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Summary on Human Tolerance to Blunt Impact

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  • Summary on Human Tolerance to Blunt Impact

    Hi All,

    Two weeks ago, I posted a question pertaining to the injury threshold of
    human body extremities when subjected to blunt impact (see the tail of this
    message for the original post). I have been provided information and
    literature search from some members on the following topics:

    - Quasi static loading condition
    - Classical “metallurgical” type of test such as Charpy impact tests
    - Automobile safety related tests

    Unfortunately, I have not yet been able to lay my hand on an extensive list
    of papers dealing with the above topic list. However, I have already at
    least a comment on each topic that I would like to share with you. Your
    further feedbacks and suggestions on this matter will remain greatly

    First, it is a known fact that bones have a viscoelastic material behavior.
    Therefore, I do not think that their failure under quasi-static bending
    force can be a reliable indication of how they would respond to a force of
    the same magnitude applied dynamically. Second, in my view, the Charpy
    impact test of cortical bone does not suffice to predict the bone fracture
    since it does not take into account the structural properties of the bone as
    a whole anatomical unit. Third, the data on the bone failure simulated for
    the automobile industry appears to be the closest to what happens during
    the blunt impact. Nonetheless, this still may not address the
    particularities of blunt impact injury. The reason for that is the latter
    involves low mass (20 kg) but low velocity (4-10 m/s).
    Also, in addition to the different rates at which the striking energy is
    delivered to the viscoelastic bone and the overlying soft tissues, the shape
    of the threat (e.g. baseball bat vs car bumper) has to be considered, since
    the energy distribution may account for the nature of the sustained injury.

    In conclusion, evaluating the threshold injury of human beings is a
    challenging task and the bone strength depends on various factors such as
    age, gender, material density, etc. However, unlike automobile users who
    form a very heterogeneous group, professional sport players, prison guards
    and anti-riot officers represent a much more homogeneous sampling of
    individuals and their tolerance to injury is higher due to their general
    good physical condition. Therefore, one may wonder if bone failure
    evaluation for automobile safety is still applicable to blunt impact injury,
    despite the clear differences between the two contexts and environments?

    Finally, I thank the few but very helpful members who contributed
    thoughtfully to orient my line of thinking in regard to this subject. The
    list of the responses is pasted next.

    Ismael El Maach

    ************************* Message 1 of 9 *******************
    I think that their is a deeper question to your loading
    conditions. You need to answer exactly what bone types Cortical or
    trabecluar and is it a long bone at mid shaft, deminsions, mineral
    density? If you get the modulus in the primary directions and the
    dimensions of the bone you wish to test,it is fairly easy to solve for the
    quazi static condition of a beam with the loading that you desire for a
    minimum. Lots of intro orthopedic biomechanics can help you step through
    this. There have been hundreds of material studies done on the anisotropic
    behavior of bone and I would definatley look at those to get the material
    one that I have seen used several times for the different stress strain
    curves for longitudinal, 30 deg, 60 deg and transverse loading was
    Frankel and Nordin, 1980 ( I have seen this reference in a chart several
    Good Luck,
    T. Withrow

    ************************** 2/9 **************************************
    Hi, Hope all is well! Don't have any answer for you, but remember
    impactor geometry has as much affects as energy, i.e. a 90 degree
    anvil will fracture a forearm with orders of magnitude less energy
    than a flat board will.

    Cheers, Trey
    Joseph Crisco

    ************************** 3/9 *******************************
    Dear Sir:

    At The University of Tennessee Engineering Institute for Trauma & Injury
    Prevention we have conducted numerous tests of the nature that you have
    described. I could mail copies of some of our published papers if you are
    interested. For now, the following numbers may help you:

    Some results of our tests indicate failure forces for the femur ranged 1.31
    8.37 kN. Bending moments averaged from approximately 100 to 500 Nm. These
    values varied depending on the speed of impact, impactor geometry, direction
    of impact, gender of specimen, etc. Several tests were performed from
    perpendicular (transverse) impacts to the mid-thigh. Intact leg specimens
    inverted and suspended against a large steel elbow plate in the test zone by
    rod passing through the tibial plateau such that impact occurred on the
    anterior or lateral surface.

    Good luck!
    -Tyler Kress

    ****************************** 4/9 *******************************

    Sport Discus had this study which compared cadaver tibia fractures. I
    remember talking to one of the authors at the ACSM meeting, and they may
    have had additional data on other bones.

    TI: Comparison of soccer shin guards in preventing tibia fracture
    AU: Francisco,-A.-C; Nightingale,-R.-W; Guilak,-F; Glisson,-R.-R;
    JN: American-journal-of-sports-medicine-(Waltham, Mass.) 28(2), Mar/Apr
    2000, 227-233 Refs:18, Total Pages: 7.
    CN: American College of Sports Medicine. Meeting (1999: Orlando, Fla.)
    PY: 1999
    AB: The goal of this study was to evaluate the effectiveness of a number of
    shin guards in protecting against tibia fracture in soccer players. A
    secondary purpose was to determine the relationship between the material and
    structural differences in shin guard design and the protection provided.
    Twenty-three commercially available shin guards were tested on a model leg
    containing a synthetic tibia that had been calibrated against human cadaver
    specimens. Each guard was categorized into one of four material types:
    plastic (N = 9), fiberglass (N = 6), compressed air (N = 4), and Kevlar (N =
    4). The maximum combined force at the ends of the tibia, the principal
    strain on the posterior side of the tibia, and the contact time of the
    impact were measured using a drop track impact simulation. Shin guards
    provided significant protection from tibia fracture at all drop heights. The
    average guard reduced force by 11 % to 17 % and strain by 45 % to 51 %
    compared with the unguarded leg. At the higher drop heights, material
    composition and structural characteristics of the shin guards showed
    significant differences in protective abilities. These findings indicate
    that all shin guards provide some measure of protection against tibia
    fracture, although the level of protection may vary significantly among the
    different guards.

    Randall Jensen, Ph.D, FACSM

    *********************** 5/9 *******************************
    Dr. Maach,

    Actually, there is a wealth of research in the literature (particularly the
    automobile safety literature) dealing with the failure strength of long
    in bending. A quick search should yield dozens of results. Here is a very
    short and incomplete list of references:

    H. Yamada, Strength of Biological Materials, Williams and Wilkins Co.,
    Baltimore, Md. 1970.

    G. W.Nyquist, "Injury Tolerance Characteristics of the Adult Human Lower
    Extremities Under Static and Dynamic Loading," Biomechanics and Medical
    Aspects of Lower Limb Injuries, SAE #861925, 1986.

    P. Schreiber, J. R. Crandall, T. Micek, S. Hurwitz, "Static and Dynamic
    Strength of the Leg," Proc. 1997 IRCOBI conference, Hannover, Germany;
    September 24-26, 1997.

    S. Duma, P. Schreiber, J. McMaster, J. R. Crandall, C. R. Bass, W. D.
    "Dynamic injury tolerances for long bones of the female upper extremity,"
    Journal of Anatomy, 194(3): 463-471, 1999.

    Good luck,

    Jim Funk

    ************************* 6/9 ***************************
    Dear sir,
    I would be interested in your replies. Please forward them to me at your
    earliest convenience. Thank you in advance for your attention to this


    Mr. Adelino Yung

    ************************* 7/9 *************************

    The auto safety industry may yet contain the answers to your questions

    shear loading of lower limb - pedestrian studies
    bending of leg - numerous studies for occupants and pedestrians
    bending/shear of upper extremity - studies of frontal airbag/forearm
    interaction, studies of side airbag/arm interaction
    I suggest searching the impact biomechanics literature related to auto
    more thoroughly.

    ************************* 8/9 ***************************
    Mr. Doug Moore forwarded the following posting to me.

    From: Alex DePaula
    >Subject: Replies: Impact testing of cortical bone
    >Date: Fri, 26 Jan 2001 14:35:00 -0500
    >Dear Biomechanics list:
    >I am looking for information about falling-mass impact testing of cortical
    >bone or people with knowledge of impact testing of bone. Any type of
    >testing information could also be helpful (Izod, Charpy or other).

    Here are the 3 replies:

    Dear Dr. DePaula:

    We have been impact testing bare bones and intact specimens for 15 years in
    our laboratories. However, we do not do the classical "metallurgical" types
    of test (Izod, Charpy, Rockwell, etc.). Our primary interest has been to
    study failure thresholds (e.g. force, energy, etc.) for various bones and
    intact specimens in order to understand mechanisms of injury and
    design criteria. We have used accelerator-cart/guiderail systems and
    drop towers in our research. Is there some specific information that you
    need? I would write more, but I am not sure what kind of information you
    looking for... Do you want data? Are you interested in experimental
    methodolgy? Let me know, and I will see if I can help more.


    Tyler Kress, Ph.D.
    Associate Director
    Engineering Institute for Trauma & Injury Prevention
    The University of Tennessee

    Tyler A. Kress, Ph.D.
    The University of Tennessee

    Yamada in Evans (Ed) Strength of Biological Materials, Williams and Williams
    pub. 1970 lists the impact snapping strength of femoral cortical bone for
    adult human, horse, bovine in the radial and tangential directions. These
    data were collected using an Izod impact machine. Values are in lbf/in^2
    (mean +- SD):
    Human radial (12.13 +- 1.35)
    Human tangential (8.87 +- 0.98)
    Horse radial (10.27 +- 0.89)
    Horse tangential (10.73 +- 0.93)
    Bovine radial (9.80 +- 0.65)
    Bovine tangential (11.20 +- 0.84)

    Hope this helps.

    Richard Kent
    University of Virginia


    We have been interested in more rigorously discriminating comminution
    patterns in high-energy injuries, based on fracture energy absorption. To
    create fractures in cortical bone segments, we use a drop tower apparatus
    that was constructed in our lab. We have also conducted tests of energy
    absorption in cortical bone beam specimens using a Balanced Hounsfield
    Impact Tester. (Some of this data is published in Beardsley et al, The Iowa
    Orthopaedic Journal, 20:24-30, 2000). I am also aware of an early paper by
    Bonfield and Datta (Journal of Applied Physics, 37:869, 1966) that reports
    on the fracture behavior of short beam compact bone specimens in a
    traditional Charpy test.

    I would be interested in reading other responses that you receive regarding
    this matter.


    Christina Beardsley

    ********************** 9/9 *********************************
    Mr. Dany Lafontaine suggested the following reference
    FUNG, y. c. biomechanical Oroperties of living tissues. New York: Spingler
    Verlag, 1981. 443 p

    **************** My original Posting *********************

    From: Ismael El Maach
    Subject: Human tolerance to blunt impact
    Date: Mon, 5 Mar 2001 13:49:19 -0500

    Dear Biomech-L members,

    Dynamic fracture forces of most body parts, as related to motor vehicle, is
    well documented in the literature (e.g. SAE reports). For instance, the
    force necessary to fracture the femur is generally determined from
    biomechanical testing where impact is delivered longitudinally through a
    flexed knee.

    *** Here is now my request:

    As opposed to the experiments carried out in the automobile industry, where
    long bones are loaded longitudinally, I am interested in knowing how much
    force (or energy) is needed to fracture the long bones of the limbs as a
    result of blunt impact delivered in a transversal manner (perpendicular to
    the bone shaft). Malicious kicks to the tibia and bat blows on the forearm
    during violent assaults are two examples among others where such forces may
    be applied.

    Any information would be much appreciated and, of course, I will post a
    summary of the responses.


    Ismael El Maach

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