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`Exhibit 1014
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`Exhibit 1014
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`Mako Surgical Corp. Ex. 1014
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`To Appear in PT--eedings of CAOS
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`'96 - Bern7 Swit,,Prland
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`FhpNav: Pre-operative Planning and Intra-operative
`Navigational Guidance for Acetabular Implant Placement
`in Total H1ip Replacement Surgery
`
`A M DiGioia M D 1 2, D A Simonl 2 B3 jaramazl 2, M Blackwe112. F Morgan2,
`R V O'Toole 3, B Colgan 1, E Kische,12
`
`'Center for Orthopaedc Research
`Shadyside Hospital
`Pittsburgh PA 15232
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`2Robotics Institute
`Carnegie Mellon University
`Pittsburgh, PA 15213
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`3Harvard Medical School
`25 Shattuck St
`Boston MA 02115
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`Abstract
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`7the Hip Navigation or HipNav system allows a surgeon to determine optimal patient specific acetabular
`implant placement and accurately achieve the desired acetabular implant placement during surgery Hip
`Nav includes three components a pre operative planner, a range of motion simulator, and an intra-oper
`ative tracking and guidance system The goals of the current HipNav system are to 1) reduce dislocations
`follotwing total hip replacement due to acetabular malposition 2) determine and potentially increase the
`'safe range of motion and 3) track in real time the position of the pelvis and acetabulum during surgery
`This information will help the surgeon achieve more reliable and accurate positioning of the acetabular
`cup and take into account specific anatomy for individual patients The HipNav system provides for a new
`class of research tools that can be us J intra operatively to permit surgeons to re examine commonly held
`assumptions concerning bone and implant motion range of motion testing and the "optial alignment
`of acetabular cups
`Keywords computer assisted surgery, total hip replacement, navigational guidance
`
`1 Introduction
`The incidence of dislocation following primary total hip replacement (THR) surgery is between 2-6% and
`even higher following revisions [5] [4] It is therefore, one of the most commonly occurring complications
`following hip replacement surgery Dislocation of a total hip replacement causes significant distress to the
`patient and physician and is associated with significant additional costs in order to relocate the hip Anoth-
`er complication of THR surgery is impingement between the neck of the femoral implant and the rim of
`the acetabular component, as shown in Figure 1 Impingement can lead to advanced wear of the acetabular
`rim resulting in polyethylene wear debris shown to accelerate loosening of implant bone interfaces The
`position at which impingement occurs is determiuned by the design and geometry of the implants (such as
`the size of the femoral head, the width of the neck, and the design of the acetabular liner), and more im-
`portantly by the relative position of the femoral and acetabular implants In certain cases, impingement
`may result in dislocation, as seen in the X-Ray of Figure 2 The causes of dislocation following total hip
`replacement are multi factorial and include not only malposition of the implants causing impingement, but
`also soft tissue and bone impingement, and soft tissue laxity [5] The most common cause of both impinge-
`ment and dislocation is malposition of the acetabular component [5]
`A system has been developed to permit accurate placement of the acetabular component during surgery
`As shown in Figure 3, the Hip Navigation or HipNav system includes three components a pre-operative
`
`This work is supported in part by a National Challenge grant from the
`National Science Foundation Award ECS-9422734
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`Figure 1 Implant impingement.
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`Figure 2 X-Ray showing pelvic dislocation
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`planner, a range of motion simulator, and an intra-operative tracking and guidance system The pre-oper
`ative planner allows the surgeon to manually specify the position of the acetabular component within the
`pelvis based upon pre operative CT images The range of motion simulator estimates femoral range of mo
`tion based upon the implant placement parameters provided by the pre-operative planner The feedback
`provided by the simulator can aid the surgeon in determining optimal, patient specific acetabular implant
`placement The intra-operative tracking and guidance system is used to accurately place the implant in the
`predetermuned optimal position regardless of the position of the patient on the operating room table
`By accurately placing the acetabular component in an optimally selected position the HipNav system has
`the potential to reduce the nsk of dislocations and the generation of wear debris caused by impingement
`resulting from malpositioned components and increase the "safe" range of motion
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`2 Current Practice
`Current planning for acetabular implant placement and size selection is performed using acetate templates
`and a single anterior-posterior X-Ray of the pelvis Acetabular templating is most commonly performed
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`.A
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`Pre-operative
`Planner
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`0
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`I L
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`Range of Motion
`SimulatorI
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`Intra-operative
`Tracking &
`Guidance
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`Figure 3 11ipNav system overview
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`to determine the approximate size of the acetabular component, but there is little effort to accurately de
`termine the ideal position of the implant
`The intra-operative positioning devices currently used by surgeons attempt to align the acetabular compo
`nent with respect to the sagittal and coronal planes of the patient [6] These devices assume that the pa
`tient'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 Use of this type of posi
`tioner can lead to a wiiie discrepancy between the desired and at-tual implant placement possibly resulting
`in reduced range of motion, impingement and subsequent dislocation
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`3 System Description
`The first step in using the HipNav system is the pre operative CT scan which is used to determine the pa
`tient s specific bony geometry The CT images are used in the pre-operative planner which allows the sur
`geon to determine appropriate implant size and placement In the current version of the planner the
`surgeon can position cross sections of the acetabular implant upon orthogonal views of the pelvis as seen
`in Figure 4 We are investigating other methods of presenting CT data to the surgeon including an ap
`proach which displays implant placement on multiple CT cross sections, each of which passes through the
`acetabulum's central axis (the axis which passes through the center of pelvic rotation and which is perpen-
`dicular to the plane of the acetabular rim)
`Once the surgeon has selected the position of the acetabular implant, the range of motion simulator is used
`to determine the femoral positions (in terms of extension/flexion, abduction/adduction and internal/exter-
`nal rotation) at which impingement would occur for that specific implant design and position Based upon
`this range of motion information the surgeon may choose to modify the selected position in an attempt to
`achieve the "optimal' cup position for the specific patient The range of motion simulator performs a k.i
`nemnatic analysis which determines an "envelope" of the safe range of motion, as seen in Figure 5 A more
`detailed description of the range of motion simulator appears in [3]
`The optimal patient specific plan is used by the HipNav System in the operating room on the day of sur-
`gery HipNav permits the surgeon to determine where the pelvis and acetabulum are in "operating room
`coordinates' at all times during surgery Knowing the position of the pelvis during all phases of surgery
`and especially during preparation and implantation of the acetabular implant, permits the surgeon to accu-
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`Figure 4 Pre-operative planner
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`Cup orientation 45* Lateral Opening
`15 Anteversion
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`Impingement
`Circle\
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`9C
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`20
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`Figure 5 Kinematic simulations Left - implant geometry Right - motion envelope
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`rately and precisely position the cup according to the pre-operative plan Alternately, using HipNav the
`surgeon can align the component to an accepted standard such as "true" 45 degrees of abduction and 20
`degrees of anteversion
`There are several high-technology devices that are used intra-operatively to allow the surgeon to accurate
`ly execute the pre-operative plan, as seen in Figure 6 One such device is an 'Optotrak' optical tracking
`camera (Northern Digital Inc , Ontano, Canada) which is capable of tracking the position of special light
`emitting diodes or "LEDs" These LEDs can be attached to bones, tools, or other pieces of operating room
`equipment to allow highly reliable tracking Optotrak can achieve accuracies of roughly 0 1mm at speeds
`of 100 measurements per second or higher
`In order to determine the location of the pelvis and the acetabular implant during surgery, Optotrak targets
`are attached to several conventional surgical tools as seen in Figure 7 The pelvis is tracked by attaching
`a target to the pelvic portion of a Hams leg length caliper (Zinmmer, Inc , Warsaw, IN), and inserting this
`device into the wing of the ilium The acetabular implant is tracked by attaching a second target to the han-
`dle of an HGP II acetabular cup holder and positioner (Zimmrer, Inc , Warsaw, IN) A third Optotrak target
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`Figure 6 Intra-operative execution
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`is required by the HipNav system to determine operating room coordinates (i e , left, right, up and down
`with respect to the surgeon)
`Several key steps are necessary to use the HipNav intra-operative guidance system One of the most im-
`portant is the registration of pre-operative information (i e , the CT scan and pre-operative plan) to the po-
`sition of the patient on the operating room table One limrutation of current registration systems used in
`orthopaedics is the need for pins to be surgically implanted into bone before pre-operative images are ac
`quired (e g [9]) An alternative technique being investigated within our group uses surface geometry to
`perform repistration [8] [7] In this approach, the surfaces of a bone (such as the pelvis or acetabulum) can
`be used to accurately align the intra-operative position of the patient to the pre-operative plan without the
`use of pins or other invasive procedures Using this technique, it is necessary to sense multiple points on
`the surface of the bone with a digitizing probe during surgery These "intra-operative data points' are then
`matched to a geometric description of the bony surface of the patient derived from the CT images used to
`plan the surgery
`The registration process is illustrated in Figure 8 The pelvic surface model was constructed from CT data
`using techniques described in 11) The discrete points were collected using a digitizing probe which was
`physically touched to the indicated points The goal of the process is to determine a "registration transfor-
`
`Figure 7 Standard surgical tools instrumented with optical tracking targets
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`Figure 8 Surface-based registration
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`mation which best aligns the discrete points with the surface model An initial estimate of this transfor-
`mation is first determined using manually specified anatomical landmarks to perform corresponding point
`registration [2] Once this initial estimate is determiuned, the surface-based registration algorithm described
`in [8] uses the pre- and intra-operative data to refine the initial transformation estimate
`Once the location of the pelvis is determined via registration, navigational feedback can be provided to the
`surgeon on a television monitor, as seen in Figure 9 This feedback is used by the surgeon to accurately
`position the acetabular implant within the acetabular cavity To accurately align the cup within the acetab
`ulum in the position determined by the pre-operative plan, the cross hairs representing the tip of wue im
`plant and the top of the handle must be aligned at the fixed cross hair in the center of the image Once
`aligned the implant is in the pre-operatively planned position and orientation
`Registration also allows the position of the pelvis to be tracked during surgery using the Optotrak system
`as demonstrated in Figure 10 This elimiunates the need for rigid fixation of the pelvis In addition, this
`tracking ability allows us to record the position of the pelvis during surgery, and especially at key times
`such as at the time of implantation of the acetabular component or during range of motion testing
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`Figure 9 Navigational feedback
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`Figure 10 Real-time tracking of the pelvis
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`4 Conclusions
`The goals of the HipNav system are to 1) reduce dislocations following total hip replacement due to im
`pingement, 2) determine and potentially increase the 'safe" range of motion, and 3) track in real time the
`position of the pelvis and acetabulum during surgery This information will help the surgeon achieve more
`reliable and accurate positioning of the acetabular cup and take into account specific anatomy for individ
`ual patients
`HipNav will also provide clinicians and researchers with a new class of tools for critically examining corn
`mon assumptions concerning range of motion bone motion and 'optimal' alignment For example the
`pelvis can be tracked during surgery to determine its position at key times such as prior to dislocation
`following dislocation, and during acetabular component implantation Using these tools we can evaluate
`the efficacy of the HipNav system in placing the acetabular implant compared to traditional techniques
`and critically examine commonly help beliefs of optimal acetabular position (i e , 45 degrees of abduction
`20 degrees of antevers ion)
`The HipNav system holds the promise of reducing dislocation rates in primar-y and revision total hip re
`placement by optimizing the relative position of the acetabular implants and minimizing impingement In
`addition
`it will provide a new category of smart" tools that will be useful to study issues in total hip re-
`placement and ultimately other procedures
`
`References
`[1] B Geiger Three dimensional modeling of human organs and its application to diagnosis and surgical plan
`ning PhD thesis Ecole des Mines de Pans April 1993
`
`[21 B K P Horn Closed form solution of absolute orientation using unit quatemions Journal of the Optical So
`ciety of America A, 4(4) 629--642 April 1987
`
`[3] B Jaramnaz S M Kladakis A M Digioia L F Kallivokas and 0 Ghattas Simulation of implant impinge-
`ment and dislocation in total hip replacement In Computer Assisted Radiology 10th International S)mpo
`
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`sium and Exhibition Pans June 1996
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`[4] D E McCollum M D and W J Gray M D Dislocation after total hip atthroplasty Clinical Orthopaedics
`(261) 159-170 1990
`[5] B F Morrey editor Reconstructive Surgery of the Joints, chapter 91- Dislocation pages 1247-1260
`Churchill Livingston 1996
`[6] B F Morrey editor Reconstructive Surgery oftihe Joints chapter Joint Replacement Arthroplasty
`pages 605-608 Churchill Livingston 1996
`[7] D A Simon M Hebert and T Kanade Real-time 3-d pose estimation using a high-speed range sensor In
`Proceedings of IEEE International Conference on Robotics and Automation, pages 2235-2241 San Diego
`CA May 1994 EEEE
`
`[8] D A Simon M Hebert and T Kanade Techniques for fast and accurate intra-surgical registration Journal
`of Image' Guided Surgery 1(l) 17-29 April 1995
`
`[9] R H Taylor B D Mittelstadt H A Paul W Hanson P Kazanzides J F Zuhars B Williamson B L
`Musits E Glassman and W L Bargar An image directed robotic system for precise orthopaedic surgery
`IEEE Transactions on Roborics and Automation, 10(3) 26 1-275 June 1994
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