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Impulse Loading With an Application in the Lower Leg using a

VIEWS: 3 PAGES: 20

									Impulse Loading on the Lower Leg
     using a Synthetic Bone
                Marley Winfield

                Department of Biochemical
                Engineering and Medical
                Biophysics

                MBP 3302
Outline

   Introduction
   Materials and
    Procedure
   Results and Discussion
   Conclusion
   Acknowledgments
   References
Introduction

   Synthetic bones have recently become available as substitutes for
    cadaveric specimens used in testing
   Many advantages, including low variability as this makes them
    more consistent, available, easy to work with, handle and store
   Have been validated for quasi-static tests, but not fracture studies




                http://www.sawbones.com/products/bio/composite.aspx
Background

   Upon axial loading of the lower leg during impact events,
    fractures of the tibia can occur

   Life altering injuries can take place depending on the
    magnitude of the axial loading

   Fracture analysis using synthetic bones to determine
    injury limits is yet to be studied

   Appropriate injury limits for lower limbs can be found
    using an apparatus designed to simulate these types of
    events
Purpose

Carrying out a fracture analysis on synthetic
 tibias, enables us to understand the impact
  that can be applied to a lower limb before
                fracture occurs.

These experimental results can be compared
    with a fracture analysis of a cadaveric
 specimen to validate whether or not synthetic
        bones are suitable substitutes.
Materials and Procedure
Potting and Alignment of Bones
 Bones were potted in
   PVC tubing
 Alignment of the anterior
   of the tibia was done
   using a laser
 PVC tubing was filled with
   cement and spread
   equally
 Important for all bones to
   be aligned and potted the
   same for consistency
Materials and Procedure
Strain Gaging




   Bone was cleaned using rubbing alcohol
   Strain gage rosettes were placed along the tibia approximately 6
    mm apart, 3 at the top and 1 at the bottom
   Gages were fixated to the bone using glue and a catalyst
   Important to make certain that the gages were completely secured
    and would not come off during testing
    Apparatus

   Can test Cadaveric and
    synthetic lower leg specimens

   Velocity the specimen is struck
    at can be varied, independent
    of the force applied

   Specimen receives a controlled
    impulse from a projectile using
    pneumatics
Data Collection

   Bone was placed in the       Data was collected
    chamber and hooked            using a data acquisition
    up to operating system        system

   The projectile was
    propelled causing            Custom-written
    impact on the bone            LabVIEW program
                                  calculated the
                                  momentum, energy,
   Projectile mass, 3.9kg,
    and force of impulse at       acceleration, force of
    16KHz                         impulse, exit velocity,
                                  and strain
Data Collection

   High speed camera records the event

   Protocol to increase impact until failure occurred –
    failure when broken into 2 or more pieces

   Impact varied by altering pressure, which correlates
    to the energy, of the pneumatic device using an
    electrically-controlled regulator

   5 sawbones were tested for comparison
Results and Discussion
                               Failure occurred at:
                               Average Exit Velocity = 5.5m/s
                               Energy = 60J
                               Average Failure Force = 4609N
Fracture Limitations
                               Standard Deviation = 505N


                   Fracture Force

            6000

            5000
                                                  Sawbone 1
            4000
Force (N)




                                                  Sawbone 2
            3000                                  Sawbone 3
            2000                                  Sawbone 4
                                                  Sawbone 5
            1000

               0
                    Sawbone
Force and Energy

                            Average Force at each Energy

                     5000
 Average Force (N)




                     4000

                     3000

                     2000

                     1000

                        0
                            20               40            60
                                          Energy (J)
Principle Strain Along Bone

                   Peak Failure Strain at each Gage

           0.012

            0.01

           0.008                                      Gage 1
  Strain




                                                      Gage 2
           0.006
                                                      Gage 3
           0.004
                                                      Gage 4
           0.002

              0
                              Strain Gage
     Strain

                          Strain at 20J

         0.0014
         0.0012
          0.001                                 Sawbone 2
Strain




         0.0008                                 Sawbone 3
         0.0006                                 Sawbone 4
         0.0004                                 Sawbone 5
         0.0002
              0
                  1   2                 3   4
                          Strain Gage
                                                                                 Strain at 20J

                                                                0.014
                                                                0.012
                                                                 0.01                                  Sawbone 2




                                                       Strain
                                                                0.008                                  Sawbone 3
                                                                0.006                                  Sawbone 4
                                                                0.004                                  Sawbone 5
                                                                0.002
                                                                    0
                                                                        1   2                  3   4
                         Strain at 40J                                           Strain Gage

         0.014
         0.012
          0.01                                 Sawbone 2
Strain




         0.008                                 Sawbone 3
         0.006                                 Sawbone 4
         0.004                                 Sawbone 5
         0.002
             0
                 1   2                 3   4
                                                                                Strain at 60J
                         Strain Gage

                                                                0.014
                                                                0.012
                                                                 0.01                                  Sawbone 2
                                                    Strain




                                                                0.008                                  Sawbone 3
                                                                0.006                                  Sawbone 4
                                                                0.004                                  Sawbone 5
                                                                0.002
                                                                    0
                                                                        1   2                  3   4
                                                                                Strain Gage
Conclusion

   Synthetic bones fractured at an energy of
    60J
   Fracture of synthetic bone occurred at an
    average force of 4609N
   Current injury limit of cadaveric lower leg is
    5.4kN (Yoganandan)
   Average exit velocity was 5.5m/s
   At fracture the highest principle strain was at
    point of impact
Conclusion

   Fracture analysis is significant when determining the
    injury limits of a bone
   Experimental results of cadaveric and synthetic
    bones can be compared, allowing for appropriate
    fracture limits to be determined
   Knowledge of fracture limitations enables
    manufacturers to improve designs, i.e. cars, to
    reduce the possibility of injury
   Understanding the properties of synthetic bones will
    increase their use in testing and research
Acknowledgments

 I would like to thank Dr. Cynthia Dunning, and Cheryl
 Quenneville for their guidance and support with the six week
 project to make it successful and enjoyable
References
   Cristofolini, L., Viceconti, M. (1999). Mechanical Validation of
    whole bone composite tibia models. Journal of Biomechanics 33
    (2000), 279-288.
   Quenneville, C., Fraser, G., Dunning, C. (2008). Development of
    an Apparatus to Produce Fractures From Short-Duration High-
    Impulse Loading With an Application in the Lower Leg. London,
    Ontario: University of Western Ontario, Department of Mechanical
    and Materials Engineering
   Sawbones Worldwide: A Division of Pacific Research Laboratories,
    Inc. (2009) Retrieved April 3, 2009, from
    http://www.sawbones.com/
   Vishay Micro-Measurements: Strain gages and Instruments
    (2008).
   Yoganandan, N. (1997). Axial Impact Biomechanics of the Human
    Foot – Ankle Complex. Journal of Biomechanical Engineering Vol
    119, 433-437

								
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