U.S. patent application number 11/030811 was filed with the patent office on 2005-07-07 for enhanced graphic features for computer assisted surgery system.
This patent application is currently assigned to GE Medical Systems Global Technology Company. Invention is credited to Kienzle, Thomas C. III.
Application Number | 20050148855 11/030811 |
Document ID | / |
Family ID | 26940269 |
Filed Date | 2005-07-07 |
United States Patent
Application |
20050148855 |
Kind Code |
A1 |
Kienzle, Thomas C. III |
July 7, 2005 |
Enhanced graphic features for computer assisted surgery system
Abstract
A computer assisted surgery system with is enhanced graphics
features is described for assisting a surgeon in orthopaedic
procedures. A system is described for use in inserting multiple
guide pins in hip fracture surgery using a single bore drill guide
that has a graphical representation comprising its real trajectory
and one or more virtual trajectories, the virtual trajectories
representing potential positions of other guide pins to be placed
during the procedure. Additionally, representations of inserted
guide pins and virtual trajectories may be retained on the display
at their inserted positions for use in aligning subsequent guide
pins. A system is also described for orientation of an acetabular
cup in a total hip replacement surgery. During cup insertion, the
surgeon is provided with information regarding the orientation of
the cup with respect to a pelvic reference frame that is based on
accepted pelvic landmarks. The positions of each landmark is
calculated by the system when a probe with a virtual tip, separate
from its physical tip, is overlaid on the landmark in roughly
orthogonal images of the pelvis.
Inventors: |
Kienzle, Thomas C. III;
(Lake Forest, IL) |
Correspondence
Address: |
MCANDREWS HELD & MALLOY, LTD
500 WEST MADISON STREET
SUITE 3400
CHICAGO
IL
60661
|
Assignee: |
GE Medical Systems Global
Technology Company
|
Family ID: |
26940269 |
Appl. No.: |
11/030811 |
Filed: |
January 7, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11030811 |
Jan 7, 2005 |
|
|
|
09683104 |
Nov 19, 2001 |
|
|
|
60249695 |
Nov 17, 2000 |
|
|
|
Current U.S.
Class: |
600/407 |
Current CPC
Class: |
A61F 2002/4681 20130101;
A61B 2034/107 20160201; A61B 34/10 20160201; A61B 34/20 20160201;
A61B 34/25 20160201; A61B 17/1742 20130101; A61B 90/36 20160201;
A61B 17/1721 20130101; A61F 2002/4668 20130101; A61F 2/4657
20130101; A61B 2090/365 20160201; A61F 2002/4632 20130101; A61B
17/1703 20130101; A61F 2/4609 20130101; A61B 2034/2055 20160201;
A61B 2034/2068 20160201; A61F 2/4603 20130101; A61F 2/34
20130101 |
Class at
Publication: |
600/407 |
International
Class: |
A61B 005/05 |
Claims
1. A computer assisted surgery system for orienting an acetabular
component during total hip replacement surgery comprising: an
imaging device for generating at least two 2-D images of a body
part; means for displaying the 2-D images of the body part; means
for specifying the locations of at least three pelvic landmarks on
the 2-D images; means for calculating a pelvic coordinate frame
based on the at least three pelvic landmarks; a positioning
instrument attachable to the acetabular component, said positioning
instrument's pose being measured by a localizing device; and means
for displaying the orientation of the acetabular component relative
to the pelvic coordinate frame.
2. The computer assisted surgery system of claim 1 wherein the
means for specifying the locations of the at least three pelvic
landmarks comprises: a probe having a real tip portion, said real
tip portion defining a virtual tip portion correlating with a point
in space located in a fixed and known relationship to the real tip
portion, the position of said probe being measured by a localizing
device; means for generating a graphic representation of the
virtual tip portion; means for superimposing the graphic
representation of the virtual tip portion over the 2-D images of
the body part; and means for signaling to the system; wherein the
surgeon uses the signaling means to indicate to the system that the
graphic representation of the virtual tip is aligned over the image
of a pelvic landmark in the 2-D images.
3. A method for orienting an acetabular component during a total
hip replacement surgery comprising the steps: (a) acquiring two
roughly orthogonal x-ray images of at least three bony landmarks of
a patient's pelvis; (b) specifying the location of each of the
three landmarks in the two x-ray images by positioning a cursor
over the landmark in both images; (c) calculating the 3-D position
of each of the three landmarks from the specified cursor positions;
(d) defining a pelvic coordinate frame based on the calculated
positions of the three landmarks; (e) attaching the acetabular
component to a positioning instrument; (f) measuring the pose of
the positioning instrument with a localizing device; (g)
calculating information regarding the orientation of the acetabular
component relative to the pelvic coordinate frame; and (h)
displaying the calculated orientation information to the surgeon;
wherein the surgeon uses the information to place the acetabular
component into a desired orientation.
4. The method of claim 3 wherein positioning the cursor is
accomplished in step (b) by manipulating a mouse, trackball,
joystick or other input device.
5. The method of claim 3 wherein the cursor is a graphic
representation of a probe and positioning the cursor in step (b)
comprises the steps of: generating a graphic representation of the
probe which indicates a virtual tip position at some known distance
from the real tip of the probe; measuring the position of the probe
with a localizing device; superimposing the graphic representation
of the virtual tip on the two x-ray images; and repositioning the
probe in space such that the virtual tip coincides with the bony
landmark in both x-ray images.
6. The method of claim 3 wherein displaying information to the
surgeon in step (g) further comprises the steps of: generating a
graphic representation of the positioning instrument and acetabular
component; and superimposing said graphic representation on one or
more images of the patient's pelvis based on the measured pose of
the positioning instrument; wherein the surgeon is able to view and
adjust the orientation of the acetabular component relative to
imaged anatomy of the pelvis.
7. The method of claim 3 wherein displaying information to the
surgeon in step (g) further comprises the steps of: defining an
axis of the acetabular component; calculating the angular
difference between the axis of the acetabular component and an axis
of the pelvic coordinate frame; and reporting the angular
difference between the axes to the surgeon.
8. The method of claim 4 wherein the three bony landmarks comprise
the left anterior superior iliac spine, the right anterior superior
iliac spine, and the anterior portion of the pubic bone.
9. A computer assisted surgery system with enhanced graphic
capabilities for noninvasively determining the location of a
specific point within a body, the system comprising: an x-ray
imaging device for generating at least two 2-D images of a body
part; means for displaying the 2-D images of the body part; a probe
having a real tip portion, said real tip portion defining a virtual
probe tip portion correlating with a point in space located in a
fixed and known relationship to the real tip portion; a localizing
device for measuring the pose of the probe relative to the imaging
device; means for generating a graphic representation of the
virtual tip portion; and means for superimposing a graphic
representation of the virtual tip portion over the 2-D images of
the body part; wherein the three-dimensional location of a specific
point within the body may be calculated from the pose of the probe
when, in the at least two images, the representation of the virtual
tip overlays the specific point within the body.
Description
RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 09/683,104, filed Nov. 19, 2001, entitled "Enhanced Graphic
Features For Computer Assisted Surgery," which is hereby expressly
incorporated herein in its entirety including the specification,
claims, drawings and abstract.
BACKGROUND OF THE INVENTION
[0002] This invention relates to a computer assisted surgery system
with enhanced graphics capabilities for use in inserting multiple
screws into a hip fracture and orienting a total hip acetabular
component.
[0003] Fractures of the femoral neck, one kind of hip fracture, are
a common injury of the elderly with over 150,000 such fractures
occurring annually. The currently accepted treatment for mildly
displaced femoral neck fractures is surgical fixation. In the
procedure, three cannulated screws are inserted in the hip, from
the lateral aspect of the femur, across the fracture site and into
the femoral head. The initial step is the placement of three guide
pins, over which the screws are inserted, in a characteristic
triangular pattern. This is typically performed under fluoroscopic
guidance, usually with the aid of a drill guide. Some surgeons
prefer to use a drill guide with a single bore, but doing so may
make it difficult to achieve the desired triangular spacing and
optimum placement of the guide pins in the femoral neck. Other
surgeons prefer a drill guide with multiple bores that are fixed in
the proper triangular spacing, but this requires a larger incision
and doesn't permit the surgeon much flexibility to modify the
preset pattern. With either drill guide, it can be difficult to
accurately predict the final guide pin placement. Further, the
surgery requires a significant number of fluoroscopic images and
x-ray exposure for the surgeon, patient and operating room
staff.
[0004] Fluoroscopic based image guided surgery systems can be of
benefit in predicting the paths of the guide pins and in
significantly reducing the amount of radiation exposure. Image
guided systems such as those taught in U.S. Pat. Nos. 5,772,594 and
6,285,902, incorporated herein by reference, employ a computer and
a localizing device to track a drill or drill guide and superimpose
a trajectory line on fluoroscopic images. U.S. Pat. No. 6,285,902
describes a system in which, preferably, orthopaedic surgical tools
outfitted with infrared LEDs are tracked by an optical localizing
device. The poses of these tools are determined and graphic
representations of the tools are superimposed on standard
intraoperative x-ray images. This allows the surgeon to view, in
real time, the position of the tool or tools with respect to an
imaged body part or another tool or tools. In the preferred
embodiment, a drill guide outfitted with infrared LEDs is tracked
and the trajectory of its bore is displayed on the x-ray image of
the involved bone. This allows a surgeon to accurately predict the
trajectory of a guide pin that passes through the bore of the drill
guide. The surgeon can see the path each guide pin will take and
can improve the accuracy and speed of insertion of the guide pin
with only a minimum number of x-ray images. These systems, however,
do not provide help in selecting paths that will lead to the
desired triangular pattern with proper spacing between screws. On
the other hand, a tracked drill guide with multiple bores may be
used, but this requires a large incision and does not leave the
surgeon with flexibility in the spacing or orientation (e.g.,
parallel vs. diverging) of the screws.
[0005] Another surgery that is very common in the elderly is total
hip replacement. Over 200,000 total hip surgeries are performed
each year. This procedure replaces the natural ball and socket
joint of the hip, with a metal ball attached to the femur and a
plastic lined cup in the socket (acetabulum) of the pelvis. A
crucial step in the procedure is the proper alignment of the
acetabular cup relative to the pelvic anatomy. Cups that are not
properly oriented can lead to dislocation of the new hip and may
require reoperation to reorient the cup. However, it can be quite
difficult to orient the acetabular cup correctly. Even though the
acetabulum is typically fully exposed, and the surgeon has the
freedom to place the cup in any orientation, the pelvic landmarks
that would give the surgeon the proper frame of reference are not
exposed. One such set of landmarks in common usage for defining a
pelvic reference frame (albeit for evaluation purposes in
post-operative x-rays) are the left and right anterior superior
iliac spines (ASIS) and the anterior portion of the pubic bone.
During surgery, however, these are not exposed and are thus hidden
under sterile draping material and the patient's soft tissue. This
problem is even worse with obese patients. Further, the pelvis may
be tilted relative to the operating table, making it difficult to
use the table or any vertical or horizontal plane as a reliable
reference. This leaves the surgeon to orient the acetabular
component based on very limited information: the pelvic anatomy
exposed in the immediate vicinity of acetabulum, the general body
orientation, any visual or palpable evidence of the orientation of
the pelvis, and any other clues the surgeon can extract based on
experience.
[0006] Numerous surgical instruments have been introduced with
features designed to assist the surgeon in orienting the acetabular
component. U.S. Pat. No. 4,475,549 describes one such instrument,
in which handles are oriented such that the cup is properly
oriented when the handles are aligned with the patient axis. Again,
however, this requires that the surgeon correctly identify the
alignment of the patient (i.e., of the patient's pelvis) under the
drape and soft tissue.
[0007] Image guided techniques have also been applied to the
problem of acetabular cup orientation. U.S. Pat. No. 6,002,859
teaches a system for orienting the acetabular cup that is based on
a CT scan to preoperatively construct a 3-D model of the pelvis and
plan the placement of the acetabular component. During surgery, a
registration step is required to correlate the position of the
patient's pelvis with the 3-D model. This currently requires the
sampling of several points on the patient with a probe and their
correlation to the 3-D model. While this system can improve the
accuracy, and even the surgical outcome of the total hip procedure,
it requires a CT scan which is not currently required, and a
potentially time consuming intraoperative registration step.
SUMMARY OF THE INVENTION
[0008] Accordingly, one objective of the present invention is to
provide a computer assisted surgery system with enhanced graphic
features for assisting a surgeon in positioning multiple guide pins
in a bone as part of a hip fracture fixation surgery and in
orienting an acetabular cup during a total hip replacement
surgery.
[0009] Another objective of the invention is to provide a technique
and apparatus for displaying a graphic representation of a drill
guide that includes a real trajectory corresponding to the bore of
the drill guide and one or more virtual trajectories relative to
the actual trajectory that indicate possible other drill guide
trajectories.
[0010] Another objective of the invention is to provide a technique
and apparatus for displaying graphic representations of implants or
instruments in positions retained from previous steps of the
procedure.
[0011] Still another objective of the invention is a method and
apparatus for accurately orienting an acetabular component relative
to the pelvis in a total hip replacement surgery.
[0012] Still another objective of the invention is a method and
apparatus for noninvasively determining the location of bony
landmarks inside a patient's body.
[0013] These and other objects of the present invention are
achieved by the use of a computer assisted surgery system,
including a computer, a localizing device and a display monitor.
The system also includes a drill guide for use in placing multiple
guide pins for hip fracture surgery and a probe and positioning
instrument for use in orienting an acetabular cup. The poses of all
three instruments are measurable by a localizing device. The system
is improved for use in the femoral neck fracture surgery and
acetabular cup orientation procedure by two enhancements to the
graphic capabilities of the original computer assisted surgery
system.
[0014] The first enhancement is inclusion in the instrument
representation of features that are not physically present on the
instrument, but that provide additional information and
functionality to the surgeon. While these virtual features are
visible only in the graphic representation, their poses are related
to the poses of real features of the instrument and their poses in
space can be calculated. A virtual feature may represent a physical
feature that is typically present on a conventional instrument but
removed in the instrument under consideration. A virtual feature
may also represent a physical feature that would improve the
function of an instrument but cannot be added, or are not desirable
to add, because of physical constraints, instrument simplicity, or
other reasons (e.g., a long probe tip for indicating points inside
of tissues) but whose function instead can be sufficiently
simulated with appropriate modeling in the instrument's graphic
representation. Further, virtual features may include modeling of
physical features that are present on physical instruments at other
times during the surgery or modeling of physical features that are
located at other poses during other steps of the surgery and are
related in position to the instrument being used in the current
step (e.g., guide pin trajectories of past or future steps of the
procedure). The representation of features virtually instead of
physically allows the surgeon to benefit from the additional
positioning information while still promoting simpler instruments
and less invasive surgical technique.
[0015] The second enhancement to the graphics features is the
ability to retain a version of the instrument representation on the
display in the position that it occupied at a given point in time.
This allows the surgeon to view representations of previously
placed hardware (e.g., guide pins) without requiring the
acquisition of new x-ray images. Further, virtual features may also
be retained in order to carry over information from one step of the
procedure to another (e.g., template information or planning
markings) or to indicate the location of previously identified
positions (e.g., selected landmarks or fiducials).
[0016] During the placement of guide pins in the hip fracture
surgery, a drill guide is used with a graphic representation that
comprises a real trajectory that corresponds to the bore of the
drill guide and that shows the path a guide pin will take when
inserted with the drill guide at its present position. The graphic
representation further comprises one or more virtual trajectories
that are defined relative to the real trajectory and represents
other possible positions for guide pins. Preferably, the virtual
trajectories are the other two positions of the desired triangular
pattern of parallel guide pins typically used in femoral neck
fracture fixation. The virtual trajectories can be redefined by the
surgeon to achieve any desired pattern and spacing of the guide
pins. During surgery, the surgeon uses the computer assisted
surgery system to insert the first guide pin by aligning the
pattern of real and virtual trajectories in an appropriate position
over the x-ray images of the femoral head and neck. Subsequent
guide pins are inserted by aligning the virtual trajectories with
x-ray images of the femur and previously placed guide pins.
Alternatively, representations of previously placed guide pins and
virtual trajectories are retained and the subsequent guide pin
placements are made by aligning the actual trajectory of the drill
guide with the retained virtual trajectories. This invention has
the advantages of assisting the surgeon in achieving a desired
screw pattern, permitting a small incision with a single bore drill
guide, and allowing the surgeon flexibility in placing the guide
pins.
[0017] During the procedure to orient the acetabular cup, a probe
is used to identify the location of three landmarks on the pelvis.
The graphic representation of the probe includes a virtual tip, at
a fixed and known distance from the real tip of the probe. Two
roughly orthogonal x-ray views of the pelvis are obtained and the
probe is moved, always above the skin, in the vicinity of the bony
landmark, until a graphic representation of the virtual probe tip
overlays the image of the landmark in both x-rays, and the 3-D
position of the landmark is calculated. This process is preferably
performed for both anterior superior iliac spines and the anterior
pubis and a pelvic coordinate frame is established. A positioning
instrument with attached acetabular cup is tracked by the localizer
and the system provides both a graphic representation of the
orientation of the acetabular cup over the x-ray images and an
alphanumeric readout of two calculated angular orientation values
familiar to the surgeon. This invention has the advantages of
non-invasively identifying accepted landmarks for establishing a
pelvic reference frame, of automatically registering the images,
and of not requiring a CT scan prior to surgery.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 1 illustrates the femur with inserted cannulated screws
as an example of prior art.
[0019] FIG. 2 illustrates the femur, drill and drill guide as an
example of prior art.
[0020] FIG. 3 illustrates the femur, drill and drill guide and an
example of a screen display of two images and superimposed
instrument representation.
[0021] FIG. 4 is an example of a screen display of two images and
superimposed actual and virtual trajectories.
[0022] FIG. 5 is an example of a screen display of two images,
superimposed actual and virtual trajectories and inserted guide
pin.
[0023] FIG. 6 is an example of a screen display of two images,
superimposed actual and virtual trajectories and inserted guide
pins.
[0024] FIG. 7 illustrates a probe and body landmark with
surrounding soft tissue and an example of a screen display of two
images with a superimposed representation of the probe.
[0025] FIG. 8 illustrates a pelvis and probe and an example of a
screen display with two images of the pelvis with a superimposed
representation of the probe.
[0026] FIG. 9 illustrates a pelvis with reference planes and a
positioning instrument and an example of a screen display of two
images of the pelvis superimposed with a representation of the
positioning instrument and text messages.
[0027] FIG. 10 is an example of a screen display with two images of
a surgical instrument with superimposed retained
representation.
[0028] FIG. 11 is an example of a screen display of two images with
a superimposed retained representation of the drill guide.
[0029] FIG. 12 is an example of a screen display of two images with
superimposed representation of the drill guide and a retained
representation of the drill guide.
DETAILED DESCRIPTION
[0030] Current surgical practice for the treatment of a femoral
neck fracture is the insertion of three cannulated screws through a
small incision on the lateral (side) aspect of the hip. As shown in
FIG. 1A, the screws (102) are inserted from the lateral aspect of
the trochanteric area of the femur (101) through the femoral neck
(103) and into the femoral head (104) in a roughly parallel manner.
When observed from a lateral view, FIG. 1B, the screws describe the
vertices of a triangle with one screw placed inferiorly (toward the
knee), one placed anteriorly (toward the front) and one placed
posteriorly (toward the back).
[0031] The first step of the procedure, shown in FIG. 2, is the
insertion of three guide pins (110) under fluoroscopic guidance.
Numerous x-ray images involving frequent reorientation of the
fluoroscope are required to monitor the progress of the guide pin
insertion in both AP (front-to-back) and lateral (side) views. A
drill guide (105) with three or more holes (106) is typically used
to assist in keeping the guide pins (110) roughly parallel during
the insertion.
[0032] As shown in FIG. 3, the computer assisted surgical system
described in the previous application can assist the surgeon in
this procedure by superimposing a graphic representation (130) of
the drill guide (123) on the images (120) of the femur (101). The
surgeon aligns the drill guide representation (130) such that the
guide pin (110) will be inserted in a position that accommodates
the remaining two guide pins in the desired triangular pattern.
Once the drill guide (123) is properly aligned, the surgeon inserts
the first guide pin (110) and obtains new AP and lateral x-rays
(120) to show the final position of the guide pin (110) relative to
the bone (101). The remaining two pins are inserted in a similar
fashion with the surgeon using the drill guide representation (130)
to align the drill guide (123).
[0033] The current invention augments the capability of the
computer assisted surgery system by providing additional
information to the surgeon in a novel manner. Whereas prior art
systems display information directly related to physical features
of the drill guide, the preferred embodiment of the current
invention includes information that is not directly derived from a
physical feature of the instrument. FIG. 4 shows the improved
graphic representation (130, 131) of the same drill guide (123)
which, in addition to a real trajectory (130) corresponding to the
sleeve of the physical drill guide, also includes virtual
trajectories (131) representing possible positions for the other
two guide pins required in the surgery. Preferably, these virtual
trajectories (131) take the form of dashed lines, but may be
displayed in any manner that allows for their differentiation from
the real trajectory (130) without departing from the instant
invention. Preferably, three different representations are
available for use in placement of the pin in the inferior,
anterior, or posterior positions. The representation of the drill
guide for placement of the inferior guide pin contains two virtual
trajectories (131) located superior to the real drill guide
trajectory (130). For placement of the anterior guide pin, the
virtual trajectories (131) are located posterior to the real
trajectory (130) while for posterior guide pin placement the
virtual trajectories (131) are located anterior to the real
trajectory (130). Alternatively, if the pin pattern is symmetric
and the drill guide is sufficiently able to rotate, a single
representation may be used by physically rotating the drill guide
about its trajectory axis. Other representations, with alternative
spacing and orientation of the virtual trajectories (131) relative
to the real drill guide trajectory (130), may be made available to
the surgeon to accommodate a range of bone sizes, fracture
patterns, or surgeon preferences.
[0034] As the surgeon positions the drill guide against the femur,
the guide's real trajectory (130) and the two virtual trajectories
(131) are superimposed on the images (121 and 122) of the femur.
With the virtual trajectories (131) included in the instrument
representation, the surgeon is able to see relative to the femur
image (125) how the positioning of the first pin will affect the
positioning of the final three-pin pattern. In the preferred
embodiment, the first guide pin placed is the inferior one.
Alternatively, any pin placement order with corresponding drill
guide representations may be used. With the guide's real trajectory
(130) shown on the display in its proper position relative to the
femur image (125), the surgeon then inserts the guide pin (110)
through the drill guide (123), and advances it into the bone
(101).
[0035] Once the first guide pin is inserted, new x-ray images are
obtained. As shown in FIG. 5 these images show the actual position
of the first guide pin (135). In preparation for the placement of
the second guide pin, the representation (130, 132 and 133) of the
drill guide is changed to one for posterior pin placement. In the
preferred embodiment, the drill guide's real trajectory (130)
represents that of the posterior guide pin, while one virtual
trajectory (132) represents the position of the previously placed
inferior guide pin (135) and the other virtual trajectory (133)
represents the proposed trajectory of the future anterior pin.
Preferably, the surgeon aligns the drill guide (110) with the femur
(101) such that the inferior virtual trajectory (132) overlays the
image of the previously placed guide pin (135), while the other
virtual trajectory (133) and the real trajectory (130) are aligned
into their proper positions relative to the femur image (125).
Then, the surgeon again advances the guide pin (110) through the
drill guide (123) and into the bone (101).
[0036] Once the first two guide pins have been placed, new x-ray
images are acquired as shown in FIG. 6. In the preferred
embodiment, the representation of the drill guide is changed to
show the virtual trajectories (131) inferiorly and posteriorly
while the drill guide's real trajectory (130) is displayed
anteriorly. Preferably, the surgeon aligns the virtual trajectories
(131) to overlay the images of the previously placed pins (135) and
advances the guide pin (110) through the drill guide (123) and into
the bone (101). The remainder of the procedure, including the
placement of the cannulated screws over the guide pins (110), is
performed in the usual manner.
[0037] In any of the guide pin placement steps described, the
surgeon should use good clinical judgment as to whether to follow
the virtual trajectories exactly, to use them merely as reference
marks, or to simply ignore them.
[0038] The major advantage of this invention is its ability to
assist the surgeon in positioning multiple guide pins relative to
one another without the necessity of a multi-bore mechanical jig.
By using a single-bore drill guide to accurately place these pins,
a smaller skin incision may be used, resulting in less trauma to
the patient, faster healing, less risk of infection, and other
advantages of minimally invasive surgery.
[0039] In the foregoing description, the assumption is made that
the body part is held immobile throughout the procedure.
Alternatively, a tracking device may be rigidly affixed to the bone
and any changes in the pose of the bone during the procedure may be
recorded and compensated for. This device may be comprised of three
LEDs affixed to an assembly that is attached to the pelvis with one
or more screws. However, any device that attaches rigidly to the
femur and tracks its changes in pose may be used. As the tracking
device changes pose, indicating a change in pose of the femur, the
software adjusts the pose of the instrument representation being
overlaid on the x-ray images in order to maintain accurate relative
superpositioning.
[0040] While the above description of the invention relates to
insertion of cannulated screws in the fixation of a femoral neck
fracture, those skilled in the art will recognize its applicability
to numerous other surgical procedures. In alternative embodiments,
the drill guide may be replaced by a probe, a drill, a bone saw, an
implant positioner, or any other surgical instrument. The drill
guide trajectory may be replaced by a representation of a probe
tip, a drill bit, a saw blade, an implant, or any other physical
feature of a surgical instrument or implant attached to a surgical
instrument. The virtual guide pin trajectories may be replaced by
graphics that represent measurements, markings, or modeling of
surgical instrument features not necessarily present on the
instrument being used nor related to an existing physical feature
of the instrument.
[0041] The virtual features may include graphics relating to
another implant or instrument not currently affixed to the first
implant or instrument, but whose position is ultimately related to
it. The other implant or instrument may be used simultaneously with
the first implant or instrument or may be involved with another
step in the procedure, either before or after the current step.
Additionally, the virtual feature may be derived from a physical
feature that has been removed from an instrument or implant or it
may represent an alternative configuration or state of the current
instrument or implant. The virtual feature may comprise any
representation that is not directly derived from the current
physical properties of the instrument or implant that it represents
without departing from the instant invention.
[0042] In the preferred embodiment, the graphic representations are
displayed overlaid on x-ray images. Alternatively, the
representations can be displayed overlaid on other medical imaging
data (CT, MRI, etc.) or relative to other instruments or implants
in a graphic picture not requiring imaging data.
[0043] In another example, an instrument with a virtual feature is
used to noninvasively determine the locations of specific points,
structures, or landmarks within the body. Often in orthopaedic
procedures it is desirable to identify the position of bony
landmarks that are hidden by soft tissue, in order to establish a
body reference frame. Current art, which includes directly touching
landmarks by a probe, is not applicable in this case because the
landmarks are covered by soft or bony tissue and therefore
inaccessible to the tip of a probe. Therefore, the current
invention, as shown in FIG. 7, includes a probe (150) which has a
graphic representation that includes a real probe tip portion (155)
and a virtual probe tip portion (156). The real probe tip portion
of the representation (155) correlates directly with the position
of the real probe tip (151). The virtual probe tip portion of the
representation (156) correlates with a point in space (152) that is
located in a fixed and known relationship to the physical probe tip
(151).
[0044] In order to identify the location of a bony landmark (154)
surrounded by soft tissue (153) two x-ray images (160 and 161) are
obtained. Preferably the two images (160 and 161) are 90 degrees
apart from one another, but may be any suitable angle apart without
departing from the instant invention. The surgeon then positions
the probe (150) in space, relative to the bony landmark (154) such
that the tip of the virtual cursor (156) is coincident with the
bony landmark's image (159) in both views (160 and 161)
simultaneously. The surgeon then presses a footswitch, or activates
some other signaling device, and the 3-D position of the point in
space (152) corresponding to the virtual probe tip (152), and
therefore the 3-D position of the bony landmark (154), is
calculated and recorded in the computer's memory.
[0045] Alternatively, the virtual probe representation can be
replaced with a straight line, a curved line, a plane, a curved
surface, or some other graphic that allows for the alignment of the
virtual probe with one or more landmarks or points. Further, those
skilled in the art will recognize that the identification of
landmarks or points with the virtual probe is applicable to other
surgeries and other imaging modalities.
[0046] In a preferred embodiment, the purpose of identifying
landmarks with the virtual probe is to establish a coordinate frame
on a patient's pelvis relative to which is oriented the acetabular
component in total hip replacement surgery. The patient is placed
on his or her side on the operating room table and draped in the
usual fashion. The surgeon then makes the usual incision and
prepares the femur and pelvic acetabulum in the standard fashion.
In the preferred embodiment, shown in FIG. 8, two modified AP x-ray
images (171 and 172) of the patient's pelvis (181) are acquired by
the C-arm fluoroscope and shown on the display (170). The first
image (171) is an "inlet view" of the pelvis (181) taken with the
C-arm aimed obliquely, approximately 40 degrees, from cephalad and
anterior to caudal and posterior. The second image (172) is an
"outlet view" of the pelvis (181) taken with the C-arm aimed from
caudal and anterior to cephalad and posterior. The surgeon then
uses a probe (150) outfitted with localizing emitters (177) to
identify three landmarks (182, 183 and 184) by positioning the
probe (150) in such a manner that the virtual probe tip (156)
overlays the image (173) of the first bony landmark (183) in both
views (171, 172). By pressing the footswitch, the system reads the
pose of the probe (150) and calculates and records the
three-dimensional location of the landmark (183). In this manner,
the surgeon records the positions of the left anterior superior
iliac spine (ASIS) (182), the right ASIS (183) and the top of the
pubic symphysis (184). Alternatively, other bony landmarks may be
selected without departing from the instant invention.
[0047] As shown in FIG. 9, the three landmarks (182, 183 and 184)
are used to define a pelvic coordinate system. The first axis (185)
of the pelvic coordinate system is contained in a line between the
left ASIS (182) and right ASIS (183), a second axis (186) is
perpendicular to the first axis and extends through the top of the
pubic symphysis (184), and the third axis (187) is orthogonal to
the first two axes (185 and 186). The "frontal" plane (188) is
defined by the first two axes (185 and 186) and is considered by
many orthopaedic surgeons to represent the standard vertical plane
of the pelvis (181) during ambulation. Likewise, the axial plane
(189) is defined by the first and last axes (185 and 187); and a
third plane, the sagittal plane (not shown), is defined by the last
two axes (186 and 187). Alternatively, other axes and planes may be
defined without departing from the instant invention.
[0048] The surgeon then attaches an acetabular component (190) to a
positioning instrument (191) outfitted with localizing emitters
(192) and then places the component (190) into the patient's
prepared acetabulum (179). The system displays a representation
(195) of the positioning instrument (191) with the attached
acetabular component (190) superimposed on the two images (171 and
172) by using the stored conic projection model of the C-arm. As
the surgeon moves the positioning instrument (191), the display is
updated in real time to show, graphically, the pose of instrument
and implant representation (195) relative to the images of the
pelvis.
[0049] At the same time, preferably, angular values (196 and 197)
are calculated and displayed to quantify for the surgeon the
orientation of the implant (190) relative to the pelvic landmarks
(182, 183 and 184). The implant axis (193) is defined as the axis
normal to the plane of the rim of the acetabular implant (190).
Preferably this axis (193) is coincident with the long axis of the
positioning instrument (191). The first value (196), the "abduction
angle" is the angle between the implant axis (193) and the second
axis (186) when both axes (193 and 186) are projected on the
frontal plane (188). A second value (197), the "forward flexion
angle" is the angle between the implant axis (193) and the
inter-ASIS axis (185) when both axes are projected on the axial
plane (189). Preferably, these values (196 and 197) are calculated
continuously and displayed in numerical form in real time.
Alternatively, other angles or values of interest to the surgeon
may be calculated. These values may be displayed in numerous ways
including numeric messages or graphic representations of angles or
distances.
[0050] Optionally, views of the pelvis from points of view other
than those available from the C-arm fluoroscope may be simulated
and the orientation of the implant positioning instrument displayed
relative to this simulated image. These simulated images may
include lateral or axial views of the pelvis and may include any of
a number of forms including bitmap pictures, previously obtained
x-rays, or projections of CT data. A graphic representation of the
implant positioning instrument is appropriately scaled and
projected onto a plane that corresponds to that of the image. The
representation is centered on the acetabulum and as the orientation
of the implant positioning instrument is changed, its
representation is reoriented in real time relative to the simulated
image.
[0051] Once the surgeon has placed the acetabular component (190)
into the proper orientation, an impacting device is used to
press-fit the implant (190) into the acetabulum (179). The rest of
the procedure, including final sizing of the components and closure
of the incision is performed in the usual fashion.
[0052] In the foregoing description, the assumption is made that
the body part is held immobile throughout the procedure.
Alternatively, a tracking device may be rigidly affixed to the bone
that records any changes in pose of the bone during the procedure.
This device may be comprised of three LEDs affixed to an assembly
that is attached to the pelvis with one or more screws. However,
any device that attaches rigidly to the pelvis and tracks its
changes in pose may be used. As the tracking device changes pose,
indicating a change in pose of the pelvis, the software adjusts the
pose of the instrument being overlaid on the x-ray images in order
to maintain accurate relative superpositiong.
[0053] In alternative embodiments, other information regarding the
fit and sizing of the implant is developed. In one alternative
embodiment, the surgeon attaches an array of tracking emitters to
the shaft of the femur prior to dislocating the hip and removing
the femoral head. The surgeon presses the footswitch while rotating
the femur around the femoral head, causing poses of the tracking
array to be recorded. The location of the center of the femoral
head relative to the tracking array is calculated by methods known
in the art. Once the femoral and acetabular components have been
placed, the sampling process and calculations are repeated. The
software then compares the data recorded before and after the
placement of the prosthetic components to provide information to
the surgeon regarding the preservation of leg length, femoral
offset, or other geometries of the replaced hip. Stored models of
the implants used may be incorporated into these calculations to
improve the accuracy and usefulness of this information.
[0054] Numerous other image-guided surgical procedures can make use
of the virtual probe as a means of identifying the locations of
internal landmarks. This invention has utility in any case where
the location of a point is to be determined, but it is impossible
or undesirable to touch the point directly with a probe tip. Those
skilled in the art will recognize the applicability of this
invention to other procedures.
[0055] Existing image guided surgery systems display real-time
graphic representations of surgical instruments overlaid on images
of the body part. As the instrument moves, so does its graphic
representation on the screen and when the instrument is removed
from the field its representation disappears from the screen.
Likewise, a representation of an implant is only valid as long as
the implant is attached to a tracked positioning device. A
capability of the computer assisted surgical system described in
U.S. Pat. No. 6,285,902 is the recording of a surgical instrument's
pose at the same time an image of the instrument is acquired. As
shown in FIG. 10, the instrument's graphic representation (201) is
then overlaid on the x-ray images (202) for a period of time that
allows the surgeon to verify the accurate functioning of the system
by comparing the position of the graphic representation (201) to
the instrument's radiographic silhouettes (203) in the x-ray images
(202).
[0056] An extension of this capability is herein described that
improves the surgeon's ability to perform surgery and reduces
intraoperative procedure time and radiation exposure. With this
invention, the recording of the pose of the instrument occurs at a
point in time specified by the surgeon, and an instrument
representation is retained immobile on the screen for the purpose
of providing the surgeon with information relating to the surgical
procedure. The retained instrument representation may be the same
as the tracked instrument representation displayed in real time
including any real or virtual features, or it may be different from
the real-time representation and comprise alternate real or virtual
features (e.g., the retained representation for a guide pin may be
the cannulated screw that fits over that pin).
[0057] In the preferred embodiment, the invention is an enhancement
to the femoral neck fracture fixation procedure previously
described. Returning to FIG. 4, the drill guide representation
including the real drill guide trajectory (130) and the two virtual
trajectories (131) is overlaid on the AP image (121) and lateral
image (122) of the femur. Once the drill guide (105) is in the
proper position, as evidenced by proper alignment of the drill
guide trajectory (130) and the two virtual trajectories (131) in
the head and neck of the femur image (125), the surgeon inserts the
first guide pin (110). Preferably, with the pin (110) inserted and
the drill guide (105) still in position, the surgeon presses a
footswitch to cause the pose of the drill guide (105) to be
recorded. Thereafter, as shown in FIG. 11, a drill guide
representation (209), including the real drill guide trajectory
(210) and the virtual trajectories (211), is displayed immobile on
the same x-ray images (121 and 122) in the position it occupied
relative to the bone (125) when the footswitch was pressed. This
retained graphic (209) represents the final position of the first
inserted guide pin (210) and the planned trajectories (211) for the
subsequent two guide pins. As shown in FIG. 12, the procedure
continues with the surgeon using a drill guide representation with
a single trajectory representation (130) to insert the final two
guide pins relative to the paths indicated by the retained virtual
trajectories (211). Additionally, by pressing the footswitch after
each remaining guide pin is inserted, a guide pin representation
(210) may be retained on the images (121 and 122) in the positions
that correspond to the final inserted poses of the guide pins.
[0058] The footswitch that the surgeon uses to indicate that the
pose of the instrument is to be recorded may be replaced with any
other signaling device without departing from the instant
invention. Other possibilities include a pushbutton on the
instrument, a keypad or keyboard button, a drill trigger, or a
voice activated switch.
[0059] In the preferred embodiment, the graphic representations are
displayed overlaid on x-ray images. Alternatively, the
representations can be displayed overlaid on other medical imaging
data (CT, MRI, etc.) or relative to other instruments in a graphic
picture not requiring imaging data.
[0060] While the described application is for insertion of
percutaneous hip screws, other surgical procedures may be addressed
without departing from the instant invention. In an alternative
embodiment, a probe tip or crosshairs representing the virtual
cursor tip described previously can be retained on the screen as a
reference marker. Likewise, multiple points, with optional
interconnecting lines, may be retained to produce a straight or
curved path relative to image or model data. In other alternative
embodiments, the graphic representation that is retained on the
screen may comprise screws used to hold reduction of a complex
fracture or affix an implanted device, an implant or individual
components of a multi-component implant, reference marks used in
subsequent steps of the procedure, or any other instrument,
implant, template, measurement, or graphic information that would
benefit the surgeon by being retained in a specified position.
Further, the graphic representation to be retained may include real
or virtual features, and may be the same or different from the
representation that was displayed prior to the recording of the
instrument's position.
[0061] This invention has utility in numerous other image-guided
surgical procedures. Those skilled in the art will recognize the
applicability of this invention to other procedures and areas of
surgery.
* * * * *