1. Robots In Spine Biomechanics
Wafa Tawackoli, Michael A.K. Liebschner
Department of Bioengineering
Rice University

2. Prediction of stress fracture risk
Motivation
In vitro study of human spine for various complex physiological loading.
Prediction of stress fracture risk
Approximately 700,000 vertebral fractures occur each year in USA
Everyday activities
Trauma (i.e. Car accident, Sports)
Occupational ($54 billion/year)
Relatively low impact office duties
High impact manual labor
Osteoporosis (~$13 billion/year)

3. Anatomy Vertebra Intervertebral Disc Annulus fibrosus
Posterior Elements
Nucleus pulposus,
Facet Joint
COR
Cortical Shell (rim)
Trabecular bone
Vertebra
Intervertebral Disc
Cramer, 1995

4. Primary Goals 3D motion path Simulation of in vivo complex loading
To understand the biomechanical behavior of spinal segments under complex physiological loading
3D motion path
Simulation of in vivo complex loading
Investigate stress fracture risk base on physiological loading

5. A 3D coordinate system Total of 6 load components may be applied
+ Z Rotation
Total of 6 load components may be applied
Three forces
Three moments
Each load component may produce 6 displacement components
Three translations
Three rotations
36 load displacement curves can be generated
+ X Direction
+ Z Direction
+ X Rotation
+ Y Rotation
+ Y Direction

6. Complications Mechanical Properties are difficult to ascertain.
Spine movies in a complex 3-Dimensional pattern.
However, it is important to apply such complex motion during in vitro studies.

7. Biomechanical Methods
In vivo experiments (including imaging studies, i.e. stereoradiography) (Tibrewan, Pearcy)
Mechanical Testing (Panjabi, Hansson, Adams)
Computational Modeling (finite element analysis) (Uppala, Williams)

8. Biomechanical Methods (cont’d)
Mechanical Testing Devices
Pulley system (Crawford, Panjabi, Patwardhan)
Uniaxial system (Adams, Panjabi, Brickmann) (Servo-Hydraulic or Pneumatic)
Mechanical Testing Methods
Uniaxial compression/tension
Shear
Bending (Flexion, Extension, Lateral, Torsion)
Compressive axial preload (Follower Load)

9. Biomechanical Methods (cont’d)
Spine Testing Machine:
Pulley system
Linear servo actuator (Parker-EBT 50)
6 DOF Transducer (ATI-Omega 160)
Bi-axial tilt sensor (range of ~60o)
Optical tracking system
Compressive axial preload capability (up to 2250 N)

10. Biomechanical Methods (cont’d)
Flexion
Force
Extension
U-Shape Bracket
Cable
guide
Side View
Top View
Force
Sagittal View
ATI-160
Dead Weights

11. Limitations
Measurement of spinal rigidity in single plane is very complex
Unconstrained Motion- 6 Degrees of Freedom (DOF)
2 DOF applied force + moment
Lack of knowledge of disc degeneration (tears or lesions)

12. Our Approach
Measurement of spinal rigidity under complex loading (Fatigue, Creep, Stress Relaxation)
Decrease DOF of unconstrained motion
Increase DOF of applied forces and moments
Apply helical axis of motion (path of minimum resistance)
Load and displacement boundary conditions.

13. Concept of KUKA Robotic Arm
6 Degree of Freedom
PC computer
Windows based program (GUI software)
Manual and automatic control
Simple modular system
Base frame
Rotating column
Link arm
Arm
Wrist

14. Coordinate Systems
Coordinate systems (can be defined by the operator):
Sensor & Tool coordinate systems
Base coordinate system
Virtual coordinate system

15. Sensing and Control Process (1)
Displacement EZ NZ
Load
Hybrid Control = { load control & displacement control }

16. Sensing and Control Process (2)
Forces and torques measured by the ATI transducer can be re-calculated to a virtual coordinate system in order to sense the real effecting forces and torques between spinal segment and the transducer.
(Fx, Fy, Fz, Tx, Ty, Tz)
Sensor ATI- OMEGA 160 LOAD CELL
The optical tracking system allows for comparison in movement between each vertebra.

17. Motion Envelope Ω Reference (Home) Position φ Foundation Points
(Manually determined)
Top View of Motion Envelope
Boundary condition (i.e. Bending moment of 5 N.m.)

18. Conclusion
Human spine is a complex system therefore complex motion behavior is expected
Hybrid control for biomechanical testing is recommended
6DOF robotic testing system can be applied to the delineation of in vitro spine kinetics

19. Acknowledgment Computational and Experimental Biomechanics Lab
KUKA USA Robotics
KUKA Development Labs
ATI Industrial Automation
Joe Gesenhues (Ryon Engineering Lab, Rice University)

20. Robots in Biomechanics
Thank You
Robots in Biomechanics
Research