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`

`TITLE OF THE INVENTION
`Computer-Assisted Surgery Planner and Intra-Operative
`Guidance System
`
`CROSS-REFERENCE TO RELATED APPLICATIONS
`This application is a continuation-in-part application
`of application Serial Number 08/803,993, filed February 21,
`1997.
`
`10
`
`STATEMENT REGARDING FEDERALLY SPONSORED
`
`RESEARCH OR DEVELOPMENT
`
`This work was supported in part by a National Challenge
`grant from the National Science Foundation Award IRI 9422734.
`
`15
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`BACKGROUND OF THE INVENTION
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`The present invention is directed generally to the
`implantation of artificial joint components, osteochondral
`grafts, and osteotomy and, more particularly,
`to computer
`assisted surgical implantation of artificial joint components
`during replacement and revision procedures, computer-assisted
`osteochondral grafts, and computer-assisted osteotomy.
`Total hip replacement
`(THR) or arthroplasty (THA)
`operations have been performed since the early 1960s to
`repair the acetabulum and the region surrounding it and to
`replace the hip components, such as the femoral head,
`that
`have degenerated. Currently, approximately 200,000 THR
`operations are performed annually in the United States alone,
`of which approximately 40,000 are redo procedures, otherwise
`known as revisions.
`The revisions become necessary due to a
`number of problems that may arise during the lifetime of the
`implanted components, such as dislocation, component wear and
`degradation, and loosening of the implant from the bone.
`Dislocation of the femoral head from the acetabular
`
`35
`
`component, or cup,
`
`is considered one of the most frequent
`
`PI-283676.01
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`

`early problems associated with THR, because of the sudden
`physical, and emotional, hardship brought on by the
`dislocation.
`The incidence of dislocation following the
`primary THR surgery is approximately 2-6% and the percentage
`is even higher for revisions. While dislocations can result
`from a variety of causes, such as soft tissue laxity and
`loosening of the implant,
`the most common cause is
`impingement of the femoral neck with either the rim of an
`acetabular cup implant, or the soft tissue or bone
`surrounding the implant.
`Impingement most frequently occurs
`as a result of the malposition of the acetabular cup
`component within the pelvis.
`Some clinicians and researchers have found incidence of
`impingement and dislocations can be lessened if the cup is
`oriented specifically to provide for approximately 15° of
`anteversion and 45° of abduction; however,
`this incidence is
`also related to the surgical approach.
`For example, McCollum
`et al. cited a comparison of THAs reported in the orthopaedic
`literature that revealed a much higher incidence of
`dislocation in patients who had THAs with a posterolateral
`approach. McCollum, D.E. and W.J. Gray, "Dislocation after
`total hip arthroplasty (causes and prevention)", Clinical
`Orthopaedics and Related Research, Vol. 261, p.159-170
`(1990). McCollum's data showed that when the patient is
`placed in the lateral position for a posterolateral THA
`approach,
`the lumbar lordotic curve is flattened and the
`pelvis may be flexed as much as 35°. If the cup was oriented
`at 15-20° of flexion with respect to the longitudinal axis of
`the body, when the patient stood up and the postoperative
`lumbar lordosis was regained,
`the cup could be retroverted as
`much as 10°-15° resulting in an unstable cup placement.
`Lewinnek et al. performed a study taking into account the
`surgical approach utilized and found that the cases falling
`in the zone of 15°+10° of anteversion and 40°+10° of
`abduction have an instability rate of 1.5%, compared with a
`6% instability rate for the cases falling outside this zone.
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`Lewinnek G.E., et al., "Dislocation after total hip-
`replacement arthroplasties", Journal of Bone and Joint
`Surgery, Vol. 60-A, No.2, p. 217-220 (March 1978).
`The
`Lewinnek work essentially verifies that dislocations can be
`
`correlated with the extent of malpositioning, as would be
`expected.
`The study does not address other variables, such
`as implant design and the anatomy of the individual, both of
`which are known to greatly affect the performance of the
`
`implant.
`The design of the implant significantly affects
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`stability as well.
`
`A number of researchers have found that
`
`the head-to-neck ratio of the femoral component is the key
`
`impingement, see Amstutz H.C., et al.,
`factor of the implant
`"Range of Motion Studies for Total Hip Replacements",
`
`15
`
`Clinical Orthopaedics and Related Research Vol. 111, p. 124-
`130 (September 1975). Krushell et al. additionally found
`that certain long and extra long neck designs of modular
`
`implants can have an adverse effect on the range of motion.
`
`Krushell, R.J., Burke D.W., and Harris W.H.,
`"Range of motion
`in contemporary total hip arthroplasty (the impact of modular
`
`20
`
`head-neck components)", The Journal of Arthroplasty, Vol. 6,
`
`p. 97-101 (February 1991). Krushell et al. also found that
`
`an optimally oriented elevated-rim liner in an acetabular cup
`implant may improve the joint stability with respect to
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`25
`
`implant
`
`impingement. Krushell, R.J., Burke D.W., and Harris
`
`W.H., "Elevated-rim acetabular components: Effect on range of
`
`motion and stability in total hip arthroplasty", The Journal
`
`of Arthroplasty, Vol.
`
`6 Supplement, p. 1-6,
`
`(October 1991).
`
`Cobb et al. have shown a statistically significant reduction
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`30
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`of dislocations in the case of elevated-rim liners, compared
`to standard liners.
`Cobb T.K., Morrey B.F., Ilstrup D.M.,
`
`"The elevated-rim acetabular liner in total hip arthroplasty:
`
`Relationship to postoperative dislocation", Journal of Bone
`
`(January 1996).
`and Joint Surgery, Vol 78-A, No. 1, p. 80-86,
`The two-year probability of dislocation was 2.19% for the
`
`35
`
`elevated liner, compared with 3.85% for standard liner.
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`

`Initial studies by Maxian et al. using a finite element model
`
`indicate that the contact stresses and therefore the
`
`polyethylene wear are not significantly increased for
`elevated rim liners; however, points of impingement and
`subsequent angles of dislocation for different liner designs
`are different as would be expected. Maxian T.A., et al.
`
`"Femoral head containment in total hip arthroplasty: Standard
`
`vs. extended lip liners", 42nd Annual meeting, Orthopaedic
`Research society, p. 420, Atlanta, Georgia (February 19-22,
`
`10
`
`1996); and Maxian T.A., et al. "Finite element modeling of
`dislocation propensity in total hip arthroplasty", 42nd
`Annual meeting, Orthopaedic Research society, p. 259-64,
`
`Atlanta, Georgia (February 19-22, 1996).
`
`An equally important concern in evaluating the
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`15
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`dislocation propensity of an implant are variations in
`individual anatomies. As a result of anatomical variations,
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`there is no single optimal design and orientation of hip
`
`replacement components and surgical procedure to minimize the
`
`the
`For example,
`dislocation propensity of the implant.
`pelvis can assume different positions and orientations
`depending or whether an individual is lying supine (as during
`a CT-scan or routine X-rays),
`in the lateral decubitis
`
`position (as during surgery) or in critical positions during
`
`activities of normal daily living (like bending over to tie
`
`shoes or during normal gait).
`The relative position of the
`pelvis and leg when defining a "neutral" plane from which the
`angles of movement, anteversion, abduction, etc., are
`
`calculated will significantly influence the measured amount
`
`of motion permitted before impingement and dislocation
`
`occurs. Therefore, it is necessary to uniquely define both
`the neutral orientation of the femur relative to the pelvis
`for relevant positions and activities, and the relations
`
`between the femur with respect to the pelvis of the patient
`
`during each segment of leg motion.
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`
`Currently, most planning for acetabular implant
`
`placement and size selection is performed using acetate
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`templates and a single anterior-posterior x-ray of the
`pelvis. Acetabular templating is most useful for determining
`the approximate size of the acetabular component; however, it
`is only of limited utility for positioning of the implant
`because the x-rays provide only a two dimensional
`image of
`the pelvis. Also,
`the variations in pelvic orientation can
`not be more fully considered as discussed above.
`Intra-operative positioning devices currently used by
`surgeons attempt to align the acetabular component with
`respect to the sagittal and coronal planes of the patient.
`B. F. Morrey, editor, "Reconstructive Surgery of the Joints",
`chapter Joint Replacement Arthroplasty, pages 605-608,
`Churchill Livingston, 1996. These devices assume that the
`patient's pelvis and trunk are aligned in a known
`orientation, and do not take into account individual
`variations in a patient's anatomy or pelvic position on the
`operating room table. These types of positioners can lead to
`a wide discrepancy between the desired and actual implant
`placement, possibly resulting in reduced range of motion,
`impingement and subsequent dislocation.
`Several attempts have been made to more precisely
`prepare the acetabular region for the implant components.
`U.S. Patent No. 5,007,936 issued to Woolson is directed to
`establishing a reference plane through which the acetabulum
`can be reamed and generally prepared to receive the
`acetabular cup implant.
`The method provides for establishing
`the reference plane based on selecting three reference
`points, preferably the 12 o'clock position on the superior
`rim of the acetabulum and two other reference points, such as
`a point in the posterior rim and the inner wall,
`that are a
`known distance from the superior rim.
`The location of the
`superior rim is determined by performing a series of computed
`tomography (CT) scans that are concentrated near the superior
`rim and other reference locations in the acetabular region.
`In the Woolson method, calculations are then performed
`to determine a plane in which the rim of the acetabular cup
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`should be positioned to allow for a predetermined rotation of
`the femoral head in the cup.
`The distances between the
`points and the plane are calculated and an orientation jig is
`calibrated to define the plane when the jig is mounted on the
`reference points. During the surgical procedure,
`the surgeon
`must identify the 12 o'clock orientation of the superior rim
`and the reference points.
`In the preferred mode,
`the jig is
`Fixed to the acetabulum by drilling a hole through the
`reference point on the inner wall of the acetabulum and
`affixing the jig to the acetabulum.
`The jig incorporates a
`drill guide to provide for reaming of the acetabulum in the
`selected plane.
`A number of difficulties exist with the Woolson method.
`For example,
`the preferred method requires drilling a hole in
`the acetabulum. Also, visual recognition of the reference
`points must be required and precision placement on the jig on
`reference points is performed in a surgical setting.
`In
`addition, proper alignment of the reaming device does not
`ensure that the implant will be properly positioned,
`thereby
`establishing a more lengthy and costly procedure with no
`guarantees of better results. These problems may be a reason
`why the Woolson method has not gained widespread acceptance
`in the medical community.
`In U.S. Patent Nos. 5,251,127 and 5,305,203 issued to
`Raab, a computer-aided surgery apparatus is disclosed in
`which a reference jig is attached to a double self indexing
`screw, previously attached to the patient,
`to provide for a
`more consistent alignment of the cutting instruments similar
`to that of Woolson. However, unlike Woolson, Raab et al.
`employ a digitizer and a computer to determine and relate the
`orientation of the reference jig and the patient during
`surgery with the skeletal shapes determined by tomography.
`Similarly, U.S. Patent Nos. 5,086,401, 5,299,288 and
`5,408,409 issued to Glassman et al. disclose an image
`directed surgical robotic system for reaming a human femur to
`accept a femoral stem and head implant using a robot cutter
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`In the system, at least three locating pins are
`system.
`inserted in the femur and CT scans of the femur in the region
`containing the locating pins are performed. During the
`implanting procedure,
`the locating pins are identified on the
`patient, as discussed in col. 9,
`lines 19-68 of Glassman's
`'401 patent.
`The location of the pins during the surgery are
`used by a computer to transform CT scan coordinates into the
`robot cutter coordinates, which are used to guide the robot
`
`cutter during reaming operations.
`While the Woolson, Raab and Glassman patents provide
`methods and apparatuses that further offer the potential for
`increased accuracy and consistency in the preparation of the
`acetabular region to receive implant components,
`there remain
`a number of difficulties with the procedures.
`A significant
`shortcoming of the methods and apparatuses is that when used
`for implanting components in a joint there are underlying
`assumptions that the proper position for the placement of the
`components in the joints has been determined and provided as
`input to the methods and apparatuses that are used to prepare
`the site. As such,
`the utility and benefit of the methods
`and apparatuses are based upon the correctness and quality of
`the implant position provided as input to the methods.
`In addition, both the Raab and Glassman methods and
`apparatuses require that fiducial markers be attached to the
`patient prior to performing tomography of the patients.
`Following the tomography,
`the markers must either remain
`attached to the patient until the surgical procedure is
`performed or the markers must be reattached at the precise
`locations to allow the transformation of the tomographic data
`to the robotic coordinate system, either of which is
`undesirable and/or difficult in practice.
`Thus,
`the need exists for apparatuses and methods which
`overcome, among others,
`the above-discussed problems so as to
`provide for the proper placement and implantation of the
`joint components to provide an improved range of motion and
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`usage of the joint following joint reconstruction,
`replacement and revision surgery.
`
`BRIEF SUMMARY OF THE INVENTION
`
`The present invention is directed to an apparatus for
`facilitating the implantation of an artificial component
`in
`one of a hip joint, a knee joint, a hand and wrist joint, an
`elbow joint, a shoulder joint, and a foot and ankle joint.
`The apparatus includes a pre-operative geometric planner and
`a pre-operative kinematic biomechanical simulator in
`communication with the pre-operative geometric planner.
`The present invention provides the medical practitioner
`a tool to precisely determine an optimal size and position of
`artificial components in a joint to provide a desired range
`of motion of the joint following surgery and to substantially
`lessen the possibility of subsequent dislocation.
`Accordingly,
`the present invention provides an effective
`solution to problems heretofore encountered with precisely
`determining the proper sizing and placement of an artificial
`component to be implanted in a joint.
`In addition,
`the
`practitioner is afforded a less invasive method for executing
`the surgical procedure in accordance with the present
`invention. These advantages and others will become apparent
`
`from the following detailed description.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`A preferred embodiment of the invention will now be
`described, by way of example only, with reference to the
`accompanying figures wherein like members bear like reference
`
`numerals and wherein:
`Fig.
`1 is a system overview of a preferred embodiment of
`the present invention;
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`2 is a flow chart illustrating the method of the
`Fig.
`present invention;
`Fig.
`3 is a schematic layout of the apparatus of the
`present
`invention being used in a hip replacement procedure;
`Fig. 3A is a diagram illustrating an embodiment of a
`system which can be used to find the coordinates of points on
`a bony surface;
`show the creation of the pelvic model using
`Figs. 4(a-c)
`two dimensional scans of the pelvis (a),
`from which skeletal
`geometric data is extracted as shown in (b) and used to
`create the pelvic model
`(c);
`Figs. 5(a-c)
`show the creation of the femur model using
`two dimensional scans of the femur (a),
`from which skeletal
`geometric data is extracted as shown in (b) and used to
`create the femur model
`(c)j;
`Fig.
`6 shows the sizing of the acetabular cup in the
`pelvic model;
`show the creation of different sized
`Figs. 7(a-e)
`femoral
`implant models
`(a) and the fitting of the femoral
`implant model into a cut femur
`(b-e) ;
`Fig.
`8 is a schematic drawing showing the range of
`motion of a femoral shaft and the impingement
`(in dotted
`
`lines) of a femoral shaft on an acetabular cup;
`Figs. 9(a-b)
`show the range of motion results from
`biomechanical simulation of two respective acetabular cup
`
`orientations;
`Figs. 10 (a) and (b)
`and femur;
`Figs. 11 (a) and (b)
`arthroplasty; and
`Figs. 12 (a-c)
`
`show the registration of the pelvis
`
`show an image guided total knee
`
`show the planning of a femoral osteotomy.
`
`
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`DETAILED DESCRIPTION OF THE INVENTION
`
`35
`
`The apparatus 10 of the present invention will be
`described generally with reference to the drawings for the
`
`9
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`purpose of illustrating the present preferred embodiments of
`the invention only and not for purposes of limiting the same.
`A system overview is provided in Figure 1 and general
`description of the method of the present invention is
`presented in flow chart form in Figure 2.
`The apparatus 10
`includes a geometric pre-operative planner 12 that is used to
`create geometric models of the joint and the components to be
`implanted based on geometric data received from a skeletal
`structure data source 13.
`The pre-operative planner 12 is
`interfaced with a pre-operative kinematic biomechanical
`simulator 14 that simulates movement of the joint using the
`geometric models for use in determining implant positions,
`including angular orientations, for the components.
`The
`implant positions are used in conjunction with the geometric
`models in intra-operative navigational software 16 to guide a
`medical practitioner in the placement of the implant
`components at the implant positions.
`the pre-
`The pre-operative geometric planner 12,
`operative kinematic biomechanical simulator 14 and the intra-
`operative navigational software are implemented using a
`computer system 20 having at least one display monitor 22, as
`shown in Figure 3.
`For example, applicants have found that a
`Silicon Graphics 02 workstation (Mountain View, CA) can be
`suitably employed as the computer system 20; however,
`the
`choice of computer system 20 will necessarily depend upon the
`resolution and calculational detail sought in practice.
`During the pre-operative stages of the method,
`the display
`monitor 22 is used for viewing and interactively creating
`and/or generating models in the pre-operative planner 12 and
`displaying the results of the biomechanical simulator 14.
`The pre-operative stages of the method may be carried out on
`a computer
`(not shown)
`remote from the surgical theater.
`During the intra-operative stages of the method,
`the
`computer system 20 is used to display the relative locations
`of the objects being tracked with a tracking device 30.
`The
`medical practitioner preferably can control the operation of
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`the computer system 20 during the procedure, such as through
`the use of a foot pedal controller 24 connected to the
`computer system 20.
`The tracking device 30 can employ any
`type of tracking method as may be known in the art, for
`example, emitter/detector systems including optic, acoustic
`or other wave forms, shape based recognition tracking
`algorithms, or video-based, mechanical, electro-magnetic and
`radio frequency (RF) systems.
`In a preferred embodiment,
`schematically shown in Figure 3,
`the tracking device 30 is an
`optical tracking system that includes at least one camera 32
`that is attached to the computer system 20 and positioned to
`detect light emitted from a number of special light emitting
`diodes, or targets 34.
`The targets 34 can be attached to
`bones,
`tools, and other objects in the operating room
`One
`equipment to provide precision tracking of the objects.
`such device that has been found to be suitable for performing
`the tracking function is the Optotrak™ 3020 system from
`Northern Digital Inc., Ontario, Canada, which is advertised
`as capable of achieving accuracies of roughly 0.1 mm at
`speeds of 100 measurements per second or higher.
`The apparatus 10 of Fig.
`1 is operated in accordance
`with the method illustrated in Fig. 2.
`The skeletal
`structure of the joint is determined at step 40 using
`tomographic data (three dimensional) or computed tomographic
`data (pseudo three dimensional data produced from a series of
`two dimensional scans) or other techniques from the skeletal
`data source 13.
`Commonly used tomographic techniques include
`computed tomography (CT), magnetic resonance imaging (MRI),
`positron emission tomographic (PET), or ultrasound scanning
`of the joint and surround structure.
`The tomographic data
`from the scanned structure generated by the skeletal data
`source 13 is provided to the geometric planner 12 for use in
`producing a model of the skeletal structure.
`It should be
`noted that,
`in a preferred embodiment,
`there is no
`requirement that fiducial markers be attached to the patient
`in the scanned region to provide a reference frame for
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`relating the tomography scans to intra-operative position of
`the patient, although markers can be used as a cross
`reference or for use with other alternative embodiments.
`At step 42, a surface model is created, or constructed,
`from the skeletal geometric data using techniques, such as
`those described by B. Geiger in "Three-dimensional modeling
`of human organs and its application to diagnosis and surgical
`planning", Ph.D.
`thesis, Ecole des Mines de Paris, April
`1993.
`The geometric models constructed from the skeletal
`data source 13 can be manually generated and input to the
`geometric planner 12, but it is preferable that the data be
`used to create the geometric models in an automated fashion.
`Also at step 42, geometric models of the artificial
`components to be implanted into the joint are
`created/generated.
`The geometric models can be created in
`any manner as is known in the art including those techniques
`described for creating joint models.
`The geometric models of
`the artificial components can be used in conjunction with the
`joint model to determine an initial static estimate of the
`proper size of the artificial components to be implanted.
`In step 44,
`the geometric models of the joint and the
`artificial components are used to perform biomechanical
`simulations of the movement of the joint containing the
`implanted artificial components.
`The biomechanical
`simulations are preferably performed at a number of test
`positions to dynamically optimize the size, position and
`orientation of the artificial components in the patient's
`joint to achieve a predetermined range of motion following
`surgery.
`The predetermined range of motion for a particular
`patient is determined based on the expected activities of the
`patient following surgery.
`For example, with regard to hip
`functions, daily activities, such as getting out of bed,
`walking, sitting and climbing stairs,
`that are performed by
`individuals requiring different ranges of motion, as will be
`discussed in further detail below.
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`The size and orientations of the implant component, and
`
`movements simulated at various test positions used in step 44
`can be fully automated or manually co