a second customized fixture 1440.
Customized fixtures 1420 and 1440 are designed and fabricated in
the manner described above to mate with mounting anchors or screws
on the pelvis and femur. For instance, anchoring screws 1442 are
inserted into femur 1430. Scanning markers are attached to
anchoring screws 1442 prior to scanning. Customized fixture 1440 is
designed to have a known geometry and to mate with anchoring screws
1442. Customized fixture 1420 is similarly designed to mate with
bone anchors that have been inserted into the pelvis.
[0110] During surgery, remote sensing device 1300 is used to
determined the relative position and orientation of the two
tracking fixtures 1210. Based on the computed registration of each
tracking fixture to the rigid part of the body to which it is
attached, the tracking system computes the relative position and
orientation of femur 1430 and pelvis 1410 and displays
representations of the femur and the pelvis on a display system
1450 in their proper geometric relationship.
[0111] Similar customized fixtures are used to attach tracking
fixtures to other parts of the body, for example to mulitple
segments of the spine. Multiple tracking fixtures can also be used
to track the configuration of skeletal joints during surgery or
during other medical procedures.
[0112] In embodiments described above, tracking fixtures, which
have integrated tracking markers, are attached to customized
fixtures. Alternatively, a customized fixture can be designed and
fabricated to directly hold the tracking markers, thereby being a
customized tracking fixture (or "tracking frame"), which has a
predetermined geometric relationship between the mounting points of
the fixture and the locations of the tracking markers.
[0113] Implementation
[0114] Referring to FIG. 11, the design and fabrication of the
fixture involves several steps and pieces of equipment. Scanner 210
produces scanned image 230 which is passed to computer 220.
Computer 220 is used by the surgeon to identify target and entry
points, and possibly other points such as marker image points. A
display and input device 1110 provides an interface for the
surgeon. For instance, multiple planar views of the scanned image
are presented to the surgeon, and the surgeon selects points using
a mouse. Program storage 1125 is coupled to computer 220 for
holding software used to implement procedures executed by computer
220. As described above, a library of standard fixtures 1120 can
optionally be attached to computer 220. These standard fixtures are
deformed using interactive procedures implemented on computer
220.
[0115] The product of the procedures executed on computer 220 is
solid model 1130 which completely specifies the shape of the
fixture. This model is passed to a fabrication computer 1140 which
derives tooling instructions 1150 which are passed to the RPT
machine 1160. The RPT machine fabricates the fixture according to
the tooling instructions.
[0116] It is to be understood that the foregoing description is
intended to illustrate and not limit the scope of the invention,
which is defined by the scope of the appended claims. Other
embodiments are within the scope of the following claims.
* * * * *