U.S. patent application number 10/570630 was filed with the patent office on 2006-12-21 for device, method and system for digitizing position and orientation information of hip joint implant components.
Invention is credited to Louis-Phillippe Amiot, Isabelle Fontaine, Herbert Andre Jansen, Daniel Odermatt.
Application Number | 20060287613 10/570630 |
Document ID | / |
Family ID | 34230727 |
Filed Date | 2006-12-21 |
United States Patent
Application |
20060287613 |
Kind Code |
A1 |
Amiot; Louis-Phillippe ; et
al. |
December 21, 2006 |
Device, method and system for digitizing position and orientation
information of hip joint implant components
Abstract
A device for digitizing a center of rotation of a hip joint
implant component with respect to a bone element in
computer-assisted surgery. The device comprises a detectable member
trackable for position and orientation by a computer-assisted
surgery system. A body is connected to the detectable member in a
known geometry. The body has a coupling portion adapted to be
coupled to the hip joint implant component in a predetermined
configuration. The center of rotation of the hip joint implant
component is calculable in the predetermined configuration as a
function of the known geometry and of the position and orientation
of the detectable member.
Inventors: |
Amiot; Louis-Phillippe;
(Quebec, CA) ; Jansen; Herbert Andre; (Quebec,
CA) ; Fontaine; Isabelle; (British Columbia, CA)
; Odermatt; Daniel; (Quebec, CA) |
Correspondence
Address: |
OGILVY RENAULT LLP
1981 MCGILL COLLEGE AVENUE
SUITE 1600
MONTREAL
QC
H3A2Y3
CA
|
Family ID: |
34230727 |
Appl. No.: |
10/570630 |
Filed: |
September 7, 2004 |
PCT Filed: |
September 7, 2004 |
PCT NO: |
PCT/CA04/01638 |
371 Date: |
March 3, 2006 |
Current U.S.
Class: |
600/587 |
Current CPC
Class: |
A61B 90/36 20160201;
A61B 2034/105 20160201; A61F 2002/4631 20130101; A61F 2310/00011
20130101; A61F 2220/0033 20130101; A61F 2002/4632 20130101; A61F
2002/3611 20130101; A61F 2002/365 20130101; A61F 2/3676 20130101;
A61B 2090/3983 20160201; A61B 2034/2068 20160201; A61F 2/4684
20130101; A61F 2/34 20130101; A61F 2002/3625 20130101; A61B
2034/2072 20160201; A61F 2310/00023 20130101; A61B 2034/102
20160201; A61F 2/367 20130101; A61F 2310/00179 20130101; A61B
2034/256 20160201; A61F 2/4657 20130101; A61B 34/20 20160201; A61F
2002/4668 20130101; A61F 2002/30332 20130101; A61F 2002/4658
20130101; A61B 2034/2055 20160201; A61B 2034/108 20160201; A61F
2/36 20130101 |
Class at
Publication: |
600/587 |
International
Class: |
A61B 5/103 20060101
A61B005/103 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 4, 2003 |
CA |
2 439 850 |
Claims
1. A device for digitizing a center of rotation of a hip joint
implant component with respect to a bone element in
computer-assisted surgery, comprising: a detectable member
trackable for position and orientation by a computer-assisted
surgery system; and a body connected to the detectable member in a
known geometry, the body having a coupling portion adapted to be
coupled to the hip joint implant component in a predetermined
configuration, the center of rotation of the hip joint implant
component being calculable in the predetermined configuration as a
function of the known geometry and of the position and orientation
of the detectable member.
2. The device according to claim 1, wherein the implant is a
femoral implant, and the coupling portion of the body is a
cylindrical receptacle in the body adapted to be releasably fitted
in said predetermined configuration to a neck of the femoral
implant prior to a ball head of the femoral implant being fixed to
the neck of the femoral implant.
3. The device according to claim 1, wherein the implant is a
femoral implant, and the coupling portion of the body is a
hemispherical receptacle in the body adapted to be releasably
fitted in said predetermined configuration to a ball head of the
femoral implant.
4. The device according to claim 1, wherein the implant is a pelvic
implant, and the coupling portion is a hemispherical member
received in any one of a shell and a liner of the pelvic implant in
said predetermined configuration.
5. The device according to claim 4, wherein the hemispherical
member has a flange at a periphery thereof, the flange being
adapted to abut a rim of the pelvic implant in said predetermined
configuration, the flange being in a known geometric relation with
the detectable member such that an orientation of the pelvic
implant is calculable with respect to said known geometric
relation, as a function of said predetermined configuration.
6. A method for digitizing a center of rotation of a pelvic implant
component with a computer-assisted surgery system, comprising the
steps of: providing a device being trackable for position and
orientation by the computer-assisted surgery system, the device
being releasably coupled in a known configuration to the pelvic
implant component; tracking a position and orientation of a pelvis
implanted with the pelvic implant component and a position and
orientation of the device; and calculating a center of rotation of
the pelvic implant component with respect to the position and
orientation of the pelvis by relating the known configuration of
the device with the position and orientation tracking of the pelvis
and of the device.
7. The method according to claim 6, further comprising the step of
calculating an orientation of the pelvic implant component with
respect to the position and orientation of the pelvis by relating
the known configuration of the device with the position and
orientation tracking of the pelvis and of the device.
8. The method according claim 6, wherein the method is performed on
an anatomical bone model or on a cadaver.
9. A method of doing surgical treatment with a position tracking
system in computer-assisted surgery for guiding an operator in
inserting a femoral implant of a hip joint implant in a resected
femur tracked for position and orientation, comprising the steps
of: positioning a trackable device on the femoral implant in a
predetermined configuration, the trackable device being trackable
in space for position and orientation; registering implant geometry
information for the femoral implant with respect to the trackable
device as a function of said predetermined configuration between
the femoral implant and the trackable device; and inserting the
femoral implant in the femur by obtaining implant position and
orientation information, the implant position and orientation
information being calculated from said implant geometry information
as a function of the tracking for position and orientation of the
trackable device with respect to a frame of reference of the
femur.
10. The method according to claim 9, wherein the step of
registering implant geometry information includes obtaining a
center of rotation of the femoral implant and a neck axis of the
implant as a function of said predetermined configuration between
the femoral implant and the trackable device, whereby the implant
position and orientation information with respect to the frame of
reference is any one of a femoral anteversion and a limb length
discrepancy.
11. The method according to claim 10, wherein the step of
registering implant geometry information includes registering
surface information on the femoral implant, said surface
information being used to calculate a longitudinal axis of the
femoral implant, whereby the implant position and orientation
information with respect to the frame of reference is any one of a
femoral anteversion, a limb length discrepancy and a varus/valgus
angle.
12. A method according to claim 9, wherein the method is performed
on an anatomical bone model or on a cadaver.
13. A computer-assisted surgery system for guiding an operator in
inserting a femoral implant of a hip joint implant in a resected
femur tracked for position and orientation, comprising: a trackable
reference device positionable onto the femoral implant in a
predetermined configuration and trackable in space for position and
orientation; a registration device trackable in space for position
and orientation and handled by the operator to register surface
information; a sensing apparatus, for tracking any one of the
devices for position and orientation; a controller connected to the
sensing apparatus, the controller being provided to: i) calculate a
position and orientation of the devices as a function of the
tracking by the sensing apparatus; ii) digitize surface information
of the femoral implant as a function of the tracking of the
registration device by the sensing apparatus; and an implant
geometry information calculator connected to the controller, for
calculating geometry information of the femoral implant from said
predetermined configuration with respect to the trackable reference
device, as a function of said surface information of the femoral
implant; whereby the geometry information is used to provide
implant position and orientation information related to a frame of
reference of the femur, so as to guide the operator in subsequently
inserting the femoral implant in the resected femur.
14. The computer-assisted surgery system according to claim 13,
wherein the geometry information is at least one of a center of
rotation of the femoral implant, a neck axis of the femoral
implant, and a longitudinal axis of the femoral implant.
15. The computer-assisted surgery system according to claim 14,
wherein the surface information is a plane digitized from points on
the femoral implant, and a tip of the femoral implant.
16. The computer-assisted surgery system according to claim 13,
wherein the implant position and orientation is at least one of
limb length discrepancy, femoral anteversion and varus/valgus
angle.
17. The computer-assisted surgery system according to claim 13,
wherein the controller stores a digital model of the femoral
implant, said geometry information calculated by the implant
geometry information calculator being associated to the digital
model through a tracking of the trackable reference device.
18. A controller computer program product comprising code means
recorded in a computer readable memory for executing the method
defined in claim 13.
Description
FIELD OF THE INVENTION
[0001] The present invention generally relates to computer-assisted
hip replacement surgery and, more particularly, to a device for
positioning hip joint implant components during surgery, and to a
system and method associated with the device.
BACKGROUND OF THE INVENTION
[0002] Computer-assisted surgery (CAS) systems provide position and
orientation information in different forms throughout the operative
steps, to guide the surgeon in his/her decision making. CAS systems
are used for instance to assist surgeons in hip replacement
surgery. In hip replacement surgery, the hip joint implants being
implanted must assure a desired posture to the patient.
Accordingly, the position and orientation information provided to
the surgeon must be precise and accurate to obtain the desired
posture.
[0003] The femoral implant and the acetabular implant generally
form a spherical joint, in which the center of a ball head of the
femoral implant coincides with the center of an hemispherical
socket of the acetabular implant, at a center of rotation of the
hip joint implant. During surgery, the femur is separated from its
associated pelvis for the implants to be implanted. Through the
separation of the femur from the pelvis, position and orientation
information is still provided from the tracking of the femur, the
pelvis and the various tools being used. For instance, a rasping
tool altering the intramedullary canal of the femur may be tracked
such that the center of rotation of the femoral implant (i.e., the
center of the ball head) may be calculated as a function of the
geometry of the femoral implant and of the altered intramedullary
canal.
[0004] Some types of femoral implants come separate with the ball
head being fixable to the femoral implant body. The femoral implant
body has a frusto-conical connector end (e.g., a Morse 12/14 taper)
upon which the ball head is slid in a friction fit. In calculating
the position of the center of rotation of the femoral implant, some
precision is lost considering that the fit between the ball head
and the frusto-conical connector end is unpredictable to some
extent.
[0005] Alternatively, it may be desired to confirm the position and
orientation of the femoral implant. Referring to the
above-described example in which the center of rotation of the
femoral implant is calculated as a function of the geometry of the
femoral implant and of the altered intramedullary canal, it is
possible that the femoral implant is not completely fitted as
expected in the altered intramedullary canal. In such a case, a
confirmation of the position and orientation of the femoral implant
would be appropriate.
SUMMARY OF THE INVENTION
[0006] Accordingly, an object of the present invention is to
provide a device for obtaining position information for hip joint
implant components in computer-assisted surgery.
[0007] It is a further object of the present invention to provide a
method and system for obtaining position information for hip joint
implant components in computer-assisted surgery.
[0008] It is a further object of the present invention to provide a
device for obtaining the center of rotation of an implant.
[0009] It is a further object of the present invention to provide a
method for obtaining the center of rotation of an implant.
[0010] Therefore, in accordance with the present application, there
is provided a device for digitizing a center of rotation of a hip
joint implant component with respect to a bone element in
computer-assisted surgery, comprising a detectable member trackable
for position and orientation by a computer-assisted surgery system;
and a body connected to the detectable member in a known geometry,
the body having a coupling portion adapted to be coupled to the hip
joint implant component in a predetermined configuration, the
center of rotation of the hip joint implant component being
calculable in the predetermined configuration as a function of the
known geometry and of the position and orientation of the
detectable member.
[0011] Further in accordance with the present invention, there is
provided a method for digitizing a center of rotation of a pelvic
implant component with a computer assisted surgery system,
comprising the steps of providing a device being trackable for
position and orientation by the computer-assisted surgery system,
the device being releasably coupled in a known configuration to the
pelvic implant component; tracking a position and orientation of a
pelvis implanted with the pelvic implant component and a position
and orientation of the device; and calculating a center of rotation
of the pelvic implant component with respect to the position and
orientation of the pelvis by relating the known configuration of
the device with the position and orientation tracking of the pelvis
and of the device.
[0012] Still further in accordance with the present invention,
there is provided a method of doing surgical treatment with a
position tracking system in computer-assisted surgery for guiding
an operator in inserting a femoral implant of a hip joint implant
in a resected femur tracked for position and orientation,
comprising the steps of positioning a trackable device on the
femoral implant in a predetermined configuration, the trackable
device being trackable in space for position and orientation;
registering implant geometry information for the femoral implant
with respect to the trackable device as a function of said
predetermined configuration between the femoral implant and the
trackable device; and inserting the femoral implant in the femur by
obtaining implant position and orientation information, the implant
position and orientation information being calculated from said
implant geometry information as a function of the tracking for
position and orientation of the trackable device with respect to a
frame of reference of the femur.
[0013] Still further in accordance with the present invention,
there is provided a computer-assisted surgery system for guiding an
operator in inserting a femoral implant of a hip joint implant in a
resected femur tracked for position and orientation, comprising a
trackable reference device positionable onto the femoral implant in
a predetermined configuration and trackable in space for position
and orientation; a registration device trackable in space for
position and orientation and handled by the operator to register
surface information; a sensing apparatus, for tracking any one of
the devices for position and orientation; a controller connected to
the sensing apparatus, the controller being provided to: i)
calculate a position and orientation of the devices as a function
of the tracking by the sensing apparatus; ii) digitize surface
information of the femoral implant as a function of the tracking of
the registration device by the sensing apparatus; and an implant
geometry information calculator connected to the controller, for
calculating geometry information of the femoral implant from said
predetermined configuration with respect to the trackable reference
device, as a function of said surface information of the femoral
implant; whereby the geometry information is used to provide
implant position and orientation information related to a frame of
reference of the femur, so as to guide the operator in subsequently
inserting the femoral implant in the resected femur.
BRIEF DESCRIPTION OF DRAWINGS
[0014] These and other features, aspects and advantages of the
present invention will become better understood with regard to the
following description and accompanying drawings wherein:
[0015] FIG. 1 is a perspective view of a device for digitizing
position and orientation information of a femoral implant, in
accordance with a preferred embodiment of the present
invention;
[0016] FIG. 2 is a perspective view of a device for digitizing
position information of an acetabular implant, in accordance with a
preferred embodiment of the present invention;
[0017] FIG. 3 is a block diagram of a computer-assisted surgery
system to be used with the devices of FIGS. 1 and 2; and
[0018] FIG. 4 is a flow chart illustrating a method of doing
surgical treatment for guiding an operator in inserting a femoral
implant in a resected femur in hip replacement surgery in
accordance with an embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0019] Referring to the drawings and, more particularly, to FIG. 1,
a device to be used for obtaining position and orientation
information for a femoral implant is generally shown at 10. A
femoral implant is shown at F, and has a body F10 and a ball head
F20. The body F10 has a stem portion F11, which is adapted to be
received in an intramedullary canal of a resected femur (not
shown). A connector end F12 projects from an end of the stem
portion F11. The connector end F12 is illustrated having a
frusto-conical shape, for instance having a Morse 12/14 taper.
[0020] The ball head F20 has a spherical outer surface, and a
connector bore F21. The connector bore F21 is illustrated having a
frusto-conical shape, so as to correspond to the shape of the
connector end F12 of the body F10. When the body F10 is suitably
received in the intramedullary canal of the femur, the ball head
F20 is secured to the connector end F12, by the complementary
shapes of the connector end F12 and the connector bore F21.
[0021] As mentioned previously, the position of the center of
rotation of the femoral implant F is useful information, even prior
to the ball head F20 being secured thereto. From the calculated
center of rotation, it may be required to further alter the
intramedullary canal in view of an anticipated leg length
discrepancy. Alternatively, the calculated center of rotation may
be used to calculate the size of ball head F20 to be used in the
femoral implant F. Femoral implant orientation information is
useful in calculating information such as the varus/valgus angle
and the offset.
[0022] Accordingly, the device 10 is to be used in digitizing the
center of rotation of the femoral implant F and/or the orientation
of the femoral implant F. The device 10 has a tubular body 11. A
tracker base 12 projects from the tubular body 11. The illustrated
tracker base 12 is of the type that receives the passive type of
tracker, i.e., in the form of three detectable devices 13 in a
known geometrical pattern. Alternatively, the tracker base 12 could
be used to secure an active tracker to the tubular body 11. The
tubular body 11 defines a cylindrical bore 14 (i.e., cylindrical
receptacle), having a circular edge 15 at its opening in the
tubular body 11. The circular edge 15 has a known diameter, and a
known position and orientation with respect to the tracker on the
tracker base 12.
[0023] The device 10 is to be positioned onto the connector end F12
of the femoral implant F. More specifically, the connector end F12
is received in the cylindrical bore 14, such that the circular edge
15 abuts against an outer surface of the connector end F12. In such
a position, the cylindrical bore 14 and the connector end F12 will
axially align themselves, considering that the connector-end F12 is
frusto-conically shaped.
[0024] Furthermore, the geometric interrelation (i.e.,
predetermined known configuration) between the connector end F12
and the cylindrical bore 14 allows the calculation of the position
and orientation of the taper of the connector end F12 with respect
to the tracker of the device 10. This position and orientation
information of the connector end F12 may then be used to calculate
the anticipated center of the ball head F20 as a function of the
size and geometry of the ball head F20. This position and
orientation information of the connector end F12 may alternatively
be related to a reference tracker on the femur to allow the
calculation of navigation information (e.g., offset, varus/valgus
angles, limb length discrepancy, etc.)
[0025] An alternative method of calculating the center of the ball
head F20 is contemplated. A device 10', having the tracker base 12
with the three detectable devices 13 with a hemispherical hole 14'
can be positioned directly on the ball head F20 once the ball head
F20 is secured to the connector end F12 of the femoral implant F.
Ball heads typically come in 3 defined sizes of 22, 28 and 32 mm,
whereby the device 10' is typically provided with corresponding
diameters for the hemispherical receptacle 14'. Therefore, when the
device 10' is mounted onto the ball head F20, the relation between
the center of the hemispherical receptacle 14' and the center of
the ball head F20 is known (e.g., the centers are coincident), such
that the center of the ball head F20 may be established with
respect to a frame of reference on the femur. The determination of
the position of the center of rotation of the femoral implant F
(through the above described procedure) can be accomplished on
trial ball heads for the calculation of other parameters (e.g.,
limb length), as well as on the definitive ball head F20 installed
on the femoral implant F.
[0026] It is also contemplated to provide an alignment mechanism
between the implants F and/or A and the devices 10 (10') and 20
(20'), respectively, for the interconnection between the implant
and its associated device to be reproducible in position and
orientation.
[0027] Referring to FIG. 2, an alternative embodiment of the
device, to be used to obtain position and orientation information
for an acetabular implant is generally shown at 20. An acetabular
implant is shown at A and has a shell A10 and a liner A20. The
shell A10 has a cup-shaped body having an outer surface A11 and a
receiving cavity A12. The acetabular implant A is to be fitted into
an acetabulum (not shown), with the outer surface A11 being in
contact with a surface of the acetabulum. The receiving cavity A12
is equipped with connector holes such that an impactor (not shown)
can be used to insert the shell A10 into the acetabulum and adjust
its position and orientation.
[0028] The liner A20 also has a cup-shaped body. The liner A20 is
sized so as to fit into the receiving cavity A20 of the shell A10.
More specifically, the liner A20 has an outer surface A21 and a
socket A22. The outer surface A21 contacts the surface of the
receiving cavity A12 when the liner A20 is fitted into the shell
A10. The socket A22 will house the ball head F20 (FIG. 1) of the
femoral implant F to form the hip joint implant.
[0029] As mentioned previously, the position of the center of
rotation of the acetabular implant A (i.e., the center of rotation
of the socket A22) is useful information prior to the liner A20
being received in the shell A10. The center of rotation of the
acetabular implant A is dependent on the socket size of the liner
A20, and on the geometry of the liner A20. The calculated center of
rotation of the acetabular implant A can be used for calculating
navigation information such as the offset and the limb length
discrepancy.
[0030] The device 20 is to be used in digitizing the center of
rotation of the acetabular implant A. The device 20 has a generally
hemispherical body 21. A tracker base 22 projects from an underside
of the hemispherical body 21. The illustrated tracker base 22 is of
the type that receives the passive type of tracker, i.e., for
instance three detectable spheres in a known geometrical pattern.
The tracker base 22 could be used to secure an active tracker to
the body 21. The hemispherical body 21 defines an outer surface
24.
[0031] The device 20 is to be positioned into the receiving cavity
A12 of the shell A10 of the acetabular implant A. More
specifically, the hemispherical body 21 is sized to fit the
receiving cavity A12 of the shell A10, such that the center of
rotation of the receiving cavity A12 of the shell A10 may be
determined. From the center of rotation of the receiving cavity
A12, the center of rotation of the liner A20 may be calculated,
knowing the geometry of the liner A20 (e.g., the CAS system being
provided with geometry data of various sizes of liners). It is also
possible that the liner A20 is of the type having its center
coincident with the center of the shell A10. Therefore, the
anticipated center of the socket A22 is calculable as a function of
the center of the receiving cavity A12 and of the geometry of the
liner A20 (stored in the CAS system).
[0032] Thereafter, the anticipated center of the rotation of the
socket A22 can be related to a reference tracker on the acetabulum
to allow the calculation of navigation information, such as the
offset and the limb length discrepancy.
[0033] It is pointed out that the device 20 may be used to
determine the center of rotation of the liner A20 directly. More
specifically, the hemispherical body 21 may be sized so as to be
received directly in the socket A22 of the liner A20, with the
liner A20 having beforehand been secured in the receiving cavity
A12. Moreover, an alternative configuration of the device 20,
herein illustrated as device 20', is provided with a flange 25 at a
periphery of the outer surface 24, so as to enable the calculation
of a plane associated to the center of rotation of the acetabular
implant A.
[0034] The setting of the femoral implant F in the intramedullary
canal of the femur is an operation that involves a plurality of
factors that will have a direct impact on the success of the hip
replacement surgery. Therefore, the setting of the femoral implant
F advantageously involves the creation of reference systems that
will be used to provide numeric data throughout the surgery to the
surgeon for such anatomical references as varus/valgus angle, limb
length discrepancy and femoral anteversion. These values are
calculable using position and orientation data of the femoral
implant, which will be available during the setting of the femoral
implant F in the femur.
[0035] Therefore, referring to FIG. 4, a method for doing surgical
treatment with a tracking system in computer-assisted surgery, for
guiding an operator in inserting a femoral implant in a femur as a
function of the limb length and the orientation of the femoral
implant is generally shown at 50.
[0036] The insertion of the femoral implant in the femur takes
place after the femoral head has been resected, and the
intramedullary canal has been altered in view of the insertion of
the implant therein. Such steps are described in International
Publication No. WO 2004/030556, published on Apr. 15, 2004, by
Jansen et al. At this point, a generic digital model of the implant
F is available through the CAS assisting the operator.
[0037] In Step 52 of the method 50, the device 10 (FIGS. 1 and 3)
is positioned on the connector end F12 of the implant F. If the
ball head F20 is already secured to the implant body F1, the device
10' is used (FIGS. 1 and 3).
[0038] In Step 54, the orientation of the neck axis of the
connector end F12, and the center of rotation of the ball head F20,
are calculable as a function of the position and orientation of the
tracker base 12.
[0039] In Step 56, a plane is digitized for the implant F. More
specifically, three non-linear points are digitized using a
registration pointer, whereby a plane may be digitized with respect
to the device 10 in which all three points lie. For instance,
points are taken at P1, P2 and P3 in FIG. 1. With these points and
with the neck axis calculated in Step 54, the position and
orientation digitized and calculated in Steps 54 and 56 may be
associated to the digital model of the implant.
[0040] In Step 58, a tip of the implant is digitized with respect
to the device 10, using the registration pointer. The tip is
illustrated at P4 in FIG. 1.
[0041] In Step 60, a longitudinal axis of the implant F is
digitized with respect to the device 10. More specifically, the CCD
angle of the implant F is generic information provided with the
digital model of the implant F. Accordingly, using the neck axis
calculated in Step 54 and the CCD angle, a line parallel to the
longitudinal axis is defined. The longitudinal axis is then
calculated with respect to the device 10 or 10 as being parallel to
this line, while lying in the plane digitized in Step 56 and
passing through the tip of the implant digitized in Step 58.
[0042] In Step 62, now that the required geometry information
pertaining to the implant F is known (i.e., longitudinal axis, neck
axis, center of rotation, with respect to the device 10), the
implant F is inserted in the altered intramedullary canal of the
femur F.
[0043] Real-time information may be provided to the operator,
whereby the device 10 (10') must be kept onto the implant F during
the insertion of the implant F in the intramedullary canal.
Accordingly, a locking mechanism should be used to secure the
device 10 to the implant F in position and orientation.
[0044] In Step 64, the geometry information gathered for the
implant F is associated to the frame of reference of the femur. By
positioning the device 10 (or 10') on the implant F, the position
of the center of rotation of the implant F is known, as well as the
position of the neck axis.
[0045] The orientation of the implant F may be calculated by
knowing the interconnection between the implant F and the device 10
(or 10') (through an alignment mechanism, as mentioned
previously).
[0046] Alternatively, the orientation of the implant F may be
calculated using the digital model of the altered intramedullary
canal with respect to the frame of reference of the femur, in
association with the position and orientation of the device 10 (or
10'). The digital model of the altered intramedullary canal is
information available as calculated during the alteration of the
intramedullary canal, as described in International Publication No.
WO 2004/030556, published on Apr. 15, 2004, by Jansen et al.
[0047] Therefore, when the geometry information of the implant F is
associated to the frame of reference of the femur, the geometry
information can be used to calculate position and orientation
information of the implant F with respect to the femur.
[0048] For instance, the longitudinal axis of the implant F, as
obtained through the method 50, can be used in the calculation of
the varus/valgus angle of the femoral implant F. More specifically,
the longitudinal axis of the femoral implant is projected onto a
frontal plane of the patient along with an axis of the
intramedullary canal (as described in International Publication No.
WO 2004/030556), with the angle between these two projections
representing the varus/valgus angle.
[0049] Also, the neck axis of the implant is projected onto the
transverse plane (as described in International Publication No. WO
2004/030556), whereby the femoral anteversion is calculable as the
angle between this projection and the intersection of the
transverse and frontal planes.
[0050] Referring to FIG. 3, a CAS system in accordance with the
present invention is generally shown at 30. The CAS system 30 has a
controller 31 that is connected to the sensing apparatus 32.
[0051] The sensing apparatus 32 tracks the devices 10, 10', 20 and
20', as well as a registration device 35 (e.g., registration tool),
and frames of reference 36 associated to bones (e.g., femoral and
pelvic frames of reference as described in International
Publication No. WO 2004/030556). For instance, the sensing
apparatus 32 is an optical sensing apparatus that visually detects
the position of the passive detectable devices, such as those
illustrated at 13 in FIG. 1). The tracking output of the sensing
apparatus 32 is calculated as position and orientation of the
devices by the controller 31, whereas registered points, as
described in Steps 56 and 58 (FIG. 4), are digitized as surface
information of the implants.
[0052] The CAS system 30 has an implant geometry information
calculator 33, that will receive the position and orientation of
the devices 10, 10', 20, 20', as well as the surface information,
so as to calculate geometry information, as mentioned in Steps 54
and 60, and transfer this data in the form of implant position and
orientation information, as described in Step 62, to an operator
through operator interface 34.
[0053] The controller 31 typically has a controller calculator 37
consisting of a processor that will calculate the above described
information, and a database 38 that will hold some information that
may be required in the calculation, such as digital model of
implants, to which the geometry information and the implant
position and orientation information may be associated, as
mentioned in the method 50.
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