Nathan Abraham

Master’s Speaking Requirement

August 6th,2004

Operating room of the past and Present

Rembrandt, The Anatomy Lesson, 1632 Jaramaz “MIS tools” 2003DiGioia (recently…)

Integration

Planners/Simulators

Biologic Implants

AugmentedRealityDisplays

Semi-active Robots

ActiveRobots

OR HCI

Robust andAccurate Tracking

Why Medical Robotics

• Improves surgeon precision and dexterity.

• Reduces motion and trembling.• Provides high repeatability.• Enables online force-control.• Reduces radiation exposure during

operation.• Enables percutaneous procedures. - Reduce patient pain and trauma. - Shorten hospital stays.

Categorization of Medical Robotics System

Robotics system Passive Semi-Active Active

Source of information systems

3D (CT, MRI) HipNavVectorVisionSurgiGATENavitrackSurgetics

AcrobotPFS

ROBODOC

2½ (Fluoro) SurgiGATEStealthStation VectorVisionSurgetics

CASPARCRIGOS

Image-free OrthopilotVectorVisionSurgeticsStryker

PiGalileo MBARS

Available Robotic Systems

• Integrated Surgical Systems• Robodoc® - Total hip replacement.• OrthoDoc® - Preoperative planning

workstation. • NeuroMateTM - Neurosurgeries (Parkinson).• Caspar - Orthopaeidic• da Vinci ® - MIS procedures

Available Robotic Systems: Precision Freehand Sculptor

PFS Tool

Position Tracking Device

Surgical plan with updates

Bone

Tracking Marker

Tracking Marker

Available Robotic Systems• Computermotion

ZEUS® - Minimally invasive procedures.

Available Robotic Systems• URSortho

CASPAR® -Bone and joint surgery.Evolution 1 + Hexapod Z ® - 10 micrometers resolution.

Major Components in a Medical Robotics Systems

Pre/Intra-operative Planning

Intraoperative robotic system

Post-operative Evaluation

Image Free SystemImage Free System

Cloud of points and Tracking the trochlear groove

Haptic device

Intra-operative planning and bone shaping

Why did we choose a parallel robot

Serial Robot

Base link

Active joints

Kinematic chain

Output link

Serial Manipulator

Base link

Close kinematicchain

Output link

Parallel Manipulator

Parallel Robot

Serial Vs. Parallel Robots

Character Serial Robot

Parallel Manipulator

Links Open Chain Close Chains

Workspace Large Small

Singularity Lose of DOF Gain uncontrollable DOF

Structure Stiffness

Low High

Load/weight ratio Small High

Accuracy Low Very high

Time respond Low High

Parameter Search

Parallel Robot

3DOF

6DOF

The application

What is it?•A parallel mechanism to be placed directly on to a patient’s knee during patellofemoral joint replacement surgery (knee surgery).

•Computer control will perform a portion of the bone milling process

•CNC machine for surgeons

Why is it?•Over 400,000 estimated knee arthroplasty procedures in the U.S. by 2030

•Invasive methods require longer healing times: more cost and discomfort to the patient

•Glorified carpentry

How your Knee Works

How your Knee Works

Current Technique

1. Surgeon traces (by hand & marker) template on to PF-surface

2. Burr/chisle used to resect the trochlear groove

3. Template is tried on knee; repeat 2 if necessary

4. Secure final implant

Our Technique1. Attach MBARS to the patients knee (making

the knee and robot a rigid body to eliminate relative motion).

2. Construct a CAD model of the patient’s knee

3. Choose from a library of implant CAD models

4. Find the model with the best fit and position on knee

5. Generate a trajectory for MBARS to follow and cover the required parts of the knee to be milled

•.sur file (points & triangles) built from CT imagery

•Can be done pre-operatively, but not covered under all insurance packages

•6 DOF force sensor

•Will be used as another appendage for MBARS to gather points and build model during surgery

Knee Model

Implant Model

•No time/money restraints

•All sizes can be preoperatively computed using CT

Fitting the Implant to the Knee

•Surgeon manually marks the trochlear groove on implant and knee model

Aligning the implant with the trochlear grove.

•Distal tip is translated to contact with knee model

Exhaustive Orientation Search

Result:

Path Generation

•Once implant is fitted to knee, find a trajectory to cover the surface needed to be milled

UniformityComplete Coverage

Sweep Line Method

•Pick an arbitrary* line and direction perpendicular to line to “sweep” line across knee surface

•Move the sweepline in equal size increments along the gradient in the chosen direction

Stuff will go here about mapping from surface to xy E R2

Final Trajectory

Cell Decomposition

Trajectory on Knee

Point to Point Navigation using Potential Fields

Local navigation of burr tip determined by the sum of 2 fictitious forces:

Forceattract

points from current burr position to target location

Forcegravity / Forcerepulse

Pulls the burr to the pattellofemoral surface if outside a set threshold

-OR-

normal force to push the burr away if within the set threshold

Following a trajectory of 100 set points. Burr locations shown in red, knee surface polygons shown in green

Simulated Gravity Example

Right figure shows the effects of choosing different gravitational constants. Smaller ones (shown by top trajectories) provide smoother paths but are not constrained tightly enough to travel along the surface.

4th order polynomial approximation of the patellofemoral surface. Has the general shape of a saddle function.

How a typical trajectory is formed. Repulsive forces in red, attractive forces in green, and gravitational forces in blue. Gravitational threshold distance shown as black dotted line.

End Result

•Alignment error is minimized computationally rather than visually

•Template step in the PFJ procedure is no longer necessary

•One time milling process instead of iterative procedure.