An Integrated Approach to Medical Robotics and
`Computer Assisted Surgery in Orthopaedics
`
`Anthony U DiGioia III, Branislav Jammaq and Robert V. O’TmIe III
`digioia @ cs.cmu.edu, branko @ cs.cmu.edu, N O @ cs.crnu .edu
`
`Center for O h o p n d i c Rcscmzh Shdyside Medical Center
`rad
`Center for Medical Robotics md Computer Assisted Surgery,
`Cwegie Mellon University,
`Pittsburgh, PA
`
`Abstrrrct
`There is great potential for medical robotics to
`have a positive impact upon surgical techniques,
`panicularly in orthopaedics. Joint replacement
`procedures occur frequently, are very expensive,
`and depend upon the accuracy and precision of
`surgical cuts to insure a successjkl clinical out-
`come. Robotic systems are emerging to address
`this need; however, there are still key components
`that are missing to insure the clinical utility of sur-
`gical robots in orthopaedics. The paper dcscribcs
`a more integrated approach to this task that in-
`cludes: I ) biomechanics-based preoperative plan-
`less
`traumatic surgical robotics
`ning, 2)
`techniques, and 3) standardized postoperative clin-
`ical tracking. The authors argue that such a system
`will improve current medical robotic systems and
`provide the long tern feedback necessary to cvalu-
`ate the clinical consequences of these system. The
`paper concludes by outlining the ongoing work on
`this project, with an emphasis on biomechanics.
`1 Introduction
`Surgical practice, and orthopaedics in particular,
`presents excellent opportunities for robotic and
`computer-based technologies to improve clinical
`techniques. Procedures such as total joint replace-
`ments are performed in large volumes and at sig-
`cost. Nearly 200,000 total hip
`nificant
`replacements and 190,OOO primary total knee
`replacements are performed in the U.S. each year
`[SI at a cost of greater than $lS,OOO each. The
`short and long tern clinical success of these proce-
`dures is very dependant on the proper placement
`and fit of the implants within bony stnrcturcs[rl].
`
`The clinical impOrtaace of precision and accuracy,
`along with the high volume of the surgical proce-
`durcs, indicates that important contributions can
`be made by surgical robots and pre-op~rative plan-
`ners that utilize computer simulations.
`Given the potential contribution, it is not surpris-
`ing that robotic mrgical devices are beginning to
`emerge in orthopaedics. Several commercial sys-
`tem exist which allow a surgeon to usc a com-
`puter to pn-operativcly plan the placement of an
`implant within a view of CT data. This plan can
`then be executed intraoperatively through a pn-
`cise robotic device[8]. These systems are technical
`successes; however, there is potential to improve
`the clinical utility of such systems by improving
`pteoperarive planning capabilities, surgical execu-
`tion techniques, and long tern clinical feedback.
`2 Problem Definition
`There arc several improvements that will help
`insure the clinical use of medical robotics and
`computer assisted systems within orthopaedics.
`First, meaningful preoperative feedback must be
`provided to the surgeon through realistic surgical
`simulations. In traditional joint replacement sur-
`geries, a surgeon makes many decisions intraoper-
`atively, based upon the “feel” of the tools and
`years of experience. In robot-assisted surgery, the
`surgmn~uscs a computer to plan the surgery so
`there is no longer any intraoperative feedback that
`can used for guidance. The robot will accurattly
`cany out a given surgical plan, but how will the
`surgeon decide what is an appropriate plan?
`A surgical simulator that incorporates biomechan-
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`ics-based analyses can do much to improve current
`preaptrative planning and address this issue.
`Existing planners do allow the surgeon to template
`the implant based upon 3D geometry’, but give no
`indication of the consequences of the proposed
`surgery on the initial stability of the system, the
`presence of implant-bone interface gaps, and the
`changes in the mechanical environment that arc
`induced in the bone.
`Little attention has been directed to providing the
`surgeon with such useful pmperative feedback.
`Without any biomechanical feedback, and with
`very little experience in the medical community at
`planning robot-assisted joint replacement proce-
`dures on a computer, it is very difficult to insure a
`successful surgical plan. The inclusion of biome-
`chanical simulations would permit the surgeon to
`make appropriate changes in the surgical plan.
`This may include changing such parameters as the
`implant placement, specifics of the bone prepara-
`tion, and type and size of the implant.
`Ideally a surgeon would be able to create a pn-
`operative plan that would be optimized for the par-
`ticular geometry and bone density of an individual
`patient. Biomechanical analyses would provide
`the surgeon with feedback concerning the distribu-
`tion of strain in the bone, and the amount of bone-
`implant contact for a given surgical plan. Biome-
`chanical analyses should consider both the implan-
`tation process (for cementless components) as well
`as the long term bone remodeling effects due to
`joint loading and varying load transfer mecha-
`nisms. Such an approach would be a great
`enhancement over cumnt capabilities and would
`provide the surgeon with some guidance as to the
`clinical significance of a proposed operation.
`Second, improvements in the surgical robotic tech-
`niques will also enhance clinical utility. For exarn-
`ple, new intraoperative registration methods are
`needed to allow “pinless” or ‘frameless” determi-
`nation of the pose (position and orientation) of a
`bone with nspect to a robot. Cumnt approaches
`suffer from the use of surgically implanted fiducial
`frames or pins to register the bone intraopera-
`tively. These markers are visible in medical
`images and are still attached to the patient at the
`
`time of surgery. By locating the markers intraoper-
`ative, a transformation between the reference
`frame of the pteopcrative plan and the reference
`frame of the actual patient can be made.
`This technique exposes the patient to additional
`trauma and risk associated with the implantation
`of markers, and tends to lengthen the duration of
`the surgical procedure over standard surgical tech-
`niques.
`New techniques arc needed that use “surface-
`based” registration to determine the bone’s pose.
`Such a technique would eliminate the need to
`implant pins, and instead rely on the intraoperative
`collection and pmssing of bone surface data to
`locate the bone accurately.
`Finally, the clinical results must be quantitatively
`analyzed to help evaluate the success of robot-
`assisted p d u r e s . Then is a need to both predict
`the long term biologic response of clinical proce-
`dures, as well as to prospectively track the actual
`clinical results of all procedures. Due to the nature
`of joint replacement failures, clinical tracking will
`not be able to convincingly demonstrate the long
`term success of the procedure until at least 10
`years in the future. However, without a method for
`obtaining valid data for comparisons, there may
`never be a valid method for judging how success-
`ful the planning and execution components have
`been.
`Cumntly there is no nationally standardized soft-
`ware or methodology for accomplishing this task,
`although attempts have recently been made to
`define the informauon all surgeons should collect
`[3]. Clinical studies arc often designed many years
`aftcr the surgery and can vary greatly in the infor-
`mation collected. It is therefore difficult to com-
`pare results. A standatdized approach would
`facilitate evaluation of the clinical results. In addi-
`tion, ttchnology assessment, including cosVbenefit
`analyses, will need to be coupled with these clini-
`cal outcome studies.
`3 Proposed Integrated Approach
`For the potential of computer assisted surgery to
`be fully realized in orthopaedics, we believe that it
`is important that several component technologies
`arc effectively integrated. As illustrated in Figure
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`Patient Data
`Implant Database
`3-D Skeleton Model
`
`W
`
`9
`
`Biomechanics-based h p e r a t i v e Planning
`
`4
`
`i
`
`.A
`
`Patient Database
`
`1 1
`
`Total Joint Registry
`
`~ Figure 1. Component technologies combine to improve surgical technique.
`
`1, these include patient data (medical imaging,
`implant databases, prc-operative patient evalua-
`tions) biomechanics-based preoperative planning,
`intraoperative robotic assistants, and long term
`clinical evaluations.
`As described in Section 2, there is an individual
`need for improvements in each of the component
`mas: preoperative planners, surgical robots, and
`clinical tracking. There is additional gain to be had
`by effectively linking each of the components
`together.
`A tight symbiotic relationship exists between sur-
`
` simulator^ and surgical robots. Improve-
`&al
`ments to either component p l y affects the
`clinical efficacy of the other.
`Improved preoperative planning capabilities arc of
`even without a robot. It would be useful for
`a surgeon to realistically simulate a surgery
`beforehand to help determine what implant size to
`use.
`However, without a robotic tool, there is no
`method for a surgeon to accurately implement a
`preoperative plan. For example, the simulation
`may help indicate an "optixd" bone cavity shape
`
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`.
`imDlant into D E D U d bone cavitv. These models
`I
`
`1
`
`.
`
`
`
`n
`
`*
`
`and implant location, but the surgeon will be
`unable to accurately perform this plan without a
`robotic device. In this manner, surgical robots
`actually improve the clinical usefulness of realistic
`surgical simulations.
`Just as surgical robots impact the usefuiness of
`prtaperative planning, surgical simulations also
`increase the utility of surgical robots. A surgical
`robot is a useful tool for executing a surgical plan,
`but the outcome will only be as good as the origi-
`nal plan. For this reason, sophisticated pnopera-
`tive planners are needed to fully develop the
`potential of robotics in oxthopacdics.
`Long term improvement in surgical technique will
`be expedited by ~areful quantitative clinical analy-
`sis. For this reason it is important to couple the
`surgical execution and planning with clinical out-
`come studies. Only by carefully tracking the clini-
`cal results of robotic (and traditional) procedures
`will it be possible to optimize the planning and
`surgical execution phases of these systems.
`All of the prc-operative patient data and post-oper-
`ative evaluations can be combined in a clinical
`database to allow long term evaluations of these
`new techniques. By combining engineering analy-
`sis, with robotic tools, and clinical databases, sig-
`nificant gains can be made in medical robotics.
`4 Current Work
`We currently are pursuing our vision of the inte-
`grated approach to medical robotics with research
`that focuses on total hip replacements. Work has
`focused on three component areas.
`4.1 Biomechanics and Surgical Simulations
`Our research concentrates on the dnite element
`analyses of the implantation procedure for cement-
`less
`acetabular and
`femoral
`components
`(1 ][4][6][9].Cementless procedures require tight
`coupling between the implant and bone. Our
`results have shown the importance of considering
`the implantation procedures and modeling friction
`effects with contact-coupled finite element models
`as illustrated in Figure 2.
`Axisymmetric models have been examined to gain
`better understanding of forceful insertion of the
`
`2 Implant k to&
`the bony cavity.
`
`into
`
`the lmpLn1 i s paaiblc
`
`Note the v a y luge
`rtninrnurtherim
`of the rcetabular
`
`Note the gapin the polar
`mgion P the cnd of the
`
`Figwe 2 Axisymmetric model of the insertion of
`a cementless acetabular cup into a prepared
`acetabular cavity.
`
`idealize the geometry of the implant and the bone
`by assuming axial ~ymrnetry, but they include
`most of the complex charactenstics of the prob-
`lem, such as frictional contact, large deformations,
`large strain and nonlinear material model. Further-
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`more, they are convenient for parametric studies
`because they allow for the effects of any parameter
`(implant size, implant oversizing, material proper-
`ties, friction, etc.) to be easily studied indepen-
`dently.
`
`3. Three-dimensional finite clement model
`
`o FF= the acetabulum and cemmtkss 8cetabulu cup.
`Cwently, we arc developing full tlme-dimen-
`sional models (of both the femur and acetabulum)
`scan data. An example acetabular
`based upon
`model is shown in Figure 3. We want to v e m the
`results of the axisymmetric studies and to further
`the study of basic biomechanics phenomena asso-
`ciated with the press fit implant insertion. In addi-
`tion, we arc working toward developing of an
`automatized procedure that will include biome-
`chanical simulation as a component of a p p m -
`tive surgical planner.
`4.2 Surgical Robotics
`registration
`We arc investigating "frameless"
`methods for surgical robotics in orthopadcs. Our
`technique is initially aimed at the robotic prepara-
`tion of the pelvis for the insertion of cementless
`acetabular components, but it is our goal to extend
`this approach to other procedures.
`We an demonstrating cutting of accurate cavities
`in bone analogs using an industrial robot. h o p e r -
`ative planning code is being developtd with a data
`
`visualization package. Additional custom code has
`been written to create surfaces from the CT data.
`We are initially concentrating on acquiring intra-
`operative surface data using a digitizing pmk to
`touch exposed surfaces of the bone; however,
`then is potential to expand this approach to many
`other data acquisition methods. Currently our
`research focuses upon integrating existing surface-
`based registration algorithms [9] into our overall
`system.
`43 Clinical Database
`We arc addressing this component through the cre-
`ation and use of a database we refer to as the
`Total Joint Regisny." This prospectively col-
`lected data will be used to examine the long term
`clinical succtss of joint replacement procedures.
`We use a research software package and a stan-
`dardized, third-party data collection called "con-
`sensus information" and endorsed by
`the
`American Academy of orthopaedic Surgeons,
`SCOT and The Hip Society. Patients have already
`enrolled in the registry and data is currently being
`collected. The incorporation of cost-benefit analy-
`sis and technology assessment into this process is
`a long term goal that may yield the ultimate mea-
`sure of the impact on the health care system.
`5. Conclusion and the Future
`Our nsearch endeavors to integrate all the compo-
`nents illustrated in Figure 1 into one complete sys-
`tem. we have made progress in many of the
`component technologies, but work remains to
`develop robust clinically practical tools and then
`to incorporatt these technologies into an overall
`system. It is our belief that the development of the
`described approach will represent a signrficant
`improvement for the field of medical robotics. Our
`c m n t work strives to make this goal a reality.
`6. References
`
`1) DiGioia AI4 El, M
` WH, Juamaz B, Orr, "E,
`s
`7bc Mechnics of the Press Fit Acetabular
`Implant", ASME Summer Bioengineering Confer-
`axe, Bnckhdge, Colodo, June, 1993.
`Jurmaz B, Visnic C, DiGioia AM III, Gham 0,
`"Finite Element Analysis of Assembly Soains in
`Acetabulum Due to Cementless Implantation" Scc-
`ond World Congress of Biomechanics, Free Univer-
`sity, Amsterdam, The Neth~dands, July, 1994.
`
`2)
`
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`3)
`
`4)
`
`5)
`
`6)
`
`7)
`
`8)
`
`9)
`
`Johnston, R.C., et d. minimi and Radiographic
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`Mow, V.C. and b y e s , W.C.. Basic Orthopaedic
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`National Center for H d t h Sutistics, Ndonal Hos-
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`Taylor, RH., Paul, H., Mittlesudt B., Hanson. W.,
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`
`1 1 1
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