Strain



- See:
      - Elastic strain:
      - Biomechanics:

- Discussion:
    - change in linear dimensions of a body resulting from the application of a force or load;
    - strain energy is the energy a body is capable of absorbing by changing its shape under the application of an external load;
    - strain is a measure of deformation, or potential energy, or amount of work deformed body is capable of doing in returning to its undeformed state;
           - more rapidly a bone is loaded, the greater will be the energy absorption prior to failure;
           - thus fractures associated with slow loading are generally linear, whereas rapid loading infuses enormous strain energy so that an explosion of the bone takes place at failure;
           - energy absorbed to produce frx of the femoral neck is approx 60 kg cm;
           - in falls, kinetic energy is far in excess of this amount, however, this energy may be dissipated by muscle action, elastic strain and plastic strain of the soft tissues;
    - load applied to a material produces stress within a material and thus invariably in deformation (strain) of the material;
    - analysis of mechanical conditions using the concept of strain allows one to understand why fractures w/single, narrow gap are very intolerant of even minute amounts of displacement;
           - such displacement may not be detected by vision but must be detected by intellect;
           - instability is better tolerated by multifragmentary (comminuted) frxs because overall displacement is shared between many fracture gaps
 
- Critical Strain Levels of Repair Tissues:
      (Elongation at rupture of different Sites)
       Granulation Tissue:                100%
       Dense Fibrous Tissue:             20%
       Cartilage:                                10%
       Cancellous Bone:                      2%
       Lamellar Bone                          2%



Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Thursday, May 24, 2012 1:03 pm