Development of the ROBODOC® System for Image-Directed SurgeryPeter KazanzidesOutlineApplication OverviewHip and Knee ImplantsTotal Hip Replacement SurgeryROBODOC Video (1991)Current Technique for THRROBODOC THR ProcedureManual Broach vs. RobotROBODOC Procedure OverviewWhat is Registration?Simple Registration MethodHow Many Points Do You Need?ROBODOC ExampleMathematical BasisMathematical Basis (Cont.)Alternate ComputationPin-Based RegistrationPin-Based RegistrationHarder Registration MethodROBODOC Pinless RegistrationIntraoperative Point CollectionPinless RegistrationHandling Re-RegistrationHandling Re-RegistrationPinless Video (1998)ROBODOC HistoryROBODOC HistoryROBODOC History (cont.)ROBODOC GenerationsCanine System GoalsCanine System DesignCanine System DesignCanine System DesignCanine System SafetyFirst Surgery - May 2, 1990Canine System LessonsBeta System GoalsBeta System DesignBeta System DesignBeta System DesignBeta System DesignSafety Design OverviewBeta System Safety DesignBeta System Safety DesignFirst Surgery - Nov 7, 1992The Press Reacts...Beta System LessonsCommercial System GoalsQuality SystemsQuality System DocumentsCommercial System DesignCommercial System DesignCommercial System DesignCommercial System DesignCommercial System Safety DesignCommercial System SurgeryCommercial System LessonsROBODOC StatusTotal Knee Surgery (2000)SummarySummaryROBODOC Video (1995)Development of the ROBODOC® System forImage-Directed SurgeryPeter Kazanzides• Ph.D. EE, Brown University (Robotics), 1988• Post-doc at IBM T.J. Watson Research Ctr., 1989• Visiting Engineer at UC Davis, 1990• Founder and Director of Robotics and Software at Integrated Surgical Systems, 1990-2002• Chief Systems and Robotics Engineer at JHU ERC for CISST• Assistant Research Professor, Computer ScienceOutline• Application Overview• Registration Methods• ROBODOC History (Design Iterations)– Design goals– System description– Safety systems– Lessons learned• SummaryApplication Overview• Total Hip and Knee Replacement Surgery– replace damaged articulating surfaces with implants• cemented - use cement to attach to bone• cementless - rely on bone ingrowth– position/orientation is important– proper fit can be important (cementless)Hip and Knee ImplantsTotal Hip Replacement SurgeryROBODOC Video (1991)Current Technique for THR• Pre-operative planning using X-rays and acetate overlays• Surgical preparation using mallet and broach or reamer• Relies on surgeon’s “feel”• Outcome depends on surgeon experienceROBODOC THR Procedure• Pre-operative planning using 3-D CT scan data and implant models (ORTHODOC®)• Surgical preparation of bone by robot using milling tool– Increased dimensional accuracy– Increased placement accuracy• Outcome more consistentManual Broach vs. RobotROBODOC Procedure Overview• Perform orthopedic procedures (hip and knee replacement):– Preoperative CT scan– Preoperative planning– Intraoperative registration– Robotic machining of boneWhat is Registration?• Establishing a transformation (conversion) from one coordinate system to another– CT coordinates (preoperative plan)– Robot coordinates (surgery)ÎAllows the robot to cut the implant in the position planned by the surgeon.Simple Registration Method• Use reference points (fiducials) that can be seen in each coordinate system• Simple example: using a mapHow Many Points Do You Need?• 2D world has 3 degrees of freedom– X, Y, θ• 3D world has 6 degrees of freedom– X, Y, Z, Rx, Ry, RzFor 2-D:Î 1 point (x1,y1) is not enough Î 2 points (x1,y1), (x2,y2) is more than enoughRedundant information: distance between pointsROBODOC Example• Using 3 reference points (fiducials)231T2YXT1XYZYZXT2-1 * T1Q: Are 3 points needed?Mathematical Basis• Define a fiducial coordinate system by some convention, e.g.,– X is unit vector from Point 1 to Point 2– Y is unit vector that is perpendicular to X and points towards Point 3.• Each observer (CT/Orthodoc and Robot) finds fiducials in its own coordinate system and computes transformation (T1 and T2).Mathematical Basis (Cont.)• Use T1 to convert implant position from CT coordinate system to fiducial coordinate system.•Use T2-1to convert implant position from fiducialcoordinate system to Robot coordinate system.• By combining transformations (T2-1 * T1), we can determine the transformation between the CT and Robot coordinate systems.– Key result for surgical navigation and robotics!Alternate ComputationDefine: A = T2-1 * T1PR= A * PCTGiven 3 points P1, P2, P3 that are located in Robot and CT coordinates, solve simultaneous equations for A(e.g., least-squares estimation)ROBODOC Pin-Based Registration• Surgery to implant pins (bone screws) prior to CT• Planning software detects pins in CT coordinates• Robot finds pins in Robot coordinates• Software checks pin distances (safety check) and then computes transformation between CT coordinates and robot coordinates• Software uses transformation to convert planned implant position (CT coordinates) to surgical position of bone (Robot coordinates)Pin-Based Registration• Q: How many pins are needed?• A: Need at least 3 “features”– 3 Pin Registration: uses center of each pin– 2 Pin Registration: uses center of each pin and axis of one pinPin-Based Registration+ Easy to implement+ Easy to use+ Very accurate (if pins far enough away)+ Very reliable- Requires extra surgery- Causes knee pain in many patientsHarder Registration Method• If there are no easily identifiable features, must find another way to establish correspondences• Example: finding a known object in the dark by probingROBODOC Pinless Registration• More complex (point-to-surface matching)• Surgeon creates surface model of bone from preoperative CT (semi-automatic software).• Surgeon uses digitizing device to collect bone surface points intraoperatively.• Software ensures good distribution of points• Surgeon verifies resultIntraoperative Point CollectionPinless RegistrationHandling Re-Registration• Problem: How to re-register if bone moves during procedure?– Required bone surfaces may have been machined away– Pinless registration can be time-consumingHandling Re-RegistrationSolution: Implant markers (pins) during surgery.1. Expose femur and implant markers2. Perform pinless registration3. Locate markers4. Use pinless registration result to transform marker positions to